You are browsing the documentation for Symfony 2.3 which is not maintained anymore.
Consider upgrading your projects to Symfony 5.3.
The Components implement common features needed to develop websites. They are the foundation of the Symfony full-stack framework, but they can also be used standalone even if you don't use the framework as they don't have any mandatory dependencies.
This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.