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From sl...@apache.org
Subject cvs commit: httpd-2.0/docs/manual content-negotiation.xml content-negotiation.html.en
Date Fri, 16 Aug 2002 00:22:45 GMT
slive       2002/08/15 17:22:45

  Modified:    docs/manual content-negotiation.html.en
  Added:       docs/manual content-negotiation.xml
  Log:
  New XML.
  
  Revision  Changes    Path
  1.32      +150 -174  httpd-2.0/docs/manual/content-negotiation.html.en
  
  Index: content-negotiation.html.en
  ===================================================================
  RCS file: /home/cvs/httpd-2.0/docs/manual/content-negotiation.html.en,v
  retrieving revision 1.31
  retrieving revision 1.32
  diff -u -d -b -u -r1.31 -r1.32
  --- content-negotiation.html.en	25 Jul 2002 21:46:37 -0000	1.31
  +++ content-negotiation.html.en	16 Aug 2002 00:22:45 -0000	1.32
  @@ -1,19 +1,8 @@
  -<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
  -    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
  -
  -<html xmlns="http://www.w3.org/1999/xhtml">
  -  <head>
  -    <meta name="generator" content="HTML Tidy, see www.w3.org" />
  -
  -    <title>Apache Content Negotiation</title>
  -  </head>
  -  <!-- Background white, links blue (unvisited), navy (visited), red (active) -->
  -
  -  <body bgcolor="#FFFFFF" text="#000000" link="#0000FF"
  -  vlink="#000080" alink="#FF0000">
  -    <!--#include virtual="header.html" -->
  -
  -    <h1 align="center">Content Negotiation</h1>
  +<html><head><META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><!--
  +        XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
  +              This file is generated from xml source: DO NOT EDIT
  +        XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
  +      --><title>Content Negotiation - Apache HTTP Server</title><link href="./style/manual.css" type="text/css" rel="stylesheet"></head><body><blockquote><div align="center"><img src="./images/sub.gif" alt="[APACHE DOCUMENTATION]"><h3>Apache HTTP Server Version 2.0</h3></div><h1 align="center">Content Negotiation</h1>
   
       <p>Apache's supports content negotiation as described in
       the HTTP/1.1 specification. It can choose the best
  @@ -23,12 +12,12 @@
       more intelligent handling of requests from browsers that send
       incomplete negotiation information.</p>
   
  -    <p>Content negotiation is provided by the <a
  -    href="mod/mod_negotiation.html">mod_negotiation</a> module,
  +    <p>Content negotiation is provided by the
  +    <code><a href="./mod/mod_negotiation.html">mod_negotiation</a></code> module.
       which is compiled in by default.</p>
  -    <hr />
  -
  -    <h2>About Content Negotiation</h2>
  +<ul><li><a href="#about">About Content Negotiation</a></li><li><a href="#negotiation">Negotiation in Apache</a><ul><li><a href="#type-map">Using a type-map file</a></li><li><a href="#multiviews">Multiviews</a></li></ul></li><li><a href="#methods">The Negotiation Methods</a><ul><li><a href="#dimensions">Dimensions of Negotiation</a></li><li><a href="#algorithm">Apache Negotiation Algorithm</a></li></ul></li><li><a href="#better">Fiddling with Quality
  +    Values</a><ul><li><a href="#wildcards">Media Types and Wildcards</a></li><li><a href="#exceptions">Language Negotiation Exceptions</a></li></ul></li><li><a href="#extensions">Extensions to Transparent Content
  +Negotiation</a></li><li><a href="#naming">Note on hyperlinks and naming conventions</a></li><li><a href="#caching">Note on Caching</a></li><li><a href="#more">More Information</a></li></ul><hr><h2><a name="about">About Content Negotiation</a></h2>
   
       <p>A resource may be available in several different
       representations. For example, it might be available in
  @@ -42,9 +31,8 @@
       if possible, else English will do. Browsers indicate their
       preferences by headers in the request. To request only French
       representations, the browser would send</p>
  -<pre>
  -  Accept-Language: fr
  -</pre>
  +
  +<blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>Accept-Language: fr</code></td></tr></table></blockquote>
   
       <p>Note that this preference will only be applied when there is
       a choice of representations and they vary by language.</p>
  @@ -55,18 +43,19 @@
       plain text or other text types, and preferring GIF or JPEG over
       other media types, but also allowing any other media type as a
       last resort:</p>
  -<pre>
  -  Accept-Language: fr; q=1.0, en; q=0.5
  -  Accept: text/html; q=1.0, text/*; q=0.8, image/gif; q=0.6,
  -        image/jpeg; q=0.6, image/*; q=0.5, */*; q=0.1
  -</pre>
  -    Apache supports 'server driven' content negotiation, as
  +
  +<blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
  +  Accept-Language: fr; q=1.0, en; q=0.5<br>
  +  Accept: text/html; q=1.0, text/*; q=0.8, image/gif; q=0.6, image/jpeg; q=0.6, image/*; q=0.5, */*; q=0.1
  +</code></td></tr></table></blockquote>
  +
  +    <p>Apache supports 'server driven' content negotiation, as
       defined in the HTTP/1.1 specification. It fully supports the
       Accept, Accept-Language, Accept-Charset and Accept-Encoding
       request headers. Apache also supports 'transparent'
       content negotiation, which is an experimental negotiation
       protocol defined in RFC 2295 and RFC 2296. It does not offer
  -    support for 'feature negotiation' as defined in these RFCs. 
  +    support for 'feature negotiation' as defined in these RFCs. </p>
   
       <p>A <strong>resource</strong> is a conceptual entity
       identified by a URI (RFC 2396). An HTTP server like Apache
  @@ -80,8 +69,7 @@
       representations is termed a <strong>variant</strong>. The ways
       in which the variants for a negotiable resource vary are called
       the <strong>dimensions</strong> of negotiation.</p>
  -
  -    <h2>Negotiation in Apache</h2>
  +<h2><a name="negotiation">Negotiation in Apache</a></h2>
   
       <p>In order to negotiate a resource, the server needs to be
       given information about each of the variants. This is done in
  @@ -97,7 +85,7 @@
         results.</li>
       </ul>
   
  -    <h3>Using a type-map file</h3>
  +   <h3><a name="type-map">Using a type-map file</a></h3>
   
       <p>A type map is a document which is associated with the
       handler named <code>type-map</code> (or, for
  @@ -106,10 +94,8 @@
       use this feature, you must have a handler set in the
       configuration that defines a file suffix as
       <code>type-map</code>; this is best done with a</p>
  -<pre>
  -  AddHandler type-map .var
  -</pre>
  -    in the server configuration file. 
  +<blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>AddHandler type-map .var</code></td></tr></table></blockquote>
  +    <p>in the server configuration file.</p>
   
       <p>Type map files should have the same name as the resource
       which they are describing, and have an entry for each available
  @@ -121,34 +107,36 @@
       present will be ignored). An example map file is shown below.
       This file would be named <code>foo.var</code>, as it describes
       a resource named <code>foo</code>.</p>
  -<pre>
  -  URI: foo
  -
  -  URI: foo.en.html
  -  Content-type: text/html
  -  Content-language: en
   
  -  URI: foo.fr.de.html
  -  Content-type: text/html;charset=iso-8859-2
  -  Content-language: fr, de
  -</pre>
  -    Note also that a typemap file will take precedence over the
  +<blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
  +  URI: foo<br>
  +<br>
  +  URI: foo.en.html<br>
  +  Content-type: text/html<br>
  +  Content-language: en<br>
  +<br>
  +  URI: foo.fr.de.html<br>
  +  Content-type: text/html;charset=iso-8859-2<br>
  +  Content-language: fr, de<br>
  +</code></td></tr></table></blockquote>
  +    <p>Note also that a typemap file will take precedence over the
       filename's extension, even when Multiviews is on. If the
       variants have different source qualities, that may be indicated
       by the "qs" parameter to the media type, as in this picture
  -    (available as jpeg, gif, or ASCII-art): 
  -<pre>
  -  URI: foo
  -
  -  URI: foo.jpeg
  -  Content-type: image/jpeg; qs=0.8
  -
  -  URI: foo.gif
  -  Content-type: image/gif; qs=0.5
  +    (available as jpeg, gif, or ASCII-art): </p>
   
  -  URI: foo.txt
  -  Content-type: text/plain; qs=0.01
  -</pre>
  +<blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
  +  URI: foo<br>
  +<br>
  +  URI: foo.jpeg<br>
  +  Content-type: image/jpeg; qs=0.8<br>
  +<br>
  +  URI: foo.gif<br>
  +  Content-type: image/gif; qs=0.5<br>
  +<br>
  +  URI: foo.txt<br>
  +  Content-type: text/plain; qs=0.01<br>
  +</code></td></tr></table></blockquote>
   
       <p>qs values can vary in the range 0.000 to 1.000. Note that
       any variant with a qs value of 0.000 will never be chosen.
  @@ -164,21 +152,19 @@
       variant depending on the nature of the resource it
       represents.</p>
   
  -    <p>The full list of headers recognized is available in the <a
  -    href="mod/mod_negotiation.html#typemaps">mod_negotation</a>
  -    documentation.</p>
  +    <p>The full list of headers recognized is available in the <a href="mod/mod_negotiation.html#typemaps">mod_negotation
  +    typemap</a> documentation.</p>
   
   
  -    <h3>Multiviews</h3>
  +<h3><a name="multiviews">Multiviews</a></h3>
   
  -    <p><code>MultiViews</code> is a per-directory option, meaning
  -    it can be set with an <code>Options</code> directive within a
  -    <code>&lt;Directory&gt;</code>, <code>&lt;Location&gt;</code>
  -    or <code>&lt;Files&gt;</code> section in
  -    <code>access.conf</code>, or (if <code>AllowOverride</code> is
  -    properly set) in <code>.htaccess</code> files. Note that
  -    <code>Options All</code> does not set <code>MultiViews</code>;
  -    you have to ask for it by name.</p>
  +    <p><code>MultiViews</code> is a per-directory option, meaning it
  +    can be set with an <a href="./mod/core.html#options" class="directive"><code class="directive">Options</code></a>
  +    directive within a <a href="./mod/core.html#directory" class="directive"><code class="directive">&lt;Directory&gt;</code></a>, <a href="./mod/core.html#location" class="directive"><code class="directive">&lt;Location&gt;</code></a> or <a href="./mod/core.html#files" class="directive"><code class="directive">&lt;Files&gt;</code></a> section in
  +    <code>access.conf</code>, or (if <a href="./mod/core.html#allowoverride" class="directive"><code class="directive">AllowOverride</code></a> is properly set) in
  +    <code>.htaccess</code> files. Note that <code>Options All</code>
  +    does not set <code>MultiViews</code>; you have to ask for it by
  +    name.</p>
   
       <p>The effect of <code>MultiViews</code> is as follows: if the
       server receives a request for <code>/some/dir/foo</code>, if
  @@ -190,36 +176,33 @@
       would have if the client had asked for one of them by name. It
       then chooses the best match to the client's requirements.</p>
   
  -    <p><code>MultiViews</code> may also apply to searches for the
  -    file named by the <code>DirectoryIndex</code> directive, if the
  -    server is trying to index a directory. If the configuration
  -    files specify</p>
  -<pre>
  -  DirectoryIndex index
  -</pre>
  -    then the server will arbitrate between <code>index.html</code>
  +    <p><code>MultiViews</code> may also apply to searches for the file
  +    named by the <a href="./mod/mod_dir.html#directoryindex" class="directive"><code class="directive">DirectoryIndex</code></a> directive, if the
  +    server is trying to index a directory. If the configuration files
  +    specify</p>
  +<blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>DirectoryIndex index</code></td></tr></table></blockquote>
  +    <p>then the server will arbitrate between <code>index.html</code>
       and <code>index.html3</code> if both are present. If neither
       are present, and <code>index.cgi</code> is there, the server
  -    will run it. 
  +    will run it.</p>
   
       <p>If one of the files found when reading the directory does not
       have an extension recognized by <code>mod_mime</code> to designate
       its Charset, Content-Type, Language, or Encoding, then the result
  -    depends on the setting of the <a
  -    href="mod/mod_mime.html#multiviewsmatch">MultiViewsMatch</a>
  -    directive.  This directive determines whether handlers, filters,
  -    and other extension types can participate in MultiViews
  -    negotiation.</p>
  +    depends on the setting of the <a href="./mod/mod_mime.html#multiviewsmatch" class="directive"><code class="directive">MultiViewsMatch</code></a> directive.  This
  +    directive determines whether handlers, filters, and other
  +    extension types can participate in MultiViews negotiation.</p>
   
  -    <h2>The Negotiation Methods</h2>
  -    After Apache has obtained a list of the variants for a given
  +<h2><a name="methods">The Negotiation Methods</a></h2>
  +
  +    <p>After Apache has obtained a list of the variants for a given
       resource, either from a type-map file or from the filenames in
       the directory, it invokes one of two methods to decide on the
       'best' variant to return, if any. It is not necessary to know
       any of the details of how negotiation actually takes place in
       order to use Apache's content negotiation features. However the
       rest of this document explains the methods used for those
  -    interested. 
  +    interested. </p>
   
       <p>There are two negotiation methods:</p>
   
  @@ -242,7 +225,7 @@
         variant selection algorithm' defined in RFC 2296.</li>
       </ol>
   
  -    <h3>Dimensions of Negotiation</h3>
  +<h3><a name="dimensions">Dimensions of Negotiation</a></h3>
   
       <table>
         <tr valign="top">
  @@ -286,7 +269,8 @@
         </tr>
       </table>
   
  -    <h3>Apache Negotiation Algorithm</h3>
  +
  +<h3><a name="algorithm">Apache Negotiation Algorithm</a></h3>
   
       <p>Apache can use the following algorithm to select the 'best'
       variant (if any) to return to the browser. This algorithm is
  @@ -371,7 +355,7 @@
         dimensions of variance.</li>
       </ol>
   
  -    <h2><a id="better" name="better">Fiddling with Quality
  +<h2><a name="better">Fiddling with Quality
       Values</a></h2>
   
       <p>Apache sometimes changes the quality values from what would
  @@ -384,36 +368,37 @@
       sends full and correct information these fiddles will not be
       applied.</p>
   
  -    <h3>Media Types and Wildcards</h3>
  +<h3><a name="wildcards">Media Types and Wildcards</a></h3>
   
       <p>The Accept: request header indicates preferences for media
       types. It can also include 'wildcard' media types, such as
       "image/*" or "*/*" where the * matches any string. So a request
       including:</p>
  -<pre>
  -  Accept: image/*, */*
  -</pre>
  -    would indicate that any type starting "image/" is acceptable,
  +
  +<blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>Accept: image/*, */*</code></td></tr></table></blockquote>
  +
  +    <p>would indicate that any type starting "image/" is acceptable,
       as is any other type (so the first "image/*" is redundant).
       Some browsers routinely send wildcards in addition to explicit
  -    types they can handle. For example: 
  -<pre>
  +    types they can handle. For example:</p>
  +
  +<blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
     Accept: text/html, text/plain, image/gif, image/jpeg, */*
  -</pre>
  -    The intention of this is to indicate that the explicitly listed
  +</code></td></tr></table></blockquote>
  +    <p>The intention of this is to indicate that the explicitly listed
       types are preferred, but if a different representation is
       available, that is ok too. However under the basic algorithm,
       as given above, the */* wildcard has exactly equal preference
       to all the other types, so they are not being preferred. The
       browser should really have sent a request with a lower quality
  -    (preference) value for *.*, such as: 
  -<pre>
  +    (preference) value for *.*, such as:</p>
  +<blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
     Accept: text/html, text/plain, image/gif, image/jpeg, */*; q=0.01
  -</pre>
  -    The explicit types have no quality factor, so they default to a
  +</code></td></tr></table></blockquote>
  +    <p>The explicit types have no quality factor, so they default to a
       preference of 1.0 (the highest). The wildcard */* is given a
       low preference of 0.01, so other types will only be returned if
  -    no variant matches an explicitly listed type. 
  +    no variant matches an explicitly listed type.</p>
   
       <p>If the Accept: header contains <em>no</em> q factors at all,
       Apache sets the q value of "*/*", if present, to 0.01 to
  @@ -424,7 +409,8 @@
       <em>not</em> applied, so requests from browsers which send the
       correct information to start with work as expected.</p>
   
  -    <h3>Language Negotiation Exceptions</h3>
  +
  +<h3><a name="exceptions">Language Negotiation Exceptions</a></h3>
   
       <p>New in Apache 2.0, some exceptions have been added to the
       negotiation algorithm to allow graceful fallback when language
  @@ -436,11 +422,10 @@
       Variant" or "Multiple Choices" response to the client.  To avoid
       these error messages, it is possible to configure Apache to ignore
       the Accept-language in these cases and provide a document that
  -    does not explictly match the client's request.  The <a
  -    href="mod/mod_negotiation.html#forcelanguagepriority">ForceLanguagePriority</a>
  +    does not explictly match the client's request.  The <a href="./mod/mod_negotiation.html#forcelanguagepriority" class="directive"><code class="directive">ForceLanguagePriority</code></a>
       directive can be used to override one or both of these error
  -    messages and subsitute the servers judgement in the form of the <a
  -    href="mod/mod_negotiation.html#languagepriority">LanguagePriority</a>
  +    messages and subsitute the servers judgement in the form of the 
  +    <a href="./mod/mod_negotiation.html#languagepriority" class="directive"><code class="directive">LanguagePriority</code></a>
       directive.</p>
   
       <p>The server will also attempt to match language-subsets when no
  @@ -455,43 +440,41 @@
       general.  Unfortunately, many current clients have default
       configurations that resemble this.)  However, if no other language
       match is possible and the server is about to return a "No
  -    Acceptable Variants" error or fallback to the
  -    <code>LanguagePriority</code>, the server will ignore the subset
  -    specification and match <code>en-GB</code> against <code>en</code>
  -    documents.  Implicitly, Apache will add the parent language to
  -    the client's acceptable language list with a very low quality
  -    value.  But note that if the client requests "en-GB; qs=0.9, fr;
  -    qs=0.8", and the server has documents designated "en" and "fr",
  -    then the "fr" document will be returned.  This is necessary to
  -    maintain compliance with the HTTP/1.1 specification and to work
  -    effectively with properly configured clients.</p>
  -
  +    Acceptable Variants" error or fallback to the <a href="./mod/mod_negotiation.html#languagepriority" class="directive"><code class="directive">LanguagePriority</code></a>, the server
  +    will ignore the subset specification and match <code>en-GB</code>
  +    against <code>en</code> documents.  Implicitly, Apache will add
  +    the parent language to the client's acceptable language list with
  +    a very low quality value.  But note that if the client requests
  +    "en-GB; qs=0.9, fr; qs=0.8", and the server has documents
  +    designated "en" and "fr", then the "fr" document will be returned.
  +    This is necessary to maintain compliance with the HTTP/1.1
  +    specification and to work effectively with properly configured
  +    clients.</p>
   
  -    <h2>Extensions to Transparent Content Negotiation</h2>
  -    Apache extends the transparent content negotiation protocol
  -    (RFC 2295) as follows. A new <code>{encoding ..}</code> element
  -    is used in variant lists to label variants which are available
  -    with a specific content-encoding only. The implementation of
  -    the RVSA/1.0 algorithm (RFC 2296) is extended to recognize
  -    encoded variants in the list, and to use them as candidate
  -    variants whenever their encodings are acceptable according to
  -    the Accept-Encoding request header. The RVSA/1.0 implementation
  -    does not round computed quality factors to 5 decimal places
  -    before choosing the best variant. 
  +<h2><a name="extensions">Extensions to Transparent Content
  +Negotiation</a></h2> 
   
  -    <h2>Note on hyperlinks and naming conventions</h2>
  +<p>Apache extends the transparent content negotiation protocol (RFC
  +2295) as follows. A new <code>{encoding ..}</code> element is used in
  +variant lists to label variants which are available with a specific
  +content-encoding only. The implementation of the RVSA/1.0 algorithm
  +(RFC 2296) is extended to recognize encoded variants in the list, and
  +to use them as candidate variants whenever their encodings are
  +acceptable according to the Accept-Encoding request header. The
  +RVSA/1.0 implementation does not round computed quality factors to 5
  +decimal places before choosing the best variant.</p>
  +<h2><a name="naming">Note on hyperlinks and naming conventions</a></h2>
   
       <p>If you are using language negotiation you can choose between
       different naming conventions, because files can have more than
       one extension, and the order of the extensions is normally
  -    irrelevant (see the <a
  -    href="mod/mod_mime.html#multipleext">mod_mime</a> documentation
  +    irrelevant (see the <a href="mod/mod_mime.html#multipleext">mod_mime</a> documentation
       for details).</p>
   
       <p>A typical file has a MIME-type extension (<em>e.g.</em>,
  -    <samp>html</samp>), maybe an encoding extension (<em>e.g.</em>,
  -    <samp>gz</samp>), and of course a language extension
  -    (<em>e.g.</em>, <samp>en</samp>) when we have different
  +    <code>html</code>), maybe an encoding extension (<em>e.g.</em>,
  +    <code>gz</code>), and of course a language extension
  +    (<em>e.g.</em>, <code>en</code>) when we have different
       language variants of this file.</p>
   
       <p>Examples:</p>
  @@ -519,7 +502,7 @@
         <tr>
           <td><em>foo.html.en</em></td>
   
  -        <td>foo<br />
  +        <td>foo<br>
            foo.html</td>
   
           <td>-</td>
  @@ -536,10 +519,10 @@
         <tr>
           <td><em>foo.html.en.gz</em></td>
   
  -        <td>foo<br />
  +        <td>foo<br>
            foo.html</td>
   
  -        <td>foo.gz<br />
  +        <td>foo.gz<br>
            foo.html.gz</td>
         </tr>
   
  @@ -548,16 +531,16 @@
   
           <td>foo</td>
   
  -        <td>foo.html<br />
  -         foo.html.gz<br />
  +        <td>foo.html<br>
  +         foo.html.gz<br>
            foo.gz</td>
         </tr>
   
         <tr>
           <td><em>foo.gz.html.en</em></td>
   
  -        <td>foo<br />
  -         foo.gz<br />
  +        <td>foo<br>
  +         foo.gz<br>
            foo.gz.html</td>
   
           <td>foo.html</td>
  @@ -566,8 +549,8 @@
         <tr>
           <td><em>foo.html.gz.en</em></td>
   
  -        <td>foo<br />
  -         foo.html<br />
  +        <td>foo<br>
  +         foo.html<br>
            foo.html.gz</td>
   
           <td>foo.gz</td>
  @@ -576,19 +559,18 @@
   
       <p>Looking at the table above you will notice that it is always
       possible to use the name without any extensions in an hyperlink
  -    (<em>e.g.</em>, <samp>foo</samp>). The advantage is that you
  +    (<em>e.g.</em>, <code>foo</code>). The advantage is that you
       can hide the actual type of a document rsp. file and can change
  -    it later, <em>e.g.</em>, from <samp>html</samp> to
  -    <samp>shtml</samp> or <samp>cgi</samp> without changing any
  +    it later, <em>e.g.</em>, from <code>html</code> to
  +    <code>shtml</code> or <code>cgi</code> without changing any
       hyperlink references.</p>
   
       <p>If you want to continue to use a MIME-type in your
  -    hyperlinks (<em>e.g.</em> <samp>foo.html</samp>) the language
  +    hyperlinks (<em>e.g.</em> <code>foo.html</code>) the language
       extension (including an encoding extension if there is one)
       must be on the right hand side of the MIME-type extension
  -    (<em>e.g.</em>, <samp>foo.html.en</samp>).</p>
  -
  -    <h2>Note on Caching</h2>
  +    (<em>e.g.</em>, <code>foo.html.en</code>).</p>
  +<h2><a name="caching">Note on Caching</a></h2>
   
       <p>When a cache stores a representation, it associates it with
       the request URL. The next time that URL is requested, the cache
  @@ -602,21 +584,15 @@
       responses.</p>
   
       <p>For requests which come from a HTTP/1.0 compliant client
  -    (either a browser or a cache), the directive
  -    <tt>CacheNegotiatedDocs</tt> can be used to allow caching of
  -    responses which were subject to negotiation. This directive can
  -    be given in the server config or virtual host, and takes no
  -    arguments. It has no effect on requests from HTTP/1.1 clients.</p>
  -
  -    <h2>More Information</h2>
  +    (either a browser or a cache), the directive <a href="./mod/mod_negotiation.html#cachenegotiateddocs" class="directive"><code class="directive">CacheNegotiatedDocs</code></a> can be
  +    used to allow caching of responses which were subject to
  +    negotiation. This directive can be given in the server config or
  +    virtual host, and takes no arguments. It has no effect on requests
  +    from HTTP/1.1 clients.</p>
  +<h2><a name="more">More Information</a></h2>
   
       <p>For more information about content negotiation, see Alan
  -    J. Flavell's <a
  -    href="http://ppewww.ph.gla.ac.uk/~flavell/www/lang-neg.html">Language
  +    J. Flavell's <a href="http://ppewww.ph.gla.ac.uk/~flavell/www/lang-neg.html">Language
       Negotiation Notes</a>.  But note that this document may not be
       updated to include changes in Apache 2.0.</p>
  -
  -    <!--#include virtual="footer.html" -->
  -  </body>
  -</html>
  -
  +<hr></blockquote><h3 align="center">Apache HTTP Server Version 2.0</h3><a href="./"><img src="./images/index.gif" alt="Index"></a><a href="./"><img src="./images/home.gif" alt="Home"></a></body></html>
  \ No newline at end of file
  
  
  
  1.1                  httpd-2.0/docs/manual/content-negotiation.xml
  
  Index: content-negotiation.xml
  ===================================================================
  <?xml version='1.0' encoding='UTF-8' ?>
  <!DOCTYPE manualpage SYSTEM "./style/manualpage.dtd">
  <?xml-stylesheet type="text/xsl" href="./style/manual.en.xsl"?>
  <manualpage>
  <relativepath href="."/>
  
  <title>Content Negotiation</title>
  
  <summary>
  
      <p>Apache's supports content negotiation as described in
      the HTTP/1.1 specification. It can choose the best
      representation of a resource based on the browser-supplied
      preferences for media type, languages, character set and
      encoding. It also implements a couple of features to give
      more intelligent handling of requests from browsers that send
      incomplete negotiation information.</p>
  
      <p>Content negotiation is provided by the
      <module>mod_negotiation</module> module.
      which is compiled in by default.</p>
  </summary>
  
  <section id="about"><title>About Content Negotiation</title>
  
      <p>A resource may be available in several different
      representations. For example, it might be available in
      different languages or different media types, or a combination.
      One way of selecting the most appropriate choice is to give the
      user an index page, and let them select. However it is often
      possible for the server to choose automatically. This works
      because browsers can send as part of each request information
      about what representations they prefer. For example, a browser
      could indicate that it would like to see information in French,
      if possible, else English will do. Browsers indicate their
      preferences by headers in the request. To request only French
      representations, the browser would send</p>
  
  <example>Accept-Language: fr</example>
  
      <p>Note that this preference will only be applied when there is
      a choice of representations and they vary by language.</p>
  
      <p>As an example of a more complex request, this browser has
      been configured to accept French and English, but prefer
      French, and to accept various media types, preferring HTML over
      plain text or other text types, and preferring GIF or JPEG over
      other media types, but also allowing any other media type as a
      last resort:</p>
  
  <example>
    Accept-Language: fr; q=1.0, en; q=0.5<br />
    Accept: text/html; q=1.0, text/*; q=0.8, image/gif; q=0.6, image/jpeg; q=0.6, image/*; q=0.5, */*; q=0.1
  </example>
  
      <p>Apache supports 'server driven' content negotiation, as
      defined in the HTTP/1.1 specification. It fully supports the
      Accept, Accept-Language, Accept-Charset and Accept-Encoding
      request headers. Apache also supports 'transparent'
      content negotiation, which is an experimental negotiation
      protocol defined in RFC 2295 and RFC 2296. It does not offer
      support for 'feature negotiation' as defined in these RFCs. </p>
  
      <p>A <strong>resource</strong> is a conceptual entity
      identified by a URI (RFC 2396). An HTTP server like Apache
      provides access to <strong>representations</strong> of the
      resource(s) within its namespace, with each representation in
      the form of a sequence of bytes with a defined media type,
      character set, encoding, etc. Each resource may be associated
      with zero, one, or more than one representation at any given
      time. If multiple representations are available, the resource
      is referred to as <strong>negotiable</strong> and each of its
      representations is termed a <strong>variant</strong>. The ways
      in which the variants for a negotiable resource vary are called
      the <strong>dimensions</strong> of negotiation.</p>
  </section>
  
  <section id="negotiation"><title>Negotiation in Apache</title>
  
      <p>In order to negotiate a resource, the server needs to be
      given information about each of the variants. This is done in
      one of two ways:</p>
  
      <ul>
        <li>Using a type map (<em>i.e.</em>, a <code>*.var</code>
        file) which names the files containing the variants
        explicitly, or</li>
  
        <li>Using a 'MultiViews' search, where the server does an
        implicit filename pattern match and chooses from among the
        results.</li>
      </ul>
  
     <section id="type-map"><title>Using a type-map file</title>
  
      <p>A type map is a document which is associated with the
      handler named <code>type-map</code> (or, for
      backwards-compatibility with older Apache configurations, the
      mime type <code>application/x-type-map</code>). Note that to
      use this feature, you must have a handler set in the
      configuration that defines a file suffix as
      <code>type-map</code>; this is best done with a</p>
  <example>AddHandler type-map .var</example>
      <p>in the server configuration file.</p>
  
      <p>Type map files should have the same name as the resource
      which they are describing, and have an entry for each available
      variant; these entries consist of contiguous HTTP-format header
      lines. Entries for different variants are separated by blank
      lines. Blank lines are illegal within an entry. It is
      conventional to begin a map file with an entry for the combined
      entity as a whole (although this is not required, and if
      present will be ignored). An example map file is shown below.
      This file would be named <code>foo.var</code>, as it describes
      a resource named <code>foo</code>.</p>
  
  <example>
    URI: foo<br />
  <br />
    URI: foo.en.html<br />
    Content-type: text/html<br />
    Content-language: en<br />
  <br />
    URI: foo.fr.de.html<br />
    Content-type: text/html;charset=iso-8859-2<br />
    Content-language: fr, de<br />
  </example>
      <p>Note also that a typemap file will take precedence over the
      filename's extension, even when Multiviews is on. If the
      variants have different source qualities, that may be indicated
      by the "qs" parameter to the media type, as in this picture
      (available as jpeg, gif, or ASCII-art): </p>
  
  <example>
    URI: foo<br />
  <br />
    URI: foo.jpeg<br />
    Content-type: image/jpeg; qs=0.8<br />
  <br />
    URI: foo.gif<br />
    Content-type: image/gif; qs=0.5<br />
  <br />
    URI: foo.txt<br />
    Content-type: text/plain; qs=0.01<br />
  </example>
  
      <p>qs values can vary in the range 0.000 to 1.000. Note that
      any variant with a qs value of 0.000 will never be chosen.
      Variants with no 'qs' parameter value are given a qs factor of
      1.0. The qs parameter indicates the relative 'quality' of this
      variant compared to the other available variants, independent
      of the client's capabilities. For example, a jpeg file is
      usually of higher source quality than an ascii file if it is
      attempting to represent a photograph. However, if the resource
      being represented is an original ascii art, then an ascii
      representation would have a higher source quality than a jpeg
      representation. A qs value is therefore specific to a given
      variant depending on the nature of the resource it
      represents.</p>
  
      <p>The full list of headers recognized is available in the <a
      href="mod/mod_negotiation.html#typemaps">mod_negotation
      typemap</a> documentation.</p>
  </section>
  
  <section id="multiviews"><title>Multiviews</title>
  
      <p><code>MultiViews</code> is a per-directory option, meaning it
      can be set with an <directive module="core">Options</directive>
      directive within a <directive module="core"
      type="section">Directory</directive>, <directive module="core"
      type="section">Location</directive> or <directive module="core"
      type="section">Files</directive> section in
      <code>access.conf</code>, or (if <directive
      module="core">AllowOverride</directive> is properly set) in
      <code>.htaccess</code> files. Note that <code>Options All</code>
      does not set <code>MultiViews</code>; you have to ask for it by
      name.</p>
  
      <p>The effect of <code>MultiViews</code> is as follows: if the
      server receives a request for <code>/some/dir/foo</code>, if
      <code>/some/dir</code> has <code>MultiViews</code> enabled, and
      <code>/some/dir/foo</code> does <em>not</em> exist, then the
      server reads the directory looking for files named foo.*, and
      effectively fakes up a type map which names all those files,
      assigning them the same media types and content-encodings it
      would have if the client had asked for one of them by name. It
      then chooses the best match to the client's requirements.</p>
  
      <p><code>MultiViews</code> may also apply to searches for the file
      named by the <directive
      module="mod_dir">DirectoryIndex</directive> directive, if the
      server is trying to index a directory. If the configuration files
      specify</p>
  <example>DirectoryIndex index</example>
      <p>then the server will arbitrate between <code>index.html</code>
      and <code>index.html3</code> if both are present. If neither
      are present, and <code>index.cgi</code> is there, the server
      will run it.</p>
  
      <p>If one of the files found when reading the directory does not
      have an extension recognized by <code>mod_mime</code> to designate
      its Charset, Content-Type, Language, or Encoding, then the result
      depends on the setting of the <directive
      module="mod_mime">MultiViewsMatch</directive> directive.  This
      directive determines whether handlers, filters, and other
      extension types can participate in MultiViews negotiation.</p>
  </section>
  </section>
  
  <section id="methods"><title>The Negotiation Methods</title>
  
      <p>After Apache has obtained a list of the variants for a given
      resource, either from a type-map file or from the filenames in
      the directory, it invokes one of two methods to decide on the
      'best' variant to return, if any. It is not necessary to know
      any of the details of how negotiation actually takes place in
      order to use Apache's content negotiation features. However the
      rest of this document explains the methods used for those
      interested. </p>
  
      <p>There are two negotiation methods:</p>
  
      <ol>
        <li><strong>Server driven negotiation with the Apache
        algorithm</strong> is used in the normal case. The Apache
        algorithm is explained in more detail below. When this
        algorithm is used, Apache can sometimes 'fiddle' the quality
        factor of a particular dimension to achieve a better result.
        The ways Apache can fiddle quality factors is explained in
        more detail below.</li>
  
        <li><strong>Transparent content negotiation</strong> is used
        when the browser specifically requests this through the
        mechanism defined in RFC 2295. This negotiation method gives
        the browser full control over deciding on the 'best' variant,
        the result is therefore dependent on the specific algorithms
        used by the browser. As part of the transparent negotiation
        process, the browser can ask Apache to run the 'remote
        variant selection algorithm' defined in RFC 2296.</li>
      </ol>
  
  <section id="dimensions"><title>Dimensions of Negotiation</title>
  
      <table>
        <tr valign="top">
          <th>Dimension</th>
  
          <th>Notes</th>
        </tr>
  
        <tr valign="top">
          <td>Media Type</td>
  
          <td>Browser indicates preferences with the Accept header
          field. Each item can have an associated quality factor.
          Variant description can also have a quality factor (the
          "qs" parameter).</td>
        </tr>
  
        <tr valign="top">
          <td>Language</td>
  
          <td>Browser indicates preferences with the Accept-Language
          header field. Each item can have a quality factor. Variants
          can be associated with none, one or more than one
          language.</td>
        </tr>
  
        <tr valign="top">
          <td>Encoding</td>
  
          <td>Browser indicates preference with the Accept-Encoding
          header field. Each item can have a quality factor.</td>
        </tr>
  
        <tr valign="top">
          <td>Charset</td>
  
          <td>Browser indicates preference with the Accept-Charset
          header field. Each item can have a quality factor. Variants
          can indicate a charset as a parameter of the media
          type.</td>
        </tr>
      </table>
  </section>
  
  <section id="algorithm"><title>Apache Negotiation Algorithm</title>
  
      <p>Apache can use the following algorithm to select the 'best'
      variant (if any) to return to the browser. This algorithm is
      not further configurable. It operates as follows:</p>
  
      <ol>
        <li>First, for each dimension of the negotiation, check the
        appropriate <em>Accept*</em> header field and assign a
        quality to each variant. If the <em>Accept*</em> header for
        any dimension implies that this variant is not acceptable,
        eliminate it. If no variants remain, go to step 4.</li>
  
        <li>
          Select the 'best' variant by a process of elimination. Each
          of the following tests is applied in order. Any variants
          not selected at each test are eliminated. After each test,
          if only one variant remains, select it as the best match
          and proceed to step 3. If more than one variant remains,
          move on to the next test. 
  
          <ol>
            <li>Multiply the quality factor from the Accept header
            with the quality-of-source factor for this variant's
            media type, and select the variants with the highest
            value.</li>
  
            <li>Select the variants with the highest language quality
            factor.</li>
  
            <li>Select the variants with the best language match,
            using either the order of languages in the
            Accept-Language header (if present), or else the order of
            languages in the <code>LanguagePriority</code> directive
            (if present).</li>
  
            <li>Select the variants with the highest 'level' media
            parameter (used to give the version of text/html media
            types).</li>
  
            <li>Select variants with the best charset media
            parameters, as given on the Accept-Charset header line.
            Charset ISO-8859-1 is acceptable unless explicitly
            excluded. Variants with a <code>text/*</code> media type
            but not explicitly associated with a particular charset
            are assumed to be in ISO-8859-1.</li>
  
            <li>Select those variants which have associated charset
            media parameters that are <em>not</em> ISO-8859-1. If
            there are no such variants, select all variants
            instead.</li>
  
            <li>Select the variants with the best encoding. If there
            are variants with an encoding that is acceptable to the
            user-agent, select only these variants. Otherwise if
            there is a mix of encoded and non-encoded variants,
            select only the unencoded variants. If either all
            variants are encoded or all variants are not encoded,
            select all variants.</li>
  
            <li>Select the variants with the smallest content
            length.</li>
  
            <li>Select the first variant of those remaining. This
            will be either the first listed in the type-map file, or
            when variants are read from the directory, the one whose
            file name comes first when sorted using ASCII code
            order.</li>
          </ol>
        </li>
  
        <li>The algorithm has now selected one 'best' variant, so
        return it as the response. The HTTP response header Vary is
        set to indicate the dimensions of negotiation (browsers and
        caches can use this information when caching the resource).
        End.</li>
  
        <li>To get here means no variant was selected (because none
        are acceptable to the browser). Return a 406 status (meaning
        "No acceptable representation") with a response body
        consisting of an HTML document listing the available
        variants. Also set the HTTP Vary header to indicate the
        dimensions of variance.</li>
      </ol>
  </section>
  </section>
  
  <section id="better"><title>Fiddling with Quality
      Values</title>
  
      <p>Apache sometimes changes the quality values from what would
      be expected by a strict interpretation of the Apache
      negotiation algorithm above. This is to get a better result
      from the algorithm for browsers which do not send full or
      accurate information. Some of the most popular browsers send
      Accept header information which would otherwise result in the
      selection of the wrong variant in many cases. If a browser
      sends full and correct information these fiddles will not be
      applied.</p>
  
  <section id="wildcards"><title>Media Types and Wildcards</title>
  
      <p>The Accept: request header indicates preferences for media
      types. It can also include 'wildcard' media types, such as
      "image/*" or "*/*" where the * matches any string. So a request
      including:</p>
  
  <example>Accept: image/*, */*</example>
  
      <p>would indicate that any type starting "image/" is acceptable,
      as is any other type (so the first "image/*" is redundant).
      Some browsers routinely send wildcards in addition to explicit
      types they can handle. For example:</p>
  
  <example>
    Accept: text/html, text/plain, image/gif, image/jpeg, */*
  </example>
      <p>The intention of this is to indicate that the explicitly listed
      types are preferred, but if a different representation is
      available, that is ok too. However under the basic algorithm,
      as given above, the */* wildcard has exactly equal preference
      to all the other types, so they are not being preferred. The
      browser should really have sent a request with a lower quality
      (preference) value for *.*, such as:</p>
  <example>
    Accept: text/html, text/plain, image/gif, image/jpeg, */*; q=0.01
  </example>
      <p>The explicit types have no quality factor, so they default to a
      preference of 1.0 (the highest). The wildcard */* is given a
      low preference of 0.01, so other types will only be returned if
      no variant matches an explicitly listed type.</p>
  
      <p>If the Accept: header contains <em>no</em> q factors at all,
      Apache sets the q value of "*/*", if present, to 0.01 to
      emulate the desired behavior. It also sets the q value of
      wildcards of the format "type/*" to 0.02 (so these are
      preferred over matches against "*/*". If any media type on the
      Accept: header contains a q factor, these special values are
      <em>not</em> applied, so requests from browsers which send the
      correct information to start with work as expected.</p>
  </section>
  
  <section id="exceptions"><title>Language Negotiation Exceptions</title>
  
      <p>New in Apache 2.0, some exceptions have been added to the
      negotiation algorithm to allow graceful fallback when language
      negotiation fails to find a match.</p>
  
      <p>When a client requests a page on your server, but the server
      cannot find a single page that matches the Accept-language sent by
      the browser, the server will return either a "No Acceptable
      Variant" or "Multiple Choices" response to the client.  To avoid
      these error messages, it is possible to configure Apache to ignore
      the Accept-language in these cases and provide a document that
      does not explictly match the client's request.  The <directive
      module="mod_negotiation">ForceLanguagePriority</directive>
      directive can be used to override one or both of these error
      messages and subsitute the servers judgement in the form of the 
      <directive module="mod_negotiation">LanguagePriority</directive>
      directive.</p>
  
      <p>The server will also attempt to match language-subsets when no
      other match can be found.  For example, if a client requests
      documents with the language <code>en-GB</code> for British
      English, the server is not normally allowed by the HTTP/1.1
      standard to match that against a document that is marked as simply
      <code>en</code>.  (Note that it is almost surely a configuration
      error to include <code>en-GB</code> and not <code>en</code> in the
      Accept-Language header, since it is very unlikely that a reader
      understands British English, but doesn't understand English in
      general.  Unfortunately, many current clients have default
      configurations that resemble this.)  However, if no other language
      match is possible and the server is about to return a "No
      Acceptable Variants" error or fallback to the <directive
      module="mod_negotiation">LanguagePriority</directive>, the server
      will ignore the subset specification and match <code>en-GB</code>
      against <code>en</code> documents.  Implicitly, Apache will add
      the parent language to the client's acceptable language list with
      a very low quality value.  But note that if the client requests
      "en-GB; qs=0.9, fr; qs=0.8", and the server has documents
      designated "en" and "fr", then the "fr" document will be returned.
      This is necessary to maintain compliance with the HTTP/1.1
      specification and to work effectively with properly configured
      clients.</p>
  </section>
  </section>
  
  <section id="extensions"><title>Extensions to Transparent Content
  Negotiation</title> 
  
  <p>Apache extends the transparent content negotiation protocol (RFC
  2295) as follows. A new <code>{encoding ..}</code> element is used in
  variant lists to label variants which are available with a specific
  content-encoding only. The implementation of the RVSA/1.0 algorithm
  (RFC 2296) is extended to recognize encoded variants in the list, and
  to use them as candidate variants whenever their encodings are
  acceptable according to the Accept-Encoding request header. The
  RVSA/1.0 implementation does not round computed quality factors to 5
  decimal places before choosing the best variant.</p>
  </section>
  
  <section id="naming"><title>Note on hyperlinks and naming conventions</title>
  
      <p>If you are using language negotiation you can choose between
      different naming conventions, because files can have more than
      one extension, and the order of the extensions is normally
      irrelevant (see the <a
      href="mod/mod_mime.html#multipleext">mod_mime</a> documentation
      for details).</p>
  
      <p>A typical file has a MIME-type extension (<em>e.g.</em>,
      <code>html</code>), maybe an encoding extension (<em>e.g.</em>,
      <code>gz</code>), and of course a language extension
      (<em>e.g.</em>, <code>en</code>) when we have different
      language variants of this file.</p>
  
      <p>Examples:</p>
  
      <ul>
        <li>foo.en.html</li>
  
        <li>foo.html.en</li>
  
        <li>foo.en.html.gz</li>
      </ul>
  
      <p>Here some more examples of filenames together with valid and
      invalid hyperlinks:</p>
  
      <table border="1" cellpadding="8" cellspacing="0">
        <tr>
          <th>Filename</th>
  
          <th>Valid hyperlink</th>
  
          <th>Invalid hyperlink</th>
        </tr>
  
        <tr>
          <td><em>foo.html.en</em></td>
  
          <td>foo<br />
           foo.html</td>
  
          <td>-</td>
        </tr>
  
        <tr>
          <td><em>foo.en.html</em></td>
  
          <td>foo</td>
  
          <td>foo.html</td>
        </tr>
  
        <tr>
          <td><em>foo.html.en.gz</em></td>
  
          <td>foo<br />
           foo.html</td>
  
          <td>foo.gz<br />
           foo.html.gz</td>
        </tr>
  
        <tr>
          <td><em>foo.en.html.gz</em></td>
  
          <td>foo</td>
  
          <td>foo.html<br />
           foo.html.gz<br />
           foo.gz</td>
        </tr>
  
        <tr>
          <td><em>foo.gz.html.en</em></td>
  
          <td>foo<br />
           foo.gz<br />
           foo.gz.html</td>
  
          <td>foo.html</td>
        </tr>
  
        <tr>
          <td><em>foo.html.gz.en</em></td>
  
          <td>foo<br />
           foo.html<br />
           foo.html.gz</td>
  
          <td>foo.gz</td>
        </tr>
      </table>
  
      <p>Looking at the table above you will notice that it is always
      possible to use the name without any extensions in an hyperlink
      (<em>e.g.</em>, <code>foo</code>). The advantage is that you
      can hide the actual type of a document rsp. file and can change
      it later, <em>e.g.</em>, from <code>html</code> to
      <code>shtml</code> or <code>cgi</code> without changing any
      hyperlink references.</p>
  
      <p>If you want to continue to use a MIME-type in your
      hyperlinks (<em>e.g.</em> <code>foo.html</code>) the language
      extension (including an encoding extension if there is one)
      must be on the right hand side of the MIME-type extension
      (<em>e.g.</em>, <code>foo.html.en</code>).</p>
  </section>
  
  <section id="caching"><title>Note on Caching</title>
  
      <p>When a cache stores a representation, it associates it with
      the request URL. The next time that URL is requested, the cache
      can use the stored representation. But, if the resource is
      negotiable at the server, this might result in only the first
      requested variant being cached and subsequent cache hits might
      return the wrong response. To prevent this, Apache normally
      marks all responses that are returned after content negotiation
      as non-cacheable by HTTP/1.0 clients. Apache also supports the
      HTTP/1.1 protocol features to allow caching of negotiated
      responses.</p>
  
      <p>For requests which come from a HTTP/1.0 compliant client
      (either a browser or a cache), the directive <directive
      module="mod_negotiation">CacheNegotiatedDocs</directive> can be
      used to allow caching of responses which were subject to
      negotiation. This directive can be given in the server config or
      virtual host, and takes no arguments. It has no effect on requests
      from HTTP/1.1 clients.</p>
  </section>
  
  <section id="more"><title>More Information</title>
  
      <p>For more information about content negotiation, see Alan
      J. Flavell's <a
      href="http://ppewww.ph.gla.ac.uk/~flavell/www/lang-neg.html">Language
      Negotiation Notes</a>.  But note that this document may not be
      updated to include changes in Apache 2.0.</p>
  </section>
  
  </manualpage>
  
  

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