# `Username`

A login handle: lower-case letters, digits, `_`, `.` and `-`, up to 64 of them.

Use it for the name someone picks to sign in or to be mentioned by. For what they are actually called, use [`PersonName`](/docs/types/type-person-name.md). For an address you can write to, use [`Email`](/docs/types/type-email.md).

## Shape

One value, held as text in one set form, with no parts: `mary.somerville_1780`.

## Example

```jadpo
Username("mary.somerville_1780")
```

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

`text.parse(raw, as: Username)` reads one from text that comes from outside. Text that isn't one at all fails `malformed`, such as `Mary`, `mary somerville` or `mary@example.com`.

## Good to know

- It refuses capitals rather than lowering them, so lower-case what a person types before you build one.
- `==` tells you whether two are the same. `<` and `list.sort_by` don't take it.
- A field that holds one counts as personal data (`identifying`), so you don't mark it yourself.

## In JSON

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

```json
"mary"
"mary.somerville_1780"
```

## Details

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

`Username` is in the group People and contact, 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: `mary` and `mary.somerville_1780`.

### How it is stored

It is stored in one column named for the field, of type `text`. `mary.somerville_1780` is stored as `'mary.somerville_1780'`.

### How it is shown to people

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

With `locale: Locale.en_gb`:

| Value | Shown |
|---|---|
| `mary` | `mary` |
| `mary.somerville_1780` | `mary.somerville_1780` |

### 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>