remark-lint-definition-case/readme.md

remark-lint rule to warn when definition labels are not lowercase

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# remark-lint-definition-case

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[`remark-lint`][github-remark-lint] rule to warn when definition labels are not lowercase.

## 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(remarkLintDefinitionCase)`](#unifieduseremarklintdefinitioncase)
* [Recommendation](#recommendation)
* [Examples](#examples)
* [Compatibility](#compatibility)
* [Contribute](#contribute)
* [License](#license)

## What is this?

This package checks the case of definition labels.

## When should I use this?

You can use this package to check that definition labels are consistent.

## Presets

This plugin is included in the following presets:

| Preset | Options |
| - | - |
| [`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-definition-case
```

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

```js
import remarkLintDefinitionCase from 'https://esm.sh/remark-lint-definition-case@4'
```

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

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

## Use

On the API:

```js
import remarkLint from 'remark-lint'
import remarkLintDefinitionCase from 'remark-lint-definition-case'
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(remarkLintDefinitionCase)
  .use(remarkStringify)
  .process(file)

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

On the CLI:

```sh
remark --frail --use remark-lint --use remark-lint-definition-case .
```

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

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

## API

This package exports no identifiers.
It exports no additional [TypeScript][typescript] types.
The default export is
[`remarkLintDefinitionCase`][api-remark-lint-definition-case].

### `unified().use(remarkLintDefinitionCase)`

Warn when definition labels are not lowercase.

###### Parameters

There are no options.

###### Returns

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

## Recommendation

Definitions and references are matched together regardless of casing.
Using uppercase in definition labels might incorrectly indicate that casing
is of importance.
Due to this, it’s recommended to use lowercase and turn this rule on.

## Examples

##### `ok.md`

###### In

```markdown
[mercury]: https://example.com "Mercury"
```

###### Out

No messages.

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

###### In

```markdown
[Mercury]: https://example.com "Mercury"
```

###### Out

```text
1:1-1:41: Unexpected uppercase characters in definition label, expected lowercase
```

##### `gfm.md`

###### In

> 👉 **Note**: this example uses
> GFM ([`remark-gfm`][github-remark-gfm]).

```markdown
[^Mercury]:
    **Mercury** is the first planet from the Sun and the smallest
    in the Solar System.
```

###### Out

```text
1:1-3:25: Unexpected uppercase characters in footnote definition label, expected lowercase
```

## 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-definition-case@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-remark-lint-definition-case]: #unifieduseremarklintdefinitioncase

[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-definition-case.svg

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

[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-definition-case

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

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

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

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

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

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