[docs] adapter-static: document prerender.default and info about disabling ssr in dev (#4304)

* [docs] document new prerender.default setting

* [docs] add explanation about dev / production discrepancy

* Remove trailing comma

* Fix weird code description

* Run prettier

* Wording

Co-authored-by: Ben McCann <[email protected]>

* make the example config syntactically valid

* shuffle things around

Co-authored-by: Ben McCann <[email protected]>
Co-authored-by: Rich Harris <[email protected]>

Author: 3 people

packages/adapter-static/README.md

@@ -18,13 +18,16 @@ export default {
 			assets: 'build',
 			fallback: null,
 			precompress: false
-		})
+		}),
+
+		prerender: {
+			// This can be false if you're using a fallback (i.e. SPA mode)
+			default: true
+		}
 	}
 };
 ```
 
-Unless you're in [SPA mode](#spa-mode), the adapter will attempt to prerender every page of your app, regardless of whether the [`prerender`](https://kit.svelte.dev/docs/page-options#prerender) option is set.
-
 > ⚠️ You must ensure SvelteKit's [`trailingSlash`](https://kit.svelte.dev/docs/configuration#trailingslash) option is set appropriately for your environment. If your host does not render `/a.html` upon receiving a request for `/a` then you will need to set `trailingSlash: 'always'` to create `/a/index.html` instead.
 
 ## Options
@@ -66,7 +69,9 @@ export default {
 };
 ```
 
-When operating in SPA mode, only pages that have the [`prerender`](https://kit.svelte.dev/docs/page-options#prerender) option set will be prerendered.
+When operating in SPA mode, you can omit `config.kit.prerender.default` (or set it to `false`, its default value), and only pages that have the [`prerender`](https://kit.svelte.dev/docs/page-options#prerender) option set will be prerendered at build time.
+
+> ⚠️ During development, SvelteKit will still attempt to server-side render your routes. This means accessing things that are only available in the browser (such as the `window` object) will result in errors, even though this would be valid in the output app. To align the behavior of SvelteKit's dev mode with your SPA, you can [call `resolve()` with a parameter of `{ssr: false}` inside the `handle()` hook](https://kit.svelte.dev/docs/hooks#handle).
 
 ## GitHub Pages