[MatmaRex]

XSLT would be a classic answer, but it's a bit of a lost ancient technology these days. I've only used it in the browser for a lark, but I suppose you'd find mature (old) libraries for working with it easily enough.

PHPTAL is another system I've heard of (but never used) that seems to be built on this idea. It is also very mature (old). https://phptal.org/

In general working with DOM doesn't seem to be very cool these days. Everyone uses template systems that are glorified string concatenators, like Mustache, and doesn't care about security issues due to bad escaping.