Modern XMPP project discussion - 2025-08-19

> But then thanks to limitations in Conversations database schema, that is basically what we have already. Wait, someone actually validates incoming XML?

Doesn't that go against the whole reason why XMPP uses XML in the first place?

I'm not sure what you mean

Validating incoming stanzas against a schema

Instead of just ignoring unknown stuff

The thing you quoted is nothing to do with "validating XML", but also yes, some implementations use schemas, and that's not against extensibility

XML extensibility works via namespaces, and each namespace has a schema

exactly

schemas can (and do) allow for extension outside their namespace

It's "against the rules" to just put unknown stuff into an existing namespace

there are SOME implementations (not pointing fingers at you, xmpp-rs) which will by default reject *anything* they don't know (even if it's in another namespace), but I consider that bad practice and will work on changing that ;)

The "just ignore unknown stuff" is what JSON-based systems basically have to do, because they don't have namespaces, and therefore can't do strict schema validation (if they also want extensibility)

XML allows both

Then stuff can break

The XSF does not allow such changes in XEPs, so that would not be an official XMPP extension

In practice, it would generally be okay, but no guarantees

Since most implementations are extremely relaxed when it comes to validation

IIRC, some XEPs had additions without changing namespace ✏

Damn, i edited the message instead of sending new one

But for the sake of ensuring interoperability and avoiding surprises, it's still good to stick to the rules. Even if it doesn't strictly validate a schema, if an implementation is developed against one schema, and then you change it in some way, you don't know if the code will correctly handle it the way you want.

MattJ, JSON schemas do have namespaces, don't they? It's just a hell to parse. Or is that only with JSON-LD?

AFAIK only JSON-LD gets you anything like that

> The XSF does not allow such changes in XEPs, so that would not be an official XMPP extension IIRC, some XEPs had things added in them without namespace changes

MattJ, right.

alexkurisu, examples would help. There may be exceptions, but they should be rare. Normally such changes incur a namespace bump.

The most recent example is XEP-0363 and the "Upload purpose" stuff

https://xmpp.org/extensions/xep-0363.html#example-7

Notice how the new element has a different namespace

Ah, wait, it adds it in its own namespace, yeah.

And that's what lack of proper sleep does to your brain…

So an implementation that validates using the old namespace will just ignore that element, and validate successfully, as intended

Which is nice, it makes the rules of extensibility well-defined, rather than a gamble every time you add something

> AFAIK only JSON-LD gets you anything like that Made a meme from that ↺

the LD in JSON-LD is for lethal dose.

https://upload.movim.eu/files/9d94237298995552fa13436420195fbca436dce7/HKyI9hCRwKA3/chat_1000008762.jpg