// LookupNs will return the full namespace string give a short code. This will
// only be useful from implementations of Unmarshaler while the namespaces
// are still in scope
func (d *Decoder) LookupNs(shortcode string) string {
	return d.ns[shortcode]
}

func TestXpath(t *testing.T) {
	x := struct {
		Y *Y `xml:"y"`
	}{}
	orig := `<x xmlns:z="zee">
	  <y xpath="z:banana/foo/z:apple"></y>
	</x>`
	d := xml.NewDecoder(strings.NewReader(orig))
	if err := d.Decode(&x); err != nil {
		t.Fail()
	}
	if x.Y.XPathLookup != "z=zee" {
		t.Error(x.Y.XPathLookup)
	}
}

type Y struct {
	XPath       string
	XPathLookup string
}

func (y *Y) UnmarshalXML(d *xml.Decoder, start xml.StartElement) error {
	copy := struct {
		XPath string
	}{}
	if err := d.DecodeElement(&copy, &start); err != nil {
		return err
	}
	y.XPath = copy.XPath
	y.XPathLookup = fmt.Sprintf("z=%s", d.LookupNs("z"))
	return nil
}