I actually sort of expected the documentation to be generated, not completely hand-written (mainly because I'm a fan of JavaDoc descendants, if they are used correctly). If this was the case, then the doc build tool would need to extract and present some additional information about the applicable traits.

The type signatures are generated, but the text and examples come from extracting documentation comments.

So I was right, it's a generated thing (obviously, a tool cannot provide the description nor usage examples).