XLSXWriter::buildWorkbookRelsXML PHP Method

    protected function buildWorkbookRelsXML()
    {
        $i = 0;
        $wkbkrels_xml = "";
        $wkbkrels_xml .= '<?xml version="1.0" encoding="UTF-8"?>' . "\n";
        $wkbkrels_xml .= '<Relationships xmlns="http://schemas.openxmlformats.org/package/2006/relationships">';
        $wkbkrels_xml .= '<Relationship Id="rId1" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/styles" Target="styles.xml"/>';
        foreach ($this->sheets as $sheet_name => $sheet) {
            $wkbkrels_xml .= '<Relationship Id="rId' . ($i + 2) . '" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/worksheet" Target="worksheets/' . $sheet->xmlname . '"/>';
            $i++;
        }
        if (!empty($this->shared_strings)) {
            $wkbkrels_xml .= '<Relationship Id="rId' . (count($this->sheets) + 2) . '" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/sharedStrings" Target="sharedStrings.xml"/>';
        }
        $wkbkrels_xml .= "\n";
        $wkbkrels_xml .= '</Relationships>';
        return $wkbkrels_xml;
    }