File extension modules handle one or several different file types.
A file extension module is called after a location, or other module
type, has returned a Stdio.File object with the correct extension.
The module type constant is MODULE_FILE_EXTENSION.
array(string) query_file_extensions()
Returns an array of strings containing the extensions this module
handles. It should be configurable by the user, the easiest way would
be to use a configuration variable of TYPE_STRING_LIST.
mapping handle_file_extension( Stdio.File file, string ext, RequestID id )
The method that will be called to do the actual work. file is the
file object that a previous module returned. ext is the extension of
the request, id the request information object. The return value is a
response mapping.
