set focus in Oracle Forms

As in Access, items in Oracle Forms have a default order of focus. I can find no way to programmatically set the focus out of order, as can be done by My.SuchAndSuch.SetFocus in Access. Is there such a method in Forms and, if so, how do I invoke it from PL/SQL?

My specific problem is that when the user inputs something invalid I want control to remain at the field of input, but it stubbornly goes to the next in default order.