Apache Reference: mod_headers, Header

Header

Control HTTP Response Header Fields
Syntax: Header operation header [value]
Example: Header set Author "John Doe"
Since: Apache 1.2

This directive can replace, merge, or remove HTTP response headers fields. It performs the operation designated by the first argument. This argument can have any of four values. The ``set'' value sets the response header to value, replacing any previous header with this name. The ``append'' value appends value to the response header of the same name; when a new value is merged into an existing header, it is separated from the existing header with a comma - the HTTP standard way of giving a header multiple values. The ``add'' value adds value to the response header in the existing set of headers, even if this header already exists. The addition can result in two (or more) headers having the same name (and lead to unforeseen consequences; in general, ``append'' should be used instead). The ``unset'' value removes the response header, if it exists. If multiple headers of the same name exist, all will be removed.

The operation argument is followed by a header name, which can include the final colon, though it is not required. Case is ignored. For ``add'', ``append'', and ``set'' operations, 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.