I was confused by the current wording. This wording
answers the question more clearly.

Thanks to Robert Griesemer for suggestions.

Fixes #16916

Change-Id: I50187c8df2db661b9581f4b3c5d5c279d2f9af41
Reviewed-on: https://go-review.googlesource.com/28052Reviewed-by: Robert Griesemer <gri@golang.org>