docs: add keepalive docs (#3090)

docs/content/3.docs/2.directory-structure/10.pages.md

@@ -199,6 +199,10 @@ definePageMeta({
 
 Of course, you are welcome to define metadata for your own use throughout your app. But some metadata defined with `definePageMeta` has a particular purpose:
 
+#### `keepalive`
+
+Nuxt will automatically wrap your page in [the Vue `<KeepAlive>` component](https://vuejs.org/guide/built-ins/keep-alive.html#keepalive) if you set `keepalive: true` in your `definePageMeta`. This might be useful to do, for example, in a parent route which has dynamic child routes, if you want to preserve page state across route changes. You can also set props to be passed to `<KeepAlive>`.
+
 #### `key`
 
 [See above](#child-route-keys).

packages/nuxt3/src/pages/runtime/composables.ts

@@ -12,10 +12,10 @@ export const useRoute = () => {
 
 export interface PageMeta {
   [key: string]: any
-  pageTransition?: false | TransitionProps
-  layoutTransition?: false | TransitionProps
+  pageTransition?: boolean | TransitionProps
+  layoutTransition?: boolean | TransitionProps
   key?: string | ((route: RouteLocationNormalizedLoaded) => string)
-  keepalive?: false | KeepAliveProps
+  keepalive?: boolean | KeepAliveProps
 }
 
 declare module 'vue-router' {