Boolean value that indicates whether the next undo action is discardable.
- iOS 5.0+
- macOS 10.7+
- tvOS 9.0+
- watchOS 2.0+
YES if the action is discardable;
Specifies that the latest undo action may be safely discarded when a document can not be saved for any reason. These are typically actions that don’t affect persistent state.
An example might be an undo action that changes the viewable area of a document.