Reference Label Generation Rules for the Sinhala Script

Overview

This document specifies a reference set of Label Generation Rules (LGR) for the Sinhala 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-Sinh]. For details and additional background on the script, see "Proposal for a Sinhala Script Root Zone Label Generation Rules-Set (LGR)" [Proposal-Sinhala]. The format of this file follows [RFC 7940].

Repertoire

The repertoire covers the Sinhala language as written with the Sinhala script and contains 72 code points for letters. In addition, 4 sequences are used in the definition of variants. The repertoire is a subset of [Unicode 6.3]. For more detail, see Section 5, "Repertoire" in [Proposal-Sinhala]. (The proposal cited has been adopted for the Sinhala script portion of the Root Zone LGR.)

For the second level, the repertoire has been augmented with the ASCII digits, U+0030 (0) to U+0039 (9), and U+002D (-) HYPHEN-MINUS, and the number of sequences increased to 112 by adding common sequences using ZWJ (U+200D), including some with variants, for a total of 195 repertoire elements.

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.

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 variants within Sinhala as described in Section 6, "Variants", in "[Proposal-Sinhala]". Additionally, some of the common conjuncts have alternates which are treated as variants.

Digit Variants: The Sinhala reference LGR does not include native digits, so there are no variants defined.

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 any other equivalent label should be blocked. There is no preference among these variants.

This LGR does not define allocatable variants.

Context Rules for Variants: for some of the variants defined in this LGR 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 reference LGR follows the guidelines in [RFC 8228].

Character Classes

As most Brahmi-derived scripts, Sinhala is an alphasyllabary writing system and written from left to right. All the categories of Consonants, Vowels, Matras, Halant, Anusvara, Visarga and Sannjakas are discussed below.

Consonants: There are 40 consonants in Sinhala alphabet and 38 of them are selected for inclusion. Its consonants imply inherent vowel a(අ) when they are used without dependent vowels. Absence of the inherent vowel is marked by adding hal kirima (remover of the inherent vowel) to the consonant; thus ක /ka/ but ක් /k/, and ව /va/ but ව් /v/. More details in Section 3.3.1, "The Consonants" in [Proposal-Sinhala].

Vowels and Matras: There are separate symbols (dependent vowels) for all the vowels except the inherent vowel අ in Sinhala. Independent vowels are used at the beginning of a word and dependent vowels (matras) are used after consonants. More details in Section 3.3.2, "The Vowels" in [Proposal-Sinhala].

Halanta: The Halanta, which is also called halkirima or hallakuna, is encoded as U+0DCA ( ් ) SINHALA SIGN AL-LAKUNA. This sign is used to remove the inherent vowel of the consonants in Sinhala, and to join consonants and form conjunct characters. More details in Section 3.3.3, "Halanta: The Inherent Vowel Remover" in [Proposal-Sinhala].

Anusvara: U+0D82 ( ං ) SINHALA SIGN ANUSVARAYA, pronounced /ŋ/, represents all the nasals. It can be preceded by any sign except halanta (U+0DCA). More details in Section 3.3.4, "The Anusvara" in [Proposal-Sinhala].

Visarga: U+0D83 ( ඃ ) SINHALA SIGN VISARGAYA is a rarely used sign and pronounced as /h/. It can be preceded by any sign except halanta (U+0DCA). More details in Section 3.3.5, "The Visarga" in [Proposal-Sinhala].

Sannjakas: There are five separate letters for prenasalized voiced stops called sannjakas in Sinhala. From among these, ඦ is not frequently used. Sannjakas cannot be followed by halanta. More details in Section 3.3.6, "Sannjakas" in [Proposal-Sinhala].

Zero Width Joiner: This character is used in the formation of certain conjuncts in Sinhala. In this LGR, U+200D (ZWJ) is not listed by itself but available as part of many defined sequences.

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].

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].

Sinhala-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 / Vowel Signs
V → Vowel
B → Anusvara (Bindu)
X → Visarga
H → Halanta / Virama
J → Sannjaka

The rules are:

• 1. H: must be preceded by C
• 2. M: must be preceded by C or J
• 3. X: must be preceded by either V, C, or M
• 4. B: must be preceded by either V, C, J or M
• 5. H: must not follow conjunct sequence

The following context rules apply to code points in variant sets to ensure the variant transitivity.

• 5. variants are undefined preceding a Halant or Matra
• 6. variants are undefined preceding an Anusvara, Visarga, Halant or Matra

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

Methodology and Contributors

This reference LGR for Sinhala for the 2nd Level has been developed by Michel Suignard and Asmus Freytag, based on the Root Zone LGR for Sinhala and information contained or referenced therein, see [RZ-LGR-4-Sinh]. Suitable extensions for the second level have been applied according to the [Guidelines]. The original proposal for a Root Zone LGR for the Sinhala script, that this reference LGR is based on, was developed by the Sinhala Generation Panel in consultation with the Neo-Brahmi Generation Panel. For more information on methodology and contributors to the underlying Root Zone LGR, see Sections 4 and 8 in [Proposal-Sinhala], 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-Sinhala]

Sinhala Generation Panel, “Proposal for a Sinhala Script Root Zone Label Generation Ruleset (LGR)”, 22 April 2019,
https://www.icann.org/en/system/files/files/proposal-sinhala-lgr-22apr19-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-Sinh]

ICANN, Root Zone Label Generation Rules for the Sinhala Script (und-Sinh) , 5 November 2020 (XML)
https://www.icann.org/sites/default/files/lgr/lgr-4-sinhala-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 Sinhala 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 [102] and above correspond to sources given in [Proposal-Sinhala] 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.