def custom_str(self, sc_expr_str_fn):
        """
        Works like MenuNode.__str__(), but allows a custom format to be used
        for all symbol/choice references. See expr_str().
        """
        return self._menu_comment_node_str(sc_expr_str_fn) \
               if self.item in _MENU_COMMENT else \
               self._sym_choice_node_str(sc_expr_str_fn)