public static function get_filetypes_browser_data_returns() {

        $type = new external_single_structure([
            'key' => new external_value(PARAM_RAW, 'The file type identifier'),
            'name' => new external_value(PARAM_RAW, 'The file type name'),
            'selected' => new external_value(PARAM_BOOL, 'Should it be marked as selected'),
            'ext' => new external_value(PARAM_RAW, 'The file extension associated with the file type'),
        ]);

        $group = new external_single_structure([
            'key' => new external_value(PARAM_RAW, 'The file type group identifier'),
            'name' => new external_value(PARAM_RAW, 'The file type group name'),
            'selectable' => new external_value(PARAM_BOOL, 'Can it be marked as selected'),
            'selected' => new external_value(PARAM_BOOL, 'Should it be marked as selected'),
            'ext' => new external_value(PARAM_RAW, 'The list of file extensions associated with the group'),
            'expanded' => new external_value(PARAM_BOOL, 'Should the group start as expanded or collapsed'),
            'types' => new external_multiple_structure($type, 'List of file types in the group'),
        ]);

        return new external_single_structure([
            'groups' => new external_multiple_structure($group, 'List of file type groups'),
        ]);
    }