Box\Spout\Writer\XLSX\Helper\FileSystemHelper::createContentTypesFile PHP Method

    public function createContentTypesFile($worksheets)
    {
        $contentTypesXmlFileContents = <<<EOD
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Types xmlns="http://schemas.openxmlformats.org/package/2006/content-types">
    <Default ContentType="application/xml" Extension="xml"/>
    <Default ContentType="application/vnd.openxmlformats-package.relationships+xml" Extension="rels"/>
    <Override ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.sheet.main+xml" PartName="/xl/workbook.xml"/>
EOD;
        /** @var Worksheet $worksheet */
        foreach ($worksheets as $worksheet) {
            $contentTypesXmlFileContents .= '<Override ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.worksheet+xml" PartName="/xl/worksheets/sheet' . $worksheet->getId() . '.xml"/>';
        }
        $contentTypesXmlFileContents .= <<<EOD
    <Override ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.styles+xml" PartName="/xl/styles.xml"/>
    <Override ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.sharedStrings+xml" PartName="/xl/sharedStrings.xml"/>
    <Override ContentType="application/vnd.openxmlformats-package.core-properties+xml" PartName="/docProps/core.xml"/>
    <Override ContentType="application/vnd.openxmlformats-officedocument.extended-properties+xml" PartName="/docProps/app.xml"/>
</Types>
EOD;
        $this->createFileWithContents($this->rootFolder, self::CONTENT_TYPES_XML_FILE_NAME, $contentTypesXmlFileContents);
        return $this;
    }