Subject matter? [Zelos gets off the chair he just dragged over and follows Yuan into the shelves.] Because... because sometimes you want the author instead. Or a time period.

[Does time period count as subject matter?

Zelos has a hand twining unconsciously in his hair as he walks. It's a little longer than it was this time last year, but it doesn't come down past his shoulders. For now, that's a good thing. His hair is wild enough with tangles as it is.]

Do you know where every single book in here is, or do you have to guess?