Tapestry.require_radio_field = function(event, field, message)
{
 if(field){
  if(field.length){
   for(var i = 0, length = field.length; i<length; i++){
    if(field[i].getAttribute("checked")){
     return;
    }
   }
   event.invalid_field(field[0], message);
  }else if(field.getAttribute("checked")){
   return;
  }else{
   event.invalid_field(field, message);
  }
 }
}