code: func ParseRoles(str string) (roles Roles, err error) {
  	for _, s := range strings.Split(str, ",") {
  		r := Role(strings.Title(strings.ToLower(strings.TrimSpace(s))))
  		if err = r.Check(); err != nil {
  			return nil, trace.Wrap(err)
  		}
  		roles = append(roles, r)
  	}
  	return roles, nil
  }
docs: // ParseRoles takes a comma-separated list of roles and returns a slice
  // of roles, or an error if parsing failed