code: func SetErrorHandler(status int, handler ErrorHandler) scaffold.Middleware {
  	return scaffold.Middleware(func(next scaffold.Handler) scaffold.Handler {
  		return scaffold.HandlerFunc(func(ctx context.Context, w http.ResponseWriter, r *http.Request) {
  			key := fmt.Sprintf("error_handler_%d", status)
  			ctx = context.WithValue(ctx, key, handler)
  
  			next.CtxServeHTTP(ctx, w, r)
  		})
  	})
  }
docs: // SetErrorHandler returns Middleware that can be used to set the error handler