`Event`’s definition

event.swift

enum Event<Output, Failure: Error> {
	case completion(Subscribers.Completion<Failure>) /// (1) Combine already tucks
	/// away completion events in their `Subscribers.Completion<Failure>` enumeration.
	/// We just wrap it as an associated value in the `Event.completion` case.

	case value(Output) /// (2) Any non-completion `Event` represents an emitted value.
	/// So, we place it in a `.value` case.
}