The YUI module is the single core dependency for all YUI 3 implementations. It must be included on all pages that use YUI — and it is the only dependency required to start writing YUI code. The YUI module contains loader functionality and a dependency calculator, allowing it to serve as a `seed` for your implementation. You provide the YUI module list you're using and the code that makes use of those modules; YUI will fetch all necessary components in a single, optimized HTTP request before executing your dependent code. While you may use some of the script- and CSS-loading facilities of the YUI module in your own implementation, this module's core purpose is to serve as a small seed from which complex, highly modular implementations can grow.