I don't know, this doesn't make much sense to me. Usually you go from a set of specifications provided by a business analyst and then presuming you have a style guide and a 'widget library', the UX designer then 'formally' implements a prototype which can then be tested asap, tweaked ad-nauseam.

Once that's done, there goes your formal specification. We know what we're doing, how we're going to do it and we can work on the impl.