code: private function readClientTextbox()
      {
          // offset: 0; size: 2; recVer and recInstance
  
          // bit: 4-15; mask: 0xFFF0; recInstance
          $recInstance = (0xFFF0 & Xls::getUInt2d($this->data, $this->pos)) >> 4;
  
          $length = Xls::getInt4d($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 ClientTextbox record.