code: function () {
              removeButtonEventHandlers.call(this);
  
              this._aButtons = null;
  
              var aForms = this.element.getElementsByTagName("form"),
                  oForm;
  
              if (aForms.length > 0) {
                  oForm = aForms[0];
  
                  if (oForm) {
                      Event.purgeElement(oForm);
                      if (oForm.parentNode) {
                          oForm.parentNode.removeChild(oForm);
                      }
                      this.form = null;
                  }
              }
              Dialog.superclass.destroy.call(this);
          }
docs: Removes the Panel element from the DOM and sets all child elements
  to null.
  @method destroy