https://github.github.com/gfm/#example-634
`xmpp` offers an optional `/` followed by a resource.
The resource can contain all alphanumeric characters, as well as `@` and `.`
......

xmpp:foo@bar.baz/txt

xmpp:foo@bar.baz/txt@bin

xmpp:foo@bar.baz/txt@bin.com

......

<p data-sourcepos="1:1-1:20"><a data-sourcepos="1:1-1:20" href="xmpp:foo@bar.baz/txt">xmpp:foo@bar.baz/txt</a></p>
<p data-sourcepos="3:1-3:24"><a data-sourcepos="3:1-3:24" href="xmpp:foo@bar.baz/txt@bin">xmpp:foo@bar.baz/txt@bin</a></p>
<p data-sourcepos="5:1-5:28"><a data-sourcepos="5:1-5:28" href="xmpp:foo@bar.baz/txt@bin.com">xmpp:foo@bar.baz/txt@bin.com</a></p>