Hi. Thank you for your reply.
Yep, that's the part of the manual I was following. I had started out with tags, but since they couldn't be nested in a hierarchy, I switched over to the genre column scheme that is described in the manual.
Having multiple tags for the genre categories seemed simpler to implement, but having the books neatly organized in subgroups struck me as an ultimately more useful way to go.
I've seen comments in this forum (as well as in that user manual entry) about applying more than one genre to a book. The problem is, none of the comments include a "how-to" followup. I've tried with commas, bars, semicolons, and ampersands, with surrounding spaces and without, but no luck to date.
Thanks again, though. I appreciate your reply.