Hi!
Thanks for pointing out that subscribe, like publish, is described as optional functionality by certain sections of XEP-0060.
I agree with you that given that (and since there are XEPs that make use of that), the feature should not be defined as REQUIRED in section 10. There's some bike-shedding to be done on OPTIONAL vs RECOMMENDED maybe (Having a XEP that is titled "publish-subscribe" for which both the "publish"as well as the "subscribe" part are optional seems... weird to me), but regardless, REQUIRED does not seem to fit at all.
That leaves us with having not a single feature that the XEP requires to be advertised for a pubsub service. As Goffi describes, the disco#info identity can be used for that purpose. I do worry that a significant amount of implementations use the (currently undocumented) '
https://jabber.org/protocol/pubsub' feature for this. For that reason, I'd still like to see the feature be explicitly named (normative) in XEP-0060.
As XEP-0060 is Stable, I don't believe this can be made a REQUIRED feature, but a RECOMMENDED one (including a note that describes how services are recommended to publish it, but that consumers should not depend on it (and use the identity instead)) should be a good improvement over the current state of the XEP.
Thoughts?
Kind regards,
Guus