68c0b5e8b37ee7daea66b3687ae27baea8f524ff
[privoxy.git] / doc / webserver / user-manual / actions-file.html
1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
2 "http://www.w3.org/TR/html4/loose.dtd">
3 <html>
4 <head>
5   <title>Actions Files</title>
6   <meta name="GENERATOR" content="Modular DocBook HTML Stylesheet Version 1.79">
7   <link rel="HOME" title="Privoxy 3.0.29 User Manual" href="index.html">
8   <link rel="PREVIOUS" title="The Main Configuration File" href="config.html">
9   <link rel="NEXT" title="Filter Files" href="filter-file.html">
10   <link rel="STYLESHEET" type="text/css" href="../p_doc.css">
11   <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
12   <link rel="STYLESHEET" type="text/css" href="p_doc.css">
13 </head>
14 <body class="SECT1" bgcolor="#EEEEEE" text="#000000" link="#0000FF" vlink="#840084" alink="#0000FF">
15   <div class="NAVHEADER">
16     <table summary="Header navigation table" width="100%" border="0" cellpadding="0" cellspacing="0">
17       <tr>
18         <th colspan="3" align="center">Privoxy 3.0.29 User Manual</th>
19       </tr>
20       <tr>
21         <td width="10%" align="left" valign="bottom"><a href="config.html" accesskey="P">Prev</a></td>
22         <td width="80%" align="center" valign="bottom"></td>
23         <td width="10%" align="right" valign="bottom"><a href="filter-file.html" accesskey="N">Next</a></td>
24       </tr>
25     </table>
26     <hr align="left" width="100%">
27   </div>
28   <div class="SECT1">
29     <h1 class="SECT1"><a name="ACTIONS-FILE" id="ACTIONS-FILE">8. Actions Files</a></h1>
30     <p>The actions files are used to define what <span class="emphasis"><i class="EMPHASIS">actions</i></span>
31     <span class="APPLICATION">Privoxy</span> takes for which URLs, and thus determines how ad images, cookies and
32     various other aspects of HTTP content and transactions are handled, and on which sites (or even parts thereof).
33     There are a number of such actions, with a wide range of functionality. Each action does something a little
34     different. These actions give us a veritable arsenal of tools with which to exert our control, preferences and
35     independence. Actions can be combined so that their effects are aggregated when applied against a given set of
36     URLs.</p>
37     <p>There are three action files included with <span class="APPLICATION">Privoxy</span> with differing purposes:</p>
38     <ul>
39       <li>
40         <p><tt class="FILENAME">match-all.action</tt> - is used to define which <span class="QUOTE">"actions"</span>
41         relating to banner-blocking, images, pop-ups, content modification, cookie handling etc should be applied by
42         default. It should be the first actions file loaded</p>
43       </li>
44       <li>
45         <p><tt class="FILENAME">default.action</tt> - defines many exceptions (both positive and negative) from the
46         default set of actions that's configured in <tt class="FILENAME">match-all.action</tt>. It is a set of rules
47         that should work reasonably well as-is for most users. This file is only supposed to be edited by the
48         developers. It should be the second actions file loaded.</p>
49       </li>
50       <li>
51         <p><tt class="FILENAME">user.action</tt> - is intended to be for local site preferences and exceptions. As an
52         example, if your ISP or your bank has specific requirements, and need special handling, this kind of thing
53         should go here. This file will not be upgraded.</p>
54       </li>
55       <li>
56         <p><span class="GUIBUTTON">Edit</span> <span class="GUIBUTTON">Set to Cautious</span> <span class=
57         "GUIBUTTON">Set to Medium</span> <span class="GUIBUTTON">Set to Advanced</span></p>
58         <p>These have increasing levels of aggressiveness <span class="emphasis"><i class="EMPHASIS">and have no
59         influence on your browsing unless you select them explicitly in the editor</i></span>. A default installation
60         should be pre-set to <tt class="LITERAL">Cautious</tt>. New users should try this for a while before adjusting
61         the settings to more aggressive levels. The more aggressive the settings, then the more likelihood there is of
62         problems such as sites not working as they should.</p>
63         <p>The <span class="GUIBUTTON">Edit</span> button allows you to turn each action on/off individually for
64         fine-tuning. The <span class="GUIBUTTON">Cautious</span> button changes the actions list to low/safe settings
65         which will activate ad blocking and a minimal set of <span class="APPLICATION">Privoxy</span>'s features, and
66         subsequently there will be less of a chance for accidental problems. The <span class="GUIBUTTON">Medium</span>
67         button sets the list to a medium level of other features and a low level set of privacy features. The
68         <span class="GUIBUTTON">Advanced</span> button sets the list to a high level of ad blocking and medium level of
69         privacy. See the chart below. The latter three buttons over-ride any changes via with the <span class=
70         "GUIBUTTON">Edit</span> button. More fine-tuning can be done in the lower sections of this internal page.</p>
71         <p>While the actions file editor allows to enable these settings in all actions files, they are only supposed
72         to be enabled in the first one to make sure you don't unintentionally overrule earlier rules.</p>
73         <p>The default profiles, and their associated actions, as pre-defined in <tt class=
74         "FILENAME">default.action</tt> are:</p>
75         <div class="TABLE">
76           <a name="AEN3124" id="AEN3124"></a>
77           <p><b>Table 1. Default Configurations</b></p>
78           <table border="1" frame="border" rules="all" class="CALSTABLE">
79             <col width="1*" title="C1">
80             <col width="1*" title="C2">
81             <col width="1*" title="C3">
82             <col width="1*" title="C4">
83             <thead>
84               <tr>
85                 <th>Feature</th>
86                 <th>Cautious</th>
87                 <th>Medium</th>
88                 <th>Advanced</th>
89               </tr>
90             </thead>
91             <tbody>
92               <tr>
93                 <td>Ad-blocking Aggressiveness</td>
94                 <td>medium</td>
95                 <td>high</td>
96                 <td>high</td>
97               </tr>
98               <tr>
99                 <td>Ad-filtering by size</td>
100                 <td>no</td>
101                 <td>yes</td>
102                 <td>yes</td>
103               </tr>
104               <tr>
105                 <td>Ad-filtering by link</td>
106                 <td>no</td>
107                 <td>no</td>
108                 <td>yes</td>
109               </tr>
110               <tr>
111                 <td>Pop-up killing</td>
112                 <td>blocks only</td>
113                 <td>blocks only</td>
114                 <td>blocks only</td>
115               </tr>
116               <tr>
117                 <td>Privacy Features</td>
118                 <td>low</td>
119                 <td>medium</td>
120                 <td>medium/high</td>
121               </tr>
122               <tr>
123                 <td>Cookie handling</td>
124                 <td>none</td>
125                 <td>session-only</td>
126                 <td>kill</td>
127               </tr>
128               <tr>
129                 <td>Referer forging</td>
130                 <td>no</td>
131                 <td>yes</td>
132                 <td>yes</td>
133               </tr>
134               <tr>
135                 <td>GIF de-animation</td>
136                 <td>no</td>
137                 <td>yes</td>
138                 <td>yes</td>
139               </tr>
140               <tr>
141                 <td>Fast redirects</td>
142                 <td>no</td>
143                 <td>no</td>
144                 <td>yes</td>
145               </tr>
146               <tr>
147                 <td>HTML taming</td>
148                 <td>no</td>
149                 <td>no</td>
150                 <td>yes</td>
151               </tr>
152               <tr>
153                 <td>JavaScript taming</td>
154                 <td>no</td>
155                 <td>no</td>
156                 <td>yes</td>
157               </tr>
158               <tr>
159                 <td>Web-bug killing</td>
160                 <td>no</td>
161                 <td>yes</td>
162                 <td>yes</td>
163               </tr>
164               <tr>
165                 <td>Image tag reordering</td>
166                 <td>no</td>
167                 <td>yes</td>
168                 <td>yes</td>
169               </tr>
170             </tbody>
171           </table>
172         </div>
173       </li>
174     </ul>
175     <p>The list of actions files to be used are defined in the main configuration file, and are processed in the order
176     they are defined (e.g. <tt class="FILENAME">default.action</tt> is typically processed before <tt class=
177     "FILENAME">user.action</tt>). The content of these can all be viewed and edited from <a href=
178     "http://config.privoxy.org/show-status" target="_top">http://config.privoxy.org/show-status</a>. The over-riding
179     principle when applying actions, is that the last action that matches a given URL wins. The broadest, most general
180     rules go first (defined in <tt class="FILENAME">default.action</tt>), followed by any exceptions (typically also in
181     <tt class="FILENAME">default.action</tt>), which are then followed lastly by any local preferences (typically in
182     <span class="emphasis"><i class="EMPHASIS">user</i></span><tt class="FILENAME">.action</tt>). Generally, <tt class=
183     "FILENAME">user.action</tt> has the last word.</p>
184     <p>An actions file typically has multiple sections. If you want to use <span class="QUOTE">"aliases"</span> in an
185     actions file, you have to place the (optional) <a href="actions-file.html#ALIASES">alias section</a> at the top of
186     that file. Then comes the default set of rules which will apply universally to all sites and pages (be <span class=
187     "emphasis"><i class="EMPHASIS">very careful</i></span> with using such a universal set in <tt class=
188     "FILENAME">user.action</tt> or any other actions file after <tt class="FILENAME">default.action</tt>, because it
189     will override the result from consulting any previous file). And then below that, exceptions to the defined
190     universal policies. You can regard <tt class="FILENAME">user.action</tt> as an appendix to <tt class=
191     "FILENAME">default.action</tt>, with the advantage that it is a separate file, which makes preserving your personal
192     settings across <span class="APPLICATION">Privoxy</span> upgrades easier.</p>
193     <p>Actions can be used to block anything you want, including ads, banners, or just some obnoxious URL whose content
194     you would rather not see. Cookies can be accepted or rejected, or accepted only during the current browser session
195     (i.e. not written to disk), content can be modified, some JavaScripts tamed, user-tracking fooled, and much more.
196     See below for a <a href="actions-file.html#ACTIONS">complete list of actions</a>.</p>
197     <div class="SECT2">
198       <h2 class="SECT2"><a name="RIGHT-MIX" id="RIGHT-MIX">8.1. Finding the Right Mix</a></h2>
199       <p>Note that some <a href="actions-file.html#ACTIONS">actions</a>, like cookie suppression or script disabling,
200       may render some sites unusable that rely on these techniques to work properly. Finding the right mix of actions
201       is not always easy and certainly a matter of personal taste. And, things can always change, requiring refinements
202       in the configuration. In general, it can be said that the more <span class="QUOTE">"aggressive"</span> your
203       default settings (in the top section of the actions file) are, the more exceptions for <span class=
204       "QUOTE">"trusted"</span> sites you will have to make later. If, for example, you want to crunch all cookies per
205       default, you'll have to make exceptions from that rule for sites that you regularly use and that require cookies
206       for actually useful purposes, like maybe your bank, favorite shop, or newspaper.</p>
207       <p>We have tried to provide you with reasonable rules to start from in the distribution actions files. But there
208       is no general rule of thumb on these things. There just are too many variables, and sites are constantly
209       changing. Sooner or later you will want to change the rules (and read this chapter again :).</p>
210     </div>
211     <div class="SECT2">
212       <h2 class="SECT2"><a name="HOW-TO-EDIT" id="HOW-TO-EDIT">8.2. How to Edit</a></h2>
213       <p>The easiest way to edit the actions files is with a browser by using our browser-based editor, which can be
214       reached from <a href="http://config.privoxy.org/show-status" target=
215       "_top">http://config.privoxy.org/show-status</a>. Note: the config file option <a href=
216       "config.html#ENABLE-EDIT-ACTIONS">enable-edit-actions</a> must be enabled for this to work. The editor allows
217       both fine-grained control over every single feature on a per-URL basis, and easy choosing from wholesale sets of
218       defaults like <span class="QUOTE">"Cautious"</span>, <span class="QUOTE">"Medium"</span> or <span class=
219       "QUOTE">"Advanced"</span>. Warning: the <span class="QUOTE">"Advanced"</span> setting is more aggressive, and
220       will be more likely to cause problems for some sites. Experienced users only!</p>
221       <p>If you prefer plain text editing to GUIs, you can of course also directly edit the the actions files with your
222       favorite text editor. Look at <tt class="FILENAME">default.action</tt> which is richly commented with many good
223       examples.</p>
224     </div>
225     <div class="SECT2">
226       <h2 class="SECT2"><a name="ACTIONS-APPLY" id="ACTIONS-APPLY">8.3. How Actions are Applied to Requests</a></h2>
227       <p>Actions files are divided into sections. There are special sections, like the <span class="QUOTE">"<a href=
228       "actions-file.html#ALIASES">alias</a>"</span> sections which will be discussed later. For now let's concentrate
229       on regular sections: They have a heading line (often split up to multiple lines for readability) which consist of
230       a list of actions, separated by whitespace and enclosed in curly braces. Below that, there is a list of URL and
231       tag patterns, each on a separate line.</p>
232       <p>To determine which actions apply to a request, the URL of the request is compared to all URL patterns in each
233       <span class="QUOTE">"action file"</span>. Every time it matches, the list of applicable actions for the request
234       is incrementally updated, using the heading of the section in which the pattern is located. The same is done
235       again for tags and tag patterns later on.</p>
236       <p>If multiple applying sections set the same action differently, the last match wins. If not, the effects are
237       aggregated. E.g. a URL might match a regular section with a heading line of <tt class="LITERAL">{ +<a href=
238       "actions-file.html#HANDLE-AS-IMAGE">handle-as-image</a> }</tt>, then later another one with just <tt class=
239       "LITERAL">{ +<a href="actions-file.html#BLOCK">block</a> }</tt>, resulting in <span class="emphasis"><i class=
240       "EMPHASIS">both</i></span> actions to apply. And there may well be cases where you will want to combine actions
241       together. Such a section then might look like:</p>
242       <table border="0" bgcolor="#E0E0E0" width="100%">
243         <tr>
244           <td>
245             <pre class="SCREEN">  { +<tt class="LITERAL">handle-as-image</tt>  +<tt class=
246             "LITERAL">block{Banner ads.}</tt> }
247   # Block these as if they were images. Send no block page.
248    banners.example.com
249    media.example.com/.*banners
250    .example.com/images/ads/</pre>
251           </td>
252         </tr>
253       </table>
254       <p>You can trace this process for URL patterns and any given URL by visiting <a href=
255       "http://config.privoxy.org/show-url-info" target="_top">http://config.privoxy.org/show-url-info</a>.</p>
256       <p>Examples and more detail on this is provided in the Appendix, <a href=
257       "appendix.html#ACTIONSANAT">Troubleshooting: Anatomy of an Action</a> section.</p>
258     </div>
259     <div class="SECT2">
260       <h2 class="SECT2"><a name="AF-PATTERNS" id="AF-PATTERNS">8.4. Patterns</a></h2>
261       <p>As mentioned, <span class="APPLICATION">Privoxy</span> uses <span class="QUOTE">"patterns"</span> to determine
262       what <span class="emphasis"><i class="EMPHASIS">actions</i></span> might apply to which sites and pages your
263       browser attempts to access. These <span class="QUOTE">"patterns"</span> use wild card type <span class=
264       "emphasis"><i class="EMPHASIS">pattern</i></span> matching to achieve a high degree of flexibility. This allows
265       one expression to be expanded and potentially match against many similar patterns.</p>
266       <p>Generally, an URL pattern has the form <tt class="LITERAL">&lt;host&gt;&lt;port&gt;/&lt;path&gt;</tt>, where
267       the <tt class="LITERAL">&lt;host&gt;</tt>, the <tt class="LITERAL">&lt;port&gt;</tt> and the <tt class=
268       "LITERAL">&lt;path&gt;</tt> are optional. (This is why the special <tt class="LITERAL">/</tt> pattern matches all
269       URLs). Note that the protocol portion of the URL pattern (e.g. <tt class="LITERAL">http://</tt>) should
270       <span class="emphasis"><i class="EMPHASIS">not</i></span> be included in the pattern. This is assumed
271       already!</p>
272       <p>The pattern matching syntax is different for the host and path parts of the URL. The host part uses a simple
273       globbing type matching technique, while the path part uses more flexible <a href=
274       "http://en.wikipedia.org/wiki/Regular_expressions" target="_top"><span class="QUOTE">"Regular
275       Expressions"</span></a> (POSIX 1003.2).</p>
276       <p>The port part of a pattern is a decimal port number preceded by a colon (<tt class="LITERAL">:</tt>). If the
277       host part contains a numerical IPv6 address, it has to be put into angle brackets (<tt class="LITERAL">&lt;</tt>,
278       <tt class="LITERAL">&gt;</tt>).</p>
279       <div class="VARIABLELIST">
280         <dl>
281           <dt><tt class="LITERAL">www.example.com/</tt></dt>
282           <dd>
283             <p>is a host-only pattern and will match any request to <tt class="LITERAL">www.example.com</tt>,
284             regardless of which document on that server is requested. So ALL pages in this domain would be covered by
285             the scope of this action. Note that a simple <tt class="LITERAL">example.com</tt> is different and would
286             NOT match.</p>
287           </dd>
288           <dt><tt class="LITERAL">www.example.com</tt></dt>
289           <dd>
290             <p>means exactly the same. For host-only patterns, the trailing <tt class="LITERAL">/</tt> may be
291             omitted.</p>
292           </dd>
293           <dt><tt class="LITERAL">www.example.com/index.html</tt></dt>
294           <dd>
295             <p>matches all the documents on <tt class="LITERAL">www.example.com</tt> whose name starts with <tt class=
296             "LITERAL">/index.html</tt>.</p>
297           </dd>
298           <dt><tt class="LITERAL">www.example.com/index.html$</tt></dt>
299           <dd>
300             <p>matches only the single document <tt class="LITERAL">/index.html</tt> on <tt class=
301             "LITERAL">www.example.com</tt>.</p>
302           </dd>
303           <dt><tt class="LITERAL">/index.html$</tt></dt>
304           <dd>
305             <p>matches the document <tt class="LITERAL">/index.html</tt>, regardless of the domain, i.e. on
306             <span class="emphasis"><i class="EMPHASIS">any</i></span> web server anywhere.</p>
307           </dd>
308           <dt><tt class="LITERAL">/</tt></dt>
309           <dd>
310             <p>Matches any URL because there's no requirement for either the domain or the path to match anything.</p>
311           </dd>
312           <dt><tt class="LITERAL">:8000/</tt></dt>
313           <dd>
314             <p>Matches any URL pointing to TCP port 8000.</p>
315           </dd>
316           <dt><tt class="LITERAL">10.0.0.1/</tt></dt>
317           <dd>
318             <p>Matches any URL with the host address <tt class="LITERAL">10.0.0.1</tt>. (Note that the real URL uses
319             plain brackets, not angle brackets.)</p>
320           </dd>
321           <dt><tt class="LITERAL">&lt;2001:db8::1&gt;/</tt></dt>
322           <dd>
323             <p>Matches any URL with the host address <tt class="LITERAL">2001:db8::1</tt>. (Note that the real URL uses
324             plain brackets, not angle brackets.)</p>
325           </dd>
326           <dt><tt class="LITERAL">index.html</tt></dt>
327           <dd>
328             <p>matches nothing, since it would be interpreted as a domain name and there is no top-level domain called
329             <tt class="LITERAL">.html</tt>. So its a mistake.</p>
330           </dd>
331         </dl>
332       </div>
333       <div class="SECT3">
334         <h3 class="SECT3"><a name="HOST-PATTERN" id="HOST-PATTERN">8.4.1. The Host Pattern</a></h3>
335         <p>The matching of the host part offers some flexible options: if the host pattern starts or ends with a dot,
336         it becomes unanchored at that end. The host pattern is often referred to as domain pattern as it is usually
337         used to match domain names and not IP addresses. For example:</p>
338         <div class="VARIABLELIST">
339           <dl>
340             <dt><tt class="LITERAL">.example.com</tt></dt>
341             <dd>
342               <p>matches any domain with first-level domain <tt class="LITERAL">com</tt> and second-level domain
343               <tt class="LITERAL">example</tt>. For example <tt class="LITERAL">www.example.com</tt>, <tt class=
344               "LITERAL">example.com</tt> and <tt class="LITERAL">foo.bar.baz.example.com</tt>. Note that it wouldn't
345               match if the second-level domain was <tt class="LITERAL">another-example</tt>.</p>
346             </dd>
347             <dt><tt class="LITERAL">www.</tt></dt>
348             <dd>
349               <p>matches any domain that <span class="emphasis"><i class="EMPHASIS">STARTS</i></span> with <tt class=
350               "LITERAL">www.</tt> (It also matches the domain <tt class="LITERAL">www</tt> but most of the time that
351               doesn't matter.)</p>
352             </dd>
353             <dt><tt class="LITERAL">.example.</tt></dt>
354             <dd>
355               <p>matches any domain that <span class="emphasis"><i class="EMPHASIS">CONTAINS</i></span> <tt class=
356               "LITERAL">.example.</tt>. And, by the way, also included would be any files or documents that exist
357               within that domain since no path limitations are specified. (Correctly speaking: It matches any FQDN that
358               contains <tt class="LITERAL">example</tt> as a domain.) This might be <tt class=
359               "LITERAL">www.example.com</tt>, <tt class="LITERAL">news.example.de</tt>, or <tt class=
360               "LITERAL">www.example.net/cgi/testing.pl</tt> for instance. All these cases are matched.</p>
361             </dd>
362           </dl>
363         </div>
364         <p>Additionally, there are wild-cards that you can use in the domain names themselves. These work similarly to
365         shell globbing type wild-cards: <span class="QUOTE">"*"</span> represents zero or more arbitrary characters
366         (this is equivalent to the <a href="http://en.wikipedia.org/wiki/Regular_expressions" target=
367         "_top"><span class="QUOTE">"Regular Expression"</span></a> based syntax of <span class="QUOTE">".*"</span>),
368         <span class="QUOTE">"?"</span> represents any single character (this is equivalent to the regular expression
369         syntax of a simple <span class="QUOTE">"."</span>), and you can define <span class="QUOTE">"character
370         classes"</span> in square brackets which is similar to the same regular expression technique. All of this can
371         be freely mixed:</p>
372         <div class="VARIABLELIST">
373           <dl>
374             <dt><tt class="LITERAL">ad*.example.com</tt></dt>
375             <dd>
376               <p>matches <span class="QUOTE">"adserver.example.com"</span>, <span class=
377               "QUOTE">"ads.example.com"</span>, etc but not <span class="QUOTE">"sfads.example.com"</span></p>
378             </dd>
379             <dt><tt class="LITERAL">*ad*.example.com</tt></dt>
380             <dd>
381               <p>matches all of the above, and then some.</p>
382             </dd>
383             <dt><tt class="LITERAL">.?pix.com</tt></dt>
384             <dd>
385               <p>matches <tt class="LITERAL">www.ipix.com</tt>, <tt class="LITERAL">pictures.epix.com</tt>, <tt class=
386               "LITERAL">a.b.c.d.e.upix.com</tt> etc.</p>
387             </dd>
388             <dt><tt class="LITERAL">www[1-9a-ez].example.c*</tt></dt>
389             <dd>
390               <p>matches <tt class="LITERAL">www1.example.com</tt>, <tt class="LITERAL">www4.example.cc</tt>,
391               <tt class="LITERAL">wwwd.example.cy</tt>, <tt class="LITERAL">wwwz.example.com</tt> etc., but
392               <span class="emphasis"><i class="EMPHASIS">not</i></span> <tt class="LITERAL">wwww.example.com</tt>.</p>
393             </dd>
394           </dl>
395         </div>
396         <p>While flexible, this is not the sophistication of full regular expression based syntax.</p>
397         <p>When compiled with FEATURE_PCRE_HOST_PATTERNS patterns can be prefixed with <span class=
398         "QUOTE">"PCRE-HOST-PATTERN:"</span> in which case full regular expression (PCRE) can be used for the host
399         pattern as well.</p>
400       </div>
401       <div class="SECT3">
402         <h3 class="SECT3"><a name="PATH-PATTERN" id="PATH-PATTERN">8.4.2. The Path Pattern</a></h3>
403         <p><span class="APPLICATION">Privoxy</span> uses <span class="QUOTE">"modern"</span> POSIX 1003.2 <a href=
404         "http://en.wikipedia.org/wiki/Regular_expressions" target="_top"><span class="QUOTE">"Regular
405         Expressions"</span></a> for matching the path portion (after the slash), and is thus more flexible.</p>
406         <p>There is an <a href="appendix.html#REGEX">Appendix</a> with a brief quick-start into regular expressions,
407         you also might want to have a look at your operating system's documentation on regular expressions (try
408         <tt class="LITERAL">man re_format</tt>).</p>
409         <p>Note that the path pattern is automatically left-anchored at the <span class="QUOTE">"/"</span>, i.e. it
410         matches as if it would start with a <span class="QUOTE">"^"</span> (regular expression speak for the beginning
411         of a line).</p>
412         <p>Please also note that matching in the path is <span class="emphasis"><i class="EMPHASIS">CASE
413         INSENSITIVE</i></span> by default, but you can switch to case sensitive at any point in the pattern by using
414         the <span class="QUOTE">"(?-i)"</span> switch: <tt class="LITERAL">www.example.com/(?-i)PaTtErN.*</tt> will
415         match only documents whose path starts with <tt class="LITERAL">PaTtErN</tt> in <span class=
416         "emphasis"><i class="EMPHASIS">exactly</i></span> this capitalization.</p>
417         <div class="VARIABLELIST">
418           <dl>
419             <dt><tt class="LITERAL">.example.com/.*</tt></dt>
420             <dd>
421               <p>Is equivalent to just <span class="QUOTE">".example.com"</span>, since any documents within that
422               domain are matched with or without the <span class="QUOTE">".*"</span> regular expression. This is
423               redundant</p>
424             </dd>
425             <dt><tt class="LITERAL">.example.com/.*/index.html$</tt></dt>
426             <dd>
427               <p>Will match any page in the domain of <span class="QUOTE">"example.com"</span> that is named
428               <span class="QUOTE">"index.html"</span>, and that is part of some path. For example, it matches
429               <span class="QUOTE">"www.example.com/testing/index.html"</span> but NOT <span class=
430               "QUOTE">"www.example.com/index.html"</span> because the regular expression called for at least two
431               <span class="QUOTE">"/'s"</span>, thus the path requirement. It also would match <span class=
432               "QUOTE">"www.example.com/testing/index_html"</span>, because of the special meta-character <span class=
433               "QUOTE">"."</span>.</p>
434             </dd>
435             <dt><tt class="LITERAL">.example.com/(.*/)?index\.html$</tt></dt>
436             <dd>
437               <p>This regular expression is conditional so it will match any page named <span class=
438               "QUOTE">"index.html"</span> regardless of path which in this case can have one or more <span class=
439               "QUOTE">"/'s"</span>. And this one must contain exactly <span class="QUOTE">".html"</span> (and end with
440               that!).</p>
441             </dd>
442             <dt><tt class="LITERAL">.example.com/(.*/)(ads|banners?|junk)</tt></dt>
443             <dd>
444               <p>This regular expression will match any path of <span class="QUOTE">"example.com"</span> that contains
445               any of the words <span class="QUOTE">"ads"</span>, <span class="QUOTE">"banner"</span>, <span class=
446               "QUOTE">"banners"</span> (because of the <span class="QUOTE">"?"</span>) or <span class=
447               "QUOTE">"junk"</span>. The path does not have to end in these words, just contain them. The path has to
448               contain at least two slashes (including the one at the beginning).</p>
449             </dd>
450             <dt><tt class="LITERAL">.example.com/(.*/)(ads|banners?|junk)/.*\.(jpe?g|gif|png)$</tt></dt>
451             <dd>
452               <p>This is very much the same as above, except now it must end in either <span class=
453               "QUOTE">".jpg"</span>, <span class="QUOTE">".jpeg"</span>, <span class="QUOTE">".gif"</span> or
454               <span class="QUOTE">".png"</span>. So this one is limited to common image formats.</p>
455             </dd>
456           </dl>
457         </div>
458         <p>There are many, many good examples to be found in <tt class="FILENAME">default.action</tt>, and more
459         tutorials below in <a href="appendix.html#REGEX">Appendix on regular expressions</a>.</p>
460       </div>
461       <div class="SECT3">
462         <h3 class="SECT3"><a name="TAG-PATTERN" id="TAG-PATTERN">8.4.3. The Request Tag Pattern</a></h3>
463         <p>Request tag patterns are used to change the applying actions based on the request's tags. Tags can be
464         created based on HTTP headers with either the <a href=
465         "actions-file.html#CLIENT-HEADER-TAGGER">client-header-tagger</a> or the <a href=
466         "actions-file.html#SERVER-HEADER-TAGGER">server-header-tagger</a> action.</p>
467         <p>Request tag patterns have to start with <span class="QUOTE">"TAG:"</span>, so <span class=
468         "APPLICATION">Privoxy</span> can tell them apart from other patterns. Everything after the colon including
469         white space, is interpreted as a regular expression with path pattern syntax, except that tag patterns aren't
470         left-anchored automatically (<span class="APPLICATION">Privoxy</span> doesn't silently add a <span class=
471         "QUOTE">"^"</span>, you have to do it yourself if you need it).</p>
472         <p>To match all requests that are tagged with <span class="QUOTE">"foo"</span> your pattern line should be
473         <span class="QUOTE">"TAG:^foo$"</span>, <span class="QUOTE">"TAG:foo"</span> would work as well, but it would
474         also match requests whose tags contain <span class="QUOTE">"foo"</span> somewhere. <span class="QUOTE">"TAG:
475         foo"</span> wouldn't work as it requires white space.</p>
476         <p>Sections can contain URL and request tag patterns at the same time, but request tag patterns are checked
477         after the URL patterns and thus always overrule them, even if they are located before the URL patterns.</p>
478         <p>Once a new request tag is added, Privoxy checks right away if it's matched by one of the request tag
479         patterns and updates the action settings accordingly. As a result request tags can be used to activate other
480         tagger actions, as long as these other taggers look for headers that haven't already be parsed.</p>
481         <p>For example you could tag client requests which use the <tt class="LITERAL">POST</tt> method, then use this
482         tag to activate another tagger that adds a tag if cookies are sent, and then use a block action based on the
483         cookie tag. This allows the outcome of one action, to be input into a subsequent action. However if you'd
484         reverse the position of the described taggers, and activated the method tagger based on the cookie tagger, no
485         method tags would be created. The method tagger would look for the request line, but at the time the cookie tag
486         is created, the request line has already been parsed.</p>
487         <p>While this is a limitation you should be aware of, this kind of indirection is seldom needed anyway and even
488         the example doesn't make too much sense.</p>
489       </div>
490       <div class="SECT3">
491         <h3 class="SECT3"><a name="NEGATIVE-TAG-PATTERNS" id="NEGATIVE-TAG-PATTERNS">8.4.4. The Negative Request Tag
492         Patterns</a></h3>
493         <p>To match requests that do not have a certain request tag, specify a negative tag pattern by prefixing the
494         tag pattern line with either <span class="QUOTE">"NO-REQUEST-TAG:"</span> or <span class=
495         "QUOTE">"NO-RESPONSE-TAG:"</span> instead of <span class="QUOTE">"TAG:"</span>.</p>
496         <p>Negative request tag patterns created with <span class="QUOTE">"NO-REQUEST-TAG:"</span> are checked after
497         all client headers are scanned, the ones created with <span class="QUOTE">"NO-RESPONSE-TAG:"</span> are checked
498         after all server headers are scanned. In both cases all the created tags are considered.</p>
499       </div>
500       <div class="SECT3">
501         <h3 class="SECT3"><a name="CLIENT-TAG-PATTERN" id="CLIENT-TAG-PATTERN">8.4.5. The Client Tag Pattern</a></h3>
502         <div class="WARNING">
503           <table class="WARNING" border="1" width="100%">
504             <tr>
505               <td align="center"><b>Warning</b></td>
506             </tr>
507             <tr>
508               <td align="left">
509                 <p>This is an experimental feature. The syntax is likely to change in future versions.</p>
510               </td>
511             </tr>
512           </table>
513         </div>
514         <p>Client tag patterns are not set based on HTTP headers but based on the client's IP address. Users can enable
515         them themselves, but the Privoxy admin controls which tags are available and what their effect is.</p>
516         <p>After a client-specific tag has been defined with the <a href=
517         "config.html#CLIENT-SPECIFIC-TAG">client-specific-tag</a>, directive, action sections can be activated based on
518         the tag by using a CLIENT-TAG pattern. The CLIENT-TAG pattern is evaluated at the same priority as URL
519         patterns, as a result the last matching pattern wins. Tags that are created based on client or server headers
520         are evaluated later on and can overrule CLIENT-TAG and URL patterns!</p>
521         <p>The tag is set for all requests that come from clients that requested it to be set. Note that "clients" are
522         differentiated by IP address, if the IP address changes the tag has to be requested again.</p>
523         <p>Clients can request tags to be set by using the CGI interface <a href=
524         "http://config.privoxy.org/client-tags" target="_top">http://config.privoxy.org/client-tags</a>.</p>
525         <p>Example:</p>
526         <table border="0" bgcolor="#E0E0E0" width="100%">
527           <tr>
528             <td>
529               <pre class="SCREEN"># If the admin defined the client-specific-tag circumvent-blocks,
530 # and the request comes from a client that previously requested
531 # the tag to be set, overrule all previous +block actions that
532 # are enabled based on URL to CLIENT-TAG patterns.
533 {-block}
534 CLIENT-TAG:^circumvent-blocks$
535
536 # This section is not overruled because it's located after
537 # the previous one.
538 {+block{Nobody is supposed to request this.}}
539 example.org/blocked-example-page</pre>
540             </td>
541           </tr>
542         </table>
543       </div>
544     </div>
545     <div class="SECT2">
546       <h2 class="SECT2"><a name="ACTIONS" id="ACTIONS">8.5. Actions</a></h2>
547       <p>All actions are disabled by default, until they are explicitly enabled somewhere in an actions file. Actions
548       are turned on if preceded with a <span class="QUOTE">"+"</span>, and turned off if preceded with a <span class=
549       "QUOTE">"-"</span>. So a <tt class="LITERAL">+action</tt> means <span class="QUOTE">"do that action"</span>, e.g.
550       <tt class="LITERAL">+block</tt> means <span class="QUOTE">"please block URLs that match the following
551       patterns"</span>, and <tt class="LITERAL">-block</tt> means <span class="QUOTE">"don't block URLs that match the
552       following patterns, even if <tt class="LITERAL">+block</tt> previously applied."</span></p>
553       <p>Again, actions are invoked by placing them on a line, enclosed in curly braces and separated by whitespace,
554       like in <tt class="LITERAL">{+some-action -some-other-action{some-parameter}}</tt>, followed by a list of URL
555       patterns, one per line, to which they apply. Together, the actions line and the following pattern lines make up a
556       section of the actions file.</p>
557       <p>Actions fall into three categories:</p>
558       <ul>
559         <li>
560           <p>Boolean, i.e the action can only be <span class="QUOTE">"enabled"</span> or <span class=
561           "QUOTE">"disabled"</span>. Syntax:</p>
562           <table border="0" bgcolor="#E0E0E0" width="90%">
563             <tr>
564               <td>
565                 <pre class="SCREEN">  +<tt class="REPLACEABLE"><i>name</i></tt>        # enable action <tt class=
566                 "REPLACEABLE"><i>name</i></tt>
567   -<tt class="REPLACEABLE"><i>name</i></tt>        # disable action <tt class="REPLACEABLE"><i>name</i></tt></pre>
568               </td>
569             </tr>
570           </table>
571           <p>Example: <tt class="LITERAL">+handle-as-image</tt></p>
572         </li>
573         <li>
574           <p>Parameterized, where some value is required in order to enable this type of action. Syntax:</p>
575           <table border="0" bgcolor="#E0E0E0" width="90%">
576             <tr>
577               <td>
578                 <pre class="SCREEN">  +<tt class="REPLACEABLE"><i>name</i></tt>{<tt class=
579                 "REPLACEABLE"><i>param</i></tt>}  # enable action and set parameter to <tt class=
580                 "REPLACEABLE"><i>param</i></tt>,
581                # overwriting parameter from previous match if necessary
582   -<tt class="REPLACEABLE"><i>name</i></tt>         # disable action. The parameter can be omitted</pre>
583               </td>
584             </tr>
585           </table>
586           <p>Note that if the URL matches multiple positive forms of a parameterized action, the last match wins, i.e.
587           the params from earlier matches are simply ignored.</p>
588           <p>Example: <tt class="LITERAL">+hide-user-agent{Mozilla/5.0 (X11; U; FreeBSD i386; en-US; rv:1.8.1.4)
589           Gecko/20070602 Firefox/2.0.0.4}</tt></p>
590         </li>
591         <li>
592           <p>Multi-value. These look exactly like parameterized actions, but they behave differently: If the action
593           applies multiple times to the same URL, but with different parameters, <span class="emphasis"><i class=
594           "EMPHASIS">all</i></span> the parameters from <span class="emphasis"><i class="EMPHASIS">all</i></span>
595           matches are remembered. This is used for actions that can be executed for the same request repeatedly, like
596           adding multiple headers, or filtering through multiple filters. Syntax:</p>
597           <table border="0" bgcolor="#E0E0E0" width="90%">
598             <tr>
599               <td>
600                 <pre class="SCREEN">  +<tt class="REPLACEABLE"><i>name</i></tt>{<tt class=
601                 "REPLACEABLE"><i>param</i></tt>}   # enable action and add <tt class=
602                 "REPLACEABLE"><i>param</i></tt> to the list of parameters
603   -<tt class="REPLACEABLE"><i>name</i></tt>{<tt class=
604 "REPLACEABLE"><i>param</i></tt>}   # remove the parameter <tt class=
605 "REPLACEABLE"><i>param</i></tt> from the list of parameters
606                 # If it was the last one left, disable the action.
607   <tt class=
608 "REPLACEABLE"><i>-name</i></tt>          # disable this action completely and remove all parameters from the list</pre>
609               </td>
610             </tr>
611           </table>
612           <p>Examples: <tt class="LITERAL">+add-header{X-Fun-Header: Some text}</tt> and <tt class=
613           "LITERAL">+filter{html-annoyances}</tt></p>
614         </li>
615       </ul>
616       <p>If nothing is specified in any actions file, no <span class="QUOTE">"actions"</span> are taken. So in this
617       case <span class="APPLICATION">Privoxy</span> would just be a normal, non-blocking, non-filtering proxy. You must
618       specifically enable the privacy and blocking features you need (although the provided default actions files will
619       give a good starting point).</p>
620       <p>Later defined action sections always over-ride earlier ones of the same type. So exceptions to any rules you
621       make, should come in the latter part of the file (or in a file that is processed later when using multiple
622       actions files such as <tt class="FILENAME">user.action</tt>). For multi-valued actions, the actions are applied
623       in the order they are specified. Actions files are processed in the order they are defined in <tt class=
624       "FILENAME">config</tt> (the default installation has three actions files). It also quite possible for any given
625       URL to match more than one <span class="QUOTE">"pattern"</span> (because of wildcards and regular expressions),
626       and thus to trigger more than one set of actions! Last match wins.</p>
627       <p>The list of valid <span class="APPLICATION">Privoxy</span> actions are:</p>
628       <div class="SECT3">
629         <h4 class="SECT3"><a name="ADD-HEADER" id="ADD-HEADER">8.5.1. add-header</a></h4>
630         <div class="VARIABLELIST">
631           <dl>
632             <dt>Typical use:</dt>
633             <dd>
634               <p>Confuse log analysis, custom applications</p>
635             </dd>
636             <dt>Effect:</dt>
637             <dd>
638               <p>Sends a user defined HTTP header to the web server.</p>
639             </dd>
640             <dt>Type:</dt>
641             <dd>
642               <p>Multi-value.</p>
643             </dd>
644             <dt>Parameter:</dt>
645             <dd>
646               <p>Any string value is possible. Validity of the defined HTTP headers is not checked. It is recommended
647               that you use the <span class="QUOTE">"<tt class="LITERAL">X-</tt>"</span> prefix for custom headers.</p>
648             </dd>
649             <dt>Notes:</dt>
650             <dd>
651               <p>This action may be specified multiple times, in order to define multiple headers. This is rarely
652               needed for the typical user. If you don't know what <span class="QUOTE">"HTTP headers"</span> are, you
653               definitely don't need to worry about this one.</p>
654               <p>Headers added by this action are not modified by other actions.</p>
655             </dd>
656             <dt>Example usage:</dt>
657             <dd>
658               <table border="0" bgcolor="#E0E0E0" width="90%">
659                 <tr>
660                   <td>
661                     <pre class="SCREEN"># Add a DNT ("Do not track") header to all requests,
662 # event to those that already have one.
663 #
664 # This is just an example, not a recommendation.
665 #
666 # There is no reason to believe that user-tracking websites care
667 # about the DNT header and depending on the User-Agent, adding the
668 # header may make user-tracking easier.
669 {+add-header{DNT: 1}}
670 /</pre>
671                   </td>
672                 </tr>
673               </table>
674             </dd>
675           </dl>
676         </div>
677       </div>
678       <div class="SECT3">
679         <h4 class="SECT3"><a name="BLOCK" id="BLOCK">8.5.2. block</a></h4>
680         <div class="VARIABLELIST">
681           <dl>
682             <dt>Typical use:</dt>
683             <dd>
684               <p>Block ads or other unwanted content</p>
685             </dd>
686             <dt>Effect:</dt>
687             <dd>
688               <p>Requests for URLs to which this action applies are blocked, i.e. the requests are trapped by
689               <span class="APPLICATION">Privoxy</span> and the requested URL is never retrieved, but is answered
690               locally with a substitute page or image, as determined by the <tt class="LITERAL"><a href=
691               "actions-file.html#HANDLE-AS-IMAGE">handle-as-image</a></tt>, <tt class="LITERAL"><a href=
692               "actions-file.html#SET-IMAGE-BLOCKER">set-image-blocker</a></tt>, and <tt class="LITERAL"><a href=
693               "actions-file.html#HANDLE-AS-EMPTY-DOCUMENT">handle-as-empty-document</a></tt> actions.</p>
694             </dd>
695             <dt>Type:</dt>
696             <dd>
697               <p>Parameterized.</p>
698             </dd>
699             <dt>Parameter:</dt>
700             <dd>
701               <p>A block reason that should be given to the user.</p>
702             </dd>
703             <dt>Notes:</dt>
704             <dd>
705               <p><span class="APPLICATION">Privoxy</span> sends a special <span class="QUOTE">"BLOCKED"</span> page for
706               requests to blocked pages. This page contains the block reason given as parameter, a link to find out why
707               the block action applies, and a click-through to the blocked content (the latter only if the force
708               feature is available and enabled).</p>
709               <p>A very important exception occurs if <span class="emphasis"><i class="EMPHASIS">both</i></span>
710               <tt class="LITERAL">block</tt> and <tt class="LITERAL"><a href=
711               "actions-file.html#HANDLE-AS-IMAGE">handle-as-image</a></tt>, apply to the same request: it will then be
712               replaced by an image. If <tt class="LITERAL"><a href=
713               "actions-file.html#SET-IMAGE-BLOCKER">set-image-blocker</a></tt> (see below) also applies, the type of
714               image will be determined by its parameter, if not, the standard checkerboard pattern is sent.</p>
715               <p>It is important to understand this process, in order to understand how <span class=
716               "APPLICATION">Privoxy</span> deals with ads and other unwanted content. Blocking is a core feature, and
717               one upon which various other features depend.</p>
718               <p>The <tt class="LITERAL"><a href="actions-file.html#FILTER">filter</a></tt> action can perform a very
719               similar task, by <span class="QUOTE">"blocking"</span> banner images and other content through rewriting
720               the relevant URLs in the document's HTML source, so they don't get requested in the first place. Note
721               that this is a totally different technique, and it's easy to confuse the two.</p>
722             </dd>
723             <dt>Example usage (section):</dt>
724             <dd>
725               <table border="0" bgcolor="#E0E0E0" width="90%">
726                 <tr>
727                   <td>
728                     <pre class="SCREEN">{+block{No nasty stuff for you.}}
729 # Block and replace with "blocked" page
730  .nasty-stuff.example.com
731
732 {+block{Doubleclick banners.} +handle-as-image}
733 # Block and replace with image
734  .ad.doubleclick.net
735  .ads.r.us/banners/
736
737 {+block{Layered ads.} +handle-as-empty-document}
738 # Block and then ignore
739  adserver.example.net/.*\.js$</pre>
740                   </td>
741                 </tr>
742               </table>
743             </dd>
744           </dl>
745         </div>
746       </div>
747       <div class="SECT3">
748         <h4 class="SECT3"><a name="CHANGE-X-FORWARDED-FOR" id="CHANGE-X-FORWARDED-FOR">8.5.3.
749         change-x-forwarded-for</a></h4>
750         <div class="VARIABLELIST">
751           <dl>
752             <dt>Typical use:</dt>
753             <dd>
754               <p>Improve privacy by not forwarding the source of the request in the HTTP headers.</p>
755             </dd>
756             <dt>Effect:</dt>
757             <dd>
758               <p>Deletes the <span class="QUOTE">"X-Forwarded-For:"</span> HTTP header from the client request, or adds
759               a new one.</p>
760             </dd>
761             <dt>Type:</dt>
762             <dd>
763               <p>Parameterized.</p>
764             </dd>
765             <dt>Parameter:</dt>
766             <dd>
767               <ul>
768                 <li>
769                   <p><span class="QUOTE">"block"</span> to delete the header.</p>
770                 </li>
771                 <li>
772                   <p><span class="QUOTE">"add"</span> to create the header (or append the client's IP address to an
773                   already existing one).</p>
774                 </li>
775               </ul>
776             </dd>
777             <dt>Notes:</dt>
778             <dd>
779               <p>It is safe and recommended to use <tt class="LITERAL">block</tt>.</p>
780               <p>Forwarding the source address of the request may make sense in some multi-user setups but is also a
781               privacy risk.</p>
782             </dd>
783             <dt>Example usage:</dt>
784             <dd>
785               <table border="0" bgcolor="#E0E0E0" width="90%">
786                 <tr>
787                   <td>
788                     <pre class="SCREEN">+change-x-forwarded-for{block}</pre>
789                   </td>
790                 </tr>
791               </table>
792             </dd>
793           </dl>
794         </div>
795       </div>
796       <div class="SECT3">
797         <h4 class="SECT3"><a name="CLIENT-HEADER-FILTER" id="CLIENT-HEADER-FILTER">8.5.4. client-header-filter</a></h4>
798         <div class="VARIABLELIST">
799           <dl>
800             <dt>Typical use:</dt>
801             <dd>
802               <p>Rewrite or remove single client headers.</p>
803             </dd>
804             <dt>Effect:</dt>
805             <dd>
806               <p>All client headers to which this action applies are filtered on-the-fly through the specified regular
807               expression based substitutions.</p>
808             </dd>
809             <dt>Type:</dt>
810             <dd>
811               <p>Multi-value.</p>
812             </dd>
813             <dt>Parameter:</dt>
814             <dd>
815               <p>The name of a client-header filter, as defined in one of the <a href="filter-file.html">filter
816               files</a>.</p>
817             </dd>
818             <dt>Notes:</dt>
819             <dd>
820               <p>Client-header filters are applied to each header on its own, not to all at once. This makes it easier
821               to diagnose problems, but on the downside you can't write filters that only change header x if header y's
822               value is z. You can do that by using tags though.</p>
823               <p>Client-header filters are executed after the other header actions have finished and use their output
824               as input.</p>
825               <p>If the request URI gets changed, <span class="APPLICATION">Privoxy</span> will detect that and use the
826               new one. This can be used to rewrite the request destination behind the client's back, for example to
827               specify a Tor exit relay for certain requests.</p>
828               <p>Please refer to the <a href="filter-file.html">filter file chapter</a> to learn which client-header
829               filters are available by default, and how to create your own.</p>
830             </dd>
831             <dt>Example usage (section):</dt>
832             <dd>
833               <table border="0" bgcolor="#E0E0E0" width="90%">
834                 <tr>
835                   <td>
836                     <pre class="SCREEN"># Hide Tor exit notation in Host and Referer Headers
837 {+client-header-filter{hide-tor-exit-notation}}
838 /</pre>
839                   </td>
840                 </tr>
841               </table>
842             </dd>
843           </dl>
844         </div>
845       </div>
846       <div class="SECT3">
847         <h4 class="SECT3"><a name="CLIENT-HEADER-TAGGER" id="CLIENT-HEADER-TAGGER">8.5.5. client-header-tagger</a></h4>
848         <div class="VARIABLELIST">
849           <dl>
850             <dt>Typical use:</dt>
851             <dd>
852               <p>Block requests based on their headers.</p>
853             </dd>
854             <dt>Effect:</dt>
855             <dd>
856               <p>Client headers to which this action applies are filtered on-the-fly through the specified regular
857               expression based substitutions, the result is used as tag.</p>
858             </dd>
859             <dt>Type:</dt>
860             <dd>
861               <p>Multi-value.</p>
862             </dd>
863             <dt>Parameter:</dt>
864             <dd>
865               <p>The name of a client-header tagger, as defined in one of the <a href="filter-file.html">filter
866               files</a>.</p>
867             </dd>
868             <dt>Notes:</dt>
869             <dd>
870               <p>Client-header taggers are applied to each header on its own, and as the header isn't modified, each
871               tagger <span class="QUOTE">"sees"</span> the original.</p>
872               <p>Client-header taggers are the first actions that are executed and their tags can be used to control
873               every other action.</p>
874             </dd>
875             <dt>Example usage (section):</dt>
876             <dd>
877               <table border="0" bgcolor="#E0E0E0" width="90%">
878                 <tr>
879                   <td>
880                     <pre class="SCREEN"># Tag every request with the User-Agent header
881 {+client-header-tagger{user-agent}}
882 /
883
884 # Tagging itself doesn't change the action
885 # settings, sections with TAG patterns do:
886 #
887 # If it's a download agent, use a different forwarding proxy,
888 # show the real User-Agent and make sure resume works.
889 {+forward-override{forward-socks5 10.0.0.2:2222 .} \
890  -hide-if-modified-since      \
891  -overwrite-last-modified     \
892  -hide-user-agent             \
893  -filter                      \
894  -deanimate-gifs              \
895 }
896 TAG:^User-Agent: NetBSD-ftp/
897 TAG:^User-Agent: Novell ZYPP Installer
898 TAG:^User-Agent: RPM APT-HTTP/
899 TAG:^User-Agent: fetch libfetch/
900 TAG:^User-Agent: Ubuntu APT-HTTP/
901 TAG:^User-Agent: MPlayer/</pre>
902                   </td>
903                 </tr>
904               </table>
905               <table border="0" bgcolor="#E0E0E0" width="90%">
906                 <tr>
907                   <td>
908                     <pre class="SCREEN"># Tag all requests with the Range header set
909 {+client-header-tagger{range-requests}}
910 /
911
912 # Disable filtering for the tagged requests.
913 #
914 # With filtering enabled Privoxy would remove the Range headers
915 # to be able to filter the whole response. The downside is that
916 # it prevents clients from resuming downloads or skipping over
917 # parts of multimedia files.
918 {-filter -deanimate-gifs}
919 TAG:^RANGE-REQUEST$</pre>
920                   </td>
921                 </tr>
922               </table>
923               <table border="0" bgcolor="#E0E0E0" width="90%">
924                 <tr>
925                   <td>
926                     <pre class="SCREEN"># Tag all requests with the client IP address
927 #
928 # (Technically the client IP address isn't included in the
929 # client headers but client-header taggers can set it anyway.
930 # For details see the tagger in default.filter)
931 {+client-header-tagger{client-ip-address}}
932 /
933
934 # Change forwarding settings for requests coming from address 10.0.0.1
935 {+forward-override{forward-socks5 127.0.1.2:2222 .}}
936 TAG:^IP-ADDRESS: 10\.0\.0\.1$</pre>
937                   </td>
938                 </tr>
939               </table>
940             </dd>
941           </dl>
942         </div>
943       </div>
944       <div class="SECT3">
945         <h4 class="SECT3"><a name="CONTENT-TYPE-OVERWRITE" id="CONTENT-TYPE-OVERWRITE">8.5.6.
946         content-type-overwrite</a></h4>
947         <div class="VARIABLELIST">
948           <dl>
949             <dt>Typical use:</dt>
950             <dd>
951               <p>Stop useless download menus from popping up, or change the browser's rendering mode</p>
952             </dd>
953             <dt>Effect:</dt>
954             <dd>
955               <p>Replaces the <span class="QUOTE">"Content-Type:"</span> HTTP server header.</p>
956             </dd>
957             <dt>Type:</dt>
958             <dd>
959               <p>Parameterized.</p>
960             </dd>
961             <dt>Parameter:</dt>
962             <dd>
963               <p>Any string.</p>
964             </dd>
965             <dt>Notes:</dt>
966             <dd>
967               <p>The <span class="QUOTE">"Content-Type:"</span> HTTP server header is used by the browser to decide
968               what to do with the document. The value of this header can cause the browser to open a download menu
969               instead of displaying the document by itself, even if the document's format is supported by the
970               browser.</p>
971               <p>The declared content type can also affect which rendering mode the browser chooses. If XHTML is
972               delivered as <span class="QUOTE">"text/html"</span>, many browsers treat it as yet another broken HTML
973               document. If it is send as <span class="QUOTE">"application/xml"</span>, browsers with XHTML support will
974               only display it, if the syntax is correct.</p>
975               <p>If you see a web site that proudly uses XHTML buttons, but sets <span class="QUOTE">"Content-Type:
976               text/html"</span>, you can use <span class="APPLICATION">Privoxy</span> to overwrite it with <span class=
977               "QUOTE">"application/xml"</span> and validate the web master's claim inside your XHTML-supporting
978               browser. If the syntax is incorrect, the browser will complain loudly.</p>
979               <p>You can also go the opposite direction: if your browser prints error messages instead of rendering a
980               document falsely declared as XHTML, you can overwrite the content type with <span class=
981               "QUOTE">"text/html"</span> and have it rendered as broken HTML document.</p>
982               <p>By default <tt class="LITERAL">content-type-overwrite</tt> only replaces <span class=
983               "QUOTE">"Content-Type:"</span> headers that look like some kind of text. If you want to overwrite it
984               unconditionally, you have to combine it with <tt class="LITERAL"><a href=
985               "actions-file.html#FORCE-TEXT-MODE">force-text-mode</a></tt>. This limitation exists for a reason, think
986               twice before circumventing it.</p>
987               <p>Most of the time it's easier to replace this action with a custom <tt class="LITERAL"><a href=
988               "actions-file.html#SERVER-HEADER-FILTER">server-header filter</a></tt>. It allows you to activate it for
989               every document of a certain site and it will still only replace the content types you aimed at.</p>
990               <p>Of course you can apply <tt class="LITERAL">content-type-overwrite</tt> to a whole site and then make
991               URL based exceptions, but it's a lot more work to get the same precision.</p>
992             </dd>
993             <dt>Example usage (sections):</dt>
994             <dd>
995               <table border="0" bgcolor="#E0E0E0" width="90%">
996                 <tr>
997                   <td>
998                     <pre class="SCREEN"># Check if www.example.net/ really uses valid XHTML
999 { +content-type-overwrite{application/xml} }
1000 www.example.net/
1001
1002 # but leave the content type unmodified if the URL looks like a style sheet
1003 {-content-type-overwrite}
1004 www.example.net/.*\.css$
1005 www.example.net/.*style</pre>
1006                   </td>
1007                 </tr>
1008               </table>
1009             </dd>
1010           </dl>
1011         </div>
1012       </div>
1013       <div class="SECT3">
1014         <h4 class="SECT3"><a name="CRUNCH-CLIENT-HEADER" id="CRUNCH-CLIENT-HEADER">8.5.7. crunch-client-header</a></h4>
1015         <div class="VARIABLELIST">
1016           <dl>
1017             <dt>Typical use:</dt>
1018             <dd>
1019               <p>Remove a client header <span class="APPLICATION">Privoxy</span> has no dedicated action for.</p>
1020             </dd>
1021             <dt>Effect:</dt>
1022             <dd>
1023               <p>Deletes every header sent by the client that contains the string the user supplied as parameter.</p>
1024             </dd>
1025             <dt>Type:</dt>
1026             <dd>
1027               <p>Parameterized.</p>
1028             </dd>
1029             <dt>Parameter:</dt>
1030             <dd>
1031               <p>Any string.</p>
1032             </dd>
1033             <dt>Notes:</dt>
1034             <dd>
1035               <p>This action allows you to block client headers for which no dedicated <span class=
1036               "APPLICATION">Privoxy</span> action exists. <span class="APPLICATION">Privoxy</span> will remove every
1037               client header that contains the string you supplied as parameter.</p>
1038               <p>Regular expressions are <span class="emphasis"><i class="EMPHASIS">not supported</i></span> and you
1039               can't use this action to block different headers in the same request, unless they contain the same
1040               string.</p>
1041               <p><tt class="LITERAL">crunch-client-header</tt> is only meant for quick tests. If you have to block
1042               several different headers, or only want to modify parts of them, you should use a <tt class=
1043               "LITERAL"><a href="actions-file.html#CLIENT-HEADER-FILTER">client-header filter</a></tt>.</p>
1044               <div class="WARNING">
1045                 <table class="WARNING" border="1" width="90%">
1046                   <tr>
1047                     <td align="center"><b>Warning</b></td>
1048                   </tr>
1049                   <tr>
1050                     <td align="left">
1051                       <p>Don't block any header without understanding the consequences.</p>
1052                     </td>
1053                   </tr>
1054                 </table>
1055               </div>
1056             </dd>
1057             <dt>Example usage (section):</dt>
1058             <dd>
1059               <table border="0" bgcolor="#E0E0E0" width="90%">
1060                 <tr>
1061                   <td>
1062                     <pre class="SCREEN"># Block the non-existent "Privacy-Violation:" client header
1063 { +crunch-client-header{Privacy-Violation:} }
1064 /</pre>
1065                   </td>
1066                 </tr>
1067               </table>
1068             </dd>
1069           </dl>
1070         </div>
1071       </div>
1072       <div class="SECT3">
1073         <h4 class="SECT3"><a name="CRUNCH-IF-NONE-MATCH" id="CRUNCH-IF-NONE-MATCH">8.5.8. crunch-if-none-match</a></h4>
1074         <div class="VARIABLELIST">
1075           <dl>
1076             <dt>Typical use:</dt>
1077             <dd>
1078               <p>Prevent yet another way to track the user's steps between sessions.</p>
1079             </dd>
1080             <dt>Effect:</dt>
1081             <dd>
1082               <p>Deletes the <span class="QUOTE">"If-None-Match:"</span> HTTP client header.</p>
1083             </dd>
1084             <dt>Type:</dt>
1085             <dd>
1086               <p>Boolean.</p>
1087             </dd>
1088             <dt>Parameter:</dt>
1089             <dd>
1090               <p>N/A</p>
1091             </dd>
1092             <dt>Notes:</dt>
1093             <dd>
1094               <p>Removing the <span class="QUOTE">"If-None-Match:"</span> HTTP client header is useful for filter
1095               testing, where you want to force a real reload instead of getting status code <span class=
1096               "QUOTE">"304"</span> which would cause the browser to use a cached copy of the page.</p>
1097               <p>It is also useful to make sure the header isn't used as a cookie replacement (unlikely but
1098               possible).</p>
1099               <p>Blocking the <span class="QUOTE">"If-None-Match:"</span> header shouldn't cause any caching problems,
1100               as long as the <span class="QUOTE">"If-Modified-Since:"</span> header isn't blocked or missing as
1101               well.</p>
1102               <p>It is recommended to use this action together with <tt class="LITERAL"><a href=
1103               "actions-file.html#HIDE-IF-MODIFIED-SINCE">hide-if-modified-since</a></tt> and <tt class=
1104               "LITERAL"><a href="actions-file.html#OVERWRITE-LAST-MODIFIED">overwrite-last-modified</a></tt>.</p>
1105             </dd>
1106             <dt>Example usage (section):</dt>
1107             <dd>
1108               <table border="0" bgcolor="#E0E0E0" width="90%">
1109                 <tr>
1110                   <td>
1111                     <pre class="SCREEN"># Let the browser revalidate cached documents but don't
1112 # allow the server to use the revalidation headers for user tracking.
1113 {+hide-if-modified-since{-60} \
1114  +overwrite-last-modified{randomize} \
1115  +crunch-if-none-match}
1116 /</pre>
1117                   </td>
1118                 </tr>
1119               </table>
1120             </dd>
1121           </dl>
1122         </div>
1123       </div>
1124       <div class="SECT3">
1125         <h4 class="SECT3"><a name="CRUNCH-INCOMING-COOKIES" id="CRUNCH-INCOMING-COOKIES">8.5.9.
1126         crunch-incoming-cookies</a></h4>
1127         <div class="VARIABLELIST">
1128           <dl>
1129             <dt>Typical use:</dt>
1130             <dd>
1131               <p>Prevent the web server from setting HTTP cookies on your system</p>
1132             </dd>
1133             <dt>Effect:</dt>
1134             <dd>
1135               <p>Deletes any <span class="QUOTE">"Set-Cookie:"</span> HTTP headers from server replies.</p>
1136             </dd>
1137             <dt>Type:</dt>
1138             <dd>
1139               <p>Boolean.</p>
1140             </dd>
1141             <dt>Parameter:</dt>
1142             <dd>
1143               <p>N/A</p>
1144             </dd>
1145             <dt>Notes:</dt>
1146             <dd>
1147               <p>This action is only concerned with <span class="emphasis"><i class="EMPHASIS">incoming</i></span> HTTP
1148               cookies. For <span class="emphasis"><i class="EMPHASIS">outgoing</i></span> HTTP cookies, use <tt class=
1149               "LITERAL"><a href="actions-file.html#CRUNCH-OUTGOING-COOKIES">crunch-outgoing-cookies</a></tt>. Use
1150               <span class="emphasis"><i class="EMPHASIS">both</i></span> to disable HTTP cookies completely.</p>
1151               <p>It makes <span class="emphasis"><i class="EMPHASIS">no sense at all</i></span> to use this action in
1152               conjunction with the <tt class="LITERAL"><a href=
1153               "actions-file.html#SESSION-COOKIES-ONLY">session-cookies-only</a></tt> action, since it would prevent the
1154               session cookies from being set. See also <tt class="LITERAL"><a href=
1155               "actions-file.html#FILTER-CONTENT-COOKIES">filter-content-cookies</a></tt>.</p>
1156             </dd>
1157             <dt>Example usage:</dt>
1158             <dd>
1159               <table border="0" bgcolor="#E0E0E0" width="90%">
1160                 <tr>
1161                   <td>
1162                     <pre class="SCREEN">+crunch-incoming-cookies</pre>
1163                   </td>
1164                 </tr>
1165               </table>
1166             </dd>
1167           </dl>
1168         </div>
1169       </div>
1170       <div class="SECT3">
1171         <h4 class="SECT3"><a name="CRUNCH-SERVER-HEADER" id="CRUNCH-SERVER-HEADER">8.5.10.
1172         crunch-server-header</a></h4>
1173         <div class="VARIABLELIST">
1174           <dl>
1175             <dt>Typical use:</dt>
1176             <dd>
1177               <p>Remove a server header <span class="APPLICATION">Privoxy</span> has no dedicated action for.</p>
1178             </dd>
1179             <dt>Effect:</dt>
1180             <dd>
1181               <p>Deletes every header sent by the server that contains the string the user supplied as parameter.</p>
1182             </dd>
1183             <dt>Type:</dt>
1184             <dd>
1185               <p>Parameterized.</p>
1186             </dd>
1187             <dt>Parameter:</dt>
1188             <dd>
1189               <p>Any string.</p>
1190             </dd>
1191             <dt>Notes:</dt>
1192             <dd>
1193               <p>This action allows you to block server headers for which no dedicated <span class=
1194               "APPLICATION">Privoxy</span> action exists. <span class="APPLICATION">Privoxy</span> will remove every
1195               server header that contains the string you supplied as parameter.</p>
1196               <p>Regular expressions are <span class="emphasis"><i class="EMPHASIS">not supported</i></span> and you
1197               can't use this action to block different headers in the same request, unless they contain the same
1198               string.</p>
1199               <p><tt class="LITERAL">crunch-server-header</tt> is only meant for quick tests. If you have to block
1200               several different headers, or only want to modify parts of them, you should use a custom <tt class=
1201               "LITERAL"><a href="actions-file.html#SERVER-HEADER-FILTER">server-header filter</a></tt>.</p>
1202               <div class="WARNING">
1203                 <table class="WARNING" border="1" width="90%">
1204                   <tr>
1205                     <td align="center"><b>Warning</b></td>
1206                   </tr>
1207                   <tr>
1208                     <td align="left">
1209                       <p>Don't block any header without understanding the consequences.</p>
1210                     </td>
1211                   </tr>
1212                 </table>
1213               </div>
1214             </dd>
1215             <dt>Example usage (section):</dt>
1216             <dd>
1217               <table border="0" bgcolor="#E0E0E0" width="90%">
1218                 <tr>
1219                   <td>
1220                     <pre class="SCREEN"># Crunch server headers that try to prevent caching
1221 { +crunch-server-header{no-cache} }
1222 /</pre>
1223                   </td>
1224                 </tr>
1225               </table>
1226             </dd>
1227           </dl>
1228         </div>
1229       </div>
1230       <div class="SECT3">
1231         <h4 class="SECT3"><a name="CRUNCH-OUTGOING-COOKIES" id="CRUNCH-OUTGOING-COOKIES">8.5.11.
1232         crunch-outgoing-cookies</a></h4>
1233         <div class="VARIABLELIST">
1234           <dl>
1235             <dt>Typical use:</dt>
1236             <dd>
1237               <p>Prevent the web server from reading any HTTP cookies from your system</p>
1238             </dd>
1239             <dt>Effect:</dt>
1240             <dd>
1241               <p>Deletes any <span class="QUOTE">"Cookie:"</span> HTTP headers from client requests.</p>
1242             </dd>
1243             <dt>Type:</dt>
1244             <dd>
1245               <p>Boolean.</p>
1246             </dd>
1247             <dt>Parameter:</dt>
1248             <dd>
1249               <p>N/A</p>
1250             </dd>
1251             <dt>Notes:</dt>
1252             <dd>
1253               <p>This action is only concerned with <span class="emphasis"><i class="EMPHASIS">outgoing</i></span> HTTP
1254               cookies. For <span class="emphasis"><i class="EMPHASIS">incoming</i></span> HTTP cookies, use <tt class=
1255               "LITERAL"><a href="actions-file.html#CRUNCH-INCOMING-COOKIES">crunch-incoming-cookies</a></tt>. Use
1256               <span class="emphasis"><i class="EMPHASIS">both</i></span> to disable HTTP cookies completely.</p>
1257               <p>It makes <span class="emphasis"><i class="EMPHASIS">no sense at all</i></span> to use this action in
1258               conjunction with the <tt class="LITERAL"><a href=
1259               "actions-file.html#SESSION-COOKIES-ONLY">session-cookies-only</a></tt> action, since it would prevent the
1260               session cookies from being read.</p>
1261             </dd>
1262             <dt>Example usage:</dt>
1263             <dd>
1264               <table border="0" bgcolor="#E0E0E0" width="90%">
1265                 <tr>
1266                   <td>
1267                     <pre class="SCREEN">+crunch-outgoing-cookies</pre>
1268                   </td>
1269                 </tr>
1270               </table>
1271             </dd>
1272           </dl>
1273         </div>
1274       </div>
1275       <div class="SECT3">
1276         <h4 class="SECT3"><a name="DEANIMATE-GIFS" id="DEANIMATE-GIFS">8.5.12. deanimate-gifs</a></h4>
1277         <div class="VARIABLELIST">
1278           <dl>
1279             <dt>Typical use:</dt>
1280             <dd>
1281               <p>Stop those annoying, distracting animated GIF images.</p>
1282             </dd>
1283             <dt>Effect:</dt>
1284             <dd>
1285               <p>De-animate GIF animations, i.e. reduce them to their first or last image.</p>
1286             </dd>
1287             <dt>Type:</dt>
1288             <dd>
1289               <p>Parameterized.</p>
1290             </dd>
1291             <dt>Parameter:</dt>
1292             <dd>
1293               <p><span class="QUOTE">"last"</span> or <span class="QUOTE">"first"</span></p>
1294             </dd>
1295             <dt>Notes:</dt>
1296             <dd>
1297               <p>This will also shrink the images considerably (in bytes, not pixels!). If the option <span class=
1298               "QUOTE">"first"</span> is given, the first frame of the animation is used as the replacement. If
1299               <span class="QUOTE">"last"</span> is given, the last frame of the animation is used instead, which
1300               probably makes more sense for most banner animations, but also has the risk of not showing the entire
1301               last frame (if it is only a delta to an earlier frame).</p>
1302               <p>You can safely use this action with patterns that will also match non-GIF objects, because no attempt
1303               will be made at anything that doesn't look like a GIF.</p>
1304             </dd>
1305             <dt>Example usage:</dt>
1306             <dd>
1307               <table border="0" bgcolor="#E0E0E0" width="90%">
1308                 <tr>
1309                   <td>
1310                     <pre class="SCREEN">+deanimate-gifs{last}</pre>
1311                   </td>
1312                 </tr>
1313               </table>
1314             </dd>
1315           </dl>
1316         </div>
1317       </div>
1318       <div class="SECT3">
1319         <h4 class="SECT3"><a name="DELAY-RESPONSE" id="DELAY-RESPONSE">8.5.13. delay-response</a></h4>
1320         <div class="VARIABLELIST">
1321           <dl>
1322             <dt>Typical use:</dt>
1323             <dd>
1324               <p>Delay responses to the client to reduce the load</p>
1325             </dd>
1326             <dt>Effect:</dt>
1327             <dd>
1328               <p>Delays responses to the client by sending the response in ca. 10 byte chunks.</p>
1329             </dd>
1330             <dt>Type:</dt>
1331             <dd>
1332               <p>Parameterized.</p>
1333             </dd>
1334             <dt>Parameter:</dt>
1335             <dd>
1336               <p><span class="QUOTE">"Number of milliseconds"</span></p>
1337             </dd>
1338             <dt>Notes:</dt>
1339             <dd>
1340               <p>Sometimes when JavaScript code is used to fetch advertisements it doesn't respect Privoxy's blocks and
1341               retries to fetch the same resource again causing unnecessary load on the client.</p>
1342               <p>This action delays responses to the client and can be combined with <tt class="LITERAL"><a href=
1343               "actions-file.html#BLOCK">blocks</a></tt> to slow down the JavaScript code, thus reducing the load on the
1344               client.</p>
1345               <p>When used without <tt class="LITERAL"><a href="actions-file.html#BLOCK">blocks</a></tt> the action can
1346               also be used to simulate a slow internet connection.</p>
1347             </dd>
1348             <dt>Example usage:</dt>
1349             <dd>
1350               <table border="0" bgcolor="#E0E0E0" width="90%">
1351                 <tr>
1352                   <td>
1353                     <pre class="SCREEN">+delay-response{100}</pre>
1354                   </td>
1355                 </tr>
1356               </table>
1357             </dd>
1358           </dl>
1359         </div>
1360       </div>
1361       <div class="SECT3">
1362         <h4 class="SECT3"><a name="DOWNGRADE-HTTP-VERSION" id="DOWNGRADE-HTTP-VERSION">8.5.14.
1363         downgrade-http-version</a></h4>
1364         <div class="VARIABLELIST">
1365           <dl>
1366             <dt>Typical use:</dt>
1367             <dd>
1368               <p>Work around (very rare) problems with HTTP/1.1</p>
1369             </dd>
1370             <dt>Effect:</dt>
1371             <dd>
1372               <p>Downgrades HTTP/1.1 client requests and server replies to HTTP/1.0.</p>
1373             </dd>
1374             <dt>Type:</dt>
1375             <dd>
1376               <p>Boolean.</p>
1377             </dd>
1378             <dt>Parameter:</dt>
1379             <dd>
1380               <p>N/A</p>
1381             </dd>
1382             <dt>Notes:</dt>
1383             <dd>
1384               <p>This is a left-over from the time when <span class="APPLICATION">Privoxy</span> didn't support
1385               important HTTP/1.1 features well. It is left here for the unlikely case that you experience
1386               HTTP/1.1-related problems with some server out there.</p>
1387               <p>Note that enabling this action is only a workaround. It should not be enabled for sites that work
1388               without it. While it shouldn't break any pages, it has an (usually negative) performance impact.</p>
1389               <p>If you come across a site where enabling this action helps, please report it, so the cause of the
1390               problem can be analyzed. If the problem turns out to be caused by a bug in <span class=
1391               "APPLICATION">Privoxy</span> it should be fixed so the following release works without the work
1392               around.</p>
1393             </dd>
1394             <dt>Example usage (section):</dt>
1395             <dd>
1396               <table border="0" bgcolor="#E0E0E0" width="90%">
1397                 <tr>
1398                   <td>
1399                     <pre class="SCREEN">{+downgrade-http-version}
1400 problem-host.example.com</pre>
1401                   </td>
1402                 </tr>
1403               </table>
1404             </dd>
1405           </dl>
1406         </div>
1407       </div>
1408       <div class="SECT3">
1409         <h4 class="SECT3"><a name="EXTERNAL-FILTER" id="EXTERNAL-FILTER">8.5.15. external-filter</a></h4>
1410         <div class="VARIABLELIST">
1411           <dl>
1412             <dt>Typical use:</dt>
1413             <dd>
1414               <p>Modify content using a programming language of your choice.</p>
1415             </dd>
1416             <dt>Effect:</dt>
1417             <dd>
1418               <p>All instances of text-based type, most notably HTML and JavaScript, to which this action applies, can
1419               be filtered on-the-fly through the specified external filter. By default plain text documents are
1420               exempted from filtering, because web servers often use the <tt class="LITERAL">text/plain</tt> MIME type
1421               for all files whose type they don't know.)</p>
1422             </dd>
1423             <dt>Type:</dt>
1424             <dd>
1425               <p>Multi-value.</p>
1426             </dd>
1427             <dt>Parameter:</dt>
1428             <dd>
1429               <p>The name of an external content filter, as defined in the <a href="filter-file.html">filter file</a>.
1430               External filters can be defined in one or more files as defined by the <tt class="LITERAL"><a href=
1431               "config.html#FILTERFILE">filterfile</a></tt> option in the <a href="config.html">config file</a>.</p>
1432               <p>When used in its negative form, and without parameters, <span class="emphasis"><i class=
1433               "EMPHASIS">all</i></span> filtering with external filters is completely disabled.</p>
1434             </dd>
1435             <dt>Notes:</dt>
1436             <dd>
1437               <p>External filters are scripts or programs that can modify the content in case common <tt class=
1438               "LITERAL"><a href="actions-file.html#FILTER">filters</a></tt> aren't powerful enough. With the exception
1439               that this action doesn't use pcrs-based filters, the notes in the <tt class="LITERAL"><a href=
1440               "actions-file.html#FILTER">filter</a></tt> section apply.</p>
1441               <div class="WARNING">
1442                 <table class="WARNING" border="1" width="90%">
1443                   <tr>
1444                     <td align="center"><b>Warning</b></td>
1445                   </tr>
1446                   <tr>
1447                     <td align="left">
1448                       <p>Currently external filters are executed with <span class="APPLICATION">Privoxy</span>'s
1449                       privileges. Only use external filters you understand and trust.</p>
1450                     </td>
1451                   </tr>
1452                 </table>
1453               </div>
1454               <p>This feature is experimental, the <tt class="LITERAL"><a href=
1455               "filter-file.html#EXTERNAL-FILTER-SYNTAX">syntax</a></tt> may change in the future.</p>
1456             </dd>
1457             <dt>Example usage:</dt>
1458             <dd>
1459               <table border="0" bgcolor="#E0E0E0" width="90%">
1460                 <tr>
1461                   <td>
1462                     <pre class="SCREEN">+external-filter{fancy-filter}</pre>
1463                   </td>
1464                 </tr>
1465               </table>
1466             </dd>
1467           </dl>
1468         </div>
1469       </div>
1470       <div class="SECT3">
1471         <h4 class="SECT3"><a name="FAST-REDIRECTS" id="FAST-REDIRECTS">8.5.16. fast-redirects</a></h4>
1472         <div class="VARIABLELIST">
1473           <dl>
1474             <dt>Typical use:</dt>
1475             <dd>
1476               <p>Fool some click-tracking scripts and speed up indirect links.</p>
1477             </dd>
1478             <dt>Effect:</dt>
1479             <dd>
1480               <p>Detects redirection URLs and redirects the browser without contacting the redirection server
1481               first.</p>
1482             </dd>
1483             <dt>Type:</dt>
1484             <dd>
1485               <p>Parameterized.</p>
1486             </dd>
1487             <dt>Parameter:</dt>
1488             <dd>
1489               <ul>
1490                 <li>
1491                   <p><span class="QUOTE">"simple-check"</span> to just search for the string <span class=
1492                   "QUOTE">"http://"</span> to detect redirection URLs.</p>
1493                 </li>
1494                 <li>
1495                   <p><span class="QUOTE">"check-decoded-url"</span> to decode URLs (if necessary) before searching for
1496                   redirection URLs.</p>
1497                 </li>
1498               </ul>
1499             </dd>
1500             <dt>Notes:</dt>
1501             <dd>
1502               <p>Many sites, like yahoo.com, don't just link to other sites. Instead, they will link to some script on
1503               their own servers, giving the destination as a parameter, which will then redirect you to the final
1504               target. URLs resulting from this scheme typically look like: <span class=
1505               "QUOTE">"http://www.example.org/click-tracker.cgi?target=http%3a//www.example.net/"</span>.</p>
1506               <p>Sometimes, there are even multiple consecutive redirects encoded in the URL. These redirections via
1507               scripts make your web browsing more traceable, since the server from which you follow such a link can see
1508               where you go to. Apart from that, valuable bandwidth and time is wasted, while your browser asks the
1509               server for one redirect after the other. Plus, it feeds the advertisers.</p>
1510               <p>This feature is currently not very smart and is scheduled for improvement. If it is enabled by
1511               default, you will have to create some exceptions to this action. It can lead to failures in several
1512               ways:</p>
1513               <p>Not every URLs with other URLs as parameters is evil. Some sites offer a real service that requires
1514               this information to work. For example a validation service needs to know, which document to validate.
1515               <tt class="LITERAL">fast-redirects</tt> assumes that every URL parameter that looks like another URL is a
1516               redirection target, and will always redirect to the last one. Most of the time the assumption is correct,
1517               but if it isn't, the user gets redirected anyway.</p>
1518               <p>Another failure occurs if the URL contains other parameters after the URL parameter. The URL:
1519               <span class="QUOTE">"http://www.example.org/?redirect=http%3a//www.example.net/&amp;foo=bar"</span>.
1520               contains the redirection URL <span class="QUOTE">"http://www.example.net/"</span>, followed by another
1521               parameter. <tt class="LITERAL">fast-redirects</tt> doesn't know that and will cause a redirect to
1522               <span class="QUOTE">"http://www.example.net/&amp;foo=bar"</span>. Depending on the target server
1523               configuration, the parameter will be silently ignored or lead to a <span class="QUOTE">"page not
1524               found"</span> error. You can prevent this problem by first using the <tt class="LITERAL"><a href=
1525               "actions-file.html#REDIRECT">redirect</a></tt> action to remove the last part of the URL, but it requires
1526               a little effort.</p>
1527               <p>To detect a redirection URL, <tt class="LITERAL">fast-redirects</tt> only looks for the string
1528               <span class="QUOTE">"http://"</span>, either in plain text (invalid but often used) or encoded as
1529               <span class="QUOTE">"http%3a//"</span>. Some sites use their own URL encoding scheme, encrypt the address
1530               of the target server or replace it with a database id. In these cases <tt class=
1531               "LITERAL">fast-redirects</tt> is fooled and the request reaches the redirection server where it probably
1532               gets logged.</p>
1533             </dd>
1534             <dt>Example usage:</dt>
1535             <dd>
1536               <table border="0" bgcolor="#E0E0E0" width="90%">
1537                 <tr>
1538                   <td>
1539                     <pre class="SCREEN"> { +fast-redirects{simple-check} }
1540    one.example.com
1541
1542  { +fast-redirects{check-decoded-url} }
1543    another.example.com/testing</pre>
1544                   </td>
1545                 </tr>
1546               </table>
1547             </dd>
1548           </dl>
1549         </div>
1550       </div>
1551       <div class="SECT3">
1552         <h4 class="SECT3"><a name="FILTER" id="FILTER">8.5.17. filter</a></h4>
1553         <div class="VARIABLELIST">
1554           <dl>
1555             <dt>Typical use:</dt>
1556             <dd>
1557               <p>Get rid of HTML and JavaScript annoyances, banner advertisements (by size), do fun text replacements,
1558               add personalized effects, etc.</p>
1559             </dd>
1560             <dt>Effect:</dt>
1561             <dd>
1562               <p>All instances of text-based type, most notably HTML and JavaScript, to which this action applies, can
1563               be filtered on-the-fly through the specified regular expression based substitutions. (Note: as of version
1564               3.0.3 plain text documents are exempted from filtering, because web servers often use the <tt class=
1565               "LITERAL">text/plain</tt> MIME type for all files whose type they don't know.)</p>
1566             </dd>
1567             <dt>Type:</dt>
1568             <dd>
1569               <p>Multi-value.</p>
1570             </dd>
1571             <dt>Parameter:</dt>
1572             <dd>
1573               <p>The name of a content filter, as defined in the <a href="filter-file.html">filter file</a>. Filters
1574               can be defined in one or more files as defined by the <tt class="LITERAL"><a href=
1575               "config.html#FILTERFILE">filterfile</a></tt> option in the <a href="config.html">config file</a>.
1576               <tt class="FILENAME">default.filter</tt> is the collection of filters supplied by the developers. Locally
1577               defined filters should go in their own file, such as <tt class="FILENAME">user.filter</tt>.</p>
1578               <p>When used in its negative form, and without parameters, <span class="emphasis"><i class=
1579               "EMPHASIS">all</i></span> filtering is completely disabled.</p>
1580             </dd>
1581             <dt>Notes:</dt>
1582             <dd>
1583               <p>For your convenience, there are a number of pre-defined filters available in the distribution filter
1584               file that you can use. See the examples below for a list.</p>
1585               <p>Filtering requires buffering the page content, which may appear to slow down page rendering since
1586               nothing is displayed until all content has passed the filters. (The total time until the page is
1587               completely rendered doesn't change much, but it may be perceived as slower since the page is not
1588               incrementally displayed.) This effect will be more noticeable on slower connections.</p>
1589               <p><span class="QUOTE">"Rolling your own"</span> filters requires a knowledge of <a href=
1590               "http://en.wikipedia.org/wiki/Regular_expressions" target="_top"><span class="QUOTE">"Regular
1591               Expressions"</span></a> and <a href="http://en.wikipedia.org/wiki/Html" target="_top"><span class=
1592               "QUOTE">"HTML"</span></a>. This is very powerful feature, and potentially very intrusive. Filters should
1593               be used with caution, and where an equivalent <span class="QUOTE">"action"</span> is not available.</p>
1594               <p>The amount of data that can be filtered is limited to the <tt class="LITERAL"><a href=
1595               "config.html#BUFFER-LIMIT">buffer-limit</a></tt> option in the main <a href="config.html">config
1596               file</a>. The default is 4096 KB (4 Megs). Once this limit is exceeded, the buffered data, and all
1597               pending data, is passed through unfiltered.</p>
1598               <p>Inappropriate MIME types, such as zipped files, are not filtered at all. (Again, only text-based types
1599               except plain text). Encrypted SSL data (from HTTPS servers) cannot be filtered either, since this would
1600               violate the integrity of the secure transaction. In some situations it might be necessary to protect
1601               certain text, like source code, from filtering by defining appropriate <tt class="LITERAL">-filter</tt>
1602               exceptions.</p>
1603               <p>Compressed content can't be filtered either, but if <span class="APPLICATION">Privoxy</span> is
1604               compiled with zlib support and a supported compression algorithm is used (gzip or deflate), <span class=
1605               "APPLICATION">Privoxy</span> can first decompress the content and then filter it.</p>
1606               <p>If you use a <span class="APPLICATION">Privoxy</span> version without zlib support, but want filtering
1607               to work on as much documents as possible, even those that would normally be sent compressed, you must use
1608               the <tt class="LITERAL"><a href="actions-file.html#PREVENT-COMPRESSION">prevent-compression</a></tt>
1609               action in conjunction with <tt class="LITERAL">filter</tt>.</p>
1610               <p>Content filtering can achieve some of the same effects as the <tt class="LITERAL"><a href=
1611               "actions-file.html#BLOCK">block</a></tt> action, i.e. it can be used to block ads and banners. But the
1612               mechanism works quite differently. One effective use, is to block ad banners based on their size (see
1613               below), since many of these seem to be somewhat standardized.</p>
1614               <p><a href="contact.html">Feedback</a> with suggestions for new or improved filters is particularly
1615               welcome!</p>
1616               <p>The below list has only the names and a one-line description of each predefined filter. There are
1617               <a href="filter-file.html#PREDEFINED-FILTERS">more verbose explanations</a> of what these filters do in
1618               the <a href="filter-file.html">filter file chapter</a>.</p>
1619             </dd>
1620             <dt>Example usage (with filters from the distribution <tt class="FILENAME">default.filter</tt> file). See
1621             <a href="filter-file.html#PREDEFINED-FILTERS">the Predefined Filters section</a> for more explanation on
1622             each:</dt>
1623             <dd>
1624               <p><a name="FILTER-JS-ANNOYANCES" id="FILTER-JS-ANNOYANCES"></a></p>
1625               <table border="0" bgcolor="#E0E0E0" width="90%">
1626                 <tr>
1627                   <td>
1628                     <pre class=
1629                     "SCREEN">+filter{js-annoyances}       # Get rid of particularly annoying JavaScript abuse.</pre>
1630                   </td>
1631                 </tr>
1632               </table>
1633               <p><a name="FILTER-JS-EVENTS" id="FILTER-JS-EVENTS"></a></p>
1634               <table border="0" bgcolor="#E0E0E0" width="90%">
1635                 <tr>
1636                   <td>
1637                     <pre class=
1638                     "SCREEN">+filter{js-events}           # Kill JavaScript event bindings and timers (Radically destructive! Only for extra nasty sites).</pre>
1639                   </td>
1640                 </tr>
1641               </table>
1642               <p><a name="FILTER-HTML-ANNOYANCES" id="FILTER-HTML-ANNOYANCES"></a></p>
1643               <table border="0" bgcolor="#E0E0E0" width="90%">
1644                 <tr>
1645                   <td>
1646                     <pre class=
1647                     "SCREEN">+filter{html-annoyances}     # Get rid of particularly annoying HTML abuse.</pre>
1648                   </td>
1649                 </tr>
1650               </table>
1651               <p><a name="FILTER-CONTENT-COOKIES" id="FILTER-CONTENT-COOKIES"></a></p>
1652               <table border="0" bgcolor="#E0E0E0" width="90%">
1653                 <tr>
1654                   <td>
1655                     <pre class=
1656                     "SCREEN">+filter{content-cookies}     # Kill cookies that come in the HTML or JS content.</pre>
1657                   </td>
1658                 </tr>
1659               </table>
1660               <p><a name="FILTER-REFRESH-TAGS" id="FILTER-REFRESH-TAGS"></a></p>
1661               <table border="0" bgcolor="#E0E0E0" width="90%">
1662                 <tr>
1663                   <td>
1664                     <pre class=
1665                     "SCREEN">+filter{refresh-tags}        # Kill automatic refresh tags if refresh time is larger than 9 seconds.</pre>
1666                   </td>
1667                 </tr>
1668               </table>
1669               <p><a name="FILTER-UNSOLICITED-POPUPS" id="FILTER-UNSOLICITED-POPUPS"></a></p>
1670               <table border="0" bgcolor="#E0E0E0" width="90%">
1671                 <tr>
1672                   <td>
1673                     <pre class="SCREEN">+filter{unsolicited-popups}  # Disable only unsolicited pop-up windows.</pre>
1674                   </td>
1675                 </tr>
1676               </table>
1677               <p><a name="FILTER-ALL-POPUPS" id="FILTER-ALL-POPUPS"></a></p>
1678               <table border="0" bgcolor="#E0E0E0" width="90%">
1679                 <tr>
1680                   <td>
1681                     <pre class="SCREEN">+filter{all-popups}          # Kill all popups in JavaScript and HTML.</pre>
1682                   </td>
1683                 </tr>
1684               </table>
1685               <p><a name="FILTER-IMG-REORDER" id="FILTER-IMG-REORDER"></a></p>
1686               <table border="0" bgcolor="#E0E0E0" width="90%">
1687                 <tr>
1688                   <td>
1689                     <pre class=
1690                     "SCREEN">+filter{img-reorder}         # Reorder attributes in &lt;img&gt; tags to make the banners-by-* filters more effective.</pre>
1691                   </td>
1692                 </tr>
1693               </table>
1694               <p><a name="FILTER-BANNERS-BY-SIZE" id="FILTER-BANNERS-BY-SIZE"></a></p>
1695               <table border="0" bgcolor="#E0E0E0" width="90%">
1696                 <tr>
1697                   <td>
1698                     <pre class="SCREEN">+filter{banners-by-size}     # Kill banners by size.</pre>
1699                   </td>
1700                 </tr>
1701               </table>
1702               <p><a name="FILTER-BANNERS-BY-LINK" id="FILTER-BANNERS-BY-LINK"></a></p>
1703               <table border="0" bgcolor="#E0E0E0" width="90%">
1704                 <tr>
1705                   <td>
1706                     <pre class=
1707                     "SCREEN">+filter{banners-by-link}     # Kill banners by their links to known clicktrackers.</pre>
1708                   </td>
1709                 </tr>
1710               </table>
1711               <p><a name="FILTER-WEBBUGS" id="FILTER-WEBBUGS"></a></p>
1712               <table border="0" bgcolor="#E0E0E0" width="90%">
1713                 <tr>
1714                   <td>
1715                     <pre class=
1716                     "SCREEN">+filter{webbugs}             # Squish WebBugs (1x1 invisible GIFs used for user tracking).</pre>
1717                   </td>
1718                 </tr>
1719               </table>
1720               <p><a name="FILTER-TINY-TEXTFORMS" id="FILTER-TINY-TEXTFORMS"></a></p>
1721               <table border="0" bgcolor="#E0E0E0" width="90%">
1722                 <tr>
1723                   <td>
1724                     <pre class=
1725                     "SCREEN">+filter{tiny-textforms}      # Extend those tiny textareas up to 40x80 and kill the hard wrap.</pre>
1726                   </td>
1727                 </tr>
1728               </table>
1729               <p><a name="FILTER-JUMPING-WINDOWS" id="FILTER-JUMPING-WINDOWS"></a></p>
1730               <table border="0" bgcolor="#E0E0E0" width="90%">
1731                 <tr>
1732                   <td>
1733                     <pre class=
1734                     "SCREEN">+filter{jumping-windows}     # Prevent windows from resizing and moving themselves.</pre>
1735                   </td>
1736                 </tr>
1737               </table>
1738               <p><a name="FILTER-FRAMESET-BORDERS" id="FILTER-FRAMESET-BORDERS"></a></p>
1739               <table border="0" bgcolor="#E0E0E0" width="90%">
1740                 <tr>
1741                   <td>
1742                     <pre class=
1743                     "SCREEN">+filter{frameset-borders}    # Give frames a border and make them resizable.</pre>
1744                   </td>
1745                 </tr>
1746               </table>
1747               <p><a name="FILTER-IFRAMES" id="FILTER-IFRAMES"></a></p>
1748               <table border="0" bgcolor="#E0E0E0" width="90%">
1749                 <tr>
1750                   <td>
1751                     <pre class=
1752                     "SCREEN">+filter{iframes}             # Removes all detected iframes. Should only be enabled for individual sites.</pre>
1753                   </td>
1754                 </tr>
1755               </table>
1756               <p><a name="FILTER-DEMORONIZER" id="FILTER-DEMORONIZER"></a></p>
1757               <table border="0" bgcolor="#E0E0E0" width="90%">
1758                 <tr>
1759                   <td>
1760                     <pre class=
1761                     "SCREEN">+filter{demoronizer}         # Fix MS's non-standard use of standard charsets.</pre>
1762                   </td>
1763                 </tr>
1764               </table>
1765               <p><a name="FILTER-SHOCKWAVE-FLASH" id="FILTER-SHOCKWAVE-FLASH"></a></p>
1766               <table border="0" bgcolor="#E0E0E0" width="90%">
1767                 <tr>
1768                   <td>
1769                     <pre class="SCREEN">+filter{shockwave-flash}     # Kill embedded Shockwave Flash objects.</pre>
1770                   </td>
1771                 </tr>
1772               </table>
1773               <p><a name="FILTER-QUICKTIME-KIOSKMODE" id="FILTER-QUICKTIME-KIOSKMODE"></a></p>
1774               <table border="0" bgcolor="#E0E0E0" width="90%">
1775                 <tr>
1776                   <td>
1777                     <pre class="SCREEN">+filter{quicktime-kioskmode} # Make Quicktime movies saveable.</pre>
1778                   </td>
1779                 </tr>
1780               </table>
1781               <p><a name="FILTER-FUN" id="FILTER-FUN"></a></p>
1782               <table border="0" bgcolor="#E0E0E0" width="90%">
1783                 <tr>
1784                   <td>
1785                     <pre class=
1786                     "SCREEN">+filter{fun}                 # Text replacements for subversive browsing fun!</pre>
1787                   </td>
1788                 </tr>
1789               </table>
1790               <p><a name="FILTER-CRUDE-PARENTAL" id="FILTER-CRUDE-PARENTAL"></a></p>
1791               <table border="0" bgcolor="#E0E0E0" width="90%">
1792                 <tr>
1793                   <td>
1794                     <pre class=
1795                     "SCREEN">+filter{crude-parental}      # Crude parental filtering. Note that this filter doesn't work reliably.</pre>
1796                   </td>
1797                 </tr>
1798               </table>
1799               <p><a name="FILTER-IE-EXPLOITS" id="FILTER-IE-EXPLOITS"></a></p>
1800               <table border="0" bgcolor="#E0E0E0" width="90%">
1801                 <tr>
1802                   <td>
1803                     <pre class=
1804                     "SCREEN">+filter{ie-exploits}         # Disable some known Internet Explorer bug exploits.</pre>
1805                   </td>
1806                 </tr>
1807               </table>
1808               <p><a name="FILTER-SITE-SPECIFICS" id="FILTER-SITE-SPECIFICS"></a></p>
1809               <table border="0" bgcolor="#E0E0E0" width="90%">
1810                 <tr>
1811                   <td>
1812                     <pre class=
1813                     "SCREEN">+filter{site-specifics}      # Cure for site-specific problems. Don't apply generally!</pre>
1814                   </td>
1815                 </tr>
1816               </table>
1817               <p><a name="FILTER-NO-PING" id="FILTER-NO-PING"></a></p>
1818               <table border="0" bgcolor="#E0E0E0" width="90%">
1819                 <tr>
1820                   <td>
1821                     <pre class=
1822                     "SCREEN">+filter{no-ping}             # Removes non-standard ping attributes in &lt;a&gt; and &lt;area&gt; tags.</pre>
1823                   </td>
1824                 </tr>
1825               </table>
1826               <p><a name="FILTER-GOOGLE" id="FILTER-GOOGLE"></a></p>
1827               <table border="0" bgcolor="#E0E0E0" width="90%">
1828                 <tr>
1829                   <td>
1830                     <pre class=
1831                     "SCREEN">+filter{google}              # CSS-based block for Google text ads. Also removes a width limitation and the toolbar advertisement.</pre>
1832                   </td>
1833                 </tr>
1834               </table>
1835               <p><a name="FILTER-YAHOO" id="FILTER-YAHOO"></a></p>
1836               <table border="0" bgcolor="#E0E0E0" width="90%">
1837                 <tr>
1838                   <td>
1839                     <pre class=
1840                     "SCREEN">+filter{yahoo}               # CSS-based block for Yahoo text ads. Also removes a width limitation.</pre>
1841                   </td>
1842                 </tr>
1843               </table>
1844               <p><a name="FILTER-MSN" id="FILTER-MSN"></a></p>
1845               <table border="0" bgcolor="#E0E0E0" width="90%">
1846                 <tr>
1847                   <td>
1848                     <pre class=
1849                     "SCREEN">+filter{msn}                 # CSS-based block for MSN text ads. Also removes tracking URLs and a width limitation.</pre>
1850                   </td>
1851                 </tr>
1852               </table>
1853               <p><a name="FILTER-BLOGSPOT" id="FILTER-BLOGSPOT"></a></p>
1854               <table border="0" bgcolor="#E0E0E0" width="90%">
1855                 <tr>
1856                   <td>
1857                     <pre class=
1858                     "SCREEN">+filter{blogspot}            # Cleans up some Blogspot blogs. Read the fine print before using this.</pre>
1859                   </td>
1860                 </tr>
1861               </table>
1862             </dd>
1863           </dl>
1864         </div>
1865       </div>
1866       <div class="SECT3">
1867         <h4 class="SECT3"><a name="FORCE-TEXT-MODE" id="FORCE-TEXT-MODE">8.5.18. force-text-mode</a></h4>
1868         <div class="VARIABLELIST">
1869           <dl>
1870             <dt>Typical use:</dt>
1871             <dd>
1872               <p>Force <span class="APPLICATION">Privoxy</span> to treat a document as if it was in some kind of
1873               <span class="emphasis"><i class="EMPHASIS">text</i></span> format.</p>
1874             </dd>
1875             <dt>Effect:</dt>
1876             <dd>
1877               <p>Declares a document as text, even if the <span class="QUOTE">"Content-Type:"</span> isn't detected as
1878               such.</p>
1879             </dd>
1880             <dt>Type:</dt>
1881             <dd>
1882               <p>Boolean.</p>
1883             </dd>
1884             <dt>Parameter:</dt>
1885             <dd>
1886               <p>N/A</p>
1887             </dd>
1888             <dt>Notes:</dt>
1889             <dd>
1890               <p>As explained <tt class="LITERAL"><a href="actions-file.html#FILTER">above</a></tt>, <span class=
1891               "APPLICATION">Privoxy</span> tries to only filter files that are in some kind of text format. The same
1892               restrictions apply to <tt class="LITERAL"><a href=
1893               "actions-file.html#CONTENT-TYPE-OVERWRITE">content-type-overwrite</a></tt>. <tt class=
1894               "LITERAL">force-text-mode</tt> declares a document as text, without looking at the <span class=
1895               "QUOTE">"Content-Type:"</span> first.</p>
1896               <div class="WARNING">
1897                 <table class="WARNING" border="1" width="90%">
1898                   <tr>
1899                     <td align="center"><b>Warning</b></td>
1900                   </tr>
1901                   <tr>
1902                     <td align="left">
1903                       <p>Think twice before activating this action. Filtering binary data with regular expressions can
1904                       cause file damage.</p>
1905                     </td>
1906                   </tr>
1907                 </table>
1908               </div>
1909             </dd>
1910             <dt>Example usage:</dt>
1911             <dd>
1912               <table border="0" bgcolor="#E0E0E0" width="90%">
1913                 <tr>
1914                   <td>
1915                     <pre class="SCREEN">+force-text-mode</pre>
1916                   </td>
1917                 </tr>
1918               </table>
1919             </dd>
1920           </dl>
1921         </div>
1922       </div>
1923       <div class="SECT3">
1924         <h4 class="SECT3"><a name="FORWARD-OVERRIDE" id="FORWARD-OVERRIDE">8.5.19. forward-override</a></h4>
1925         <div class="VARIABLELIST">
1926           <dl>
1927             <dt>Typical use:</dt>
1928             <dd>
1929               <p>Change the forwarding settings based on User-Agent or request origin</p>
1930             </dd>
1931             <dt>Effect:</dt>
1932             <dd>
1933               <p>Overrules the forward directives in the configuration file.</p>
1934             </dd>
1935             <dt>Type:</dt>
1936             <dd>
1937               <p>Parameterized.</p>
1938             </dd>
1939             <dt>Parameter:</dt>
1940             <dd>
1941               <ul>
1942                 <li>
1943                   <p><span class="QUOTE">"forward ."</span> to use a direct connection without any additional
1944                   proxies.</p>
1945                 </li>
1946                 <li>
1947                   <p><span class="QUOTE">"forward 127.0.0.1:8123"</span> to use the HTTP proxy listening at 127.0.0.1
1948                   port 8123.</p>
1949                 </li>
1950                 <li>
1951                   <p><span class="QUOTE">"forward-socks4a 127.0.0.1:9050 ."</span> to use the socks4a proxy listening
1952                   at 127.0.0.1 port 9050. Replace <span class="QUOTE">"forward-socks4a"</span> with <span class=
1953                   "QUOTE">"forward-socks4"</span> to use a socks4 connection (with local DNS resolution) instead, use
1954                   <span class="QUOTE">"forward-socks5"</span> for socks5 connections (with remote DNS resolution).</p>
1955                 </li>
1956                 <li>
1957                   <p><span class="QUOTE">"forward-socks4a 127.0.0.1:9050 proxy.example.org:8000"</span> to use the
1958                   socks4a proxy listening at 127.0.0.1 port 9050 to reach the HTTP proxy listening at proxy.example.org
1959                   port 8000. Replace <span class="QUOTE">"forward-socks4a"</span> with <span class=
1960                   "QUOTE">"forward-socks4"</span> to use a socks4 connection (with local DNS resolution) instead, use
1961                   <span class="QUOTE">"forward-socks5"</span> for socks5 connections (with remote DNS resolution).</p>
1962                 </li>
1963                 <li>
1964                   <p><span class="QUOTE">"forward-webserver 127.0.0.1:80"</span> to use the HTTP server listening at
1965                   127.0.0.1 port 80 without adjusting the request headers.</p>
1966                   <p>This makes it more convenient to use Privoxy to make existing websites available as onion services
1967                   as well.</p>
1968                   <p>Many websites serve content with hardcoded URLs and can't be easily adjusted to change the domain
1969                   based on the one used by the client.</p>
1970                   <p>Putting Privoxy between Tor and the webserver (or an stunnel that forwards to the webserver)
1971                   allows to rewrite headers and content to make client and server happy at the same time.</p>
1972                   <p>Using Privoxy for webservers that are only reachable through onion addresses and whose location is
1973                   supposed to be secret is not recommended and should not be necessary anyway.</p>
1974                 </li>
1975               </ul>
1976             </dd>
1977             <dt>Notes:</dt>
1978             <dd>
1979               <p>This action takes parameters similar to the <a href="config.html#FORWARDING">forward</a> directives in
1980               the configuration file, but without the URL pattern. It can be used as replacement, but normally it's
1981               only used in cases where matching based on the request URL isn't sufficient.</p>
1982               <div class="WARNING">
1983                 <table class="WARNING" border="1" width="90%">
1984                   <tr>
1985                     <td align="center"><b>Warning</b></td>
1986                   </tr>
1987                   <tr>
1988                     <td align="left">
1989                       <p>Please read the description for the <a href="config.html#FORWARDING">forward</a> directives
1990                       before using this action. Forwarding to the wrong people will reduce your privacy and increase
1991                       the chances of man-in-the-middle attacks.</p>
1992                       <p>If the ports are missing or invalid, default values will be used. This might change in the
1993                       future and you shouldn't rely on it. Otherwise incorrect syntax causes Privoxy to exit. Due to
1994                       design limitations, invalid parameter syntax isn't detected until the action is used the first
1995                       time.</p>
1996                       <p>Use the <a href="http://config.privoxy.org/show-url-info" target="_top">show-url-info CGI
1997                       page</a> to verify that your forward settings do what you thought the do.</p>
1998                     </td>
1999                   </tr>
2000                 </table>
2001               </div>
2002             </dd>
2003             <dt>Example usage:</dt>
2004             <dd>
2005               <table border="0" bgcolor="#E0E0E0" width="90%">
2006                 <tr>
2007                   <td>
2008                     <pre class="SCREEN"># Use an ssh tunnel for requests previously tagged as
2009 # <span class="QUOTE">"User-Agent: fetch libfetch/2.0"</span> and make sure
2010 # resuming downloads continues to work.
2011 #
2012 # This way you can continue to use Tor for your normal browsing,
2013 # without overloading the Tor network with your FreeBSD ports updates
2014 # or downloads of bigger files like ISOs.
2015 #
2016 # Note that HTTP headers are easy to fake and therefore their
2017 # values are as (un)trustworthy as your clients and users.
2018 {+forward-override{forward-socks5 10.0.0.2:2222 .} \
2019  -hide-if-modified-since      \
2020  -overwrite-last-modified     \
2021 }
2022 TAG:^User-Agent: fetch libfetch/2\.0$</pre>
2023                   </td>
2024                 </tr>
2025               </table>
2026             </dd>
2027           </dl>
2028         </div>
2029       </div>
2030       <div class="SECT3">
2031         <h4 class="SECT3"><a name="HANDLE-AS-EMPTY-DOCUMENT" id="HANDLE-AS-EMPTY-DOCUMENT">8.5.20.
2032         handle-as-empty-document</a></h4>
2033         <div class="VARIABLELIST">
2034           <dl>
2035             <dt>Typical use:</dt>
2036             <dd>
2037               <p>Mark URLs that should be replaced by empty documents <span class="emphasis"><i class="EMPHASIS">if
2038               they get blocked</i></span></p>
2039             </dd>
2040             <dt>Effect:</dt>
2041             <dd>
2042               <p>This action alone doesn't do anything noticeable. It just marks URLs. If the <tt class=
2043               "LITERAL"><a href="actions-file.html#BLOCK">block</a></tt> action <span class="emphasis"><i class=
2044               "EMPHASIS">also applies</i></span>, the presence or absence of this mark decides whether an HTML
2045               <span class="QUOTE">"BLOCKED"</span> page, or an empty document will be sent to the client as a
2046               substitute for the blocked content. The <span class="emphasis"><i class="EMPHASIS">empty</i></span>
2047               document isn't literally empty, but actually contains a single space.</p>
2048             </dd>
2049             <dt>Type:</dt>
2050             <dd>
2051               <p>Boolean.</p>
2052             </dd>
2053             <dt>Parameter:</dt>
2054             <dd>
2055               <p>N/A</p>
2056             </dd>
2057             <dt>Notes:</dt>
2058             <dd>
2059               <p>Some browsers complain about syntax errors if JavaScript documents are blocked with <span class=
2060               "APPLICATION">Privoxy's</span> default HTML page; this option can be used to silence them. And of course
2061               this action can also be used to eliminate the <span class="APPLICATION">Privoxy</span> BLOCKED message in
2062               frames.</p>
2063               <p>The content type for the empty document can be specified with <tt class="LITERAL"><a href=
2064               "actions-file.html#CONTENT-TYPE-OVERWRITE">content-type-overwrite{}</a></tt>, but usually this isn't
2065               necessary.</p>
2066             </dd>
2067             <dt>Example usage:</dt>
2068             <dd>
2069               <table border="0" bgcolor="#E0E0E0" width="90%">
2070                 <tr>
2071                   <td>
2072                     <pre class="SCREEN"># Block all documents on example.org that end with ".js",
2073 # but send an empty document instead of the usual HTML message.
2074 {+block{Blocked JavaScript} +handle-as-empty-document}
2075 example.org/.*\.js$</pre>
2076                   </td>
2077                 </tr>
2078               </table>
2079             </dd>
2080           </dl>
2081         </div>
2082       </div>
2083       <div class="SECT3">
2084         <h4 class="SECT3"><a name="HANDLE-AS-IMAGE" id="HANDLE-AS-IMAGE">8.5.21. handle-as-image</a></h4>
2085         <div class="VARIABLELIST">
2086           <dl>
2087             <dt>Typical use:</dt>
2088             <dd>
2089               <p>Mark URLs as belonging to images (so they'll be replaced by images <span class="emphasis"><i class=
2090               "EMPHASIS">if they do get blocked</i></span>, rather than HTML pages)</p>
2091             </dd>
2092             <dt>Effect:</dt>
2093             <dd>
2094               <p>This action alone doesn't do anything noticeable. It just marks URLs as images. If the <tt class=
2095               "LITERAL"><a href="actions-file.html#BLOCK">block</a></tt> action <span class="emphasis"><i class=
2096               "EMPHASIS">also applies</i></span>, the presence or absence of this mark decides whether an HTML
2097               <span class="QUOTE">"blocked"</span> page, or a replacement image (as determined by the <tt class=
2098               "LITERAL"><a href="actions-file.html#SET-IMAGE-BLOCKER">set-image-blocker</a></tt> action) will be sent
2099               to the client as a substitute for the blocked content.</p>
2100             </dd>
2101             <dt>Type:</dt>
2102             <dd>
2103               <p>Boolean.</p>
2104             </dd>
2105             <dt>Parameter:</dt>
2106             <dd>
2107               <p>N/A</p>
2108             </dd>
2109             <dt>Notes:</dt>
2110             <dd>
2111               <p>The below generic example section is actually part of <tt class="FILENAME">default.action</tt>. It
2112               marks all URLs with well-known image file name extensions as images and should be left intact.</p>
2113               <p>Users will probably only want to use the handle-as-image action in conjunction with <tt class=
2114               "LITERAL"><a href="actions-file.html#BLOCK">block</a></tt>, to block sources of banners, whose URLs don't
2115               reflect the file type, like in the second example section.</p>
2116               <p>Note that you cannot treat HTML pages as images in most cases. For instance, (in-line) ad frames
2117               require an HTML page to be sent, or they won't display properly. Forcing <tt class=
2118               "LITERAL">handle-as-image</tt> in this situation will not replace the ad frame with an image, but lead to
2119               error messages.</p>
2120             </dd>
2121             <dt>Example usage (sections):</dt>
2122             <dd>
2123               <table border="0" bgcolor="#E0E0E0" width="90%">
2124                 <tr>
2125                   <td>
2126                     <pre class="SCREEN"># Generic image extensions:
2127 #
2128 {+handle-as-image}
2129 /.*\.(gif|jpg|jpeg|png|bmp|ico)$
2130
2131 # These don't look like images, but they're banners and should be
2132 # blocked as images:
2133 #
2134 {+block{Nasty banners.} +handle-as-image}
2135 nasty-banner-server.example.com/junk.cgi\?output=trash</pre>
2136                   </td>
2137                 </tr>
2138               </table>
2139             </dd>
2140           </dl>
2141         </div>
2142       </div>
2143       <div class="SECT3">
2144         <h4 class="SECT3"><a name="HIDE-ACCEPT-LANGUAGE" id="HIDE-ACCEPT-LANGUAGE">8.5.22.
2145         hide-accept-language</a></h4>
2146         <div class="VARIABLELIST">
2147           <dl>
2148             <dt>Typical use:</dt>
2149             <dd>
2150               <p>Pretend to use different language settings.</p>
2151             </dd>
2152             <dt>Effect:</dt>
2153             <dd>
2154               <p>Deletes or replaces the <span class="QUOTE">"Accept-Language:"</span> HTTP header in client
2155               requests.</p>
2156             </dd>
2157             <dt>Type:</dt>
2158             <dd>
2159               <p>Parameterized.</p>
2160             </dd>
2161             <dt>Parameter:</dt>
2162             <dd>
2163               <p>Keyword: <span class="QUOTE">"block"</span>, or any user defined value.</p>
2164             </dd>
2165             <dt>Notes:</dt>
2166             <dd>
2167               <p>Faking the browser's language settings can be useful to make a foreign User-Agent set with <tt class=
2168               "LITERAL"><a href="actions-file.html#HIDE-USER-AGENT">hide-user-agent</a></tt> more believable.</p>
2169               <p>However some sites with content in different languages check the <span class=
2170               "QUOTE">"Accept-Language:"</span> to decide which one to take by default. Sometimes it isn't possible to
2171               later switch to another language without changing the <span class="QUOTE">"Accept-Language:"</span>
2172               header first.</p>
2173               <p>Therefore it's a good idea to either only change the <span class="QUOTE">"Accept-Language:"</span>
2174               header to languages you understand, or to languages that aren't wide spread.</p>
2175               <p>Before setting the <span class="QUOTE">"Accept-Language:"</span> header to a rare language, you should
2176               consider that it helps to make your requests unique and thus easier to trace. If you don't plan to change
2177               this header frequently, you should stick to a common language.</p>
2178             </dd>
2179             <dt>Example usage (section):</dt>
2180             <dd>
2181               <table border="0" bgcolor="#E0E0E0" width="90%">
2182                 <tr>
2183                   <td>
2184                     <pre class="SCREEN"># Pretend to use Canadian language settings.
2185 {+hide-accept-language{en-ca} \
2186 +hide-user-agent{Mozilla/5.0 (X11; U; OpenBSD i386; en-CA; rv:1.8.0.4) Gecko/20060628 Firefox/1.5.0.4} \
2187 }
2188 /</pre>
2189                   </td>
2190                 </tr>
2191               </table>
2192             </dd>
2193           </dl>
2194         </div>
2195       </div>
2196       <div class="SECT3">
2197         <h4 class="SECT3"><a name="HIDE-CONTENT-DISPOSITION" id="HIDE-CONTENT-DISPOSITION">8.5.23.
2198         hide-content-disposition</a></h4>
2199         <div class="VARIABLELIST">
2200           <dl>
2201             <dt>Typical use:</dt>
2202             <dd>
2203               <p>Prevent download menus for content you prefer to view inside the browser.</p>
2204             </dd>
2205             <dt>Effect:</dt>
2206             <dd>
2207               <p>Deletes or replaces the <span class="QUOTE">"Content-Disposition:"</span> HTTP header set by some
2208               servers.</p>
2209             </dd>
2210             <dt>Type:</dt>
2211             <dd>
2212               <p>Parameterized.</p>
2213             </dd>
2214             <dt>Parameter:</dt>
2215             <dd>
2216               <p>Keyword: <span class="QUOTE">"block"</span>, or any user defined value.</p>
2217             </dd>
2218             <dt>Notes:</dt>
2219             <dd>
2220               <p>Some servers set the <span class="QUOTE">"Content-Disposition:"</span> HTTP header for documents they
2221               assume you want to save locally before viewing them. The <span class=
2222               "QUOTE">"Content-Disposition:"</span> header contains the file name the browser is supposed to use by
2223               default.</p>
2224               <p>In most browsers that understand this header, it makes it impossible to <span class=
2225               "emphasis"><i class="EMPHASIS">just view</i></span> the document, without downloading it first, even if
2226               it's just a simple text file or an image.</p>
2227               <p>Removing the <span class="QUOTE">"Content-Disposition:"</span> header helps to prevent this annoyance,
2228               but some browsers additionally check the <span class="QUOTE">"Content-Type:"</span> header, before they
2229               decide if they can display a document without saving it first. In these cases, you have to change this
2230               header as well, before the browser stops displaying download menus.</p>
2231               <p>It is also possible to change the server's file name suggestion to another one, but in most cases it
2232               isn't worth the time to set it up.</p>
2233               <p>This action will probably be removed in the future, use server-header filters instead.</p>
2234             </dd>
2235             <dt>Example usage:</dt>
2236             <dd>
2237               <table border="0" bgcolor="#E0E0E0" width="90%">
2238                 <tr>
2239                   <td>
2240                     <pre class="SCREEN"># Disarm the download link in Sourceforge's patch tracker
2241 { -filter \
2242  +content-type-overwrite{text/plain}\
2243  +hide-content-disposition{block} }
2244  .sourceforge.net/tracker/download\.php</pre>
2245                   </td>
2246                 </tr>
2247               </table>
2248             </dd>
2249           </dl>
2250         </div>
2251       </div>
2252       <div class="SECT3">
2253         <h4 class="SECT3"><a name="HIDE-IF-MODIFIED-SINCE" id="HIDE-IF-MODIFIED-SINCE">8.5.24.
2254         hide-if-modified-since</a></h4>
2255         <div class="VARIABLELIST">
2256           <dl>
2257             <dt>Typical use:</dt>
2258             <dd>
2259               <p>Prevent yet another way to track the user's steps between sessions.</p>
2260             </dd>
2261             <dt>Effect:</dt>
2262             <dd>
2263               <p>Deletes the <span class="QUOTE">"If-Modified-Since:"</span> HTTP client header or modifies its
2264               value.</p>
2265             </dd>
2266             <dt>Type:</dt>
2267             <dd>
2268               <p>Parameterized.</p>
2269             </dd>
2270             <dt>Parameter:</dt>
2271             <dd>
2272               <p>Keyword: <span class="QUOTE">"block"</span>, or a user defined value that specifies a range of
2273               hours.</p>
2274             </dd>
2275             <dt>Notes:</dt>
2276             <dd>
2277               <p>Removing this header is useful for filter testing, where you want to force a real reload instead of
2278               getting status code <span class="QUOTE">"304"</span>, which would cause the browser to use a cached copy
2279               of the page.</p>
2280               <p>Instead of removing the header, <tt class="LITERAL">hide-if-modified-since</tt> can also add or
2281               subtract a random amount of time to/from the header's value. You specify a range of minutes where the
2282               random factor should be chosen from and <span class="APPLICATION">Privoxy</span> does the rest. A
2283               negative value means subtracting, a positive value adding.</p>
2284               <p>Randomizing the value of the <span class="QUOTE">"If-Modified-Since:"</span> makes it less likely that
2285               the server can use the time as a cookie replacement, but you will run into caching problems if the random
2286               range is too high.</p>
2287               <p>It is a good idea to only use a small negative value and let <tt class="LITERAL"><a href=
2288               "actions-file.html#OVERWRITE-LAST-MODIFIED">overwrite-last-modified</a></tt> handle the greater
2289               changes.</p>
2290               <p>It is also recommended to use this action together with <tt class="LITERAL"><a href=
2291               "actions-file.html#CRUNCH-IF-NONE-MATCH">crunch-if-none-match</a></tt>, otherwise it's more or less
2292               pointless.</p>
2293             </dd>
2294             <dt>Example usage (section):</dt>
2295             <dd>
2296               <table border="0" bgcolor="#E0E0E0" width="90%">
2297                 <tr>
2298                   <td>
2299                     <pre class="SCREEN"># Let the browser revalidate but make tracking based on the time less likely.
2300 {+hide-if-modified-since{-60} \
2301  +overwrite-last-modified{randomize} \
2302  +crunch-if-none-match}
2303 /</pre>
2304                   </td>
2305                 </tr>
2306               </table>
2307             </dd>
2308           </dl>
2309         </div>
2310       </div>
2311       <div class="SECT3">
2312         <h4 class="SECT3"><a name="HIDE-FROM-HEADER" id="HIDE-FROM-HEADER">8.5.25. hide-from-header</a></h4>
2313         <div class="VARIABLELIST">
2314           <dl>
2315             <dt>Typical use:</dt>
2316             <dd>
2317               <p>Keep your (old and ill) browser from telling web servers your email address</p>
2318             </dd>
2319             <dt>Effect:</dt>
2320             <dd>
2321               <p>Deletes any existing <span class="QUOTE">"From:"</span> HTTP header, or replaces it with the specified
2322               string.</p>
2323             </dd>
2324             <dt>Type:</dt>
2325             <dd>
2326               <p>Parameterized.</p>
2327             </dd>
2328             <dt>Parameter:</dt>
2329             <dd>
2330               <p>Keyword: <span class="QUOTE">"block"</span>, or any user defined value.</p>
2331             </dd>
2332             <dt>Notes:</dt>
2333             <dd>
2334               <p>The keyword <span class="QUOTE">"block"</span> will completely remove the header (not to be confused
2335               with the <tt class="LITERAL"><a href="actions-file.html#BLOCK">block</a></tt> action).</p>
2336               <p>Alternately, you can specify any value you prefer to be sent to the web server. If you do, it is a
2337               matter of fairness not to use any address that is actually used by a real person.</p>
2338               <p>This action is rarely needed, as modern web browsers don't send <span class="QUOTE">"From:"</span>
2339               headers anymore.</p>
2340             </dd>
2341             <dt>Example usage:</dt>
2342             <dd>
2343               <table border="0" bgcolor="#E0E0E0" width="90%">
2344                 <tr>
2345                   <td>
2346                     <pre class="SCREEN">+hide-from-header{block}</pre>
2347                   </td>
2348                 </tr>
2349               </table>
2350               <p>or</p>
2351               <table border="0" bgcolor="#E0E0E0" width="90%">
2352                 <tr>
2353                   <td>
2354                     <pre class="SCREEN">+hide-from-header{spam-me-senseless@sittingduck.example.com}</pre>
2355                   </td>
2356                 </tr>
2357               </table>
2358             </dd>
2359           </dl>
2360         </div>
2361       </div>
2362       <div class="SECT3">
2363         <h4 class="SECT3"><a name="HIDE-REFERRER" id="HIDE-REFERRER">8.5.26. hide-referrer</a></h4><a name=
2364         "HIDE-REFERER" id="HIDE-REFERER"></a>
2365         <div class="VARIABLELIST">
2366           <dl>
2367             <dt>Typical use:</dt>
2368             <dd>
2369               <p>Conceal which link you followed to get to a particular site</p>
2370             </dd>
2371             <dt>Effect:</dt>
2372             <dd>
2373               <p>Deletes the <span class="QUOTE">"Referer:"</span> (sic) HTTP header from the client request, or
2374               replaces it with a forged one.</p>
2375             </dd>
2376             <dt>Type:</dt>
2377             <dd>
2378               <p>Parameterized.</p>
2379             </dd>
2380             <dt>Parameter:</dt>
2381             <dd>
2382               <ul>
2383                 <li>
2384                   <p><span class="QUOTE">"conditional-block"</span> to delete the header completely if the host has
2385                   changed.</p>
2386                 </li>
2387                 <li>
2388                   <p><span class="QUOTE">"conditional-forge"</span> to forge the header if the host has changed.</p>
2389                 </li>
2390                 <li>
2391                   <p><span class="QUOTE">"block"</span> to delete the header unconditionally.</p>
2392                 </li>
2393                 <li>
2394                   <p><span class="QUOTE">"forge"</span> to pretend to be coming from the homepage of the server we are
2395                   talking to.</p>
2396                 </li>
2397                 <li>
2398                   <p>Any other string to set a user defined referrer.</p>
2399                 </li>
2400               </ul>
2401             </dd>
2402             <dt>Notes:</dt>
2403             <dd>
2404               <p><tt class="LITERAL">conditional-block</tt> is the only parameter, that isn't easily detected in the
2405               server's log file. If it blocks the referrer, the request will look like the visitor used a bookmark or
2406               typed in the address directly.</p>
2407               <p>Leaving the referrer unmodified for requests on the same host allows the server owner to see the
2408               visitor's <span class="QUOTE">"click path"</span>, but in most cases she could also get that information
2409               by comparing other parts of the log file: for example the User-Agent if it isn't a very common one, or
2410               the user's IP address if it doesn't change between different requests.</p>
2411               <p>Always blocking the referrer, or using a custom one, can lead to failures on servers that check the
2412               referrer before they answer any requests, in an attempt to prevent their content from being embedded or
2413               linked to elsewhere.</p>
2414               <p>Both <tt class="LITERAL">conditional-block</tt> and <tt class="LITERAL">forge</tt> will work with
2415               referrer checks, as long as content and valid referring page are on the same host. Most of the time
2416               that's the case.</p>
2417               <p><tt class="LITERAL">hide-referer</tt> is an alternate spelling of <tt class=
2418               "LITERAL">hide-referrer</tt> and the two can be can be freely substituted with each other. (<span class=
2419               "QUOTE">"referrer"</span> is the correct English spelling, however the HTTP specification has a bug - it
2420               requires it to be spelled as <span class="QUOTE">"referer"</span>.)</p>
2421             </dd>
2422             <dt>Example usage:</dt>
2423             <dd>
2424               <table border="0" bgcolor="#E0E0E0" width="90%">
2425                 <tr>
2426                   <td>
2427                     <pre class="SCREEN">+hide-referrer{forge}</pre>
2428                   </td>
2429                 </tr>
2430               </table>
2431               <p>or</p>
2432               <table border="0" bgcolor="#E0E0E0" width="90%">
2433                 <tr>
2434                   <td>
2435                     <pre class="SCREEN">+hide-referrer{http://www.yahoo.com/}</pre>
2436                   </td>
2437                 </tr>
2438               </table>
2439             </dd>
2440           </dl>
2441         </div>
2442       </div>
2443       <div class="SECT3">
2444         <h4 class="SECT3"><a name="HIDE-USER-AGENT" id="HIDE-USER-AGENT">8.5.27. hide-user-agent</a></h4>
2445         <div class="VARIABLELIST">
2446           <dl>
2447             <dt>Typical use:</dt>
2448             <dd>
2449               <p>Try to conceal your type of browser and client operating system</p>
2450             </dd>
2451             <dt>Effect:</dt>
2452             <dd>
2453               <p>Replaces the value of the <span class="QUOTE">"User-Agent:"</span> HTTP header in client requests with
2454               the specified value.</p>
2455             </dd>
2456             <dt>Type:</dt>
2457             <dd>
2458               <p>Parameterized.</p>
2459             </dd>
2460             <dt>Parameter:</dt>
2461             <dd>
2462               <p>Any user-defined string.</p>
2463             </dd>
2464             <dt>Notes:</dt>
2465             <dd>
2466               <div class="WARNING">
2467                 <table class="WARNING" border="1" width="90%">
2468                   <tr>
2469                     <td align="center"><b>Warning</b></td>
2470                   </tr>
2471                   <tr>
2472                     <td align="left">
2473                       <p>This can lead to problems on web sites that depend on looking at this header in order to
2474                       customize their content for different browsers (which, by the way, is <span class=
2475                       "emphasis"><i class="EMPHASIS">NOT</i></span> the right thing to do: good web sites work
2476                       browser-independently).</p>
2477                     </td>
2478                   </tr>
2479                 </table>
2480               </div>
2481               <p>Using this action in multi-user setups or wherever different types of browsers will access the same
2482               <span class="APPLICATION">Privoxy</span> is <span class="emphasis"><i class="EMPHASIS">not
2483               recommended</i></span>. In single-user, single-browser setups, you might use it to delete your OS version
2484               information from the headers, because it is an invitation to exploit known bugs for your OS. It is also
2485               occasionally useful to forge this in order to access sites that won't let you in otherwise (though there
2486               may be a good reason in some cases).</p>
2487               <p>More information on known user-agent strings can be found at <a href="http://www.user-agents.org/"
2488               target="_top">http://www.user-agents.org/</a> and <a href="http://en.wikipedia.org/wiki/User_agent"
2489               target="_top">http://en.wikipedia.org/wiki/User_agent</a>.</p>
2490             </dd>
2491             <dt>Example usage:</dt>
2492             <dd>
2493               <table border="0" bgcolor="#E0E0E0" width="90%">
2494                 <tr>
2495                   <td>
2496                     <pre class="SCREEN">+hide-user-agent{Netscape 6.1 (X11; I; Linux 2.4.18 i686)}</pre>
2497                   </td>
2498                 </tr>
2499               </table>
2500             </dd>
2501           </dl>
2502         </div>
2503       </div>
2504       <div class="SECT3">
2505         <h4 class="SECT3"><a name="HTTPS-INSPECTION" id="HTTPS-INSPECTION">8.5.28. https-inspection</a></h4>
2506         <div class="VARIABLELIST">
2507           <dl>
2508             <dt>Typical use:</dt>
2509             <dd>
2510               <p>Filter encrypted requests and responses</p>
2511             </dd>
2512             <dt>Effect:</dt>
2513             <dd>
2514               <p>Encrypted requests are decrypted, filtered and forwarded encrypted.</p>
2515             </dd>
2516             <dt>Type:</dt>
2517             <dd>
2518               <p>Boolean.</p>
2519             </dd>
2520             <dt>Parameter:</dt>
2521             <dd>
2522               <p>N/A</p>
2523             </dd>
2524             <dt>Notes:</dt>
2525             <dd>
2526               <p>This action allows <span class="APPLICATION">Privoxy</span> to filter encrypted requests and
2527               responses. For this to work <span class="APPLICATION">Privoxy</span> has to generate a certificate and
2528               send it to the client which has to accept it.</p>
2529               <p>Before this works the directives in the <tt class="LITERAL"><a href="config.html#TLS" target=
2530               "_top">TLS section</a></tt> of the config file have to be configured.</p>
2531               <p>Note that the action has to be enabled based on the CONNECT request which doesn't contain a path.
2532               Enabling it based on a pattern with path doesn't work as the path is only seen by <span class=
2533               "APPLICATION">Privoxy</span> if the action is already enabled.</p>
2534               <p>This is an experimental feature.</p>
2535             </dd>
2536             <dt>Example usage (section):</dt>
2537             <dd>
2538               <table border="0" bgcolor="#E0E0E0" width="90%">
2539                 <tr>
2540                   <td>
2541                     <pre class="SCREEN">{+https-inspection}
2542 www.example.com</pre>
2543                   </td>
2544                 </tr>
2545               </table>
2546             </dd>
2547           </dl>
2548         </div>
2549       </div>
2550       <div class="SECT3">
2551         <h4 class="SECT3"><a name="IGNORE-CERTIFICATE-ERRORS" id="IGNORE-CERTIFICATE-ERRORS">8.5.29.
2552         ignore-certificate-errors</a></h4>
2553         <div class="VARIABLELIST">
2554           <dl>
2555             <dt>Typical use:</dt>
2556             <dd>
2557               <p>Filter encrypted requests and responses without verifying the certificate</p>
2558             </dd>
2559             <dt>Effect:</dt>
2560             <dd>
2561               <p>Encrypted requests are forwarded to sites without verifying the certificate.</p>
2562             </dd>
2563             <dt>Type:</dt>
2564             <dd>
2565               <p>Boolean.</p>
2566             </dd>
2567             <dt>Parameter:</dt>
2568             <dd>
2569               <p>N/A</p>
2570             </dd>
2571             <dt>Notes:</dt>
2572             <dd>
2573               <p>When the <a href="actions-file.html#HTTPS-INSPECTION"><span class=
2574               "QUOTE">"+https-inspection"</span></a> action is used <span class="APPLICATION">Privoxy</span> by default
2575               verifies that the remote site uses a valid certificate.</p>
2576               <p>If the certificate can't be validated by <span class="APPLICATION">Privoxy</span> the connection is
2577               aborted.</p>
2578               <p>This action disables the certificate check so requests to sites with certificates that can't be
2579               validated are allowed.</p>
2580               <p>Note that enabling this action allows Man-in-the-middle attacks.</p>
2581             </dd>
2582             <dt>Example usage:</dt>
2583             <dd>
2584               <table border="0" bgcolor="#E0E0E0" width="90%">
2585                 <tr>
2586                   <td>
2587                     <pre class="SCREEN">    {+ignore-certificate-errors}
2588     www.example.org
2589    </pre>
2590                   </td>
2591                 </tr>
2592               </table>
2593             </dd>
2594           </dl>
2595         </div>
2596       </div>
2597       <div class="SECT3">
2598         <h4 class="SECT3"><a name="LIMIT-CONNECT" id="LIMIT-CONNECT">8.5.30. limit-connect</a></h4>
2599         <div class="VARIABLELIST">
2600           <dl>
2601             <dt>Typical use:</dt>
2602             <dd>
2603               <p>Prevent abuse of <span class="APPLICATION">Privoxy</span> as a TCP proxy relay or disable SSL for
2604               untrusted sites</p>
2605             </dd>
2606             <dt>Effect:</dt>
2607             <dd>
2608               <p>Specifies to which ports HTTP CONNECT requests are allowable.</p>
2609             </dd>
2610             <dt>Type:</dt>
2611             <dd>
2612               <p>Parameterized.</p>
2613             </dd>
2614             <dt>Parameter:</dt>
2615             <dd>
2616               <p>A comma-separated list of ports or port ranges (the latter using dashes, with the minimum defaulting
2617               to 0 and the maximum to 65K).</p>
2618             </dd>
2619             <dt>Notes:</dt>
2620             <dd>
2621               <p>By default, i.e. if no <tt class="LITERAL">limit-connect</tt> action applies, <span class=
2622               "APPLICATION">Privoxy</span> allows HTTP CONNECT requests to all ports. Use <tt class=
2623               "LITERAL">limit-connect</tt> if fine-grained control is desired for some or all destinations.</p>
2624               <p>The CONNECT methods exists in HTTP to allow access to secure websites (<span class=
2625               "QUOTE">"https://"</span> URLs) through proxies. It works very simply: the proxy connects to the server
2626               on the specified port, and then short-circuits its connections to the client and to the remote server.
2627               This means CONNECT-enabled proxies can be used as TCP relays very easily.</p>
2628               <p><span class="APPLICATION">Privoxy</span> relays HTTPS traffic without seeing the decoded content.
2629               Websites can leverage this limitation to circumvent <span class="APPLICATION">Privoxy</span>'s filters.
2630               By specifying an invalid port range you can disable HTTPS entirely.</p>
2631             </dd>
2632             <dt>Example usages:</dt>
2633             <dd>
2634               <table border="0" bgcolor="#E0E0E0" width="90%">
2635                 <tr>
2636                   <td>
2637                     <pre class="SCREEN">+limit-connect{443}                   # Port 443 is OK.
2638 +limit-connect{80,443}                # Ports 80 and 443 are OK.
2639 +limit-connect{-3, 7, 20-100, 500-}   # Ports less than 3, 7, 20 to 100 and above 500 are OK.
2640 +limit-connect{-}                     # All ports are OK
2641 +limit-connect{,}                     # No HTTPS/SSL traffic is allowed</pre>
2642                   </td>
2643                 </tr>
2644               </table>
2645             </dd>
2646           </dl>
2647         </div>
2648       </div>
2649       <div class="SECT3">
2650         <h4 class="SECT3"><a name="LIMIT-COOKIE-LIFETIME" id="LIMIT-COOKIE-LIFETIME">8.5.31.
2651         limit-cookie-lifetime</a></h4>
2652         <div class="VARIABLELIST">
2653           <dl>
2654             <dt>Typical use:</dt>
2655             <dd>
2656               <p>Limit the lifetime of HTTP cookies to a couple of minutes or hours.</p>
2657             </dd>
2658             <dt>Effect:</dt>
2659             <dd>
2660               <p>Overwrites the expires field in Set-Cookie server headers if it's above the specified limit.</p>
2661             </dd>
2662             <dt>Type:</dt>
2663             <dd>
2664               <p>Parameterized.</p>
2665             </dd>
2666             <dt>Parameter:</dt>
2667             <dd>
2668               <p>The lifetime limit in minutes, or 0.</p>
2669             </dd>
2670             <dt>Notes:</dt>
2671             <dd>
2672               <p>This action reduces the lifetime of HTTP cookies coming from the server to the specified number of
2673               minutes, starting from the time the cookie passes Privoxy.</p>
2674               <p>Cookies with a lifetime below the limit are not modified. The lifetime of session cookies is set to
2675               the specified limit.</p>
2676               <p>The effect of this action depends on the server.</p>
2677               <p>In case of servers which refresh their cookies with each response (or at least frequently), the
2678               lifetime limit set by this action is updated as well. Thus, a session associated with the cookie
2679               continues to work with this action enabled, as long as a new request is made before the last limit set is
2680               reached.</p>
2681               <p>However, some servers send their cookies once, with a lifetime of several years (the year 2037 is a
2682               popular choice), and do not refresh them until a certain event in the future, for example the user
2683               logging out. In this case this action may limit the absolute lifetime of the session, even if requests
2684               are made frequently.</p>
2685               <p>If the parameter is <span class="QUOTE">"0"</span>, this action behaves like <tt class=
2686               "LITERAL"><a href="actions-file.html#SESSION-COOKIES-ONLY">session-cookies-only</a></tt>.</p>
2687             </dd>
2688             <dt>Example usages:</dt>
2689             <dd>
2690               <table border="0" bgcolor="#E0E0E0" width="90%">
2691                 <tr>
2692                   <td>
2693                     <pre class="SCREEN">+limit-cookie-lifetime{60}</pre>
2694                   </td>
2695                 </tr>
2696               </table>
2697             </dd>
2698           </dl>
2699         </div>
2700       </div>
2701       <div class="SECT3">
2702         <h4 class="SECT3"><a name="PREVENT-COMPRESSION" id="PREVENT-COMPRESSION">8.5.32. prevent-compression</a></h4>
2703         <div class="VARIABLELIST">
2704           <dl>
2705             <dt>Typical use:</dt>
2706             <dd>
2707               <p>Ensure that servers send the content uncompressed, so it can be passed through <tt class=
2708               "LITERAL"><a href="actions-file.html#FILTER">filter</a></tt>s.</p>
2709             </dd>
2710             <dt>Effect:</dt>
2711             <dd>
2712               <p>Removes the Accept-Encoding header which can be used to ask for compressed transfer.</p>
2713             </dd>
2714             <dt>Type:</dt>
2715             <dd>
2716               <p>Boolean.</p>
2717             </dd>
2718             <dt>Parameter:</dt>
2719             <dd>
2720               <p>N/A</p>
2721             </dd>
2722             <dt>Notes:</dt>
2723             <dd>
2724               <p>More and more websites send their content compressed by default, which is generally a good idea and
2725               saves bandwidth. But the <tt class="LITERAL"><a href="actions-file.html#FILTER">filter</a></tt> and
2726               <tt class="LITERAL"><a href="actions-file.html#DEANIMATE-GIFS">deanimate-gifs</a></tt> actions need
2727               access to the uncompressed data.</p>
2728               <p>When compiled with zlib support (available since <span class="APPLICATION">Privoxy</span> 3.0.7),
2729               content that should be filtered is decompressed on-the-fly and you don't have to worry about this action.
2730               If you are using an older <span class="APPLICATION">Privoxy</span> version, or one that hasn't been
2731               compiled with zlib support, this action can be used to convince the server to send the content
2732               uncompressed.</p>
2733               <p>Most text-based instances compress very well, the size is seldom decreased by less than 50%, for
2734               markup-heavy instances like news feeds saving more than 90% of the original size isn't unusual.</p>
2735               <p>Not using compression will therefore slow down the transfer, and you should only enable this action if
2736               you really need it. As of <span class="APPLICATION">Privoxy</span> 3.0.7 it's disabled in all predefined
2737               action settings.</p>
2738               <p>Note that some (rare) ill-configured sites don't handle requests for uncompressed documents correctly.
2739               Broken PHP applications tend to send an empty document body, some IIS versions only send the beginning of
2740               the content and some content delivery networks let the connection time out. If you enable <tt class=
2741               "LITERAL">prevent-compression</tt> per default, you might want to add exceptions for those sites. See the
2742               example for how to do that.</p>
2743             </dd>
2744             <dt>Example usage (sections):</dt>
2745             <dd>
2746               <table border="0" bgcolor="#E0E0E0" width="90%">
2747                 <tr>
2748                   <td>
2749                     <pre class="SCREEN"># Selectively turn off compression, and enable a filter
2750 #
2751 { +filter{tiny-textforms} +prevent-compression }
2752 # Match only these sites
2753  .google.
2754  sourceforge.net
2755  sf.net
2756
2757 # Or instead, we could set a universal default:
2758 #
2759 { +prevent-compression }
2760  / # Match all sites
2761
2762 # Then maybe make exceptions for broken sites:
2763 #
2764 { -prevent-compression }
2765 .compusa.com/</pre>
2766                   </td>
2767                 </tr>
2768               </table>
2769             </dd>
2770           </dl>
2771         </div>
2772       </div>
2773       <div class="SECT3">
2774         <h4 class="SECT3"><a name="OVERWRITE-LAST-MODIFIED" id="OVERWRITE-LAST-MODIFIED">8.5.33.
2775         overwrite-last-modified</a></h4>
2776         <div class="VARIABLELIST">
2777           <dl>
2778             <dt>Typical use:</dt>
2779             <dd>
2780               <p>Prevent yet another way to track the user's steps between sessions.</p>
2781             </dd>
2782             <dt>Effect:</dt>
2783             <dd>
2784               <p>Deletes the <span class="QUOTE">"Last-Modified:"</span> HTTP server header or modifies its value.</p>
2785             </dd>
2786             <dt>Type:</dt>
2787             <dd>
2788               <p>Parameterized.</p>
2789             </dd>
2790             <dt>Parameter:</dt>
2791             <dd>
2792               <p>One of the keywords: <span class="QUOTE">"block"</span>, <span class=
2793               "QUOTE">"reset-to-request-time"</span> and <span class="QUOTE">"randomize"</span></p>
2794             </dd>
2795             <dt>Notes:</dt>
2796             <dd>
2797               <p>Removing the <span class="QUOTE">"Last-Modified:"</span> header is useful for filter testing, where
2798               you want to force a real reload instead of getting status code <span class="QUOTE">"304"</span>, which
2799               would cause the browser to reuse the old version of the page.</p>
2800               <p>The <span class="QUOTE">"randomize"</span> option overwrites the value of the <span class=
2801               "QUOTE">"Last-Modified:"</span> header with a randomly chosen time between the original value and the
2802               current time. In theory the server could send each document with a different <span class=
2803               "QUOTE">"Last-Modified:"</span> header to track visits without using cookies. <span class=
2804               "QUOTE">"Randomize"</span> makes it impossible and the browser can still revalidate cached documents.</p>
2805               <p><span class="QUOTE">"reset-to-request-time"</span> overwrites the value of the <span class=
2806               "QUOTE">"Last-Modified:"</span> header with the current time. You could use this option together with
2807               <tt class="LITERAL"><a href="actions-file.html#HIDE-IF-MODIFIED-SINCE">hide-if-modified-since</a></tt> to
2808               further customize your random range.</p>
2809               <p>The preferred parameter here is <span class="QUOTE">"randomize"</span>. It is safe to use, as long as
2810               the time settings are more or less correct. If the server sets the <span class=
2811               "QUOTE">"Last-Modified:"</span> header to the time of the request, the random range becomes zero and the
2812               value stays the same. Therefore you should later randomize it a second time with <tt class=
2813               "LITERAL"><a href="actions-file.html#HIDE-IF-MODIFIED-SINCE">hided-if-modified-since</a></tt>, just to be
2814               sure.</p>
2815               <p>It is also recommended to use this action together with <tt class="LITERAL"><a href=
2816               "actions-file.html#CRUNCH-IF-NONE-MATCH">crunch-if-none-match</a></tt>.</p>
2817             </dd>
2818             <dt>Example usage:</dt>
2819             <dd>
2820               <table border="0" bgcolor="#E0E0E0" width="90%">
2821                 <tr>
2822                   <td>
2823                     <pre class="SCREEN"># Let the browser revalidate without being tracked across sessions
2824 { +hide-if-modified-since{-60} \
2825  +overwrite-last-modified{randomize} \
2826  +crunch-if-none-match}
2827 /</pre>
2828                   </td>
2829                 </tr>
2830               </table>
2831             </dd>
2832           </dl>
2833         </div>
2834       </div>
2835       <div class="SECT3">
2836         <h4 class="SECT3"><a name="REDIRECT" id="REDIRECT">8.5.34. redirect</a></h4>
2837         <div class="VARIABLELIST">
2838           <dl>
2839             <dt>Typical use:</dt>
2840             <dd>
2841               <p>Redirect requests to other sites.</p>
2842             </dd>
2843             <dt>Effect:</dt>
2844             <dd>
2845               <p>Convinces the browser that the requested document has been moved to another location and the browser
2846               should get it from there.</p>
2847             </dd>
2848             <dt>Type:</dt>
2849             <dd>
2850               <p>Parameterized</p>
2851             </dd>
2852             <dt>Parameter:</dt>
2853             <dd>
2854               <p>An absolute URL or a single pcrs command.</p>
2855             </dd>
2856             <dt>Notes:</dt>
2857             <dd>
2858               <p>Requests to which this action applies are answered with a HTTP redirect to URLs of your choosing. The
2859               new URL is either provided as parameter, or derived by applying a single pcrs command to the original
2860               URL.</p>
2861               <p>The syntax for pcrs commands is documented in the <a href="filter-file.html">filter file</a>
2862               section.</p>
2863               <p>Requests can't be blocked and redirected at the same time, applying this action together with
2864               <tt class="LITERAL"><a href="actions-file.html#BLOCK">block</a></tt> is a configuration error. Currently
2865               the request is blocked and an error message logged, the behavior may change in the future and result in
2866               Privoxy rejecting the action file.</p>
2867               <p>This action can be combined with <tt class="LITERAL"><a href=
2868               "actions-file.html#FAST-REDIRECTS">fast-redirects{check-decoded-url}</a></tt> to redirect to a decoded
2869               version of a rewritten URL.</p>
2870               <p>Use this action carefully, make sure not to create redirection loops and be aware that using your own
2871               redirects might make it possible to fingerprint your requests.</p>
2872               <p>In case of problems with your redirects, or simply to watch them working, enable <a href=
2873               "config.html#DEBUG">debug 128</a>.</p>
2874             </dd>
2875             <dt>Example usages:</dt>
2876             <dd>
2877               <table border="0" bgcolor="#E0E0E0" width="90%">
2878                 <tr>
2879                   <td>
2880                     <pre class="SCREEN"># Replace example.com's style sheet with another one
2881 { +redirect{http://localhost/css-replacements/example.com.css} }
2882  example.com/stylesheet\.css
2883
2884 # Create a short, easy to remember nickname for a favorite site
2885 # (relies on the browser to accept and forward invalid URLs to <span class="APPLICATION">Privoxy</span>)
2886 { +redirect{https://www.privoxy.org/user-manual/actions-file.html} }
2887  a
2888
2889 # Always use the expanded view for Undeadly.org articles
2890 # (Note the $ at the end of the URL pattern to make sure
2891 # the request for the rewritten URL isn't redirected as well)
2892 {+redirect{s@$@&amp;mode=expanded@}}
2893 undeadly.org/cgi\?action=article&amp;sid=\d*$
2894
2895 # Redirect Google search requests to MSN
2896 {+redirect{s@^http://[^/]*/search\?q=([^&amp;]*).*@http://search.msn.com/results.aspx?q=$1@}}
2897 .google.com/search
2898
2899 # Redirect MSN search requests to Yahoo
2900 {+redirect{s@^http://[^/]*/results\.aspx\?q=([^&amp;]*).*@http://search.yahoo.com/search?p=$1@}}
2901 search.msn.com//results\.aspx\?q=
2902
2903 # Redirect http://example.com/&amp;bla=fasel&amp;toChange=foo (and any other value but "bar")
2904 # to       http://example.com/&amp;bla=fasel&amp;toChange=bar
2905 #
2906 # The URL pattern makes sure that the following request isn't redirected again.
2907 {+redirect{s@toChange=[^&amp;]+@toChange=bar@}}
2908 example.com/.*toChange=(?!bar)
2909
2910 # Add a shortcut to look up illumos bugs
2911 {+redirect{s@^http://i([0-9]+)/.*@https://www.illumos.org/issues/$1@}}
2912 # Redirected URL = http://i4974/
2913 # Redirect Destination = https://www.illumos.org/issues/4974
2914 i[0-9][0-9][0-9][0-9]*/
2915
2916 # Redirect remote requests for this manual
2917 # to the local version delivered by Privoxy
2918 {+redirect{s@^http://www@http://config@}}
2919 www.privoxy.org/user-manual/</pre>
2920                   </td>
2921                 </tr>
2922               </table>
2923             </dd>
2924           </dl>
2925         </div>
2926       </div>
2927       <div class="SECT3">
2928         <h4 class="SECT3"><a name="SERVER-HEADER-FILTER" id="SERVER-HEADER-FILTER">8.5.35.
2929         server-header-filter</a></h4>
2930         <div class="VARIABLELIST">
2931           <dl>
2932             <dt>Typical use:</dt>
2933             <dd>
2934               <p>Rewrite or remove single server headers.</p>
2935             </dd>
2936             <dt>Effect:</dt>
2937             <dd>
2938               <p>All server headers to which this action applies are filtered on-the-fly through the specified regular
2939               expression based substitutions.</p>
2940             </dd>
2941             <dt>Type:</dt>
2942             <dd>
2943               <p>Multi-value.</p>
2944             </dd>
2945             <dt>Parameter:</dt>
2946             <dd>
2947               <p>The name of a server-header filter, as defined in one of the <a href="filter-file.html">filter
2948               files</a>.</p>
2949             </dd>
2950             <dt>Notes:</dt>
2951             <dd>
2952               <p>Server-header filters are applied to each header on its own, not to all at once. This makes it easier
2953               to diagnose problems, but on the downside you can't write filters that only change header x if header y's
2954               value is z. You can do that by using tags though.</p>
2955               <p>Server-header filters are executed after the other header actions have finished and use their output
2956               as input.</p>
2957               <p>Please refer to the <a href="filter-file.html">filter file chapter</a> to learn which server-header
2958               filters are available by default, and how to create your own.</p>
2959             </dd>
2960             <dt>Example usage (section):</dt>
2961             <dd>
2962               <table border="0" bgcolor="#E0E0E0" width="90%">
2963                 <tr>
2964                   <td>
2965                     <pre class="SCREEN">{+server-header-filter{html-to-xml}}
2966 example.org/xml-instance-that-is-delivered-as-html
2967
2968 {+server-header-filter{xml-to-html}}
2969 example.org/instance-that-is-delivered-as-xml-but-is-not</pre>
2970                   </td>
2971                 </tr>
2972               </table>
2973             </dd>
2974           </dl>
2975         </div>
2976       </div>
2977       <div class="SECT3">
2978         <h4 class="SECT3"><a name="SERVER-HEADER-TAGGER" id="SERVER-HEADER-TAGGER">8.5.36.
2979         server-header-tagger</a></h4>
2980         <div class="VARIABLELIST">
2981           <dl>
2982             <dt>Typical use:</dt>
2983             <dd>
2984               <p>Enable or disable filters based on the Content-Type header.</p>
2985             </dd>
2986             <dt>Effect:</dt>
2987             <dd>
2988               <p>Server headers to which this action applies are filtered on-the-fly through the specified regular
2989               expression based substitutions, the result is used as tag.</p>
2990             </dd>
2991             <dt>Type:</dt>
2992             <dd>
2993               <p>Multi-value.</p>
2994             </dd>
2995             <dt>Parameter:</dt>
2996             <dd>
2997               <p>The name of a server-header tagger, as defined in one of the <a href="filter-file.html">filter
2998               files</a>.</p>
2999             </dd>
3000             <dt>Notes:</dt>
3001             <dd>
3002               <p>Server-header taggers are applied to each header on its own, and as the header isn't modified, each
3003               tagger <span class="QUOTE">"sees"</span> the original.</p>
3004               <p>Server-header taggers are executed before all other header actions that modify server headers. Their
3005               tags can be used to control all of the other server-header actions, the content filters and the crunch
3006               actions (<a href="actions-file.html#REDIRECT">redirect</a> and <a href=
3007               "actions-file.html#BLOCK">block</a>).</p>
3008               <p>Obviously crunching based on tags created by server-header taggers doesn't prevent the request from
3009               showing up in the server's log file.</p>
3010             </dd>
3011             <dt>Example usage (section):</dt>
3012             <dd>
3013               <table border="0" bgcolor="#E0E0E0" width="90%">
3014                 <tr>
3015                   <td>
3016                     <pre class="SCREEN"># Tag every request with the content type declared by the server
3017 {+server-header-tagger{content-type}}
3018 /
3019
3020 # If the response has a tag starting with 'image/' enable an external
3021 # filter that only applies to images.
3022 #
3023 # Note that the filter is not available by default, it's just a
3024 # <tt class="LITERAL"><a href="filter-file.html#EXTERNAL-FILTER-SYNTAX">silly example</a></tt>.
3025 {+external-filter{rotate-image} +force-text-mode}
3026 TAG:^image/</pre>
3027                   </td>
3028                 </tr>
3029               </table>
3030             </dd>
3031           </dl>
3032         </div>
3033       </div>
3034       <div class="SECT3">
3035         <h4 class="SECT3"><a name="SESSION-COOKIES-ONLY" id="SESSION-COOKIES-ONLY">8.5.37.
3036         session-cookies-only</a></h4>
3037         <div class="VARIABLELIST">
3038           <dl>
3039             <dt>Typical use:</dt>
3040             <dd>
3041               <p>Allow only temporary <span class="QUOTE">"session"</span> cookies (for the current browser session
3042               <span class="emphasis"><i class="EMPHASIS">only</i></span>).</p>
3043             </dd>
3044             <dt>Effect:</dt>
3045             <dd>
3046               <p>Deletes the <span class="QUOTE">"expires"</span> field from <span class="QUOTE">"Set-Cookie:"</span>
3047               server headers. Most browsers will not store such cookies permanently and forget them in between
3048               sessions.</p>
3049             </dd>
3050             <dt>Type:</dt>
3051             <dd>
3052               <p>Boolean.</p>
3053             </dd>
3054             <dt>Parameter:</dt>
3055             <dd>
3056               <p>N/A</p>
3057             </dd>
3058             <dt>Notes:</dt>
3059             <dd>
3060               <p>This is less strict than <tt class="LITERAL"><a href=
3061               "actions-file.html#CRUNCH-INCOMING-COOKIES">crunch-incoming-cookies</a></tt> / <tt class=
3062               "LITERAL"><a href="actions-file.html#CRUNCH-OUTGOING-COOKIES">crunch-outgoing-cookies</a></tt> and allows
3063               you to browse websites that insist or rely on setting cookies, without compromising your privacy too
3064               badly.</p>
3065               <p>Most browsers will not permanently store cookies that have been processed by <tt class=
3066               "LITERAL">session-cookies-only</tt> and will forget about them between sessions. This makes profiling
3067               cookies useless, but won't break sites which require cookies so that you can log in for transactions.
3068               This is generally turned on for all sites, and is the recommended setting.</p>
3069               <p>It makes <span class="emphasis"><i class="EMPHASIS">no sense at all</i></span> to use <tt class=
3070               "LITERAL">session-cookies-only</tt> together with <tt class="LITERAL"><a href=
3071               "actions-file.html#CRUNCH-INCOMING-COOKIES">crunch-incoming-cookies</a></tt> or <tt class=
3072               "LITERAL"><a href="actions-file.html#CRUNCH-OUTGOING-COOKIES">crunch-outgoing-cookies</a></tt>. If you
3073               do, cookies will be plainly killed.</p>
3074               <p>Note that it is up to the browser how it handles such cookies without an <span class=
3075               "QUOTE">"expires"</span> field. If you use an exotic browser, you might want to try it out to be
3076               sure.</p>
3077               <p>This setting also has no effect on cookies that may have been stored previously by the browser before
3078               starting <span class="APPLICATION">Privoxy</span>. These would have to be removed manually.</p>
3079               <p><span class="APPLICATION">Privoxy</span> also uses the <a href=
3080               "actions-file.html#FILTER-CONTENT-COOKIES">content-cookies filter</a> to block some types of cookies.
3081               Content cookies are not effected by <tt class="LITERAL">session-cookies-only</tt>.</p>
3082             </dd>
3083             <dt>Example usage:</dt>
3084             <dd>
3085               <table border="0" bgcolor="#E0E0E0" width="90%">
3086                 <tr>
3087                   <td>
3088                     <pre class="SCREEN">+session-cookies-only</pre>
3089                   </td>
3090                 </tr>
3091               </table>
3092             </dd>
3093           </dl>
3094         </div>
3095       </div>
3096       <div class="SECT3">
3097         <h4 class="SECT3"><a name="SET-IMAGE-BLOCKER" id="SET-IMAGE-BLOCKER">8.5.38. set-image-blocker</a></h4>
3098         <div class="VARIABLELIST">
3099           <dl>
3100             <dt>Typical use:</dt>
3101             <dd>
3102               <p>Choose the replacement for blocked images</p>
3103             </dd>
3104             <dt>Effect:</dt>
3105             <dd>
3106               <p>This action alone doesn't do anything noticeable. If <span class="emphasis"><i class=
3107               "EMPHASIS">both</i></span> <tt class="LITERAL"><a href="actions-file.html#BLOCK">block</a></tt>
3108               <span class="emphasis"><i class="EMPHASIS">and</i></span> <tt class="LITERAL"><a href=
3109               "actions-file.html#HANDLE-AS-IMAGE">handle-as-image</a></tt> <span c