[Zope] Folder-specific metatypes?

[Nolan Darilek]

I'm working on a product in Python which implements a folder, but
restricts the metatypes of the objects which can be added. How,
exactly, do I go about doing this? I've tried overriding the
filtered_meta_types method, but I'm returning a list, and it seems
that I should return a list of dictionaries instead, but I'm not entirely sure
how the metatype is converted into a dictionary. I also noticed the
_product_meta_types variable, but rgreps of the zope code didn't
reveal anything about this variable. Am I on the right track with
these?

Thanks.