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Label Generation Rules for the Hindi language

Overview

This document specifies a set of Label Generation Rules (LGR) for the Hindi 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-Deva]. Note that while it is the Devanagari Script Root Zone LGR that forms the starting point, the LGR defined here covers the Hindi Language. The format of this file follows [RFC 7940]. This LGR is adapted from the “Reference LGR for the Second Level for the Hindi Language” [Ref-LGR-hi-Deva], for details, see Change History below.

For details and additional background on the Devanagari script, see “Proposal for a Devanagari Script Root Zone Label Generation Rule-Set (LGR)" [Proposal-Devanagari].

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

The repertoire contains 61 code points for letters for use in the Hindi language in addition to 7 sequences used for in-script variants (see “Variants” below). The repertoire is a subset of [Unicode 11.0.0]. For details, see Section 5, “Repertoire” in [Proposal-Devanagari]. (The proposal cited has been adopted for the Devanagari script portion of the Root Zone LGR.)

For the second level, the repertoire has been augmented with the HYPHEN-MINUS, and two sets of decimal digits:

• European (common) digits
• Devanagari digits

for a total of 91 repertoire elements.

Any code points outside the Hindi 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.

Repertoire Listing: Each code point or range is tagged with the script or scripts with which the code point is used, one or more tag values denoting character category, 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.

Variants

This LGR is designed for use in zones shared by more than one script. For details, see Section 3, “Use of Multiple Reference LGRs in the Same Zone” in [Level-2-Overview]. Where appropriate, cross-script variants have been defined to mutually exclude labels from different scripts that could otherwise be substituted by the users. Once a label has been delegated for one script, any of its variant labels consisting entirely of cross-script variants would be blocked. Any label containing at least one code point that is not a cross-script variant would be considered distinct. Because of that, even large numbers of defined cross-script variants generally do not lead to a high percentage of labels experiencing a collision.

This LGR defines in-script variants variants as described in Section 6, “Variants”, in “[Proposal-Devanagari]”. The in-script variants are based on Candrabindu and Candra Vowel Signs followed by Anusvara plus digit variants.

Digit Variants: All Devanagari digits are treated as semantic variants of the corresponding common (ASCII) digits. By transitivity, they are also semantic variants of any native digits in scripts that also include the common digits. Such variant relations are deemed to exist implicitly by transitivity but are not listed explicitly in each reference LGR. Instead, if needed, they are applied by using the Common LGR in label processing.

In particular, Devanagari digit ZERO is a cross-script homoglyph or near homoglyph of digit ZERO in many other scripts; these are already implicit semantic variants by transitivity and therefore not listed here.

Note that in addition to a transitive semantic variant relation, Devanagari digits ZERO, TWO, FOUR, FIVE and EIGHT reperesent cross-script homoglyph or near homoglyph forms of the corresponding Gujarati digits.

To keep digit variant sets manageable in zones where multiple scripts are present, no attempt has been made at identifying cross-script variants among digits of different numeric value or between a digit in one script and a letter in another, such as between digit zero and Latin letter ‘o’. Other mechanisms may be required to prevent homograph labels.

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

This LGR does not define allocatable variants.

Context Rules for Variants: some of the variants defined in this LGR are “effective null variants”, that is, some code points in the source map to “nothing” in the target with all other code points unchanged. (Because mappings are symmetric, it does not matter whether it is the forward or reverse mapping that maps to “null”.) Such variants require a context rule to keep the variant set well behaved.

In other cases, the sequences or code points making up source and target are constrained by explicit context rules on the code points (or by implicit context rules defined for the adjacent code points). In such a case, any variants may require context rules that match the intersection between the effective contexts for both source and target; otherwise, a sequence might be considered valid in some variant label when it would not be valid in an equivalent context in an original label. Symmetry requires the same context rule for both forward and reverse mappings.

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

Character Classes

Devanagari is an alphasyllabary and the heart of the writing system is the akshar. This is the unit which is instinctively recognized by users of the script. As encoded, the writing system of Devanagari is composed of Consonants, Halant, Vowels, Anusvara, Candrabindu, Nukta and Visarga.

Consonants: Devanagari consonants all contain an implicit schwa /ə/. To make a full syllable, consonants may be followed by certain code points from one or more of the other groups (see “WLE rules” below). See Section 3.3.1, “The Consonants” in [Proposal-Devanagari].

Halant: Because all consonants contain an implicit vowel /ə/, a special sign is needed to denote that this implicit vowel is stripped off. This sign is the Halant, encoded as U+094D  ्  DEVANAGARI SIGN VIRAMA. The Halant thus joins two consonants and creates conjuncts, which can be generally from 2 to 4 consonant combinations. In rare cases, it can join up to 5 consonants. However, this LGR will not enforce any length limit. See Section 3.3.2, “The Implicit Vowel Killer: Halant” in [Proposal-Devanagari].

Vowels and Matras: There are separate code points for vowels that are pronounced independently at the beginning of a syllable or after a vowel sound. To indicate a vowel sound following a consonant other than the implicit shwa sound, a vowel sign (matra) is attached to the consonant. There is an equivalent matra for each vowel excepting U+0905 अ DEVANAGARI VOWEL A. See Section 3.3.3, “Vowels” in [Proposal-Devanagari].

Anusvara: The Anusvara shows a nasal at the end of a syllable. See Section 3.3.4, “The Anusvara” of the [Proposal-Devanagari].

Candrabindu: A Candrabindu denotes nasalization of the preceding vowel. Present-day Hindi users tend to replace the Candrabindu by the Anusvara. See Section 3.3.5, “Nasalization: Candrabindu” in [Proposal-Devanagari].

Nukta: The nukta sign is placed below a certain number of consonants to represent sounds found only in words borrowed from Perso-Arabic, English and other non-Aryan sources. It is also placed under the consonants U+0921 ड and U+0922 ढ to indicate flapped sounds. See Section 3.3.6, “Nukta” in [Proposal-Devanagari].

Visarga: U+0903  ः  DEVANAGARI SIGN VISARGA, representing an aspiration at the end of a syllable, is frequently used in Sanskrit. See Section 3.3.7, “Visarga and Avagraha” in [Proposal-Devanagari].

Devanagari Digits: U+0966 ० to U+096F ९ are a set of Devanagari-specific digits. They are used in alternation with the European (common) digits.

Common Digits: U+0030 0 to U+0039 9 are the set of digits from the ASCII range.

Whole Label Evaluation (WLE) and Context Rules

Common Rules

The LGR includes the rules and actions to implement the following restrictions, some of which are mandated by the IDNA protocol. They are marked with ⍟ and included here by default.

• 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].
• Digit-mixing — no mixing between different digit sets (European and Devanagari digits) is allowed; implemented here as a WLE rule with associated action.

Default Actions

This LGR includes the complete set 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] and [150]. An additional action is triggered by mixed digit labels.

Hindi-specific Rules

These rules ensure that the Hindi label conforms to akshar formation norms for the Devanagari script. These norms are exclusively presented as context rules.

The following symbols are used in the names and comments for WLE rules:

• C → Consonant
• M → Matra
• V → Vowel
• B → Anusvara (Bindu)
• D → Candrabindu
• X → Visarga
• H → Halant / Virama
• N → Nukta

The rules are:

• 1. N: must be preceded by C1
• 2. H: must be preceded by C or CN
• 3. M: must be preceded by C or CN
• 4. X: must be preceded by any of V, C, N or M
• 5. B: must be preceded by any of V, C, N or M
• 6. D: must be preceded by any of V, C, N or M
• 7. V: Can NOT be preceded by H

See Section 7, “Whole Label Evaluation Rules (WLE)” in [Proposal-Devanagari].

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 Hindi Language was developed by Michel Suignard and Asmus Freytag, based on the Root Zone LGR for the Devanagari script and information contained or referenced therein; see [RZ-LGR-Deva]. 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 Devanagari script, that this LGR is based on, was developed by the Devanagari Generation Panel. For more information on methodology and contributors to the underlying Root Zone LGR, see Sections 4 and 8 in [Proposal-Devanagari], as well as [RZ-LGR-Overview].

Changes from Version Dated 15 December 2020

Language tag has been updated.

Changes from Version Dated 18 May 2021

Unicode Version has been updated.

Changes from Version Dated 24 January 2024

Adopted from the Second Level Reference LGR for the Hindi Language [Ref-LGR-hi-Deva] 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

[Proposal-Devanagari]

Neo-Brahmi Generation Panel, “Proposal for a Devanagari Script Root Zone Label Generation Rule-Set (LGR)”, 22 April 2019,
https://www.icann.org/en/system/files/files/proposal-devanagari-lgr-22apr19-en.pdf

[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-Deva]

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

[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

[Ref-LGR-hi-Deva]

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

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

Reference [0] refers to the Unicode Standard versions in which the corresponding code points were initially encoded. References [100] and above correspond to sources given in [Proposal-Devanagari] justifying the inclusion of the corresponding 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.

Character Classes

Number of named classes	8
Implicit (except script)	3
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
C	Tag=Consonant	33	{0915-0928 092A-0930 0932 0935-0939}		Any Devanagari consonant
C1	Tag=C1	9	{0915-0917 091A-091C 0921-0922 092B}		Consonants followed by Devanagari Nukta
V	Tag=Vowel	13	{0905-090B 090D 090F-0911 0913-0914}		Any Devanagari independent vowel
M	Tag=Matra	12	{093E-0943 0945 0947-0949 094B-094C}		Any Devanagari vowel sign (matra)
H	Tag=Halant	1	{094D}		The Devanagari Halant (VIRAMA)
N	Tag=Nukta	1	{093C}		The Devanagari Nukta
common-digits	Tag=Common-digit	10	{0030-0039}		Digits from the ASCII range; ⍟
devanagari-digits	Tag=Devanagari-digit	10	{0966-096F}		Devanagari digits
implicit	Tag=Anusvara	1	{0902}		The character tagged as Anusvara
implicit	Tag=Candrabindu	1	{0901}		The character tagged as Candrabindu
implicit	Tag=Visarga	1	{0903}		The character tagged as Visarga
implicit	Tag=sc:Deva	73	{0901-0903 0905-090B 090D 090F-0911 0913-0928 092A-0930 0932 0935-0939 093C 093E-0943 0945 0947-0949 094B-094D 0966-096F}		Any character tagged as Devanagari
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	7
Used to trigger actions	2
Used as context rule (C)	5
Used as context rule (V)	1
Anchored context rules	5

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 - ⍟
follows-C1	([:C1:])← ⚓︎		✔	C		Section 7, WLE 1: Rule for Nukta which restricts its preceding characters
follows-C-or-CN	([:C:]|([:C:][:N:]))← ⚓︎		✔	C, V		Section 7, WLE 2, 3: Halant or matra characters can only be preceded by consonant or a Nukta which is preceded by a consonant
follows-V-or-C-or-N-or-M	([:V:]|[:C:]|[:N:]|[:M:])← ⚓︎		✔	C		Section 7, WLE 4, 5, 6: Anusvara, Candrabindu or Visarga characters can only be preceded by either vowel or consonant or Nukta or matra
preceded-by-H	([:H:])← ⚓︎		✔	C		Section 7, WLE 7: A vowel is not allowed to follow an H
digit-mixing	([:common-digits:].*[:devanagari-digits:])|([:devanagari-digits:].*[:common-digits:])	✔				restrictions on mixing digits

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.

*, +, ?, {n,m} - count operators

* indicates 0 or more, + indicates one or more, and ? indicates up to one instance. {n,m} indicates at least n and at most m instances.

[: :] - named or implicit character set

Reference to a named character set [:name:] or an implicit character set [:tag:]. A leading “^” before name or tag indicates the set complement.

[\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).

⍟ - 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	[150]	labels with leading combining marks are invalid ⍟
2	if label matches	digit-mixing	→	invalid		a label violating the restriction on digit mixing is invalid
3	if at least one variant is in	{out-of-repertoire-var}	→	invalid		any variant label with a code point out of repertoire is invalid ⍟
4	if at least one variant is in	{blocked}	→	blocked		any variant label containing blocked variants is blocked ⍟
5	if each variant is in	{allocatable}	→	allocatable		variant labels with all variants allocatable are allocatable ⍟
6	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.