As always, Undo is available from the Edit menu and can also be invoked using the keyboard with Command-Z. Redo is also in the Edit menu and can be done with the Command-Shift-Z keyboard shortcut.
I have no earlier version available for testing, but am confident 9.2 is when the feature I've noted was added. I regularly invoke the Undo keyboard shortcut just as a habitual response to a mistake, and I never witnessed the behavior prior to 9.2.
[crarko adds: I tested this, and it works as described.]

