UserAgent: Mozilla/5.0 (X11; CrOS x86_64 10176.61.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/64.0.3282.122 Safari/537.36
Platform: 10176.61.0 (Official Build) beta-channel zako

Steps to reproduce the problem:
1. Open the Settings app
2. Search for [input methods]
3. Click [Manage input methods]

What is the expected behavior?
All of the available options should be adequately documented, including descriptions of their distinguishing behavior.

That documentation could appear in the Settings app, the system Help app, or the Chromebook Help center (https://support.google.com/chromebook).

What went wrong?
The documentation for the "US International" keyboard in the Chromebook Help center mentions the accent marks it makes available, but not the letters to which they apply, and does not mention the other 3rd-level characters it enables.

The "US International (PC)" and "US Extended" options appear to be completely undocumented.
(The former may be the one added in response to https://bugs.chromium.org/p/chromium/issues/detail?id=718368. I have no idea about the latter.)

Did this work before? N/A 

Chrome version: 64.0.3282.122  Channel: n/a
OS Version: 10176.61.0
Flash Version: