Helvellyn |
The section on multi-classing the hybrid classes held in the new Advanced Class Guide is on page 2 of that PDF.
Effectively you can't take any class levels of a class from which the hybrid is made from, nor take any hybrid levels if you already have one of those classes.
For example:
If you already have class levels as a sorcerer you can't be an Arcanist.
If you're Swashbuckler you can't then take levels as a Fighter or Gunslinger.
Starglim |
If your favoured class is an alternate class or hybrid class and you take one level of that class, you get one favoured class bonus. If you take one level of any other class, you get no bonus.
If you are a half-elf, you have two classes that work in this way but nothing else changes. If you picked a hybrid class and one of its alternates as favoured classes, you'd waste your racial ability because you could never have levels in both of those classes. If you picked both alternates of a hybrid class and took levels in the hybrid class, you wouldn't receive a favoured class bonus at all.
As Quandary mentioned, if your favoured class is a hybrid class, by one or two steps of interpretation, you might have access to optional favoured class bonuses for both of its alternates. You'd pick one bonus to apply for each level out of the standard benefits and the options available to you.