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Label Generation Rules for the Bengali (Bangla) script

Overview

This document specifies a set of Label Generation Rules (LGR) for the Bengali (Bangla) 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-Beng]. [Proposal-Bengali]. The format of this file follows [RFC 7940]. This LGR is adapted from the “Reference LGR for the Second Level for the Bengali Script” [Ref-LGR-und-Beng], for details, see Change History below.

This LGR covers Assamese, Bengali, Manipuri and a number of other languages written with the Bengali script. For details and additional background on the Bengali script, see “Proposal for a Bangla (or Bengali) Script Root Zone Label Generation Ruleset (LGR)” [Proposal-Bengali].

Repertoire

The repertoire contains 61 code points for letters, as well as 9 code point sequences. Out of the nine sequences, two sequences override a WLE constraint; four sequences were defined for in-script variants; and the other three sequences were defined to restrict U+09BC  ়  NUKTA from appearing in any context other than these sequences. Accordingly, while U+09BC  ়  is not listed by itself, it brings the total of code points available for letters to 62. The repertoire is a subset of [Unicode 11.0.0]. For details, see Section 5, “Repertoire” in [Proposal-Bengali]. (The proposal cited has been adopted for the Bengali script portion of the Root Zone LGR.)

Note that the code points U+09DC ড়, U+09DD ঢ় and U+09DF য় are not in Normalization Form NFC and thus not PVALID under IDNA2008. Before performing lookup, any user agent accepting these code points will normalize them into the equivalent sequences with an explicit U+09BC  ়  Nukta code point. Accordingly, this LGR does not reference these code points, but instead includes only the sequences.

For the second level, the repertoire has been augmented with the Bengali digits, U+09E6 ০ to U+09EF ৯, ASCII digits U+0030 0 to U+0039 9, and U+002D - HYPHEN-MINUS, for a total of 91 repertoire elements.

Any code points outside the Bengali 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, 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

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 Gurmukhi and Devanagari in the same zone will create potential cross-script issues. For details, see Section 6, “Variants” in [Proposal-Bengali]. Mitigation of these 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 required for concurrent use with the Gurmukhi and Devanagari LGR(s) can be found in the following LGR: [Ref-LGR-Devanagari-Full-Variant-Script]

This LGR defines in-script variants as described in Section 6, “Variants” in [Proposal-Bengali]. There are three in-script variants; two sequence sets and one set for variation of RA. See Section 6.1 in [Proposal-Bengali].

Digit Variants: All Bengali 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, Bengali 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.

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: The in-script variant pair U+09B0 র / U+09F0 ৰ is of type “allocatable”, thus allowing access to either user community. All other 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, the other one equivalent variant label should be blocked. There is no preference among these variants.

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

Character Classes

Consonants: All consonants contain an implicit vowel. More details in Section 3.3.1, “ The Consonants” of [Proposal-Bengali].

Hasanta: A special sign is needed whenever the implicit vowel in the preceding consonant is stripped off. This symbol is also known as the Halant or “Virama”. More details in Section 3.3.2, “The Implicit Vowel Killer: Hasanta” of [Proposal-Bengali].

Vowels: Separate symbols exist for all “Swara” or Vowels in Bengali, which are pronounced independently either at the beginning of the word or after another vowel or consonant sound. To indicate a Vowel sound other than the implicit one, a Vowel sign (Matra) is attached to the consonant. More details in Section 3.3.3, “Vowels” of [Proposal-Bengali].

Anusvara: The Anusvara represents a homorganic nasal. It replaces a conjunct group of a Nasal Consonant+Halant+Consonant belonging to that particular barga or set. Before a non-barga consonant, the anusvara represents a nasal sound. More details in Section 3.3.4, “The Anusvara” of [Proposal-Bengali].

Candrabindu: Candrabindu denotes nasalization of the preceding vowel as in চাঁদ /cãd/ “moon” (U+099A U+09BE U+0981 U+09A6). This sign with a dot inside the half-moon mark is used as nasalization marker in many Indian scripts. More details in Section 3.3.5, “Nasalization: Candrabindu” of [Proposal-Bengali].

Visarga and Avagraha: The Visarga U+0983  ঃ  is frequently used in Bengali loanwords borrowed from Sanskrit and represents a sound very close to /h/. More details in Section 3.3.7, “Visarga and Avagraha” of [Proposal-Bengali].

Ya-phala: There are two instances in Bangla where a Hasanta is preceded by a full vowel (U+0985 অ BENGALI LETTER A and U+098F এ BENGALI LETTER E). More details in Section 3.3.9, “Use of Ya-phala” of [Proposal-Bengali].

Ra-phala and Ref Sequences: RA+Hasanta (Repha or Ra-phala sequences). More details in Section 3.3.10, “Ra-phala and Ref Sequences” of [Proposal-Bengali].

Nukta: Nukta is not listed by itself in the repertoire; it is only included in three sequences. More details in Section 3.3.6, “Nukta” of [Proposal-Bengali].

Zero Width Non-joiner (ZWNJ) and Zero Width Joiner (ZWJ): These are not included in the repertoire. More details in Section 3.3.8, “Zero Width Non-joiner (U+200C) and Zero Width Joiner (U+200D)” of [Proposal-Bengali].

Bengali Digits: U+09E6 ০ to U+09EF ৯ are a set of Bengali-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 Bengali 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.

Bengali-specific Rules

These rules have been formulated as context rules suitable for adoption into an LGR specification.

The following symbols are used in the WLE rules:

• C → Consonant
• M → Kar (Matra)
• V → Vowel
• B → Onushshar (Anusvara)
• X → Bisarga (Visarga)
• D → Candrabindu
• H → Hasanta (Halant)
• Z → KhandaTa
• P → Ra-Hasanta
• S → (a/e) Ya-phala

The rules are:

• 1. C: C is a set of C and CN where CN is the set of normalized forms of {ড়,ঢ়,য়}
• 2. H: must be preceded by C
• 3. M: must be preceded by C
• 4. D: must be preceded by any of V, C, M
• 5. X: must be preceded by any of V, C, M, D
• 6. B: must be preceded by any of V, C, M, D
• 7. Z: must be preceded by any of V, C, M, D, B, X, P
• 8. V: CANNOT be preceded by H
• 9. S: CANNOT be preceded by H
• 10. U+09B0 র and U+09F0 ৰ CANNOT be mixed in the same label

More details in Section 7, “Whole Label Evaluation Rules (WLE)” of [Proposal-Bengali].

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 Bengali (Bangla) Script was developed by Michel Suignard and Asmus Freytag, based on the Root Zone LGR for the Bengali script and information contained or referenced therein; see [RZ-LGR-Beng]. 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 Bengali script, that this reference LGR is based on, was developed by the Neo-Brahmi Generation Panel (NBGP). For more information on methodology and contributors to the underlying Root Zone LGR, see Sections 4 and 8 in [Proposal-Bengali], as well as [RZ-LGR-Overview].

Changes from Version Dated 15 December 2020

Unicode Version has been updated. U+0994 ঔ Letter AU has been corrected to be a vowel with corresponding context rule.

Changes from Version Dated 24 January 2024

Adopted from the Second Level Reference LGR for the Bengali (Bangla) Script [Ref-LGR-und-Beng] without normative changes.

References

The following general references are cited in this document:

[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-Bengali]

Neo-Brahmi Generation Panel, “Proposal for a Bangla (or Bengali) Script Root Zone Label Generation Ruleset (LGR)”, 20 May 2020,
https://www.icann.org/en/system/files/files/proposal-bangla-lgr-20may20-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

[Ref-LGR-und-Beng]

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

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

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

[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-Beng]

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

[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 Bengali (Bangla) Script for the second level please see details in the Table of References below.

References [0] and [7] refer to the Unicode Standard versions in which the corresponding code points were initially encoded. References [101] and above correspond to sources given in [Proposal-Bengali] 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	10
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
C-single	Tag=Consonant	35	{0995-09A8 09AA-09B0 09B2 09B6-09B9 09CE 09F0-09F1}		Any Bengali consonant
V	Tag=Vowel	11	{0985-098B 098F-0990 0993-0994}		Any Bengali vowel letter
M	Tag=Matra	11	{09BE-09C4 09C7-09C8 09CB-09CC}		Any Bengali vowel sign (matra)
H	Tag=Halant	1	{09CD}		The Bengali Hasanta (Halant / Virama)
B	Tag=Anusvara	1	{0982}		The Bengali Onushshar (Anusvara)
X	Tag=Visarga	1	{0983}		The Bengali Bisarga (Visarga)
D	Tag=Candrabindu	1	{0981}		The Bengali Candrabindu
C2	Tag=C2	2	{09B0 09F0}		Any Bengali consonant from set C2
common-digits	Tag=Common-digit	10	{0030-0039}		Digits from the ASCII range; ⍟
bengali-digits	Tag=Bengali-digit	10	{09E6-09EF}		Bengali digits
implicit	Tag=KhandaTa	1	{09CE}		The character tagged as KhandaTa
implicit	Tag=sc:Beng	71	{0981-0983 0985-098B 098F-0990 0993-09A8 09AA-09B0 09B2 09B6-09B9 09BE-09C4 09C7-09C8 09CB-09CE 09E6-09F1}		Any character tagged as Bengali
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	14
Used to trigger actions	3
Used as context rule (C)	6
Anchored context rules	6
Used only in another rule	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
C-RRA	\u09A1\u09BC					NFC form of BENGALI LETTER RRA
C-RHA	\u09A2\u09BC					NFC form of BENGALI LETTER RHA
C-YYA	\u09AF\u09BC					NFC form of BENGALI LETTER YYA
C	[:C-single:]|(:C-RRA:)|(:C-RHA:)|(:C-YYA:)					Section 7, WLE1: All consonants in the LGR repertoire; single code points and sequences
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-only-C	((:C:))← ⚓︎		✔	C		Section 7, WLE 2: H: must be preceded by C ; WLE 3: M: must be preceded by C
follows-only-V-C-M	([:V:]|(:C:)|[:M:])← ⚓︎		✔	C		Section 7, WLE 4: D: must be preceded by any of V, C, M
follows-only-V-C-M-D	([:V:]|(:C:)|[:M:]|[:D:])← ⚓︎		✔	C		Section 7, WLE 5: X: must be preceded by any of V, C, M, D; WLE 6: B: must be preceded by any of V, C, M, D
P	[:C2:][:H:]					Ra-Hasanta, defined for use in WLE-7
follows-only-V-C-M-D-B-X-P	([:V:]|(:C:)|[:M:]|[:D:]|[:B:]|[:X:]|(:P:))← ⚓︎		✔	C		Section 7, WLE 7: Khanda Ta must be preceded by V, C, M, D, B, X, P
follows-H	([:H:])← ⚓︎		✔	C		Section 7, WLE 8: V cannot be preceded by H, WLE 9: S cannot be preceded by H
no-mix-09B0-09F0	(\u09B0.*\u09F0)|(\u09F0.*\u09B0)	✔				Section 7, WLE 10: U+09B0 র and U+09F0 ৰ cannot be mixed.
digit-mixing	([:common-digits:].*[:bengali-digits:])|([:bengali-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.

(: :) - rule reference

Non-recursive reference to a named rule.

( ) - 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 label matches	no-mix-09B0-09F0	→	invalid		WLE 10: U+09B0 র and U+09F0 ৰ cannot be mixed.
4	if at least one variant is in	{out-of-repertoire-var}	→	invalid		any variant label with a code point out of repertoire is invalid ⍟
5	if at least one variant is in	{blocked}	→	blocked		any variant label containing blocked variants is blocked ⍟
6	if each variant is in	{allocatable}	→	allocatable		variant labels with all variants allocatable are allocatable ⍟
7	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: out-of-repertoire-var. This is not necessarily an error.