stylelint/lib/rules/declaration-block-no-duplicate-properties/README.md

A mighty, modern CSS linter.

# declaration-block-no-duplicate-properties

Disallow duplicate properties within declaration blocks.

<!-- prettier-ignore -->
```css
a { color: pink; color: orange; }
/** ↑            ↑
 * These duplicated properties */
```

This rule ignores variables (`$sass`, `@less`, `--custom-property`).

## Options

### `true`

The following patterns are considered violations:

<!-- prettier-ignore -->
```css
a { color: pink; color: orange; }
```

<!-- prettier-ignore -->
```css
a { color: pink; background: orange; color: orange }
```

The following patterns are _not_ considered violations:

<!-- prettier-ignore -->
```css
a { color: pink; }
```

<!-- prettier-ignore -->
```css
a { color: pink; background: orange; }
```

## Optional secondary options

### `ignore: ["consecutive-duplicates"]`

Ignore consecutive duplicated properties.

They can prove to be useful fallbacks for older browsers.

The following patterns are considered violations:

<!-- prettier-ignore -->
```css
p {
  font-size: 16px;
  font-weight: 400;
  font-size: 1rem;
}
```

The following patterns are _not_ considered violations:

<!-- prettier-ignore -->
```css
p {
  font-size: 16px;
  font-size: 1rem;
  font-weight: 400;
}
```

### `ignore: ["consecutive-duplicates-with-different-values"]`

Ignore consecutive duplicated properties with different values.

Including duplicate properties (fallbacks) is useful to deal with older browsers support for CSS properties. E.g. using `px` units when `rem` isn't available.

The following patterns are considered violations:

<!-- prettier-ignore -->
```css
/* properties with the same value */
p {
  font-size: 16px;
  font-size: 16px;
  font-weight: 400;
}
```

<!-- prettier-ignore -->
```css
/* nonconsecutive duplicates */
p {
  font-size: 16px;
  font-weight: 400;
  font-size: 1rem;
}
```

The following patterns are _not_ considered violations:

<!-- prettier-ignore -->
```css
p {
  font-size: 16px;
  font-size: 1rem;
  font-weight: 400;
}
```

### `ignoreProperties: ["/regex/", "non-regex"]`

Ignore duplicates of specific properties.

Given:

```
["color", "/background-/"]
```

The following patterns are considered violations:

<!-- prettier-ignore -->
```css
a { color: pink; background: orange; background: white; }
```

<!-- prettier-ignore -->
```css
a { background: orange; color: pink; background: white; }
```

The following patterns are _not_ considered violations:

<!-- prettier-ignore -->
```css
a { color: pink; color: orange; background-color: orange; background-color: white; }
```

<!-- prettier-ignore -->
```css
a { color: pink; background-color: orange; color: orange; background-color: white; }
```