> RBTransformationRule (you need to activate that verificationBlock > when > you create your rewriter).
Yes, and this is the tricky bit :-) Because there's no guarantee that this block is functional. For example, it may access context ivar which, by the time UI is retrieving intervals is already nilled out or even filled again with some other unrelated context if you're reusing rule instances (but if not, you may run into performance problems...)
