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Label Generation Rules for the Cyrillic Script

Overview

This document specifies a set of Label Generation Rules (LGR) for the Cyrillic script for the second level domain or domains identified above. The starting point for the development of this LGR can be found in the related Root Zone LGR [RZ-LGR-Cyrl]. The format of this file follows [RFC 7940]. This LGR is adapted from the “Reference LGR for the Second Level for the Cyrillic Script” [Ref-LGR-und-Cyrl], for details, see Change History below.

For details and additional background on the Cyrillic script, see “Proposal for a Cyrillic Script Root Zone LGR” [Proposal-Cyrillic].

Repertoire

The repertoire includes 86 code points used by languages written in the Cyrillic script.

The repertoire only includes code points used by languages that are actively written in the Cyrillic script. All languages with [EGIDS] level 1 through 4 were included. Level 5 languages were analyzed and included on a case by case basis. The repertoire is a subset of [Unicode 11.0.0]. For details, see Section 5, “Repertoire” in [Proposal-Cyrillic]. (The proposal cited has been adopted for the Cyrillic script portion of the Root Zone LGR.)

Note that, while U+02BC ʼ MODIFIER LETTER APOSTROPHE is used in Belarusian and 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.

For the second level, the repertoire has been augmented with the ASCII digits, U+0030 0 to U+0039 9, plus U+002D - HYPHEN-MINUS, for a total of 97 repertoire elements.

The following language-based reference LGRs for the Second Level were also reviewed:

• Second Level Reference Label Generation Ruleset for Language bel-Cyrl (Belorusian) [301]
• Second Level Reference Label Generation Ruleset for Language bos-Cryl (Bosnian) [302]
• Second Level Reference Label Generation Ruleset for Language bul-Cyrl (Bulgarian) [303]
• Second Level Reference Label Generation Ruleset for Language mkd-Cyrl (Macedonian) [304]
• Second Level Reference Label Generation Ruleset for Language cnr-Cyrl (Montenegrin) [305]
• Second Level Reference Label Generation Ruleset for Language rus-Cyrl (Russian) [306]
• Second Level Reference Label Generation Ruleset for Language srp-Cyrk (Serbian) [307]
• Second Level Reference Label Generation Ruleset for Language ukr-Cyrl (Ukranian) [308]

The core repertoire of these LGRs is covered here, except for a few rarely used code points where this LGR follows [RZ-LGR-Cyrl] in excluding them.

Any code points outside the Cyrillic Script 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.

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 references documenting sufficient justification for inclusion in the repertoire, see “References” below. For code points that are part of the repertoire, comments identify the languages using the code point along with their [EGIDS] level.

Variants

The variants defined in this LGR are limited to those required for use in zones not shared with any other script. As such, this LGR does not define cross-script variants. However, using this LGR concurrently with any LGR for Armenian, Greek, and Latin in the same zone will introduce some in-script variants due to cross-script variant transitivity. This will also create potential cross-script issues when used with the same LGRs. For details, see Section 6, “Variants” in [Proposal-Cyrillic]. Mitigation of these in-script and cross-script variants can be addressed by using the Common LGR. For details, see Section 3, “Use of Multiple Reference LGRs in the Same Zone” in [Level-2-Overview]. In addition to variants defined by this LGR, the full variant information related to this script and added by concurrent use with the Armenian, Greek, and Latin LGR(s) can be found in the following LGR: [Ref-LGR-Latin-Full-Variant-Script]

In particular, the Cyrillic LGR inherits the following in-script variants as result of concurrent use with the Latin and Greek LGRs:

• Blocked: U+0456 і — U+0457 ї.
• Blocked: U+0443 у — U+04AF ү.

These variant definitions are required when using this LGR together with the Common LGR in label processing, but they also reflect a certain consistency in the approach to variants across typographically related scripts.

Implicit Variant Sequences: The full set of inherited cross script variants would include certain otherwise redundant sequences. These are defined as having a partition into other repertoire elements, where each element has a cross-script variant of its own, making a concatenation of these variants an implicit cross-script variant for the sequence. Where such sequences do not contribute to the set of available valid labels, where they produce the same index variant as all of their valid partitions, and where they do not participate in allocatable variants, they are not listed anywhere. See Section 4.5.8 “Implicit Cross-script Variants” of [Level-2-Overview] for further details.

Affected sequences in this LGR include: U+0455 U+0455 ѕѕ and U+04CF U+04CF ӏӏ.

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.

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].

Cyrillic-specific Rules

This LGR does not define rules specific to the Cyrillic script.

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 Cyrillic Script was developed by Michel Suignard and Asmus Freytag, based on the Root Zone LGR for the Cyrillic script and information contained or referenced therein; see [RZ-LGR-Cyrl]. Suitable extensions for the second level have been applied according to the [Guidelines] and with community input. The original proposal for a Root Zone LGR for the Cyrillic script, that this LGR is based on, was developed by the Cyrillic Generation Panel. For more information on methodology and contributors to the underlying Root Zone LGR, see Sections 4 and 8 in [Proposal-Cyrillic], as well as [RZ-LGR-Overview].

Changes from Version Dated 24 January 2024

Adopted from the Second Level Reference LGR for the Cyrillic Script [Ref-LGR-und-Cyrl] without normative changes.

References

The following general references are cited in this document:

[EGIDS]

Lewis and Simons, “EGIDS: Expanded Graded Intergenerational Disruption Scale,” documented in [SIL-Ethnologue] and summarized here:
https://en.wikipedia.org/wiki/Expanded_Graded_Intergenerational_Disruption_Scale_(EGIDS)

[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

[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

[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-Cyrillic]

Cyrillic Generation Panel, “Proposal for Cyrillic Script Root Zone Label Generation Rules”, 3 April 2018,
https://www.icann.org/en/system/files/files/proposal-cyrillic-lgr-03apr18-en.pdf

[Ref-LGR-und-Cyrl]

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

[Ref-LGR-Latin-Full-Variant-Script]

ICANN, Second Level Reference Label Generation Rules for the Latin Script (und-Latn), 24 January 2024 (XML)
https://www.icann.org/sites/default/files/packages/lgr/lgr-second-level-latin-full-variant-script-24jan24-en.xml
non-normative HTML presentation:
https://www.icann.org/sites/default/files/packages/lgr/lgr-second-level-latin-full-variant-script-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

[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

[RZ-LGR-Cyrl]

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

[RZ-LGR-Greek]

“Root Zone Label Generation Rules for the Greek Script”, 26 May 2022 (XML),
https://www.icann.org/sites/default/files/lgr/rz-lgr-5-greek-script-26may22-en.xml
non-normative HTML presentation:
https://www.icann.org/sites/default/files/lgr/rz-lgr-5-greek-script-26may22-en.html

[RZ-LGR-Latin]

“Root Zone Label Generation Rules for the Latin Script”, 26 May 2022 (XML),
https://www.icann.org/sites/default/files/lgr/rz-lgr-5-latin-script-26may22-en.xml
non-normative HTML presentation:
https://www.icann.org/sites/default/files/lgr/rz-lgr-5-latin-script-26may22-en.html

[SIL-Ethnologue]

David M. Eberhard, Gary F. Simons & Charles D. Fennig (eds.). 2021. Ethnologue: Languages of the World, Twenty fourth edition. Dallas, Texas: SIL International. Online version available as
https://www.ethnologue.com

[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/

For references consulted particularly in designing the repertoire for the Cyrillic Script for the second level please see details in the Table of References below.

Reference [0] refers to the Unicode Standard version in which corresponding code points were initially encoded. References [100] to [122] correspond to sources given in [Proposal-Cyrillic] for justifying the inclusion of for the corresponding code points. Single code points or ranges may have multiple source reference values.

Character Classes

Implicit (except script)	1
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=Common-digit	10	{0030-0039}		Any character tagged as Common-digit
implicit	Tag=sc:Cyrl	86	{0430-044F 0451-045C 045E-045F 0491 0493 0495 0497 0499 049B 049F 04A1 04A3 04A5 04A9 04AB 04AD 04AF 04B1 04B3 04B5 04B7 04BB 04BD 04BF 04CF 04D1 04D3 04D5 ...}		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	2
Used to trigger actions	1
Used as context rule (C)	1
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 - ⍟

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.

⍟ - 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		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 each variant is in	{allocatable}	→	allocatable		variant labels with all variants allocatable are allocatable ⍟
5	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: allocatable, out-of-repertoire-var. This is not necessarily an error.