mux.go
func (mx *Mux) updateSubRoutes(fn func(subMux *Mux)) {
	for _, r := range mx.tree.routes() {
		subMux, ok := r.SubRoutes.(*Mux)
		if !ok {
			continue
		}
		fn(subMux)
	}
}
func (mx *Mux) updateSubRoutes(fn func(subMux *Mux)) {
	for _, r := range mx.tree.routes() {
		subMux, ok := r.SubRoutes.(*Mux)
		if !ok {
			continue
		}
		fn(subMux)
	}
}
// Recursively update data on child routers.