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229 lines
8.8 KiB
HTML
229 lines
8.8 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta name="generator" content="HTML Tidy, see www.w3.org" />
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<title>Apache module mod_negotiation</title>
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</head>
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<!-- Background white, links blue (unvisited), navy (visited), red (active) -->
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<body bgcolor="#FFFFFF" text="#000000" link="#0000FF"
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<!--#include virtual="header.html" -->
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<h1 align="CENTER">Module mod_negotiation</h1>
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<p>This module provides for <a
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href="../content-negotiation.html">content negotiation</a>.</p>
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<p><a href="module-dict.html#Status"
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rel="Help"><strong>Status:</strong></a> Base<br />
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<a href="module-dict.html#SourceFile"
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rel="Help"><strong>Source File:</strong></a>
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mod_negotiation.c<br />
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<a href="module-dict.html#ModuleIdentifier"
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rel="Help"><strong>Module Identifier:</strong></a>
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negotiation_module</p>
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<h2>Summary</h2>
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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.
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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 <a
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href="core.html#options">Option</a>, 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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<h2>Directives</h2>
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<ul>
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<li><a
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href="#cachenegotiateddocs">CacheNegotiatedDocs</a></li>
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<li><a href="#languagepriority">LanguagePriority</a></li>
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</ul>
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<strong>See also</strong>: <a
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href="./mod_mime.html#defaultlanguage">DefaultLanguage</a>, <a
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href="./mod_mime.html#addencoding">AddEncoding</a>, <a
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href="./mod_mime.html#addlanguage">AddLanguage</a>, <a
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href="./mod_mime.html#addtype">AddType</a>, and <a
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href="core.html#options">Options</a>.
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<h2>Type maps</h2>
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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:
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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 <a
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href="mod_mime.html#addencoding">AddEncoding</a> 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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<blockquote>
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<code>Content-Type: image/jpeg; qs=0.8</code>
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</blockquote>
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</dd>
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<dt>URI:</dt>
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<dd>The path to the file containing this variant, relative to
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the map file.</dd>
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</dl>
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<h2>MultiViews</h2>
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A MultiViews search is enabled by the MultiViews <a
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href="core.html#options">Option</a>. 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.
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<hr />
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<h2><a id="cachenegotiateddocs"
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name="cachenegotiateddocs">CacheNegotiatedDocs</a>
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directive</h2>
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<a href="directive-dict.html#Syntax"
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rel="Help"><strong>Syntax:</strong></a> CacheNegotiatedDocs
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on|off<br />
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<a href="directive-dict.html#Default"
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rel="Help"><strong>Default:</strong></a>
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<code>CacheNegotiatedDocs off</code><br />
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<a href="directive-dict.html#Context"
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rel="Help"><strong>Context:</strong></a> server config<br />
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<a href="directive-dict.html#Status"
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rel="Help"><strong>Status:</strong></a> Base<br />
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<a href="directive-dict.html#Module"
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rel="Help"><strong>Module:</strong></a> mod_negotiation<br />
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<a href="directive-dict.html#Compatibility"
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rel="Help"><strong>Compatibility:</strong></a>
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CacheNegotiatedDocs is only available in Apache 1.1 and later.
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The syntax changed in version 2.0.
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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, CacheNegotiatedDocs 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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<hr />
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<h2><a id="languagepriority"
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name="languagepriority">LanguagePriority</a> directive</h2>
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<!--%plaintext <?INDEX {\tt LanguagePriority} directive> -->
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<a href="directive-dict.html#Syntax"
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rel="Help"><strong>Syntax:</strong></a> LanguagePriority
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<em>MIME-lang</em> [<em>MIME-lang</em>] ...<br />
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<a href="directive-dict.html#Context"
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rel="Help"><strong>Context:</strong></a> server config, virtual
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host, directory, .htaccess<br />
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<a href="directive-dict.html#Override"
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rel="Help"><strong>Override:</strong></a> FileInfo<br />
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<a href="directive-dict.html#Status"
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rel="Help"><strong>Status:</strong></a> Base<br />
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<a href="directive-dict.html#Module"
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rel="Help"><strong>Module:</strong></a> mod_negotiation
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<p>The LanguagePriority sets the precedence of language
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variants for the case where the client does not express a
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preference, when handling a MultiViews request. The list of
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<em>MIME-lang</em> are in order of decreasing preference.
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Example:</p>
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<blockquote>
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<code>LanguagePriority en fr de</code>
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</blockquote>
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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.
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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. Correctly
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implemented HTTP/1.1 requests will mean this directive has no
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effect.</p>
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<p><strong>See also</strong>: <a
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href="./mod_mime.html#defaultlanguage">DefaultLanguage</a> and
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<a href="./mod_mime.html#addlanguage">AddLanguage</a>
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<!--#include virtual="footer.html" -->
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</p>
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</body>
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</html>
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