code: func APIVersions(resp *http.Response, versionHeader string) []APIVersion {
  	versions := []APIVersion{}
  	if versionHeader != "" {
  		for _, supportedVersions := range resp.Header[http.CanonicalHeaderKey(versionHeader)] {
  			for _, version := range strings.Fields(supportedVersions) {
  				versions = append(versions, ParseAPIVersion(version))
  			}
  		}
  	}
  	return versions
  }
docs: // APIVersions gets the API versions out of an HTTP response using the provided
  // version header as the key for the HTTP header.