[css-sizing-4][css-values-4] Define 0 & infinite ratios as degenerate, and define that degenerate ratios do nothing.

Author: tabatkins

css-sizing-4/Overview.bs

@@ -182,6 +182,9 @@ Preferred Aspect Ratios: the 'aspect-ratio' property</h3>
 			Size calculations involving the aspect ratio
 			work with the dimensions of the box specified by 'box-sizing'.
 
+			If the <<ratio>> is [=degenerate ratio|degenerate=],
+			the property instead behaves as ''aspect-ratio/auto''.
+
 		<dt><dfn>auto && <<ratio>></dfn>
 		<dd>
 			If both ''auto'' and a <<ratio>> are specified together,
@@ -191,6 +194,9 @@ Preferred Aspect Ratios: the 'aspect-ratio' property</h3>
 			in which case that aspect ratio is used instead.
 			In all cases, size calculations involving the aspect ratio
 			work with the [=content box=] dimensions always.
+
+			If the <<ratio>> is [=degenerate ratio|degenerate=],
+			the property instead behaves as ''aspect-ratio/auto''.
 	</dl>
 
 	Note: Having a [=preferred aspect ratio=] does not make a box into a [=replaced element=];

css-values-4/Overview.bs

@@ -1293,14 +1293,10 @@ Ratios: the <<ratio>> type</h3>
 	However, <<ratio>> is always serialized with both components.
 
 	The computed value of a <<ratio>> is the pair of numbers provided.
-	However, a ratio of ''0 / 0'' behaves as the ratio ''1 / 0'' instead.
 
-	Note: This makes the behavior of ''calc(0 / 0)''
-	(an ordinary division,
-	which resolves to ''NaN''
-	and is then "censored" to ''infinity'')
-	consistent with the ratio ''0 / 0'';
-	this consistency is generally true in all other cases.
+	If either number in the <<ratio>> is 0 or infinite,
+	it represents a <dfn export>degenerate ratio</dfn>
+	(and, generally, won't do anything).
 
 	If two <<ratio>>s need to be compared,
 	divide the first number by the second,
@@ -1325,6 +1321,9 @@ Combination of <<ratio>></h4>
 	then interpreting the result as a <<ratio>>
 	with the result as the first value and ''1'' as the second value.
 
+	If either <<ratio>> is [=degenerate ratio|degenerate=],
+	the values cannot be interpolated.
+
 	<div class='example'>
 		For example,
 		halfway through a linear interpolation from ''5 / 1'' to ''3 / 2'',