This post is part of a series about new changes in XI 2.1. See also:
Raw events were introduced in XI 2.0 to allow clients to track direct device data, before the server gets its hands on it. The prime target for these was games that needed relative mouse events.
However, there was one flaw with raw events: they were delivered either to the root window or to the grabbing client only. Which made them less-than-useful, since grabs are virtually everywhere: active grabs by clients, passive grabs whenever a popup or dropdown menu appears, implicit grabs whenever the button is down.
This behaviour changes in XI 2.1. If a client announces support for XI 2.1, it will get raw events delivered to the root window at all times.
The second change to raw event behaviour is that the events now have the sourceid set (Bug 34420). The libXi interface catered for this but we never sent the value down the wire. This is fixed now in XI 2.1.