Other characters might have broad immunities to certain attack sources as well. In such cases, it’s best to make the attack immunity as an explicit power fact, and to state the exact limits of the immunity to avoid confusion during play.
Example: Bill sees his character Mack Atlas as the traditional 'brick' style hero, and thus immune to mundane attack sources like knives and bullets. He writes 'Invulnerability' as a power fact to reflect this. The GM thinks that this is too broad, so Bill clarifies the power-fact as 'Invulnerability (bulletproof)'. So although Mack can now safely ignore the threat provided by a mugger's pistol, something like a rocket-launcher or equivalent force can still be used to make attacks against the hero.