remark-lint-emphasis-marker/readme.md

remark-lint rule to warn when emphasis markers violate the given style

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# remark-lint-emphasis-marker

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[`remark-lint`][github-remark-lint] rule to warn when emphasis markers are inconsistent.

## Contents

* [What is this?](#what-is-this)
* [When should I use this?](#when-should-i-use-this)
* [Presets](#presets)
* [Install](#install)
* [Use](#use)
* [API](#api)
  * [`unified().use(remarkLintEmphasisMarker[, options])`](#unifieduseremarklintemphasismarker-options)
  * [`Marker`](#marker)
  * [`Options`](#options)
* [Recommendation](#recommendation)
* [Fix](#fix)
* [Examples](#examples)
* [Compatibility](#compatibility)
* [Contribute](#contribute)
* [License](#license)

## What is this?

This package checks the style of emphasis markers.

## When should I use this?

You can use this package to check that emphasis is consistent.

## Presets

This plugin is included in the following presets:

| Preset | Options |
| - | - |
| [`remark-preset-lint-consistent`](https://github.com/remarkjs/remark-lint/tree/main/packages/remark-preset-lint-consistent) | `'consistent'` |
| [`remark-preset-lint-markdown-style-guide`](https://github.com/remarkjs/remark-lint/tree/main/packages/remark-preset-lint-markdown-style-guide) | `'*'` |

## Install

This package is [ESM only][github-gist-esm].
In Node.js (version 16+),
install with [npm][npm-install]:

```sh
npm install remark-lint-emphasis-marker
```

In Deno with [`esm.sh`][esm-sh]:

```js
import remarkLintEmphasisMarker from 'https://esm.sh/remark-lint-emphasis-marker@4'
```

In browsers with [`esm.sh`][esm-sh]:

```html
<script type="module">
  import remarkLintEmphasisMarker from 'https://esm.sh/remark-lint-emphasis-marker@4?bundle'
</script>
```

## Use

On the API:

```js
import remarkLint from 'remark-lint'
import remarkLintEmphasisMarker from 'remark-lint-emphasis-marker'
import remarkParse from 'remark-parse'
import remarkStringify from 'remark-stringify'
import {read} from 'to-vfile'
import {unified} from 'unified'
import {reporter} from 'vfile-reporter'

const file = await read('example.md')

await unified()
  .use(remarkParse)
  .use(remarkLint)
  .use(remarkLintEmphasisMarker)
  .use(remarkStringify)
  .process(file)

console.error(reporter(file))
```

On the CLI:

```sh
remark --frail --use remark-lint --use remark-lint-emphasis-marker .
```

On the CLI in a config file (here a `package.json`):

```diff
 …
 "remarkConfig": {
   "plugins": [
     …
     "remark-lint",
+    "remark-lint-emphasis-marker",
     …
   ]
 }
 …
```

## API

This package exports no identifiers.
It exports the [TypeScript][typescript] types
[`Marker`][api-marker] and
[`Options`][api-options].
The default export is
[`remarkLintEmphasisMarker`][api-remark-lint-emphasis-marker].

### `unified().use(remarkLintEmphasisMarker[, options])`

Warn when emphasis markers are inconsistent.

###### Parameters

* `options` ([`Options`][api-options], default: `'consistent'`)
  — preferred style or whether to detect the first style and warn for
  further differences

###### Returns

Transform ([`Transformer` from `unified`][github-unified-transformer]).

### `Marker`

Marker (TypeScript type).

###### Type

```ts
type Marker = '*' | '_'
```

### `Options`

Configuration (TypeScript type).

###### Type

```ts
type Options = Marker | 'consistent'
```

## Recommendation

Whether asterisks or underscores are used affects how and whether emphasis
works.
Underscores are sometimes used to represent normal underscores inside words,
so there are extra rules in markdown to support that.
Asterisks are not used in natural language,
so they don’t need these rules,
and thus can form emphasis in more cases.
Asterisks can also be used as the marker of more constructs than underscores:
lists.
Due to having simpler parsing rules,
looking more like syntax,
and that they can be used for more constructs,
it’s recommended to prefer asterisks.

## Fix

[`remark-stringify`][github-remark-stringify] formats emphasis with
asterisks by default.
Pass `emphasis: '_'` to always use underscores.

## Examples

##### `ok-asterisk.md`

When configured with `'*'`.

###### In

```markdown
*Mercury*.
```

###### Out

No messages.

##### `not-ok-asterisk.md`

When configured with `'*'`.

###### In

```markdown
_Mercury_.
```

###### Out

```text
1:1-1:10: Unexpected emphasis marker `_`, expected `*`
```

##### `ok-underscore.md`

When configured with `'_'`.

###### In

```markdown
_Mercury_.
```

###### Out

No messages.

##### `not-ok-underscore.md`

When configured with `'_'`.

###### In

```markdown
*Mercury*.
```

###### Out

```text
1:1-1:10: Unexpected emphasis marker `*`, expected `_`
```

##### `not-ok-consistent.md`

###### In

```markdown
*Mercury* and _Venus_.
```

###### Out

```text
1:15-1:22: Unexpected emphasis marker `_`, expected `*`
```

##### `not-ok.md`

When configured with `'🌍'`.

###### Out

```text
1:1: Unexpected value `🌍` for `options`, expected `'*'`, `'_'`, or `'consistent'`
```

## Compatibility

Projects maintained by the unified collective are compatible with maintained
versions of Node.js.

When we cut a new major release, we drop support for unmaintained versions of
Node.
This means we try to keep the current release line,
`remark-lint-emphasis-marker@4`,
compatible with Node.js 16.

## Contribute

See [`contributing.md`][github-dotfiles-contributing] in [`remarkjs/.github`][github-dotfiles-health] for ways
to get started.
See [`support.md`][github-dotfiles-support] for ways to get help.

This project has a [code of conduct][github-dotfiles-coc].
By interacting with this repository, organization, or community you agree to
abide by its terms.

## License

[MIT][file-license] © [Titus Wormer][author]

[api-marker]: #marker

[api-options]: #options

[api-remark-lint-emphasis-marker]: #unifieduseremarklintemphasismarker-options

[author]: https://wooorm.com

[badge-build-image]: https://github.com/remarkjs/remark-lint/workflows/main/badge.svg

[badge-build-url]: https://github.com/remarkjs/remark-lint/actions

[badge-chat-image]: https://img.shields.io/badge/chat-discussions-success.svg

[badge-chat-url]: https://github.com/remarkjs/remark/discussions

[badge-coverage-image]: https://img.shields.io/codecov/c/github/remarkjs/remark-lint.svg

[badge-coverage-url]: https://codecov.io/github/remarkjs/remark-lint

[badge-downloads-image]: https://img.shields.io/npm/dm/remark-lint-emphasis-marker.svg

[badge-downloads-url]: https://www.npmjs.com/package/remark-lint-emphasis-marker

[badge-funding-backers-image]: https://opencollective.com/unified/backers/badge.svg

[badge-funding-sponsors-image]: https://opencollective.com/unified/sponsors/badge.svg

[badge-funding-url]: https://opencollective.com/unified

[badge-size-image]: https://img.shields.io/bundlejs/size/remark-lint-emphasis-marker

[badge-size-url]: https://bundlejs.com/?q=remark-lint-emphasis-marker

[esm-sh]: https://esm.sh

[file-license]: https://github.com/remarkjs/remark-lint/blob/main/license

[github-dotfiles-coc]: https://github.com/remarkjs/.github/blob/main/code-of-conduct.md

[github-dotfiles-contributing]: https://github.com/remarkjs/.github/blob/main/contributing.md

[github-dotfiles-health]: https://github.com/remarkjs/.github

[github-dotfiles-support]: https://github.com/remarkjs/.github/blob/main/support.md

[github-gist-esm]: https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c

[github-remark-lint]: https://github.com/remarkjs/remark-lint

[github-remark-stringify]: https://github.com/remarkjs/remark/tree/main/packages/remark-stringify

[github-unified-transformer]: https://github.com/unifiedjs/unified#transformer

[npm-install]: https://docs.npmjs.com/cli/install

[typescript]: https://www.typescriptlang.org