[css-values-5] Tweak the wording of <progress> to only allow literal percentage tokens to be equivalent to a number. #10017

Author: tabatkins

css-values-5/Overview.bs

@@ -317,13 +317,21 @@ Representing Interpolation Progress: the <<progress>> type</h2>
 	where:
 
 	<dl dfn-type=value dfn-for="<progress>">
-		<dt><dfn><<percentage>></dfn>
+		<dt><dfn><<percentage-token>></dfn>
 		<dd>
 			Computes to the equivalent <<number>>:
 			''0%'' becomes ''0'',
 			''100%'' becomes ''1'',
 			etc.
 
+			Note: This only allows literal percentages,
+			like ''15%'';
+			calculations like ''calc(100% / 7)'' will not work,
+			as they will instead attempt to use the normal rules
+			for resolving a percentage against another type
+			(such as <<length>>, in 'width').
+			Use expressions like ''calc(1 / 7)'' instead.
+
 		<dt><dfn><<number>></dfn>
 		<dd>
 			Represents the [=mix progress value=].
@@ -332,15 +340,6 @@ Representing Interpolation Progress: the <<progress>> type</h2>
 			''media-progress()'',
 			and ''container-progress()'' notations.
 
-			For this purpose,
-			a value is allowed to match <<number>>
-			regardless of its [=CSSNumericValue/type=]’s [=percent hint=].
-
-			Note: This means that a value like ''progress(50% from 100px to 200px)''
-			will match,
-			despite its type having a [=percent hint=] of "length".
-
-
 		<dt><dfn><<'animation-timeline'>></dfn>
 		<dd>
 			Represents the [=mix progress value=]
@@ -361,6 +360,13 @@ Representing Interpolation Progress: the <<progress>> type</h2>
 	they allow representing interpolation beyond the range
 	defined by the start and end values.
 
+	Note: While <<progress>> itself can be a <<percentage>>,
+	mapping directly to the equivalent <<number>>,
+	a function that <em>resolves</em> to a <<number>>,
+	like ''progress()'',
+	resolves <<percentage>>s using the normal rules for the context;
+	for example, in 'width', they would be resolved against a length.
+
 	The [=computed value=] of a <<progress>> value specified with <<percentage>> or <<number>>
 	is the computed <<number>> converted through the <<easing-function>> (if any).
 	The [=computed value=] of a <<progress>> value specified with <<'animation-timeline'>>