Page Includes (Advanced) is accessed from the Admin Panel by clicking on the Page Includes (Advanced) tab. This is used to inject either javascript or css includes into the page at runtime. It is intended to be a way to customize the page without modifying markup. You can include a reference to a js file, css file or script out raw javascript. You can define a page you want this script on and whether you want it to be in the Header or at the end of the page.