i have seen those in annotated javascript documentation. but it was the other way around. (comment on the left, and code on the right). they all seem to use docco[0] with the option to display comment in "parallel". the author of docco used it in their library underscore[1].

[0]: https://github.com/jashkenas/docco

[1]: https://underscorejs.org/docs/underscore-esm.html