Now that you know symfony very well, you are already able to dig into its code to understand its core design and discover new hidden abilities. But before extending the symfony classes to match your own requirements, you should take a closer look at some of the configuration files. Many features are already built into symfony and can be activated by just changing configuration settings. This means that you can tweak the symfony core behavior without overriding its classes. This chapter takes you deep into the configuration files and their powerful capabilities.