How to Undo a Mistake While Typing on a Mac

What you need: A Mac and a box on a website, an email or a document where you were typing and something changed that you did not want, such as words that disappeared.

1. Stop typing as soon as you notice the change you did not want. Anything you type after it must be undone first.
2. Click once inside the box, email or document where the change happened. A thin blinking line (the text cursor) appears.
3. Hold down the Command key (marked with the ⌘ symbol, beside the space bar). While holding it, press the Z key once (the first letter at the left end of the bottom row of letters), then let go of both keys. The most recent change is reversed.
4. Look at the words. If they are not all back yet, hold down Command and press Z once more. Repeat until the words are back, then stop, because each further press reverses an earlier change too.

Expected result: The words are back the way they were before the change.