code: function(items) {
              var $items = $(items);
  
              for (var i = 0; i < $items.length; i++) {
                  var item = $items[i];
  
                  // Make sure this element doesn't belong to another selector
                  if ($.data(item, 'select')) {
                      Garnish.log('Element was added to more than one selector');
                      $.data(item, 'select').removeItems(item);
                  }
  
                  // Add the item
                  $.data(item, 'select', this);
  
                  // Get the handle
                  var $handle;
  
                  if (this.settings.handle) {
                      if (typeof this.settings.handle === 'object') {
                          $handle = $(this.settings.handle);
                      }
                      else if (typeof this.settings.handle === 'string') {
                          $handle = $(item).find(this.settings.handle);
                      }
                      else if (typeof this.settings.handle === 'function') {
                          $handle = $(this.settings.handle(item));
                      }
                  }
                  else {
                      $handle = $(item);
                  }
  
                  $.data(item, 'select-handle', $handle);
                  $handle.data('select-item', item);
  
                  this.addListener($handle, 'mousedown', 'onMouseDown');
                  this.addListener($handle, 'mouseup', 'onMouseUp');
                  this.addListener($handle, 'click', function() {
                      this.ignoreClick = true;
                  });
  
                  this.addListener(item, 'keydown', 'onKeyDown');
              }
  
              this.$items = this.$items.add($items);
              this.updateIndexes();
          }
docs: Add Items