Label Generation Rules for Ukrainian

Overview

This document specifies a reference set of Label Generation Rules for Ukrainian using a limited repertoire as appropriate for a second level domain.

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 protocol valid (PVALID) in IDNA2008; other forms of apostrophes such as U+0027 (') APOSTROPHE or U+2019 (’) RIGHT SINGLE QUOTATION MARK are DISALLOWED. As [RFC6912] 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 Comments, 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 extended code points. To support extended single code points or code point sequences, delete the context "extended-cp" from their repertoire definition.

Variants

None.

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.

Character Classes

This LGR defines no named character classes.

Rules

Common rules:

• 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 RFC5891 [120]. 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 RFC5891 [120].

Actions

Actions included are the default actions for LGRs as well as those needed to invalidate labels with misplaced combining marks and apostrophe modifiers.

Methodology and Contributors

This reference LGR for Ukrainian for the 2nd Level has been developed by Michel Suignard and Asmus Freytag, verified in expert reviews by Michael Everson, Nicholas Ostler, and Wil Tan, and based on multiple open public consultations.

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).
http://archive.icann.org/en/topics/new-gtlds/cyrillic-vip-issues-report-06oct11-en.pdf.

[HARD-SIGN]

Wikipedia, "Hard sign",
http://en.wikipedia.org/wiki/Hard_sign

[YKP]

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

[RFC6912]

RFC6912, "Principles for Unicode Code Point Inclusion in Labels in the DNS",
http://www.rfc-base.org/txt/rfc-6912.txt

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. For more details, see the Table of References below.

Character Classes

The following table lists all named 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:Zyyy	11 Elements:	{002D 0030-0039}
implicit	Tag=sc:Cyrl	39 Elements:	{0430-044F 0451 0454 0456-0457 045E 0491 04C2}

Whole label evaluation and context rules

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. (Any use of context rules for variants is not indicated).

Name	Used as Trigger	Used as Context	Anchor	Regular Expression	Ref	Comment
leading-combining-mark	✔			(^[∅=[[∅=\p{gc=Mn}][∅=\p{gc=Mc}]]])	[120]	RFC5891 restrictions on placement of combining marks
hyphen-minus-disallowed		✔	✔	((((?<=^)⚓)|(⚓(?=$))|((?<=^..\u002D)⚓)))	[120]	RFC5891 restrictions on placement of U+002D
extended-cp		✔		(^$)		code points from the extended range

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 any label (catch-all)		→	valid		catch all (default action)