>>>>> On Sun, 17 Sep 2023, Florian Schmaus wrote:

> <upstream>
>   <reference uri='doi:10.17487/rfc6120'/>
> </upstream>

> sounds perfectly fine.

Don't use an attribute if you can put the information in the (otherwise
empty) element. Especially, when other elements like <doc> already do it
that way.

> It would require (minor) adjustments to the schema and DTD.

Also an update of GLEP 68, in the first place.