Where is the latest docker images specification?

After unpacking a tarball that is emitted by docker save, I notice that it has a set of layer directories and a repositories file as well as a manifest.json . After reading the image specification linked on the main github page (https://github.com/docker/docker/blob/master/image/spec/v1.md) I’m not sure what the manifest file contains and how it supercedes the repositories file (which is my understanding). Is there an updated doc which describes the format of the tarball emitted by docker save ?