(luhn-valid? "79927398713")          ;=> true
(luhn-check-digit "7992739871")       ;=> "3"
(iso7064-mod11-2-check "000000021825009") ;=> "7"   (ORCID)

Standalone check-digit algorithms (Luhn, Verhoeff, ISO 7064), usable directly
when you need the primitive rather than a typed identifier validator.

Each algorithm has a `*-valid?` predicate over a complete string (payload plus
the trailing check character). Where it applies, an algorithm also has a
`*-check-digit` or `*-check` calculator. The calculator returns the check
character for a bare payload.

    (luhn-valid? "79927398713")          ;=> true
    (luhn-check-digit "7992739871")       ;=> "3"
    (iso7064-mod11-2-check "000000021825009") ;=> "7"   (ORCID)

(valid?  :iban "GB82 WEST 1234 5698 7654 32")  ;=> true
(parse   :credit-card "4111111111111111")      ;=> {:valid? true :network :visa}
(format  :iban "GB82WEST12345698765432")       ;=> "GB82 WEST 1234 5698 7654 32"
(detect  "4111111111111111")                   ;=> [:credit-card :luhn]

Validate, parse, and format standard identifier numbers.

This API supports credit cards, IBAN/BIC, ISBN, ISSN, ISIN, US bank routing
(ABA), IMEI, and the raw Luhn check. A type keyword selects the identifier
type. The API uses Clojure data. It is a facade over Apache Commons Validator
and iban4j. It does not reimplement their algorithms.

    (valid?  :iban "GB82 WEST 1234 5698 7654 32")  ;=> true
    (parse   :credit-card "4111111111111111")      ;=> {:valid? true :network :visa}
    (format  :iban "GB82WEST12345698765432")       ;=> "GB82 WEST 1234 5698 7654 32"
    (detect  "4111111111111111")                   ;=> [:credit-card :luhn]

`valid?`, `parse`, and `format` throw only for an unknown identifier type.
Bad input data does not throw. `valid?` returns false, `parse` returns
{:valid? false}, and `format` returns nil.

(parse "(01)09521234543213(15)170331(10)ABC123")
;=> [{:ai "01" :label "GTIN"        :value "09521234543213"}
;    {:ai "15" :label "BEST BEFORE" :value "170331"}
;    {:ai "10" :label "BATCH/LOT"   :value "ABC123"}]

A parser for GS1-128 (formerly UCC/EAN-128) element strings. These strings use
the Application Identifier (AI) encoding on logistics and retail barcodes.

`parse` accepts the human-readable parenthesized form or the raw scanned form.
In the raw form, FNC1 (the ASCII group separator 0x1D) ends a variable-length
field. `parse` returns a vector of segment maps, in order:

    (parse "(01)09521234543213(15)170331(10)ABC123")
    ;=> [{:ai "01" :label "GTIN"        :value "09521234543213"}
    ;    {:ai "15" :label "BEST BEFORE" :value "170331"}
    ;    {:ai "10" :label "BATCH/LOT"   :value "ABC123"}]

Weight, measure, and amount AIs carry an implied decimal place: the last digit
of the AI. Those segments also report `:decimals` and a numeric
`:decimal-value`.

(require '[stdnum.vies :as vies])
(vies/check "DE136695976")
;=> {:valid? true, :country "DE", :vat-number "136695976", :name "...", ...}

Online EU VAT validation against the official VIES service
(https://ec.europa.eu/taxation_customs/vies/). This namespace is the one part
of the library that does network I/O. It stays separate, so that
`stdnum.core` stays pure and keeps few dependencies. `check` confirms that a
VAT number *exists* in the member-state registry, which a checksum cannot do.
It also returns the trader name and address if the member state gives them.

    (require '[stdnum.vies :as vies])
    (vies/check "DE136695976")
    ;=> {:valid? true, :country "DE", :vat-number "136695976", :name "...", ...}

Requires JDK 11+ (it uses java.net.http). On a network failure or a service
failure, `check` returns `{:error <message>}` and does not throw.