xforms

    and output filters are run, allowing outgoing headers to be

    modified.</p>

    <p>By default, this directive only affects successful responses (responses

    in the <code>2<var>xx</var></code> range).  The optional <var>condition</var>

    can be either <code>onsuccess</code> (default) or <code>always</code> (all

    status codes, including successful responses).  A value of <code>always</code>

    may be needed to influence headers set by some internal modules even for

    successful responses, and is always needed to affect non-<code>2<var>xx</var></code> 

    responses such as redirects or client errors.</p>

    <div class="note"><h3>CGI</h3>

      <p>To manipulate headers set by CGI scripts, it is necessary to specify 

      <code>always</code> for the first parameter.</p>

    </div>

    <p> The optional <var>condition</var> argument determines which internal

    table of responses headers this directive will operate against.  Other

    components of the server may have stored their response headers in either

    the table that corresponds to <code>onsuccess</code> or the table that

    corresponds to <code>always</code>.  "Always" in this context refers to

    whether headers you add will be sent during both a successful and unsucessful 

    response, but if your action is a function of an existing header, you

    will have to read on for further complications.</p>

    <p> The default value of <code>onsuccess</code> may need to be changed to 

    <code>always</code> under the circumstances similar to those listed below

    Note also that repeating this directive with both conditions makes sense in

    some scenarios because <code>always</code> is not a superset of 

    <code>onsuccess</code> with respect to existing headers:</p>

    <ul>

       <li> You're adding a header to a non-success (non-2xx) response, such 

            as a redirect, in which case only the table corresponding to 

            <code>always</code> is used in the ultimate response.</li>

       <li> You're modifying or removing a header generated by a CGI script,

            in which case the CGI scripts are in the table corresponding to 

            <code>always</code> and not in the default table.</li>

       <li> You're modifying or removing a header generated by some piece of 

            the server but that header is not being found by the default 

            <code>onsuccess</code> condition.</li>

    </ul>

    <p>The action it performs is determined by the first

    argument (second argument if a <var>condition</var> is specified).