I'm not sure what you mean by Prototype.
BIAB has a feature in stylepicker called prototype...I know this because when the new StylePicker came out, it was removed as a feature and I asked that it be put back in and they did.
Basically, what it does is to mark a selected style as a "prototype", meaning a way to select styles that match the prototype in various ways. When you select the command "Mark as Prototype and sort by Similar Styles...", the StylePicker will then sort and filter the list by best to worst match based on the prototype's style tempo, feel, genre, time signature, and other factors.
It lets you choose a style that is close to what you want (based on those criteria) and display a list of other styles that match that criteria.
In the original StylePicker (before the new interface), you could set a prototype, and then all the styles that were similar displayed with an asterisk next to them. That's how you knew which ones matched.
That being said, I haven't tried it in the latest build, so I don't know if it would throw an exception error. If I get a chance, I'll try it out tonight.