Regenerate user manual with recent changes
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24         <th colspan="3" align="center">Privoxy 3.0.25 User Manual</th>
25       </tr>
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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="AEN2681" id="AEN2681"></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="RIGHT-MIX" id="RIGHT-MIX">8.1. Finding the
318       Right 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="HOW-TO-EDIT" id="HOW-TO-EDIT">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="PATH-PATTERN" id="PATH-PATTERN">8.4.2. The
648         Path 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         Request Tag Pattern</a></h3>
748
749         <p>Request tag patterns are used to change the applying actions based
750         on the request's tags. Tags can be created based on HTTP headers with
751         either the <a href=
752         "actions-file.html#CLIENT-HEADER-TAGGER">client-header-tagger</a> or
753         the <a href=
754         "actions-file.html#SERVER-HEADER-TAGGER">server-header-tagger</a>
755         action.</p>
756
757         <p>Request tag patterns have to start with <span class=
758         "QUOTE">"TAG:"</span>, so <span class="APPLICATION">Privoxy</span>
759         can tell them apart from other patterns. Everything after the colon
760         including white space, is interpreted as a regular expression with
761         path pattern syntax, except that tag patterns aren't left-anchored
762         automatically (<span class="APPLICATION">Privoxy</span> doesn't
763         silently add a <span class="QUOTE">"^"</span>, you have to do it
764         yourself if you need it).</p>
765
766         <p>To match all requests that are tagged with <span class=
767         "QUOTE">"foo"</span> your pattern line should be <span class=
768         "QUOTE">"TAG:^foo$"</span>, <span class="QUOTE">"TAG:foo"</span>
769         would work as well, but it would also match requests whose tags
770         contain <span class="QUOTE">"foo"</span> somewhere. <span class=
771         "QUOTE">"TAG: foo"</span> wouldn't work as it requires white
772         space.</p>
773
774         <p>Sections can contain URL and request tag patterns at the same
775         time, but request tag patterns are checked after the URL patterns and
776         thus always overrule them, even if they are located before the URL
777         patterns.</p>
778
779         <p>Once a new request tag is added, Privoxy checks right away if it's
780         matched by one of the request tag patterns and updates the action
781         settings accordingly. As a result request tags can be used to
782         activate other tagger actions, as long as these other taggers look
783         for headers that haven't already be parsed.</p>
784
785         <p>For example you could tag client requests which use the <tt class=
786         "LITERAL">POST</tt> method, then use this tag to activate another
787         tagger that adds a tag if cookies are sent, and then use a block
788         action based on the cookie tag. This allows the outcome of one
789         action, to be input into a subsequent action. However if you'd
790         reverse the position of the described taggers, and activated the
791         method tagger based on the cookie tagger, no method tags would be
792         created. The method tagger would look for the request line, but at
793         the time the cookie tag is created, the request line has already been
794         parsed.</p>
795
796         <p>While this is a limitation you should be aware of, this kind of
797         indirection is seldom needed anyway and even the example doesn't make
798         too much sense.</p>
799       </div>
800
801       <div class="SECT3">
802         <h3 class="SECT3"><a name="NEGATIVE-TAG-PATTERNS" id=
803         "NEGATIVE-TAG-PATTERNS">8.4.4. The Negative Request Tag
804         Patterns</a></h3>
805
806         <p>To match requests that do not have a certain request tag, specify
807         a negative tag pattern by prefixing the tag pattern line with either
808         <span class="QUOTE">"NO-REQUEST-TAG:"</span> or <span class=
809         "QUOTE">"NO-RESPONSE-TAG:"</span> instead of <span class=
810         "QUOTE">"TAG:"</span>.</p>
811
812         <p>Negative request tag patterns created with <span class=
813         "QUOTE">"NO-REQUEST-TAG:"</span> are checked after all client headers
814         are scanned, the ones created with <span class=
815         "QUOTE">"NO-RESPONSE-TAG:"</span> are checked after all server
816         headers are scanned. In both cases all the created tags are
817         considered.</p>
818       </div>
819
820       <div class="SECT3">
821         <h3 class="SECT3"><a name="CLIENT-TAG-PATTERN" id=
822         "CLIENT-TAG-PATTERN">8.4.5. The Client Tag Pattern</a></h3>
823
824         <div class="WARNING">
825           <table class="WARNING" border="1" width="100%">
826             <tr>
827               <td align="center"><b>Warning</b></td>
828             </tr>
829
830             <tr>
831               <td align="left">
832                 <p>This is an experimental feature. The syntax is likely to
833                 change in future versions.</p>
834               </td>
835             </tr>
836           </table>
837         </div>
838
839         <p>Client tag patterns are not set based on HTTP headers but based on
840         the client's IP address. Users can enable them themselves, but the
841         Privoxy admin controls which tags are available and what their effect
842         is.</p>
843
844         <p>After a client-specific tag has been defined with the <a href=
845         "config.html#CLIENT-SPECIFIC-TAG">client-specific-tag</a>, directive,
846         action sections can be activated based on the tag by using a
847         CLIENT-TAG pattern. The CLIENT-TAG pattern is evaluated at the same
848         priority as URL patterns, as a result the last matching pattern wins.
849         Tags that are created based on client or server headers are evaluated
850         later on and can overrule CLIENT-TAG and URL patterns!</p>
851
852         <p>The tag is set for all requests that come from clients that
853         requested it to be set. Note that "clients" are differentiated by IP
854         address, if the IP address changes the tag has to be requested
855         again.</p>
856
857         <p>Clients can request tags to be set by using the CGI interface
858         <a href="http://config.privoxy.org/show-client-tags" target=
859         "_top">http://config.privoxy.org/show-client-tags</a>.</p>
860
861         <p>Example:</p>
862
863         <table border="0" bgcolor="#E0E0E0" width="100%">
864           <tr>
865             <td>
866               <pre class="SCREEN">
867 # If the admin defined the client-specific-tag circumvent-blocks,
868 # and the request comes from a client that previously requested
869 # the tag to be set, overrule all previous +block actions that
870 # are enabled based on URL to CLIENT-TAG patterns.
871 {-block}
872 CLIENT-TAG:^circumvent-blocks$
873
874 # This section is not overruled because it's located after
875 # the previous one.
876 {+block{Nobody is supposed to request this.}}
877 example.org/blocked-example-page
878 </pre>
879             </td>
880           </tr>
881         </table>
882       </div>
883     </div>
884
885     <div class="SECT2">
886       <h2 class="SECT2"><a name="ACTIONS" id="ACTIONS">8.5. Actions</a></h2>
887
888       <p>All actions are disabled by default, until they are explicitly
889       enabled somewhere in an actions file. Actions are turned on if preceded
890       with a <span class="QUOTE">"+"</span>, and turned off if preceded with
891       a <span class="QUOTE">"-"</span>. So a <tt class="LITERAL">+action</tt>
892       means <span class="QUOTE">"do that action"</span>, e.g. <tt class=
893       "LITERAL">+block</tt> means <span class="QUOTE">"please block URLs that
894       match the following patterns"</span>, and <tt class=
895       "LITERAL">-block</tt> means <span class="QUOTE">"don't block URLs that
896       match the following patterns, even if <tt class="LITERAL">+block</tt>
897       previously applied."</span></p>
898
899       <p>Again, actions are invoked by placing them on a line, enclosed in
900       curly braces and separated by whitespace, like in <tt class=
901       "LITERAL">{+some-action -some-other-action{some-parameter}}</tt>,
902       followed by a list of URL patterns, one per line, to which they apply.
903       Together, the actions line and the following pattern lines make up a
904       section of the actions file.</p>
905
906       <p>Actions fall into three categories:</p>
907
908       <ul>
909         <li>
910           <p>Boolean, i.e the action can only be <span class=
911           "QUOTE">"enabled"</span> or <span class="QUOTE">"disabled"</span>.
912           Syntax:</p>
913
914           <table border="0" bgcolor="#E0E0E0" width="90%">
915             <tr>
916               <td>
917                 <pre class="SCREEN">
918   +<tt class="REPLACEABLE"><i>name</i></tt>        # enable action <tt class=
919 "REPLACEABLE"><i>name</i></tt>
920   -<tt class=
921 "REPLACEABLE"><i>name</i></tt>        # disable action <tt class="REPLACEABLE"><i>name</i></tt>
922 </pre>
923               </td>
924             </tr>
925           </table>
926
927           <p>Example: <tt class="LITERAL">+handle-as-image</tt></p>
928         </li>
929
930         <li>
931           <p>Parameterized, where some value is required in order to enable
932           this type of action. Syntax:</p>
933
934           <table border="0" bgcolor="#E0E0E0" width="90%">
935             <tr>
936               <td>
937                 <pre class="SCREEN">
938   +<tt class="REPLACEABLE"><i>name</i></tt>{<tt class=
939 "REPLACEABLE"><i>param</i></tt>}  # enable action and set parameter to <tt class="REPLACEABLE"><i>param</i></tt>,
940                # overwriting parameter from previous match if necessary
941   -<tt class=
942 "REPLACEABLE"><i>name</i></tt>         # disable action. The parameter can be omitted
943 </pre>
944               </td>
945             </tr>
946           </table>
947
948           <p>Note that if the URL matches multiple positive forms of a
949           parameterized action, the last match wins, i.e. the params from
950           earlier matches are simply ignored.</p>
951
952           <p>Example: <tt class="LITERAL">+hide-user-agent{Mozilla/5.0 (X11;
953           U; FreeBSD i386; en-US; rv:1.8.1.4) Gecko/20070602
954           Firefox/2.0.0.4}</tt></p>
955         </li>
956
957         <li>
958           <p>Multi-value. These look exactly like parameterized actions, but
959           they behave differently: If the action applies multiple times to
960           the same URL, but with different parameters, <span class=
961           "emphasis"><i class="EMPHASIS">all</i></span> the parameters from
962           <span class="emphasis"><i class="EMPHASIS">all</i></span> matches
963           are remembered. This is used for actions that can be executed for
964           the same request repeatedly, like adding multiple headers, or
965           filtering through multiple filters. Syntax:</p>
966
967           <table border="0" bgcolor="#E0E0E0" width="90%">
968             <tr>
969               <td>
970                 <pre class="SCREEN">
971   +<tt class="REPLACEABLE"><i>name</i></tt>{<tt class=
972 "REPLACEABLE"><i>param</i></tt>}   # enable action and add <tt class=
973 "REPLACEABLE"><i>param</i></tt> to the list of parameters
974   -<tt class="REPLACEABLE"><i>name</i></tt>{<tt class=
975 "REPLACEABLE"><i>param</i></tt>}   # remove the parameter <tt class=
976 "REPLACEABLE"><i>param</i></tt> from the list of parameters
977                 # If it was the last one left, disable the action.
978   <tt class=
979 "REPLACEABLE"><i>-name</i></tt>          # disable this action completely and remove all parameters from the list
980 </pre>
981               </td>
982             </tr>
983           </table>
984
985           <p>Examples: <tt class="LITERAL">+add-header{X-Fun-Header: Some
986           text}</tt> and <tt class=
987           "LITERAL">+filter{html-annoyances}</tt></p>
988         </li>
989       </ul>
990
991       <p>If nothing is specified in any actions file, no <span class=
992       "QUOTE">"actions"</span> are taken. So in this case <span class=
993       "APPLICATION">Privoxy</span> would just be a normal, non-blocking,
994       non-filtering proxy. You must specifically enable the privacy and
995       blocking features you need (although the provided default actions files
996       will give a good starting point).</p>
997
998       <p>Later defined action sections always over-ride earlier ones of the
999       same type. So exceptions to any rules you make, should come in the
1000       latter part of the file (or in a file that is processed later when
1001       using multiple actions files such as <tt class=
1002       "FILENAME">user.action</tt>). For multi-valued actions, the actions are
1003       applied in the order they are specified. Actions files are processed in
1004       the order they are defined in <tt class="FILENAME">config</tt> (the
1005       default installation has three actions files). It also quite possible
1006       for any given URL to match more than one <span class=
1007       "QUOTE">"pattern"</span> (because of wildcards and regular
1008       expressions), and thus to trigger more than one set of actions! Last
1009       match wins.</p>
1010
1011       <p>The list of valid <span class="APPLICATION">Privoxy</span> actions
1012       are:</p>
1013
1014       <div class="SECT3">
1015         <h4 class="SECT3"><a name="ADD-HEADER" id="ADD-HEADER">8.5.1.
1016         add-header</a></h4>
1017
1018         <div class="VARIABLELIST">
1019           <dl>
1020             <dt>Typical use:</dt>
1021
1022             <dd>
1023               <p>Confuse log analysis, custom applications</p>
1024             </dd>
1025
1026             <dt>Effect:</dt>
1027
1028             <dd>
1029               <p>Sends a user defined HTTP header to the web server.</p>
1030             </dd>
1031
1032             <dt>Type:</dt>
1033
1034             <dd>
1035               <p>Multi-value.</p>
1036             </dd>
1037
1038             <dt>Parameter:</dt>
1039
1040             <dd>
1041               <p>Any string value is possible. Validity of the defined HTTP
1042               headers is not checked. It is recommended that you use the
1043               <span class="QUOTE">"<tt class="LITERAL">X-</tt>"</span> prefix
1044               for custom headers.</p>
1045             </dd>
1046
1047             <dt>Notes:</dt>
1048
1049             <dd>
1050               <p>This action may be specified multiple times, in order to
1051               define multiple headers. This is rarely needed for the typical
1052               user. If you don't know what <span class="QUOTE">"HTTP
1053               headers"</span> are, you definitely don't need to worry about
1054               this one.</p>
1055
1056               <p>Headers added by this action are not modified by other
1057               actions.</p>
1058             </dd>
1059
1060             <dt>Example usage:</dt>
1061
1062             <dd>
1063               <table border="0" bgcolor="#E0E0E0" width="90%">
1064                 <tr>
1065                   <td>
1066                     <pre class="SCREEN">
1067 # Add a DNT ("Do not track") header to all requests,
1068 # event to those that already have one.
1069 #
1070 # This is just an example, not a recommendation.
1071 #
1072 # There is no reason to believe that user-tracking websites care
1073 # about the DNT header and depending on the User-Agent, adding the
1074 # header may make user-tracking easier.
1075 {+add-header{DNT: 1}}
1076 /
1077 </pre>
1078                   </td>
1079                 </tr>
1080               </table>
1081             </dd>
1082           </dl>
1083         </div>
1084       </div>
1085
1086       <div class="SECT3">
1087         <h4 class="SECT3"><a name="BLOCK" id="BLOCK">8.5.2. block</a></h4>
1088
1089         <div class="VARIABLELIST">
1090           <dl>
1091             <dt>Typical use:</dt>
1092
1093             <dd>
1094               <p>Block ads or other unwanted content</p>
1095             </dd>
1096
1097             <dt>Effect:</dt>
1098
1099             <dd>
1100               <p>Requests for URLs to which this action applies are blocked,
1101               i.e. the requests are trapped by <span class=
1102               "APPLICATION">Privoxy</span> and the requested URL is never
1103               retrieved, but is answered locally with a substitute page or
1104               image, as determined by the <tt class="LITERAL"><a href=
1105               "actions-file.html#HANDLE-AS-IMAGE">handle-as-image</a></tt>,
1106               <tt class="LITERAL"><a href=
1107               "actions-file.html#SET-IMAGE-BLOCKER">set-image-blocker</a></tt>,
1108               and <tt class="LITERAL"><a href=
1109               "actions-file.html#HANDLE-AS-EMPTY-DOCUMENT">handle-as-empty-document</a></tt>
1110               actions.</p>
1111             </dd>
1112
1113             <dt>Type:</dt>
1114
1115             <dd>
1116               <p>Parameterized.</p>
1117             </dd>
1118
1119             <dt>Parameter:</dt>
1120
1121             <dd>
1122               <p>A block reason that should be given to the user.</p>
1123             </dd>
1124
1125             <dt>Notes:</dt>
1126
1127             <dd>
1128               <p><span class="APPLICATION">Privoxy</span> sends a special
1129               <span class="QUOTE">"BLOCKED"</span> page for requests to
1130               blocked pages. This page contains the block reason given as
1131               parameter, a link to find out why the block action applies, and
1132               a click-through to the blocked content (the latter only if the
1133               force feature is available and enabled).</p>
1134
1135               <p>A very important exception occurs if <span class=
1136               "emphasis"><i class="EMPHASIS">both</i></span> <tt class=
1137               "LITERAL">block</tt> and <tt class="LITERAL"><a href=
1138               "actions-file.html#HANDLE-AS-IMAGE">handle-as-image</a></tt>,
1139               apply to the same request: it will then be replaced by an
1140               image. If <tt class="LITERAL"><a href=
1141               "actions-file.html#SET-IMAGE-BLOCKER">set-image-blocker</a></tt>
1142               (see below) also applies, the type of image will be determined
1143               by its parameter, if not, the standard checkerboard pattern is
1144               sent.</p>
1145
1146               <p>It is important to understand this process, in order to
1147               understand how <span class="APPLICATION">Privoxy</span> deals
1148               with ads and other unwanted content. Blocking is a core
1149               feature, and one upon which various other features depend.</p>
1150
1151               <p>The <tt class="LITERAL"><a href=
1152               "actions-file.html#FILTER">filter</a></tt> action can perform a
1153               very similar task, by <span class="QUOTE">"blocking"</span>
1154               banner images and other content through rewriting the relevant
1155               URLs in the document's HTML source, so they don't get requested
1156               in the first place. Note that this is a totally different
1157               technique, and it's easy to confuse the two.</p>
1158             </dd>
1159
1160             <dt>Example usage (section):</dt>
1161
1162             <dd>
1163               <table border="0" bgcolor="#E0E0E0" width="90%">
1164                 <tr>
1165                   <td>
1166                     <pre class="SCREEN">
1167 {+block{No nasty stuff for you.}}
1168 # Block and replace with "blocked" page
1169  .nasty-stuff.example.com
1170
1171 {+block{Doubleclick banners.} +handle-as-image}
1172 # Block and replace with image
1173  .ad.doubleclick.net
1174  .ads.r.us/banners/
1175
1176 {+block{Layered ads.} +handle-as-empty-document}
1177 # Block and then ignore
1178  adserver.example.net/.*\.js$
1179 </pre>
1180                   </td>
1181                 </tr>
1182               </table>
1183             </dd>
1184           </dl>
1185         </div>
1186       </div>
1187
1188       <div class="SECT3">
1189         <h4 class="SECT3"><a name="CHANGE-X-FORWARDED-FOR" id=
1190         "CHANGE-X-FORWARDED-FOR">8.5.3. change-x-forwarded-for</a></h4>
1191
1192         <div class="VARIABLELIST">
1193           <dl>
1194             <dt>Typical use:</dt>
1195
1196             <dd>
1197               <p>Improve privacy by not forwarding the source of the request
1198               in the HTTP headers.</p>
1199             </dd>
1200
1201             <dt>Effect:</dt>
1202
1203             <dd>
1204               <p>Deletes the <span class="QUOTE">"X-Forwarded-For:"</span>
1205               HTTP header from the client request, or adds a new one.</p>
1206             </dd>
1207
1208             <dt>Type:</dt>
1209
1210             <dd>
1211               <p>Parameterized.</p>
1212             </dd>
1213
1214             <dt>Parameter:</dt>
1215
1216             <dd>
1217               <ul>
1218                 <li>
1219                   <p><span class="QUOTE">"block"</span> to delete the
1220                   header.</p>
1221                 </li>
1222
1223                 <li>
1224                   <p><span class="QUOTE">"add"</span> to create the header
1225                   (or append the client's IP address to an already existing
1226                   one).</p>
1227                 </li>
1228               </ul>
1229             </dd>
1230
1231             <dt>Notes:</dt>
1232
1233             <dd>
1234               <p>It is safe and recommended to use <tt class=
1235               "LITERAL">block</tt>.</p>
1236
1237               <p>Forwarding the source address of the request may make sense
1238               in some multi-user setups but is also a privacy risk.</p>
1239             </dd>
1240
1241             <dt>Example usage:</dt>
1242
1243             <dd>
1244               <table border="0" bgcolor="#E0E0E0" width="90%">
1245                 <tr>
1246                   <td>
1247                     <pre class="SCREEN">
1248 +change-x-forwarded-for{block}
1249 </pre>
1250                   </td>
1251                 </tr>
1252               </table>
1253             </dd>
1254           </dl>
1255         </div>
1256       </div>
1257
1258       <div class="SECT3">
1259         <h4 class="SECT3"><a name="CLIENT-HEADER-FILTER" id=
1260         "CLIENT-HEADER-FILTER">8.5.4. client-header-filter</a></h4>
1261
1262         <div class="VARIABLELIST">
1263           <dl>
1264             <dt>Typical use:</dt>
1265
1266             <dd>
1267               <p>Rewrite or remove single client headers.</p>
1268             </dd>
1269
1270             <dt>Effect:</dt>
1271
1272             <dd>
1273               <p>All client headers to which this action applies are filtered
1274               on-the-fly through the specified regular expression based
1275               substitutions.</p>
1276             </dd>
1277
1278             <dt>Type:</dt>
1279
1280             <dd>
1281               <p>Multi-value.</p>
1282             </dd>
1283
1284             <dt>Parameter:</dt>
1285
1286             <dd>
1287               <p>The name of a client-header filter, as defined in one of the
1288               <a href="filter-file.html">filter files</a>.</p>
1289             </dd>
1290
1291             <dt>Notes:</dt>
1292
1293             <dd>
1294               <p>Client-header filters are applied to each header on its own,
1295               not to all at once. This makes it easier to diagnose problems,
1296               but on the downside you can't write filters that only change
1297               header x if header y's value is z. You can do that by using
1298               tags though.</p>
1299
1300               <p>Client-header filters are executed after the other header
1301               actions have finished and use their output as input.</p>
1302
1303               <p>If the request URI gets changed, <span class=
1304               "APPLICATION">Privoxy</span> will detect that and use the new
1305               one. This can be used to rewrite the request destination behind
1306               the client's back, for example to specify a Tor exit relay for
1307               certain requests.</p>
1308
1309               <p>Please refer to the <a href="filter-file.html">filter file
1310               chapter</a> to learn which client-header filters are available
1311               by default, and how to create your own.</p>
1312             </dd>
1313
1314             <dt>Example usage (section):</dt>
1315
1316             <dd>
1317               <table border="0" bgcolor="#E0E0E0" width="90%">
1318                 <tr>
1319                   <td>
1320                     <pre class="SCREEN">
1321 # Hide Tor exit notation in Host and Referer Headers
1322 {+client-header-filter{hide-tor-exit-notation}}
1323 /
1324
1325 </pre>
1326                   </td>
1327                 </tr>
1328               </table>
1329             </dd>
1330           </dl>
1331         </div>
1332       </div>
1333
1334       <div class="SECT3">
1335         <h4 class="SECT3"><a name="CLIENT-HEADER-TAGGER" id=
1336         "CLIENT-HEADER-TAGGER">8.5.5. client-header-tagger</a></h4>
1337
1338         <div class="VARIABLELIST">
1339           <dl>
1340             <dt>Typical use:</dt>
1341
1342             <dd>
1343               <p>Block requests based on their headers.</p>
1344             </dd>
1345
1346             <dt>Effect:</dt>
1347
1348             <dd>
1349               <p>Client headers to which this action applies are filtered
1350               on-the-fly through the specified regular expression based
1351               substitutions, the result is used as tag.</p>
1352             </dd>
1353
1354             <dt>Type:</dt>
1355
1356             <dd>
1357               <p>Multi-value.</p>
1358             </dd>
1359
1360             <dt>Parameter:</dt>
1361
1362             <dd>
1363               <p>The name of a client-header tagger, as defined in one of the
1364               <a href="filter-file.html">filter files</a>.</p>
1365             </dd>
1366
1367             <dt>Notes:</dt>
1368
1369             <dd>
1370               <p>Client-header taggers are applied to each header on its own,
1371               and as the header isn't modified, each tagger <span class=
1372               "QUOTE">"sees"</span> the original.</p>
1373
1374               <p>Client-header taggers are the first actions that are
1375               executed and their tags can be used to control every other
1376               action.</p>
1377             </dd>
1378
1379             <dt>Example usage (section):</dt>
1380
1381             <dd>
1382               <table border="0" bgcolor="#E0E0E0" width="90%">
1383                 <tr>
1384                   <td>
1385                     <pre class="SCREEN">
1386 # Tag every request with the User-Agent header
1387 {+client-header-tagger{user-agent}}
1388 /
1389
1390 # Tagging itself doesn't change the action
1391 # settings, sections with TAG patterns do:
1392 #
1393 # If it's a download agent, use a different forwarding proxy,
1394 # show the real User-Agent and make sure resume works.
1395 {+forward-override{forward-socks5 10.0.0.2:2222 .} \
1396  -hide-if-modified-since      \
1397  -overwrite-last-modified     \
1398  -hide-user-agent             \
1399  -filter                      \
1400  -deanimate-gifs              \
1401 }
1402 TAG:^User-Agent: NetBSD-ftp/
1403 TAG:^User-Agent: Novell ZYPP Installer
1404 TAG:^User-Agent: RPM APT-HTTP/
1405 TAG:^User-Agent: fetch libfetch/
1406 TAG:^User-Agent: Ubuntu APT-HTTP/
1407 TAG:^User-Agent: MPlayer/
1408
1409 </pre>
1410                   </td>
1411                 </tr>
1412               </table>
1413
1414               <table border="0" bgcolor="#E0E0E0" width="90%">
1415                 <tr>
1416                   <td>
1417                     <pre class="SCREEN">
1418 # Tag all requests with the Range header set
1419 {+client-header-tagger{range-requests}}
1420 /
1421
1422 # Disable filtering for the tagged requests.
1423 #
1424 # With filtering enabled Privoxy would remove the Range headers
1425 # to be able to filter the whole response. The downside is that
1426 # it prevents clients from resuming downloads or skipping over
1427 # parts of multimedia files.
1428 {-filter -deanimate-gifs}
1429 TAG:^RANGE-REQUEST$
1430
1431 </pre>
1432                   </td>
1433                 </tr>
1434               </table>
1435             </dd>
1436           </dl>
1437         </div>
1438       </div>
1439
1440       <div class="SECT3">
1441         <h4 class="SECT3"><a name="CONTENT-TYPE-OVERWRITE" id=
1442         "CONTENT-TYPE-OVERWRITE">8.5.6. content-type-overwrite</a></h4>
1443
1444         <div class="VARIABLELIST">
1445           <dl>
1446             <dt>Typical use:</dt>
1447
1448             <dd>
1449               <p>Stop useless download menus from popping up, or change the
1450               browser's rendering mode</p>
1451             </dd>
1452
1453             <dt>Effect:</dt>
1454
1455             <dd>
1456               <p>Replaces the <span class="QUOTE">"Content-Type:"</span> HTTP
1457               server header.</p>
1458             </dd>
1459
1460             <dt>Type:</dt>
1461
1462             <dd>
1463               <p>Parameterized.</p>
1464             </dd>
1465
1466             <dt>Parameter:</dt>
1467
1468             <dd>
1469               <p>Any string.</p>
1470             </dd>
1471
1472             <dt>Notes:</dt>
1473
1474             <dd>
1475               <p>The <span class="QUOTE">"Content-Type:"</span> HTTP server
1476               header is used by the browser to decide what to do with the
1477               document. The value of this header can cause the browser to
1478               open a download menu instead of displaying the document by
1479               itself, even if the document's format is supported by the
1480               browser.</p>
1481
1482               <p>The declared content type can also affect which rendering
1483               mode the browser chooses. If XHTML is delivered as <span class=
1484               "QUOTE">"text/html"</span>, many browsers treat it as yet
1485               another broken HTML document. If it is send as <span class=
1486               "QUOTE">"application/xml"</span>, browsers with XHTML support
1487               will only display it, if the syntax is correct.</p>
1488
1489               <p>If you see a web site that proudly uses XHTML buttons, but
1490               sets <span class="QUOTE">"Content-Type: text/html"</span>, you
1491               can use <span class="APPLICATION">Privoxy</span> to overwrite
1492               it with <span class="QUOTE">"application/xml"</span> and
1493               validate the web master's claim inside your XHTML-supporting
1494               browser. If the syntax is incorrect, the browser will complain
1495               loudly.</p>
1496
1497               <p>You can also go the opposite direction: if your browser
1498               prints error messages instead of rendering a document falsely
1499               declared as XHTML, you can overwrite the content type with
1500               <span class="QUOTE">"text/html"</span> and have it rendered as
1501               broken HTML document.</p>
1502
1503               <p>By default <tt class="LITERAL">content-type-overwrite</tt>
1504               only replaces <span class="QUOTE">"Content-Type:"</span>
1505               headers that look like some kind of text. If you want to
1506               overwrite it unconditionally, you have to combine it with
1507               <tt class="LITERAL"><a href=
1508               "actions-file.html#FORCE-TEXT-MODE">force-text-mode</a></tt>.
1509               This limitation exists for a reason, think twice before
1510               circumventing it.</p>
1511
1512               <p>Most of the time it's easier to replace this action with a
1513               custom <tt class="LITERAL"><a href=
1514               "actions-file.html#SERVER-HEADER-FILTER">server-header
1515               filter</a></tt>. It allows you to activate it for every
1516               document of a certain site and it will still only replace the
1517               content types you aimed at.</p>
1518
1519               <p>Of course you can apply <tt class=
1520               "LITERAL">content-type-overwrite</tt> to a whole site and then
1521               make URL based exceptions, but it's a lot more work to get the
1522               same precision.</p>
1523             </dd>
1524
1525             <dt>Example usage (sections):</dt>
1526
1527             <dd>
1528               <table border="0" bgcolor="#E0E0E0" width="90%">
1529                 <tr>
1530                   <td>
1531                     <pre class="SCREEN">
1532 # Check if www.example.net/ really uses valid XHTML
1533 { +content-type-overwrite{application/xml} }
1534 www.example.net/
1535
1536 # but leave the content type unmodified if the URL looks like a style sheet
1537 {-content-type-overwrite}
1538 www.example.net/.*\.css$
1539 www.example.net/.*style
1540 </pre>
1541                   </td>
1542                 </tr>
1543               </table>
1544             </dd>
1545           </dl>
1546         </div>
1547       </div>
1548
1549       <div class="SECT3">
1550         <h4 class="SECT3"><a name="CRUNCH-CLIENT-HEADER" id=
1551         "CRUNCH-CLIENT-HEADER">8.5.7. crunch-client-header</a></h4>
1552
1553         <div class="VARIABLELIST">
1554           <dl>
1555             <dt>Typical use:</dt>
1556
1557             <dd>
1558               <p>Remove a client header <span class=
1559               "APPLICATION">Privoxy</span> has no dedicated action for.</p>
1560             </dd>
1561
1562             <dt>Effect:</dt>
1563
1564             <dd>
1565               <p>Deletes every header sent by the client that contains the
1566               string the user supplied as parameter.</p>
1567             </dd>
1568
1569             <dt>Type:</dt>
1570
1571             <dd>
1572               <p>Parameterized.</p>
1573             </dd>
1574
1575             <dt>Parameter:</dt>
1576
1577             <dd>
1578               <p>Any string.</p>
1579             </dd>
1580
1581             <dt>Notes:</dt>
1582
1583             <dd>
1584               <p>This action allows you to block client headers for which no
1585               dedicated <span class="APPLICATION">Privoxy</span> action
1586               exists. <span class="APPLICATION">Privoxy</span> will remove
1587               every client header that contains the string you supplied as
1588               parameter.</p>
1589
1590               <p>Regular expressions are <span class="emphasis"><i class=
1591               "EMPHASIS">not supported</i></span> and you can't use this
1592               action to block different headers in the same request, unless
1593               they contain the same string.</p>
1594
1595               <p><tt class="LITERAL">crunch-client-header</tt> is only meant
1596               for quick tests. If you have to block several different
1597               headers, or only want to modify parts of them, you should use a
1598               <tt class="LITERAL"><a href=
1599               "actions-file.html#CLIENT-HEADER-FILTER">client-header
1600               filter</a></tt>.</p>
1601
1602               <div class="WARNING">
1603                 <table class="WARNING" border="1" width="90%">
1604                   <tr>
1605                     <td align="center"><b>Warning</b></td>
1606                   </tr>
1607
1608                   <tr>
1609                     <td align="left">
1610                       <p>Don't block any header without understanding the
1611                       consequences.</p>
1612                     </td>
1613                   </tr>
1614                 </table>
1615               </div>
1616             </dd>
1617
1618             <dt>Example usage (section):</dt>
1619
1620             <dd>
1621               <table border="0" bgcolor="#E0E0E0" width="90%">
1622                 <tr>
1623                   <td>
1624                     <pre class="SCREEN">
1625 # Block the non-existent "Privacy-Violation:" client header
1626 { +crunch-client-header{Privacy-Violation:} }
1627 /
1628
1629 </pre>
1630                   </td>
1631                 </tr>
1632               </table>
1633             </dd>
1634           </dl>
1635         </div>
1636       </div>
1637
1638       <div class="SECT3">
1639         <h4 class="SECT3"><a name="CRUNCH-IF-NONE-MATCH" id=
1640         "CRUNCH-IF-NONE-MATCH">8.5.8. crunch-if-none-match</a></h4>
1641
1642         <div class="VARIABLELIST">
1643           <dl>
1644             <dt>Typical use:</dt>
1645
1646             <dd>
1647               <p>Prevent yet another way to track the user's steps between
1648               sessions.</p>
1649             </dd>
1650
1651             <dt>Effect:</dt>
1652
1653             <dd>
1654               <p>Deletes the <span class="QUOTE">"If-None-Match:"</span> HTTP
1655               client header.</p>
1656             </dd>
1657
1658             <dt>Type:</dt>
1659
1660             <dd>
1661               <p>Boolean.</p>
1662             </dd>
1663
1664             <dt>Parameter:</dt>
1665
1666             <dd>
1667               <p>N/A</p>
1668             </dd>
1669
1670             <dt>Notes:</dt>
1671
1672             <dd>
1673               <p>Removing the <span class="QUOTE">"If-None-Match:"</span>
1674               HTTP client header is useful for filter testing, where you want
1675               to force a real reload instead of getting status code
1676               <span class="QUOTE">"304"</span> which would cause the browser
1677               to use a cached copy of the page.</p>
1678
1679               <p>It is also useful to make sure the header isn't used as a
1680               cookie replacement (unlikely but possible).</p>
1681
1682               <p>Blocking the <span class="QUOTE">"If-None-Match:"</span>
1683               header shouldn't cause any caching problems, as long as the
1684               <span class="QUOTE">"If-Modified-Since:"</span> header isn't
1685               blocked or missing as well.</p>
1686
1687               <p>It is recommended to use this action together with
1688               <tt class="LITERAL"><a href=
1689               "actions-file.html#HIDE-IF-MODIFIED-SINCE">hide-if-modified-since</a></tt>
1690               and <tt class="LITERAL"><a href=
1691               "actions-file.html#OVERWRITE-LAST-MODIFIED">overwrite-last-modified</a></tt>.</p>
1692             </dd>
1693
1694             <dt>Example usage (section):</dt>
1695
1696             <dd>
1697               <table border="0" bgcolor="#E0E0E0" width="90%">
1698                 <tr>
1699                   <td>
1700                     <pre class="SCREEN">
1701 # Let the browser revalidate cached documents but don't
1702 # allow the server to use the revalidation headers for user tracking.
1703 {+hide-if-modified-since{-60} \
1704  +overwrite-last-modified{randomize} \
1705  +crunch-if-none-match}
1706 /
1707 </pre>
1708                   </td>
1709                 </tr>
1710               </table>
1711             </dd>
1712           </dl>
1713         </div>
1714       </div>
1715
1716       <div class="SECT3">
1717         <h4 class="SECT3"><a name="CRUNCH-INCOMING-COOKIES" id=
1718         "CRUNCH-INCOMING-COOKIES">8.5.9. crunch-incoming-cookies</a></h4>
1719
1720         <div class="VARIABLELIST">
1721           <dl>
1722             <dt>Typical use:</dt>
1723
1724             <dd>
1725               <p>Prevent the web server from setting HTTP cookies on your
1726               system</p>
1727             </dd>
1728
1729             <dt>Effect:</dt>
1730
1731             <dd>
1732               <p>Deletes any <span class="QUOTE">"Set-Cookie:"</span> HTTP
1733               headers from server replies.</p>
1734             </dd>
1735
1736             <dt>Type:</dt>
1737
1738             <dd>
1739               <p>Boolean.</p>
1740             </dd>
1741
1742             <dt>Parameter:</dt>
1743
1744             <dd>
1745               <p>N/A</p>
1746             </dd>
1747
1748             <dt>Notes:</dt>
1749
1750             <dd>
1751               <p>This action is only concerned with <span class=
1752               "emphasis"><i class="EMPHASIS">incoming</i></span> HTTP
1753               cookies. For <span class="emphasis"><i class=
1754               "EMPHASIS">outgoing</i></span> HTTP cookies, use <tt class=
1755               "LITERAL"><a href=
1756               "actions-file.html#CRUNCH-OUTGOING-COOKIES">crunch-outgoing-cookies</a></tt>.
1757               Use <span class="emphasis"><i class="EMPHASIS">both</i></span>
1758               to disable HTTP cookies completely.</p>
1759
1760               <p>It makes <span class="emphasis"><i class="EMPHASIS">no sense
1761               at all</i></span> to use this action in conjunction with the
1762               <tt class="LITERAL"><a href=
1763               "actions-file.html#SESSION-COOKIES-ONLY">session-cookies-only</a></tt>
1764               action, since it would prevent the session cookies from being
1765               set. See also <tt class="LITERAL"><a href=
1766               "actions-file.html#FILTER-CONTENT-COOKIES">filter-content-cookies</a></tt>.</p>
1767             </dd>
1768
1769             <dt>Example usage:</dt>
1770
1771             <dd>
1772               <table border="0" bgcolor="#E0E0E0" width="90%">
1773                 <tr>
1774                   <td>
1775                     <pre class="SCREEN">
1776 +crunch-incoming-cookies
1777 </pre>
1778                   </td>
1779                 </tr>
1780               </table>
1781             </dd>
1782           </dl>
1783         </div>
1784       </div>
1785
1786       <div class="SECT3">
1787         <h4 class="SECT3"><a name="CRUNCH-SERVER-HEADER" id=
1788         "CRUNCH-SERVER-HEADER">8.5.10. crunch-server-header</a></h4>
1789
1790         <div class="VARIABLELIST">
1791           <dl>
1792             <dt>Typical use:</dt>
1793
1794             <dd>
1795               <p>Remove a server header <span class=
1796               "APPLICATION">Privoxy</span> has no dedicated action for.</p>
1797             </dd>
1798
1799             <dt>Effect:</dt>
1800
1801             <dd>
1802               <p>Deletes every header sent by the server that contains the
1803               string the user supplied as parameter.</p>
1804             </dd>
1805
1806             <dt>Type:</dt>
1807
1808             <dd>
1809               <p>Parameterized.</p>
1810             </dd>
1811
1812             <dt>Parameter:</dt>
1813
1814             <dd>
1815               <p>Any string.</p>
1816             </dd>
1817
1818             <dt>Notes:</dt>
1819
1820             <dd>
1821               <p>This action allows you to block server headers for which no
1822               dedicated <span class="APPLICATION">Privoxy</span> action
1823               exists. <span class="APPLICATION">Privoxy</span> will remove
1824               every server header that contains the string you supplied as
1825               parameter.</p>
1826
1827               <p>Regular expressions are <span class="emphasis"><i class=
1828               "EMPHASIS">not supported</i></span> and you can't use this
1829               action to block different headers in the same request, unless
1830               they contain the same string.</p>
1831
1832               <p><tt class="LITERAL">crunch-server-header</tt> is only meant
1833               for quick tests. If you have to block several different
1834               headers, or only want to modify parts of them, you should use a
1835               custom <tt class="LITERAL"><a href=
1836               "actions-file.html#SERVER-HEADER-FILTER">server-header
1837               filter</a></tt>.</p>
1838
1839               <div class="WARNING">
1840                 <table class="WARNING" border="1" width="90%">
1841                   <tr>
1842                     <td align="center"><b>Warning</b></td>
1843                   </tr>
1844
1845                   <tr>
1846                     <td align="left">
1847                       <p>Don't block any header without understanding the
1848                       consequences.</p>
1849                     </td>
1850                   </tr>
1851                 </table>
1852               </div>
1853             </dd>
1854
1855             <dt>Example usage (section):</dt>
1856
1857             <dd>
1858               <table border="0" bgcolor="#E0E0E0" width="90%">
1859                 <tr>
1860                   <td>
1861                     <pre class="SCREEN">
1862 # Crunch server headers that try to prevent caching
1863 { +crunch-server-header{no-cache} }
1864 /
1865 </pre>
1866                   </td>
1867                 </tr>
1868               </table>
1869             </dd>
1870           </dl>
1871         </div>
1872       </div>
1873
1874       <div class="SECT3">
1875         <h4 class="SECT3"><a name="CRUNCH-OUTGOING-COOKIES" id=
1876         "CRUNCH-OUTGOING-COOKIES">8.5.11. crunch-outgoing-cookies</a></h4>
1877
1878         <div class="VARIABLELIST">
1879           <dl>
1880             <dt>Typical use:</dt>
1881
1882             <dd>
1883               <p>Prevent the web server from reading any HTTP cookies from
1884               your system</p>
1885             </dd>
1886
1887             <dt>Effect:</dt>
1888
1889             <dd>
1890               <p>Deletes any <span class="QUOTE">"Cookie:"</span> HTTP
1891               headers from client requests.</p>
1892             </dd>
1893
1894             <dt>Type:</dt>
1895
1896             <dd>
1897               <p>Boolean.</p>
1898             </dd>
1899
1900             <dt>Parameter:</dt>
1901
1902             <dd>
1903               <p>N/A</p>
1904             </dd>
1905
1906             <dt>Notes:</dt>
1907
1908             <dd>
1909               <p>This action is only concerned with <span class=
1910               "emphasis"><i class="EMPHASIS">outgoing</i></span> HTTP
1911               cookies. For <span class="emphasis"><i class=
1912               "EMPHASIS">incoming</i></span> HTTP cookies, use <tt class=
1913               "LITERAL"><a href=
1914               "actions-file.html#CRUNCH-INCOMING-COOKIES">crunch-incoming-cookies</a></tt>.
1915               Use <span class="emphasis"><i class="EMPHASIS">both</i></span>
1916               to disable HTTP cookies completely.</p>
1917
1918               <p>It makes <span class="emphasis"><i class="EMPHASIS">no sense
1919               at all</i></span> to use this action in conjunction with the
1920               <tt class="LITERAL"><a href=
1921               "actions-file.html#SESSION-COOKIES-ONLY">session-cookies-only</a></tt>
1922               action, since it would prevent the session cookies from being
1923               read.</p>
1924             </dd>
1925
1926             <dt>Example usage:</dt>
1927
1928             <dd>
1929               <table border="0" bgcolor="#E0E0E0" width="90%">
1930                 <tr>
1931                   <td>
1932                     <pre class="SCREEN">
1933 +crunch-outgoing-cookies
1934 </pre>
1935                   </td>
1936                 </tr>
1937               </table>
1938             </dd>
1939           </dl>
1940         </div>
1941       </div>
1942
1943       <div class="SECT3">
1944         <h4 class="SECT3"><a name="DEANIMATE-GIFS" id=
1945         "DEANIMATE-GIFS">8.5.12. deanimate-gifs</a></h4>
1946
1947         <div class="VARIABLELIST">
1948           <dl>
1949             <dt>Typical use:</dt>
1950
1951             <dd>
1952               <p>Stop those annoying, distracting animated GIF images.</p>
1953             </dd>
1954
1955             <dt>Effect:</dt>
1956
1957             <dd>
1958               <p>De-animate GIF animations, i.e. reduce them to their first
1959               or last image.</p>
1960             </dd>
1961
1962             <dt>Type:</dt>
1963
1964             <dd>
1965               <p>Parameterized.</p>
1966             </dd>
1967
1968             <dt>Parameter:</dt>
1969
1970             <dd>
1971               <p><span class="QUOTE">"last"</span> or <span class=
1972               "QUOTE">"first"</span></p>
1973             </dd>
1974
1975             <dt>Notes:</dt>
1976
1977             <dd>
1978               <p>This will also shrink the images considerably (in bytes, not
1979               pixels!). If the option <span class="QUOTE">"first"</span> is
1980               given, the first frame of the animation is used as the
1981               replacement. If <span class="QUOTE">"last"</span> is given, the
1982               last frame of the animation is used instead, which probably
1983               makes more sense for most banner animations, but also has the
1984               risk of not showing the entire last frame (if it is only a
1985               delta to an earlier frame).</p>
1986
1987               <p>You can safely use this action with patterns that will also
1988               match non-GIF objects, because no attempt will be made at
1989               anything that doesn't look like a GIF.</p>
1990             </dd>
1991
1992             <dt>Example usage:</dt>
1993
1994             <dd>
1995               <table border="0" bgcolor="#E0E0E0" width="90%">
1996                 <tr>
1997                   <td>
1998                     <pre class="SCREEN">
1999 +deanimate-gifs{last}
2000 </pre>
2001                   </td>
2002                 </tr>
2003               </table>
2004             </dd>
2005           </dl>
2006         </div>
2007       </div>
2008
2009       <div class="SECT3">
2010         <h4 class="SECT3"><a name="DOWNGRADE-HTTP-VERSION" id=
2011         "DOWNGRADE-HTTP-VERSION">8.5.13. downgrade-http-version</a></h4>
2012
2013         <div class="VARIABLELIST">
2014           <dl>
2015             <dt>Typical use:</dt>
2016
2017             <dd>
2018               <p>Work around (very rare) problems with HTTP/1.1</p>
2019             </dd>
2020
2021             <dt>Effect:</dt>
2022
2023             <dd>
2024               <p>Downgrades HTTP/1.1 client requests and server replies to
2025               HTTP/1.0.</p>
2026             </dd>
2027
2028             <dt>Type:</dt>
2029
2030             <dd>
2031               <p>Boolean.</p>
2032             </dd>
2033
2034             <dt>Parameter:</dt>
2035
2036             <dd>
2037               <p>N/A</p>
2038             </dd>
2039
2040             <dt>Notes:</dt>
2041
2042             <dd>
2043               <p>This is a left-over from the time when <span class=
2044               "APPLICATION">Privoxy</span> didn't support important HTTP/1.1
2045               features well. It is left here for the unlikely case that you
2046               experience HTTP/1.1-related problems with some server out
2047               there.</p>
2048
2049               <p>Note that enabling this action is only a workaround. It
2050               should not be enabled for sites that work without it. While it
2051               shouldn't break any pages, it has an (usually negative)
2052               performance impact.</p>
2053
2054               <p>If you come across a site where enabling this action helps,
2055               please report it, so the cause of the problem can be analyzed.
2056               If the problem turns out to be caused by a bug in <span class=
2057               "APPLICATION">Privoxy</span> it should be fixed so the
2058               following release works without the work around.</p>
2059             </dd>
2060
2061             <dt>Example usage (section):</dt>
2062
2063             <dd>
2064               <table border="0" bgcolor="#E0E0E0" width="90%">
2065                 <tr>
2066                   <td>
2067                     <pre class="SCREEN">
2068 {+downgrade-http-version}
2069 problem-host.example.com
2070 </pre>
2071                   </td>
2072                 </tr>
2073               </table>
2074             </dd>
2075           </dl>
2076         </div>
2077       </div>
2078
2079       <div class="SECT3">
2080         <h4 class="SECT3"><a name="EXTERNAL-FILTER" id=
2081         "EXTERNAL-FILTER">8.5.14. external-filter</a></h4>
2082
2083         <div class="VARIABLELIST">
2084           <dl>
2085             <dt>Typical use:</dt>
2086
2087             <dd>
2088               <p>Modify content using a programming language of your
2089               choice.</p>
2090             </dd>
2091
2092             <dt>Effect:</dt>
2093
2094             <dd>
2095               <p>All instances of text-based type, most notably HTML and
2096               JavaScript, to which this action applies, can be filtered
2097               on-the-fly through the specified external filter. By default
2098               plain text documents are exempted from filtering, because web
2099               servers often use the <tt class="LITERAL">text/plain</tt> MIME
2100               type for all files whose type they don't know.)</p>
2101             </dd>
2102
2103             <dt>Type:</dt>
2104
2105             <dd>
2106               <p>Multi-value.</p>
2107             </dd>
2108
2109             <dt>Parameter:</dt>
2110
2111             <dd>
2112               <p>The name of an external content filter, as defined in the
2113               <a href="filter-file.html">filter file</a>. External filters
2114               can be defined in one or more files as defined by the
2115               <tt class="LITERAL"><a href=
2116               "config.html#FILTERFILE">filterfile</a></tt> option in the
2117               <a href="config.html">config file</a>.</p>
2118
2119               <p>When used in its negative form, and without parameters,
2120               <span class="emphasis"><i class="EMPHASIS">all</i></span>
2121               filtering with external filters is completely disabled.</p>
2122             </dd>
2123
2124             <dt>Notes:</dt>
2125
2126             <dd>
2127               <p>External filters are scripts or programs that can modify the
2128               content in case common <tt class="LITERAL"><a href=
2129               "actions-file.html#FILTER">filters</a></tt> aren't powerful
2130               enough. With the exception that this action doesn't use
2131               pcrs-based filters, the notes in the <tt class=
2132               "LITERAL"><a href="actions-file.html#FILTER">filter</a></tt>
2133               section apply.</p>
2134
2135               <div class="WARNING">
2136                 <table class="WARNING" border="1" width="90%">
2137                   <tr>
2138                     <td align="center"><b>Warning</b></td>
2139                   </tr>
2140
2141                   <tr>
2142                     <td align="left">
2143                       <p>Currently external filters are executed with
2144                       <span class="APPLICATION">Privoxy</span>'s privileges.
2145                       Only use external filters you understand and trust.</p>
2146                     </td>
2147                   </tr>
2148                 </table>
2149               </div>
2150
2151               <p>This feature is experimental, the <tt class=
2152               "LITERAL"><a href=
2153               "filter-file.html#EXTERNAL-FILTER-SYNTAX">syntax</a></tt> may
2154               change in the future.</p>
2155             </dd>
2156
2157             <dt>Example usage:</dt>
2158
2159             <dd>
2160               <table border="0" bgcolor="#E0E0E0" width="90%">
2161                 <tr>
2162                   <td>
2163                     <pre class="SCREEN">
2164 +external-filter{fancy-filter}
2165 </pre>
2166                   </td>
2167                 </tr>
2168               </table>
2169             </dd>
2170           </dl>
2171         </div>
2172       </div>
2173
2174       <div class="SECT3">
2175         <h4 class="SECT3"><a name="FAST-REDIRECTS" id=
2176         "FAST-REDIRECTS">8.5.15. fast-redirects</a></h4>
2177
2178         <div class="VARIABLELIST">
2179           <dl>
2180             <dt>Typical use:</dt>
2181
2182             <dd>
2183               <p>Fool some click-tracking scripts and speed up indirect
2184               links.</p>
2185             </dd>
2186
2187             <dt>Effect:</dt>
2188
2189             <dd>
2190               <p>Detects redirection URLs and redirects the browser without
2191               contacting the redirection server first.</p>
2192             </dd>
2193
2194             <dt>Type:</dt>
2195
2196             <dd>
2197               <p>Parameterized.</p>
2198             </dd>
2199
2200             <dt>Parameter:</dt>
2201
2202             <dd>
2203               <ul>
2204                 <li>
2205                   <p><span class="QUOTE">"simple-check"</span> to just search
2206                   for the string <span class="QUOTE">"http://"</span> to
2207                   detect redirection URLs.</p>
2208                 </li>
2209
2210                 <li>
2211                   <p><span class="QUOTE">"check-decoded-url"</span> to decode
2212                   URLs (if necessary) before searching for redirection
2213                   URLs.</p>
2214                 </li>
2215               </ul>
2216             </dd>
2217
2218             <dt>Notes:</dt>
2219
2220             <dd>
2221               <p>Many sites, like yahoo.com, don't just link to other sites.
2222               Instead, they will link to some script on their own servers,
2223               giving the destination as a parameter, which will then redirect
2224               you to the final target. URLs resulting from this scheme
2225               typically look like: <span class=
2226               "QUOTE">"http://www.example.org/click-tracker.cgi?target=http%3a//www.example.net/"</span>.</p>
2227
2228               <p>Sometimes, there are even multiple consecutive redirects
2229               encoded in the URL. These redirections via scripts make your
2230               web browsing more traceable, since the server from which you
2231               follow such a link can see where you go to. Apart from that,
2232               valuable bandwidth and time is wasted, while your browser asks
2233               the server for one redirect after the other. Plus, it feeds the
2234               advertisers.</p>
2235
2236               <p>This feature is currently not very smart and is scheduled
2237               for improvement. If it is enabled by default, you will have to
2238               create some exceptions to this action. It can lead to failures
2239               in several ways:</p>
2240
2241               <p>Not every URLs with other URLs as parameters is evil. Some
2242               sites offer a real service that requires this information to
2243               work. For example a validation service needs to know, which
2244               document to validate. <tt class="LITERAL">fast-redirects</tt>
2245               assumes that every URL parameter that looks like another URL is
2246               a redirection target, and will always redirect to the last one.
2247               Most of the time the assumption is correct, but if it isn't,
2248               the user gets redirected anyway.</p>
2249
2250               <p>Another failure occurs if the URL contains other parameters
2251               after the URL parameter. The URL: <span class=
2252               "QUOTE">"http://www.example.org/?redirect=http%3a//www.example.net/&amp;foo=bar"</span>.
2253               contains the redirection URL <span class=
2254               "QUOTE">"http://www.example.net/"</span>, followed by another
2255               parameter. <tt class="LITERAL">fast-redirects</tt> doesn't know
2256               that and will cause a redirect to <span class=
2257               "QUOTE">"http://www.example.net/&amp;foo=bar"</span>. Depending
2258               on the target server configuration, the parameter will be
2259               silently ignored or lead to a <span class="QUOTE">"page not
2260               found"</span> error. You can prevent this problem by first
2261               using the <tt class="LITERAL"><a href=
2262               "actions-file.html#REDIRECT">redirect</a></tt> action to remove
2263               the last part of the URL, but it requires a little effort.</p>
2264
2265               <p>To detect a redirection URL, <tt class=
2266               "LITERAL">fast-redirects</tt> only looks for the string
2267               <span class="QUOTE">"http://"</span>, either in plain text
2268               (invalid but often used) or encoded as <span class=
2269               "QUOTE">"http%3a//"</span>. Some sites use their own URL
2270               encoding scheme, encrypt the address of the target server or
2271               replace it with a database id. In theses cases <tt class=
2272               "LITERAL">fast-redirects</tt> is fooled and the request reaches
2273               the redirection server where it probably gets logged.</p>
2274             </dd>
2275
2276             <dt>Example usage:</dt>
2277
2278             <dd>
2279               <table border="0" bgcolor="#E0E0E0" width="90%">
2280                 <tr>
2281                   <td>
2282                     <pre class="SCREEN">
2283  { +fast-redirects{simple-check} }
2284    one.example.com
2285
2286  { +fast-redirects{check-decoded-url} }
2287    another.example.com/testing
2288 </pre>
2289                   </td>
2290                 </tr>
2291               </table>
2292             </dd>
2293           </dl>
2294         </div>
2295       </div>
2296
2297       <div class="SECT3">
2298         <h4 class="SECT3"><a name="FILTER" id="FILTER">8.5.16.
2299         filter</a></h4>
2300
2301         <div class="VARIABLELIST">
2302           <dl>
2303             <dt>Typical use:</dt>
2304
2305             <dd>
2306               <p>Get rid of HTML and JavaScript annoyances, banner
2307               advertisements (by size), do fun text replacements, add
2308               personalized effects, etc.</p>
2309             </dd>
2310
2311             <dt>Effect:</dt>
2312
2313             <dd>
2314               <p>All instances of text-based type, most notably HTML and
2315               JavaScript, to which this action applies, can be filtered
2316               on-the-fly through the specified regular expression based
2317               substitutions. (Note: as of version 3.0.3 plain text documents
2318               are exempted from filtering, because web servers often use the
2319               <tt class="LITERAL">text/plain</tt> MIME type for all files
2320               whose type they don't know.)</p>
2321             </dd>
2322
2323             <dt>Type:</dt>
2324
2325             <dd>
2326               <p>Multi-value.</p>
2327             </dd>
2328
2329             <dt>Parameter:</dt>
2330
2331             <dd>
2332               <p>The name of a content filter, as defined in the <a href=
2333               "filter-file.html">filter file</a>. Filters can be defined in
2334               one or more files as defined by the <tt class=
2335               "LITERAL"><a href="config.html#FILTERFILE">filterfile</a></tt>
2336               option in the <a href="config.html">config file</a>. <tt class=
2337               "FILENAME">default.filter</tt> is the collection of filters
2338               supplied by the developers. Locally defined filters should go
2339               in their own file, such as <tt class=
2340               "FILENAME">user.filter</tt>.</p>
2341
2342               <p>When used in its negative form, and without parameters,
2343               <span class="emphasis"><i class="EMPHASIS">all</i></span>
2344               filtering is completely disabled.</p>
2345             </dd>
2346
2347             <dt>Notes:</dt>
2348
2349             <dd>
2350               <p>For your convenience, there are a number of pre-defined
2351               filters available in the distribution filter file that you can
2352               use. See the examples below for a list.</p>
2353
2354               <p>Filtering requires buffering the page content, which may
2355               appear to slow down page rendering since nothing is displayed
2356               until all content has passed the filters. (The total time until
2357               the page is completely rendered doesn't change much, but it may
2358               be perceived as slower since the page is not incrementally
2359               displayed.) This effect will be more noticeable on slower
2360               connections.</p>
2361
2362               <p><span class="QUOTE">"Rolling your own"</span> filters
2363               requires a knowledge of <a href=
2364               "http://en.wikipedia.org/wiki/Regular_expressions" target=
2365               "_top"><span class="QUOTE">"Regular Expressions"</span></a> and
2366               <a href="http://en.wikipedia.org/wiki/Html" target=
2367               "_top"><span class="QUOTE">"HTML"</span></a>. This is very
2368               powerful feature, and potentially very intrusive. Filters
2369               should be used with caution, and where an equivalent
2370               <span class="QUOTE">"action"</span> is not available.</p>
2371
2372               <p>The amount of data that can be filtered is limited to the
2373               <tt class="LITERAL"><a href=
2374               "config.html#BUFFER-LIMIT">buffer-limit</a></tt> option in the
2375               main <a href="config.html">config file</a>. The default is 4096
2376               KB (4 Megs). Once this limit is exceeded, the buffered data,
2377               and all pending data, is passed through unfiltered.</p>
2378
2379               <p>Inappropriate MIME types, such as zipped files, are not
2380               filtered at all. (Again, only text-based types except plain
2381               text). Encrypted SSL data (from HTTPS servers) cannot be
2382               filtered either, since this would violate the integrity of the
2383               secure transaction. In some situations it might be necessary to
2384               protect certain text, like source code, from filtering by
2385               defining appropriate <tt class="LITERAL">-filter</tt>
2386               exceptions.</p>
2387
2388               <p>Compressed content can't be filtered either, but if
2389               <span class="APPLICATION">Privoxy</span> is compiled with zlib
2390               support and a supported compression algorithm is used (gzip or
2391               deflate), <span class="APPLICATION">Privoxy</span> can first
2392               decompress the content and then filter it.</p>
2393
2394               <p>If you use a <span class="APPLICATION">Privoxy</span>
2395               version without zlib support, but want filtering to work on as
2396               much documents as possible, even those that would normally be
2397               sent compressed, you must use the <tt class="LITERAL"><a href=
2398               "actions-file.html#PREVENT-COMPRESSION">prevent-compression</a></tt>
2399               action in conjunction with <tt class="LITERAL">filter</tt>.</p>
2400
2401               <p>Content filtering can achieve some of the same effects as
2402               the <tt class="LITERAL"><a href=
2403               "actions-file.html#BLOCK">block</a></tt> action, i.e. it can be
2404               used to block ads and banners. But the mechanism works quite
2405               differently. One effective use, is to block ad banners based on
2406               their size (see below), since many of these seem to be somewhat
2407               standardized.</p>
2408
2409               <p><a href="contact.html">Feedback</a> with suggestions for new
2410               or improved filters is particularly welcome!</p>
2411
2412               <p>The below list has only the names and a one-line description
2413               of each predefined filter. There are <a href=
2414               "filter-file.html#PREDEFINED-FILTERS">more verbose
2415               explanations</a> of what these filters do in the <a href=
2416               "filter-file.html">filter file chapter</a>.</p>
2417             </dd>
2418
2419             <dt>Example usage (with filters from the distribution <tt class=
2420             "FILENAME">default.filter</tt> file). See <a href=
2421             "filter-file.html#PREDEFINED-FILTERS">the Predefined Filters
2422             section</a> for more explanation on each:</dt>
2423
2424             <dd>
2425               <p><a name="FILTER-JS-ANNOYANCES" id=
2426               "FILTER-JS-ANNOYANCES"></a></p>
2427
2428               <table border="0" bgcolor="#E0E0E0" width="90%">
2429                 <tr>
2430                   <td>
2431                     <pre class="SCREEN">
2432 +filter{js-annoyances}       # Get rid of particularly annoying JavaScript abuse.
2433 </pre>
2434                   </td>
2435                 </tr>
2436               </table>
2437
2438               <p><a name="FILTER-JS-EVENTS" id="FILTER-JS-EVENTS"></a></p>
2439
2440               <table border="0" bgcolor="#E0E0E0" width="90%">
2441                 <tr>
2442                   <td>
2443                     <pre class="SCREEN">
2444 +filter{js-events}           # Kill JavaScript event bindings and timers (Radically destructive! Only for extra nasty sites).
2445 </pre>
2446                   </td>
2447                 </tr>
2448               </table>
2449
2450               <p><a name="FILTER-HTML-ANNOYANCES" id=
2451               "FILTER-HTML-ANNOYANCES"></a></p>
2452
2453               <table border="0" bgcolor="#E0E0E0" width="90%">
2454                 <tr>
2455                   <td>
2456                     <pre class="SCREEN">
2457 +filter{html-annoyances}     # Get rid of particularly annoying HTML abuse.
2458 </pre>
2459                   </td>
2460                 </tr>
2461               </table>
2462
2463               <p><a name="FILTER-CONTENT-COOKIES" id=
2464               "FILTER-CONTENT-COOKIES"></a></p>
2465
2466               <table border="0" bgcolor="#E0E0E0" width="90%">
2467                 <tr>
2468                   <td>
2469                     <pre class="SCREEN">
2470 +filter{content-cookies}     # Kill cookies that come in the HTML or JS content.
2471 </pre>
2472                   </td>
2473                 </tr>
2474               </table>
2475
2476               <p><a name="FILTER-REFRESH-TAGS" id=
2477               "FILTER-REFRESH-TAGS"></a></p>
2478
2479               <table border="0" bgcolor="#E0E0E0" width="90%">
2480                 <tr>
2481                   <td>
2482                     <pre class="SCREEN">
2483 +filter{refresh-tags}        # Kill automatic refresh tags if refresh time is larger than 9 seconds.
2484 </pre>
2485                   </td>
2486                 </tr>
2487               </table>
2488
2489               <p><a name="FILTER-UNSOLICITED-POPUPS" id=
2490               "FILTER-UNSOLICITED-POPUPS"></a></p>
2491
2492               <table border="0" bgcolor="#E0E0E0" width="90%">
2493                 <tr>
2494                   <td>
2495                     <pre class="SCREEN">
2496 +filter{unsolicited-popups}  # Disable only unsolicited pop-up windows.
2497 </pre>
2498                   </td>
2499                 </tr>
2500               </table>
2501
2502               <p><a name="FILTER-ALL-POPUPS" id="FILTER-ALL-POPUPS"></a></p>
2503
2504               <table border="0" bgcolor="#E0E0E0" width="90%">
2505                 <tr>
2506                   <td>
2507                     <pre class="SCREEN">
2508 +filter{all-popups}          # Kill all popups in JavaScript and HTML.
2509 </pre>
2510                   </td>
2511                 </tr>
2512               </table>
2513
2514               <p><a name="FILTER-IMG-REORDER" id=
2515               "FILTER-IMG-REORDER"></a></p>
2516
2517               <table border="0" bgcolor="#E0E0E0" width="90%">
2518                 <tr>
2519                   <td>
2520                     <pre class="SCREEN">
2521 +filter{img-reorder}         # Reorder attributes in &lt;img&gt; tags to make the banners-by-* filters more effective.
2522 </pre>
2523                   </td>
2524                 </tr>
2525               </table>
2526
2527               <p><a name="FILTER-BANNERS-BY-SIZE" id=
2528               "FILTER-BANNERS-BY-SIZE"></a></p>
2529
2530               <table border="0" bgcolor="#E0E0E0" width="90%">
2531                 <tr>
2532                   <td>
2533                     <pre class="SCREEN">
2534 +filter{banners-by-size}     # Kill banners by size.
2535 </pre>
2536                   </td>
2537                 </tr>
2538               </table>
2539
2540               <p><a name="FILTER-BANNERS-BY-LINK" id=
2541               "FILTER-BANNERS-BY-LINK"></a></p>
2542
2543               <table border="0" bgcolor="#E0E0E0" width="90%">
2544                 <tr>
2545                   <td>
2546                     <pre class="SCREEN">
2547 +filter{banners-by-link}     # Kill banners by their links to known clicktrackers.
2548 </pre>
2549                   </td>
2550                 </tr>
2551               </table>
2552
2553               <p><a name="FILTER-WEBBUGS" id="FILTER-WEBBUGS"></a></p>
2554
2555               <table border="0" bgcolor="#E0E0E0" width="90%">
2556                 <tr>
2557                   <td>
2558                     <pre class="SCREEN">
2559 +filter{webbugs}             # Squish WebBugs (1x1 invisible GIFs used for user tracking).
2560 </pre>
2561                   </td>
2562                 </tr>
2563               </table>
2564
2565               <p><a name="FILTER-TINY-TEXTFORMS" id=
2566               "FILTER-TINY-TEXTFORMS"></a></p>
2567
2568               <table border="0" bgcolor="#E0E0E0" width="90%">
2569                 <tr>
2570                   <td>
2571                     <pre class="SCREEN">
2572 +filter{tiny-textforms}      # Extend those tiny textareas up to 40x80 and kill the hard wrap.
2573 </pre>
2574                   </td>
2575                 </tr>
2576               </table>
2577
2578               <p><a name="FILTER-JUMPING-WINDOWS" id=
2579               "FILTER-JUMPING-WINDOWS"></a></p>
2580
2581               <table border="0" bgcolor="#E0E0E0" width="90%">
2582                 <tr>
2583                   <td>
2584                     <pre class="SCREEN">
2585 +filter{jumping-windows}     # Prevent windows from resizing and moving themselves.
2586 </pre>
2587                   </td>
2588                 </tr>
2589               </table>
2590
2591               <p><a name="FILTER-FRAMESET-BORDERS" id=
2592               "FILTER-FRAMESET-BORDERS"></a></p>
2593
2594               <table border="0" bgcolor="#E0E0E0" width="90%">
2595                 <tr>
2596                   <td>
2597                     <pre class="SCREEN">
2598 +filter{frameset-borders}    # Give frames a border and make them resizable.
2599 </pre>
2600                   </td>
2601                 </tr>
2602               </table>
2603
2604               <p><a name="FILTER-IFRAMES" id="FILTER-IFRAMES"></a></p>
2605
2606               <table border="0" bgcolor="#E0E0E0" width="90%">
2607                 <tr>
2608                   <td>
2609                     <pre class="SCREEN">
2610 +filter{iframes}             # Removes all detected iframes. Should only be enabled for individual sites.
2611 </pre>
2612                   </td>
2613                 </tr>
2614               </table>
2615
2616               <p><a name="FILTER-DEMORONIZER" id=
2617               "FILTER-DEMORONIZER"></a></p>
2618
2619               <table border="0" bgcolor="#E0E0E0" width="90%">
2620                 <tr>
2621                   <td>
2622                     <pre class="SCREEN">
2623 +filter{demoronizer}         # Fix MS's non-standard use of standard charsets.
2624 </pre>
2625                   </td>
2626                 </tr>
2627               </table>
2628
2629               <p><a name="FILTER-SHOCKWAVE-FLASH" id=
2630               "FILTER-SHOCKWAVE-FLASH"></a></p>
2631
2632               <table border="0" bgcolor="#E0E0E0" width="90%">
2633                 <tr>
2634                   <td>
2635                     <pre class="SCREEN">
2636 +filter{shockwave-flash}     # Kill embedded Shockwave Flash objects.
2637 </pre>
2638                   </td>
2639                 </tr>
2640               </table>
2641
2642               <p><a name="FILTER-QUICKTIME-KIOSKMODE" id=
2643               "FILTER-QUICKTIME-KIOSKMODE"></a></p>
2644
2645               <table border="0" bgcolor="#E0E0E0" width="90%">
2646                 <tr>
2647                   <td>
2648                     <pre class="SCREEN">
2649 +filter{quicktime-kioskmode} # Make Quicktime movies saveable.
2650 </pre>
2651                   </td>
2652                 </tr>
2653               </table>
2654
2655               <p><a name="FILTER-FUN" id="FILTER-FUN"></a></p>
2656
2657               <table border="0" bgcolor="#E0E0E0" width="90%">
2658                 <tr>
2659                   <td>
2660                     <pre class="SCREEN">
2661 +filter{fun}                 # Text replacements for subversive browsing fun!
2662 </pre>
2663                   </td>
2664                 </tr>
2665               </table>
2666
2667               <p><a name="FILTER-CRUDE-PARENTAL" id=
2668               "FILTER-CRUDE-PARENTAL"></a></p>
2669
2670               <table border="0" bgcolor="#E0E0E0" width="90%">
2671                 <tr>
2672                   <td>
2673                     <pre class="SCREEN">
2674 +filter{crude-parental}      # Crude parental filtering. Note that this filter doesn't work reliably.
2675 </pre>
2676                   </td>
2677                 </tr>
2678               </table>
2679
2680               <p><a name="FILTER-IE-EXPLOITS" id=
2681               "FILTER-IE-EXPLOITS"></a></p>
2682
2683               <table border="0" bgcolor="#E0E0E0" width="90%">
2684                 <tr>
2685                   <td>
2686                     <pre class="SCREEN">
2687 +filter{ie-exploits}         # Disable some known Internet Explorer bug exploits.
2688 </pre>
2689                   </td>
2690                 </tr>
2691               </table>
2692
2693               <p><a name="FILTER-SITE-SPECIFICS" id=
2694               "FILTER-SITE-SPECIFICS"></a></p>
2695
2696               <table border="0" bgcolor="#E0E0E0" width="90%">
2697                 <tr>
2698                   <td>
2699                     <pre class="SCREEN">
2700 +filter{site-specifics}      # Cure for site-specific problems. Don't apply generally!
2701 </pre>
2702                   </td>
2703                 </tr>
2704               </table>
2705
2706               <p><a name="FILTER-NO-PING" id="FILTER-NO-PING"></a></p>
2707
2708               <table border="0" bgcolor="#E0E0E0" width="90%">
2709                 <tr>
2710                   <td>
2711                     <pre class="SCREEN">
2712 +filter{no-ping}             # Removes non-standard ping attributes in &lt;a&gt; and &lt;area&gt; tags.
2713 </pre>
2714                   </td>
2715                 </tr>
2716               </table>
2717
2718               <p><a name="FILTER-GOOGLE" id="FILTER-GOOGLE"></a></p>
2719
2720               <table border="0" bgcolor="#E0E0E0" width="90%">
2721                 <tr>
2722                   <td>
2723                     <pre class="SCREEN">
2724 +filter{google}              # CSS-based block for Google text ads. Also removes a width limitation and the toolbar advertisement.
2725 </pre>
2726                   </td>
2727                 </tr>
2728               </table>
2729
2730               <p><a name="FILTER-YAHOO" id="FILTER-YAHOO"></a></p>
2731
2732               <table border="0" bgcolor="#E0E0E0" width="90%">
2733                 <tr>
2734                   <td>
2735                     <pre class="SCREEN">
2736 +filter{yahoo}               # CSS-based block for Yahoo text ads. Also removes a width limitation.
2737 </pre>
2738                   </td>
2739                 </tr>
2740               </table>
2741
2742               <p><a name="FILTER-MSN" id="FILTER-MSN"></a></p>
2743
2744               <table border="0" bgcolor="#E0E0E0" width="90%">
2745                 <tr>
2746                   <td>
2747                     <pre class="SCREEN">
2748 +filter{msn}                 # CSS-based block for MSN text ads. Also removes tracking URLs and a width limitation.
2749 </pre>
2750                   </td>
2751                 </tr>
2752               </table>
2753
2754               <p><a name="FILTER-BLOGSPOT" id="FILTER-BLOGSPOT"></a></p>
2755
2756               <table border="0" bgcolor="#E0E0E0" width="90%">
2757                 <tr>
2758                   <td>
2759                     <pre class="SCREEN">
2760 +filter{blogspot}            # Cleans up some Blogspot blogs. Read the fine print before using this.
2761 </pre>
2762                   </td>
2763                 </tr>
2764               </table>
2765             </dd>
2766           </dl>
2767         </div>
2768       </div>
2769
2770       <div class="SECT3">
2771         <h4 class="SECT3"><a name="FORCE-TEXT-MODE" id=
2772         "FORCE-TEXT-MODE">8.5.17. force-text-mode</a></h4>
2773
2774         <div class="VARIABLELIST">
2775           <dl>
2776             <dt>Typical use:</dt>
2777
2778             <dd>
2779               <p>Force <span class="APPLICATION">Privoxy</span> to treat a
2780               document as if it was in some kind of <span class=
2781               "emphasis"><i class="EMPHASIS">text</i></span> format.</p>
2782             </dd>
2783
2784             <dt>Effect:</dt>
2785
2786             <dd>
2787               <p>Declares a document as text, even if the <span class=
2788               "QUOTE">"Content-Type:"</span> isn't detected as such.</p>
2789             </dd>
2790
2791             <dt>Type:</dt>
2792
2793             <dd>
2794               <p>Boolean.</p>
2795             </dd>
2796
2797             <dt>Parameter:</dt>
2798
2799             <dd>
2800               <p>N/A</p>
2801             </dd>
2802
2803             <dt>Notes:</dt>
2804
2805             <dd>
2806               <p>As explained <tt class="LITERAL"><a href=
2807               "actions-file.html#FILTER">above</a></tt>, <span class=
2808               "APPLICATION">Privoxy</span> tries to only filter files that
2809               are in some kind of text format. The same restrictions apply to
2810               <tt class="LITERAL"><a href=
2811               "actions-file.html#CONTENT-TYPE-OVERWRITE">content-type-overwrite</a></tt>.
2812               <tt class="LITERAL">force-text-mode</tt> declares a document as
2813               text, without looking at the <span class=
2814               "QUOTE">"Content-Type:"</span> first.</p>
2815
2816               <div class="WARNING">
2817                 <table class="WARNING" border="1" width="90%">
2818                   <tr>
2819                     <td align="center"><b>Warning</b></td>
2820                   </tr>
2821
2822                   <tr>
2823                     <td align="left">
2824                       <p>Think twice before activating this action. Filtering
2825                       binary data with regular expressions can cause file
2826                       damage.</p>
2827                     </td>
2828                   </tr>
2829                 </table>
2830               </div>
2831             </dd>
2832
2833             <dt>Example usage:</dt>
2834
2835             <dd>
2836               <table border="0" bgcolor="#E0E0E0" width="90%">
2837                 <tr>
2838                   <td>
2839                     <pre class="SCREEN">
2840 +force-text-mode
2841
2842 </pre>
2843                   </td>
2844                 </tr>
2845               </table>
2846             </dd>
2847           </dl>
2848         </div>
2849       </div>
2850
2851       <div class="SECT3">
2852         <h4 class="SECT3"><a name="FORWARD-OVERRIDE" id=
2853         "FORWARD-OVERRIDE">8.5.18. forward-override</a></h4>
2854
2855         <div class="VARIABLELIST">
2856           <dl>
2857             <dt>Typical use:</dt>
2858
2859             <dd>
2860               <p>Change the forwarding settings based on User-Agent or
2861               request origin</p>
2862             </dd>
2863
2864             <dt>Effect:</dt>
2865
2866             <dd>
2867               <p>Overrules the forward directives in the configuration
2868               file.</p>
2869             </dd>
2870
2871             <dt>Type:</dt>
2872
2873             <dd>
2874               <p>Parameterized.</p>
2875             </dd>
2876
2877             <dt>Parameter:</dt>
2878
2879             <dd>
2880               <ul>
2881                 <li>
2882                   <p><span class="QUOTE">"forward ."</span> to use a direct
2883                   connection without any additional proxies.</p>
2884                 </li>
2885
2886                 <li>
2887                   <p><span class="QUOTE">"forward 127.0.0.1:8123"</span> to
2888                   use the HTTP proxy listening at 127.0.0.1 port 8123.</p>
2889                 </li>
2890
2891                 <li>
2892                   <p><span class="QUOTE">"forward-socks4a 127.0.0.1:9050
2893                   ."</span> to use the socks4a proxy listening at 127.0.0.1
2894                   port 9050. Replace <span class=
2895                   "QUOTE">"forward-socks4a"</span> with <span class=
2896                   "QUOTE">"forward-socks4"</span> to use a socks4 connection
2897                   (with local DNS resolution) instead, use <span class=
2898                   "QUOTE">"forward-socks5"</span> for socks5 connections
2899                   (with remote DNS resolution).</p>
2900                 </li>
2901
2902                 <li>
2903                   <p><span class="QUOTE">"forward-socks4a 127.0.0.1:9050
2904                   proxy.example.org:8000"</span> to use the socks4a proxy
2905                   listening at 127.0.0.1 port 9050 to reach the HTTP proxy
2906                   listening at proxy.example.org port 8000. Replace
2907                   <span class="QUOTE">"forward-socks4a"</span> with
2908                   <span class="QUOTE">"forward-socks4"</span> to use a socks4
2909                   connection (with local DNS resolution) instead, use
2910                   <span class="QUOTE">"forward-socks5"</span> for socks5
2911                   connections (with remote DNS resolution).</p>
2912                 </li>
2913
2914                 <li>
2915                   <p><span class="QUOTE">"forward-webserver
2916                   127.0.0.1:80"</span> to use the HTTP server listening at
2917                   127.0.0.1 port 80 without adjusting the request
2918                   headers.</p>
2919
2920                   <p>This makes it more convenient to use Privoxy to make
2921                   existing websites available as onion services as well.</p>
2922
2923                   <p>Many websites serve content with hardcoded URLs and
2924                   can't be easily adjusted to change the domain based on the
2925                   one used by the client.</p>
2926
2927                   <p>Putting Privoxy between Tor and the webserver (or an
2928                   stunnel that forwards to the webserver) allows to rewrite
2929                   headers and content to make client and server happy at the
2930                   same time.</p>
2931
2932                   <p>Using Privoxy for webservers that are only reachable
2933                   through onion addresses and whose location is supposed to
2934                   be secret is not recommended and should not be necessary
2935                   anyway.</p>
2936                 </li>
2937               </ul>
2938             </dd>
2939
2940             <dt>Notes:</dt>
2941
2942             <dd>
2943               <p>This action takes parameters similar to the <a href=
2944               "config.html#FORWARDING">forward</a> directives in the
2945               configuration file, but without the URL pattern. It can be used
2946               as replacement, but normally it's only used in cases where
2947               matching based on the request URL isn't sufficient.</p>
2948
2949               <div class="WARNING">
2950                 <table class="WARNING" border="1" width="90%">
2951                   <tr>
2952                     <td align="center"><b>Warning</b></td>
2953                   </tr>
2954
2955                   <tr>
2956                     <td align="left">
2957                       <p>Please read the description for the <a href=
2958                       "config.html#FORWARDING">forward</a> directives before
2959                       using this action. Forwarding to the wrong people will
2960                       reduce your privacy and increase the chances of
2961                       man-in-the-middle attacks.</p>
2962
2963                       <p>If the ports are missing or invalid, default values
2964                       will be used. This might change in the future and you
2965                       shouldn't rely on it. Otherwise incorrect syntax causes
2966                       Privoxy to exit. Due to design limitations, invalid
2967                       parameter syntax isn't detected until the action is
2968                       used the first time.</p>
2969
2970                       <p>Use the <a href=
2971                       "http://config.privoxy.org/show-url-info" target=
2972                       "_top">show-url-info CGI page</a> to verify that your
2973                       forward settings do what you thought the do.</p>
2974                     </td>
2975                   </tr>
2976                 </table>
2977               </div>
2978             </dd>
2979
2980             <dt>Example usage:</dt>
2981
2982             <dd>
2983               <table border="0" bgcolor="#E0E0E0" width="90%">
2984                 <tr>
2985                   <td>
2986                     <pre class="SCREEN">
2987 # Use an ssh tunnel for requests previously tagged as
2988 # <span class="QUOTE">"User-Agent: fetch libfetch/2.0"</span> and make sure
2989 # resuming downloads continues to work.
2990 #
2991 # This way you can continue to use Tor for your normal browsing,
2992 # without overloading the Tor network with your FreeBSD ports updates
2993 # or downloads of bigger files like ISOs.
2994 #
2995 # Note that HTTP headers are easy to fake and therefore their
2996 # values are as (un)trustworthy as your clients and users.
2997 {+forward-override{forward-socks5 10.0.0.2:2222 .} \
2998  -hide-if-modified-since      \
2999  -overwrite-last-modified     \
3000 }
3001 TAG:^User-Agent: fetch libfetch/2\.0$
3002
3003 </pre>
3004                   </td>
3005                 </tr>
3006               </table>
3007             </dd>
3008           </dl>
3009         </div>
3010       </div>
3011
3012       <div class="SECT3">
3013         <h4 class="SECT3"><a name="HANDLE-AS-EMPTY-DOCUMENT" id=
3014         "HANDLE-AS-EMPTY-DOCUMENT">8.5.19. handle-as-empty-document</a></h4>
3015
3016         <div class="VARIABLELIST">
3017           <dl>
3018             <dt>Typical use:</dt>
3019
3020             <dd>
3021               <p>Mark URLs that should be replaced by empty documents
3022               <span class="emphasis"><i class="EMPHASIS">if they get
3023               blocked</i></span></p>
3024             </dd>
3025
3026             <dt>Effect:</dt>
3027
3028             <dd>
3029               <p>This action alone doesn't do anything noticeable. It just
3030               marks URLs. If the <tt class="LITERAL"><a href=
3031               "actions-file.html#BLOCK">block</a></tt> action <span class=
3032               "emphasis"><i class="EMPHASIS">also applies</i></span>, the
3033               presence or absence of this mark decides whether an HTML
3034               <span class="QUOTE">"BLOCKED"</span> page, or an empty document
3035               will be sent to the client as a substitute for the blocked
3036               content. The <span class="emphasis"><i class=
3037               "EMPHASIS">empty</i></span> document isn't literally empty, but
3038               actually contains a single space.</p>
3039             </dd>
3040
3041             <dt>Type:</dt>
3042
3043             <dd>
3044               <p>Boolean.</p>
3045             </dd>
3046
3047             <dt>Parameter:</dt>
3048
3049             <dd>
3050               <p>N/A</p>
3051             </dd>
3052
3053             <dt>Notes:</dt>