code: public static InfoPopup error (String message, Position pos, Widget source)
      {
          if (source instanceof FocusWidget) {
              ((FocusWidget)source).setFocus(true);
          }
          return show(new InfoPopup(message).toError(), pos, source);
      }
docs: Displays error feedback to the user in a non-offensive way. The error feedback is displayed
  near the supplied component and if the component supports focus, it is focused.