At the moment anyway, that XML link won't render per an XML parsing error. For anyone who wants a quick look at what these XML docs look like here's one for UUID6 [0].
[0] https://github.com/uuid6/uuid6-ietf-draft/blob/master/draft-...
The reason it's showing that is because the document says
<?xml-stylesheet type="text/xsl" href="rfc2629.xslt" ?>
But rfc2629.xslt isn't uploaded in the same directory (and Firefox gets real unhappy when it tries to parse the HTML 404 page as an XSLT file). Which is fine, the XML file isn't there to show it rendered, it's to download the source. So you can still just save it.
So the authors wrote this XML https://www.ietf.org/archive/id/draft-peabody-dispatch-new-u...
That XML got turned in to this plaintext https://www.ietf.org/archive/id/draft-peabody-dispatch-new-u... by the xml2rfc tool https://xml2rfc.tools.ietf.org/
And then that plaintext got turned in to the linked HTML by the datatracker.ietf.org server software, which can be found in SVN https://svn.ietf.org/svn/tools/ietfdb/