Perform validation on ``value``. Raise a :exc:`ValidationError` if validation
        does not succeed.

def _validate(self, value):
        """Perform validation on ``value``. Raise a :exc:`ValidationError` if validation
        does not succeed.
        """
        errors = []
        kwargs = {}
        for validator in self.validators:
            try:
                r = validator(value)
                if not isinstance(validator, Validator) and r is False:
                    self.fail('validator_failed')
            except ValidationError as err:
                kwargs.update(err.kwargs)
                if isinstance(err.messages, dict):
                    errors.append(err.messages)
                else:
                    errors.extend(err.messages)
        if errors:
            raise ValidationError(errors, **kwargs)