B2G/gecko/browser/components/tabview/groupitems.js
// if there are no children.
if there are no children.
if there are no children .
function GroupItem_setActiveTab(tab) {
    Utils.assertThrow((!tab && this._children.length == 0) || tab.isATabItem,
        "tab must be null (if no children) or a TabItem");
    this._activeTab = tab;
    if (this.isStacked())
      this.arrange({immediately: true});
  }
function GroupItem_setActiveTab ( tab ) { Utils . assertThrow ( ( ! tab && this . _children . length == 0 ) || tab . isATabItem , "tab must be null (if no children) or a TabItem" ) ; this . _activeTab = tab ; if ( this . isStacked ( ) ) this . arrange ( { immediately : true } ) ; }
if there are no children.
if there are no children .