@baldur That’s a thought-provoking post. I’ve been experimenting with <details> and <summary> tags for notes. They have the disadvantage that they can’t be anchored to particular words or phrases in the text and can be displayed only between paragraphs (<details> is a block element) but that’s not a deal breaker for me. I also like the idea of using <aside> with CSS to position it in the margin and create a marginal note. Again, it’s a block element that can’t be anchored to a word or phrase. But the main reason I’ve avoided <aside> so far is that it probably wouldn’t display well on mobile without additional CSS.
@artkavanagh Yeah, it's also a topic I've been thinking about as I really like the idea of notes/sidenotes. I don't know if I'll end up using this solution but it's useful to have as a reference.