docs: def netengine(self):
          """ access netengine instance """
          # return None if no backend chosen yet
          if not self.backend:
              return None
  
          # init instance of the netengine backend if not already done
          if not self.__netengine:
              NetengineBackend = self.backend_class
              arguments = self._build_netengine_arguments()
  
              self.__netengine = NetengineBackend(**arguments)
  
          # return netengine instance
          return self.__netengine