Emit triggers the handlers of listeners that match the event, passing the event to them.

Listen adds a listener to receive events on the default emitter.

Unlisten removes a listener from receiving events on the default emitter.

Emitter is a collection of Listeners that you can Emit events to.

Listener wraps an event handler callback, optionally specifying how it receives events from an Emitter.

Event interface is used to identify events.

Signal is a builtin event that is just a name with no other payload.