[Standards] Extending XEP-0313 with trimming support

Hi folks, There are a few limitations with XEP-0313 which I've been hoping to address for a while, mostly around giving users more control and making it easier for operators to comply with various data protection requirements. Users have control over most account data in XMPP. However archives are, generally, read-only. In particular, user data should generally be deleted upon request. Currently such requests would have to be manually sent to the service operator, as there is no in-band method for this yet. My proposal is to support an in-band 'trim' command, which allows removal of all archived messages, or up to (and including) a specific archived message, or deletion of the entire archive. The functionality is optional and discoverable, so shouldn't affect backwards compatibility. This has some limitations. For example, it wouldn't allow selectively deleting all messages with a specific contact, which is occasionally requested. Such an operation would leave holes in the archive (which XEP-0313 forbids to ensure sync points don't get removed). But I'm in favour of solving what we easily can for now. There are other things I would like to improve around archiving, such as exposing retention configuration. But I plan for these to live in new XEPs. As XEP-0313 is stable and almost universally implemented, I wanted to raise awareness of this proposal and seek some consensus from the community before pushing it forward to Council. The PR can be found at https://github.com/xsf/xeps/pull/1514 The new section is rendered at https://matthewwild.co.uk/uploads/xep-0313.html#trim Regards, Matthew