mod_negotiation.html revision c9ba2370d003b2c4d07e295d30b313566386a194
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
This file is generated from xml source: DO NOT EDIT
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
--><title>mod_negotiation - Apache HTTP Server</title><link rel="stylesheet" type="text/css" href="/style/manual.css"/></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">Apache Module mod_negotiation</h1><table bgcolor="#cccccc" cellpadding="0" cellspacing="1"><tr><td><table bgcolor="#ffffff"><tr><td valign="top"><span class="help">Description:</span></td><td>Provides for <a href="/content-negotiation.html">content negotiation</a></td></tr><tr><td><a class="help" href="module-dict.html#Status">Status:</a></td><td>Base</td></tr><tr><td><a class="help" href="module-dict.html#ModuleIdentifier">Module Identifier:</a></td><td>negotiation_module</td></tr></table></td></tr></table><h2>Summary</h2>
<p>Content negotiation, or more accurately content selection, is
the selection of the document that best matches the clients
capabilities, from one of several available documents. There
are two implementations of this.</p>
<ul>
<li>A type map (a file with the handler
<code>type-map</code>) which explicitly lists the files
containing the variants.</li>
<li>A MultiViews search (enabled by the MultiViews <a class="directive" href="core.html#options"><code class="directive">Options</code></a>, where the server does an
implicit filename pattern match, and choose from amongst the
results.</li>
</ul>
<h2>Directives</h2><ul><li><a href="#cachenegotiateddocs">CacheNegotiatedDocs</a></li><li><a href="#forcelangaugepriority">ForceLangaugePriority</a></li><li><a href="#languagepriority">LanguagePriority</a></li></ul><p><strong>See also </strong></p><ul><li><a class="directive" href="mod_mime.html#defaultlangauge"><code class="directive">DefaultLangauge</code></a></li><li><a class="directive" href="mod_mime.html#addencoding"><code class="directive">AddEncoding</code></a></li><li><a class="directive" href="mod_mime.html#addlanguage"><code class="directive">AddLanguage</code></a></li><li><a class="directive" href="mod_mime.html#addtype"><code class="directive">AddType</code></a></li></ul><h2>Type maps</h2>
<p>A type map has the same format as RFC822 mail headers. It
contains document descriptions separated by blank lines, with
lines beginning with a hash character ('#') treated as
comments. A document description consists of several header
records; records may be continued on multiple lines if the
continuation lines start with spaces. The leading space will be
deleted and the lines concatenated. A header record consists of
a keyword name, which always ends in a colon, followed by a
value. Whitespace is allowed between the header name and value,
and between the tokens of value. The headers allowed are: </p>
<dl>
<dt>Content-Encoding:</dt>
<dd>The encoding of the file. Apache only recognizes
encodings that are defined by an <a class="directive" href="mod_mime.html#addencoding"><code class="directive">AddEncoding</code></a> directive.
This normally includes the encodings <code>x-compress</code>
for compress'd files, and <code>x-gzip</code> for gzip'd
files. The <code>x-</code> prefix is ignored for encoding
comparisons.</dd>
<dt>Content-Language:</dt>
<dd>The language of the variant, as an Internet standard
language tag (RFC 1766). An example is <code>en</code>,
meaning English.</dd>
<dt>Content-Length:</dt>
<dd>The length of the file, in bytes. If this header is not
present, then the actual length of the file is used.</dd>
<dt>Content-Type:</dt>
<dd>
The MIME media type of the document, with optional
parameters. Parameters are separated from the media type
and from one another by a semi-colon, with a syntax of
<code>name=value</code>. Common parameters include:
<dl>
<dt>level</dt>
<dd>an integer specifying the version of the media type.
0.</dd>
<dt>qs</dt>
<dd>a floating-point number with a value in the range 0.0
to 1.0, indicating 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 ascii art, then an ascii
file would have a higher source quality than a jpeg file.
All qs values are therefore specific to a given
resource.</dd>
</dl>
Example:
<blockquote>
</blockquote>
</dd>
<dt>URI:</dt>
<dd>The path to the file containing this variant, relative to
the map file.</dd>
</dl>
<h2>MultiViews</h2>
<p>A MultiViews search is enabled by the MultiViews <a class="directive" href="core.html#options"><code class="directive">Options</code></a>. If the server receives a
server reads the directory looking for all files named
<code>foo.*</code>, 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, and returns that document.</p>
<hr/><h2><a name="CacheNegotiatedDocs">CacheNegotiatedDocs</a> <a name="cachenegotiateddocs">Directive</a></h2><table bgcolor="#cccccc" border="0" cellspacing="0" cellpadding="1"><tr><td><table bgcolor="#ffffff"><tr><td><strong>Description: </strong></td><td>Allows content-negotiated documents to be
cached by proxy servers</td></tr><tr><td><a class="help" href="directive-dict.html#Syntax">Syntax:</a></td><td>CacheNegotiatedDocs on|off</td></tr><tr><td><a class="help" href="directive-dict.html#Default">Default:</a></td><td><code>CacheNegotiatedDocs off</code></td></tr><tr><td><a class="help" href="directive-dict.html#Context">Context:</a></td><td>server config</td></tr><tr><td><a class="help" href="directive-dict.html#Status">Status:</a></td><td>Base</td></tr><tr><td><a class="help" href="directive-dict.html#Module">Module:</a></td><td>mod_negotiation</td></tr><tr><td valign="top" align="left"><a class="help" href="directive-dict.html#Compatibility">Compatibility:</a></td><td>The syntax changed in version 2.0.</td></tr></table></td></tr></table>
<p>If set, this directive allows content-negotiated documents
to be cached by proxy servers. This could mean that clients
behind those proxys could retrieve versions of the documents
that are not the best match for their abilities, but it will
make caching more efficient.</p>
<p>This directive only applies to requests which come from
the caching of negotiated documents, and this directive has no
<p>Prior to version 2.0,
<code class="directive">CacheNegotiatedDocs</code> did not take an
argument; it was turned on by the presence of the directive by
itself.</p>
<hr/><h2><a name="ForceLangaugePriority">ForceLangaugePriority</a> <a name="forcelangaugepriority">Directive</a></h2><table bgcolor="#cccccc" border="0" cellspacing="0" cellpadding="1"><tr><td><table bgcolor="#ffffff"><tr><td><strong>Description: </strong></td><td>Action to take if a single acceptable document is not
found</td></tr><tr><td><a class="help" href="directive-dict.html#Syntax">Syntax:</a></td><td>ForceLanguagePriority None|Prefer|Fallback [Prefer|Fallback]</td></tr><tr><td><a class="help" href="directive-dict.html#Default">Default:</a></td><td><code>ForceLangaugePriority None</code></td></tr><tr><td><a class="help" href="directive-dict.html#Context">Context:</a></td><td>server config, virtual host, directory, .htaccess</td></tr><tr><td><a class="help" href="directive-dict.html#Override">Override:</a></td><td>FileInfo</td></tr><tr><td><a class="help" href="directive-dict.html#Status">Status:</a></td><td>Base</td></tr><tr><td><a class="help" href="directive-dict.html#Module">Module:</a></td><td>mod_negotiation</td></tr><tr><td valign="top" align="left"><a class="help" href="directive-dict.html#Compatibility">Compatibility:</a></td><td>Available in version 2.0.30 and later</td></tr></table></td></tr></table>
<p>The <code class="directive">ForceLanguagePriority</code> directive uses
the given <a class="directive" href="#languagepriority"><code class="directive">LanguagePriority</code></a> to satisfy
negotation where the server could otherwise not return a single
matching document.</p>
<p><code>ForceLanguagePriority Prefer</code> uses
<code>LanguagePriority</code> to serve a one valid result, rather
than returning an HTTP result 300 (MULTIPLE CHOICES) when there
are several equally valid choices. If the directives below were
given, and the user's Accept-Language header assigned en and de
each as quality .500 (equally acceptable) then then first matching
variant, en, will be served.</p>
<blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
LanguagePriority en fr de<br/>
ForceLanguagePriority Prefer
</code></td></tr></table></blockquote>
<p><code>ForceLanguagePriority Fallback</code> uses
<code>LanguagePriority</code> to serve a valid result, rather than
returning an HTTP result 406 (NOT ACCEPTABLE). If the directives
below were given, and the user's Accept-Language only permitted an
es langauge response, but such a variant isn't found, then the
first variant from the LanguagePriority list below will be
served.</p>
<blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
LanguagePriority en fr de<br/>
ForceLanguagePriority Fallback
</code></td></tr></table></blockquote>
<p>Both options, Prefer and Fallback, may be specified, so either the
first matching variant from LanguagePriority will be served if more
that one variant is acceptable, or first available document will be
served if none of the variants matched the client's acceptable list of
languages.</p>
<hr/><h2><a name="LanguagePriority">LanguagePriority</a> <a name="languagepriority">Directive</a></h2><table bgcolor="#cccccc" border="0" cellspacing="0" cellpadding="1"><tr><td><table bgcolor="#ffffff"><tr><td><strong>Description: </strong></td><td>The precendence of language variants for cases where
the client does not express a preference</td></tr><tr><td><a class="help" href="directive-dict.html#Syntax">Syntax:</a></td><td>LanguagePriority <em>MIME-lang</em> [<em>MIME-lang</em>] ...</td></tr><tr><td><a class="help" href="directive-dict.html#Context">Context:</a></td><td>server config, virtual host, directory, .htaccess</td></tr><tr><td><a class="help" href="directive-dict.html#Override">Override:</a></td><td>FileInfo</td></tr><tr><td><a class="help" href="directive-dict.html#Status">Status:</a></td><td>Base</td></tr><tr><td><a class="help" href="directive-dict.html#Module">Module:</a></td><td>mod_negotiation</td></tr></table></td></tr></table>
<p>The <code class="directive">LanguagePriority</code> sets the precedence
of language variants for the case where the client does not
express a preference, when handling a MultiViews request. The list
of <em>MIME-lang</em> are in order of decreasing preference.
Example:</p>
<blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>LanguagePriority en fr de</code></td></tr></table></blockquote>
existed, but the browser did not express a language preference,
<p>Note that this directive only has an effect if a 'best'
language cannot be determined by any other means or the <a class="directive" href="#forcelanguagepriority"><code class="directive">ForceLanguagePriority</code></a> directive
will mean this directive has no effect.</p>
