Reference Label Generation Rules for the Kannada Script

Overview

This document specifies a reference set of Label Generation Rules (LGR) for the Kannada script for the second level. The starting point for the development of this LGR can be found in the related Root Zone LGR [RZ-LGR-4-Knda]. For details and additional background on the script, see "Proposal for a Kannada Script Root Zone Label Generation Ruleset (LGR)" [Proposal-Kannada]. The format of this file follows [RFC 7940].

Repertoire

The repertoire contains 62 code points for letters covering Kannada, Tulu, Beary, Konkani, Havyaka, Kodava, among other languages written using the Kannada script. The repertoire is a subset of [Unicode 6.3]. For more details, see Section 5, "Repertoire" in [Proposal-Kannada]. (The proposal cited has been adopted for the Kannada 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
• Kannada digits

for a total of 83 repertoire elements.

Code points outside the Kannada 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. Comments provide alternate names for some code points.

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.

The Kannada and Telugu scripts are closely related to each other and there are many code points in both scripts which can be confused with code points in the other script. This LGR defines many cross-script variants with Telugu as described in Section 6, "Variants", in "[Proposal-Kannada]". There are no in-script variants defined for Kannada.

Digit Variants: All Kannada 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 transitive relations are deemed to exist implicitly 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.) There is a homoglyph relation between most Telugu and Kannada digits, but as the Telugu LGR does not support native digits, this does not give rise to variants. In addition, Kannada digit ZERO is a cross-script homoglyph or near homoglyph of digit ZERO in many other scripts; all of 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: 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 variant label should be blocked. There is no preference among these variants.

This LGR does not define allocatable variants.

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

Character Classes

The structure of the Kannada script is similar to that of other Indian scripts; it is particularly closely related to Telugu. The heart of the writing system is the akshar. The basic characters are classified into three main categories: swara (vowels), vyanjana (consonants) and yogavahas (semiconsonants).

Swaras (vowels): There are thirteen vowels. When a vowel follows a consonant, it is written with a diacritic rather than as a separate letter. Sometimes these are referred to as vowel signs or matras. More details in Section 3.4.1, "Swaras (vowels)" in [Proposal-Kannada].

Yogavahas (semiconsonants): The Yogavaha (part-vowel, part consonant) include two letters:

1. The anusvara: ಅಂ /aṁ/.
2. The visarga: ಅಃ /aḥ/.

See Section 3.4.2, "Yogavahas" in [Proposal-Kannada].

Vyanjanas (consonants): Two categories of consonant characters are defined in Kannada: the structured consonants (vargeeya vyanjana) and the unstructured consonants (avargeeya vyanjana). For the purpose of this LGR, all consonants are treated the same. More details in Section 3.4.3, "Vyanjanas (consonants)" of the [Proposal-Kannada].

Halant / Virama: All consonant code points in Kannada contain an implicit vowel ಅ /a/. The Unicode character U+0CCD (್), which is the Kannada equivalent of the Devanagari Halant (or Virama), U+094D (्), is applied to consonants to remove the implicit vowel. More details in Section 3.4.4, "Implicit vowel ಅ (a) in consonants" in [Proposal-Kannada].

Kannada Digits: U+0CE6 (೦) to U+0CEF (೯) are a set of Kannada-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].
• Digit-mixing — no mixing between different digit sets (European and Kannada 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].

Kannada-specific Rules

These rules have been formulated so that they can be adopted for LGR specification.

The following symbols are used in the WLE rules:
C → Consonant
M → Matra
V → Vowel
B → Anusvara
X → Visarga
H → Halant / Virama

The rules are:

• 1. H: must be preceded by C
• 2. M: must be preceded by C
• 3. B: must be preceded by C, V or M
• 4. X: must be preceded by C, V or M
• 5. V: cannot be preceded by H

More details in Section 7, "Whole Label Evaluation Rules (WLE)" of [Proposal-Kannada].

Methodology and Contributors

This reference LGR for Kannada for the 2nd Level has been developed by Michel Suignard and Asmus Freytag, based on the Root Zone LGR for Kannada and information contained or referenced therein, see [RZ-LGR-4-Knda]. Suitable extensions for the second level have been applied according to the [Guidelines]. The original proposal for a Root Zone LGR for the Kannada 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 [Proposal-Kannada].

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-Kannada]

Neo-Brahmi Generation Panel, “Proposal for a Kannada Script Root Zone Label Generation Ruleset (LGR)”, 6 March 2019,
https://www.icann.org/en/system/files/files/proposal-kannada-lgr-06mar19-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-4: Overview and Summary", 5 November 2020 (PDF),
https://www.icann.org/sites/default/files/lgr/lgr-4-overview-05nov20-en.pdf

[RZ-LGR-4-Knda]

ICANN, Root Zone Label Generation Rules for the Kannada Script (und-Knda) , 5 November 2020 (XML)
https://www.icann.org/sites/default/files/lgr/lgr-4-kannada-script-05nov20-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 Kannada script for the second level please see details in the Table of References below. Reference [0] refers to the Unicode Standard version in which the corresponding code points were initially encoded. References [110] and above correspond to sources given in [Proposal-Kannada] justifying the inclusion of the corresponding code points. Entries in the table may have multiple source reference values. Reference [150] indicates the source for common rules.

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.