Along with the field tag cleanup, it seems like encoding/xml might also want to
structure its API the same way that encoding/gob and encoding/json have before Go 1
comes out, so that we're not stuck with the current API.

In particular:

package xml

func Marshal(v interface{}) ([]byte, error)
func Indent(w io.WriteStringer, src []byte, pfx, ind string)
func Unmarshal(data []byte, v interface{}) error

type Decoder struct {
    // contains filtered or unexported fields
}
func NewDecoder(r io.Reader) *Decoder
func (dec *Decoder) Decode(v interface{}) error

type Encoder struct {
    // contains filtered or unexported fields
}
func NewEncoder(w io.Writer) *Encoder
func (*Encoder) Encode
func (enc *Encoder) Encode(v interface{}) error

type Marshaler interface {
    MarshalXML() ([]byte, error)
}

type Unmarshaler interface {
    UnmarshalXML([]byte) (error)
}