# Code collapse

> Fold long code blocks until the reader asks for more.

<CodePreview>
<CodeCollapse>
```ts [lib/path.ts]
const ORDER_PREFIX = /^(\d+)\./;
const EXTENSION = /\.mdx?$/;

export interface Segment {
  order: number;
  name: string;
}

export function parseSegment(raw: string): Segment {
  const match = raw.match(ORDER_PREFIX);
  const name = raw.replace(ORDER_PREFIX, '').replace(EXTENSION, '');
  return { order: match ? Number(match[1]) : Infinity, name };
}

export function toSlug(entryPath: string) {
  const names = entryPath.split('/').map((raw) => parseSegment(raw).name);
  if (names.length > 1 && names.at(-1) === 'index') names.pop();
  return names.join('/');
}
```
</CodeCollapse>

````mdx
<CodeCollapse>
```ts [lib/path.ts]
// long file
```
</CodeCollapse>
````
</CodePreview>