[scrabble]

Ok, let's say that the code can double as documentation (which is what I stated), and not that the code doubles as all of the documentation.

The code should be able to provide you with the how and the why (supplied with proper testing that covers planned use cases, and comments when testing and code are insufficient.) When code is well written it will answer a lot of questions, I encounter this almost daily when reviewing code.

What code is not is a manual or instructions on plugin writing, etc. You are right on the money there. It's also not API documentation, again, right on the money.