Checking contextual integrity

[Tom Zeller]

> ... I think that
> understanding flow and semantics is easier of it's tri-state.

I guess the reason for me suggesting true|false|throw is that I am not
sure what the third state in the troolean is.

Thinking of the tri-state as an enum makes me feel better ? Or
perhaps, as Rod originally hinted, the return value could be an Action
@Event.

> I don't think maintaining the Predicate interface is really terribly
> valuable. It's not as though it's particularly complex.

Agreed.