Checks to see if a selection is a valid index or choice of a combo
        preference

def change_combo_val(self, new_val):
        """
        Checks to see if a selection is a valid index or choice of a combo
        preference
        """
        choice_obj = self._intern.value
        assert isinstance(self._intern.value, PrefChoice), 'must be a choice'
        return choice_obj.get_tuple()