[privoxy.git] / doc / source / user-manual.sgml

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<!--
 File        :  doc/source/user-manual.sgml

 Purpose     :  user manual

 Copyright (C) 2001-2021 Privoxy Developers https://www.privoxy.org/
 See LICENSE.

 ========================================================================
 NOTE: Please read developer-manual/documentation.html before touching
 anything in this, or other Privoxy documentation.
 ========================================================================

-->

<article id="index">
<artheader>

<title>Privoxy &p-version; User Manual</title>

<pubdate>
 <subscript>
<!-- Completely the wrong markup, but very little is allowed  -->
<!-- in this part of an article. FIXME -->
 <link linkend="copyright">Copyright</link> &my-copy; 2001-2021 by
 <ulink url="https://www.privoxy.org/">Privoxy Developers</ulink>
 </subscript>
</pubdate>

<!--

Note: the following should generate a separate page, and a live link to it,
all nicely done. But it doesn't for some mysterious reason. Please leave
commented unless it can be fixed proper. For the time being, the
copyright/license declarations will be in their own sgml.

Hal.


-->


<abstract>

<![%dummy;[
 <para>
 <comment>
  This is here to keep vim syntax file from breaking :/
  If I knew enough to fix it, I would.
  PLEASE DO NOT REMOVE! HB: hal@foobox.net
 </comment>
 </para>
]]>

 <para>
  The <citetitle>Privoxy User Manual</citetitle> gives users information on how to
  install, configure and use <ulink
  url="https://www.privoxy.org/">Privoxy</ulink>.
 </para>

<!-- Include privoxy.sgml boilerplate: -->
 &p-intro;
<!-- end privoxy.sgml -->

 <para>
  You can find the latest version of the <citetitle>Privoxy User Manual</citetitle> at  <ulink
  url="https://www.privoxy.org/user-manual/">https://www.privoxy.org/user-manual/</ulink>.
  Please see the <link linkend="contact">Contact section</link> on how to
  contact the developers.
 </para>

</abstract>

</artheader>

<!--   ~~~~~       New section      ~~~~~     -->
<sect1 label="1" id="introduction"><title>Introduction</title>
<para>
 This documentation is included with the current &p-status; version of
 <application>Privoxy</application>, &p-version;<![%p-not-stable;[,
 and is mostly complete at this point. The most up to date reference for the
 time being is still the comments in the source files and in the individual
 configuration files. Development of a new version is currently nearing
 completion, and includes significant changes and enhancements over
 earlier versions]]>.
</para>

<!-- include only in non-stable versions -->
<![%p-not-stable;[
<para>
 Since this is a &p-status; version, not all new features are well tested. This
 documentation may be slightly out of sync as a result (especially with
 <ulink url="https://www.privoxy.org/gitweb/?p=privoxy.git;a=summary">git sources</ulink>).
 And there <emphasis>may be</emphasis> bugs, though hopefully
 not many!
</para>
]]>

<!--   ~~~~~       New section      ~~~~~     -->
<sect2 id="features"><title>Features</title>
<para>
 In addition to the core
 features of ad blocking and
 <ulink url="https://en.wikipedia.org/wiki/Browser_cookie">cookie</ulink> management,
 <application>Privoxy</application> provides many supplemental
 features<![%p-not-stable;[, some of them currently under development]]>,
 that give the end-user more control, more privacy and more freedom:
</para>
<!-- Include newfeatures.sgml boilerplate here: -->
 &newfeatures;
<!-- end boilerplate -->
</sect2>

</sect1>

<!--  ~  End section  ~  -->


<!--   ~~~~~       New section      ~~~~~     -->
<sect1 id="installation"><title>Installation</title>

<para>
 <application>Privoxy</application> is available both in convenient pre-compiled
 packages for a wide range of operating systems, and as raw source code.
 For most users, we recommend using the packages, which can be downloaded from our
 <ulink url="https://sourceforge.net/projects/ijbswa/">Privoxy Project
 Page</ulink>.
</para>

<para>
 Note:
 On some platforms, the installer may remove previously installed versions, if
 found. (See below for your platform). In any case <emphasis>be sure to backup
 your old configuration if it is valuable to you.</emphasis> See the <link
 linkend="upgradersnote">note to upgraders</link> section below.
</para>

<!--   ~~~~~       New section      ~~~~~     -->
<sect2 id="installation-packages"><title>Binary Packages</title>
<para>
How to install the binary packages depends on your operating system:
</para>

<!-- XXX: The installation sections should be sorted -->

<!--   ~~~~~       New section      ~~~~~     -->
<sect3 id="installation-deb"><title>Debian and Ubuntu</title>
<para>
 DEBs can be installed with <literal>apt-get install privoxy</literal>,
 and will use <filename>/etc/privoxy</filename> for the location of
 configuration files.
</para>
</sect3>

<!--   ~~~~~       New section      ~~~~~     -->
<sect3 id="installation-pack-win"><title>Windows</title>

<para>
 Just double-click the installer, which will guide you through
 the installation process. You will find the configuration files
 in the same directory as you installed <application>Privoxy</application> in.
</para>
<para>
 Version 3.0.5 beta introduced full <application>Windows</application> service
 functionality. On Windows only, the <application>Privoxy</application>
 program has two new command line arguments to install and uninstall
 <application>Privoxy</application> as a <emphasis>service</emphasis>.
</para>
 <variablelist>
  <varlistentry>
   <term>Arguments:</term>
   <listitem>
    <para>
     <replaceable class="parameter">--install</replaceable>[:<replaceable class="parameter">service_name</replaceable>]
    </para>
    <para>
     <replaceable class="parameter">--uninstall</replaceable>[:<replaceable class="parameter">service_name</replaceable>]
    </para>
   </listitem>
  </varlistentry>
 </variablelist>
 <para>
 After invoking <application>Privoxy</application> with
 <command>--install</command>, you will need to bring up the
 <application>Windows</application> service console to assign the user you
 want <application>Privoxy</application> to run under, and whether or not you
 want it to run whenever the system starts. You can start the
 <application>Windows</application> services console with the following
 command: <command>services.msc</command>.  If you do not take the manual step
 of modifying <application>Privoxy's</application> service settings, it will
 not start.  Note too that you will need to give Privoxy a user account that
 actually exists, or it will not be permitted to
 write to its log and configuration files.
</para>

</sect3>

<!--   ~~~~~       New section      ~~~~~     -->
<sect3 id="installation-mac"><title>Mac OS X</title>
<para>
 Installation instructions for the OS X platform depend upon whether
 you downloaded a ready-built installation package (.pkg or .mpkg) or have
 downloaded the source code.
</para>
</sect3>
<sect3 renderas="sect4" id="OS-X-install-from-package">
<title>Installation from ready-built package</title>
<para>
 The downloaded file will either be a .pkg (for OS X 10.5 upwards) or a bzipped
 .mpkg file (for OS X 10.4). The former can be double-clicked as is and the
 installation will start; double-clicking the latter will unzip the .mpkg file
 which can then be double-clicked to commence the installation.
</para>
<para>
 The privoxy service will automatically start after a successful installation
 (and thereafter every time your computer starts up) however you will need to
 configure your web browser(s) to use it. To do so, configure them to use a
 proxy for HTTP and HTTPS at the address 127.0.0.1:8118.
</para>
<para>
 To prevent the privoxy service from automatically starting when your computer
 starts up, remove or rename the file <literal>/Library/LaunchDaemons/org.ijbswa.privoxy.plist</literal>
 (on OS X 10.5 and higher) or the folder named
 <literal>/Library/StartupItems/Privoxy</literal> (on OS X 10.4 'Tiger').
</para>
<para>
 To manually start or stop the privoxy service, use the scripts startPrivoxy.sh
 and stopPrivoxy.sh supplied in /Applications/Privoxy. They must be run from an
 administrator account, using sudo.
</para>
<para>
 To uninstall, run /Applications/Privoxy/uninstall.command as sudo from an
 administrator account.
</para>
</sect3>
<sect3 renderas="sect4" id="OS-X-install-from-source">
<title>Installation from source</title>
<para>
 To build and install the Privoxy source code on OS X you will need to obtain
 the macsetup module from the Privoxy Sourceforge CVS repository (refer to
 Sourceforge help for details of how to set up a CVS client to have read-only
 access to the repository). This module contains scripts that leverage the usual
 open-source tools (available as part of Apple's free of charge Xcode
 distribution or via the usual open-source software package managers for OS X
 (MacPorts, Homebrew, Fink etc.) to build and then install the privoxy binary
 and associated files. The macsetup module's README file contains complete
 instructions for its use.
</para>
<para>
 The privoxy service will automatically start after a successful installation
 (and thereafter every time your computer starts up) however you will need to
 configure your web browser(s) to use it. To do so, configure them to use a
 proxy for HTTP and HTTPS at the address 127.0.0.1:8118.
</para>
<para>
 To prevent the privoxy service from automatically starting when your computer
 starts up, remove or rename the file <literal>/Library/LaunchDaemons/org.ijbswa.privoxy.plist</literal>
 (on OS X 10.5 and higher) or the folder named
 <literal>/Library/StartupItems/Privoxy</literal> (on OS X 10.4 'Tiger').
</para>
<para>
 To manually start or stop the privoxy service, use the Privoxy Utility
 for Mac OS X (also part of the macsetup module).  This application can start
 and stop the privoxy service and display its log and configuration files.
</para>
<para>
 To uninstall, run the macsetup module's uninstall.sh as sudo from an
 administrator account.
</para>
</sect3>

<!--   ~~~~~       New section      ~~~~~     -->
<sect3 id="installation-freebsd"><title>FreeBSD</title>

<para>
 Privoxy is part of FreeBSD's Ports Collection, you can build and install
 it with <literal>cd /usr/ports/www/privoxy; make install clean</literal>.
</para>
</sect3>

</sect2>

<!--   ~~~~~       New section      ~~~~~     -->
<sect2 id="installation-source"><title>Building from Source</title>

<para>
 The most convenient way to obtain the <application>Privoxy</application> source
 code is to download the source tarball from our
 <ulink url="https://sourceforge.net/projects/ijbswa/files/Sources/">
    project download page</ulink>,
 or you can get the up-to-the-minute, possibly unstable, development version from
 <ulink url="https://www.privoxy.org/">https://www.privoxy.org/</ulink>.
</para>

<!-- include buildsource.sgml boilerplate: -->
&buildsource;
<!-- end boilerplate -->


    <sect3 id="WINBUILD-CYGWIN"><title>Windows</title>

    <sect4 id="WINBUILD-SETUP"><title>Setup</title>
      <para>
        Install the Cygwin utilities needed to build <application>Privoxy</application>.
        If you have a 64 bit CPU (which most people do by now), get the
        Cygwin setup-x86_64.exe program <ulink url="https://cygwin.com/setup-x86_64.exe">here</ulink>
        (the .sig file is <ulink url="https://cygwin.com/setup-x86_64.exe.sig">here</ulink>).
      </para>
      <para>
        Run the setup program and from View / Category select:
      </para>
      <screen>
  Devel
    autoconf 2.5
    automake 1.15
    binutils
    cmake
    gcc-core
    gcc-g++
    git
    make
    mingw64-i686-gcc-core
    mingw64-i686-zlib
  Editors
    vim
  Libs
    libxslt: GNOME XSLT library (runtime)
  Net
    curl
    openssh
  Text
    docbook-dssl
    docbook-sgml31
    docbook-utils
    openjade
  Utils
    gnupg
  Web
    w3m
</screen>

      <para>
        If you haven't already downloaded the Privoxy source code, get it now:
      </para>
      <screen>
  mkdir &lt;root-dir>
  cd &lt;root-dir>
  git clone https://www.privoxy.org/git/privoxy.git
</screen>

      <para>
        Get the source code (.zip or .tar.gz) for tidy from
        <ulink url="https://github.com/htacg/tidy-html5/releases">
                    https://github.com/htacg/tidy-html5/releases</ulink>,
        unzip into &lt;root-dir> and build the software:
      </para>
      <screen>
  cd &lt;root-dir>
  cd tidy-html5-x.y.z/build/cmake
  cmake ../.. -DCMAKE_BUILD_TYPE=Release -DBUILD_SHARED_LIB:BOOL=OFF -DCMAKE_INSTALL_PREFIX=/usr/local
  make && make install
</screen>

      <para>
        If you want to be able to make a Windows release package, get the NSIS .zip file from
            <!-- FIXME:  which version(s) are known to work? -->
        <ulink url="https://sourceforge.net/projects/nsis/files/NSIS%203/">
                    https://sourceforge.net/projects/nsis/files/NSIS%203/</ulink>
        and extract the NSIS directory to <literal>privoxy/windows</literal>.
        Then edit the windows/GNUmakefile to set the location of the NSIS executable - eg:
      </para>
      <screen>
# Path to NSIS
MAKENSIS = ./nsis/makensis.exe
</screen>

      </sect4>

      <sect4 id="WINBUILD-BUILD"><title>Build</title>

      <para>
        To build just the Privoxy executable and not the whole installation package, do:
      </para>
      <programlisting>
  cd &lt;root-dir>/privoxy
  ./windows/MYconfigure && make
</programlisting>

      <para>
        Privoxy uses the <ulink url="https://en.wikipedia.org/wiki/GNU_build_system">GNU Autotools</ulink>
        for building software, so the process is:
      </para>
      <programlisting>
  $ autoheader              # creates config.h.in
  $ autoconf                # uses config.h.in to create the configure shell script
  $ ./configure [options]   # creates GNUmakefile
  $ make        [options]   # builds the program
</programlisting>

      <para>
        The usual <literal>configure</literal> options for building a native Windows application under cygwin are
      </para>

      <literallayout class="Monospaced">
  --host=i686-w64-mingw32
  --enable-mingw32
  --enable-zlib
  --enable-static-linking
  --disable-pthread
  --disable-dynamic-pcre
</literallayout>

      <para>
        You can set the <literal>CFLAGS</literal> and <literal>LDFLAGS</literal> envars before
        running <literal>configure</literal> to set compiler and linker flags.  For example:
      </para>

      <programlisting>
  $ export CFLAGS="-O2"              # set gcc optimization level
  $ export LDFLAGS="-Wl,--nxcompat"  # Enable DEP
  $ ./configure --host=i686-w64-mingw32 --enable-mingw32  --enable-zlib \
  >             --enable-static-linking --disable-pthread --disable-dynamic-pcre
  $ make                             # build Privoxy
</programlisting>

      <para>
        See the <ulink url="../developer-manual/newrelease.html#NEWRELEASE-WINDOWS">Developer's Manual</ulink>
        for building a Windows release package.
      </para>

    </sect4>
    </sect3>
</sect2>


<!--   ~~~~~       New section      ~~~~~     -->
<sect2 id="installation-keepupdated"><title>Keeping your Installation Up-to-Date</title>

<para>
 If you wish to receive an email notification whenever we release updates of
 <application>Privoxy</application> or the actions file, <ulink
 url="https://lists.privoxy.org/mailman/listinfo/privoxy-announce">subscribe
 to our announce mailing list</ulink>, privoxy-announce@lists.privoxy.org.
</para>

<para>
 In order not to lose your personal changes and adjustments when updating
 to the latest <literal>default.action</literal> file we <emphasis>strongly
 recommend</emphasis> that you use <literal>user.action</literal> and
 <literal>user.filter</literal> for your local
 customizations of <application>Privoxy</application>. See the <link
 linkend="actions-file">Chapter on actions files</link> for details.
</para>

</sect2>


</sect1>

<!--  ~  End section  ~  -->

<!--   ~~~~~       New section      ~~~~~     -->
<sect1 id="whatsnew">
<title>What's New in this Release</title>

&changelog;

<!--   ~~~~~       New section      ~~~~~     -->

<sect2 id="upgradersnote">
<title>Note to Upgraders</title>

<para>
 A quick list of things to be aware of before upgrading from earlier
 versions of <application>Privoxy</application>:
</para>

 <itemizedlist>

 <listitem>
  <para>
   The recommended way to upgrade &my-app; is to backup your old
   configuration files, install the new ones, verify that &my-app;
   is working correctly and finally merge back your changes using
   <application>diff</application> and maybe <application>patch</application>.
  </para>
  <para>
   There are a number of new features in each &my-app; release and
   most of them have to be explicitly enabled in the configuration
   files. Old configuration files obviously don't do that and due
   to syntax changes using old configuration files with a new
   &my-app; isn't always possible anyway.
  </para>
 </listitem>
 <listitem>
  <para>
    Note that some installers remove earlier versions completely,
    including configuration files, therefore you should really save
    any important configuration files!
  </para>
 </listitem>
 <listitem>
  <para>
   On the other hand, other installers don't overwrite existing configuration
   files, thinking you will want to do that yourself.
  </para>
 </listitem>
 <listitem>
  <para>
   In the default configuration only fatal errors are logged now.
   You can change that in the <link linkend="DEBUG">debug section</link>
   of the configuration file. You may also want to enable more verbose
   logging until you verified that the new &my-app; version is working
   as expected.
  </para>
 </listitem>

 <listitem>
    <para>
     Three other config file settings are now off by default:
     <link linkend="enable-remote-toggle">enable-remote-toggle</link>,
     <link linkend="enable-remote-http-toggle">enable-remote-http-toggle</link>,
     and  <link linkend="enable-edit-actions">enable-edit-actions</link>.
     If you use or want these, you will need to explicitly enable them, and
     be aware of the security issues involved.
    </para>
  </listitem>

<!--
 <listitem>
  <para>
   What constitutes a <quote>default</quote> configuration has changed,
   and you may want to review which actions are <quote>on</quote> by
   default. This is primarily a matter of emphasis, but some features
   you may have been used to, may now be <quote>off</quote> by default.
   There are also a number of new actions and filters you may want to
   consider, most of which are not fully incorporated into the default
   settings as yet (see above).
  </para>
 </listitem>
-->
<!--
  <listitem>
   <para>
    The default actions setting is now <literal>Cautious</literal>. Previous
    releases had a default setting of <literal>Medium</literal>. Experienced
    users may want to adjust this, as it is fairly conservative by &my-app;
    standards and past practices. See <ulink
    url="http://config.privoxy.org/edit-actions-list?f=default">
    http://config.privoxy.org/edit-actions-list?f=default</ulink>. New users
    should try the default settings for a while before turning up the volume.
   </para>
  </listitem>

  <listitem>
   <para>
    The default setting has filtering turned <emphasis>off</emphasis>, which
    subsequently means that compression is <emphasis>on</emphasis>. Remember
    that filtering does not work on compressed pages, so if you use, or want to
    use, filtering, you will need to force compression off. Example:
   </para>
 <screen>
  { +<link linkend="filter">filter</link>{google}  +<link linkend="prevent-compression">prevent-compression</link> }
   .google.</screen>
   <para>
    Or if you use a number of filters, or filter many sites, you may just want
    to turn off compression for all sites in
    <filename>default.action</filename> (or
    <filename>user.action</filename>).
   </para>

  </listitem>

  <listitem>
  <para>
   Also, <link linkend="SESSION-COOKIES-ONLY">session-cookies-only</link> is
   off by default now. If you've liked this feature in the past, you may want
   to turn it back on in <filename>user.action</filename> now.
  </para>
  </listitem>


  <listitem>
  <para>
   Some installers may not automatically start
   <application>Privoxy</application> after installation.
  </para>
 </listitem>
-->

 </itemizedlist>

</sect2>
</sect1>

<!--   ~~~~~       New section      ~~~~~     -->
<sect1 id="quickstart"><title>Quickstart to Using Privoxy</title>

 <itemizedlist>

 <listitem>
  <para>
  Install <application>Privoxy</application>. See the <link
  linkend="installation">Installation Section</link> below for platform specific
  information.
 </para>
 </listitem>

 <listitem>
  <para>
   Advanced users and those who want to offer <application>Privoxy</application>
   service to more than just their local machine should check the <link
   linkend="config">main config file</link>, especially the <link
   linkend="access-control">security-relevant</link> options. These are
   off by default.
  </para>
 </listitem>

 <listitem>
  <para>
  Start <application>Privoxy</application>, if the installation program has
  not done this already (may vary according to platform). See the section
  <link linkend="startup">Starting <application>Privoxy</application></link>.
  </para>
 </listitem>

 <listitem>
  <para>
   Set your browser to use <application>Privoxy</application> as HTTP and
   HTTPS (SSL)  <ulink url="https://en.wikipedia.org/wiki/Proxy_server">proxy</ulink>
   by setting the proxy configuration for address of
   <literal>127.0.0.1</literal> and port <literal>8118</literal>.
   <emphasis>DO NOT</emphasis> activate proxying for <literal>FTP</literal> or
   any protocols besides HTTP and HTTPS (SSL) unless you intend to prevent your
   browser from using these protocols.
  </para>
 </listitem>

 <listitem>
  <para>
    Flush your browser's disk and memory caches, to remove any cached ad images.
    If using <application>Privoxy</application> to manage
    <ulink url="https://en.wikipedia.org/wiki/Browser_cookie">cookies</ulink>,
    you should remove any currently stored cookies too.
  </para>
 </listitem>

 <listitem>
  <para>
   A default installation should provide a reasonable starting point for
   most. There will undoubtedly be occasions where you will want to adjust the
   configuration, but that can be dealt with as the need arises. Little
   to no initial configuration is required in most cases, you may want
   to enable the
   <ulink url="config.html#ENABLE-EDIT-ACTIONS">web-based action editor</ulink> though.
   Be sure to read the warnings first.
  </para>
  <para>
   See the <link linkend="configuration">Configuration section</link> for more
   configuration options, and how to customize your installation.
   You might also want to look at the <link
   linkend="quickstart-ad-blocking">next section</link> for a quick
   introduction to how <application>Privoxy</application> blocks ads and
   banners.
</para>
 </listitem>

 <listitem>
  <para>
    If you experience ads that slip through, innocent images that are
    blocked, or otherwise feel the need to fine-tune
    <application>Privoxy's</application> behavior, take a look at the <link
    linkend="actions-file">actions files</link>. As a quick start, you might
    find the <link linkend="act-examples">richly commented examples</link>
    helpful. You can also view and edit the actions files through the <ulink
    url="http://config.privoxy.org">web-based user interface</ulink>. The
    Appendix <quote><link linkend="actionsanat">Troubleshooting: Anatomy of an
    Action</link></quote> has hints on how to understand and debug actions that
    <quote>misbehave</quote>.
  </para>
 </listitem>

 <listitem>
  <para>
   Please see the section <link linkend="contact">Contacting the
   Developers</link> on how to report bugs, problems with websites or to get
   help.
  </para>
 </listitem>

 <listitem>
  <para>
   Now enjoy surfing with enhanced control, comfort and privacy!
  </para>
 </listitem>

 </itemizedlist>


<!--   ~~~~~       New section      ~~~~~     -->

<sect2 id="quickstart-ad-blocking">
<title>Quickstart to Ad Blocking</title>
<!--
 NOTE:  This section is deliberately redundant for those that don't
 want to read the whole thing (which is getting lengthy).
-->
<para>
 Ad blocking is but one of <application>Privoxy's</application>
 array of features. Many of these features are for the technically minded advanced
 user. But, ad and banner blocking is surely common ground for everybody.
</para>
<para>
 This section will provide a quick summary of ad blocking so
 you can get up to speed quickly without having to read the more extensive
 information provided below, though this is highly recommended.
</para>
<para>
 First a bit of a warning ... blocking ads is much like blocking SPAM: the
 more aggressive you are about it, the more likely you are to block
 things that were not intended. And the more likely that some things
 may not work as intended. So there is a trade off here. If you want
 extreme ad free browsing, be prepared to deal with more
 <quote>problem</quote> sites, and to spend more time adjusting the
 configuration to solve these unintended consequences. In short, there is
 not an easy way to eliminate <emphasis>all</emphasis> ads. Either take
 the easy way and settle for <emphasis>most</emphasis> ads blocked with the
 default configuration, or jump in and tweak it for your personal surfing
 habits and preferences.
</para>
<para>
 Secondly, a brief explanation of <application>Privoxy's </application>
 <quote>actions</quote>. <quote>Actions</quote> in this context, are
 the directives we use to tell <application>Privoxy</application> to perform
 some task relating to HTTP transactions (i.e. web browsing). We tell
 <application>Privoxy</application> to take some <quote>action</quote>. Each
 action has a unique name and function. While there are many potential
 <application>actions</application> in <application>Privoxy's</application>
 arsenal, only a few are used for ad blocking. <link
 linkend="actions">Actions</link>, and <link linkend="actions-file">action
 configuration files</link>, are explained in depth below.
</para>
<para>
 Actions are specified in <application>Privoxy's</application> configuration,
 followed by one or more URLs to which the action should apply. URLs
 can actually be URL type <link linkend="af-patterns">patterns</link> that use
 wildcards so they can apply potentially to a range of similar URLs. The
 actions, together with the URL patterns are called a section.
</para>
<para>
 When you connect to a website, the full URL will either match one or more
 of the sections as defined in <application>Privoxy's</application> configuration,
 or not. If so, then <application>Privoxy</application> will perform the
 respective actions. If not, then nothing special happens. Furthermore, web
 pages may contain embedded, secondary URLs that your web browser will
 use to load additional components of the page, as it parses the
 original page's HTML content. An ad image for instance, is just an URL
 embedded in the page somewhere. The image itself may be on the same server,
 or a server somewhere else on the Internet. Complex web pages will have many
 such embedded URLs. &my-app; can deal with each URL individually, so, for
 instance, the main page text is not touched, but images from such-and-such
 server are blocked.
</para>

<para>
 The most important actions for basic ad blocking are:  <literal><link
 linkend="block">block</link></literal>, <literal><link
 linkend="handle-as-image">handle-as-image</link></literal>,
 <literal><link
 linkend="handle-as-empty-document">handle-as-empty-document</link></literal>,and
 <literal><link linkend="set-image-blocker">set-image-blocker</link></literal>:
</para>

 <itemizedlist>

 <listitem>
  <para>
   <literal><link linkend="block">block</link></literal> - this is perhaps
   the single most used action, and is particularly important for ad blocking.
   This action stops any contact between your browser and any URL patterns
   that match this action's configuration. It can be used for blocking ads,
   but also anything that is determined to be unwanted. By itself, it simply
   stops any communication with the remote server and sends
   <application>Privoxy</application>'s own built-in BLOCKED page instead to
   let you now what has happened (with some exceptions, see below).
  </para>
 </listitem>

 <listitem>
  <para>
   <literal><link linkend="handle-as-image">handle-as-image</link></literal> -
   tells <application>Privoxy</application> to treat this URL as an image.
   <application>Privoxy</application>'s default configuration already does this
   for all common image types (e.g. GIF), but there are many situations where this
   is not so easy to determine. So we'll force it in these cases. This is particularly
   important for ad blocking, since  only if we know that it's an image of
   some kind, can we replace it with an image of our choosing, instead of the
   <application>Privoxy</application> BLOCKED page (which would only result in
   a <quote>broken image</quote> icon). There are some limitations to this
   though. For instance, you can't just brute-force an image substitution for
   an entire HTML page in most situations.
  </para>
 </listitem>

 <listitem>
  <para>
   <literal><link linkend="handle-as-empty-document">handle-as-empty-document</link></literal> -
   sends an empty document instead of <application>Privoxy's</application>
   normal BLOCKED HTML page. This is useful for file types that are neither
   HTML nor images, such as blocking JavaScript files.
  </para>
 </listitem>

 <listitem>
  <para>
   <literal><link
   linkend="set-image-blocker">set-image-blocker</link></literal> - tells
   <application>Privoxy</application> what to display in place of an ad image that
   has hit a block rule. For this to come into play, the URL must match a
   <literal><link linkend="block">block</link></literal> action somewhere in the
   configuration, <emphasis>and</emphasis>, it must also match an
   <literal><link linkend="handle-as-image">handle-as-image</link></literal> action.
  </para>
  <para>
   The configuration options on what to display instead of the ad are:
  </para>
  <simplelist>
   <member>
    &nbsp;&nbsp;&nbsp;<emphasis>pattern</emphasis> - a checkerboard pattern, so that an ad
    replacement is obvious. This is the default.
   </member>
  </simplelist>
  <simplelist>
   <member>
    &nbsp;&nbsp;&nbsp;<emphasis>blank</emphasis> - A very small empty GIF image is displayed.
    This is the so-called <quote>invisible</quote> configuration option.
   </member>
  </simplelist>
  <simplelist>
   <member>
    &nbsp;&nbsp;&nbsp;<emphasis>http://&lt;URL&gt;</emphasis> - A redirect to any image anywhere
    of the user's choosing (advanced usage).
   </member>
  </simplelist>
  </listitem>

</itemizedlist>

<para>
 Advanced users will eventually want to explore &my-app;
 <literal><link linkend="filter">filters</link></literal> as well. Filters
 are very different from <literal><link
 linkend="block">blocks</link></literal>.
 A <quote>block</quote> blocks a site, page, or unwanted contented. Filters
 are a way of filtering or modifying what is actually on the page. An example
 filter usage: a text replacement of <quote>no-no</quote> for
 <quote>nasty-word</quote>. That is a very simple example. This process can be
 used for ad blocking, but it is more in the realm of advanced usage and has
 some pitfalls to be wary off.
</para>

<para>
 The quickest way to adjust any of these settings is with your browser through
 the special <application>Privoxy</application> editor at <ulink
 url="http://config.privoxy.org/show-status">http://config.privoxy.org/show-status</ulink>
 (shortcut: <ulink url="http://p.p/">http://p.p/show-status</ulink>). This
 is an internal page, and does not require Internet access.
</para>

<para>
 Note that as of <application>Privoxy</application> 3.0.7 beta the
 action editor is disabled by default. Check the
 <ulink url="config.html#ENABLE-EDIT-ACTIONS">enable-edit-actions
  section in the configuration file</ulink> to learn why and in which
 cases it's safe to enable again.
</para>

<para>
 If you decided to enable the action editor, select the appropriate
 <quote>actions</quote> file, and click
 <quote><guibutton>Edit</guibutton></quote>. It is best to put personal or
 local preferences in <filename>user.action</filename> since this is not
 meant to be overwritten during upgrades, and will over-ride the settings in
 other files. Here you can insert new <quote>actions</quote>, and URLs for ad
 blocking or other purposes, and make other adjustments to the configuration.
 <application>Privoxy</application> will detect these changes automatically.
</para>

<para>
 A quick and simple step by step example:
</para>

 <itemizedlist>

  <listitem>
   <para>
     Right click on the ad image to be blocked, then select
     <quote><guimenuitem>Copy Link Location</guimenuitem></quote> from the
     pop-up menu.
   </para>
  </listitem>
  <listitem>
   <para>
    Set your browser to
    <ulink
 url="http://config.privoxy.org/show-status">http://config.privoxy.org/show-status</ulink>
   </para>
  </listitem>
  <listitem>
   <para>
    Find <filename>user.action</filename> in the top section, and click
    on <quote><guibutton>Edit</guibutton></quote>:
   </para>

 <!-- image of editor and actions files selections -->
  <figure pgwide="0" float="0"><title>Actions Files in Use</title>
   <mediaobject>
     <imageobject>
      <imagedata  fileref="files-in-use.jpg" format="jpg">
       </imageobject>
       <textobject>
        <phrase>[ Screenshot of Actions Files in Use ]</phrase>
      </textobject>
   </mediaobject>
  </figure>
 </listitem>

 <listitem>
  <para>
   You should have a section with only
   <literal><link linkend="block">block</link></literal> listed under
   <quote>Actions:</quote>.
   If not, click a <quote><guibutton>Insert new section below</guibutton></quote>
   button, and in the new section that just appeared, click the
   <guibutton>Edit</guibutton> button right under the word <quote>Actions:</quote>.
   This will bring up a list of all actions. Find
   <literal><link linkend="block">block</link></literal> near the top, and click
   in the <quote>Enabled</quote> column, then <quote><guibutton>Submit</guibutton></quote>
   just below the list.
  </para>
 </listitem>
 <listitem>
  <para>
   Now, in the <literal><link linkend="block">block</link></literal> actions section,
   click the <quote><guibutton>Add</guibutton></quote> button, and paste the URL the
   browser got from <quote><guimenuitem>Copy Link Location</guimenuitem></quote>.
   Remove the <literal>http://</literal> at the beginning of the URL. Then, click
   <quote><guibutton>Submit</guibutton></quote> (or
   <quote><guibutton>OK</guibutton></quote> if in a pop-up window).
  </para>
 </listitem>
 <listitem>
  <para>
   Now go back to the original page, and press <keycap>SHIFT-Reload</keycap>
   (or flush all browser caches). The image should be gone now.
  </para>
 </listitem>

 </itemizedlist>

<para>
 This is a very crude and simple example. There might be good reasons to use a
 wildcard pattern match to include potentially similar images from the same
 site. For a more extensive explanation of <quote>patterns</quote>, and
 the entire actions concept, see <link linkend="actions-file">the Actions
 section</link>.
</para>

<para>
 For advanced users who want to hand edit their config files, you might want
 to now go to the <link linkend="act-examples">Actions Files Tutorial</link>.
 The ideas explained therein also apply to the web-based editor.
</para>
<para>
 There are also various
 <link linkend="filter">filters</link> that can be used for ad blocking
 (filters are a special subset of actions). These
 fall into the <quote>advanced</quote> usage category, and are explained in
 depth in later sections.
</para>

</sect2>

</sect1>

<!--  ~  End section  ~  -->


<!--   ~~~~~       New section      ~~~~~     -->
<sect1 id="startup">
<title>Starting Privoxy</title>
<para>
 Before launching <application>Privoxy</application> for the first time, you
 will want to configure your browser(s) to use
 <application>Privoxy</application> as a HTTP and HTTPS (SSL)
 <ulink url="https://en.wikipedia.org/wiki/Proxy_server">proxy</ulink>. The default is
 127.0.0.1 (or localhost) for the proxy address, and port 8118 (earlier versions
 used port 8000). This is the one configuration step <emphasis>that must be done
</emphasis>!
</para>
<para>
 Please note that <application>Privoxy</application> can only proxy HTTP and
 HTTPS traffic. It will not work with FTP or other protocols.
</para>

 <!-- image of Mozilla Proxy configuration -->
  <figure pgwide="0" float="0"><title>Proxy Configuration Showing
  Mozilla Firefox HTTP and HTTPS (SSL) Settings</title>
   <mediaobject>
     <imageobject>
      <imagedata  fileref="proxy_setup.jpg" format="jpg">
       </imageobject>
       <textobject>
        <phrase>[ Screenshot of Mozilla Firefox Proxy Configuration ]</phrase>
      </textobject>
   </mediaobject>
  </figure>


<para>
 With <application>Firefox</application>, this is typically set under:
</para>

<literallayout>
 <guibutton>Edit</guibutton> -> <guibutton>Preferences</guibutton> ->  <guibutton>Network Settings</guibutton> -> <guibutton>Settings</guibutton>
</literallayout>

<para>
 Or optionally on some platforms:
</para>

<literallayout>
 <guibutton>Edit</guibutton> -> <guibutton>Preferences</guibutton> -> <guibutton>General</guibutton> -> <guibutton>Connection Settings</guibutton> -> <guibutton>Manual Proxy Configuration</guibutton>
</literallayout>


<para>
 With <application>Netscape</application> (and
 <application>Mozilla</application>), this can be set under:
</para>


<literallayout>
<!-- Mix ascii and gui art, something for everybody -->
<!-- spacing on this is tricky -->
 <guibutton>Edit</guibutton> -> <guibutton>Preferences</guibutton> -> <guibutton>Advanced</guibutton> -> <guibutton>Proxies</guibutton> -> <guibutton>HTTP Proxy</guibutton>
</literallayout>

<para>
 For <application>Internet Explorer v.5-7</application>:
</para>

<literallayout>
 <guibutton>Tools</guibutton> -> <guibutton>Internet Options</guibutton> -> <guibutton>Connections</guibutton> -> <guibutton>LAN Settings</guibutton>
</literallayout>

<para>
 Then, check <quote>Use Proxy</quote> and fill in the appropriate info
 (Address: 127.0.0.1, Port: 8118). Include HTTPS (SSL), if you want HTTPS
 proxy support too (sometimes labeled <quote>Secure</quote>). Make sure any
 checkboxes like <quote>Use the same proxy server for all protocols</quote> is
 <emphasis>UNCHECKED</emphasis>. You want only HTTP and HTTPS (SSL)!
</para>

 <!-- image of IE Proxy configuration -->
  <figure pgwide="0" float="0"><title>Proxy Configuration Showing
  Internet Explorer HTTP and HTTPS (Secure) Settings</title>
   <mediaobject>
     <imageobject>
      <imagedata  fileref="proxy2.jpg" format="jpg">
       </imageobject>
       <textobject>
        <phrase>[ Screenshot of IE Proxy Configuration ]</phrase>
      </textobject>
   </mediaobject>
  </figure>


<para>
 After doing this, flush your browser's disk and memory caches to force a
 re-reading of all pages and to get rid of any ads that may be cached. Remove
 any <ulink url="https://en.wikipedia.org/wiki/Browser_cookie">cookies</ulink>,
 if you want <application>Privoxy</application> to manage that. You are now
 ready to start enjoying the benefits of using
 <application>Privoxy</application>!
</para>

<para>
 <application>Privoxy</application> itself is typically started by specifying the
 main configuration file to be used on the command line. If no configuration
 file is specified on the command line, <application>Privoxy</application>
 will look for a file named <filename>config</filename> in the current
 directory. Except on Win32 where it will try <filename>config.txt</filename>.
</para>

<sect2 id="start-debian">
<title>Debian</title>
<para>
 We use a script. Note that Debian typically starts &my-app; upon booting per
 default.  It will use the file
 <filename>/etc/privoxy/config</filename> as its main configuration
 file.
</para>
 <screen>
 # /etc/init.d/privoxy start
</screen>
</sect2>

<sect2 id="start-freebsd">
<title>FreeBSD and ElectroBSD</title>
<para>
 To start <application>Privoxy</application> upon booting, add
 "privoxy_enable='YES'" to <filename>/etc/rc.conf</filename>.
 <application>Privoxy</application> will use
 <filename>/usr/local/etc/privoxy/config</filename> as its main
 configuration file.
</para>
<para>
 If you installed <application>Privoxy</application> into a jail, the
 paths above are relative to the jail root.
</para>
<para>
 To start <application>Privoxy</application> manually, run:
</para>
 <screen>
 # service privoxy onestart
</screen>
</sect2>

<sect2 id="start-windows">
<title>Windows</title>
<para>
Click on the &my-app; Icon to start <application>Privoxy</application>. If no configuration file is
 specified on the command line, <application>Privoxy</application> will look
 for a file named <filename>config.txt</filename>. Note that Windows will
 automatically start &my-app; when the system starts if you chose that option
 when installing.
</para>
<para>
 <application>Privoxy</application> can run with full Windows service functionality.
 On Windows only, the &my-app; program has two new command line arguments
 to install and uninstall &my-app; as a service. See the
 <link linkend="installation-pack-win">Windows Installation
 instructions</link> for details.
</para>
</sect2>

<sect2 id="start-unices">
<title>Generic instructions for Unix derivates (Solaris, NetBSD, HP-UX etc.)</title>
<para>
Example Unix startup command:
</para>
 <screen>
 # /usr/sbin/privoxy --user privoxy /etc/privoxy/config
</screen>
<para>
 Note that if you installed <application>Privoxy</application> through
 a package manager, the package will probably contain a platform-specific
 script or configuration file to start <application>Privoxy</application>
 upon boot.
</para>
</sect2>

<sect2 id="start-macosx">
<title>Mac OS X</title>
<para>
 The privoxy service will automatically start after a successful installation
 (and thereafter every time your computer starts up) however you will need to
 configure your web browser(s) to use it. To do so, configure them to use a
 proxy for HTTP and HTTPS at the address 127.0.0.1:8118.
</para>
<para>
 To prevent the privoxy service from automatically starting when your computer
 starts up, remove or rename the file <literal>/Library/LaunchDaemons/org.ijbswa.privoxy.plist</literal>
 (on OS X 10.5 and higher) or the folder named
 <literal>/Library/StartupItems/Privoxy</literal> (on OS X 10.4 'Tiger').
</para>
<para>
 To manually start or stop the privoxy service, use the scripts startPrivoxy.sh
 and stopPrivoxy.sh supplied in /Applications/Privoxy. They must be run from an
 administrator account, using sudo.
</para>
</sect2>


<!--

<para>
 See the section <link linkend="cmdoptions">Command line options</link> for
 further info.
</para>

must find a better place for this paragraph

<para>
 The included default configuration files should give a reasonable starting
 point. Most of the per site configuration is done in the
 <ulink url="actions-file.html"><quote>actions</quote></ulink> files. These are
 where various cookie actions are defined, ad and banner blocking, and other
 aspects of <application>Privoxy</application> configuration. There are several
 such files included, with varying levels of aggressiveness.
</para>

<para>
 You will probably want to keep an eye out for sites for which you may prefer
 persistent cookies, and add these to your actions configuration as needed. By
 default, most of these will be accepted only during the current browser
 session (aka <quote>session cookies</quote>), unless you add them to the
 configuration. If you want the browser to handle this instead, you will need
 to edit <filename>user.action</filename> (or through the web based interface)
 and disable this feature. If you use more than one browser, it would make
 more sense to let <application>Privoxy</application> handle this. In which
 case, the browser(s) should be set to accept all cookies.
</para>

<para>
 Another feature where you will probably want to define exceptions for trusted
 sites is the popup-killing (through  <ulink
 url="actions-file.html#FILTER-POPUPS"><quote>+filter{popups}</quote></ulink>),
 because your favorite shopping, banking, or leisure site may need
 popups (explained below).
</para>

<para>
 <application>Privoxy</application> does not support all of the optional HTTP/1.1
 features yet. In the unlikely event that you experience inexplicable problems
 with browsers that use HTTP/1.1 per default
 (like <application>Mozilla</application> or recent versions of I.E.), you might
 try to force HTTP/1.0 compatibility. For Mozilla, look under <literal>Edit -&gt;
 Preferences -&gt; Debug -&gt; Networking</literal>.
 Alternatively, set the <quote>+downgrade-http-version</quote> config option in
 <filename>default.action</filename> which will downgrade your browser's HTTP
 requests from HTTP/1.1 to HTTP/1.0 before processing them.
</para>

<para>
 After running <application>Privoxy</application> for a while, you can
 start to fine tune the configuration to suit your personal, or site,
 preferences and requirements. There are many, many aspects that can
 be customized. <quote>Actions</quote>
 can be adjusted by pointing your browser to
 <ulink url="http://config.privoxy.org/">http://config.privoxy.org/</ulink>
 (shortcut: <ulink url="http://p.p/">http://p.p/</ulink>),
 and then follow the link to <quote>View &#38; Change the Current Configuration</quote>.
 (This is an internal page and does not require Internet access.)
</para>

<para>
 In fact, various aspects of <application>Privoxy</application>
 configuration can be viewed from this page, including
 current configuration parameters, source code version numbers,
 the browser's request headers, and <quote>actions</quote> that apply
 to a given URL. In addition to the actions file
 editor mentioned above, <application>Privoxy</application> can also
 be turned <quote>on</quote> and <quote>off</quote> (toggled) from this page.
</para>

<para>
 If you encounter problems, try loading the page without
 <application>Privoxy</application>. If that helps, enter the URL where
 you have the problems into <ulink url="http://p.p/show-url-info">the browser
 based rule tracing utility</ulink>. See which rules apply and why, and
 then try turning them off for that site one after the other, until the problem
 is gone. When you have found the culprit, you might want to turn the rest on
 again.
</para>

<para>
 If the above paragraph sounds gibberish to you, you might want to <link
 linkend="actions-file">read more about the actions concept</link>
 or even dive deep into the <link linkend="actionsanat">Appendix
 on actions</link>.
</para>

<para>
 If you can't get rid of the problem at all, think you've found a bug in
 Privoxy, want to propose a new feature or smarter rules, please see the
 section <link linkend="contact"><quote>Contacting the
 Developers</quote></link> below.
</para>

-->

<!--   ~~~~~       New section      ~~~~~     -->
<sect2 id="cmdoptions">
<title>Command Line Options</title>
<para>
 <application>Privoxy</application> may be invoked with the following
 command-line options:
</para>

 <itemizedlist>

 <listitem>
  <para>
   <emphasis>--config-test</emphasis>
  </para>
  <para>
   Exit after loading the configuration files before binding to
   the listen address. The exit code signals whether or not the
   configuration files have been successfully loaded.
  </para>
  <para>
   If the exit code is 1, at least one of the configuration files
   is invalid, if it is 0, all the configuration files have been
   successfully loaded (but may still contain errors that can
   currently only be detected at run time).
  </para>
  <para>
   This option doesn't affect the log setting, combination with
   <emphasis>--no-daemon</emphasis> is recommended if a configured
   log file shouldn't be used.
  </para>
 </listitem>
 <listitem>
  <para>
    <emphasis>--version</emphasis>
  </para>
  <para>
     Print version info and exit. Unix only.
  </para>
 </listitem>
 <listitem>
  <para>
    <emphasis>--help</emphasis>
  </para>
  <para>
   Print short usage info and exit. Unix only.
  </para>
 </listitem>
 <listitem>
  <para>
   <emphasis>--no-daemon</emphasis>
  </para>
  <para>
   Don't become a daemon, i.e. don't fork and become process group
   leader, and don't detach from controlling tty. Unix only.
  </para>
 </listitem>
 <listitem>
  <para>
   <emphasis>--pidfile FILE</emphasis>
  </para>
  <para>
   On startup, write the process ID to <emphasis>FILE</emphasis>. Delete the
   <emphasis>FILE</emphasis> on exit. Failure to create or delete the
   <emphasis>FILE</emphasis> is non-fatal. If no <emphasis>FILE</emphasis>
   option is given, no PID file will be used. Unix only.
  </para>
 </listitem>
 <listitem>
  <para>
   <emphasis>--user USER[.GROUP]</emphasis>
  </para>
  <para>
   After (optionally) writing the PID file, assume the user  ID  of
   <emphasis>USER</emphasis>, and if included the GID of GROUP.  Exit if the
   privileges are not sufficient to do so. Unix only.
  </para>
 </listitem>
 <listitem>
  <para>
   <emphasis>--chroot</emphasis>
  </para>
  <para>
   Before changing to the user ID given in the <emphasis>--user</emphasis> option,
   chroot to that user's home directory, i.e. make the kernel pretend to the &my-app;
   process that the directory tree starts there. If set up carefully, this can limit
   the impact of possible vulnerabilities in &my-app; to the files contained in that hierarchy.
   Unix only.
  </para>
 </listitem>
 <listitem>
  <para>
   <emphasis>--pre-chroot-nslookup hostname</emphasis>
  </para>
  <para>
   Specifies a hostname (for example www.privoxy.org) to look up before doing a chroot.
   On some systems, initializing the resolver library involves reading config files from
   /etc and/or loading additional shared libraries from /lib.
   On these systems, doing a hostname lookup before the chroot reduces
   the number of files that must be copied into the chroot tree.
  </para>
  <para>
   For fastest startup speed, a good value is a hostname that is not in /etc/hosts but that
   your local name server (listed in /etc/resolv.conf) can resolve without recursion
   (that is, without having to ask any other name servers). The hostname need not exist,
   but if it doesn't, an error message (which can be ignored) will be output.
  </para>
 </listitem>

 <listitem>
  <para>
    <emphasis>configfile</emphasis>
  </para>
  <para>
    If no <emphasis>configfile</emphasis> is included on the command line,
    <application>Privoxy</application> will look for a file named
    <quote>config</quote> in the current directory (except on Win32
    where it will look for <quote>config.txt</quote> instead). Specify
    full path to avoid confusion. If no config file is found,
    <application>Privoxy</application> will fail to start.
  </para>
 </listitem>

 </itemizedlist>

<para>
 On <application>MS Windows</application> only there are two additional
 command-line options to allow <application>Privoxy</application> to install and
 run as a <emphasis>service</emphasis>. See the
<link linkend="installation-pack-win">Window Installation section</link>
for details.
</para>

</sect2>

</sect1>

<!--  ~  End section  ~  -->


<!--   ~~~~~       New section      ~~~~~     -->
<sect1 id="configuration"><title>Privoxy Configuration</title>
 <para>
  All <application>Privoxy</application> configuration is stored
  in text files. These files can be edited with a text editor.
  Many important aspects of <application>Privoxy</application> can
  also be controlled easily with a web browser.
 </para>


<!--   ~~~~~       New section      ~~~~~     -->

<sect2 id="control-with-webbrowser">
<title>Controlling Privoxy with Your Web Browser</title>
<para>
 <application>Privoxy</application>'s user interface can be reached through the special
 URL <ulink url="http://config.privoxy.org/">http://config.privoxy.org/</ulink>
 (shortcut: <ulink url="http://p.p/">http://p.p/</ulink>),
 which is a built-in page and works without Internet access.
 You will see the following section:
</para>

<!-- Needs to be put in a table and colorized  -->
<screen><!-- want the background color that goes with screen -->
 <msgtext>
 <bridgehead renderas="sect2">&nbsp;&nbsp;&nbsp;&nbsp;Privoxy Menu</bridgehead>
 <simplelist>
 <member>
  &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&squf;&nbsp;&nbsp;<ulink url="http://config.privoxy.org/show-status">View & change the current configuration</ulink>
 </member>
 <member>
  &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&squf;&nbsp;&nbsp;<ulink url="http://config.privoxy.org/client-tags">View or toggle the tags that can be set based on the client's address</ulink>
 </member>
 <member>
  &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&squf;&nbsp;&nbsp;<ulink url="http://config.privoxy.org/show-request">View the request headers.</ulink>
 </member>
 <member>
  &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&squf;&nbsp;&nbsp;<ulink url="http://config.privoxy.org/show-url-info">Look up which actions apply to a URL and why</ulink>
 </member>
 <member>
  &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&squf;&nbsp;&nbsp;<ulink url="http://config.privoxy.org/toggle">Toggle Privoxy on or off</ulink>
 </member>
 <member>
  &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&squf;&nbsp;&nbsp;<ulink
  url="https://www.privoxy.org/&p-version;/user-manual/">Documentation</ulink>
 </member>
 </simplelist>
 </msgtext>
</screen>


<para>
 This should be self-explanatory. Note the first item leads to an editor for the
 <link linkend="actions-file">actions files</link>, which is where the ad, banner,
 cookie, and URL blocking magic is configured as well as other advanced features of
 <application>Privoxy</application>. This is an easy way to adjust various
 aspects of <application>Privoxy</application> configuration. The actions
 file, and other configuration files, are explained in detail below.
</para>

<para>
 <quote>Toggle Privoxy On or Off</quote> is handy for sites that might
 have problems with your current actions and filters. You can in fact use
 it as a test to see whether it is <application>Privoxy</application>
 causing the problem or not. <application>Privoxy</application> continues
 to run as a proxy in this case, but all manipulation is disabled, i.e.
 <application>Privoxy</application> acts like a normal forwarding proxy.
</para>

<para>
 Note that several of the features described above are disabled by default
 in <application>Privoxy</application> 3.0.7 beta and later.
 Check the
 <ulink url="config.html">configuration file</ulink> to learn why
 and in which cases it's safe to enable them again.
</para>

</sect2>

<!--  ~  End section  ~  -->




<!--   ~~~~~       New section      ~~~~~     -->

<sect2 id="confoverview">
<title>Configuration Files Overview</title>
<para>
 For Unix, *BSD and GNU/Linux, all configuration files are located in
 <filename>/etc/privoxy/</filename> by default. For MS Windows
 these are all in the same directory as the
 <application>Privoxy</application> executable. <![%p-not-stable;[ The name
 and number of configuration files has changed from previous versions, and is
 subject to change as development progresses.]]>
</para>

<para>
 The installed defaults provide a reasonable starting point, though
 some settings may be aggressive by some standards. For the time being, the
 principle configuration files are:
</para>

 <itemizedlist>

  <listitem>
   <para>
     The <link linkend="config">main configuration file</link> is named <filename>config</filename>
     on GNU/Linux, Unix, BSD, and <filename>config.txt</filename>
     on Windows. This is a required file.
   </para>
  </listitem>

  <listitem>
   <para>
    <filename>match-all.action</filename> is used to define which <quote>actions</quote>
    relating to banner-blocking, images, pop-ups, content modification, cookie handling
    etc should be applied by default. It should be the first actions file loaded.
   </para>
   <para>
    <filename>default.action</filename> defines many exceptions (both positive and negative)
    from the default set of actions that's configured in <filename>match-all.action</filename>.
    It should be the second actions file loaded and shouldn't be edited by the user.
   </para>
   <para>
    Multiple actions files may be defined in <filename>config</filename>. These
    are processed in the order they are defined. Local customizations and locally
    preferred exceptions to the default policies as defined in
    <filename>match-all.action</filename> (which you will most probably want
    to define sooner or later) are best applied in <filename>user.action</filename>,
    where you can preserve them across upgrades. The file isn't installed by all
    installers, but you can easily create it yourself with a text editor.
   </para>
   <para>
    There is also a web based editor that can be accessed from
    <ulink
    url="http://config.privoxy.org/show-status">http://config.privoxy.org/show-status</ulink>
    (Shortcut: <ulink
    url="http://p.p/show-status">http://p.p/show-status</ulink>) for the
    various actions files.
   </para>
  </listitem>

  <listitem>
   <para>
    <quote>Filter files</quote> (the <link linkend="filter-file">filter
    file</link>) can be used to re-write the raw page content, including
    viewable text as well as embedded HTML and JavaScript, and whatever else
    lurks on any given web page. The filtering jobs are only pre-defined here;
    whether to apply them or not is up to the actions files.
    <filename>default.filter</filename> includes various filters made
    available for use by the developers. Some are much more intrusive than
    others, and all should be used with caution. You may define additional
    filter files in <filename>config</filename> as you can with
    actions files. We suggest <filename>user.filter</filename> for any
    locally defined filters or customizations.
   </para>
  </listitem>

 </itemizedlist>

<para>
 The syntax of the configuration and filter files may change between different
 Privoxy versions, unfortunately some enhancements cost backwards compatibility.
 <!-- Add link to documentation-->
</para>

<para>
 All files use the <quote><literal>#</literal></quote> character to denote a
 comment (the rest of the line will be ignored) and understand line continuation
 through placing a backslash ("<literal>\</literal>") as the very last character
 in a line. If the <literal>#</literal> is preceded by a backslash, it looses
 its special function. Placing a <literal>#</literal> in front of an otherwise
 valid configuration line to prevent it from being interpreted is called "commenting
 out" that line. Blank lines are ignored.
</para>

<para>
 The actions files and filter files
 can use Perl style <link linkend="regex">regular expressions</link> for
 maximum flexibility.
</para>

<para>
 After making any changes, there is no need to restart
 <application>Privoxy</application> in order for the changes to take
 effect. <application>Privoxy</application> detects such changes
 automatically. Note, however, that it may take one or two additional
 requests for the change to take effect. When changing the listening address
 of <application>Privoxy</application>, these <quote>wake up</quote> requests
 must obviously be sent to the <emphasis>old</emphasis> listening address.
</para>

<![%p-not-stable;[
<para>
 While under development, the configuration content is subject to change.
 The below documentation may not be accurate by the time you read this.
 Also, what constitutes a <quote>default</quote> setting, may change, so
 please check all your configuration files on important issues.
</para>
]]>

</sect2>
</sect1>
<!--  ~  End section  ~  -->


<!--   ~~~~~~~~       New section Header    ~~~~~~~~~     -->

<!-- **************************************************** -->
<!-- Include config.sgml here -->
<!-- This is where the entire config file is detailed. -->
 &config;
<!-- end include  -->


<!--  ~  End section  ~  -->



<!--   ~~~~~~~~       New section Header    ~~~~~~~~~     -->

<sect1 id="actions-file"><title>Actions Files</title>


<!--
  XXX: similar descriptions are in the Configuration Files sections.
  We should only describe them at one place.
-->
<para>
 The actions files are used to define what <emphasis>actions</emphasis>
 <application>Privoxy</application> takes for which URLs, and thus determines
 how ad images, cookies and various other aspects of HTTP content and
 transactions are handled, and on which sites (or even parts thereof).
 There are a number of such actions, with a wide range of functionality.
 Each action does something a little different.
 These actions give us a veritable arsenal of tools with which to exert
 our control, preferences and independence. Actions can be combined so that
 their effects are aggregated when applied against a given set of URLs.
</para>
<para>
 There
 are three action files included with <application>Privoxy</application> with
 differing purposes:
</para>
 <itemizedlist>
  <listitem>
   <para>
    <filename>match-all.action</filename> - is used to define which
    <quote>actions</quote> relating to banner-blocking, images, pop-ups,
    content modification, cookie handling etc should be applied by default.
    It should be the first actions file loaded
   </para>
  </listitem>
  <listitem>
   <para>
    <filename>default.action</filename> - defines many exceptions (both
    positive and negative) from the default set of actions that's configured
    in <filename>match-all.action</filename>. It is a set of rules that should
    work reasonably well as-is for most users. This file is only supposed to
    be edited by the developers. It should be the second actions file loaded.
   </para>
  </listitem>
  <listitem>
   <para>
    <filename>user.action</filename> - is intended to be for local site
    preferences and exceptions. As an example, if your ISP or your bank
    has specific requirements, and need special handling, this kind of
    thing should go here. This file will not be upgraded.
   </para>
  </listitem>
  <listitem>
   <para>
    <guibutton>Edit</guibutton>  <guibutton>Set to Cautious</guibutton> <guibutton>Set to Medium</guibutton>  <guibutton>Set to Advanced</guibutton>
   </para>
   <para>
    These have increasing levels of aggressiveness <emphasis>and have no
    influence on your browsing unless you select them explicitly in the
    editor</emphasis>. A default installation should be pre-set to
    <literal>Cautious</literal>. New users should try this for a while before
    adjusting the settings to more aggressive levels. The more aggressive
    the settings, then the more likelihood there is of problems such as sites
    not working as they should.
   </para>
   <para>
    The <guibutton>Edit</guibutton> button allows you to turn each
    action on/off individually for fine-tuning. The <guibutton>Cautious</guibutton>
    button changes the actions list to low/safe settings which will activate
    ad blocking and a minimal set of &my-app;'s features, and subsequently
    there will be less of a chance for accidental problems. The
    <guibutton>Medium</guibutton> button sets the list to a medium level of
    other features and a low level set of privacy features. The
    <guibutton>Advanced</guibutton> button sets the list to a high level of
    ad blocking and medium level of privacy. See the chart below. The latter
    three buttons over-ride any changes via with the
    <guibutton>Edit</guibutton> button. More fine-tuning can be done in the
    lower sections of this internal page.
   </para>
   <para>
    While the actions file editor allows to enable these settings in all
    actions files, they are only supposed to be enabled in the first one
    to make sure you don't unintentionally overrule earlier rules.
   </para>
   <para>
    The default profiles, and their associated actions, as pre-defined in
    <filename>default.action</filename> are:
   </para>
    <table frame=all id="default-configurations"><title>Default Configurations</title>
    <tgroup cols=4 align=left colsep=1 rowsep=1>
    <colspec colname=c1>
    <colspec colname=c2>
    <colspec colname=c3>
    <colspec colname=c4>
    <thead>
    <row>
      <entry>Feature</entry>
      <entry>Cautious</entry>
      <entry>Medium</entry>
      <entry>Advanced</entry>
    </row>
    </thead>
    <!--  <tfoot> -->
    <!--  <row> -->
    <!--    <entry>f1</entry> -->
    <!--    <entry>f2</entry> -->
    <!--    <entry>f3</entry> -->
    <!--    <entry>f4</entry> -->
    <!--  </row> -->
    <!--  </tfoot> -->
    <tbody>

    <row>
      <entry>Ad-blocking Aggressiveness</entry>
      <entry>medium</entry>
      <entry>high</entry>
      <entry>high</entry>
    </row>

    <row>
      <entry>Ad-filtering by size</entry>
      <entry>no</entry>
      <entry>yes</entry>
      <entry>yes</entry>
    </row>

    <row>
      <entry>Ad-filtering by link</entry>
      <entry>no</entry>
      <entry>no</entry>
      <entry>yes</entry>
    </row>
    <row>
      <entry>Pop-up killing</entry>
      <entry>blocks only</entry>
      <entry>blocks only</entry>
      <entry>blocks only</entry>
    </row>

    <row>
      <entry>Privacy Features</entry>
      <entry>low</entry>
      <entry>medium</entry>
      <entry>medium/high</entry>
    </row>

    <row>
      <entry>Cookie handling</entry>
      <entry>none</entry>
      <entry>session-only</entry>
      <entry>kill</entry>
    </row>

    <row>
      <entry>Referer forging</entry>
      <entry>no</entry>
      <entry>yes</entry>
      <entry>yes</entry>
    </row>

    <row>
      <entry>GIF de-animation</entry>
      <entry>no</entry>
      <entry>yes</entry>
      <entry>yes</entry>
    </row>

    <row>
      <entry>Fast redirects</entry>
      <entry>no</entry>
      <entry>no</entry>
      <entry>yes</entry>
    </row>

    <row>
      <entry>HTML taming</entry>
      <entry>no</entry>
      <entry>no</entry>
      <entry>yes</entry>
    </row>

    <row>
      <entry>JavaScript taming</entry>
      <entry>no</entry>
      <entry>no</entry>
      <entry>yes</entry>
    </row>

    <row>
      <entry>Web-bug killing</entry>
      <entry>no</entry>
      <entry>yes</entry>
      <entry>yes</entry>
    </row>

    <row>
      <entry>Image tag reordering</entry>
      <entry>no</entry>
      <entry>yes</entry>
      <entry>yes</entry>
    </row>

    </tbody>
    </tgroup>
    </table>

  </listitem>
 </itemizedlist>

<para>
 The list of actions files to be used are defined in the main configuration
 file, and are processed in the order they are defined (e.g.
 <filename>default.action</filename> is typically processed before
 <filename>user.action</filename>). The content of these can all be viewed and
 edited from <ulink
 url="http://config.privoxy.org/show-status">http://config.privoxy.org/show-status</ulink>.
 The over-riding principle when applying actions, is that the last action that
 matches a given URL wins. The broadest, most general rules go first
 (defined in <filename>default.action</filename>),
 followed by any exceptions (typically also in
 <filename>default.action</filename>), which are then followed lastly by any
 local preferences (typically in <emphasis>user</emphasis><filename>.action</filename>).
 Generally, <filename>user.action</filename> has the last word.
 </para>

<para>
 An actions file typically has multiple sections. If you want to use
 <quote>aliases</quote> in an actions file, you have to place the (optional)
 <link linkend="aliases">alias section</link> at the top of that file.
 Then comes the default set of rules which will apply universally to all
 sites and pages (be <emphasis>very careful</emphasis> with using such a
 universal set in <filename>user.action</filename> or any other actions file after
 <filename>default.action</filename>, because it will override the result
 from consulting any previous file). And then below that,
 exceptions to the defined universal policies. You can regard
 <filename>user.action</filename> as an appendix to <filename>default.action</filename>,
 with the advantage that it is a separate file, which makes preserving your
 personal settings across <application>Privoxy</application> upgrades easier.
</para>

<para>
 Actions can be used to block anything you want, including ads, banners, or
 just some obnoxious URL whose content you would rather not see. Cookies can be accepted
 or rejected, or accepted only during the current browser session (i.e. not
 written to disk), content can be modified, some JavaScripts tamed, user-tracking
 fooled, and much more. See below for a <link linkend="actions">complete list
 of actions</link>.
</para>

<!--   ~~~~~       New section      ~~~~~     -->
<sect2 id="right-mix">
<title>Finding the Right Mix</title>
<para>
 Note that some <link linkend="actions">actions</link>, like cookie suppression
 or script disabling, may render some sites unusable that rely on these
 techniques to work properly. Finding the right mix of actions is not always easy and
 certainly a matter of personal taste. And, things can always change, requiring
 refinements in the configuration. In general, it can be said that the more
 <quote>aggressive</quote> your default settings (in the top section of the
 actions file) are, the more exceptions for <quote>trusted</quote> sites you
 will have to make later. If, for example, you want to crunch all cookies per
 default, you'll have to make exceptions from that rule for sites that you
 regularly use and that require cookies for actually useful purposes, like maybe
 your bank, favorite shop, or newspaper.
</para>

<para>
 We have tried to provide you with reasonable rules to start from in the
 distribution actions files. But there is no general rule of thumb on these
 things. There just are too many variables, and sites are constantly changing.
 Sooner or later you will want to change the rules (and read this chapter again :).
</para>
</sect2>

<!--   ~~~~~       New section      ~~~~~     -->
<sect2 id="how-to-edit">
<title>How to Edit</title>
<para>
 The easiest way to edit the actions files is with a browser by
 using our browser-based editor, which can be reached from <ulink
 url="http://config.privoxy.org/show-status">http://config.privoxy.org/show-status</ulink>.
 Note: the config file option <link
 linkend="enable-edit-actions">enable-edit-actions</link> must be enabled for
 this to work. The editor allows both fine-grained control over every single
 feature on a per-URL basis, and easy choosing from wholesale sets of defaults
 like <quote>Cautious</quote>, <quote>Medium</quote> or
 <quote>Advanced</quote>. Warning: the <quote>Advanced</quote> setting is more
 aggressive, and will be more likely to cause problems for some sites.
 Experienced users only!
 </para>

<para>
 If you prefer plain text editing to GUIs, you can of course also directly edit the
 the actions files with your favorite text editor. Look at
 <filename>default.action</filename> which is richly commented with many
 good examples.
</para>
</sect2>


<sect2 id="actions-apply">
<title>How Actions are Applied to Requests</title>
<para>
 Actions files are divided into sections. There are special sections,
 like the <quote><link linkend="aliases">alias</link></quote> sections which will
 be discussed later. For now let's concentrate on regular sections: They have a
 heading line (often split up to multiple lines for readability) which consist
 of a list of actions, separated by whitespace and enclosed in curly braces.
 Below that, there is a list of URL and tag patterns, each on a separate line.
</para>

<para>
 To determine which actions apply to a request, the URL of the request is
 compared to all URL patterns in each <quote>action file</quote>.
 Every time it matches, the list of applicable actions for the request is
 incrementally updated, using the heading of the section in which the
 pattern is located. The same is done again for tags and tag patterns later on.
</para>

<para>
 If multiple applying sections set the same action differently,
 the last match wins. If not, the effects are aggregated.
 E.g. a URL might match a regular section with a heading line of <literal>{
 +<link linkend="handle-as-image">handle-as-image</link> }</literal>,
 then later another one with just <literal>{
 +<link linkend="block">block</link> }</literal>, resulting
 in <emphasis>both</emphasis> actions to apply. And there may well be
 cases where you will want to combine actions together. Such a section then
 might look like:
</para>

 <screen>
  { +<literal>handle-as-image</literal>  +<literal>block{Banner ads.}</literal> }
  # Block these as if they were images. Send no block page.
   banners.example.com
   media.example.com/.*banners
   .example.com/images/ads/</screen>

<para>
 You can trace this process for URL patterns and any given URL by visiting <ulink
 url="http://config.privoxy.org/show-url-info">http://config.privoxy.org/show-url-info</ulink>.
</para>

<para>
 Examples and more detail on this is provided in the Appendix, <link linkend="ACTIONSANAT">
 Troubleshooting: Anatomy of an Action</link> section.
</para>
</sect2>

<!--   ~~~~~       New section      ~~~~~     -->
<sect2 id="af-patterns">
<title>Patterns</title>
<para>
 As mentioned, <application>Privoxy</application> uses <quote>patterns</quote>
 to determine what <emphasis>actions</emphasis> might apply to which sites and
 pages your browser attempts to access. These <quote>patterns</quote> use wild
 card type <emphasis>pattern</emphasis> matching to achieve a high degree of
 flexibility. This allows one expression to be expanded and potentially match
 against many similar patterns.
</para>

<para>
 Generally, an URL pattern has the form
 <literal>&lt;host&gt;&lt;port&gt;/&lt;path&gt;</literal>, where the
 <literal>&lt;host&gt;</literal>, the <literal>&lt;port&gt;</literal>
 and the <literal>&lt;path&gt;</literal> are optional. (This is why the special
 <literal>/</literal> pattern matches all URLs). Note that the protocol
 portion of the URL pattern (e.g. <literal>http://</literal>) should
 <emphasis>not</emphasis> be included in the pattern. This is assumed already!
</para>
<para>
 The pattern matching syntax is different for the host and path parts of
 the URL. The host part uses a simple globbing type matching technique,
 while the path part uses more flexible
 <ulink url="https://en.wikipedia.org/wiki/Regular_expressions"><quote>Regular
  Expressions</quote></ulink> (POSIX 1003.2).
</para>
<para>
 The port part of a pattern is a decimal port number preceded by a colon
 (<literal>:</literal>). If the host part contains a numerical IPv6 address,
 it has to be put into angle brackets
 (<literal>&lt;</literal>, <literal>&gt;</literal>).
</para>

<variablelist>
 <varlistentry>
  <term><literal>www.example.com/</literal></term>
  <listitem>
   <para>
    is a host-only pattern and will match any request to <literal>www.example.com</literal>,
    regardless of which document on that server is requested. So ALL pages in
    this domain would be covered by the scope of this action. Note that a
    simple <literal>example.com</literal> is different and would NOT match.
   </para>
  </listitem>
 </varlistentry>
 <varlistentry>
  <term><literal>www.example.com</literal></term>
  <listitem>
   <para>
    means exactly the same. For host-only patterns, the trailing <literal>/</literal> may
    be omitted.
   </para>
  </listitem>
 </varlistentry>
 <varlistentry>
  <term><literal>www.example.com/index.html</literal></term>
  <listitem>
   <para>
    matches all the documents on <literal>www.example.com</literal>
    whose name starts with <literal>/index.html</literal>.
   </para>
  </listitem>
 </varlistentry>
 <varlistentry>
  <term><literal>www.example.com/index.html$</literal></term>
  <listitem>
   <para>
    matches only the single document <literal>/index.html</literal>
    on <literal>www.example.com</literal>.
   </para>
  </listitem>
 </varlistentry>
 <varlistentry>
  <term><literal>/index.html$</literal></term>
  <listitem>
   <para>
    matches the document <literal>/index.html</literal>, regardless of the domain,
    i.e. on <emphasis>any</emphasis> web server anywhere.
   </para>
  </listitem>
 </varlistentry>
 <varlistentry>
  <term><literal>/</literal></term>
  <listitem>
   <para>
    Matches any URL because there's no requirement for either the
    domain or the path to match anything.
   </para>
  </listitem>
 </varlistentry>
 <varlistentry>
  <term><literal>:8000/</literal></term>
  <listitem>
   <para>
    Matches any URL pointing to TCP port 8000.
   </para>
  </listitem>
 </varlistentry>
 <varlistentry>
  <term><literal>10.0.0.1/</literal></term>
  <listitem>
   <para>
    Matches any URL with the host address <literal>10.0.0.1</literal>.
    (Note that the real URL uses plain brackets, not angle brackets.)
   </para>
  </listitem>
 </varlistentry>
 <varlistentry>
  <term><literal>&lt;2001:db8::1&gt;/</literal></term>
  <listitem>
   <para>
    Matches any URL with the host address <literal>2001:db8::1</literal>.
    (Note that the real URL uses plain brackets, not angle brackets.)
   </para>
  </listitem>
 </varlistentry>
 <varlistentry>
  <term><literal>index.html</literal></term>
  <listitem>
   <para>
    matches nothing, since it would be interpreted as a domain name and
    there is no top-level domain called <literal>.html</literal>. So its
    a mistake.
   </para>
  </listitem>
 </varlistentry>
</variablelist>


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 id="host-pattern"><title>The Host Pattern</title>

<para>
 The matching of the host part offers some flexible options: if the
 host pattern starts or ends with a dot, it becomes unanchored at that end.
 The host pattern is often referred to as domain pattern as it is usually
 used to match domain names and not IP addresses.
 For example:
</para>

<variablelist>
 <varlistentry>
  <term><literal>.example.com</literal></term>
  <listitem>
   <para>
    matches any domain with first-level domain <literal>com</literal>
    and second-level domain <literal>example</literal>.
    For example <literal>www.example.com</literal>,
    <literal>example.com</literal> and <literal>foo.bar.baz.example.com</literal>.
    Note that it wouldn't match if the second-level domain was <literal>another-example</literal>.
   </para>
  </listitem>
 </varlistentry>
 <varlistentry>
  <term><literal>www.</literal></term>
  <listitem>
   <para>
    matches any domain that <emphasis>STARTS</emphasis> with
    <literal>www.</literal> (It also matches the domain
    <literal>www</literal> but most of the time that doesn't matter.)
   </para>
  </listitem>
 </varlistentry>
 <varlistentry>
  <term><literal>.example.</literal></term>
  <listitem>
   <para>
    matches any domain that <emphasis>CONTAINS</emphasis> <literal>.example.</literal>.
    And, by the way, also included would be any files or documents that exist
    within that domain since no path limitations are specified. (Correctly
    speaking: It matches any FQDN that contains <literal>example</literal> as
    a domain.) This might be <literal>www.example.com</literal>,
    <literal>news.example.de</literal>, or
    <literal>www.example.net/cgi/testing.pl</literal> for instance. All these
    cases are matched.
   </para>
  </listitem>
 </varlistentry>
</variablelist>

<para>
 Additionally, there are wild-cards that you can use in the domain names
 themselves. These work similarly to shell globbing type wild-cards:
 <quote>*</quote> represents zero or more arbitrary characters (this is
 equivalent to the
 <ulink url="https://en.wikipedia.org/wiki/Regular_expressions"><quote>Regular
 Expression</quote></ulink> based syntax of <quote>.*</quote>),
 <quote>?</quote>  represents any single character (this is equivalent to the
 regular expression syntax of a simple <quote>.</quote>), and you can define
 <quote>character classes</quote> in square brackets which is similar to
 the same regular expression technique. All of this can be freely mixed:
</para>

<variablelist>
 <varlistentry>
  <term><literal>ad*.example.com</literal></term>
  <listitem>
   <para>
    matches <quote>adserver.example.com</quote>,
    <quote>ads.example.com</quote>, etc but not <quote>sfads.example.com</quote>
   </para>
  </listitem>
 </varlistentry>
 <varlistentry>
  <term><literal>*ad*.example.com</literal></term>
  <listitem>
   <para>
    matches all of the above, and then some.
   </para>
  </listitem>
 </varlistentry>
 <varlistentry>
  <term><literal>.?pix.com</literal></term>
  <listitem>
   <para>
    matches <literal>www.ipix.com</literal>,
    <literal>pictures.epix.com</literal>, <literal>a.b.c.d.e.upix.com</literal> etc.
   </para>
  </listitem>
 </varlistentry>
 <varlistentry>
  <term><literal>www[1-9a-ez].example.c*</literal></term>
  <listitem>
   <para>
     matches <literal>www1.example.com</literal>,
     <literal>www4.example.cc</literal>, <literal>wwwd.example.cy</literal>,
     <literal>wwwz.example.com</literal> etc., but <emphasis>not</emphasis>
     <literal>wwww.example.com</literal>.
   </para>
  </listitem>
 </varlistentry>
</variablelist>

<para>
 While flexible, this is not the sophistication of full regular expression based syntax.
</para>

<para>
 When compiled with FEATURE_PCRE_HOST_PATTERNS patterns can be prefixed with
 <quote>PCRE-HOST-PATTERN:</quote> in which case full regular expression
 (PCRE) can be used for the host pattern as well.
</para>

</sect3>

<!--  ~  End section  ~  -->


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 id="path-pattern"><title>The Path Pattern</title>

<para>
 <application>Privoxy</application> uses <quote>modern</quote> POSIX 1003.2
  <ulink url="https://en.wikipedia.org/wiki/Regular_expressions"><quote>Regular
  Expressions</quote></ulink> for matching the path portion (after the slash),
  and is thus more flexible.
</para>

<para>
 There is an <link linkend="regex">Appendix</link> with a brief quick-start into regular
 expressions, you also might want to have a look at your operating system's documentation
 on regular expressions (try <literal>man re_format</literal>).
</para>

<para>
 Note that the path pattern is automatically left-anchored at the <quote>/</quote>,
 i.e. it matches as if it would start with a <quote>^</quote> (regular expression speak
 for the beginning of a line).
</para>

<para>
 Please also note that matching in the path is <emphasis>CASE INSENSITIVE</emphasis>
 by default, but you can switch to case sensitive at any point in the pattern by using the
 <quote>(?-i)</quote> switch: <literal>www.example.com/(?-i)PaTtErN.*</literal> will match
 only documents whose path starts with <literal>PaTtErN</literal> in
 <emphasis>exactly</emphasis> this capitalization.
</para>

<variablelist>
 <varlistentry>
  <term><literal>.example.com/.*</literal></term>
  <listitem>
   <para>
     Is equivalent to just <quote>.example.com</quote>, since any documents
     within that domain are matched with or without the <quote>.*</quote>
     regular expression. This is redundant
   </para>
  </listitem>
 </varlistentry>
 <varlistentry>
  <term><literal>.example.com/.*/index.html$</literal></term>
  <listitem>
   <para>
    Will match any page in the domain of <quote>example.com</quote> that is
    named <quote>index.html</quote>, and that is part of some path. For
    example, it matches <quote>www.example.com/testing/index.html</quote> but
    NOT <quote>www.example.com/index.html</quote> because the regular
    expression called for at least two <quote>/'s</quote>, thus the path
    requirement. It also would match
    <quote>www.example.com/testing/index_html</quote>, because of the
    special meta-character <quote>.</quote>.
   </para>
  </listitem>
 </varlistentry>
 <varlistentry>
  <term><literal>.example.com/(.*/)?index\.html$</literal></term>
  <listitem>
   <para>
    This regular expression is conditional so it will match any page
    named <quote>index.html</quote> regardless of path which in this case can
    have one or more <quote>/'s</quote>. And this one must contain exactly
    <quote>.html</quote> (and end with that!).
   </para>
  </listitem>
 </varlistentry>
 <varlistentry>
  <term><literal>.example.com/(.*/)(ads|banners?|junk)</literal></term>
  <listitem>
   <para>
    This regular expression will match any path of <quote>example.com</quote>
    that contains any of the words <quote>ads</quote>, <quote>banner</quote>,
    <quote>banners</quote> (because of the <quote>?</quote>) or <quote>junk</quote>.
    The path does not have to end in these words, just contain them.
    The path has to contain at least two slashes (including the one at the beginning).
   </para>
  </listitem>
 </varlistentry>
 <varlistentry>
  <term><literal>.example.com/(.*/)(ads|banners?|junk)/.*\.(jpe?g|gif|png)$</literal></term>
  <listitem>
   <para>
    This is very much the same as above, except now it must end in either
    <quote>.jpg</quote>, <quote>.jpeg</quote>, <quote>.gif</quote> or <quote>.png</quote>. So this
    one is limited to common image formats.
   </para>
  </listitem>
 </varlistentry>

</variablelist>
<para>
 There are many, many good examples to be found in <filename>default.action</filename>,
 and more tutorials below in <link linkend="regex">Appendix on regular expressions</link>.
</para>

</sect3>

<!--  ~  End section  ~  -->


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 id="tag-pattern"><title>The Request Tag Pattern</title>

<para>
 Request tag patterns are used to change the applying actions based on the
 request's tags. Tags can be created based on HTTP headers with either
 the <link linkend="CLIENT-HEADER-TAGGER">client-header-tagger</link>
 or the  <link linkend="SERVER-HEADER-TAGGER">server-header-tagger</link> action.
</para>

<para>
 Request tag patterns have to start with <quote>TAG:</quote>, so &my-app;
 can tell them apart from other patterns. Everything after the colon
 including white space, is interpreted as a regular expression with
 path pattern syntax, except that tag patterns aren't left-anchored
 automatically (&my-app; doesn't silently add a <quote>^</quote>,
 you have to do it yourself if you need it).
</para>

<para>
 To match all requests that are tagged with <quote>foo</quote>
 your pattern line should be <quote>TAG:^foo$</quote>,
 <quote>TAG:foo</quote> would work as well, but it would also
 match requests whose tags contain <quote>foo</quote> somewhere.
 <quote>TAG: foo</quote> wouldn't work as it requires white space.
</para>

<para>
 Sections can contain URL and request tag patterns at the same time,
 but request tag patterns are checked after the URL patterns and thus
 always overrule them, even if they are located before the URL patterns.
</para>

<para>
 Once a new request tag is added, Privoxy checks right away if it's matched by one
 of the request tag patterns and updates the action settings accordingly. As a result
 request tags can be used to activate other tagger actions, as long as these other
 taggers look for headers that haven't already be parsed.
</para>

<para>
 For example you could tag client requests which use the
 <literal>POST</literal> method,
 then use this tag to activate another tagger that adds a tag if cookies
 are sent, and then use a block action based on the cookie tag. This allows
 the outcome of one action, to be input into a subsequent action. However if
 you'd reverse the position of the described taggers, and activated the
 method tagger based on the cookie tagger, no method tags would be created.
 The method tagger would look for the request line, but at the time
 the cookie tag is created, the request line has already been parsed.
</para>

<para>
 While this is a limitation you should be aware of, this kind of
 indirection is seldom needed anyway and even the example doesn't
 make too much sense.
</para>

</sect3>

<!--   ~~~~~       New section      ~~~~~     -->
<sect3 id="negative-tag-patterns"><title>The Negative Request Tag Patterns</title>

<para>
 To match requests that do not have a certain request tag, specify a negative tag pattern
 by prefixing the tag pattern line with either <quote>NO-REQUEST-TAG:</quote>
 or <quote>NO-RESPONSE-TAG:</quote> instead of <quote>TAG:</quote>.
</para>

<para>
 Negative request tag patterns created with <quote>NO-REQUEST-TAG:</quote> are checked
 after all client headers are scanned, the ones created with <quote>NO-RESPONSE-TAG:</quote>
 are checked after all server headers are scanned. In both cases all the created
 tags are considered.
</para>
</sect3>

<!--   ~~~~~       New section      ~~~~~     -->
<sect3 id="client-tag-pattern"><title>The Client Tag Pattern</title>

<!-- XXX: This section contains duplicates content from the
          client-specific-tag documentation. -->

<warning>
<para>
 This is an experimental feature. The syntax is likely to change in future versions.
</para>
</warning>

<para>
 Client tag patterns are not set based on HTTP headers but based on
 the client's IP address. Users can enable them themselves, but the
 Privoxy admin controls which tags are available and what their effect
 is.
</para>

<para>
 After a client-specific tag has been defined with the
 <link linkend="client-specific-tag">client-specific-tag</link>,
 directive, action sections can be activated based on the tag by using a
 CLIENT-TAG pattern. The CLIENT-TAG pattern is evaluated at the same priority
 as URL patterns, as a result the last matching pattern wins. Tags that
 are created based on client or server headers are evaluated later on
 and can overrule CLIENT-TAG and URL patterns!
</para>
<para>
 The tag is set for all requests that come from clients that requested
 it to be set. Note that "clients" are  differentiated by IP address,
 if the IP address changes the tag has to be requested again.
</para>
<para>
 Clients can request tags to be set by using the CGI interface <ulink
  url="http://config.privoxy.org/client-tags">http://config.privoxy.org/client-tags</ulink>.
</para>

<para>
 Example:
</para>

 <screen>
# If the admin defined the client-specific-tag circumvent-blocks,
# and the request comes from a client that previously requested
# the tag to be set, overrule all previous +block actions that
# are enabled based on URL to CLIENT-TAG patterns.
{-block}
CLIENT-TAG:^circumvent-blocks$

# This section is not overruled because it's located after
# the previous one.
{+block{Nobody is supposed to request this.}}
example.org/blocked-example-page</screen>

</sect3>

</sect2>

<!--  ~  End section  ~  -->


<!--   ~~~~~       New section      ~~~~~     -->

<sect2 id="actions">
<title>Actions</title>
<para>
 All actions are disabled by default, until they are explicitly enabled
 somewhere in an actions file. Actions are turned on if preceded with a
 <quote>+</quote>, and turned off if preceded with a <quote>-</quote>. So a
 <literal>+action</literal> means <quote>do that action</quote>, e.g.
 <literal>+block</literal> means <quote>please block URLs that match the
 following patterns</quote>, and <literal>-block</literal> means <quote>don't
 block URLs that match the following patterns, even if <literal>+block</literal>
 previously applied.</quote>
</para>

<para>
 Again, actions are invoked by placing them on a line, enclosed in curly braces and
 separated by whitespace, like in
 <literal>{+some-action -some-other-action{some-parameter}}</literal>,
 followed by a list of URL patterns, one per line, to which they apply.
 Together, the actions line and the following pattern lines make up a section
 of the actions file.
</para>

<para>
 Actions fall into three categories:
</para>

 <itemizedlist>
 <listitem>
  <para>
   Boolean, i.e the action can only be <quote>enabled</quote> or
   <quote>disabled</quote>. Syntax:
  </para>
   <screen>
  +<replaceable class="function">name</replaceable>        # enable action <replaceable class="parameter">name</replaceable>
  -<replaceable class="function">name</replaceable>        # disable action <replaceable class="parameter">name</replaceable></screen>
  <para>
   Example: <literal>+handle-as-image</literal>
  </para>
 </listitem>


 <listitem>
  <para>
   Parameterized, where some value is required in order to enable this type of action.
   Syntax:
  </para>
   <screen>
  +<replaceable class="function">name</replaceable>{<replaceable class="parameter">param</replaceable>}  # enable action and set parameter to <replaceable class="parameter">param</replaceable>,
               # overwriting parameter from previous match if necessary
  -<replaceable class="function">name</replaceable>         # disable action. The parameter can be omitted</screen>
  <para>
   Note that if the URL matches multiple positive forms of a parameterized action,
   the last match wins, i.e. the params from earlier matches are simply ignored.
  </para>
  <para>
   Example: <literal>+hide-user-agent{Mozilla/5.0 (X11; U; FreeBSD i386; en-US; rv:1.8.1.4) Gecko/20070602 Firefox/2.0.0.4}</literal>
  </para>
 </listitem>

 <listitem>
  <para>
   Multi-value. These look exactly like parameterized actions,
   but they behave differently: If the action applies multiple times to the
   same URL, but with different parameters, <emphasis>all</emphasis> the parameters
   from <emphasis>all</emphasis> matches are remembered. This is used for actions
   that can be executed for the same request repeatedly, like adding multiple
   headers, or filtering through multiple filters. Syntax:
  </para>
   <screen>
  +<replaceable class="function">name</replaceable>{<replaceable class="parameter">param</replaceable>}   # enable action and add <replaceable class="parameter">param</replaceable> to the list of parameters
  -<replaceable class="function">name</replaceable>{<replaceable class="parameter">param</replaceable>}   # remove the parameter <replaceable class="parameter">param</replaceable> from the list of parameters
                # If it was the last one left, disable the action.
  <replaceable class="parameter">-name</replaceable>          # disable this action completely and remove all parameters from the list</screen>
  <para>
   Examples: <literal>+add-header{X-Fun-Header: Some text}</literal> and
   <literal>+filter{html-annoyances}</literal>
  </para>
 </listitem>

 </itemizedlist>

<para>
 If nothing is specified in any actions file, no <quote>actions</quote> are
 taken. So in this case <application>Privoxy</application> would just be a
 normal, non-blocking, non-filtering proxy. You must specifically enable the
 privacy and blocking features you need (although the provided default actions
 files will give a good starting point).
</para>

<para>
 Later defined action sections always over-ride earlier ones of the same type.
 So exceptions to any rules you make, should come in the latter part of the file (or
 in a file that is processed later when using multiple actions files such
 as <filename>user.action</filename>). For multi-valued actions, the actions
 are applied in the order they are specified. Actions files are processed in
 the order they are defined in <filename>config</filename> (the default
 installation has three actions files). It also quite possible for any given
 URL to match more than one <quote>pattern</quote> (because of wildcards and
 regular expressions), and thus to trigger more than one set of actions! Last
 match wins.
</para>

<!-- start actions listing -->
<para>
 The list of valid <application>Privoxy</application> actions are:
</para>


<!-- ********************************************************** -->
<!-- Please note the below defined actions use id's that are    -->
<!-- probably linked from other places, so please don't change. -->
<!--                                                            -->
<!-- ********************************************************** -->


<!--   ~~~~~       New section      ~~~~~     -->

<sect3 renderas="sect4" id="add-header">
<title>add-header</title>

<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>Confuse log analysis, custom applications</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    Sends a user defined HTTP header to the web server.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Type:</term>
  <!-- boolean, parameterized, Multi-value -->
  <listitem>
   <para>Multi-value.</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Parameter:</term>
  <listitem>
   <para>
    Any string value is possible. Validity of the defined HTTP headers is not checked.
    It is recommended that you use the <quote><literal>X-</literal></quote> prefix
    for custom headers.
   </para>
  </listitem>
 </varlistentry>

<varlistentry>
  <term>Notes:</term>
  <listitem>
   <para>
    This action may be specified multiple times, in order to define multiple
    headers. This is rarely needed for the typical user. If you don't know what
    <quote>HTTP headers</quote> are, you definitely don't need to worry about this
    one.
   </para>
   <para>
    Headers added by this action are not modified by other actions.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage:</term>
  <listitem>
     <screen># Add a DNT ("Do not track") header to all requests,
# event to those that already have one.
#
# This is just an example, not a recommendation.
#
# There is no reason to believe that user-tracking websites care
# about the DNT header and depending on the User-Agent, adding the
# header may make user-tracking easier.
{+add-header{DNT: 1}}
/</screen>
  </listitem>
 </varlistentry>
</variablelist>
</sect3>


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 renderas="sect4" id="block">
<title>block</title>

<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>Block ads or other unwanted content</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    Requests for URLs to which this action applies are blocked, i.e. the
    requests are trapped by &my-app; and the requested URL is never retrieved,
    but is answered locally with a substitute page or image, as determined by
    the <literal><link
    linkend="handle-as-image">handle-as-image</link></literal>,
    <literal><link
    linkend="set-image-blocker">set-image-blocker</link></literal>, and
    <literal><link
    linkend="handle-as-empty-document">handle-as-empty-document</link></literal> actions.

   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Type:</term>
  <!-- boolean, parameterized, Multi-value -->
  <listitem>
   <para>Parameterized.</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Parameter:</term>
  <listitem>
   <para>A block reason that should be given to the user.</para>
  </listitem>
 </varlistentry>

<varlistentry>
  <term>Notes:</term>
  <listitem>
   <para>
    <application>Privoxy</application> sends a special <quote>BLOCKED</quote> page
    for requests to blocked pages. This page contains the block reason given as
    parameter, a link to find out why the block action applies, and a click-through
    to the blocked content (the latter only if the force feature is available and
    enabled).
   </para>
   <para>
    A very important exception occurs if <emphasis>both</emphasis>
    <literal>block</literal> and <literal><link linkend="handle-as-image">handle-as-image</link></literal>,
    apply to the same request: it will then be replaced by an image. If
    <literal><link linkend="set-image-blocker">set-image-blocker</link></literal>
    (see below) also applies, the type of image will be determined by its parameter,
    if not, the standard checkerboard pattern is sent.
   </para>
   <para>
    It is important to understand this process, in order
    to understand how <application>Privoxy</application> deals with
    ads and other unwanted content. Blocking is a core feature, and one
    upon which various other features depend.
   </para>
   <para>
    The <literal><link linkend="filter">filter</link></literal>
    action can perform a very similar task, by <quote>blocking</quote>
    banner images and other content through rewriting the relevant URLs in the
    document's HTML source, so they don't get requested in the first place.
    Note that this is a totally different technique, and it's easy to confuse the two.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage (section):</term>
  <listitem>
     <screen>{+block{No nasty stuff for you.}}
# Block and replace with "blocked" page
 .nasty-stuff.example.com

{+block{Doubleclick banners.} +handle-as-image}
# Block and replace with image
 .ad.doubleclick.net
 .ads.r.us/banners/

{+block{Layered ads.} +handle-as-empty-document}
# Block and then ignore
 adserver.example.net/.*\.js$</screen>
  </listitem>
 </varlistentry>


</variablelist>
</sect3>


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 renderas="sect4" id="change-x-forwarded-for">
<title>change-x-forwarded-for</title>

<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>Improve privacy by not forwarding the source of the request in the HTTP headers.</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    Deletes the <quote>X-Forwarded-For:</quote> HTTP header from the client request,
    or adds a new one.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Type:</term>
  <!-- Boolean, Parameterized, Multi-value -->
  <listitem>
   <para>Parameterized.</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Parameter:</term>
  <listitem>
   <itemizedlist>
    <listitem>
     <para><quote>block</quote> to delete the header.</para>
    </listitem>
    <listitem>
     <para>
       <quote>add</quote> to create the header (or append
       the client's IP address to an already existing one).
     </para>
    </listitem>
   </itemizedlist>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Notes:</term>
  <listitem>
   <para>
    It is safe and recommended to use <literal>block</literal>.
   </para>
   <para>
    Forwarding the source address of the request may make
    sense in some multi-user setups but is also a privacy risk.
   </para>
  </listitem>
 </varlistentry>
 <varlistentry>
  <term>Example usage:</term>
  <listitem>
     <screen>+change-x-forwarded-for{block}</screen>
  </listitem>
 </varlistentry>
</variablelist>
</sect3>

<!--   ~~~~~       New section      ~~~~~     -->
<sect3 renderas="sect4" id="client-header-filter">
<title>client-header-filter</title>

<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>
   Rewrite or remove single client headers.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    All client headers to which this action applies are filtered on-the-fly through
    the specified regular expression based substitutions.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Type:</term>
  <!-- boolean, parameterized, Multi-value -->
  <listitem>
   <para>Multi-value.</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Parameter:</term>
  <listitem>
   <para>
    The name of a client-header filter, as defined in one of the
    <link linkend="filter-file">filter files</link>.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Notes:</term>
  <listitem>
   <para>
    Client-header filters are applied to each header on its own, not to
    all at once. This makes it easier to diagnose problems, but on the downside
    you can't write filters that only change header x if header y's value is z.
    You can do that by using tags though.
   </para>
   <para>
    Client-header filters are executed after the other header actions have finished
    and use their output as input.
   </para>
   <para>
    If the request URI gets changed, &my-app; will detect that and use the new
    one. This can be used to rewrite the request destination behind the client's
    back, for example to specify a Tor exit relay for certain requests.
   </para>
   <para>
    Note that to change the destination host for
    <link linkend="HTTPS-INSPECTION">https-inspected</link>
    requests a protocol and host has to be added to the URI.
   </para>
   <para>
    If <link linkend="HTTPS-INSPECTION">https inspection</link>
    is enabled, the protocol can be downgraded from https to http
    but upgrading a request from http to https is currently not
    supported.
   </para>
   <para>
    After detecting a rewrite, &my-app; does not update the actions
    used for the request based on the new host.
   </para>
   <para>
    Please refer to the <link linkend="filter-file">filter file chapter</link>
    to learn which client-header filters are available by default, and how to
    create your own.
   </para>

  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage (section):</term>
  <listitem>
     <screen>
# Hide Tor exit notation in Host and Referer Headers
{+client-header-filter{hide-tor-exit-notation}}
/
</screen>
  </listitem>
 </varlistentry>

</variablelist>
</sect3>

<!--   ~~~~~       New section      ~~~~~     -->
<sect3 renderas="sect4" id="client-body-filter">
<title>client-body-filter</title>

<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>
   Rewrite or remove client request body.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    All request bodies to which this action applies are filtered on-the-fly through
    the specified regular expression based substitutions.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Type:</term>
  <!-- boolean, parameterized, Multi-value -->
  <listitem>
   <para>Multi-value.</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Parameter:</term>
  <listitem>
   <para>
    The name of a client-body filter, as defined in one of the
    <link linkend="filter-file">filter files</link>.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Notes:</term>
  <listitem>
   <para>
    Please refer to the <link linkend="filter-file">filter file chapter</link>
    to learn how to create your own client-body filters.
   </para>
   <para>
    The distribution <filename>default.filter</filename> file contains a selection of
    client-body filters for example purposes.
   </para>
   <para>
    The amount of data that can be filtered is limited by the
    <literal><link linkend="buffer-limit">buffer-limit</link></literal>
    option in the main <link linkend="config">config file</link>. The
    default is 4096 KB (4 Megs). Once this limit is exceeded, the whole
    request body is passed through unfiltered.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage (section):</term>
  <listitem>
     <screen>
# Remove "test" everywhere in the request body
{+client-body-filter{remove-test}}
/
</screen>
  </listitem>
 </varlistentry>

</variablelist>
</sect3>


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 renderas="sect4" id="client-header-tagger">
<title>client-header-tagger</title>

<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>
   Block requests based on their headers.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    Client headers to which this action applies are filtered on-the-fly through
    the specified regular expression based substitutions, the result is used as
    tag.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Type:</term>
  <!-- boolean, parameterized, Multi-value -->
  <listitem>
   <para>Multi-value.</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Parameter:</term>
  <listitem>
   <para>
    The name of a client-header tagger, as defined in one of the
    <link linkend="filter-file">filter files</link>.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Notes:</term>
  <listitem>
   <para>
    Client-header taggers are applied to each header on its own,
    and as the header isn't modified, each tagger <quote>sees</quote>
    the original.
   </para>
   <para>
    Client-header taggers are the first actions that are executed
    and their tags can be used to control every other action.
   </para>
 </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage (section):</term>
  <listitem>
     <screen>
# Tag every request with the User-Agent header
{+client-header-tagger{user-agent}}
/

# Tagging itself doesn't change the action
# settings, sections with TAG patterns do:
#
# If it's a download agent, use a different forwarding proxy,
# show the real User-Agent and make sure resume works.
{+forward-override{forward-socks5 10.0.0.2:2222 .} \
 -hide-if-modified-since      \
 -overwrite-last-modified     \
 -hide-user-agent             \
 -filter                      \
 -deanimate-gifs              \
}
TAG:^User-Agent: NetBSD-ftp/
TAG:^User-Agent: Novell ZYPP Installer
TAG:^User-Agent: RPM APT-HTTP/
TAG:^User-Agent: fetch libfetch/
TAG:^User-Agent: Ubuntu APT-HTTP/
TAG:^User-Agent: MPlayer/
</screen>

     <screen>
# Tag all requests with the Range header set
{+client-header-tagger{range-requests}}
/

# Disable filtering for the tagged requests.
#
# With filtering enabled Privoxy would remove the Range headers
# to be able to filter the whole response. The downside is that
# it prevents clients from resuming downloads or skipping over
# parts of multimedia files.
{-filter -deanimate-gifs}
TAG:^RANGE-REQUEST$
</screen>

     <screen>
# Tag all requests with the client IP address
#
# (Technically the client IP address isn't included in the
# client headers but client-header taggers can set it anyway.
# For details see the tagger in default.filter)
{+client-header-tagger{client-ip-address}}
/

# Change forwarding settings for requests coming from address 10.0.0.1
{+forward-override{forward-socks5 127.0.1.2:2222 .}}
TAG:^IP-ADDRESS: 10\.0\.0\.1$
</screen>
  </listitem>
 </varlistentry>

</variablelist>
</sect3>


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 renderas="sect4" id="content-type-overwrite">
<title>content-type-overwrite</title>

<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>Stop useless download menus from popping up, or change the browser's rendering mode</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    Replaces the <quote>Content-Type:</quote> HTTP server header.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Type:</term>
  <!-- Boolean, Parameterized, Multi-value -->
  <listitem>
   <para>Parameterized.</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Parameter:</term>
  <listitem>
   <para>
    Any string.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Notes:</term>
  <listitem>
   <para>
    The <quote>Content-Type:</quote> HTTP server header is used by the
    browser to decide what to do with the document. The value of this
    header can cause the browser to open a download menu instead of
    displaying the document by itself, even if the document's format is
    supported by the browser.
   </para>
   <para>
    The declared content type can also affect which rendering mode
    the browser chooses. If XHTML is delivered as <quote>text/html</quote>,
    many browsers treat it as yet another broken HTML document.
    If it is send as <quote>application/xml</quote>, browsers with
    XHTML support will only display it, if the syntax is correct.
   </para>
   <para>
    If you see a web site that proudly uses XHTML buttons, but sets
    <quote>Content-Type: text/html</quote>, you can use &my-app;
    to overwrite it with <quote>application/xml</quote> and validate
    the web master's claim inside your XHTML-supporting browser.
    If the syntax is incorrect, the browser will complain loudly.
   </para>
   <para>
    You can also go the opposite direction: if your browser prints
    error messages instead of rendering a document falsely declared
    as XHTML, you can overwrite the content type with
    <quote>text/html</quote> and have it rendered as broken HTML document.
   </para>
   <para>
    By default <literal>content-type-overwrite</literal> only replaces
    <quote>Content-Type:</quote> headers that look like some kind of text.
    If you want to overwrite it unconditionally, you have to combine it with
    <literal><link linkend="force-text-mode">force-text-mode</link></literal>.
    This limitation exists for a reason, think twice before circumventing it.
   </para>
   <para>
    Most of the time it's easier to replace this action with a custom
    <literal><link linkend="server-header-filter">server-header filter</link></literal>.
    It allows you to activate it for every document of a certain site and it will still
    only replace the content types you aimed at.
   </para>
   <para>
    Of course you can apply <literal>content-type-overwrite</literal>
    to a whole site and then make URL based exceptions, but it's a lot
    more work to get the same precision.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage (sections):</term>
  <listitem>
     <screen># Check if www.example.net/ really uses valid XHTML
{ +content-type-overwrite{application/xml} }
www.example.net/

# but leave the content type unmodified if the URL looks like a style sheet
{-content-type-overwrite}
www.example.net/.*\.css$
www.example.net/.*style
</screen>
  </listitem>
 </varlistentry>
</variablelist>
</sect3>


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 renderas="sect4" id="crunch-client-header">
<!--
new action
-->
<title>crunch-client-header</title>

<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>Remove a client header <application>Privoxy</application> has no dedicated action for.</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    Deletes every header sent by the client that contains the string the user supplied as parameter.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Type:</term>
  <!-- Boolean, Parameterized, Multi-value -->
  <listitem>
   <para>Parameterized.</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Parameter:</term>
  <listitem>
   <para>
    Any string.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Notes:</term>
  <listitem>
   <para>
    This action allows you to block client headers for which no dedicated
    <application>Privoxy</application> action exists.
    <application>Privoxy</application> will remove every client header that
    contains the string you supplied as parameter.
   </para>
   <para>
    Regular expressions are <emphasis>not supported</emphasis> and you can't
    use this action to block different headers in the same request, unless
    they contain the same string.
   </para>
   <para>
    <literal>crunch-client-header</literal> is only meant for quick tests.
    If you have to block several different headers, or only want to modify
    parts of them, you should use a
    <literal><link linkend="client-header-filter">client-header filter</link></literal>.
   </para>
    <warning>
     <para>
      Don't block any header without understanding the consequences.
     </para>
    </warning>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage (section):</term>
  <listitem>
     <screen># Block the non-existent "Privacy-Violation:" client header
{ +crunch-client-header{Privacy-Violation:} }
/
</screen>
  </listitem>
 </varlistentry>
</variablelist>
</sect3>


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 renderas="sect4" id="crunch-if-none-match">
<title>crunch-if-none-match</title>
<!--
new action
-->
<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>Prevent yet another way to track the user's steps between sessions.</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    Deletes the <quote>If-None-Match:</quote> HTTP client header.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Type:</term>
  <!-- Boolean, Parameterized, Multi-value -->
  <listitem>
   <para>Boolean.</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Parameter:</term>
  <listitem>
   <para>
    N/A
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Notes:</term>
  <listitem>
   <para>
    Removing the <quote>If-None-Match:</quote> HTTP client header
    is useful for filter testing, where you want to force a real
    reload instead of getting status code <quote>304</quote> which
    would cause the browser to use a cached copy of the page.
   </para>
   <para>
    It is also useful to make sure the header isn't used as a cookie
    replacement (unlikely but possible).
   </para>
   <para>
    Blocking the <quote>If-None-Match:</quote> header shouldn't cause any
    caching problems, as long as the <quote>If-Modified-Since:</quote> header
    isn't blocked or missing as well.
   </para>
   <para>
    It is recommended to use this action together with
    <literal><link linkend="hide-if-modified-since">hide-if-modified-since</link></literal>
    and
    <literal><link linkend="overwrite-last-modified">overwrite-last-modified</link></literal>.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage (section):</term>
  <listitem>
     <screen># Let the browser revalidate cached documents but don't
# allow the server to use the revalidation headers for user tracking.
{+hide-if-modified-since{-60} \
 +overwrite-last-modified{randomize} \
 +crunch-if-none-match}
/
</screen>
  </listitem>
 </varlistentry>
</variablelist>
</sect3>


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 renderas="sect4" id="crunch-incoming-cookies">
<title>crunch-incoming-cookies</title>

<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>
    Prevent the web server from setting HTTP cookies on your system
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    Deletes any <quote>Set-Cookie:</quote> HTTP headers from server replies.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Type:</term>
  <!-- Boolean, Parameterized, Multi-value -->
  <listitem>
   <para>Boolean.</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Parameter:</term>
  <listitem>
   <para>
    N/A
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Notes:</term>
  <listitem>
   <para>
    This action is only concerned with <emphasis>incoming</emphasis> HTTP cookies. For
    <emphasis>outgoing</emphasis> HTTP cookies, use
    <literal><link linkend="crunch-outgoing-cookies">crunch-outgoing-cookies</link></literal>.
    Use <emphasis>both</emphasis> to disable HTTP cookies completely.
   </para>
   <para>
    It makes <emphasis>no sense at all</emphasis> to use this action in conjunction
    with the <literal><link linkend="session-cookies-only">session-cookies-only</link></literal> action,
    since it would prevent the session cookies from being set. See also
    <literal><link linkend="filter-content-cookies">filter-content-cookies</link></literal>.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage:</term>
  <listitem>
    <screen>+crunch-incoming-cookies</screen>
  </listitem>
 </varlistentry>
</variablelist>
</sect3>


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 renderas="sect4" id="crunch-server-header">
<title>crunch-server-header</title>
<!--
new action
-->
<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>Remove a server header <application>Privoxy</application> has no dedicated action for.</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    Deletes every header sent by the server that contains the string the user supplied as parameter.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Type:</term>
  <!-- Boolean, Parameterized, Multi-value -->
  <listitem>
   <para>Parameterized.</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Parameter:</term>
  <listitem>
   <para>
    Any string.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Notes:</term>
  <listitem>
   <para>
    This action allows you to block server headers for which no dedicated
    <application>Privoxy</application> action exists. <application>Privoxy</application>
    will remove every server header that contains the string you supplied as parameter.
   </para>
   <para>
    Regular expressions are <emphasis>not supported</emphasis> and you can't
    use this action to block different headers in the same request, unless
    they contain the same string.
   </para>
   <para>
    <literal>crunch-server-header</literal> is only meant for quick tests.
    If you have to block several different headers, or only want to modify
    parts of them, you should use a custom
    <literal><link linkend="server-header-filter">server-header filter</link></literal>.
   </para>
    <warning>
     <para>
     Don't block any header without understanding the consequences.
     </para>
    </warning>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage (section):</term>
  <listitem>
     <screen># Crunch server headers that try to prevent caching
{ +crunch-server-header{no-cache} }
/
</screen>
  </listitem>
 </varlistentry>
</variablelist>
</sect3>


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 renderas="sect4" id="crunch-outgoing-cookies">
<title>crunch-outgoing-cookies</title>

<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>
    Prevent the web server from reading any HTTP cookies from your system
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    Deletes any <quote>Cookie:</quote> HTTP headers from client requests.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Type:</term>
  <!-- Boolean, Parameterized, Multi-value -->
  <listitem>
   <para>Boolean.</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Parameter:</term>
  <listitem>
   <para>
    N/A
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Notes:</term>
  <listitem>
   <para>
    This action is only concerned with <emphasis>outgoing</emphasis> HTTP cookies. For
    <emphasis>incoming</emphasis> HTTP cookies, use
    <literal><link linkend="crunch-incoming-cookies">crunch-incoming-cookies</link></literal>.
    Use <emphasis>both</emphasis> to disable HTTP cookies completely.
   </para>
   <para>
    It makes <emphasis>no sense at all</emphasis> to use this action in conjunction
    with the <literal><link linkend="session-cookies-only">session-cookies-only</link></literal> action,
    since it would prevent the session cookies from being read.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage:</term>
  <listitem>
    <screen>+crunch-outgoing-cookies</screen>
  </listitem>
 </varlistentry>

</variablelist>
</sect3>


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 renderas="sect4" id="deanimate-gifs">
<title>deanimate-gifs</title>

<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>Stop those annoying, distracting animated GIF images.</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    De-animate GIF animations, i.e. reduce them to their first or last image.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Type:</term>
  <!-- boolean, parameterized, Multi-value -->
  <listitem>
   <para>Parameterized.</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Parameter:</term>
  <listitem>
   <para>
    <quote>last</quote> or <quote>first</quote>
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Notes:</term>
  <listitem>
   <para>
    This will also shrink the images considerably (in bytes, not pixels!). If
    the option <quote>first</quote> is given, the first frame of the animation
    is used as the replacement. If <quote>last</quote> is given, the last
    frame of the animation is used instead, which probably makes more sense for
    most banner animations, but also has the risk of not showing the entire
    last frame (if it is only a delta to an earlier frame).
   </para>
   <para>
    You can safely use this action with patterns that will also match non-GIF
    objects, because no attempt will be made at anything that doesn't look like
    a GIF.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage:</term>
  <listitem>
      <screen>+deanimate-gifs{last}</screen>
  </listitem>
 </varlistentry>
</variablelist>
</sect3>


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 renderas="sect4" id="delay-response">
<title>delay-response</title>

<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>Delay responses to the client to reduce the load</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    Delays responses to the client by sending the response in ca. 10 byte chunks.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Type:</term>
  <!-- boolean, parameterized, Multi-value -->
  <listitem>
   <para>Parameterized.</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Parameter:</term>
  <listitem>
   <para>
    <quote>Number of milliseconds</quote>
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Notes:</term>
  <listitem>
   <para>
    Sometimes when JavaScript code is used to fetch advertisements
    it doesn't respect Privoxy's blocks and retries to fetch the
    same resource again causing unnecessary load on the client.
   </para>
   <para>
    This action delays responses to the client and can be combined
    with <literal><link linkend="block">blocks</link></literal>
    to slow down the JavaScript code, thus reducing
    the load on the client.
   </para>
   <para>
    When used without <literal><link linkend="block">blocks</link></literal>
    the action can also be used to simulate a slow internet connection.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage:</term>
  <listitem>
      <screen>+delay-response{100}</screen>
  </listitem>
 </varlistentry>
</variablelist>
</sect3>


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 renderas="sect4" id="downgrade-http-version">
<title>downgrade-http-version</title>

<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>Work around (very rare) problems with HTTP/1.1</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    Downgrades HTTP/1.1 client requests and server replies to HTTP/1.0.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Type:</term>
  <!-- boolean, parameterized, Multi-value -->
  <listitem>
   <para>Boolean.</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Parameter:</term>
  <listitem>
   <para>
    N/A
   </para>
  </listitem>
 </varlistentry>

<varlistentry>
  <term>Notes:</term>
  <listitem>
   <para>
    This is a left-over from the time when <application>Privoxy</application>
    didn't support important HTTP/1.1 features well. It is left here for the
    unlikely case that you experience HTTP/1.1-related problems with some server
    out there.
   </para>
   <para>
    Note that enabling this action is only a workaround. It should not
    be enabled for sites that work without it. While it shouldn't break
    any pages, it has an (usually negative) performance impact.
  </para>
  <para>
    If you come across a site where enabling this action helps, please report it,
    so the cause of the problem can be analyzed. If the problem turns out to be
    caused by a bug in  <application>Privoxy</application> it should be
    fixed so the following release works without the work around.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage (section):</term>
  <listitem>
     <screen>{+downgrade-http-version}
problem-host.example.com</screen>
  </listitem>
 </varlistentry>

</variablelist>
</sect3>


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 renderas="sect4" id="external-filter">
<title>external-filter</title>

<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>Modify content using a programming language of your choice.</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    All instances of text-based type, most notably HTML and JavaScript, to which
    this action applies, can be filtered on-the-fly through the specified external
    filter.
    By default plain text documents are exempted from filtering, because web
    servers often use the <literal>text/plain</literal> MIME type for all files
    whose type they don't know.)
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Type:</term>
  <!-- boolean, parameterized, Multi-value -->
  <listitem>
   <para>Multi-value.</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Parameter:</term>
  <listitem>
   <para>
    The name of an external content filter, as defined in the
    <link linkend="filter-file">filter file</link>.
    External filters can be defined in one or more files as defined by the
    <literal><link linkend="filterfile">filterfile</link></literal>
    option in the <link linkend="config">config file</link>.
   </para>
   <para>
    When used in its negative form,
    and without parameters, <emphasis>all</emphasis> filtering with external
    filters is completely disabled.
  </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Notes:</term>
  <listitem>
   <para>
    External filters are scripts or programs that can modify the content in
    case common <literal><link linkend="filter">filters</link></literal>
    aren't powerful enough. With the exception that this action doesn't
    use pcrs-based filters, the notes in the
    <literal><link linkend="filter">filter</link></literal> section apply.
   </para>
   <warning>
    <para>
     Currently external filters are executed with &my-app;'s privileges.
     Only use external filters you understand and trust.
    </para>
   </warning>
   <para>
    This feature is experimental, the <literal><link
    linkend="external-filter-syntax">syntax</link></literal>
    may change in the future.
   </para>

  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage:</term>
  <listitem>
    <screen>+external-filter{fancy-filter}</screen>
  </listitem>
 </varlistentry>
</variablelist>
</sect3>

<!--   ~~~~~       New section      ~~~~~     -->
<sect3 renderas="sect4" id="fast-redirects">
<title>fast-redirects</title>

<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>Fool some click-tracking scripts and speed up indirect links.</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    Detects redirection URLs and redirects the browser without contacting
    the redirection server first.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Type:</term>
  <!-- boolean, parameterized, Multi-value -->
  <listitem>
   <para>Parameterized.</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Parameter:</term>
  <listitem>
   <itemizedlist>
    <listitem>
     <para>
      <quote>simple-check</quote> to just search for the string <quote>http://</quote>
      to detect redirection URLs.
     </para>
    </listitem>
    <listitem>
     <para>
      <quote>check-decoded-url</quote> to decode URLs (if necessary) before searching
      for redirection URLs.
     </para>
    </listitem>
   </itemizedlist>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Notes:</term>
  <listitem>
   <para>
    Many sites, like yahoo.com, don't just link to other sites. Instead, they
    will link to some script on their own servers, giving the destination as a
    parameter, which will then redirect you to the final target. URLs
    resulting from this scheme typically look like:
    <quote>http://www.example.org/click-tracker.cgi?target=http%3a//www.example.net/</quote>.
  </para>
   <para>
    Sometimes, there are even multiple consecutive redirects encoded in the
    URL. These redirections via scripts make your web browsing more traceable,
    since the server from which you follow such a link can see where you go
    to. Apart from that, valuable bandwidth and time is wasted, while your
    browser asks the server for one redirect after the other. Plus, it feeds
    the advertisers.
   </para>
   <para>
    This feature is currently not very smart and is scheduled for improvement.
    If it is enabled by default, you will have to create some exceptions to
    this action. It can lead to failures in several ways:
   </para>
   <para>
    Not every URLs with other URLs as parameters is evil.
    Some sites offer a real service that requires this information to work.
    For example a validation service needs to know, which document to validate.
    <literal>fast-redirects</literal> assumes that every URL parameter that
    looks like another URL is a redirection target, and will always redirect to
    the last one. Most of the time the assumption is correct, but if it isn't,
    the user gets redirected anyway.
   </para>
   <para>
    Another failure occurs if the URL contains other parameters after the URL parameter.
    The URL:
    <quote>http://www.example.org/?redirect=http%3a//www.example.net/&amp;foo=bar</quote>.
    contains the redirection URL <quote>http://www.example.net/</quote>,
    followed by another parameter. <literal>fast-redirects</literal> doesn't know that
    and will cause a redirect to <quote>http://www.example.net/&amp;foo=bar</quote>.
    Depending on the target server configuration, the parameter will be silently ignored
    or lead to a <quote>page not found</quote> error. You can prevent this problem by
    first using the <literal><link linkend="redirect">redirect</link></literal> action
    to remove the last part of the URL, but it requires a little effort.
   </para>
   <para>
    To detect a redirection URL, <literal>fast-redirects</literal> only
    looks for the string <quote>http://</quote>, either in plain text
    (invalid but often used) or encoded as <quote>http%3a//</quote>.
    Some sites use their own URL encoding scheme, encrypt the address
    of the target server or replace it with a database id. In these cases
    <literal>fast-redirects</literal> is fooled and the request reaches the
    redirection server where it probably gets logged.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage:</term>
  <listitem>
     <screen>
 { +fast-redirects{simple-check} }
   one.example.com

 { +fast-redirects{check-decoded-url} }
   another.example.com/testing</screen>
  </listitem>
 </varlistentry>

</variablelist>
</sect3>


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 renderas="sect4" id="filter">
<title>filter</title>

<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>Get rid of HTML and JavaScript annoyances, banner advertisements (by size),
         do fun text replacements, add personalized effects, etc.</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    All instances of text-based type, most notably HTML and JavaScript, to which
    this action applies, can be filtered on-the-fly through the specified regular
    expression based substitutions. (Note: as of version 3.0.3 plain text documents
    are exempted from filtering, because web servers often use the
   <literal>text/plain</literal> MIME type for all files whose type they don't know.)
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Type:</term>
  <!-- boolean, parameterized, Multi-value -->
  <listitem>
   <para>Multi-value.</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Parameter:</term>
  <listitem>
   <para>
    The name of a content filter, as defined in the <link linkend="filter-file">filter file</link>.
    Filters can be defined in one or more  files as defined by the
    <literal><link linkend="filterfile">filterfile</link></literal>
    option in the <link linkend="config">config file</link>.
    <filename>default.filter</filename> is the collection of filters
    supplied by the developers. Locally defined filters should go
    in their own file, such as <filename>user.filter</filename>.
   </para>
   <para>
     When used in its negative form,
     and without parameters, <emphasis>all</emphasis> filtering is completely disabled.
  </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Notes:</term>
  <listitem>
   <para>
    For your convenience, there are a number of pre-defined filters available
    in the distribution filter file that you can use. See the examples below for
    a list.
   </para>
   <para>
    Filtering requires buffering the page content, which may appear to
    slow down page rendering since nothing is displayed until all content has
    passed the filters. (The total time until the page is completely rendered
    doesn't change much, but it may be perceived as slower since the page is
    not incrementally displayed.)
    This effect will be more noticeable on slower connections.
   </para>
   <para>
   <quote>Rolling your own</quote>
    filters requires a knowledge of
     <ulink url="https://en.wikipedia.org/wiki/Regular_expressions"><quote>Regular
     Expressions</quote></ulink> and
      <ulink url="https://en.wikipedia.org/wiki/Html"><quote>HTML</quote></ulink>.
    This is very powerful feature, and potentially very intrusive.
    Filters should be used with caution, and where an equivalent
    <quote>action</quote> is not available.
   </para>
   <para>
    The amount of data that can be filtered is limited by the
    <literal><link linkend="buffer-limit">buffer-limit</link></literal>
    option in the main <link linkend="config">config file</link>. The
    default is 4096 KB (4 Megs). Once this limit is exceeded, the buffered
    data, and all pending data, is passed through unfiltered.
   </para>
   <para>
    Inappropriate MIME types, such as zipped files, are not filtered at all.
    (Again, only text-based types except plain text). Encrypted SSL data
    (from HTTPS servers) cannot be filtered either, since this would violate
    the integrity of the secure transaction. In some situations it might
    be necessary to protect certain text, like source code, from filtering
    by defining appropriate <literal>-filter</literal> exceptions.
   </para>
   <para>
    Compressed content can't be filtered either, but if &my-app;
    is compiled with zlib support and a supported compression algorithm
    is used (gzip or deflate), &my-app; can first decompress the content
    and then filter it.
   </para>
   <para>
    If you use a &my-app; version without zlib support, but want filtering to work on
    as much documents as possible, even those that would normally be sent compressed,
    you must use the <literal><link linkend="prevent-compression">prevent-compression</link></literal>
    action in conjunction with <literal>filter</literal>.
   </para>
   <para>
    Content filtering can achieve some of the same effects as the
    <literal><link linkend="block">block</link></literal>
    action, i.e. it can be used to block ads and banners. But the mechanism
    works quite differently. One effective use, is to block ad banners
    based on their size (see below), since many of these seem to be somewhat
    standardized.
   </para>
   <para>
    <link linkend="contact">Feedback</link> with suggestions for new or
    improved filters is particularly welcome!
   </para>
   <para>
    The below list has only the names and a one-line description of each
    predefined filter. There are <link linkend="predefined-filters">more
    verbose explanations</link> of what these filters do in the <link
    linkend="filter-file">filter file chapter</link>.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage (with filters from the distribution <filename>default.filter</filename> file).
  See <link linkend="PREDEFINED-FILTERS">the Predefined Filters section</link> for
  more explanation on each:</term>
  <listitem>
   <para>
    <anchor id="filter-js-annoyances">
   </para>
    <screen>+filter{js-annoyances}       # Get rid of particularly annoying JavaScript abuse.</screen>
   <para>
    <anchor id="filter-js-events">
   </para>
    <screen>+filter{js-events}           # Kill JavaScript event bindings and timers (Radically destructive! Only for extra nasty sites).</screen>
   <para>
    <anchor id="filter-html-annoyances">
   </para>
    <screen>+filter{html-annoyances}     # Get rid of particularly annoying HTML abuse.</screen>
   <para>
    <anchor id="filter-content-cookies">
   </para>
    <screen>+filter{content-cookies}     # Kill cookies that come in the HTML or JS content.</screen>
   <para>
    <anchor id="filter-refresh-tags">
   </para>
    <screen>+filter{refresh-tags}        # Kill automatic refresh tags if refresh time is larger than 9 seconds.</screen>
   <para>
    <anchor id="filter-unsolicited-popups">
   </para>
    <screen>+filter{unsolicited-popups}  # Disable only unsolicited pop-up windows.</screen>
   <para>
    <anchor id="filter-all-popups">
   </para>
    <screen>+filter{all-popups}          # Kill all popups in JavaScript and HTML.</screen>
   <para>
    <anchor id="filter-img-reorder">
   </para>
    <screen>+filter{img-reorder}         # Reorder attributes in &lt;img&gt; tags to make the banners-by-* filters more effective.</screen>
   <para>
    <anchor id="filter-banners-by-size">
   </para>
    <screen>+filter{banners-by-size}     # Kill banners by size.</screen>
   <para>
    <anchor id="filter-banners-by-link">
   </para>
    <screen>+filter{banners-by-link}     # Kill banners by their links to known clicktrackers.</screen>
   <para>
    <anchor id="filter-webbugs">
   </para>
    <screen>+filter{webbugs}             # Squish WebBugs (1x1 invisible GIFs used for user tracking).</screen>
   <para>
    <anchor id="filter-tiny-textforms">
   </para>
    <screen>+filter{tiny-textforms}      # Extend those tiny textareas up to 40x80 and kill the hard wrap.</screen>
   <para>
    <anchor id="filter-jumping-windows">
   </para>
    <screen>+filter{jumping-windows}     # Prevent windows from resizing and moving themselves.</screen>
   <para>
    <anchor id="filter-frameset-borders">
   </para>
    <screen>+filter{frameset-borders}    # Give frames a border and make them resizable.</screen>
   <para>
    <anchor id="filter-iframes">
   </para>
    <screen>+filter{iframes}             # Removes all detected iframes. Should only be enabled for individual sites.</screen>
   <para>
    <anchor id="filter-demoronizer">
   </para>
    <screen>+filter{demoronizer}         # Fix MS's non-standard use of standard charsets.</screen>
   <para>
    <anchor id="filter-shockwave-flash">
   </para>
    <screen>+filter{shockwave-flash}     # Kill embedded Shockwave Flash objects.</screen>
   <para>
    <anchor id="filter-quicktime-kioskmode">
   </para>
    <screen>+filter{quicktime-kioskmode} # Make Quicktime movies saveable.</screen>
   <para>
    <anchor id="filter-fun">
   </para>
    <screen>+filter{fun}                 # Text replacements for subversive browsing fun!</screen>
   <para>
    <anchor id="filter-crude-parental">
   </para>
    <screen>+filter{crude-parental}      # Crude parental filtering. Note that this filter doesn't work reliably.</screen>
   <para>
    <anchor id="filter-ie-exploits">
   </para>
    <screen>+filter{ie-exploits}         # Disable some known Internet Explorer bug exploits.</screen>
   <para>
    <anchor id="filter-site-specifics">
   </para>
    <screen>+filter{site-specifics}      # Cure for site-specific problems. Don't apply generally!</screen>
   <para>
    <anchor id="filter-no-ping">
   </para>
    <screen>+filter{no-ping}             # Removes non-standard ping attributes in &lt;a&gt; and &lt;area&gt; tags.</screen>
   <para>
    <anchor id="filter-github">