docs: def characterize(cls, record):
          """Load the record in a concrete subclass of this type.
          """
          classes = list(cls.__subclasses__())
          if not isabstract(cls):
              classes.append(cls)
          for subclass in classes:
              entity = subclass(record)
              if entity.is_valid():
                  return entity
          raise RuntimeError("could not find the type for '{}'".format(record.id))