public function filter(&$value) {
        $accepted_types = optional_param_array('accepted_types', '', PARAM_RAW);
        if (isset($value['children'])) {
            if (!empty($value['children'])) {
                $value['children'] = array_filter($value['children'], array($this, 'filter'));
            }
            return true; // always return directories
        } else {
            if ($accepted_types == '*' or empty($accepted_types)
                or (is_array($accepted_types) and in_array('*', $accepted_types))) {
                return true;
            } else {
                foreach ($accepted_types as $ext) {
                    if (preg_match('#'.$ext.'$#i', $value['title'])) {
                        return true;
                    }
                }
            }
        }
        return false;
    }