code: def validate(self, value):
          
          # check object type
          if not isinstance(value, list):
              raise tldap.exceptions.ValidationError(
                  "is not a list and max_instances is %s" %
                  self._max_instances)
          # check maximum instances
          if (self._max_instances is not None and
                  len(value) > self._max_instances):
              raise tldap.exceptions.ValidationError(
                  "exceeds max_instances of %d" %
                  self._max_instances)
          # check this required value is given
          if self._required:
              if len(value) == 0:
                  raise tldap.exceptions.ValidationError(
                      "is required")
          # validate the value
          for i, v in enumerate(value):
              self.value_validate(v)
docs: Validates value and throws ValidationError. Subclasses should override
          this to provide validation logic.