I bet this is something easy I've missed but I want to get everyone's vote on it to be certain I have it right.
Let's say a player has spellcasting from their Class (Sorc), and another from an Archetype (Wiz). Sorc's Key ability is Charisma, and what they use to cast spells. Wizard's Key is Intelligence.
When casting spells, my understanding rules as written is that the spellcasting modifier they use would be Charisma regardless if they're casting Wizard spells or Sorc spells, because the magic is coming from their "class" even though it's a Feat. (Core pg. 447 "If your Class grants you spellcasting, use your key ability modifier.")
I'm clarifying this interpretation is correct, would make things a lot simpler for me and my players. I'm struggling with it a lot given previous rules systems I learned growing up. Thank you!