Code block

The <CodeBlock> component displays code examples with syntax highlighting. Code blocks support line highlighting, focusing, titles, and deep linking to make your code examples more readable and interactive.

Usage

Use three backticks with an optional language identifier.

1
console.log("hello world")

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```js
2
console.log("hello world")
3
```

Variants

Titles

Add a title to your code snippet by adding a title after the language identifier. Alternatively, use a title prop (title="Snippet with title") or filename prop (filename="Snippet with title") to achieve the same result.

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console.log("hello world")

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```js Snippet with title
2
console.log("hello world")
3
```

Line highlighting

Highlight specific lines in your code snippet by placing a numeric range inside {} after the language identifier. The range is inclusive and can be a single number, a comma-separated list of numbers, or ranges.

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console.log("Line 1");
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console.log("Line 2");
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console.log("Line 3");
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console.log("Line 4");
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console.log("Line 5");
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console.log("Line 6");

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```javascript {2-4, 6}
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console.log("Line 1");
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console.log("Line 2");
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console.log("Line 3");
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console.log("Line 4");
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console.log("Line 5");
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console.log("Line 6");
8
```

Line focusing

Focus on specific lines by adding a comment [!code focus] or by adding a focus attribute after the language identifier.

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console.log("Line 1");
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console.log("Line 2");
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console.log("Line 3");
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console.log("Line 4");
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console.log("Line 5");

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```javascript focus={2-4}
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console.log("Line 1");
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console.log("Line 2");
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console.log("Line 3");
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console.log("Line 4");
6
console.log("Line 5");
7
```

Start line

Control which line appears first in your code block by adding a startLine attribute after the language identifier. This is useful for longer code snippets where you want to highlight the main logic while still providing the complete context.

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    console.log("Line 1");
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    console.log("Line 2");
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    console.log("Line 3");
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    console.log("Line 4");
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    console.log("Line 5");
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    console.log("Line 6");
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    console.log("Line 7");
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    console.log("Line 8");
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    console.log("Line 9");
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    console.log("Line 10");
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    console.log("Line 11");
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    console.log("Line 12");
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    console.log("Line 13");
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    console.log("Line 14");
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    console.log("Line 15");
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    console.log("Line 16");
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    console.log("Line 17");
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    console.log("Line 18");
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    console.log("Line 19");
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    console.log("Line 20");
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    console.log("Line 21");
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    console.log("Line 22");
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    console.log("Line 23");
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    console.log("Line 24");
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    console.log("Line 25");
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    console.log("Line 26");
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    console.log("Line 27");
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    console.log("Line 28")

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```javascript startLine={6}
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console.log("Line 1");
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console.log("Line 2");
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console.log("Line 3");
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console.log("Line 4");
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console.log("Line 5");
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console.log("Line 6");
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console.log("Line 7");
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console.log("Line 8");
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console.log("Line 9");
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console.log("Line 10");
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console.log("Line 11");
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console.log("Line 12");
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console.log("Line 13");
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console.log("Line 14");
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console.log("Line 15");
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console.log("Line 16");
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console.log("Line 17");
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console.log("Line 18");
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console.log("Line 19");
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console.log("Line 20");
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console.log("Line 21");
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console.log("Line 22");
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console.log("Line 23");
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console.log("Line 24");
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console.log("Line 25");
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console.log("Line 26");
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console.log("Line 27");
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console.log("Line 28")
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```

Max height

Control the max height of the code block by adding a maxLines attribute after the language identifier. The maxLines attribute should be a number representing the maximum number of lines to display. By default, the code block will display up to 20 lines. (To disable the default 20 lines limit, set maxLines to 0.)

When you use maxLines, an expand button automatically appears on hover in the top-right corner, allowing users to view the full code content in an expanded overlay that displays over the page.

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def is_prime(num):
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    """Check if a number is prime."""
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    if num <= 1:
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        return False
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    for i in range(2, num):
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        if num % i == 0:
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            return False
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    return True
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start = 10
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end = 50
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print(f"Prime numbers between {start} and {end} are:")
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prime_numbers = []
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for num in range(start, end+1):
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    if is_prime(num):
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        prime_numbers.append(num)
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for prime in prime_numbers:
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    print(prime)

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```python maxLines=10
2
def is_prime(num):
3
    """Check if a number is prime."""
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    if num <= 1:
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        return False
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    for i in range(2, num):
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        if num % i == 0:
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            return False
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    return True
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start = 10
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end = 50
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print(f"Prime numbers between {start} and {end} are:")
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prime_numbers = []
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for num in range(start, end+1):
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    if is_prime(num):
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        prime_numbers.append(num)
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for prime in prime_numbers:
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    print(prime)
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```

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/* Hide the expand button */
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.fern-expand-button {
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  display: none;
4
}

Wrap overflow

By default, long lines that exceed the width of the code block become scrollable:

A very very very long line of text that may cause the code block to overflow and scroll as a result.

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```txt title="Without wordWrap"
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A very very very long line of text that may cause the code block to overflow and scroll as a result. 
3
```

To disable scrolling and wrap overflow onto the next line, use the wordWrap prop:

A very very very long line of text that may cause the code block to overflow and scroll as a result.

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```txt title="With wordWrap" wordWrap
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A very very very long line of text that may cause the code block to overflow and scroll as a result. 
3
```

Hide line numbers

By default, code blocks display line numbers (and $ / > prefixes in bash/shell code blocks) in the gutter. To hide line numbers and prefixes, set showLineNumbers to false:

npm install plantstore
npm run build \
    --output dist

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```bash showLineNumbers={false}
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npm install plantstore
3
npm run build \
4
    --output dist
5
```

Deep linking

Make specific text within code blocks clickable by defining a links map. This is useful for linking to documentation, API references, or related resources directly from your code examples.

The links property accepts a map where keys are matching patterns (exact strings or regex) and values are the URLs to link to.

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import { PlantClient } from "@plantstore/sdk";
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const client = new PlantClient({ apiKey: "YOUR_API_KEY" });
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const plant = await client.createPlant({
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  name: "Monstera",
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  species: "Monstera deliciosa"
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});

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<CodeBlock
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  links={{"PlantClient": "/learn/docs/writing-content/demo#plantclient", "createPlant": "/learn/docs/writing-content/demo#create_plant"}}
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>
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```typescript 
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import { PlantClient } from "@plantstore/sdk";
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const client = new PlantClient({ apiKey: "YOUR_API_KEY" });
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const plant = await client.createPlant({
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  name: "Monstera",
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  species: "Monstera deliciosa"
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});
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```
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</CodeBlock>

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from plantstore import PlantStore, PlantClientfrom plantstore import PlantStore, PlantClient
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store = PlantStore(api_key="YOUR_API_KEY")
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client = PlantClient(store)
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plant = store.getPlant(plant_id="123")
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garden = store.getGarden(garden_id="456")

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<CodeBlock
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   links={{"/get\\w+/": "/learn/docs/writing-content/demo#get-methods", "/Plant(Store|Client)/": "/learn/docs/writing-content/demo#type-definitions"}}
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>
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```python
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from plantstore import PlantStore, PlantClient
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store = PlantStore(api_key="YOUR_API_KEY")
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client = PlantClient(store)
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plant = store.getPlant(plant_id="123")
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garden = store.getGarden(garden_id="456")
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```
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</CodeBlock>

Embedding code files

You can embed code from local or external files using the <Code> component with the src prop. For local files, reference files relative to your docs directory. For external files, use full URLs to pull code samples directly from remote sources like GitHub.

The <Code> component supports the same props as <CodeBlock>, including title, language, and maxLines.

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console.log("I love Fern!");

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console.log("I also love Fern!"); 

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```js
2
3
console.log("I love Fern!");
4
```
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<Code src="snippets/example-code.js">

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name: fern-check
2
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on:
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  pull_request:
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  push:
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    branches:
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      - main
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jobs:
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  run:
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    runs-on: ubuntu-latest
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    steps:
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      - name: Checkout repository
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        uses: actions/checkout@v5
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      - name: Setup Node.js
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        uses: actions/setup-node@v5
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        with:
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          node-version: "24"
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      - name: Setup Fern CLI
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        uses: fern-api/setup-fern-cli@v1
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      - name: Check API is valid
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        run: fern check

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<Code
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  src="https://raw.githubusercontent.com/fern-api/docs-starter/refs/heads/main/.github/workflows/check.yml"
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  title="GitHub Actions workflow"
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  language="yaml"
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  maxLines={15}
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>

Code blocks with tabs

Display multiple code blocks in a tabbed interface.

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puts "Hello World"

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<CodeBlocks>
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  ```ruby title="hello_world.rb"
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  puts "Hello World"
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  ```
5
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  ```php title="hello_world.php"
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  <?php
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  echo "Hello World";
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  ?>
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  ```
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  ```rust title="hello_world.rs"
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  fn main() {
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      println!("Hello World");
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  }
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  ```
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</CodeBlocks>

Language synchronization

Code blocks with the same language automatically synchronize across your documentation site. When a user selects a language, all code blocks with that language switch to match. Language preferences persist across browser sessions.

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print("First code block!")

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print("Second code block - syncs with the one above!")

$
npm install plantstore

$
npm uninstall plantstore

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<CodeGroup>
2
  ```bash title="Install using npm" for="npm"
3
  npm install plantstore
4
  ```
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  ```bash title="Install using pnpm" for="pnpm"
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  pnpm add plantstore
7
  ```
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  ```bash title="Install using yarn" for="yarn"
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  yarn add plantstore
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  ```
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</CodeGroup>
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<CodeGroup>
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  ```bash title="Uninstall using npm" for="npm"
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  npm uninstall plantstore
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  ```
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  ```bash title="Uninstall using pnpm" for="pnpm"
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  pnpm remove plantstore
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  ```
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  ```bash title="Uninstall using yarn" for="yarn"
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  yarn remove plantstore
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  ```
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</CodeGroup>

Properties

Code block attributes

These can be added after the language identifier in markdown code blocks or as props on the <CodeBlock> component.

<Code> properties

The <Code> component is used for embedding code from files. It accepts all code block attributes listed above, plus: