RBTransformationRule inst var changes initialization

Hello,

I have a rewrite rule - subclass of RBTransformationRule. And I want to apply it to specific scope, but before applying it, would be nice to see ChangesBrowser with all future changes. For that I need to have changes inst var initialized, but they are nil. So, the question is, where is inst var "changes" of RBTransformationRule initialized?

Thanks,
Mark