Comment by emfree

You piqued my curiosity :) A comment in the source for the release notes (https://github.com/golang/go/blob/master/doc/go1.9.html#L922) points to the relevant change: https://go-review.googlesource.com/c/go/+/34310, which in turn links to this issue: https://github.com/golang/go/issues/13086