Forms :: Setting Mouse Position And Restricting Checkbox Update?

what name is used to reverence the mouse cursor in Forms. I am trying to state that if the user reaches the last record in a file and clicks the mouse on the empty record below that they will get a message saying they are at the last record (basically so it means they have to manually click an add record button before they can add a new record)

I currently have this:

IF :SYSTEM.LAST_RECORD = 'TRUE'
THEN
<something here> := :SYSTEM.LAST_RECORD;
MESSAGE('You are at the last record.');
ELSE
DOWN;
END IF;

Where i have <something here> is where i assume the refence for the mouse cursor should go, of which i dont know the name, am i correct?

Another thing is that I have a checkbox that is originally NO but when set to YES cannot be turned back to NO.

I have accomplished this by putting the following code in the WHEN_CHECKBOX_CHANGED trigger and it works fine. However it also updates the checkbox to NO and then back to YES, , as a result this brings up my Are you sure you want to update message. I originally thought that if i took out the :in_active := 'Y'; the FORM_TRIGGER_FAILURE would stop the checkbox being changed in the first place but this didnt appear to be the case. how to accomplish this without letting it update at all (perhaps put something in the WHEN_VALIDATE trigger?

DECLARE
return_alert number;
BEGIN
if :in_active = 'N' THEN
return_alert := SHOW_ALERT('checkbox_alert');
:in_active := 'Y';
RAISE FORM_TRIGGER_FAILURE;
END if;
END;