Register a class with a function.

        :param klass: The class
        :type klass: class

        :param callback: The callable
        :type callback: callable

        :param name: The short name
        :type name: str

def register(self, klass, callback, name="default"):
        """
        Register a class with a function.

        :param klass: The class
        :type klass: class

        :param callback: The callable
        :type callback: callable

        :param name: The short name
        :type name: str
        """
        if klass not in self._definitions:
            self._definitions[klass] = {}

        self._definitions[klass][name] = callback