Hi Eliot,
I agree, the documentation could surely be more precise here. Would you possibly be interested in editing it? We are always interested in external contributions (the only reason for enforcing a registration is that we had to stop spamming activities in the past).
In the case of URNs, the token separator is ":", so you could treat each token as a directory name.
Sounds reasonable; I've added an issue for that (https://github.com/BaseXdb/basex/issues/1124).
Cheers, Christian