code: func (r *Router) ServeHTTPContext(ctx context.Context, w http.ResponseWriter, req *http.Request) error {
  	route, h, vars := r.Handler(req)
  	ctx = WithVars(ctx, vars)
  	ctx = WithRoute(ctx, route)
  	return h.ServeHTTPContext(ctx, w, req)
  }
docs: // ServeHTTPContext implements the Handler interface.