if seems that this event is triggered when undo'ing the contents of a
form, but before the data is undone
simplified example,

if I have txtA with a value of 1 and its afterUpdate event that sets
txtB to apple
now I change txtA to a value of 2, and the afterUpdate sets txtB to
banana
now if I click a button that does me.undo, txtA returns to 1
and I was hoping to use the onUndo event to set txtB to apple, but
txtA is still 2 when that event fires
what event can I use to set txtB to apple

note, that there are 3 ways to undo the contents of a form, and if
possible, I'd like to use just one event to deal with resetting txtB