Index: trunk/data/validator/deprecated.mapcss
===================================================================
--- trunk/data/validator/deprecated.mapcss	(revision 8184)
+++ trunk/data/validator/deprecated.mapcss	(revision 8185)
@@ -437,2 +437,7 @@
   throwWarning: tr("{0} together with {1}", "{0.tag}", "{1.tag}");
 }
+
+/* see #11234 */
+*[/=|\+|\/|&|<|>|;|'|"|%|#|@|\\|,|\./] {
+  throwWarning: tr("key with uncommon character");
+}