Reference Label Generation Rules for the Bengali (Bangla) script

Overview

This document specifies a reference set of Label Generation Rules (LGR) for the Bengali (Bangla) script. This LGR covers Assamese, Bengali, Manipuri and a number of other languages written with the Bengali script. The starting point for the development of this LGR can be found in the related Root Zone LGR [RZ-LGR-3-Beng]. For details and additional background on the script, see "Proposal for a Bengali Script Root Zone Label Generation Ruleset (LGR)" [Proposal-Bengali]. The format of this file follows [RFC 7940].

This is a DRAFT document released for public comments and not final. Please see the announcement on the ICANN website for public comments on the Second Level Reference LGRs for details on how to submit comments.

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. For more detail, see Section 5, "Repertoire" in [Proposal-Bengali]. (The proposal cited has been adopted for the Bengali script portion of the Root Zone LGR.)

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.

Code points outside the Bengali script that are listed in this file are targets for out-of-script variants and are identified by a reflexive (identity) variant of type "out-of-repertoire-var". They do not form part of the repertoire.

Each code point or range is tagged with the script or scripts that the code point is used with, 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 reference LGR is designed for use in zones shared by more than one script. 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 variant labels from other scripts consisting 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 and cross-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]. There are four cross-script variants; two sets with Gurmukhi and the other two sets with Devanagari. See Section 6.2 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. (Omitting the listing of these other cross script digit variants does not affect index variant calculation, as the ASCII digit variant being smallest would always be the index variant.) 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, such as between Bengali digit SEVEN and Gujarati digit ONE; or between a digit in one script and a letter in another, such as between digit zero and Latin letter 'o'.

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 reference 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

• 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].
• One non-ASCII code point — An IDN label must contain one non-ASCII code point, as described in Section 4.2.4 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

Actions include the default actions for LGRs as well as that needed to invalidate labels with misplaced combining marks. They are marked with ⍟. For a description see [RFC 7940].

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

This reference LGR for Bengali for the 2nd Level has been developed by Michel Suignard and Asmus Freytag, based on the Root Zone LGR for Bengali and information contained or referenced therein, see [RZ-LGR-3-Beng]. Suitable extensions for the second level have been applied according to the [Guidelines]. 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].

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-06jan16-en.pdf

[Proposal-Bengali]

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

[RFC 7940]

Davies, K. and A. Freytag, "Representing Label Generation Rulesets Using XML", RFC 7940, August 2016,
http://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 - LGR-3: Overview and Summary", 01 March 2020 (PDF),
https://www.icann.org/sites/default/files/lgr/lgr-3-overview-10jul19-en.pdf

[RZ-LGR-3-Beng]

ICANN, Root Zone Label Generation Rules for the Bengali Script (und-Beng) , 10 July 2019 (XML)
https://www.icann.org/sites/default/files/lgr/lgr-3-bengali-script-10jul19-en.xml

[Unicode 6.3]

The Unicode Consortium. The Unicode Standard, Version 6.3.0, (Mountain View, CA: The Unicode Consortium, 2013. ISBN 978-1-936213-08-5)
http://www.unicode.org/versions/Unicode6.3.0/

For references consulted particularly in designing the repertoire for the Bengali 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.

4.1 Character Classes

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).

4.2 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 or variant.

4.3 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.