code: function (val) {
              var carousel = this;
  
              if (val >= 0 && val < carousel.get("numItems")) {
                  carousel.scrollTo(val);
              } else {
                  val = carousel.get("firstVisible");
              }
              return val;
          }
docs: Set the value for the Carousel's first visible item.
  
  @method _setFirstVisible
  @param val {Number} The new value for firstVisible
  @return {Number} The new value that would be set
  @protected