Kind of like how you can do [in-line links](a website) to link people to a website, allow the user to use the same syntax to create contextual information that appears when the user mouses over. This way users who know the context won’t have to slog through a massive wall of text while those who don’t can optionally bring themselves up to speed.
This is definitely a cool but very niche feature that I and nerds like me would use, but the vast majority of normal* folk never would. So for that reason it’s probably not going to be any kind of priority to add. But hey, in the meantime, we’ve always got footnotes!
* “normal” by Lemming standards, anyway