The added bonus of the current matching is that it does allow for the
selector to "leak" should you want that for whatever reason.
This isn't really important since this result can already be achieved in another manner,
using .compareDocumentPosition() or .contains() (in IE). However, leaving it "broken
by default because it would be hard to specify" doesn't really seem to mesh well.
True, though this would be significantly slower since the implementation
would match against all nodes in the whole document, only to have many
of them filtered out.
/ Jonas
