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Label Generation Rules for Ukrainian

Overview

This document specifies a set of Label Generation Rules (LGR) for the Ukrainian language using a language-specific repertoire for the second level domain or domains identified above. The format of this file follows [RFC 7940]. This LGR is adapted from the “Reference LGR for the Second Level for the Ukrainian Language” [Ref-LGR-uk-Cyrl], for details, see Change History below.

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. This LGR lacks features that would allow its use in the context of another LGR in the same zone, and it may contain other features incompatible with such use.

Repertoire

Most references converge on 33 Cyrillic code points. There is some disagreement concerning U+044A ъ CYRILLIC SMALL LETTER HARD SIGN and U+0451 ё CYRILLIC SMALL LETTER IO. While CLDR considers U+0451 ё CYRILLIC SMALL LETTER IO part of the main alphabet, these appear to be used in Russian words or names, not in Ukrainian words and names themselves. Both of these letters are part of the extended repertoire as defined here along with many letters used for Ukrainian. In Russian, the hard sign indicates the non-palatalization of a consonant preceding a morpheme beginning with a iotated vowel; in Ukrainian this function is met by the use of an apostrophe or of U+02BC ʼ MODIFIER LETTER APOSTROPHE.

Note that, while U+02BC ʼ MODIFIER LETTER APOSTROPHE is used in Ukrainian and is protocol valid (PVALID) in IDNA2008; other forms of apostrophes such as U+0027 ' APOSTROPHE or U+2019 ’ RIGHT SINGLE QUOTATION MARK are DISALLOWED. As [RFC 6912] points out, in a public zone, many users may read U+02BC ʼ as indistinguishable from the regular apostrophe. Therefore, following the principle of conservatism, and in response to a comment made by the IAB during public comment proceedings, the code point U+02BC ʼ is not included here.

An IDN table published in the IANA Repository of IDN Practices for Ukrainian by .ua (Ukrainian cctld) in [700] contains many code points beyond what would be used in Ukrainian and even languages used in adjacent areas. Code points not corroborated by any other reference but used for Belarusian, Russian, and Moldovan have been added to the extended repertoire. South Slavic characters are excluded here.

For other IDNA TLD dedicated to Ukrainian: see .укр [YKP] and the IDNA table in [701]. That table shows a repertoire combining Russian and Ukrainian.

In Ukrainian, the acute accent may be used as a stress mark on the vowel of a syllable or to disambiguate between minimal pairs. However, as in Russian, it is restricted to dictionaries and educational materials. See Stress and Disambiguation in [ACUTE].

Excluded code points

Letters documented in some references but not included:

• U+02BC ʼ MODIFIER LETTER APOSTROPHE

• U+0450 ѐ CYRILLIC SMALL LETTER IE WITH GRAVE

• U+0452 ђ CYRILLIC SMALL LETTER DJE

• U+0453 ѓ CYRILLIC SMALL LETTER GJE

• U+0455 ѕ CYRILLIC SMALL LETTER DZE

• U+0458 ј CYRILLIC SMALL LETTER JE

• U+0459 љ CYRILLIC SMALL LETTER LJE

• U+045A њ CYRILLIC SMALL LETTER NJE

• U+045B ћ CYRILLIC SMALL LETTER TSHE

• U+045C ќ CYRILLIC SMALL LETTER KJE

• U+045D ѝ CYRILLIC SMALL LETTER I WITH GRAVE

• U+045F џ CYRILLIC SMALL LETTER DZHE

• U+0430 U+0301 а́ CYRILLIC SMALL LETTER A WITH ACUTE ACCENT

• U+0435 U+0301 е́ CYRILLIC SMALL LETTER IE WITH ACUTE ACCENT

• U+0438 U+0301 и́ CYRILLIC SMALL LETTER I WITH ACUTE ACCENT

• U+043E U+0301 о́ CYRILLIC SMALL LETTER O WITH ACUTE ACCENT

• U+0443 U+0301 у́ CYRILLIC SMALL LETTER U WITH ACUTE ACCENT

• U+044E U+0301 ю́ CYRILLIC SMALL LETTER YU WITH ACUTE ACCENT

• U+044F U+0301 я́ CYRILLIC SMALL LETTER YA WITH ACUTE ACCENT

• U+0454 U+0301 є́ CYRILLIC SMALL LETTER UKRAINIAN IE WITH ACUTE ACCENT

• U+0456 U+0301 і́ CYRILLIC SMALL LETTER BYELORUSSIAN-UKRAINIAN I WITH ACUTE ACCENT

• U+0457 U+0301 ї́ CYRILLIC SMALL LETTER YI WITH ACUTE ACCENT

Extended code points

A number of letters not considered essential to writing the core vocabulary of the language are nevertheless in common use. Where they have not been added to the core repertoire, they are flagged as “extended-cp” in the table of code points. A context rule is provided that by default will prohibit labels with such extended code points. To support extended single code points or code point sequences, delete the context “extended-cp” from their repertoire definition.

Any code points outside the Ukrainian Language repertoire that are targets for out-of-repertoire variants would be included here only if the variant is listed in this file. In this case they are identified as a reflexive (identity) variant of type “out-of-repertoire-var”. Whether or not they are listed, they do not form part of the repertoire.

Variants

There are no variants defined between Cyrillic letters.

No ASCII Variants: This LGR does not contain definitions for “blocked” variants for letters that look indistinguishable from ASCII letters (homoglyphs). If concurrent use of LDH labels is desired, the resulting conflicts can be handled by using the “Common LGR” in processing. For details, see Section 3, “Use of Multiple Reference LGRs in the Same Zone” in [Level-2-Overview].

Note: a study of a possible variant relationship concerning U+0433 г CYRILLIC SMALL LETTER GHE and U+0491 ґ CYRILLIC SMALL LETTER GHE WITH UPTURN was undertaken in the context of Ukrainian by a Cyrillic case study team in [CYRILLIC-VIP] (page 6, section 3.2). The experts point to some instability concerning the encoding of the GHE WITH UPTURN and the possible confusion between the two code points by non-Ukrainian users. However, in the context of a Ukrainian LGR it does not seem necessary to establish such a variant relationship between these two code points.

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].

Character Classes

This LGR does not define named character classes.

Rules

Common 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].

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].

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 Ukrainian Language was developed by Michel Suignard and Asmus Freytag, including input by Michael Everson, Nicholas Ostler, and Wil Tan, and based on multiple open public consultations.

Changes from Version Dated 19 December 2016

Language tag has been updated.

Changes from Version Dated 18 May 2021

Unicode Version has been updated.

Blocked variants have been added for homoglyphs of ASCII letters. These have no effect unless the LGR is used together with LDH labels in the same zone.

Changes from Version Dated 24 January 2024

Adopted from the Second Level Reference LGR for the Ukrainian Language [Ref-LGR-uk-Cyrl] without normative changes.

References

General reference for the language:

• Shevelov, George Y. 1993. “Ukrainian”, in Bernard Comrie & Greville G. Corbett, eds. The Slavonic languages. London; New York: Routledge. ISBN 0-415-04755-2

Other references cited in this document:

[ACUTE]

Wikipedia, “Acute accent”
https://en.wikipedia.org/wiki/Acute_accent

[CYRILLIC-VIP]

Sozonov, A. et al., “IDN Variant TLDs – Cyrillic Script Issues”. (Marina del Rey, California: ICANN, October 2011).
https://archive.icann.org/en/topics/new-gtlds/cyrillic-vip-issues-report-06oct11-en.pdf

[HARD-SIGN]

Wikipedia, “Hard sign”,
https://en.wikipedia.org/wiki/Hard_sign

[Level-2-Overview]

Internet Corporation for Assigned Names and Numbers, (ICANN),“Reference Label Generation Rules (LGR) for the Second Level: Overview and Summary” (PDF), (Los Angeles, California: ICANN, 24 January 2024),
https://www.icann.org/en/system/files/files/level2-lgr-overview-summary-24jan24-en.pdf

[Ref-LGR-uk-Cyrl]

ICANN, Second Level Reference Label Generation Rules for the Ukrainian Language (uk-Cyrl), 24 January 2024 (XML)
https://www.icann.org/sites/default/files/packages/lgr/lgr-second-level-ukrainian-language-24jan24-en.xml
non-normative HTML presentation:
https://www.icann.org/sites/default/files/packages/lgr/lgr-second-level-ukrainian-language-24jan24-en.html

[RFC 6912]

Sullivan, A., Thaler, D., Klensin, J., and O. Kolkman, "Principles for Unicode Code Point Inclusion in Labels in the DNS", RFC 6912, April 2013,
https://www.rfc-editor.org/info/rfc6912

[RFC 7940]

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

[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

[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/

[YKP]

U-Regristry.com website (in Ukrainian)
https://namestore.u-registry.com/

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.

Character Classes

Implict defined by script tag	2

The following table lists all named and implicit classes with their definition and a list of their members intersected with the current repertoire (for larger classes, this list is elided).

Name	Definition	Count	Members or Ranges	Ref	Comment
implicit	Tag=sc:Cyrl	39	{0430-044F 0451 0454 0456-0457 045E 0491 04C2}		Any character tagged as Cyrillic
implicit	Tag=sc:Zyyy	11	{002D 0030-0039}		Any character tagged as Common

Legend

Members or Ranges

Lists the members of the class as code points (xxx) or as ranges of code points (xxx-yyy). Any class too numerous to list in full is elided with "...".

Tag=ttt

A named or implicit class defined by all code points that share the given tag value (ttt).

Implicit

An anonymous class implicitly defined based on tag value and for which there is no named equivalent.

Whole label evaluation and context rules

Number of rules	3
Used to trigger actions	1
Used as context rule (C)	2
Anchored context rules	1

The following table lists all named rules defined in the LGR and indicates whether they are used as trigger in an action or as context (when or not-when) for a code point or variant.

Name	Regular Expression	Used as Trigger	Anchor	Used as Context	Ref	Comment
leading-combining-mark	(start)[∅=[[∅=\p{gc=Mn}] ∪ [∅=\p{gc=Mc}]]]	✔			[150]	RFC 5891 restrictions on placement of combining marks ⍟
hyphen-minus-disallowed	(((start))← ⚓︎)|(⚓︎ →((end)))|(((start)..\u002D)← ⚓︎)		✔	C	[150]	RFC 5891 restrictions on placement of U+002D - ⍟
extended-cp	(start)(end)			C		context to gate off code points from the extended range, matches no label ⍟

Legend

Used as Trigger

This rule triggers one of the actions listed below.

Used as Context

This rule defines a required or prohibited context for a code point C or variant V.

Anchor

This rule has a placeholder for the code point for which it is evaluated.

Regular Expression

A regular expression equivalent to the rule, shown in a modified notation as noted:

⚓︎ - context anchor

Placeholder for the actual code point when a context is evaluated. The code point must occur at the position corresponding to the anchor. Rules containing an anchor cannot be used as triggers.

(...)← - look-behind

If present encloses required context preceding the anchor.

→(..) - look-ahead

If present encloses required context following the anchor.

( ) - group

An anonymous nested rule is used to group match operators.

(... | ...) - choice

When there is more than one alternative in a rule, the choices are separated by the alternation operator (...|...).

start or end

(start) matches the start of the label; (end) matches the end of the label.

. - any code point

. matches any code point.

[\p{ }] - property

Set of all characters matching a given value for a Unicode property [\p{prop=val}]. Note: uppercase “\P” defines the complement of a property set.

∪, ∩, ∖, ∆ - set operators

Sets may be combined by set operators (∪ = union, ∩ = intersection, ∖ = difference, ∆ = symmetric difference).

∅= - empty set

Indicates that the following set is empty because of the result of set operations, or because none of its elements is part of the repertoire defined here. A rule with a non-optional empty set never matches.

(^$) - empty label

The regex (^$) matches the empty label. Used as a context rule, it always fails to match, thus disallowing the affected code point in any label. By convention, it is used for context rules that disable code points that are not part of the repertoire, yet explicitly listed in the LGR as excluded or for optional future extension.

⍟ - default rule

Rules marked with ⍟ are included by default and may or may not be triggered by any possible label under this LGR.

Actions

The following table lists the actions that are used to assign dispositions to labels and variant labels based on the specified conditions. The order of actions defines their precedence: the first action triggered by a label is the one defining its disposition.

#	Condition	Rule / Variant Set		Disposition	Ref	Comment
1	if label matches	leading-combining-mark	→	invalid		by default, labels with leading combining marks are invalid
2	if at least one variant is in	{out-of-repertoire-var}	→	invalid		any variant label with a code point out of repertoire is invalid ⍟
3	if at least one variant is in	{blocked}	→	blocked		any variant label containing blocked variants is blocked ⍟
4	if any label (catch-all)		→	valid		catch all (default action)

Legend

{...} - variant type set

In the “Rule/Variant Set” column, the notation {...} means a set of variant types.

⍟ - default action

Actions marked with ⍟ are included by default and may or may not be triggered by any possible label under this LGR.

Note: The following variant types are used in one or more actions, but are not defined in this LGR: blocked, out-of-repertoire-var. This is not necessarily an error.