Under what circumstances does DR protect against spell damage?

[ruleslawyer]

Funny; IMO, the intention was precisely the opposite: i.e., that barbarian DR should protect against all attacks. It bothers me that there's a direct contradiction between the DMG and the PHB glossary on this, but I think the glossary language is better spelled out, since it's a specific description of barb DR and not the mere use of barb DR as an example.

Anyway, YMMV.