Code Plugin Requirements?

Is there a new FAQ / Submission Guidelines Doc that tells us what the requirements are for Code Plugins on Marketplace?

In particular I want to know if we have to distribute source with the plug-in (I doubt Substance Designer has, but I wanna check just in case), and what programming guidelines there are.

Well Substance goes the library route. They provide sources of the glue code and prebuilt libraries of their propriatary stuff. And that, im my opinion, would make sense to be the rule.