Register a regex for processing HTTP POST
        requests.  If the callback is None, any
        existing registration is removed.

        The callback will be called as:

            callback(path, postmap)

def register_post(self, regex, callback):
        """
        Register a regex for processing HTTP POST
        requests.  If the callback is None, any
        existing registration is removed.

        The callback will be called as:

            callback(path, postmap)
    """
        if callback is None:                                                                    # pragma: no cover
            if regex in self.post_registrations:
                del self.post_registrations[regex]
        else:
            self.post_registrations[regex] = (re.compile(regex), callback)