function Roller(location, targetElement)
      {
      var userData = new roller_user_data(targetElement);
      this.ajax = new Ajax(location, roller_on_success, roller_on_failure, roller_on_completion, true, userData);
      
      this.roll = roller_roll;
      }
      
    function roller_roll()
      {
      this.ajax.execute();
      }
          
    function roller_on_success(responseText, status, statusText, userData)
      {
      var targetElement = userData.targetElement;
      targetElement.innerHTML = responseText;
      }
      
    function roller_on_failure(status, statusText, userData)
      {
      var textStatus =  statusText + ' \(' + status + '\)';
      
      var targetElement = userData.targetElement;
      targetElement.innerHTML = 'Unable to load content \(' + textStatus + '\).';
      }
      
    function roller_on_completion(responseText, status, statusText, userData)
      {
      }
      
    function roller_user_data(targetElement)
      {
      this.targetElement = targetElement;
      }