# Code Highlighting

Milkdown supports syntax highlighting for code blocks through the `@milkdown/plugin-highlight` plugin. This plugin provides several options for highlighting code with different syntax highlighters.

## Installation

```bash
npm install @milkdown/plugin-highlight
```

## Basic Usage

The highlight plugin requires a parser to be configured. Here's a basic example using the Shiki parser:

```typescript
import { Editor } from "@milkdown/core";
import { commonmark } from "@milkdown/preset-commonmark";
import { highlight, highlightPluginConfig } from "@milkdown/plugin-highlight";
import { createParser } from "@milkdown/plugin-highlight/shiki";

const editor = Editor.make()
  .config(async (ctx) => {
    const parser = await createParser({
      theme: "github-light",
      langs: ["javascript", "typescript", "python", "html", "css"],
    });
    ctx.set(highlightPluginConfig.key, { parser });
  })
  .use(commonmark)
  .use(highlight)
  .create();
```

## Available Parsers

The plugin supports multiple syntax highlighting libraries:

### Shiki

Provides high-quality syntax highlighting with VS Code themes. Learn more at [Shiki](https://shiki.style/):

```typescript
import { createParser } from "@milkdown/plugin-highlight/shiki";

const parser = await createParser({
  theme: "github-light",
  langs: ["javascript", "typescript", "python"],
});
ctx.set(highlightPluginConfig.key, { parser });
```

### Lowlight

Based on [highlight.js](https://highlightjs.org/), supports many languages:

```typescript
import { createParser } from "@milkdown/plugin-highlight/lowlight";
import { common } from "lowlight";

const parser = createParser({ common });
ctx.set(highlightPluginConfig.key, { parser });
```

Learn more about Lowlight at [lowlight](https://github.com/wooorm/lowlight).

### Refractor

Based on [Prism.js](https://prismjs.com/):

```typescript
import { createParser } from "@milkdown/plugin-highlight/refractor";
import { refractor } from "refractor";

const parser = createParser({ refractor });
ctx.set(highlightPluginConfig.key, { parser });
```

Learn more about Refractor at [refractor](https://github.com/wooorm/refractor).

### Sugar High

A lightweight and fast syntax highlighter. Learn more at [Sugar High](https://github.com/huozhi/sugar-high):

```typescript
import { createParser } from "@milkdown/plugin-highlight/sugar-high";

const parser = createParser();
ctx.set(highlightPluginConfig.key, { parser });
```

## Styling

The highlighted code will have CSS classes applied based on the chosen parser. You'll need to include appropriate CSS to style the highlighted tokens.

### Sugar High Classes

Sugar High uses classes like:

- `sh__token--identifier`
- `sh__token--string`
- `sh__token--keyword`
- `sh__token--sign`
- `sh__token--property`

You can style these using CSS variables:

```css
.sh__token--identifier {
  color: var(--sh-identifier);
}
.sh__token--string {
  color: var(--sh-string);
}
.sh__token--keyword {
  color: var(--sh-keyword);
}
```

### Other Parsers

For Lowlight, Refractor, and Shiki, refer to their respective documentation for styling information.

## Example

Here's a complete example with Shiki:

```typescript
import { Editor } from "@milkdown/core";
import { commonmark } from "@milkdown/preset-commonmark";
import { highlight, highlightPluginConfig } from "@milkdown/plugin-highlight";
import { createParser } from "@milkdown/plugin-highlight/shiki";

async function createHighlightedEditor() {
  const parser = await createParser({
    theme: "github-light",
    langs: ["javascript", "typescript", "python", "html", "css", "json"],
  });

  const editor = Editor.make()
    .config((ctx) => {
      ctx.set(highlightPluginConfig.key, { parser });
    })
    .use(commonmark)
    .use(highlight);

  await editor.create();
  return editor;
}
```

With this setup, your code blocks will be automatically highlighted:

````markdown
```javascript
console.log("Hello, world!");
const greeting = (name) => `Hello, ${name}!`;
```
````

The code above will render with syntax highlighting applied to keywords, strings, and other language constructs.