How to I implement with FO lists like

I.
I.a.
I.a.a.
I.b.
I.b.a.
I.b.b.
I.b.c.

II.
II.a.
etc...

Silly example, - I do not care about the exact symbols used, only
that there should be support for branching.

thanx

-- 
Eric Smith

 XSL-List info and archive:  http://www.mulberrytech.com/xsl/xsl-list