code: private function writeHeader()
      {
          $record = 0x0014; // Record identifier
  
          /* removing for now
          // need to fix character count (multibyte!)
          if (strlen($this->phpSheet->getHeaderFooter()->getOddHeader()) <= 255) {
              $str      = $this->phpSheet->getHeaderFooter()->getOddHeader();       // header string
          } else {
              $str = '';
          }
          */
  
          $recordData = StringHelper::UTF8toBIFF8UnicodeLong($this->phpSheet->getHeaderFooter()->getOddHeader());
          $length = strlen($recordData);
  
          $header = pack('vv', $record, $length);
  
          $this->append($header . $recordData);
      }
docs: Store the header caption BIFF record.