It’s a markup language(ish) but it’s not a programming language. XML would be closer to programming, IMHO, since you could have simple things like recursion.

One could also view it a different way:

XML merely provides abstract structure. It doesn’t direct that anything be done. By itself, it doesn’t program anything.

HTML, on the other hand, directs web layout engines to produce outputs. It programs them.

SQL is in the same category for me.

SQL directs databases to manipulate data and relations, and to produce results. It programs them.

Imperative and functional programming are often what come to mind first, at least for many of us, but declarative programming is nevertheless programming.