[css-values-5] mix() should be restricted to <keyframes-name> w3c#11121

Author: fantasai

css-values-5/Overview.bs

@@ -1145,7 +1145,7 @@ Interpolated Property Values: the ''mix()'' notation</h3>
 	<pre class="prod">
 		<dfn><<mix()>></dfn> =
 		  mix( <<progress>> , <<whole-value>> , <<whole-value>> ) |
-		  mix( <<progress>> && of <<'animation-name'>> )
+		  mix( <<progress>> && of <<keyframes-name>> )
 	</pre>
 
 	The first syntax alternative, like other [=mix notations=],