[Zope] Creating attributes in ZClass instances

I have a ZClass named Event. Event objects need to keep a list of people signed up for them, so they had a lines property named 'people'. But lines properties have odd semantics, and I want to store arbitrary objects rather than strings (i.e. it shouldn't be edited through the web like a lines property is). So I would like for the 'people' attributes of Event objects to be regular Python lists. It seems that I should create this attribute in the Event_add constructor in my Product. But how do I do that? Thanks, David Bustos