If you don't know for sure how to use a certain filter, be sure to check out the examples folder in the plugin.
If you're a developer, we have some extra goodies for you [...]
If you're a developer, you are probably developing your site locally. The we have some good news for you. We have thought of that [...]
With this filter you can set a pre-filled email address on the registration form.
With this filter you can set a pre-filled username on the registration form.