Webmaster in a Nutshell, Third Edition

The mod_headers module allows administrators to merge, remove, or replace customizable HTTP response headers to be distributed with documents from the server.

Header <setappendaddunset>: header [ value ]

[ server config , or within <VirtualHost> or <Directory>, or .htaccess ]

This directive allows administrators to merge, remove, or replace HTTP headers that are transmitted with server documents. The header action performed is specified after the Header directive; it can be one of four choices:

set

The header specified is reset to the value specified.

append

A header is appended to the specified response header, if it exists. The new value is listed after the old value and is separated by a comma.

add

A new header is created and added to the response headers, even if one already exists.

unset

This option deletes the first occurrence of the header in question.

Headers such as Date and Server cannot be overridden using this directive.