code: def _validate_check_with(self, checks, field, value):
          
          if isinstance(checks, _str_type):
              try:
                  value_checker = self.__get_rule_handler('check_with', checks)
              # TODO remove on next major release
              except RuntimeError:
                  value_checker = self.__get_rule_handler('validator', checks)
                  warn(
                      "The 'validator' rule was renamed to 'check_with'. Please update "
                      "your schema and method names accordingly.",
                      DeprecationWarning,
                  )
              value_checker(field, value)
          elif isinstance(checks, Iterable):
              for v in checks:
                  self._validate_check_with(v, field, value)
          else:
              checks(field, value, self._error)
docs: {'oneof': [
                  {'type': 'callable'},
                  {'type': 'list',
                   'schema': {'oneof': [{'type': 'callable'},
                                        {'type': 'string'}]}},
                  {'type': 'string'}
                  ]}