code: private function writeMarginLeft()
      {
          $record = 0x0026; // Record identifier
          $length = 0x0008; // Bytes to follow
  
          $margin = $this->phpSheet->getPageMargins()->getLeft(); // Margin in inches
  
          $header = pack('vv', $record, $length);
          $data = pack('d', $margin);
          if (self::getByteOrder()) { // if it's Big Endian
              $data = strrev($data);
          }
  
          $this->append($header . $data);
      }
docs: Store the LEFTMARGIN BIFF record.