forName() is used to bind a window object to a window using the identifier specified in the OPEN WINDOW statement. It requires a single parameter that is the name of the window opened using OPEN WINDOW. The method is used in combination with the LET statement and needs namespace specification:
DEFINE wo ui.Window
OPEN WINDOW orders AT 2,2 WITH FORM "f_orders"
LET wo = ui.Window.ForName("orders")