HTML might be getting a new type of tag, which… hasn't happened this millennium. Here's the new syntax, and how it works.

And here's the explainer on HTML patching https://github.com/WICG/declarative-partial-updates/blob/main/patching-explainer.md

@firefoxwebdevs @jaffathecake How would out-of-order HTML patching work with a start/end processing instruction node pair with different parent elements? In the last example, what would happen to the closing em tag when HTML was patched?
@timsev @jaffathecake currently, it wouldn't. The plan is, for that feature, to require the markers to be direct children of the parent with the marker attribute.