docs: function () {
              if (!this._popup || !this._popup.isOpen || this._draggable) {
                  // maybe the popup was closed while loading aria.utils.dragdrop.Drag,
                  // or it was closed and re-opened very quickly (and we should avoid
                  // creating the _draggable object twice)
                  return;
              }
              this._draggable = new aria.utils.dragdrop.Drag(this._domElt, {
                  handle : this._titleBarDomElt,
                  cursor : "move",
                  proxy : this._cfg.movableProxy,
                  constrainTo : this._popupContainer.getContainerRef(),
                  dragOverIFrame : true
              });
              this._draggable.$on({
                  "dragstart" : {
                      fn : this._onDragStart,
                      scope : this
                  },
                  "move" : {
                      fn : this._onDragMove,
                      scope : this
                  },
                  "dragend" : {
                      fn : this._onDragEnd,
                      scope : this
                  }
              });
          }