Missing documentation

I stumbled onto something that works but is not documented and I'd like to understand if it should be avoided.

The setup: Non react application renders various react components in few places.

I've noticed couple of components that do the following:

function Foo(props){
    return <div>
        Some content
        <div id="placeholder"></div>
    </div>
}
ReactDOM.render(<Foo/>, domRef)

Somewhere else in the application ReactDOM.render(<Bar/>, document.getElementById("placeholder")). The "placeholder" being the dom element rendered by the <Foo /> component.

I couldn't find anything in the React docs and Stackoverflow describing how/if this should work. Any light on the subject would be much appreciated.

I have also opened a this: https://stackoverflow.com/questions/66134211/reactdom-render-one-react-component-inside-the-render-tree-of-another

Commencez par les exemples de ReactDOM.render décrits dans l’issue et comparez-les à la documentation React existante. Déterminez si le rendu dans un élément DOM produit par un autre composant est pris en charge ou s’il doit être évité, puis documentez les recommandations et vérifiez que la page traite le cas de rendu imbriqué soulevé ici.