code: private function writeNumFmt(XMLWriter $objWriter, NumberFormat $pNumberFormat, $pId = 0)
      {
          // Translate formatcode
          $formatCode = $pNumberFormat->getFormatCode();
  
          // numFmt
          if ($formatCode !== null) {
              $objWriter->startElement('numFmt');
              $objWriter->writeAttribute('numFmtId', ($pId + 164));
              $objWriter->writeAttribute('formatCode', $formatCode);
              $objWriter->endElement();
          }
      }
docs: Write NumberFormat.
  
  @param XMLWriter $objWriter XML Writer
  @param NumberFormat $pNumberFormat Number Format
  @param int $pId Number Format identifier