def _validate_oneof(self, definitions, field, value):
        """ {'type': 'list', 'logical': 'oneof'} """
        valids, _errors = \
            self.__validate_logical('oneof', definitions, field, value)
        if valids != 1:
            self._error(field, errors.ONEOF, _errors,
                        valids, len(definitions))
{'type': 'list', 'logical': 'oneof'}