As far as possible, these classes should use encapsulation to hide the implementation details from the user; for example, users of your module don't need to be aware of individual resource names. In software engineering, we call this encapsulation. For example, in a config class, we can use several resources, but the user doesn't need to know all about them. Rather, they just simply know that they should use the config class for the configuration of the software to work correctly.

Having classes contain other classes can be very useful, especially in larger modules where you want to improve code readability. You can move chunks of functionality into separate files, and then use the contain keyword to refer to these separated chunks of functionality.