What I was suggesting was not a popup expansion, but rather a "fold out"
expansion, like the kind you see in the MSWin file manager's directory tree
browser. See eg. http://www.ii.uib.no/~torgeir/work/outline.html for a
description of what I'm thinking about. The rendering method could vary from
browser to browser though.
-- Torgeir @ http://www.ii.uib.no/~torgeir/