Asking about sandbox and core design

[cod3beat]

Im not sure if this is the appropriate place to ask. After reading some presentation from Addy Osmany about Module, Facade, Mediator, and then after reading how AuraJS seperates the components into extension, sandbox, and core, I was very interested how you guys can seperate the application code from the core code.

In aurajs documentation, it says that a sandbox:

A sandbox is just a way to implement the facade pattern on top of features provided by core. It lets you expose the parts of a JavaScript library that are safe to use instead of exposing the entire API

But when i read the aura-github example (for example this one: https://github.com/aurajs/examples/blob/master/aura-github/public/widgets/alerts/main.js), I saw that the widget can access jquery API, such as:

this.$el.show();

Is that correct? Isn't that exposing the underlying core library API?

Hopefully you guys understand what I mean, and in by no way I'm saying that I know what the good way, or bad way is.

So please help me to see this architectural idea correctly.

thanks in advance