code: @Override
    protected void toggleTooltip(Node reference, Control below) {
      String fieldTooltip = field.getTooltip();
  
      if ((reference.isFocused() || reference.isHover())
          && (!fieldTooltip.equals("") || field.getErrorMessages().size() > 0)) {
        tooltip.setText((!fieldTooltip.equals("") ? fieldTooltip + "\n" : "")
            + String.join("\n", field.getErrorMessages()));
  
        if (tooltip.isShowing()) {
          return;
        }
  
        Point2D p = below.localToScene(0.0, 0.0);
  
        tooltip.show(
            reference.getScene().getWindow(),
            p.getX() + reference.getScene().getX() + reference.getScene().getWindow().getX(),
            p.getY() + reference.getScene().getY() + reference.getScene().getWindow().getY()
                + below.getHeight() + 5
        );
      } else {
        tooltip.hide();
      }
    }
docs: Sets the error message as tooltip for the matching control.
  
  @param below     The control needed for positioning the tooltip.
  @param reference The control which gets the tooltip.