Index: trunk/src/org/openstreetmap/josm/gui/mappaint/mapcss/Expression.java
===================================================================
--- trunk/src/org/openstreetmap/josm/gui/mappaint/mapcss/Expression.java	(revision 4007)
+++ trunk/src/org/openstreetmap/josm/gui/mappaint/mapcss/Expression.java	(revision 4008)
@@ -129,4 +129,12 @@
             public float blue(Color c) {
                 return Utils.color_int2float(c.getBlue());
+            }
+
+            public String concat(Object... args) {
+                StringBuilder res = new StringBuilder();
+                for (Object f : args) {
+                    res.append(f.toString());
+                }
+                return res.toString();
             }