> I like to write commentary in the margins

Oh man, tangent into one of my favorite library book experiences. I checked out a sci-fi book at the library. It was good I was enjoying it. Then a few chapters in, I found a previous library patron had written nit-picky notes in the margin, poking holes in the author's fictional science tech explanations. And these weren't little one-word exclamations, they were whole sentences written in perfectly legible, almost impossibly-tiny pencil handwriting. Some of them even had little drawn diagrams! It went through the whole book, every hundred pages or so some little margin notes about how such-and-such sci-fi babble didn't reflect how space-time actually works or whatever. It was a hoot, a little bonus on top of the book itself.

I had a similar experience with a second-hand copy of House of Leaves [0].

This was a special treat because the book itself already uses copious footnotes and cross-references from fictional characters to create a maze. And now a real person added to the effect by trying to make sense of it themselves.

[0]: https://en.wikipedia.org/wiki/House_of_Leaves