code: func ServeXml(w http.ResponseWriter, v interface{}) {
  	content, err := xml.Marshal(v)
  	if err != nil {
  		http.Error(w, err.Error(), http.StatusInternalServerError)
  		return
  	}
  	w.Header().Set("Content-Length", strconv.Itoa(len(content)))
  	w.Header().Set("Content-Type", "text/xml; charset=utf-8")
  	w.Write(content)
  }
docs: // ServeXml replies to the request with an XML
  // representation of resource v.