The idea is that the URL can do something, like link to specification or something. However, there is nothing mandatory the URL has to do whatsoever. I think i

The idea is that the URL can do something, like link to specification or something. However, there is nothing mandatory the URL has to do whatsoever. I think in practice you can treat it as an opaque blob and if you want to just declare a namespace as "bar.foo.example.com" I think it would work just about everywhere. There's enough legacy, but still in use, namespaces that aren't full legal URIs that libraries will never be able to start enforcing it, and since there's effectively no utility in forcing them to be URIs anyhow I doubt it'll suddenly become an issue when all the libraries decide to become compliant. Given that it's a bit bizarre to have a URI to something that doesn't have to even so much as exist, I can't see the standards bodies every getting very fussy about this either. Backing it down to just being "some agreed-upon blob value" would be backwards compatible anyhow.