A tag envelope field is set by your requestor application to identify the request event that it is sending. When a server application receives the request event and prepares the reply event, it ensures that the same tag field is set for the reply as was received on the request event. If your requestor sends several different request events, it should set each with a different tag field. When your requestor receives a reply event, it can check the tag field to determine the original request with which the reply is associated.