Is there any API documentation on the next() function? #197

I want to see what is capable with the next() function besides bubbling errors to a Stormpath form. More specifically I want to not only send a new Error to the form from an express preRegistrationHandler (which I know how to do because it is in the documentation), but I also want to fire a function within scope of the form from the preRegistrationHandler.

Now I know that there is a next() call in my client-side onFormSubmit which then passes data to the preRegistrationHandler in express, but how can I access the scope of the form again from the preRegistrationHandler? I am unsure if I should be passing a function or some type of callback into the client-side next() prior to the preRegistrationHandler.