undocumented expectation for webfinger of domain

[Johann150]

When I use the Follow button whithout being logged in, I am prompted to enter my instance's domain name. (I think previously I was asked my full profile handle?) From what I understand if I enter domain.example, the JavaScript will then try to web-finger https://domain.example (see https://github.com/mastodon/mastodon/blob/b1dec09d203d535a3b0bc61e520e520ba7643878/app/javascript/packs/remote_interaction_helper.ts#L77-L92).

The expectation that https://domain.example will resolve to anything is not documented on the webfinger page, for example in the list at the end it should have a case saying something like this:

• Asking example.com for the resource https://example.com yields a link with rel of http://ostatus.org/schema/1.0/subscribe.

I did not check if this is expected in other places too (to resolve to a full link to the instance actor) or if the ostatus subscribe template is enough.

NB: This expectation does not currently hold with Misskey and breaks the feature because it redirects to a non-existent URL.