XI2 relative motion events documentation

[Rendaw]

  Hello,
http://www.x.org/wiki/XI2 lists "Support for relative motion events" as 
a feature of XI2.  I've googled around quite a bit but I haven't been 
able to find any more information on this.  The spec doesn't seem to 
list anything related to it either.  The closest I've been able to find 
is valuators, but for the (my) master mouse, none seem to be relative.

I imagined, from reading that webpage, that I could get relative motion 
events for all cursor devices.  Is this, or something similar, 
possible?  Are there any webpages or resources that document this?

I'd appreciate any tips greatly.

Thanks,
Rendaw