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<H1 ALIGN="CENTER">Module mod_headers</H1>

The optional headers module allows for the customization of HTTP
response headers. Headers can be merged, replaced or removed. The
directives described in this document are only available if Apache is
compiled with <STRONG>mod_headers.c</STRONG>.

<HR>

<H2>Directive</H2>
<UL>
<LI><A HREF="#header">Header</A>
</UL>

<HR>

<H2><A NAME="header">Header</A></H2>
<A
 HREF="directive-dict.html#Syntax"
 REL="Help"
><STRONG>Syntax:</STRONG></A> Header [ set | append | add ]
 <EM>header</EM> <EM>value</EM><BR>
<A
 HREF="directive-dict.html#Syntax"
 REL="Help"
><STRONG>Syntax:</STRONG></A> Header unset <EM>header</EM><BR>
<A
 HREF="directive-dict.html#Context"
 REL="Help"
><STRONG>Context:</STRONG></A> server config, virtual host, access.conf,
 .htaccess<BR>
<A
 HREF="directive-dict.html#Status"
 REL="Help"
><STRONG>Status:</STRONG></A> optional<BR>
<A
 HREF="directive-dict.html#Module"
 REL="Help"
><STRONG>Module:</STRONG></A> mod_header<P>

This directive can replace, merge or remove HTTP response headers. The
action it performs is determined by the first argument. This can be one
of the following values:

<UL>
<LI><STRONG>set</STRONG><BR>
  The response header is set, replacing any previous header with this name

<LI><STRONG>append</STRONG><BR>
  The response header is appended to any existing header of the same
  name. When a new value is merged onto an existing header it is
  separated from the existing header with a comma. This is the HTTP standard
  way of giving a header multiple values.

<LI><STRONG>add</STRONG><BR>
  The response header is added to the existing set of headers, even if
  this header already exists. This can result in two (or more) headers
  having the same name. This can lead to unforeseen consequences, and in
  general "append" should be used instead.

<LI><STRONG>unset</STRONG><BR>
  The response header of this name is removed, if it exists. If there are
  multiple headers of the same name, all will be removed.
</UL>

This argument is followed by a header name, which can include the
final colon, but it is not required. Case is ignored. For
add, append and set a value is given as the third argument. If this
value contains spaces, it should be surrounded by double quotes.
For unset, no value should be given.

<H3>Order of Processing</H3>

The Header directive can occur almost anywhere within the server
configuration. It is valid in the main server config and virtual host
sections, inside &lt;Directory&gt;, &lt;Location&gt; and &lt;Files&gt;
sections, and within .htaccess files.
<P>
The Header directives are processed in the following order:
<OL>
<LI>main server
<LI>virtual host
<LI>&lt;Directory&gt; sections and .htaccess
<LI>&lt;Location&gt;
<LI>&lt;Files&gt;
</OL>

Order is important. These two headers have a different effect if reversed:
<PRE>
Header append Author "John P. Doe"
Header unset Author
</PRE>

This way round, the Author header is not set. If reversed, the Author
header is set to "John P. Doe".
<P>

The Header directives are processed just before the response is sent
by its handler. These means that some headers that are added just
before the response is sent cannot be unset or overridden. This
includes headers such as "Date" and "Server".
<P>

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