protected function filter_rights($a_folders, $rights)
    {
        $regex = '/('.$rights.')/';

        foreach ($a_folders as $idx => $folder) {
            if ($this->folder_namespace($folder) == 'personal') {
                continue;
            }

            $myrights = join('', (array)$this->my_rights($folder));

            if ($myrights !== null && !preg_match($regex, $myrights)) {
                unset($a_folders[$idx]);
            }
        }

        return $a_folders;
    }