static S wordAtMouse() {
  ret (S) swing(func {
    Component c = componentAtMouse();
    if (c instanceof JTextComponent) {
      JTextComponent tc = cast c;
      Point d = mouseLocation();
      SwingUtilities.convertPointFromScreen(d, c);
      int idx = tc.viewToModel(d);
      S text = tc.getText();
      ret wordAroundIndex(text, idx);
    }
    ret "";
  });
}