code: func PlainText(w http.ResponseWriter, r *http.Request, v string) {
  	w.Header().Set("Content-Type", "text/plain; charset=utf-8")
  	if status, ok := r.Context().Value(StatusCtxKey).(int); ok {
  		w.WriteHeader(status)
  	}
  	w.Write([]byte(v))
  }
docs: // PlainText writes a string to the response, setting the Content-Type as
  // text/plain.