# `HttpHeaderName`

An HTTP header's name, in lower case: `content-type`.

Use it to name a header in a list or in logs. Capitals are refused, so lower-case any you read.

## Shape

One value, held as text in one set form, with no parts: `x-request-id`.

## Example

```jadpo
HttpHeaderName("content-type")
```

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

`text.parse(raw, as: HttpHeaderName)` reads one from text that comes from outside. Text that isn't one at all fails `malformed`, such as `Content-Type`, `content type` or `content-type:`.

## Good to know

- `==` 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
"content-type"
"accept-language"
"x-request-id"
```

## Details

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

`HttpHeaderName` 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: `content-type`, `accept-language` and `x-request-id`.

### How it is stored

It is stored in one column named for the field, of type `text`. `accept-language` is stored as `'accept-language'`.

### How it is shown to people

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

With `locale: Locale.en_gb`:

| Value | Shown |
|---|---|
| `content-type` | `content-type` |
| `accept-language` | `accept-language` |
| `x-request-id` | `x-request-id` |

### 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>