def save(self, filename=None):
        filename = Path(filename) if filename is not None else self.filename
        with filename.open("w") as f:
            f.write(self.yaml)
def main(self):
      UI.OpenDialog(
        VBox(
          Heading("This Is a Heading."),
          Label("This is a Label."),
          PushButton("&OK")
        )
      )
      UI.UserInput()
      UI.CloseDialog()