docs: def check(self, defn):
          """Performs the uniqueness check against the value list
          maintained in this rule objects
          """
          val = getattr(defn, self.attr)
          if val is not None and val in self.val_list:
              self.messages.append(self.msg % str(val))
              # TODO self.messages.append("TBD location message")
              self.valid = False
          elif val is not None:
              self.val_list.append(val)
              log.debug(self.val_list)