Al blinked. Well, it seemed like a rather... persistent personal choice. Even if it did narrow down the collection of all the books in the world to a very small share of acceptable reading material.
"Usually, I read everything at least once," Al said. "It's imprudent to trust a second opinion without seeing things for myself and then forming my own. Occasionally I do select a book, from that range of multitudes, to be re-read a second time, or even referenced persistently. Those usually make it into my personal collection."
He bit his lip.
"Hm, I suppose there are collections of books in Severus' library that I've been asked not to interact with. The old, Dark, and dangerous kind."