Summary: This is a fairly common question but I think it's the right product
behavior, document it so I can reference the docs next time it comes up.
Test Plan: Generated and read documentation.
Reviewers: btrahan, jungejason
Reviewed By: jungejason
CC: aran, jungejason
Maniphest Tasks: T735
Differential Revision: https://secure.phabricator.com/D1310
