# `DomainName`

A domain name: `example.com`.

Use it for a customer's or a company's domain. To allow an IP address or `localhost` as well, use [`Hostname`](/docs/types/type-hostname.md). For a whole address, use [`Url`](/docs/types/type-url.md).

## Shape

One value, held as text in one set form, with no parts: `localhost`.

## Example

```jadpo
DomainName("example.com")
```

`DomainName(raw)` checks the text, and text that isn't one breaks the `format` rule.

`text.parse(raw, as: DomainName)` reads one from text that comes from outside. Text that isn't one at all fails `malformed`, such as `Example.com`, `example.com.` or `-example.com`.

## Good to know

- It is lower case with no dot at the end. A non-ASCII label is held in its `xn--` form, such as `xn--mnchen-3ya.de`.
- `==` tells you whether two are the same. `<` and `list.sort_by` don't take it.

## In JSON

A string, in a request, a response or `json.write`:

```json
"example.com"
"www.example.co.uk"
"xn--mnchen-3ya.de"
```

## Details

<details>
<summary>Text form, storage, how it is shown, and operations</summary>

`DomainName` is in the group Web and network, and has been in Jadpo since 0.1.0.

### Text form

`text.from` writes one standard text form, the same form `text.parse` reads back: `example.com`, `www.example.co.uk` and `xn--mnchen-3ya.de`.

### How it is stored

It is stored in one column named for the field, of type `text`. `xn--mnchen-3ya.de` is stored as `'xn--mnchen-3ya.de'`.

### How it is shown to people

`text.format(value, locale:)` shows it to people in their locale.

With `locale: Locale.en_gb`:

| Value | Shown |
|---|---|
| `example.com` | `example.com` |
| `www.example.co.uk` | `www.example.co.uk` |
| `xn--mnchen-3ya.de` | `xn--mnchen-3ya.de` |
| `localhost` | `localhost` |

### Operations

It also takes `text.parse`, `text.from`, `text.format`, `json.read`, `json.write` and `==`. [How every standard type behaves](/docs/every-standard-type-meets-one-contract.md) says how they work.

</details>