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447 lines
14 KiB
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447 lines
14 KiB
Text
# mdast-util-to-markdown
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[![Build][build-badge]][build]
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[![Coverage][coverage-badge]][coverage]
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[![Downloads][downloads-badge]][downloads]
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[![Size][size-badge]][size]
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[![Sponsors][sponsors-badge]][collective]
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[![Backers][backers-badge]][collective]
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[![Chat][chat-badge]][chat]
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**[mdast][]** utility that turns a syntax tree into markdown.
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## Contents
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* [What is this?](#what-is-this)
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* [When should I use this?](#when-should-i-use-this)
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* [Install](#install)
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* [Use](#use)
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* [API](#api)
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* [`toMarkdown(tree[, options])`](#tomarkdowntree-options)
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* [List of extensions](#list-of-extensions)
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* [Syntax](#syntax)
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* [Syntax tree](#syntax-tree)
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* [Types](#types)
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* [Security](#security)
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* [Related](#related)
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* [Contribute](#contribute)
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* [License](#license)
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## What is this?
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This package is a utility that takes an [mdast][] syntax tree as input and turns
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it into serialized markdown.
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This utility is a low level project.
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It’s used in [`remark-stringify`][remark-stringify], which focusses on making it
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easier to transform content by abstracting these internals away.
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## When should I use this?
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If you want to handle syntax trees manually, use this.
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For an easier time processing content, use the **[remark][]** ecosystem instead.
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## Install
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This package is [ESM only][esm].
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In Node.js (version 12.20+, 14.14+, or 16.0+), install with [npm][]:
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```sh
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npm install mdast-util-to-markdown
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```
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In Deno with [Skypack][]:
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```js
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import {toMarkdown} from 'https://cdn.skypack.dev/mdast-util-to-markdown@1?dts'
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```
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In browsers with [Skypack][]:
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```html
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<script type="module">
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import {toMarkdown} from 'https://cdn.skypack.dev/mdast-util-to-markdown@1?min'
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</script>
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```
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## Use
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Say our module `example.js` looks as follows:
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```js
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import {toMarkdown} from 'mdast-util-to-markdown'
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/** @type {import('mdast').Root} */
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const tree = {
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type: 'root',
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children: [
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{
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type: 'blockquote',
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children: [
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{type: 'thematicBreak'},
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{
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type: 'paragraph',
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children: [
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{type: 'text', value: '- a\nb !'},
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{
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type: 'link',
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url: 'example.com',
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children: [{type: 'text', value: 'd'}]
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}
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]
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}
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]
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}
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]
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}
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console.log(toMarkdown(tree))
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```
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…now running `node example.js` yields:
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```markdown
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> ***
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>
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> \- a
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> b \
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```
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> 👉 **Note**: observe the properly escaped characters which would otherwise
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> turn into a list and image respectively.
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## API
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This package exports the following identifier: `toMarkdown`.
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There is no default export.
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### `toMarkdown(tree[, options])`
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Turn an **[mdast][]** syntax tree into markdown.
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##### Formatting options
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###### `options.bullet`
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Marker to use for bullets of items in unordered lists (`'*'`, `'+'`, or `'-'`,
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default: `'*'`).
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###### `options.bulletOther`
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Marker to use in certain cases where the primary bullet doesn’t work (`'*'`,
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`'+'`, or `'-'`, default: depends).
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There are three cases where the primary bullet can’t be used:
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* When three list items are on their own, the last one is empty, and `bullet`
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is also a valid `rule`: `* - +`.
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This would turn into a thematic break if serialized with three primary
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bullets.
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As this is an edge case unlikely to appear in normal markdown, the last list
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item will be given a different bullet.
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* When a thematic break is the first child of one of the list items, and
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`bullet` is the same character as `rule`: `- ***`.
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This would turn into a single thematic break if serialized with primary
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bullets.
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As this is an edge case unlikely to appear in normal markdown this markup is
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always fixed, even if `bulletOther` is not passed
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* When two unordered lists appear next to each other: `* a\n- b`.
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CommonMark sees different bullets as different lists, but several markdown
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parsers parse it as one list.
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To solve for both, we instead inject an empty comment between the two lists:
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`* a\n<!---->\n* b`, but if `bulletOther` is given explicitly, it will be
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used instead
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###### `options.bulletOrdered`
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Marker to use for bullets of items in ordered lists (`'.'` or `')'`, default:
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`'.'`).
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###### `options.bulletOrderedOther`
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Marker to use in certain cases where the primary bullet for ordered items
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doesn’t work (`'.'` or `')'`, default: none).
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There is one case where the primary bullet for ordered items can’t be used:
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* When two ordered lists appear next to each other: `1. a\n2) b`.
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CommonMark added support for `)` as a marker, but other markdown parsers
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do not support it.
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To solve for both, we instead inject an empty comment between the two lists:
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`1. a\n<!---->\n1. b`, but if `bulletOrderedOther` is given explicitly, it
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will be used instead
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###### `options.closeAtx`
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Whether to add the same number of number signs (`#`) at the end of an ATX
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heading as the opening sequence (`boolean`, default: `false`).
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###### `options.emphasis`
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Marker to use for emphasis (`'*'` or `'_'`, default: `'*'`).
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###### `options.fence`
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Marker to use for fenced code (``'`'`` or `'~'`, default: ``'`'``).
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###### `options.fences`
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Whether to use fenced code always (`boolean`, default: `false`).
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The default is to use fenced code if there is a language defined, if the code is
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empty, or if it starts or ends in blank lines.
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###### `options.incrementListMarker`
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Whether to increment the counter of ordered lists items (`boolean`, default:
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`true`).
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###### `options.listItemIndent`
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How to indent the content of list items (`'one'`, `'tab'`, or `'mixed'`,
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default: `'tab'`).
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Either with the size of the bullet plus one space (when `'one'`), a tab stop
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(`'tab'`), or depending on the item and its parent list (`'mixed'`, uses `'one'`
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if the item and list are tight and `'tab'` otherwise).
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###### `options.quote`
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Marker to use for titles (`'"'` or `"'"`, default: `'"'`).
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###### `options.resourceLink`
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Whether to always use resource links (`boolean`, default: `false`).
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The default is to use autolinks (`<https://example.com>`) when possible
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and resource links (`[text](url)`) otherwise.
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###### `options.rule`
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Marker to use for thematic breaks (`'*'`, `'-'`, or `'_'`, default: `'*'`).
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###### `options.ruleRepetition`
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Number of markers to use for thematic breaks (`number`, default: `3`, min: `3`).
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###### `options.ruleSpaces`
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Whether to add spaces between markers in thematic breaks (`boolean`, default:
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`false`).
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###### `options.setext`
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Whether to use setext headings when possible (`boolean`, default: `false`).
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The default is to always use ATX headings (`# heading`) instead of setext
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headings (`heading\n=======`).
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Setext headings can’t be used for empty headings or headings with a rank of
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three or more.
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###### `options.strong`
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Marker to use for strong (`'*'` or `'_'`, default: `'*'`).
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###### `options.tightDefinitions`
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Whether to join definitions without a blank line (`boolean`, default: `false`).
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The default is to add blank lines between any flow (“block”) construct.
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Turning this option on is a shortcut for a join function like so:
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```js
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function joinTightDefinitions(left, right) {
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if (left.type === 'definition' && right.type === 'definition') {
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return 0
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}
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}
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```
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###### `options.handlers`
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Object mapping node types to custom handlers (`Record<string, Handle>`, default:
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`{}`).
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Useful for syntax extensions.
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This option is a bit advanced.
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It’s recommended to look at the code in [`lib/handle/`][handlers] for examples.
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###### `options.join`
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List of functions used to determine what to place between two flow nodes
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(`Array<Join>`, default: `[]`).
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“Blocks” are typically joined by one blank line.
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Sometimes it’s nicer to have them flush next to each other, yet other times
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they can’t occur together at all.
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Join functions receive two adjacent siblings and their parent and can return
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`number` or `boolean`, to signal how many blank lines to use between them.
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A return value of `true` is as passing `1`.
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A return value of `false` means the nodes cannot be joined by a blank line, such
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as two adjacent block quotes or indented code after a list, in which case a
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comment will be injected to break them up:
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```markdown
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> Quote 1
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<!---->
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> Quote 2
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```
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###### `options.unsafe`
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List of patterns to escape (`Array<Unsafe>`).
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Useful for syntax extensions.
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This option is quite advanced.
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It’s recommended to look at the code in [`lib/unsafe.js`][unsafe] for examples.
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##### Extension options
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###### `options.extensions`
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List of extensions (`Array<ToMarkdownExtension>`, default: `[]`).
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Each `ToMarkdownExtension` is an object with the same interface as `options`
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here.
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##### Returns
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Serialized markdown (`string`).
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## List of extensions
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* [`syntax-tree/mdast-util-directive`](https://github.com/syntax-tree/mdast-util-directive)
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— directives
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* [`syntax-tree/mdast-util-frontmatter`](https://github.com/syntax-tree/mdast-util-frontmatter)
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— frontmatter (YAML, TOML, more)
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* [`syntax-tree/mdast-util-gfm`](https://github.com/syntax-tree/mdast-util-gfm)
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— GFM
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* [`syntax-tree/mdast-util-gfm-autolink-literal`](https://github.com/syntax-tree/mdast-util-gfm-autolink-literal)
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— GFM autolink literals
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* [`syntax-tree/mdast-util-gfm-footnote`](https://github.com/syntax-tree/mdast-util-gfm-footnote)
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— GFM footnotes
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* [`syntax-tree/mdast-util-gfm-strikethrough`](https://github.com/syntax-tree/mdast-util-gfm-strikethrough)
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— GFM strikethrough
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* [`syntax-tree/mdast-util-gfm-table`](https://github.com/syntax-tree/mdast-util-gfm-table)
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— GFM tables
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* [`syntax-tree/mdast-util-gfm-task-list-item`](https://github.com/syntax-tree/mdast-util-gfm-task-list-item)
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— GFM task list items
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* [`syntax-tree/mdast-util-math`](https://github.com/syntax-tree/mdast-util-math)
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— math
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* [`syntax-tree/mdast-util-mdx`](https://github.com/syntax-tree/mdast-util-mdx)
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— MDX
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* [`syntax-tree/mdast-util-mdx-expression`](https://github.com/syntax-tree/mdast-util-mdx-expression)
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— MDX expressions
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* [`syntax-tree/mdast-util-mdx-jsx`](https://github.com/syntax-tree/mdast-util-mdx-jsx)
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— MDX JSX
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* [`syntax-tree/mdast-util-mdxjs-esm`](https://github.com/syntax-tree/mdast-util-mdxjs-esm)
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— MDX ESM
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## Syntax
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Markdown is serialized according to CommonMark but care is taken to format in
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such a way that the resulting markdown should work with most markdown parsers.
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Extensions can add support for custom syntax.
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## Syntax tree
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The syntax tree is [mdast][].
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## Types
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This package is fully typed with [TypeScript][].
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It exports the types `Options`, `Map`, `Unsafe`, `Join`, `Handlers`, `Handle`,
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`Context`, `SafeOptions`, which model the interfaces used by options and
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extensions.
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## Security
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`mdast-util-to-markdown` will do its best to serialize markdown to match the
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syntax tree, but there are several cases where that is impossible.
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It’ll do its best, but complete roundtripping is impossible given that any value
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could be injected into the tree.
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As markdown is sometimes used for HTML, and improper use of HTML can open you up
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to a [cross-site scripting (XSS)][xss] attack, use of `mdast-util-to-markdown`
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and parsing it again later could potentially be unsafe.
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When parsing markdown afterwards and then going to HTML, use something like
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[`hast-util-sanitize`][hast-util-sanitize] to make the tree safe.
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## Related
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* [`syntax-tree/mdast-util-from-markdown`](https://github.com/syntax-tree/mdast-util-from-markdown)
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— parse markdown to mdast
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* [`micromark/micromark`](https://github.com/micromark/micromark)
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— parse markdown
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* [`remarkjs/remark`](https://github.com/remarkjs/remark)
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— process markdown
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## Contribute
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See [`contributing.md` in `syntax-tree/.github`][contributing] for ways to get
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started.
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See [`support.md`][support] for ways to get help.
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This project has a [code of conduct][coc].
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By interacting with this repository, organization, or community you agree to
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abide by its terms.
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## License
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[MIT][license] © [Titus Wormer][author]
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<!-- Definitions -->
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[build-badge]: https://github.com/syntax-tree/mdast-util-to-markdown/workflows/main/badge.svg
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[build]: https://github.com/syntax-tree/mdast-util-to-markdown/actions
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[coverage-badge]: https://img.shields.io/codecov/c/github/syntax-tree/mdast-util-to-markdown.svg
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[coverage]: https://codecov.io/github/syntax-tree/mdast-util-to-markdown
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[downloads-badge]: https://img.shields.io/npm/dm/mdast-util-to-markdown.svg
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[downloads]: https://www.npmjs.com/package/mdast-util-to-markdown
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[size-badge]: https://img.shields.io/bundlephobia/minzip/mdast-util-to-markdown.svg
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[size]: https://bundlephobia.com/result?p=mdast-util-to-markdown
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[sponsors-badge]: https://opencollective.com/unified/sponsors/badge.svg
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[backers-badge]: https://opencollective.com/unified/backers/badge.svg
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[collective]: https://opencollective.com/unified
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[chat-badge]: https://img.shields.io/badge/chat-discussions-success.svg
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[chat]: https://github.com/syntax-tree/unist/discussions
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[npm]: https://docs.npmjs.com/cli/install
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[skypack]: https://www.skypack.dev
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[license]: license
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[author]: https://wooorm.com
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[contributing]: https://github.com/syntax-tree/.github/blob/HEAD/contributing.md
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[support]: https://github.com/syntax-tree/.github/blob/HEAD/support.md
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[coc]: https://github.com/syntax-tree/.github/blob/HEAD/code-of-conduct.md
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[esm]: https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c
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[typescript]: https://www.typescriptlang.org
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[mdast]: https://github.com/syntax-tree/mdast
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[xss]: https://en.wikipedia.org/wiki/Cross-site_scripting
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[hast-util-sanitize]: https://github.com/syntax-tree/hast-util-sanitize
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[handlers]: lib/handle
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[unsafe]: lib/unsafe.js
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[remark]: https://github.com/remarkjs/remark
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[remark-stringify]: https://github.com/remarkjs/remark/tree/main/packages/remark-stringify
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