def add_to_cat_group(self, cat, cat_group, def_name):
self.cat_groups.setdefault(cat, {}).setdefault(cat_group, deque()).append(def_name)<EOL>
Associate the provided rule definition name ``def_name`` with the
        category group ``cat_group`` in the category ``cat``.

        :param str cat: The category the rule definition was declared in
        :param str cat_group: The group within the category the rule belongs to
        :param str def_name: The name of the rule definition