public UiTopoLayoutId parent() {
        String p = get(PARENT, null);
        return p == null ? UiTopoLayoutId.DEFAULT_ID : UiTopoLayoutId.layoutId(p);
    }
@Test
    public void setParent() {
        loadLayout(L1);
        assertEquals("parent not default layout", UiTopoLayoutId.DEFAULT_ID, cfg.parent());
        cfg.parent(NEW_PARENT);
        assertEquals("not new parent", NEW_PARENT, cfg.parent());
        cfg.parent(null);
        assertEquals("parent not reset to default", UiTopoLayoutId.DEFAULT_ID, cfg.parent());
    }