FDC3 for Web currently offers request/response message types for both the new PrivateChannel.addEventListener function and the deprecated PrivateChannel.onAddContextListener/onUnsubscribe/onDisconnect functions

The current message schema for privateChannelAddEventListenerRequest doesn't currently support registering listeners for all event types, where the API function does (by passing null for the type argument):

addEventListener(type: PrivateChannelEventTypes  | null, handler: EventHandler): Promise<Listener>;