NSUndoManagerWillUndoChange
Posted just before an undo manager performs an undo operation.
Declaration
static let NSUndoManagerWillUndoChange: NSNotification.NameDiscussion
If you invoke undo() or undoNestedGroup(), this notification is posted. The notification object is the UndoManager object. This notification doesn’t contain a userInfo dictionary.
The system posts this notification on the actor, thread, or dispatch queue that calls undo().