code: function (val) {
              var carousel   = this,
                  isCircular = carousel.get("isCircular"),
                  numItems   = carousel.get("numItems"),
                  sentinel   = numItems - 1;
  
              if (val < 0) {
                  if (isCircular) {
                      val = numItems + val;
                  } else {
                      val = carousel.get("selectedItem");
                  }
              } else if (val > sentinel) {
                  if (isCircular) {
                      val = val - numItems;
                  } else {
                      val = carousel.get("selectedItem");
                  }
              }
              return val;
          }
docs: Get the value for the selected item.
  
  @method _getSelectedItem
  @param val {Number} The new value for "selected" item
  @return {Number} The new value that would be set
  @protected