Blackberry Playbook WebWorks How to make a textfield open a different virtual keyboard?

Question

I'm developing a WebWorks application for the Blackberry Playbook. This page in their documentation says

You can display a specific type of virtual keyboard, depending on the type of input that is required. In addition to the default keyboard, you can choose from a selection of keyboards, such as a keyboard designed for typing in an email or a keyboard designed for typing in a browser.

https://bdsc.webapps.blackberry.com/html5/documentation/ww_best_practices/ui_components_tablet_microsites_1877108_11.html

However, I can't find any documentation on how to actually DO that. I have some fields for entering an email address, so I'd like to give the user an email focused keyboard.

This is a WebWorks app, not Flash. Any ideas?