A Message sent to the current card when the Undo action changes. If there is a message handler by the same name in the message path, then it will be executed.
Message[]
Syntax:
undoChanged
Undoable actions include painting actions, deletion of objects, moving of controls, and editing actions in a field. When the user performs one of these actions, thus changing what happens as a result of choosing Edit → Undo from the menubar, LiveCode sends the undoChanged message to the current card.
Message handler[]
Examples:
on undoChanged global lastFieldState put field "Edit" into lastFieldState end undoChanged
Use the undoChanged Message handler to intercept the "Undo" menu item, providing your own Undo stack.