does anyone have strong opinions on chat application message formatting wire formats

discord using markdown, matrix using (a subset of) HTML (generally speaking), telegram having character ranges

i think the telegram approach of "the body is plaintext and you have attributes attached to characters" is interesting, though i'm not sure how well that works for inserting formatting that doesn't really correspond to any particular text

something that lets you explicitly define fallbacks would be interesting. like

<first-supported>
<geoloc coord="125,64" />
<a href="geo:125,64">Location</a>
<span>Location (125,64)</span>
</first-supported>

for better backwards compatibility with old clients seeing new messages