Rails 2.3 nested forms and transactions

Hi all,

Does anyone know if the new nested object forms in Rails 2.3 supports
transactions on save? (http://guides.rubyonrails.org/
2_3_release_notes.html#nested-object-forms)

Supposing you had a form that let users of an app create an account
and the admin user account in the same screen, nested object forms
seem like a good fit. However, creating the customer account and the
user need to be done as a transaction (you wouldn’t want a customer
without an admin user or vice versa).

How is this handled? Is this the default? Does it need to be
implemented in a :reject_if proc?

Thanks!