+<section id="early"><title>Early and Late Processing</title>
+ <p><module>mod_headers</module> can be applied either early or late
+ in the request. The normal mode is late, when Request Headers are
+ set immediately before running the content generator and Response
+ Headers just as the response is sent down the wire. Always use
+ Late mode in an operational server.</p>
+
+ <p>Early mode is designed as a test/debugging aid for developers.
+ Directives defined using the <code>early</code> keyword are set
+ right at the beginning of processing the request. This means
+ they can be used to simulate different requests and set up test
+ cases, but it also means that headers may be changed at any time
+ by other modules before generating a Response.</p>
+
+ <p>Because early directives are processed before the request path's
+ configuration is traversed, early headers can only be set in a
+ main server or virtual host context. Early directives cannot depend
+ on a request path, so they will fail in contexts such as
+ <code><Directory></code> or <code><Location></code>.</p>
+</section>
+