code: function moveHighlight(dropdown, delta) {
          var results = dropdown.results;
          if (!results.length) {
              return;
          }
  
          var resultItems = [].slice.call(dropdown.el.querySelectorAll('.selectivity-result-item'));
  
          function scrollToHighlight() {
              var el;
              if (dropdown.highlightedResult) {
                  el = findResultItem(resultItems, dropdown.highlightedResult.id);
              } else if (dropdown.loadMoreHighlighted) {
                  el = dropdown.$('.selectivity-load-more');
              }
  
              if (el && el.scrollIntoView) {
                  el.scrollIntoView(delta < 0);
              }
          }
  
          if (dropdown.submenu) {
              moveHighlight(dropdown.submenu, delta);
              return;
          }
  
          var defaultIndex = delta > 0 ? 0 : resultItems.length - 1;
          var index = defaultIndex;
          var highlightedResult = dropdown.highlightedResult;
          if (highlightedResult) {
              var highlightedResultItem = findResultItem(resultItems, highlightedResult.id);
              index = resultItems.indexOf(highlightedResultItem) + delta;
              if (delta > 0 ? index >= resultItems.length : index < 0) {
                  if (dropdown.hasMore) {
                      dropdown.highlightLoadMore();
                      scrollToHighlight();
                      return;
                  } else {
                      index = defaultIndex;
                  }
              }
          }
  
          var resultItem = resultItems[index];
          var result = Selectivity.findNestedById(results, selectivity.getRelatedItemId(resultItem));
          if (result) {
              dropdown.highlight(result, { delay: !!result.submenu });
              scrollToHighlight();
          }
      }
docs: Moves a dropdown's highlight to the next or previous result item.
  
  @param delta Either 1 to move to the next item, or -1 to move to the previous item.