onOpenEnd = function onOpenEnd() {
          listen(target$$1, 'transitionend', onOpenEnd, false);
          _this.lock = false;
          _this.target.upgradeSource();

          if (_this.options.enableGrab) {
            toggleGrabListeners(document, _this.handler, true);
          }

          cb(target$$1);
        }
Open (zoom in) the Element.
@param  {Element} el The Element to open.
@param  {Function} [cb=this.options.onOpen] A callback function that will
be called when a target is opened and transition has ended. It will get
the target element as the argument.
@return {this}