Prestige Classes and Spellcasting Advancement

[Shiv]

I haven't been able to find any official errata or clarifications on this.

In the case of a prestige class where you could (or in some cases, must) have more than one spellcasting classes...

I know you don't advance multiple spellcasting classes at the same time. However, do you only get to advance one of the spellcasting classes as you advance the prestige class. That is, do you choose a class to advance and each time you level the prestige class, you level the chosen spellcasting class?

Or, can you choose to level whichever ONE of your spellcasting classes you want each time you level the prestige class?

 

[Caliber]

You choose which class each +1 spellcasting level goes to.

So a Wizard 5/Cleric 5 could who is taking a PrC that gives +1 spellcasting every level could eventually end up casting as a Wizard 10/Cleric 10 (if he split the +1 spellcasting levels evenly.)