Notifications represent resumable exceptional conditions that are non-fatal, and for information purposes only.
By default Notifications are sent to the trace device if not handled, though once again this is up to the SessionManager, which can override #onUnhandledNotification: as appropriate.
On a development system, the trace device is the Transcript. The default run-time trace device is the kernel provided one (i.e. that to which output is written by OutputDebugString()).
The class Notification, which like Error contains a displayable description, represents the most general form of notification. Again it is not normally necessary to subclass Notification.