If there were somehow a strict definition of the Article spec, mastodon would simply ignore it.

It’s just basically just a link. (For mastodon. I think hometown inlines it somewhat properly.)

No (not yet), I haven’t found a need for that.

Ignore the replies saying you did tag evan. If you look at the AP object, it’s clear he wasn’t tagged. If your intention was to notify him, what some random client does to the html later obviously won’t do that.