Rebuild HTML docs for 3.0.22 UNSTABLE
[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
4 <html>
5 <head>
6   <title>Actions Files</title>
7   <meta name="GENERATOR" content=
8   "Modular DocBook HTML Stylesheet Version 1.79">
9   <link rel="HOME" title="Privoxy 3.0.22 User Manual" href="index.html">
10   <link rel="PREVIOUS" title="The Main Configuration File" href=
11   "config.html">
12   <link rel="NEXT" title="Filter Files" href="filter-file.html">
13   <link rel="STYLESHEET" type="text/css" href="../p_doc.css">
14   <meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
15   <link rel="STYLESHEET" type="text/css" href="p_doc.css">
16 </head>
17
18 <body class="SECT1" bgcolor="#EEEEEE" text="#000000" link="#0000FF" vlink=
19 "#840084" alink="#0000FF">
20   <div class="NAVHEADER">
21     <table summary="Header navigation table" width="100%" border="0"
22     cellpadding="0" cellspacing="0">
23       <tr>
24         <th colspan="3" align="center">Privoxy 3.0.22 User Manual</th>
25       </tr>
26
27       <tr>
28         <td width="10%" align="left" valign="bottom"><a href="config.html"
29         accesskey="P">Prev</a></td>
30
31         <td width="80%" align="center" valign="bottom"></td>
32
33         <td width="10%" align="right" valign="bottom"><a href=
34         "filter-file.html" accesskey="N">Next</a></td>
35       </tr>
36     </table>
37     <hr align="left" width="100%">
38   </div>
39
40   <div class="SECT1">
41     <h1 class="SECT1"><a name="ACTIONS-FILE" id="ACTIONS-FILE">8. Actions
42     Files</a></h1>
43
44     <p>The actions files are used to define what <span class=
45     "emphasis"><i class="EMPHASIS">actions</i></span> <span class=
46     "APPLICATION">Privoxy</span> takes for which URLs, and thus determines
47     how ad images, cookies and various other aspects of HTTP content and
48     transactions are handled, and on which sites (or even parts thereof).
49     There are a number of such actions, with a wide range of functionality.
50     Each action does something a little different. These actions give us a
51     veritable arsenal of tools with which to exert our control, preferences
52     and independence. Actions can be combined so that their effects are
53     aggregated when applied against a given set of URLs.</p>
54
55     <p>There are three action files included with <span class=
56     "APPLICATION">Privoxy</span> with differing purposes:</p>
57
58     <ul>
59       <li>
60         <p><tt class="FILENAME">match-all.action</tt> - is used to define
61         which <span class="QUOTE">"actions"</span> relating to
62         banner-blocking, images, pop-ups, content modification, cookie
63         handling etc should be applied by default. It should be the first
64         actions file loaded</p>
65       </li>
66
67       <li>
68         <p><tt class="FILENAME">default.action</tt> - defines many exceptions
69         (both positive and negative) from the default set of actions that's
70         configured in <tt class="FILENAME">match-all.action</tt>. It is a set
71         of rules that should work reasonably well as-is for most users. This
72         file is only supposed to be edited by the developers. It should be
73         the second actions file loaded.</p>
74       </li>
75
76       <li>
77         <p><tt class="FILENAME">user.action</tt> - is intended to be for
78         local site preferences and exceptions. As an example, if your ISP or
79         your bank has specific requirements, and need special handling, this
80         kind of thing should go here. This file will not be upgraded.</p>
81       </li>
82
83       <li>
84         <p><span class="GUIBUTTON">Edit</span> <span class="GUIBUTTON">Set to
85         Cautious</span> <span class="GUIBUTTON">Set to Medium</span>
86         <span class="GUIBUTTON">Set to Advanced</span></p>
87
88         <p>These have increasing levels of aggressiveness <span class=
89         "emphasis"><i class="EMPHASIS">and have no influence on your browsing
90         unless you select them explicitly in the editor</i></span>. A default
91         installation should be pre-set to <tt class="LITERAL">Cautious</tt>.
92         New users should try this for a while before adjusting the settings
93         to more aggressive levels. The more aggressive the settings, then the
94         more likelihood there is of problems such as sites not working as
95         they should.</p>
96
97         <p>The <span class="GUIBUTTON">Edit</span> button allows you to turn
98         each action on/off individually for fine-tuning. The <span class=
99         "GUIBUTTON">Cautious</span> button changes the actions list to
100         low/safe settings which will activate ad blocking and a minimal set
101         of <span class="APPLICATION">Privoxy</span>'s features, and
102         subsequently there will be less of a chance for accidental problems.
103         The <span class="GUIBUTTON">Medium</span> button sets the list to a
104         medium level of other features and a low level set of privacy
105         features. The <span class="GUIBUTTON">Advanced</span> button sets the
106         list to a high level of ad blocking and medium level of privacy. See
107         the chart below. The latter three buttons over-ride any changes via
108         with the <span class="GUIBUTTON">Edit</span> button. More fine-tuning
109         can be done in the lower sections of this internal page.</p>
110
111         <p>While the actions file editor allows to enable these settings in
112         all actions files, they are only supposed to be enabled in the first
113         one to make sure you don't unintentionally overrule earlier
114         rules.</p>
115
116         <p>The default profiles, and their associated actions, as pre-defined
117         in <tt class="FILENAME">default.action</tt> are:</p>
118
119         <div class="TABLE">
120           <a name="AEN2863" id="AEN2863"></a>
121
122           <p><b>Table 1. Default Configurations</b></p>
123
124           <table border="1" frame="border" rules="all" class="CALSTABLE">
125             <col width="1*" title="C1">
126             <col width="1*" title="C2">
127             <col width="1*" title="C3">
128             <col width="1*" title="C4">
129
130             <thead>
131               <tr>
132                 <th>Feature</th>
133
134                 <th>Cautious</th>
135
136                 <th>Medium</th>
137
138                 <th>Advanced</th>
139               </tr>
140             </thead>
141
142             <tbody>
143               <tr>
144                 <td>Ad-blocking Aggressiveness</td>
145
146                 <td>medium</td>
147
148                 <td>high</td>
149
150                 <td>high</td>
151               </tr>
152
153               <tr>
154                 <td>Ad-filtering by size</td>
155
156                 <td>no</td>
157
158                 <td>yes</td>
159
160                 <td>yes</td>
161               </tr>
162
163               <tr>
164                 <td>Ad-filtering by link</td>
165
166                 <td>no</td>
167
168                 <td>no</td>
169
170                 <td>yes</td>
171               </tr>
172
173               <tr>
174                 <td>Pop-up killing</td>
175
176                 <td>blocks only</td>
177
178                 <td>blocks only</td>
179
180                 <td>blocks only</td>
181               </tr>
182
183               <tr>
184                 <td>Privacy Features</td>
185
186                 <td>low</td>
187
188                 <td>medium</td>
189
190                 <td>medium/high</td>
191               </tr>
192
193               <tr>
194                 <td>Cookie handling</td>
195
196                 <td>none</td>
197
198                 <td>session-only</td>
199
200                 <td>kill</td>
201               </tr>
202
203               <tr>
204                 <td>Referer forging</td>
205
206                 <td>no</td>
207
208                 <td>yes</td>
209
210                 <td>yes</td>
211               </tr>
212
213               <tr>
214                 <td>GIF de-animation</td>
215
216                 <td>no</td>
217
218                 <td>yes</td>
219
220                 <td>yes</td>
221               </tr>
222
223               <tr>
224                 <td>Fast redirects</td>
225
226                 <td>no</td>
227
228                 <td>no</td>
229
230                 <td>yes</td>
231               </tr>
232
233               <tr>
234                 <td>HTML taming</td>
235
236                 <td>no</td>
237
238                 <td>no</td>
239
240                 <td>yes</td>
241               </tr>
242
243               <tr>
244                 <td>JavaScript taming</td>
245
246                 <td>no</td>
247
248                 <td>no</td>
249
250                 <td>yes</td>
251               </tr>
252
253               <tr>
254                 <td>Web-bug killing</td>
255
256                 <td>no</td>
257
258                 <td>yes</td>
259
260                 <td>yes</td>
261               </tr>
262
263               <tr>
264                 <td>Image tag reordering</td>
265
266                 <td>no</td>
267
268                 <td>yes</td>
269
270                 <td>yes</td>
271               </tr>
272             </tbody>
273           </table>
274         </div>
275       </li>
276     </ul>
277
278     <p>The list of actions files to be used are defined in the main
279     configuration file, and are processed in the order they are defined (e.g.
280     <tt class="FILENAME">default.action</tt> is typically processed before
281     <tt class="FILENAME">user.action</tt>). The content of these can all be
282     viewed and edited from <a href="http://config.privoxy.org/show-status"
283     target="_top">http://config.privoxy.org/show-status</a>. The over-riding
284     principle when applying actions, is that the last action that matches a
285     given URL wins. The broadest, most general rules go first (defined in
286     <tt class="FILENAME">default.action</tt>), followed by any exceptions
287     (typically also in <tt class="FILENAME">default.action</tt>), which are
288     then followed lastly by any local preferences (typically in <span class=
289     "emphasis"><i class="EMPHASIS">user</i></span><tt class=
290     "FILENAME">.action</tt>). Generally, <tt class=
291     "FILENAME">user.action</tt> has the last word.</p>
292
293     <p>An actions file typically has multiple sections. If you want to use
294     <span class="QUOTE">"aliases"</span> in an actions file, you have to
295     place the (optional) <a href="actions-file.html#ALIASES">alias
296     section</a> at the top of that file. Then comes the default set of rules
297     which will apply universally to all sites and pages (be <span class=
298     "emphasis"><i class="EMPHASIS">very careful</i></span> with using such a
299     universal set in <tt class="FILENAME">user.action</tt> or any other
300     actions file after <tt class="FILENAME">default.action</tt>, because it
301     will override the result from consulting any previous file). And then
302     below that, exceptions to the defined universal policies. You can regard
303     <tt class="FILENAME">user.action</tt> as an appendix to <tt class=
304     "FILENAME">default.action</tt>, with the advantage that it is a separate
305     file, which makes preserving your personal settings across <span class=
306     "APPLICATION">Privoxy</span> upgrades easier.</p>
307
308     <p>Actions can be used to block anything you want, including ads,
309     banners, or just some obnoxious URL whose content you would rather not
310     see. Cookies can be accepted or rejected, or accepted only during the
311     current browser session (i.e. not written to disk), content can be
312     modified, some JavaScripts tamed, user-tracking fooled, and much more.
313     See below for a <a href="actions-file.html#ACTIONS">complete list of
314     actions</a>.</p>
315
316     <div class="SECT2">
317       <h2 class="SECT2"><a name="AEN2962" id="AEN2962">8.1. Finding the Right
318       Mix</a></h2>
319
320       <p>Note that some <a href="actions-file.html#ACTIONS">actions</a>, like
321       cookie suppression or script disabling, may render some sites unusable
322       that rely on these techniques to work properly. Finding the right mix
323       of actions is not always easy and certainly a matter of personal taste.
324       And, things can always change, requiring refinements in the
325       configuration. In general, it can be said that the more <span class=
326       "QUOTE">"aggressive"</span> your default settings (in the top section
327       of the actions file) are, the more exceptions for <span class=
328       "QUOTE">"trusted"</span> sites you will have to make later. If, for
329       example, you want to crunch all cookies per default, you'll have to
330       make exceptions from that rule for sites that you regularly use and
331       that require cookies for actually useful purposes, like maybe your
332       bank, favorite shop, or newspaper.</p>
333
334       <p>We have tried to provide you with reasonable rules to start from in
335       the distribution actions files. But there is no general rule of thumb
336       on these things. There just are too many variables, and sites are
337       constantly changing. Sooner or later you will want to change the rules
338       (and read this chapter again :).</p>
339     </div>
340
341     <div class="SECT2">
342       <h2 class="SECT2"><a name="AEN2969" id="AEN2969">8.2. How to
343       Edit</a></h2>
344
345       <p>The easiest way to edit the actions files is with a browser by using
346       our browser-based editor, which can be reached from <a href=
347       "http://config.privoxy.org/show-status" target=
348       "_top">http://config.privoxy.org/show-status</a>. Note: the config file
349       option <a href=
350       "config.html#ENABLE-EDIT-ACTIONS">enable-edit-actions</a> must be
351       enabled for this to work. The editor allows both fine-grained control
352       over every single feature on a per-URL basis, and easy choosing from
353       wholesale sets of defaults like <span class="QUOTE">"Cautious"</span>,
354       <span class="QUOTE">"Medium"</span> or <span class=
355       "QUOTE">"Advanced"</span>. Warning: the <span class=
356       "QUOTE">"Advanced"</span> setting is more aggressive, and will be more
357       likely to cause problems for some sites. Experienced users only!</p>
358
359       <p>If you prefer plain text editing to GUIs, you can of course also
360       directly edit the the actions files with your favorite text editor.
361       Look at <tt class="FILENAME">default.action</tt> which is richly
362       commented with many good examples.</p>
363     </div>
364
365     <div class="SECT2">
366       <h2 class="SECT2"><a name="ACTIONS-APPLY" id="ACTIONS-APPLY">8.3. How
367       Actions are Applied to Requests</a></h2>
368
369       <p>Actions files are divided into sections. There are special sections,
370       like the <span class="QUOTE">"<a href=
371       "actions-file.html#ALIASES">alias</a>"</span> sections which will be
372       discussed later. For now let's concentrate on regular sections: They
373       have a heading line (often split up to multiple lines for readability)
374       which consist of a list of actions, separated by whitespace and
375       enclosed in curly braces. Below that, there is a list of URL and tag
376       patterns, each on a separate line.</p>
377
378       <p>To determine which actions apply to a request, the URL of the
379       request is compared to all URL patterns in each <span class=
380       "QUOTE">"action file"</span>. Every time it matches, the list of
381       applicable actions for the request is incrementally updated, using the
382       heading of the section in which the pattern is located. The same is
383       done again for tags and tag patterns later on.</p>
384
385       <p>If multiple applying sections set the same action differently, the
386       last match wins. If not, the effects are aggregated. E.g. a URL might
387       match a regular section with a heading line of <tt class="LITERAL">{
388       +<a href="actions-file.html#HANDLE-AS-IMAGE">handle-as-image</a>
389       }</tt>, then later another one with just <tt class="LITERAL">{
390       +<a href="actions-file.html#BLOCK">block</a> }</tt>, resulting in
391       <span class="emphasis"><i class="EMPHASIS">both</i></span> actions to
392       apply. And there may well be cases where you will want to combine
393       actions together. Such a section then might look like:</p>
394
395       <table border="0" bgcolor="#E0E0E0" width="100%">
396         <tr>
397           <td>
398             <pre class="SCREEN">
399   { +<tt class="LITERAL">handle-as-image</tt>  +<tt class=
400 "LITERAL">block{Banner ads.}</tt> }
401   # Block these as if they were images. Send no block page.
402    banners.example.com
403    media.example.com/.*banners
404    .example.com/images/ads/
405 </pre>
406           </td>
407         </tr>
408       </table>
409
410       <p>You can trace this process for URL patterns and any given URL by
411       visiting <a href="http://config.privoxy.org/show-url-info" target=
412       "_top">http://config.privoxy.org/show-url-info</a>.</p>
413
414       <p>Examples and more detail on this is provided in the Appendix,
415       <a href="appendix.html#ACTIONSANAT">Troubleshooting: Anatomy of an
416       Action</a> section.</p>
417     </div>
418
419     <div class="SECT2">
420       <h2 class="SECT2"><a name="AF-PATTERNS" id="AF-PATTERNS">8.4.
421       Patterns</a></h2>
422
423       <p>As mentioned, <span class="APPLICATION">Privoxy</span> uses
424       <span class="QUOTE">"patterns"</span> to determine what <span class=
425       "emphasis"><i class="EMPHASIS">actions</i></span> might apply to which
426       sites and pages your browser attempts to access. These <span class=
427       "QUOTE">"patterns"</span> use wild card type <span class=
428       "emphasis"><i class="EMPHASIS">pattern</i></span> matching to achieve a
429       high degree of flexibility. This allows one expression to be expanded
430       and potentially match against many similar patterns.</p>
431
432       <p>Generally, an URL pattern has the form <tt class=
433       "LITERAL">&lt;host&gt;&lt;port&gt;/&lt;path&gt;</tt>, where the
434       <tt class="LITERAL">&lt;host&gt;</tt>, the <tt class=
435       "LITERAL">&lt;port&gt;</tt> and the <tt class=
436       "LITERAL">&lt;path&gt;</tt> are optional. (This is why the special
437       <tt class="LITERAL">/</tt> pattern matches all URLs). Note that the
438       protocol portion of the URL pattern (e.g. <tt class=
439       "LITERAL">http://</tt>) should <span class="emphasis"><i class=
440       "EMPHASIS">not</i></span> be included in the pattern. This is assumed
441       already!</p>
442
443       <p>The pattern matching syntax is different for the host and path parts
444       of the URL. The host part uses a simple globbing type matching
445       technique, while the path part uses more flexible <a href=
446       "http://en.wikipedia.org/wiki/Regular_expressions" target=
447       "_top"><span class="QUOTE">"Regular Expressions"</span></a> (POSIX
448       1003.2).</p>
449
450       <p>The port part of a pattern is a decimal port number preceded by a
451       colon (<tt class="LITERAL">:</tt>). If the host part contains a
452       numerical IPv6 address, it has to be put into angle brackets
453       (<tt class="LITERAL">&lt;</tt>, <tt class="LITERAL">&gt;</tt>).</p>
454
455       <div class="VARIABLELIST">
456         <dl>
457           <dt><tt class="LITERAL">www.example.com/</tt></dt>
458
459           <dd>
460             <p>is a host-only pattern and will match any request to
461             <tt class="LITERAL">www.example.com</tt>, regardless of which
462             document on that server is requested. So ALL pages in this domain
463             would be covered by the scope of this action. Note that a simple
464             <tt class="LITERAL">example.com</tt> is different and would NOT
465             match.</p>
466           </dd>
467
468           <dt><tt class="LITERAL">www.example.com</tt></dt>
469
470           <dd>
471             <p>means exactly the same. For host-only patterns, the trailing
472             <tt class="LITERAL">/</tt> may be omitted.</p>
473           </dd>
474
475           <dt><tt class="LITERAL">www.example.com/index.html</tt></dt>
476
477           <dd>
478             <p>matches all the documents on <tt class=
479             "LITERAL">www.example.com</tt> whose name starts with <tt class=
480             "LITERAL">/index.html</tt>.</p>
481           </dd>
482
483           <dt><tt class="LITERAL">www.example.com/index.html$</tt></dt>
484
485           <dd>
486             <p>matches only the single document <tt class=
487             "LITERAL">/index.html</tt> on <tt class=
488             "LITERAL">www.example.com</tt>.</p>
489           </dd>
490
491           <dt><tt class="LITERAL">/index.html$</tt></dt>
492
493           <dd>
494             <p>matches the document <tt class="LITERAL">/index.html</tt>,
495             regardless of the domain, i.e. on <span class=
496             "emphasis"><i class="EMPHASIS">any</i></span> web server
497             anywhere.</p>
498           </dd>
499
500           <dt><tt class="LITERAL">/</tt></dt>
501
502           <dd>
503             <p>Matches any URL because there's no requirement for either the
504             domain or the path to match anything.</p>
505           </dd>
506
507           <dt><tt class="LITERAL">:8000/</tt></dt>
508
509           <dd>
510             <p>Matches any URL pointing to TCP port 8000.</p>
511           </dd>
512
513           <dt><tt class="LITERAL">10.0.0.1/</tt></dt>
514
515           <dd>
516             <p>Matches any URL with the host address <tt class=
517             "LITERAL">10.0.0.1</tt>. (Note that the real URL uses plain
518             brackets, not angle brackets.)</p>
519           </dd>
520
521           <dt><tt class="LITERAL">&lt;2001:db8::1&gt;/</tt></dt>
522
523           <dd>
524             <p>Matches any URL with the host address <tt class=
525             "LITERAL">2001:db8::1</tt>. (Note that the real URL uses plain
526             brackets, not angle brackets.)</p>
527           </dd>
528
529           <dt><tt class="LITERAL">index.html</tt></dt>
530
531           <dd>
532             <p>matches nothing, since it would be interpreted as a domain
533             name and there is no top-level domain called <tt class=
534             "LITERAL">.html</tt>. So its a mistake.</p>
535           </dd>
536         </dl>
537       </div>
538
539       <div class="SECT3">
540         <h3 class="SECT3"><a name="HOST-PATTERN" id="HOST-PATTERN">8.4.1. The
541         Host Pattern</a></h3>
542
543         <p>The matching of the host part offers some flexible options: if the
544         host pattern starts or ends with a dot, it becomes unanchored at that
545         end. The host pattern is often referred to as domain pattern as it is
546         usually used to match domain names and not IP addresses. For
547         example:</p>
548
549         <div class="VARIABLELIST">
550           <dl>
551             <dt><tt class="LITERAL">.example.com</tt></dt>
552
553             <dd>
554               <p>matches any domain with first-level domain <tt class=
555               "LITERAL">com</tt> and second-level domain <tt class=
556               "LITERAL">example</tt>. For example <tt class=
557               "LITERAL">www.example.com</tt>, <tt class=
558               "LITERAL">example.com</tt> and <tt class=
559               "LITERAL">foo.bar.baz.example.com</tt>. Note that it wouldn't
560               match if the second-level domain was <tt class=
561               "LITERAL">another-example</tt>.</p>
562             </dd>
563
564             <dt><tt class="LITERAL">www.</tt></dt>
565
566             <dd>
567               <p>matches any domain that <span class="emphasis"><i class=
568               "EMPHASIS">STARTS</i></span> with <tt class="LITERAL">www.</tt>
569               (It also matches the domain <tt class="LITERAL">www</tt> but
570               most of the time that doesn't matter.)</p>
571             </dd>
572
573             <dt><tt class="LITERAL">.example.</tt></dt>
574
575             <dd>
576               <p>matches any domain that <span class="emphasis"><i class=
577               "EMPHASIS">CONTAINS</i></span> <tt class=
578               "LITERAL">.example.</tt>. And, by the way, also included would
579               be any files or documents that exist within that domain since
580               no path limitations are specified. (Correctly speaking: It
581               matches any FQDN that contains <tt class="LITERAL">example</tt>
582               as a domain.) This might be <tt class=
583               "LITERAL">www.example.com</tt>, <tt class=
584               "LITERAL">news.example.de</tt>, or <tt class=
585               "LITERAL">www.example.net/cgi/testing.pl</tt> for instance. All
586               these cases are matched.</p>
587             </dd>
588           </dl>
589         </div>
590
591         <p>Additionally, there are wild-cards that you can use in the domain
592         names themselves. These work similarly to shell globbing type
593         wild-cards: <span class="QUOTE">"*"</span> represents zero or more
594         arbitrary characters (this is equivalent to the <a href=
595         "http://en.wikipedia.org/wiki/Regular_expressions" target=
596         "_top"><span class="QUOTE">"Regular Expression"</span></a> based
597         syntax of <span class="QUOTE">".*"</span>), <span class=
598         "QUOTE">"?"</span> represents any single character (this is
599         equivalent to the regular expression syntax of a simple <span class=
600         "QUOTE">"."</span>), and you can define <span class=
601         "QUOTE">"character classes"</span> in square brackets which is
602         similar to the same regular expression technique. All of this can be
603         freely mixed:</p>
604
605         <div class="VARIABLELIST">
606           <dl>
607             <dt><tt class="LITERAL">ad*.example.com</tt></dt>
608
609             <dd>
610               <p>matches <span class="QUOTE">"adserver.example.com"</span>,
611               <span class="QUOTE">"ads.example.com"</span>, etc but not
612               <span class="QUOTE">"sfads.example.com"</span></p>
613             </dd>
614
615             <dt><tt class="LITERAL">*ad*.example.com</tt></dt>
616
617             <dd>
618               <p>matches all of the above, and then some.</p>
619             </dd>
620
621             <dt><tt class="LITERAL">.?pix.com</tt></dt>
622
623             <dd>
624               <p>matches <tt class="LITERAL">www.ipix.com</tt>, <tt class=
625               "LITERAL">pictures.epix.com</tt>, <tt class=
626               "LITERAL">a.b.c.d.e.upix.com</tt> etc.</p>
627             </dd>
628
629             <dt><tt class="LITERAL">www[1-9a-ez].example.c*</tt></dt>
630
631             <dd>
632               <p>matches <tt class="LITERAL">www1.example.com</tt>,
633               <tt class="LITERAL">www4.example.cc</tt>, <tt class=
634               "LITERAL">wwwd.example.cy</tt>, <tt class=
635               "LITERAL">wwwz.example.com</tt> etc., but <span class=
636               "emphasis"><i class="EMPHASIS">not</i></span> <tt class=
637               "LITERAL">wwww.example.com</tt>.</p>
638             </dd>
639           </dl>
640         </div>
641
642         <p>While flexible, this is not the sophistication of full regular
643         expression based syntax.</p>
644       </div>
645
646       <div class="SECT3">
647         <h3 class="SECT3"><a name="AEN3163" id="AEN3163">8.4.2. The Path
648         Pattern</a></h3>
649
650         <p><span class="APPLICATION">Privoxy</span> uses <span class=
651         "QUOTE">"modern"</span> POSIX 1003.2 <a href=
652         "http://en.wikipedia.org/wiki/Regular_expressions" target=
653         "_top"><span class="QUOTE">"Regular Expressions"</span></a> for
654         matching the path portion (after the slash), and is thus more
655         flexible.</p>
656
657         <p>There is an <a href="appendix.html#REGEX">Appendix</a> with a
658         brief quick-start into regular expressions, you also might want to
659         have a look at your operating system's documentation on regular
660         expressions (try <tt class="LITERAL">man re_format</tt>).</p>
661
662         <p>Note that the path pattern is automatically left-anchored at the
663         <span class="QUOTE">"/"</span>, i.e. it matches as if it would start
664         with a <span class="QUOTE">"^"</span> (regular expression speak for
665         the beginning of a line).</p>
666
667         <p>Please also note that matching in the path is <span class=
668         "emphasis"><i class="EMPHASIS">CASE INSENSITIVE</i></span> by
669         default, but you can switch to case sensitive at any point in the
670         pattern by using the <span class="QUOTE">"(?-i)"</span> switch:
671         <tt class="LITERAL">www.example.com/(?-i)PaTtErN.*</tt> will match
672         only documents whose path starts with <tt class=
673         "LITERAL">PaTtErN</tt> in <span class="emphasis"><i class=
674         "EMPHASIS">exactly</i></span> this capitalization.</p>
675
676         <div class="VARIABLELIST">
677           <dl>
678             <dt><tt class="LITERAL">.example.com/.*</tt></dt>
679
680             <dd>
681               <p>Is equivalent to just <span class=
682               "QUOTE">".example.com"</span>, since any documents within that
683               domain are matched with or without the <span class=
684               "QUOTE">".*"</span> regular expression. This is redundant</p>
685             </dd>
686
687             <dt><tt class="LITERAL">.example.com/.*/index.html$</tt></dt>
688
689             <dd>
690               <p>Will match any page in the domain of <span class=
691               "QUOTE">"example.com"</span> that is named <span class=
692               "QUOTE">"index.html"</span>, and that is part of some path. For
693               example, it matches <span class=
694               "QUOTE">"www.example.com/testing/index.html"</span> but NOT
695               <span class="QUOTE">"www.example.com/index.html"</span> because
696               the regular expression called for at least two <span class=
697               "QUOTE">"/'s"</span>, thus the path requirement. It also would
698               match <span class=
699               "QUOTE">"www.example.com/testing/index_html"</span>, because of
700               the special meta-character <span class="QUOTE">"."</span>.</p>
701             </dd>
702
703             <dt><tt class="LITERAL">.example.com/(.*/)?index\.html$</tt></dt>
704
705             <dd>
706               <p>This regular expression is conditional so it will match any
707               page named <span class="QUOTE">"index.html"</span> regardless
708               of path which in this case can have one or more <span class=
709               "QUOTE">"/'s"</span>. And this one must contain exactly
710               <span class="QUOTE">".html"</span> (but does not have to end
711               with that!).</p>
712             </dd>
713
714             <dt><tt class=
715             "LITERAL">.example.com/(.*/)(ads|banners?|junk)</tt></dt>
716
717             <dd>
718               <p>This regular expression will match any path of <span class=
719               "QUOTE">"example.com"</span> that contains any of the words
720               <span class="QUOTE">"ads"</span>, <span class=
721               "QUOTE">"banner"</span>, <span class="QUOTE">"banners"</span>
722               (because of the <span class="QUOTE">"?"</span>) or <span class=
723               "QUOTE">"junk"</span>. The path does not have to end in these
724               words, just contain them.</p>
725             </dd>
726
727             <dt><tt class=
728             "LITERAL">.example.com/(.*/)(ads|banners?|junk)/.*\.(jpe?g|gif|png)$</tt></dt>
729
730             <dd>
731               <p>This is very much the same as above, except now it must end
732               in either <span class="QUOTE">".jpg"</span>, <span class=
733               "QUOTE">".jpeg"</span>, <span class="QUOTE">".gif"</span> or
734               <span class="QUOTE">".png"</span>. So this one is limited to
735               common image formats.</p>
736             </dd>
737           </dl>
738         </div>
739
740         <p>There are many, many good examples to be found in <tt class=
741         "FILENAME">default.action</tt>, and more tutorials below in <a href=
742         "appendix.html#REGEX">Appendix on regular expressions</a>.</p>
743       </div>
744
745       <div class="SECT3">
746         <h3 class="SECT3"><a name="TAG-PATTERN" id="TAG-PATTERN">8.4.3. The
747         Tag Pattern</a></h3>
748
749         <p>Tag patterns are used to change the applying actions based on the
750         request's tags. Tags can be created with either the <a href=
751         "actions-file.html#CLIENT-HEADER-TAGGER">client-header-tagger</a> or
752         the <a href=
753         "actions-file.html#SERVER-HEADER-TAGGER">server-header-tagger</a>
754         action.</p>
755
756         <p>Tag patterns have to start with <span class="QUOTE">"TAG:"</span>,
757         so <span class="APPLICATION">Privoxy</span> can tell them apart from
758         URL patterns. Everything after the colon including white space, is
759         interpreted as a regular expression with path pattern syntax, except
760         that tag patterns aren't left-anchored automatically (<span class=
761         "APPLICATION">Privoxy</span> doesn't silently add a <span class=
762         "QUOTE">"^"</span>, you have to do it yourself if you need it).</p>
763
764         <p>To match all requests that are tagged with <span class=
765         "QUOTE">"foo"</span> your pattern line should be <span class=
766         "QUOTE">"TAG:^foo$"</span>, <span class="QUOTE">"TAG:foo"</span>
767         would work as well, but it would also match requests whose tags
768         contain <span class="QUOTE">"foo"</span> somewhere. <span class=
769         "QUOTE">"TAG: foo"</span> wouldn't work as it requires white
770         space.</p>
771
772         <p>Sections can contain URL and tag patterns at the same time, but
773         tag patterns are checked after the URL patterns and thus always
774         overrule them, even if they are located before the URL patterns.</p>
775
776         <p>Once a new tag is added, Privoxy checks right away if it's matched
777         by one of the tag patterns and updates the action settings
778         accordingly. As a result tags can be used to activate other tagger
779         actions, as long as these other taggers look for headers that haven't
780         already be parsed.</p>
781
782         <p>For example you could tag client requests which use the <tt class=
783         "LITERAL">POST</tt> method, then use this tag to activate another
784         tagger that adds a tag if cookies are sent, and then use a block
785         action based on the cookie tag. This allows the outcome of one
786         action, to be input into a subsequent action. However if you'd
787         reverse the position of the described taggers, and activated the
788         method tagger based on the cookie tagger, no method tags would be
789         created. The method tagger would look for the request line, but at
790         the time the cookie tag is created, the request line has already been
791         parsed.</p>
792
793         <p>While this is a limitation you should be aware of, this kind of
794         indirection is seldom needed anyway and even the example doesn't make
795         too much sense.</p>
796       </div>
797
798       <div class="SECT3">
799         <h3 class="SECT3"><a name="NEGATIVE-TAG-PATTERNS" id=
800         "NEGATIVE-TAG-PATTERNS">8.4.4. The Negative Tag Patterns</a></h3>
801
802         <p>To match requests that do not have a certain tag, specify a
803         negative tag pattern by prefixing the tag pattern line with either
804         <span class="QUOTE">"NO-REQUEST-TAG:"</span> or <span class=
805         "QUOTE">"NO-RESPONSE-TAG:"</span> instead of <span class=
806         "QUOTE">"TAG:"</span>.</p>
807
808         <p>Negative tag patterns created with <span class=
809         "QUOTE">"NO-REQUEST-TAG:"</span> are checked after all client headers
810         are scanned, the ones created with <span class=
811         "QUOTE">"NO-RESPONSE-TAG:"</span> are checked after all server
812         headers are scanned. In both cases all the created tags are
813         considered.</p>
814       </div>
815     </div>
816
817     <div class="SECT2">
818       <h2 class="SECT2"><a name="ACTIONS" id="ACTIONS">8.5. Actions</a></h2>
819
820       <p>All actions are disabled by default, until they are explicitly
821       enabled somewhere in an actions file. Actions are turned on if preceded
822       with a <span class="QUOTE">"+"</span>, and turned off if preceded with
823       a <span class="QUOTE">"-"</span>. So a <tt class="LITERAL">+action</tt>
824       means <span class="QUOTE">"do that action"</span>, e.g. <tt class=
825       "LITERAL">+block</tt> means <span class="QUOTE">"please block URLs that
826       match the following patterns"</span>, and <tt class=
827       "LITERAL">-block</tt> means <span class="QUOTE">"don't block URLs that
828       match the following patterns, even if <tt class="LITERAL">+block</tt>
829       previously applied."</span></p>
830
831       <p>Again, actions are invoked by placing them on a line, enclosed in
832       curly braces and separated by whitespace, like in <tt class=
833       "LITERAL">{+some-action -some-other-action{some-parameter}}</tt>,
834       followed by a list of URL patterns, one per line, to which they apply.
835       Together, the actions line and the following pattern lines make up a
836       section of the actions file.</p>
837
838       <p>Actions fall into three categories:</p>
839
840       <ul>
841         <li>
842           <p>Boolean, i.e the action can only be <span class=
843           "QUOTE">"enabled"</span> or <span class="QUOTE">"disabled"</span>.
844           Syntax:</p>
845
846           <table border="0" bgcolor="#E0E0E0" width="90%">
847             <tr>
848               <td>
849                 <pre class="SCREEN">
850   +<tt class="REPLACEABLE"><i>name</i></tt>        # enable action <tt class=
851 "REPLACEABLE"><i>name</i></tt>
852   -<tt class=
853 "REPLACEABLE"><i>name</i></tt>        # disable action <tt class="REPLACEABLE"><i>name</i></tt>
854 </pre>
855               </td>
856             </tr>
857           </table>
858
859           <p>Example: <tt class="LITERAL">+handle-as-image</tt></p>
860         </li>
861
862         <li>
863           <p>Parameterized, where some value is required in order to enable
864           this type of action. Syntax:</p>
865
866           <table border="0" bgcolor="#E0E0E0" width="90%">
867             <tr>
868               <td>
869                 <pre class="SCREEN">
870   +<tt class="REPLACEABLE"><i>name</i></tt>{<tt class=
871 "REPLACEABLE"><i>param</i></tt>}  # enable action and set parameter to <tt class="REPLACEABLE"><i>param</i></tt>,
872                # overwriting parameter from previous match if necessary
873   -<tt class=
874 "REPLACEABLE"><i>name</i></tt>         # disable action. The parameter can be omitted
875 </pre>
876               </td>
877             </tr>
878           </table>
879
880           <p>Note that if the URL matches multiple positive forms of a
881           parameterized action, the last match wins, i.e. the params from
882           earlier matches are simply ignored.</p>
883
884           <p>Example: <tt class="LITERAL">+hide-user-agent{Mozilla/5.0 (X11;
885           U; FreeBSD i386; en-US; rv:1.8.1.4) Gecko/20070602
886           Firefox/2.0.0.4}</tt></p>
887         </li>
888
889         <li>
890           <p>Multi-value. These look exactly like parameterized actions, but
891           they behave differently: If the action applies multiple times to
892           the same URL, but with different parameters, <span class=
893           "emphasis"><i class="EMPHASIS">all</i></span> the parameters from
894           <span class="emphasis"><i class="EMPHASIS">all</i></span> matches
895           are remembered. This is used for actions that can be executed for
896           the same request repeatedly, like adding multiple headers, or
897           filtering through multiple filters. Syntax:</p>
898
899           <table border="0" bgcolor="#E0E0E0" width="90%">
900             <tr>
901               <td>
902                 <pre class="SCREEN">
903   +<tt class="REPLACEABLE"><i>name</i></tt>{<tt class=
904 "REPLACEABLE"><i>param</i></tt>}   # enable action and add <tt class=
905 "REPLACEABLE"><i>param</i></tt> to the list of parameters
906   -<tt class="REPLACEABLE"><i>name</i></tt>{<tt class=
907 "REPLACEABLE"><i>param</i></tt>}   # remove the parameter <tt class=
908 "REPLACEABLE"><i>param</i></tt> from the list of parameters
909                 # If it was the last one left, disable the action.
910   <tt class=
911 "REPLACEABLE"><i>-name</i></tt>          # disable this action completely and remove all parameters from the list
912 </pre>
913               </td>
914             </tr>
915           </table>
916
917           <p>Examples: <tt class="LITERAL">+add-header{X-Fun-Header: Some
918           text}</tt> and <tt class=
919           "LITERAL">+filter{html-annoyances}</tt></p>
920         </li>
921       </ul>
922
923       <p>If nothing is specified in any actions file, no <span class=
924       "QUOTE">"actions"</span> are taken. So in this case <span class=
925       "APPLICATION">Privoxy</span> would just be a normal, non-blocking,
926       non-filtering proxy. You must specifically enable the privacy and
927       blocking features you need (although the provided default actions files
928       will give a good starting point).</p>
929
930       <p>Later defined action sections always over-ride earlier ones of the
931       same type. So exceptions to any rules you make, should come in the
932       latter part of the file (or in a file that is processed later when
933       using multiple actions files such as <tt class=
934       "FILENAME">user.action</tt>). For multi-valued actions, the actions are
935       applied in the order they are specified. Actions files are processed in
936       the order they are defined in <tt class="FILENAME">config</tt> (the
937       default installation has three actions files). It also quite possible
938       for any given URL to match more than one <span class=
939       "QUOTE">"pattern"</span> (because of wildcards and regular
940       expressions), and thus to trigger more than one set of actions! Last
941       match wins.</p>
942
943       <p>The list of valid <span class="APPLICATION">Privoxy</span> actions
944       are:</p>
945
946       <div class="SECT3">
947         <h4 class="SECT3"><a name="ADD-HEADER" id="ADD-HEADER">8.5.1.
948         add-header</a></h4>
949
950         <div class="VARIABLELIST">
951           <dl>
952             <dt>Typical use:</dt>
953
954             <dd>
955               <p>Confuse log analysis, custom applications</p>
956             </dd>
957
958             <dt>Effect:</dt>
959
960             <dd>
961               <p>Sends a user defined HTTP header to the web server.</p>
962             </dd>
963
964             <dt>Type:</dt>
965
966             <dd>
967               <p>Multi-value.</p>
968             </dd>
969
970             <dt>Parameter:</dt>
971
972             <dd>
973               <p>Any string value is possible. Validity of the defined HTTP
974               headers is not checked. It is recommended that you use the
975               <span class="QUOTE">"<tt class="LITERAL">X-</tt>"</span> prefix
976               for custom headers.</p>
977             </dd>
978
979             <dt>Notes:</dt>
980
981             <dd>
982               <p>This action may be specified multiple times, in order to
983               define multiple headers. This is rarely needed for the typical
984               user. If you don't know what <span class="QUOTE">"HTTP
985               headers"</span> are, you definitely don't need to worry about
986               this one.</p>
987
988               <p>Headers added by this action are not modified by other
989               actions.</p>
990             </dd>
991
992             <dt>Example usage:</dt>
993
994             <dd>
995               <table border="0" bgcolor="#E0E0E0" width="90%">
996                 <tr>
997                   <td>
998                     <pre class="SCREEN">
999 +add-header{X-User-Tracking: sucks}
1000 </pre>
1001                   </td>
1002                 </tr>
1003               </table>
1004             </dd>
1005           </dl>
1006         </div>
1007       </div>
1008
1009       <div class="SECT3">
1010         <h4 class="SECT3"><a name="BLOCK" id="BLOCK">8.5.2. block</a></h4>
1011
1012         <div class="VARIABLELIST">
1013           <dl>
1014             <dt>Typical use:</dt>
1015
1016             <dd>
1017               <p>Block ads or other unwanted content</p>
1018             </dd>
1019
1020             <dt>Effect:</dt>
1021
1022             <dd>
1023               <p>Requests for URLs to which this action applies are blocked,
1024               i.e. the requests are trapped by <span class=
1025               "APPLICATION">Privoxy</span> and the requested URL is never
1026               retrieved, but is answered locally with a substitute page or
1027               image, as determined by the <tt class="LITERAL"><a href=
1028               "actions-file.html#HANDLE-AS-IMAGE">handle-as-image</a></tt>,
1029               <tt class="LITERAL"><a href=
1030               "actions-file.html#SET-IMAGE-BLOCKER">set-image-blocker</a></tt>,
1031               and <tt class="LITERAL"><a href=
1032               "actions-file.html#HANDLE-AS-EMPTY-DOCUMENT">handle-as-empty-document</a></tt>
1033               actions.</p>
1034             </dd>
1035
1036             <dt>Type:</dt>
1037
1038             <dd>
1039               <p>Parameterized.</p>
1040             </dd>
1041
1042             <dt>Parameter:</dt>
1043
1044             <dd>
1045               <p>A block reason that should be given to the user.</p>
1046             </dd>
1047
1048             <dt>Notes:</dt>
1049
1050             <dd>
1051               <p><span class="APPLICATION">Privoxy</span> sends a special
1052               <span class="QUOTE">"BLOCKED"</span> page for requests to
1053               blocked pages. This page contains the block reason given as
1054               parameter, a link to find out why the block action applies, and
1055               a click-through to the blocked content (the latter only if the
1056               force feature is available and enabled).</p>
1057
1058               <p>A very important exception occurs if <span class=
1059               "emphasis"><i class="EMPHASIS">both</i></span> <tt class=
1060               "LITERAL">block</tt> and <tt class="LITERAL"><a href=
1061               "actions-file.html#HANDLE-AS-IMAGE">handle-as-image</a></tt>,
1062               apply to the same request: it will then be replaced by an
1063               image. If <tt class="LITERAL"><a href=
1064               "actions-file.html#SET-IMAGE-BLOCKER">set-image-blocker</a></tt>
1065               (see below) also applies, the type of image will be determined
1066               by its parameter, if not, the standard checkerboard pattern is
1067               sent.</p>
1068
1069               <p>It is important to understand this process, in order to
1070               understand how <span class="APPLICATION">Privoxy</span> deals
1071               with ads and other unwanted content. Blocking is a core
1072               feature, and one upon which various other features depend.</p>
1073
1074               <p>The <tt class="LITERAL"><a href=
1075               "actions-file.html#FILTER">filter</a></tt> action can perform a
1076               very similar task, by <span class="QUOTE">"blocking"</span>
1077               banner images and other content through rewriting the relevant
1078               URLs in the document's HTML source, so they don't get requested
1079               in the first place. Note that this is a totally different
1080               technique, and it's easy to confuse the two.</p>
1081             </dd>
1082
1083             <dt>Example usage (section):</dt>
1084
1085             <dd>
1086               <table border="0" bgcolor="#E0E0E0" width="90%">
1087                 <tr>
1088                   <td>
1089                     <pre class="SCREEN">
1090 {+block{No nasty stuff for you.}}
1091 # Block and replace with "blocked" page
1092  .nasty-stuff.example.com
1093
1094 {+block{Doubleclick banners.} +handle-as-image}
1095 # Block and replace with image
1096  .ad.doubleclick.net
1097  .ads.r.us/banners/
1098
1099 {+block{Layered ads.} +handle-as-empty-document}
1100 # Block and then ignore
1101  adserver.example.net/.*\.js$
1102 </pre>
1103                   </td>
1104                 </tr>
1105               </table>
1106             </dd>
1107           </dl>
1108         </div>
1109       </div>
1110
1111       <div class="SECT3">
1112         <h4 class="SECT3"><a name="CHANGE-X-FORWARDED-FOR" id=
1113         "CHANGE-X-FORWARDED-FOR">8.5.3. change-x-forwarded-for</a></h4>
1114
1115         <div class="VARIABLELIST">
1116           <dl>
1117             <dt>Typical use:</dt>
1118
1119             <dd>
1120               <p>Improve privacy by not forwarding the source of the request
1121               in the HTTP headers.</p>
1122             </dd>
1123
1124             <dt>Effect:</dt>
1125
1126             <dd>
1127               <p>Deletes the <span class="QUOTE">"X-Forwarded-For:"</span>
1128               HTTP header from the client request, or adds a new one.</p>
1129             </dd>
1130
1131             <dt>Type:</dt>
1132
1133             <dd>
1134               <p>Parameterized.</p>
1135             </dd>
1136
1137             <dt>Parameter:</dt>
1138
1139             <dd>
1140               <ul>
1141                 <li>
1142                   <p><span class="QUOTE">"block"</span> to delete the
1143                   header.</p>
1144                 </li>
1145
1146                 <li>
1147                   <p><span class="QUOTE">"add"</span> to create the header
1148                   (or append the client's IP address to an already existing
1149                   one).</p>
1150                 </li>
1151               </ul>
1152             </dd>
1153
1154             <dt>Notes:</dt>
1155
1156             <dd>
1157               <p>It is safe and recommended to use <tt class=
1158               "LITERAL">block</tt>.</p>
1159
1160               <p>Forwarding the source address of the request may make sense
1161               in some multi-user setups but is also a privacy risk.</p>
1162             </dd>
1163
1164             <dt>Example usage:</dt>
1165
1166             <dd>
1167               <table border="0" bgcolor="#E0E0E0" width="90%">
1168                 <tr>
1169                   <td>
1170                     <pre class="SCREEN">
1171 +change-x-forwarded-for{block}
1172 </pre>
1173                   </td>
1174                 </tr>
1175               </table>
1176             </dd>
1177           </dl>
1178         </div>
1179       </div>
1180
1181       <div class="SECT3">
1182         <h4 class="SECT3"><a name="CLIENT-HEADER-FILTER" id=
1183         "CLIENT-HEADER-FILTER">8.5.4. client-header-filter</a></h4>
1184
1185         <div class="VARIABLELIST">
1186           <dl>
1187             <dt>Typical use:</dt>
1188
1189             <dd>
1190               <p>Rewrite or remove single client headers.</p>
1191             </dd>
1192
1193             <dt>Effect:</dt>
1194
1195             <dd>
1196               <p>All client headers to which this action applies are filtered
1197               on-the-fly through the specified regular expression based
1198               substitutions.</p>
1199             </dd>
1200
1201             <dt>Type:</dt>
1202
1203             <dd>
1204               <p>Parameterized.</p>
1205             </dd>
1206
1207             <dt>Parameter:</dt>
1208
1209             <dd>
1210               <p>The name of a client-header filter, as defined in one of the
1211               <a href="filter-file.html">filter files</a>.</p>
1212             </dd>
1213
1214             <dt>Notes:</dt>
1215
1216             <dd>
1217               <p>Client-header filters are applied to each header on its own,
1218               not to all at once. This makes it easier to diagnose problems,
1219               but on the downside you can't write filters that only change
1220               header x if header y's value is z. You can do that by using
1221               tags though.</p>
1222
1223               <p>Client-header filters are executed after the other header
1224               actions have finished and use their output as input.</p>
1225
1226               <p>If the request URI gets changed, <span class=
1227               "APPLICATION">Privoxy</span> will detect that and use the new
1228               one. This can be used to rewrite the request destination behind
1229               the client's back, for example to specify a Tor exit relay for
1230               certain requests.</p>
1231
1232               <p>Please refer to the <a href="filter-file.html">filter file
1233               chapter</a> to learn which client-header filters are available
1234               by default, and how to create your own.</p>
1235             </dd>
1236
1237             <dt>Example usage (section):</dt>
1238
1239             <dd>
1240               <table border="0" bgcolor="#E0E0E0" width="90%">
1241                 <tr>
1242                   <td>
1243                     <pre class="SCREEN">
1244 # Hide Tor exit notation in Host and Referer Headers
1245 {+client-header-filter{hide-tor-exit-notation}}
1246 /
1247
1248 </pre>
1249                   </td>
1250                 </tr>
1251               </table>
1252             </dd>
1253           </dl>
1254         </div>
1255       </div>
1256
1257       <div class="SECT3">
1258         <h4 class="SECT3"><a name="CLIENT-HEADER-TAGGER" id=
1259         "CLIENT-HEADER-TAGGER">8.5.5. client-header-tagger</a></h4>
1260
1261         <div class="VARIABLELIST">
1262           <dl>
1263             <dt>Typical use:</dt>
1264
1265             <dd>
1266               <p>Block requests based on their headers.</p>
1267             </dd>
1268
1269             <dt>Effect:</dt>
1270
1271             <dd>
1272               <p>Client headers to which this action applies are filtered
1273               on-the-fly through the specified regular expression based
1274               substitutions, the result is used as tag.</p>
1275             </dd>
1276
1277             <dt>Type:</dt>
1278
1279             <dd>
1280               <p>Parameterized.</p>
1281             </dd>
1282
1283             <dt>Parameter:</dt>
1284
1285             <dd>
1286               <p>The name of a client-header tagger, as defined in one of the
1287               <a href="filter-file.html">filter files</a>.</p>
1288             </dd>
1289
1290             <dt>Notes:</dt>
1291
1292             <dd>
1293               <p>Client-header taggers are applied to each header on its own,
1294               and as the header isn't modified, each tagger <span class=
1295               "QUOTE">"sees"</span> the original.</p>
1296
1297               <p>Client-header taggers are the first actions that are
1298               executed and their tags can be used to control every other
1299               action.</p>
1300             </dd>
1301
1302             <dt>Example usage (section):</dt>
1303
1304             <dd>
1305               <table border="0" bgcolor="#E0E0E0" width="90%">
1306                 <tr>
1307                   <td>
1308                     <pre class="SCREEN">
1309 # Tag every request with the User-Agent header
1310 {+client-header-tagger{user-agent}}
1311 /
1312
1313 # Tagging itself doesn't change the action
1314 # settings, sections with TAG patterns do:
1315 #
1316 # If it's a download agent, use a different forwarding proxy,
1317 # show the real User-Agent and make sure resume works.
1318 {+forward-override{forward-socks5 10.0.0.2:2222 .} \
1319  -hide-if-modified-since      \
1320  -overwrite-last-modified     \
1321  -hide-user-agent             \
1322  -filter                      \
1323  -deanimate-gifs              \
1324 }
1325 TAG:^User-Agent: NetBSD-ftp/
1326 TAG:^User-Agent: Novell ZYPP Installer
1327 TAG:^User-Agent: RPM APT-HTTP/
1328 TAG:^User-Agent: fetch libfetch/
1329 TAG:^User-Agent: Ubuntu APT-HTTP/
1330 TAG:^User-Agent: MPlayer/
1331
1332 </pre>
1333                   </td>
1334                 </tr>
1335               </table>
1336
1337               <table border="0" bgcolor="#E0E0E0" width="90%">
1338                 <tr>
1339                   <td>
1340                     <pre class="SCREEN">
1341 # Tag all requests with the Range header set
1342 {+client-header-tagger{range-requests}}
1343 /
1344
1345 # Disable filtering for the tagged requests.
1346 #
1347 # With filtering enabled Privoxy would remove the Range headers
1348 # to be able to filter the whole response. The downside is that
1349 # it prevents clients from resuming downloads or skipping over
1350 # parts of multimedia files.
1351 {-filter -deanimate-gifs}
1352 TAG:^RANGE-REQUEST$
1353
1354 </pre>
1355                   </td>
1356                 </tr>
1357               </table>
1358             </dd>
1359           </dl>
1360         </div>
1361       </div>
1362
1363       <div class="SECT3">
1364         <h4 class="SECT3"><a name="CONTENT-TYPE-OVERWRITE" id=
1365         "CONTENT-TYPE-OVERWRITE">8.5.6. content-type-overwrite</a></h4>
1366
1367         <div class="VARIABLELIST">
1368           <dl>
1369             <dt>Typical use:</dt>
1370
1371             <dd>
1372               <p>Stop useless download menus from popping up, or change the
1373               browser's rendering mode</p>
1374             </dd>
1375
1376             <dt>Effect:</dt>
1377
1378             <dd>
1379               <p>Replaces the <span class="QUOTE">"Content-Type:"</span> HTTP
1380               server header.</p>
1381             </dd>
1382
1383             <dt>Type:</dt>
1384
1385             <dd>
1386               <p>Parameterized.</p>
1387             </dd>
1388
1389             <dt>Parameter:</dt>
1390
1391             <dd>
1392               <p>Any string.</p>
1393             </dd>
1394
1395             <dt>Notes:</dt>
1396
1397             <dd>
1398               <p>The <span class="QUOTE">"Content-Type:"</span> HTTP server
1399               header is used by the browser to decide what to do with the
1400               document. The value of this header can cause the browser to
1401               open a download menu instead of displaying the document by
1402               itself, even if the document's format is supported by the
1403               browser.</p>
1404
1405               <p>The declared content type can also affect which rendering
1406               mode the browser chooses. If XHTML is delivered as <span class=
1407               "QUOTE">"text/html"</span>, many browsers treat it as yet
1408               another broken HTML document. If it is send as <span class=
1409               "QUOTE">"application/xml"</span>, browsers with XHTML support
1410               will only display it, if the syntax is correct.</p>
1411
1412               <p>If you see a web site that proudly uses XHTML buttons, but
1413               sets <span class="QUOTE">"Content-Type: text/html"</span>, you
1414               can use <span class="APPLICATION">Privoxy</span> to overwrite
1415               it with <span class="QUOTE">"application/xml"</span> and
1416               validate the web master's claim inside your XHTML-supporting
1417               browser. If the syntax is incorrect, the browser will complain
1418               loudly.</p>
1419
1420               <p>You can also go the opposite direction: if your browser
1421               prints error messages instead of rendering a document falsely
1422               declared as XHTML, you can overwrite the content type with
1423               <span class="QUOTE">"text/html"</span> and have it rendered as
1424               broken HTML document.</p>
1425
1426               <p>By default <tt class="LITERAL">content-type-overwrite</tt>
1427               only replaces <span class="QUOTE">"Content-Type:"</span>
1428               headers that look like some kind of text. If you want to
1429               overwrite it unconditionally, you have to combine it with
1430               <tt class="LITERAL"><a href=
1431               "actions-file.html#FORCE-TEXT-MODE">force-text-mode</a></tt>.
1432               This limitation exists for a reason, think twice before
1433               circumventing it.</p>
1434
1435               <p>Most of the time it's easier to replace this action with a
1436               custom <tt class="LITERAL"><a href=
1437               "actions-file.html#SERVER-HEADER-FILTER">server-header
1438               filter</a></tt>. It allows you to activate it for every
1439               document of a certain site and it will still only replace the
1440               content types you aimed at.</p>
1441
1442               <p>Of course you can apply <tt class=
1443               "LITERAL">content-type-overwrite</tt> to a whole site and then
1444               make URL based exceptions, but it's a lot more work to get the
1445               same precision.</p>
1446             </dd>
1447
1448             <dt>Example usage (sections):</dt>
1449
1450             <dd>
1451               <table border="0" bgcolor="#E0E0E0" width="90%">
1452                 <tr>
1453                   <td>
1454                     <pre class="SCREEN">
1455 # Check if www.example.net/ really uses valid XHTML
1456 { +content-type-overwrite{application/xml} }
1457 www.example.net/
1458
1459 # but leave the content type unmodified if the URL looks like a style sheet
1460 {-content-type-overwrite}
1461 www.example.net/.*\.css$
1462 www.example.net/.*style
1463 </pre>
1464                   </td>
1465                 </tr>
1466               </table>
1467             </dd>
1468           </dl>
1469         </div>
1470       </div>
1471
1472       <div class="SECT3">
1473         <h4 class="SECT3"><a name="CRUNCH-CLIENT-HEADER" id=
1474         "CRUNCH-CLIENT-HEADER">8.5.7. crunch-client-header</a></h4>
1475
1476         <div class="VARIABLELIST">
1477           <dl>
1478             <dt>Typical use:</dt>
1479
1480             <dd>
1481               <p>Remove a client header <span class=
1482               "APPLICATION">Privoxy</span> has no dedicated action for.</p>
1483             </dd>
1484
1485             <dt>Effect:</dt>
1486
1487             <dd>
1488               <p>Deletes every header sent by the client that contains the
1489               string the user supplied as parameter.</p>
1490             </dd>
1491
1492             <dt>Type:</dt>
1493
1494             <dd>
1495               <p>Parameterized.</p>
1496             </dd>
1497
1498             <dt>Parameter:</dt>
1499
1500             <dd>
1501               <p>Any string.</p>
1502             </dd>
1503
1504             <dt>Notes:</dt>
1505
1506             <dd>
1507               <p>This action allows you to block client headers for which no
1508               dedicated <span class="APPLICATION">Privoxy</span> action
1509               exists. <span class="APPLICATION">Privoxy</span> will remove
1510               every client header that contains the string you supplied as
1511               parameter.</p>
1512
1513               <p>Regular expressions are <span class="emphasis"><i class=
1514               "EMPHASIS">not supported</i></span> and you can't use this
1515               action to block different headers in the same request, unless
1516               they contain the same string.</p>
1517
1518               <p><tt class="LITERAL">crunch-client-header</tt> is only meant
1519               for quick tests. If you have to block several different
1520               headers, or only want to modify parts of them, you should use a
1521               <tt class="LITERAL"><a href=
1522               "actions-file.html#CLIENT-HEADER-FILTER">client-header
1523               filter</a></tt>.</p>
1524
1525               <div class="WARNING">
1526                 <table class="WARNING" border="1" width="90%">
1527                   <tr>
1528                     <td align="center"><b>Warning</b></td>
1529                   </tr>
1530
1531                   <tr>
1532                     <td align="left">
1533                       <p>Don't block any header without understanding the
1534                       consequences.</p>
1535                     </td>
1536                   </tr>
1537                 </table>
1538               </div>
1539             </dd>
1540
1541             <dt>Example usage (section):</dt>
1542
1543             <dd>
1544               <table border="0" bgcolor="#E0E0E0" width="90%">
1545                 <tr>
1546                   <td>
1547                     <pre class="SCREEN">
1548 # Block the non-existent "Privacy-Violation:" client header
1549 { +crunch-client-header{Privacy-Violation:} }
1550 /
1551
1552 </pre>
1553                   </td>
1554                 </tr>
1555               </table>
1556             </dd>
1557           </dl>
1558         </div>
1559       </div>
1560
1561       <div class="SECT3">
1562         <h4 class="SECT3"><a name="CRUNCH-IF-NONE-MATCH" id=
1563         "CRUNCH-IF-NONE-MATCH">8.5.8. crunch-if-none-match</a></h4>
1564
1565         <div class="VARIABLELIST">
1566           <dl>
1567             <dt>Typical use:</dt>
1568
1569             <dd>
1570               <p>Prevent yet another way to track the user's steps between
1571               sessions.</p>
1572             </dd>
1573
1574             <dt>Effect:</dt>
1575
1576             <dd>
1577               <p>Deletes the <span class="QUOTE">"If-None-Match:"</span> HTTP
1578               client header.</p>
1579             </dd>
1580
1581             <dt>Type:</dt>
1582
1583             <dd>
1584               <p>Boolean.</p>
1585             </dd>
1586
1587             <dt>Parameter:</dt>
1588
1589             <dd>
1590               <p>N/A</p>
1591             </dd>
1592
1593             <dt>Notes:</dt>
1594
1595             <dd>
1596               <p>Removing the <span class="QUOTE">"If-None-Match:"</span>
1597               HTTP client header is useful for filter testing, where you want
1598               to force a real reload instead of getting status code
1599               <span class="QUOTE">"304"</span> which would cause the browser
1600               to use a cached copy of the page.</p>
1601
1602               <p>It is also useful to make sure the header isn't used as a
1603               cookie replacement (unlikely but possible).</p>
1604
1605               <p>Blocking the <span class="QUOTE">"If-None-Match:"</span>
1606               header shouldn't cause any caching problems, as long as the
1607               <span class="QUOTE">"If-Modified-Since:"</span> header isn't
1608               blocked or missing as well.</p>
1609
1610               <p>It is recommended to use this action together with
1611               <tt class="LITERAL"><a href=
1612               "actions-file.html#HIDE-IF-MODIFIED-SINCE">hide-if-modified-since</a></tt>
1613               and <tt class="LITERAL"><a href=
1614               "actions-file.html#OVERWRITE-LAST-MODIFIED">overwrite-last-modified</a></tt>.</p>
1615             </dd>
1616
1617             <dt>Example usage (section):</dt>
1618
1619             <dd>
1620               <table border="0" bgcolor="#E0E0E0" width="90%">
1621                 <tr>
1622                   <td>
1623                     <pre class="SCREEN">
1624 # Let the browser revalidate cached documents but don't
1625 # allow the server to use the revalidation headers for user tracking.
1626 {+hide-if-modified-since{-60} \
1627  +overwrite-last-modified{randomize} \
1628  +crunch-if-none-match}
1629 /
1630 </pre>
1631                   </td>
1632                 </tr>
1633               </table>
1634             </dd>
1635           </dl>
1636         </div>
1637       </div>
1638
1639       <div class="SECT3">
1640         <h4 class="SECT3"><a name="CRUNCH-INCOMING-COOKIES" id=
1641         "CRUNCH-INCOMING-COOKIES">8.5.9. crunch-incoming-cookies</a></h4>
1642
1643         <div class="VARIABLELIST">
1644           <dl>
1645             <dt>Typical use:</dt>
1646
1647             <dd>
1648               <p>Prevent the web server from setting HTTP cookies on your
1649               system</p>
1650             </dd>
1651
1652             <dt>Effect:</dt>
1653
1654             <dd>
1655               <p>Deletes any <span class="QUOTE">"Set-Cookie:"</span> HTTP
1656               headers from server replies.</p>
1657             </dd>
1658
1659             <dt>Type:</dt>
1660
1661             <dd>
1662               <p>Boolean.</p>
1663             </dd>
1664
1665             <dt>Parameter:</dt>
1666
1667             <dd>
1668               <p>N/A</p>
1669             </dd>
1670
1671             <dt>Notes:</dt>
1672
1673             <dd>
1674               <p>This action is only concerned with <span class=
1675               "emphasis"><i class="EMPHASIS">incoming</i></span> HTTP
1676               cookies. For <span class="emphasis"><i class=
1677               "EMPHASIS">outgoing</i></span> HTTP cookies, use <tt class=
1678               "LITERAL"><a href=
1679               "actions-file.html#CRUNCH-OUTGOING-COOKIES">crunch-outgoing-cookies</a></tt>.
1680               Use <span class="emphasis"><i class="EMPHASIS">both</i></span>
1681               to disable HTTP cookies completely.</p>
1682
1683               <p>It makes <span class="emphasis"><i class="EMPHASIS">no sense
1684               at all</i></span> to use this action in conjunction with the
1685               <tt class="LITERAL"><a href=
1686               "actions-file.html#SESSION-COOKIES-ONLY">session-cookies-only</a></tt>
1687               action, since it would prevent the session cookies from being
1688               set. See also <tt class="LITERAL"><a href=
1689               "actions-file.html#FILTER-CONTENT-COOKIES">filter-content-cookies</a></tt>.</p>
1690             </dd>
1691
1692             <dt>Example usage:</dt>
1693
1694             <dd>
1695               <table border="0" bgcolor="#E0E0E0" width="90%">
1696                 <tr>
1697                   <td>
1698                     <pre class="SCREEN">
1699 +crunch-incoming-cookies
1700 </pre>
1701                   </td>
1702                 </tr>
1703               </table>
1704             </dd>
1705           </dl>
1706         </div>
1707       </div>
1708
1709       <div class="SECT3">
1710         <h4 class="SECT3"><a name="CRUNCH-SERVER-HEADER" id=
1711         "CRUNCH-SERVER-HEADER">8.5.10. crunch-server-header</a></h4>
1712
1713         <div class="VARIABLELIST">
1714           <dl>
1715             <dt>Typical use:</dt>
1716
1717             <dd>
1718               <p>Remove a server header <span class=
1719               "APPLICATION">Privoxy</span> has no dedicated action for.</p>
1720             </dd>
1721
1722             <dt>Effect:</dt>
1723
1724             <dd>
1725               <p>Deletes every header sent by the server that contains the
1726               string the user supplied as parameter.</p>
1727             </dd>
1728
1729             <dt>Type:</dt>
1730
1731             <dd>
1732               <p>Parameterized.</p>
1733             </dd>
1734
1735             <dt>Parameter:</dt>
1736
1737             <dd>
1738               <p>Any string.</p>
1739             </dd>
1740
1741             <dt>Notes:</dt>
1742
1743             <dd>
1744               <p>This action allows you to block server headers for which no
1745               dedicated <span class="APPLICATION">Privoxy</span> action
1746               exists. <span class="APPLICATION">Privoxy</span> will remove
1747               every server header that contains the string you supplied as
1748               parameter.</p>
1749
1750               <p>Regular expressions are <span class="emphasis"><i class=
1751               "EMPHASIS">not supported</i></span> and you can't use this
1752               action to block different headers in the same request, unless
1753               they contain the same string.</p>
1754
1755               <p><tt class="LITERAL">crunch-server-header</tt> is only meant
1756               for quick tests. If you have to block several different
1757               headers, or only want to modify parts of them, you should use a
1758               custom <tt class="LITERAL"><a href=
1759               "actions-file.html#SERVER-HEADER-FILTER">server-header
1760               filter</a></tt>.</p>
1761
1762               <div class="WARNING">
1763                 <table class="WARNING" border="1" width="90%">
1764                   <tr>
1765                     <td align="center"><b>Warning</b></td>
1766                   </tr>
1767
1768                   <tr>
1769                     <td align="left">
1770                       <p>Don't block any header without understanding the
1771                       consequences.</p>
1772                     </td>
1773                   </tr>
1774                 </table>
1775               </div>
1776             </dd>
1777
1778             <dt>Example usage (section):</dt>
1779
1780             <dd>
1781               <table border="0" bgcolor="#E0E0E0" width="90%">
1782                 <tr>
1783                   <td>
1784                     <pre class="SCREEN">
1785 # Crunch server headers that try to prevent caching
1786 { +crunch-server-header{no-cache} }
1787 /
1788 </pre>
1789                   </td>
1790                 </tr>
1791               </table>
1792             </dd>
1793           </dl>
1794         </div>
1795       </div>
1796
1797       <div class="SECT3">
1798         <h4 class="SECT3"><a name="CRUNCH-OUTGOING-COOKIES" id=
1799         "CRUNCH-OUTGOING-COOKIES">8.5.11. crunch-outgoing-cookies</a></h4>
1800
1801         <div class="VARIABLELIST">
1802           <dl>
1803             <dt>Typical use:</dt>
1804
1805             <dd>
1806               <p>Prevent the web server from reading any HTTP cookies from
1807               your system</p>
1808             </dd>
1809
1810             <dt>Effect:</dt>
1811
1812             <dd>
1813               <p>Deletes any <span class="QUOTE">"Cookie:"</span> HTTP
1814               headers from client requests.</p>
1815             </dd>
1816
1817             <dt>Type:</dt>
1818
1819             <dd>
1820               <p>Boolean.</p>
1821             </dd>
1822
1823             <dt>Parameter:</dt>
1824
1825             <dd>
1826               <p>N/A</p>
1827             </dd>
1828
1829             <dt>Notes:</dt>
1830
1831             <dd>
1832               <p>This action is only concerned with <span class=
1833               "emphasis"><i class="EMPHASIS">outgoing</i></span> HTTP
1834               cookies. For <span class="emphasis"><i class=
1835               "EMPHASIS">incoming</i></span> HTTP cookies, use <tt class=
1836               "LITERAL"><a href=
1837               "actions-file.html#CRUNCH-INCOMING-COOKIES">crunch-incoming-cookies</a></tt>.
1838               Use <span class="emphasis"><i class="EMPHASIS">both</i></span>
1839               to disable HTTP cookies completely.</p>
1840
1841               <p>It makes <span class="emphasis"><i class="EMPHASIS">no sense
1842               at all</i></span> to use this action in conjunction with the
1843               <tt class="LITERAL"><a href=
1844               "actions-file.html#SESSION-COOKIES-ONLY">session-cookies-only</a></tt>
1845               action, since it would prevent the session cookies from being
1846               read.</p>
1847             </dd>
1848
1849             <dt>Example usage:</dt>
1850
1851             <dd>
1852               <table border="0" bgcolor="#E0E0E0" width="90%">
1853                 <tr>
1854                   <td>
1855                     <pre class="SCREEN">
1856 +crunch-outgoing-cookies
1857 </pre>
1858                   </td>
1859                 </tr>
1860               </table>
1861             </dd>
1862           </dl>
1863         </div>
1864       </div>
1865
1866       <div class="SECT3">
1867         <h4 class="SECT3"><a name="DEANIMATE-GIFS" id=
1868         "DEANIMATE-GIFS">8.5.12. deanimate-gifs</a></h4>
1869
1870         <div class="VARIABLELIST">
1871           <dl>
1872             <dt>Typical use:</dt>
1873
1874             <dd>
1875               <p>Stop those annoying, distracting animated GIF images.</p>
1876             </dd>
1877
1878             <dt>Effect:</dt>
1879
1880             <dd>
1881               <p>De-animate GIF animations, i.e. reduce them to their first
1882               or last image.</p>
1883             </dd>
1884
1885             <dt>Type:</dt>
1886
1887             <dd>
1888               <p>Parameterized.</p>
1889             </dd>
1890
1891             <dt>Parameter:</dt>
1892
1893             <dd>
1894               <p><span class="QUOTE">"last"</span> or <span class=
1895               "QUOTE">"first"</span></p>
1896             </dd>
1897
1898             <dt>Notes:</dt>
1899
1900             <dd>
1901               <p>This will also shrink the images considerably (in bytes, not
1902               pixels!). If the option <span class="QUOTE">"first"</span> is
1903               given, the first frame of the animation is used as the
1904               replacement. If <span class="QUOTE">"last"</span> is given, the
1905               last frame of the animation is used instead, which probably
1906               makes more sense for most banner animations, but also has the
1907               risk of not showing the entire last frame (if it is only a
1908               delta to an earlier frame).</p>
1909
1910               <p>You can safely use this action with patterns that will also
1911               match non-GIF objects, because no attempt will be made at
1912               anything that doesn't look like a GIF.</p>
1913             </dd>
1914
1915             <dt>Example usage:</dt>
1916
1917             <dd>
1918               <table border="0" bgcolor="#E0E0E0" width="90%">
1919                 <tr>
1920                   <td>
1921                     <pre class="SCREEN">
1922 +deanimate-gifs{last}
1923 </pre>
1924                   </td>
1925                 </tr>
1926               </table>
1927             </dd>
1928           </dl>
1929         </div>
1930       </div>
1931
1932       <div class="SECT3">
1933         <h4 class="SECT3"><a name="DOWNGRADE-HTTP-VERSION" id=
1934         "DOWNGRADE-HTTP-VERSION">8.5.13. downgrade-http-version</a></h4>
1935
1936         <div class="VARIABLELIST">
1937           <dl>
1938             <dt>Typical use:</dt>
1939
1940             <dd>
1941               <p>Work around (very rare) problems with HTTP/1.1</p>
1942             </dd>
1943
1944             <dt>Effect:</dt>
1945
1946             <dd>
1947               <p>Downgrades HTTP/1.1 client requests and server replies to
1948               HTTP/1.0.</p>
1949             </dd>
1950
1951             <dt>Type:</dt>
1952
1953             <dd>
1954               <p>Boolean.</p>
1955             </dd>
1956
1957             <dt>Parameter:</dt>
1958
1959             <dd>
1960               <p>N/A</p>
1961             </dd>
1962
1963             <dt>Notes:</dt>
1964
1965             <dd>
1966               <p>This is a left-over from the time when <span class=
1967               "APPLICATION">Privoxy</span> didn't support important HTTP/1.1
1968               features well. It is left here for the unlikely case that you
1969               experience HTTP/1.1-related problems with some server out
1970               there.</p>
1971
1972               <p>Note that enabling this action is only a workaround. It
1973               should not be enabled for sites that work without it. While it
1974               shouldn't break any pages, it has an (usually negative)
1975               performance impact.</p>
1976
1977               <p>If you come across a site where enabling this action helps,
1978               please report it, so the cause of the problem can be analyzed.
1979               If the problem turns out to be caused by a bug in <span class=
1980               "APPLICATION">Privoxy</span> it should be fixed so the
1981               following release works without the work around.</p>
1982             </dd>
1983
1984             <dt>Example usage (section):</dt>
1985
1986             <dd>
1987               <table border="0" bgcolor="#E0E0E0" width="90%">
1988                 <tr>
1989                   <td>
1990                     <pre class="SCREEN">
1991 {+downgrade-http-version}
1992 problem-host.example.com
1993 </pre>
1994                   </td>
1995                 </tr>
1996               </table>
1997             </dd>
1998           </dl>
1999         </div>
2000       </div>
2001
2002       <div class="SECT3">
2003         <h4 class="SECT3"><a name="FAST-REDIRECTS" id=
2004         "FAST-REDIRECTS">8.5.14. fast-redirects</a></h4>
2005
2006         <div class="VARIABLELIST">
2007           <dl>
2008             <dt>Typical use:</dt>
2009
2010             <dd>
2011               <p>Fool some click-tracking scripts and speed up indirect
2012               links.</p>
2013             </dd>
2014
2015             <dt>Effect:</dt>
2016
2017             <dd>
2018               <p>Detects redirection URLs and redirects the browser without
2019               contacting the redirection server first.</p>
2020             </dd>
2021
2022             <dt>Type:</dt>
2023
2024             <dd>
2025               <p>Parameterized.</p>
2026             </dd>
2027
2028             <dt>Parameter:</dt>
2029
2030             <dd>
2031               <ul>
2032                 <li>
2033                   <p><span class="QUOTE">"simple-check"</span> to just search
2034                   for the string <span class="QUOTE">"http://"</span> to
2035                   detect redirection URLs.</p>
2036                 </li>
2037
2038                 <li>
2039                   <p><span class="QUOTE">"check-decoded-url"</span> to decode
2040                   URLs (if necessary) before searching for redirection
2041                   URLs.</p>
2042                 </li>
2043               </ul>
2044             </dd>
2045
2046             <dt>Notes:</dt>
2047
2048             <dd>
2049               <p>Many sites, like yahoo.com, don't just link to other sites.
2050               Instead, they will link to some script on their own servers,
2051               giving the destination as a parameter, which will then redirect
2052               you to the final target. URLs resulting from this scheme
2053               typically look like: <span class=
2054               "QUOTE">"http://www.example.org/click-tracker.cgi?target=http%3a//www.example.net/"</span>.</p>
2055
2056               <p>Sometimes, there are even multiple consecutive redirects
2057               encoded in the URL. These redirections via scripts make your
2058               web browsing more traceable, since the server from which you
2059               follow such a link can see where you go to. Apart from that,
2060               valuable bandwidth and time is wasted, while your browser asks
2061               the server for one redirect after the other. Plus, it feeds the
2062               advertisers.</p>
2063
2064               <p>This feature is currently not very smart and is scheduled
2065               for improvement. If it is enabled by default, you will have to
2066               create some exceptions to this action. It can lead to failures
2067               in several ways:</p>
2068
2069               <p>Not every URLs with other URLs as parameters is evil. Some
2070               sites offer a real service that requires this information to
2071               work. For example a validation service needs to know, which
2072               document to validate. <tt class="LITERAL">fast-redirects</tt>
2073               assumes that every URL parameter that looks like another URL is
2074               a redirection target, and will always redirect to the last one.
2075               Most of the time the assumption is correct, but if it isn't,
2076               the user gets redirected anyway.</p>
2077
2078               <p>Another failure occurs if the URL contains other parameters
2079               after the URL parameter. The URL: <span class=
2080               "QUOTE">"http://www.example.org/?redirect=http%3a//www.example.net/&amp;foo=bar"</span>.
2081               contains the redirection URL <span class=
2082               "QUOTE">"http://www.example.net/"</span>, followed by another
2083               parameter. <tt class="LITERAL">fast-redirects</tt> doesn't know
2084               that and will cause a redirect to <span class=
2085               "QUOTE">"http://www.example.net/&amp;foo=bar"</span>. Depending
2086               on the target server configuration, the parameter will be
2087               silently ignored or lead to a <span class="QUOTE">"page not
2088               found"</span> error. You can prevent this problem by first
2089               using the <tt class="LITERAL"><a href=
2090               "actions-file.html#REDIRECT">redirect</a></tt> action to remove
2091               the last part of the URL, but it requires a little effort.</p>
2092
2093               <p>To detect a redirection URL, <tt class=
2094               "LITERAL">fast-redirects</tt> only looks for the string
2095               <span class="QUOTE">"http://"</span>, either in plain text
2096               (invalid but often used) or encoded as <span class=
2097               "QUOTE">"http%3a//"</span>. Some sites use their own URL
2098               encoding scheme, encrypt the address of the target server or
2099               replace it with a database id. In theses cases <tt class=
2100               "LITERAL">fast-redirects</tt> is fooled and the request reaches
2101               the redirection server where it probably gets logged.</p>
2102             </dd>
2103
2104             <dt>Example usage:</dt>
2105
2106             <dd>
2107               <table border="0" bgcolor="#E0E0E0" width="90%">
2108                 <tr>
2109                   <td>
2110                     <pre class="SCREEN">
2111  { +fast-redirects{simple-check} }
2112    one.example.com
2113
2114  { +fast-redirects{check-decoded-url} }
2115    another.example.com/testing
2116 </pre>
2117                   </td>
2118                 </tr>
2119               </table>
2120             </dd>
2121           </dl>
2122         </div>
2123       </div>
2124
2125       <div class="SECT3">
2126         <h4 class="SECT3"><a name="FILTER" id="FILTER">8.5.15.
2127         filter</a></h4>
2128
2129         <div class="VARIABLELIST">
2130           <dl>
2131             <dt>Typical use:</dt>
2132
2133             <dd>
2134               <p>Get rid of HTML and JavaScript annoyances, banner
2135               advertisements (by size), do fun text replacements, add
2136               personalized effects, etc.</p>
2137             </dd>
2138
2139             <dt>Effect:</dt>
2140
2141             <dd>
2142               <p>All instances of text-based type, most notably HTML and
2143               JavaScript, to which this action applies, can be filtered
2144               on-the-fly through the specified regular expression based
2145               substitutions. (Note: as of version 3.0.3 plain text documents
2146               are exempted from filtering, because web servers often use the
2147               <tt class="LITERAL">text/plain</tt> MIME type for all files
2148               whose type they don't know.)</p>
2149             </dd>
2150
2151             <dt>Type:</dt>
2152
2153             <dd>
2154               <p>Parameterized.</p>
2155             </dd>
2156
2157             <dt>Parameter:</dt>
2158
2159             <dd>
2160               <p>The name of a content filter, as defined in the <a href=
2161               "filter-file.html">filter file</a>. Filters can be defined in
2162               one or more files as defined by the <tt class=
2163               "LITERAL"><a href="config.html#FILTERFILE">filterfile</a></tt>
2164               option in the <a href="config.html">config file</a>. <tt class=
2165               "FILENAME">default.filter</tt> is the collection of filters
2166               supplied by the developers. Locally defined filters should go
2167               in their own file, such as <tt class=
2168               "FILENAME">user.filter</tt>.</p>
2169
2170               <p>When used in its negative form, and without parameters,
2171               <span class="emphasis"><i class="EMPHASIS">all</i></span>
2172               filtering is completely disabled.</p>
2173             </dd>
2174
2175             <dt>Notes:</dt>
2176
2177             <dd>
2178               <p>For your convenience, there are a number of pre-defined
2179               filters available in the distribution filter file that you can
2180               use. See the examples below for a list.</p>
2181
2182               <p>Filtering requires buffering the page content, which may
2183               appear to slow down page rendering since nothing is displayed
2184               until all content has passed the filters. (The total time until
2185               the page is completely rendered doesn't change much, but it may
2186               be perceived as slower since the page is not incrementally
2187               displayed.) This effect will be more noticeable on slower
2188               connections.</p>
2189
2190               <p><span class="QUOTE">"Rolling your own"</span> filters
2191               requires a knowledge of <a href=
2192               "http://en.wikipedia.org/wiki/Regular_expressions" target=
2193               "_top"><span class="QUOTE">"Regular Expressions"</span></a> and
2194               <a href="http://en.wikipedia.org/wiki/Html" target=
2195               "_top"><span class="QUOTE">"HTML"</span></a>. This is very
2196               powerful feature, and potentially very intrusive. Filters
2197               should be used with caution, and where an equivalent
2198               <span class="QUOTE">"action"</span> is not available.</p>
2199
2200               <p>The amount of data that can be filtered is limited to the
2201               <tt class="LITERAL"><a href=
2202               "config.html#BUFFER-LIMIT">buffer-limit</a></tt> option in the
2203               main <a href="config.html">config file</a>. The default is 4096
2204               KB (4 Megs). Once this limit is exceeded, the buffered data,
2205               and all pending data, is passed through unfiltered.</p>
2206
2207               <p>Inappropriate MIME types, such as zipped files, are not
2208               filtered at all. (Again, only text-based types except plain
2209               text). Encrypted SSL data (from HTTPS servers) cannot be
2210               filtered either, since this would violate the integrity of the
2211               secure transaction. In some situations it might be necessary to
2212               protect certain text, like source code, from filtering by
2213               defining appropriate <tt class="LITERAL">-filter</tt>
2214               exceptions.</p>
2215
2216               <p>Compressed content can't be filtered either, but if
2217               <span class="APPLICATION">Privoxy</span> is compiled with zlib
2218               support and a supported compression algorithm is used (gzip or
2219               deflate), <span class="APPLICATION">Privoxy</span> can first
2220               decompress the content and then filter it.</p>
2221
2222               <p>If you use a <span class="APPLICATION">Privoxy</span>
2223               version without zlib support, but want filtering to work on as
2224               much documents as possible, even those that would normally be
2225               sent compressed, you must use the <tt class="LITERAL"><a href=
2226               "actions-file.html#PREVENT-COMPRESSION">prevent-compression</a></tt>
2227               action in conjunction with <tt class="LITERAL">filter</tt>.</p>
2228
2229               <p>Content filtering can achieve some of the same effects as
2230               the <tt class="LITERAL"><a href=
2231               "actions-file.html#BLOCK">block</a></tt> action, i.e. it can be
2232               used to block ads and banners. But the mechanism works quite
2233               differently. One effective use, is to block ad banners based on
2234               their size (see below), since many of these seem to be somewhat
2235               standardized.</p>
2236
2237               <p><a href="contact.html">Feedback</a> with suggestions for new
2238               or improved filters is particularly welcome!</p>
2239
2240               <p>The below list has only the names and a one-line description
2241               of each predefined filter. There are <a href=
2242               "filter-file.html#PREDEFINED-FILTERS">more verbose
2243               explanations</a> of what these filters do in the <a href=
2244               "filter-file.html">filter file chapter</a>.</p>
2245             </dd>
2246
2247             <dt>Example usage (with filters from the distribution <tt class=
2248             "FILENAME">default.filter</tt> file). See <a href=
2249             "filter-file.html#PREDEFINED-FILTERS">the Predefined Filters
2250             section</a> for more explanation on each:</dt>
2251
2252             <dd>
2253               <p><a name="FILTER-JS-ANNOYANCES" id=
2254               "FILTER-JS-ANNOYANCES"></a></p>
2255
2256               <table border="0" bgcolor="#E0E0E0" width="90%">
2257                 <tr>
2258                   <td>
2259                     <pre class="SCREEN">
2260 +filter{js-annoyances}       # Get rid of particularly annoying JavaScript abuse.
2261 </pre>
2262                   </td>
2263                 </tr>
2264               </table>
2265
2266               <p><a name="FILTER-JS-EVENTS" id="FILTER-JS-EVENTS"></a></p>
2267
2268               <table border="0" bgcolor="#E0E0E0" width="90%">
2269                 <tr>
2270                   <td>
2271                     <pre class="SCREEN">
2272 +filter{js-events}           # Kill JavaScript event bindings and timers (Radically destructive! Only for extra nasty sites).
2273 </pre>
2274                   </td>
2275                 </tr>
2276               </table>
2277
2278               <p><a name="FILTER-HTML-ANNOYANCES" id=
2279               "FILTER-HTML-ANNOYANCES"></a></p>
2280
2281               <table border="0" bgcolor="#E0E0E0" width="90%">
2282                 <tr>
2283                   <td>
2284                     <pre class="SCREEN">
2285 +filter{html-annoyances}     # Get rid of particularly annoying HTML abuse.
2286 </pre>
2287                   </td>
2288                 </tr>
2289               </table>
2290
2291               <p><a name="FILTER-CONTENT-COOKIES" id=
2292               "FILTER-CONTENT-COOKIES"></a></p>
2293
2294               <table border="0" bgcolor="#E0E0E0" width="90%">
2295                 <tr>
2296                   <td>
2297                     <pre class="SCREEN">
2298 +filter{content-cookies}     # Kill cookies that come in the HTML or JS content.
2299 </pre>
2300                   </td>
2301                 </tr>
2302               </table>
2303
2304               <p><a name="FILTER-REFRESH-TAGS" id=
2305               "FILTER-REFRESH-TAGS"></a></p>
2306
2307               <table border="0" bgcolor="#E0E0E0" width="90%">
2308                 <tr>
2309                   <td>
2310                     <pre class="SCREEN">
2311 +filter{refresh-tags}        # Kill automatic refresh tags if refresh time is larger than 9 seconds.
2312 </pre>
2313                   </td>
2314                 </tr>
2315               </table>
2316
2317               <p><a name="FILTER-UNSOLICITED-POPUPS" id=
2318               "FILTER-UNSOLICITED-POPUPS"></a></p>
2319
2320               <table border="0" bgcolor="#E0E0E0" width="90%">
2321                 <tr>
2322                   <td>
2323                     <pre class="SCREEN">
2324 +filter{unsolicited-popups}  # Disable only unsolicited pop-up windows.
2325 </pre>
2326                   </td>
2327                 </tr>
2328               </table>
2329
2330               <p><a name="FILTER-ALL-POPUPS" id="FILTER-ALL-POPUPS"></a></p>
2331
2332               <table border="0" bgcolor="#E0E0E0" width="90%">
2333                 <tr>
2334                   <td>
2335                     <pre class="SCREEN">
2336 +filter{all-popups}          # Kill all popups in JavaScript and HTML.
2337 </pre>
2338                   </td>
2339                 </tr>
2340               </table>
2341
2342               <p><a name="FILTER-IMG-REORDER" id=
2343               "FILTER-IMG-REORDER"></a></p>
2344
2345               <table border="0" bgcolor="#E0E0E0" width="90%">
2346                 <tr>
2347                   <td>
2348                     <pre class="SCREEN">
2349 +filter{img-reorder}         # Reorder attributes in &lt;img&gt; tags to make the banners-by-* filters more effective.
2350 </pre>
2351                   </td>
2352                 </tr>
2353               </table>
2354
2355               <p><a name="FILTER-BANNERS-BY-SIZE" id=
2356               "FILTER-BANNERS-BY-SIZE"></a></p>
2357
2358               <table border="0" bgcolor="#E0E0E0" width="90%">
2359                 <tr>
2360                   <td>
2361                     <pre class="SCREEN">
2362 +filter{banners-by-size}     # Kill banners by size.
2363 </pre>
2364                   </td>
2365                 </tr>
2366               </table>
2367
2368               <p><a name="FILTER-BANNERS-BY-LINK" id=
2369               "FILTER-BANNERS-BY-LINK"></a></p>
2370
2371               <table border="0" bgcolor="#E0E0E0" width="90%">
2372                 <tr>
2373                   <td>
2374                     <pre class="SCREEN">
2375 +filter{banners-by-link}     # Kill banners by their links to known clicktrackers.
2376 </pre>
2377                   </td>
2378                 </tr>
2379               </table>
2380
2381               <p><a name="FILTER-WEBBUGS" id="FILTER-WEBBUGS"></a></p>
2382
2383               <table border="0" bgcolor="#E0E0E0" width="90%">
2384                 <tr>
2385                   <td>
2386                     <pre class="SCREEN">
2387 +filter{webbugs}             # Squish WebBugs (1x1 invisible GIFs used for user tracking).
2388 </pre>
2389                   </td>
2390                 </tr>
2391               </table>
2392
2393               <p><a name="FILTER-TINY-TEXTFORMS" id=
2394               "FILTER-TINY-TEXTFORMS"></a></p>
2395
2396               <table border="0" bgcolor="#E0E0E0" width="90%">
2397                 <tr>
2398                   <td>
2399                     <pre class="SCREEN">
2400 +filter{tiny-textforms}      # Extend those tiny textareas up to 40x80 and kill the hard wrap.
2401 </pre>
2402                   </td>
2403                 </tr>
2404               </table>
2405
2406               <p><a name="FILTER-JUMPING-WINDOWS" id=
2407               "FILTER-JUMPING-WINDOWS"></a></p>
2408
2409               <table border="0" bgcolor="#E0E0E0" width="90%">
2410                 <tr>
2411                   <td>
2412                     <pre class="SCREEN">
2413 +filter{jumping-windows}     # Prevent windows from resizing and moving themselves.
2414 </pre>
2415                   </td>
2416                 </tr>
2417               </table>
2418
2419               <p><a name="FILTER-FRAMESET-BORDERS" id=
2420               "FILTER-FRAMESET-BORDERS"></a></p>
2421
2422               <table border="0" bgcolor="#E0E0E0" width="90%">
2423                 <tr>
2424                   <td>
2425                     <pre class="SCREEN">
2426 +filter{frameset-borders}    # Give frames a border and make them resizable.
2427 </pre>
2428                   </td>
2429                 </tr>
2430               </table>
2431
2432               <p><a name="FILTER-IFRAMES" id="FILTER-IFRAMES"></a></p>
2433
2434               <table border="0" bgcolor="#E0E0E0" width="90%">
2435                 <tr>
2436                   <td>
2437                     <pre class="SCREEN">
2438 +filter{iframes}             # Removes all detected iframes. Should only be enabled for individual sites.
2439 </pre>
2440                   </td>
2441                 </tr>
2442               </table>
2443
2444               <p><a name="FILTER-DEMORONIZER" id=
2445               "FILTER-DEMORONIZER"></a></p>
2446
2447               <table border="0" bgcolor="#E0E0E0" width="90%">
2448                 <tr>
2449                   <td>
2450                     <pre class="SCREEN">
2451 +filter{demoronizer}         # Fix MS's non-standard use of standard charsets.
2452 </pre>
2453                   </td>
2454                 </tr>
2455               </table>
2456
2457               <p><a name="FILTER-SHOCKWAVE-FLASH" id=
2458               "FILTER-SHOCKWAVE-FLASH"></a></p>
2459
2460               <table border="0" bgcolor="#E0E0E0" width="90%">
2461                 <tr>
2462                   <td>
2463                     <pre class="SCREEN">
2464 +filter{shockwave-flash}     # Kill embedded Shockwave Flash objects.
2465 </pre>
2466                   </td>
2467                 </tr>
2468               </table>
2469
2470               <p><a name="FILTER-QUICKTIME-KIOSKMODE" id=
2471               "FILTER-QUICKTIME-KIOSKMODE"></a></p>
2472
2473               <table border="0" bgcolor="#E0E0E0" width="90%">
2474                 <tr>
2475                   <td>
2476                     <pre class="SCREEN">
2477 +filter{quicktime-kioskmode} # Make Quicktime movies saveable.
2478 </pre>
2479                   </td>
2480                 </tr>
2481               </table>
2482
2483               <p><a name="FILTER-FUN" id="FILTER-FUN"></a></p>
2484
2485               <table border="0" bgcolor="#E0E0E0" width="90%">
2486                 <tr>
2487                   <td>
2488                     <pre class="SCREEN">
2489 +filter{fun}                 # Text replacements for subversive browsing fun!
2490 </pre>
2491                   </td>
2492                 </tr>
2493               </table>
2494
2495               <p><a name="FILTER-CRUDE-PARENTAL" id=
2496               "FILTER-CRUDE-PARENTAL"></a></p>
2497
2498               <table border="0" bgcolor="#E0E0E0" width="90%">
2499                 <tr>
2500                   <td>
2501                     <pre class="SCREEN">
2502 +filter{crude-parental}      # Crude parental filtering. Note that this filter doesn't work reliably.
2503 </pre>
2504                   </td>
2505                 </tr>
2506               </table>
2507
2508               <p><a name="FILTER-IE-EXPLOITS" id=
2509               "FILTER-IE-EXPLOITS"></a></p>
2510
2511               <table border="0" bgcolor="#E0E0E0" width="90%">
2512                 <tr>
2513                   <td>
2514                     <pre class="SCREEN">
2515 +filter{ie-exploits}         # Disable some known Internet Explorer bug exploits.
2516 </pre>
2517                   </td>
2518                 </tr>
2519               </table>
2520
2521               <p><a name="FILTER-SITE-SPECIFICS" id=
2522               "FILTER-SITE-SPECIFICS"></a></p>
2523
2524               <table border="0" bgcolor="#E0E0E0" width="90%">
2525                 <tr>
2526                   <td>
2527                     <pre class="SCREEN">
2528 +filter{site-specifics}      # Cure for site-specific problems. Don't apply generally!
2529 </pre>
2530                   </td>
2531                 </tr>
2532               </table>
2533
2534               <p><a name="FILTER-NO-PING" id="FILTER-NO-PING"></a></p>
2535
2536               <table border="0" bgcolor="#E0E0E0" width="90%">
2537                 <tr>
2538                   <td>
2539                     <pre class="SCREEN">
2540 +filter{no-ping}             # Removes non-standard ping attributes in &lt;a&gt; and &lt;area&gt; tags.
2541 </pre>
2542                   </td>
2543                 </tr>
2544               </table>
2545
2546               <p><a name="FILTER-GOOGLE" id="FILTER-GOOGLE"></a></p>
2547
2548               <table border="0" bgcolor="#E0E0E0" width="90%">
2549                 <tr>
2550                   <td>
2551                     <pre class="SCREEN">
2552 +filter{google}              # CSS-based block for Google text ads. Also removes a width limitation and the toolbar advertisement.
2553 </pre>
2554                   </td>
2555                 </tr>
2556               </table>
2557
2558               <p><a name="FILTER-YAHOO" id="FILTER-YAHOO"></a></p>
2559
2560               <table border="0" bgcolor="#E0E0E0" width="90%">
2561                 <tr>
2562                   <td>
2563                     <pre class="SCREEN">
2564 +filter{yahoo}               # CSS-based block for Yahoo text ads. Also removes a width limitation.
2565 </pre>
2566                   </td>
2567                 </tr>
2568               </table>
2569
2570               <p><a name="FILTER-MSN" id="FILTER-MSN"></a></p>
2571
2572               <table border="0" bgcolor="#E0E0E0" width="90%">
2573                 <tr>
2574                   <td>
2575                     <pre class="SCREEN">
2576 +filter{msn}                 # CSS-based block for MSN text ads. Also removes tracking URLs and a width limitation.
2577 </pre>
2578                   </td>
2579                 </tr>
2580               </table>
2581
2582               <p><a name="FILTER-BLOGSPOT" id="FILTER-BLOGSPOT"></a></p>
2583
2584               <table border="0" bgcolor="#E0E0E0" width="90%">
2585                 <tr>
2586                   <td>
2587                     <pre class="SCREEN">
2588 +filter{blogspot}            # Cleans up some Blogspot blogs. Read the fine print before using this.
2589 </pre>
2590                   </td>
2591                 </tr>
2592               </table>
2593             </dd>
2594           </dl>
2595         </div>
2596       </div>
2597
2598       <div class="SECT3">
2599         <h4 class="SECT3"><a name="FORCE-TEXT-MODE" id=
2600         "FORCE-TEXT-MODE">8.5.16. force-text-mode</a></h4>
2601
2602         <div class="VARIABLELIST">
2603           <dl>
2604             <dt>Typical use:</dt>
2605
2606             <dd>
2607               <p>Force <span class="APPLICATION">Privoxy</span> to treat a
2608               document as if it was in some kind of <span class=
2609               "emphasis"><i class="EMPHASIS">text</i></span> format.</p>
2610             </dd>
2611
2612             <dt>Effect:</dt>
2613
2614             <dd>
2615               <p>Declares a document as text, even if the <span class=
2616               "QUOTE">"Content-Type:"</span> isn't detected as such.</p>
2617             </dd>
2618
2619             <dt>Type:</dt>
2620
2621             <dd>
2622               <p>Boolean.</p>
2623             </dd>
2624
2625             <dt>Parameter:</dt>
2626
2627             <dd>
2628               <p>N/A</p>
2629             </dd>
2630
2631             <dt>Notes:</dt>
2632
2633             <dd>
2634               <p>As explained <tt class="LITERAL"><a href=
2635               "actions-file.html#FILTER">above</a></tt>, <span class=
2636               "APPLICATION">Privoxy</span> tries to only filter files that
2637               are in some kind of text format. The same restrictions apply to
2638               <tt class="LITERAL"><a href=
2639               "actions-file.html#CONTENT-TYPE-OVERWRITE">content-type-overwrite</a></tt>.
2640               <tt class="LITERAL">force-text-mode</tt> declares a document as
2641               text, without looking at the <span class=
2642               "QUOTE">"Content-Type:"</span> first.</p>
2643
2644               <div class="WARNING">
2645                 <table class="WARNING" border="1" width="90%">
2646                   <tr>
2647                     <td align="center"><b>Warning</b></td>
2648                   </tr>
2649
2650                   <tr>
2651                     <td align="left">
2652                       <p>Think twice before activating this action. Filtering
2653                       binary data with regular expressions can cause file
2654                       damage.</p>
2655                     </td>
2656                   </tr>
2657                 </table>
2658               </div>
2659             </dd>
2660
2661             <dt>Example usage:</dt>
2662
2663             <dd>
2664               <table border="0" bgcolor="#E0E0E0" width="90%">
2665                 <tr>
2666                   <td>
2667                     <pre class="SCREEN">
2668 +force-text-mode
2669
2670 </pre>
2671                   </td>
2672                 </tr>
2673               </table>
2674             </dd>
2675           </dl>
2676         </div>
2677       </div>
2678
2679       <div class="SECT3">
2680         <h4 class="SECT3"><a name="FORWARD-OVERRIDE" id=
2681         "FORWARD-OVERRIDE">8.5.17. forward-override</a></h4>
2682
2683         <div class="VARIABLELIST">
2684           <dl>
2685             <dt>Typical use:</dt>
2686
2687             <dd>
2688               <p>Change the forwarding settings based on User-Agent or
2689               request origin</p>
2690             </dd>
2691
2692             <dt>Effect:</dt>
2693
2694             <dd>
2695               <p>Overrules the forward directives in the configuration
2696               file.</p>
2697             </dd>
2698
2699             <dt>Type:</dt>
2700
2701             <dd>
2702               <p>Multi-value.</p>
2703             </dd>
2704
2705             <dt>Parameter:</dt>
2706
2707             <dd>
2708               <ul>
2709                 <li>
2710                   <p><span class="QUOTE">"forward ."</span> to use a direct
2711                   connection without any additional proxies.</p>
2712                 </li>
2713
2714                 <li>
2715                   <p><span class="QUOTE">"forward 127.0.0.1:8123"</span> to
2716                   use the HTTP proxy listening at 127.0.0.1 port 8123.</p>
2717                 </li>
2718
2719                 <li>
2720                   <p><span class="QUOTE">"forward-socks4a 127.0.0.1:9050
2721                   ."</span> to use the socks4a proxy listening at 127.0.0.1
2722                   port 9050. Replace <span class=
2723                   "QUOTE">"forward-socks4a"</span> with <span class=
2724                   "QUOTE">"forward-socks4"</span> to use a socks4 connection
2725                   (with local DNS resolution) instead, use <span class=
2726                   "QUOTE">"forward-socks5"</span> for socks5 connections
2727                   (with remote DNS resolution).</p>
2728                 </li>
2729
2730                 <li>
2731                   <p><span class="QUOTE">"forward-socks4a 127.0.0.1:9050
2732                   proxy.example.org:8000"</span> to use the socks4a proxy
2733                   listening at 127.0.0.1 port 9050 to reach the HTTP proxy
2734                   listening at proxy.example.org port 8000. Replace
2735                   <span class="QUOTE">"forward-socks4a"</span> with
2736                   <span class="QUOTE">"forward-socks4"</span> to use a socks4
2737                   connection (with local DNS resolution) instead, use
2738                   <span class="QUOTE">"forward-socks5"</span> for socks5
2739                   connections (with remote DNS resolution).</p>
2740                 </li>
2741               </ul>
2742             </dd>
2743
2744             <dt>Notes:</dt>
2745
2746             <dd>
2747               <p>This action takes parameters similar to the <a href=
2748               "config.html#FORWARDING">forward</a> directives in the
2749               configuration file, but without the URL pattern. It can be used
2750               as replacement, but normally it's only used in cases where
2751               matching based on the request URL isn't sufficient.</p>
2752
2753               <div class="WARNING">
2754                 <table class="WARNING" border="1" width="90%">
2755                   <tr>
2756                     <td align="center"><b>Warning</b></td>
2757                   </tr>
2758
2759                   <tr>
2760                     <td align="left">
2761                       <p>Please read the description for the <a href=
2762                       "config.html#FORWARDING">forward</a> directives before
2763                       using this action. Forwarding to the wrong people will
2764                       reduce your privacy and increase the chances of
2765                       man-in-the-middle attacks.</p>
2766
2767                       <p>If the ports are missing or invalid, default values
2768                       will be used. This might change in the future and you
2769                       shouldn't rely on it. Otherwise incorrect syntax causes
2770                       Privoxy to exit.</p>
2771
2772                       <p>Use the <a href=
2773                       "http://config.privoxy.org/show-url-info" target=
2774                       "_top">show-url-info CGI page</a> to verify that your
2775                       forward settings do what you thought the do.</p>
2776                     </td>
2777                   </tr>
2778                 </table>
2779               </div>
2780             </dd>
2781
2782             <dt>Example usage:</dt>
2783
2784             <dd>
2785               <table border="0" bgcolor="#E0E0E0" width="90%">
2786                 <tr>
2787                   <td>
2788                     <pre class="SCREEN">
2789 # Always use direct connections for requests previously tagged as
2790 # <span class="QUOTE">"User-Agent: fetch libfetch/2.0"</span> and make sure
2791 # resuming downloads continues to work.
2792 # This way you can continue to use Tor for your normal browsing,
2793 # without overloading the Tor network with your FreeBSD ports updates
2794 # or downloads of bigger files like ISOs.
2795 # Note that HTTP headers are easy to fake and therefore their
2796 # values are as (un)trustworthy as your clients and users.
2797 {+forward-override{forward .} \
2798  -hide-if-modified-since      \
2799  -overwrite-last-modified     \
2800 }
2801 TAG:^User-Agent: fetch libfetch/2\.0$
2802
2803 </pre>
2804                   </td>
2805                 </tr>
2806               </table>
2807             </dd>
2808           </dl>
2809         </div>
2810       </div>
2811
2812       <div class="SECT3">
2813         <h4 class="SECT3"><a name="HANDLE-AS-EMPTY-DOCUMENT" id=
2814         "HANDLE-AS-EMPTY-DOCUMENT">8.5.18. handle-as-empty-document</a></h4>
2815
2816         <div class="VARIABLELIST">
2817           <dl>
2818             <dt>Typical use:</dt>
2819
2820             <dd>
2821               <p>Mark URLs that should be replaced by empty documents
2822               <span class="emphasis"><i class="EMPHASIS">if they get
2823               blocked</i></span></p>
2824             </dd>
2825
2826             <dt>Effect:</dt>
2827
2828             <dd>
2829               <p>This action alone doesn't do anything noticeable. It just
2830               marks URLs. If the <tt class="LITERAL"><a href=
2831               "actions-file.html#BLOCK">block</a></tt> action <span class=
2832               "emphasis"><i class="EMPHASIS">also applies</i></span>, the
2833               presence or absence of this mark decides whether an HTML
2834               <span class="QUOTE">"BLOCKED"</span> page, or an empty document
2835               will be sent to the client as a substitute for the blocked
2836               content. The <span class="emphasis"><i class=
2837               "EMPHASIS">empty</i></span> document isn't literally empty, but
2838               actually contains a single space.</p>
2839             </dd>
2840
2841             <dt>Type:</dt>
2842
2843             <dd>
2844               <p>Boolean.</p>
2845             </dd>
2846
2847             <dt>Parameter:</dt>
2848
2849             <dd>
2850               <p>N/A</p>
2851             </dd>
2852
2853             <dt>Notes:</dt>
2854
2855             <dd>
2856               <p>Some browsers complain about syntax errors if JavaScript
2857               documents are blocked with <span class=
2858               "APPLICATION">Privoxy's</span> default HTML page; this option
2859               can be used to silence them. And of course this action can also
2860               be used to eliminate the <span class=
2861               "APPLICATION">Privoxy</span> BLOCKED message in frames.</p>
2862
2863               <p>The content type for the empty document can be specified
2864               with <tt class="LITERAL"><a href=
2865               "actions-file.html#CONTENT-TYPE-OVERWRITE">content-type-overwrite{}</a></tt>,
2866               but usually this isn't necessary.</p>
2867             </dd>
2868
2869             <dt>Example usage:</dt>
2870
2871             <dd>
2872               <table border="0" bgcolor="#E0E0E0" width="90%">
2873                 <tr>
2874                   <td>
2875                     <pre class="SCREEN">
2876 # Block all documents on example.org that end with ".js",
2877 # but send an empty document instead of the usual HTML message.
2878 {+block{Blocked JavaScript} +handle-as-empty-document}
2879 example.org/.*\.js$
2880
2881 </pre>
2882                   </td>
2883                 </tr>
2884               </table>
2885             </dd>
2886           </dl>
2887         </div>
2888       </div>
2889
2890       <div class="SECT3">
2891         <h4 class="SECT3"><a name="HANDLE-AS-IMAGE" id=
2892         "HANDLE-AS-IMAGE">8.5.19. handle-as-image</a></h4>
2893
2894         <div class="VARIABLELIST">
2895           <dl>
2896             <dt>Typical use:</dt>
2897
2898             <dd>
2899               <p>Mark URLs as belonging to images (so they'll be replaced by
2900               images <span class="emphasis"><i class="EMPHASIS">if they do
2901               get blocked</i></span>, rather than HTML pages)</p>
2902             </dd>
2903
2904             <dt>Effect:</dt>
2905
2906             <dd>
2907               <p>This action alone doesn't do anything noticeable. It just
2908               marks URLs as images. If the <tt class="LITERAL"><a href=
2909               "actions-file.html#BLOCK">block</a></tt> action <span class=
2910               "emphasis"><i class="EMPHASIS">also applies</i></span>, the
2911               presence or absence of this mark decides whether an HTML
2912               <span class="QUOTE">"blocked"</span> page, or a replacement
2913               image (as determined by the <tt class="LITERAL"><a href=
2914               "actions-file.html#SET-IMAGE-BLOCKER">set-image-blocker</a></tt>
2915               action) will be sent to the client as a substitute for the
2916               blocked content.</p>
2917             </dd>
2918
2919             <dt>Type:</dt>
2920
2921             <dd>
2922               <p>Boolean.</p>
2923             </dd>
2924
2925             <dt>Parameter:</dt>
2926
2927             <dd>
2928               <p>N/A</p>
2929             </dd>
2930
2931             <dt>Notes:</dt>
2932
2933             <dd>
2934               <p>The below generic example section is actually part of
2935               <tt class="FILENAME">default.action</tt>. It marks all URLs
2936               with well-known image file name extensions as images and should
2937               be left intact.</p>
2938
2939               <p>Users will probably only want to use the handle-as-image
2940               action in conjunction with <tt class="LITERAL"><a href=
2941               "actions-file.html#BLOCK">block</a></tt>, to block sources of
2942               banners, whose URLs don't reflect the file type, like in the
2943               second example section.</p>
2944
2945               <p>Note that you cannot treat HTML pages as images in most
2946               cases. For instance, (in-line) ad frames require an HTML page
2947               to be sent, or they won't display properly. Forcing <tt class=
2948               "LITERAL">handle-as-image</tt> in this situation will not
2949               replace the ad frame with an image, but lead to error
2950               messages.</p>
2951             </dd>
2952
2953             <dt>Example usage (sections):</dt>
2954
2955             <dd>
2956               <table border="0" bgcolor="#E0E0E0" width="90%">
2957                 <tr>
2958                   <td>
2959                     <pre class="SCREEN">
2960 # Generic image extensions:
2961 #
2962 {+handle-as-image}
2963 /.*\.(gif|jpg|jpeg|png|bmp|ico)$
2964
2965 # These don't look like images, but they're banners and should be
2966 # blocked as images:
2967 #
2968 {+block{Nasty banners.} +handle-as-image}
2969 nasty-banner-server.example.com/junk.cgi\?output=trash
2970 </pre>
2971                   </td>
2972                 </tr>
2973               </table>
2974             </dd>
2975           </dl>
2976         </div>
2977       </div>
2978
2979       <div class="SECT3">
2980         <h4 class="SECT3"><a name="HIDE-ACCEPT-LANGUAGE" id=
2981         "HIDE-ACCEPT-LANGUAGE">8.5.20. hide-accept-language</a></h4>
2982
2983         <div class="VARIABLELIST">
2984           <dl>
2985             <dt>Typical use:</dt>
2986
2987             <dd>
2988               <p>Pretend to use different language settings.</p>
2989             </dd>
2990
2991             <dt>Effect:</dt>
2992
2993             <dd>
2994               <p>Deletes or replaces the <span class=
2995               "QUOTE">"Accept-Language:"</span> HTTP header in client
2996               requests.</p>
2997             </dd>
2998
2999             <dt>Type:</dt>
3000
3001             <dd>
3002               <p>Parameterized.</p>
3003             </dd>
3004
3005             <dt>Parameter:</dt>
3006
3007             <dd>
3008               <p>Keyword: <span class="QUOTE">"block"</span>, or any user
3009               defined value.</p>
3010             </dd>
3011
3012             <dt>Notes:</dt>
3013
3014             <dd>
3015               <p>Faking the browser's language settings can be useful to make
3016               a foreign User-Agent set with <tt class="LITERAL"><a href=
3017               "actions-file.html#HIDE-USER-AGENT">hide-user-agent</a></tt>
3018               more believable.</p>
3019
3020               <p>However some sites with content in different languages check
3021               the <span class="QUOTE">"Accept-Language:"</span> to decide
3022               which one to take by default. Sometimes it isn't possible to
3023               later switch to another language without changing the
3024               <span class="QUOTE">"Accept-Language:"</span> header first.</p>
3025
3026               <p>Therefore it's a good idea to either only change the
3027               <span class="QUOTE">"Accept-Language:"</span> header to
3028               languages you understand, or to languages that aren't wide
3029               spread.</p>
3030
3031               <p>Before setting the <span class=
3032               "QUOTE">"Accept-Language:"</span> header to a rare language,
3033               you should consider that it helps to make your requests unique
3034               and thus easier to trace. If you don't plan to change this
3035               header frequently, you should stick to a common language.</p>
3036             </dd>
3037
3038             <dt>Example usage (section):</dt>
3039
3040             <dd>
3041               <table border="0" bgcolor="#E0E0E0" width="90%">
3042                 <tr>
3043                   <td>
3044                     <pre class="SCREEN">
3045 # Pretend to use Canadian language settings.
3046 {+hide-accept-language{en-ca} \
3047 +hide-user-agent{Mozilla/5.0 (X11; U; OpenBSD i386; en-CA; rv:1.8.0.4) Gecko/20060628 Firefox/1.5.0.4} \
3048 }
3049 /
3050 </pre>
3051                   </td>
3052                 </tr>
3053               </table>
3054             </dd>
3055           </dl>
3056         </div>
3057       </div>