docs: add csr warning list (#11130)

documentation/docs/20-core-concepts/40-page-options.md

@@ -121,6 +121,7 @@ Normally, SvelteKit renders your page on the server first and sends that HTML to
 ```js
 /// file: +page.js
 export const ssr = false;
+// If both `ssr` and `csr` are `false`, nothing will be rendered!
 ```
 
 If you add `export const ssr = false` to your root `+layout.js`, your entire app will only be rendered on the client — which essentially means you turn your app into an SPA.
@@ -132,9 +133,15 @@ Ordinarily, SvelteKit [hydrates](glossary#hydration) your server-rendered HTML i
 ```js
 /// file: +page.js
 export const csr = false;
+// If both `csr` and `ssr` are `false`, nothing will be rendered!
 ```
 
-> If both `ssr` and `csr` are `false`, nothing will be rendered!
+Disabling CSR does not ship any JavaScript to the client. This means:
+
+* The webpage should work with HTML and CSS only.
+* `<script>` tags inside all Svelte components are removed.
+* `<form>` elements cannot be [progressively enhanced](form-actions#progressive-enhancement).
+* Links are handled by the browser with a full-page navigation.
 
 ## trailingSlash