[css-ui-4] Allow button to act as auto when otherwise impractical

Author: frivoal

css-ui-4/Overview.bs

@@ -1843,8 +1843,13 @@ Animation type: discrete
 		The element is rendered with the look and feel of a push button,
 		similar to the ''appearance: auto'' rendering of the [[HTML]] <{button}> element.
 
-		Issue: Are there some form controls or other replaced elements
-		on which this value should be a no&#x2011;op?
+		UAs may treat this value as ''appearance/auto'' on form controls
+		or replaced elements
+		for which it is impractical or nonsensical.
+
+		Issue: Are there some elements
+		on which this value <em>must</em> be treated as auto for web compat requirements?
+		The phrasing above alows it, and that's probably enough.
 
 	<dt><dfn type="">&lt;compat></dfn>
 	<dd>