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While React Server Components in React 19 are stable and will not break between minor versions, the underlying APIs used to implement a React Server Components bundler or framework do not follow semver and may break between minors in React 19.x.
In the above example, a ref is created in the parent component, `MyForm`, and is passed to the child component, `MyInput`. `MyInput`then passes the ref to`<input>`. Because `<input>`is a [built-in component](/reference/react-dom/components/common)React sets the `.current`property of the ref to the `<input>` DOM element.
The `inputRef` created in `MyForm` now points to the `<input>` DOM element returned by `MyInput`. A click handler created in `MyForm` can access `inputRef` and call `focus()` to set the focus on `<input>`.
In the above example, the ref passed to `MyInput` is passed on to the original DOM input element. This lets the parent component call `focus()` on it. However, this also lets the parent component do something else--for example, change its CSS styles. In uncommon cases, you may want to restrict the exposed functionality. You can do that with [`useImperativeHandle`](/reference/react/useImperativeHandle):
Here, `realInputRef` inside `MyInput` holds the actual input DOM node. However, [`useImperativeHandle`](/reference/react/useImperativeHandle) instructs React to provide your own special object as the value of a ref to the parent component. So `inputRef.current` inside the `Form` component will only have the `focus` method. In this case, the ref "handle" is not the DOM node, but the custom object you create inside [`useImperativeHandle`](/reference/react/useImperativeHandle) call.
[React DevTools](/learn/react-developer-tools) (v5.0+) and [React Native DevTools](https://reactnative.dev/docs/react-native-devtools) have built-in support for React Compiler and will display a "Memo ✨" badge next to components that have been optimized by the compiler.
{/*FIXME: this doesn't appear to actually work -- I guess precedence isn't implemented yet?*/}
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Stylesheets can conflict with each other, and when they do, the browser goes with the one that comes later in the document. React lets you control the order of stylesheets with the `precedence` prop. In this example, three components render stylesheets, and the ones with the same precedence are grouped together in the `<head>`.
Note the `precedence` values themselves are arbitrary and their naming is up to you. React will infer that precedence values it discovers first are "lower" and precedence values it discovers later are "higher".
- Data fetching with Suspense-enabled frameworks like [Relay](https://relay.dev/docs/guided-tour/rendering/loading-states/) and [Next.js](https://nextjs.org/docs/app/building-your-application/routing/loading-ui-and-streaming#streaming-with-suspense)
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- Lazy-loading component code with [`lazy`](/reference/react/lazy)
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- Reading the value of a cached Promise with [`use`](/reference/react/use)
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