code: func (ns *Namespace) Contains(s, substr interface{}) (bool, error) {
  	ss, err := cast.ToStringE(s)
  	if err != nil {
  		return false, err
  	}
  
  	su, err := cast.ToStringE(substr)
  	if err != nil {
  		return false, err
  	}
  
  	return _strings.Contains(ss, su), nil
  }
docs: // Contains reports whether substr is in s.