> > I'd like to modify it so that the root of the tree is fixed (as in the
> > help system), and so that only folders which do not have the 'hidden'
> > property set are shown.
I figured out the last part:
<!--#tree branches_expr="objectValues(['Folder'])"-->
<!--#unless hidden-->
<A HREF="<!--#var tree-item-url-->">
<!--#var title_or_id-->
</A>
<!--#/unless-->
<!--#/tree-->