More questions about contextual reference nodes

[Boris Zbarsky]

I have two questions about 
http://www.w3.org/TR/selectors-api2/#determine-contextual-reference-nodes

1)  What are the use cases for supplying more than one contextual 
reference node, exactly?  It seems weird to allow more than one node to 
match :scope.

2)  If we do want to allow the multiple node thing, can we please do it 
in IDL instead of the (currently pretty vague) prose?  Something like:

  Element querySelector(in DOMString selectors,
                        in optional Element refElement);
  Element querySelector(in DOMString selectors,
                        in optional NodeList refElements);
  Element querySelector(in DOMString selectors,
                        in optional sequence<Element> refElements);

or some such?  It's not quite clear to me whether we want a 
"sequence<Element>" or a "T[]"; that's worth checking.  In either case, 
the prose will need to define what happens with the NodeList or 
sequence/array cases, but there will be no ambiguity about how one gets 
Elements out of what's passed in.  The one difference is that in the 
array case if non-elements are present in the array an exception will be 
thrown.  I think that's fine, myself.

-Boris