[css-syntax][css-nesting] Design of @nest rule

[chromium-helper]

CSSWG added the following resolution(s):

• RESOLVED: 1. Introduce a CSSNestedDeclarations object inheriting from CSSRule and having a .style accessor, and use that to represent the declaration lists in a CSSStyleRule. It serializes as a raw declaration list. 2. Extend .insertRule() to parse declarations (or, if Web-compat requires, add .insertDeclarations()) into a CSSNestedDeclarations Object. 3. Open a new issue wrt the first declarations block.

in w3c/csswg-drafts#10234 (comment)

[chromium-helper]

I have filed issues.chromium.org/343463516

That is all that can be done here, closing issue.