# `PiiCatalog.Pattern`
[🔗](https://github.com/signalvaultio/pii_catalog/blob/v0.1.0/lib/pii_catalog/pattern.ex#L1)

One identifier in the catalog: a regex that finds values of its shape, and
the check a value must pass before it counts.

## Fields

  * `name` – the stable identifier, an atom such as `:iban` or
    `:personnummer_se`. Once a pattern is released its name never changes,
    so it can be stored.
  * `label`, `short_label`, `plural` – how to name it in a full sentence
    ("US Social Security number"), in a compact list ("SSN") and in running
    text ("US social security numbers").
  * `regex` – finds candidate values. Compiled without the `u` flag, so it
    matches bytewise; see `PiiCatalog.Patterns` for the boundaries this
    implies.
  * `regions` – where the identifier is used, as region atoms
    (`PiiCatalog.regions/0`). The first is the region it is listed under.
  * `confidence` – how a match is confirmed:
    * `:checksum` – a validator confirms the value (a check digit or a
      structure the regex cannot express);
    * `:format` – the regex alone decides;
    * `:format_with_context` – the identifier has no check digit, or one
      too weak on its own, so the regex also requires a word naming it
      directly before the value, and starts the match after that word with
      `\K`. The validator still runs on the value.
  * `check` – what the validator checks: `:check_digit` (a check digit,
    letter or character computed from the rest of the value),
    `:structure` (a structure only, such as a date of birth or ranges that
    are never issued, with no check digit), `:mixed` (a check digit for
    some values and a structure only for others, as for EU VAT numbers,
    where some member states' numbers have no check), or `nil` (no
    validator).
  * `keyword_required` – `true` when the regex matches only directly
    after a word naming the identifier. That is every
    `:format_with_context` pattern, where the word is not part of the
    match, and `:date_of_birth`, where it is.
  * `validator` – the name of the check in `PiiCatalog.Validators`, or
    `nil` when the format alone decides.
  * `requires` – what a text must contain for the pattern to be scanned at
    all: a literal every match contains (`"@"`), or a list of regexes, one
    of which every text holding a match also matches. `nil` means always
    scan.
  * `example` – a test or invented value, never a real person's. For a
    `:format_with_context` pattern it includes the keyword.
  * `notes` – what the regex accepts, in a sentence or two.

# `check`

```elixir
@type check() :: :check_digit | :mixed | :structure | nil
```

# `confidence`

```elixir
@type confidence() :: :checksum | :format | :format_with_context
```

# `t`

```elixir
@type t() :: %PiiCatalog.Pattern{
  check: check(),
  confidence: confidence(),
  example: String.t(),
  keyword_required: boolean(),
  label: String.t(),
  name: atom(),
  notes: String.t() | nil,
  plural: String.t(),
  regex: Regex.t(),
  regions: [atom(), ...],
  requires: String.t() | [Regex.t()] | nil,
  short_label: String.t(),
  validator: atom() | nil
}
```

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*Consult [api-reference.md](api-reference.md) for complete listing*