docs: def _label_from_kvlayer(self, key, val):
          '''Make a label from a kvlayer row.
          '''
          (content_id1, content_id2, annotator_id,
           inverted_epoch_ticks) = key
          epoch_ticks = time_complement(inverted_epoch_ticks)
  
          rel_strength, meta = cbor.loads(val)
          return RelationLabel(content_id1, content_id2, annotator_id,
                               RelationStrength(rel_strength),
                               epoch_ticks=epoch_ticks, meta=meta)