In the conclusion of the second part of this series, I've talked about one great benefit of using the Symfony2 components: the interoperability between all frameworks and applications using them. Let's do a big step towards this goal by making our framework implement HttpKernelInterface.

By changing up the custom framework just a bit to use HttpKernelInterface, you get built-in HTTP caching (HttpCache). He shows how to use this class to create some custom caching rules and how to use Edge Side Includes to only cache partial parts of the page.