This is cool, but it’d be cooler (and more usable) if it had a way for the right frame to go directly to the context of the left one.
Line numbers and manual scrolling are still workable, but it sure feels unpolished.
I missed that too and have made an improved version for myself: https://matracas.org/tmp/lions-/
I added the reverse links from source to notes, and also extra links from the note text to the source code.
There are some issues pending, for instance that for some lines there are several links to them and the reverse link goes only to one. That’s a limitation of HTML but it could be worked around.
I’m trying to figure out its copyright status: it would be nice to make a new edition in the same style of my re-edition of the Xanadu description “Xanadu Hypertext Documents” https://lobste.rs/s/wsmudg/xanadu_hypertext_documents