}
	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
		if err := e.EncodeElement(f.Prefix, xml.StartElement{Name: xml.Name{Local: "Prefix"}}); err != nil {
			return err
		}
	}

	return e.EncodeToken(xml.EndElement{Name: start.Name})
}

		predCount++
	}
	if f.ObjectSizeLessThan != 0 {
		pType = sizeLtPred
		predCount++
	}
	// Note: S3 supports empty <Filter></Filter>, so predCount == 0 is
	// valid.
	if predCount > 1 {
		return errInvalidFilter
	}

	var err error
	switch pType {
	case nonePred:
	// S3 supports empty <Filter></Filter>
	case prefixPred:
	case andPred:
		err = f.And.Validate()
	case tagPred: