Embed links to third party identities with rel="me" for cross verification.

[Half-Shot]

E.g. GitHub allows you to link a URL in your profile (like so: https://github.com/Half-Shot) which shows up as a

<a rel="nofollow me" class="Link--primary" href="https://mastodon.half-shot.uk/@halfy">https://mastodon.half-shot.uk/@halfy</a>

This is handy because on the other service it can cross reference your ownership of the identity, like so:

Obviously this kind of thing is tricky to support in matrix.to because:

• We still don't have a way to set arbitrary profile keys ( e.g. WIPish: MSC1769: Extensible profiles as rooms matrix-spec-proposals#1769 )
• If we used ^, we'd need a way to fetch state while being unauthenticated and in a fairly cache friendly manner.

[Mikaela]

I mostly see rel=me page by Indieweb.org which attributes the specification to https://microformats.org/wiki/rel-me