{
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  "title": "核心概念",
  "description": "了解 unifast 的多阶段编译管线、内置处理阶段以及 MdAst 和 HAst 转换的工作方式。",
  "section": "introduction",
  "body": "unifast 通过一条多阶段管线来编译 Markdown。理解这些阶段有助于你配置编译器并选择合适的插件。\n\n### 编译管线\n\n```\nInput text\n  → Parse (Markdown or MDX)\n  → IR0: MdAst (Markdown structure)\n  → Normalize + Built-in MdAst passes\n  → Lower to IR1: HAst (HTML structure)\n  → HAst passes (sanitize, highlight, etc.)\n  → Emit (HTML string)\n```\n\n每个阶段都会通过一层中间表示（IR）对文档进行转换。\n\n### 中间表示\n\n| IR | 名称 | 用途 |\n|----|------|---------|\n| **IR0** | MdAst | Markdown 结构 —— 标题、段落、列表、代码块 |\n| **IR1** | HAst | HTML 结构 —— 元素、属性、文本节点 |\n| **IR2** | JsAst | 仅 MDX 使用 —— ESM 导入和 JSX 表达式 |\n\n解析器首先生成 **MdAst**，再降级为 **HAst** 以便输出 HTML。MDX 输入还会额外生成用于 JavaScript 输出的 **JsAst** 节点。\n\n### 处理阶段\n\n处理阶段是在 AST 的特定阶段上执行的转换。unifast 为常见任务内置了以下处理阶段：\n\n**MdAst 阶段**（降级为 HTML 之前）：\n\n- **Normalize** —— 为下游阶段提供一致的结构\n- **Slug** —— 根据文本内容生成标题 ID\n- **TOC** —— 从标题中提取目录\n- **Definition Resolution** —— 解析链接/图像的引用定义\n\n**HAst 阶段**（降级为 HTML 之后）：\n\n- **Sanitize** —— 移除不允许的 HTML 元素和属性\n- **Highlight** —— 为代码块应用语法高亮\n- **Cleanup** —— 清理多余的节点和空白字符\n\n处理阶段按照所属阶段自动排序 —— 你无需关心它们的执行顺序。\n\n### 插件\n\n插件是用于配置内置处理阶段的 TypeScript 包。它们不会在编译期间执行任意 JavaScript 代码 —— 而是通过设置选项来控制 Rust 核心处理文档的方式。\n\n```ts\nimport { compile, gfm, sanitize } from \"@unifast/node\";\n\nconst result = compile(source, {\n  plugins: [gfm(), sanitize()],\n});\n```\n\n每个插件都会返回一个配置对象，在 Rust 核心运行之前被合并到编译选项中。这样就能保证热路径完全运行在原生代码中。\n\n### 输出格式\n\n编译器通过 `outputKind` 选项支持多种输出格式：\n\n| 格式 | 描述 |\n|--------|-------------|\n| `\"html\"` | HTML 字符串（默认） |\n| `\"hast\"` | HAst JSON —— 用于自定义渲染的 HTML AST |\n| `\"mdast\"` | MdAst JSON —— 用于分析的 Markdown AST |\n| `\"mdx-js\"` | JavaScript 模块字符串（仅 MDX） |\n\n### 诊断信息\n\n编译器会通过结果中的 `diagnostics` 数组报告各类问题。每条诊断都包含严重级别、消息，以及可选的源码位置范围，用于精确定位错误。\n\n```ts\nconst result = compile(source);\n\nfor (const d of result.diagnostics) {\n  console.warn(`[${d.level}] ${d.message}`);\n}\n```",
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