Handling different client and server content - not showing initial render

In the hydrateRoot page, it is mentioned that
"This way the initial render pass will render the same content as the server, avoiding mismatches, but an additional pass will happen synchronously right after hydration."

which means that the initial render on the playground should show "Is Server", but it shows directly "Is Client" which is very confusing for learners and doesn't show the real behavior.
I tired opening the sandbox in external window, and it indeed shows "Is Server" first and then changing to "Is Client" as expected.

hydrateRoot ページに埋め込まれた playground から始め、外部で開いた同じ sandbox とその動作を比較します。初回レンダリングで "Is Server" が表示され、その後 "Is Client" に変わることを確認します。埋め込まれた例がドキュメント化された hydration のシーケンスを示せば完了です。