diff --git a/src/layer/interface/module/view/navigation.ts b/src/layer/interface/module/view/navigation.ts
index e4f576e2..b28466e1 100644
--- a/src/layer/interface/module/view/navigation.ts
+++ b/src/layer/interface/module/view/navigation.ts
@@ -12,6 +12,7 @@ export class NavigationView extends Coroutine<never> {
     super(async function* () {
       return this.finally(bind(window, 'popstate', ev => {
         if (!isTransitable(page.state) || !isTransitable(window.history.state)) return;
+        // Prevent updates by frames.
         if (standardize(window.location.href) === page.url.href) return;
         listener(ev);
       }));