We had a little dicussion recently on which parts play toghether when booting a Symfony2-based application. In particular, there's the front controller, the "AppKernel" and the choice of a particular "environment".
For us, it was important to sort this out and get the naming straight because of the way we do configuration management and partially code generation when we deploy our projects.
Instead of putting the summary on our internal wiki, we thought the Symfony2 documentation might be a much better place. So we're proud that our addition was accepted and is now available for everyone :-).
By the way – if you love Symfony2 as much as we do, maybe you would like to join our team?