Anne van Kesteren

Who has access to the event target?

That kinda works I think, but I think the problem is that people might start using this mechanism in specifications for something it's not intended for.

I suspect what implementations have is more similar to "event groups" in https://www.w3.org/TR/2003/NOTE-DOM-Level-3-Events-20031107/events.html in that userland cannot prevent those listeners from being run and that ordering is independent from userland...

Are there benchmarks for this? @smaug---- @rniwa thoughts?

Thanks everyone for weighing in. It seems like the next steps here would be a PR to change the DOM Standard as well as corresponding tests in the web-platform-tests project.

@smaug---- @domenic any updates here?

Looking at https://html.spec.whatwg.org/#create-an-element-for-the-token, I'm not sure. It won't be able to find a weird definition as that also uses the local name and it eventually delegates to this algorithm.

@wessberg how is https://github.com/whatwg/dom/issues/533#issuecomment-405530738 solved by extensions to `MutationObserver`? You'd still not know about shadow tree mutations. Having reread the thread it's not entirely clear to me everyone is on...

So by synchronous you mean equivalent timing to custom elements, not equivalent timing to mutation events? Why is mutation observer timing insufficient? Why would you need to polyfill/emulate custom elements...

As I mentioned there, I don't think we should add this feature to this API. XMLHttpRequest is essentially frozen and new functionality should go into `fetch()` if applicable, but I...