docs: dev vs build target (#14997)

Author: patak-dev

docs/guide/dep-pre-bundling.md

@@ -60,7 +60,7 @@ A typical use case for `optimizeDeps.include` or `optimizeDeps.exclude` is when
 
 Both `include` and `exclude` can be used to deal with this. If the dependency is large (with many internal modules) or is CommonJS, then you should include it; If the dependency is small and is already valid ESM, you can exclude it and let the browser load it directly.
 
-You can further customize esbuild too with the [`optimizeDeps.esbuildOptions` option](/config/dep-optimization-options.md#optimizedeps-esbuildoptions). For example, adding an esbuild plugin to handle special files in dependencies.
+You can further customize esbuild too with the [`optimizeDeps.esbuildOptions` option](/config/dep-optimization-options.md#optimizedeps-esbuildoptions). For example, adding an esbuild plugin to handle special files in dependencies or changing the [build `target`](https://esbuild.github.io/api/#target).
 
 ## Caching
 

docs/guide/index.md

@@ -20,7 +20,9 @@ You can learn more about the rationale behind the project in the [Why Vite](./wh
 
 ## Browser Support
 
-The default build targets browsers that support [native ES Modules](https://caniuse.com/es6-module), [native ESM dynamic import](https://caniuse.com/es6-module-dynamic-import), and [`import.meta`](https://caniuse.com/mdn-javascript_operators_import_meta). Legacy browsers can be supported via the official [@vitejs/plugin-legacy](https://github.com/vitejs/vite/tree/main/packages/plugin-legacy) - see the [Building for Production](./build) section for more details.
+During development, Vite sets [`esnext` as the transform target](https://esbuild.github.io/api/#target), because we assume a modern browser is used and it supports all of the latest JavaScript and CSS features. This prevents syntax lowering, letting Vite serve modules as close as possible to the original source code.
+
+For the production build, by default Vite targets browsers that support [native ES Modules](https://caniuse.com/es6-module), [native ESM dynamic import](https://caniuse.com/es6-module-dynamic-import), and [`import.meta`](https://caniuse.com/mdn-javascript_operators_import_meta). Legacy browsers can be supported via the official [@vitejs/plugin-legacy](https://github.com/vitejs/vite/tree/main/packages/plugin-legacy). See the [Building for Production](./build) section for more details.
 
 ## Trying Vite Online