Index: trunk/data/validator/deprecated.mapcss
===================================================================
--- trunk/data/validator/deprecated.mapcss	(revision 11409)
+++ trunk/data/validator/deprecated.mapcss	(revision 11476)
@@ -1119,4 +1119,10 @@
 }
 
+way[area][area!=yes][area!=no] {
+  throwError: tr("wrong value: {0}", "{0.tag}");
+  suggestAlternative: "area=yes";
+  suggestAlternative: "area=no";
+}
+
 /* #13953 */
 *[amenity=hunting_stand][lock=yes],