Thank you Richard, this was brilliant. I learned new techniques. Like usual, very elegant solutions.
I will be implementing the undo this week.

I would like to see two things if possible:

1- the use of tabledef to guard against future table changes as you mentioned in the video.
2- explore the possibility of turning this into a seminar/template where it could be implemented on an existing database. I know I would pay good money for that.

Thanks again for great developer lesson.