The register method is used to ask the system to request a new endpoint for notifications. This method has been superceded by PushManager.subscribe().
The registrations method is used to ask the system about existing push endpoint registrations.
The unregister() method was used to ask the system to unregister and delete the specified endpoint. In the updated API, a subscription is can be unregistered via the PushSubscription.unsubscribe() method.