In-response-to-base:
Date: Wed, 31 May 1995 07:35:39 GMT
From: Nigel Hutchison (nwoh@software-ag.de)

Server Callbacks - to support Notification

HTTP/1.1 200 OK Date: Mon, 21 May 2012 09:07:23 GMT Server: Apache/2.2.6 (Fedora) Last-Modified: Thu, 30 Oct 1997 19:45:03 GMT ETag: "248437-1fc-59212dc0" Accept-Ranges: bytes Content-Length: 508 Connection: close Content-Type: text/html; charset=UTF-8

Suppose two or more users are working on the same object.
1. It is advantageous for some scenarios that the each 
   user is made aware of this and the users are identified.
2. It is even more advantageous that when one user _updates_
   the object that that the other users are notified.
   Depending on the scenario the client might automatically
   update the users view of it.

This does not scale well for the Internet but would be 
interesting for a corporate WAN using web technology