docs: def write_example_yaml(cls, dest, skip=()):
          """
          Write a file containing an example yaml string for a Serializable
          subclass.
          """
          # Make sure we can make an instance before we open a file.
          inst = cls.example_instance(skip=skip)
          with open(dest, 'w') as f:
              inst.to_yaml(stream=f, skip=skip)