Connects the given selector to this event.
Disconnects the given selector from this event.
Registers a live observer with this event.
Registers a live observer with this event. The method is called with the
observing function which receives the event's update messages, and the
method generates an opaque Disposable
instance, which may be used to
remove the observer eventually (through the dispose
method).
A rooted event does not have sources. This trait provides a simple implementation of
pull
which merely checks if this event has fired or not.