The node reference associated with the process.
The node reference associated with the process. A Some value indicates that
at least one instance view is playing, whereas a None value indicates that
there is no actively playing instance view at the moment.
The view must store a handle to its underlying model.
Registers a live observer with this observable.
Registers a live observer with this observable. The method is called with the
observing function which receives the observable's update message of type A, and the
method generates an opaque Disposable instance, which may be used to
remove the observer eventually (through the dispose method).