With this

> This discussion conflates comments with highlights, which are two different animals altogether.

And this

> The distinguishing feature of highlights is that they are anchored to a specific passage in a (hyper)text

And this

> Comments are an entirely different animal

And this

> Binning bookmarks, highlights, and comments together as "content" is like calling wedding cake, bobcats and lighter fluid different kinds of "matter"; it's reductive to the point of uselessness.