BUG HAD WRONG DESCRIPTION. NEW DESC FORTHCOMING.
Ammend and modify the Nimbus API as necessary to allow third party components to implement UIDelegates for Nimbus. In particular, ensure that they can: register delegates, use Painters, use custom states, use AbstractRegionPainter.

None of this API is "public" in the sense that it is supported, but it is "public" in the java sense.