If routingKey is provided when publishing a message, the message will be delivered only to peers that have provided the same routing key or no routing key during subscription. If routingKey is provided when subscribing for a topic, only messages that have been published with a matching routing key or no routing key at all will be received by the subscriber. If target is provided when publishing a message, the message will be delivered only to subscribers for which all properties of the target object match the respective fields on the subscribers identity. If target is provided when subscribing for a topic, the provided object will be compared to the identity of the publishers of the messages and only if they match will the messages be received by the subscriber.