docs: def passes(self, value):
          """Does the given value pass this constraint?
  
          :return: True,None if so; False,<expected> if not
          :rtype: tuple
          """
          try:
              if self._op.compare(value, self.value):
                  return True, None
              else:
                  return False, self.value
          except ValueError as err:
              return False, str(err)