[css-cascade-6] Make CSSScopeRule.start/end optional (w3c#8716)

w3c#8626

Author: andruud

css-cascade-6/Overview.bs

@@ -746,31 +746,23 @@ The <code>CSSScopeRule</code> interface</h3>
 	<pre class='idl' export>
 	[Exposed=Window]
 	interface CSSScopeRule : CSSGroupingRule {
-	  readonly attribute CSSOMString start;
-	  readonly attribute CSSOMString end;
+	  readonly attribute CSSOMString? start;
+	  readonly attribute CSSOMString? end;
 	};
 	</pre>
 
 	<dl class='idl-attributes'>
 		<dt><code>start</code> of type <code>CSSOMString</code>
-		<dd>The <code>start</code> attribute must return a value as follows:
-
-			<dl class="switch">
-				<dt data-md>The ''@scope'' rule has an associated <<scope-start>>
-				<dd data-md>The result of serializing that <<scope-start>>.
-				<dt data-md>Otherwise
-				<dd data-md>An empty string.
-			</dl>
+		<dd>The <code>start</code> attribute
+		returns the result of serializing the <<scope-start>> of the rule
+		(without the enclosing parentheses),
+		or null if there is no <<scope-start>>.
 
 		<dt><code>end</code> of type <code>CSSOMString</code>
-		<dd>The <code>end</code> attribute must return a value as follows:
-
-			<dl class="switch">
-				<dt data-md>The ''@scope'' rule has an associated <<scope-end>>
-				<dd data-md>The result of serializing that <<scope-end>>.
-				<dt data-md>Otherwise
-				<dd data-md>An empty string.
-			</dl>
+		<dd>The <code>end</code> attribute
+		returns the result of serializing the <<scope-end>> of the rule
+		(without the enclosing parentheses),
+		or null if there is no <<scope-end>>.
 	</dl>
 
 <!--
@@ -804,6 +796,7 @@ Changes since the 21 December 2021 First Public Working Draft</h3>
 		(<a href="https://github.com/w3c/csswg-drafts/issues/6895">Issue 6895</a>)
 
 	* Added the {{CSSScopeRule}} interface.
+		(<a href="https://github.com/w3c/csswg-drafts/issues/8626">Issue 8626</a>)
 
 	* Added implicit scopes by making ''<<scope-start>>'' optional.
 		(<a href="https://github.com/w3c/csswg-drafts/issues/6606">Issue 6606</a>)