def add_behavior_for_pclass(self, cls):
        """
        Define an additional base class for the Python class created for a
        particular definition.

        :param type cls: The additional base class.  Its name must exactly
            match the name of a definition with a version matching this
            object's version.

        :return: ``None``
        """
        kind = cls.__name__
        for version in sorted(self.versions):
            try:
                self.spec.add_behavior_for_pclass(self.full_name(version, kind), cls)
            except NoSuchDefinition:
                pass
            else:
                return None
        raise NoSuchDefinition(kind)