The content of sub-pages is displayed using Page placeholder web parts. The result of this approach is that the sub-page content is "nested" inside the content of higher‑level pages. The following picture shows the root (master page) without nested content:

 

 

... and here's the home page nested inside the master page:

 

 

Please note how the pages are structured in the content tree: the root (master page) is the parent of the Home page which is loaded inside the master page. You can perform nesting recursively at any level of the content tree. A necessary component for page nesting is the Page placeholder web part. This web part must be placed on the master page and it specifies the place where the underlying page will be inserted. The Page placeholder on the Corporate Site root loads the sub-pages between the main menu and footer: