Next come the four button triggers you defined yourself. Just look at the first of them to confirm the syntax of the ON statement:

ON CHOOSE OF BtnFirst IN FRAME CustQuery /* First */
DO:
  GET FIRST CustQuery.
  IF AVAILABLE Customer THEN 
    DISPLAY Customer.Name Customer.CustNum Customer.Address Customer.City 
          Customer.State 
      WITH FRAME CustQuery IN WINDOW CustWin.
  {&OPEN-BROWSERS-IN-QUERY-CustQuery}  
END.

When you define triggers in the Section Editor, it masks the syntax of the ON statement somewhat by putting the event name and the object name into fill-ins that you can select. It also automatically adds the IN FRAME qualifier for you, based on which frame contains the object.