docs: def worker(self):
          """
          Returns the worker object for loading records for this record box.
          
          :return     <XOrbLookupWorker>
          """
          if self._worker is None:
              self._worker = XOrbLookupWorker(self.isThreadEnabled())
              self._worker.setBatchSize(self._batchSize)
              self._worker.setBatched(not self.isThreadEnabled())
              
              # connect the worker
              self.loadRequested.connect(self._worker.loadRecords)
              self._worker.loadingStarted.connect(self.markLoadingStarted)
              self._worker.loadingFinished.connect(self.markLoadingFinished)
              self._worker.loadedRecords.connect(self.addRecordsFromThread)
          
          return self._worker