code: func (v *Notebook) AppendPageMenu(child IWidget, tabLabel IWidget, menuLabel IWidget) int {
  	c := C.gtk_notebook_append_page_menu(v.native(), child.toWidget(),
  		tabLabel.toWidget(), menuLabel.toWidget())
  	return int(c)
  }
docs: // AppendPageMenu() is a wrapper around gtk_notebook_append_page_menu().