public static function get_content_pages_viewed_parameters() {
        return new external_function_parameters (
            array(
                'lessonid' => new external_value(PARAM_INT, 'lesson instance id'),
                'lessonattempt' => new external_value(PARAM_INT, 'lesson attempt number'),
                'userid' => new external_value(PARAM_INT, 'the user id (empty for current user)', VALUE_DEFAULT, null),
            )
        );
    }