Index: trunk/data/validator/numeric.mapcss
===================================================================
--- trunk/data/validator/numeric.mapcss	(revision 6534)
+++ trunk/data/validator/numeric.mapcss	(revision 6548)
@@ -1,3 +1,9 @@
 /* measurement values and units warnings (ticket #8687) */
+
+*[/^[0-9]+$/] {
+  throwWarning: tr("numerical key");
+  assertMatch: "way 123=foo";
+  assertNoMatch: "way ref.1=foo";
+}
 
 *[layer =~ /\+.*/] {