[Suggestion]: Clarify SSR metadata hoisting behavior for fragment-based rendering

Summary

React 19's documentation for tags title, meta and link states that they are automatically hoisted to the document </head/>. However, there is a critical nuance regarding Server-Side Rendering (SSR) that should be explicitly documented.

When React is used to render only a fragment of a page (e.g., mounted inside </div id="root"/> rather than controlling the full HTML document), metadata tags are not hoisted to the actual HTML during SSR. Instead, they appear at the top of React's rendered tree (which is inside the </body/> in the initial HTML response).

Page

https://react.dev/reference/react-dom/components/title

Details

You can watch it at any basic SSR template, I also created an example
If you run it, you will see, that <title> and will not be hoisted to the actual HTML .

This is server html response

This is browser render

I propose adding a note in the React 19 documentation under the "Rendering Metadata" section that clarifies:

Important: React 19's automatic hoisting works at the React tree level, not the HTML document level. During SSR with renderToString renderToPipeableStream and others, metadata tags are placed at the top of React's rendered output. If React controls the entire document, this means </head/>. If React renders only a fragment (e.g., inside a </div id="root"/>), the tags will be in this fragment and will no be moved to </head/>. For SEO-critical metadata that must appear in the initial HTML </head/>, server-side integration (e.g., rendering these tags in your backend framework's layout) is still required in fragment-based setups.

React 19 の title、meta、link のドキュメントページから始め、特に "Rendering Metadata" セクションを確認してください。issue で説明されている SSR の動作を確認し、renderToString または renderToPipeableStream を使用するリンク先の例と比較してください。ドキュメントで、フラグメントベースの SSR 配置と完全なドキュメントのレンダリングの違い、および必要に応じたサーバー側統合の必要性が明確に説明されていれば完了です。