Bert, Roel -
After talking with a colleague it appears that you can
indeed not
"take away" permissions in a subfolder, all permissions are inherited.
Actually - you can. My smallwiki 1 (Squeak) does just that: its root
folder is viewable by all, and one of its subfolder is private. I
don't have direct access to its image right now, but as I remember the
key is to re-specify (override) a role's permissions on the subfolder.
Michal