class with `tf.experimental.ExtensionType` as its base, and use type
        annotations to specify the type for each field. E.g.: `python class
        MaskedTensor(tf.experimental.ExtensionType): values: tf.Tensor mask:
        tf.Tensor` The `tf.ExtensionType` base class works similarly to
        [`typing.NamedTuple`](https://docs.python.org/3/library/typing.html#typing.NamedTuple)