Well, `handler` in this circumstance is e.g., ``RestContoller._handle_get``, ``RestController._handle_post``, etc... all of which have similar behavior that:

*  Tries to find an instance method defined that matches the HTTP method (e.g., ``def get_all``, ``def_one``, ``def post``).
*  When one isn't found, raises an ``HTTPNotFound``.

In this way, if you write a RestController like:

    class MyController(RestController):
    
        @pecan.expose()
        def post(self):
            return 'Hello, World!'

...it would respond to an ``HTTP POST``, but return a ``404 Not Found`` for any other type of request.  My code addition implements the check for a ``_lookup`` as a fallback for when the controller can't find a matching route based on the HTTP method itself.  If you look at the way ``_lookup``'s are routed in pecan's core routing (https://github.com/dreamhost/pecan/blob/master/pecan/routing.py#L35), the approach is very similar.