That sentence raised the same question for me. I interpreted it as not meaning code comments.
However, I think it's a good idea to justify certain design decisions in code comments, for example where a design choice might cause another developer looking at your code to think "why did he do it that way?" or "how does this bit work then?"
I’ve looked at a lot of different solutions, and in my humble opinion Aspose is the way to go. Here’s the link: http://aspose.com
subject: Where to document minor design descisions