code: private function readDefault()
      {
          // offset 0; size: 2; recVer and recInstance
          $verInstance = Xls::getUInt2d($this->data, $this->pos);
  
          // offset: 2; size: 2: Record Type
          $fbt = Xls::getUInt2d($this->data, $this->pos + 2);
  
          // bit: 0-3; mask: 0x000F; recVer
          $recVer = (0x000F & $verInstance) >> 0;
  
          $length = Xls::getInt4d($this->data, $this->pos + 4);
          $recordData = substr($this->data, $this->pos + 8, $length);
  
          // move stream pointer to next record
          $this->pos += 8 + $length;
      }
docs: Read a generic record.