@Override
    public void swapState(Routable rhs) {
        super.swapState(rhs);
        if (rhs instanceof DocumentMessage) {
            DocumentMessage msg = (DocumentMessage)rhs;

            DocumentProtocol.Priority pri = this.priority;
            this.priority = msg.priority;
            msg.priority = pri;
        }
    }
Creates and returns a reply to this message.

@return The created reply.
documentapi/src/main/java/com/yahoo/documentapi/messagebus/protocol/DocumentMessage.java