I'm still in planning phase, but I've seen that the effect of a focus should be an object. But looking at the code, I can't find an Effect class. Also, details of the structure of how an class would become affectable isn't clear: add an member effect list in every affectable class? Maybe a purely virtual affectable class, parent to all affectable classes, that only contains a linked list (or map) of effects (and a static list) would be better (I'd go with that one).
After that is determined, it should be pretty straightforward to add the effect of foci.
Should I post that to the mailing list? I consider myself a bit too green to touch the class hierarchy without any green light!