def __init__(self, filename=None):
        self.filename = None
        if filename:
            self.load(filename)
def main(self):
      UI.OpenDialog(
        VBox(
          Heading("This Is a Heading."),
          Label("This is a Label."),
          PushButton("&OK")
        )
      )
      UI.UserInput()
      UI.CloseDialog()