How do class skills work with multi-classing?

[Codanous]

Hey how do skills work with multi classing? Do I get both sets of skills as class skills or do one set go away when I move into the new class? And do I lose the +3 if it stops being a class skill for a skill that was previously a class skill but might not be now?

To sum it up as that might be confusing I am wondering if class skills continue being class skills if you start multi-classing.

[Some Random Dood]

You get both sets as class skills.

[Roberta Yang]

You get all the class skills of all of your classes.

[Elvis Aron Manypockets]

Plus, not only do you not lose the +3 for the old class skills, you get a +3 for any new class skills you already had a rank in when it wasn't a class skill, in addition to any old or new class skills you put a first rank in going forward.

[mcv]

Basically, multiclassing to a class with a completely different set of class skills is pure win. (Except that you'll never have enough skill points to be really good at all of them, but at low levels, you can be decent at almost everything.)

[Quandary]

it's similar to weapon proficiencies from different classes, once you get them you can't lose them,
except unlike weapons where non-proficiency gives penalty and proficiency is zero modifier,
class skills give no penalty for not having them, but give a bonus if you do have them.