[Zope] propertyIds() of a ZClass propertysheet

How do I get the propertyIds() of a ZClass propertysheet (class, not instance) ? I have a ZClass with 90 properties, and I'd like to contain instances of these in a another ZClass (group container). From this container I'd like to make a manage page that can edit a user selected subset of properties in the contained ZClasses. So I thought that I could make a multiple selection (list) field in the container class, that select the properties I'd like to work with. To make it short - how can I access the ZClasses (products) definitions. Regards