code: def allows_simple_recursion(self):
          
          rec_level = self.aggregate.config["recursionlevel"]
          if rec_level >= 0 and self.recursion_level >= rec_level:
              log.debug(LOG_CHECK, "... no, maximum recursion level reached.")
              return False
          if self.extern[0]:
              log.debug(LOG_CHECK, "... no, extern.")
              return False
          return True
docs: Check recursion level and extern status.