In fact, I was wondering if it's possible to use it for other purposes than check required fields. For example, I have a python function performing a check on the values entered, and I'd like to use this kind of popup instead of the usual messagebox. What interests me in this popup is that it doesn't take the focus and oblige the user to click ok before doing something else.

just add required in your field

example :

 'name': fields.char("Name ",size=128,required=True),

and this popup is automatically displayed.