Thanks! One follow up: during Revision, you reorder your spellbooks AND upgrade a spell to a master spell, or do you only get to perform one or the other?
You can only choose one of these two action
According to the rulebook, you can do both things:
Instead of learning a new spell, current player may revise his spellbook by discarding 4 gems.
Current player can rearrange his/her spells freely in any order.
Spellbooks can be emptied in this process
After that, he/she may flip one spell over and that spell become a Mastered Spell."
That you have to chose is between to learn a spell or make a revision. I guess that Chan Pak Hei (Percy Chan) has misread your question and he was meaning about this choice.