elemental equilibrium

question about the mechanics of EE. The effect happens after the damage of the spell is registered correct? So the target of a fireball would take full damage from that spell then receive the buff to fire resist and debuffs to cold and lite?? then casting arc on that target would deal full lite damage including the previous lite debuff, then trigger a new debuff for fire and cold and buff to lite damage??

it seems intuitive but i've figured things wrong before. want to make sure if i build a dual elemental witch that i know what i'm doing.