[Zope] Populating selection-style property with list of folders

[Gary Duke Speer]

Hi -
Perhaps someone can help ...
What dtml method produces a list of folders that is compatible with the
'selection' property type?

My goal is to add a proprty to the ZMI property sheet for a folder that is
a drop-down listing of available subfolders.

I have no problem creating a property called ThemeFolder of type
'selection' that points to another property called FolderList of type
'lines' that has the names of the folders.

The documentation says the selection can come from either a property or a
method.

When the selection property it is pointed to a DTML Method called
DTMLFolderList with the code:
_dtml-in "objectValues(['Folder'])"_ _dtml-var id_
_/dtml-in_

It reports an error.
I have tried _dtml-var objectItems_ and several other variations with
similar results.
What dtml method produces a list that is compatible with the 'selection'
property type?

I'm stumped.  Thank you for any assistance you can provide or point me to
expanded documentation!  A full surch of the mailing list archives didn't
report any suggestions.
Thank you,
Gary