How to delete or control "x" button

[mech]

Hi everyone,

I am a novice in prism, and i would like to know if it's possible to
use "onbeforeunload" by a click on "x" button ?
Also, is it possible to "freeze" this button or give it another
function like reduce the page ? I've already search in webrunner.js,
but i didn't find anything.

Thanks by advance !

Antoine.