The linked article suggests a potential syntax:

  <template for="footer" patchsrc="/partials/footer.html">

But the road ahead for this is still quite bumpy. Here's a good video from a year ago, talking through the obstacles. https://www.youtube.com/watch?v=t0NBcve0enY

I can't really tell how you'd even use this. Is it supposed to be some sort of micro-optimisation thing to do with how HTML is parsed (now you can download chunks out of order, presumably with some performance gains since it's browser native?).

When I saw the title I was hoping it was going to be a very simple React-like API for constantly updating parts of the DOM with maximum performance since the browser devs are now involved. It doesn't look like that's what this is at all. And all these years later I'm still wondering why browsers aren't implementing an API like that when it's been obvious for over a decade now that real-time DOM updates are a vital browser feature that needs to be performant, and that developers vastly prefer a declarative model to a procedural one. Why after 15-16 years are we still building 100 versions of the same abstraction in user-land to turn Element.append into "refresh these elements when this data changes"?