[css-transforms-2] Copy the range limitation to the term's personal definition.

Author: tabatkins

css-transforms-2/Overview.bs

@@ -770,7 +770,7 @@ Animation type: by computed value
 </pre>
 
 <dl dfn-type=value dfn-for="perspective">
-	: <dfn><<length>></dfn>
+	: <dfn><<length [0, ∞]>></dfn>
 	:: Distance to the center of projection.
 
 		Issue: Verify that projection is the distance to the center of projection.