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184 lines
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
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This file is generated from xml source: DO NOT EDIT
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--><title>mod_expires - Apache HTTP Server</title><link href="../style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" /><link href="../images/favicon.ico" rel="shortcut icon" /></head><body><div id="page-header"><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><p class="apache">Apache HTTP Server Version 2.0</p><img alt="" src="../images/feather.gif" /></div><div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div><div id="path"><a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs-project/">Documentation</a> > <a href="../">Version 2.0</a> > <a href="./">Modules</a></div><div id="page-content"><div id="preamble"><h1>Apache Module mod_expires</h1><table class="module"><tr><th>Description:
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</th><td>Generation of
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<code>Expires</code> HTTP headers according to user-specified
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criteria</td></tr><tr><th><a href="module-dict.html#Status">Status:
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</a></th><td>Extension</td></tr><tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:
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</a></th><td>expires_module</td></tr></table><h3>Summary</h3>
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<p>This module controls the setting of the <code>Expires</code>
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HTTP header in server responses. The expiration date can set to
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be relative to either the time the source file was last
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modified, or to the time of the client access.</p>
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<p>The <code>Expires</code> HTTP header is an instruction to
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the client about the document's validity and persistence. If
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cached, the document may be fetched from the cache rather than
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from the source until this time has passed. After that, the
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cache copy is considered "expired" and invalid, and a new copy
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must be obtained from the source.</p>
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</div><div id="quickview"><h3 class="directives">Directives</h3><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#expiresactive">ExpiresActive</a></li><li><img alt="" src="../images/down.gif" /> <a href="#expiresbytype">ExpiresByType</a></li><li><img alt="" src="../images/down.gif" /> <a href="#expiresdefault">ExpiresDefault</a></li></ul><h3>Topics</h3><ul id="topics"><li><img alt="" src="../images/down.gif" /> <a href="#AltSyn">Alternate Interval
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Syntax</a></li></ul></div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div><div class="section"><h2><a name="AltSyn" id="AltSyn">Alternate Interval
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Syntax</a></h2>
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<p>The <code class="directive"><a href="#expiresdefault">ExpiresDefault</a></code> and
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<code class="directive"><a href="#expiresbytype">ExpiresByType</a></code> directives
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can also be defined in a more readable syntax of the form:</p>
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<div class="example"><p><code>
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ExpiresDefault "<base> [plus] {<num>
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<type>}*"<br />
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ExpiresByType type/encoding "<base> [plus]
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{<num> <type>}*"
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</code></p></div>
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<p>where <base> is one of:</p>
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<ul>
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<li><code>access</code></li>
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<li><code>now</code> (equivalent to
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'<code>access</code>')</li>
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<li><code>modification</code></li>
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</ul>
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<p>The '<code>plus</code>' keyword is optional. <num>
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should be an integer value [acceptable to <code>atoi()</code>],
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and <type> is one of:</p>
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<ul>
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<li><code>years</code></li>
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<li><code>months</code></li>
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<li><code>weeks</code></li>
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<li><code>days</code></li>
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<li><code>hours</code></li>
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<li><code>minutes</code></li>
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<li><code>seconds</code></li>
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</ul>
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<p>For example, any of the following directives can be used to
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make documents expire 1 month after being accessed, by
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default:</p>
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<div class="example"><p><code>
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ExpiresDefault "access plus 1 month"<br />
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ExpiresDefault "access plus 4 weeks"<br />
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ExpiresDefault "access plus 30 days"
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</code></p></div>
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<p>The expiry time can be fine-tuned by adding several
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'<num> <type>' clauses:</p>
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<div class="example"><p><code>
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ExpiresByType text/html "access plus 1 month 15
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days 2 hours"<br />
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ExpiresByType image/gif "modification plus 5 hours 3
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minutes"
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</code></p></div>
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<p>Note that if you use a modification date based setting, the
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Expires header will <strong>not</strong> be added to content
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that does not come from a file on disk. This is due to the fact
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that there is no modification time for such content.</p>
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</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div><div class="directive-section"><h2><a name="ExpiresActive" id="ExpiresActive">ExpiresActive</a> <a name="expiresactive" id="expiresactive">Directive</a></h2><table class="directive"><tr><th>Description:
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</th><td>Enables generation of Expires headers</td></tr><tr><th><a href="directive-dict.html#Syntax">Syntax:
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</a></th><td>ExpiresActive On|Off</td></tr><tr><th><a href="directive-dict.html#Context">Context:
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</a></th><td>server config, virtual host, directory, .htaccess</td></tr><tr><th><a href="directive-dict.html#Override">Override:
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</a></th><td>Indexes</td></tr><tr><th><a href="directive-dict.html#Status">Status:
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</a></th><td>Extension</td></tr><tr><th><a href="directive-dict.html#Module">Module:
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</a></th><td>mod_expires</td></tr></table>
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<p>This directive enables or disables the generation of the
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<code>Expires</code> header for the document realm in question.
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(That is, if found in an <code>.htaccess</code> file, for
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instance, it applies only to documents generated from that
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directory.) If set to <em><code>Off</code></em>, no
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<code>Expires</code> header will be generated for any document
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in the realm (unless overridden at a lower level, such as an
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<code>.htaccess</code> file overriding a server config file).
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If set to <em><code>On</code></em>, the header will be added to
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served documents according to the criteria defined by the
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<code class="directive"><a href="#expiresbytype">ExpiresByType</a></code> and
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<code class="directive"><a href="#expiresdefault">ExpiresDefault</a></code> directives
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(<em>q.v.</em>).</p>
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<p>Note that this directive does not guarantee that an
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<code>Expires</code> header will be generated. If the criteria
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aren't met, no header will be sent, and the effect will be as
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though this directive wasn't even specified.</p>
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</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div><div class="directive-section"><h2><a name="ExpiresByType" id="ExpiresByType">ExpiresByType</a> <a name="expiresbytype" id="expiresbytype">Directive</a></h2><table class="directive"><tr><th>Description:
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</th><td>Value of the Expires header configured
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by MIME type</td></tr><tr><th><a href="directive-dict.html#Syntax">Syntax:
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</a></th><td>ExpiresByType
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<em>MIME-type <code>seconds</em></td></tr><tr><th><a href="directive-dict.html#Context">Context:
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</a></th><td>server config, virtual host, directory, .htaccess</td></tr><tr><th><a href="directive-dict.html#Override">Override:
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</a></th><td>Indexes</td></tr><tr><th><a href="directive-dict.html#Status">Status:
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</a></th><td>Extension</td></tr><tr><th><a href="directive-dict.html#Module">Module:
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</a></th><td>mod_expires</td></tr></table>
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<p>This directive defines the value of the <code>Expires</code>
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header generated for documents of the specified type
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(<em>e.g.</em>, <code>text/html</code>). The second argument
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sets the number of seconds that will be added to a base time to
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construct the expiration date.</p>
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<p>The base time is either the last modification time of the
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file, or the time of the client's access to the document. Which
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should be used is specified by the
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<code><em><code></em></code> field; <strong>M</strong>
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means that the file's last modification time should be used as
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the base time, and <strong>A</strong> means the client's access
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time should be used.</p>
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<p>The difference in effect is subtle. If <em>M</em> is used,
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all current copies of the document in all caches will expire at
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the same time, which can be good for something like a weekly
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notice that's always found at the same URL. If <em>A</em> is
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used, the date of expiration is different for each client; this
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can be good for image files that don't change very often,
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particularly for a set of related documents that all refer to
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the same images (<em>i.e.</em>, the images will be accessed
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repeatedly within a relatively short timespan).</p>
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<p><strong>Example:</strong></p>
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<div class="example"><p><code>
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# enable expirations<br />
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ExpiresActive On<br />
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# expire GIF images after a month in the client's cache<br />
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ExpiresByType image/gif A2592000<br />
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# HTML documents are good for a week from the time they were changed<br />
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ExpiresByType text/html M604800
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</code></p></div>
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<p>Note that this directive only has effect if
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<code>ExpiresActive On</code> has been specified. It overrides,
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for the specified MIME type <em>only</em>, any expiration date
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set by the <code class="directive"><a href="#expiresdefault">ExpiresDefault</a></code>
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directive.</p>
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<p>You can also specify the expiration time calculation using
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an <a href="#AltSyn">alternate syntax</a>, described earlier in
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this document.</p>
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</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div><div class="directive-section"><h2><a name="ExpiresDefault" id="ExpiresDefault">ExpiresDefault</a> <a name="expiresdefault" id="expiresdefault">Directive</a></h2><table class="directive"><tr><th>Description:
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</th><td>Default algorithm for calculating expiration time</td></tr><tr><th><a href="directive-dict.html#Syntax">Syntax:
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</a></th><td>ExpiresDefault <em><code>seconds</em></td></tr><tr><th><a href="directive-dict.html#Context">Context:
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</a></th><td>server config, virtual host, directory, .htaccess</td></tr><tr><th><a href="directive-dict.html#Override">Override:
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</a></th><td>Indexes</td></tr><tr><th><a href="directive-dict.html#Status">Status:
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</a></th><td>Extension</td></tr><tr><th><a href="directive-dict.html#Module">Module:
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</a></th><td>mod_expires</td></tr></table>
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<p>This directive sets the default algorithm for calculating the
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expiration time for all documents in the affected realm. It can be
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overridden on a type-by-type basis by the <code class="directive"><a href="#expiresbytype">ExpiresByType</a></code> directive. See the
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description of that directive for details about the syntax of the
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argument, and the <a href="#AltSyn">alternate syntax</a>
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description as well.</p>
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</div></div><div id="footer"><p class="apache">Maintained by the <a href="http://httpd.apache.org/docs-project/">Apache HTTP Server Documentation Project</a></p><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></div></body></html> |