[jQuery] [Validate] Custom error message for a group of fields

[Bizzy]

Hi,

let's take this example :

$("#myform").validate({
  groups: {
    username: "fname lname"
  },
  errorPlacement: function(error, element) {
     if (element.attr("name") == "fname"
                 || element.attr("name") == "lname" )
       error.insertAfter("#lastname");
     else
       error.insertAfter(element);
   },
   debug:true
 })

I want to c$("#myform").validate({
  groups: {
    username: "fname lname"
  },
  errorPlacement: function(error, element) {
     if (element.attr("name") == "fname"
                 || element.attr("name") == "lname" )
       error.insertAfter("#lastname");
     else
       error.insertAfter(element);
   },
   debug:true
 })

If i want to declare a custom message that will be shown for the whole
goup if one of the group elements is not filled ?
thanks in advance!