Type: Integer
If the notification was registered by the Object class beginClassNotificationForIF, beginClassesNotificationForIF, or beginNotificationForIF method, the read-only featureNumber property of the Notification class contains the identifying number of the interface method that was mapped by the subscriber to receive an event notification.
If the notification was registered by the Object class beginClassNotification, beginClassesNotification, or beginNotification method, this property contains zero (0).