When Spell Resistance Applies
Each spell includes an entry that indicates whether spell resistance applies to the spell. In general, whether spell resistance applies depends on what the spell does:
Spell resistance applies if the spell is targeted at the creature. Some individually targeted spells can be directed at several creatures simultaneously. In such cases, a creature’s spell resistance applies only to the portion of the spell actually targeted at that creature. If several different resistant creatures are subjected to such a spell, each checks its spell resistance separately.
Spell resistance applies if the resistant creature is within the spell’s area. It protects the resistant creature without affecting the spell itself.
Multi-target spells against multiple foes with SR get checked separately vs each foe. What about area affect spells? Do you just check once, even if you're laying a lightning bolt down on a whole column of tanarukk?