code: def _validate_validator(self, validator, field, value):
          
          if isinstance(validator, _str_type):
              validator = self.__get_rule_handler('validator', validator)
              validator(field, value)
          elif isinstance(validator, Iterable):
              for v in validator:
                  self._validate_validator(v, field, value)
          else:
              validator(field, value, self._error)
docs: {'oneof': [
                  {'type': 'callable'},
                  {'type': 'list',
                   'schema': {'oneof': [{'type': 'callable'},
                                        {'type': 'string'}]}},
                  {'type': 'string'}
                  ]}