Label Generation Rules for the Japanese Language

Overview

This document specifies a set of Label Generation Rules (LGR) for the Japanese language for the second level domain or domains identified above. The ultimate starting point for the development of this LGR can be found in the related Root Zone LGR [RZ-LGR-Jpan]. Note that while it is the Japanese Script Root Zone LGR that forms the starting point, the LGR defined here covers the Japanese Language. The format of this file follows [RFC 7940]. This LGR is adapted from the “Reference LGR for the Second Level for the Japanese Language” [Ref-LGR-ja-Jpan], for details, see Change History below.

The Japanese language is written in a combination of elements from three Unicode scripts: Han (Kanji), Hiragana and Katakana. Collectively they have the script code “Jpan” for Japanese. For details and additional background on the Japanese script, see “Proposal for a Japanese Script Root Zone LGR” [Proposal-Japanese], including the appendices [Proposal-Japanese-Appendices].

Standalone LGR: This LGR is designed to be used in a zone that does not cater to IDNs other than those valid under this LGR. Following existing practice, this LGR also supports ASCII letters and where applicable accounts for any interaction with the remainder of the repertoire.

Repertoire

The repertoire contains the code points used in writing the Japanese language using a repertoire appropriate for the Second Level. It is part of JIS X 0208:1997 [100] and it includes 6,356 Han characters, 85 Hiragana characters, 89 Katakana characters, and 2 Common (quasi-Kanji) characters for a subtotal of 6,532 repertoire elements. One of the common characters is shared between Han, Hiragana, and Katakana while the other one is shared between Hiragana and Katakana.

The repertoire is a subset of [Unicode 11.0.0]. For details, see Section 5, “Repertoire” in [Proposal-Japanese]. (The proposal cited has been adopted for the Japanese script portion of the Root Zone LGR.)

For the second level, the repertoire has been augmented with the ASCII digits, U+0030 0 to U+0039 9; the ASCII lowercase letters, U+0061 a to U+007A z; U+002D - HYPHEN-MINUS, U+3007 〇 IDEOGRAPHIC NUMBER ZERO, and U+30FB ・ KATAKANA MIDDLE DOT for a total of 6,571 repertoire elements.

Unlike many other non-Latin Second Level Reference LGRs, the Japanese Language LGR includes the basic ASCII Latin letters (a to z) because it is common practice in Japanese text to mix Japanese and ASCII. Therefore including these letters is not seen as creating added confusability or security risks in the context of a Second Level LGR for the Japanese language. It is also supported by current IDNA practice; see [700], for example.

Repertoire Listing: Each code point or range is tagged with the script or scripts with which the code point is used and one or more other character categories. For each repertoire element, one or more references document sufficient justification for inclusion in the repertoire; see the “References” below.

Variants

This LGR defines visually identical variants within the Japanese script. For Details, see Sections 6, 7, and 8 of [Proposal-Japanese]. In addition, adding the ideographic number zero to the repertoire resulted in an additional variant association with the Latin letter “o”.

Variant Disposition: All variants are of type “blocked”, making labels that differ only by these variants mutually exclusive: whichever label containing either of these variants is chosen earlier would be delegated, while any other equivalent labels should be blocked. There is no preference among these labels.

This LGR does not define allocatable variants.

The specification of variants in this LGR follows the guidelines in [RFC 8228].

Source References for Variants

The following source reference is used for variant entries in this LGR:

• [101] - visually identical variants within the Japanese script

Character Classes

The following classes are defined for use in WLE and context rules:

• hiragana, the set of Hiragana code points
• katakana, the set of Katakana code points
• japanese, the union of the hiragana, katakana and kanji
• kanji, the set of Kanji code points
• kanji-numeral, the set of ideographs that are used numerically, plus U+3007 〇 IDEOGRAPHIC NUMBER ZERO

Whole Label Evaluation (WLE) and Context Rules

Default Whole Label Evaluation Rules

By default, the LGR includes the rules and actions to implement the following restrictions mandated by the IDNA protocol. They are marked with ⍟.

• Hyphen Restrictions — restrictions on the allowable placement of hyphens (no leading/ending hyphen and no hyphen in positions 3 and 4). These restrictions are described in Section 4.2.3.1 of RFC 5891 [150]. They are implemented here as context rule on U+002D (-) HYPHEN-MINUS.
• Leading Combining Marks — restrictions on the allowable placement of combining marks (no leading combining mark). This rule is described in Section 4.2.3.2 of RFC 5891 [150].

Japanese-specific Context Rules

The LGR defines the following context rules.

• at-start-of-word — No small kana, iteration mark or prolonged sound mark may start a label or word.
• follows-kanji-numeral — U+3007 〇 IDEOGRAPHIC NUMBER ZERO must follow a Kanji numeral.
• middle-dot-context — U+30FB ・ KATAKANA MIDDLE DOT is only used between Japanese characters and does not follow itself.

Note that U+30FB ・ KATAKANA MIDDLE DOT is used to separate words. Therefore, the letters following a KATAKANA MIDDLE DOT must be restricted to the same set as for the start of label. For the second level, the context rule “at-start-of-word” has been defined which covers the start of a label as well as the context following a KATAKANA MIDDLE DOT.

Iteration marks: The iteration marks, U+3005 々, U+309D ゝ, U+309E ゞ, U+30FD ヽ, and U+30FE ヾ, are used to reiterate the pronunciation or meaning of the preceding character. As such, these characters have neither particular pronunciation nor meanings by themselves. Similar considerations apply to the prolonged sound mark (U+30FC). Accordingly, any sequence of two or more iteration marks and/or the prolonged sound mark has no meaning and is disallowed by the following WLE rule:

• repeated-mark — repeated iteration or prolonged sound marks are disallowed

The following WLE rule implements an additional restriction on HYPHEN-MINUS in a Japanese context.

• hyphen-minus-restriction — a hyphen is disallowed adjacent to Japanese characters

Actions

Default Actions

This LGR includes the default actions for LGRs as well as the action needed to invalidate labels with misplaced combining marks. They are marked with ⍟. For a description see [RFC 7940].

Japanese-specific actions

The LGR defines a Japanese-specific action invalidating any label containing a hyphen adjacent to Japanese characters.

Methodology and Contributors

The LGR in this document has been adapted from the corresponding Reference LGR for the Second Level. The Second Level Reference LGR for the Japanese Language was developed by Michel Suignard and Asmus Freytag, based on the Root Zone LGR for the Japanese script and information contained or referenced therein; see [RZ-LGR-Jpan]. Suitable extensions for the second level have been applied according to the [Guidelines] and with community input. As part of that process, features have been removed or modified as appropriate for the target language. The original proposal for a Root Zone LGR for the Japanese script, that this LGR is based on, was developed by the Japanese Generation Panel. For more information on methodology and contributors to the underlying Root Zone LGR, see Sections 4 and 8 in [Proposal-Japanese], as well as [RZ-LGR-Overview].

Changes from Version Dated 25 October 2024

This version modifies the Second Level Reference LGR for the Japanese Language [Ref-LGR-ja-Jpan] by injecting the complete (maximal) set of cross-repertoire variants, including any imposed by transitivity. Injected variants are marked by special comments. Any character classes, context and WLE rules required for testing are also imported. In all other respects, description or annotations have not been updated to reflect the injected variants. Any LGR elements that might pose a possible conflict when the LGR is used with the Common LGR for cross-repertoire variant resolution are clearly marked. All modifications are carried out mechanically; there may be an occasional context rule or similar that is injected because its definition relates to some repertoire element even though it can never be triggered by any label valid under the modified LGR.

References

References [0] and up refer to the Unicode Standard versions in which corresponding code points were initially encoded. For example, a reference value of [0] means a character was first encoded in Unicode Version 1.1. References [100] and up indicate that the code point is included in one of the following source references: JIS X 0208:1997, Survey on the user perception of the homographic character set specified by JGP. Entries in the table may have multiple source reference values.

In addition, the following general references are cited in this document:

[CLGR]

Root Zone Label Generation Rules for Chinese, 26 May 2020,
https://www.icann.org/en/system/files/files/proposal-chinese-lgr-26may20-en.xml

[Guidelines]

ICANN, “Guidelines for Developing Reference LGRs for the Second Level”, (Los Angeles, California: ICANN, 27 May 2020),
https://www.icann.org/en/system/files/files/lgr-guidelines-second-level-27may20-en.pdf

[KLGR]

Root Zone Label Generation Rules for Korean, 1 May 2021,
https://www.icann.org/en/system/files/files/proposal-korean-lgr-01may21-en.xml

[MSR-5]

Integration Panel, “Maximal Starting Repertoire — MSR-5 Overview and Rationale”, 24 June 2021,
https://www.icann.org/en/system/files/files/msr-5-overview-24jun21-en.pdf

[Proposal-Japanese]

Japanese Script Generation Panel (JGP), “Proposal for a Japanese Script Root Zone LGR”, 20 December 2021 (PDF),
https://www.icann.org/en/system/files/files/proposal-japanese-lgr-20dec21-en.pdf

[Proposal-Japanese-Appendices]

Appendices to “Proposal for a Japanese Script Root Zone LGR”, 20 December 2021 (ZIP),
https://www.icann.org/en/system/files/files/proposal-japanese-lgr-appendices-20dec21-en.zip

[RFC 7940]

Davies, K. and A. Freytag, “Representing Label Generation Rulesets Using XML”, RFC 7940, August 2016,
https://www.rfc-editor.org/info/rfc7940

[RZ-LGR-Jpan]

ICANN, Root Zone Label Generation Rules for the Japanese Script (und-Jpan), 26 May 2022 (XML)
https://www.icann.org/sites/default/files/lgr/rz-lgr-5-japanese-script-26may22-en.xml

[RFC 8228]

A. Freytag, “Guidance on Designing Label Generation Rulesets (LGRs) Supporting Variant Labels”, RFC 8228, August 2017,
https://www.rfc-editor.org/info/rfc8228

[RZ-LGR-Overview]

Integration Panel, “Root Zone Label Generation Rules (RZ LGR-5): Overview and Summary”, 26 May 2022 (PDF),
https://www.icann.org/sites/default/files/lgr/rz-lgr-5-overview-26may22-en.pdf

[RZ-LGR-5]

Integration Panel, “Root Zone Label Generation Rules (RZ-LGR-5)”, 26 May 2022 (XML),
https://www.icann.org/sites/default/files/lgr/rz-lgr-5-common-26may22-en.xml
non-normative HTML presentation:
https://www.icann.org/sites/default/files/lgr/rz-lgr-5-common-26may22-en.html

[Ref-LGR-ja-Jpan]

ICANN, Second Level Reference Label Generation Rules for the Japanese Language (ja-Jpan), 25 October 2024 (XML)
https://www.icann.org/sites/default/files/packages/lgr/lgr-second-level-japanese-language-25oct24-en.xml
non-normative HTML presentation:
https://www.icann.org/sites/default/files/packages/lgr/lgr-second-level-japanese-language-25oct24-en.html

[Unicode 11.0.0]

The Unicode Consortium. The Unicode Standard, Version 11.0.0, (Mountain View, CA: The Unicode Consortium, 2018. ISBN 978-1-936213-19-1)
https://www.unicode.org/versions/Unicode11.0.0/

In the listing of the repertoire by code point, references starting from [0] refer to the version of the Unicode Standard in which the corresponding code point was initially encoded. Other references (starting from [100]) document usage of code points. Entries in the table may have multiple source reference values. In the listing of whole label evaluation and context rules, reference [150] indicates the source for common rules. For more details, see the Table of References below.

Where links to certain references are not available, the data may be archived as part of [Proposal-Japanese].