Adding custom collection operation which restricts element type of the input collection (documentation needs improving)

[oxbowlakes]

The documentation on adding custom operations to collections does not go into any detail about how to add operations to collections of particular element types. As per my stackoverflow question, I don't know how to translate the 2.12 method signature:

def split[X, CC[X] <: Traversable[X], A, B](l : CC[Either[A, B]])(implicit bfa : CanBuildFrom[Nothing, A, CC[A]], bfb : CanBuildFrom[Nothing, B, CC[B]]) : (CC[A], CC[B])

Into 2.13 idiomatic style and implement it. The SO question demonstrates one way I solved the problem using the documentation but it requires type parameters to be supplied at the use-site.

It would be good if the documentation could expressly demonstrate how to solve this sort of thing