Reference Issue 282 in the spec (w3c#291)

Author: nainar

css-properties-values-api/Overview.bs

@@ -129,7 +129,7 @@ However, "3em" is not (depending on the environment, 3em could compute to
 multiple different values). Additionally, "var(--foo)" is not computationally idempotent.
 </div>
 
-Issue: define computational idempotency.
+Issue(282): define computational idempotency.
 
 Issue(121): Is computational idempotency the right thing to do here? We could also just
 resolve any relative values once (against all the other initial values) and use