[selectors-4] Tweak changes list, add link.

Author: fantasai

selectors-4/Overview.bs

@@ -3935,12 +3935,10 @@ Changes</h2>
 		<li>Rewrote selectors grammar using the CSS Value Definition Syntax.
 		<li>Split out <a>relative selectors</a> from <a>scoped selectors</a>,
 			as these are different concepts that can be independently invoked.
-		<li>Changed rules for absolutizing a relative selector.
-
-		Issue: List changes + rationale?
 		<li>Moved definition of <<An+B>> microsyntax to CSS Syntax.
 
 		Issue: Semantic definition should probably move back here.
+
 		<li>Added new sections:
 			<ul>
 				<li>[[#data-model]]
@@ -3955,9 +3953,8 @@ Changes</h2>
 					</ul>
 				</li>
 			</ul>
-		<li>Removed restriction on combinators within '':matches()'' and '':not()''.
-
-			Issue: Do we have implementations of this? If not, maybe it's better to keep the restriction for level 4?
+		<li>Removed restriction on combinators within '':matches()'' and '':not()'';
+			see <a href="https://lists.w3.org/Archives/Public/www-style/2014Jan/0607.html">discussion</a>.
 		<li>Defined <a>specificity</a> of a <a>selector list</a>. (Why?)
 		<li>Required quotes around '':lang()'' values involving an asterisk;
 			only language codes which happen to bhe CSS identifiers can be used unquoted.