[cssom][css-nesting] Per #8940, CSSStyleRule inherits from CSSGroupingRule, so remove the now extraneous definitions from Nesting.

Author: tabatkins

css-nesting-1/Overview.bs

@@ -18,6 +18,10 @@ spec:css-values-4; type:dfn; text:identifier
 spec:cssom-1; type:dfn;
 	text:child css rules
 	text:specified order
+spec:selectors-4; type:dfn;
+	text: combinators
+	text: simple selector
+	text: type selector
 </pre>
 
 <h2 id="intro">
@@ -663,7 +667,7 @@ Nesting Other At-Rules {#conditionals}
 	and placed before all other child rules.
 	This includes in the OM.
 	(That is,
-	the {{CSSContainerRule/childRules}} attribute
+	the {{CSSGroupingRule/cssRules}} attribute
 	actually starts with this [=nested style rule=],
 	containing all the directly-nested properties.)
 
@@ -759,7 +763,7 @@ Mixing Nesting Rules and Declarations {#mixing}
 -----------------------------------------------
 
 	When a style rule contains both declarations
-	and [=nested style rules=] or [=nested conditional group rules=],
+	and [=nested style rules=] or [=nested group rules=],
 	all three can be arbitrarily mixed.
 	However, the relative order of declarations
 	vs other rules
@@ -786,7 +790,7 @@ Mixing Nesting Rules and Declarations {#mixing}
 	</div>
 
 	For the purpose of determining the [[css-cascade-4#cascade-sort|Order Of Appearance]],
-	[=nested style rules=] and [=nested conditional group rules=]
+	[=nested style rules=] and [=nested group rules=]
 	are considered to come <em>after</em> their parent rule.
 
 	<div>
@@ -1064,48 +1068,47 @@ Nesting Selector: the ''&'' selector {#nest-selector}
 CSSOM {#cssom}
 ==============
 
-Modifications to {{CSSStyleRule}} {#cssom-style}
----------------------------------------------
+Note: [[CSSOM-1]] now defines
+that {{CSSStyleRule}} can have child rules.
 
-CSS style rules gain the ability to have nested rules:
-
-<pre class=idl>
-partial interface CSSStyleRule {
-	[SameObject] readonly attribute CSSRuleList cssRules;
-	unsigned long insertRule(CSSOMString rule, optional unsigned long index = 0);
-	undefined deleteRule(unsigned long index);
-};
-</pre>
-
-The <dfn attribute for=CSSStyleRule>cssRules</dfn> attribute
-must return a {{CSSRuleList}} object for the [=CSSRule/child CSS rules=].
-
-The <dfn method for=CSSStyleRule>insertRule(<var>rule</var>, <var>index</var>)</dfn> method
-must return the result of
-invoking [=insert a CSS rule=] <var>rule</var>
-into the [=CSSRule/child CSS rules=] at <var>index</var>.
+When serializing a [=relative selector=] in a [=nested style rule=],
+the selector must be absolutized,
+with the implied [=nesting selector=] inserted.
 
+When serializing a [=nested group rule=],
+it must serialize solely with child rules.
 
-The <dfn method for=CSSStyleRule>deleteRule(<var>index</var>)</dfn> method
-must [=remove a CSS rule=] from the [=CSSRule/child CSS rules=] at <var>index</var>.
+<div class=example>
+	For example, the selector ''> .foo''
+	will serialize as ''& > .foo''.
 
-Note: Serialization of {{CSSStyleRule}} with nested rules
-are already well-defined by [[CSSOM]],
-via [=serialize a CSS rule=].
+	A [=nested group rule=] like:
 
-Note: The restriction on what a [=nested style rule's=]
-selector can start with
-counts as a "constraint imposed by CSS"
-in step 5 of [=insert a CSS rule=]
-(when invoked by anything that takes [=nested style rules=],
-not just {{CSSStyleRule}} itself).
+	<pre class=lang-css>
+	.foo {
+		@media (prefers-color-scheme: dark) {
+			color: white;
+			background: black;
+		}
+	}
+	</pre>
 
-When setting {{CSSStyleRule/selectorText}},
-if the {{CSSStyleRule}} is a [=nested style rule=],
-and the returned group of selectors
-starts with a selector
-that starts with an ident or function token,
-do nothing and return.
+	will serialize as:
 
-Issue: The above paragraph will be inlined into the CSSOM algo,
-rather than monkey-patched.
+	<pre class=lang-css>
+	.foo {
+		@media (prefers-color-scheme: dark) {
+			& {
+				color: white;
+				background: black;
+			}
+		}
+	}
+	</pre>
+</div>
+
+Note: These rules ensure that the rules in question
+are valid to be moved to other contexts,
+including non-nested ones.
+It also ensures that the serialization
+closely matches the structure of the CSSOM.

cssom-1/Overview.bs

@@ -1998,7 +1998,7 @@ The <code>CSSStyleRule</code> interface represents a style rule.
 
 <pre class=idl>
 [Exposed=Window]
-interface CSSStyleRule : CSSRule {
+interface CSSStyleRule : CSSGroupingRule {
   attribute CSSOMString selectorText;
   [SameObject, PutForwards=cssText] readonly attribute CSSStyleDeclaration style;
 };