private function _mod_folder_name(&$list, $folder, $new_name)
    {
        foreach ($list as $idx => $item) {
            if ($item['id'] == $folder) {
                $list[$idx]['name'] = $new_name;
                return true;
            }
            else if (!empty($item['folders'])) {
                if ($this->_mod_folder_name($list[$idx]['folders'], $folder, $new_name)) {
                    return true;
                }
            }
        }

        return false;
    }