code: private function writeAutoFilterInfo()
      {
          $record = 0x009D; // Record identifier
          $length = 0x0002; // Bytes to follow
  
          $rangeBounds = Coordinate::rangeBoundaries($this->phpSheet->getAutoFilter()->getRange());
          $iNumFilters = 1 + $rangeBounds[1][0] - $rangeBounds[0][0];
  
          $header = pack('vv', $record, $length);
          $data = pack('v', $iNumFilters);
          $this->append($header . $data);
      }
docs: Write the AUTOFILTERINFO BIFF record. This is used to configure the number of autofilter select used in the sheet.