On Sun, 9 Jan 2022 at 13:38, Marvin W <[email protected]> wrote: > On 09.01.22 13:24, Dave Cridland wrote: > > Still, as written, the ability send a message which is rendered in > > *radically* different ways in different clients just fills me with > > unease. Fallback bodies are nasty like this - it's why I've never been > > happy with the "multipart/alternative" style of XHTML-IM, for example > > "multipart/alternative" style as you call it is being used in e-Mail for > centuries. I might also be worth looking at other modern messengers like > Matrix, which transports html and plain text as alternatives > [https://spec.matrix.org/unstable/client-server-api/#mroommessage-msgtypes > ]. >
Yes, I'm aware that "multipart/alternative" is used in email, hence my usage of that particular MIME type to describe the style (I wouldn't say centuries though - I remember MUAs getting MIME support as an exciting new feature). It doesn't surprise me that it's repeated in Matrix - it seems like a practical, sensible idea at first, and it was the only reasonable option for email, which prior to this had just plaintext ASCII email bodies. It was generally impossible to update software on your workstation as well, since (for most people) you only had user level access. I'd still argue that it's a bad idea these days, even if Matrix haven't learned from the trouble it's caused in email. Most other proprietary messaging apps just have one form, the only reason email (and us, and Matrix) went for alternatives is because of an existing deployed base that only understood plaintext. This causes not only the problem of messages having potentially wildly different meanings between the alternatives, but also you can never get rid of the compatibility layer. We (like Matrix) would have been better off without it - content negotiation or graceful degradation are always better options when available, and upgrading client software is vastly simpler than it used to be as well. RFC 1341, which introduced multipart/alternative, also introduced the MIME-Version header. We repeated that error too - both our versions are stuck forever at "1.0". (Mark Crispin actually predicted that one back in 1990 or so). Dave.
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