Currently, if there are 3 levels of pages (eg. Top Page > Sub Page > Details Page) and a user is on the Details Page, only the Top Page and the Details page will indicate that it's selected. This is accomplished through the NavItem's isSelected() method.
This improvement adds a new method to NavItem, isChildSelected(), that allows developers to check if Sub Page is selected.
#if ($nav_item.isSelected() || $nav_item.isChildSelected())
#set ($nav_item_class = "selected")
#set ($nav_item_class = "")