[css-nesting] Include CSSNestedDeclarations?

[andruud]

Test List

(Add) css/css-nesting/nested-declarations-cssom.html
(Add) css/css-nesting/nested-declarations-matching.html

Rationale

Possibly a bit late to include in 2024, but checking to see if there's interest anyway. cc @emilio @mdubet

CC'd people already know, but I'll include some examples of potential interop pain anyway:

---

The implicit rule inside @media (color:green) now matches <div> with the specificity of div, not the specificty of :is(div, #unrelated):

div, #unrelated {
  color: red;
  @media (width > 400px) {
     color: green;
  }
}

---

The implicit rule inside @media can now match pseudo-elements:

div::before {
  content: "narrow";
  @media (width > 400px) {
     content: "wide"; /* Works now, didn't before */
  }
}

[emilio]

Fwiw it's already kind of included since you fixed the parsing tests, so WebKit and gecko are at ninety something percent now.

I think it's fine on our end, I plan to implement this change sooner rather than later anyways

[andruud]

Fwiw it's already kind of included since you fixed the parsing tests, so WebKit and gecko are at ninety something percent now.

Indeed. But if we don't agree to include CSSNestedDeclarations here, I can remove those tests (from interop, not from WPT), per #604.

[mdubet]

Fine on our side also 👍

[emilio]

@andruud I just noticed that some of these tests have a dependency on @scope (which is not on by default in Firefox and not part of interop). Would you be fine if I made the test not depend on it (by either moving the test, or checking for window.CSSScopeRule or so)?

[andruud]

@emilio Oh, my bad. Yes, please move it.