[Yuan doesn't so much wait patiently as start off down the line of shelves, deeper into the archive.]

We can't copy every book. Here. Look at the spine.

[He turns as he goes, to pass the book in question to Zelos, spine-first. At the base of the spine someone has made some careful notations in a light hand, neat enough to be legible even now.]

[Almost against his will, the grin gets an answering smile from Yuan, even if it's only a faint curve.]

The code tells you where it goes, if you know how to read it. Every book here is tagged this way. Does that begin to make sense?