XLSXWriter::buildWorkbookXML PHP Method

    protected function buildWorkbookXML()
    {
        $i = 0;
        $workbook_xml = "";
        $workbook_xml .= '<?xml version="1.0" encoding="UTF-8" standalone="yes"?>' . "\n";
        $workbook_xml .= '<workbook xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main" xmlns:r="http://schemas.openxmlformats.org/officeDocument/2006/relationships">';
        $workbook_xml .= '<fileVersion appName="Calc"/><workbookPr backupFile="false" showObjects="all" date1904="false"/><workbookProtection/>';
        $workbook_xml .= '<bookViews><workbookView activeTab="0" firstSheet="0" showHorizontalScroll="true" showSheetTabs="true" showVerticalScroll="true" tabRatio="212" windowHeight="8192" windowWidth="16384" xWindow="0" yWindow="0"/></bookViews>';
        $workbook_xml .= '<sheets>';
        foreach ($this->sheets as $sheet_name => $sheet) {
            $workbook_xml .= '<sheet name="' . self::xmlspecialchars($sheet->sheetname) . '" sheetId="' . ($i + 1) . '" state="visible" r:id="rId' . ($i + 2) . '"/>';
            $i++;
        }
        $workbook_xml .= '</sheets>';
        $workbook_xml .= '<calcPr iterateCount="100" refMode="A1" iterate="false" iterateDelta="0.001"/></workbook>';
        return $workbook_xml;
    }