> In fact Vladimir's question (about the order of items within 
> a group) is not as well answered in the spec as I would like. 
> For each of the four grouping methods a procedural algorithm 
> is given, and the order of items in a group depends on you 
> understanding that when items are "added to a group", they 
> are added at the end. 

I've logged a bug on this:

http://www.w3.org/Bugs/Public/show_bug.cgi?id=9140

Regards,

Michael Kay
http://www.saxonica.com/
http://twitter.com/michaelhkay