Update the change counter by indicating the kind of change.
A constant that indicates whether a change has been made, cleared, undone, or redone. See
UIDocumentChangeKind for more information.
Calling this method can affect the value returned by
hasUnsavedChanges. You should not need to call method this if you access an
UndoManager object from the
undoManager property (or assign a custom one to it) and register changes with the undo manager.
Tracking Changes and Autosaving