The Aid Another rules discuss how one character can make a special attack against AC 10 to grant +2 to attack rolls or AC to an ally. These rules have an addendum at the end (emphasis mine):
You can also use this standard action to help a friend in other ways, such as when he is affected by a spell, or to assist another character’s skill check.
The case for skills is adequately described - you roll a skill check against DC 10. But what do you roll when you want to help your ally "when he is affected by a spell"?
I'm looking for written rules, not rulings. A DM might rule that you make a saving throw against DC 10, or still make an attack roll, or require a Spellcraft skill check, and that's fine, but what (if anything) do the rules actually say about this?