[selectors] Add spec text for :user-valid.

Author: emilio

selectors-4/Overview.bs

@@ -2606,21 +2606,29 @@ The Optionality Pseudo-classes: '':required'' and '':optional''</h4>
 	form elements are neither required nor optional.
 
 <h4 id="user-pseudos">
-The User-interaction Pseudo-class: '':user-invalid''</h4>
+The User-interaction Pseudo-classes: '':user-valid'' and '':user-invalid''</h4>
+
+	The <dfn id="user-invalid-pseudo">:user-invalid</dfn>
+	and the <dfn id="user-valid-pseudo">:user-valid</dfn> pseudo-classes
+	represent an element with incorrect or correct input, respectively,
+	but only <em>after</em> the user has significantly interacted with it.
 
-	The <dfn id="user-invalid-pseudo">:user-invalid</dfn> pseudo-class
-	represents an element with incorrect input, but only
-	<em>after</em> the user has significantly interacted with it.
 	The '':user-invalid'' pseudo-class
-	must match an '':invalid'', '':out-of-range'', or blank-but-'':required'' elements
-	between the time the user has attempted to submit the form
-	and before the user has interacted again with the form element.
-	User-agents may allow it to match such elements at other times,
+	must match an '':invalid'', '':out-of-range'', or
+	blank-but-'':required'' elements between the time the user has attempted
+	to submit the form and before the user has interacted again with the
+	form element.
+
+	The '':user-valid'' pseudo-class must match a '':valid'' element between the
+	time the user has attempted to submit the form and before the user has
+	interacted again with the form element.
+
+	User-agents may allow them to match such elements at other times,
 	as would be appropriate for highlighting an error to the user.
-	For example, a UA may choose to have '':user-invalid'' match
-	an '':invalid'' element once the user has typed some text into it
-	and changed the focus to another element,
-	and to stop matching only after the user has successfully corrected the input.
+	For example, a UA may choose to have '':user-invalid'' match an
+	'':invalid'' element once the user has typed some text into it and
+	changed the focus to another element, and to stop matching only after
+	the user has successfully corrected the input.
 
 	<div class='example'>
 		For example, the input in the following document fragment
@@ -2642,8 +2650,6 @@ The User-interaction Pseudo-class: '':user-invalid''</h4>
 
 	Issue: Cross-check with <a href="https://developer.mozilla.org/en-US/docs/Web/CSS/%3A-moz-ui-invalid">'':-moz-ui-invalid''</a>.
 
-	Issue: Add <a href="https://developer.mozilla.org/en-US/docs/Web/CSS/%3A-moz-ui-valid">:-moz-ui-valid</a> as '':user-valid'' per WG resolution.
-
 	Issue: Evaluate proposed <a href="https://lists.w3.org/Archives/Public/www-style/2014Feb/0511.html">:dirty pseudo-class</a>
 
 	Issue: Clarify that this (and '':invalid''/'':valid'') can apply to form and fieldset elements.