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270 lines
10 KiB
XML
270 lines
10 KiB
XML
<?xml version="1.0"?>
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<!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd">
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<?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>
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<modulesynopsis>
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<name>mod_negotiation</name>
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<description>Provides for <a
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href="../content-negotiation.html">content negotiation</a></description>
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<status>Base</status>
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<sourcefile>mod_negotiation.c</sourcefile>
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<identifier>negotiation_module</identifier>
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<summary>
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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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<ul>
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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 MultiViews <directive
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module="core">Options</directive>, where the server does an
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implicit filename pattern match, and choose from amongst the
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results.</li>
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</ul>
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</summary>
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<seealso><directive module="mod_mime">DefaultLanguage</directive></seealso>
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<seealso><directive module="mod_mime">AddEncoding</directive></seealso>
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<seealso><directive module="mod_mime">AddLanguage</directive></seealso>
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<seealso><directive module="mod_mime">AddType</directive></seealso>
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<seealso><directive module="mod_mime">MultiViewsMatch</directive></seealso>
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<section id="typemaps"><title>Type maps</title>
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<p>A type map has the same format as 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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<dl>
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<dt>Content-Encoding:</dt>
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<dd>The encoding of the file. Apache only recognizes
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encodings that are defined by an <directive
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module="mod_mime">AddEncoding</directive> 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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comparisons.</dd>
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<dt>Content-Language:</dt>
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<dd>The language of the variant, as an Internet standard
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language tag (RFC 1766). An example is <code>en</code>,
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meaning English.</dd>
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<dt>Content-Length:</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>Content-Type:</dt>
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<dd>
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The MIME media type of the document, with optional
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parameters. Parameters are separated from the media type
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and from one another by a semi-colon, with a syntax of
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<code>name=value</code>. Common parameters include:
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<dl>
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<dt>level</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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0.</dd>
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<dt>qs</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 qs values are therefore specific to a given
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resource.</dd>
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</dl>
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Example:
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<example>Content-Type: image/jpeg; qs=0.8</example>
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</dd>
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<dt>URI:</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>Body:</dt>
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<dd><p>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.</p>
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<p>Example:</p>
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<example>
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Body:----xyz----<br />
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<html><br />
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<body><br />
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<p>Content of the page.</p><br />
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</body><br />
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</html><br />
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----xyz----
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</example>
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</dd>
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</dl>
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</section>
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<section id="multiviews">
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<title>MultiViews</title>
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<p>A MultiViews search is enabled by the MultiViews <directive
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module="core">Options</directive>. 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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</section>
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<directivesynopsis>
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<name>CacheNegotiatedDocs</name>
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<description>Allows content-negotiated documents to be
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cached by proxy servers</description>
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<syntax>CacheNegotiatedDocs on|off</syntax>
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<default>CacheNegotiatedDocs off</default>
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<contextlist><context>server config</context><context>virtual host</context>
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</contextlist>
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<compatibility>The syntax changed in version 2.0.</compatibility>
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<usage>
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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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<directive>CacheNegotiatedDocs</directive> did not take an
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argument; it was turned on by the presence of the directive by
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itself.</p>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>ForceLanguagePriority</name>
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<description>Action to take if a single acceptable document is not
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found</description>
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<syntax>ForceLanguagePriority None|Prefer|Fallback [Prefer|Fallback]</syntax>
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<default>ForceLanguagePriority Prefer</default>
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<contextlist><context>server config</context>
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<context>virtual host</context>
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<context>directory</context>
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<context>.htaccess</context>
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</contextlist>
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<override>FileInfo</override>
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<compatibility>Available in version 2.0.30 and later</compatibility>
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<usage>
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<p>The <directive>ForceLanguagePriority</directive> directive uses
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the given <directive
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module="mod_negotiation">LanguagePriority</directive> 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 Accept-Language header assigned en and de
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each as quality .500 (equally acceptable) then the first matching
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variant, en, will be served.</p>
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<example>
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LanguagePriority en fr de<br />
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ForceLanguagePriority Prefer
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</example>
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<p><code>ForceLanguagePriority Fallback</code> uses
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<code>LanguagePriority</code> to serve a valid result, rather than
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returning an HTTP result 406 (NOT ACCEPTABLE). If the directives
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below were given, and the user's Accept-Language only permitted an
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es language response, but such a variant isn't found, then the
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first variant from the LanguagePriority list below will be
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served.</p>
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<example>
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LanguagePriority en fr de<br />
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ForceLanguagePriority Fallback
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</example>
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<p>Both options, Prefer and Fallback, may be specified, so either the
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first matching variant from LanguagePriority will be served if more
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that one variant is acceptable, or first available document will be
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served if none of the variants matched the client's acceptable list of
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languages.</p>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>LanguagePriority</name>
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<description>The precendence of language variants for cases where
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the client does not express a preference</description>
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<syntax>LanguagePriority <em>MIME-lang</em> [<em>MIME-lang</em>] ...</syntax>
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<contextlist><context>server config</context>
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<context>virtual host</context>
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<context>directory</context>
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<context>.htaccess</context>
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</contextlist>
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<override>FileInfo</override>
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<usage>
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<p>The <directive>LanguagePriority</directive> 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 <em>MIME-lang</em> are in order of decreasing preference.
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Example:</p>
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<example>LanguagePriority en fr de</example>
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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 <directive
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module="mod_negotiation">ForceLanguagePriority</directive> directive
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is not <code>None</code>. Correctly implemented HTTP/1.1 requests
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will mean this directive has no effect.</p>
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</usage>
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</directivesynopsis>
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</modulesynopsis>
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