<https://jetpack.com/blog/how-to-use-email-subscriptions-in-jetpack-1-2/#primaryimage>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://jetpack.com/blog/how-to-use-email-subscriptions-in-jetpack-1-2/?like_comment=1593&_wpnonce=55228851bd>