What is the issue with the HTML Standard?

The <selectedoption> element is discussed more generally here, and this issue is for a topic which has been split out: w3c/csswg-drafts#10242

When the author modifies content inside an <option> element, we will clone the contents of that <option> into the <selectedoption>, but the timing at which we do this cloning has not yet been decided.

The timing will be web observable. For example, if the author modifies an option and then tries to query the layout of <selectedoption>, they will have to wait until the cloning happens.

Some possible options for cloning timing are:

1. Synchronously
2. Microtask timing
3. CustomElements reaction timing
4. Something slower?

I think that we should do microtask timing because I am planning on using a MutationObserver internally to implement this, and MutationObserver already uses microtask timing: https://dom.spec.whatwg.org/#queue-a-mutation-observer-compound-microtask

If we diverge from microtask timing, we would have to make a special kind of mutationobserver that does different timing, right?

@emilio @smaug----