message: Link to the optimizer base class for examples.
diff: # limitations under the License.
  # ==============================================================================
  # pylint: disable=invalid-name
  -"""Built-in optimizer classes."""
  +"""Built-in optimizer classes.
  +
  +For more examples see the base class `tf.keras.optimizers.Optimizer`.
  +"""
  from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  