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<title>mod_negotiation - Apache HTTP Server</title>
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<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p>
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<p class="apache">Apache HTTP Server Version 2.2</p>
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<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.2</a> > <a href="./">Modules</a></div>
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<div id="page-content">
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<div id="preamble"><h1>Apache Module mod_negotiation</h1>
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<p><span>Available Languages: </span><a href="../en/mod/mod_negotiation.html" title="English"> en </a> |
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<a href="../ja/mod/mod_negotiation.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a></p>
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<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Provides for <a href="../content-negotiation.html">content negotiation</a></td></tr>
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<tr><th><a href="module-dict.html#Status">Status:</a></th><td>Base</td></tr>
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<tr><th><a href="module-dict.html#ModuleIdentifier">Module�Identifier:</a></th><td>negotiation_module</td></tr>
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<tr><th><a href="module-dict.html#SourceFile">Source�File:</a></th><td>mod_negotiation.c</td></tr></table>
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<p>Content negotiation, or more accurately content selection, is
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the selection of the document that best matches the clients
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capabilities, from one of several available documents. There
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are two implementations of this.</p>
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<li>A type map (a file with the handler
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<code>type-map</code>) which explicitly lists the files
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containing the variants.</li>
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<li>A MultiViews search (enabled by the <code>MultiViews</code>
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<code class="directive"><a href="../mod/core.html#options">Options</a></code>), where the server does
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an implicit filename pattern match, and choose from amongst the
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<div id="quickview"><h3 class="directives">Directives</h3>
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<li><img alt="" src="../images/down.gif" /> <a href="#cachenegotiateddocs">CacheNegotiatedDocs</a></li>
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<li><img alt="" src="../images/down.gif" /> <a href="#forcelanguagepriority">ForceLanguagePriority</a></li>
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<li><img alt="" src="../images/down.gif" /> <a href="#languagepriority">LanguagePriority</a></li>
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<li><img alt="" src="../images/down.gif" /> <a href="#typemaps">Type maps</a></li>
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<li><img alt="" src="../images/down.gif" /> <a href="#multiviews">MultiViews</a></li>
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</ul><h3>See also</h3>
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<li><code class="directive"><a href="../mod/core.html#options">Options</a></code></li>
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<li><code class="module"><a href="../mod/mod_mime.html">mod_mime</a></code></li>
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<li><a href="../content-negotiation.html">Content
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<li><a href="../env.html">Environment Variables</a></li>
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<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<h2><a name="typemaps" id="typemaps">Type maps</a></h2>
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<p>A type map has a format similar to RFC822 mail headers. It
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contains document descriptions separated by blank lines, with
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lines beginning with a hash character ('#') treated as
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comments. A document description consists of several header
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records; records may be continued on multiple lines if the
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continuation lines start with spaces. The leading space will be
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deleted and the lines concatenated. A header record consists of
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a keyword name, which always ends in a colon, followed by a
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value. Whitespace is allowed between the header name and value,
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and between the tokens of value. The headers allowed are: </p>
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<dt><code>Content-Encoding:</code></dt>
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<dd>The encoding of the file. Apache only recognizes
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encodings that are defined by an <code class="directive"><a href="../mod/mod_mime.html#addencoding">AddEncoding</a></code> directive.
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This normally includes the encodings <code>x-compress</code>
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for compress'd files, and <code>x-gzip</code> for gzip'd
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files. The <code>x-</code> prefix is ignored for encoding
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<dt><code>Content-Language:</code></dt>
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<dd>The language(s) of the variant, as an Internet standard
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language tag (<a href="http://www.ietf.org/rfc/rfc1766.txt">RFC 1766</a>). An example is <code>en</code>,
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meaning English. If the variant contains more than one
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language, they are separated by a comma.</dd>
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<dt><code>Content-Length:</code></dt>
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<dd>The length of the file, in bytes. If this header is not
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present, then the actual length of the file is used.</dd>
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<dt><code>Content-Type:</code></dt>
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The <a class="glossarylink" href="../glossary.html#mime-type" title="see glossary">MIME media type</a> of
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the document, with optional parameters. Parameters are
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separated from the media type and from one another by a
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semi-colon, with a syntax of <code>name=value</code>. Common
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<dt><code>level</code></dt>
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<dd>an integer specifying the version of the media type.
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For <code>text/html</code> this defaults to 2, otherwise
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<dt><code>qs</code></dt>
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<dd>a floating-point number with a value in the range 0.0
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to 1.0, indicating the relative 'quality' of this variant
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compared to the other available variants, independent of
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the client's capabilities. For example, a jpeg file is
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usually of higher source quality than an ascii file if it
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is attempting to represent a photograph. However, if the
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resource being represented is ascii art, then an ascii
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file would have a higher source quality than a jpeg file.
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All <code>qs</code> values are therefore specific to a given
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<div class="example"><h3>Example</h3><p><code>
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Content-Type: image/jpeg; qs=0.8
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<dt><code>URI:</code></dt>
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<dd>uri of the file containing the variant (of the given
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media type, encoded with the given content encoding). These
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are interpreted as URLs relative to the map file; they must
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be on the same server (!), and they must refer to files to
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which the client would be granted access if they were to be
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requested directly.</dd>
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<dt><code>Body:</code></dt>
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<dd>New in Apache 2.0, the actual content of the resource may
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be included in the type-map file using the Body header. This
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header must contain a string that designates a delimiter for
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the body content. Then all following lines in the type map
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file will be considered part of the resource body until the
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delimiter string is found.
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<div class="example"><h3>Example:</h3><p><code>
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Body:----xyz----<br />
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<p>Content of the page.</p><br />
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</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<div class="section">
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<h2><a name="multiviews" id="multiviews">MultiViews</a></h2>
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<p>A MultiViews search is enabled by the <code>MultiViews</code>
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<code class="directive"><a href="../mod/core.html#options">Options</a></code>. If the server receives a
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request for <code>/some/dir/foo</code> and
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<code>/some/dir/foo</code> does <em>not</em> exist, then the
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server reads the directory looking for all files named
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<code>foo.*</code>, and effectively fakes up a type map which
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names all those files, assigning them the same media types and
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content-encodings it would have if the client had asked for one
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of them by name. It then chooses the best match to the client's
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requirements, and returns that document.</p>
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<p>The <code class="directive"><a href="../mod/mod_mime.html#multiviewsmatch">MultiViewsMatch</a></code>
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directive configures whether Apache will consider files
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that do not have content negotiation meta-information assigned
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to them when choosing files.</p>
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<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<div class="directive-section"><h2><a name="CacheNegotiatedDocs" id="CacheNegotiatedDocs">CacheNegotiatedDocs</a> <a name="cachenegotiateddocs" id="cachenegotiateddocs">Directive</a></h2>
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<table class="directive">
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<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Allows content-negotiated documents to be
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cached by proxy servers</td></tr>
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<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheNegotiatedDocs On|Off</code></td></tr>
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<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheNegotiatedDocs Off</code></td></tr>
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<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
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<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Base</td></tr>
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<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_negotiation</td></tr>
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<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>The syntax changed in version 2.0.</td></tr>
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<p>If set, this directive allows content-negotiated documents
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to be cached by proxy servers. This could mean that clients
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behind those proxys could retrieve versions of the documents
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that are not the best match for their abilities, but it will
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make caching more efficient.</p>
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<p>This directive only applies to requests which come from
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HTTP/1.0 browsers. HTTP/1.1 provides much better control over
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the caching of negotiated documents, and this directive has no
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effect in responses to HTTP/1.1 requests.</p>
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<p>Prior to version 2.0,
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<code class="directive">CacheNegotiatedDocs</code> did not take an
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argument; it was turned on by the presence of the directive by
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<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<div class="directive-section"><h2><a name="ForceLanguagePriority" id="ForceLanguagePriority">ForceLanguagePriority</a> <a name="forcelanguagepriority" id="forcelanguagepriority">Directive</a></h2>
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<table class="directive">
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<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Action to take if a single acceptable document is not
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<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ForceLanguagePriority None|Prefer|Fallback [Prefer|Fallback]</code></td></tr>
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<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>ForceLanguagePriority Prefer</code></td></tr>
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<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
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<tr><th><a href="directive-dict.html#Override">Override:</a></th><td>FileInfo</td></tr>
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<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Base</td></tr>
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<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_negotiation</td></tr>
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<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.0.30 and later</td></tr>
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<p>The <code class="directive">ForceLanguagePriority</code> directive uses
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the given <code class="directive"><a href="#languagepriority">LanguagePriority</a></code> to satisfy
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negotation where the server could otherwise not return a single
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matching document.</p>
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<p><code>ForceLanguagePriority Prefer</code> uses
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<code>LanguagePriority</code> to serve a one valid result, rather
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than returning an HTTP result 300 (MULTIPLE CHOICES) when there
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are several equally valid choices. If the directives below were
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given, and the user's <code>Accept-Language</code> header assigned
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<code>en</code> and <code>de</code> each as quality <code>.500</code>
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(equally acceptable) then the first matching variant, <code>en</code>,
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<div class="example"><p><code>
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LanguagePriority en fr de<br />
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ForceLanguagePriority Prefer
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<p><code>ForceLanguagePriority Fallback</code> uses
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<code class="directive"><a href="#languagepriority">LanguagePriority</a></code> to
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serve a valid result, rather than returning an HTTP result 406
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(NOT ACCEPTABLE). If the directives below were given, and the user's
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<code>Accept-Language</code> only permitted an <code>es</code>
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language response, but such a variant isn't found, then the first
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variant from the <code class="directive"><a href="#languagepriority">LanguagePriority</a></code> list below will be served.</p>
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<div class="example"><p><code>
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LanguagePriority en fr de<br />
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ForceLanguagePriority Fallback
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<p>Both options, <code>Prefer</code> and <code>Fallback</code>, may be
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specified, so either the first matching variant from <code class="directive"><a href="#languagepriority">LanguagePriority</a></code> will be served if
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more than one variant is acceptable, or first available document will
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be served if none of the variants matched the client's acceptable list
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<li><code class="directive"><a href="../mod/mod_mime.html#addlanguage">AddLanguage</a></code></li>
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<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<div class="directive-section"><h2><a name="LanguagePriority" id="LanguagePriority">LanguagePriority</a> <a name="languagepriority" id="languagepriority">Directive</a></h2>
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<table class="directive">
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<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The precendence of language variants for cases where
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the client does not express a preference</td></tr>
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<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>LanguagePriority <var>MIME-lang</var> [<var>MIME-lang</var>]
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<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
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<tr><th><a href="directive-dict.html#Override">Override:</a></th><td>FileInfo</td></tr>
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<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Base</td></tr>
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<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_negotiation</td></tr>
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<p>The <code class="directive">LanguagePriority</code> sets the precedence
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of language variants for the case where the client does not
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express a preference, when handling a MultiViews request. The list
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of <var>MIME-lang</var> are in order of decreasing preference.</p>
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<div class="example"><h3>Example:</h3><p><code>
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LanguagePriority en fr de
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<p>For a request for <code>foo.html</code>, where
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<code>foo.html.fr</code> and <code>foo.html.de</code> both
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existed, but the browser did not express a language preference,
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then <code>foo.html.fr</code> would be returned.</p>
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<p>Note that this directive only has an effect if a 'best'
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language cannot be determined by any other means or the <code class="directive"><a href="#forcelanguagepriority">ForceLanguagePriority</a></code> directive
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is not <code>None</code>. In general, the client determines the
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language preference, not the server.</p>
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<li><code class="directive"><a href="../mod/mod_mime.html#addlanguage">AddLanguage</a></code></li>
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<div class="bottomlang">
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<p><span>Available Languages: </span><a href="../en/mod/mod_negotiation.html" title="English"> en </a> |
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<a href="../ja/mod/mod_negotiation.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a></p>
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</div><div id="footer">
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<p class="apache">Copyright 2006 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
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