code: private function readSharedFmla()
      {
          $length = self::getUInt2d($this->data, $this->pos + 2);
          $recordData = $this->readRecordData($this->data, $this->pos + 4, $length);
  
          // move stream pointer to next record
          $this->pos += 4 + $length;
  
          // offset: 0, size: 6; cell range address of the area used by the shared formula, not used for anything
          $cellRange = substr($recordData, 0, 6);
          $cellRange = $this->readBIFF5CellRangeAddressFixed($cellRange); // note: even BIFF8 uses BIFF5 syntax
  
          // offset: 6, size: 1; not used
  
          // offset: 7, size: 1; number of existing FORMULA records for this shared formula
          $no = ord($recordData[7]);
  
          // offset: 8, size: var; Binary token array of the shared formula
          $formula = substr($recordData, 8);
  
          // at this point we only store the shared formula for later use
          $this->sharedFormulas[$this->baseCell] = $formula;
      }
docs: Read a SHAREDFMLA record. This function just stores the binary shared formula in the reader,
  which usually contains relative references.
  These will be used to construct the formula in each shared formula part after the sheet is read.