scala/scala.github.com — comment on commit c9f4e7828c67289ee27c320fde6524a8a6963d6a
File: overviews/parallel-collections/introduction.md line 66
By heathermiller:

Perhaps a nice motivating example would be to give an example of the collections hierarchy when parallel collections were added there weren't yet any Gen traits? For example, in the old design, you could have some method on Seq which you could pass a ParSeq to. (Not sure if it's overkill to add all of this discussion though.)