code: func ValidateTag(k, v string) error {
  	if err := StreamName(k).Validate(); err != nil {
  		return fmt.Errorf("invalid tag key: %s", err)
  	}
  	if len(k) > MaxTagKeySize {
  		return fmt.Errorf("tag key exceeds maximum size (%d > %d)", len(k), MaxTagKeySize)
  	}
  	if len(v) > MaxTagValueSize {
  		return fmt.Errorf("tag value exceeds maximum size (%d > %d)", len(v), MaxTagValueSize)
  	}
  	return nil
  }
docs: // ValidateTag returns an error if a tag contains a nonconfirming value.