Mention the github filter in the user-manual

[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">
   </para>
    <screen>+filter{github}              # Removes the annoying "Sign-Up" banner and the Cookie disclaimer.</screen>
   <para>
    <anchor id="filter-google">
   </para>
    <screen>+filter{google}              # CSS-based block for Google text ads. Also removes a width limitation and the toolbar advertisement.</screen>
   <para>
    <anchor id="filter-yahoo">
   </para>
    <screen>+filter{yahoo}               # CSS-based block for Yahoo text ads. Also removes a width limitation.</screen>
   <para>
    <anchor id="filter-msn">
   </para>
    <screen>+filter{msn}                 # CSS-based block for MSN text ads. Also removes tracking URLs and a width limitation.</screen>
   <para>
    <anchor id="filter-blogspot">
   </para>
    <screen>+filter{blogspot}            # Cleans up some Blogspot blogs. Read the fine print before using this.</screen>
  </listitem>
 </varlistentry>
</variablelist>
</sect3>


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 renderas="sect4" id="force-text-mode">
<title>force-text-mode</title>
<!--
new action
-->
<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>Force <application>Privoxy</application> to treat a document as if it was in some kind of <emphasis>text</emphasis> format.   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    Declares a document as text, even if the <quote>Content-Type:</quote> isn't detected as such.
   </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>
    As explained <literal><link linkend="filter">above</link></literal>,
    <application>Privoxy</application> tries to only filter files that are
    in some kind of text format. The same restrictions apply to
    <literal><link linkend="content-type-overwrite">content-type-overwrite</link></literal>.
    <literal>force-text-mode</literal> declares a document as text,
    without looking at the <quote>Content-Type:</quote> first.
   </para>
   <warning>
    <para>
     Think twice before activating this action. Filtering binary data
     with regular expressions can cause file damage.
    </para>
   </warning>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage:</term>
  <listitem>
     <screen>
+force-text-mode
</screen>
  </listitem>
 </varlistentry>
</variablelist>
</sect3>


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 renderas="sect4" id="forward-override">
<title>forward-override</title>
<!--
new action
-->
<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>Change the forwarding settings based on User-Agent or request origin</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    Overrules the forward directives in the configuration file.
   </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>forward .</quote> to use a direct connection without any additional proxies.</para>
    </listitem>
    <listitem>
     <para>
      <quote>forward 127.0.0.1:8123</quote> to use the HTTP proxy listening at 127.0.0.1 port 8123.
     </para>
    </listitem>
    <listitem>
     <para>
      <quote>forward-socks4a 127.0.0.1:9050 .</quote> to use the socks4a proxy listening at
      127.0.0.1 port 9050. Replace <quote>forward-socks4a</quote> with <quote>forward-socks4</quote>
      to use a socks4 connection  (with local DNS resolution) instead, use <quote>forward-socks5</quote>
      for socks5 connections (with remote DNS resolution).
     </para>
    </listitem>
    <listitem>
     <para>
      <quote>forward-socks4a 127.0.0.1:9050 proxy.example.org:8000</quote> to use the socks4a proxy
      listening at 127.0.0.1 port 9050 to reach the HTTP proxy listening at proxy.example.org port 8000.
      Replace <quote>forward-socks4a</quote> with <quote>forward-socks4</quote> to use a socks4 connection
      (with local DNS resolution) instead, use <quote>forward-socks5</quote>
      for socks5 connections (with remote DNS resolution).
     </para>
    </listitem>
    <listitem>
     <para>
      <quote>forward-webserver 127.0.0.1:80</quote> to use the HTTP
      server listening at 127.0.0.1 port 80 without adjusting the
      request headers.
     </para>
     <para>
      This makes it more convenient to use Privoxy to make
      existing websites available as onion services as well.
     </para>
     <para>
      Many websites serve content with hardcoded URLs and
      can't be easily adjusted to change the domain based
      on the one used by the client.
     </para>
     <para>
      Putting Privoxy between Tor and the webserver (or an stunnel
      that forwards to the webserver) allows to rewrite headers and
      content to make client and server happy at the same time.
     </para>
     <para>
      Using Privoxy for webservers that are only reachable through
      onion addresses and whose location is supposed to be secret
      is not recommended and should not be necessary anyway.
     </para>
    </listitem>
   </itemizedlist>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Notes:</term>
  <listitem>
   <para>
    This action takes parameters similar to the
    <link linkend="forwarding">forward</link> directives in the configuration
    file, but without the URL pattern. It can be used as replacement, but normally it's only
    used in cases where matching based on the request URL isn't sufficient.
   </para>
   <warning>
    <para>
     Please read the description for the <link linkend="forwarding">forward</link> directives before
     using this action. Forwarding to the wrong people will reduce your privacy and increase the
     chances of man-in-the-middle attacks.
    </para>
    <para>
     If the ports are missing or invalid, default values will be used. This might change
     in the future and you shouldn't rely on it. Otherwise incorrect syntax causes Privoxy
     to exit. Due to design limitations, invalid parameter syntax isn't detected until the
     action is used the first time.
    </para>
    <para>
     Use the <ulink url="http://config.privoxy.org/show-url-info">show-url-info CGI page</ulink>
     to verify that your forward settings do what you thought the do.
    </para>
   </warning>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage:</term>
  <listitem>
     <screen>
# Use an ssh tunnel for requests previously tagged as
# <quote>User-Agent: fetch libfetch/2.0</quote> and make sure
# resuming downloads continues to work.
#
# This way you can continue to use Tor for your normal browsing,
# without overloading the Tor network with your FreeBSD ports updates
# or downloads of bigger files like ISOs.
#
# Note that HTTP headers are easy to fake and therefore their
# values are as (un)trustworthy as your clients and users.
{+forward-override{forward-socks5 10.0.0.2:2222 .} \
 -hide-if-modified-since      \
 -overwrite-last-modified     \
}
TAG:^User-Agent: fetch libfetch/2\.0$
</screen>
  </listitem>
 </varlistentry>
</variablelist>
</sect3>


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 renderas="sect4" id="handle-as-empty-document">
<title>handle-as-empty-document</title>
<!--
new action
-->
<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>Mark URLs that should be replaced by empty documents <emphasis>if they get blocked</emphasis></para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    This action alone doesn't do anything noticeable. It just marks URLs.
    If the <literal><link linkend="block">block</link></literal> action <emphasis>also applies</emphasis>,
    the presence or absence of this mark decides whether an HTML <quote>BLOCKED</quote>
    page, or an empty document will be sent to the client as a substitute for the blocked content.
    The <emphasis>empty</emphasis> document isn't literally empty, but actually contains a single space.
   </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>
    Some browsers complain about syntax errors if JavaScript documents
    are blocked with <application>Privoxy's</application>
    default HTML page; this option can be used to silence them.
    And of course this action can also be used to eliminate the &my-app;
    BLOCKED message in frames.
   </para>
   <para>
    The content type for the empty document can be specified with
    <literal><link linkend="content-type-overwrite">content-type-overwrite{}</link></literal>,
    but usually this isn't necessary.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage:</term>
  <listitem>
     <screen># Block all documents on example.org that end with ".js",
# but send an empty document instead of the usual HTML message.
{+block{Blocked JavaScript} +handle-as-empty-document}
example.org/.*\.js$
</screen>
  </listitem>
 </varlistentry>
</variablelist>
</sect3>


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 renderas="sect4" id="handle-as-image">
<title>handle-as-image</title>

<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>Mark URLs as belonging to images (so they'll be replaced by images <emphasis>if they do get blocked</emphasis>, rather than HTML pages)</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    This action alone doesn't do anything noticeable. It just marks URLs as images.
    If the <literal><link linkend="block">block</link></literal> action <emphasis>also applies</emphasis>,
    the presence or absence of this mark decides whether an HTML <quote>blocked</quote>
    page, or a replacement image (as determined by the <literal><link
    linkend="set-image-blocker">set-image-blocker</link></literal> action) will be sent to the
    client as a substitute for the blocked content.
   </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>
    The below generic example section is actually part of <filename>default.action</filename>.
    It marks all URLs with well-known image file name extensions as images and should
    be left intact.
   </para>
   <para>
    Users will probably only want to use the handle-as-image action in conjunction with
    <literal><link linkend="block">block</link></literal>, to block sources of banners, whose URLs don't
    reflect the file type, like in the second example section.
   </para>
   <para>
    Note that you cannot treat HTML pages as images in most cases. For instance, (in-line) ad
    frames require an HTML page to be sent, or they won't display properly.
    Forcing <literal>handle-as-image</literal> in this situation will not replace the
    ad frame with an image, but lead to error messages.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage (sections):</term>
  <listitem>
     <screen># Generic image extensions:
#
{+handle-as-image}
/.*\.(gif|jpg|jpeg|png|bmp|ico)$

# These don't look like images, but they're banners and should be
# blocked as images:
#
{+block{Nasty banners.} +handle-as-image}
nasty-banner-server.example.com/junk.cgi\?output=trash
</screen>
  </listitem>
 </varlistentry>
</variablelist>
</sect3>


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 renderas="sect4" id="hide-accept-language">
<title>hide-accept-language</title>
<!--
new action
-->
<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>Pretend to use different language settings.</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    Deletes or replaces the <quote>Accept-Language:</quote> HTTP header in client requests.
   </para>
  </listitem>
 </varlistentry>

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

 <varlistentry>
  <term>Parameter:</term>
  <listitem>
   <para>
    Keyword: <quote>block</quote>, or any user defined value.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Notes:</term>
  <listitem>
   <para>
    Faking the browser's language settings can be useful to make a
    foreign User-Agent set with
    <literal><link linkend="hide-user-agent">hide-user-agent</link></literal>
    more believable.
   </para>
   <para>
    However some sites with content in different languages check the
    <quote>Accept-Language:</quote> to decide which one to take by default.
    Sometimes it isn't possible to later switch to another language without
    changing the <quote>Accept-Language:</quote> header first.
   </para>
   <para>
    Therefore it's a good idea to either only change the
    <quote>Accept-Language:</quote> header to languages you understand,
    or to languages that aren't wide spread.
   </para>
   <para>
    Before setting the <quote>Accept-Language:</quote> header
    to a rare language, you should consider that it helps to
    make your requests unique and thus easier to trace.
    If you don't plan to change this header frequently,
    you should stick to a common language.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage (section):</term>
  <listitem>
     <screen># Pretend to use Canadian language settings.
{+hide-accept-language{en-ca} \
+hide-user-agent{Mozilla/5.0 (X11; U; OpenBSD i386; en-CA; rv:1.8.0.4) Gecko/20060628 Firefox/1.5.0.4} \
}
/
</screen>
  </listitem>
 </varlistentry>
</variablelist>
</sect3>


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 renderas="sect4" id="hide-content-disposition">
<title>hide-content-disposition</title>
<!--
new action
-->
<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>Prevent download menus for content you prefer to view inside the browser.</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    Deletes or replaces the <quote>Content-Disposition:</quote> HTTP header set by some servers.
   </para>
  </listitem>
 </varlistentry>

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

 <varlistentry>
  <term>Parameter:</term>
  <listitem>
   <para>
    Keyword: <quote>block</quote>, or any user defined value.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Notes:</term>
  <listitem>
   <para>
    Some servers set the <quote>Content-Disposition:</quote> HTTP header for
    documents they assume you want to save locally before viewing them.
    The <quote>Content-Disposition:</quote> header contains the file name
    the browser is supposed to use by default.
   </para>
   <para>
    In most browsers that understand this header, it makes it impossible to
    <emphasis>just view</emphasis> the document, without downloading it first,
    even if it's just a simple text file or an image.
   </para>
   <para>
    Removing the <quote>Content-Disposition:</quote> header helps
    to prevent this annoyance, but some browsers additionally check the
    <quote>Content-Type:</quote> header, before they decide if they can
    display a document without saving it first. In these cases, you have
    to change this header as well, before the browser stops displaying
    download menus.
   </para>
   <para>
    It is also possible to change the server's file name suggestion
    to another one, but in most cases it isn't worth the time to set
    it up.
   </para>
   <para>
    This action will probably be removed in the future,
    use server-header filters instead.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage:</term>
  <listitem>
     <screen># Disarm the download link in Sourceforge's patch tracker
{ -filter \
 +content-type-overwrite{text/plain}\
 +hide-content-disposition{block} }
 .sourceforge.net/tracker/download\.php</screen>
  </listitem>
 </varlistentry>
</variablelist>
</sect3>


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 renderas="sect4" id="hide-if-modified-since">
<title>hide-if-modified-since</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-Modified-Since:</quote> HTTP client header or modifies its value.
   </para>
  </listitem>
 </varlistentry>

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

 <varlistentry>
  <term>Parameter:</term>
  <listitem>
   <para>
    Keyword: <quote>block</quote>, or a user defined value that specifies a range of hours.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Notes:</term>
  <listitem>
   <para>
    Removing this 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>
    Instead of removing the header, <literal>hide-if-modified-since</literal> can
    also add or subtract a random amount of time to/from the header's value.
    You specify a range of minutes where the random factor should be chosen from and
    <application>Privoxy</application> does the rest. A negative value means
    subtracting, a positive value adding.
   </para>
   <para>
    Randomizing the value of the <quote>If-Modified-Since:</quote> makes
    it less likely that the server can use the time as a cookie replacement,
    but you will run into caching problems if the random range is too high.
   </para>
   <para>
    It is a good idea to only use a small negative value and let
    <literal><link linkend="overwrite-last-modified">overwrite-last-modified</link></literal>
    handle the greater changes.
   </para>
   <para>
    It is also recommended to use this action together with
    <literal><link linkend="crunch-if-none-match">crunch-if-none-match</link></literal>,
    otherwise it's more or less pointless.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage (section):</term>
  <listitem>
     <screen># Let the browser revalidate but make tracking based on the time less likely.
{+hide-if-modified-since{-60} \
 +overwrite-last-modified{randomize} \
 +crunch-if-none-match}
/</screen>
  </listitem>
 </varlistentry>
</variablelist>
</sect3>


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

<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>Keep your (old and ill) browser from telling web servers your email address</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    Deletes any existing <quote>From:</quote> HTTP header, or replaces it with the
    specified string.
   </para>
  </listitem>
 </varlistentry>

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

 <varlistentry>
  <term>Parameter:</term>
  <listitem>
   <para>
    Keyword: <quote>block</quote>, or any user defined value.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Notes:</term>
  <listitem>
   <para>
    The keyword <quote>block</quote> will completely remove the header
    (not to be confused with the <literal><link linkend="block">block</link></literal>
    action).
   </para>
   <para>
    Alternately, you can specify any value you prefer to be sent to the web
    server. If you do, it is a matter of fairness not to use any address that
    is actually used by a real person.
   </para>
   <para>
    This action is rarely needed, as modern web browsers don't send
    <quote>From:</quote> headers anymore.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage:</term>
  <listitem>
    <screen>+hide-from-header{block}</screen>
    <para>or</para>
    <screen>+hide-from-header{spam-me-senseless@sittingduck.example.com}</screen>
  </listitem>
 </varlistentry>
</variablelist>
</sect3>


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 renderas="sect4" id="hide-referrer">
<title>hide-referrer</title>
<anchor id="hide-referer">
<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>Conceal which link you followed to get to a particular site</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    Deletes the <quote>Referer:</quote> (sic) HTTP header from the client request,
    or replaces it with a forged 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>conditional-block</quote> to delete the header completely if the host has changed.</para>
    </listitem>
    <listitem>
     <para><quote>conditional-forge</quote> to forge the header if the host has changed.</para>
    </listitem>
    <listitem>
     <para><quote>block</quote> to delete the header unconditionally.</para>
    </listitem>
    <listitem>
     <para><quote>forge</quote> to pretend to be coming from the homepage of the server we are talking to.</para>
    </listitem>
    <listitem>
     <para>Any other string to set a user defined referrer.</para>
    </listitem>
   </itemizedlist>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Notes:</term>
  <listitem>
   <para>
    <literal>conditional-block</literal> is the only parameter,
    that isn't easily detected in the server's log file. If it blocks the
    referrer, the request will look like the visitor used a bookmark or
    typed in the address directly.
   </para>
   <para>
    Leaving the referrer unmodified for requests on the same host
    allows the server owner to see the visitor's <quote>click path</quote>,
    but in most cases she could also get that information by comparing
    other parts of the log file: for example the User-Agent if it isn't
    a very common one, or the user's IP address if it doesn't change between
    different requests.
   </para>
   <para>
    Always blocking the referrer, or using a custom one, can lead to
    failures on servers that check the referrer before they answer any
    requests, in an attempt to prevent their content from being
    embedded or linked to elsewhere.
   </para>
   <para>
    Both <literal>conditional-block</literal> and <literal>forge</literal>
    will work with referrer checks, as long as content and valid referring page
    are on the same host. Most of the time that's the case.
   </para>
   <para>
    <literal>hide-referer</literal> is an alternate spelling of
    <literal>hide-referrer</literal> and the two can be can be freely
    substituted with each other. (<quote>referrer</quote> is the
    correct English spelling, however the HTTP specification has a bug - it
    requires it to be spelled as <quote>referer</quote>.)
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage:</term>
  <listitem>
     <screen>+hide-referrer{forge}</screen>
     <para>or</para>
     <screen>+hide-referrer{http://www.yahoo.com/}</screen>
  </listitem>
 </varlistentry>
</variablelist>
</sect3>


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 renderas="sect4" id="hide-user-agent">
<title>hide-user-agent</title>

<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>Try to conceal your type of browser and client operating system</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    Replaces the value of the <quote>User-Agent:</quote> HTTP header
    in client requests with the specified value.
   </para>
  </listitem>
 </varlistentry>

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

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

 <varlistentry>
  <term>Notes:</term>
  <listitem>
   <warning>
    <para>
     This can lead to problems on web sites that depend on looking at this header in
     order to customize their content for different browsers (which, by the
     way, is <emphasis>NOT</emphasis> the right thing to do: good web sites
     work browser-independently).
    </para>
   </warning>
   <para>
    Using this action in multi-user setups or wherever different types of
    browsers will access the same <application>Privoxy</application> is
    <emphasis>not recommended</emphasis>. In single-user, single-browser
    setups, you might use it to delete your OS version information from
    the headers, because it is an invitation to exploit known bugs for your
    OS. It is also occasionally useful to forge this in order to access
    sites that won't let you in otherwise (though there may be a good
    reason in some cases).
   </para>
   <para>
     More information on known user-agent strings can be found at
     <ulink url="http://www.user-agents.org/">http://www.user-agents.org/</ulink>
     and
     <ulink url="https://en.wikipedia.org/wiki/User_agent">http://en.wikipedia.org/wiki/User_agent</ulink>.
   </para>
   </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage:</term>
  <listitem>
     <screen>+hide-user-agent{Mozilla/5.0 (X11; ElectroBSD i386; rv:78.0) Gecko/20100101 Firefox/78.0}</screen>
  </listitem>
 </varlistentry>
</variablelist>
</sect3>


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

<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>Filter encrypted requests and responses</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    Encrypted requests are decrypted, filtered and forwarded encrypted.
   </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 allows &my-app; to filter encrypted requests and responses.
    For this to work &my-app; has to generate a certificate and send it
    to the client which has to accept it.
   </para>
   <para>
    Before this works the directives in the
    <literal><ulink url="config.html#HTTPS-INSPECTION-DIRECTIVES">HTTPS inspection section</ulink></literal>
    of the config file have to be configured.
   </para>
   <para>
    Note that the action has to be enabled based on the CONNECT
    request which doesn't contain a path. Enabling it based on
    a pattern with path doesn't work as the path is only seen
    by &my-app; if the action is already enabled.
   </para>
   <para>
    This is an experimental feature.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage (section):</term>
  <listitem>
     <screen>{+https-inspection}
www.example.com</screen>
  </listitem>
 </varlistentry>

</variablelist>
</sect3>


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 renderas="sect4" id="ignore-certificate-errors">
<title>ignore-certificate-errors</title>

<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>Filter encrypted requests and responses without verifying the certificate</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    Encrypted requests are forwarded to sites without verifying the certificate.
   </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>
    When the
    <link linkend="HTTPS-INSPECTION"><quote>+https-inspection</quote></link>
    action is used &my-app; by default verifies that the remote site uses a valid
    certificate.
   </para>
   <para>
    If the certificate can't be validated by &my-app; the connection is aborted.
   </para>
   <para>
    This action disables the certificate check so requests to sites
    with certificates that can't be validated are allowed.
   </para>
   <para>
    Note that enabling this action allows Man-in-the-middle attacks.
   </para>
   </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage:</term>
  <listitem>
   <screen>
    {+ignore-certificate-errors}
    www.example.org
   </screen>
  </listitem>
 </varlistentry>
</variablelist>
</sect3>


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

<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>Prevent abuse of <application>Privoxy</application> as a TCP proxy relay or disable SSL for untrusted sites</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    Specifies to which ports HTTP CONNECT requests are allowable.
   </para>
  </listitem>
 </varlistentry>

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

 <varlistentry>
  <term>Parameter:</term>
  <listitem>
   <para>
    A comma-separated list of ports or port ranges (the latter using dashes, with the minimum
    defaulting to 0 and the maximum to 65K).
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Notes:</term>
  <listitem>
   <para>
    By default, i.e. if no <literal>limit-connect</literal> action applies,
    <application>Privoxy</application> allows HTTP CONNECT requests to all
    ports. Use <literal>limit-connect</literal> if fine-grained control
    is desired for some or all destinations.
   </para>
   <para>
    The CONNECT methods exists in HTTP to allow access to secure websites
    (<quote>https://</quote> URLs) through proxies. It works very simply:
    the proxy connects to the server on the specified port, and then
    short-circuits its connections to the client and to the remote server.
    This means CONNECT-enabled proxies can be used as TCP relays very easily.
  </para>
  <para>
   <application>Privoxy</application> relays HTTPS traffic without seeing
   the decoded content. Websites can leverage this limitation to circumvent &my-app;'s
   filters. By specifying an invalid port range you can disable HTTPS entirely.
  </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usages:</term>
  <listitem>
   <!-- I had trouble getting the spacing to look right in my browser -->
   <!-- I probably have the wrong font setup, bollocks. -->
   <!-- Apparently the emphasis tag uses a proportional font no matter what -->
     <screen>+limit-connect{443}                   # Port 443 is OK.
+limit-connect{80,443}                # Ports 80 and 443 are OK.
+limit-connect{-3, 7, 20-100, 500-}   # Ports less than 3, 7, 20 to 100 and above 500 are OK.
+limit-connect{-}                     # All ports are OK
+limit-connect{,}                     # No HTTPS/SSL traffic is allowed</screen>
  </listitem>
 </varlistentry>
</variablelist>
</sect3>


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 renderas="sect4" id="limit-cookie-lifetime">
<title>limit-cookie-lifetime</title>

<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>Limit the lifetime of HTTP cookies to a couple of minutes or hours.</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    Overwrites the expires field in Set-Cookie server headers if it's above the specified limit.
   </para>
  </listitem>
 </varlistentry>

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

 <varlistentry>
  <term>Parameter:</term>
  <listitem>
   <para>
    The lifetime limit in minutes, or 0.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Notes:</term>
  <listitem>
   <para>
    This action reduces the lifetime of HTTP cookies coming from the
    server to the specified number of minutes, starting from the time
    the cookie passes Privoxy.
   </para>
   <para>
    Cookies with a lifetime below the limit are not modified.
    The lifetime of session cookies is set to the specified limit.
   </para>
   <para>
    The effect of this action depends on the server.
   </para>
   <para>
    In case of servers which refresh their cookies with each response
    (or at least frequently), the lifetime limit set by this action
    is updated as well.
    Thus, a session associated with the cookie continues to work with
    this action enabled, as long as a new request is made before the
    last limit set is reached.
   </para>
   <para>
    However, some servers send their cookies once, with a lifetime of several
    years (the year 2037 is a popular choice), and do not refresh them
    until a certain event in the future, for example the user logging out.
    In this case this action may limit the absolute lifetime of the session,
    even if requests are made frequently.
   </para>
   <para>
    If the parameter is <quote>0</quote>, this action behaves like
    <literal><link linkend="session-cookies-only">session-cookies-only</link></literal>.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usages:</term>
  <listitem>
     <screen>+limit-cookie-lifetime{60}</screen>
  </listitem>
 </varlistentry>
</variablelist>
</sect3>

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

<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>
    Ensure that servers send the content uncompressed, so it can be
    passed through <literal><link linkend="filter">filter</link></literal>s.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    Removes the Accept-Encoding header which can be used to ask for compressed transfer.
   </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>
    More and more websites send their content compressed by default, which
    is generally a good idea and saves bandwidth. But the <literal><link
    linkend="filter">filter</link></literal> and
    <literal><link linkend="deanimate-gifs">deanimate-gifs</link></literal>
    actions need access to the uncompressed data.
   </para>
   <para>
    When compiled with zlib support (available since &my-app; 3.0.7), content that should be
    filtered is decompressed on-the-fly and you don't have to worry about this action.
    If you are using an older &my-app; version, or one that hasn't been compiled with zlib
    support, this action can be used to convince the server to send the content uncompressed.
   </para>
   <para>
    Most text-based instances compress very well, the size is seldom decreased by less than 50%,
    for markup-heavy instances like news feeds saving more than 90% of the original size isn't
    unusual.
   </para>
   <para>
    Not using compression will therefore slow down the transfer, and you should only
    enable this action if you really need it. As of &my-app; 3.0.7 it's disabled in all
    predefined action settings.
   </para>
   <para>
    Note that some (rare) ill-configured sites don't handle requests for uncompressed
    documents correctly. Broken PHP applications tend to send an empty document body,
    some IIS versions only send the beginning of the content and some content delivery
    networks let the connection time out.
    If you enable <literal>prevent-compression</literal> per default, you might
    want to add exceptions for those sites. See the example for how to do that.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage (sections):</term>
  <listitem>
    <screen>
# Selectively turn off compression, and enable a filter
#
{ +filter{tiny-textforms} +prevent-compression }
# Match only these sites
 .google.
 sourceforge.net
 sf.net

# Or instead, we could set a universal default:
#
{ +prevent-compression }
 / # Match all sites

# Then maybe make exceptions for broken sites:
#
{ -prevent-compression }
.compusa.com/</screen>
  </listitem>
 </varlistentry>

</variablelist>
</sect3>


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 renderas="sect4" id="overwrite-last-modified">
<title>overwrite-last-modified</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>Last-Modified:</quote> HTTP server header or modifies its value.
   </para>
  </listitem>
 </varlistentry>

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

 <varlistentry>
  <term>Parameter:</term>
  <listitem>
   <para>
    One of the keywords: <quote>block</quote>, <quote>reset-to-request-time</quote>
    and <quote>randomize</quote>
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Notes:</term>
  <listitem>
   <para>
    Removing the <quote>Last-Modified:</quote> 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 reuse the old
    version of the page.
   </para>
   <para>
    The <quote>randomize</quote> option overwrites the value of the
    <quote>Last-Modified:</quote> header with a randomly chosen time
    between the original value and the current time. In theory the server
    could send each document with a different <quote>Last-Modified:</quote>
    header to track visits without using cookies. <quote>Randomize</quote>
    makes it impossible and the browser can still revalidate cached documents.
   </para>
   <para>
    <quote>reset-to-request-time</quote> overwrites the value of the
    <quote>Last-Modified:</quote> header with the current time. You could use
    this option together with
    <literal><link linkend="hide-if-modified-since">hide-if-modified-since</link></literal>
    to further customize your random range.
   </para>
   <para>
    The preferred parameter here is <quote>randomize</quote>. It is safe
    to use, as long as the time settings are more or less correct.
    If the server sets the <quote>Last-Modified:</quote> header to the time
    of the request, the random range becomes zero and the value stays the same.
    Therefore you should later randomize it a second time with
    <literal><link linkend="hide-if-modified-since">hided-if-modified-since</link></literal>,
    just to be sure.
   </para>
   <para>
    It is also recommended to use this action together with
    <literal><link linkend="crunch-if-none-match">crunch-if-none-match</link></literal>.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage:</term>
  <listitem>
     <screen># Let the browser revalidate without being tracked across sessions
{ +hide-if-modified-since{-60} \
 +overwrite-last-modified{randomize} \
 +crunch-if-none-match}
/</screen>
  </listitem>
 </varlistentry>
</variablelist>
</sect3>


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 renderas="sect4" id="redirect">
<title>redirect</title>
<!--
new action
-->
<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>
    Redirect requests to other sites.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    Convinces the browser that the requested document has been moved
    to another location and the browser should get it from there.
   </para>
  </listitem>
 </varlistentry>

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

 <varlistentry>
  <term>Parameter:</term>
  <listitem>
   <para>
    An absolute URL or a single pcrs command.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Notes:</term>
  <listitem>
   <para>
    Requests to which this action applies are answered with a
    HTTP redirect to URLs of your choosing. The new URL is
    either provided as parameter, or derived by applying a
    single pcrs command to the original URL.
   </para>
   <para>
    The syntax for pcrs commands is documented in the
    <link linkend="filter-file">filter file</link> section.
   </para>
   <para>
    Requests can't be blocked and redirected at the same time,
    applying this action together with
    <literal><link linkend="block">block</link></literal>
    is a configuration error. Currently the request is blocked
    and an error message logged, the behavior may change in the
    future and result in Privoxy rejecting the action file.
   </para>
   <para>
    This action can be combined with
    <literal><link linkend="fast-redirects">fast-redirects{check-decoded-url}</link></literal>
    to redirect to a decoded version of a rewritten URL.
   </para>
   <para>
    Use this action carefully, make sure not to create redirection loops
    and be aware that using your own redirects might make it
    possible to fingerprint your requests.
   </para>
   <para>
    In case of problems with your redirects, or simply to watch
    them working, enable <link linkend="DEBUG">debug 128</link>.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usages:</term>
  <listitem>
    <screen># Replace example.com's style sheet with another one
{ +redirect{http://localhost/css-replacements/example.com.css} }
 example.com/stylesheet\.css

# Create a short, easy to remember nickname for a favorite site
# (relies on the browser to accept and forward invalid URLs to &my-app;)
{ +redirect{https://www.privoxy.org/user-manual/actions-file.html} }
 a

# Always use the expanded view for Undeadly.org articles
# (Note the $ at the end of the URL pattern to make sure
# the request for the rewritten URL isn't redirected as well)
{+redirect{s@$@&amp;mode=expanded@}}
undeadly.org/cgi\?action=article&amp;sid=\d*$

# Redirect Google search requests to MSN
{+redirect{s@^http://[^/]*/search\?q=([^&amp;]*).*@http://search.msn.com/results.aspx?q=$1@}}
.google.com/search

# Redirect MSN search requests to Yahoo
{+redirect{s@^http://[^/]*/results\.aspx\?q=([^&amp;]*).*@http://search.yahoo.com/search?p=$1@}}
search.msn.com//results\.aspx\?q=

# Redirect http://example.com/&amp;bla=fasel&amp;toChange=foo (and any other value but "bar")
# to       http://example.com/&amp;bla=fasel&amp;toChange=bar
#
# The URL pattern makes sure that the following request isn't redirected again.
{+redirect{s@toChange=[^&amp;]+@toChange=bar@}}
example.com/.*toChange=(?!bar)

# Add a shortcut to look up illumos bugs
{+redirect{s@^http://i([0-9]+)/.*@https://www.illumos.org/issues/$1@}}
# Redirected URL = http://i4974/
# Redirect Destination = https://www.illumos.org/issues/4974
i[0-9][0-9][0-9][0-9]*/

# Redirect requests for the old Tor Hidden Service of the Privoxy website to the new one
{+redirect{s@^http://jvauzb4sb3bwlsnc.onion/@http://l3tczdiiwoo63iwxty4lhs6p7eaxop5micbn7vbliydgv63x5zrrrfyd.onion/@}}
jvauzb4sb3bwlsnc.onion/

# Redirect remote requests for this manual
# to the local version delivered by Privoxy
{+redirect{s@^http://www@http://config@}}
www.privoxy.org/user-manual/</screen>
  </listitem>
 </varlistentry>

</variablelist>
</sect3>


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

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

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    All server 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 server-header filter, as defined in one of the
    <link linkend="filter-file">filter files</link>.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Notes:</term>
  <listitem>
   <para>
    Server-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>
    Server-header filters are executed after the other header actions have finished
    and use their output as input.
   </para>
   <para>
    Please refer to the <link linkend="filter-file">filter file chapter</link>
    to learn which server-header filters are available by default, and how to
    create your own.
   </para>
 </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage (section):</term>
  <listitem>
     <screen>
{+server-header-filter{html-to-xml}}
example.org/xml-instance-that-is-delivered-as-html

{+server-header-filter{xml-to-html}}
example.org/instance-that-is-delivered-as-xml-but-is-not
</screen>
  </listitem>
 </varlistentry>

</variablelist>
</sect3>


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

<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>
   Enable or disable filters based on the Content-Type header.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    Server 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 server-header tagger, as defined in one of the
    <link linkend="filter-file">filter files</link>.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Notes:</term>
  <listitem>
   <para>
    Server-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>
    Server-header taggers are executed before all other header actions
    that modify server headers. Their tags can be used to control
    all of the other server-header actions, the content filters
    and the crunch actions (<link linkend="redirect">redirect</link>
    and <link linkend="block">block</link>).
   </para>
   <para>
    Obviously crunching based on tags created by server-header taggers
    doesn't prevent the request from showing up in the server's log file.
   </para>

 </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage (section):</term>
  <listitem>
     <screen>
# Tag every request with the content type declared by the server
{+server-header-tagger{content-type}}
/

# If the response has a tag starting with 'image/' enable an external
# filter that only applies to images.
#
# Note that the filter is not available by default, it's just a
# <literal><link linkend="external-filter-syntax">silly example</link></literal>.
{+external-filter{rotate-image} +force-text-mode}
TAG:^image/
</screen>
  </listitem>
 </varlistentry>

</variablelist>
</sect3>


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

<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>
   Suppress client or server tag.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    Server or client tags to which this action applies are not added to the request,
    thus making all actions that are specific to these request tags inactive.
   </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 result tag of a server-header or client-header tagger, as defined in one of the
    <link linkend="filter-file">filter files</link>.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage (section):</term>
  <listitem>
     <screen>
# Suppress tag produced by range-requests client-header tagger for requests coming from address 10.0.0.1
{+suppress-tag{RANGE-REQUEST}}
TAG:^IP-ADDRESS: 10\.0\.0\.1$
</screen>
  </listitem>
 </varlistentry>

</variablelist>
</sect3>


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

<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>
    Allow only temporary <quote>session</quote> cookies (for the current
    browser session <emphasis>only</emphasis>).
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
    Deletes the <quote>expires</quote> field from <quote>Set-Cookie:</quote>
    server headers. Most browsers will not store such cookies permanently and
    forget them in between sessions.
   </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 less strict than <literal><link linkend="crunch-incoming-cookies">crunch-incoming-cookies</link></literal> /
    <literal><link linkend="crunch-outgoing-cookies">crunch-outgoing-cookies</link></literal> and allows you to browse
    websites that insist or rely on setting cookies, without compromising your privacy too badly.
   </para>
   <para>
    Most browsers will not permanently store cookies that have been processed by
    <literal>session-cookies-only</literal> and will forget about them between sessions.
    This makes profiling cookies useless, but won't break sites which require cookies so
    that you can log in for transactions. This is generally turned on for all
    sites, and is the recommended setting.
   </para>
   <para>
    It makes <emphasis>no sense at all</emphasis> to use <literal>session-cookies-only</literal>
    together with <literal><link linkend="crunch-incoming-cookies">crunch-incoming-cookies</link></literal> or
    <literal><link linkend="crunch-outgoing-cookies">crunch-outgoing-cookies</link></literal>. If you do, cookies
    will be plainly killed.
   </para>
   <para>
    Note that it is up to the browser how it handles such cookies without an <quote>expires</quote>
    field. If you use an exotic browser, you might want to try it out to be sure.
   </para>
   <para>
    This setting also has no effect on cookies that may have been stored
    previously by the browser before starting <application>Privoxy</application>.
    These would have to be removed manually.
   </para>
   <para>
     <application>Privoxy</application> also uses
     the <link linkend="filter-content-cookies">content-cookies filter</link>
     to block some types of cookies. Content cookies are not effected by
     <literal>session-cookies-only</literal>.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage:</term>
  <listitem>
     <screen>+session-cookies-only</screen>
  </listitem>
 </varlistentry>
</variablelist>
</sect3>


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 renderas="sect4" id="set-image-blocker">
<title>set-image-blocker</title>

<variablelist>
 <varlistentry>
  <term>Typical use:</term>
  <listitem>
   <para>Choose the replacement for blocked images</para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Effect:</term>
  <listitem>
   <para>
     This action alone doesn't do anything noticeable. If <emphasis>both</emphasis>
     <literal><link linkend="block">block</link></literal> <emphasis>and</emphasis> <literal><link
     linkend="handle-as-image">handle-as-image</link></literal> <emphasis>also</emphasis>
     apply, i.e. if the request is to be blocked as an image,
     <emphasis>then</emphasis> the parameter of this action decides what will be
     sent as a replacement.
   </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>pattern</quote> to send a built-in checkerboard pattern image. The image is visually
      decent, scales very well, and makes it obvious where banners were busted.
     </para>
    </listitem>
    <listitem>
     <para>
      <quote>blank</quote> to send a built-in transparent image. This makes banners disappear
      completely, but makes it hard to detect where <application>Privoxy</application> has blocked
      images on a given page and complicates troubleshooting if <application>Privoxy</application>
      has blocked innocent images, like navigation icons.
     </para>
    </listitem>
    <listitem>
     <para>
      <quote><replaceable class="parameter">target-url</replaceable></quote> to
      send a redirect to <replaceable class="parameter">target-url</replaceable>. You can redirect
      to any image anywhere, even in your local filesystem via <quote>file:///</quote> URL.
      (But note that not all browsers support redirecting to a local file system).
     </para>
     <para>
      A good application of redirects is to use special <application>Privoxy</application>-built-in
      URLs, which send the built-in images, as <replaceable class="parameter">target-url</replaceable>.
      This has the same visual effect as specifying <quote>blank</quote> or <quote>pattern</quote> in
      the first place, but enables your browser to cache the replacement image, instead of requesting
      it over and over again.
     </para>
    </listitem>
   </itemizedlist>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Notes:</term>
  <listitem>
   <para>
    The URLs for the built-in images are <quote>http://config.privoxy.org/send-banner?type=<replaceable
    class="parameter">type</replaceable></quote>, where <replaceable class="parameter">type</replaceable> is
    either <quote>blank</quote> or <quote>pattern</quote>.
   </para>
   <para>
    There is a third (advanced) type, called <quote>auto</quote>. It is <emphasis>NOT</emphasis> to be
    used in <literal>set-image-blocker</literal>, but meant for use from <link linkend="filter-file">filters</link>.
    Auto will select the type of image that would have applied to the referring page, had it been an image.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term>Example usage:</term>
  <listitem>
   <para>
    Built-in pattern:
   </para>
    <screen>+set-image-blocker{pattern}</screen>
   <para>
    Redirect to the BSD daemon:
   </para>
    <screen>+set-image-blocker{http://www.freebsd.org/gifs/dae_up3.gif}</screen>
   <para>
    Redirect to the built-in pattern for better caching:
   </para>
    <screen>+set-image-blocker{http://config.privoxy.org/send-banner?type=pattern}</screen>
  </listitem>
 </varlistentry>
</variablelist>
</sect3>


<!--   ~~~~~       New section      ~~~~~     -->
<sect3 id="summary">
<title>Summary</title>
<para>
 Note that many of these actions have the potential to cause a page to
 misbehave, possibly even not to display at all. There are many ways
 a site designer may choose to design his site, and what HTTP header
 content, and other criteria, he may depend on. There is no way to have hard
 and fast rules for all sites. See the <link
 linkend="ACTIONSANAT">Appendix</link> for a brief example on troubleshooting
 actions.
</para>
</sect3>
</sect2>

<!--   ~~~~~       New section      ~~~~~     -->
<sect2 id="aliases">
<title>Aliases</title>
<para>
 Custom <quote>actions</quote>, known to <application>Privoxy</application>
 as <quote>aliases</quote>, can be defined by combining other actions.
 These can in turn be invoked just like the built-in actions.
 Currently, an alias name can contain any character except space, tab,
 <quote>=</quote>,
 <quote>{</quote> and <quote>}</quote>, but we <emphasis>strongly
 recommend</emphasis> that you only use <quote>a</quote> to <quote>z</quote>,
 <quote>0</quote> to <quote>9</quote>, <quote>+</quote>, and <quote>-</quote>.
 Alias names are not case sensitive, and are not required to start with a
 <quote>+</quote> or <quote>-</quote> sign, since they are merely textually
 expanded.
</para>
<para>
 Aliases can be used throughout the actions file, but they <emphasis>must be
 defined in a special section at the top of the file!</emphasis>
 And there can only be one such section per actions file. Each actions file may
 have its own alias section, and the aliases defined in it are only visible
 within that file.
</para>
<para>
 There are two main reasons to use aliases: One is to save typing for frequently
 used combinations of actions, the other one is a gain in flexibility: If you
 decide once how you want to handle shops by defining an alias called
 <quote>shop</quote>, you can later change your policy on shops in
 <emphasis>one</emphasis> place, and your changes will take effect everywhere
 in the actions file where the <quote>shop</quote> alias is used. Calling aliases
 by their purpose also makes your actions files more readable.
</para>
<para>
 Currently, there is one big drawback to using aliases, though:
 <application>Privoxy</application>'s built-in web-based action file
 editor honors aliases when reading the actions files, but it expands
 them before writing. So the effects of your aliases are of course preserved,
 but the aliases themselves are lost when you edit sections that use aliases
 with it.
</para>

<para>
 Now let's define some aliases...
</para>

 <screen>
 # Useful custom aliases we can use later.
 #
 # Note the (required!) section header line and that this section
 # must be at the top of the actions file!
 #
 {{alias}}

 # These aliases just save typing later:
 # (Note that some already use other aliases!)
 #
 +crunch-all-cookies = +<link linkend="CRUNCH-INCOMING-COOKIES">crunch-incoming-cookies</link> +<link linkend="CRUNCH-OUTGOING-COOKIES">crunch-outgoing-cookies</link>
 -crunch-all-cookies = -<link linkend="CRUNCH-INCOMING-COOKIES">crunch-incoming-cookies</link> -<link linkend="CRUNCH-OUTGOING-COOKIES">crunch-outgoing-cookies</link>
 +block-as-image      = +block{Blocked image.} +handle-as-image
 allow-all-cookies   = -crunch-all-cookies -<link linkend="SESSION-COOKIES-ONLY">session-cookies-only</link> -<link linkend="FILTER-CONTENT-COOKIES">filter{content-cookies}</link>

 # These aliases define combinations of actions
 # that are useful for certain types of sites:
 #
 fragile     = -<link linkend="BLOCK">block</link> -<link linkend="FILTER">filter</link> -crunch-all-cookies -<link linkend="FAST-REDIRECTS">fast-redirects</link> -<link linkend="HIDE-REFERER">hide-referrer</link> -<link linkend="PREVENT-COMPRESSION">prevent-compression</link>

 shop        = -crunch-all-cookies -<link linkend="FILTER-ALL-POPUPS">filter{all-popups}</link>

 # Short names for other aliases, for really lazy people ;-)
 #
 c0 = +crunch-all-cookies
 c1 = -crunch-all-cookies</screen>

<para>
 ...and put them to use. These sections would appear in the lower part of an
 actions file and define exceptions to the default actions (as specified further
 up for the <quote>/</quote> pattern):
</para>

 <screen>
 # These sites are either very complex or very keen on
 # user data and require minimal interference to work:
 #
 {fragile}
 .office.microsoft.com
 .windowsupdate.microsoft.com
 # Gmail is really mail.google.com, not gmail.com
 mail.google.com

 # Shopping sites:
 # Allow cookies (for setting and retrieving your customer data)
 #
 {shop}
 .quietpc.com
 .worldpay.com   # for quietpc.com
 mybank.example.com

 # These shops require pop-ups:
 #
 {-filter{all-popups} -filter{unsolicited-popups}}
  .dabs.com
  .overclockers.co.uk</screen>

<para>
 Aliases like <quote>shop</quote> and <quote>fragile</quote> are typically used for
 <quote>problem</quote> sites that require more than one action to be disabled
 in order to function properly.
</para>
</sect2>
<!--
hal stop here
-->
<!--   ~~~~~       New section      ~~~~~     -->
<sect2 id="act-examples">
<title>Actions Files Tutorial</title>
<para>
 The above chapters have shown <link linkend="actions-file">which actions files
 there are and how they are organized</link>, how actions are <link
 linkend="actions">specified</link> and <link linkend="actions-apply">applied
 to URLs</link>, how <link linkend="af-patterns">patterns</link> work, and how to
 define and use <link linkend="aliases">aliases</link>. Now, let's look at an
 example <filename>match-all.action</filename>, <filename>default.action</filename>
 and <filename>user.action</filename> file and see how all these pieces come together:
</para>

<sect3 id="match-all">
<title>match-all.action</title>
<para>
 Remember <emphasis>all actions are disabled when matching starts</emphasis>,
 so we have to explicitly enable the ones we want.
</para>

<para>
 While the <filename>match-all.action</filename> file only contains a
 single section, it is probably the most important one. It has only one
 pattern, <quote><literal>/</literal></quote>, but this pattern
 <link linkend="af-patterns">matches all URLs</link>. Therefore, the set of
 actions used in this <quote>default</quote> section <emphasis>will
 be applied to all requests as a start</emphasis>. It can  be partly or
 wholly overridden by other actions files like <filename>default.action</filename>
 and <filename>user.action</filename>, but it will still be largely responsible
 for your overall browsing experience.
</para>

<para>
 Again, at the start of matching, all actions are disabled, so there is
 no need to disable any actions here. (Remember: a <quote>+</quote>
 preceding the action name enables the action, a <quote>-</quote> disables!).
 Also note how this long line has been made more readable by splitting it into
 multiple lines with line continuation.
</para>

 <screen>
{ \
 +<link linkend="CHANGE-X-FORWARDED-FOR">change-x-forwarded-for{block}</link> \
 +<link linkend="HIDE-FROM-HEADER">hide-from-header{block}</link> \
 +<link linkend="SET-IMAGE-BLOCKER">set-image-blocker{pattern}</link> \
}
/ # Match all URLs
</screen>

<para>
 The default behavior is now set.
</para>
</sect3>

<sect3 id="default-action">
<title>default.action</title>

<para>
 If you aren't a developer, there's no need for you to edit the
 <filename>default.action</filename> file. It is maintained by
 the &my-app; developers and if you disagree with some of the
 sections, you should overrule them in your <filename>user.action</filename>.
</para>

<para>
 Understanding the <filename>default.action</filename> file can
 help you with your <filename>user.action</filename>, though.
</para>

<para>
 The first section in this file is a special section for internal use
 that prevents older &my-app; versions from reading the file:
</para>

 <screen>
##########################################################################
# Settings -- Don't change! For internal Privoxy use ONLY.
##########################################################################
{{settings}}
for-privoxy-version=3.0.11</screen>

<para>
 After that comes the (optional) alias section. We'll use the example
 section from the above <link linkend="aliases">chapter on aliases</link>,
 that also explains why and how aliases are used:
</para>

 <screen>
##########################################################################
# Aliases
##########################################################################
{{alias}}

 # These aliases just save typing later:
 # (Note that some already use other aliases!)
 #
 +crunch-all-cookies = +<link linkend="CRUNCH-INCOMING-COOKIES">crunch-incoming-cookies</link> +<link linkend="CRUNCH-OUTGOING-COOKIES">crunch-outgoing-cookies</link>
 -crunch-all-cookies = -<link linkend="CRUNCH-INCOMING-COOKIES">crunch-incoming-cookies</link> -<link linkend="CRUNCH-OUTGOING-COOKIES">crunch-outgoing-cookies</link>
 +block-as-image      = +block{Blocked image.} +handle-as-image
 mercy-for-cookies   = -crunch-all-cookies -<link linkend="SESSION-COOKIES-ONLY">session-cookies-only</link> -<link linkend="FILTER-CONTENT-COOKIES">filter{content-cookies}</link>

 # These aliases define combinations of actions
 # that are useful for certain types of sites:
 #
 fragile     = -<link linkend="BLOCK">block</link> -<link linkend="FILTER">filter</link> -crunch-all-cookies -<link linkend="FAST-REDIRECTS">fast-redirects</link> -<link linkend="HIDE-REFERER">hide-referrer</link>
 shop        = -crunch-all-cookies -<link linkend="FILTER-ALL-POPUPS">filter{all-popups}</link></screen>

<para>
 The first of our specialized sections is concerned with <quote>fragile</quote>
 sites, i.e. sites that require minimum interference, because they are either
 very complex or very keen on tracking you (and have mechanisms in place that
 make them unusable for people who avoid being tracked). We will use
 our pre-defined <literal>fragile</literal> alias instead of stating the list
 of actions explicitly:
</para>

 <screen>
##########################################################################
# Exceptions for sites that'll break under the default action set:
##########################################################################

# "Fragile" Use a minimum set of actions for these sites (see alias above):
#
{ fragile }
.office.microsoft.com           # surprise, surprise!
.windowsupdate.microsoft.com
mail.google.com</screen>

<para>
 Shopping sites are not as fragile, but they typically
 require cookies to log in, and pop-up windows for shopping
 carts or item details. Again, we'll use a pre-defined alias:
</para>

 <screen>
# Shopping sites:
#
{ shop }
.quietpc.com
.worldpay.com   # for quietpc.com
.jungle.com
.scan.co.uk</screen>

<para>
 The <literal><link linkend="FAST-REDIRECTS">fast-redirects</link></literal>
 action, which may have been enabled in <filename>match-all.action</filename>,
 breaks some sites. So disable it for popular sites where we know it misbehaves:
</para>

 <screen>
{ -<link linkend="FAST-REDIRECTS">fast-redirects</link> }
login.yahoo.com
edit.*.yahoo.com
.google.com
.altavista.com/.*(like|url|link):http
.altavista.com/trans.*urltext=http
.nytimes.com</screen>

<para>
 It is important that <application>Privoxy</application> knows which
 URLs belong to images, so that <emphasis>if</emphasis> they are to
 be blocked, a substitute image can be sent, rather than an HTML page.
 Contacting the remote site to find out is not an option, since it
 would destroy the loading time advantage of banner blocking, and it
 would feed the advertisers information about you. We can mark any
 URL as an image with the <literal><link
 linkend="handle-as-image">handle-as-image</link></literal> action,
 and marking all URLs that end in a known image file extension is a
 good start:
</para>

 <screen>
##########################################################################
# Images:
##########################################################################

# Define which file types will be treated as images, in case they get
# blocked further down this file:
#
{ +<link linkend="HANDLE-AS-IMAGE">handle-as-image</link> }
/.*\.(gif|jpe?g|png|bmp|ico)$</screen>

<para>
 And then there are known banner sources. They often use scripts to
 generate the banners, so it won't be visible from the URL that the
 request is for an image. Hence we block them <emphasis>and</emphasis>
 mark them as images in one go, with the help of our
 <literal>+block-as-image</literal> alias defined above. (We could of
 course just as well use <literal>+<link linkend="block">block</link>
 +<link linkend="handle-as-image">handle-as-image</link></literal> here.)
 Remember that the type of the replacement image is chosen by the
 <literal><link linkend="set-image-blocker">set-image-blocker</link></literal>
 action. Since all URLs have matched the default section with its
 <literal>+<link linkend="set-image-blocker">set-image-blocker</link>{pattern}</literal>
 action before, it still applies and needn't be repeated:
</para>

 <screen>
# Known ad generators:
#
{ +block-as-image }
ar.atwola.com
.ad.doubleclick.net
.ad.*.doubleclick.net
.a.yimg.com/(?:(?!/i/).)*$
.a[0-9].yimg.com/(?:(?!/i/).)*$
bs*.gsanet.com
.qkimg.net</screen>

<para>
 One of the most important jobs of <application>Privoxy</application>
 is to block banners. Many of these can be <quote>blocked</quote>
 by the <literal><link linkend="filter">filter</link>{banners-by-size}</literal>
 action, which we enabled above, and which deletes the references to banner
 images from the pages while they are loaded, so the browser doesn't request
 them anymore, and hence they don't need to be blocked here. But this naturally
 doesn't catch all banners, and some people choose not to use filters, so we
 need a comprehensive list of patterns for banner URLs here, and apply the
 <literal><link linkend="block">block</link></literal> action to them.
</para>
<para>
 First comes many generic patterns, which do most of the work, by
 matching typical domain and path name components of banners. Then comes
 a list of individual patterns for specific sites, which is omitted here
 to keep the example short:
</para>

 <screen>
##########################################################################
# Block these fine banners:
##########################################################################
{ <link linkend="BLOCK">+block{Banner ads.}</link> }

# Generic patterns:
#
ad*.
.*ads.
banner?.
count*.
/.*count(er)?\.(pl|cgi|exe|dll|asp|php[34]?)
/(?:.*/)?(publicite|werbung|rekla(ma|me|am)|annonse|maino(kset|nta|s)?)/

# Site-specific patterns (abbreviated):
#
.hitbox.com</screen>

<para>
 It's quite remarkable how many advertisers actually call their banner
 servers ads.<replaceable>company</replaceable>.com, or call the directory
 in which the banners are stored literally <quote>banners</quote>. So the above
 generic patterns are surprisingly effective.
</para>
<para>
 But being very generic, they necessarily also catch URLs that we don't want
 to block. The pattern <literal>.*ads.</literal> e.g. catches
 <quote>nasty-<emphasis>ads</emphasis>.nasty-corp.com</quote> as intended,
 but also <quote>downlo<emphasis>ads</emphasis>.sourcefroge.net</quote> or
 <quote><emphasis>ads</emphasis>l.some-provider.net.</quote> So here come some
 well-known exceptions to the <literal>+<link linkend="BLOCK">block</link></literal>
 section above.
</para>
<para>
 Note that these are exceptions to exceptions from the default! Consider the URL
 <quote>downloads.sourcefroge.net</quote>: Initially, all actions are deactivated,
 so it wouldn't get blocked. Then comes the defaults section, which matches the
 URL, but just deactivates the <literal><link linkend="BLOCK">block</link></literal>
 action once again. Then it matches <literal>.*ads.</literal>, an exception to the
 general non-blocking policy, and suddenly
 <literal><link linkend="BLOCK">+block</link></literal> applies. And now, it'll match
 <literal>.*loads.</literal>, where <literal><link linkend="BLOCK">-block</link></literal>
 applies, so (unless it matches <emphasis>again</emphasis> further down) it ends up
 with no <literal><link linkend="BLOCK">block</link></literal> action applying.
</para>

 <screen>
##########################################################################
# Save some innocent victims of the above generic block patterns:
##########################################################################

# By domain:
#
{ -<link linkend="BLOCK">block</link> }
adv[io]*.  # (for advogato.org and advice.*)
adsl.      # (has nothing to do with ads)
adobe.     # (has nothing to do with ads either)
ad[ud]*.   # (adult.* and add.*)
.edu       # (universities don't host banners (yet!))
.*loads.   # (downloads, uploads etc)

# By path:
#
/.*loads/

# Site-specific:
#
www.globalintersec.com/adv # (adv = advanced)
www.ugu.com/sui/ugu/adv</screen>

<para>
 Filtering source code can have nasty side effects,
 so make an exception for our friends at sourceforge.net,
 and all paths with <quote>cvs</quote> in them. Note that
 <literal>-<link linkend="FILTER">filter</link></literal>
 disables <emphasis>all</emphasis> filters in one fell swoop!
</para>

 <screen>
# Don't filter code!
#
{ -<link linkend="FILTER">filter</link> }
/(.*/)?cvs
bugzilla.
developer.
wiki.
.sourceforge.net</screen>

<para>
 The actual <filename>default.action</filename> is of course much more
 comprehensive, but we hope this example made clear how it works.
</para>

</sect3>

<sect3 id="user-action"><title>user.action</title>

<para>
 So far we are painting with a broad brush by setting general policies,
 which would be a reasonable starting point for many people. Now,
 you might want to be more specific and have customized rules that
 are more suitable to your personal habits and preferences. These would
 be for narrowly defined situations like your ISP or your bank, and should
 be placed in <filename>user.action</filename>, which is parsed after all other
 actions files and hence has the last word, over-riding any previously
 defined actions. <filename>user.action</filename> is also a
 <emphasis>safe</emphasis> place for your personal settings, since
 <filename>default.action</filename> is actively maintained by the
 <application>Privoxy</application> developers and you'll probably want
 to install updated versions from time to time.
</para>

<para>
 So let's look at a few examples of things that one might typically do in
 <filename>user.action</filename>:
</para>


<!-- brief sample user.action here -->

 <screen>
# My user.action file. &lt;fred@example.com&gt;</screen>

<para>
 As <link linkend="aliases">aliases</link> are local to the actions
 file that they are defined in, you can't use the ones from
 <filename>default.action</filename>, unless you repeat them here:
</para>

 <screen>
# Aliases are local to the file they are defined in.
# (Re-)define aliases for this file:
#
{{alias}}
#
# These aliases just save typing later, and the alias names should
# be self explanatory.
#
+crunch-all-cookies = +crunch-incoming-cookies +crunch-outgoing-cookies
-crunch-all-cookies = -crunch-incoming-cookies -crunch-outgoing-cookies
 allow-all-cookies  = -crunch-all-cookies -session-cookies-only
 allow-popups       = -filter{all-popups}
+block-as-image     = +block{Blocked as image.} +handle-as-image
-block-as-image     = -block

# These aliases define combinations of actions that are useful for
# certain types of sites:
#
fragile     = -block -crunch-all-cookies -filter -fast-redirects -hide-referrer
shop        = -crunch-all-cookies allow-popups

# Allow ads for selected useful free sites:
#
allow-ads   = -block -filter{banners-by-size} -filter{banners-by-link}

# Alias for specific file types that are text, but might have conflicting
# MIME types. We want the browser to force these to be text documents.
handle-as-text = -<link linkend="FILTER">filter</link> +-<link linkend="content-type-overwrite">content-type-overwrite{text/plain}</link> +-<link linkend="FORCE-TEXT-MODE">force-text-mode</link> -<link linkend="HIDE-CONTENT-DISPOSITION">hide-content-disposition</link></screen>

<para>
 Say you have accounts on some sites that you visit regularly, and
 you don't want to have to log in manually each time. So you'd like
 to allow persistent cookies for these sites. The
 <literal>allow-all-cookies</literal> alias defined above does exactly
 that, i.e. it disables crunching of cookies in any direction, and the
 processing of cookies to make them only temporary.
</para>

 <screen>
{ allow-all-cookies }
 sourceforge.net
 .yahoo.com
 .msdn.microsoft.com
 .redhat.com</screen>

<para>
 Your bank is allergic to some filter, but you don't know which, so you disable them all:
</para>

 <screen>
{ -<link linkend="FILTER">filter</link> }
 .your-home-banking-site.com</screen>

<para>
 Some file types you may not want to filter for various reasons:
</para>

 <screen>
# Technical documentation is likely to contain strings that might
# erroneously get altered by the JavaScript-oriented filters:
#
.tldp.org
/(.*/)?selfhtml/

# And this stupid host sends streaming video with a wrong MIME type,
# so that Privoxy thinks it is getting HTML and starts filtering:
#
stupid-server.example.com/</screen>

<para>
 Example of a simple <link linkend="BLOCK">block</link> action. Say you've
 seen an ad on your favourite page on example.com that you want to get rid of.
 You have right-clicked the image, selected <quote>copy image location</quote>
 and pasted the URL below while removing the leading http://, into a
 <literal>{ +block{} }</literal> section. Note that <literal>{ +handle-as-image
 }</literal> need not be specified, since all URLs ending in
 <literal>.gif</literal> will be tagged as images by the general rules as set
 in default.action anyway:
</para>

 <screen>
{ +<link linkend="BLOCK">block</link>{Nasty ads.} }
 www.example.com/nasty-ads/sponsor\.gif
 another.example.net/more/junk/here/</screen>

<para>
 The URLs of dynamically generated banners, especially from large banner
 farms, often don't use the well-known image file name extensions, which
 makes it impossible for <application>Privoxy</application> to guess
 the file type just by looking at the URL.
 You can use the <literal>+block-as-image</literal> alias defined above for
 these cases.
 Note that objects which match this rule but then turn out NOT to be an
 image are typically rendered as a <quote>broken image</quote> icon by the
 browser. Use cautiously.
</para>

 <screen>
{ +block-as-image }
 .doubleclick.net
 .fastclick.net
 /Realmedia/ads/
 ar.atwola.com/</screen>

<para>
 Now you noticed that the default configuration breaks Forbes Magazine,
 but you were too lazy to find out which action is the culprit, and you
 were again too lazy to give <link linkend="contact">feedback</link>, so
 you just used the <literal>fragile</literal> alias on the site, and
 -- <emphasis>whoa!</emphasis> -- it worked. The <literal>fragile</literal>
 aliases disables those actions that are most likely to break a site. Also,
 good for testing purposes to see if it is <application>Privoxy</application>
 that is causing the problem or not. We later find other regular sites
 that misbehave, and add those to our personalized list of troublemakers:
</para>

<screen>
{ fragile }
 .forbes.com
 webmail.example.com
 .mybank.com</screen>

<para>
 You like the <quote>fun</quote> text replacements in <filename>default.filter</filename>,
 but it is disabled in the distributed actions file.
 So you'd like to turn it on in your private,
 update-safe config, once and for all:
</para>

<screen>
{ +<link linkend="filter-fun">filter{fun}</link> }
 / # For ALL sites!</screen>

<para>
 Note that the above is not really a good idea: There are exceptions
 to the filters in <filename>default.action</filename> for things that
 really shouldn't be filtered, like code on CVS->Web interfaces. Since
 <filename>user.action</filename> has the last word, these exceptions
 won't be valid for the <quote>fun</quote> filtering specified here.
</para>

<para>
 You might also worry about how your favourite free websites are
 funded, and find that they rely on displaying banner advertisements
 to survive. So you might want to specifically allow banners for those
 sites that you feel provide value to you:
</para>

<screen>
{ allow-ads }
 .sourceforge.net
 .slashdot.org
 .osdn.net</screen>

<para>
 Note that <literal>allow-ads</literal> has been aliased to
 <literal>-<link linkend="block">block</link></literal>,
 <literal>-<link linkend="filter-banners-by-size">filter{banners-by-size}</link></literal>, and
 <literal>-<link linkend="filter-banners-by-link">filter{banners-by-link}</link></literal> above.
</para>

<para>
 Invoke another alias here to force an over-ride of the MIME type <literal>
 application/x-sh</literal> which typically would open a download type
 dialog. In my case, I want to look at the shell script, and then I can save
 it should I choose to.
</para>

<screen>
{ handle-as-text }
 /.*\.sh$</screen>

<para>
 <filename>user.action</filename> is generally the best place to define
 exceptions and additions to the default policies of
 <filename>default.action</filename>. Some actions are safe to have their
 default policies set here though. So let's set a default policy to have a
 <quote>blank</quote> image as opposed to the checkerboard pattern for
 <emphasis>ALL</emphasis> sites. <quote>/</quote> of course matches all URL
 paths and patterns:
</para>

<screen>
{ +<link linkend="set-image-blocker">set-image-blocker{blank}</link> }
/ # ALL sites</screen>

</sect3>
</sect2>

<!--  ~  End section  ~  -->

</sect1>

<!--  ~  End section  ~  -->

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

<sect1 id="filter-file">
<title>Filter Files</title>

<para>
 On-the-fly text substitutions need
 to be defined in a <quote>filter file</quote>. Once defined, they
 can then be invoked as an <quote>action</quote>.
</para>

<para>
 &my-app; supports four different pcrs-based filter actions:
 <literal><link linkend="filter">filter</link></literal> to
 rewrite the content that is send to the client,
 <literal><link linkend="client-header-filter">client-header-filter</link></literal>
 to rewrite headers that are send by the client,
 <literal><link linkend="server-header-filter">server-header-filter</link></literal>
 to rewrite headers that are send by the server, and
 <literal><link linkend="client-body-filter">client-body-filter</link></literal>
 to rewrite client request body.
</para>

<para>
 &my-app; also supports two tagger actions:
 <literal><link linkend="client-header-tagger">client-header-tagger</link></literal>
 and
 <literal><link linkend="server-header-tagger">server-header-tagger</link></literal>.
 Taggers and filters use the same syntax in the filter files, the difference
 is that taggers don't modify the text they are filtering, but use a rewritten
 version of the filtered text as tag. The tags can then be used to change the
 applying actions through sections with <link linkend="tag-pattern">tag-patterns</link>.
</para>

<para>
 Finally &my-app; supports the
 <literal><link linkend="external-filter">external-filter</link></literal> action
 to enable <literal><link linkend="external-filter-syntax">external filters</link></literal>
 written in proper programming languages.
</para>


<para>
 Multiple filter files can be defined through the <literal> <link
 linkend="filterfile">filterfile</link></literal> config directive. The filters
 as supplied by the developers are located in
 <filename>default.filter</filename>. It is recommended that any locally
 defined or modified filters go in a separately defined file such as
 <filename>user.filter</filename>.
 </para>

<para>
 Common tasks for content filters are to eliminate common annoyances in
 HTML and JavaScript, such as pop-up windows,
 exit consoles, crippled windows without navigation tools, the
 infamous &lt;BLINK&gt; tag etc, to suppress images with certain
 width and height attributes (standard banner sizes or web-bugs),
 or just to have fun.
</para>

<para>
 Enabled content filters are applied to any content whose
 <quote>Content Type</quote> header is recognised as a sign
 of text-based content, with the exception of <literal>text/plain</literal>.
 Use the <link linkend="FORCE-TEXT-MODE">force-text-mode</link> action
 to also filter other content.
</para>

<para>
 Substitutions are made at the source level, so if you want to <quote>roll
 your own</quote> filters, you should first be familiar with HTML syntax,
 and, of course, regular expressions.
</para>

<para>
 Just like the <link linkend="actions-file">actions files</link>, the
 filter file is organized in sections, which are called <emphasis>filters</emphasis>
 here. Each filter consists of a heading line, that starts with one of the
 <emphasis>keywords</emphasis> <literal>FILTER:</literal>,
 <literal>CLIENT-HEADER-FILTER:</literal>, <literal>SERVER-HEADER-FILTER:</literal> or
 <literal>CLIENT-BODY-FILTER:</literal>
 followed by the filter's <emphasis>name</emphasis>, and a short (one line)
 <emphasis>description</emphasis> of what it does. Below that line
 come the <emphasis>jobs</emphasis>, i.e. lines that define the actual
 text substitutions. By convention, the name of a filter
 should describe what the filter <emphasis>eliminates</emphasis>. The
 comment is used in the <ulink url="http://config.privoxy.org/">web-based
 user interface</ulink>.
</para>

<para>
 Once a filter called <replaceable>name</replaceable> has been defined
 in the filter file, it can be invoked by using an action of the form
 +<literal><link linkend="filter">filter</link>{<replaceable>name</replaceable>}</literal>
 in any <link linkend="actions-file">actions file</link>.
</para>

<para>
 Filter definitions start with a header line that contains the filter
 type, the filter name and the filter description.
 A content filter header line for a filter called <quote>foo</quote> could look
 like this:
</para>

 <screen>FILTER: foo Replace all "foo" with "bar"</screen>

<para>
 Below that line, and up to the next header line, come the jobs that
 define what text replacements the filter executes. They are specified
 in a syntax that imitates <ulink url="http://www.perl.org/">Perl</ulink>'s
 <literal>s///</literal> operator. If you are familiar with Perl, you
 will find this to be quite intuitive, and may want to look at the
 PCRS documentation for the subtle differences to Perl behaviour.
</para>

<para>
 Most notably, the non-standard option letter <literal>U</literal> is supported,
 which turns the default to ungreedy matching (add <literal>?</literal> to
 quantifiers to turn them greedy again).
</para>

<para>
 The non-standard option letter <literal>D</literal> (dynamic) allows
 to use the variables $host, $origin (the IP address the request came from),
 $path, $url and $listen-address (the address on which Privoxy accepted the
 client request. Example: 127.0.0.1:8118).
 They will be replaced with the value they refer to before the filter
 is executed.
</para>

<para>
 Note that '$' is a bad choice for a delimiter in a dynamic filter as you
 might end up with unintended variables if you use a variable name
 directly after the delimiter. Variables will be resolved without
 escaping anything, therefore you also have to be careful not to chose
 delimiters that appear in the replacement text. For example '<' should
 be save, while '?' will sooner or later cause conflicts with $url.
</para>

<para>
 The non-standard option letter <literal>T</literal> (trivial) prevents
 parsing for backreferences in the substitute. Use it if you want to include
 text like '$&' in your substitute without quoting.
</para>

<para>
 If you are new to
  <ulink url="https://en.wikipedia.org/wiki/Regular_expressions"><quote>Regular
  Expressions</quote></ulink>, you might want to take a look at
 the <link linkend="regex">Appendix on regular expressions</link>, and
 see the <ulink url="http://perldoc.perl.org/perlre.html">Perl
 manual</ulink> for
 <ulink url="http://perldoc.perl.org/perlop.html">the
 <literal>s///</literal> operator's syntax</ulink> and <ulink
 url="http://perldoc.perl.org/perlre.html">Perl-style regular
 expressions</ulink> in general.
 The below examples might also help to get you started.
</para>


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

<sect2 id="filter-file-tut"><title>Filter File Tutorial</title>
<para>
 Now, let's complete our <quote>foo</quote> content filter. We have already defined
 the heading, but the jobs are still missing. Since all it does is to replace
 <quote>foo</quote> with <quote>bar</quote>, there is only one (trivial) job
 needed:
</para>

 <screen>s/foo/bar/</screen>

<para>
 But wait! Didn't the comment say that <emphasis>all</emphasis> occurrences
 of <quote>foo</quote> should be replaced? Our current job will only take
 care of the first <quote>foo</quote> on each page. For global substitution,
 we'll need to add the <literal>g</literal> option:
</para>

 <screen>s/foo/bar/g</screen>

<para>
 Our complete filter now looks like this:
</para>

 <screen>FILTER: foo Replace all "foo" with "bar"
s/foo/bar/g</screen>

<para>
 Let's look at some real filters for more interesting examples. Here you see
 a filter that protects against some common annoyances that arise from JavaScript
 abuse. Let's look at its jobs one after the other:
</para>


 <screen>
FILTER: js-annoyances Get rid of particularly annoying JavaScript abuse

# Get rid of JavaScript referrer tracking. Test page: http://www.randomoddness.com/untitled.htm
#
s|(&lt;script.*)document\.referrer(.*&lt;/script&gt;)|$1"Not Your Business!"$2|Usg</screen>

<para>
 Following the header line and a comment, you see the job. Note that it uses
 <literal>|</literal> as the delimiter instead of <literal>/</literal>, because
 the pattern contains a forward slash, which would otherwise have to be escaped
 by a backslash (<literal>\</literal>).
</para>

<para>
 Now, let's examine the pattern: it starts with the text <literal>&lt;script.*</literal>
 enclosed in parentheses. Since the dot matches any character, and <literal>*</literal>
 means: <quote>Match an arbitrary number of the element left of myself</quote>, this
 matches <quote>&lt;script</quote>, followed by <emphasis>any</emphasis> text, i.e.
 it matches the whole page, from the start of the first &lt;script&gt; tag.
</para>

<para>
 That's more than we want, but the pattern continues: <literal>document\.referrer</literal>
 matches only the exact string <quote>document.referrer</quote>. The dot needed to
 be <emphasis>escaped</emphasis>, i.e. preceded by a backslash, to take away its
 special meaning as a joker, and make it just a regular dot. So far, the meaning is:
 Match from the start of the first &lt;script&gt; tag in a the page, up to, and including,
 the text <quote>document.referrer</quote>, if <emphasis>both</emphasis> are present
 in the page (and appear in that order).
</para>

<para>
 But there's still more pattern to go. The next element, again enclosed in parentheses,
 is <literal>.*&lt;/script&gt;</literal>. You already know what <literal>.*</literal>
 means, so the whole pattern translates to: Match from the start of the first  &lt;script&gt;
 tag in a page to the end of the last &lt;script&gt; tag, provided that the text
 <quote>document.referrer</quote> appears somewhere in between.
</para>

<para>
 This is still not the whole story, since we have ignored the options and the parentheses:
 The portions of the page matched by sub-patterns that are enclosed in parentheses, will be
 remembered and be available through the variables <literal>$1, $2, ...</literal> in
 the substitute. The <literal>U</literal> option switches to ungreedy matching, which means
 that the first <literal>.*</literal> in the pattern will only <quote>eat up</quote> all
 text in between <quote>&lt;script</quote> and the <emphasis>first</emphasis> occurrence
 of <quote>document.referrer</quote>, and that the second <literal>.*</literal> will
 only span the text up to the <emphasis>first</emphasis> <quote>&lt;/script&gt;</quote>
 tag. Furthermore, the <literal>s</literal> option says that the match may span
 multiple lines in the page, and the <literal>g</literal> option again means that the
 substitution is global.
</para>

<para>
 So, to summarize, the pattern means: Match all scripts that contain the text
 <quote>document.referrer</quote>. Remember the parts of the script from
 (and including) the start tag up to (and excluding) the string
 <quote>document.referrer</quote> as <literal>$1</literal>, and the part following
 that string, up to and including the closing tag, as <literal>$2</literal>.
</para>

<para>
 Now the pattern is deciphered, but wasn't this about substituting things? So
 lets look at the substitute: <literal>$1"Not Your Business!"$2</literal> is
 easy to read: The text remembered as <literal>$1</literal>, followed by
 <literal>"Not Your Business!"</literal> (<emphasis>including</emphasis>
 the quotation marks!), followed by the text remembered as <literal>$2</literal>.
 This produces an exact copy of the original string, with the middle part
 (the <quote>document.referrer</quote>) replaced by <literal>"Not Your
 Business!"</literal>.
</para>

<para>
 The whole job now reads: Replace <quote>document.referrer</quote> by
 <literal>"Not Your Business!"</literal> wherever it appears inside a
 &lt;script&gt tag. Note that this job won't break JavaScript syntax,
 since both the original and the replacement are syntactically valid
 string objects. The script just won't have access to the referrer
 information anymore.
</para>

<para>
 We'll show you two other jobs from the JavaScript taming department, but
 this time only point out the constructs of special interest:
</para>

 <screen>
# The status bar is for displaying link targets, not pointless blahblah
#
s/window\.status\s*=\s*(['"]).*?\1/dUmMy=1/ig</screen>

<para>
 <literal>\s</literal> stands for whitespace characters (space, tab, newline,
 carriage return, form feed), so that <literal>\s*</literal> means: <quote>zero
 or more whitespace</quote>. The <literal>?</literal> in <literal>.*?</literal>
 makes this matching of arbitrary text ungreedy. (Note that the <literal>U</literal>
 option is not set). The <literal>['"]</literal> construct means: <quote>a single
 <emphasis>or</emphasis> a double quote</quote>. Finally, <literal>\1</literal> is
 a back-reference to the first parenthesis just like <literal>$1</literal> above,
 with the difference that in the <emphasis>pattern</emphasis>, a backslash indicates
 a back-reference, whereas in the <emphasis>substitute</emphasis>, it's the dollar.
</para>

<para>
 So what does this job do? It replaces assignments of single- or double-quoted
 strings to the <quote>window.status</quote> object with a dummy assignment
 (using a variable name that is hopefully odd enough not to conflict with
 real variables in scripts). Thus, it catches many cases where e.g. pointless
 descriptions are displayed in the status bar instead of the link target when
 you move your mouse over links.
</para>

 <screen>
# Kill OnUnload popups. Yummy. Test: http://www.zdnet.com/zdsubs/yahoo/tree/yfs.html
#
s/(&lt;body [^&gt;]*)onunload(.*&gt;)/$1never$2/iU</screen>

<para>
 Including the
 <ulink url="http://www.w3.org/TR/2000/REC-DOM-Level-2-Events-20001113/events.html#Events-eventgroupings-htmlevents">OnUnload
 event binding</ulink> in the HTML DOM was a <emphasis>CRIME</emphasis>.
 When I close a browser window, I want it to close and die. Basta.
 This job replaces the <quote>onunload</quote> attribute in
 <quote>&lt;body&gt</quote> tags with the dummy word <literal>never</literal>.
 Note that the <literal>i</literal> option makes the pattern matching
 case-insensitive. Also note that ungreedy matching alone doesn't always guarantee
 a minimal match: In the first parenthesis, we had to use <literal>[^&gt;]*</literal>
 instead of <literal>.*</literal> to prevent the match from exceeding the
 &lt;body&gt tag if it doesn't contain <quote>OnUnload</quote>, but the page's
 content does.
</para>

<para>
 The last example is from the fun department:
</para>

 <screen>
FILTER: fun Fun text replacements

# Spice the daily news:
#
s/microsoft(?!\.com)/MicroSuck/ig</screen>

<para>
 Note the <literal>(?!\.com)</literal> part (a so-called negative lookahead)
 in the job's pattern, which means: Don't match, if the string
 <quote>.com</quote> appears directly following <quote>microsoft</quote>
 in the page. This prevents links to microsoft.com from being trashed, while
 still replacing the word everywhere else.
</para>

 <screen>
# Buzzword Bingo (example for extended regex syntax)
#
s* industry[ -]leading \
|  cutting[ -]edge \
|  customer[ -]focused \
|  market[ -]driven \
|  award[ -]winning # Comments are OK, too! \
|  high[ -]performance \
|  solutions[ -]based \
|  unmatched \
|  unparalleled \
|  unrivalled \
*&lt;font color="red"&gt;&lt;b&gt;BINGO!&lt;/b&gt;&lt;/font&gt; \
*igx</screen>

<para>
 The <literal>x</literal> option in this job turns on extended syntax, and allows for
 e.g. the liberal use of (non-interpreted!) whitespace for nicer formatting.
</para>

<para>
 You get the idea?
</para>
</sect2>

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

<sect2 id="predefined-filters"><title>The Pre-defined Filters</title>

<!--

 Note each filter is also listed in the +filter action section above. Please
 keep these listings in sync.

-->

<para>
The distribution <filename>default.filter</filename> file contains a selection of
pre-defined filters for your convenience:
</para>

<variablelist>
 <varlistentry>
  <term><emphasis>js-annoyances</emphasis></term>
  <listitem>
   <para>
    The purpose of this filter is to get rid of particularly annoying JavaScript abuse.
    To that end, it
   </para>
   <itemizedlist>
    <listitem>
     <para>
      replaces JavaScript references to the browser's referrer information
      with the string "Not Your Business!". This compliments the <literal><link
      linkend="hide-referrer">hide-referrer</link></literal> action on the content level.
     </para>
    </listitem>
    <listitem>
     <para>
      removes the bindings to the DOM's
      <ulink url="http://www.w3.org/TR/2000/REC-DOM-Level-2-Events-20001113/events.html#Events-eventgroupings-htmlevents">unload
      event</ulink> which we feel has no right to exist and is responsible for most <quote>exit consoles</quote>, i.e.
      nasty windows that pop up when you close another one.
     </para>
    </listitem>
    <listitem>
     <para>
      removes code that causes new windows to be opened with undesired properties, such as being
      full-screen, non-resizeable, without location, status or menu bar etc.
     </para>
    </listitem>
   </itemizedlist>
   <para>
    Use with caution. This is an aggressive filter, and can break sites that
    rely heavily on JavaScript.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term><emphasis>js-events</emphasis></term>
  <listitem>
   <para>
    This is a very radical measure. It removes virtually all JavaScript event bindings, which
    means that scripts can not react to user actions such as mouse movements or clicks, window
    resizing etc, anymore. Use with caution!
   </para>
   <para>
    We <emphasis>strongly discourage</emphasis> using this filter as a default since it breaks
    many legitimate scripts. It is meant for use only on extra-nasty sites (should you really
    need to go there).
   </para>
  </listitem>
 </varlistentry>

<varlistentry>
  <term><emphasis>html-annoyances</emphasis></term>
  <listitem>
   <para>
    This filter will undo many common instances of HTML based abuse.
   </para>
   <para>
    The <literal>BLINK</literal> and <literal>MARQUEE</literal> tags
    are neutralized (yeah baby!), and browser windows will be created as
    resizeable (as of course they should be!), and will have location,
    scroll and menu bars -- even if specified otherwise.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term><emphasis>content-cookies</emphasis></term>
  <listitem>
   <para>
    Most cookies are set in the HTTP dialog, where they can be intercepted
    by the
    <literal><link linkend="crunch-incoming-cookies">crunch-incoming-cookies</link></literal>
    and <literal><link linkend="crunch-outgoing-cookies">crunch-outgoing-cookies</link></literal>
    actions. But web sites increasingly make use of HTML meta tags and JavaScript
    to sneak cookies to the browser on the content level.
   </para>
   <para>
    This filter disables most HTML and JavaScript code that reads or sets
    cookies. It cannot detect all clever uses of these types of code, so it
    should not be relied on as an absolute fix. Use it wherever you would also
    use the cookie crunch actions.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term><emphasis>refresh-tags</emphasis></term>
  <listitem>
   <para>
    Disable any refresh tags if the interval is greater than nine seconds (so
    that redirections done via refresh tags are not destroyed). This is useful
    for dial-on-demand setups, or for those who find this HTML feature
    annoying.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term><emphasis>unsolicited-popups</emphasis></term>
  <listitem>
   <para>
    This filter attempts to prevent only <quote>unsolicited</quote> pop-up
    windows from opening, yet still allow pop-up windows that the user
    has explicitly chosen to open. It was added in version 3.0.1,
    as an improvement over earlier such filters.
   </para>
   <para>
    Technical note: The filter works by redefining the window.open JavaScript
    function to a dummy function, <literal>PrivoxyWindowOpen()</literal>,
    during the loading and rendering phase of each HTML page access, and
    restoring the function afterward.
   </para>
   <para>
    This is recommended only for browsers that cannot perform this function
    reliably themselves. And be aware that some sites require such windows
    in order to function normally. Use with caution.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term><emphasis>all-popups</emphasis></term>
  <listitem>
   <para>
    Attempt to prevent <emphasis>all</emphasis> pop-up windows from opening.
    Note this should be used with even more discretion than the above, since
    it is more likely to break some sites that require pop-ups for normal
    usage. Use with caution.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term><emphasis>img-reorder</emphasis></term>
  <listitem>
   <para>
    This is a helper filter that has no value if used alone. It makes the
    <literal>banners-by-size</literal> and <literal>banners-by-link</literal>
    (see below) filters more effective and should be enabled together with them.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term><emphasis>banners-by-size</emphasis></term>
  <listitem>
   <para>
    This filter removes image tags purely based on what size they are. Fortunately
    for us, many ads and banner images tend to conform to certain standardized
    sizes, which makes this filter quite effective for ad stripping purposes.
   </para>
   <para>
    Occasionally this filter will cause false positives on images that are not ads,
    but just happen to be of one of the standard banner sizes.
   </para>
   <para>
    Recommended only for those who require extreme ad blocking. The default
    block rules should catch 95+% of all ads <emphasis>without</emphasis> this filter enabled.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term><emphasis>banners-by-link</emphasis></term>
  <listitem>
   <para>
    This is an experimental filter that attempts to kill any banners if
    their URLs seem to point to known or suspected click trackers. It is currently
    not of much value and is not recommended for use by default.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term><emphasis>webbugs</emphasis></term>
  <listitem>
   <para>
    Webbugs are small, invisible images (technically 1X1 GIF images), that
    are used to track users across websites, and collect information on them.
    As an HTML page is loaded by the browser, an embedded image tag causes the
    browser to contact a third-party site, disclosing the tracking information
    through the requested URL and/or cookies for that third-party domain, without
    the user ever becoming aware of the interaction with the third-party site.
    HTML-ized spam also uses a similar technique to verify email addresses.
   </para>
   <para>
    This filter removes the HTML code that loads such <quote>webbugs</quote>.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term><emphasis>tiny-textforms</emphasis></term>
  <listitem>
   <para>
    A rather special-purpose filter that can be used to enlarge textareas (those
    multi-line text boxes in web forms) and turn off hard word wrap in them.
    It was written for the sourceforge.net tracker system where such boxes are
    a nuisance, but it can be handy on other sites, too.
   </para>
   <para>
    It is not recommended to use this filter as a default.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term><emphasis>jumping-windows</emphasis></term>
  <listitem>
   <para>
    Many consider windows that move, or resize themselves to be abusive. This filter
    neutralizes the related JavaScript code. Note that some sites might not display
    or behave as intended when using this filter. Use with caution.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term><emphasis>frameset-borders</emphasis></term>
  <listitem>
   <para>
    Some web designers seem to assume that everyone in the world will view their
    web sites using the same browser brand and version, screen resolution etc,
    because only that assumption could explain why they'd use static frame sizes,
    yet prevent their frames from being resized by the user, should they be too
    small to show their whole content.
   </para>
   <para>
    This filter removes the related HTML code. It should only be applied to sites
    which need it.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term><emphasis>demoronizer</emphasis></term>
  <listitem>
   <para>
    Many Microsoft products that generate HTML use non-standard extensions (read:
    violations) of the ISO 8859-1 aka Latin-1 character set. This can cause those
    HTML documents to display with errors on standard-compliant platforms.
   </para>
   <para>
    This filter translates the MS-only characters into Latin-1 equivalents.
    It is not necessary when using MS products, and will cause corruption of
    all documents that use 8-bit character sets other than Latin-1. It's mostly
    worthwhile for Europeans on non-MS platforms, if weird garbage characters
    sometimes appear on some pages, or user agents that don't correct for this on
    the fly.
<!--
    My version of Mozilla (ancient) shows little square boxes for quote
    characters, and apostrophes on moronized pages. So many pages have this, I
    can read them fine now. HB 08/27/06
-->
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term><emphasis>shockwave-flash</emphasis></term>
  <listitem>
   <para>
    A filter for shockwave haters. As the name suggests, this filter strips code
    out of web pages that is used to embed shockwave flash objects.
   </para>
   <para>
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term><emphasis>quicktime-kioskmode</emphasis></term>
  <listitem>
   <para>
    Change HTML code that embeds Quicktime objects so that kioskmode, which
    prevents saving, is disabled.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term><emphasis>fun</emphasis></term>
  <listitem>
   <para>
    Text replacements for subversive browsing fun. Make fun of your favorite
    Monopolist or play buzzword bingo.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term><emphasis>crude-parental</emphasis></term>
  <listitem>
   <para>
    A demonstration-only filter that shows how <application>Privoxy</application>
    can be used to delete web content on a keyword basis.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term><emphasis>ie-exploits</emphasis></term>
  <listitem>
   <para>
    An experimental collection of text replacements to disable malicious HTML and JavaScript
    code that exploits known security holes in Internet Explorer.
   </para>
   <para>
    Presently, it only protects against Nimda and a cross-site scripting bug, and
    would need active maintenance to provide more substantial protection.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term><emphasis>site-specifics</emphasis></term>
  <listitem>
   <para>
    Some web sites have very specific problems, the cure for which doesn't apply
    anywhere else, or could even cause damage on other sites.
   </para>
   <para>
    This is a collection of such site-specific cures which should only be applied
    to the sites they were intended for, which is what the supplied
    <filename>default.action</filename> file does. Users shouldn't need to change
    anything regarding this filter.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term><emphasis>google</emphasis></term>
  <listitem>
   <para>
    A CSS based block for Google text ads. Also removes a width limitation
    and the toolbar advertisement.
   </para>
  </listitem>
 </varlistentry>

  <varlistentry>
  <term><emphasis>yahoo</emphasis></term>
  <listitem>
   <para>
    Another CSS based block, this time for Yahoo text ads. And removes
    a width limitation as well.
   </para>
  </listitem>
 </varlistentry>

  <varlistentry>
  <term><emphasis>msn</emphasis></term>
  <listitem>
   <para>
    Another CSS based block, this time for MSN text ads. And removes
    tracking URLs, as well as a width limitation.
   </para>
  </listitem>
 </varlistentry>

 <varlistentry>
  <term><emphasis>blogspot</emphasis></term>
  <listitem>
   <para>
    Cleans up some Blogspot blogs. Read the fine print before using this one!
   </para>
   <para>
    This filter also intentionally removes some navigation stuff and sets the
    page width to 100%. As a result, some rounded <quote>corners</quote> would
    appear to early or not at all and as fixing this would require a browser
    that understands background-size (CSS3), they are removed instead.
   </para>
  </listitem>
 </varlistentry>

  <varlistentry>
  <term><emphasis>xml-to-html</emphasis></term>
  <listitem>
   <para>
    Server-header filter to change the Content-Type from xml to html.
   </para>
  </listitem>
 </varlistentry>

  <varlistentry>
  <term><emphasis>html-to-xml</emphasis></term>
  <listitem>
   <para>
    Server-header filter to change the Content-Type from html to xml.
   </para>
  </listitem>
 </varlistentry>

  <varlistentry>
  <term><emphasis>no-ping</emphasis></term>
  <listitem>
   <para>
    Removes the non-standard <literal>ping</literal> attribute from
    anchor and area HTML tags.
   </para>
  </listitem>
 </varlistentry>

  <varlistentry>
  <term><emphasis>hide-tor-exit-notation</emphasis></term>
  <listitem>
   <para>
    Client-header filter to remove the <command>Tor</command> exit node notation
    found in Host and Referer headers.
   </para>
   <para>
    If &my-app; and <command>Tor</command> are chained and &my-app;
    is configured to use socks4a, one can use <quote>http://www.example.org.foobar.exit/</quote>
    to access the host <quote>www.example.org</quote> through the
    <command>Tor</command> exit node <quote>foobar</quote>.
   </para>
   <para>
    As the HTTP client isn't aware of this notation, it treats the
    whole string <quote>www.example.org.foobar.exit</quote> as host and uses it
    for the <quote>Host</quote> and <quote>Referer</quote> headers. From the
    server's point of view the resulting headers are invalid and can cause problems.
   </para>
   <para>
    An invalid <quote>Referer</quote> header can trigger <quote>hot-linking</quote>
    protections, an invalid <quote>Host</quote> header will make it impossible for
    the server to find the right vhost (several domains hosted on the same IP address).
   </para>
   <para>
    This client-header filter removes the <quote>foo.exit</quote> part in those headers
    to prevent the mentioned problems. Note that it only modifies
    the HTTP headers, it doesn't make it impossible for the server
    to detect your <command>Tor</command> exit node based on the IP address
    the request is coming from.
   </para>
  </listitem>
 </varlistentry>

<!--
 <varlistentry>
  <term><emphasis> </emphasis></term>
  <listitem>
   <para>
   </para>
   <para>
   </para>
  </listitem>
 </varlistentry>
-->
</variablelist>

</sect2>

<!--   ~~~~~~~~       New section Header    ~~~~~~~~~     -->
<sect2 id="external-filter-syntax"><title>External filter syntax</title>
<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.
</para>
<para>
 External filters can be written in any language the platform &my-app; runs
 on supports.
</para>
<para>
 They are controlled with the
 <literal><link linkend="external-filter">external-filter</link></literal> action
 and have to be defined in the <literal><link linkend="filterfile">filterfile</link></literal>
 first.
</para>
<para>
 The header looks like any other filter, but instead of pcrs jobs, external
 filters contain a single job which can be a program or a shell script (which
 may call other scripts or programs).
</para>
<para>
 External filters read the content from STDIN and write the rewritten
 content to STDOUT.
 The environment variables PRIVOXY_URL, PRIVOXY_PATH, PRIVOXY_HOST,
 PRIVOXY_ORIGIN, PRIVOXY_LISTEN_ADDRESS can be used to get some details
 about the client request.
</para>
<para>
 &my-app; will temporary store the content to filter in the
 <literal><link linkend="temporary-directory">temporary-directory</link></literal>.
</para>

 <screen>
EXTERNAL-FILTER: cat Pointless example filter that doesn't actually modify the content
/bin/cat

# Incorrect reimplementation of the filter above in POSIX shell.
#
# Note that it's a single job that spans multiple lines, the line
# breaks are not passed to the shell, thus the semicolons are required.
#
# If the script isn't trivial, it is recommended to put it into an external file.
#
# In general, writing external filters entirely in POSIX shell is not
# considered a good idea.
EXTERNAL-FILTER: cat2 Pointless example filter that despite its name may actually modify the content
while read line; \
do \
  echo "$line"; \
done

EXTERNAL-FILTER: rotate-image Rotate an image by 180 degree. Test filter with limited value.
/usr/local/bin/convert - -rotate 180 -

EXTERNAL-FILTER: citation-needed Adds a "[citation needed]" tag to an image. The coordinates may need adjustment.
/usr/local/bin/convert - -pointsize 16 -fill white  -annotate +17+418 "[citation needed]" -
</screen>

<warning>
 <para>
  Currently external filters are executed with &my-app;'s privileges!
  Only use external filters you understand and trust.
 </para>
</warning>
<para>
 External filters are experimental and the syntax may change in the future.
</para>
</sect2>

</sect1>

<!--  ~  End section  ~  -->



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

<sect1 id="templates">
<title>Privoxy's Template Files</title>
<para>
 All <application>Privoxy</application> built-in pages, i.e. error pages such as the
 <ulink url="http://show-the-404-error.page"><quote>404 - No Such Domain</quote>
 error page</ulink>, the <ulink
 url="http://ads.bannerserver.example.com/nasty-ads/sponsor.html"><quote>BLOCKED</quote>
 page</ulink>
 and all pages of its <ulink url="http://config.privoxy.org/">web-based
 user interface</ulink>, are generated from <emphasis>templates</emphasis>.
 (<application>Privoxy</application> must be running for the above links to work as
 intended.)
</para>

<para>
 These templates are stored in a subdirectory of the <link linkend="confdir">configuration
 directory</link> called <filename>templates</filename>. On Unixish platforms,
 this is typically
 <ulink url="file:///etc/privoxy/templates/"><filename>/etc/privoxy/templates/</filename></ulink>.
</para>

<para>
 The templates are basically normal HTML files, but with place-holders (called symbols
 or exports), which <application>Privoxy</application> fills at run time. It
 is possible to edit the templates with a normal text editor, should you want
 to customize them. (<emphasis>Not recommended for the casual
 user</emphasis>). Should you create your own custom templates, you should use
 the <filename>config</filename> setting <link linkend="templdir">templdir</link>
 to specify an alternate location, so your templates do not get overwritten
 during upgrades.
 </para>
 <para>
 Note that just like in configuration files, lines starting
 with <literal>#</literal> are ignored when the templates are filled in.
</para>

<para>
 The place-holders are of the form <literal>@name@</literal>, and you will
 find a list of available symbols, which vary from template to template,
 in the comments at the start of each file. Note that these comments are not
 always accurate, and that it's probably best to look at the existing HTML
 code to find out which symbols are supported and what they are filled in with.
</para>

<para>
 A special application of this substitution mechanism is to make whole
 blocks of HTML code disappear when a specific symbol is set. We use this
 for many purposes, one of them being to include the beta warning in all
 our user interface (CGI) pages when <application>Privoxy</application>
 is in an alpha or beta development stage:
</para>

 <screen>
&lt;!-- @if-unstable-start --&gt;

  ... beta warning HTML code goes here ...

&lt;!-- if-unstable-end@ --&gt;</screen>

<para>
 If the "unstable" symbol is set, everything in between and including
 <literal>@if-unstable-start</literal> and <literal>if-unstable-end@</literal>
 will disappear, leaving nothing but an empty comment:
</para>

 <screen>&lt;!--  --&gt;</screen>

<para>
 There's also an if-then-else construct and an <literal>#include</literal>
 mechanism, but you'll sure find out if you are inclined to edit the
 templates ;-)
</para>

<para>
 All templates refer to a style located at
 <ulink url="http://config.privoxy.org/send-stylesheet"><literal>http://config.privoxy.org/send-stylesheet</literal></ulink>.
 This is, of course, locally served by <application>Privoxy</application>
 and the source for it can be found and edited in the
 <filename>cgi-style.css</filename> template.
</para>

</sect1>

<!--  ~  End section  ~  -->



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

<sect1 id="contact"><title>Contacting the Developers, Bug Reporting and Feature
Requests</title>

<!-- Include contacting.sgml boilerplate: -->
 &contacting;
<!-- end boilerplate -->

</sect1>

<!--  ~  End section  ~  -->


<!--   ~~~~~       New section      ~~~~~     -->
<sect1 id="copyright"><title>Privoxy Copyright, License and History</title>

<!-- Include copyright.sgml: -->
 &copyright;
<!-- end copyright -->

<para>
 <application>Privoxy</application> is free software; you can
 redistribute and/or modify its source code under the terms
 of the <citetitle>GNU General Public License</citetitle>
 as published by the Free Software Foundation, either version 2
 of the license, or (at your option) any later version.
</para>

<para>
 The same is true for <application>Privoxy</application> binaries
 unless they are linked with a
 <ulink url="https://tls.mbed.org/">mbed TLS</ulink> version
 that is licensed under the Apache 2.0 license in which
 case you can redistribute and/or modify the <application>Privoxy</application>
 binaries under the terms of the <citetitle>GNU General Public License</citetitle>
 as published by the Free Software Foundation, either version 3
 of the license, or (at your option) any later version.
</para>

<para>
 Both licenses are included in the next section.
</para>

<!--   ~~~~~       New section      ~~~~~     -->
<sect2 id="license"><title>License</title>

<sect3 id="gplv2"><title>GNU General Public License version 2</title>
 <screen><![ RCDATA [ &GPLv2; ]]></screen>
</sect3>

<sect3 id="gplv3"><title>GNU General Public License version 3</title>
 <screen><![ RCDATA [ &GPLv3; ]]></screen>
</sect3>

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


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

<sect2 id="history"><title>History</title>
<!-- Include history.sgml: -->
 &history;
<!-- end history -->
</sect2>

<sect2 id="authors"><title>Authors</title>
<!-- Include p-authors.sgml: -->
 &p-authors;
<!-- end authors -->
</sect2>

</sect1>

<!--  ~  End section  ~  -->


<!--   ~~~~~       New section      ~~~~~     -->
<sect1 id="seealso"><title>See Also</title>
<!-- Include seealso.sgml: -->
 &seealso;
<!-- end seealso -->
</sect1>



<!--   ~~~~~       New section      ~~~~~     -->
<sect1 id="appendix"><title>Appendix</title>


<!--   ~~~~~       New section      ~~~~~     -->
<sect2 id="regex">
<title>Regular Expressions</title>
<para>
 <application>Privoxy</application> uses Perl-style <quote>regular
 expressions</quote> in its <link linkend="actions-file">actions
 files</link> and <link linkend="filter-file">filter file</link>,
 through the <ulink url="http://www.pcre.org/">PCRE</ulink> and
<!--
 dead 08/27/06
 <ulink url="http://www.oesterhelt.org/pcrs/">PCRS</ulink> libraries.
-->
 <application>PCRS</application> libraries.
</para>

<para>
 If you are reading this, you probably don't understand what <quote>regular
 expressions</quote> are, or what they can do. So this will be a very brief
 introduction only. A full explanation would require a <ulink
 url="http://www.oreilly.com/catalog/regex/">book</ulink> ;-)
</para>

<para>
 Regular expressions provide a language to describe patterns that can be
 run against strings of characters (letter, numbers, etc), to see if they
 match the string or not. The  patterns are themselves (sometimes complex)
 strings of literal characters, combined with  wild-cards, and other special
 characters, called meta-characters. The <quote>meta-characters</quote> have
 special meanings and are used to build complex patterns to be matched against.
 Perl Compatible Regular Expressions are an especially convenient
 <quote>dialect</quote> of the regular expression language.
</para>

<para>
 To make a simple analogy, we do something similar when we use wild-card
 characters when listing files with the <command>dir</command> command in DOS.
 <literal>*.*</literal> matches all filenames. The <quote>special</quote>
 character here is the asterisk which matches any and all characters. We can be
 more specific and use <literal>?</literal> to match just individual
 characters. So <quote>dir file?.text</quote> would match
 <quote>file1.txt</quote>, <quote>file2.txt</quote>, etc. We are pattern
 matching, using a similar technique to <quote>regular expressions</quote>!
</para>

<para>
 Regular expressions do essentially the same thing, but are much, much more
 powerful. There are many more <quote>special characters</quote> and ways of
 building complex patterns however. Let's look at a few of the common ones,
 and then some examples:
</para>

<simplelist>
 <member>
  <emphasis>.</emphasis> - Matches any single character, e.g. <quote>a</quote>,
  <quote>A</quote>, <quote>4</quote>, <quote>:</quote>, or <quote>@</quote>.
 </member>
</simplelist>

<simplelist>
 <member>
  <emphasis>?</emphasis> - The preceding character or expression is matched ZERO or ONE
  times. Either/or.
 </member>
</simplelist>

<simplelist>
 <member>
  <emphasis>+</emphasis> - The preceding character or expression is matched ONE or MORE
  times.
 </member>
</simplelist>

<simplelist>
 <member>
  <emphasis>*</emphasis> - The preceding character or expression is matched ZERO or MORE
  times.
 </member>
</simplelist>

<simplelist>
 <member>
  <emphasis>\</emphasis> - The <quote>escape</quote> character denotes that
  the following character should be taken literally. This is used where one of the
  special characters (e.g. <quote>.</quote>) needs to be taken literally and
  not as a special meta-character. Example: <quote>example\.com</quote>, makes
  sure the period is recognized only as a period (and not expanded to its
  meta-character meaning of any single character).
 </member>
</simplelist>

<simplelist>
 <member>
  <emphasis>[ ]</emphasis> - Characters enclosed in brackets will be matched if
  any of the enclosed characters are encountered. For instance, <quote>[0-9]</quote>
  matches any numeric digit (zero through nine). As an example, we can combine
  this with <quote>+</quote> to match any digit one of more times: <quote>[0-9]+</quote>.
 </member>
</simplelist>

<simplelist>
 <member>
  <emphasis>( )</emphasis> - parentheses are used to group a sub-expression,
  or multiple sub-expressions.
 </member>
</simplelist>

<simplelist>
 <member>
  <emphasis>|</emphasis> - The <quote>bar</quote> character works like an
  <quote>or</quote> conditional statement. A match is successful if the
  sub-expression on either side of <quote>|</quote> matches. As an example:
  <quote>/(this|that) example/</quote> uses grouping and the bar character
  and would match either <quote>this example</quote> or <quote>that
  example</quote>, and nothing else.
 </member>
</simplelist>

<para>
 These are just some of the ones you are likely to use when matching URLs with
 <application>Privoxy</application>, and is a long way from a definitive
 list. This is enough to get us started with a few simple examples which may
 be more illuminating:
</para>

<para>
 <emphasis><literal>/.*/banners/.*</literal></emphasis> - A  simple example
 that uses the common combination of <quote>.</quote> and <quote>*</quote> to
 denote any character, zero or more times. In other words, any string at all.
 So we start with a literal forward slash, then our regular expression pattern
 (<quote>.*</quote>) another literal forward slash, the string
 <quote>banners</quote>, another forward slash, and lastly another
 <quote>.*</quote>. We are building
 a directory path here. This will match any file with the path that has a
 directory named <quote>banners</quote> in it. The <quote>.*</quote> matches
 any characters, and this could conceivably be more forward slashes, so it
 might expand into a much longer looking path. For example, this could match:
 <quote>/eye/hate/spammers/banners/annoy_me_please.gif</quote>, or just
 <quote>/banners/annoying.html</quote>, or almost an infinite number of other
 possible combinations, just so it has <quote>banners</quote> in the path
 somewhere.
</para>

<para>
 And now something a little more complex:
</para>

<para>
 <emphasis><literal>/.*/adv((er)?ts?|ertis(ing|ements?))?/</literal></emphasis> -
 We have several literal forward slashes again (<quote>/</quote>), so we are
 building another expression that is a file path statement. We have another
 <quote>.*</quote>, so we are matching against any conceivable sub-path, just so
 it matches our expression. The only true literal that <emphasis>must
 match</emphasis> our pattern is <application>adv</application>, together with
 the forward slashes. What comes after the <quote>adv</quote> string is the
 interesting part.
</para>

<para>
 Remember the <quote>?</quote> means the preceding expression (either a
 literal character or anything grouped with <quote>(...)</quote> in this case)
 can exist or not, since this means either zero or one match. So
 <quote>((er)?ts?|ertis(ing|ements?))</quote> is optional, as are the
 individual sub-expressions: <quote>(er)</quote>,
 <quote>(ing|ements?)</quote>, and the <quote>s</quote>. The <quote>|</quote>
 means <quote>or</quote>. We have two of those. For instance,
 <quote>(ing|ements?)</quote>, can expand to match either <quote>ing</quote>
 <emphasis>OR</emphasis> <quote>ements?</quote>. What is being done here, is an
 attempt at matching as many variations of <quote>advertisement</quote>, and
 similar, as possible. So this would expand to match just <quote>adv</quote>,
 or <quote>advert</quote>, or <quote>adverts</quote>, or
 <quote>advertising</quote>, or <quote>advertisement</quote>, or
 <quote>advertisements</quote>. You get the idea. But it would not match
 <quote>advertizements</quote> (with a <quote>z</quote>). We could fix that by
 changing our regular expression to:
 <quote>/.*/adv((er)?ts?|erti(s|z)(ing|ements?))?/</quote>, which would then match
 either spelling.
</para>

<para>
 <emphasis><literal>/.*/advert[0-9]+\.(gif|jpe?g)</literal></emphasis> - Again
 another path statement with forward slashes. Anything in the square brackets
 <quote>[ ]</quote> can be matched. This is using <quote>0-9</quote> as a
 shorthand expression to mean any digit one through nine. It is the same as
 saying <quote>0123456789</quote>. So any digit matches. The <quote>+</quote>
 means one or more of the preceding expression must be included. The preceding
 expression here is what is in the square brackets -- in this case, any digit
 one through nine. Then, at the end, we have a grouping: <quote>(gif|jpe?g)</quote>.
 This includes a <quote>|</quote>, so this needs to match the expression on
 either side of that bar character also. A simple <quote>gif</quote> on one side, and the other
 side will in turn match either <quote>jpeg</quote> or <quote>jpg</quote>,
 since the <quote>?</quote> means the letter <quote>e</quote> is optional and
 can be matched once or not at all. So we are building an expression here to
 match image GIF or JPEG type image file. It must include the literal
 string <quote>advert</quote>, then one or more digits, and a <quote>.</quote>
 (which is now a literal, and not a special character, since it is escaped
 with <quote>\</quote>), and lastly either <quote>gif</quote>, or
 <quote>jpeg</quote>, or <quote>jpg</quote>. Some possible matches would
 include: <quote>//advert1.jpg</quote>,
 <quote>/nasty/ads/advert1234.gif</quote>,
 <quote>/banners/from/hell/advert99.jpg</quote>. It would not match
 <quote>advert1.gif</quote> (no leading slash), or
 <quote>/adverts232.jpg</quote> (the expression does not include an
 <quote>s</quote>), or <quote>/advert1.jsp</quote> (<quote>jsp</quote> is not
 in the expression anywhere).
</para>

<para>
 We are barely scratching the surface of regular expressions here so that you
 can understand the default <application>Privoxy</application>
 configuration files, and maybe use this knowledge to customize your own
 installation. There is much, much more that can be done with regular
 expressions. Now that you know enough to get started, you can learn more on
 your own :/
</para>

<para>
 More reading on Perl Compatible Regular expressions:
 <ulink url="http://perldoc.perl.org/perlre.html">http://perldoc.perl.org/perlre.html</ulink>
</para>

<para>
 For information on regular expression based substitutions and their applications
 in filters, please see the <link linkend="filter-file">filter file tutorial</link>
 in this manual.
</para>
</sect2>

<!--  ~  End section  ~  -->


<!--   ~~~~~       New section      ~~~~~     -->
<sect2 id="internal-pages">
<title>Privoxy's Internal Pages</title>

<para>
 Since <application>Privoxy</application> proxies each requested
 web page, it is easy for <application>Privoxy</application> to
 trap certain special URLs. In this way, we can talk directly to
 <application>Privoxy</application>, and see how it is
 configured, see how our rules are being applied, change these
 rules and other configuration options, and even turn
 <application>Privoxy's</application> filtering off, all with
 a web browser.
</para>

<para>
 The URLs listed below are the special ones that allow direct access
 to <application>Privoxy</application>. Of course,
 <application>Privoxy</application> must be running to access these. If
 not, you will get a friendly error message. Internet access is not
 necessary either.
</para>

 <itemizedlist>

 <listitem>
  <para>
   Privoxy main page:
  </para>
  <blockquote>
   <para>
     <ulink url="http://config.privoxy.org/">http://config.privoxy.org/</ulink>
   </para>
  </blockquote>
  <para>
   There is a shortcut: <ulink url="http://p.p/">http://p.p/</ulink> (But it
   doesn't provide a fall-back to a real page, in case the request is not
   sent through <application>Privoxy</application>)
  </para>
 </listitem>

 <listitem>
  <para>
    View and toggle client tags:
  </para>
   <blockquote>
   <para>
    <ulink url="http://config.privoxy.org/client-tags">http://config.privoxy.org/client-tags</ulink>
   </para>
  </blockquote>
 </listitem>

 <listitem>
  <para>
    Show information about the current configuration, including viewing and
    editing of actions files:
  </para>
   <blockquote>
   <para>
    <ulink url="http://config.privoxy.org/show-status">http://config.privoxy.org/show-status</ulink>
   </para>
  </blockquote>
 </listitem>

 <listitem>
  <para>
   Show the browser's request headers:
  </para>
  <blockquote>
   <para>
    <ulink url="http://config.privoxy.org/show-request">http://config.privoxy.org/show-request</ulink>
   </para>
  </blockquote>
 </listitem>

 <listitem>
  <para>
   Show which actions apply to a URL and why:
  </para>
   <blockquote>
   <para>
    <ulink url="http://config.privoxy.org/show-url-info">http://config.privoxy.org/show-url-info</ulink>
   </para>
  </blockquote>
 </listitem>

 <listitem>
  <para>
   Toggle Privoxy on or off. This feature can be turned off/on in the main
   <filename>config</filename> file. When toggled <quote>off</quote>, <quote>Privoxy</quote>
   continues to run, but only as a pass-through proxy, with no actions taking
   place:
  </para>
   <blockquote>
   <para>
    <ulink url="http://config.privoxy.org/toggle">http://config.privoxy.org/toggle</ulink>
   </para>
  </blockquote>
  <para>
   Short cuts. Turn off, then on:
  </para>
   <blockquote>
   <para>
     <ulink url="http://config.privoxy.org/toggle?set=disable">http://config.privoxy.org/toggle?set=disable</ulink>
   </para>
  </blockquote>
   <blockquote>
   <para>
     <ulink url="http://config.privoxy.org/toggle?set=enable">http://config.privoxy.org/toggle?set=enable</ulink>
   </para>
  </blockquote>
 </listitem>

 </itemizedlist>

</sect2>


<!--   ~~~~~       New section      ~~~~~     -->
<sect2 id="chain">
<title>Chain of Events</title>
<para>
 Let's take a quick look at how some of <application>Privoxy's</application>
 core features are triggered, and the ensuing sequence of events when a web
 page is requested by your browser:
</para>

 <itemizedlist>
 <listitem>
  <para>
   First, your web browser requests a web page. The browser knows to send
   the request to <application>Privoxy</application>, which will in turn,
   relay the request to the remote web server after passing the following
   tests:
  </para>
 </listitem>
 <listitem>
  <para>
   <application>Privoxy</application> traps any request for its own internal CGI
   pages (e.g <ulink url="http://p.p/">http://p.p/</ulink>) and sends the CGI page back to the browser.
  </para>
 </listitem>
 <listitem>
  <para>
   Next, <application>Privoxy</application> checks to see if the URL
   matches any <link
   linkend="BLOCK"><quote>+block</quote></link> patterns. If
   so, the URL is then blocked, and the remote web server will not be contacted.
   <link linkend="HANDLE-AS-IMAGE"><quote>+handle-as-image</quote></link>
   and
   <link linkend="HANDLE-AS-EMPTY-DOCUMENT"><quote>+handle-as-empty-document</quote></link>
   are then checked, and if there is no match, an
   HTML <quote>BLOCKED</quote> page is sent back to the browser. Otherwise, if
   it does match, an image is returned for the former, and an empty text
   document for the latter. The type of image would depend on the setting of
   <link linkend="SET-IMAGE-BLOCKER"><quote>+set-image-blocker</quote></link>
   (blank, checkerboard pattern, or an HTTP redirect to an image elsewhere).
  </para>
 </listitem>
 <listitem>
  <para>
   Untrusted URLs are blocked. If URLs are being added to the
   <filename>trust</filename> file, then that is done.
  </para>
 </listitem>
 <listitem>
  <para>
   If the URL pattern matches the <link
   linkend="FAST-REDIRECTS"><quote>+fast-redirects</quote></link> action,
   it is then processed. Unwanted parts of the requested URL are stripped.
  </para>
 </listitem>
 <listitem>
  <para>
   Now the rest of the client browser's request headers are processed. If any
   of these match any of the relevant actions (e.g. <link
   linkend="HIDE-USER-AGENT"><quote>+hide-user-agent</quote></link>,
   etc.), headers are suppressed or forged as determined by these actions and
   their parameters.
  </para>
 </listitem>
 <listitem>
  <para>
   Now the web server starts sending its response back (i.e. typically a web
   page).
  </para>
 </listitem>
 <listitem>
  <para>
   First, the server headers are read and processed to determine, among other
   things, the MIME type (document type) and encoding. The headers are then
   filtered as determined by the
   <link linkend="CRUNCH-INCOMING-COOKIES"><quote>+crunch-incoming-cookies</quote></link>,
   <link linkend="SESSION-COOKIES-ONLY"><quote>+session-cookies-only</quote></link>,
   and <link linkend="DOWNGRADE-HTTP-VERSION"><quote>+downgrade-http-version</quote></link>
   actions.
  </para>
 </listitem>
 <listitem>
  <para>
   If any <link linkend="FILTER"><quote>+filter</quote></link> action
   or <link
   linkend="DEANIMATE-GIFS"><quote>+deanimate-gifs</quote></link>
   action applies (and the document type fits the action), the rest of the page is
   read into memory (up to a configurable limit). Then the filter rules (from
   <filename>default.filter</filename> and any other filter files) are
   processed against the buffered content. Filters are applied in the order
   they are specified in one of the filter files. Animated GIFs, if present,
   are reduced to either the first or last frame, depending on the action
   setting.The entire page, which is now filtered, is then sent by
   <application>Privoxy</application> back to your browser.
  </para>
  <para>
   If neither a <link linkend="FILTER"><quote>+filter</quote></link> action
   or <link
   linkend="DEANIMATE-GIFS"><quote>+deanimate-gifs</quote></link>
   matches, then <application>Privoxy</application> passes the raw data through
   to the client browser as it becomes available.
  </para>
 </listitem>
 <listitem>
  <para>
   As the browser receives the now (possibly filtered) page content, it
   reads and then requests any URLs that may be embedded within the page
   source, e.g. ad images, stylesheets, JavaScript, other HTML documents (e.g.
   frames), sounds, etc. For each of these objects, the browser issues a
   separate request (this is easily viewable in <application>Privoxy's</application>
   logs). And each such request is in turn processed just as above. Note that a
   complex web page will have many, many such embedded URLs. If these
   secondary requests are to a different server, then quite possibly a very
   differing set of actions is triggered.
  </para>
 </listitem>

 </itemizedlist>

<para>
 NOTE: This is somewhat of a simplistic overview of what happens with each URL
 request. For the sake of brevity and simplicity, we have focused on
 <application>Privoxy's</application> core features only.
</para>

</sect2>


<!--   ~~~~~       New section      ~~~~~     -->
<sect2 id="actionsanat">
<title>Troubleshooting: Anatomy of an Action</title>

<para>
 The way <application>Privoxy</application> applies
 <link linkend="ACTIONS">actions</link> and <link linkend="FILTER">filters</link>
 to any given URL can be complex, and not always so
 easy to understand what is happening. And sometimes we need to be able to
 <emphasis>see</emphasis> just what <application>Privoxy</application> is
 doing. Especially, if something <application>Privoxy</application> is doing
 is causing us a problem inadvertently. It can be a little daunting to look at
 the actions and filters files themselves, since they tend to be filled with
 <link linkend="regex">regular expressions</link> whose consequences are not
 always so obvious.
</para>

<para>
 One quick test to see if <application>Privoxy</application> is causing a problem
 or not, is to disable it temporarily. This should be the first troubleshooting
 step (be sure to flush caches afterward!). Looking at the
 logs is a good idea too. (Note that both the toggle feature and logging are
 enabled via <filename>config</filename> file settings, and may need to be
 turned <quote>on</quote>.)
</para>
<para>
 Another easy troubleshooting step to try is if you have done any
 customization of your installation, revert back to the installed
 defaults and see if that helps. There are times the developers get complaints
 about one thing or another, and the problem is more related to a customized
 configuration issue.
</para>

<para>
 <application>Privoxy</application> also provides the
 <ulink url="http://config.privoxy.org/show-url-info">http://config.privoxy.org/show-url-info</ulink>
 page that can show us very specifically how <application>actions</application>
 are being applied to any given URL. This is a big help for troubleshooting.
</para>

<para>
 First, enter one URL (or partial URL) at the prompt, and then
 <application>Privoxy</application> will tell us
 how the current configuration will handle it. This will not
 help with filtering effects (i.e. the <link
 linkend="FILTER"><quote>+filter</quote></link> action) from
 one of the filter files since this is handled very
 differently and not so easy to trap! It also will not tell you about any other
 URLs that may be embedded within the URL you are testing. For instance, images
 such as ads are expressed as URLs within the raw page source of HTML pages. So
 you will only get info for the actual URL that is pasted into the prompt area
 -- not any sub-URLs. If you want to know about embedded URLs like ads, you
 will have to dig those out of the HTML source. Use your browser's <quote>View
 Page Source</quote> option for this. Or right click on the ad, and grab the
 URL.
</para>

<para>
 Let's try an example, <ulink url="http://google.com">google.com</ulink>,
 and look at it one section at a time in a sample configuration (your real
 configuration may vary):
</para>

 <screen>
 Matches for http://www.google.com:

 In file: default.action <guibutton>[ View ]</guibutton> <guibutton>[ Edit ]</guibutton>

 {+change-x-forwarded-for{block}
 +deanimate-gifs {last}
 +fast-redirects {check-decoded-url}
 +filter {refresh-tags}
 +filter {img-reorder}
 +filter {banners-by-size}
 +filter {webbugs}
 +filter {jumping-windows}
 +filter {ie-exploits}
 +hide-from-header {block}
 +hide-referrer {forge}
 +session-cookies-only
 +set-image-blocker {pattern}
/

 { -session-cookies-only }
 .google.com

 { -fast-redirects }
 .google.com

In file: user.action <guibutton>[ View ]</guibutton> <guibutton>[ Edit ]</guibutton>
(no matches in this file)
</screen>

<para>
 This is telling us how we have defined our
 <link linkend="ACTIONS"><quote>actions</quote></link>, and
 which ones match for our test case, <quote>google.com</quote>.
 Displayed is all the actions that are available to us. Remember,
 the <literal>+</literal> sign denotes <quote>on</quote>. <literal>-</literal>
 denotes <quote>off</quote>. So some are <quote>on</quote> here, but many
 are <quote>off</quote>. Each example we try may provide a slightly different
 end result, depending on our configuration directives.
</para>
<para>
 The first listing
  is for our <filename>default.action</filename> file. The large, multi-line
  listing, is how the actions are set to match for all URLs, i.e. our default
  settings. If you look at your <quote>actions</quote> file, this would be the
  section just below the <quote>aliases</quote> section near the top. This
  will apply to all URLs as signified by the single forward slash at the end
  of the listing -- <quote> / </quote>.
</para>

<para>
 But we have defined additional actions that would be exceptions to these general
 rules, and then we list specific URLs (or patterns) that these exceptions
 would apply to. Last match wins. Just below this then are two explicit
 matches for <quote>.google.com</quote>. The first is negating our previous
 cookie setting, which was for <link
 linkend="SESSION-COOKIES-ONLY"><quote>+session-cookies-only</quote></link>
 (i.e. not persistent). So we will allow persistent cookies for google, at
 least that is how it is in this example. The second turns
 <emphasis>off</emphasis> any <link
 linkend="FAST-REDIRECTS"><quote>+fast-redirects</quote></link>
 action, allowing this to take place unmolested. Note that there is a leading
 dot here -- <quote>.google.com</quote>. This will match any hosts and
 sub-domains, in the google.com domain also, such as
 <quote>www.google.com</quote> or <quote>mail.google.com</quote>. But it would not
 match <quote>www.google.de</quote>! So, apparently, we have these two actions
 defined as exceptions to the general rules at the top somewhere in the lower
 part of our <filename>default.action</filename> file, and
 <quote>google.com</quote> is referenced somewhere in these latter sections.
</para>

<para>
 Then, for our <filename>user.action</filename> file, we again have no hits.
 So there is nothing google-specific that we might have added to our own, local
 configuration. If there was, those actions would over-rule any actions from
 previously processed files, such as <filename>default.action</filename>.
 <filename>user.action</filename> typically has the last word. This is the
 best place to put hard and fast exceptions,
</para>

<para>
 And finally we pull it all together in the bottom section and summarize how
 <application>Privoxy</application> is applying all its <quote>actions</quote>
 to <quote>google.com</quote>:
</para>

 <screen>
 Final results:

 -add-header
 -block
 +change-x-forwarded-for{block}
 -client-header-filter{hide-tor-exit-notation}
 -content-type-overwrite
 -crunch-client-header
 -crunch-if-none-match
 -crunch-incoming-cookies
 -crunch-outgoing-cookies
 -crunch-server-header
 +deanimate-gifs {last}
 -downgrade-http-version
 -fast-redirects
 -filter {js-events}
 -filter {content-cookies}
 -filter {all-popups}
 -filter {banners-by-link}
 -filter {tiny-textforms}
 -filter {frameset-borders}
 -filter {demoronizer}
 -filter {shockwave-flash}
 -filter {quicktime-kioskmode}
 -filter {fun}
 -filter {crude-parental}
 -filter {site-specifics}
 -filter {js-annoyances}
 -filter {html-annoyances}
 +filter {refresh-tags}
 -filter {unsolicited-popups}
 +filter {img-reorder}
 +filter {banners-by-size}
 +filter {webbugs}
 +filter {jumping-windows}
 +filter {ie-exploits}
 -filter {google}
 -filter {yahoo}
 -filter {msn}
 -filter {blogspot}
 -filter {no-ping}
 -force-text-mode
 -handle-as-empty-document
 -handle-as-image
 -hide-accept-language
 -hide-content-disposition
 +hide-from-header {block}
 -hide-if-modified-since
 +hide-referrer {forge}
 -hide-user-agent
 -limit-connect
 -overwrite-last-modified
 -prevent-compression
 -redirect
 -server-header-filter{xml-to-html}
 -server-header-filter{html-to-xml}
 -session-cookies-only
 +set-image-blocker {pattern}
</screen>

<para>
 Notice the only difference here to the previous listing, is to
 <quote>fast-redirects</quote> and <quote>session-cookies-only</quote>,
 which are activated specifically for this site in our configuration,
 and thus show in the <quote>Final Results</quote>.
</para>

<para>
 Now another example, <quote>ad.doubleclick.net</quote>:
</para>

 <screen>
 { +block{Domains starts with "ad"} }
  ad*.

 { +block{Domain contains "ad"} }
  .ad.

 { +block{Doubleclick banner server} +handle-as-image }
  .[a-vx-z]*.doubleclick.net
</screen>

<para>
 We'll just show the interesting part here - the explicit matches. It is
 matched three different times. Two <quote>+block{}</quote> sections,
 and a <quote>+block{} +handle-as-image</quote>,
 which is the expanded form of one of our aliases that had been defined as:
 <quote>+block-as-image</quote>. (<link
 linkend="ALIASES"><quote>Aliases</quote></link> are defined in
 the first section of the actions file and typically used to combine more
 than one action.)
</para>

<para>
 Any one of these would have done the trick and blocked this as an unwanted
 image. This is unnecessarily redundant since the last case effectively
 would also cover the first. No point in taking chances with these guys
 though ;-) Note that if you want an ad or obnoxious
 URL to be invisible, it should be defined as <quote>ad.doubleclick.net</quote>
 is done here -- as both a <link
 linkend="BLOCK"><quote>+block{}</quote></link>
 <emphasis>and</emphasis> an
 <link linkend="HANDLE-AS-IMAGE"><quote>+handle-as-image</quote></link>.
 The custom alias <quote><literal>+block-as-image</literal></quote> just
 simplifies the process and make it more readable.
</para>

<para>
 One last example. Let's try <quote>http://www.example.net/adsl/HOWTO/</quote>.
 This one is giving us problems. We are getting a blank page. Hmmm ...
</para>

 <screen>
 Matches for http://www.example.net/adsl/HOWTO/:

 In file: default.action <guibutton>[ View ]</guibutton> <guibutton>[ Edit ]</guibutton>

 {-add-header
  -block
  +change-x-forwarded-for{block}
  -client-header-filter{hide-tor-exit-notation}
  -content-type-overwrite
  -crunch-client-header
  -crunch-if-none-match
  -crunch-incoming-cookies
  -crunch-outgoing-cookies
  -crunch-server-header
  +deanimate-gifs
  -downgrade-http-version
  +fast-redirects {check-decoded-url}
  -filter {js-events}
  -filter {content-cookies}
  -filter {all-popups}
  -filter {banners-by-link}
  -filter {tiny-textforms}
  -filter {frameset-borders}
  -filter {demoronizer}
  -filter {shockwave-flash}
  -filter {quicktime-kioskmode}
  -filter {fun}
  -filter {crude-parental}
  -filter {site-specifics}
  -filter {js-annoyances}
  -filter {html-annoyances}
  +filter {refresh-tags}
  -filter {unsolicited-popups}
  +filter {img-reorder}
  +filter {banners-by-size}
  +filter {webbugs}
  +filter {jumping-windows}
  +filter {ie-exploits}
  -filter {google}
  -filter {yahoo}
  -filter {msn}
  -filter {blogspot}
  -filter {no-ping}
  -force-text-mode
  -handle-as-empty-document
  -handle-as-image
  -hide-accept-language
  -hide-content-disposition
  +hide-from-header{block}
  +hide-referer{forge}
  -hide-user-agent
  -overwrite-last-modified
  +prevent-compression
  -redirect
  -server-header-filter{xml-to-html}
  -server-header-filter{html-to-xml}
  +session-cookies-only
  +set-image-blocker{blank} }
   /

 { +block{Path contains "ads".} +handle-as-image }
  /ads
</screen>

<para>
 Ooops, the <quote>/adsl/</quote> is matching <quote>/ads</quote> in our
 configuration! But we did not want this at all! Now we see why we get the
 blank page. It is actually triggering two different actions here, and
 the effects are aggregated so that the URL is blocked, and &my-app; is told
 to treat the block as if it were an image. But this is, of course, all wrong.
  We could now add a new action below this (or better in our own
  <filename>user.action</filename> file) that explicitly
  <emphasis>un</emphasis> blocks (
  <link linkend="BLOCK"><quote>{-block}</quote></link>) paths with
  <quote>adsl</quote> in them (remember, last match in the configuration
  wins). There are various ways to handle such exceptions. Example:
</para>

 <screen>
 { -block }
  /adsl
</screen>

<para>
 Now the page displays ;-)
 Remember to flush your browser's caches when making these kinds of changes to
 your configuration to insure that you get a freshly delivered page! Or, try
 using <literal>Shift+Reload</literal>.
</para>

<para>
 But now what about a situation where we get no explicit matches like
 we did with:
</para>

 <screen>
 { +block{Path starts with "ads".} +handle-as-image }
 /ads
</screen>

<para>
 That actually was very helpful and pointed us quickly to where the problem
 was. If you don't get this kind of match, then it means one of the default
 rules in the first section of <filename>default.action</filename> is causing
 the problem. This would require some guesswork, and maybe a little trial and
 error to isolate the offending rule. One likely cause would be one of the
 <link linkend="FILTER"><quote>+filter</quote></link> actions.
 These tend to be harder to troubleshoot.
 Try adding the URL for the site to one of aliases that turn off
 <link linkend="FILTER"><quote>+filter</quote></link>:
</para>

 <screen>
 { shop }
 .quietpc.com
 .worldpay.com   # for quietpc.com
 .jungle.com
 .scan.co.uk
 .forbes.com
</screen>

<para>
 <quote><literal>{ shop }</literal></quote> is an <quote>alias</quote> that expands to
 <quote><literal>{ -filter -session-cookies-only }</literal></quote>.
 Or you could do your own exception to negate filtering:
</para>

 <screen>
 { -filter }
 # Disable ALL filter actions for sites in this section
 .forbes.com
 developer.ibm.com
 localhost
</screen>

<para>
 This would turn off all filtering for these sites. This is best
 put in <filename>user.action</filename>, for local site
 exceptions. Note that when a simple domain pattern is used by itself (without
 the subsequent path portion), all sub-pages within that domain are included
 automatically in the scope of the action.
</para>

<para>
 Images that are inexplicably being blocked, may well be hitting the
<link linkend="FILTER-BANNERS-BY-SIZE"><quote>+filter{banners-by-size}</quote></link>
 rule, which assumes
 that images of certain sizes are ad banners (works well
 <emphasis>most of the time</emphasis>  since these tend to be standardized).
</para>

<para>
 <quote><literal>{ fragile }</literal></quote> is an alias that disables most
 actions that are the most likely to cause trouble. This can be used as a
 last resort for problem sites.
</para>

 <screen>
 { fragile }
 # Handle with care: easy to break
 mail.google.
 mybank.example.com</screen>


<para>
 <emphasis>Remember to flush caches!</emphasis> Note that the
 <literal>mail.google</literal> reference lacks the TLD portion (e.g.
 <quote>.com</quote>). This will effectively match any TLD with
 <literal>google</literal> in it, such as <literal>mail.google.de.</literal>,
 just as an example.
</para>
<para>
 If this still does not work, you will have to go through the remaining
 actions one by one to find which one(s) is causing the problem.
</para>

</sect2>

</sect1>

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</article>