[css-cascade-5] Clarify that revert-layer does not merge author and preshint origins. w3c#7087

Author: tabatkins

css-cascade-5/Overview.bs

@@ -1732,8 +1732,9 @@ Precedence of Non-CSS Presentational Hints</h3>
 	the [=UA-origin=] or a special-purpose <dfn>author presentational hint origin</dfn>
 	between the regular [=user origin=] and the [=author origin=].
 	For the purpose of [=cascading=]
-	this [=author presentational hint origin=] is treated as an independent [=origin=],
-	but for the purpose of the ''revert'' keyword
+	this [=author presentational hint origin=] is treated as an independent [=origin=];
+	however for the purpose of the ''revert'' keyword
+	(but not for the ''revert-layer'' keyword)
 	it is considered part of the [=author origin=].
 
 	A document language may define whether such a presentational hint