UndoManager.DidOpenUndoGroupMessage
A message that an undo manager sends after opening an undo group.
Declaration
struct DidOpenUndoGroupMessageOverview
The undo manager posts this message after you call beginUndoGrouping(). Because this is a “did”-style message, the undo manager sends the message after it opens the undo group.
Observe this message with the identifier didOpenUndoGroup, or specify its type directly to the addObserver(of:for:using:) method. The Subject of this message type is UndoManager.
This message interoperates with the notification NSUndoManagerDidOpenUndoGroup. The system notifies observers of the message when the NotificationCenter posts the notification. Similarly, the system notifies observers of the notification when it posts the message.