[css-values] Clamp calc() values at both computed and used value time per WG resolution. #434

Author: fantasai

css-values-3/Overview.bs

@@ -1740,8 +1740,12 @@ Range Checking
 
 	Parse-time range-checking of values is not performed within ''calc()'',
 	and therefore out-of-range values do not cause the declaration to become invalid.
-	However, the used value resulting from an expression
+	However, the value resulting from an expression
 	must be clamped to the range allowed in the target context.
+	Clamping is performed on computed values to the extent possible,
+	and also on used values
+	if computation was unable to sufficiently simplify the expression
+	to allow range-checking.
 
 	Note: This requires all contexts accepting ''calc()''
 	to define their allowable values as a closed (not open) interval.
@@ -2140,6 +2144,9 @@ Changes
 		Reverted previous change to allow zero angles to drop their unit;
 			this will instead be special-cased where needed for backwards-compatibility.
 			(See discussion)
+		Defined that range checking, and any resulting clamping, of ''calc()'' values
+			is performed both at computed time and at used time.
+			(Issue #434)
 		Fixed grammar error that disallowed numeric expressions as denominators in ''calc()''.
 			(Issue 12)
 		Defined handling of font-relative units outside the context of an element.

css-values-4/Overview.bs

@@ -1880,8 +1880,12 @@ Range Checking
 
 	Parse-time range-checking of values is not performed within [=math functions=],
 	and therefore out-of-range values do not cause the declaration to become invalid.
-	However, the used value resulting from an expression
+	However, the value resulting from an expression
 	must be clamped to the range allowed in the target context.
+	Clamping is performed on computed values to the extent possible,
+	and also on used values
+	if computation was unable to sufficiently simplify the expression
+	to allow range-checking.
 
 	Note: This requires all contexts accepting ''calc()''
 	to define their allowable values as a closed (not open) interval.