private function writePrintGridlines()
    {
        $record = 0x002b; // Record identifier
        $length = 0x0002; // Bytes to follow

        $fPrintGrid = $this->phpSheet->getPrintGridlines() ? 1 : 0; // Boolean flag

        $header = pack('vv', $record, $length);
        $data = pack('v', $fPrintGrid);
        $this->append($header . $data);
    }