private function sanitize($st){
    $st = trim((string)$st);
    if ( strpos($st, ';') !== false ){
      return '';
    }
    if ( strpos($st, '<') !== false ){
      return '';
    }
    if ( strpos($st, '"') !== false ){
      return '';
    }
    if ( strpos($st, "'") !== false ){
      return '';
    }
    return $st;
  }