Donna, it seems to be able to handle non-spiral-bound just fine too. If you're already a member of the JFAMC Facebook group, this link should take you to those other pics I mentioned, showing at least one non-spiral book on the stand.
https://www.facebook.com/groups/JFAMC/permalink/1539093206398083/
So I think the coding handbook being on the desk in front of
the laptop in the pic is simply a matter of his number of books overall
and the stand only being able to handle 4 at a time (on the sides -- more could be
plopped on top while closed), not due to that one not being spiral-bound.
I'm planning on ordering one of these myself in the next couple of weeks, as soon as my finances permit.