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224 lines
7.6 KiB
HTML
224 lines
7.6 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
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<HTML>
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<HEAD>
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<TITLE>Apache module mod_negotiation</TITLE>
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<!-- Background white, links blue (unvisited), navy (visited), red (active) -->
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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
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HREF="module-dict.html#Status"
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REL="Help"
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><STRONG>Status:</STRONG></A> Base
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<BR>
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<A
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HREF="module-dict.html#SourceFile"
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REL="Help"
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><STRONG>Source File:</STRONG></A> mod_negotiation.c
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<BR>
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<A
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HREF="module-dict.html#ModuleIdentifier"
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REL="Help"
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><STRONG>Module Identifier:</STRONG></A> negotiation_module
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</P>
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<H2>Summary</H2>
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Content negotiation, or more accurately content selection, is the
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selection of the document that best matches the clients
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capabilities, from one of several available documents.
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There are two implementations of this.
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<UL>
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<LI> A type map (a file with the handler <CODE>type-map</CODE>)
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which explicitly lists the files containing the variants.
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<LI> A MultiViews search (enabled by the MultiViews
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<A HREF="core.html#options">Option</A>, where the server does an implicit
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filename pattern match, and choose from amongst the results.
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</UL>
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<H2>Directives</H2>
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<UL>
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<LI><A HREF="#cachenegotiateddocs">CacheNegotiatedDocs</A>
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<LI><A HREF="#languagepriority">LanguagePriority</A>
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</UL>
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<STRONG>See also</STRONG>:
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<A HREF="./mod_mime.html#defaultlanguage">DefaultLanguage</A>,
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<A HREF="./mod_mime.html#addencoding">AddEncoding</A>,
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<A HREF="./mod_mime.html#addlanguage">AddLanguage</A>,
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<A HREF="./mod_mime.html#addtype">AddType</A>, and
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<A 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 contains document
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descriptions separated by blank lines, with lines beginning with a hash
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character ('#') treated as comments. A document description consists of
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several header records; records may be continued on multiple lines if the
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continuation lines start with spaces. The leading space will be deleted
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and the lines concatenated. A header record consists of a keyword
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name, which always ends in a colon, followed by a value. Whitespace is allowed
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between the header name and value, and between the tokens of value.
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The headers allowed are:
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<DL>
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<DT>Content-Encoding:
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<DD>The encoding of the file. Apache only recognizes encodings that are
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defined by an <A HREF="mod_mime.html#addencoding">AddEncoding</A> directive.
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This normally includes the encodings <CODE>x-compress</CODE> for compress'd
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files, and <CODE>x-gzip</CODE> for gzip'd files. The <CODE>x-</CODE> prefix
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is ignored for encoding comparisons.
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<DT>Content-Language:
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<DD>The language of the variant, as an Internet standard language tag
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(RFC 1766). An example is <CODE>en</CODE>, meaning English.
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<DT>Content-Length:
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<DD>The length of the file, in bytes. If this header is not present, then
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the actual length of the file is used.
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<DT>Content-Type:
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<DD>The MIME media type of the document, with optional parameters.
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Parameters are 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 parameters
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include:
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<DL>
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<DT>level
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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 0.
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<DT>qs
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<DD>a floating-point number with a value in the range 0.0 to 1.0,
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indicating the relative 'quality' of this variant
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compared to the other available variants, independent of the client's
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capabilities. For example, a jpeg file is usually of higher source
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quality than an ascii file if it is attempting to represent a
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photograph. However, if the resource being represented is ascii art,
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then an ascii file would have a higher source quality than a jpeg file.
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All qs values are therefore specific to a given resource.
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</DL>
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Example:
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<BLOCKQUOTE><CODE>Content-Type: image/jpeg; qs=0.8</CODE></BLOCKQUOTE>
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<DT>URI:
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<DD>The path to the file containing this variant, relative to the map file.
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</DL>
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<H2>MultiViews</H2>
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A MultiViews search is enabled by the MultiViews
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<A HREF="core.html#options">Option</A>.
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If the server receives a request for <CODE>/some/dir/foo</CODE> and
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<CODE>/some/dir/foo</CODE> does <EM>not</EM> exist, then the server reads the
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directory looking for all files named <CODE>foo.*</CODE>, and effectively
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fakes up a type map which names all those files, assigning them the same media
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types and content-encodings it would have if the client had asked for
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one 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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<HR>
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<H2><A NAME="cachenegotiateddocs">CacheNegotiatedDocs</A> directive</H2>
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<A
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HREF="directive-dict.html#Syntax"
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REL="Help"
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><STRONG>Syntax:</STRONG></A> CacheNegotiatedDocs on|off<BR>
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<A
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HREF="directive-dict.html#Default"
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REL="Help"
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><STRONG>Default:</STRONG></A> <CODE>CacheNegotiatedDocs off</CODE><BR>
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<A
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HREF="directive-dict.html#Context"
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REL="Help"
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><STRONG>Context:</STRONG></A> server config<BR>
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<A
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HREF="directive-dict.html#Status"
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REL="Help"
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><STRONG>Status:</STRONG></A> Base<BR>
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<A
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HREF="directive-dict.html#Module"
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REL="Help"
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><STRONG>Module:</STRONG></A> mod_negotiation<BR>
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<A
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HREF="directive-dict.html#Compatibility"
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REL="Help"
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><STRONG>Compatibility:</STRONG></A> CacheNegotiatedDocs is only available
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in Apache 1.1 and later. The syntax changed in version 2.0.<P>
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<P>If set, this directive allows content-negotiated documents to be
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cached by proxy servers. This could mean that clients behind those
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proxys could retrieve versions of the documents that are not the best
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match for their abilities, but it will make caching more
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efficient.
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<P>This directive only applies to requests which come from HTTP/1.0 browsers.
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HTTP/1.1 provides much better control over the caching of negotiated
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documents, and this directive has no effect in responses to
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HTTP/1.1 requests.
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<P>Prior to version 2.0, CacheNegotiatedDocs did not take an argument;
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it was turned on by the presence of the directive by itself.
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<hr>
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<H2><A NAME="languagepriority">LanguagePriority</A> directive</H2>
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<!--%plaintext <?INDEX {\tt LanguagePriority} directive> -->
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<A
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HREF="directive-dict.html#Syntax"
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REL="Help"
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><STRONG>Syntax:</STRONG></A> LanguagePriority <EM>MIME-lang</em>
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[<em>MIME-lang</EM>] ...<BR>
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<A
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HREF="directive-dict.html#Context"
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REL="Help"
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><STRONG>Context:</STRONG></A> server config, virtual host, directory, .htaccess<BR>
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<A
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HREF="directive-dict.html#Override"
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REL="Help"
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><STRONG>Override:</STRONG></A> FileInfo<BR>
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<A
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HREF="directive-dict.html#Status"
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REL="Help"
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><STRONG>Status:</STRONG></A> Base<BR>
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<A
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HREF="directive-dict.html#Module"
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REL="Help"
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><STRONG>Module:</STRONG></A> mod_negotiation<P>
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The LanguagePriority sets the precedence of language variants for the case
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where the client does not express a preference, when handling a
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MultiViews request. The list of <EM>MIME-lang</EM> are in order of decreasing
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preference. Example:
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<BLOCKQUOTE><CODE>LanguagePriority en fr de</CODE></BLOCKQUOTE>
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For a request for <CODE>foo.html</CODE>, where <CODE>foo.html.fr</CODE>
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and <CODE>foo.html.de</CODE> both existed, but the browser did not express
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a language preference, then <CODE>foo.html.fr</CODE> would be returned.<P>
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<P>
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Note that this directive only has an effect if a 'best' language
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cannot be determined by any other means. Correctly implemented
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HTTP/1.1 requests will mean this directive has no effect.
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<P>
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<STRONG>See also</STRONG>:
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<A 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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</BODY>
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</HTML>
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