A repository name is broken up into path components. A component of a repository name must be at least one lowercase, alpha-numeric characters, optionally separated by periods, dashes or underscores. More strictly, it must match the regular expression [a-z0-9]+(?:[._-][a-z0-9]+)*.
Please update the regex mentioned in docs because it is outdated.
https://docs.docker.com/registry/spec/api/#overview
Now multiple dashes and double underscore is allowed.
https://github.com/docker/distribution/blob/master/reference/regexp.go#L18
I used the go playground which gave me as an output this regex
[a-z0-9]+(?:(?:(?:[._]|__|[-]*)[a-z0-9]+)+)?https://play.golang.org/p/wQ4w431jvS