Normally this method is only called for the benefit of the GoUndoManager to record larger or more complex state before a change than can easily or efficiently be passed as the "old" or "previous" value in a call to Changed. This method does nothing if SuspendsUpdates is true. If you intend to turn on SuspendsUpdates for a while, to reduce the overhead of repeated notifications, you probably should call this method first and make sure the CopyOldValueForUndo and CopyNewValueForRedo methods can remember all of the relevant state before the unrecorded changes occur.