# Collapsible

A section that opens and shuts under a one-line summary, the browser's details element.

A collapsible keeps secondary detail out of the way until someone asks for it. It is a <details> with its summary, so it works by keyboard and without script, and open sets whether it starts expanded. Keep the summary short and specific about what is inside.

## Use it

Web:

```rust
use ocean_ui_web::Collapsible;
Collapsible { summary: "Advanced", open: false }.render(&mut out, |out| out.push_str("…"))
```

Native:

```rust
use ocean_ui_native::containers::Collapsible;
Collapsible { summary: "production".into(), open: &mut open }.show(ui, |ui| ui.label("ocean-web, deployed 1 h ago"))
```

Cargo feature `base`; since 2026-10-29.

## Props

| Name | Type | Default | What |
|---|---|---|---|
| `summary` | `&str` | `—` | The line that stays in view and opens and shuts the section. |
| `open` | `bool` | `false` | Starts expanded. |

On the Mac: ![Collapsible, dark](/ui/native/collapsible-dark.png) ![Collapsible, light](/ui/native/collapsible-light.png)

## Examples

### Closed

The summary names what opens.

```rust
Collapsible { summary: "Advanced settings", open: false }.render(
    out,
    |out| out.push_str("<p>Retries, timeouts and the model.</p>"),
);
```

### Open

Starts open when the content matters first.

```rust
Collapsible { summary: "What the agent may do", open: true }.render(
    out,
    |out| out.push_str("<p>Read tickets, draft replies, ask a person before refunds.</p>"),
);
```

### Stacked

Several in a row read like a list of questions.

```rust
for (q, a) in [
    ("Is it free?", "The builder is free; runs are metered."),
    ("Where is data kept?", "In your Ocean Base database."),
] {
    Collapsible { summary: q, open: false }.render(
        out,
        |out| { out.push_str("<p>"); out.push_str(a); out.push_str("</p>"); },
    );,
}
```

## Accessibility

- The summary is the browser's own disclosure control; Enter or Space toggles it and its expanded state is reported.
- The content of a closed section is hidden from assistive technology until it opens.

## Related

- [Card](/ui/components/card.md)
- [Tabs](/ui/components/tabs.md)
- [Popover](/ui/components/popover.md)