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# checkpoint

An identifier for a message about an undo manager reaching a checkpoint.

```
static var checkpoint: NotificationCenter.BaseMessageIdentifier<UndoManager.CheckpointMessage> { get }
```

## Discussion

Use this identifier with [`NotificationCenter`](/documentation/Foundation/NotificationCenter)’s `addObserver(of:for:using:)` or `messages(of:for:bufferSize:)` methods to observe messages of type [`UndoManager.CheckpointMessage`](/documentation/Foundation/UndoManager/CheckpointMessage).

---

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