I've seen it before, but I can't remember which project or which documentor they used (if any). I'm pretty sure it was a JS project, probably a Node.JS module.
Anyhow, the documentation was listed by file, and each page displayed as 2 columns, one with the inline documentation, and the other with the code.
Does anyone know which tools allow for this?
"Annotated Documentation" is what I was trying to think of!
The tool was docco.
The above link is docco's documentation as documented using docco.