Merge "Clarify some UCE API docs" into sc-dev am: 3e2c6580a5 am: 0f802d8b34

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/14629229

Change-Id: I35efe1bb0a966e5537fd48a2acab48637e79c26b