The context binding of children is the same for repeat and group, so I'll dig
into that one first.
First try without attribute-based repeats is in bug 269132.
Current status is that basic functionality is checked in. We still need support
for copy, itemset, etc., and of course attribute-based repeats.
itemset is part of bug 270572.
Depends on select, bug 270572, as it implements <itemset>.