message: Minor update in docstring of `Input` to address user confusion.
diff: @@ -317,14 +317,18 @@ def Input( # pylint: disable=invalid-name
  Note that even if eager execution is enabled,
  `Input` produces a symbolic tensor-like object (i.e. a placeholder).
  - This symbolic tensor-like object can be used with other
  - TensorFlow ops, as such:
  + This symbolic tensor-like object can be used with lower-level
  + TensorFlow ops that take tensors as inputs, as such:
  ```python
  x = Input(shape=(32,))
  - y = tf.square(x)
  + y = tf.square(x) # This op will be treated like a layer
  + model = Model(x, y)
  ```
  + (This behavior does not work for higher-order TensorFlow APIs such as
  + control flow and being directly watched by a `tf.GradientTape`).
  +
  However, the resulting model will not track any variables that were
  used as inputs to TensorFlow ops. All variable usages must happen within
  Keras layers to make sure they will be tracked by the model's weights.
  