'event' for a component event (the spec's events), 'state' for a state change, 'initialized' when it
finished loading, 'selected' when the user switched to this component's tab, 'closed' when the user closed it.
OptionalNameThe event type or state path.
OptionalPayloadThe event payload or new state value (already untyped JSON-ish; the channel bounds it).
Something the user did inside a rendered component, reported by the host to the channel.