NSUndoManagerCheckpoint
Posted whenever an undo manager opens or closes an undo group (except when it opens a top-level group) and when checking the redo stack.
Declaration
static let NSUndoManagerCheckpoint: NSNotification.NameDiscussion
The notification object is the NSUndoManager object. This notification doesn’t contain a userInfo dictionary.
The system posts this notification on the actor, thread, or dispatch queue that calls beginUndoGrouping(), endUndoGrouping(), or canRedo.