Regarding the handling of IRIs as XML namespaces

[funkyfuture]

before i dump an attempt to validate declared namespaces as IRIs (RFC 3987) in #68, i want to leave some notes about the problem.

• lxml doesn't seem to validate namespace values, after all the test suite is full with invalid ones
• rdflib validates URIs like this, it doesn't really
• there's also uritools that focuses on parsing rather than validation and has no type annotations or support for RFC 3687 yet
• delb's namepace validation logic (as part of a parser implementation) would also have to consider xml:base and thus require a function to resolve relative IRIs
• in the Rust realm there are iref, iri-string, oxiri & sophia_iri

whatever a design decision will be, i'd rather like to see it late on the roadmap.