required fields + alerts

Hi!

1) Is there a way to give an alert when the user attempt to submit a form
without filling a required field?
I'm using firefox 1.6a2 with the latest nightly build of the XForms plugin (
0.4) and the following example doesn't works as I spected to.

2) The field marked as boolean starts as
invalid, is it right? I supose it's because the model instance is empty and
this empty field does not match with the boolean type (as an empty string
match whith the string type).

Thanks a lot,

Moski