private function finalizeDefaultXmls()
    {
        $this->zip->addFromString('[Content_Types].xml', DefaultXml::CONTENT_TYPES);
        $this->zip->addFromString('docProps/core.xml',
            sprintf(DefaultXml::DOCPROPS_CORE, date(DATE_ISO8601), date(DATE_ISO8601)));
        $this->zip->addFromString('docProps/app.xml', DefaultXml::DOCPROPS_APP);
        $this->zip->addFromString('_rels/.rels', DefaultXml::RELS_RELS);
        $this->zip->addFromString('xl/_rels/workbook.xml.rels', DefaultXml::XL_RELS_WORKBOOK);
        $this->zip->addFromString('xl/workbook.xml', DefaultXml::XL_WORKBOOK);
    }