As an example of how this works, later this month there's an event called IndieWebCamp 2020 West[archived], a "two days meeting up online to share ideas, create & improve personal websites, and build upon each other's creations." One of the ways of signing up is to make a post on your own weblog RSVPing yes, like I did here. My blog then notifies the IndieWebCamp website that I mentioned them using a W3C Recommendation[archived], and they check my answer to the event by extracting metadata from my post. Isn't that awesome?