docs: def check(self, defn, msg=None):
          """Uses the definitions slice() method to determine its start/stop
          range.
          """
          # Check enum does not contain boolean keys
          if (defn.slice().start != self.prevstop):
              self.messages.append(self.msg % str(defn.name))
              # TODO self.messages.append("TBD location message")
              self.valid = False
  
          self.prevstop = defn.slice().stop