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

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

Author: dummdidumm

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

@@ -171,7 +171,7 @@ Exports from runes mode components cannot be bound to directly. For example, hav
 
 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 [`$bindable`](/docs/runes#$bindable) rune.
 
-If a property is bindable and has a default value (e.g. `let { foo = $bindable('bar') } = $props();`), you need to pass a non-`undefined` value to that property, if you're binding to it. This prevents undefined behavior and results in more performant code (in Svelte 4, the default value was propagated back up, which on the server and client could result in more render cycles).
+If a bindable property has a default value (e.g. `let { foo = $bindable('bar') } = $props();`), you need to pass a non-`undefined` value to that property if you're binding to it. This prevents ambiguous behavior — the parent and child must have the same value — and results in better performance (in Svelte 4, the default value was reflected back to the parent, resulting in wasteful additional render cycles).
 
 ### `accessors` option is ignored