public static function get_files_parameters() {
        return new external_function_parameters(
            array(
                'contextid'    => new external_value(PARAM_INT, 'context id Set to -1 to use contextlevel and instanceid.'),
                'component'    => new external_value(PARAM_TEXT, 'component'),
                'filearea'     => new external_value(PARAM_TEXT, 'file area'),
                'itemid'       => new external_value(PARAM_INT, 'associated id'),
                'filepath'     => new external_value(PARAM_PATH, 'file path'),
                'filename'     => new external_value(PARAM_TEXT, 'file name'),
                'modified'     => new external_value(PARAM_INT, 'timestamp to return files changed after this time.', VALUE_DEFAULT, null),
                'contextlevel' => new external_value(PARAM_ALPHA, 'The context level for the file location.', VALUE_DEFAULT, null),
                'instanceid'   => new external_value(PARAM_INT, 'The instance id for where the file is located.', VALUE_DEFAULT, null)

            )
        );
    }