references this - Stalwart and Improved Stalwart feats work for base Barbarian class, but not Invulnerable Rager. Please implement for Invulnerable Rager Barbarian archetype. It's probably the most played Barb. archetype, and one that benefits the most from the DR stacking.
Sneaky... filing this under code almost meant the next release would not have had this... data = book content; code = java engine.