Sorry I'm still not following. There is no chain, no "next".

The idea is that every callback *can* invoke any other callback. So, for example, a success callback could decide that it wants to invoke an error (and explicitly does so). There really isn't a chain per-se. Success is success.

In other words, passing a `callbacks` object gives us the ability to re-route the success callback into an error. That's all this does.

There is a bug in my code though, let me fix that first. It'll clear things up.