code: func NewRoles(in []string) (Roles, error) {
  	var roles Roles
  	for _, val := range in {
  		role := Role(val)
  		if err := role.Check(); err != nil {
  			return nil, trace.Wrap(err)
  		}
  		roles = append(roles, role)
  	}
  	return roles, nil
  }
docs: // NewRoles return a list of roles from slice of strings