docs(api): add definePageMeta util (#6931)

Co-authored-by: Daniel Roe <daniel@roe.dev>
Co-authored-by: Damian Głowala <48835293+DamianGlowala@users.noreply.github.com>

docs/content/3.api/3.utils/define-page-meta.md

@@ -1,7 +1,152 @@
 # `definePageMeta`
 
+`definePageMeta` is a compiler macro that you can use to set metadata for your **page** components located in the `pages/` directory (unless [set otherwise](https://v3.nuxtjs.org/api/configuration/nuxt.config#pages)). This way you can set custom metadata for each static or dynamic route of your Nuxt application.
+
+```vue [pages/some-page.vue]
+<script setup>
+  definePageMeta({
+    title: 'Articles'
+  })
+</script>
+```
+
+::ReadMore{link="/guide/directory-structure/pages/#page-metadata"}
+::
+
+## Type
+
+```ts
+definePageMeta(meta: PageMeta) => void
+
+interface PageMeta {
+  pageTransition?: boolean | TransitionProps
+  layoutTransition?: boolean | TransitionProps
+  key?: false | string | ((route: RouteLocationNormalizedLoaded) => string)
+  keepalive?: boolean | KeepAliveProps
+  layout?: false | LayoutKey | Ref<LayoutKey> | ComputedRef<LayoutKey>
+  middleware?: MiddlewareKey | NavigationGuard | Array<MiddlewareKey | NavigationGuard>
+  [key: string]: any
+}
+```
+
+## Parameters
+
+### `meta`
+
+- **Type**: `PageMeta`
+
+  An object accepting the following page metadata:
+
+  **`pageTransition`**
+  
+  - **Type**: `boolean` | [`TransitionProps`](https://vuejs.org/api/built-in-components.html#transition)
+  
+    Set name of the transition to apply for current page. You can also set this value to `false` to disable the page transition.
+
+  **`layoutTransition`**
+
+  - **Type**: `boolean` | [`TransitionProps`](https://vuejs.org/api/built-in-components.html#transition)
+
+    Set name of the transition to apply for current layout. You can also set this value to `false` to disable the layout transition.
+
+  **`key`**
+
+  - **Type**: `false` | `string` | `((route: RouteLocationNormalizedLoaded) => string)`
+
+    Set `key` value when you need more control over when the `<NuxtPage>` component is re-rendered.
+
+  **`keepalive`**
+
+  - **Type**: `boolean` | [`KeepAliveProps`](https://vuejs.org/api/built-in-components.html#keepalive)
+
+    Set to `true` when you want to preserve page state across route changes or use the [`KeepAliveProps`](https://vuejs.org/api/built-in-components.html#keepalive) for a fine-grained control.
+
+  **`layout`**
+
+  - **Type**: `false` | `LayoutKey` | `Ref<LayoutKey>` | `ComputedRef<LayoutKey>`
+
+    Set a static or dynamic name of the layout for each route. This can be set to `false` in case the default layout needs to be disabled.
+
+  **`middleware`**
+
+  - **Type**: `MiddlewareKey` | [`NavigationGuard`](https://router.vuejs.org/api/interfaces/NavigationGuard.html#navigationguard) | `Array<MiddlewareKey | NavigationGuard>`
+
+    Define anonymous or named middleware directly within `definePageMeta`. Learn more about [route middleware](/docs/directory-structure/middleware).
+
+  **`[key: string]`**
+
+  - **Type**: `any`
+
+    Apart from the above properties, you can also set **custom** metadata. You may wish to do so in a type-safe way by [augmenting the type of the `meta` object](/guide/directory-structure/pages/#typing-custom-metadata).
+
+## Examples
+
+### Basic Usage
+
+The example below demonstrates:
+
+- how `key` can be a function that returns a value;
+- how `keepalive` property makes sure that the `<modal>` component is not cached when switching between multiple components;
+- adding `pageType` as a custom property:
+
+```vue [pages/some-page.vue]
+<script setup>
+  definePageMeta({
+    key: (route) => route.fullPath,
+
+    keepalive: {
+      exclude: ['modal']
+    },
+
+    pageType: 'Checkout'
+  })
+</script>
+```
+
+### Defining Middleware
+
+The example below shows how the middleware can be defined using a `function` directly within the `definePageMeta` or set as a `string` that matches the middleware file name located in the `middleware/` directory:
+
+```vue [pages/some-page.vue]
+<script setup>
+  definePageMeta({
+    // define middleware as a function
+    middleware: [
+      function (to, from) {
+        const auth = useState('auth')
+        
+        if (!auth.value.authenticated) {
+            return navigateTo('/login')
+        }
+        
+        return navigateTo('/checkout')
+      }
+    ],
+
+    // ... or a string
+    middleware: 'auth'
+    
+    // ... or multiple strings
+    middleware: ['auth', 'another-named-middleware']
+})
+</script>
+```
+
+### Defining Layout
+
+You can define the layout that matches the layout's file name located (by default) in the `layouts/` directory. You can also disable the layout by setting the `layout` to `false`:
+
+```vue [pages/some-page.vue]
+<script setup>
+  definePageMeta({
+    // set custom layout
+    layout: 'admin'
+    
+    // ... or disable a default layout
+    layout: false
+  })
+</script>
+```
+
 ::ReadMore{link="/guide/features/routing"}
 ::
-
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