docs: def example_value(self):
          """
          If we're an instance of a Serializable, fall back to its
          `example_instance()` method.
          """
          from .serializable import Serializable
          inst = self._static_example_value()
          if inst is tr.Undefined and issubclass(self.klass, Serializable):
              return self.klass.example_instance()
          return inst