code: function() {
  
              Dialog.superclass.setFirstLastFocusable.call(this);
  
              var i, l, el, elements = this.focusableElements;
  
              this.firstFormElement = null;
              this.lastFormElement = null;
  
              if (this.form && elements && elements.length > 0) {
                  l = elements.length;
  
                  for (i = 0; i < l; ++i) {
                      el = elements[i];
                      if (this.form === el.form) {
                          this.firstFormElement = el;
                          break;
                      }
                  }
  
                  for (i = l-1; i >= 0; --i) {
                      el = elements[i];
                      if (this.form === el.form) {
                          this.lastFormElement = el;
                          break;
                      }
                  }
              }
          }
docs: Configures instance properties, pointing to the
  first and last focusable elements in the Dialog's form.
  
  @method setFirstLastFocusable