In my latest meeting with the Drupal people, we talked about their native support for buttons in forms which is currently missing in Symfony. They support things like:

• Different buttons lead to different validation groups being executed. E.g. a "Previous" button in a multi-step form would not trigger validation, while a "Next" button would.
• Support for adding/removing rows to/from a collection form using server round-trips when JavaScript is not available.

This ticket needs more research, but we should look into supporting these use cases in future releases.