[css-values-4] Per WG resolution, censor NaNs to 0. Closes #7067

css-values-4/Overview.bs

@@ -3990,7 +3990,7 @@ Type Checking</h3>
 	If a <dfn export>top-level calculation</dfn>
 	(a [=math function=] not nested inside of another [=math function=])
 	would produce a value whose numeric part is NaN,
-	it instead act as though the numeric part is +∞.
+	it instead act as though the numeric part is 0.
 	If a [=top-level calculation=]
 	would produce a value whose numeric part is 0⁻,
 	it instead acts as though the numeric part is the standard "unsigned" zero.