}
}
```

Here, the command `animal-names` returns the appropriate list of names. `$context` is a string where the value is the command-line that has been typed so far.

```nu
>| my-command
cat                 dog                 eel
>| my-command dog
Lulu                Enzo
>my-command dog enzo
The dog is named Enzo
```

On the second line, after pressing the <kbd>tab</kbd> key, the argument `"my-command dog"` is passed to the `animal-names` completer as context.

::: tip
Completers can also obtain the current cursor position on the command-line using:

```nu
def completer [context:string, position:int] {}
```

:::

## Custom Completion and [`extern`](/commands/docs/extern.md)

A powerful combination is adding custom completions to [known `extern` commands](externs.md). These work the same way as adding a custom completion to a custom command: by creating the custom completion and then attaching it with a `@` to the type of one of the positional or flag arguments of the `extern`.

If you look closely at the examples in the default config, you'll see this:

```nu
export extern "git push" [
    remote?: string@"nu-complete git remotes",  # the name of the remote
    refspec?: string@"nu-complete git branches" # the branch / refspec
    ...
]
```

Custom completions will serve the same role in this example as in the previous examples. The examples above call into two different custom completions, based on the position the user is currently in.

## Custom Descriptions and Styles

As an alternative to returning a list of strings, a completion function can also return a list of records with a `value` field as well as optional `description` and `style` fields. The style can be one of the following:

- A string with the foreground color, either a hex code or a color name such as `yellow`. For a list of valid color names, see `ansi --list`.
- A record with the fields `fg` (foreground color), `bg` (background color), and `attr` (attributes such as underline and bold). This record is in the same format that `ansi --escape` accepts. See the [`ansi`](/commands/docs/ansi) command reference for a list of possible values for the `attr` field.