Edward Tufte's sidenotes. https://edwardtufte.github.io/tufte-css/ https://edwardtufte.github.io/tufte-css/ "Sidenotes are like footnotes, except they don’t for

Edward Tufte's sidenotes. https://edwardtufte.github.io/tufte-css/ https://edwardtufte.github.io/tufte-css/ "Sidenotes are like footnotes, except they don’t force the reader to jump their eye to the bottom of the page, but instead display off to the side in the margin."