Destination 5250 form arrival scripts use this JavaScript method to display themselves:
SHOW_CURRENT_FORM(true);
They can specify that a form wrapper should be used to display the details instead, like this:
SHOW_CURRENT_FORM(true, "VL Wrapper Id", "Additional information to be passed to wrapper" );
Note that it's the wrapper's id (which is often not the same as its name) that you have to specify in the second parameter.