XML can be great, but there is more to know about it than most people realize (namespaces for instance). There is a reason why .NET Core switched back from JSON to XML for projects descriptions... When done well I think it can be close to the sweet spot between human and machine readability (if you need that). It has comments, and can natively handle many data types that JSON cannot (like dates). If bandwidth is you primary concern then perhaps you should consider binary serialization? When done bad you get almost any of the OGC Standards[^]... The best thing about JSON is its tight integration with Javascript, which is a nice feature (and why it "won" the web).

Mathieu Cartoixa