# PostCSS Extend Rule [<img src="https://postcss.github.io/postcss/logo.svg" alt="PostCSS Logo" width="90" height="90" align="right">][postcss]

[![NPM Version][npm-img]][npm-url]
[![Build Status][cli-img]][cli-url]
[![Gitter Chat][git-img]][git-url]

[PostCSS Extend Rule] lets you use the `@extend` at-rule and
[Functional Selectors] in CSS, following the speculative
[CSS Extend Rules Specification].

```css
%thick-border {
  border: thick dotted red;
}

.serious-modal {
  font-style: normal;
  font-weight: bold;

  @media (max-width: 240px) {
    @extend .modal:hover;
  }
}

.modal {
  @extend %thick-border;

  color: red;
}

.modal:hover:not(:focus) {
  outline: none;
}

/* becomes */

.serious-modal {
  font-style: normal;
  font-weight: bold;
}

@media (max-width: 240px) {
  .serious-modal:not(:focus) {
    outline: none;
  }
}

.modal {
  border: thick dotted red;
  color: red;
}

.modal:hover:not(:focus) {
  outline: none;
}
```

## Usage

Add [PostCSS Extend Rule] to your build tool:

```bash
npm install postcss-extend-rule --save-dev
```

#### Node

Use [PostCSS Extend Rule] to process your CSS:

```js
require('postcss-extend-rule').process(YOUR_CSS /*, PostCSS Options, Options */);
```

#### PostCSS

Add [PostCSS] to your build tool:

```bash
npm install postcss --save-dev
```

Use [PostCSS Extend Rule] as a plugin:

```js
postcss([
  require('postcss-extend-rule')(/* Options */)
]).process(YOUR_CSS);
```

#### Gulp

Add [Gulp PostCSS] to your build tool:

```bash
npm install gulp-postcss --save-dev
```

Use [PostCSS Extend Rule] in your Gulpfile:

```js
var postcss = require('gulp-postcss');

gulp.task('css', function () {
  return gulp.src('./src/*.css').pipe(
    postcss([
      require('postcss-extend-rule')(/* Options */)
    ])
  ).pipe(
    gulp.dest('.')
  );
});
```

#### Grunt

Add [Grunt PostCSS] to your build tool:

```bash
npm install grunt-postcss --save-dev
```

Use [PostCSS Extend Rule] in your Gruntfile:

```js
grunt.loadNpmTasks('grunt-postcss');

grunt.initConfig({
  postcss: {
    options: {
      use: [
        require('postcss-extend-rule')(/* Options */)
      ]
    },
    dist: {
      src: '*.css'
    }
  }
});
```

## Options

### onFunctionalSelector

The `onFunctionalSelector` option determines how functional selectors should be
handled. Its options are:

- `remove` (default) removes any functional selector
- `ignore` ignores any functional selector and moves on
- `warn` warns the user whenever it encounters a functional selector
- `throw` throws an error if ever it encounters a functional selector

### onRecursiveExtend

The `onRecursiveExtend` option determines how recursive extend at-rules should
be handled. Its options are:

- `remove` (default) removes any recursive extend at-rules
- `ignore` ignores any recursive extend at-rules and moves on
- `warn` warns the user whenever it encounters a recursive extend at-rules
- `throw` throws an error if ever it encounters a recursive extend at-rules

### onUnusedExtend

The `onUnusedExtend` option determines how an unused extend at-rule should be
handled. Its options are:

- `remove` (default) removes any unused extend at-rule
- `ignore` ignores any unused extend at-rule and moves on
- `warn` warns the user whenever it encounters an unused extend at-rule
- `throw` throws an error if ever it encounters an unused extend at-rule

[npm-url]: https://www.npmjs.com/package/postcss-extend-rule
[npm-img]: https://img.shields.io/npm/v/postcss-extend-rule.svg
[cli-url]: https://travis-ci.org/jonathantneal/postcss-extend-rule
[cli-img]: https://img.shields.io/travis/jonathantneal/postcss-extend-rule.svg
[git-url]: https://gitter.im/postcss/postcss
[git-img]: https://img.shields.io/badge/chat-gitter-blue.svg

[CSS Extend Rules Specification]: https://jonathantneal.github.io/specs/css-extend-rule/
[Functional Selectors]: https://jonathantneal.github.io/specs/css-extend-rule/#functional-selector
[Gulp PostCSS]: https://github.com/postcss/gulp-postcss
[Grunt PostCSS]: https://github.com/nDmitry/grunt-postcss
[PostCSS]: https://github.com/postcss/postcss
[PostCSS Extend Rule]: https://github.com/jonathantneal/postcss-extend-rule