Enable lossless markdown editing with Extensible Events

[ShadowJonathan]

Your use case

With MSC1767, it is now possible to represent events in more formats than plain + HTML, this would enable also sending/setting the raw markdown into the event itself, as it's being sent out;

{
    "type": "m.message",
    "content": {

        "m.message": [
            {
                "mimetype": "text/html",
                "body": "i am a <b>fish</b>"
            },
            {
                "mimetype": "text/x-markdown",
                "body": "i am a *fish*"
            },
            {
                "mimetype": "text/plain",
                "body": "i am a *fish*"
            }
        ],
    }
}

Or alternatively (with an MSC);

{
    "type": "m.message",
    "content": {

        "m.text": "i am a *fish*",
        "m.md": "i am a *fish*",
        "m.html": "i am a <b>fish</b>"
    }
}

This would preserve the markdown perfectly, and allow seamless editing without a long tail of lossy html-to-markdown conversion errors (such as element-hq/element-web#12535, element-hq/element-web#17242, etc.)

This would fix element-hq/element-web#10725

This would be extra duplication per message, but until/unless the matrix ecosystem as a whole goes off of HTML, this is unavoidable.

This solution would allow some compatible viewing of events, but an edit of a non-markdown-aware client on such an event like this would still make a lossy conversion of the HTML, instead of using the markdown in full.

Have you considered any alternatives?

Immediate jump to GFM (#330) while speccing the GFM ExtEv keys as well;

The above, but GFM

{
    "type": "m.message",
    "content": {

        "m.message": [
            {
                "mimetype": "text/html",
                "body": "i am a <b>fish</b>"
            },
            {
                "mimetype": "text/x-gfm",
                "body": "i am a *fish*"
            },
            {
                "mimetype": "text/plain",
                "body": "i am a *fish*"
            }
        ],
    }
}

Or alternatively;

{
    "type": "m.message",
    "content": {
        "m.text": "i am a *fish*",
        "m.gfm": "i am a *fish*",
        "m.html": "i am a <b>fish</b>"
    }
}

Additional context

No response