The toot I just tooted, about 5–7 things? I got it from social.targaryen.house/@chrisgrace, who credited it to “@HedgeMage”, with no instance marker. That’s a Twitter habit, but doesn’t work on Mastodon, where there could be any number of people on different instances with the same handle. I tracked down which HedgeMage seemed to be the originator, but I think there needs to be an easy automated way of quoting a Mastodon user with the instance intact.
Aaaaand a couple new things: @foo links to the user with the handle foo on your instance, and (I think) only works if the reader is reading on the same instance. instance/@foo only works as a link with the https-colon-slash-slash in front of it.