code: def list_extra_features(self):
          '''
          Returns
          -------
          List of dicts.  One dict for each document, keys are metadata, values are counts
          '''
          return FeatureLister(self._mX,
                               self._metadata_idx_store,
                               self.get_num_docs()).output(f list_extra_features(self):
          '''
          Returns
          -------
          List of dicts.  One dict for each document, keys are metadata, values are counts
          '''
          return FeatureLister(self._mX,
                               self._metadata_idx_store,
                               self.get_num_docs()).output()
docs: Returns
          -------
          List of dicts.  One dict for each document, keys are metadata, values are counts