Enabled navigation on click of navigation key.

http://webix.com/snippet/031f6073 please find this snippet.
Action:-
If I click on the combo button and then press down arrow key.
Behavior Wanted.
I want to move to the down cell.
Observed Behavior
It is opening popup.
Note :- I have hook up the onKeyPress event which is not get fired in this case.
Advice Needed:-
can you guide me how can i get onkeypress event here. So I can hook up my code here.

Please consider closed I got my ans.
http://webix.com/snippet/823670de