I was revising this answer, and decided not to go through with the changes I was planning to make. I pressed Ctrl+Z, then clicked the Save Edit button, knowing that it would not add an additional revision (since the body of the post had not changed).
Surprisingly it let the revision go through, and added another revision identical to the original. The automated edit summary reads:
added 15 characters in body
even though there are no additional characters. What usually happens if you click "Save Edit" without changing the body of the post at all is nothing (no additional revisions).