All of them - we haven't been too consistent about enforcing that, and there are a lot of docstrings left over, but generally:
 * if a user would need to know it, put it in the manual
 * if other developers of other components would need to know it (e.g., it's providing an API), put it in the developer docs
 * if developers of this source would need to know it (e.g., it's a utility method, like this one), put it in comments