private function writeWorkbookProtection(XMLWriter $objWriter, Spreadsheet $spreadsheet)
    {
        if ($spreadsheet->getSecurity()->isSecurityEnabled()) {
            $objWriter->startElement('workbookProtection');
            $objWriter->writeAttribute('lockRevision', ($spreadsheet->getSecurity()->getLockRevision() ? 'true' : 'false'));
            $objWriter->writeAttribute('lockStructure', ($spreadsheet->getSecurity()->getLockStructure() ? 'true' : 'false'));
            $objWriter->writeAttribute('lockWindows', ($spreadsheet->getSecurity()->getLockWindows() ? 'true' : 'false'));

            if ($spreadsheet->getSecurity()->getRevisionsPassword() != '') {
                $objWriter->writeAttribute('revisionsPassword', $spreadsheet->getSecurity()->getRevisionsPassword());
            }

            if ($spreadsheet->getSecurity()->getWorkbookPassword() != '') {
                $objWriter->writeAttribute('workbookPassword', $spreadsheet->getSecurity()->getWorkbookPassword());
            }

            $objWriter->endElement();
        }
    }