code: private function readPane()
      {
          $length = self::getUInt2d($this->data, $this->pos + 2);
          $recordData = $this->readRecordData($this->data, $this->pos + 4, $length);
  
          // move stream pointer to next record
          $this->pos += 4 + $length;
  
          if (!$this->readDataOnly) {
              // offset: 0; size: 2; position of vertical split
              $px = self::getUInt2d($recordData, 0);
  
              // offset: 2; size: 2; position of horizontal split
              $py = self::getUInt2d($recordData, 2);
  
              // offset: 4; size: 2; top most visible row in the bottom pane
              $rwTop = self::getUInt2d($recordData, 4);
  
              // offset: 6; size: 2; first visible left column in the right pane
              $colLeft = self::getUInt2d($recordData, 6);
  
              if ($this->frozen) {
                  // frozen panes
                  $cell = Coordinate::stringFromColumnIndex($px + 1) . ($py + 1);
                  $topLeftCell = Coordinate::stringFromColumnIndex($colLeft + 1) . ($rwTop + 1);
                  $this->phpSheet->freezePane($cell, $topLeftCell);
              }
              // unfrozen panes; split windows; not supported by PhpSpreadsheet core
          }
      }
docs: Read PANE record.