[Zope] How to limit types of classes added to a Folder

I'm building a class (Site) that contains a Folder (Called screenshots) in which I will be storing instances of a class I've built called ScreenShot. The problem is that I can't figure out how to make the Folder interface in the ZMI limit the instance types to ScreenShot. In the Site class __init__ method, I have : OFS.Folder.manage_addFolder(self, 'screenshots', 'Screen Shots') self.screenshots.meta_types=('ScreenShot') However, this isn't working. I looked into the Folder class, and discovered that it's base class ObjectManager has a class property (not instance) called meta-types that is a tuple. do I need to sub-class Folder and set meta_types at the class level ? Russell Fine