private function buildNetscapeExtension()
    {
        $extension = "\x21";
        $extension .= "\xFF";
        $extension .= "\x0B";
        $extension .= 'NETSCAPE2.0';
        $extension .= "\x03";
        $extension .= "\x01";
        $extension .= pack('v', $this->loops);
        $extension .= "\x00";

        return $extension;
    }