Class Reply. Used for a Command that is a Reply in a Request-Reply exchange. Brighter supports publish-subscribe as its main approach to producers and consumers, but it is possible to support request-reply semantics as well. The key is that the sender must include a ReplyAddress in the Request (the IAmAMessageMapper then populates that into the MessageHeader as the replyTo address). When we create a Reply then we set the ReplyAddress from the Request onto the Reply and the IAmAMessageMapper for the Reply sets this as the topic so that it is routed correctly.