private function writeBookViews(XMLWriter $objWriter, Spreadsheet $spreadsheet)
    {
        // bookViews
        $objWriter->startElement('bookViews');

        // workbookView
        $objWriter->startElement('workbookView');

        $objWriter->writeAttribute('activeTab', $spreadsheet->getActiveSheetIndex());
        $objWriter->writeAttribute('autoFilterDateGrouping', '1');
        $objWriter->writeAttribute('firstSheet', '0');
        $objWriter->writeAttribute('minimized', '0');
        $objWriter->writeAttribute('showHorizontalScroll', '1');
        $objWriter->writeAttribute('showSheetTabs', '1');
        $objWriter->writeAttribute('showVerticalScroll', '1');
        $objWriter->writeAttribute('tabRatio', '600');
        $objWriter->writeAttribute('visibility', 'visible');

        $objWriter->endElement();

        $objWriter->endElement();
    }