358 lines
9.8 KiB
Markdown
358 lines
9.8 KiB
Markdown
# rehype-external-links
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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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**[rehype][]** plugin to add `rel` (and `target`) to external links.
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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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* [`unified().use(rehypeExternalLinks[, options])`](#unifieduserehypeexternallinks-options)
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* [`CreateContent`](#createcontent)
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* [`CreateProperties`](#createproperties)
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* [`CreateRel`](#createrel)
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* [`CreateTarget`](#createtarget)
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* [`Options`](#options)
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* [`Target`](#target)
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* [Types](#types)
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* [Compatibility](#compatibility)
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* [Security](#security)
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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 [unified][] ([rehype][]) plugin to add `rel` (and `target`)
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attributes to external links.
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It is particularly useful when displaying user content on your reputable site,
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because users could link to disreputable sources (spam, scams, etc), as search
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engines and other bots will discredit your site for linking to them (or
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legitimize their sites).
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In short: linking to something signals trust, but you can’t trust users.
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This plugin adds certain `rel` attributes to prevent that from happening.
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**unified** is a project that transforms content with abstract syntax trees
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(ASTs).
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**rehype** adds support for HTML to unified.
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**hast** is the HTML AST that rehype uses.
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This is a rehype plugin that adds `rel` (and `target`) to `<a>`s in the AST.
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## When should I use this?
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This project is useful when you want to display user content from authors you
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don’t trust (such as comments), as they might include links you don’t endorse,
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on your website.
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## Install
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This package is [ESM only][esm].
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In Node.js (version 16+), install with [npm][]:
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```sh
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npm install rehype-external-links
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```
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In Deno with [`esm.sh`][esmsh]:
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```js
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import rehypeExternalLinks from 'https://esm.sh/rehype-external-links@3'
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```
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In browsers with [`esm.sh`][esmsh]:
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```html
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<script type="module">
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import rehypeExternalLinks from 'https://esm.sh/rehype-external-links@3?bundle'
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</script>
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```
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## Use
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Say our module `example.js` contains:
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```js
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import rehypeExternalLinks from 'rehype-external-links'
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import remarkParse from 'remark-parse'
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import remarkRehype from 'remark-rehype'
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import rehypeStringify from 'rehype-stringify'
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import {unified} from 'unified'
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const file = await unified()
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.use(remarkParse)
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.use(remarkRehype)
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.use(rehypeExternalLinks, {rel: ['nofollow']})
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.use(rehypeStringify)
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.process('[rehype](https://github.com/rehypejs/rehype)')
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console.log(String(file))
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```
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…then running `node example.js` yields:
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```html
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<p><a href="https://github.com/rehypejs/rehype" rel="nofollow">rehype</a></p>
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```
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## API
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This package exports no identifiers.
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The default export is [`rehypeExternalLinks`][api-rehype-external-links].
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### `unified().use(rehypeExternalLinks[, options])`
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Automatically add `rel` (and `target`?) to external links.
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###### Parameters
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* `options` ([`Options`][api-options], optional)
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— configuration
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###### Returns
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Transform ([`Transformer`][unified-transformer]).
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###### Notes
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You should [likely not configure `target`][css-tricks].
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You should at least set `rel` to `['nofollow']`.
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When using a `target`, add `noopener` and `noreferrer` to avoid exploitation
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of the `window.opener` API.
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When using a `target`, you should set `content` to adhere to accessibility
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guidelines by [giving users advanced warning when opening a new window][g201].
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### `CreateContent`
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Create a target for the element (TypeScript type).
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###### Parameters
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* `element` ([`Element`][hast-element])
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— element to check
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###### Returns
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Content to add (`Array<Node>` or `Node`, optional).
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### `CreateProperties`
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Create properties for an element (TypeScript type).
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###### Parameters
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* `element` ([`Element`][hast-element])
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— element to check
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###### Returns
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Properties to add ([`Properties`][hast-properties], optional).
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### `CreateRel`
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Create a `rel` for the element (TypeScript type).
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###### Parameters
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* `element` ([`Element`][hast-element])
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— element to check
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###### Returns
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`rel` to use (`Array<string>`, optional).
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### `CreateTarget`
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Create a `target` for the element (TypeScript type).
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###### Parameters
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* `element` ([`Element`][hast-element])
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— element to check
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###### Returns
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`target` to use ([`Target`][api-target], optional).
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### `Options`
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Configuration (TypeScript type).
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###### Fields
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* `content` (`Array<Node>`, [`CreateContent`][api-create-content], or `Node`,
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optional)
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— content to insert at the end of external links; will be inserted in a
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`<span>` element; useful for improving accessibility by giving users
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advanced warning when opening a new window
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* `contentProperties` ([`CreateProperties`][api-create-properties] or
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[`Properties`][hast-properties], optional)
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— properties to add to the `span` wrapping `content`
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* `properties` ([`CreateProperties`][api-create-properties] or
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[`Properties`][hast-properties], optional)
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— properties to add to the link itself
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* `protocols` (`Array<string>`, default: `['http', 'https']`)
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— protocols to see as external, such as `mailto` or `tel`
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* `rel` (`Array<string>`, [`CreateRel`][api-create-rel], or `string`,
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default: `['nofollow']`)
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— [link types][mdn-rel] to hint about the referenced documents; pass an
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empty array (`[]`) to not set `rel`s on links; when using a `target`, add `noopener`
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and `noreferrer` to avoid exploitation of the `window.opener` API
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* `target` ([`CreateTarget`][api-create-target] or [`Target`][api-target],
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optional)
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— how to display referenced documents; the default (nothing) is to not set
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`target`s on links
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* `test` ([`Test`][is-test], optional)
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— extra test to define which external link elements are modified; any test
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that can be given to `hast-util-is-element` is supported
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### `Target`
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Target (TypeScript type).
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###### Type
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```ts
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type Target = '_blank' | '_parent' | '_self' | '_top'
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```
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## Types
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This package is fully typed with [TypeScript][].
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It exports the additional types
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[`CreateContent`][api-create-content],
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[`CreateProperties`][api-create-properties],
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[`CreateRel`][api-create-rel],
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[`CreateTarget`][api-create-target],
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[`Options`][api-options], and
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[`Target`][api-target].
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## Compatibility
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Projects maintained by the unified collective are compatible with maintained
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versions of Node.js.
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When we cut a new major release, we drop support for unmaintained versions of
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Node.
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This means we try to keep the current release line, `rehype-external-links@^3`,
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compatible with Node.js 16.
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This plugin works with `rehype-parse` version 3+, `rehype-stringify` version 3+,
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`rehype` version 4+, and `unified` version 6+.
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## Security
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Improper use of `rehype-external-links` can open you up to a
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[cross-site scripting (XSS)][xss] attack.
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Either do not combine this plugin with user content or use
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[`rehype-sanitize`][rehype-sanitize].
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## Contribute
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See [`contributing.md`][contributing] in [`rehypejs/.github`][health] for ways
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to get 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/rehypejs/rehype-external-links/workflows/main/badge.svg
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[build]: https://github.com/rehypejs/rehype-external-links/actions
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[coverage-badge]: https://img.shields.io/codecov/c/github/rehypejs/rehype-external-links.svg
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[coverage]: https://codecov.io/github/rehypejs/rehype-external-links
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[downloads-badge]: https://img.shields.io/npm/dm/rehype-external-links.svg
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[downloads]: https://www.npmjs.com/package/rehype-external-links
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[size-badge]: https://img.shields.io/bundlejs/size/rehype-external-links
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[size]: https://bundlejs.com/?q=rehype-external-links
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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/rehypejs/rehype/discussions
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[npm]: https://docs.npmjs.com/cli/install
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[esm]: https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c
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[esmsh]: https://esm.sh
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[health]: https://github.com/rehypejs/.github
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[contributing]: https://github.com/rehypejs/.github/blob/HEAD/contributing.md
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[support]: https://github.com/rehypejs/.github/blob/HEAD/support.md
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[coc]: https://github.com/rehypejs/.github/blob/HEAD/code-of-conduct.md
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[license]: license
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[author]: https://wooorm.com
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[hast-properties]: https://github.com/syntax-tree/hast#properties
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[is-test]: https://github.com/syntax-tree/hast-util-is-element#test
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[mdn-rel]: https://developer.mozilla.org/en-US/docs/Web/HTML/Link_types
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[rehype]: https://github.com/rehypejs/rehype
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[rehype-sanitize]: https://github.com/rehypejs/rehype-sanitize
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[typescript]: https://www.typescriptlang.org
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[unified]: https://github.com/unifiedjs/unified
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[unified-transformer]: https://github.com/unifiedjs/unified#transformer
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[xss]: https://en.wikipedia.org/wiki/Cross-site_scripting
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[hast-element]: https://github.com/syntax-tree/hast#element
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[g201]: https://www.w3.org/WAI/WCAG21/Techniques/general/G201
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[css-tricks]: https://css-tricks.com/use-target_blank/
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[api-create-content]: #createcontent
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[api-create-properties]: #createproperties
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[api-create-rel]: #createrel
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[api-create-target]: #createtarget
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[api-options]: #options
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[api-target]: #target
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[api-rehype-external-links]: #unifieduserehypeexternallinks-options
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