public static function message_search_users_parameters() {
        return new external_function_parameters(
            array(
                'userid' => new external_value(PARAM_INT, 'The id of the user who is performing the search'),
                'search' => new external_value(PARAM_RAW, 'The string being searched'),
                'limitfrom' => new external_value(PARAM_INT, 'Limit from', VALUE_DEFAULT, 0),
                'limitnum' => new external_value(PARAM_INT, 'Limit number', VALUE_DEFAULT, 0),
            )
        );
    }