public static function group_description() {
        return new external_single_structure(
            array(
                'id' => new external_value(PARAM_INT, 'group record id'),
                'name' => new external_value(PARAM_TEXT, 'multilang compatible name, course unique'),
                'description' => new external_value(PARAM_RAW, 'group description text'),
                'descriptionformat' => new external_format_value('description'),
                'idnumber' => new external_value(PARAM_RAW, 'id number'),
                'courseid' => new external_value(PARAM_INT, 'course id', VALUE_OPTIONAL),
            )
        );
    }