union, intersect, and except

Why are the union, intersect, and except operations limited to working 
on sequences of nodes? It seems to me that they are perfectly well 
defined operations for sequences of arbitrary types, and that these 
three operators should be declared to work on sequences of item type. If 
there's no good reason for limiting them to node()*, I would ask that 
the signatures of these operators be revised to item()* instead.

--
Elliotte Rusty Harold