[selectors-4] Update Changes list

Author: fantasai

selectors-4/Overview.bs

@@ -4005,9 +4005,26 @@ Changes since the 21 November 2018 Working Draft</h3>
 
 	<ul>
 		<li>Removed the Selector profiles, marked '':has()'' as optional and at-risk instead.
-		(<a href="https://github.com/w3c/csswg-drafts/issues/3925">Issue 3925</a>)
+			(<a href="https://github.com/w3c/csswg-drafts/issues/3925">Issue 3925</a>)
 		<li>Added [[#sub-pseudo-elements]] to define [=sub-pseudo-elements=] and related terminology.
 		<li>Added '':defined''.
+			(<a href="https://github.com/w3c/csswg-drafts/issues/2258">Issue 2258</a>)
+		<li>Added '':seeking'', '':buffering'', and ':stalled'' media playback state pseudo-classes.
+			(<a href="https://github.com/w3c/csswg-drafts/issues/3821">Issue 3821</a>)
+		<li>Added '':muted'' and '':volume-locked'' sound state pseudo-classes.
+			(<a href="https://github.com/w3c/csswg-drafts/issues/3821">Issue 3821</a> and <a href="https://github.com/w3c/csswg-drafts/issues/3933">Issue 3933</a>)
+		<li>Added '':user-valid''.
+			(<a href="https://lists.w3.org/Archives/Public/www-style/2015Sep/0111.html">Discussion</a>)
+		<li>Defined '':is()'', '':where()'', '':has()'', '':nth-child()'', and '':nth-last-child()''
+			to not be themselves invalidated when containing an invalid selector.
+			(<a href="https://github.com/w3c/csswg-drafts/issues/3264">Issue 3264</a>)
+		<li>Clarified case-sensitive string matching by referencing string identity as defined in [[INFRA]].
+		<li>Clarified that UA-provided placeholder text still triggers '':placeholder-shown''.
+		<li>Rewrote '':focus-visible'' definition for clarity.
+		<li>Switched reminder note in the grammar section to normative text
+			describing the requirement of whitespace between <<compound-selector>>s
+			when a <<combinator>> token is missing.
+		<li>
 	</ul>
 
 <h3 id="changes-2018-02">