# length-zero-no-unit

Disallow units for zero lengths.

<!-- prettier-ignore -->
```css
a { top: 0px; }
/**      ↑↑
 * This zero and this type of length unit */
```

_Lengths_ refer to distance measurements. A length is a _dimension_, which is a _number_ immediately followed by a _unit identifier_. However, for zero lengths the unit identifier is optional. The length units are: `em`, `ex`, `ch`, `vw`, `vh`, `cm`, `mm`, `in`, `pt`, `pc`, `px`, `rem`, `vmin`, and `vmax`.

This rule ignores lengths within math functions (e.g. `calc`).

The [`fix` option](../../../docs/user-guide/options.md#fix) can automatically fix all of the problems reported by this rule.

## Options

### `true`

The following patterns are considered problems:

<!-- prettier-ignore -->
```css
a { top: 0px }
```

<!-- prettier-ignore -->
```css
a { top: 0.000em }
```

The following patterns are _not_ considered problems:

<!-- prettier-ignore -->
```css
a { top: 0 } /* no unit */
```

<!-- prettier-ignore -->
```css
a { transition-delay: 0s; } /* dimension */
```

<!-- prettier-ignore -->
```css
a { top: 2in; }
```

<!-- prettier-ignore -->
```css
a { top: 1.001vh }
```

## Optional secondary options

### `ignore: ["custom-properties"]`

#### `"custom-properties"`

Ignore units for zero length in custom properties.

The following pattern is _not_ considered a problem:

<!-- prettier-ignore -->
```css
a { --x: 0px; }
```

### `ignoreFunctions: ["/regex/", /regex/, "string"]`

Given:

```json
["var", "/^--/"]
```

The following patterns are _not_ considered problems:

<!-- prettier-ignore -->
```css
a { top: var(--foo, 0px); }
```

<!-- prettier-ignore -->
```css
a { top: --bar(0px); }
```