- FormLayout: We prevent the 'submit' event unconditionally, which means that the underlying HTML <form> element can not actually be submitted.
- ButtonInputWidget: We prevent the 'click' event unconditionally, which means that the button can not be used to submit a form (form 'submit' event is not fired if the 'click' event is prevented).
- (maybe others?)
We need to allow the OOUI event handlers to decide whether the DOM events should be prevented. Making the current behavior configurable with config options would also help, but might not be sufficient?
Broken reverted attempt at fixing a part of this: https://gerrit.wikimedia.org/r/#/c/191834/