I think the main problem with CMSes supporting XHTML would be that basically every single one uses template engine that treats HTML as a string of characters.

I think the main problem with CMSes supporting XHTML would be that basically every single one uses template engine that treats HTML as a string of characters. Is there a templating system that’s easy to use (think Jinja or something Svelte-like), but parses templates as XML instead of just concatenating a bunch of strings?