Show sub-page content on page

It’s often useful, for example on a staff page showing bios, to show subpage content on the parent page. This way a sub-page can be created for a staff member and all staff can then be featured on the main page. This technique can work just as well for products or projects. The code snippet I use looks like this:

I use if(_is_child()) to restrict this feature to second-level child pages so that only third-level grandchild pages are shown.