The source code of Zend Framework 3 is stored in GitHub repositories. There is a separate repository per each ZF3 component.
In most cases you won't need to get the code of Zend Framework 3 manually. Instead, you will install it with Composer dependency manager. We will become familiar with Composer later in a chapter called Zend Skeleton Application.
It is a good practice to introduce some common coding standard for all your code. This standard would define class naming rules, code formatting rules, etc. Zend Framework 3 defines such standard here. All the code in ZF3 follows the rules described in that document.
If you plan to write a ZF3-based website, it is recommended that you follow the same standard for your own code. This will make your code consistent and easier to extend and support by other people.