atom/docs/packages/wrap-guide.md

### Wrap Guide

The `wrap-guide` extension places a vertical line in each editor at a certain
column to guide your formatting so lines do not exceed a certain width.

By default the wrap-guide is placed at the 80th column.

#### Configuration

You can customize where the column is placed using the `wrapGuide.columns`
config option.

```json
{
  "wrapGuide": {
    "columns": [
      { "pattern": "\.mm$", "column": 200 },
      { "pattern": "\.cc$", "column": 120 }
    ]
  }
}
```

The above config example would place the guide at the 200th column for paths
that end with `.mm` and place the guide at the 120th column for paths that end
with `.cc`.

You can configure the color and/or width of the line by adding the following
CSS to a custom stylesheet:

```css
.wrap-guide {
  width: 10px;
  background-color: red;
}
```