code: func (h *handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
  	panic(fmt.Sprintf("httpx: ServeHTTP called on %v", h))
  }
docs: // ServeHTTP implements the http.Handler interface. This method is never
  // actually called by this package, it's only used as a means to pass a Handler
  // in and out of mux.