[selectors-4] Refer explicitly to the 'document element' concept. #7787

Author: tabatkins

selectors-4/Overview.bs

@@ -2838,8 +2838,8 @@ Tree-Structural pseudo-classes</h2>
 	the root of the document.
 
 	For example, in a DOM document,
-	the '':root'' pseudo-class matches the root element of the <a interface>Document</a> object.
-	In HTML, this would be the <a element>html</a> element
+	the '':root'' pseudo-class matches the [=document element=].
+	In HTML, this will be the <{html}> element
 	(unless scripting has been used to modify the document).
 
 <h3 id="the-empty-pseudo">