Yarnabrina, I was asking for a way to do this just with Markdown, but that's not so important. Doing it with kableExtra would work out just as well and really it's more versatile and a more common use case. That said, the page you pointed to is very helpful. The grouped columns should do exactly what I need, and the grouped rows should work well enough, though they're rather unsatisfying. I think that that may just be a limitation I have to live with.