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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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<title>Filters - Apache HTTP Server Version 2.5</title>
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<link href="./style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" />
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<link href="./style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" />
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</script>
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<link href="./images/favicon.ico" rel="shortcut icon" /></head>
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<body id="manual-page"><div id="page-header">
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<p class="menu"><a href="./mod/">Modules</a> | <a href="./mod/quickreference.html">Directives</a> | <a href="http://wiki.apache.org/httpd/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 2.5</p>
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<img alt="" src="./images/feather.gif" /></div>
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<div class="up"><a href="./"><img title="<-" alt="<-" src="./images/left.gif" /></a></div>
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<div id="path">
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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 2.5</a></div><div id="page-content"><div id="preamble"><h1>Filters</h1>
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<div class="toplang">
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<p><span>Available Languages: </span><a href="./en/filter.html" title="English"> en </a> |
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<a href="./es/filter.html" hreflang="es" rel="alternate" title="Espa<70>ol"> es </a> |
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<a href="./fr/filter.html" hreflang="fr" rel="alternate" title="Fran<61>ais"> fr </a> |
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<a href="./ja/filter.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
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<a href="./ko/filter.html" hreflang="ko" rel="alternate" title="Korean"> ko </a> |
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<a href="./tr/filter.html" hreflang="tr" rel="alternate" title="T<>rk<72>e"> tr </a></p>
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</div>
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<p>This document describes the use of filters in Apache.</p>
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</div>
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<div id="quickview"><ul id="toc"><li><img alt="" src="./images/down.gif" /> <a href="#intro">Filtering in Apache 2</a></li>
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<li><img alt="" src="./images/down.gif" /> <a href="#smart">Smart Filtering</a></li>
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<li><img alt="" src="./images/down.gif" /> <a href="#service">Exposing Filters as an HTTP Service</a></li>
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<li><img alt="" src="./images/down.gif" /> <a href="#using">Using Filters</a></li>
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</ul><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div>
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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="section">
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<h2><a name="intro" id="intro">Filtering in Apache 2</a></h2>
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<table class="related"><tr><th>Related Modules</th><th>Related Directives</th></tr><tr><td><ul><li><code class="module"><a href="./mod/mod_filter.html">mod_filter</a></code></li><li><code class="module"><a href="./mod/mod_deflate.html">mod_deflate</a></code></li><li><code class="module"><a href="./mod/mod_ext_filter.html">mod_ext_filter</a></code></li><li><code class="module"><a href="./mod/mod_include.html">mod_include</a></code></li><li><code class="module"><a href="./mod/mod_charset_lite.html">mod_charset_lite</a></code></li><li><code class="module"><a href="./mod/mod_reflector.html">mod_reflector</a></code></li><li><code class="module"><a href="./mod/mod_buffer.html">mod_buffer</a></code></li><li><code class="module"><a href="./mod/mod_data.html">mod_data</a></code></li><li><code class="module"><a href="./mod/mod_ratelimit.html">mod_ratelimit</a></code></li><li><code class="module"><a href="./mod/mod_reqtimeout.html">mod_reqtimeout</a></code></li><li><code class="module"><a href="./mod/mod_request.html">mod_request</a></code></li><li><code class="module"><a href="./mod/mod_sed.html">mod_sed</a></code></li><li><code class="module"><a href="./mod/mod_substitute.html">mod_substitute</a></code></li><li><code class="module"><a href="./mod/mod_xml2enc.html">mod_xml2enc</a></code></li><li><code class="module"><a href="./mod/mod_proxy_html.html">mod_proxy_html</a></code></li><li><code class="module"><a href="./mod/mod_policy.html">mod_policy</a></code></li></ul></td><td><ul><li><code class="directive"><a href="./mod/mod_filter.html#filterchain">FilterChain</a></code></li><li><code class="directive"><a href="./mod/mod_filter.html#filterdeclare">FilterDeclare</a></code></li><li><code class="directive"><a href="./mod/mod_filter.html#filterprotocol">FilterProtocol</a></code></li><li><code class="directive"><a href="./mod/mod_filter.html#filterprovider">FilterProvider</a></code></li><li><code class="directive"><a href="./mod/mod_mime.html#addinputfilter">AddInputFilter</a></code></li><li><code class="directive"><a href="./mod/mod_mime.html#addoutputfilter">AddOutputFilter</a></code></li><li><code class="directive"><a href="./mod/mod_mime.html#removeinputfilter">RemoveInputFilter</a></code></li><li><code class="directive"><a href="./mod/mod_mime.html#removeoutputfilter">RemoveOutputFilter</a></code></li><li><code class="directive"><a href="./mod/mod_reflector.html#reflectorheader">ReflectorHeader</a></code></li><li><code class="directive"><a href="./mod/mod_ext_filter.html#extfilterdefine">ExtFilterDefine</a></code></li><li><code class="directive"><a href="./mod/mod_ext_filter.html#extfilteroptions">ExtFilterOptions</a></code></li><li><code class="directive"><a href="./mod/core.html#setinputfilter">SetInputFilter</a></code></li><li><code class="directive"><a href="./mod/core.html#setoutputfilter">SetOutputFilter</a></code></li></ul></td></tr></table>
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<p>The Filter Chain is available in Apache 2.0 and higher,
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and enables applications to process incoming and outgoing data
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in a highly flexible and configurable manner, regardless of
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where the data comes from. We can pre-process incoming data,
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and post-process outgoing data, at will. This is basically
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independent of the traditional request processing phases.</p>
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<p class="figure">
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<img src="images/filter_arch.png" width="569" height="392" alt="Filters can be chained, in a Data Axis orthogonal to request processing" />
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</p>
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<p>Some examples of filtering in the standard Apache distribution are:</p>
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<ul>
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<li><code class="module"><a href="./mod/mod_include.html">mod_include</a></code>, implements server-side includes.</li>
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<li><code class="module"><a href="./mod/mod_ssl.html">mod_ssl</a></code>, implements SSL encryption (https).</li>
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<li><code class="module"><a href="./mod/mod_deflate.html">mod_deflate</a></code>, implements compression/decompression on the fly.</li>
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<li><code class="module"><a href="./mod/mod_charset_lite.html">mod_charset_lite</a></code>, transcodes between different character sets.</li>
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<li><code class="module"><a href="./mod/mod_ext_filter.html">mod_ext_filter</a></code>, runs an external program as a filter.</li>
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</ul>
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<p>Apache also uses a number of filters internally to perform
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functions like chunking and byte-range handling.</p>
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<p>A wider range of applications are implemented by third-party filter
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modules available from <a href="http://modules.apache.org/">modules.apache.org</a> and
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elsewhere. A few of these are:</p>
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<ul>
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<li>HTML and XML processing and rewriting</li>
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<li>XSLT transforms and XIncludes</li>
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<li>XML Namespace support</li>
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<li>File Upload handling and decoding of HTML Forms</li>
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<li>Image processing</li>
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<li>Protection of vulnerable applications such as PHP scripts</li>
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<li>Text search-and-replace editing</li>
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</ul>
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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="smart" id="smart">Smart Filtering</a></h2>
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<p class="figure">
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<img src="images/mod_filter_new.png" width="423" height="331" alt="Smart filtering applies different filter providers according to the state of request processing" />
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</p>
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<p><code class="module"><a href="./mod/mod_filter.html">mod_filter</a></code>, included in Apache 2.1 and later,
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enables the filter chain to be configured dynamically at run time.
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So for example you can set up a proxy to rewrite
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HTML with an HTML filter and JPEG images with a completely
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separate filter, despite the proxy having no prior information
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about what the origin server will send. This works by using a
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filter harness, that dispatches to different providers according
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to the actual contents at runtime. Any filter may be either
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inserted directly in the chain and run unconditionally, or
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used as a provider and inserted dynamically. For example,</p>
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<ul>
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<li>an HTML processing filter will only run if the content is
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text/html or application/xhtml+xml</li>
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<li>A compression filter will only run if the input is a
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compressible type and not already compressed</li>
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<li>A charset conversion filter will be inserted if a text
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document is not already in the desired charset</li>
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</ul>
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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="service" id="service">Exposing Filters as an HTTP Service</a></h2>
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<p>Filters can be used to process content originating from the client in
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addition to processing content originating on the server using the
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<code class="module"><a href="./mod/mod_reflector.html">mod_reflector</a></code> module.</p>
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<p><code class="module"><a href="./mod/mod_reflector.html">mod_reflector</a></code> accepts POST requests from clients, and reflects
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the content request body received within the POST request back in the response,
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passing through the output filter stack on the way back to the client.</p>
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<p>This technique can be used as an alternative to a web service running within
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an application server stack, where an output filter provides the transformation
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required on the request body. For example, the <code class="module"><a href="./mod/mod_deflate.html">mod_deflate</a></code>
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module might be used to provide a general compression service, or an image
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transformation filter might be turned into an image transformation service.</p>
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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="using" id="using">Using Filters</a></h2>
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<p>There are two ways to use filtering: Simple and Dynamic.
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In general, you should use one or the other; mixing them can
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have unexpected consequences (although simple Input filtering
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can be mixed freely with either simple or dynamic Output filtering).</p>
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<p>The Simple Way is the only way to configure input filters, and is
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sufficient for output filters where you need a static filter chain.
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Relevant directives are
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<code class="directive"><a href="./mod/core.html#setinputfilter">SetInputFilter</a></code>,
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<code class="directive"><a href="./mod/core.html#setoutputfilter">SetOutputFilter</a></code>,
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<code class="directive"><a href="./mod/mod_mime.html#addinputfilter">AddInputFilter</a></code>,
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<code class="directive"><a href="./mod/mod_mime.html#addoutputfilter">AddOutputFilter</a></code>,
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<code class="directive"><a href="./mod/mod_mime.html#removeinputfilter">RemoveInputFilter</a></code>, and
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<code class="directive"><a href="./mod/mod_mime.html#removeoutputfilter">RemoveOutputFilter</a></code>.</p>
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<p>The Dynamic Way enables both static and flexible, dynamic configuration
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of output filters, as discussed in the <code class="module"><a href="./mod/mod_filter.html">mod_filter</a></code> page.
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Relevant directives are
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<code class="directive"><a href="./mod/mod_filter.html#filterchain">FilterChain</a></code>,
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<code class="directive"><a href="./mod/mod_filter.html#filterdeclare">FilterDeclare</a></code>, and
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<code class="directive"><a href="./mod/mod_filter.html#filterprovider">FilterProvider</a></code>.</p>
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<p>One further directive <code class="directive"><a href="./mod/mod_filter.html#addoutputfilterbytype">AddOutputFilterByType</a></code> is still supported,
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but deprecated. Use dynamic configuration instead.</p>
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</div></div>
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<div class="bottomlang">
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<p><span>Available Languages: </span><a href="./en/filter.html" title="English"> en </a> |
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<a href="./es/filter.html" hreflang="es" rel="alternate" title="Espa<70>ol"> es </a> |
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<a href="./fr/filter.html" hreflang="fr" rel="alternate" title="Fran<61>ais"> fr </a> |
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<a href="./ja/filter.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
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<a href="./ko/filter.html" hreflang="ko" rel="alternate" title="Korean"> ko </a> |
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<a href="./tr/filter.html" hreflang="tr" rel="alternate" title="T<>rk<72>e"> tr </a></p>
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</div><div class="top"><a href="#page-header"><img src="./images/up.gif" alt="top" /></a></div><div class="section"><h2><a id="comments_section" name="comments_section">Comments</a></h2><div class="warning"><strong>Notice:</strong><br />This is not a Q&A section. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed again by our moderators if they are either implemented or considered invalid/off-topic. Questions on how to manage the Apache HTTP Server should be directed at either our IRC channel, #httpd, on Freenode, or sent to our <a href="http://httpd.apache.org/lists.html">mailing lists</a>.</div>
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