XLSXWriter::buildContentTypesXML PHP Method

    protected function buildContentTypesXML()
    {
        $content_types_xml = "";
        $content_types_xml .= '<?xml version="1.0" encoding="UTF-8"?>' . "\n";
        $content_types_xml .= '<Types xmlns="http://schemas.openxmlformats.org/package/2006/content-types">';
        $content_types_xml .= '<Override PartName="/_rels/.rels" ContentType="application/vnd.openxmlformats-package.relationships+xml"/>';
        $content_types_xml .= '<Override PartName="/xl/_rels/workbook.xml.rels" ContentType="application/vnd.openxmlformats-package.relationships+xml"/>';
        foreach ($this->sheets as $sheet_name => $sheet) {
            $content_types_xml .= '<Override PartName="/xl/worksheets/' . $sheet->xmlname . '" ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.worksheet+xml"/>';
        }
        if (!empty($this->shared_strings)) {
            $content_types_xml .= '<Override PartName="/xl/sharedStrings.xml" ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.sharedStrings+xml"/>';
        }
        $content_types_xml .= '<Override PartName="/xl/workbook.xml" ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.sheet.main+xml"/>';
        $content_types_xml .= '<Override PartName="/xl/styles.xml" ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.styles+xml"/>';
        $content_types_xml .= '<Override PartName="/docProps/app.xml" ContentType="application/vnd.openxmlformats-officedocument.extended-properties+xml"/>';
        $content_types_xml .= '<Override PartName="/docProps/core.xml" ContentType="application/vnd.openxmlformats-package.core-properties+xml"/>';
        $content_types_xml .= "\n";
        $content_types_xml .= '</Types>';
        return $content_types_xml;
    }