You are inserting this unconditionally... Don't you need to check whether the sheet is applicable first?

In all other places you call this function after changing the servo styles. I understand that this function doesn't need to see the changes as it just marks things dirty. But I would prefer we keep it consistent that we invoke it only after we apply the changes.

Just move this to the end of the function and add an additional call before the return should be enough.

Please add a note here that for shadow root, we don't add non-applicable sheets into the style rule map, which is different than what we do for style set.

Or you can just change the handling here to match what we do in style set, since it doesn't really have any problem to add non-applicable sheet into it, given they are not dangling.

Maybe just

c++
if (!mDisabled) {
  ApplicableStateChanged(true);
}

In general we have title="Your Name" in the author link element as well.

It doesn't seem to me <style> element may have disabled attribute. Neither MDN nor the HTML spec says so. And according to my test, we don't support it either, actually...

You can still disable a <style> element via giving it a non-empty title attribute and [setting the default style via <meta>](https://html.spec.whatwg.org/multipage/semantics.html#attr-meta-http-equiv-default-style) to something different.