switch {
	case !f.And.isEmpty():
		if err := e.EncodeElement(f.And, xml.StartElement{Name: xml.Name{Local: "And"}}); err != nil {
			return err
		}
	case !f.Tag.IsEmpty():
		if err := e.EncodeElement(f.Tag, xml.StartElement{Name: xml.Name{Local: "Tag"}}); err != nil {
			return err
		}
	default:
		// Always print Prefix field when both And & Tag are empty

	switch {
	case !f.And.isEmpty():
		if err := e.EncodeElement(f.And, xml.StartElement{Name: xml.Name{Local: "And"}}); err != nil {
			return err
		}
	case !f.Tag.IsEmpty():
		if err := e.EncodeElement(f.Tag, xml.StartElement{Name: xml.Name{Local: "Tag"}}); err != nil {
			return err
		}
	default:
		// Always print Prefix field when both And & Tag are empty

func (n NoncurrentVersionExpiration) MarshalXML(e *xml.Encoder, start xml.StartElement) error {
	if n.IsNull() {
		return nil
	}
	type noncurrentVersionExpirationWrapper NoncurrentVersionExpiration
	return e.EncodeElement(noncurrentVersionExpirationWrapper(n), start)
}

// UnmarshalXML decodes NoncurrentVersionExpiration
func (n *NoncurrentVersionExpiration) UnmarshalXML(d *xml.Decoder, startElement xml.StartElement) error {

	*p = Prefix{string: s, set: true}
	return nil
}

// MarshalXML - decodes XML data.
func (p Prefix) MarshalXML(e *xml.Encoder, startElement xml.StartElement) error {
	if !p.set {
		return nil
	}
	return e.EncodeElement(p.string, startElement)
}

// String returns the prefix string
func (p Prefix) String() string {
	return p.string

	if err := e.EncodeToken(start); err != nil {
		return err
	}
	if err := e.EncodeElement(d.String(), xml.StartElement{Name: xml.Name{Local: "Bucket"}}); err != nil {
		return err
	}
	if d.StorageClass != "" {
		if err := e.EncodeElement(d.StorageClass, xml.StartElement{Name: xml.Name{Local: "StorageClass"}}); err != nil {
			return err
		}
	}

// encodes empty string otherwise
func (eDays ExpirationDays) MarshalXML(e *xml.Encoder, startElement xml.StartElement) error {
	if eDays == 0 {
		return nil
	}
	return e.EncodeElement(int(eDays), startElement)
}

// ExpirationDate is a embedded type containing time.Time to unmarshal
// Date in Expiration
type ExpirationDate struct {
	time.Time
}

// empty string otherwise
func (tDate TransitionDate) MarshalXML(e *xml.Encoder, startElement xml.StartElement) error {
	if tDate.Time.IsZero() {
		return nil
	}
	return e.EncodeElement(tDate.Format(time.RFC3339), startElement)
}

// TransitionDays is a type alias to unmarshal Days in Transition
type TransitionDays int

// UnmarshalXML parses number of days from Transition and validates if
// >= 0

func (filter FilterRule) MarshalXML(e *xml.Encoder, start xml.StartElement) error {
	if filter.isEmpty() {
		return nil
	}
	type filterRuleWrapper FilterRule
	return e.EncodeElement(filterRuleWrapper(filter), start)
}

// UnmarshalXML - decodes XML data.
func (filter *FilterRule) UnmarshalXML(d *xml.Decoder, start xml.StartElement) error {
	// Make subtype to avoid recursive UnmarshalXML().

func (de DelMarkerExpiration) MarshalXML(enc *xml.Encoder, start xml.StartElement) error {
	if de.Empty() {
		return nil
	}

	type delMarkerExpiration DelMarkerExpiration
	return enc.EncodeElement(delMarkerExpiration(de), start)
}

// NextDue returns upcoming DelMarkerExpiration date for obj if
// applicable, returns false otherwise.
func (de DelMarkerExpiration) NextDue(obj ObjectOpts) (time.Time, bool) {

// empty string otherwise
func (t DeleteMarkerMTime) MarshalXML(e *xml.Encoder, startElement xml.StartElement) error {
	if t.Time.IsZero() {
		return nil
	}
	return e.EncodeElement(t.Time.Format(time.RFC3339), startElement)
}

// ObjectV object version key/versionId
type ObjectV struct {
	ObjectName string `xml:"Key"`
	VersionID  string `xml:"VersionId"`
}