Note that, although popup menus may be created easily to be triggered in various ways, attaching submenus doesn’t work. See this thread from 2½ years ago in which Jim put me straight on several misconceptions:
He wrote then, ‘For now, the documentation is wrong, submenus cannot be used with a popup menu. Well, sort of, with the hack you’ve discovered, but that is not by design and not supported. It’s possible (perhaps probable) that if/when this bug is fixed, your hack may stop working. Sorry.’
And that ‘hack’ no longer works, as predicted.