docs: @JSFunction
      public static Object varargs(Context cx, Scriptable thisObj,
                                              Object[] args, Function funObj)
      {
          StringBuilder buf = new StringBuilder();
          buf.append("this = ");
          buf.append(Context.toString(thisObj));
          buf.append("; args = [");
          for (int i=0; i < args.length; i++) {
              buf.append(Context.toString(args[i]));
              if (i+1 != args.length)
                  buf.append(", ");
          }
          buf.append("]");
          return buf.toString();
      }