code: func (w *Window) Parent() (*Window, error) {
  	tree, err := xproto.QueryTree(w.X.Conn(), w.Id).Reply()
  	if err != nil {
  		return nil, fmt.Errorf("ParentWindow: Error retrieving parent window "+
  			"for %x: %s", w.Id, err)
  	}
  	return New(w.X, tree.Parent), nil
  }
docs: // Parent queries the QueryTree and finds the parent window.