SELECT structures with lots of OPTIONs

I just read through
   http://lists.w3.org/Archives/Public/w3c-wai-ig/1997JulSep/0031.html

In general, I like the proposal and I think it just needs some more
detailed wording on the way axis/axes determine the hierarchy.

I have one concern:

> You know how you can nest lists with most windowing systems?  Like
> in NS bookmarks when you can have an arrow on the right which has a
> sublist; so that you can have a hierarchical organization for pick
> lists.

The way I understand it, SELECT are implemented as list boxes when
multiple-selection is used and as drop-down menu for single-selection.

I know that nested option menu is supported on most if not all
systems, but in order to support nested multiple list, one would have
to move from a single list boxes to a more powerful "outliner" widget
(like the one used on most systems to _manage_ the bookmark list in a
separate static window).

My concern is that there's going to be push-back from the implementors
because this requires non-trivial changes to their browser at a late
stage.