Index: trunk/data/validator/numeric.mapcss
===================================================================
--- trunk/data/validator/numeric.mapcss	(revision 8725)
+++ trunk/data/validator/numeric.mapcss	(revision 9050)
@@ -175,2 +175,9 @@
   assertNoMatch: "node amenity=cinema screen=8";
 }
+*[admin_level][admin_level !~ /^(1|2|3|4|5|6|7|8|9|10|11|12)$/] {
+  throwWarning: tr("unusual value of {0}", "admin_level");
+  assertMatch: "node admin_level=0";
+  assertMatch: "node admin_level=-1";
+  assertMatch: "node admin_level=13";
+  assertNoMatch: "node admin_level=5";
+}