code: function activate($article, expandParents) {
      var $item;
  
      if ($active) {
        $item = $active.data('ndoc.item') || $empty;
        $item.removeClass('current');
        eachParent($item, function ($parent) {
          $parent.removeClass('current-parent');
        });
      }
  
      // set new active article
      $active = $article;
  
      // update title
      document.title = getTitle($article);
  
      $item = $active.data('ndoc.item') || $empty;
      $item.addClass('current');
      eachParent($item, function ($parent) {
        $parent.addClass('current-parent');
        if (expandParents) {
          $parent.data('ndoc.childs')
            .data('ndoc.collapsed', false)
            .animate({
              height: 'show',
              opacity: 'show'
            });
        }
      });
    }
docs: activates item (used upon scrolling)