Very tasteful web design, too. I was curious how the layout was done, and the answer is the venerable <table>

Could it be a framework / library? Since it looks exactly like [0]

[0] https://khamidou.com/compilers/lisp.py/

Made with pycco, a variant of docco:

https://pycco-docs.github.io/pycco/

I agree, it's a really cool way to lay out code with commentary. I wonder if it would be useful to generate a layout like this from code interleaved with comments, moving the comments to the sidebar.