While I was digging around my file server, I came across XNS Technical Specs version 1.0 (July 2002, 7 edition), so I'm posting it here.
If the XDI.org site was still up and running I would have been able to download it from there, but since the site has been abandoned I am providing a repository instead.
XNS later became XRI/XDI, and is the technology that became the core specification of OpenID 2.0. The current DID is also an extension of that. I think there are many things that are quite useful. If you are talking about decentralized IDs these days, I think this is a good specification to read.