Talk:Job Classes/@comment-49.145.174.82-20180209013856/@comment-94.189.253.74-20180408093111

I think this refers to the point that is similar to DnD system. Let's say you want to achieve a wizard 10th tier spell. You start as a wizard and get to level 15, then you pick a prestige class that is an upgrade of a wizard and you get higher tier spells. Let's say that at level 15 wizard you unlock 3rd tier of wizard spells, with some prestige class you might unlock 4th, 5th and so on tiers of wizard spells.

So in this case you were quite correct that it means that there are other 'spellbook' systems, but some classes share those spellbooks and upgrade upon each other, while you can't automatically advance in other spellbooks.