[compiler] Move React 17/18 section to its own subheading (#7230)

Currently it's a little hidden, let's move it to its own subheading for
more prominence

Author: poteto

src/content/learn/react-compiler.md

@@ -192,61 +192,63 @@ export default function App() {
 
 When you have more confidence with rolling out the compiler, you can expand coverage to other directories as well and slowly roll it out to your whole app.
 
-#### New projects {/*new-projects*/}
-
-If you're starting a new project, you can enable the compiler on your entire codebase, which is the default behavior.
+### Using React Compiler with React 17 or 18 {/*using-react-compiler-with-react-17-or-18*/}
 
-## Usage {/*installation*/}
-
-### Babel {/*usage-with-babel*/}
+React Compiler works best with React 19 RC. If you are unable to upgrade, you can install the extra `react-compiler-runtime` package which will allow the compiled code to run on versions prior to 19. However, note that the minimum supported version is 17.
 
 <TerminalBlock>
-npm install babel-plugin-react-compiler@experimental
+npm install react-compiler-runtime@experimental
 </TerminalBlock>
 
-The compiler includes a Babel plugin which you can use in your build pipeline to run the compiler.
-
-After installing, add it to your Babel config. Please note that it's critical that the compiler run **first** in the pipeline:
+You should also add the correct `target` to your compiler config, where `target` is the major version of React you are targeting:
 
-```js {7}
+```js {3}
 // babel.config.js
-const ReactCompilerConfig = { /* ... */ };
+const ReactCompilerConfig = {
+  target: '18' // '17' | '18' | '19'
+};
 
 module.exports = function () {
   return {
     plugins: [
-      ['babel-plugin-react-compiler', ReactCompilerConfig], // must run first!
-      // ...
+      ['babel-plugin-react-compiler', ReactCompilerConfig],
     ],
   };
 };
 ```
 
-`babel-plugin-react-compiler` should run first before other Babel plugins as the compiler requires the input source information for sound analysis.
+#### New projects {/*new-projects*/}
 
-React Compiler works best with React 19 RC. If you are unable to upgrade, you can install the extra `react-compiler-runtime` package which will allow the compiled code to run on versions prior to 19. However, note that the minimum supported version is 17.
+If you're starting a new project, you can enable the compiler on your entire codebase, which is the default behavior.
+
+## Usage {/*installation*/}
+
+### Babel {/*usage-with-babel*/}
 
 <TerminalBlock>
-npm install react-compiler-runtime@experimental
+npm install babel-plugin-react-compiler@experimental
 </TerminalBlock>
 
-You should also add the correct `target` to your compiler config, where `target` is the major version of React you are targeting:
+The compiler includes a Babel plugin which you can use in your build pipeline to run the compiler.
 
-```js {3}
+After installing, add it to your Babel config. Please note that it's critical that the compiler run **first** in the pipeline:
+
+```js {7}
 // babel.config.js
-const ReactCompilerConfig = {
-  target: '18' // '17' | '18' | '19'
-};
+const ReactCompilerConfig = { /* ... */ };
 
 module.exports = function () {
   return {
     plugins: [
-      ['babel-plugin-react-compiler', ReactCompilerConfig],
+      ['babel-plugin-react-compiler', ReactCompilerConfig], // must run first!
+      // ...
     ],
   };
 };
 ```
 
+`babel-plugin-react-compiler` should run first before other Babel plugins as the compiler requires the input source information for sound analysis.
+
 ### Vite {/*usage-with-vite*/}
 
 If you use Vite, you can add the plugin to vite-plugin-react:
@@ -392,12 +394,6 @@ To report issues, please first create a minimal repro on the [React Compiler Pla
 
 You can also provide feedback in the React Compiler Working Group by applying to be a member. Please see [the README for more details on joining](https://github.com/reactwg/react-compiler).
 
-### `(0 , _c) is not a function` error {/*0--_c-is-not-a-function-error*/}
-
-This occurs if you are not using React 19 RC and up. To fix this, [upgrade your app to React 19 RC](https://react.dev/blog/2024/04/25/react-19-upgrade-guide) first.
-
-If you are unable to upgrade to React 19, you may try a userspace implementation of the cache function as described in the [Working Group](https://github.com/reactwg/react-compiler/discussions/6). However, please note that this is not recommended and you should upgrade to React 19 when possible.
-
 ### How do I know my components have been optimized? {/*how-do-i-know-my-components-have-been-optimized*/}
 
 [React Devtools](/learn/react-developer-tools) (v5.0+) has built-in support for React Compiler and will display a "Memo ✨" badge next to components that have been optimized by the compiler.