public static function get_files_returns() {
        return new external_single_structure(
            array(
                'parents' => new external_multiple_structure(
                    new external_single_structure(
                        array(
                            'contextid' => new external_value(PARAM_INT, ''),
                            'component' => new external_value(PARAM_COMPONENT, ''),
                            'filearea'  => new external_value(PARAM_AREA, ''),
                            'itemid'    => new external_value(PARAM_INT, ''),
                            'filepath'  => new external_value(PARAM_TEXT, ''),
                            'filename'  => new external_value(PARAM_TEXT, ''),
                        )
                    )
                ),
                'files' => new external_multiple_structure(
                    new external_single_structure(
                        array(
                            'contextid' => new external_value(PARAM_INT, ''),
                            'component' => new external_value(PARAM_COMPONENT, ''),
                            'filearea'  => new external_value(PARAM_AREA, ''),
                            'itemid'   => new external_value(PARAM_INT, ''),
                            'filepath' => new external_value(PARAM_TEXT, ''),
                            'filename' => new external_value(PARAM_TEXT, ''),
                            'isdir'    => new external_value(PARAM_BOOL, ''),
                            'url'      => new external_value(PARAM_TEXT, ''),
                            'timemodified' => new external_value(PARAM_INT, ''),
                            'timecreated' => new external_value(PARAM_INT, 'Time created', VALUE_OPTIONAL),
                            'filesize' => new external_value(PARAM_INT, 'File size', VALUE_OPTIONAL),
                            'author' => new external_value(PARAM_TEXT, 'File owner', VALUE_OPTIONAL),
                            'license' => new external_value(PARAM_TEXT, 'File license', VALUE_OPTIONAL),
                        )
                    )
                )
            )
        );
    }