code: public function writeData($data)
      {
          if (strlen($data) - 4 > $this->limit) {
              $data = $this->addContinue($data);
          }
          $this->_datasize += strlen($data);
  
          return $data;
      }
docs: General storage function like append, but returns string instead of modifying $this->_data.
  
  @param string $data binary data to write
  
  @return string