View Source LiveQuery.Protocol.CallbackRegistered (LiveQuery v0.3.1)
Sent in response to a LiveQuery.Protocol.RegisterCallback call.
The callback's return value is discarded by the query.
The cb_key is used to identify the callback when unregistering it. It is namespaced to the client_pid.
That is, different clients can register callbacks with the same cb_key at the same time and they will not interfere with each other.