Genero Web Front End and popups dialog box - how to ?

Hi all,
 
In the Genero Web Front End, is there any way to pop up a confirmation
dialog box on top of the browser window which the user is working on ? What
I would like to do is that after the user made changes to a screenful of
information on the browser window (using a default html template) but then
clicked the "Cancel" button on the top toolbar, I want to pop up a dialog
box to ask him/her to confirm the cancellation. If  the user picks "Yes",
then the 4GL code will discard the modification. If "No", then the 4GL code
will CONTINUE INPUT.
 
From what I have found so far in the documentation, Web Front End only
supports SDI and such a popup is not possible.
 
 
Thanks.
 
 
Fred