The 'attack' and 'guard' skills can differ depending on the actor. That’s why I didn’t just use 1 and 2 there for their ID.
It’s only an extension point in the engine for plugins though, so you can’t change this in the editor by default. There’s a WeaponSkill.js plugin floating around that makes use of this, for example. (I’d link the original page but I’m not sure where it is from.)