[Zope] propertyIds() of a ZClass propertysheet

[Kenneth Ellested]

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