[css-ui-4] Disregarding a property means ignoring it, not overriding it

See #9919

css-ui-4/Overview.bs

@@ -2270,11 +2270,17 @@ Switching appearance: the 'appearance' property</h3>
 		and activating (for example by clicking) the element would toggle the state as usual.
 	</div>
 
-	User agents may disregard some CSS properties
+	User agents may [=disregard=] some CSS properties
 	on [=widgets=] rendered with their [=native appearance=]
 	to ensure that the intended appearance is preserved,
 	or because these properties may not be meaningful for the chosen appearance.
-	However, the following properties must not be disregarded:
+	<dfn>Disregarding</dfn> a property means that
+	the user agent treats it as if it didn't [=apply to=] the widget in question.
+	Nevertheless,
+	unless an explicit exception is specified (for compatibility reasons),
+	the user agent must still determine the [=computed value=] of any [=disregarded=] property
+	according to the usual rules.
+	However, the following properties must not be [=disregarded=]:
 
 	<ul>
 		<li>'appearance'