[css-nesting] Why does CSSStyleRule not inherit from CSSGroupingRule?

[emilio]

https://drafts.csswg.org/css-nesting/#cssom-style has:

partial interface CSSStyleRule {
  [SameObject] readonly attribute CSSRuleList cssRules;
  unsigned long insertRule(CSSOMString rule, optional unsigned long index = 0);
  undefined deleteRule(unsigned long index);
};

Why doing that rather than inheriting from CSSGroupingRule, which gives you that?

cc @tabatkins @sesse

[emilio]

cc @mdubet

[mdubet]

I've asked the same question during a WG meeting : #8350 (comment)

[tabatkins]

I honestly just didn't think about changing the inheritance tree? It feels like doing that to such an old rule might have compat implications, but then again CSSMediaRule is just as old and we changed it. So yeah, probably we can just do it this way.

[css-meeting-bot]

The CSS Working Group just discussed [css-nesting] Why does CSSStyleRule not inherit from CSSGroupingRule?, and agreed to the following:

• RESOLVED: Change CSSStyleRule to inherit from CSSGroupingRule, modulo any discovered compat impact

The full IRC log of that discussion

<TabAtkins> emilio: Nesting spec extends CSSSTyleRule by copypasting CSSGroupingRule API
<TabAtkins> emilio: Think there was a point in the past we discussed enhancing CSSSTyleRule but discarded that
<TabAtkins> emilio: So maybe instead we could have CSSStyleRule inherit from CSSGroupingRule? Then enhancements from either come to both.
<TabAtkins> emilio: Would make it more likely that changes (like using observablearray) would apply to both
<TabAtkins> emilio: This is all assuming there's no compat impact.
<TabAtkins> emilio: Assuming that, I think this is the right thing to do.
<TabAtkins> No objections from me, modulo possible compat impact we'll find.
<TabAtkins> (it would be *relatively* hard to have a compat impact here, I imagine)
<TabAtkins> astearns: Objections?
<TabAtkins> RESOLVED: Change CSSStyleRule to inherit from CSSGroupingRule, modulo any discovered compat impact
<TabAtkins> emilio: I'd also expect compat to be rare
<TabAtkins> emilio: Few people use instanceof, they use duck-typing
<TabAtkins> emilio: And we shipped .cssRules on CSSStyleRule without issue

[emilio]

This has tests now, and spec text, so closing.

FWIW Gecko shipped this without issues.