[Standards] Proposed XMPP Extension: Channel Binding Pseudomechanisms

Florian Schmaus flo at geekplace.eu
Sat May 9 16:09:45 UTC 2020


On 5/9/20 4:58 PM, Marvin W wrote:> On 07.05.20 18:34, Sam Whited wrote:
>> Can we modify the mechanisms feature? Having this be an extension to the
>> mechanisms feature seems problematic to me.
> 
> Extensibility inside the <mechanisms> element is part of RFC6120. The
> schema at https://www.rfc-editor.org/rfc/rfc6120.html#appendix-A.4
> explicitly allows for arbitrary elements inside it.

Thanks for pointing this out Marvin.

> Any client, server
> or library not allowing unknown elements to be present in <mechanisms>
> can therefor be considered RFC non-compliant. Any strict validator that
> fails to validate such unknown element inside <mechanisms> is either
> broken or fed with an invalid schema.

Actually the schema is irrelevant when it comes to RFC compliance.
Schemas are non-normative. This is explicitly noted in the RFC.

But this demonstrates the extensibility spirit of XMPP. As I said
before, we do add new elements and attributes without a namespace bump
if possible all the time. And it is one of the key strengths of XMPP,
that we have that ability to extend XML elements without namespace bumps
whenever possible.

That is why you will find many schemas in XEPs without the explicit
declaration of <xs:any namespace='##other/>, and yet those will be
extended without namespace bumps (if possible).

- Florian


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