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docs: clarify class attribute usage in Svelte templates #1404

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16 changes: 16 additions & 0 deletions ...svelte.dev/content/tutorial/01-svelte/07-classes-and-styles/01-classes/index.md
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Expand Up @@ -26,4 +26,20 @@ We can make it nicer though. Adding or removing a class based on some condition

This means 'always add the `card` class, and add the `flipped` class whenever `flipped` is truthy'.

> **Note:** When using multiple expressions inside a `class={}` attribute, make sure to combine them within a single array or object.
> Avoid separating expressions with commas at the top level (for example: `class={['foo'], 'bar'}`), as this creates a JavaScript sequence expression, which can cause errors in Runes mode and result in unintended behavior.
>
> ✅ Correct:
>
> ```svelte
> <div class={["foo", condition && "bar", "baz"]}></div>
> ```
>
> ❌ Avoid:
>
> ```svelte
> <div class={["foo"], "bar"}></div>
> ```
>

For more examples of how to combine conditional classes, [consult the `class` documentation](/docs/svelte/class).