2.7.7-2 UNDO to Reverse Control Actions

Any user action should be immediately reversible by an UNDO command.

Additional Information:
UNDO itself should be reversible, so that a second UNDO action will do again whatever was just undone. Even with an UNDO capability, however, a user may make an irretrievable mistake, if succeeding actions intervene before a prior destructive action is noticed. If a user is too hasty in confirming a destructive action, and realizes the mistake right away (i.e., before taking another action), then an UNDO action might be taken to reverse the damage.