private function unhandledElement($type, $line, $element) {
    // warn only about unknown and missed elements, not about unuseful
    if (!in_array($element['id'], $this->unuseful_elements)) {
      $this->warning('Unhandled '.$type.' element ['.basename(__FILE__).':'.$line.'] ('.$element['id'].'::'.$element['id_name'].' ['.$element['length'].' bytes]) at '.$element['offset']);
    }

    // increase offset for unparsed elements
    if (!isset($element['data'])) {
      $this->current_offset = $element['end'];
    }
  }