Specify a whitelist of allowed combinators.

```
a + b {}
/** ↑
* This combinator */
```

This rule normalizes the whitespace descendant combinator to be a single space.

This rule ignores reference combinators e.g. `/for/`

.

`array|string`

: `["array", "of", "combinators"]|"combinator"`

Given:

`[">", " "]`

The following patterns are considered violations:

`a + b {}`

`a ~ b {}`

The following patterns are *not* considered violations:

`a > b {}`

`a b {}`

```
a
b {}
```