[css-sizing-3] Don't override CSS2 sizing rules. Only supplement them.

Author: fantasai

css-sizing-3/Overview.bs

@@ -824,7 +824,7 @@ Intrinsic Sizes</h3>
 
 	If the <a>max-content size</a> would depend
 	on the size of the containing block
-	(as it does for images with an intrinsic aspect ratio but no intrinsic size,
+	(as it sometimes does for images with an intrinsic aspect ratio but no intrinsic size,
 	see <a href="https://www.w3.org/TR/CSS2/visudet.html#inline-replaced-width">CSS2&sect;10.3.2</a>)
 	and therefore can't be calculated against an infinitely-sized containing block
 	then: