"edit undo" for a GUI form

http://www.chrisgreaves.com/Downloads/GUIundo.zip is a link to a ZIPped file you can download, inspect and adapt.
It represents a simple model for providing an Edit-Undo facility on GUI forms.

In my real-world situation we had a GUI form with several interlocking options; changing this and that meant that those were modified.

I decided to permit the user to reverse successive decisions back to a valid restart point.