code: function (index) {
              var choices = this.findHighlightableChoices(),
                  choice,
                  data;
  
              if (arguments.length === 0) {
                  return indexOf(choices.filter(".select2-highlighted")[0], choices.get());
              }
  
              if (index >= choices.length) index = choices.length - 1;
              if (index < 0) index = 0;
  
              this.results.find(".select2-highlighted").removeClass("select2-highlighted");
  
              choice = $(choices[index]);
              choice.addClass("select2-highlighted");
  
              this.ensureHighlightVisible();
  
              data = choice.data("select2-data");
              if (data) {
                  this.opts.element.trigger({ type: "select2-highlight", val: this.id(data), choice: data });
              }
          }
docs: abstract