[1] [[IDNA]] の[[ラベル]]に関する要件をすべて満たす[[文字列]]は[DFN[[RUBYB[IDNA 妥当]@en[IDNA-valid]]]]であるといいます。
[SRC[>>2]]

* 仕様書

- [2] [CITE@en[RFC 5890 - Internationalized Domain Names for Applications (IDNA): Definitions and Document Framework]] 
<http://tools.ietf.org/html/rfc5890#section-2.3.2.1>

* 分類

[6] [[IDNA妥当]]である[[ラベル]]は次の3種類です [SRC[>>2]]。

- [3] [[Aラベル]]
- [4] [[Uラベル]]
- [5] [[NR-LDHラベル]]

[7] [[IDNA]] に対応した[[アプリケーション]]や[[文脈]]ではこれら3種類だけを認めることになっています。
[SRC[>>2]]

[FIG(quote)[
[FIGCAPTION[
[8] [CITE@en[RFC 7542 - The Network Access Identifier]]
([TIME[2015-10-18 15:17:56 +09:00]] 版)
<https://tools.ietf.org/html/rfc7542#section-3.2>
]FIGCAPTION]

> The NAI does not make a distinction between A-labels and U-labels, as
>    those are terms specific to DNS.  It is instead an IDNA-valid label,
>    as per the first item in Section 2.3.2.1 of '''['''RFC5890''']'''.  As noted in
>    that section, the term "IDNA-valid label" encompasses both "A-label"
>    and "U-label".

]FIG]