--- /dev/null
+<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
+<HTML>
+ <HEAD>
+ <TITLE>Apache module mod_expires</TITLE>
+ </HEAD>
+ <BODY>
+ <!--#include virtual="header.html" -->
+ <H1>Module mod_expires</H1>
+ <P>
+ This module is contained in the <CODE>mod_expires.c</CODE> file, and
+ is <STRONG>not</STRONG> compiled in by default. It provides for the
+ generation of <CODE>Expires</CODE> headers according to user-specified
+ criteria.
+ </P>
+ <H2>Summary</H2>
+ <P>
+ This module controls the setting of the <CODE>Expires</CODE> HTTP
+ header in server responses. The expiration date can set to be
+ relative to either the time the source file was last modified, or to
+ the time of the client access.
+ </P>
+ <P>
+ The <CODE>Expires</CODE> HTTP header is an instruction to the client
+ about the document's validity and persistence. If cached, the document
+ may be fetched from the cache rather than from the source until this
+ time has passed. After that, the cache copy is considered
+ "expired" and invalid, and a new copy must be obtained from
+ the source.
+ </P>
+ <H2>Directives</H2>
+ <P>
+ <MENU>
+ <LI><A
+ HREF="#expiresactive"
+ >ExpiresActive</A>
+ </LI>
+ <LI><A
+ HREF="#expiresbytype"
+ >ExpiresByType</A>
+ </LI>
+ <LI><A
+ HREF="#expiresdefault"
+ >ExpiresDefault</A>
+ </LI>
+ </MENU>
+ <HR>
+ <A NAME="expiresactive">
+ <H2>ExpiresActive directive</H2>
+ </A>
+ <!--%plaintext <?INDEX {\tt ExpiresActive} directive> -->
+ <P>
+ <STRONG>Syntax:</STRONG> ExpiresActive <EM>boolean</EM>
+ <BR>
+ <STRONG>Context:</STRONG> server config, virtual host, directory, .htaccess
+ <br>
+ <STRONG>Override:</STRONG> Indexes
+ <br>
+ <STRONG>Status:</STRONG> Extension
+ <br>
+ <STRONG>Module:</STRONG> mod_expires
+ </P>
+ <P>
+ This directive enables or disables the generation of the
+ <CODE>Expires</CODE> header for the document realm in question. (That
+ is, if found in an <CODE>.htaccess</CODE> file, for instance, it
+ applies only to documents generated from that directory.) If set to
+ <EM><CODE>Off</CODE></EM>, no <CODE>Expires</CODE> header will be
+ generated for any document in the realm (unless overridden at a lower
+ level, such as an <CODE>.htaccess</CODE> file overriding a server
+ config file). If set to <EM><CODE>On</CODE></EM>, the header will be
+ added to served documents according to the criteria defined by the
+ <A
+ HREF="expiresbytype"
+ >ExpiresByType</A>
+ and
+ <A
+ HREF="#expiresdefault"
+ >ExpiresDefault</A>
+ directives (<EM>q.v.</EM>).
+ </P>
+ <P>
+ Note that this directive does not guarantee that an
+ <CODE>Expires</CODE> header will be generated. If the criteria aren't
+ met, no header will be sent, and the effect will be as though this
+ directive wasn't even specified.
+ </P>
+ <HR>
+ <A NAME="expiresbytype">
+ <H2>ExpiresByType directive</H2>
+ </A>
+ <!--%plaintext <?INDEX {\tt ExpiresByType} directive> -->
+ <P>
+ <STRONG>Syntax:</STRONG> ExpiresByType <EM>mime-type <code>seconds</EM>
+ <BR>
+ <STRONG>Context:</STRONG> server config, virtual host, directory, .htaccess
+ <br>
+ <STRONG>Override:</STRONG> Indexes
+ <br>
+ <STRONG>Status:</STRONG> Extension
+ <br>
+ <STRONG>Module:</STRONG> mod_expires
+ </P>
+ <P>
+ This directive defines the value of the <CODE>Expires</CODE> header
+ generated for documents of the specified type (<EM>e.g.</EM>,
+ <CODE>text/html</CODE>). The second argument sets the number of
+ seconds that will be added to a base time to construct the expiration
+ date.
+ </P>
+ <P>
+ The base time is either the last modification time of the file, or the
+ time of the client's access to the document. Which should be used is
+ specified by the <CODE><EM><code></EM></CODE> field;
+ <STRONG>M</STRONG> means that the file's last modification time should
+ be used as the base time, and <STRONG>A</STRONG> means the client's
+ access time should be used.
+ </P>
+ <P>
+ The difference in effect is subtle. If <EM>M</EM> is used, all current
+ copies of the document in all caches will expire at the same time,
+ which can be good for something like a weekly notice that's always
+ found at the same URL. If <EM>A</EM> is used, the date of expiration
+ is different for each client; this can be good for image files that
+ don't change very often, particularly for a set of related documents
+ that all refer to the same images (<EM>i.e.</EM>, the images will be
+ accessed repeatedly within a relatively short timespan).
+ </P>
+ <P>
+ <STRONG>Example:</STRONG>
+ </P>
+ <P>
+ <PRE>
+ ExpiresActive On # enable expirations
+ ExpiresByType image/gif A2592000 # expire GIF images after a month
+ # in the client's cache
+ ExpiresByType text/html M604800 # HTML documents are good for a
+ # week from the time they were
+ # changed, period
+ </PRE>
+ </P>
+ <P>
+ Note that this directive only has effect if <CODE>ExpiresActive
+ On</CODE> has been specified. It overrides, for the specified MIME
+ type <EM>only</EM>, any expiration date set by the
+ <A
+ HREF="#expiresdefault"
+ >ExpiresDefault</A>
+ directive.
+ </P>
+ <HR>
+ <A NAME="expiresdefault">
+ <H2>ExpiresDefault directive</H2>
+ </A>
+ <!--%plaintext <?INDEX {\tt ExpiresDefault} directive> -->
+ <P>
+ <STRONG>Syntax:</STRONG> ExpiresDefault <EM><code>seconds</EM>
+ <BR>
+ <STRONG>Context:</STRONG> server config, virtual host, directory, .htaccess
+ <br>
+ <STRONG>Override:</STRONG> Indexes
+ <br>
+ <STRONG>Status:</STRONG> Extension
+ <br>
+ <STRONG>Module:</STRONG> mod_expires
+ </P>
+ <P>
+ This directive sets the default algorithm for calculating the
+ expiration time for all documents in the affected realm. It can be
+ overridden on a type-by-type basis by the
+ <A
+ HREF="#expiresbytype"
+ >ExpiresByType</A>
+ directive. See the description of that directive for details about
+ the syntax of the argument.
+ </P>
+ <!--#include virtual="footer.html" -->
+ </BODY>
+</HTML>
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