[css-values-4][editorial] Clarify that positive zeros also exist, and are produced unless otherwise specified. #8034

Author: tabatkins

css-values-4/Overview.bs

@@ -4241,8 +4241,9 @@ Type Checking</h3>
 	* Any operation with at least one NaN argument produces NaN.
 
 	Additionally,
-	IEEE-754 introduces the concept of "negative zero",
-	which must be tracked within a calculation
+	IEEE-754 introduces the concept of a "signed zero",
+	which is specifically positive or negative,
+	and which must be tracked within a calculation
 	and between nested calculations:
 
 	* Negative zero
@@ -4275,13 +4276,16 @@ Type Checking</h3>
 		For example, ''min(0⁺, 0⁻)'' must produce 0⁻,
 		''max(0⁺, 0⁻)'' must produce 0⁺,
 		and ''clamp(0⁺, 0⁻, 1)'' must produce 0⁺.
+	* Unless otherwise specified,
+		any other operation that produces a zero
+		produces positive zero (0⁺).
 
 	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 0.
 	If a [=top-level calculation=]
-	would produce a value whose numeric part is 0⁻,
+	would produce a value whose numeric part is 0⁻ or 0⁺,
 	it instead acts as though the numeric part is the standard "unsigned" zero.
 
 	<div class=example>