[css-values-4] Don't imply that NaN and -0 censoring rules only apply to <number> calculations.

Author: tabatkins

css-values-4/Overview.bs

@@ -3485,10 +3485,11 @@ Type Checking</h3>
 
 	If a <dfn export>top-level calculation</dfn>
 	(a [=math function=] not nested inside of another [=math function=])
-	would produce a NaN,
-	it instead produces +∞.
-	If a [=top-level calculation=] would produce 0⁻,
-	it instead produces the standard "unsigned" zero.
+	would produce a value whose numeric part is NaN,
+	it instead act as though the numeric part is +∞.
+	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.
 
 	<div class=example>
 		For example, ''calc(-5 * 0)'' produces an unsigned zero--