Attempted to create a docker repository named “some–thing” and syntax checker failed the name. A single dash (“some-thing”) did work. Bug?
The hub message isn’t as comprehensive as it probably could be, but I did notice that this also seems to be a restriction in the docker engine’s regex:
$ docker tag busybox foo--bar
repository name component must match "[a-z0-9]+(?:[._-][a-z0-9]+)*"