<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
        "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [

<!ENTITY RCL "<application>Recoll</application>">
<!ENTITY RCLAPPS "<ulink url='http://www.recoll.org/pages/features.html#doctypes'>http://www.recoll.org/pages/features.html</ulink>">
<!ENTITY RCLVERSION "1.29">
<!ENTITY XAP "<application>Xapian</application>">
<!ENTITY WIN "<application>Windows</application>">
<!ENTITY LIN "<application>Unix</application>-like systems">
<!ENTITY FAQS "https://www.lesbonscomptes.com/recoll/faqsandhowtos/">
<!ENTITY RCLCONF SYSTEM "recoll.conf.xml">
]>

<book lang="en">


  <!-- A nice overview of docbook elements:

       https://tdg.docbook.org/tdg/4.5/ch02.html#ch02-logdiv -->
  
  <bookinfo>
    <title>Recoll user manual</title>

    <author>
      <firstname>Jean-Francois</firstname>
      <surname>Dockes</surname>
      <affiliation>
        <address><email>jfd@recoll.org</email></address>
      </affiliation>
    </author>

    <copyright>
      <year>2005-2020</year>
      <holder role="mailto:jfd@recoll.org">Jean-Francois Dockes</holder>
    </copyright>

    <abstract>
      <para><literal>Permission is granted to copy, distribute and/or
      modify this document under the terms of the GNU Free Documentation
      License, Version 1.3 or any later version published by the Free
      Software Foundation; with no Invariant Sections, no Front-Cover
      Texts, and no Back-Cover Texts.  A copy of the license can be
      found at the following
      location: <ulink url="http://www.gnu.org/licenses/fdl.html">GNU
      web site</ulink>.</literal></para>

      <para>This document introduces full text search notions
      and describes the installation and use of the &RCL;
      application. This version describes &RCL; &RCLVERSION;.</para>
    </abstract>


  </bookinfo>
  
  <chapter id="RCL.INTRODUCTION">
    <title>Introduction</title>

    <para>This document introduces full text search notions
    and describes the installation and use of the &RCL;
    application. It is updated for &RCL; &RCLVERSION;.</para>

    <para>&RCL; was for a long time dedicated to Unix-like systems. It
      was only lately (2015) ported to
      <application>MS-Windows</application>. Many references in this
      manual, especially file locations, are specific to Unix, and not
      valid on &WIN;, where some described features are also not available.
      The manual will be progressively updated. Until this happens, on
      &WIN;, most references to shared files can be translated by looking
      under the Recoll installation directory (Typically <filename>C:/Program
        Files (x86)/Recoll</filename>, esp. anything referenced
      in <filename>/usr/share</filename> in this document will be found int
      the <filename>Share</filename> subdirectory). The user configuration is
      stored by default under <filename>AppData/Local/Recoll</filename>
      inside the user directory, along with the index itself.</para>
    
    <sect1 id="RCL.INTRODUCTION.TRYIT">
      <title>Giving it a try</title>
      
      <para>If you do not like reading manuals (who does?) but 
      wish to give &RCL; a try, just
      <link linkend="RCL.INSTALL.BINARY">install</link> the application
      and start the <command>recoll</command> graphical user
      interface (GUI), which will ask permission to index your home
      directory, allowing you to search immediately after
      indexing completes.</para>

      <para>Do not do this if your home directory contains a huge
      number of documents and you do not want to wait or are very
      short on disk space. In this case, you may first want to customize
      the <link linkend="RCL.INDEXING.CONFIG">configuration</link>
      to restrict the indexed area (shortcut: from the
      <command>recoll</command> GUI go to:
      <menuchoice> 
        <guimenu>Preferences</guimenu>
        <guimenuitem>Indexing configuration</guimenuitem>
        </menuchoice>, then adjust the <guilabel>Top
      directories</guilabel> section).</para>

      <para>On &LIN;, you may need to install the
      appropriate
      <link linkend="RCL.INSTALL.EXTERNAL">supporting applications</link> 
      for document types that need them (for
      example <application>antiword</application> for
      <application>Microsoft Word</application> files).
      The &RCL; for &WIN; package is self-contained and includes
      most useful auxiliary programs.</para>

    </sect1>

    <sect1 id="RCL.INTRODUCTION.SEARCH"> 
      <title>Full text search</title>

      <para>&RCL; is a full text search application, which means that it
      finds your data by content rather than by external attributes
      (like the file name). You specify words
      (terms) which should or should not appear in the text you are
      looking for, and receive in return a list of matching
      documents, ordered so that the most
      <emphasis>relevant</emphasis> documents will appear
      first.</para>

      <para>You do not need to remember in what file or email message you
      stored a given piece of information. You just ask for related
      terms, and the tool will return a list of documents where
      these terms are prominent, in a similar way to Internet search
      engines.</para>

      <para>Full text search applications try to determine which
      documents are most relevant to the search terms you
      provide. Computer algorithms for determining relevance can be
      very complex, and in general are inferior to the power of the
      human mind to rapidly determine relevance. The quality of
      relevance guessing is probably the most important aspect when
      evaluating a search application. &RCL; relies on the &XAP;
      probabilistic information retrieval library to determine
      relevance.</para> 

      <para>In many cases, you are looking for all the forms of a
      word, including plurals, different tenses for a verb, or terms
      derived from the same root or <emphasis>stem</emphasis>
      (example: <replaceable>floor, floors, floored,
      flooring...</replaceable>). Queries are usually automatically
      expanded to all such related terms (words that reduce to the
      same stem). This can be prevented for searching for a specific
      form.</para>

      <para>Stemming, by itself, does not accommodate for misspellings or
      phonetic searches. A full text search application may also support
      this form of approximation. For example, a search for
      <replaceable>aliterattion</replaceable> returning no result might
      propose <replaceable>alliteration, alteration, alterations, or
      altercation</replaceable> as possible replacement terms. &RCL; bases
      its suggestions on the actual index contents, so that suggestions may
      be made for words which would not appear in a standard dictionary.</para>

    </sect1>

    <sect1 id="RCL.INTRODUCTION.RECOLL">
      <title>Recoll overview</title>

      <para>&RCL; uses the 
      <ulink url="http://www.xapian.org">&XAP;</ulink> information retrieval
      library as its storage and retrieval engine. &XAP; is a very
      mature package using <ulink
      url="http://www.xapian.org/docs/intro_ir.html">a sophisticated
      probabilistic ranking model</ulink>.</para>
      
      <para>The &XAP; library manages an index database which
      describes where terms appear in your document files. It
      efficiently processes the complex queries which are produced by
      the &RCL; query expansion mechanism, and is in charge of the
      all-important relevance computation task.</para>

      <para>&RCL; provides the mechanisms and interface to get data
      into and out of the index. This includes translating the many
      possible document formats into pure text, handling term
      variations (using &XAP; stemmers), and spelling approximations
      (using the <application>aspell</application> speller),
      interpreting user queries and presenting results.</para>

      <para>In a shorter way, &RCL; does the dirty footwork, &XAP;
      deals with the intelligent parts of the process.</para>

      <para>The &XAP; index can be big (roughly the size of the original
      document set), but it is not a document archive. &RCL; can only
      display documents that still exist at the place from which they were
      indexed.</para>

      <para>&RCL; stores all internal data in <application>Unicode
      UTF-8</application> format, and it can index many types of files
      with different character sets, encodings, and languages into the
      same index. It can process documents embedded inside other
      documents (for example a PDF document stored inside a Zip
      archive sent as an email attachment...), down to an arbitrary
      depth.</para>
      
      <para>Stemming is the process by which &RCL; reduces words to
      their radicals so that searching does not depend, for example, on a
      word being singular or plural (floor, floors), or on a verb tense
      (flooring, floored). Because the mechanisms used for stemming
      depend on the specific grammatical rules for each language, there
      is a separate &XAP; stemmer module for most common languages where
      stemming makes sense.</para>

      <para>&RCL; stores the unstemmed versions of terms in the main index
      and uses auxiliary databases for term expansion (one for each
      stemming language), which means that you can switch stemming
      languages between searches, or add a language without needing a
      full reindex.</para>

      <para>Storing documents written in different languages in the same
      index is possible, and commonly done. In this situation, you can
      specify several stemming languages for the index. </para>

      <para>&RCL; currently makes no attempt at automatic language
      recognition, which means that the stemmer will sometimes be applied
      to terms from other languages with potentially strange results. In
      practise, even if this introduces possibilities of confusion, this
      approach has been proven quite useful, and it is much less
      cumbersome than separating your documents according to what
      language they are written in.</para>

      <para>By default, &RCL; strips most accents and
      diacritics from terms, and converts them to lower case before
      either storing them in the index or searching for them. As a
      consequence, it is impossible to search for a particular
      capitalization of a term (<literal>US</literal> /
      <literal>us</literal>), or to discriminate two terms based on
      diacritics (<literal>sake</literal> / <literal>saké</literal>, 
      <literal>mate</literal> / <literal>maté</literal>).</para>
      
      <para>&RCL; can optionally store the raw terms, without accent
      stripping or case conversion. In this configuration, default searches
      will behave as before, but it is possible to perform searches
      sensitive to case and diacritics. This is described in more detail in
      the section about
      <link linkend="RCL.INDEXING.CONFIG.SENS">index case and diacritics sensitivity</link>.
      </para>

      <para>&RCL; uses many parameters to define exactly what to index,
        and how to classify and decode the source documents. These are kept
        in <link linkend="RCL.INDEXING.CONFIG">configuration files</link>.  A
        default configuration is copied into a standard location (usually
        something like <filename>/usr/share/recoll/examples</filename>)
        during installation. The default values set by the configuration
        files in this directory may be overridden by values set inside your
        personal configuration. With the default configuration, &RCL; will
        index your home directory with generic parameters. Most common
        parameters can be set by using
        configuration menus in the <command>recoll</command> GUI. Some less
        common parameters can only be set by editing the text files (the
        new values will be preserved by the GUI).</para>

      <para>The <link linkend="RCL.INDEXING.PERIODIC.EXEC">indexing process</link>
      is started automatically (after asking permission), the
      first time you execute the <command>recoll</command> GUI. Indexing
      can also be performed by executing the <command>recollindex</command>
      command. &RCL; indexing is multithreaded by default when appropriate
      hardware resources are available, and can perform in parallel
      multiple tasks for text extraction, segmentation and index
      updates.</para>

      <para><link linkend="RCL.SEARCH">Searches</link> are usually
      performed inside the <command>recoll</command> GUI, which has many
      options to help you find what you are looking for. However, there
      are other ways to query the index:
      <itemizedlist>
        <listitem><para>A
        <link linkend="RCL.SEARCH.COMMANDLINE">command line interface</link>.
        </para></listitem>
        <listitem><para>A
        <link linkend="RCL.PROGRAM.PYTHONAPI"><application>Python</application> programming interface</link>
        </para></listitem>
        <listitem><para>A <link linkend="RCL.SEARCH.KIO"><application>KDE</application> KIO slave module</link>.
        </para></listitem> 
        <listitem><para>A Ubuntu Unity
        <ulink url="https://www.lesbonscomptes.com/recoll/pages/download.html">Scope</ulink>
        module.</para></listitem>
        <listitem><para>A Gnome Shell
        <ulink url="https://www.lesbonscomptes.com/recoll/pages/download.html">Search Provider</ulink>.
        </para></listitem>
        <listitem><para>A
        <ulink url="https://framagit.org/medoc92/recollwebui">Web interface</ulink>.
        </para></listitem>
      </itemizedlist>
      </para>

    </sect1>
  </chapter>


  <chapter id="RCL.INDEXING">
    <title>Indexing</title>

    <sect1 id="RCL.INDEXING.INTRODUCTION">
      <title>Introduction</title>

      <para>Indexing is the process by which the set of documents is
      analyzed and the data entered into the database. &RCL;
      indexing is normally incremental: documents will only be
      processed if they have been modified since the last run. On
      the first execution, all documents will need processing. A
      full index build can be forced later by specifying an option
      to the indexing command (<command>recollindex</command>
      <option>-z</option> or <option>-Z</option>).</para>

      <para><command>recollindex</command> skips files which caused an
      error during a previous pass. This is a performance optimization, and
      the command line option <option>-k</option> can be set to retry
      failed files, for example after updating an input handler.</para>

      <para>The following sections give an overview of different
      aspects of the indexing processes and configuration, with links
      to detailed sections.</para>

      <para>Depending on your data, temporary files may be needed during
      indexing, some of them possibly quite big. You can use the
      <envar>RECOLL_TMPDIR</envar> or <envar>TMPDIR</envar> environment
      variables to determine where they are created (the default is to
      use <filename>/tmp</filename>). Using <envar>TMPDIR</envar> has
      the nice property that it may also be taken into account by 
      auxiliary commands executed by <command>recollindex</command>.</para>

      <sect2 id="RCL.INDEXING.INTRODUCTION.MODES">
        <title>Indexing modes</title> 

        <para>&RCL; indexing can be performed along two main modes:</para>
        <itemizedlist>
          <listitem>
            <formalpara><title>
              <link linkend="RCL.INDEXING.PERIODIC">Periodic (or batch) indexing</link>
            </title> <para><command>recollindex</command> is executed at
                discrete times. On &LIN;, the typical usage is to have a
                nightly run
                <link linkend="RCL.INDEXING.PERIODIC.AUTOMAT">
                  programmed</link>
                into your <command>cron</command> file. On &WIN;, this is
                the only mode available, and the Windows Task Scheduler can
                be used to run indexing. In both cases, the GUI includes an
                easy interface to the system batch scheduler.</para>
            </formalpara>
          </listitem>
          <listitem>
            <formalpara><title>
              <link linkend="RCL.INDEXING.MONITOR">Real time indexing</link>
            </title>
            <para>(Only available on &LIN;). <command>recollindex</command> runs
            permanently as a daemon and uses a file system alteration monitor
            (e.g. <application>inotify</application>) to detect file
            changes. New or updated files are indexed at once. Monitoring a
            big file system tree can consume 
            significant system resources. </para>
            </formalpara>
          </listitem>
        </itemizedlist>

        <simplesect><title>&LIN;: choosing an indexing mode</title>
        <para>The choice between the two methods is mostly a matter of
        preference, and they can be combined by setting up multiple
        indexes (ie: use periodic indexing on a big documentation
        directory, and real time indexing on a small home
        directory), or, with &RCL; 1.24 and newer, by
        <link linkend="RCL.INDEXING.MONITOR">configuring the index so that only a subset of the tree will be monitored.</link>
        </para>
        <para>The choice of method and the parameters used can be
        configured from the <command>recoll</command> GUI:
        <menuchoice>
          <guimenu>Preferences</guimenu>
          <guimenuitem>Indexing schedule</guimenuitem>
        </menuchoice> dialog.
        </para>
        </simplesect>

      </sect2>

      <sect2 id="RCL.INDEXING.INTRODUCTION.CONFIG">
        <title>Configurations, multiple indexes</title>

        <para>&RCL; supports defining multiple indexes, each defined by its
        own configuration directory. A configuration directory contains
        <link linkend="RCL.INDEXING.CONFIG">several files</link> which
        describe what should be indexed and how.</para>

        <para>When <command>recoll</command> or
        <command>recollindex</command> is first executed, it creates a
        default configuration directory. This configuration is the one used
        for indexing and querying when no specific configuration is
        specified. It is located in <filename>$HOME/.recoll/</filename> for
        &LIN; and <filename>%LOCALAPPDATA%\Recoll</filename> on &WIN;
        (typically
        <filename>C:\Users\[me]\Appdata\Local\Recoll</filename>).</para> 

        <para>All configuration parameters have defaults, defined in
        system-wide files. Without further customisation, the default
        configuration will process your complete home directory, with a
        reasonable set of defaults. It can be adjusted to process a
        different area of the file system, select files in different ways,
        and many other things.</para>

        <para>In some cases, it may be useful to create additional
        configuration directories, for example, to separate personal and
        shared indexes, or to take advantage of the organization of your
        data to improve search precision.</para>

        <para>In order to do this, you would create an empty directory in a
        location of your choice, and then instruct
        <command>recoll</command> or <command>recollindex</command> to use
        it by setting either a command line option (<literal>-c</literal>
        <replaceable>/some/directory</replaceable>), or an environment
        variable
        (<envar>RECOLL_CONFDIR</envar>=<replaceable>/some/directory</replaceable>).
        Any modification performed by the commands (e.g. configuration
        customisation or searches by <command>recoll</command> or index
        creation by <command>recollindex</command>) would then apply to the
        new directory and not to the default one.</para>

        <para>Once multiple indexes are created, you can use each of them
        separately by setting the <literal>-c</literal> option or the
        <envar>RECOLL_CONFDIR</envar> environment variable when starting a
        command, to select the desired index.</para>

        <para>It is also possible to instruct one configuration to
        query one or several other indexes in addition to its own, by using
        the <guimenuitem>External index</guimenuitem> function in the
        <command>recoll</command> GUI, or some other functions in the
        command line and programming tools.</para>
        
        <para>A plausible usage scenario for the multiple index feature
        would be for a system administrator to set up a central index for
        shared data, that you choose to search or not in addition to your
        personal data. Of course, there are other possibilities. for
        example, there are many cases where you know the subset of files
        that should be searched, and where narrowing the search can improve
        the results. You can achieve approximately the same effect with the
        directory filter in advanced search, but multiple indexes may have
        better performance and may be worth the trouble in some
        cases.</para>

        <para>A more advanced use case would be to use multiple index to
        improve indexing performance, by updating several indexes in
        parallel (using multiple CPU cores and disks, or possibly several
        machines), and then merging them, or querying them in
        parallel.</para>

        <para>See the section about
        <link linkend="RCL.INDEXING.CONFIG.MULTIPLE">configuring multiple indexes</link>
        for more detail</para>

      </sect2>

      <sect2>
        <title>Document types</title>

        <para>&RCL; knows about quite a few different document
          types. The parameters for document types recognition and
          processing are set in <link linkend="RCL.INDEXING.CONFIG">
            configuration files</link>.
        </para>

        <para>Most file types, like HTML or word processing files, only hold
        one document. Some file types, like email folders or zip
        archives, can hold many individually indexed documents, which may
        themselves be compound ones. Such hierarchies can go quite
        deep, and &RCL; can process, for example, a
        <application>LibreOffice</application> 
        document stored as an attachment to an email message inside an
        email folder archived in a zip file...</para>

        <para><command>recollindex</command> processes plain text, HTML,
        OpenDocument (Open/LibreOffice), email formats, and a few others
        internally.</para>

        <para>Other file types (ie: postscript, pdf, ms-word, rtf ...) 
        need external applications for preprocessing. The list is in the
        <link linkend="RCL.INSTALL.EXTERNAL">installation</link>
        section. After every indexing operation, &RCL; updates a list of
        commands that would be needed for indexing existing files
        types. This list can be displayed by selecting the menu option
        <menuchoice>
          <guimenu>File</guimenu>
          <guimenuitem>Show Missing Helpers</guimenuitem>
        </menuchoice>
        in the <command>recoll</command> GUI. It is stored in the
        <filename>missing</filename> text file inside the configuration
        directory.</para>

        <para>After installing a missing handler, you may need to
          tell <command>recollindex</command> 
          to retry the failed files, by adding option <literal>-k</literal>
          to the command line, or by using the GUI
        <menuchoice>
          <guimenu>File</guimenu>
          <guimenuitem>Special indexing</guimenuitem> 
        </menuchoice> menu. This is because <command>recollindex</command>,
        in its default operation mode, will not retry files which caused an
        error during an earlier pass. In special cases, it may be useful to
        reset the data for a category of files before indexing. See
        the <command>recollindex</command> manual page. If your index is
        not too big, it may be simpler to just reset it.</para>
          
        <para>By default, &RCL; will try to index any file type that
        it has a way to read. This is sometimes not desirable, and
        there are ways to either exclude some types, or on the
        contrary define a positive list of types to be
        indexed. In the latter case, any type not in the list will
        be ignored.</para>

        <para>Excluding files by name can be done by adding wildcard name
        patterns to the
        <link linkend="RCL.INSTALL.CONFIG.RECOLLCONF.SKIPPEDNAMES">
          skippedNames</link> 
        list, which can be done from the GUI Index configuration
        menu. Excluding by type can be done by setting the 
        <link linkend="RCL.INSTALL.CONFIG.RECOLLCONF.EXCLUDEDMIMETYPES">
          excludedmimetypes</link> 
        list in the configuration file (1.20 and later). This can be
        redefined for subdirectories.</para>

        <para>You can also define an exclusive list of MIME types to be
        indexed (no others will be indexed), by setting 
        the <link linkend="RCL.INSTALL.CONFIG.RECOLLCONF.INDEXEDMIMETYPES">
            indexedmimetypes</link>
        configuration variable. Example:<programlisting>
        indexedmimetypes = text/html application/pdf
      </programlisting>
      It is possible to redefine this parameter for
      subdirectories. Example:<programlisting>
      [/path/to/my/dir]
      indexedmimetypes = application/pdf
    </programlisting>
    (When using sections like this, don't forget that they remain
    in effect until the end of the file or another section
    indicator).
        </para>

        <para><literal>excludedmimetypes</literal> or
        <literal>indexedmimetypes</literal>, can be set either by editing
        the <link linkend="RCL.INSTALL.CONFIG.RECOLLCONF">configuration file (<filename>recoll.conf</filename>)</link>
        for the index, or by using the GUI index configuration tool.</para>

        <note><title>Note about MIME types</title>
        <para>When editing the <literal>indexedmimetypes</literal>
        or <literal>excludedmimetypes</literal> lists, you should use the
        MIME values listed in the <filename>mimemap</filename> file
        or in Recoll result lists in preference to <literal>file -i</literal>
        output: there are a number of differences. The
        <literal>file -i</literal> output should only be used for files
        without extensions, or for which the extension is not listed in
        <filename>mimemap</filename></para></note> 

      </sect2>


      <sect2>
        <title>Indexing failures</title>

        <para>Indexing may fail for some documents, for a number of
        reasons: a helper program may be missing, the document may be
        corrupt, we may fail to uncompress a file because no file
        system space is available, etc.</para>
        
        <para>The &RCL; indexer in versions 1.21 and later does not
          retry failed files by default, because some indexing failures
          can be quite costly (for example failing to uncompress a big
          file because of insufficient disk space).
          Retrying will only occur if an explicit option
          (<option>-k</option>) is set on
          the <command>recollindex</command> command line, or if a script
          executed when <command>recollindex</command> starts up says
          so. The script is defined by a configuration variable
          (<literal>checkneedretryindexscript</literal>), and makes a
          rather lame attempt at deciding if a helper command may have been
          installed, by checking if any of the
          common <filename>bin</filename> directories have changed.</para>

      </sect2>

      <sect2>
        <title>Recovery</title>

        <para>In the rare case where the index becomes corrupted (which can
        signal itself by weird search results or crashes), the index files
        need to be erased before restarting a clean indexing pass. Just delete
        the <filename>xapiandb</filename> directory (see 
        <link linkend="RCL.INDEXING.STORAGE">next section</link>), or, 
        alternatively, start the next <command>recollindex</command> with the 
        <option>-z</option> option, which will reset the database before
        indexing. The difference between the two methods is that the
        second will not change the current index format, which may be
        undesirable if a newer format is supported by the &XAP;
        version.</para>

      </sect2>

    </sect1>

    <sect1 id="RCL.INDEXING.STORAGE">
      <title>Index storage</title>

      <para>The default location for the index data is the
      <filename>xapiandb</filename> subdirectory of the &RCL;
      configuration directory, typically
      <filename>$HOME/.recoll/xapiandb/</filename>. This can be
      changed via two different methods (with different purposes):
      <orderedlist>

        <listitem><para>For a given configuration directory, you can
        specify a non-default storage location for the index by setting
        the <varname>dbdir</varname> parameter in the configuration file
        (see the
        <link linkend="RCL.INSTALL.CONFIG.RECOLLCONF">configuration section</link>).
        This method would mainly be of use if you wanted
        to keep the configuration directory in its default location, but
        desired another location for the index, typically out of disk
        occupation or performance concerns.</para>
        </listitem>

        <listitem><para>You can specify a different configuration
        directory by setting the <envar>RECOLL_CONFDIR</envar>
        environment variable, or using the <option>-c</option>
        option to the &RCL; commands. This method would typically be
        used to index different areas of the file system to
        different indexes. For example, if you were to issue the
        following command: 
        <programlisting>recoll -c ~/.indexes-email</programlisting> Then
        &RCL; would use configuration files 
        stored in <filename>~/.indexes-email/</filename> and,
        (unless specified otherwise in
        <filename>recoll.conf</filename>) would look for 
        the index in
        <filename>~/.indexes-email/xapiandb/</filename>.</para>

        <para>Using multiple configuration directories and
        <link linkend="RCL.INSTALL.CONFIG.RECOLLCONF">configuration options</link>
        allows you to tailor multiple configurations and
        indexes to handle whatever subset of the available data you wish
        to make searchable.</para>
        </listitem>

      </orderedlist>
      </para>

      <para>The size of the index is determined by the size of the set
      of documents, but the ratio can vary a lot. For a typical
      mixed set of documents, the index size will often be close to
      the data set size. In specific cases (a set of compressed mbox
      files for example), the index can become much bigger than the
      documents. It may also be much smaller if the documents
      contain a lot of images or other non-indexed data (an extreme
      example being a set of mp3 files where only the tags would be
      indexed).</para>

      <para>Of course, images, sound and video do not increase the index
      size, which means that in most cases, the space used by the index
      will be negligible compared to the total amount of data on the
      computer.</para>
      
      <para>The index data directory (<filename>xapiandb</filename>)
      only contains data that can be completely rebuilt by an index run
      (as long as the original documents exist), and it can always be
      destroyed safely.</para>
      
      <sect2 id="RCL.INDEXING.STORAGE.FORMAT">
        <title>&XAP; index formats</title>

        <para>&XAP; versions usually support several formats for index
        storage. A given major &XAP; version will have a current format,
        used to create new indexes, and will also support the format from
        the previous major version.</para>

        <para>&XAP; will not convert automatically an existing index from
        the older format to the newer one. If you want to upgrade to the
        new format, or if a very old index needs to be converted because
        its format is not supported any more, you will have to explicitly
        delete the old index (typically
        <filename>~/.recoll/xapiandb</filename>), then run a normal
        indexing command. Using <command>recollindex</command> option
        <option>-z</option> would not work in this situation.</para>


      </sect2>

      <sect2 id="RCL.INDEXING.STORAGE.SECURITY">
        <title>Security aspects</title>

        <para>The &RCL; index does not hold complete copies of the indexed
        documents (it almost does after version 1.24). But it does
        hold enough data to allow for an almost complete reconstruction. If
        confidential data is indexed, access to the database directory
        should be restricted. </para>

        <para>&RCL; will create the configuration directory with a mode of
        0700 (access by owner only). As the index data directory is by
        default a sub-directory of the configuration directory, this should
        result in appropriate protection.</para>

        <para>If you use another setup, you should think of the kind
        of protection you need for your index, set the directory
        and files access modes appropriately, and also maybe adjust
        the <literal>umask</literal> used during index updates.</para>

      </sect2>

      <sect2 id="RCL.INDEXING.STORAGE.BIG">
        <title>Special considerations for big indexes</title>

        <para>This only needs concern you if your index is going to be
        bigger than around 5 GBytes. Beyond 10 GBytes, it becomes a serious
        issue. Most people have much smaller indexes. For reference, 5
        GBytes would be around 2000 bibles, a lot of text.  If you have a
        huge text dataset (remember: images don't count, the text content
        of PDFs is typically less than 5% of the file size), read on.</para>

        <para>The amount of writing performed by Xapian during index
        creation is not linear with the index size (it is somewhere between
        linear and quadratic). For big indexes this becomes a performance
        issue, and may even be an SSD disk wear issue.</para>

        <para>The problem can be mitigated by observing the following
        rules:</para>
        <itemizedlist>
          <listitem><para>Partition the data set and create several indexes
          of reasonable size rather than a huge one. These indexes can then
          be queried in parallel (using the &RCL; external indexes
          facility), or merged using
          <command>xapian-compact</command>.</para></listitem> 
          <listitem><para>Have a lot of RAM available and set the
          <literal>idxflushmb</literal> &RCL; configuration parameter as
          high as you can without swapping (experimentation will be
          needed). 200 would be a minimum in this
          context.</para></listitem>
          <listitem><para>Use Xapian 1.4.10 or newer, as this version
          brought a significant improvement in the amount of writes.</para>
          </listitem>
        </itemizedlist>

      </sect2>
      
    </sect1>

    <sect1 id="RCL.INDEXING.CONFIG">
      <title>Index configuration</title>

      <para>Variables stored inside the 
        <link linkend="RCL.INSTALL.CONFIG">&RCL; configuration files</link>
        control which areas of the file system are indexed, and how files
        are processed. The values can be set by editing the text
        files. Most of the more commonly used ones can also be adjusted by
        using the <link linkend="RCL.INDEXING.CONFIG.GUI">
          dialogs in the <command>recoll</command> GUI</link>.</para>

      <para>The first time you start <command>recoll</command>, you will be
      asked whether or not you would like it to build the index. If you
      want to adjust the configuration before indexing, just click
      <guilabel>Cancel</guilabel> at this point, which will get you into
      the configuration interface. If you exit at this point,
      <filename>recoll</filename> will have created a default configuration
      directory with empty configuration files, which you can then
      edit.</para>

      <para>The configuration is documented inside the 
      <link linkend="RCL.INSTALL.CONFIG">installation chapter</link> 
      of this document, or in the
      <ulink url="https://www.lesbonscomptes.com/recoll/manpages/recoll.conf.5.html"><citerefentry><refentrytitle>recoll.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry></ulink>
      manual page. Both documents are automatically generated from
      the comments inside the configuration file.</para>

      <para>The most immediately useful variable
      is probably
      <link linkend="RCL.INSTALL.CONFIG.RECOLLCONF.TOPDIRS"><varname>topdirs</varname></link>, 
      which lists the subtrees and files to be indexed.</para>

      <para>The applications needed to index file types other than
      text, HTML or email (ie: pdf, postscript, ms-word...) are
      described in the <link linkend="RCL.INSTALL.EXTERNAL">external packages section</link>.
      </para>

      <para>There are two incompatible types of Recoll
        indexes, depending on the treatment of character case and
        diacritics. A <link linkend="RCL.INDEXING.CONFIG.SENS">further
        section</link> describes the two types in more detail. The default
        type is appropriate in most cases.</para>

      <sect2 id="RCL.INDEXING.CONFIG.MULTIPLE">
        <title>Multiple indexes</title>

        <para>Multiple &RCL; indexes can be created by using several
        configuration directories which are typically set to index
        different areas of the file system.</para>

        <para>A specific index can be selected by setting the
        <envar>RECOLL_CONFDIR</envar> environment variable or giving the
        <option>-c</option> option to <command>recoll</command> and
        <command>recollindex</command>.</para>

        <para>The <command>recollindex</command> program, used for creating
        or updating indexes, always works on a single index. The different
        configurations are entirely independent (no parameters are ever
        shared between configurations when indexing). </para>

        <para>All the search interfaces (<command>recoll</command>,
        <command>recollq</command>, the Python API, etc.) operate with a
        main configuration, from which both configuration and index data
        are used, and can also query data from multiple additional
        indexes. Only the index data from the latter is used, their
        configuration parameters are ignored. This implies that some
        parameters should be consistent among index configurations which
        are to be used together.</para>

        <para>When searching, the current main index (defined by
        <envar>RECOLL_CONFDIR</envar> or <option>-c</option>) is always
        active. If this is undesirable, you can set up your base
        configuration to index an empty directory.</para>

        <para>Index configuration parameters can be set either by using a
        text editor on the files, or, for most parameters, by using the
        <link linkend="RCL.INDEXING.CONFIG.GUI"><command>recoll</command> index configuration GUI</link>.
        In the latter case, the configuration directory for which
        parameters are modified is the one which was selected by
        <envar>RECOLL_CONFDIR</envar> or the <option>-c</option> parameter,
        and there is no way to switch configurations within the GUI.</para>

        <para>See the <link linkend="RCL.INSTALL.CONFIG.RECOLLCONF">configuration section</link>
        for a detailed description of the parameters</para>

        <para>Some configuration parameters must be consistent among a set
        of multiple indexes used together for searches.  Most importantly,
        all indexes to be queried concurrently must have the same option
        concerning character case and diacritics stripping, but there are
        other constraints. Most of the relevant parameters affect the
        <link linkend="RCL.INSTALL.CONFIG.RECOLLCONF.TERMS">term generation</link>.
        </para>

        <para>Using multiple configurations implies a small
        level of command line or file manager usage. The user must
        explicitly create additional configuration directories, the GUI
        will not do it. This is to avoid mistakenly creating additional
        directories when an argument is mistyped. Also, the GUI or the
        indexer must be launched with a specific option or environment to
        work on the right configuration.</para>

        <simplesect>
          <title>In practise: creating and using an additional index</title>


        <para>Initially creating the configuration and index:<programlisting>
mkdir <replaceable>/path/to/my/new/config</replaceable></programlisting></para>
        
        <para>Configuring the new index can be done from the
        <command>recoll</command> GUI, launched from the
        command line to pass the <literal>-c</literal> option
        (you could create a desktop file to do it for you), and then using the
        <link linkend="RCL.INDEXING.CONFIG.GUI">GUI index configuration tool</link>
        to set up the index.
        <programlisting>
recoll -c <replaceable>/path/to/my/new/config</replaceable></programlisting>
</para>
    

         <para>Alternatively, you can just start a text editor on the main
         configuration file:
         <programlisting>
<replaceable>someEditor</replaceable> <replaceable>/path/to/my/new/config</replaceable>/<link linkend="RCL.INSTALL.CONFIG.RECOLLCONF"><filename>recoll.conf</filename></link>
</programlisting>
         </para>


<para>Creating and updating the index can be done from the command line:

<programlisting>recollindex -c <replaceable>/path/to/my/new/config</replaceable>
</programlisting>
or from the File menu of a GUI launched with the same option
(<command>recoll</command>, see above).</para>

          <para>The same GUI would also let you set up batch indexing for
          the new index. Real time indexing can only be set up from the GUI
          for the default index (the menu entry will be inactive if the GUI
          was started with a non-default <literal>-c</literal>
          option).</para>

          <para>The new index can be queried alone with<programlisting>
recoll -c <replaceable>/path/to/my/new/config</replaceable></programlisting>
          Or, in parallel with the default index, by starting
          <command>recoll</command> without a <literal>-c</literal> option,
          and using the 
        <menuchoice>
          <guimenu>Preferences</guimenu>
          <guimenuitem>External Index Dialog</guimenuitem> 
        </menuchoice> menu.</para> 
      </simplesect>
      </sect2>


      <sect2 id="RCL.INDEXING.CONFIG.SENS">
        <title>Index case and diacritics sensitivity</title>

        <para>As of &RCL; version 1.18 you have a choice of building an
        index with terms stripped of character case and diacritics, or
        one with raw terms. For a source term of
        <literal>Résumé</literal>, the former will store
        <literal>resume</literal>, the latter
        <literal>Résumé</literal>.</para>
        
        <para>Each type of index allows performing searches insensitive to
        case and diacritics: with a raw index, the user entry will be
        expanded to match all case and diacritics variations present in
        the index. With a stripped index, the search term will be stripped
        before searching.</para>
        
        <para>A raw index allows using case and diacritics to discriminate
        between terms, e.g., returning different results when searching for
        <literal>US</literal> and <literal>us</literal> or
        <literal>resume</literal> and <literal>résumé</literal>.
        Read the
        <link linkend="RCL.SEARCH.CASEDIAC">section about search case and diacritics sensitivity</link> 
        for more details.</para>

        <para>The type of index to be created is controlled by the
        <literal>indexStripChars</literal> configuration
        variable which can only be changed by editing the
        configuration file. Any change implies an index reset (not
        automated by &RCL;), and all indexes in a search must be set
        in the same way (again, not checked by &RCL;). </para>

        <para>&RCL; creates a stripped index by default if
        <literal>indexStripChars</literal> is not set.</para>

        <para>As a cost for added capability, a raw index will be slightly
        bigger than a stripped one (around 10%). Also, searches will be
        more complex, so probably slightly slower, and the feature is
        relatively little used, so that a certain amount of weirdness
        cannot be excluded.</para>

        <para>One of the most adverse consequence of using a raw index
        is that some phrase and proximity searches may become
        impossible: because each term needs to be expanded, and all
        combinations searched for, the multiplicative expansion may
        become unmanageable.</para>

      </sect2>





      <sect2 id="RCL.INDEXING.CONFIG.THREADS">
        <title>Indexing threads configuration (&LIN;)</title>

        <para>The &RCL; indexing process 
        <command>recollindex</command> can use multiple threads to
        speed up indexing on multiprocessor systems. The work done
        to index files is divided in several stages and some of the
        stages can be executed by multiple threads. The stages are:
        <orderedlist>
          <listitem><para>File system walking: this is always performed by
          the main thread.</para></listitem>
          <listitem><para>File conversion and data
          extraction.</para></listitem>
          <listitem><para>Text processing (splitting, stemming,
          etc.).</para></listitem>
          <listitem><para>&XAP; index update.</para></listitem>
        </orderedlist>
        </para>
        <para>You can also read a 
        <ulink url="http://www.recoll.org/pages/idxthreads/threadingRecoll.html">
          longer document</ulink> about the transformation of
        &RCL; indexing to multithreading.</para>

        <para>The threads configuration is controlled by two
        configuration file parameters.</para>

        <variablelist>

          <varlistentry><term><varname>thrQSizes</varname></term>
          <listitem><para>This variable defines the job input queues
          configuration. There are three possible queues for stages
          2, 3 and 4, and this parameter should give the queue depth
          for each stage (three integer values). If a value of -1 is
          used for a given stage, no queue is used, and the thread
          will go on performing the next stage. In practise, deep
          queues have not been shown to increase performance. A value
          of 0 for the first queue tells &RCL; to perform
          autoconfiguration (no need for anything else in this case,
          thrTCounts is not used) - this is the default
          configuration.</para>
          </listitem>
          </varlistentry>

          <varlistentry><term><varname>thrTCounts</varname></term>
          <listitem><para>This defines the number of threads used
          for each stage. If a value of -1 is used for one of
          the queue depths, the corresponding thread count is
          ignored. It makes no sense to use a value other than 1
          for the last stage because updating the &XAP; index is
          necessarily single-threaded (and protected by a
          mutex).</para>
          </listitem>
          </varlistentry>

        </variablelist>

        <note><para>If the first value in <varname>thrQSizes</varname> is
        0, <varname>thrTCounts</varname> is ignored.</para></note>
        
        <para>The following example would use three queues (of depth 2),
        and 4 threads for converting source documents, 2 for
        processing their text, and one to update the index. This was
        tested to be the best configuration on the test system
        (quadri-processor with multiple disks).
        <programlisting>
          thrQSizes = 2 2 2
          thrTCounts =  4 2 1
        </programlisting>
        </para>

        <para>The following example would use a single queue, and the
        complete processing for each document would be performed by
        a single thread (several documents will still be processed
        in parallel in most cases). The threads will use mutual
        exclusion when entering the index update stage. In practise
        the performance would be close to the precedent case in
        general, but worse in certain cases (e.g. a Zip archive
        would be performed purely sequentially), so the previous
        approach is preferred. YMMV...  The 2 last values for
        thrTCounts are ignored.
        <programlisting>
          thrQSizes = 2 -1 -1
          thrTCounts =  6 1 1
        </programlisting>
        </para>

        <para>The following example would disable
        multithreading. Indexing will be performed by a single
        thread.
        <programlisting>
          thrQSizes = -1 -1 -1
        </programlisting>
        </para>

      </sect2>



      <sect2 id="RCL.INDEXING.CONFIG.GUI">
        <title>The index configuration GUI</title>

        <para>Most parameters for a given index configuration can
        be set from a <command>recoll</command> GUI running on this
        configuration (either as default, or by setting
        <envar>RECOLL_CONFDIR</envar> or the <option>-c</option>
        option.)</para> 

        <para>The interface is started from the
        <menuchoice>
          <guimenu>Preferences</guimenu>
          <guimenuitem>Index Configuration</guimenuitem> 
        </menuchoice>
        menu entry. It is divided in four tabs,
        <guilabel>Global parameters</guilabel>, <guilabel>Local
        parameters</guilabel>, <guilabel>Web history</guilabel>
        (which is explained in the next section) and <guilabel>Search
        parameters</guilabel>.</para>

        <para>The <guilabel>Global parameters</guilabel> tab allows setting
        global variables, like the lists of top directories, skipped paths,
        or stemming languages.</para> 

        <para>The <guilabel>Local parameters</guilabel> tab allows setting
        variables that can be redefined for subdirectories. This second tab
        has an initially empty list of customisation directories, to which
        you can add. The variables are then set for the currently selected
        directory (or at the top level if the empty line is
        selected).</para>

        <para>The <guilabel>Search parameters</guilabel> section defines
        parameters which are used at query time, but are global to an
        index and affect all search tools, not only the GUI.</para>

        <para>The meaning for most entries in the interface is 
        self-evident and documented by a <literal>ToolTip</literal>
        popup on the text label. For more detail, you will need to
        refer to the
        <link linkend="RCL.INSTALL.CONFIG">configuration section</link>
        of this guide.</para>

        <para>The configuration tool normally respects the comments
        and most of the formatting inside the configuration file, so
        that it is quite possible to use it on hand-edited files,
        which you might nevertheless want to backup first...</para>

      </sect2>
    </sect1>

    <sect1 id="RCL.INDEXING.REMOVABLE">
      <title>Removable volumes</title>

      <para>&RCL; used to have no support for indexing removable volumes
      (portable disks, USB keys, etc.). Recent versions have improved the
      situation and support indexing removable volumes in two different
      ways:</para>

    <itemizedlist>
      <listitem><para>By indexing the volume in the main, fixed, index, and
      ensuring that the volume data is not purged if the indexing runs
      while the volume is mounted. (since &RCL; 1.25.2).</para></listitem>
      <listitem><para>By storing a volume index on the volume
      itself (since &RCL; 1.24).</para></listitem>
    </itemizedlist>

    <simplesect id="RCL.INDEXING.REMOVABLE.MAIN">
      <title>Indexing removable volumes in the main index</title>

      <para>As of version 1.25.2, &RCL; provides a simple way to ensure
      that the index data for an absent volume will not be purged. Two
      conditions must be met:
      <itemizedlist>
        <listitem><para>The volume mount 
        point must be a member of the <literal>topdirs</literal>
        list.</para></listitem> 
        <listitem><para>The mount directory must be empty (when the volume
        is not mounted).</para></listitem>
      </itemizedlist>
      </para>

      <para>If <command>recollindex</command> finds that one of the
      <literal>topdirs</literal> is empty when starting up, any existing
      data for the tree will be preserved by the indexing
      pass (no purge for this area).</para> 

    </simplesect>
    
    <simplesect id="RCL.INDEXING.REMOVABLE.SELF">
      <title>Self contained volumes</title>
      
      <para>As of &RCL; 1.24, it has become possible to build
      self-contained datasets including a &RCL; configuration directory and
      index together with the indexed documents, and to move such a dataset
      around (for example copying it to an USB drive), without having to
      adjust the configuration for querying the index.</para>

      <note><para>This is a query-time feature only. The index must only be
      updated in its original location. If an update is necessary in a
      different location, the index must be reset.</para></note>

      <para>The principle of operation is that the configuration stores the
      location of the original configuration directory, which must reside
      on the movable volume. If the volume is later mounted elsewhere,
      &RCL; adjusts the paths stored inside the index by the difference
      between the original and current locations of the configuration
      directory.</para>
      
      <para>To make a long story short, here follows a script to create a
      &RCL; configuration and index under a given directory (given as single
      parameter). The resulting data set (files + recoll directory) can later
      to be moved to a CDROM or thumb drive. Longer explanations come after
      the script.</para>
      
    <programlisting>#!/bin/sh

fatal()
{
    echo $*;exit 1
}
usage()
{
    fatal "Usage: init-recoll-volume.sh &lt;top-directory>"
}

test $# = 1 || usage
topdir=$1
test -d "$topdir" || fatal $topdir should be a directory

confdir="$topdir/recoll-config"
test ! -d "$confdir" || fatal $confdir should not exist

mkdir "$confdir"
cd "$topdir"
topdir=`pwd`
cd "$confdir"
confdir=`pwd`

(echo topdirs = '"'$topdir'"'; \
 echo orgidxconfdir = $topdir/recoll-config) > "$confdir/recoll.conf"

recollindex -c "$confdir"
</programlisting>
    
    <para>The examples below will assume that you have a dataset under
    <filename>/home/me/mydata/</filename>, with the index configuration and
    data stored inside
    <filename>/home/me/mydata/recoll-confdir</filename>.</para> 
    
    <para>In order to be able to run queries after the dataset has been
    moved, you must ensure the following:
    <itemizedlist>
      <listitem><para>The main configuration file must define the
      <link linkend="RCL.INSTALL.CONFIG.RECOLLCONF.ORGIDXCONFDIR">orgidxconfdir</link>
      variable to be the original location of the configuration directory
      (<filename>orgidxconfdir=/home/me/mydata/recoll-confdir</filename>
      must be set inside
      <filename>/home/me/mydata/recoll-confdir/recoll.conf</filename> in
      the example above).</para></listitem>

      <listitem><para>The configuration directory must exist with the
      documents, somewhere under the directory which will be
      moved. E.g. if you are moving <filename>/home/me/mydata</filename>
      around, the configuration directory must exist somewhere below this
      point, for example
      <filename>/home/me/mydata/recoll-confdir</filename>, or
      <filename>/home/me/mydata/sub/recoll-confdir</filename>.</para></listitem>

      <listitem><para>You should keep the default locations for the index
      elements which are relative to the configuration directory by
      default (principally <literal>dbdir</literal>). Only the paths
      referring to the documents themselves
      (e.g. <literal>topdirs</literal> values) should be absolute (in
      general, they are only used when indexing anyway).</para></listitem>
      
    </itemizedlist>
    </para>

    <para>Only the first point needs an explicit user action, the &RCL;
    defaults are compatible with the third one, and the second is
    natural.</para>
    
    <para>If, after the move, the configuration directory needs to be
    copied out of the dataset (for example because the thumb drive is too
    slow), you can set the
    <link linkend="RCL.INSTALL.CONFIG.RECOLLCONF.CURIDXCONFDIR">curidxconfdir</link>,
    variable inside the copied configuration to
    define the location of the moved one. For example if
    <filename>/home/me/mydata</filename> is now mounted onto
    <filename>/media/me/somelabel</filename>, but the configuration
    directory and index has been copied to
    <filename>/tmp/tempconfig</filename>, you would set
    <literal>curidxconfdir</literal> to
    <filename>/media/me/somelabel/recoll-confdir</filename> inside
    <filename>/tmp/tempconfig/recoll.conf</filename>.
    <literal>orgidxconfdir</literal> would still be
    <filename>/home/me/mydata/recoll-confdir</filename> in the original and
    the copy.</para>

    <para>If you are regularly copying the configuration out of the
    dataset, it will be useful to write a script to automate the
    procedure. This can't really be done inside &RCL; because there are
    probably many possible variants. One example would be to copy the
    configuration to make it writable, but keep the index data on the
    medium because it is too big - in this case, the script would also need
    to set <literal>dbdir</literal> in the copied configuration.</para>
    
    <para>The same set of modifications (&RCL; 1.24) has also made it
    possible to run queries from a readonly configuration directory (with
    slightly reduced function of course, such as not recording the query
    history).</para>
  </simplesect>
  </sect1>

    <sect1 id="RCL.INDEXING.WebQUEUE">
      <title>&LIN;: indexing visited Web pages</title>

      <para>With the help of a <application>Firefox</application>
        extension, &RCL; can index the Internet pages that you visit. The
        extension has a long history: it was initially designed for
        the <application>Beagle</application> indexer, then adapted to
        &RCL; and
        the <application>Firefox</application> <application>XUL</application>
        API. The current version of the extension is located in
        the <ulink url="https://addons.mozilla.org/en-US/firefox/addon/recoll-we/">Mozilla
        add-ons repository</ulink> uses
        the <application>WebExtensions</application> API, and works with
        current <application>Firefox</application> versions.</para>

      <para>The extension works by copying visited Web pages to an indexing
        queue directory, which &RCL; then processes, storing the data into a
        local cache, then indexing it, then removing the file from the
        queue.</para>
      
      <note><title>The local cache is not an archive</title><para>As
          mentioned above, a copy of the indexed Web pages is retained by
          Recoll in a local cache (from which data is fetched for previews,
          or when resetting the index). The cache is not changed by an
          index reset, just read for indexing. The cache has a maximum
          size, which can be adjusted from the <guilabel>Index
          configuration</guilabel> / <guilabel>Web history</guilabel> panel
          (<literal>webcachemaxmbs</literal> parameter
          in <filename>recoll.conf</filename>). Once the maximum size is
          reached, old pages are erased to make room for new ones.  The
          pages which you want to keep indefinitely need to be explicitly
          archived elsewhere. Using a very high value for the cache size
          can avoid data erasure, but see the above 'Howto' page for more
          details and gotchas.</para></note>

      <para>The visited Web pages indexing feature can be enabled on the
        &RCL; side from the GUI <guilabel>Index configuration</guilabel>
        panel, or by editing the configuration file (set
        <varname>processwebqueue</varname> to 1).</para>

      <para>The &RCL; GUI has a tool to list and edit the contents of the
        Web cache. (<menuchoice><guimenu>Tools</guimenu><guimenuitem>Webcache
        editor</guimenuitem></menuchoice>)</para>
      <para>The <command>recollindex</command> command has two options to
        help manage the Web cache:</para>
      <itemizedlist>
        <listitem><option>--webcache-compact</option> will recover
            the space from erased entries. It may need to use twice the disk space
            currently needed for the Web cache.</listitem>
        <listitem><option>--webcache-burst <replaceable>destdir</replaceable></option>
            will extract all current entries into pairs of metadata and data
            files created
            inside <replaceable>destdir</replaceable></listitem>
      </itemizedlist>

      <para>You can find more details on Web indexing, its usage and configuration
        in a <ulink url="&FAQS;IndexWebHistory">Recoll 'Howto'
        entry</ulink>.</para> 


    </sect1>

    <sect1 id="RCL.INDEXING.EXTATTR">
      <title>&LIN;: using extended attributes</title>

      <para>User extended attributes are named pieces of information
      that most modern file systems can attach to any file.</para>

      <para>&RCL; processes extended attributes as document fields by
      default.</para>

      <para>A 
      <ulink url="http://www.freedesktop.org/wiki/CommonExtendedAttributes">
        freedesktop standard</ulink> defines a few special
        attributes, which are handled as such by &RCL;:
        <variablelist>
          <varlistentry>
            <term>mime_type</term>
            <listitem><para>If set, this overrides any other
            determination of the file MIME type.</para></listitem>
          </varlistentry>
          <varlistentry>
            <term>charset</term>
            <listitem><para>If set, this defines the file character set
            (mostly useful for plain text files).</para></listitem>
          </varlistentry>
        </variablelist>
      </para>

      <para>By default, other attributes are handled as &RCL; fields of the
      same name.</para>

      <para>On Linux, the <literal>user</literal> prefix is removed from
      the name.</para>

      <para>The name translation can be configured more precisely inside the
      <link linkend="RCL.INSTALL.CONFIG.FIELDS"><filename>fields</filename> configuration file</link>.
      </para>

    </sect1>

    <sect1 id="RCL.INDEXING.EXTTAGS">
      <title>&LIN;: importing external tags</title>

      <para>During indexing, it is possible to import metadata for each
      file by executing commands. This allows, for example, extracting tag
      data from an external application and storing it in a field for
      indexing.</para>

      <para>See the 
      <link linkend="RCL.INSTALL.CONFIG.RECOLLCONF.METADATACMDS">section about the <literal>metadatacmds</literal> field</link> 
      in the main configuration chapter for a description of the
      configuration syntax.</para>

      <para>For example, if you would want &RCL; to use tags managed by
      <application>tmsu</application> in a field named
      <replaceable>tags</replaceable>, you would add the following to the
      configuration file:</para>

      <programlisting>[/some/area/of/the/fs]
metadatacmds = ; <replaceable>tags</replaceable> = tmsu tags %f
      </programlisting>

      <note><para>Depending on the <application>tmsu</application> version,
      you may need/want to add options like
      <literal>--database=/some/db</literal>.</para></note>
      
      <para>You may want to restrict this processing to a subset of
      the directory tree, because it may slow down indexing a bit
      (<literal>[some/area/of/the/fs]</literal>).</para>
      <para>Note the initial semi-colon after the equal sign.</para>

      <para>In the example above, the output of <command>tmsu</command> is
      used to set a field named <replaceable>tags</replaceable>. The field
      name is arbitrary and could be <replaceable>tmsu</replaceable> or
      <replaceable>myfield</replaceable> just the same, but
      <replaceable>tags</replaceable> is an alias for the standard &RCL;
      <literal>keywords</literal> field, and the <command>tmsu</command>
      output will just augment its contents. This will avoid the need to
      extend the <link linkend="RCL.PROGRAM.FIELDS">field
      configuration</link>.</para>

      <para>Once re-indexing is performed (you will need to force the file
      reindexing, &RCL; will not detect the need by itself), you will be
      able to search from the query language, through any of its aliases:
      <replaceable>tags:some/alternate/values</replaceable> or
      <replaceable>tags:all,these,values</replaceable> (the compact field search
      syntax is supported for recoll 1.20 and later. For older versions,
      you would need to repeat the <replaceable>tags:</replaceable>
      specifier for each term, e.g.  <replaceable>tags:some</replaceable>
      <literal>OR</literal>
      <replaceable>tags:alternate</replaceable>).</para>

      <para>Tags changes will not be detected by
      the indexer if the file itself did not change. One possible
      workaround would be to update the file <literal>ctime</literal> when
      you modify the tags, which 
      would be consistent with how extended attributes function. A pair of
      <command>chmod</command> commands could accomplish this, or a
      <literal>touch -a</literal> . Alternatively, just
      couple the tag update with a
      <literal>recollindex -e -i</literal> <replaceable>/path/to/the/file</replaceable>.</para>

    </sect1>


    <sect1 id="RCL.INDEXING.PDF">
      <title>The PDF input handler</title>

      <para>The PDF format is very important for scientific and technical
        documentation, and document archival. It has extensive
        facilities for storing metadata along with the document, and these
        facilities are actually used in the real world.</para>

      <para>In consequence, the <command>rclpdf.py</command> PDF input
        handler has more complex capabilities than most others, and it is
        also more configurable. Specifically, <command>rclpdf.py</command>
        has the following features:
        <itemizedlist>
          <listitem><para>It can be configured to extract
              specific metadata tags from an XMP packet.</para></listitem>
          <listitem><para>It can extract PDF
              attachments.</para></listitem>
          <listitem><para>It can automatically perform
              OCR if the document text is empty. This is done by 
              executing an external program and is now described in a 
              <link linkend="RCL.INDEXING.OCR">separate
                section</link>, because the OCR framework can also be used
                with non-PDF image files.</para></listitem>
        </itemizedlist>
      </para>
      
      <sect2 id="RCL.INDEXING.PDF.XMP">
        <title>XMP fields extraction</title>

        <para>The <filename>rclpdf.py</filename> script in &RCL; version
        1.23.2 and later can extract XMP metadata fields by executing the
        <command>pdfinfo</command> command (usually found with
        <application>poppler-utils</application>). This is controlled by
        the
        <link linkend="RCL.INSTALL.CONFIG.RECOLLCONF.PDFEXTRAMETA">pdfextrameta</link>
        configuration variable, which specifies which tags to extract and,
        possibly, how to rename them.</para>

        <para>The
        <link linkend="RCL.INSTALL.CONFIG.RECOLLCONF.PDFEXTRAMETAFIX">pdfextrametafix</link>
        variable can be used to designate a file with Python code to edit
        the metadata fields (available for &RCL; 1.23.3 and later. 1.23.2
        has equivalent code inside the handler script). Example:</para>

        <programlisting>import sys
        import re

        class MetaFixer(object):
            def __init__(self):
                pass

            def metafix(self, nm, txt):
                if nm == 'bibtex:pages':
                    txt = re.sub(r'--', '-', txt)
                elif nm == 'someothername':
                    # do something else
                    pass
                elif nm == 'stillanother':
                    # etc.
                    pass
        
                return txt
            def wrapup(self, metaheaders):
                pass
        </programlisting>

        <para>If the 'metafix()' method is defined, it is called for each
        metadata field. A new MetaFixer object is created for each PDF
        document (so the object can keep state for, for example,
        eliminating duplicate values). If the 'wrapup()' method is defined, it
        is called at the end of XMP fields processing with the whole
        metadata as parameter, as an array of '(nm, val)' pairs, allowing
        an alternate approach for editing or adding/deleting fields.</para>
        
        <!-- <para> There is a <ulink url="&FAQS;PDFXMP.wiki">complete example of XMP
             tags setup</ulink>, including a  nice result list paragraph format in the 
             &RCL; Wiki </para> -->
        

      </sect2>

      <sect2 id="RCL.INDEXING.PDF.ATTACH">
        <title>PDF attachment indexing</title>

        <para>If <application>pdftk</application> is installed, and if the
          the
        <link linkend="RCL.INSTALL.CONFIG.RECOLLCONF.PDFATTACH">pdfattach</link>
        configuration variable is set, the PDF input handler will try to
        extract PDF attachments for indexing as sub-documents of the PDF
        file. This is disabled by default, because it slows down PDF
        indexing a bit even if not one attachment is ever found (PDF
        attachments are uncommon in my experience).</para>

      </sect2>
      
    </sect1>


    <sect1 id="RCL.INDEXING.OCR">
      <title>Recoll and OCR</title>

      <para>This is new in &RCL; 1.26.5. Older versions had a more limited,
      non-caching capability to execute an external OCR program in the PDF
      handler. The new function has the following features:

      <itemizedlist>
        <listitem><para>The OCR output is cached, stored as separate
        files. The caching is ultimately based on a hash value of the
        original file contents, so that it is immune to file renames. A
        first path-based layer ensures fast operation for unchanged
        (unmoved files), and the data hash (which is still orders of
        magnitude faster than OCR) is only re-computed if the file has
        moved. OCR is only performed if the file was not previously
        processed or if it changed.</para></listitem>
        <listitem><para>The support for a specific program is implemented
        in a simple Python module. It should be straightforward to add
        support for any OCR engine with a capability to run from the
        command line.</para></listitem>
        <listitem><para>Modules initially exist for
        <application>tesseract</application> (Linux and Windows), and
        <application>ABBYY FineReader</application> (Linux, tested with
        version 11). ABBYY FineReader is a commercial closed source
        program, but it sometimes perform better than
        tesseract.</para></listitem>
        <listitem><para>The OCR is currently only called from the PDF
        handler, but there should be no problem using it for other image
        types.</para></listitem>
      </itemizedlist>
    </para>

      <para>To enable this feature, you need to install one of
        the supported OCR applications
        (<application>tesseract</application>
        or <application>ABBYY</application>), enable OCR in the PDF
        handler, and tell &RCL; where the appropriate command resides. The
        last parts are done by setting configuration variables. See the
        <link linkend="RCL.INSTALL.CONFIG.RECOLLCONF.OCR">
        relevant section</link>. All parameters can be localized in
        subdirectories through the usual main configuration mechanism (path
        sections).</para>

    </sect1>


    <sect1 id="RCL.INDEXING.PERIODIC">
      <title>Periodic indexing</title>

      <simplesect id="RCL.INDEXING.PERIODIC.EXEC">
        <title>Running the indexer</title>

        <para>The <command>recollindex</command> program performs index
        updates. You can start it either from the command line or from the
        <guimenu>File</guimenu> menu in the <command>recoll</command> GUI
        program. When started from the GUI, the indexing will run on the
        same configuration <command>recoll</command> was started on. When
        started from the command line, <command>recollindex</command> will
        use the <envar>RECOLL_CONFDIR</envar> variable or accept a
        <option>-c</option> <replaceable>confdir</replaceable> option to
        specify a non-default configuration directory.</para>

        <para>If the <command>recoll</command> program finds no index
        when it starts, it will automatically start indexing (except
        if canceled).</para>

        <para>The GUI <menuchoice><guimenu>File</guimenu> </menuchoice>
        menu has entries to start or stop the current indexing
        operation. When indexing is not currently running, you have a
        choice between <guimenuitem>Update
            Index</guimenuitem> or <guimenuitem>Rebuild Index</guimenuitem>.
          The first choice only processes changed files, the second one
          erases the index before starting so that all files are
          processed.</para>

        <para>On Linux and Windows, the GUI can be used to manage the indexing
        operation. Stopping the indexer can be done
        from the <command>recoll</command> GUI
        <menuchoice>
          <guimenu>File</guimenu>
          <guimenuitem>Stop Indexing</guimenuitem>
        </menuchoice>
        menu entry.
        </para>

        <para>On Linux, the <command>recollindex</command> indexing process
        can be interrupted by sending an interrupt
        (<keysym>Ctrl-C</keysym>, SIGINT) or terminate (SIGTERM)
        signal. 
        </para>

        <para>When stopped, some time may elapse before
        <command>recollindex</command> exits, because it needs to properly
        flush and close the index.</para>
        
        <para>After an interruption, the index will be somewhat
        inconsistent because some operations which are normally
        performed at the end of the indexing pass will have been
        skipped (for example, the stemming and spelling databases
        will be inexistent or out of date). You just need to restart
        indexing at a later time to restore consistency. The
        indexing will restart at the interruption point (the full
        file tree will be traversed, but files that were indexed up
        to the interruption and for which the index is still up to
        date will not need to be reindexed).</para>
      </simplesect>

      <simplesect id="RCL.INDEXING.PERIODIC.CMDLINE">
          <title>recollindex command line</title>

        <para><command>recollindex</command> has many options
        which are listed in its
        <ulink url="https://www.lesbonscomptes.com/recoll/manpages/recollindex.1.html">manual page</ulink>.
        Only a few will be described here.</para>
        
        <para>Option <option>-z</option> will reset the index when
        starting. This is almost the same as destroying the index
        files (the nuance is that the &XAP; format version will not
        be changed).</para>
        <para>Option <option>-Z</option> will force the update of all
        documents without resetting the index first. This will not
        have the "clean start" aspect of <option>-z</option>, but
        the advantage is that the index will remain available for
        querying while it is rebuilt, which can be a significant
        advantage if it is very big (some installations need days
        for a full index rebuild).</para>

        <para>Option <option>-k</option> will force retrying files
        which previously failed to be indexed, for example because
        of a missing helper program.</para>

        <para>Of special interest also, maybe, are
        the <option>-i</option> and <option>-f</option>
        options. <option>-i</option> allows indexing an explicit
        list of files (given as command line parameters or read on
        <literal>stdin</literal>).  <option>-f</option> tells
        <command>recollindex</command> to ignore file selection
        parameters from the configuration. Together, these options
        allow building a custom file selection process for some area
        of the file system, by adding the top directory to the
        <varname>skippedPaths</varname> list and using an
        appropriate file selection method to build the file list to
        be fed to <command>recollindex</command>
        <option>-if</option>.  Trivial example:</para>

        <programlisting>
          find . -name indexable.txt -print | recollindex -if
        </programlisting>

        <para><command>recollindex</command> <option>-i</option> will 
        not descend into subdirectories specified as parameters, 
        but just add them as index entries. It is
        up to the external file selection method to build the complete
        file list.</para>
      </simplesect>

      <simplesect id="RCL.INDEXING.PERIODIC.AUTOMAT">
        <title>Linux: using <command>cron</command> to automate indexing</title>

        <para>The most common way to set up indexing is to have a cron
        task execute it every night. For example the following
        <filename>crontab</filename> entry would do it every day at
        3:30AM (supposing <command>recollindex</command> is in your
        PATH):

        <screen><![CDATA[
        30 3 * * * recollindex > /some/tmp/dir/recolltrace 2>&1
        ]]></screen>

        Or, using <command>anacron</command>:
        <screen><![CDATA[
        1  15  su mylogin -c "recollindex recollindex > /tmp/rcltraceme 2>&1"
        ]]></screen>
        </para>

        <para>The &RCL; GUI has dialogs to manage
        <filename>crontab</filename> entries for
        <command>recollindex</command>. You can reach them from the
        <menuchoice>
          <guimenu>Preferences</guimenu>
          <guimenuitem>Indexing Schedule</guimenuitem> 
        </menuchoice> 
        menu. They only 
        work with the good old <command>cron</command>, and do not give
        access to all features of <command>cron</command>
        scheduling. Entries created via the tool are marked with
        a <literal>RCLCRON_RCLINDEX=</literal> marker so that the tool
        knows which entries belong to it. As a side effect, this sets an
        environment variable for the process, but it's not actually used,
        this is just a marker.</para> 

        <para>The usual command to edit your
        <filename>crontab</filename> is <command>crontab</command>
        <option>-e</option> (which will usually start the
        <command>vi</command> editor to edit the file). You may have
        more sophisticated tools available on your system.</para>

        <para>Please be aware that there may be differences between your
        usual interactive command line environment and the one seen by
        crontab commands. Especially the PATH variable may be of
        concern. Please check the crontab manual pages about possible
        issues.</para>


      </simplesect>
    </sect1>

    <sect1 id="RCL.INDEXING.MONITOR">
      <title>&LIN;: real time indexing</title>

      <para>Real time monitoring/indexing is performed by starting the
      <command>recollindex</command> <option>-m</option> command.
      With this option, <command>recollindex</command> will detach
      from the terminal and become a daemon, permanently monitoring
      file changes and updating the index.</para>

      <para>In this situation, the <command>recoll</command>
      GUI <menuchoice><guimenu>File</guimenu></menuchoice> menu makes two
      operations available: <guimenuitem>Stop</guimenuitem>
      and <guimenuitem>Trigger incremental pass</guimenuitem>.
      </para>

      <para><guimenuitem>Trigger incremental pass</guimenuitem> has the
        same effect as restarting the indexer, and will cause a complete
        walk of the indexed area, processing the changed files, then switch
        to monitoring. This is only marginally useful, maybe in cases where
        the indexer is configured to delay updates, or to force an
        immediate rebuild of the stemming and phonetic data, which are only
        processed at intervals by the real time indexer.</para>

      <para>While it is convenient that data is indexed in real time,
      repeated indexing can generate a significant load on the
      system when files such as email folders change. Also,
      monitoring large file trees by itself significantly taxes
      system resources. You probably do not want to enable it if
      your system is short on resources. Periodic indexing is
      adequate in most cases.</para>

      <para>As of &RCL; 1.24, you can set the
      <link linkend="RCL.INSTALL.CONFIG.RECOLLCONF.MONITORDIRS">monitordirs</link>
      configuration variable to specify that only a subset of your indexed
      files will be monitored for instant indexing.  In this situation, an
      incremental pass on the full tree can be triggered by either
      restarting the indexer, or just running 
      <command>recollindex</command>, which will notify the running
      process. The <command>recoll</command> GUI also has a menu entry for
      this.</para>

      <simplesect id="RCL.INDEXING.MONITOR.START">
        <title>Automatic daemon start</title>

        <para>Under <application>KDE</application>,
        <application>Gnome</application> and some other desktop
        environments, the daemon can automatically started when you log
        in, by creating a desktop file inside the
        <filename>~/.config/autostart</filename> directory.  This can be
        done for you by the &RCL; GUI. Use the
        <guimenu>Preferences->Indexing Schedule</guimenu> menu.</para>
        
        <para>With older <application>X11</application> setups, starting
        the daemon is normally performed as part of the user session
        script.</para>

        <para>The <filename>rclmon.sh</filename> script can be used to
        easily start and stop the daemon. It can be found in the
        <filename>examples</filename> directory (typically
        <filename>/usr/local/[share/]recoll/examples</filename>).</para>

        <para>For example, a good old <application>xdm</application>-based
        session could have a <filename>.xsession</filename> script with the
        following lines  at the end:</para>

        <programlisting>recollconf=$HOME/.recoll-home
recolldata=/usr/local/share/recoll
RECOLL_CONFDIR=$recollconf $recolldata/examples/rclmon.sh start

fvwm 
</programlisting>

        <para>The indexing daemon gets started, then the window manager,
        for which the session waits.</para> <para>By default the
        indexing daemon will monitor the state of the X11 session, and
        exit when it finishes, it is not necessary to kill it
        explicitly. (The <application>X11</application> server
        monitoring can be disabled with option <option>-x</option> to
        <command>recollindex</command>).</para>

        <para>If you use the daemon completely out of an
        <application>X11</application> session, you need to add option
        <option>-x</option> to disable <application>X11</application>
        session monitoring (else the daemon will not start).</para>
      </simplesect>
      
      <simplesect id="RCL.INDEXING.MONITOR.DETAILS">
        <title>Miscellaneous details</title>

        <para>By default, the messages from the indexing daemon will be
        sent to the same file as those from the interactive commands
        (<literal>logfilename</literal>).  You may want to change this
        by setting the <varname>daemlogfilename</varname> and
        <varname>daemloglevel</varname> configuration parameters. Also
        the log file will only be truncated when the daemon starts. If
        the daemon runs permanently, the log file may grow quite big,
        depending on the log level.</para>

        <formalpara><title>Increasing resources for inotify</title>
        <para>On Linux systems, monitoring a big tree may need
        increasing the resources available to inotify, which are
        normally defined in <filename>/etc/sysctl.conf</filename>.
        <programlisting>
### inotify
#
# cat  /proc/sys/fs/inotify/max_queued_events   - 16384
# cat  /proc/sys/fs/inotify/max_user_instances  - 128
# cat  /proc/sys/fs/inotify/max_user_watches    - 16384
#
# -- Change to:
#
fs.inotify.max_queued_events=32768
fs.inotify.max_user_instances=256
fs.inotify.max_user_watches=32768
        </programlisting>
        
        Especially, you will need to trim your tree or adjust
        the <literal>max_user_watches</literal> value if indexing exits with
        a message about errno <literal>ENOSPC</literal> (28) from
        <function>inotify_add_watch</function>.
        </para>
        </formalpara>

        
        <formalpara><title>Slowing down the reindexing rate for fast changing
        files</title>
        <para>When using the real time monitor, it may happen that some
        files need to be indexed, but change so often that they impose an
        excessive load for the system.

        &RCL; provides a configuration option to specify the minimum
        time before which a file, specified by a wildcard pattern, cannot be
        reindexed. See the <varname>mondelaypatterns</varname> parameter in
        the <link linkend="RCL.INSTALL.CONFIG.RECOLLCONF.MISC">configuration section</link>.
        </para>
        </formalpara>
      
      </simplesect>
      
    </sect1>

  </chapter>

  <chapter id="RCL.SEARCH">
    <title>Searching</title>

    <sect1 id="RCL.SEARCH.INTRODUCTION">
      <title>Introduction</title>

      <para>Getting answers to specific queries is of course the whole
      point of &RCL;. The multiple provided interfaces always understand
      simple queries made of one or several words, and return appropriate
      results in most cases.</para>

      <para>In order to make the most of &RCL; though, it may be worthwhile
      to understand how it processes your input. Five different modes
      exist:
      <itemizedlist>
        <listitem><para>In <literal>All Terms</literal> mode, &RCL; looks
        for documents containing all your input terms.</para></listitem>
        <listitem><para><literal>Query Language</literal> mode behaves like

        <literal>All Terms</literal> in the absence of special input, but
        it can also do much more. This is the best mode for getting the
        most of &RCL;.</para></listitem>
        
        <listitem><para>In <literal>Any Term</literal> mode, &RCL; looks
        for documents containing any your input terms, preferring those
        which contain more.</para></listitem>
        
        <listitem><para>In <literal>File Name</literal> mode, &RCL; will
        only match file names, not content. Using a small subset of the
        index allows things like left-hand wildcards without performance
        issues, and may sometimes be useful.</para></listitem>

        <listitem><para>The GUI <literal>Advanced Search</literal> mode is
        actually not more powerful than the query language, but it helps
        you build complex queries without having to remember the language,
        and avoids any interpretation ambiguity, as it bypasses the user
        input parser.</para></listitem>

      </itemizedlist>
      </para>

      <para>These five input modes are supported by the different user
      interfaces which are described in the following sections.</para>
      
    </sect1>


    <sect1 id="RCL.SEARCH.GUI">
      <title>Searching with the Qt graphical user interface</title>

      <para>The <command>recoll</command> program provides the main user
        interface for searching. It is based on the
        <application>Qt</application> library.</para>

      <para><command>recoll</command> has two search interfaces:</para>
      <itemizedlist>
        <listitem><para>Simple search (the default, on the main screen) has
            a single entry field where you can enter multiple words.</para>
        </listitem>
        <listitem><para>Advanced search (a panel accessed through the
            <guilabel>Tools</guilabel> menu or the toolbox bar icon) has
            multiple entry fields, which you may use to build a logical
            condition, with additional filtering on file type, location
            in the file system, modification date, and size.</para>
        </listitem>
      </itemizedlist>

      <para>In most cases, you can enter the terms as you think them, even
      if they contain embedded punctuation or other non-textual characters
      (e.g. &RCL; can handle things like email addresses).</para>

      <para>The main case where you should enter text differently from
      how it is printed is for east-asian languages (Chinese,
      Japanese, Korean). Words composed of single or multiple
      characters should be entered separated by white space in this
      case (they would typically be printed without white
      space).</para>

      <para>Some searches can be quite complex, and you may want to re-use
      them later, perhaps with some tweaking. &RCL; can save and restore
      searches. See <link linkend="RCL.SEARCH.SAVING">Saving and restoring
      queries</link>.
      </para>

      <sect2 id="RCL.SEARCH.GUI.SIMPLE">
        <title>Simple search</title>

        <procedure>
          <step><para>Start the <command>recoll</command> program.</para>
          </step>
          <step><para>Possibly choose a search mode: <guilabel>Any
          term</guilabel>, <guilabel>All terms</guilabel>, 
          <guilabel>File name</guilabel> or
          <guilabel>Query language</guilabel>.</para>
          </step>
          <step><para>Enter search term(s) in the text field at the top of the
          window.</para>
          </step>
          <step><para>Click the <guilabel>Search</guilabel> button or
          hit the <keycap>Enter</keycap> key to start the search.</para>
          </step>
        </procedure>

        <para>The initial default search mode is <guilabel>Query
        language</guilabel>. Without special directives, this will look for
        documents containing all of the search terms (the ones with more
        terms will get better scores), just like the <guilabel>All
        terms</guilabel> mode. <guilabel>Any term</guilabel> will search
        for documents where at least one of the terms
        appear. <guilabel>File name</guilabel> will exclusively look for
        file names, not contents</para>

        <para>All search modes allow terms to be expanded with wildcards
        characters (<literal>*</literal>, <literal>?</literal>,
        <literal>[]</literal>). See the
        <link linkend="RCL.SEARCH.WILDCARDS">section about wildcards</link> for
        more details.</para>

        <para>In all modes except <guilabel>File name</guilabel>, you can
        search for exact phrases (adjacent words in a given order) by
        enclosing the input inside double quotes. Ex:
        <literal>"virtual reality"</literal>.</para>

        <para>The <guilabel>Query Language</guilabel> features are
        described in
        <link linkend="RCL.SEARCH.LANG">a separate section</link>.
        </para>  

        <para>When using a stripped index (the default), character case has
        no influence on search, except that you can disable stem expansion
        for any term by capitalizing it. Ie: a search for
        <literal>floor</literal> will also normally look for
        <literal>flooring</literal>, <literal>floored</literal>, etc., but
        a search for <literal>Floor</literal> will only look for
        <literal>floor</literal>, in any character case. Stemming can also
        be disabled globally in the preferences. When using a raw index,
        <link linkend="RCL.SEARCH.CASEDIAC">the rules are a bit more complicated</link>.</para>

        <para>&RCL; remembers the last few searches that you performed. You
        can directly access the search history by clicking the clock button
        on the right of the search entry, while the latter is
        empty. Otherwise, the history is used for entry completion (see
        next). Only the search texts are remembered, not the mode
        (all/any/file name).</para>

        <para>While text is entered in the search area,
        <command>recoll</command> will display possible completions,
        filtered from the history and the index search terms. This can be
        disabled with a GUI Preferences option.</para>

        <para>Double-clicking on a word in the result list or a preview
        window will insert it into the simple search entry field.</para>

        <para>You can cut and paste any text into an <guilabel>All
        terms</guilabel> or <guilabel>Any term</guilabel> search field,
        punctuation, newlines and all - except for wildcard characters
        (single <literal>?</literal> characters are ok). &RCL; will process
        it and produce a meaningful search. This is what most differentiates
        this mode from the <guilabel>Query Language</guilabel> mode, where
        you have to care about the syntax.</para>

        <para>You can use the <link linkend="RCL.SEARCH.GUI.COMPLEX"><menuchoice><guimenu>Tools</guimenu><guimenuitem>Advanced search</guimenuitem></menuchoice></link>
        dialog for more complex searches.</para>

        <para>The <guilabel>File name</guilabel> search mode will
        specifically look for file names. The point of having a separate
        file name search is that wild card expansion can be performed more
        efficiently on a small subset of the index (allowing wild cards on
        the left of terms without excessive cost). Things to know:
        <itemizedlist>
          <listitem><para>White space in the entry should match white
          space in the file name, and is not treated specially.</para>
          </listitem>
          <listitem><para>The search is insensitive to character case and
          accents, independently of the type of index.</para>
          </listitem>
          <listitem><para>An entry without any wild card
          character and not capitalized will be prepended and appended
          with '*' (ie: <replaceable>etc</replaceable> ->
          <replaceable>*etc*</replaceable>, but
          <replaceable>Etc</replaceable> ->
          <replaceable>etc</replaceable>).</para> 
          </listitem>
          <listitem><para>If you have a big index (many files),
          excessively generic fragments may result in inefficient
          searches.</para>
          </listitem>
        </itemizedlist>
        </para>

      </sect2>

      <sect2 id="RCL.SEARCH.GUI.RESLIST">
        <title>The result list</title>

        <para>After starting a search, a list of results will instantly
          be displayed in the main window.</para> 

        <para>By default, the document list is presented in order of
        relevance (how well the system estimates that the document
        matches the query). You can sort the result by ascending or
        descending date by using the vertical arrows in the toolbar.</para>

        <para>Clicking the <literal>Preview</literal> link for an entry
          will open an internal preview window for the document. Further
          <literal>Preview</literal> clicks for the same search will open
          tabs in the existing preview window. You can use
          <keycap>Shift</keycap>+Click to force the creation of another
          preview window, which may be useful to view the documents side
          by side. (You can also browse successive results in a single
          preview window by typing
          <keycap>Shift</keycap>+<keycap>ArrowUp/Down</keycap> in the
          window).</para> 

        <para>Clicking the <literal>Open</literal> link will
          start an external viewer for the document. By default, &RCL; lets
          the desktop choose the appropriate application for most document
          types. See 
          <link linkend="RCL.SEARCH.GUI.RESLIST.APPLICATIONS">further</link>
          for customizing the applications.</para>

        <para>You can click on the <literal>Query details</literal> link
          at the top of the results page to see the query actually 
          performed, after stem expansion and other processing.</para>

        <para>Double-clicking on any word inside the result list or a
          preview window will insert it into the simple search text.</para>

        <para>The result list is divided into pages (the size of which
          you can change in the preferences). Use the arrow buttons in the
          toolbar or the links at the bottom of the page to browse the
          results.</para>

        <para>The <literal>Preview</literal> and <literal>Open</literal>
          edit links may not be present for all entries, meaning that
          &RCL; has no configured way to preview a given file type (which
          was indexed by name only), or no configured external editor for
          the file type. This can sometimes be adjusted simply by tweaking
          the <link linkend="RCL.INSTALL.CONFIG.MIMEMAP">
            <filename>mimemap</filename></link>
          and  <link linkend="RCL.INSTALL.CONFIG.MIMEVIEW">
            <filename>mimeview</filename></link>
          configuration files (the latter can be modified with the user
          preferences dialog).</para>

        <para>The format of the result list entries is entirely
          configurable by using the preference dialog to 
        <link linkend="RCL.SEARCH.GUI.CUSTOM.RESLIST">
          edit an HTML fragment</link>.</para>

        <simplesect id="RCL.SEARCH.GUI.RESLIST.APPLICATIONS">
          <title>Customising the applications</title>

          <para>By default &RCL; lets the desktop choose what
            application should be used to open a given document, with
            exceptions.</para> 

          <para>The details of this behaviour can be customized with the
            <menuchoice>
              <guimenu>Preferences</guimenu>
              <guimenuitem>GUI configuration</guimenuitem>
              <guimenuitem>User interface</guimenuitem>
              <guimenuitem>Choose editor applications</guimenuitem>
            </menuchoice> dialog or by editing
            the <link linkend="RCL.INSTALL.CONFIG.MIMEVIEW">
              <filename>mimeview</filename> configuration file.</link></para>

          <para>When <guilabel>Use desktop preferences</guilabel>, at the
            top of the dialog, is checked, the desktop default is generally
            used, but there is a small default list of exceptions, for MIME
            types where the &RCL; choice should override the desktop
            one. These are applications which are well integrated with
            &RCL;, for example, on Linux, <application>evince</application>
            for viewing PDF and Postscript files because of its support for
            opening the document at a specific page and passing a search
            string as an argument. You can add or remove document types to
            the exceptions by using the dialog.</para>

          <para>If you prefer to completely customize the choice of
            applications, you can uncheck <guilabel>Use desktop
            preferences</guilabel>, in which case the &RCL; predefined
            applications will be used, and can be changed for each document
            type. This is probably not the most convenient approach in most
            cases.</para> 

          <para>In all cases, the applications choice dialog accepts
            multiple selections of MIME types in the top section, and lets
            you define how they are processed in the bottom one. In most
            cases, you will be using <literal>%f</literal> as a place
            holder to be replaced by the file name in the application
            command line.</para>

          <para>You may also change the choice of applications by editing
            the
            <link linkend="RCL.INSTALL.CONFIG.MIMEVIEW">
              <filename>mimeview</filename></link> 
            configuration file if you find this more convenient.</para>

          <para>Under &LIN;, each result list entry also has a right-click
            menu with an
            <guilabel>Open With</guilabel> entry. This lets you choose an
            application from the list of those which registered with the desktop
            for the document MIME type, on a case by case basis.</para>
        </simplesect>


        <sect3 id="RCL.SEARCH.GUI.RESLIST.SUGGS">
          <title>No results: the spelling suggestions</title>

          <para>When a search yields no result, and if the
          <application>aspell</application> dictionary is configured, &RCL;
          will try to check for misspellings among the query terms, and
          will propose lists of replacements. Clicking on one of the
          suggestions will replace the word and restart the search. You can
          hold any of the modifier keys (Ctrl, Shift, etc.) while clicking
          if you would rather stay on the suggestion screen because several
          terms need replacement.</para>

        </sect3>


        <sect3 id="RCL.SEARCH.GUI.RESULTLIST.MENU">
          <title>The result list right-click menu</title>

          <para>Apart from the preview and edit links, you can display a
          pop-up menu by right-clicking over a paragraph in the result
          list. This menu has the following entries:</para>

          <itemizedlist>
            <listitem><para><guilabel>Preview</guilabel></para></listitem>
            <listitem><para><guilabel>Open</guilabel></para></listitem>
            <listitem><para><guilabel>Open With</guilabel></para></listitem>
            <listitem><para><guilabel>Run Script</guilabel></para></listitem>
            <listitem><para><guilabel>Copy File Name</guilabel></para></listitem>
            <listitem><para><guilabel>Copy Url</guilabel></para></listitem>
            <listitem><para><guilabel>Save to File</guilabel></para></listitem>
            <listitem><para><guilabel>Find similar</guilabel></para></listitem>
            <listitem><para><guilabel>Preview Parent
            document</guilabel></para></listitem> 
            <listitem><para><guilabel>Open Parent
            document</guilabel></para></listitem> 
            <listitem><para><guilabel>Open Snippets
            Window</guilabel></para></listitem>  
          </itemizedlist>

          <para>The <guilabel>Preview</guilabel> and
          <guilabel>Open</guilabel> entries do the same thing as the 
          corresponding links.</para>

          <para><guilabel>Open With</guilabel> (&LIN;) lets you open the
          document with one of the applications claiming to be able to
          handle its MIME type (the information comes from
          the <literal>.desktop</literal> files
          in <filename>/usr/share/applications</filename>).</para>

          <para><guilabel>Run Script</guilabel> (&LIN;) allows starting an
          arbitrary command on the result file. It will only appear for
          results which are top-level
          files. See <link linkend="RCL.SEARCH.GUI.RUNSCRIPT">further</link>
          for a more detailed description.</para>

          <para>The <guilabel>Copy File Name</guilabel> and
          <guilabel>Copy Url</guilabel> copy the relevant data to the
          clipboard, for later pasting.</para> 

          <para><guilabel>Save to File</guilabel> allows saving the
          contents of a result document to a chosen file. This entry
          will only appear if the document does not correspond to an
          existing file, but is a subdocument inside such a file (ie: an
          email attachment). It is especially useful to extract attachments
          with no associated editor.</para> 

          <para>The <guilabel>Open/Preview Parent document</guilabel> entries
          allow working with the higher level document (e.g. the email
          message an attachment comes from). &RCL; is sometimes not totally
          accurate as to what it can or can't do in this area.  For example
          the <guilabel>Parent</guilabel> entry will also appear for an
          email which is part of an mbox folder file, but you can't actually
          visualize the mbox (there will be an error dialog if you
          try).</para>

          <para>If the document is a top-level file, <guilabel>Open
          Parent</guilabel> will start the default file manager on the
          enclosing filesystem directory.</para>

          <para>The <guilabel>Find similar</guilabel> entry will select
          a number of relevant term from the current document and enter
          them into the simple search field. You can then start a simple
          search, with a good chance of finding documents related to the
          current result. I can't remember a single instance where this
          function was actually useful to me...</para>

          <para id="RCL.SEARCH.GUI.RESULTLIST.MENU.SNIPPETS">The
          <guilabel>Open Snippets Window</guilabel> entry will only 
          appear for documents which support page breaks (typically
          PDF, Postscript, DVI). The snippets window lists extracts from
          the document, taken around search terms occurrences, along with the
          corresponding page number, as links which can be used to start
          the native viewer on the appropriate page. If the viewer supports
          it, its search function will also be primed with one of the
          search terms.</para>

        </sect3>

      </sect2>

      <sect2 id="RCL.SEARCH.GUI.RESTABLE">
        <title>The result table</title>

        <para>As an alternative to the result list, the results can also be
          displayed in spreadsheet-like fashion. You can switch to this
          presentation by clicking the table-like icon in the toolbar (this
          is a toggle, click again to restore the list).</para>

        <para>Clicking on the column headers will allow sorting by the
        values in the column. You can click again to invert the order, and
        use the header right-click menu to reset sorting to the default
        relevance order (you can also use the sort-by-date arrows to do
        this).</para>

        <para>Both the list and the table display the same underlying
        results. The sort order set from the table is still active if you
        switch back to the list mode. You can click twice on a date sort
        arrow to reset it from there.</para>

        <para>The header right-click menu allows adding or deleting
        columns. The columns can be resized, and their order can be changed
        (by dragging). All the changes are recorded when you quit
        <command>recoll</command></para> 
        
        <para>Hovering over a table row will update the detail area at the
        bottom of the window with the corresponding values. You can click
        the row to freeze the display. The bottom area is equivalent to a
        result list paragraph, with links for starting a preview or a
        native application, and an equivalent right-click menu. Typing
        <keycap>Esc</keycap> (the Escape key) will unfreeze the
        display.</para>

      </sect2>

      <sect2 id="RCL.SEARCH.GUI.RUNSCRIPT">
        <title>&LIN;: running arbitrary commands on result files</title> 

        <para>Apart from the <guilabel>Open</guilabel> and <guilabel>Open
        With</guilabel> operations, which allow starting an application on a
        result document (or a temporary copy), based on its MIME type, it is
        also possible to run arbitrary commands on results which are
        top-level files, using the <guilabel>Run Script</guilabel> entry in
        the results pop-up menu.</para>

        <para>The commands which will appear in the <guilabel>Run
        Script</guilabel> submenu must be defined by
        <literal>.desktop</literal> files inside the
        <filename>scripts</filename> subdirectory of the current
        configuration directory.</para>

        <para>Here follows an example of a <literal>.desktop</literal> file,
        which could be named for example,
        <filename>~/.recoll/scripts/myscript.desktop</filename> (the exact
        file name inside the directory is irrelevant):
        <programlisting>
          [Desktop Entry]
          Type=Application
          Name=MyFirstScript
          Exec=/home/me/bin/tryscript %F
          MimeType=*/*
        </programlisting>
        The <literal>Name</literal> attribute defines the label which will
        appear inside the <guilabel>Run Script</guilabel> menu. The
        <literal>Exec</literal> attribute defines the program to be run,
        which does not need to actually be a script, of course. The
        <literal>MimeType</literal> attribute is not used, but needs to exist.
        </para>

        <para>The commands defined this way can also be used from links
        inside the
        <link linkend="RCL.SEARCH.GUI.CUSTOM.RESLIST.PARA">result paragraph</link>.
        </para>
        
        <para>As an example, it might make sense to write a script which
        would move the document to the trash and purge it from the &RCL;
        index.</para>

      </sect2>

      <sect2 id="RCL.SEARCH.GUI.THUMBNAILS">
        <title>&LIN;: displaying thumbnails</title>

        <para>The default format for the result list entries and the
        detail area of the result table display an icon for each result
        document. The icon is either a generic one determined from the
        MIME type, or a thumbnail of the document appearance. Thumbnails
        are only displayed if found in the standard
        <application>freedesktop</application> location, where they would
        typically have been created by a file manager.</para>

        <para>Recoll has no capability to create thumbnails. A relatively
        simple trick is to use the <guilabel>Open parent
        document/folder</guilabel> entry in the result list popup
        menu. This should open a file manager window on the containing
        directory, which should in turn create the thumbnails (depending on
        your settings). Restarting the search should then display the
        thumbnails.</para>
        
        <para>There are also <ulink url="&FAQS;ResultsThumbnails.html">some
            pointers about thumbnail generation</ulink> in the &RCL;
            FAQ.</para> 

      </sect2>

      <sect2 id="RCL.SEARCH.GUI.PREVIEW">
        <title>The preview window</title>

        <para>The preview window opens when you first click a
        <literal>Preview</literal> link inside the result list.</para>

        <para>Subsequent preview requests for a given search open new
        tabs in the existing window (except if you hold the
        <keycap>Shift</keycap> key while clicking which will open a new
        window for side by side viewing).</para>
        
        <para>Starting another search and requesting a preview will
        create a new preview window. The old one stays open until you
        close it.</para>

        <para>You can close a preview tab by typing <keycap>Ctrl-W</keycap>
        (<keycap>Ctrl</keycap> + <keycap>W</keycap>) in the window. Closing
        the last tab, or using the window manager button in the top of the
        frame will also close the window.</para>

        <para>You can display successive or previous documents from the
        result list inside a preview tab by typing
        <keycap>Shift</keycap>+<keycap>Down</keycap> or
        <keycap>Shift</keycap>+<keycap>Up</keycap> (<keycap>Down</keycap>
        and <keycap>Up</keycap> are the arrow keys).</para> 

        <para>A right-click menu in the text area allows switching
        between displaying the main text or the contents of fields
        associated to the document (ie: author, abtract, etc.). This is
        especially useful in cases where the term match did not occur in
        the main text but in one of the fields. In the case of
        images, you can switch between three displays: the image
        itself, the image metadata as extracted
        by <command>exiftool</command> and the fields, which is the
        metadata stored in the index.</para>


        <para>You can print the current preview window contents by typing
        <keycap>Ctrl-P</keycap> (<keycap>Ctrl</keycap> +
        <keycap>P</keycap>) in  the window text.</para> 


        <sect3 id="RCL.SEARCH.GUI.PREVIEW.SEARCH">
          <title>Searching inside the preview</title>

          <para>The preview window has an internal search capability,
          mostly controlled by the panel at the bottom of the window,
          which works in two modes: as a classical editor incremental
          search, where we look for the text entered in the entry
          zone, or as a way to walk the matches between the document
          and the &RCL; query that found it.</para>

          <variablelist>
            <varlistentry>
              <term>Incremental text search</term>
              <listitem><para>The preview tabs have an internal incremental search
              function. You initiate the search either by typing a
              <keycap>/</keycap> (slash) or <keycap>CTL-F</keycap>
              inside the text area or by clicking into
              the <guilabel>Search for:</guilabel> text field and
              entering the search string. You can then use the 
              <guilabel>Next</guilabel>
              and <guilabel>Previous</guilabel> buttons 
              to find the next/previous occurrence. You can also type
              <keycap>F3</keycap> inside the text area to get to the next
              occurrence.</para>
              <para>If you have a search string entered and you use
              Ctrl-Up/Ctrl-Down to browse the results, the search is
              initiated for each successive document. If the string is
              found, the cursor will be positioned at the first
              occurrence of the search string.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term>Walking the match lists</term>
              <listitem><para>If the entry area is empty when you click
              the <guilabel>Next</guilabel>
              or <guilabel>Previous</guilabel> buttons, the editor will
              be scrolled to show the next match to any search term
              (the next highlighted zone). If you select a search group
              from the dropdown list and click <guilabel>Next</guilabel>
              or <guilabel>Previous</guilabel>, the match list for this
              group will be walked. This is not the same as a text
              search, because the occurrences will include non-exact
              matches (as caused by stemming or wildcards). The search
              will revert to the text mode as soon as you edit the
              entry area.</para></listitem>
            </varlistentry>
          </variablelist>


        </sect3>        
        
      </sect2>

      <sect2 id="RCL.SEARCH.GUI.FRAGBUTS">
        <title>The Query Fragments window</title>

        <para>Selecting the <menuchoice><guimenu>Tools</guimenu> 
        <guimenuitem>Query Fragments</guimenuitem></menuchoice> menu
        entry will open a window with radio- and check-buttons which
        can be used to activate query language fragments for
        filtering the current query. This can be useful if you have
        frequent reusable selectors, for example, filtering on
        alternate directories, or searching just one category of
        files, not covered by the standard category
        selectors.</para>

        <para>The contents of the window are entirely customizable, and
        defined by the contents of the <filename>fragbuts.xml</filename>
        file inside the configuration directory. The sample file
        distributed with &RCL; (which you should be able to find under
        <filename>/usr/share/recoll/examples/fragbuts.xml</filename>),
        contains an example which filters the results from the Web
        history.</para>


        <para>Here follows an example:
        <programlisting><![CDATA[
<?xml version="1.0" encoding="UTF-8"?>
<fragbuts version="1.0">

  <radiobuttons>
    <!-- Actually useful: toggle Web queue results inclusion -->
    <fragbut>
      <label>Include Web Results</label>
      <frag></frag>
    </fragbut>

    <fragbut>
      <label>Exclude Web Results</label>
      <frag>-rclbes:BGL</frag>
    </fragbut>

    <fragbut>
      <label>Only Web Results</label>
      <frag>rclbes:BGL</frag>
    </fragbut>

  </radiobuttons>

  <buttons>

    <fragbut>
      <label>Example: Year 2010</label>
      <frag>date:2010-01-01/2010-12-31</frag>
    </fragbut>

    <fragbut>
      <label>Example: c++ files</label>
      <frag>ext:cpp OR ext:cxx</frag>
    </fragbut>

    <fragbut>
      <label>Example: My Great Directory</label>
      <frag>dir:/my/great/directory</frag>
    </fragbut>

  </buttons>

</fragbuts>
        ]]></programlisting>
        </para>
        
        <para>Each <literal>radiobuttons</literal> or
        <literal>buttons</literal> section defines a line of
        checkbuttons or radiobuttons inside the window. Any number of
        buttons can be selected, but the radiobuttons in a line are
        exclusive.</para>
        
        <para>Each <literal>fragbut</literal> section defines the label
        for a button, and the Query Language fragment which will be
        added (as an AND filter) before performing the query if the
        button is active.</para>

      </sect2>


      <sect2 id="RCL.SEARCH.GUI.COMPLEX">
        <title>Complex/advanced search</title>

        <para>The advanced search dialog helps you build more complex queries
        without memorizing the search language constructs. It can be opened
        through the <guilabel>Tools</guilabel> menu or through the main
        toolbar.</para>

        <para>&RCL; keeps a history of searches. See 
        <link linkend="RCL.SEARCH.GUI.COMPLEX.HISTORY">Advanced search history</link>.
        </para> 

        <para>The dialog has two tabs:</para> 

        <orderedlist>

          <listitem><para>The first tab lets you specify terms to search
          for, and permits specifying multiple clauses which are combined
          to build the search.</para>
          </listitem> 

          <listitem><para>The second tab lets filter the results according
          to file size, date of modification, MIME type, or
          location.</para>
          </listitem>
          
        </orderedlist>

        <para>Click on the <guilabel>Start Search</guilabel> button in
        the advanced search dialog, or type <keycap>Enter</keycap> in
        any text field to start the search. The button in
        the main window always performs a simple search.</para>

        <para>Click on the <literal>Show query details</literal> link at
        the top of the result page to see the query expansion.</para>

        <sect3 id="RCL.SEARCH.GUI.COMPLEX.TERMS">
          <title>Advanced search: the "find" tab</title>

          <para>This part of the dialog lets you constructc a query by
          combining multiple clauses of different types.  Each entry
          field is configurable for the following modes:</para>

          <itemizedlist>
            <listitem><para>All terms.</para>
            </listitem>
            <listitem><para>Any term.</para>
            </listitem>
            <listitem><para>None of the terms.</para>
            </listitem>
            <listitem><para>Phrase (exact terms in order within an
            adjustable window).</para>
            </listitem>
            <listitem><para>Proximity (terms in any order within an
            adjustable window).</para>
            </listitem>
            <listitem><para>Filename search.</para>
            </listitem>
          </itemizedlist>

          <para>Additional entry fields can be created by clicking the
          <guilabel>Add clause</guilabel> button.</para>

          <para>When searching, the non-empty clauses will be
          combined either with an AND or an OR conjunction, depending on
          the choice made on the left (<guilabel>All clauses</guilabel> or
          <guilabel>Any clause</guilabel>).</para>

          <para>Entries of all types except "Phrase" and "Near" accept
          a mix of single words and phrases enclosed in double quotes. 
          Stemming and wildcard expansion will be performed as for simple
          search. </para>

          <formalpara><title>Phrases and Proximity searches</title>
          <para>These two clauses work in similar ways, with the difference
          that proximity searches do not impose an order on the words. In
          both cases, an adjustable number (slack) of non-matched words may
          be accepted between the searched ones (use the counter on the
          left to adjust this count). For phrases, the default count is
          zero (exact match). For proximity it is ten (meaning that two
          search terms, would be matched if found within a window of twelve
          words). Examples: a phrase search for
          <literal>quick fox</literal> with a slack of 0 will match
          <literal>quick fox</literal> but not
          <literal>quick brown fox</literal>. With
          a slack of 1 it will match the latter, but not
          <literal>fox quick</literal>. A proximity search for
          <literal>quick fox</literal> with the default slack will 
          match the latter, and also
          <literal>a fox is a cunning and quick animal</literal>.</para> 
          </formalpara>

        </sect3>

        <sect3 id="RCL.SEARCH.GUI.COMPLEX.FILTER">
          <title>Advanced search: the "filter" tab</title>

          <para>This part of the dialog has several sections which allow
          filtering the results of a search according to a number of
          criteria</para>

          <itemizedlist>

            <listitem>
              <para>The first section allows filtering by dates of last
              modification. You can specify both a minimum and a maximum
              date. The initial values are set according to the oldest and
              newest documents found in the index.</para>
            </listitem>

            <listitem>
              <para>The next section allows filtering the results by
              file size. There are two entries for minimum and maximum
              size. Enter decimal numbers. You can use suffix multipliers:
              <literal>k/K</literal>, <literal>m/M</literal>,
              <literal>g/G</literal>, <literal>t/T</literal> for 1E3, 1E6,
              1E9, 1E12 respectively.</para>
            </listitem>

            <listitem>   
              <para>The next section allows filtering the results by their MIME
              types, or MIME categories (ie: media/text/message/etc.).</para>
              <para>You can transfer the types between two boxes, to define
              which will be included or excluded by the search.</para>
              <para>The state of the file type selection can be saved as
              the default (the file type filter will not be activated at
              program start-up, but the lists will be in the restored
              state).</para> 
            </listitem>

            <listitem>
              <para>The bottom section allows restricting the search results to a
              sub-tree of the indexed area. You can use the
              <guilabel>Invert</guilabel> checkbox to search for files not in
              the sub-tree instead. If you use directory filtering often and on
              big subsets of the file system, you may think of setting up
              multiple indexes instead, as the performance may be
              better.</para>
              <para>You can use relative/partial paths for filtering. Ie,
              entering <literal>dirA/dirB</literal> would match either
              <filename>/dir1/dirA/dirB/myfile1</filename> or
              <filename>/dir2/dirA/dirB/someother/myfile2</filename>.</para> 
            </listitem>

          </itemizedlist>

        </sect3>

        <sect3 id="RCL.SEARCH.GUI.COMPLEX.HISTORY">
          <title>Advanced search history</title>

          <para>The advanced search tool memorizes the last 100 searches
          performed. You can walk the saved searches by using the up and
          down arrow keys while the keyboard focus belongs to the advanced
          search dialog.</para>

          <para>The complex search history can be erased, along with the
          one for simple search, by selecting the <menuchoice>
          <guimenu>File</guimenu>
          <guimenuitem>Erase Search History</guimenuitem>
          </menuchoice> menu entry.</para>

        </sect3>

      </sect2>

      <sect2 id="RCL.SEARCH.GUI.TERMEXPLORER">
        <title>The term explorer tool</title>

        <para>&RCL; automatically manages the expansion of search terms
        to their derivatives (ie: plural/singular, verb
        inflections). But there are other cases where the exact search
        term is not known. For example, you may not remember the exact
        spelling, or only know the beginning of the name.</para>

        <para>The search will only propose replacement terms with
        spelling variations when no matching document were found. In some
        cases, both proper spellings and mispellings are present in the
        index, and it may be interesting to look for them explicitly.</para>

        <para>The term explorer tool (started from the toolbar icon or
        from the <guilabel>Term explorer</guilabel> entry of the
        <guilabel>Tools</guilabel> menu) can be used to search the full index
        terms list. It has three modes of operations:</para>
        <variablelist>

          <varlistentry>
            <term>Wildcard</term>
            <listitem><para>In this mode of operation, you can enter a
            search string with shell-like wildcards (*, ?, []). ie:
            <replaceable>xapi*</replaceable> would display all index terms
            beginning with <replaceable>xapi</replaceable>. (More
            about wildcards
            <link linkend="RCL.SEARCH.WILDCARDS">here</link>
            ).</para></listitem> 
          </varlistentry>

          <varlistentry>
            <term>Regular expression</term>
            <listitem><para>This mode will accept a regular expression
            as input. Example:
            <replaceable>word[0-9]+</replaceable>. The expression is
            implicitly anchored at the beginning. Ie:
            <replaceable>press</replaceable> will match
            <replaceable>pression</replaceable> but not
            <replaceable>expression</replaceable>. You can use
            <replaceable>.*press</replaceable> to match the latter,
            but be aware that this will cause a full index term list
            scan, which can be quite long.</para>
            </listitem>
          </varlistentry>

          <varlistentry>
            <term>Stem expansion</term>
            <listitem><para>This mode will perform the usual stem expansion
            normally done as part user input processing. As such it is
            probably mostly useful to demonstrate the process.
            </para></listitem>
          </varlistentry>

          <varlistentry>
            <term>Spelling/Phonetic</term> <listitem><para>In this
            mode, you enter the term as you think it is spelled, and
            &RCL; will do its best to find index terms that sound like
            your entry. This mode uses the
            <application>Aspell</application> spelling application,
            which must be installed on your system for things to work
            (if your documents contain non-ascii characters, &RCL;
            needs an aspell version newer than 0.60 for UTF-8
            support). The language which is used to build the
            dictionary out of the index terms (which is done at the
            end of an indexing pass) is the one defined by your NLS
            environment. Weird things will probably happen if
            languages are mixed up.</para></listitem>
          </varlistentry>
          <varlistentry>
            <term>Show index statistics</term> <listitem><para>This will
                print a long list of boring numbers about the index</para>
          </listitem></varlistentry>
          <varlistentry>
            <term>List files which could not be indexed</term>
            <listitem><para>This will show the files which caused errors,
                usually because <command>recollindex</command> could not
                translate their format into text.</para>
          </listitem></varlistentry>
        </variablelist>

        <para>Note that in cases where &RCL; does not know the beginning
        of the string to search for (ie a wildcard expression like
        <replaceable>*coll</replaceable>), the expansion can take quite
        a long time because the full index term list will have to be
        processed. The expansion is currently limited at 10000 results for
        wildcards and regular expressions. It is possible to change the
        limit in the configuration file.</para>
        
        <para>Double-clicking on a term in the result list will insert
        it into the simple search entry field. You can also cut/paste
        between the result list and any entry field (the end of lines
        will be taken care of).</para>

      </sect2>

      <sect2 id="RCL.SEARCH.GUI.MULTIDB">
        <title>Multiple indexes</title>

        <para>See the section describing
        <link linkend="RCL.INDEXING.CONFIG.MULTIPLE">the use of multiple indexes</link> for
        generalities. Only the aspects concerning the
        <command>recoll</command> GUI are described here.</para>

        <para>A <command>recoll</command> program instance is always
        associated with a specific index, which is the one to be updated
        when requested from the <guimenu>File</guimenu> menu, but it can
        use any number of &RCL; indexes for searching. The external
        indexes can be selected through the <guilabel>external
        indexes</guilabel> tab in the preferences dialog.</para>

        <para>Index selection is performed in two phases. A set of all usable
        indexes must first be defined, and then the subset of indexes to be
        used for searching. These parameters are retained across program
        executions (there are kept separately for each &RCL;
        configuration). The set of all indexes is usually quite stable, while
        the active ones might typically be adjusted quite frequently.</para>

        <para>The main index (defined by
        <envar>RECOLL_CONFDIR</envar>) is always active. If this is
        undesirable, you can set up your base configuration to index
        an empty directory.</para>

        <para>When adding a new index to the set, you can select either
        a &RCL; configuration directory, or directly a &XAP; index
        directory. In the first case, the &XAP; index directory will
        be obtained from the selected configuration.</para>

        <para>As building the set of all indexes can be a little tedious
        when done through the user interface, you can use the
        <envar>RECOLL_EXTRA_DBS</envar> environment
        variable to provide an initial set. This might typically be
        set up by a system administrator so that every user does not
        have to do it. The variable should define a colon-separated list
        of index  directories, ie: 
        </para>
        <screen>export RECOLL_EXTRA_DBS=/some/place/xapiandb:/some/other/db</screen> 

        <para>Another environment
        variable, <envar>RECOLL_ACTIVE_EXTRA_DBS</envar> allows adding to
        the active list of indexes. This variable was suggested and
        implemented by a &RCL; user. It is mostly useful if you use scripts
        to mount external volumes with &RCL; indexes. By
        using <envar>RECOLL_EXTRA_DBS</envar>
        and <envar>RECOLL_ACTIVE_EXTRA_DBS</envar>, you can add and
        activate the index for the mounted volume when
        starting <command>recoll</command>. Unreachable indexes will 
        automatically be deactivated  when starting up.</para>

      </sect2>

      <sect2 id="RCL.SEARCH.GUI.HISTORY">
        <title>Document history</title>

        <para>Documents that you actually view (with the internal preview
        or an external tool) are entered into the document history,
        which is remembered.</para> 
        <para>You can display the history list by using
        the <guilabel>Tools/</guilabel><guilabel>Doc History</guilabel> menu
        entry.</para> 
        <para>You can erase the document history by using the
        <guilabel>Erase document history</guilabel> entry in the
        <guimenu>File</guimenu> menu.</para>

      </sect2>

      <sect2 id="RCL.SEARCH.GUI.SORT">
        <title>Sorting search results and collapsing duplicates</title>

        <para>The documents in a result list are normally sorted in
        order of relevance. It is possible to specify a different sort
        order, either by using the vertical arrows in the GUI toolbox to
        sort by date, or switching to the result table display and clicking
        on any header. The sort order chosen inside the result table
        remains active if you switch back to the result list, until you
        click one of the vertical arrows, until both are unchecked (you are
        back to sort by relevance).</para>

        <para>Sort parameters are remembered between program
        invocations, but result sorting is normally always inactive
        when the program starts. It is possible to keep the sorting
        activation state between program invocations by checking the
        <guilabel>Remember sort activation state</guilabel> option in
        the preferences.</para>

        <para>It is also possible to hide duplicate entries inside
        the result list (documents with the exact same contents as the
        displayed one). The test of identity is based on an MD5 hash
        of the document container, not only of the text contents (so
        that ie, a text document with an image added will not be a
        duplicate of the text only). Duplicates hiding is controlled
        by an entry in the <guilabel>GUI configuration</guilabel>
        dialog, and is off by default.</para>

        <para>When a result document does have undisplayed duplicates,
          a <literal>Dups</literal> link will be shown with the result list
          entry. Clicking the link will display the paths (URLs + ipaths)
          for the duplicate entries.</para>

      </sect2>

      <sect2 id="RCL.SEARCH.GUI.SHORTCUTS">
        <title>Keyboard shortcuts</title>

        <para>A number of common actions within the graphical interface can
          be triggered through keyboard shortcuts. As of &RCL; 1.29, many
          of the shortcut values can be customised from a screen in the GUI
          preferences. Most shortcuts are specific to a given context
          (e.g. within a preview window, within the result table).</para>

        <table frame='all'>
          <title>Keyboard shortcuts</title>
          <tgroup cols='2' align='left' colsep='1' rowsep='1'>
            <colspec colname='c1'/>
            <colspec colname='c2'/>
            <thead>
              <row><entry>Description</entry><entry>Default value</entry></row>
            </thead>

            <tbody>

              <row><entry namest="c1" nameend="c2">
                  <command>Context: almost everywhere</command></entry></row> 
              <row>
                <entry>Program exit</entry>
                <entry>Ctrl+Q</entry>
              </row>

              <row><entry namest="c1" nameend="c2">
                  <command>Context: advanced search</command></entry></row> 
              <row>
                <entry>Load the next entry from the search history</entry>
                <entry>Up</entry>
              </row>
              <row>
                <entry>Load the previous entry from the search history</entry>
                <entry>Down</entry>
              </row>

              <row><entry namest="c1" nameend="c2">
                  <command>Context: main window</command></entry>
              </row>
              <row>
                <entry>Clear search. This will move the keyboard cursor to
                the simple search entry and erase the current text</entry>
                <entry>Ctrl+S</entry>
              </row>
              <row>
                <entry>Move the keyboard cursor to the search entry area
                without erasing the current text</entry>
                <entry>Ctrl+L</entry>
              </row>
              <row>
                <entry>Move the keyboard cursor to the search entry area
                without erasing the current text</entry>
                <entry>Ctrl+Shift+S</entry>
              </row>
              <row>
                <entry>Toggle displaying the current results as a table or
                as a list</entry>
                <entry>Ctrl+T</entry>
              </row>

              <row><entry namest="c1" nameend="c2">
                  <command>Context: main window, when showing the results
                    as a table</command></entry>
              </row>
              <row>
                <entry>Move the keyboard cursor to currently the selected row
                in the table, or to the first one if none is selected</entry>
                <entry>Ctrl+R</entry>
              </row>
              <row>
                <entry>Jump to row 0-9 or a-z in the table</entry>
                <entry>Ctrl+[0-9] or Ctrl+Shift+[a-z]</entry>
              </row>
              <row>
                <entry>Cancel the current selection</entry><entry>Esc</entry>
              </row>


              <row><entry namest="c1" nameend="c2">
                  <command>Context: preview window</command></entry> 
              </row>
              <row>
                <entry>Close the preview window</entry>
                <entry>Esc</entry>
              </row>
              <row>
                <entry>Close the current tab</entry>
                <entry>Ctrl+W</entry>
              </row>
              <row>
                <entry>Open a print dialog for the current tab contents</entry>
                <entry>Ctrl+P</entry>
              </row>
              <row>
                <entry>Load the next result from the list to the current tab</entry>
                <entry>Shift+Down</entry>
              </row>
              <row>
                <entry>Load the previous result from the list to the current tab</entry>
                <entry>Shift+Up</entry>
              </row>

              <row><entry namest="c1" nameend="c2">
                  <command>Context: result table</command></entry></row>
              <row>
                <entry>Copy the text contained in the selected
                  document to the clipboard</entry> <entry>Ctrl+G</entry>
              </row>
              <row>
                <entry>Open the current document and exit Recoll</entry>
                <entry>Ctrl+Shift+O</entry>
              </row>
              <row>
                <entry>Open the current document</entry>
                <entry>Ctrl+O</entry>
              </row>
              <row>
                <entry>Show a full preview for the current document</entry>
                <entry>Ctrl+D</entry>
              </row>
              <row>
                <entry>Toggle showing the column names</entry>
                <entry>Ctrl+H</entry>
              </row>
              <row>
                <entry>Show a snippets (keyword in context) list for the current document</entry>
                <entry>Ctrl+E</entry>
              </row>
              <row>
                <entry>Toggle showing the row letters/numbers</entry>
                <entry>Ctrl+V</entry>
              </row>

              <row><entry namest="c1" nameend="c2">
                  <command>Context: snippets window</command></entry></row>
              <row>
                <entry>Close the snippets window</entry>
                <entry>Esc</entry>
              </row>
              <row>
                <entry>Find in the snippets list (method #1)</entry>
                <entry>Ctrl+F</entry>
              </row>
              <row>
                <entry>Find in the snippets list (method #2)</entry>
                <entry>/</entry>
              </row>
              <row>
                <entry>Find the next instance of the search term</entry>
                <entry>F3</entry>
              </row>
              <row>
                <entry>Find the previous instance of the search term</entry>
                <entry>Shift+F3</entry>
              </row>
            </tbody>
          </tgroup>
        </table>

      </sect2>

      <sect2 id="RCL.SEARCH.GUI.TIPS">
        <title>Search tips</title>

        <sect3 id="RCL.SEARCH.GUI.TIPS.TERMS">
          <title>Terms and search expansion</title>

          <formalpara><title>Term completion</title>
          <para>While typing into the
          simple search entry, a popup menu will appear and show
          completions for the current string. Values preceded by a clock
          icon come from the history, those preceded by a magnifier icon
          come from the index terms. This can be disabled in the
          preferences.</para> 
          </formalpara>

          <formalpara><title>Picking up new terms from result or preview 
          text</title>
          <para>Double-clicking on a word in the result list or in a
          preview window will copy it to the simple search entry field.</para>
          </formalpara>

          <formalpara><title>Wildcards</title>
          <para>Wildcards can be used inside search terms in all forms
          of searches. <link linkend="RCL.SEARCH.WILDCARDS">More about wildcards</link>.
          </para>
          </formalpara>

          <formalpara><title>Automatic suffixes</title>
          <para>Words like <literal>odt</literal> or <literal>ods</literal>
          can be automatically turned into query language
          <literal>ext:xxx</literal> clauses. This can be enabled in the
          <guilabel>Search preferences</guilabel> panel in the GUI.
          </para>
          </formalpara>

          <formalpara><title>Disabling stem expansion</title>
          <para>Entering a capitalized word in any search field will prevent
          stem expansion (no search for
          <literal>gardening</literal> if you enter
          <literal>Garden</literal> instead of
          <literal>garden</literal>). This is the only case where
          character case should make a difference for a &RCL;
          search. You can also disable stem expansion or change the
          stemming language in the preferences.</para>
          </formalpara>

          <formalpara><title>Finding related documents</title>
          <para>Selecting the <guilabel>Find similar documents</guilabel> entry
          in the result list paragraph right-click menu will select a
          set of "interesting" terms from the current result, and insert
          them into the simple search entry field. You can then possibly
          edit the list and start a search to find documents which may
          be apparented to the current result.</para>
          </formalpara>

          <formalpara><title>File names</title>
          <para>File names are added as terms during indexing, and you can
          specify them as ordinary terms in normal search fields (&RCL; used
          to index all directories in the file path as terms. This has been
          abandoned as it did not seem really useful). Alternatively, you
          can use the specific file name search which will
          <emphasis>only</emphasis> look for file names, and may be
          faster than the generic search especially when using wildcards.</para>
          </formalpara>

        </sect3>


        <sect3 id="RCL.SEARCH.GUI.TIPS.PHRASES">
          <title>Working with phrases and proximity</title>

          <formalpara><title>Phrases searches</title>
            <para>A phrase can be
              looked for by enclosing a number of terms in double
              quotes. Example: <literal>"user manual"</literal> will look only
              for occurrences of <literal>user</literal> immediately followed
              by <literal>manual</literal>. You can use
              the <guilabel>"Phrase"</guilabel> field of the advanced search
              dialog to the same effect. Phrases can be entered along simple
              terms in all simple or advanced search entry fields,
              except <guilabel>"Phrase"</guilabel>. </para></formalpara>

          <formalpara><title>Proximity searches</title>
          <para>A proximity search differs from a phrase search in that 
            it does not impose an order on the terms. Proximity searches
            can be entered by specifying
            the <guilabel>"Proximity"</guilabel> type in the advanced
            search, or by postfixing a phrase search with a 'p'. Example:
            "user manual"p would also match "manual user". Also
            see <link linkend="RCL.SEARCH.LANG.MODIFIERS">the modifier
            section</link> from the query language
            documentation.</para></formalpara>

          <formalpara><title>AutoPhrases</title>
            <para>This option can be set in the preferences dialog. If it is
              set, a phrase will be automatically built and added to simple
              searches when looking for <literal>Any terms</literal>. This
              will not change radically the results, but will give a relevance
              boost to the results where the search terms appear as a
              phrase. Ie: searching for <literal>virtual reality</literal>
              will still find all documents where either
              <literal>virtual</literal> or <literal>reality</literal> or 
              both appear, but those which contain
              <literal>virtual reality</literal> should appear sooner in the
              list.</para></formalpara>

          <para>Phrase searches can slow down a query if most of the
            terms in the phrase are common. If
            the <varname>autophrase</varname> option is on, very common
            terms will be removed from the automatically constructed
            phrase. The removal threshold can be adjusted from the search
            preferences.</para>

          <formalpara><title>Phrases and abbreviations</title> 
            <para>Dotted abbreviations like
              <literal>I.B.M.</literal> are also automatically indexed as a
              word without the dots: <literal>IBM</literal>. Searching for
              the word inside a phrase (ie: <literal>"the IBM
              company"</literal>) will only match the dotted abrreviation
              if you increase the phrase slack (using the advanced search
              panel control, or the <literal>o</literal> query language
              modifier). Literal occurrences of the word will be matched
              normally.</para>
          </formalpara>

        </sect3>

        <sect3 id="RCL.SEARCH.GUI.TIPS.MISC">
          <title>Others</title>

          <formalpara><title>Using fields</title>
          <para>You can use the <link linkend="RCL.SEARCH.LANG">query
              language </link> and field specifications
            to only search certain parts of documents. This can be
            especially helpful with email, for example only searching
            emails from a specific originator:
            <literal>search tips from:helpfulgui</literal>
          </para></formalpara>

          <formalpara><title>Adjusting the result table columns</title>
          <para>When displaying results in table mode, you can use a
          right click on the table headers to activate a pop-up menu
          which will let you adjust what columns are displayed. You can
          drag the column headers to adjust their order. You can click
          them to sort by the field displayed in the column.  You can
          also save the result list in CSV format.</para> 
          </formalpara>


          <formalpara><title>Changing the GUI geometry</title>
          <para>It is possible to configure the GUI in wide form
          factor by dragging the toolbars to one of the sides (their
          location is remembered between sessions), and moving the
          category filters to a menu (can be set in the 
          <menuchoice>
            <guimenu>Preferences</guimenu>
            <guimenuitem>GUI configuration</guimenuitem>
            <guimenuitem>User interface</guimenuitem>
          </menuchoice> panel).</para>
          </formalpara>

          <formalpara><title>Query explanation</title>
          <para>You can get an exact description of what the query
          looked for, including stem expansion, and Boolean operators
          used, by clicking on the result list header.</para>
          </formalpara>

          <formalpara><title>Advanced search history</title> <para>You can
              display any of the last 100 complex searches performed by
              using the up and down arrow keys while the advanced search
              panel is active.</para>
          </formalpara>
          
          <formalpara><title>Forced opening of a preview window</title>
          <para>You can use <keycap>Shift</keycap>+Click on a result list
          <literal>Preview</literal> link to force the creation of a
          preview window instead of a new tab in the existing one.</para>
          </formalpara>

        </sect3>
      </sect2>

      <sect2 id="RCL.SEARCH.SAVING">
        <title>Saving and restoring queries (1.21 and later)</title>

        <para>Both simple and advanced query dialogs save recent
        history, but the amount is limited: old queries will eventually
        be forgotten. Also, important queries may be difficult to find
        among others. This is why both types of queries can also be
        explicitly saved to files, from the GUI menus:
        <menuchoice>
          <guimenu>File</guimenu>
          <guimenuitem>Save last query / Load last query</guimenuitem>
        </menuchoice>
        </para>

        <para>The default location for saved queries is a subdirectory
        of the current configuration directory, but saved queries are
        ordinary files and can be written or moved anywhere.</para>

        <para>Some of the saved query parameters are part of the
        preferences (e.g. <literal>autophrase</literal> or the active
        external indexes), and may differ when the query is
        loaded from the time it was saved. In this case, &RCL; will warn
        of the differences, but will not change the user
        preferences.</para>

      </sect2>

      <sect2 id="RCL.SEARCH.GUI.CUSTOM">
        <title>Customizing the search interface</title>

        <para>You can customize some aspects of the search interface by using
        the <guimenu>GUI configuration</guimenu> entry in the
        <guimenu>Preferences</guimenu> menu.</para>

        <para>There are several tabs in the dialog, dealing with the
        interface itself, the parameters used for searching and
        returning results, and what indexes are searched.</para> 


        <formalpara id="RCL.SEARCH.GUI.CUSTOM.UI">
          <title>User interface parameters:</title>
          <para>
            <itemizedlist>

              <listitem><para><guilabel>Highlight color for query
              terms</guilabel>: Terms from the user query are highlighted in
              the result list samples and the preview window. The color can
              be chosen here. Any Qt color string should work (ie
              <literal>red</literal>, <literal>#ff0000</literal>). The
              default is <literal>blue</literal>.</para>
              </listitem>

              <listitem><para><guilabel>Style sheet</guilabel>:
              The name of a <application>Qt</application> style sheet
              text file which is applied to the whole Recoll application
              on startup. The default value is empty, but there is a
              skeleton style sheet (<filename>recoll.qss</filename>)
              inside the <filename>/usr/share/recoll/examples</filename>
              directory. Using a style sheet, you can change most
              <command>recoll</command> graphical parameters:
              colors, fonts, etc. See the sample file for a few
              simple examples.</para> 
              <para>You should be aware that parameters (e.g.: the
              background color) set inside the &RCL; GUI style sheet
              will override global system preferences, with possible
              strange side effects: for example if you set the
              foreground to a light color and the background to a
              dark one in the desktop preferences, but only the
              background is set inside the &RCL; style sheet, and it
              is light too, then text will appear light-on-light
              inside the &RCL; GUI.</para>
              </listitem>

              <listitem><para><guilabel>Maximum text size highlighted for
              preview</guilabel> Inserting highlights on search term inside
              the text before inserting it in the preview window involves
              quite a lot of processing, and can be disabled over the given
              text size to speed up loading.</para>
              </listitem>

              <listitem><para><guilabel>Prefer HTML to plain text for
              preview</guilabel> if set, Recoll will display HTML as such
              inside the preview window. If this causes problems with the Qt
              HTML display, you can uncheck it to display the plain text
              version instead. </para>
              </listitem>

              <listitem><para><guilabel>Activate links in
              preview</guilabel> if set, Recoll will turn HTTP links found
              inside plain text into proper HTML anchors, and clicking a
              link inside a preview window will start the default browser
              on the link target.</para> </listitem>

              <listitem><para><guilabel>Plain text to HTML line
              style</guilabel>: when displaying plain text inside the
              preview window, &RCL; tries to preserve some of the original
              text line breaks and indentation. It can either use PRE HTML
              tags, which will well preserve the indentation but will force
              horizontal scrolling for long lines, or use BR tags to break
              at the original line breaks, which will let the editor
              introduce other line breaks according to the window width,
              but will lose some of the original indentation. The third
              option has been available in recent releases and is probably
              now the best one: use PRE tags with line wrapping.</para>
              </listitem>

              <listitem><para><guilabel>Choose editor
              application</guilabel>: this opens a dialog which allows you
              to select the application to be used to open each MIME
              type. The default is to use the <command>xdg-open</command>
              utility, but you can use this dialog to override it, setting
              exceptions for MIME types that will still be opened according
              to &RCL; preferences. This is useful for passing parameters
              like page numbers or search strings to applications that
              support them (e.g. <application>evince</application>). This
              cannot be done with <command>xdg-open</command> which only
              supports passing one parameter.</para>
              </listitem>

              <listitem><para><guilabel>Disable Qt autocompletion in search
              entry</guilabel>: this will disable the completion popup. Il
              will only appear, and display the full history, either if you
              enter only white space in the search area, or if you click
              the clock button on the right of the area.</para>
              </listitem>

              <listitem><para><guilabel>Document filter choice
              style</guilabel>: this will let you choose if the document
              categories are displayed as a list or a set of buttons, or a
              menu.</para>
              </listitem>

              <listitem><para><guilabel>Start with simple search
              mode</guilabel>: this lets you choose the value of the simple
              search type on program startup. Either a fixed value
              (e.g. <literal>Query Language</literal>, or the value in use
              when the program last exited.</para></listitem>

              <listitem><para><guilabel>Start with advanced search dialog open
              </guilabel>: If you use this dialog frequently, checking
              the entries will get it to open when recoll starts.</para>
              </listitem>
              
              <listitem><para><guilabel>Remember sort activation
              state</guilabel> if set, Recoll will remember the sort tool
              stat between invocations. It normally starts with sorting
              disabled.</para>
              </listitem>

            </itemizedlist>
          </para>
        </formalpara>


        <formalpara id="RCL.SEARCH.GUI.CUSTOM.RL">
          <title>Result list parameters:</title>
          <para>
            <itemizedlist>
              
              <listitem><para><guilabel>Number of results in a result
              page</guilabel></para>
              </listitem>

              <listitem><para><guilabel>Result list font</guilabel>: There is
              quite a lot of information shown in the result list, and you
              may want to customize the font and/or font size. The rest of
              the fonts used by &RCL; are determined by your generic Qt
              config (try the <command>qtconfig</command> command).</para>
              </listitem>

              <listitem id="RCL.SEARCH.GUI.CUSTOM.RESULTPARA">
                <para><guilabel>Edit result list paragraph format string</guilabel>:
                allows you to change the presentation of each result list
                entry. See the
                <link linkend="RCL.SEARCH.GUI.CUSTOM.RESLIST">result list customisation section</link>.
                </para>
              </listitem>

              <listitem id="RCL.SEARCH.GUI.CUSTOM.RESULTHEAD">
                <para><guilabel>Edit result page HTML header insert</guilabel>:
                allows you to define text inserted at the end of the result
                page HTML header.  
                More detail in the
                <link linkend="RCL.SEARCH.GUI.CUSTOM.RESLIST">result list customisation section</link>.
                </para>
              </listitem>

              <listitem>
                <para><guilabel>Date format</guilabel>: allows specifying the
                format used for displaying dates inside the result list. This
                should be specified as an strftime() string (man strftime).</para>
              </listitem>

              <listitem id="RCL.SEARCH.GUI.CUSTOM.ABSSEP">
                <para><guilabel>Abstract snippet separator</guilabel>:
                for synthetic abstracts built from index data, which are
                usually made of several snippets from different parts of the
                document, this defines the snippet separator, an ellipsis by
                default. </para>
              </listitem>

          </itemizedlist></para>
        </formalpara>

        <formalpara id="RCL.SEARCH.GUI.CUSTOM.SEARCH">
          <title>Search parameters:</title>
          <para>
            <itemizedlist>

              <listitem><para><guilabel>Hide duplicate results</guilabel>:
              decides if result list entries are shown for identical
              documents found in different places.</para>
              </listitem>

              <listitem><para><guilabel>Stemming language</guilabel>:
              stemming obviously depends on the document's language. This
              listbox will let you chose among the stemming databases which
              were built during indexing (this is set in the
              <link linkend="RCL.INSTALL.CONFIG.RECOLLCONF">main configuration file</link>), 
              or later added with
              <command>recollindex -s</command> (See the recollindex
              manual). Stemming languages
              which are dynamically added will be deleted at the next
              indexing pass unless they are also added in the configuration
              file.</para>
              </listitem>

              <listitem><para>
                <guilabel>Automatically add phrase to simple searches</guilabel>:
                a phrase will be automatically built and
              added to simple searches when looking for
              <literal>Any terms</literal>. This will give a relevance
              boost to the results where the search terms appear as a
              phrase (consecutive and in order).</para>
              </listitem>

              <listitem><para><guilabel>Autophrase term frequency threshold
              percentage</guilabel>: very frequent terms should not be included
              in automatic phrase searches for performance reasons. The
              parameter defines the cutoff percentage (percentage of the
              documents where the term appears).</para>
              </listitem>

              <listitem><para><guilabel>Replace abstracts from
              documents</guilabel>: this decides if we should synthesize and
              display an abstract in place of an explicit abstract found
              within the document itself.</para>
              </listitem>

              <listitem><para><guilabel>Dynamically build
              abstracts</guilabel>: this decides if &RCL; tries to build
              document abstracts (lists of <emphasis>snippets</emphasis>)
              when displaying the result list. Abstracts are constructed by
              taking context from the document information, around the search
              terms.</para>
              </listitem>

              <listitem><para><guilabel>Synthetic abstract size</guilabel>:
              adjust to taste...</para>
              </listitem>

              <listitem><para><guilabel>Synthetic abstract context
              words</guilabel>: how many words should be displayed around
              each term occurrence.</para>
              </listitem>

              <listitem><para><guilabel>Query language magic file name 
              suffixes</guilabel>: a list of words which automatically get
              turned into <literal>ext:xxx</literal> file name suffix clauses
              when starting a query language query (e.g.:
              <literal>doc xls xlsx...</literal>). 
              This will save some typing for people who
              use file types a lot when querying.</para>
              </listitem>
            </itemizedlist>
          </para>
        </formalpara>

        <formalpara id="RCL.SEARCH.GUI.CUSTOM.EXTRADB">
          <title>External indexes:</title> 
          <para>This panel will let you browse for additional indexes
          that you may want to search. External indexes are designated by
          their database directory (ie:
          <filename>/home/someothergui/.recoll/xapiandb</filename>,
          <filename>/usr/local/recollglobal/xapiandb</filename>).</para>
        </formalpara>

        <para>Once entered, the indexes will appear in the
        <guilabel>External indexes</guilabel> list, and you can
        chose which ones you want to use at any moment by checking or
        unchecking their entries.</para> 

        <para>Your main database (the one the current configuration
        indexes to), is always implicitly active. If this is not
        desirable, you can set up your configuration so that it indexes,
        for example, an empty directory. An alternative indexer may also
        need to implement a way of purging the index from stale data,
        </para>

        <sect3 id="RCL.SEARCH.GUI.CUSTOM.RESLIST">
          <title>The result list format</title>

          <para>Recoll normally uses a full function HTML processor to
            display the result list and the 
          <link linkend="RCL.SEARCH.GUI.RESULTLIST.MENU.SNIPPETS">
            snippets window</link>. Depending on the version, this may be
          based on either Qt WebKit or Qt WebEngine.
          It is then possible to completely customise the result list with full
          support for CSS and Javascript.</para>

          <para>It is also possible to build &RCL; to use a simpler Qt
            QTextBrowser widget to display the HTML, which may be necessary
            if the ones above are not ported on the system, or to reduce
            the application size and dependencies. There are limits to what
            you can do in this case, but it is still possible to decide
            what data each result will contain, and how it will be
            displayed.</para>

          <para>The result list presentation can be customized
            by adjusting two elements:

          <itemizedlist>
            <listitem><para>The paragraph format</para></listitem>
            <listitem><para>HTML code inside the header section. For
            versions 1.21 and later, this is also used for the
            <link linkend="RCL.SEARCH.GUI.RESULTLIST.MENU.SNIPPETS">snippets window</link>.
            </para></listitem>
          </itemizedlist>
          The paragraph format and the header fragment can be edited
          from the <guilabel>Result list</guilabel> tab of the
          <guilabel>GUI configuration</guilabel>.
          </para>

          <para>The header fragment is used both for the result list and
          the snippets window. The snippets list is a table and has a
          <literal>snippets</literal> class attribute. Each paragraph in
          the result list is a table, with class
          <literal>respar</literal>, but this can be changed by editing
          the paragraph format.</para>

          <para>There are a few examples on the 
          <ulink url="http://www.recoll.org/pages/custom.html">page about 
          customising the result list</ulink> on the &RCL; web site.</para>

          <sect4 id="RCL.SEARCH.GUI.CUSTOM.RESLIST.PARA">
            <title>The paragraph format</title>

            <para>This is an arbitrary HTML string where the following printf-like
            <literal>%</literal> substitutions will be performed:

            <itemizedlist>
              <listitem>
                <formalpara><title>%A</title><para>Abstract</para></formalpara>
              </listitem>
              <listitem><formalpara><title>%D</title><para>Date</para></formalpara>
              </listitem>
              <listitem><formalpara><title>%I</title><para>Icon image
              name. This is normally determined from the MIME type. The
              associations are defined inside the 
              <link linkend="RCL.INSTALL.CONFIG.MIMECONF"><filename>mimeconf</filename> configuration file</link>. 
                If a thumbnail for the file is found at
                the standard Freedesktop location, this will be displayed
                instead.</para></formalpara> 
              </listitem>
              <listitem><formalpara><title>%K</title><para>Keywords (if
              any)</para></formalpara> 
              </listitem>
              <listitem><formalpara><title>%L</title><para>Precooked Preview,
              Edit, and possibly Snippets links</para></formalpara> 
              </listitem>
              <listitem><formalpara><title>%M</title><para>MIME
              type</para></formalpara> 
              </listitem>
              <listitem><formalpara><title>%N</title><para>result Number inside
              the result page</para></formalpara> 
              </listitem>
              <listitem><formalpara><title>%P</title><para>Parent folder
              Url. In the case of an embedded document, this is the parent folder
              for the top level container file.</para></formalpara>
              </listitem>
              <listitem><formalpara><title>%R</title><para>Relevance
              percentage</para></formalpara> 
              </listitem>
              <listitem><formalpara><title>%S</title><para>Size
              information</para></formalpara> 
              </listitem>
              <listitem><formalpara><title>%T</title><para>Title or Filename if
              not set.</para></formalpara> 
              </listitem>
              <listitem><formalpara><title>%t</title><para>Title or empty.
              </para></formalpara> 
              </listitem>
              <listitem><formalpara><title>%(filename)</title><para>File name.
              </para></formalpara> 
              </listitem>
              <listitem><formalpara><title>%U</title><para>Url</para></formalpara>
              </listitem>
            </itemizedlist>

            The format of the Preview, Edit, and Snippets links is 
            <literal>&lt;a href="P%N"&gt;</literal>,
            <literal>&lt;a href="E%N"&gt;</literal>
            and 
            <literal>&lt;a href="A%N"&gt;</literal>
            where <replaceable>docnum</replaceable> (%N) expands to the document
            number inside the result page).</para>

            <para>A link target defined as <literal>"F%N"</literal> will open
            the document corresponding to the <literal>%P</literal> parent
            folder expansion, usually creating a file manager window on the
            folder where the container file resides. E.g.:
            <programlisting>&lt;a href="F%N"&gt;%P&lt;/a&gt;</programlisting>
            </para>

            <para>A link target defined as
            <literal>R%N|<replaceable>scriptname</replaceable></literal> will
            run the corresponding script on the result file (if the document is
            embedded, the script will be started on the top-level parent).
            See the <link linkend="RCL.SEARCH.GUI.RUNSCRIPT">section about defining scripts</link>.</para>

            <para>In addition to the predefined values above, all strings
            like <literal>%(fieldname)</literal> will be replaced by the
            value of the field named <literal>fieldname</literal> for this
            document. Only stored fields can be accessed in this way, the
            value of indexed but not stored fields is not known at this
            point in the search process
            (see <link linkend="RCL.PROGRAM.FIELDS">field configuration</link>). There are currently very few fields
            stored by default, apart from the values above
            (only <literal>author</literal>
            and <literal>filename</literal>), so this feature will need
            some custom local configuration to be useful. An example
            candidate would be the <literal>recipient</literal> field
            which is generated by the message input handlers.</para>

            <para>The default value for the paragraph format string is:
            <screen><![CDATA[
            "<table class=\"respar\">\n"
            "<tr>\n"
            "<td><a href='%U'><img src='%I' width='64'></a></td>\n"
            "<td>%L &nbsp;<i>%S</i> &nbsp;&nbsp;<b>%T</b><br>\n"
            "<span style='white-space:nowrap'><i>%M</i>&nbsp;%D</span>&nbsp;&nbsp;&nbsp; <i>%U</i>&nbsp;%i<br>\n"
            "%A %K</td>\n"
            "</tr></table>\n"
            ]]></screen>

            You may, for example, try the following for a more web-like
            experience:

            <screen><![CDATA[
            <u><b><a href="P%N">%T</a></b></u><br>
            %A<font color=#008000>%U - %S</font> - %L
            ]]></screen>

            Note that the P%N link in the above paragraph makes the title a
            preview link. Or the clean looking:

            <screen><![CDATA[
            <img src="%I" align="left">%L <font color="#900000">%R</font>
            &nbsp;&nbsp;<b>%T&</b><br>%S&nbsp;
            <font color="#808080"><i>%U</i></font>
            <table bgcolor="#e0e0e0">
            <tr><td><div>%A</div></td></tr>
            </table>%K
            ]]></screen>
            </para>

            <para>These samples, and some others are 
            <ulink url="http://www.recoll.org/pages/custom.html">on the web
            site, with pictures to show how they look.</ulink></para>

            <para>It is also possible to 
            <link linkend="RCL.SEARCH.GUI.CUSTOM.ABSSEP">define the value of the snippet separator inside the abstract section</link>.</para>
          </sect4>
        </sect3>
      </sect2>

    </sect1> <!-- search GUI -->

    <sect1 id="RCL.SEARCH.KIO">
      <title>Searching with the KDE KIO slave</title>

      <sect2 id="RCL.SEARCH.KIO.INTRO">
        <title>What's this</title>

        <para>The &RCL; KIO slave allows performing a &RCL; search
        by entering an appropriate URL in a KDE open dialog, or with an
        HTML-based interface displayed in
        <command>Konqueror</command>.</para>  

        <para>The HTML-based interface is similar to the Qt-based
        interface, but slightly less powerful for now. Its advantage is
        that you can perform your search while staying fully within the
        KDE framework: drag and drop from the result list works normally
        and you have your normal choice of applications for opening
        files.</para>

        <para>The alternative interface uses a directory view of search
        results. Due to limitations in the current KIO slave interface,
        it is currently not obviously useful (to me).</para>

        <para>The interface is described in more detail inside a help
        file which you can access by entering
        <filename>recoll:/</filename> inside the
        <command>konqueror</command> URL line (this works only if the
        recoll KIO slave has been previously installed).</para>


        <para>The instructions for building this module are located in the
        source tree. See:
        <filename>kde/kio/recoll/00README.txt</filename>. Some Linux
        distributions do package the kio-recoll module, so check before
        diving into the build process, maybe it's already out there ready for
        one-click installation.</para>
      </sect2>


      <sect2 id="RCL.SEARCH.KIO.SEARCHABLEDOCS">
        <title>Searchable documents</title>

        <para>As a sample application, the &RCL; KIO slave could allow
        preparing a set of HTML documents (for example a manual) so that
        they become their own search interface inside
        <command>konqueror</command>.</para>

        <para>This can be done by either explicitly inserting
        <literal><![CDATA[<a href="recoll://...">]]></literal> links 
        around some document areas, or automatically by adding a
        very small <application>javascript</application> program to the
        documents, like the following example, which would initiate a search by
        double-clicking any term:</para>
        
        <programlisting>&lt;script language="JavaScript">
        function recollsearch() {
        var t = document.getSelection();
        window.location.href = 'recoll://search/query?qtp=a&amp;p=0&amp;q=' +
        encodeURIComponent(t);
        }
        &lt;/script>
        ....
        &lt;body ondblclick="recollsearch()">

        </programlisting>
      </sect2>
    </sect1>


    <sect1 id="RCL.SEARCH.COMMANDLINE">
      <title>Searching on the command line</title>

      <para>There are several ways to obtain search results as a text
      stream, without a graphical interface:</para>
      <itemizedlist>
        <listitem><para>By passing option <option>-t</option> to the
        <command>recoll</command> program, or by calling it as
        <command>recollq</command> (through a link).</para>
        </listitem>
        <listitem><para>By using the <command>recollq</command> program.</para>
        </listitem>
        <listitem><para>By writing a custom
        <application>Python</application> program, using the 
        <link linkend="RCL.PROGRAM.PYTHONAPI">Recoll Python API</link>.</para>
        </listitem>
      </itemizedlist>

      <para>The first two methods work in the same way and accept/need the same
      arguments (except for the additional <option>-t</option> to
      <command>recoll</command>). The query to be executed is specified
      as command line arguments.</para> 

      <para><command>recollq</command> is not always built by default. You
      can use the <filename>Makefile</filename> in the
      <filename>query</filename> directory to build it. This is a very
      simple program, and if you can program a little c++, you may find it
      useful to taylor its output format to your needs. Apart from being
      easily customised, <command>recollq</command> is only really useful
      on systems where the Qt libraries are not available, else it is
      redundant with <literal>recoll -t</literal>.</para>

      <para><command>recollq</command> has a
      <ulink url="https://www.lesbonscomptes.com/recoll/manpages/recollq.1.html">man page</ulink>. 

      The Usage string follows:</para>
      <programlisting><![CDATA[
recollq: usage:
 -P: Show the date span for all the documents present in the index
 [-o|-a|-f] [-q] <query string>
 Runs a recoll query and displays result lines. 
  Default: will interpret the argument(s) as a xesam query string
  Query elements: 
   * Implicit AND, exclusion, field spec:  t1 -t2 title:t3
   * OR has priority: t1 OR t2 t3 OR t4 means (t1 OR t2) AND (t3 OR t4)
   * Phrase: "t1 t2" (needs additional quoting on cmd line)
 -o Emulate the GUI simple search in ANY TERM mode
 -a Emulate the GUI simple search in ALL TERMS mode
 -f Emulate the GUI simple search in filename mode
 -q is just ignored (compatibility with the recoll GUI command line)
Common options:
 -c <configdir> : specify config directory, overriding $RECOLL_CONFDIR
 -d also dump file contents
 -n [first-]<cnt> define the result slice. The default value for [first]
    is 0. Without the option, the default max count is 2000.
    Use n=0 for no limit
 -b : basic. Just output urls, no mime types or titles
 -Q : no result lines, just the processed query and result count
 -m : dump the whole document meta[] array for each result
 -A : output the document abstracts
 -S fld : sort by field <fld>
   -D : sort descending
 -s stemlang : set stemming language to use (must exist in index...)
    Use -s "" to turn off stem expansion
 -T <synonyms file>: use the parameter (Thesaurus) for word expansion 
 -i <dbdir> : additional index, several can be given
 -e use url encoding (%xx) for urls
 -F <field name list> : output exactly these fields for each result.
    The field values are encoded in base64, output in one line and 
    separated by one space character. This is the recommended format 
    for use by other programs. Use a normal query with option -m to 
    see the field names. Use -F '' to output all fields, but you probably
    also want option -N in this case
  -N : with -F, print the (plain text) field names before the field values
      ]]></programlisting>

      <para>Sample execution:</para>
      <programlisting>
recollq 'ilur -nautique mime:text/html'
Recoll query: ((((ilur:(wqf=11) OR ilurs) AND_NOT (nautique:(wqf=11) OR nautiques OR nautiqu OR nautiquement)) FILTER Ttext/html))
4 results
text/html       [file:///Users/uncrypted-dockes/projets/bateaux/ilur/comptes.html]      [comptes.html]  18593   bytes   
text/html       [file:///Users/uncrypted-dockes/projets/nautique/webnautique/articles/ilur1/index.html] [Constructio...
text/html       [file:///Users/uncrypted-dockes/projets/pagepers/index.html]    [psxtcl/writemime/recoll]...
text/html       [file:///Users/uncrypted-dockes/projets/bateaux/ilur/factEtCie/recu-chasse-maree....
      </programlisting>
    </sect1>


    <sect1 id="RCL.SEARCH.LANG">
      <title>The query language</title>

      <para>The query language processor is activated in the GUI
      simple search entry when the search mode selector is set to
      <guilabel>Query Language</guilabel>. It can also be used with the KIO
      slave or the command line search. It broadly has the same
      capabilities as the complex search interface in the
      GUI.</para>

      <para>The language was based on the now defunct
      <ulink url="http://www.xesam.org/main/XesamUserSearchLanguage95">
      Xesam</ulink> user search language specification.</para>

      <para>If the results of a query language search puzzle you and you
      doubt what has been actually searched for, you can use the GUI
      <literal>Show Query</literal> link at the top of the result list to
      check the exact query which was finally executed by Xapian.</para>

      <para>Here follows a sample request that we are going to
      explain:</para>

      <programlisting>
        author:"john doe" Beatles OR Lennon Live OR Unplugged -potatoes
      </programlisting>

      <para>This would search for all documents with 
      <replaceable>John Doe</replaceable>
      appearing as a phrase in the author field (exactly what this is
      would depend on the document type, ie: the
      <literal>From:</literal> header, for an email message),
      and containing either <replaceable>beatles</replaceable> or
      <replaceable>lennon</replaceable> and either
      <replaceable>live</replaceable> or
      <replaceable>unplugged</replaceable> but not
      <replaceable>potatoes</replaceable> (in any part of the document).</para>

      <para>An element is composed of an optional field specification,
      and a value, separated by a colon (the field separator is the last
      colon in the element). Examples:
      <replaceable>Eugenie</replaceable>,
      <replaceable>author:balzac</replaceable>,
      <replaceable>dc:title:grandet</replaceable> 
      <replaceable>dc:title:"eugenie grandet"</replaceable> 
      </para>

      <para>The colon, if present, means "contains". Xesam defines other
      relations, which are mostly unsupported for now (except in special
      cases, described further down).</para>

      <para>All elements in the search entry are normally combined
      with an implicit AND. It is possible to specify that elements be
      OR'ed instead, as in <replaceable>Beatles</replaceable>
      <literal>OR</literal> <replaceable>Lennon</replaceable>. The
      <literal>OR</literal> must be entered literally (capitals), and
      it has priority over the AND associations:
      <replaceable>word1</replaceable>
      <replaceable>word2</replaceable> <literal>OR</literal>
      <replaceable>word3</replaceable> 
      means 
      <replaceable>word1</replaceable> AND 
      (<replaceable>word2</replaceable> <literal>OR</literal>
      <replaceable>word3</replaceable>)
      not 
      (<replaceable>word1</replaceable> AND
      <replaceable>word2</replaceable>) <literal>OR</literal>
      <replaceable>word3</replaceable>. </para>

      <para>&RCL; versions 1.21 and later, allow using parentheses to
      group elements, which will sometimes make things clearer, and may
      allow expressing combinations which would have been difficult
      otherwise.</para>

      <para>An element preceded by a <literal>-</literal> specifies a
      term that should <emphasis>not</emphasis> appear.</para>

      <para>As usual, words inside quotes define a phrase
      (the order of words is significant), so that
      <replaceable>title:"prejudice pride"</replaceable> is not the same as
      <replaceable>title:prejudice title:pride</replaceable>, and is
      unlikely to find a result.</para> 

      <para>Words inside phrases and capitalized words are not
      stem-expanded. Wildcards may be used anywhere inside a term.
      Specifying a wild-card on the left of a term can produce a very
      slow search (or even an incorrect one if the expansion is
      truncated because of excessive size). Also see 
      <link linkend="RCL.SEARCH.WILDCARDS">More about wildcards</link>.
      </para>

      <para>To save you some typing, recent &RCL; versions (1.20 and later)
      interpret a comma-separated list of terms for a field as an AND list
      inside the field. Use slash characters ('/') for an OR list. No white
      space is allowed. So
      <programlisting>author:john,lennon</programlisting> will search for
      documents with <literal>john</literal> and <literal>lennon</literal>
      inside the <literal>author</literal> field (in any order), and
      <programlisting>author:john/ringo</programlisting> would search for
      <literal>john</literal> or <literal>ringo</literal>. This behaviour
      only happens for field queries (input without a field, comma- or
      slash- separated input will produce a phrase search). You can use a
      <literal>text</literal> field name to search the main text this
      way.</para>

      <para>Modifiers can be set on a double-quote value, for example to specify
      a proximity search (unordered). See 
      <link linkend="RCL.SEARCH.LANG.MODIFIERS">the modifier section</link>.
      No space must separate the final double-quote and the modifiers
      value, e.g. <replaceable>"two one"po10</replaceable></para>

      <para>&RCL; currently manages the following default fields:</para>

      <itemizedlist>

        <listitem><para><literal>title</literal>,
        <literal>subject</literal> or <literal>caption</literal> are
        synonyms which specify data to be searched for in the
        document title or subject.</para>
        </listitem>

        <listitem><para><literal>author</literal> or
        <literal>from</literal> for searching the documents
        originators.</para>
        </listitem>

        <listitem><para><literal>recipient</literal> or
        <literal>to</literal> for searching the documents
        recipients.</para>
        </listitem>

        <listitem><para><literal>keyword</literal> for searching the
        document-specified keywords (few documents actually have
        any).</para>
        </listitem>

        <listitem><para><literal>filename</literal> for the document's
        file name. This is not necessarily set for all documents:
        internal documents contained inside a compound one (for example
        an EPUB section) do not inherit the container file name any more,
        this was replaced by an explicit field (see next). Sub-documents
        can still have a specific <literal>filename</literal>, if it is
        implied by the document format, for example the attachment file
        name for an email attachment.</para></listitem> 

        <listitem><para><literal>containerfilename</literal>. This is
            set for all documents, both top-level and contained
            sub-documents, and is always the name of the filesystem directory
            entry which contains the data. The terms from this field can
            only be matched by an explicit field specification (as opposed
            to terms from <literal>filename</literal> which are also indexed
            as general document content). This avoids getting matches for
            all the sub-documents when searching for the container file
            name.</para></listitem> 
        
        <listitem><para><literal>ext</literal> specifies the file
            name extension
            (Ex: <literal>ext:html</literal>).</para></listitem>

        <listitem><para><literal>rclmd5</literal> the MD5 checksum for the
            document. This is used for displaying the duplicates of a
            search result (when querying with the option to collapse
            duplicate results). Incidentally, this could be used to find
            the duplicates of any given file by computing its MD5 checksum
            and executing a query with just the <literal>rclmd5</literal>
            value.</para>
        </listitem>

      </itemizedlist>

      <para>&RCL; 1.20 and later have a way to specify aliases for the
        field names, which will save typing, for example by aliasing
        <literal>filename</literal> to <replaceable>fn</replaceable> or
        <literal>containerfilename</literal> to
        <replaceable>cfn</replaceable>. See the
        <link linkend="RCL.INSTALL.CONFIG.FIELDS">section about the <filename>fields</filename> file</link>.
      </para> 

      <para>The document input handlers used while indexing have the
      possibility to create other fields with arbitrary names, and
      aliases may be defined in the configuration, so that the exact
      field search possibilities may be different for you if someone
      took care of the customisation.</para>

      <para>The field syntax also supports a few field-like, but
      special, criteria:</para>

      <itemizedlist>

        <listitem><para><literal>dir</literal> for filtering the
        results on file location
        (Ex: <literal>dir:/home/me/somedir</literal>). 
        <literal>-dir</literal>
        also works to find results not in the specified directory
        (release >= 1.15.8). Tilde expansion will be performed as
        usual (except for a bug in versions 1.19 to
        1.19.11p1). Wildcards will be expanded, but
        please
        <link linkend="RCL.SEARCH.WILDCARDS.PATH"> have a look</link>
        at an important limitation of wildcards in path filters.</para>

        <para>Relative paths also make sense, for example, 
        <literal>dir:share/doc</literal> would match either
        <filename>/usr/share/doc</filename> or
        <filename>/usr/local/share/doc</filename> </para>

        <para>Several <literal>dir</literal> clauses can be specified,
        both positive and negative. For example the following makes sense:
        <programlisting>
          dir:recoll dir:src -dir:utils -dir:common
          </programlisting> This would select results which have both
          <filename>recoll</filename> and <filename>src</filename> in the
          path (in any order), and which have not either
          <filename>utils</filename> or
        <filename>common</filename>.</para>
        
        <para>You can also use <literal>OR</literal> conjunctions
        with <literal>dir:</literal> clauses.</para>

        <para>A special aspect of <literal>dir</literal> clauses is
        that the values in the index are not transcoded to UTF-8, and
        never lower-cased or unaccented, but stored as binary. This means
        that you need to enter the values in the exact lower or upper
        case, and that searches for names with diacritics may sometimes
        be impossible because of character set conversion
        issues. Non-ASCII UNIX file paths are an unending source of
        trouble and are best avoided.</para> 

        <para>You need to use double-quotes around the path value if it
        contains space characters.</para> 

        </listitem>

        <listitem><para><literal>size</literal> for filtering the
        results on file size. Example: 
        <literal>size&lt;10000</literal>. You can use
        <literal>&lt;</literal>, <literal>&gt;</literal> or
        <literal>=</literal> as operators. You can specify a range like the
        following: <literal>size>100 size&lt;1000</literal>. The usual
        <literal>k/K, m/M, g/G, t/T</literal> can be used as (decimal)
        multipliers. Ex: <literal>size&gt;1k</literal> to search for files
        bigger than 1000 bytes.</para>
        </listitem>

        <listitem><para><literal>date</literal> for searching or filtering
        on dates. The syntax for the argument is based on the ISO8601
        standard for dates and time intervals. Only dates are supported, no
        times. The general syntax is 2 elements separated by a
        <literal>/</literal> character. Each element can be a date or a
        period of time. Periods are specified as 
        <literal>P</literal><replaceable>n</replaceable><literal>Y</literal><replaceable>n</replaceable><literal>M</literal><replaceable>n</replaceable><literal>D</literal>. 
        The <replaceable>n</replaceable> numbers are the respective numbers
        of years, months or days, any of which may be missing. Dates are
        specified as  
        <replaceable>YYYY</replaceable>-<replaceable>MM</replaceable>-<replaceable>DD</replaceable>. 
        The days and months parts may be missing. If the
        <literal>/</literal> is present but an element is missing, the
        missing element is interpreted as the lowest or highest date in the
        index. Examples:</para>

        <itemizedlist>
          <listitem><para><literal>2001-03-01/2002-05-01</literal> the
          basic syntax for an interval of dates.</para>
          </listitem>
          <listitem><para><literal>2001-03-01/P1Y2M</literal> the
          same specified with a period.</para>
          </listitem>
          <listitem><para><literal>2001/</literal> from the beginning of
          2001 to the latest date in the index.</para>
          </listitem>
          <listitem><para><literal>2001</literal> the whole year of
          2001</para></listitem>
          <listitem><para><literal>P2D/</literal> means 2 days ago up to
          now if there are no documents with dates in the future.</para>
          </listitem>
          <listitem><para><literal>/2003</literal> all documents from
          2003 or older.</para>
          </listitem>
        </itemizedlist>
        <para>Periods can also be specified with small letters (ie:
        p2y).</para> 
        </listitem>

        <listitem><para><literal>mime</literal> or
        <literal>format</literal> for specifying the
        MIME type. These clauses are processed besides the normal
        Boolean logic of the search. Multiple values will be OR'ed
        (instead of the normal AND). You can specify types to be
        excluded, with the usual <literal>-</literal>, and use
        wildcards. Example: <replaceable>mime:text/*
        -mime:text/plain</replaceable> 
        Specifying an explicit boolean
        operator before a <literal>mime</literal> specification is not
        supported and will produce strange results. </para>
        </listitem>

        <listitem><para><literal>type</literal> or
        <literal>rclcat</literal> for specifying the category (as in
        text/media/presentation/etc.). The classification of MIME
        types in categories is defined in the &RCL; configuration
        (<filename>mimeconf</filename>), and can be modified or
        extended. The default category names are those which permit
        filtering results in the main GUI screen. Categories are OR'ed
        like MIME types above, and can be negated with
        <literal>-</literal>.</para>
        </listitem>

      </itemizedlist>

      <note><para>
        <literal>mime</literal>, <literal>rclcat</literal>,
        <literal>size</literal> and <literal>date</literal> criteria
        always affect the whole query (they are applied as a final
        filter), even if set with other terms inside a parenthese.</para>
      </note>

      <note><para>
        <literal>mime</literal> (or the equivalent
        <literal>rclcat</literal>) is the <emphasis>only</emphasis>
        field with an <literal>OR</literal> default. You do need to use
        <literal>OR</literal> with <literal>ext</literal> terms for
      example.</para> </note>

      <sect2 id="RCL.SEARCH.LANG.RANGES">
        <title>Range clauses</title>

        <para>&RCL; 1.24 and later support range clauses on fields which
        have been configured to support it. No default field uses them
        currently, so this paragraph is only interesting if you modified
        the fields configuration and possibly use a custom input
        handler.</para>

        <para>A range clause looks like one of the following:</para>
        <programlisting><replaceable>myfield</replaceable>:<replaceable>small</replaceable>..<replaceable>big</replaceable>
<replaceable>myfield</replaceable>:<replaceable>small</replaceable>..
<replaceable>myfield</replaceable>:..<replaceable>big</replaceable>
        </programlisting>

        <para>The nature of the clause is indicated by the two dots
        <literal>..</literal>, and the effect is to filter the results for
        which the <replaceable>myfield</replaceable> value is in the
        possibly open-ended interval.</para>

        <para>See the section about the
        <link linkend="RCL.INSTALL.CONFIG.FIELDS"><filename>fields</filename> configuration file</link>
        for the details of configuring a field for range searches (list
        them in the [values] section).</para> 

        
      </sect2>
      
      <sect2 id="RCL.SEARCH.LANG.MODIFIERS">
        <title>Modifiers</title>

        <para>Some characters are recognized as search modifiers when found
        immediately after the closing double quote of a phrase, as in
        <literal>"some term"modifierchars</literal>. The actual "phrase"
        can be a single term of course. Supported modifiers:

        <itemizedlist>
          <listitem><para><literal>l</literal> can be used to turn off
          stemming (mostly makes sense with <literal>p</literal> because
          stemming is off by default for phrases).</para>
          </listitem>

          <listitem><para><literal>s</literal> can be used to turn off
          synonym expansion, if a synonyms file is in place (only for
          &RCL; 1.22 and later).</para>
          </listitem>

          <listitem><para><literal>o</literal> can be used to specify a
          "slack" for phrase and proximity searches: the number of
          additional terms that may be found between the specified
          ones. If <literal>o</literal> is followed by an integer number,
          this is the slack, else the default is 10.</para>
          </listitem>

          <listitem><para><literal>p</literal> can be used to turn the
          default phrase search into a proximity one
          (unordered). Example: <literal>"order any in"p</literal></para>
          </listitem>

          <listitem><para><literal>C</literal> will turn on case
          sensitivity (if the index supports it).</para></listitem>

          <listitem><para><literal>D</literal> will turn on diacritics
          sensitivity (if the index supports it).</para></listitem>

          <listitem><para>A weight can be specified for a query element
          by specifying a decimal value at the start of the
          modifiers. Example: <literal>"Important"2.5</literal>.</para>
          </listitem>
        </itemizedlist>
        </para>


      </sect2> <!-- search modifiers -->

    </sect1> <!-- rcl.search.lang -->
    
    <sect1 id="RCL.SEARCH.ANCHORWILD">
      <title>Anchored searches and wildcards</title>

      <para>Some special characters are interpreted by &RCL; in search
      strings to expand or specialize the search. Wildcards expand a root
      term in controlled ways. Anchor characters can restrict a search to
      succeed only if the match is found at or near the beginning of the
      document or one of its fields.</para>

      <sect2 id="RCL.SEARCH.WILDCARDS">
        <title>More about wildcards</title>

        <para>All words entered in &RCL; search fields will be processed
        for wildcard expansion before the request is finally
        executed.</para>

        <para>The wildcard characters are:</para>

        <itemizedlist>
          <listitem><para><literal>*</literal> which matches 0 or more 
          characters.</para>
          </listitem>
          <listitem><para><literal>?</literal> which matches
          a single character.</para>
          </listitem>
          <listitem><para><literal>[]</literal> which allow
          defining sets of characters to be matched (ex:
          <literal>[</literal><userinput>abc</userinput><literal>]</literal> 
          matches a single character which may be 'a' or 'b' or 'c',
          <literal>[</literal><userinput>0-9</userinput><literal>]</literal>
          matches any number.</para>
          </listitem>
        </itemizedlist>

        <para>You should be aware of a few things when using
        wildcards.</para>

        <itemizedlist>
          <listitem><para>Using a wildcard character at the beginning of
          a word can make for a slow search because &RCL; will have to
          scan the whole index term list to find the
          matches. However, this is much less a problem for field
          searches, and queries
          like <replaceable>author:*@domain.com</replaceable> can
          sometimes be very useful.</para></listitem>

          <listitem><para>For &RCL; version 18 only, when working with a
          raw index (preserving character case and diacritics), the
          literal part of a wildcard expression will be matched
          exactly for case and diacritics. This is not true any
          more for versions 19 and later.</para></listitem>

          <listitem><para>Using a <literal>*</literal> at the end of a
          word can produce more matches than you would think, and
          strange search results. You can use the 
          <link linkend="RCL.SEARCH.GUI.TERMEXPLORER">term explorer</link>
          tool to check what completions exist for
          a given term. You can also see exactly what search was
          performed by clicking on the link at the top of the result
          list. In general, for natural language terms, stem
          expansion will produce better results than an
          ending <literal>*</literal> (stem expansion is turned off
          when any wildcard character appears in the
          term).</para></listitem> 
        </itemizedlist>

        <sect3 id="RCL.SEARCH.WILDCARDS.PATH">
          <title>Wildcards and path filtering</title>

          <para>Due to the way that &RCL; processes wildcards
          inside <literal>dir</literal> path filtering clauses, they
          will have a multiplicative effect on the query size. A clause
          containing wildcards in several paths elements, like, for
          example,
          <literal>dir:</literal><replaceable>/home/me/*/*/docdir</replaceable>,
          will almost certainly fail if your indexed tree is of any realistic
          size.</para>

          <para>Depending on the case, you may be able to work around
          the issue by specifying the paths elements more narrowly, with
          a constant prefix, or by using 2
          separate <literal>dir:</literal> clauses instead of multiple
          wildcards, as
          in <literal>dir:</literal><replaceable>/home/me</replaceable> <literal>dir:</literal><replaceable>docdir</replaceable>. The
          latter query is not equivalent to the initial one because it
          does not specify a number of directory levels, but that's
          the best we can do (and it may be actually more useful in
          some cases).</para>

        </sect3>

      </sect2> <!-- wildchars -->

      <sect2 id="RCL.SEARCH.ANCHOR">
        <title>Anchored searches</title>

        <para>Two characters are used to specify that a search hit should
        occur at the beginning or at the end of the
        text. <literal>^</literal> at the beginning of a term or phrase
        constrains the search to happen at the start, <literal>$</literal>
        at the end force it to happen at the end.</para>
        
        <para>As this function is implemented as a phrase search it is
        possible to specify a maximum distance at which the hit should
        occur, either through the controls of the advanced search panel, or
        using the query language, for example, as in:
        <programlisting>"^someterm"o10</programlisting> which would force
        <literal>someterm</literal> to be found within 10 terms of the
        start of the text. This can be combined with a field search as in
        <literal>somefield:"^someterm"o10</literal> or
        <literal>somefield:someterm$</literal>.</para>

        <para>This feature can also be used with an actual phrase search,
        but in this case, the distance applies to the whole phrase and
        anchor, so that, for example,
        <literal>bla bla my unexpected term</literal> at the
        beginning of the text would be a match for
        <literal>"^my term"o5</literal>.</para>

        <para>Anchored searches can be very useful for searches inside
        somewhat structured documents like scientific articles, in case
        explicit metadata has not been supplied (a most frequent case), for
        example for looking for matches inside the abstract or the list of
        authors (which occur at the top of the document).</para>


      </sect2>

    </sect1> <!-- wildchars and anchors -->


    
    <sect1 id="RCL.SEARCH.SYNONYMS">
      <title>Using Synonyms (1.22)</title>

      <formalpara><title>Term synonyms and text search:</title> <para>in
      general, there are two main ways to use term synonyms for
      searching text:
      <itemizedlist>
        <listitem><para>At index creation time, they can be used to alter the 
        indexed terms, either increasing or decreasing their number, by
        expanding the original terms to all synonyms, or by
        reducing all synonym terms to a canonical one.</para></listitem>
        <listitem><para>At query time, they can be used to match texts
        containing terms which are synonyms of the ones specified by the user,
        either by expanding the query for all synonyms, or by reducing the user
        entry to canonical terms (the latter only works if the corresponding
        processing has been performed while creating the
        index).</para></listitem> 
      </itemizedlist>
      </para>
      </formalpara>
      
      <para>&RCL; only uses synonyms at query time. A user query term which
      part of a synonym group will be optionally expanded into an
      <literal>OR</literal> query for all terms in the group.</para>

      <para>Synonym groups are defined inside ordinary text files. Each line
      in the file defines a group.</para> 

      <para>Example:
      <programlisting>
        hi hello "good morning"

        # not sure about "au revoir" though. Is this english ?
        bye goodbye "see you" \
        "au revoir" 
      </programlisting>
      </para>

      <para>As usual, lines beginning with a <literal>#</literal> are comments,
      empty lines are ignored, and lines can be continued by ending them with
      a backslash.
      </para>

      <para>Multi-word synonyms are supported, but be aware that these will
      generate phrase queries, which may degrade performance and will disable
      stemming expansion for the phrase terms.</para>

      <para>The contents of the synonyms file must be casefolded (not only
      lowercased), because this is what expected at the point in the query
      processing where it is used. There are a few cases where this makes a
      difference, for example, German sharp s should be expressed as
      <literal>ss</literal>, Greek final sigma as sigma. For reference,
      Python3 has an easy way to casefold words (str.casefold()).</para>
      
      <para>The synonyms file can be specified in the <guilabel>Search
      parameters</guilabel> tab of the <guilabel>GUI configuration</guilabel>
      <guilabel>Preferences</guilabel> menu entry, or as an option for
      command-line searches.</para>

      <para>Once the file is defined, the use of synonyms can be enabled or
      disabled directly from the <guilabel>Preferences</guilabel>
      menu.</para>
      
      <para>The synonyms are searched for matches with user terms after the
      latter are stem-expanded, but the contents of the synonyms file itself
      is not subjected to stem expansion. This means that a match will not be
      found if the form present in the synonyms file is not present anywhere
      in the document set (same with accents when using a raw index).</para>

      <para>The synonyms function is probably not going to help you find your
      letters to Mr. Smith. It is best used for domain-specific searches. For
      example, it was initially suggested by a user performing searches among
      historical documents: the synonyms file would contains nicknames and
      aliases for each of the persons of interest.</para>

      
    </sect1>
    
    <sect1 id="RCL.SEARCH.PTRANS">
      <title>Path translations</title>
      
      <para>In some cases, the document paths stored inside the index do
      not match the actual ones, so that document
      previews and accesses will fail. This can occur in a number of
      circumstances:</para>
      <itemizedlist>
        <listitem><para>When using multiple indexes it is a relatively common
        occurrence that some will actually reside on a remote volume, for
        example mounted via NFS. In this case, the paths used to access
        the documents on the local machine are not necessarily the same
        than the ones used while indexing on the remote machine. For
        example, <filename>/home/me</filename> may have been used as
        a <literal>topdirs</literal> elements while indexing, but the
        directory might be mounted
        as <filename>/net/server/home/me</filename> on the local
        machine.</para></listitem>

        <listitem><para>The case may also occur with removable
        disks. It is perfectly possible to configure an index to
        live with the documents on the removable disk, but it may
        happen that the disk is not mounted at the same place so
        that the documents paths from the index are
        invalid.</para></listitem>
        
        <listitem><para>As a last example, one could imagine that a big
        directory has been moved, but that it is currently
        inconvenient to run the indexer.</para></listitem>
      </itemizedlist>

      <para>&RCL; has a facility for rewriting access paths when
      extracting the data from the index. The translations can be
      defined for the main index and for any additional query
      index.</para>

      <para>The path translation facility will be useful
      whenever the documents paths seen by the indexer are not the same
      as the ones which should be used at query time.</para>

      <para>In the above NFS example, &RCL; could be instructed to
      rewrite any <filename>file:///home/me</filename> URL from the
      index to <filename>file:///net/server/home/me</filename>,
      allowing accesses from the client.</para>

      <para>The translations are defined in the 
      <link linkend="RCL.INSTALL.CONFIG.PTRANS"><filename>ptrans</filename></link>
      configuration file, which
        can be edited by hand or from the GUI external indexes
        configuration dialog: <menuchoice>
        <guimenu>Preferences</guimenu>
        <guimenuitem>External index dialog</guimenuitem>
        </menuchoice>, then click the <guilabel>Paths
        translations</guilabel> button on the right below the index
      list.</para>

      <note><para>Due to a current bug, the GUI must be restarted
      after changing the <filename>ptrans</filename> values (even when they
      were changed from the GUI).</para></note>
    </sect1>

    <sect1 id="RCL.SEARCH.CASEDIAC">
      <title>Search case and diacritics sensitivity</title>

      <para>For &RCL; versions 1.18 and later, and <emphasis>when working
      with a raw index</emphasis> (not the default), searches can be
      sensitive to character case and diacritics. How this happens
      is controlled by configuration variables and what search data is
      entered.</para>

      <para>The general default is that searches entered without upper-case
      or accented characters are insensitive to case and diacritics. An
      entry of <literal>resume</literal> will match any of
      <literal>Resume</literal>, <literal>RESUME</literal>,
      <literal>résumé</literal>, <literal>Résumé</literal> etc.</para>

      <para>Two configuration variables can automate switching on
      sensitivity (they were documented but actually did nothing until
      &RCL; 1.22):</para>

      <variablelist>

        <varlistentry>
          <term>autodiacsens</term><listitem><para>If this is set, search
          sensitivity to diacritics will be turned on as soon as an
          accented character exists in a search term. When the variable
          is set to true, <literal>resume</literal> will start a
          diacritics-unsensitive search, but <literal>résumé</literal>
          will be matched exactly. The default value is
          <emphasis>false</emphasis>.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term>autocasesens</term><listitem><para>If this is set, search
          sensitivity to character case will be turned on as soon as an
          upper-case character exists in a search term <emphasis>except
          for the first one</emphasis>. When the variable is set to
          true, <literal>us</literal> or <literal>Us</literal> will
          start a diacritics-unsensitive search, but
          <literal>US</literal> will be matched exactly. The default
          value is <emphasis>true</emphasis> (contrary to
          <literal>autodiacsens</literal>).</para></listitem>
        </varlistentry>

      </variablelist>
      
      <para>As in the past, capitalizing the first letter of a word will
      turn off its stem expansion and have no effect on
      case-sensitivity.</para>

      <para>You can also explicitly activate case and diacritics
      sensitivity by using modifiers with the query
      language. <literal>C</literal> will make the term case-sensitive, and
      <literal>D</literal> will make it
      diacritics-sensitive. Examples:</para>
      <programlisting>
        "us"C
      </programlisting>

      <para>will search for the term <literal>us</literal> exactly
      (<literal>Us</literal> will not be a match).</para>

      <programlisting>
        "resume"D
      </programlisting>
      <para>will search for the term <literal>resume</literal> exactly
      (<literal>résumé</literal> will not be a match).</para>


      <para>When either case or diacritics sensitivity is activated, stem
      expansion is turned off. Having both does not make much sense.</para>

    </sect1>


    <sect1 id="RCL.SEARCH.DESKTOP">
      <title>Desktop integration</title>

      <para>Being independent of the desktop type has its drawbacks: &RCL;
      desktop integration is minimal. However there are a few tools
      available:
      <itemizedlist>
        <listitem>
          <para>Users of recent Ubuntu-derived distributions, or
            any other Gnome desktop systems (e.g. Fedora) can install the
            <ulink 
              url="https://www.lesbonscomptes.com/recoll/pages/download.html#gssp">
              Recoll GSSP</ulink> (Gnome Shell Search Provider).</para>
        </listitem>
        <listitem>
          <para>The <application>KDE</application> KIO Slave was described
            in a <link linkend="RCL.SEARCH.KIO">previous
              section</link>. It can provide search results
              inside <command>Dolphin</command>. </para>
        </listitem>
        <listitem>
          <para>If you use an oldish version of Ubuntu Linux, you may
          find the <ulink url="&FAQS;UnityLens">Ubuntu Unity
          Lens</ulink> module useful.</para>
        </listitem>
        <listitem>
          <para>There is also an independently developed
          <ulink
              url="http://kde-apps.org/content/show.php/recollrunner?content=128203">
          Krunner plugin</ulink>.</para>
        </listitem>
      </itemizedlist>
      </para>

      <para>Here follow a few other things that may help.</para>

      <sect2 id="RCL.SEARCH.SHORTCUT">
        <title>Hotkeying recoll</title>

        <para>It is surprisingly convenient to be able to show or hide the
        &RCL; GUI with a single keystroke. Recoll comes with a small
        Python script, based on the <application>libwnck</application> window
        manager interface library, which will allow you to do just
        this. The detailed instructions are on
        <ulink url="&FAQS;HotRecoll">this wiki page</ulink>.</para>

      </sect2>

      <sect2 id="RCL.KICKER-APPLET">
        <title>The KDE Kicker Recoll applet</title>

        <para>This is probably obsolete now. Anyway:</para>
        <para>The &RCL; source tree contains the source code to the
        <application>recoll_applet</application>, a small application derived
        from the <application>find_applet</application>. This can be used to
        add a small &RCL; launcher to the KDE panel.</para>

        <para>The applet is not automatically built with the main &RCL;
        programs, nor is it included with the main source distribution
        (because the KDE build boilerplate makes it relatively big). You can
        download its source from the recoll.org download page. Use the
        omnipotent <userinput>configure;make;make install</userinput>
        incantation to build and install.</para>
        
        <para>You can then add the applet to the panel by right-clicking the
        panel and choosing the <guilabel>Add applet</guilabel> entry.</para>

        <para>The <application>recoll_applet</application> has a small text
        window where you can type a &RCL; query (in query language form),
        and an icon which can be used to restrict the search to certain
        types of files. It is quite primitive, and launches a new recoll
        GUI instance every time (even if it is already running). You may
        find it useful anyway.</para>

      </sect2>

    </sect1> <!-- rcl.search.desktop -->

  </chapter> <!-- Search -->

  <chapter id="RCL.PROGRAM">
    <title>Programming interface</title>

    <para>&RCL; has an Application Programming Interface, usable both
    for indexing and searching, currently accessible from the
    <application>Python</application> language.</para>

    <para>Another less radical way to extend the application is to
    write input handlers for new types of documents.</para>

    <para>The processing of metadata attributes for documents
    (<literal>fields</literal>) is highly configurable.</para>



    <sect1 id="RCL.PROGRAM.FILTERS">
      <title>Writing a document input handler</title>
      
      <note><title>Terminology</title><para>The small programs or pieces
      of code which handle the processing of the different document
      types for &RCL; used to be called <literal>filters</literal>,
      which is still reflected in the name of the directory which
      holds them and many configuration variables. They were named
      this way because one of their primary functions is to filter
      out the formatting directives and keep the text
      content. However these modules may have other behaviours, and
      the term <literal>input handler</literal> is now progressively
      substituted in the documentation. <literal>filter</literal> is
      still used in many places though.</para></note>

      <para>&RCL; input handlers cooperate to translate from the multitude
      of input document formats, simple ones as
      <application>opendocument</application>,
      <application>acrobat</application>, or compound ones such as
      <application>Zip</application> or <application>Email</application>,
      into the final &RCL; indexing input format, which is plain text (in
      many cases the processing pipeline has an intermediary HTML step,
      which may be used for better previewing presentation).  Most input
      handlers are executable programs or scripts. A few handlers are coded
      in C++ and live inside <command>recollindex</command>. This latter
      kind will not be described here.</para>

      <para>There are two kinds of external executable input handlers:
      <itemizedlist>
        <listitem><para>Simple <literal>exec</literal> handlers
        run once and exit. They can be bare programs like
        <command>antiword</command>, or scripts using other
        programs. They are very simple to write, because they just
        need to print the converted document to the standard
        output. Their output can be plain text or HTML. HTML is
        usually preferred because it can store metadata fields and
        it allows preserving some of the formatting for the GUI
        preview. However, these handlers have limitations:
        <itemizedlist>
          <listitem><para>They can only process one document
          per file.</para></listitem>
          <listitem><para>The output MIME type must be known and
          fixed.</para></listitem>
          <listitem><para>The character encoding, if relevant, must be
          known and fixed (or possibly just depending on
          location).</para></listitem>
        </itemizedlist>
        </para>
        </listitem>
        <listitem><para>Multiple <literal>execm</literal> handlers can
        process multiple files (sparing the process startup time which can
        be very significant), or multiple documents per file (e.g.: for
        archives or multi-chapter publications). They communicate with the
        indexer through a simple protocol, but are nevertheless a bit more
        complicated than the older kind. Most of the new handlers are
        written in <application>Python</application> (exception:
        <command>rclimg</command> which is written in Perl because
        <literal>exiftool</literal> has no real Python equivalent). The
        Python handlers use common modules to factor out the boilerplate,
        which can make them very simple in favorable cases. The
        subdocuments output by these handlers can be directly indexable
        (text or HTML), or they can be other simple or compound documents
        that will need to be processed by another handler.</para>
        </listitem>
      </itemizedlist>
      </para>

      <para>In both cases, handlers deal with regular file system
      files, and can process either a single document, or a
      linear list of documents in each file. &RCL; is responsible
      for performing up to date checks, deal with more complex
      embedding and other upper level issues.</para>

      <para>A simple handler returning a
      document in <literal>text/plain</literal> format, can transfer
      no metadata to the indexer. Generic metadata, like document
      size or modification date, will be gathered and stored by
      the indexer.</para>

      <para>Handlers that produce  <literal>text/html</literal>
      format can return an arbitrary amount of metadata inside HTML
      <literal>meta</literal> tags. These will be processed
      according to the directives found in 
      the <link linkend="RCL.PROGRAM.FIELDS"><filename>fields</filename> configuration file</link>.
      </para>

      <para>The handlers that can handle multiple documents per file
      return a single piece of data to identify each document inside
      the file. This piece of data, called
      an <literal>ipath</literal> will be sent back by
      &RCL; to extract the document at query time, for previewing,
      or for creating a temporary file to be opened by a
      viewer. These handlers can also return metadata either as HTML
      <literal>meta</literal> tags, or as named data through the
      communication protocol.</para>

      <para>The following section describes the simple
      handlers, and the next one gives a few explanations about
      the <literal>execm</literal> ones. You could conceivably
      write a simple handler with only the elements in the
      manual. This will not be the case for the other ones, for
      which you will have to look at the code.</para>

      <sect2 id="RCL.PROGRAM.FILTERS.SIMPLE">
        <title>Simple input handlers</title>

        <para>&RCL; simple handlers are usually shell-scripts, but this is in
        no way necessary. Extracting the text from the native format is the
        difficult part. Outputting the format expected by &RCL; is
        trivial. Happily enough, most document formats have translators or
        text extractors which can be called from the handler. In some cases
        the output of the translating program is completely appropriate,
        and no intermediate shell-script is needed.</para>

        <para>Input handlers are called with a single argument which is the
        source file name. They should output the result to stdout.</para>

        <para>When writing a handler, you should decide if it will output
        plain text or HTML. Plain text is simpler, but you will not be able
        to add metadata or vary the output character encoding (this will be
        defined in a configuration file). Additionally, some formatting may
        be easier to preserve when previewing HTML. Actually the deciding factor
        is metadata: &RCL; has a way to
        <link linkend="RCL.PROGRAM.FILTERS.HTML">extract metadata from the HTML header and use it for field searches.</link>.
        </para>

        <para>The <envar>RECOLL_FILTER_FORPREVIEW</envar> environment
        variable (values <literal>yes</literal>, <literal>no</literal>)
        tells the handler if the operation is for indexing or
        previewing. Some handlers use this to output a slightly different
        format, for example stripping uninteresting repeated keywords (ie:
        <literal>Subject:</literal> for email) when indexing. This is not
        essential.</para>

        <para>You should look at one of the simple handlers, for example
        <command>rclps</command> for a starting point.</para>

        <para>Don't forget to make your handler executable before 
        testing !</para>

      </sect2>

      <sect2 id="RCL.PROGRAM.FILTERS.MULTIPLE">
        <title>"Multiple" handlers</title>

        <para>If you can program and want to write
        an <literal>execm</literal> handler, it should not be too
        difficult to make sense of one of the existing handlers.</para>

        <para>The existing handlers differ in the amount of helper code
        which they are using:
        <itemizedlist>
          <listitem><para><literal>rclimg</literal> is written in Perl and
          handles the execm protocol all by itself (showing how trivial it
          is).</para></listitem> <listitem><para>All the Python handlers
          share at least the <filename>rclexecm.py</filename> module, which
          handles the communication. Have a look at, for
          example, <filename>rclzip</filename> for a handler which
          uses <filename>rclexecm.py</filename>
          directly.</para></listitem> <listitem><para>Most Python handlers
          which process single-document files by executing another command
          are further abstracted by using
          the <filename>rclexec1.py</filename> module. See for
          example <filename>rclrtf.py</filename> for a simple one,
          or <filename>rcldoc.py</filename> for a slightly more complicated
          one (possibly executing several
          commands).</para></listitem> <listitem><para>Handlers which
          extract text from an XML document by using an XSLT style sheet
          are now executed inside <command>recollindex</command>, with only
          the style sheet stored in the <filename>filters/</filename>
          directory. These can use a single style sheet
          (e.g. <filename>abiword.xsl</filename>), or two sheets for the
          data and metadata (e.g. <filename>opendoc-body.xsl</filename>
          and <filename>opendoc-meta.xsl</filename>). The <filename>mimeconf</filename>
          configuration file defines how the sheets are used, have a
          look. Before the C++ import, the xsl-based handlers used a common
          module <filename>rclgenxslt.py</filename>, it is still around but
          unused at the moment. The handler for OpenXML presentations is
          still the Python version because the format did not fit with what
          the C++ code does. It would be a good base for another similar
          issue.</para></listitem>
        </itemizedlist>
        </para>

        <para>There is a sample trivial handler based on
        <filename>rclexecm.py</filename>, with many comments, not actually
        used by &RCL;. It would index a text file as one document per
        line. Look for <filename>rcltxtlines.py</filename> in the
        <filename>src/filters</filename> directory in the online &RCL;
        <ulink url="https://framagit.org/medoc92/recoll">Git
        repository</ulink> (the sample not in the distributed release at
        the moment).</para>

        <para>You can also have a look at the slightly more complex
        <command>rclzip</command> which uses Zip
        file paths as identifiers (<literal>ipath</literal>).</para>

        <para><literal>execm</literal> handlers sometimes need to make
        a choice for the nature of the <literal>ipath</literal>
        elements that they use in communication with the
        indexer. Here are a few guidelines:
        <itemizedlist>
          <listitem><para>Use ASCII or UTF-8 (if the identifier is an
          integer print it, for example, like printf %d would
          do).</para></listitem>
          <listitem><para>If at all possible, the data should make some
          kind of sense when printed to a log file to help with 
          debugging.</para></listitem>
          <listitem><para>&RCL; uses a colon (<literal>:</literal>) as a
          separator to store a complex path internally (for
          deeper embedding). Colons inside
          the <literal>ipath</literal> elements output by a
          handler will be escaped, but would be a bad choice as a
          handler-specific separator (mostly, again, for
          debugging issues).</para></listitem>
        </itemizedlist>
        In any case, the main goal is that it should
        be easy for the handler to extract the target document, given
        the file name and the <literal>ipath</literal>
        element.</para>

        <para><literal>execm</literal> handlers will also produce
        a document with a null <literal>ipath</literal>
        element. Depending on the type of document, this may have
        some associated data (e.g. the body of an email message), or
        none (typical for an archive file). If it is empty, this
        document will be useful anyway for some operations, as the
        parent of the actual data documents.</para>
      </sect2>

      <sect2 id="RCL.PROGRAM.FILTERS.ASSOCIATION">
        <title>Telling &RCL; about the handler</title>

        <para>There are two elements that link a file to the handler which
        should process it: the association of file to MIME type and the
        association of a MIME type with a handler.</para>

        <para>The association of files to MIME types is mostly based on
        name suffixes. The types are defined inside the
        <link linkend="RCL.INSTALL.CONFIG.MIMEMAP"><filename>mimemap</filename> file</link>. 
        Example:
          <programlisting>

            .doc = application/msword
          </programlisting>
          If no suffix association is found for the file name, &RCL; will try
          to execute a system command (typically <command>file -i</command> or
        <command>xdg-mime</command>) to determine a MIME type.</para>

        <para>The second element is the association of MIME types to handlers
        in the <link linkend="RCL.INSTALL.CONFIG.MIMECONF"><filename>mimeconf</filename> file</link>. 
        A sample will probably be  better than a long explanation:</para>
        <programlisting>

          [index]
          application/msword = exec antiword -t -i 1 -m UTF-8;\
          mimetype = text/plain ; charset=utf-8

          application/ogg = exec rclogg

          text/rtf = exec unrtf --nopict --html; charset=iso-8859-1; mimetype=text/html

          application/x-chm = execm rclchm
        </programlisting>

        <para>The fragment specifies that:

        <itemizedlist>
          <listitem><para><literal>application/msword</literal> files
          are processed by executing the <command>antiword</command>
          program, which outputs
          <literal>text/plain</literal> encoded in
          <literal>utf-8</literal>.</para> 
          </listitem>
          
          <listitem><para><literal>application/ogg</literal> files are
          processed by the <command>rclogg</command> script, with
          default output type (<literal>text/html</literal>, with
          encoding specified in the header, or <literal>utf-8</literal>
          by default).</para>
          </listitem>
          
          <listitem><para><literal>text/rtf</literal> is processed by
          <command>unrtf</command>, which outputs
          <literal>text/html</literal>. The 
          <literal>iso-8859-1</literal> encoding is specified because it
          is not the <literal>utf-8</literal> default, and not output by
          <command>unrtf</command> in the HTML header section.</para>
          </listitem>
          <listitem><para><literal>application/x-chm</literal> is processed
          by a persistent handler. This is determined by the
          <literal>execm</literal> keyword.</para>
          </listitem>
        </itemizedlist>
        </para> 

      </sect2>

      <sect2 id="RCL.PROGRAM.FILTERS.HTML">
        <title>Input handler output</title>

        <para>Both the simple and persistent input handlers can return any
        MIME type to Recoll, which will further process the data according
        to the MIME configuration.</para>

        <para>Most input filters filters produce either
        <literal>text/plain</literal> or <literal>text/html</literal>
        data. There are exceptions, for example, filters which process
        archive file (<literal>zip</literal>, <literal>tar</literal>, etc.)
        will usually return the documents as they are found, without
        processing them further.</para>

        <para>There is nothing to say about <literal>text/plain</literal>
        output, except that its character encoding should be consistent
        with what is specified in the <filename>mimeconf</filename>
        file.</para>
        
        <para>For filters producing HTML, the output could be very minimal
        like the following example:
          <programlisting><![CDATA[
          <html>
            <head>
              <meta http-equiv="Content-Type" content="text/html;charset=UTF-8"/>
            </head>
            <body>
              Some text content
            </body>
          </html>
          ]]></programlisting>
        </para>

        <para>You should take care to escape some
        characters inside the text by transforming them into
        appropriate entities. At the very minimum,
        "<literal>&amp;</literal>" should be transformed into
        "<literal>&amp;amp;</literal>", "<literal>&lt;</literal>"
        should be transformed into
        "<literal>&amp;lt;</literal>". This is not always properly
        done by external helper programs which output HTML, and of
        course never by those which output plain text. </para>

        <para>When encapsulating plain text in an HTML body, 
        the display of a preview may be improved by enclosing the
        text inside <literal>&lt;pre></literal> tags.</para>

        <para>The character set needs to be specified in the
        header. It does not need to be UTF-8 (&RCL; will take care
        of translating it), but it must be accurate for good
        results.</para>

        <para>&RCL; will process <literal>meta</literal> tags inside
        the header as possible document fields candidates. Documents
        fields can be processed by the indexer in different ways,
        for searching or displaying inside query results. This is
        described in a <link linkend="RCL.PROGRAM.FIELDS">following section.</link>
        </para>

        <para>By default, the indexer will process the standard header
        fields if they are present: <literal>title</literal>,
        <literal>meta/description</literal>,
        and <literal>meta/keywords</literal> are both indexed and stored
        for query-time display.</para>

        <para>A predefined non-standard <literal>meta</literal> tag
        will also be processed by &RCL; without further
        configuration: if a <literal>date</literal> tag is present
        and has the right format, it will be used as the document
        date (for display and sorting), in preference to the file
        modification date. The date format should be as follows:
        <programlisting>
          &lt;meta name="date" content="YYYY-mm-dd HH:MM:SS">
          or
          &lt;meta name="date" content="YYYY-mm-ddTHH:MM:SS">
        </programlisting>
        Example:
        <programlisting>
          &lt;meta name="date" content="2013-02-24 17:50:00">
        </programlisting>
        </para>

        <para>Input handlers also have the possibility to "invent" field
        names. This should also be output as meta tags:</para>

        <programlisting>
          &lt;meta name="somefield" content="Some textual data" /&gt;
        </programlisting>

        <para>You can embed HTML markup inside the content of custom
        fields, for improving the display inside result lists. In this
        case, add a (wildly non-standard) <literal>markup</literal>
        attribute to tell &RCL; that the value is HTML and should not
        be escaped for display.</para>

        <programlisting>
          &lt;meta name="somefield" markup="html" content="Some &lt;i>textual&lt;/i> data" /&gt;
        </programlisting>

        <para>As written above, the processing of fields is described
        in a <link linkend="RCL.PROGRAM.FIELDS">further section</link>.</para> 


        <para>Persistent filters can use another, probably simpler,
        method to produce metadata, by calling the
        <literal>setfield()</literal> helper method. This avoids the
        necessity to produce HTML, and any issue with HTML quoting. See,
        for example, <filename>rclaudio</filename> in &RCL; 1.23 and
        later for an example of handler which outputs
        <literal>text/plain</literal> and uses
        <literal>setfield()</literal> to produce metadata.</para>
        
      </sect2>

      <sect2 id="RCL.PROGRAM.FILTERS.PAGES">
        <title>Page numbers</title>

        <para>The indexer will interpret <literal>^L</literal> characters
        in the handler output as indicating page breaks, and will record
        them. At query time, this allows starting a viewer on the right
        page for a hit or a snippet. Currently, only the PDF, Postscript
        and DVI handlers generate page breaks.</para>

      </sect2>

    </sect1>

    <sect1 id="RCL.PROGRAM.FIELDS">
      <title>Field data processing</title>

      <para><literal>Fields</literal> are named pieces of information
      in or about documents, like <literal>title</literal>,
      <literal>author</literal>, <literal>abstract</literal>.</para> 

      <para>The field values for documents can appear in several ways
      during indexing: either output by input handlers
      as <literal>meta</literal> fields in the HTML header section, or
      extracted from file extended attributes, or added as attributes
      of the <literal>Doc</literal> object when using the API, or
      again synthetized internally by &RCL;.</para>

      <para>The &RCL; query language allows searching for text in a
      specific field.</para>

      <para>&RCL; defines a number of default fields. Additional
      ones can be output by handlers, and described in the
      <filename>fields</filename> configuration file.</para>

      <para>Fields can be:</para>
      <itemizedlist>

        <listitem><para><literal>indexed</literal>, meaning that their
        terms are separately stored in inverted lists (with a specific
        prefix), and that a field-specific search is possible.</para>
        </listitem>

        <listitem><para><literal>stored</literal>, meaning that their
        value is recorded in the index data record for the document,
        and can be returned and displayed with search results.</para>
        </listitem>

      </itemizedlist>

      <para>A field can be either or both indexed and stored. This and 
      other aspects of fields handling is defined inside the
      <filename>fields</filename> configuration file.</para>

      <para>Some fields may also designated as supporting range queries,
      meaning that the results may be selected for an interval of its
      values. See the <link linkend="RCL.INSTALL.CONFIG.FIELDS">configuration section</link> for more details.</para>
      
      <para>The sequence of events for field processing is as follows:
      <itemizedlist>
        <listitem><para>During indexing, 
        <command>recollindex</command> scans all <literal>meta</literal>
        fields in HTML documents (most document types are transformed
        into HTML at some point). It compares the name for each element
        to the configuration defining what should be done with fields
        (the <filename>fields</filename> file)</para>
        </listitem>
        <listitem><para>If the name for the <literal>meta</literal>
        element matches one for a field that should be indexed, the
        contents are processed and the terms are entered into the index
        with the prefix defined in the <filename>fields</filename>
        file.</para>
        </listitem>
        <listitem><para>If the name for the <literal>meta</literal> element
        matches one for a field that should be stored, the content of the
        element is stored with the document data record, from which it
        can be extracted and displayed at query time.</para>
        </listitem>
        <listitem><para>At query time, if a field search is performed, the
        index prefix is computed and the match is only performed against
        appropriately prefixed terms in the index.</para>
        </listitem>
        <listitem><para>At query time, the field can be displayed inside
        the result list by using the appropriate directive in the
        definition of the
        <link linkend="RCL.SEARCH.GUI.CUSTOM.RESLIST">result list paragraph format</link>.
        All fields are displayed on the fields screen of
        the preview window (which you can reach through the right-click
        menu). This is independent of the fact that the search which
        produced the results used the field or not.</para>  
        </listitem>
      </itemizedlist>
      </para>

      <para>You can find more information in the 
      <link linkend="RCL.INSTALL.CONFIG.FIELDS">section about the <filename>fields</filename> file</link>, 
      or in comments inside the file.</para> 

      <para>You can also have a look at the 
      <ulink url="&FAQS;HandleCustomField">example in the FAQs area</ulink>, 
      detailing how one could add a <emphasis>page count</emphasis> field
      to pdf documents for displaying inside result lists.</para>

    </sect1>


    <sect1 id="RCL.PROGRAM.PYTHONAPI">
      <title>Python API</title>

      <sect2 id="RCL.PROGRAM.PYTHONAPI.INTRO">
        <title>Introduction</title>

        <para>The &RCL; Python programming interface can be used both for
        searching and for creating/updating an index. Bindings exist for
        Python2 and Python3 (Jan 2021: python2 support will be dropped
        soon).</para>

        <para>The search interface is used in a number of active projects:
        the <ulink 
              url="https://www.lesbonscomptes.com/recoll/pages/download.html#gssp">
            &RCL; <application>Gnome Shell Search Provider</application>
          </ulink>,
        the <ulink url="https://framagit.org/medoc92/recollwebui">
            &RCL; Web UI</ulink>, and the 
          <ulink 
       url="https://www.lesbonscomptes.com/upmpdcli/upmpdcli-manual.html#UPRCL">
            upmpdcli UPnP Media Server</ulink>, in addition 
          to many small scripts.</para>

        <para>The index update section of the API may be used to create and
        update &RCL; indexes on specific configurations (separate from the
        ones created by <command>recollindex</command>). The resulting
        databases can be queried alone, or in conjunction with regular
        ones, through the GUI or any of the query interfaces.</para>

        <para>The search API is modeled along the Python database API
        version 2.0 specification (early versions used the version 1.0 spec).</para>

        <para>The <literal>recoll</literal> package contains two modules:</para>
        <itemizedlist>
          <listitem><para>The <literal>recoll</literal> module contains
          functions and classes used to query (or update) the
          index.</para></listitem>

          <listitem><para>The <literal>rclextract</literal> module contains
          functions and classes used at query time to access document
          data. The <literal>recoll</literal> module must be imported
          before <literal>rclextract</literal></para>
          </listitem>
        </itemizedlist>

        <para>There is a good chance that your system repository has
        packages for the Recoll Python API, sometimes in a package separate
        from the main one (maybe named something like python-recoll).  Else
        refer to the <link linkend="RCL.INSTALL.BUILDING">Building from source chapter</link>.</para>

        <para>As an introduction, the following small sample will run a
        query and list the title and url for each of the results. The
        <filename>python/samples</filename> source directory contains
        several examples of Python programming with &RCL;, exercising the
        extension more completely, and especially its data extraction
        features.</para>

<programlisting><![CDATA[
#!/usr/bin/python3

from recoll import recoll

db = recoll.connect()
query = db.query()
nres = query.execute("some query")
results = query.fetchmany(20)
for doc in results:
    print("%s %s" % (doc.url, doc.title))
]]></programlisting>

        <para>You can also take a look at the source for the
        <ulink 
	  url="https://framagit.org/medoc92/recollwebui/-/blob/master/webui.py">
		  Recoll WebUI</ulink>, the
        <ulink url="https://framagit.org/medoc92/upmpdcli/-/blob/master/src/mediaserver/cdplugins/uprcl/uprclfolders.py">
		  upmpdcli local media server</ulink>, or the
        <ulink 
  url="https://framagit.org/medoc92/recoll-gssp/-/blob/master/gssp-recoll.py">
		  Gnome Shell Search Provider</ulink>.</para>
        
      </sect2>
      
      <sect2 id="RCL.PROGRAM.PYTHONAPI.ELEMENTS">
        <title>Interface elements</title>

        <para>A few elements in the interface are specific and and need
        an explanation.</para>

        <variablelist>

          <varlistentry id="RCL.PROGRAM.PYTHONAPI.ELEMENTS.IPATH">
            <term>ipath</term> 
            <listitem><para>This data value (set as a field in the Doc
            object) is stored, along with the URL, but not indexed by
            &RCL;. Its contents are not interpreted by the index layer, and
            its use is up to the application. For example, the &RCL; file
            system indexer uses the <literal>ipath</literal> to store the
            part of the document access path internal to (possibly
            imbricated) container documents. <literal>ipath</literal> in
            this case is a vector of access elements (e.g, the first part
            could be a path inside a zip file to an archive member which
            happens to be an mbox file, the second element would be the
            message sequential number inside the mbox
            etc.). <literal>url</literal> and <literal>ipath</literal> are 
            returned in every search result and define the access to the
            original document. <literal>ipath</literal> is empty for
            top-level document/files (e.g. a PDF document which is a
            filesystem file). The &RCL; GUI knows about the structure of the
            <literal>ipath</literal> values used by the filesystem indexer,
            and uses it for such functions as opening the parent of a given
            document.</para>
            </listitem>
          </varlistentry>

          <varlistentry id="RCL.PROGRAM.PYTHONAPI.ELEMENTS.UDI">
            <term>udi</term>
            <listitem><para>An <literal>udi</literal> (unique document
            identifier) identifies a document. Because of limitations inside
            the index engine, it is restricted in length (to 200 bytes),
            which is why a regular URI cannot be used. The structure and
            contents of the <literal>udi</literal> is defined by the
            application and opaque to the index engine. For example, the
            internal file system indexer uses the complete document path
            (file path + internal path), truncated to length, the suppressed
            part being replaced by a hash value. The <literal>udi</literal>
            is not explicit in the query interface (it is used "under the
            hood" by the <filename>rclextract</filename> module), but it is
            an explicit element of the update interface.</para> </listitem>
          </varlistentry>

          <varlistentry id="RCL.PROGRAM.PYTHONAPI.ELEMENTS.PARENTUDI">
            <term>parent_udi</term>
            <listitem><para>If this attribute is set on a document when
            entering it in the index, it designates its physical container
            document. In a multilevel hierarchy, this may not be the
            immediate parent. <literal>parent_udi</literal> is optional, but
            its use by an indexer may simplify index maintenance, as &RCL;
            will automatically delete all children defined by
            <literal>parent_udi == udi</literal> when the document designated
            by <literal>udi</literal> is destroyed. e.g. if a
            <literal>Zip</literal> archive contains entries which are
            themselves containers, like <literal>mbox</literal> files, all
            the subdocuments inside the <literal>Zip</literal> file (mbox,
            messages, message attachments, etc.) would have the same
            <literal>parent_udi</literal>, matching the
            <literal>udi</literal> for the <literal>Zip</literal> file, and
            all would be destroyed when the <literal>Zip</literal> file
            (identified by its <literal>udi</literal>) is removed from the
            index. The standard filesystem indexer uses
            <literal>parent_udi</literal>.</para></listitem>
          </varlistentry>

          <varlistentry> 
            <term>Stored and indexed fields</term> 
            <listitem><para>The
            <link linkend="RCL.INSTALL.CONFIG.FIELDS"><filename>fields</filename> file</link>
            inside the &RCL; configuration defines which
            document fields are either <literal>indexed</literal>
            (searchable), <literal>stored</literal> (retrievable with
            search results), or both. Apart from a few standard/internal
            fields, only the <literal>stored</literal> fields are
            retrievable through the Python search interface.</para>
            </listitem>
          </varlistentry>

        </variablelist>

      </sect2>

      <sect2 id="RCL.PROGRAM.PYTHONAPI.LOG">
        <title>Log messages for Python scripts</title>

      <para>Two specific configuration variables:
      <literal>pyloglevel</literal> and <literal>pylogfilename</literal>
      allow overriding the generic values for Python programs. Set
      <literal>pyloglevel</literal> to 2 to suppress default startup messages
      (printed at level 3).</para>

      </sect2>
      
      <sect2 id="RCL.PROGRAM.PYTHONAPI.SEARCH">
        <title>Python search interface</title>

        <sect3 id="RCL.PROGRAM.PYTHONAPI.RECOLL">
          <title>The recoll module</title>

        <simplesect id="RCL.PROGRAM.PYTHONAPI.RECOLL.CONNECT">
          <title>connect(confdir=None, extra_dbs=None, writable = False)</title>

          <para>The <literal>connect()</literal> function connects to
          one or several &RCL; index(es) and returns
          a <literal>Db</literal> object.</para>
          <para>This call initializes the recoll module, and it should
          always be performed before any other call or object
          creation.</para> 
          <itemizedlist>
            <listitem><para><literal>confdir</literal> may specify
            a configuration directory. The usual defaults
            apply.</para></listitem> 
            <listitem><para><literal>extra_dbs</literal> is a list of
            additional indexes (Xapian directories).</para></listitem>
            <listitem><para><literal>writable</literal> decides if
            we can index new data through this
            connection.</para></listitem>
          </itemizedlist> 
        </simplesect>

        <simplesect id="RCL.PROGRAM.PYTHONAPI.RECOLL.DB">
          <title>The Db class</title>

          <para>A Db object is created by a <literal>connect()</literal>
          call and holds a  connection to a Recoll index.</para>
          <variablelist>
            <varlistentry>
              <term>Db.close()</term>
              <listitem><para>Closes the connection. You can't do anything
              with the <literal>Db</literal> object after
              this.</para></listitem>
            </varlistentry>
            <varlistentry>
              <term>Db.query(), Db.cursor()</term> <listitem><para>These
              aliases return a blank <literal>Query</literal> object
              for this index.</para></listitem>
            </varlistentry>

            <varlistentry>
              <term>Db.setAbstractParams(maxchars,
              contextwords)</term> <listitem><para>Set the parameters used
              to build snippets (sets of keywords in context text
              fragments). <literal>maxchars</literal> defines the
              maximum total size of the abstract. 
              <literal>contextwords</literal> defines how many
              terms are shown around the keyword.</para></listitem>
            </varlistentry>

            <varlistentry>
<term>Db.termMatch(match_type, expr, field='', maxlen=-1, casesens=False, diacsens=False, lang='english')</term> 
              <listitem><para>Expand an expression against the
              index term list. Performs the basic function from the
              GUI term explorer tool. <literal>match_type</literal>
              can be either
              of <literal>wildcard</literal>, <literal>regexp</literal>
              or <literal>stem</literal>. Returns a list of terms
              expanded from the input expression.
              </para></listitem>
            </varlistentry>

          </variablelist>

        </simplesect>
        <simplesect id="RCL.PROGRAM.PYTHONAPI.RECOLL.CLASSES.QUERY">
          <title>The Query class</title>

          <para>A <literal>Query</literal> object (equivalent to a
          cursor in the Python DB API) is created by
          a <literal>Db.query()</literal> call. It is used to
          execute index searches.</para>

          <variablelist>

            <varlistentry>
              <term>Query.sortby(fieldname, ascending=True)</term>
              <listitem><para>Sort results
              by <replaceable>fieldname</replaceable>, in ascending
              or descending order. Must be called before executing
              the search.</para></listitem>
            </varlistentry>
            
            <varlistentry>
<term>Query.execute(query_string, stemming=1, stemlang="english", fetchtext=False, collapseduplicates=False)</term>
              <listitem><para>Starts a search
              for <replaceable>query_string</replaceable>, a &RCL;
              search language string. If the index stores the document
              texts and <literal>fetchtext</literal> is True, store the
              document extracted text in
              <literal>doc.text</literal>.</para></listitem> 
            </varlistentry>

            <varlistentry>
              <term>Query.executesd(SearchData, fetchtext=False, collapseduplicates=False)</term>
              <listitem><para>Starts a search for the query defined by
              the SearchData object. If the index stores the document
              texts and <literal>fetchtext</literal> is True, store the
              document extracted text in
              <literal>doc.text</literal>.</para></listitem>
            </varlistentry>

            <varlistentry>
              <term>Query.fetchmany(size=query.arraysize)</term> 
              <listitem><para>Fetches
              the next <literal>Doc</literal> objects in the current
              search results, and returns them as an array of the
              required size, which is by default the value of
              the <literal>arraysize</literal> data member.</para></listitem>
            </varlistentry>

            <varlistentry>
              <term>Query.fetchone()</term> <listitem><para>Fetches the
              next <literal>Doc</literal> object from the current
              search results. Generates a StopIteration exception if
              there are no results left.</para></listitem>
            </varlistentry>

            <varlistentry>
              <term>Query.close()</term>
              <listitem><para>Closes the query. The object is unusable
              after the call.</para></listitem>
            </varlistentry>

            <varlistentry>
              <term>Query.scroll(value, mode='relative')</term>
              <listitem><para>Adjusts the position in the current result
              set. <literal>mode</literal> can
              be <literal>relative</literal>
              or <literal>absolute</literal>. </para></listitem>
            </varlistentry>

            <varlistentry>
              <term>Query.getgroups()</term>
              <listitem><para>Retrieves the expanded query terms as a list
              of pairs. Meaningful only after executexx In each
              pair, the first entry is a list of user terms (of size
              one for simple terms, or more for group and phrase
              clauses), the second a list of query terms as derived
              from the user terms and used in the Xapian
              Query.</para></listitem>
            </varlistentry>
            
            <varlistentry>
              <term>Query.getxquery()</term>
              <listitem><para>Return the Xapian query description as a
              Unicode string. 
              Meaningful only after executexx.</para></listitem>
            </varlistentry>

            <varlistentry>
              <term>Query.highlight(text, ishtml = 0, methods = object)</term>
              <listitem><para>Will insert &lt;span "class=rclmatch">,
              &lt;/span> tags around the match areas in the input text
              and return the modified text.  <literal>ishtml</literal>
              can be set to indicate that the input text is HTML and
              that HTML special characters should not be escaped.
              <literal>methods</literal> if set should be an object
              with methods startMatch(i) and endMatch() which will be
              called for each match and should return a begin and end
              tag</para></listitem>
            </varlistentry>

            <varlistentry>
              <term>Query.makedocabstract(doc, methods = object))</term>
              <listitem><para>Create a snippets abstract
              for <literal>doc</literal> (a <literal>Doc</literal>
              object) by selecting text around the match terms.
              If methods is set, will also perform highlighting. See
              the highlight method.
              </para></listitem>
            </varlistentry>
            
            <varlistentry>
             <term>Query.getsnippets(doc, maxoccs = -1, ctxwords = -1,
               sortbypage=False, methods = object)</term>
             <listitem><para>Will return a list of extracts from the result
                 document by selecting text around the match terms.  Each
                 entry in the result list is a triple: page number, term,
                 text. By default, the most relevants snippets appear first
                 in the list. Set <literal>sortbypage</literal> to sort by
                 page number instead. If <literal>methods</literal> is set,
                 the fragments will be highlighted (see the highlight
                 method). If <literal>maxoccs</literal> is set, it defines
                 the maximum result list
                 length. <literal>ctxwords</literal> allows adjusting the
                 individual snippet context size. </para></listitem>
            </varlistentry>
            
            <varlistentry>
              <term>Query.__iter__() and Query.next()</term>
              <listitem><para>So that things like
              <literal>for doc in query:</literal>
              will work.</para></listitem>
            </varlistentry>
          </variablelist>

          <variablelist>

            <varlistentry>
              <term>Query.arraysize</term>
              <listitem><para>Default number of records processed by
              fetchmany (r/w).</para></listitem>  
            </varlistentry>

            <varlistentry>
              <term>Query.rowcount</term>
              <listitem><para>Number of records returned by the last
              execute.</para></listitem>
            </varlistentry>

            <varlistentry>
              <term>Query.rownumber</term>
              <listitem><para>Next index to be fetched from
              results. Normally increments after each fetchone() call, but
              can be set/reset before the call to effect seeking
              (equivalent to using <literal>scroll()</literal>). Starts at
              0.</para></listitem>
            </varlistentry>

          </variablelist>

        </simplesect>
        <simplesect id="RCL.PROGRAM.PYTHONAPI.RECOLL.CLASSES.DOC">
          <title>The Doc class</title>

          <para>A <literal>Doc</literal> object contains index data
          for a given document. The data is extracted from the
          index when searching, or set by the indexer program when
          updating. The Doc object has many attributes to be read or
          set by its user. It mostly matches the Rcl::Doc C++
          object. Some of the attributes are predefined, but,
          especially when indexing, others can be set, the name of
          which will be processed as field names by the indexing
          configuration.  Inputs can be specified as Unicode or
          strings. Outputs are Unicode objects. All dates are
          specified as Unix timestamps, printed as strings. Please
          refer to the <filename>rcldb/rcldoc.cpp</filename> C++ file
          for a full description of the predefined attributes. Here
          follows a short list.</para>

          <para><itemizedlist>
            <listitem><para><literal>url</literal> the document URL but
            see also <literal>getbinurl()</literal></para></listitem>
            
            <listitem><para><literal>ipath</literal> the document
            <literal>ipath</literal> for embedded
            documents.</para></listitem> 

            <listitem><para><literal>fbytes, dbytes</literal> the document
            file and text sizes.</para></listitem> 
            <listitem><para><literal>fmtime, dmtime</literal> the document
            file and document times.</para></listitem> 
            
            <listitem><para><literal>xdocid</literal> the document
            Xapian document ID. This is useful if you want to access
            the document through a direct Xapian
            operation.</para></listitem>

            <listitem><para><literal>mtype</literal> the document
            MIME type.</para></listitem>

            <listitem><para>Fields stored by default:
            <literal>author</literal>, <literal>filename</literal>,
            <literal>keywords</literal>,
            <literal>recipient</literal></para></listitem>

          </itemizedlist>                
          </para>
          
          <para>At query time, only the fields that are defined as
          <literal>stored</literal> either by default or in the
          <filename>fields</filename> configuration file will be meaningful
          in the <literal>Doc</literal> object. The document processed text
          may be present or not, depending if the index stores the text at
          all, and if it does, on the <literal>fetchtext</literal> query
          execute option. See also the <literal>rclextract</literal> module
          for accessing document contents.</para>

          <variablelist>

            <varlistentry>
              <term>get(key), [] operator</term>

              <listitem><para>Retrieve the named document
              attribute. You can also use
              <literal>getattr(doc, key)</literal> or
              <literal>doc.key</literal>.</para></listitem>
            </varlistentry>

            <varlistentry>
              <term>doc.key = value</term>

              <listitem><para>Set the the named document attribute. You
              can also use
              <literal>setattr(doc, key, value)</literal>.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term>getbinurl()</term>

              <listitem><para>Retrieve the URL in byte array format (no
              transcoding), for use as parameter to a system
              call.</para></listitem>
            </varlistentry>

            <varlistentry>
              <term>setbinurl(url)</term>

              <listitem><para>Set the URL in byte array format (no
              transcoding).</para></listitem>
            </varlistentry>

            <varlistentry>
              <term>items()</term>
              <listitem><para>Return a dictionary of doc object
              keys/values</para></listitem> 
            </varlistentry>

            <varlistentry>
              <term>keys()</term>
              <listitem><para>list of doc object keys (attribute
              names).</para></listitem>
            </varlistentry>
          </variablelist>

        </simplesect> <!-- Doc -->

        <simplesect id="RCL.PROGRAM.PYTHONAPI.RECOLL.CLASSES.SEARCHDATA">
          <title>The SearchData class</title>

          <para>A <literal>SearchData</literal> object allows building
          a query by combining clauses, for execution
          by <literal>Query.executesd()</literal>. It can be used
          in replacement of the query language approach. The
          interface is going to change a little, so no detailed doc
          for now...</para>

          <variablelist>

            <varlistentry>
              <term>addclause(type='and'|'or'|'excl'|'phrase'|'near'|'sub',
              qstring=string, slack=0, field='', stemming=1,
              subSearch=SearchData)</term>
              <listitem><para></para></listitem>
            </varlistentry>
          </variablelist>

        </simplesect> <!-- SearchData -->

      </sect3> <!-- Recoll module -->

        <sect3 id="RCL.PROGRAM.PYTHONAPI.RCLEXTRACT">
          <title>The rclextract module</title>

          
          <para>Prior to &RCL; 1.25, index queries could not provide document
          content because it was never stored. &RCL; 1.25 and later usually
          store the document text, which can be optionally retrieved when
          running a query (see <literal>query.execute()</literal>
          above - the result is always plain text).</para>

          <para>The <literal>rclextract</literal> module can give access to
          the original document and to the document text content (if not
          stored by the index, or to access an HTML version of the text).
          Accessing the original document is particularly useful if it is
          embedded (e.g. an email attachment).</para>

          <para>You need to import the <literal>recoll</literal> module
          before the <literal>rclextract</literal> module.</para>
          
          <simplesect id="RCL.PROGRAM.PYTHONAPI.RCLEXTRACT.CLASSES.EXTRACTOR">
            <title>The Extractor class</title>

            <variablelist>

              <varlistentry>
                <term>Extractor(doc)</term>
                <listitem><para>An <literal>Extractor</literal> object is
                built from a <literal>Doc</literal> object, output
                from a query.</para></listitem>
              </varlistentry>
              <varlistentry>
                <term>Extractor.textextract(ipath)</term>
                <listitem><para>Extract document defined by
                <replaceable>ipath</replaceable> and return a
                <literal>Doc</literal> object. The
                <literal>doc.text</literal> field has the document text
                converted to either text/plain or text/html according to
                <literal>doc.mimetype</literal>. The typical use would be
                as follows:</para>
<programlisting>
from recoll import recoll, rclextract

qdoc = query.fetchone()
extractor = recoll.Extractor(qdoc)
doc = extractor.textextract(qdoc.ipath)
# use doc.text, e.g. for previewing</programlisting>

                <para>Passing <literal>qdoc.ipath</literal> to
                  <literal>textextract()</literal> is redundant, but
                  reflects the fact that the <literal>Extractor</literal>
                  object actually has the capability to access the other
                  entries in a compound document.</para>
                </listitem>
              </varlistentry>
              <varlistentry>
                <term>Extractor.idoctofile(ipath, targetmtype, outfile='')</term>
                <listitem><para>Extracts document into an output file,
                    which can be given explicitly or will be created as a
                    temporary file to be deleted by the caller. Typical
                    use:</para> 
<programlisting>
from recoll import recoll, rclextract

qdoc = query.fetchone()
extractor = recoll.Extractor(qdoc)
filename = extractor.idoctofile(qdoc.ipath, qdoc.mimetype)</programlisting>
 
                  <para>In all cases the output is a copy, even if the
                  requested document is a regular system file, which may be
                  wasteful in some cases. If you want to avoid this, you
                  can test for a simple file document as follows:
<programlisting>
not doc.ipath and (not "rclbes" in doc.keys() or doc["rclbes"] == "FS")
</programlisting>
                  </para></listitem>
                </varlistentry>

              </variablelist>

          </simplesect>
        </sect3> <!-- rclextract module -->


        <sect3 id="RCL.PROGRAM.PYTHONAPI.SEARCH.EXAMPLE">
          <title>Search API usage example</title>

          <para>The following sample would query the index with a user
          language string. See the <filename>python/samples</filename>
          directory inside the &RCL; source for other
          examples. The <filename>recollgui</filename> subdirectory
          has a very embryonic GUI which demonstrates the
          highlighting and data extraction functions.</para>

<programlisting><![CDATA[
#!/usr/bin/python3

from recoll import recoll

db = recoll.connect()
db.setAbstractParams(maxchars=80, contextwords=4)

query = db.query()
nres = query.execute("some user question")
print("Result count: %d" % nres)
if nres > 5:
    nres = 5
for i in range(nres):
    doc = query.fetchone()
    print("Result #%d" % (query.rownumber))
    for k in ("title", "size"):
        print("%s : %s" % (k, getattr(doc, k)))
    print("%s\n" % db.makeDocAbstract(doc, query))
]]></programlisting>

        </sect3>
      </sect2>


      <sect2 id="RCL.PROGRAM.PYTHONAPI.UPDATE">
        <title>Creating Python external indexers</title>

        <para>The update API can be used to create an index from data which
        is not accessible to the regular &RCL; indexer, or structured to
        present difficulties to the &RCL; input handlers.</para>

        <para>An indexer created using this API will be have equivalent work
        to do as the the Recoll file system indexer: look for modified
        documents, extract their text, call the API for indexing it, take
        care of purging the index out of data from documents which do not
        exist in the document store any more.</para>
        
        <para>The data for such an external indexer should be stored in an
        index separate from any used by the &RCL; internal file system
        indexer. The reason is that the main document indexer purge pass
        (removal of deleted documents) would also remove all the documents
        belonging to the external indexer, as they were not seen during the
        filesystem walk. The main indexer documents would also probably be a
        problem for the external indexer own purge operation.</para>

        <para>While there would be ways to enable multiple foreign indexers
        to cooperate on a single index, it is just simpler to use separate
        ones, and use the multiple index access capabilities of the query
        interface, if needed.</para>

        <para>There are two parts in the update interface:</para>

        <itemizedlist>
          <listitem><para>Methods inside the <filename>recoll</filename>
          module allow inserting data into the index, to make it accessible by
          the normal query interface.</para></listitem>
          <listitem><para>An interface based on scripts execution is defined
          to allow either the GUI or the <filename>rclextract</filename>
          module to access original document data for previewing or
          editing.</para></listitem>
        </itemizedlist>

        <sect3 id="RCL.PROGRAM.PYTHONAPI.UPDATE.UPDATE">
          <title>Python update interface</title>

          <para>The update methods are part of the
          <filename>recoll</filename> module described above. The connect()
          method is used with a <literal>writable=true</literal> parameter to
          obtain a writable <literal>Db</literal> object. The following
          <literal>Db</literal> object methods are then available.</para>

          <variablelist>

            <varlistentry>
              <term>addOrUpdate(udi, doc, parent_udi=None)</term>
              <listitem><para>Add or update index data for a given document
              The
              <literal><link linkend="RCL.PROGRAM.PYTHONAPI.ELEMENTS.UDI">udi</link></literal> 
              string must define a unique id for
                the document. It is an opaque interface element and not
                interpreted inside Recoll. <literal>doc</literal> is a
                <literal><link linkend="RCL.PROGRAM.PYTHONAPI.RECOLL.CLASSES.DOC">Doc</link></literal> 
                object, created from the data to be
                    indexed (the main text should be in
                    <literal>doc.text</literal>). If
                    <literal><link linkend="RCL.PROGRAM.PYTHONAPI.ELEMENTS.PARENTUDI">parent_udi</link></literal>
                    is set, this is a unique identifier for the top-level
                    container (e.g. for the filesystem indexer, this would
                    be the one which is an actual file).</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term>delete(udi)</term>
              <listitem><para>Purge index from all data for
              <literal>udi</literal>, and all documents (if any) which have a
              matrching <literal>parent_udi</literal>.  </para> </listitem>
            </varlistentry>

            <varlistentry>
              <term>needUpdate(udi, sig)</term>
              <listitem><para>Test if the index needs to be updated for the
              document identified by <literal>udi</literal>. If this call is
              to be used, the <literal>doc.sig</literal> field should contain
              a signature value when calling
              <literal>addOrUpdate()</literal>. The
              <literal>needUpdate()</literal> call then compares its
              parameter value with the stored <literal>sig</literal> for
              <literal>udi</literal>. <literal>sig</literal> is an opaque
              value, compared as a string.</para>
              <para>The filesystem indexer uses a
              concatenation of the decimal string values for file size and
              update time, but a hash of the contents could also be
              used.</para>
              <para>As a side effect, if the return value is false (the index
              is up to date), the call will set the existence flag for the
              document (and any subdocument defined by its
              <literal>parent_udi</literal>), so that a later
              <literal>purge()</literal> call will preserve them).</para>
              <para>The use of <literal>needUpdate()</literal> and
              <literal>purge()</literal> is optional, and the indexer may use
              another method for checking the need to reindex or to delete
              stale entries.</para></listitem>
            </varlistentry>
            
            <varlistentry>
              <term>purge()</term>
              <listitem><para>Delete all documents that were not touched
              during the just finished indexing pass (since
              open-for-write). These are the documents for the needUpdate()
              call was not performed, indicating that they no longer exist in
              the primary storage system.</para></listitem> 
            </varlistentry>

          </variablelist>
          
        </sect3>

        <sect3 id="RCL.PROGRAM.PYTHONAPI.UPDATE.ACCESS">
          <title>Query data access for external indexers (1.23)</title>

          <para>&RCL; has internal methods to access document data for its
          internal (filesystem) indexer. An external indexer needs to provide
          data access methods if it needs integration with the GUI
          (e.g. preview function), or support for the
          <filename>rclextract</filename> module.</para>

          <para>The index data and the access method are linked by the
          <literal>rclbes</literal> (recoll backend storage) 
          <literal>Doc</literal> field. You should set this to a short string
          value identifying your indexer (e.g. the filesystem indexer uses either
          "FS" or an empty value, the Web history indexer uses "BGL").</para>

          <para>The link is actually performed inside a
          <filename>backends</filename> configuration file (stored in the
          configuration directory). This defines commands to execute to
          access data from the specified indexer. Example, for the mbox
          indexing sample found in the Recoll source (which sets
          <literal>rclbes="MBOX"</literal>):</para>
<programlisting>[MBOX]
fetch = /path/to/recoll/src/python/samples/rclmbox.py fetch
makesig = path/to/recoll/src/python/samples/rclmbox.py makesig
</programlisting>

          <para><literal>fetch</literal> and <literal>makesig</literal>
          define two commands to execute to respectively retrieve the
          document text and compute the document signature (the example
          implementation uses the same script with different first parameters
          to perform both operations).</para>

          <para>The scripts are called with three additional arguments:
          <literal>udi</literal>, <literal>url</literal>,
          <literal>ipath</literal>, stored with the document when it was
          indexed, and may use any or all to perform the requested
          operation. The caller expects the result data on
          <literal>stdout</literal>.</para>

        </sect3>

        <sect3 id="RCL.PROGRAM.PYTHONAPI.UPDATE.SAMPLES">
          <title>External indexer samples</title>

          <para>The Recoll source tree has two samples of external indexers
          in the <filename>src/python/samples</filename> directory. The more
          interesting one is <filename>rclmbox.py</filename> which indexes a
          directory containing <literal>mbox</literal> folder files. It
          exercises most features in the update interface, and has a data
          access interface.</para>

          <para>See the comments inside the file for more information.</para>
        </sect3>
      </sect2>
      
      <sect2 id="RCL.PROGRAM.PYTHONAPI.COMPAT">
        <title>Package compatibility with the previous version</title>
        
        <para>The following code fragments can be used to ensure that
        code can run with both the old and the new API (as long as it
        does not use the new abilities of the new API of
        course).</para>

        <para>Adapting to the new package structure:</para>
<programlisting><![CDATA[
try:
from recoll import recoll
from recoll import rclextract
hasextract = True
except:
import recoll
hasextract = False
]]></programlisting>

        <para>Adapting to the change of nature of
        the <literal>next</literal> <literal>Query</literal>
        member. The same test can be used to choose to use
        the <literal>scroll()</literal> method (new) or set
        the <literal>next</literal> value (old).</para>

        <programlisting><![CDATA[rownum = query.next if type(query.next) == int else query.rownumber]]></programlisting>

      </sect2> <!-- compat with previous version -->

      
    </sect1>
  </chapter>


  <chapter id="RCL.INSTALL">
    <title>Installation and configuration</title>

    <sect1 id="RCL.INSTALL.BINARY">
      <title>Installing a binary copy</title>

      
      <para>&RCL; binary copies are always distributed as regular
      packages for your system. They can be obtained either through
      the system's normal software distribution framework (e.g.
      <application>Debian/Ubuntu apt</application>,
      <application>FreeBSD</application> ports, etc.), or from some type
      of "backports" repository providing versions newer than the standard
      ones, or found on the &RCL; Web site in some
      cases. The most up-to-date information about Recoll packages can
      usually be found on the
      <ulink url="http://www.recoll.org/pages/download.html">
        <application>Recoll</application> Web site downloads
      page</ulink></para> 

      <para>The &WIN; version of Recoll comes in a self-contained setup
      file, there is nothing else to install.</para>
      
      <para>On &LIN;, the package management tools will automatically
      install hard dependencies for packages obtained from a proper package
      repository. You will have to deal with them by hand for downloaded
      packages (for example, when <command>dpkg</command> complains about
      missing dependencies).</para>

      <para>In all cases, you will have to check or install
      <link linkend="RCL.INSTALL.EXTERNAL">supporting applications</link>
      for the file types that you want to index beyond those that are
      natively processed by &RCL; (text, HTML, email files, and a few
      others).</para>

      <para>You should also maybe have a look at the 
      <link linkend="RCL.INSTALL.CONFIG">configuration section</link>
      (but this may not be necessary for a quick test with default
      parameters). Most parameters can be more conveniently set from the
      GUI interface.</para>

    </sect1>

    <sect1 id="RCL.INSTALL.EXTERNAL">
      <title>Supporting packages</title>

      <note><para>The &WIN; installation of &RCL; is self-contained.
      &WIN; users can skip this section.</para></note>
      
      <para>&RCL; uses external applications to index some file
      types. You need to install them for the file types that you wish to
      have indexed (these are run-time optional dependencies. None is
      needed for building or running &RCL; except for indexing their
      specific file type).</para>

      <para>After an indexing pass, the commands that were found
      missing can be displayed from the <command>recoll</command>
      <guilabel>File</guilabel> menu. The list is stored in the
      <filename>missing</filename> text file inside the configuration
      directory.</para>

      <para>The past has proven that I was unable to maintain an up to date
      application list in this manual. Please check &RCLAPPS; for a
      complete list along with links to the home pages or best
      source/patches pages, and misc tips. What follows is only a
      very short extract of the stable essentials.</para>

      <itemizedlist>

        <listitem><para>PDF files need <command>pdftotext</command>
        which is part of <application>Poppler</application> (usually
        comes with the <literal>poppler-utils</literal>
        package). Avoid the original one from 
        <application>Xpdf</application>.</para></listitem>

        <listitem><para>MS Word documents need
        <command>antiword</command>. It is also useful to have
        <command>wvWare</command> installed as it may be 
        be used as a fallback for some files which
        <command>antiword</command> does not handle.</para></listitem>

        <listitem><para>RTF files need <command>unrtf</command>,
        which, in its older versions, has much trouble with
        non-western character sets. Many Linux distributions carry
        outdated <command>unrtf</command> versions. Check
        &RCLAPPS; for details.</para></listitem>

        <listitem><para>Pictures: &RCL; uses the 
        <application>Exiftool</application>
        <application>Perl</application> package to extract tag
        information. Most image file formats are
        supported.</para></listitem> 

        <listitem><para>Up to &RCL; 1.24, many XML-based formats need the
        <command>xsltproc</command> command, which usually comes with
        <application>libxslt</application>. These are: abiword, fb2
        ebooks, kword, openoffice, opendocument svg. &RCL; 1.25 and later
        process them internally (using libxslt).</para>
        </listitem>
      </itemizedlist>


    </sect1>


    <sect1 id="RCL.INSTALL.BUILDING">
      <title>Building from source</title>

      <sect2 id="RCL.INSTALL.BUILDING.PREREQS">
        <title>Prerequisites</title>

        <para>The following prerequisites are described in broad terms and
        not as specific package names (which will depend on the exact
        platform). The dependencies should be available as packages on most
        common Unix derivatives, and it should be quite uncommon that you
        would have to build one of them.</para>

        <para>If you do not need the GUI, you can avoid all GUI
        dependencies by disabling its build. (See the configure section
        further).</para>
        
        <para>The shopping list:</para>
        <itemizedlist>

          <listitem><para>If you start from git code, you will need the
          <command>autoconf</command>, <command>automake</command> and
          <command>libtool</command> triad. They are not needed for
          building from tar distributions.</para></listitem>

          <listitem><para>C++ compiler. Recent versions require C++11
          compatibility (1.23 and later).</para></listitem>

          <listitem><para><command>bison</command> command (for &RCL; 1.21
          and later).</para></listitem>

          <listitem><para>For building the documentation: the
          <command>xsltproc</command> command, and the Docbook XML and
          style sheet files. You can avoid this dependency by disabling
          documentation building with the
          <literal>--disable-userdoc</literal> <command>configure</command>
          option.</para></listitem>
          
          <listitem><para>Development files
          for <ulink url="http://www.xapian.org"> <application>Xapian
          core</application></ulink>.</para> 
          <important>
            <para>If you are
            building Xapian for an older CPU (before Pentium 4 or Athlon
            64), you need to add the <option>--disable-sse</option> flag
            to the configure command. Else all Xapian application will
            crash with an <literal>illegal instruction</literal>
            error.</para> 
          </important>
          </listitem>

          <listitem> <para>Development files for 
            <ulink url="http://qt-project.org/downloads"><application>Qt 5</application> </ulink>.
            and its own dependencies (X11 etc.)</para> </listitem>

          <listitem><para>Development files for libxslt</para></listitem>

          <listitem><para>Development files for
          <application>zlib</application>.</para> </listitem> 

          <listitem><para>Development files for
          <application>Python</application> (or use
          <literal>--disable-python-module</literal>).</para></listitem>

          <listitem><para>Development files for libchm</para></listitem>
          
          <listitem><para>You may also need 
            <ulink url="http://www.gnu.org/software/libiconv/">libiconv</ulink>.

            On <application>Linux</application> systems, the iconv
            interface is part of libc and you should not need to do
            anything special.</para></listitem>

        </itemizedlist>

        <para>Check the <ulink url="http://www.recoll.org/pages/download.html">
        &RCL; download page</ulink> for up to date version
        information.</para>

      </sect2>

      <sect2 id="RCL.INSTALL.BUILDING.BUILDING">
        <title>Building</title>

        <para>&RCL; has been built on Linux, FreeBSD, Mac OS X, and Solaris,
        most versions after 2005 should be ok, maybe some older ones too
        (Solaris 8 used to be ok). If you build on another system, and
        need to modify things,
        <ulink url="mailto:jfd@recoll.org">I would
        very much welcome patches</ulink>.</para>


        <formalpara>
          <title>Configure options:</title>
          <para>
            <itemizedlist>

              <listitem><para><option>--without-aspell</option> 
              will disable the code for phonetic matching of search
              terms. </para></listitem>

              <listitem><para><option>--with-fam</option> or
              <option>--with-inotify</option> will enable the code for real
              time indexing. Inotify support is enabled by default on Linux
              systems.</para></listitem>
              

              <listitem><para><option>--with-qzeitgeist</option> will
              enable sending <application>Zeitgeist</application>
              events about the visited search results, and needs
              the <application>qzeitgeist</application>
              package.</para></listitem> 

              <listitem><para><option>--disable-webkit</option> is available
              from version 1.17 to implement the result list with a
              <application>Qt</application> QTextBrowser instead of a
              WebKit widget if you do not or can't depend on the
              latter.</para></listitem>

              <listitem><para><option>--disable-qtgui</option> Disable the Qt
              interface. Will allow building the indexer and the command line
              search program in absence of a Qt environment.</para> 
              </listitem>

              <listitem><para><option>--enable-webengine</option> Enable the
              use of Qt Webengine (only meaningful if the Qt GUI 
              is enabled), in place or Qt Webkit.</para></listitem>

              <listitem><para><option>--disable-idxthreads</option> is available
              from version 1.19 to suppress multithreading inside the
              indexing process. You can also use the run-time
              configuration to restrict <command>recollindex</command>
              to using a single thread, but the compile-time option
              may disable a few more unused locks. This only applies
              to the use of multithreading for the core index
              processing (data input). The &RCL; monitor mode always
              uses at least two threads of execution.</para></listitem>

              <listitem><para><option>--disable-python-module</option> will 
              avoid building the <application>Python</application>
              module.</para></listitem>

              <listitem><para><option>--disable-python-chm</option> will
              avoid building the Python libchm interface used to index CHM
              files.</para></listitem>

              <listitem><para><option>--enable-camelcase</option> will enable
              splitting <replaceable>camelCase</replaceable> words. This
              is not enabled by default as it has the unfortunate
              side-effect of making some phrase searches quite
              confusing: ie, <literal>"MySQL manual"</literal> would be
              matched by <literal>"MySQL manual"</literal> and
              <literal>"my sql manual"</literal> but not
              <literal>"mysql manual"</literal> (only inside phrase
              searches).</para>
              </listitem>

              <listitem><para><option>--with-file-command</option> Specify
              the version of the 'file' command to use (ie:
              --with-file-command=/usr/local/bin/file). Can be useful to
              enable the gnu version on systems where the native one is
              bad.</para> </listitem>

              <listitem><para><option>--disable-x11mon</option> Disable
              <application>X11</application> connection monitoring
              inside recollindex. Together with --disable-qtgui, this
              allows building recoll without
              <application>Qt</application> and
              <application>X11</application>.</para> </listitem>

              <listitem><para><option>--disable-userdoc</option> 
              will avoid building the user manual. This avoids having to
              install the Docbook XML/XSL files and the TeX toolchain used for
              translating the manual to PDF.</para></listitem>

              <listitem><para><option>--enable-recollq</option> Enable
              building the <command>recollq</command> command line query
              tool (recoll -t without need for Qt). This is done by 
              default if --disable-qtgui is set but this option
              enables forcing it.</para></listitem>

              <listitem><para><option>--disable-pic</option> (&RCL; versions up
              to 1.21 only) will compile
              &RCL; with position-dependant code. This is incompatible with
              building the KIO or the <application>Python</application>
              or <application>PHP</application> extensions, but might
              yield very marginally faster code.</para></listitem>

              <listitem><para>Of course the usual 
              <application>autoconf</application> <command>configure</command>
              options, like <option>--prefix</option> apply.</para> 
              </listitem>
            </itemizedlist>
          </para>
        </formalpara>

        <para>Normal procedure (for source extracted from a tar
        distribution):</para>
        <screen>
          <userinput>cd recoll-xxx</userinput>
          <userinput>./configure</userinput>
          <userinput>make</userinput>
          <userinput>(practices usual hardship-repelling invocations)</userinput>
        </screen>

        <para>When building from source cloned from the git repository,
        you also need to install <application>autoconf</application>,
        <application>automake</application>, and
        <application>libtool</application> and you must execute
        <literal>sh autogen.sh</literal> in the top source directory
        before running <literal>configure</literal>.</para>
      </sect2>
      
      <sect2 id="RCL.INSTALL.BUILDING.INSTALL">
        <title>Installing</title>
        
        <para>Use <userinput>make install</userinput>
        in the root 
        of the source tree. This will copy the commands to
        <filename><replaceable>prefix</replaceable>/bin</filename>
        and the sample configuration files, scripts and other shared
        data to
        <filename><replaceable>prefix</replaceable>/share/recoll</filename>.
        </para>

      </sect2>

      <sect2 id="RCL.INSTALL.BUILDING.PYTHON">
        <title>Python API package</title>

        <para>The Python interface can be found in the source tree,
        under the <filename>python/recoll</filename> directory.</para>

        <para>As of &RCL; 1.19, the module can be compiled for
        Python3.</para>

        <para>The normal &RCL; build procedure (see above) installs the API
        package for the default system version (python) along with the main
        code. The package for other Python versions (e.g. python3 if the
        system default is python2) must be explicitly built and
        installed.</para>

        <para>The <filename>python/recoll/</filename> directory contains
        the usual <filename>setup.py</filename>. After configuring and
        building the main &RCL; code, you can use the script to build and
        install the Python module:
        <screen>
          <userinput>cd recoll-xxx/python/recoll</userinput>
          <userinput>pythonX setup.py build</userinput>
          <userinput>sudo pythonX setup.py install</userinput>
        </screen>
        </para> 

      </sect2>

      <sect2 id="RCL.INSTALL.BUILDING.SOLARIS">
        <title>Building on Solaris</title>

        <para>We did not test building the GUI on Solaris for recent
        versions. You will need at least Qt 4.4. There are some hints
        on <ulink url="http://www.recoll.org/download-1.14.html">an old
        web site page</ulink>, they may still be valid.</para>

        <para>Someone did test the 1.19 indexer and Python module build,
        they do work, with a few minor glitches. Be sure to use
        GNU <command>make</command> and <command>install</command>.</para> 
      </sect2>

    </sect1>

    <sect1 id="RCL.INSTALL.CONFIG">
      <title>Configuration overview</title>

      <para>Most of the parameters specific to the
      <command>recoll</command> GUI are set through the
      <guilabel>Preferences</guilabel> menu and stored in the standard Qt
      place (<filename>$HOME/.config/Recoll.org/recoll.conf</filename>).
      You probably do not want to edit this by hand.</para>

      <para>&RCL; indexing options are set inside text configuration
      files located in a configuration directory. There can be
      several such directories, each of which defines the parameters
      for one index.</para>

      <para>The configuration files can be edited by hand or through
      the <guilabel>Index configuration</guilabel> dialog 
      (<guilabel>Preferences</guilabel> menu). The GUI tool will try
      to respect your formatting and comments as much as possible,
      so it is quite possible to use both approaches on the same
      configuration.</para> 

      <para>The most accurate documentation for the
      configuration parameters is given by comments inside the default
      files, and we will just give a general overview here.</para>

      <para>For each index, there are at least two sets of
      configuration files. System-wide configuration files are kept
      in a directory named
      like <filename>/usr/share/recoll/examples</filename>,
      and define default values, shared by all indexes. For each
      index, a parallel set of files defines the customized
      parameters.</para>

      <para>The default location of the customized configuration is the
      <filename>.recoll</filename>
      directory in your home. Most people will only use this
      directory.</para> 

      <para>This location can be changed, or others can be added with the
      <envar>RECOLL_CONFDIR</envar> environment variable or the
      <option>-c</option> option parameter to <command>recoll</command> and
      <command>recollindex</command>.</para>

      <para>In addition (as of &RCL; version 1.19.7), it is possible
      to specify two additional configuration directories which will
      be stacked before and after the user configuration
      directory. These are defined by
      the <envar>RECOLL_CONFTOP</envar>
      and <envar>RECOLL_CONFMID</envar> environment
      variables. Values from configuration files inside the top
      directory will override user ones, values from configuration
      files inside the middle directory will override system ones
      and be overridden by user ones. These two variables may be of
      use to applications which augment &RCL; functionality, and
      need to add configuration data without disturbing the user's
      files. Please note that the two, currently single, values will
      probably be interpreted as colon-separated lists in the
      future: do not use colon characters inside the directory
      paths.</para>

      <para>If the <filename>.recoll</filename> directory does not
      exist when <command>recoll</command> or
      <command>recollindex</command> are started, it will be created
      with a set of empty configuration files.
      <command>recoll</command> will give you a chance to edit the
      configuration file before starting
      indexing. <command>recollindex</command> will proceed
      immediately. To avoid mistakes, the automatic directory
      creation will only occur for the
      default location, not if <option>-c</option> or
      <envar>RECOLL_CONFDIR</envar> were used (in the latter
      cases, you will have to create the directory).</para>

      <para>All configuration files share the same format. For
      example, a short extract of the main configuration file might
      look as follows:</para> 
      <programlisting>
        # Space-separated list of files and directories to index.
        topdirs =  ~/docs /usr/share/doc

        [~/somedirectory-with-utf8-txt-files]
        defaultcharset = utf-8
      </programlisting>

      <para>There are three kinds of lines: </para>
      <itemizedlist>
        <listitem><para>Comment (starts with
        <emphasis>#</emphasis>) or empty.</para> 
        </listitem>
        <listitem><para>Parameter affectation (<emphasis>name =
        value</emphasis>).</para> 
        </listitem>
        <listitem><para>Section definition
        ([<emphasis>somedirname</emphasis>]).</para> 
        </listitem>
      </itemizedlist>

      <para>Long lines can be broken by ending each incomplete part with
      a backslash (<literal>\</literal>).</para>
      
      <para>Depending on the type of configuration file, section
      definitions either separate groups of parameters or allow
      redefining some parameters for a directory sub-tree. They stay
      in effect until another section definition, or the end of
      file, is encountered. Some of the parameters used for indexing
      are looked up hierarchically from the current directory
      location upwards. Not all parameters can be meaningfully
      redefined, this is specified for each in the next
      section. </para>

      <important>
        <para>Global parameters <emphasis>must not</emphasis> be defined in
        a directory subsection, else they will not be found at all by the
        &RCL; code, which looks for them at the top level
        (e.g. <literal>skippedPaths</literal>).</para> 
      </important>

      <para>When found at the beginning of a file path, the tilde
      character (~) is expanded to the name of the user's home
      directory, as a shell would do.</para> 
      
      <para>Some parameters are lists of strings. White space is used for
      separation. List elements with embedded spaces can be quoted using
      double-quotes. Double quotes inside these elements can be escaped
      with a backslash.</para>

      <para>No value inside a configuration file can contain a newline
      character. Long lines can be continued by escaping the
      physical newline with backslash, even inside quoted strings.</para>
      <programlisting>
        astringlist =  "some string \
        with spaces"
        thesame = "some string with spaces"        
      </programlisting>

      <para>Parameters which are not part of string lists can't be
      quoted, and leading and trailing space characters are
      stripped before the value is used.</para>

      <formalpara>
        <title>Encoding issues</title>
        <para>Most of the configuration parameters are plain ASCII. Two
        particular sets of values may cause encoding issues:</para>
      </formalpara>


      <para>
        <itemizedlist>
          <listitem><para>File path parameters may contain non-ascii
          characters and should use the exact same byte values as found in
          the file system directory. Usually, this means that the
          configuration file should use the system default locale
          encoding.</para>
          </listitem>
          <listitem><para>The <envar>unac_except_trans</envar> parameter
          should be encoded in UTF-8. If your system locale is not UTF-8, and
          you need to also specify non-ascii file paths, this poses a
          difficulty because common text editors cannot handle multiple
          encodings in a single file. In this relatively unlikely case, you
          can edit the configuration file as two separate text files with
          appropriate encodings, and concatenate them to create the complete
          configuration.</para>
          </listitem>
        </itemizedlist>
      </para>
      
      <sect2 id="RCL.INSTALL.CONFIG.ENVIR">
        <title>Environment variables</title>

        <variablelist>
          <varlistentry>
            <term><varname>RECOLL_CONFDIR</varname></term>
            <listitem><para>Defines the main configuration
            directory.</para></listitem>
          </varlistentry>

          <varlistentry>
            <term><varname>RECOLL_TMPDIR, TMPDIR</varname></term>
            <listitem><para>Locations for temporary files, in this order
            of priority. The default if none of these is set is to use
            <filename>/tmp</filename>. Big temporary files may be created
            during indexing, mostly for decompressing, and also for
            processing, e.g. email attachments.</para></listitem>
          </varlistentry>

          <varlistentry>
            <term><varname>RECOLL_CONFTOP, RECOLL_CONFMID</varname></term>
            <listitem><para>Allow adding configuration directories with
            priorities below and above the user directory (see above the
            Configuration overview section for details).</para></listitem>
          </varlistentry>

          <varlistentry>
            <term><varname>RECOLL_EXTRA_DBS, RECOLL_ACTIVE_EXTRA_DBS</varname></term>
            <listitem><para>
              Help for setting up external indexes. See
              <link linkend="RCL.SEARCH.GUI.MULTIDB">this paragraph</link> for
              explanations.
            </para></listitem>
          </varlistentry>

          <varlistentry>
            <term><varname>RECOLL_DATADIR</varname></term>
            <listitem><para>Defines replacement for the default location
            of Recoll data files, normally found in, e.g.,
            <filename>/usr/share/recoll</filename>).</para></listitem>
          </varlistentry>

          <varlistentry>
            <term><varname>RECOLL_FILTERSDIR</varname></term>
            <listitem><para>Defines replacement for the default location
            of Recoll filters, normally found in, e.g.,
            <filename>/usr/share/recoll/filters</filename>).</para></listitem>
          </varlistentry>

          <varlistentry>
            <term><varname>ASPELL_PROG</varname></term>
            <listitem><para><command>aspell</command> program to use for
            creating the spelling dictionary. The result has to be
            compatible with the <filename>libaspell</filename> which &RCL;
            is using.</para></listitem>
          </varlistentry>

        </variablelist>

      </sect2>

      <!-- <sect2 id="RCL.INSTALL.CONFIG.RECOLLCONF"> -->
&RCLCONF;


      <sect2 id="RCL.INSTALL.CONFIG.FIELDS">
        <title>The fields file</title>

        <para>This file contains information about dynamic fields handling
        in &RCL;. Some very basic fields have hard-wired behaviour,
        and, mostly, you should not change the original data inside the
        <filename>fields</filename> file. But you can create custom fields
        fitting your data and handle them just like they were native
        ones.</para>

        <para>The <filename>fields</filename> file has several sections,
        which each define an aspect of fields processing. Quite often,
        you'll have to modify several sections to obtain the desired
        behaviour.</para>

        <para>We will only give a short description here, you should refer
        to the comments inside the default file for more detailed
        information.</para>

        <para>Field names should be lowercase alphabetic ASCII.</para>

        <variablelist>

          <varlistentry>
            <term>[prefixes]</term>
            <listitem><para>A field becomes indexed (searchable) by having
            a prefix defined in this section. There is a more complete
            explanation of what prefixes are in used by a standard recoll
            installation. In a nutshell: extension prefixes should be all
            caps, begin with XY, and short. E.g. XYMFLD.</para>
            </listitem>
          </varlistentry>
          <varlistentry>
            <term>[values]</term>
            <listitem><para>Fields listed in this section will be stored as
            &XAP; <literal>values</literal> inside the index. This makes
            them available for range queries, allowing to filter results
            according to the field value. This feature currently supports
            string and integer data. See the comments in the file for more
            detail</para> 
            </listitem>
          </varlistentry>
          <varlistentry>
            <term>[stored]</term>
            <listitem><para>A field becomes stored (displayable inside
            results) by having its name listed in this section (typically
            with an empty value).</para>
            </listitem>
          </varlistentry>
          <varlistentry>
            <term>[aliases]</term>
            <listitem><para>This section defines lists of synonyms for the
            canonical names used inside the <literal>[prefixes]</literal>
            and <literal>[stored]</literal> sections</para>
            </listitem>
          </varlistentry>
          <varlistentry>
            <term>[queryaliases]</term>
            <listitem><para>This section also defines aliases for the
            canonic field names, with the difference that the substitution
            will only be used at query time, avoiding any possibility that
            the value would pick-up random metadata from documents.</para>
            </listitem>
          </varlistentry>
          <varlistentry>
            <term>handler-specific sections</term>
            <listitem><para>Some input handlers may need specific
            configuration for handling fields. Only the email message handler
            currently has such a section (named
            <literal>[mail]</literal>). It allows indexing arbitrary email
            headers in addition to the ones indexed by default. Other such
            sections may appear in the future.</para>
            </listitem>
          </varlistentry>

        </variablelist>

        <para>Here follows a small example of a personal
        <filename>fields</filename> 
        file. This would extract a specific email header and
        use it as a searchable field, with data displayable inside result
        lists. (Side note: as the email handler does no decoding on the values,
        only plain ascii headers can be indexed, and only the
        first occurrence will be used for headers that occur several times).

        <programlisting>[prefixes]
        # Index mailmytag contents (with the given prefix)
        mailmytag = XMTAG

        [stored]
        # Store mailmytag inside the document data record (so that it can be
        # displayed - as %(mailmytag) - in result lists).
        mailmytag = 

        [queryaliases]
        filename = fn
        containerfilename = cfn

        [mail]
        # Extract the X-My-Tag mail header, and use it internally with the
        # mailmytag field name
        x-my-tag = mailmytag
        </programlisting>
        </para>


        <sect3 id="RCL.INSTALL.CONFIG.FIELDS.XATTR">
          <title>Extended attributes in the fields file</title>

          <para>&RCL; versions 1.19 and later process user extended
          file attributes as documents fields by default.</para>

          <para>Attributes are processed as fields of the same name,
          after removing the <literal>user</literal> prefix on
          Linux.</para>

          <para>The <literal>[xattrtofields]</literal>
          section of the <filename>fields</filename> file allows
          specifying translations from extended attributes names to
          &RCL; field names. An empty translation disables use of the
          corresponding attribute data.</para>

        </sect3>

      </sect2>

      <sect2 id="RCL.INSTALL.CONFIG.MIMEMAP">
        <title>The mimemap file</title>

        <para><filename>mimemap</filename> specifies the
        file name extension to MIME type mappings.</para> 
        
        <para>For file names without an extension, or with an unknown one,
        a system command (<command>file</command> <option>-i</option>, or
        <command>xdg-mime</command>) will be executed to determine the MIME
        type (this can be switched off, or the command changed inside the
        main configuration file).</para>

        <para>All extension values in <filename>mimemap</filename> must be
        entered in lower case. File names extensions are lower-cased for
        comparison during indexing, meaning that an upper case
        <filename>mimemap</filename> entry will never be matched.</para>

        <para>The mappings can be specified on a per-subtree basis,
        which may be useful in some cases. Example:
        <application>okular</application> notes have a
        <filename>.xml</filename> extension but 
        should be handled specially, which is possible because they
        are usually all located in one place. Example:
        <programlisting>[~/.kde/share/apps/okular/docdata]
        .xml = application/x-okular-notes</programlisting></para>

        <para>The <varname>recoll_noindex</varname>
        <filename>mimemap</filename> variable has been moved to
        <filename>recoll.conf</filename> and renamed to
        <varname>noContentSuffixes</varname>, while keeping the same
        function, as of &RCL; version 1.21. For older &RCL; versions,
        see the documentation for <varname>noContentSuffixes</varname>
        but use <varname>recoll_noindex</varname> in
        <filename>mimemap</filename>.</para>

      </sect2>

      <sect2 id="RCL.INSTALL.CONFIG.MIMECONF">
        <title>The mimeconf file</title>

        <para>The main purpose of the <filename>mimeconf</filename> file is
        to specify how the different MIME types are handled for
        indexing. This is done in the <literal>[index]</literal>
        section, which should not be modified casually. See the comments in
        the file.</para>

        <para>The file also contains other definitions which affect the
        query language and the GUI, and which, in retrospect, should have
        been stored elsewhere.</para>

        <para>The <literal>[icons]</literal> section allows you to change
        the icons which are displayed by the <command>recoll</command> GUI
        in the result lists (the values are the basenames of the
        <literal>png</literal> images inside the
        <filename>iconsdir</filename> directory (which is itself defined
        in <filename>recoll.conf</filename>).</para>

        <para>The <literal>[categories]</literal> section defines the
        groupings of MIME types into <literal>categories</literal> as used
        when adding an <literal>rclcat</literal> clause to a
        <link linkend="RCL.SEARCH.LANG">query language</link>
        query. <literal>rclcat</literal> clauses are also used by the
        default <literal>guifilters</literal> buttons in the GUI (see
        next).</para>

        <para>The filter controls appear at the top of the
        <command>recoll</command> GUI, either as checkboxes just above the
        result list, or as a dropbox in the tool area.</para>

        <para>By default, they are labeled: <literal>media</literal>,
        <literal>message</literal>, <literal>other</literal>,
        <literal>presentation</literal>, <literal>spreadsheet</literal> and
        <literal>text</literal>, and each maps to a document category. This
        is determined in the <literal>[guifilters]</literal> section, where
        each control is defined by a variable naming a query language
        fragment.</para>

        <para>A simple example will hopefully make things clearer.</para>

        <programlisting>[guifilters]

Big Books = dir:"~/My Books" size&gt;10K
My Docs = dir:"~/My Documents"
Small Books = dir:"~/My Books" size&lt;10K
System Docs = dir:/usr/share/doc
        </programlisting>


        <para>The above definition would create four filter checkboxes,
        labelled <literal>Big Books</literal>, <literal>My Docs</literal>,
        etc.</para>

        <para>The text after the equal sign must be a valid query language
        fragment, and, when the button is checked, it will be combined with
        the rest of the query with an AND conjunction.</para>

        <para>Any name text before a colon character will be erased in the
        display, but used for sorting. You can use this to display the
        checkboxes in any order you like. For example, the following would
        do exactly the same as above, but ordering the checkboxes in the
        reverse order.</para>

        <programlisting>[guifilters]

d:Big Books = dir:"~/My Books" size&gt;10K
c:My Docs = dir:"~/My Documents"
b:Small Books = dir:"~/My Books" size&lt;10K
a:System Docs = dir:/usr/share/doc
        </programlisting>

        <para>As you may have guessed, The default
        <literal>[guifilters]</literal> section looks like:</para>
        <programlisting>[guifilters]
text = rclcat:text
spreadsheet = rclcat:spreadsheet
presentation = rclcat:presentation
media = rclcat:media
message = rclcat:message
other = rclcat:other
        </programlisting>
        
      </sect2>


      <sect2 id="RCL.INSTALL.CONFIG.MIMEVIEW">
        <title>The mimeview file</title>

        <para><filename>mimeview</filename> specifies which programs
        are started when you click on an <guilabel>Open</guilabel> link
        in a result list. Ie: HTML is normally displayed using
        <application>firefox</application>, but you may prefer
        <application>Konqueror</application>, your
        <application>openoffice.org</application> 
        program might be named <command>oofice</command> instead of
        <command>openoffice</command> etc.</para>

        <para>Changes to this file can be done by direct editing, or
        through the <command>recoll</command> GUI preferences dialog.</para>

        <para>If <guilabel>Use desktop preferences to choose document
        editor</guilabel> is checked in the &RCL; GUI preferences, all
        <filename>mimeview</filename> entries will be ignored except the
        one labelled <literal>application/x-all</literal> (which is set to
        use <command>xdg-open</command> by default).</para>

        <para>In this case, the <literal>xallexcepts</literal> top level
        variable defines a list of MIME type exceptions which
        will be processed according to the local entries instead of being
        passed to the desktop. This is so that specific &RCL; options
        such as a page number or a search string can be passed to
        applications that support them, such as the
        <application>evince</application> viewer.</para>

        <para>As for the other configuration files, the normal usage
        is to have a <filename>mimeview</filename> inside your own
        configuration directory, with just the non-default entries,
        which will override those from the central configuration
        file.</para>

        <para>All viewer definition entries must be placed under a
        <literal>[view]</literal> section.</para>

        <para>The keys in the file are normally MIME types. You can add an
        application tag to specialize the choice for an area of the
        filesystem (using a <varname>localfields</varname> specification
        in <filename>mimeconf</filename>). The syntax for the key is 
        <replaceable>mimetype</replaceable><literal>|</literal><replaceable>tag</replaceable></para>

        <para>The <varname>nouncompforviewmts</varname> entry, (placed at
        the top level, outside of the <literal>[view]</literal> section),
        holds a list of MIME types that should not be uncompressed before
        starting the viewer (if they are found compressed, ie:
        <replaceable>mydoc.doc.gz</replaceable>).</para>

        <para>The right side of each assignment holds a command to be
        executed for opening the file. The following substitutions are
        performed:</para> 

        <itemizedlist>
          <listitem>
            <formalpara><title>%D</title>
            <para>Document date</para></formalpara>
          </listitem> 

          <listitem><formalpara><title>%f</title>
          <para>File name. This may be the name of a temporary file if
          it was  necessary to create one (ie: to extract a subdocument
          from a  container).</para></formalpara>
          </listitem>

          <listitem><formalpara><title>%i</title>
          <para>Internal path, for subdocuments of containers. The
          format depends on the container type. If this appears in the
          command line, &RCL; will not create a temporary file to
          extract the subdocument, expecting the called application
          (possibly a script) to be able to handle it.</para></formalpara>
          </listitem>

          <listitem><formalpara><title>%M</title>
          <para>MIME type</para></formalpara> 
          </listitem>

          <listitem><formalpara><title>%p</title>
          <para>Page index. Only significant for a subset of document
          types, currently only PDF, Postscript and DVI files. Can be
          used to start the editor at the right page for a match or
          snippet.</para></formalpara>
          </listitem>

          <listitem><formalpara><title>%s</title>
          <para>Search term. The value will only be set for documents
          with indexed page numbers (ie: PDF). The value will be one of
          the matched search terms. It would allow pre-setting the
          value in the "Find" entry inside Evince for example, for easy
          highlighting of the term.</para></formalpara>  
          </listitem>

          <listitem><formalpara><title>%u</title>
          <para>Url.</para></formalpara> 
          </listitem>
        </itemizedlist>

        <para>In addition to the predefined values above, all strings like
        <literal>%(fieldname)</literal> will be replaced by the value of
        the field named <literal>fieldname</literal> for the
        document. This could be used in combination with field
        customisation to help with opening the document.</para> 

      </sect2>

      <sect2 id="RCL.INSTALL.CONFIG.PTRANS">
        <title>The <filename>ptrans</filename> file</title>

        <para><filename>ptrans</filename> specifies query-time path
        translations. These can be useful
        in <link linkend="RCL.SEARCH.PTRANS">multiple cases</link>.
        </para>

        <para>The file has a section for any index which needs
        translations, either the main one or additional query
        indexes. The sections are named with the &XAP; index
        directory names. No slash character should exist at the end
        of the paths (all comparisons are textual). An example
        should make things sufficiently clear</para>

        <programlisting>
          [/home/me/.recoll/xapiandb]
          /this/directory/moved = /to/this/place

          [/path/to/additional/xapiandb]
          /server/volume1/docdir = /net/server/volume1/docdir
          /server/volume2/docdir = /net/server/volume2/docdir
        </programlisting>

      </sect2>


      <sect2 id="RCL.INSTALL.CONFIG.EXAMPLES">
        <title>Examples of configuration adjustments</title>

        <sect3 id="RCL.INSTALL.CONFIG.EXAMPLES.ADDVIEW">
          <title>Adding an external viewer for an non-indexed type</title>

          <para>Imagine that you have some kind of file which does not
          have indexable content, but for which you would like to have a
          functional <guilabel>Open</guilabel> link in the result list
          (when found by file name). The file names end in
          <replaceable>.blob</replaceable> and can be displayed by
          application <replaceable>blobviewer</replaceable>.</para>

          <para>You need two entries in the configuration files for this
          to work:</para>

          <itemizedlist>
            <listitem><para>In <filename>$RECOLL_CONFDIR/mimemap</filename>
            (typically <filename>~/.recoll/mimemap</filename>), add the
            following line:<programlisting>
            .blob = application/x-blobapp
          </programlisting>
          Note that the MIME type is made up here, and you could
          call it <replaceable>diesel/oil</replaceable> just the
          same.</para>
            </listitem>
            <listitem><para>In <filename>$RECOLL_CONFDIR/mimeview</filename>
            under the <literal>[view]</literal> section, add:</para>
            <programlisting>
              application/x-blobapp = blobviewer %f
            </programlisting>
            <para>We are supposing
            that <replaceable>blobviewer</replaceable> wants a file
            name parameter here, you would use <literal>%u</literal> if
            it liked URLs better.</para>
            </listitem>
          </itemizedlist>

          <para>If you just wanted to change the application used by
          &RCL; to display a MIME type which it already knows, you
          would just need to edit <filename>mimeview</filename>. The
          entries you add in your personal file override those in the
          central configuration, which you do not need to
          alter. <filename>mimeview</filename> can also be modified
          from the Gui.</para>

        </sect3>

        <sect3 id="RCL.INSTALL.CONFIG.EXAMPLES.ADDINDEX">
          <title>Adding indexing support for a new file type</title>

          <para>Let us now imagine that the above
          <replaceable>.blob</replaceable> files actually contain
          indexable text and that you know how to extract it with a
          command line program. Getting &RCL; to index the files is
          easy. You need to perform the above alteration, and also to
          add data to the <filename>mimeconf</filename> file
          (typically in <filename>~/.recoll/mimeconf</filename>):</para>
          <itemizedlist>
            <listitem><para>Under the <literal>[index]</literal>
            section, add the following line (more about the
            <replaceable>rclblob</replaceable> indexing script
            later):<programlisting>
application/x-blobapp = exec rclblob</programlisting>
          Or if the files are mostly text and you don't need to process them
          for indexing:<programlisting>
application/x-blobapp = internal text/plain</programlisting>
          </para>
            </listitem>
            <listitem><para>Under the <literal>[icons]</literal>
            section, you should choose an icon to be displayed for the
            files inside the result lists. Icons are normally 64x64
            pixels PNG files which live in
            <filename>/usr/share/recoll/images</filename>.</para>
            </listitem>
            <listitem><para>Under the <literal>[categories]</literal>
            section, you should add the MIME type where it makes sense
            (you can also create a category). Categories may be used
            for filtering in advanced search.</para>
            </listitem>
          </itemizedlist>

          <para>The <replaceable>rclblob</replaceable> handler should
          be an executable program or script which exists inside
          <filename>/usr/share/recoll/filters</filename>. It
          will be given a file name as argument and should output the
          text or html contents on the standard output.</para>

          <para>The <link linkend="RCL.PROGRAM.FILTERS">filter programming</link>
          section describes in more detail how to write an input handler.</para> 

          
        </sect3>
      </sect2>
    </sect1>
  </chapter>
</book>
