This directive enables or disables the generation of the Expires and Cache-Control headers for the document realm in question. (That is, if found in an .htaccess file, for instance, it applies only to documents generated from that directory.) If set to Off, the headers will not be generated for any document in the realm (unless overridden at a lower level, such as an .htaccess file overriding a server config file). If set to On, the headers will be added to served documents according to the criteria defined by the ExpiresByType and ExpiresDefault directives (q.v.).