note breaking change

Author: dummdidumm

.changeset/heavy-ducks-leave.md

@@ -2,4 +2,4 @@
 "svelte": patch
 ---
 
-fix: robustify interop of exports and props
+breaking: robustify interop of exports and props in runes mode

sites/svelte-5-preview/src/routes/docs/content/03-appendix/02-breaking-changes.md

@@ -117,6 +117,18 @@ Svelte now use Mutation Observers instead of IFrames to measure dimensions for `
 
 Content inside component tags becomes a [snippet prop](/docs/snippets) called `children`. You cannot have a separate prop by that name.
 
+## Breaking changes in runes mode
+
+Some breaking changes only apply once your component is in runes mode.
+
+### Bindings to component exports don't show up in rest props
+
+In runes mode, bindings to component exports don't show up in rest props. For example, `rest` in `let { foo, bar, ...rest } = $props();` would not contain `baz` if `baz` was defined as `export const baz = ...;` inside the component. In Svelte 4 syntax, the equivalent to `rest` would be `$$restProps`, which contains these component exports.
+
+### Bindings need to be explicitly defined using `$bindable()`
+
+In Svelte 4 syntax, every property (declared via `export let`) is bindable, meaning you can `bind:` to it. In runes mode, properties are not bindable by default: you need to denote bindable props with the [/docs/runes#$bindable](`$bindable`) rune.
+
 ## Other breaking changes
 
 ### Stricter `@const` assignment validation