code: function (index) {
              var count = this.insertedOptionsCount();
  
              if (index < 1 || index > count) {
                  this.$logError(this.INDEX_OUT_OF_BOUNDS, [count, index]);
                  return;
              }
  
              this.removeHighlight();
  
              var suggestionNode = this._getSuggestionsContainer().children[index - 1];
  
              this._addClass(suggestionNode, 'highlight');
              suggestionNode.firstChild.setAttribute('tabindex', 0);
              suggestionNode.firstChild.focus();
          }
docs: Exclusively highlights the inserted option located at the given index. That means that any other highlighted
  option will not be highlighted anymore, and this even if the targeted option is already highlighted.
  @param {Number} index Index of the option to highlight. 1-based.
  @see removeHighlight
  @see addHighlight