code: private function writeMsoDrawingGroup()
      {
          // write the Escher stream if necessary
          if (isset($this->escher)) {
              $writer = new Escher($this->escher);
              $data = $writer->close();
  
              $record = 0x00EB;
              $length = strlen($data);
              $header = pack('vv', $record, $length);
  
              return $this->writeData($header . $data);
          }
  
          return '';
      }
docs: Writes the MSODRAWINGGROUP record if needed. Possibly split using CONTINUE records.