URL modules are called after first modules. URL modules change data in the request object, for example the URL being fetched. The module type constant is MODULE_URL. The available API method is:

void|object|mixed remap_url( object id )

id is the request information object. remap_url() either returns zero, a changed request information object or a normal response, as documented in the response chapter. If the method returns a request information object Challenger will call all URL modules again, so care must be taken so infinite loops are not created.