Root Zone LGR for script und-Taml (Tamil) | lgr-3-tamil-script-10jul19-en

This document is mechanically formatted from the above XML file for the LGR. It provides additional summary data and explanatory text. The XML file remains the sole normative specification of the LGR.

Date | 2019-07-10
LGR Version | 3
Language | und-Taml
Scope | domain: "." (Root)
Unicode Version | 6.3.0

## Table of Contents

# 1 Description

# Root Zone Label Generation Rules for the Tamil Script

## Overview

This file contains Label Generation Rules (LGR) for the Tamil script for the Root zone. For more details on this LGR and its development, see "Proposal for a Tamil Script Root Zone Label Generation Rule-Set (LGR)" [Proposal]. This file is one of a set of LGR files that together form an integrated LGR for the DNS Root Zone [RZ-LGR-3]. The format of this file follows [RFC 7940].

## Repertoire

According to Section 5, "Repertoire" in [Proposal] the Tamil LGR contains 48 unique code points and 4 sequences. This LGR caters to the Tamil language written using Tamil script.

The repertoire is based on [MSR-4], which is a subset of [Unicode 6.3].

Code points outside the Tamil 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 is tagged with the script or scripts that the code point is used with, a category value, 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

According to Section 6, "Variants", in [Proposal], this LGR defines four sequences as in-script variants. Two of them are variants to single code points; the other two are variants of each other; all defined variants look exactly alike and can cause confusion even to a careful observer.

In addition to these, this LGR defines 6 cross-script variants with the Malayalam script.

Variant Disposition: Except as noted, 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 label should be blocked.

For historical reasons, there are two sequences that both represent the same akshar (Shri) with exactly the same rendered form. These two sequences are thus semantically identical and users may choose either one, except that a single label must use one of these forms consistently. This variant pair is thus being defined as "allocatable" variant. (For more details see Section 6.1 in [Proposal].)

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

## Character Classes

Tamil 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. The writing system of Tamil could be summed up as composed of Consonants, the Implicit Vowel Killer: Halant, Vowels and Visarga/Aytham.

Consonants: More details in Section 3.3.1, "The Consonants" in [Proposal].

Halant / Virama: All consonants contain an implicit vowel (a). A special sign is needed to denote that this implicit vowel is stripped off. This is known as the Pulli and encoded as U+0BCD ( ் ) TAMIL SIGN VIRAMA. The virama thus joins two adjacent consonants. In Tamil, there are only two cases where this forms conjuncts. More details in Section 3.3.2, "Virama/Pulli" of the [Proposal].

Vowels and Matras: Separate symbols exist for all Vowels that are pronounced independently either at the beginning or after another vowel sound. To indicate a Vowel sound other than the implicit one following a consonant, a Vowel sign (matra) is attached to the consonant. Since the consonant has a built in ‘a’, there are equivalent Matras for all vowels excepting the அ. More details in Section 3.3.3, "Vowels" in [Proposal].

Visarga: The Visarga (or Aytham) is used in Tamil to represent a sound very close to /ḵ/. More details in Section 3.3.4, "Visarga/Aytham" in [Proposal].

## Whole Label Evaluation (WLE) and Context Rules

### Default Whole Label Evaluation Rules and Actions

The LGR includes the set of required default WLE rules and actions applicable to the Root Zone and defined in [MSR-4]. They are marked with ⍟. The default prohibition on leading combining marks is equivalent to ensuring that a label only starts with a consonant or vowel.

### Tamil-specific Rules and Action

These rules have been drafted to ensure that the prospective Tamil label conforms to akshar formation norms as desired in Tamil script. These norms are exclusively presented as context rules.

The following symbols are used in the WLE rules:
C → Consonant
M → Matra
H → Haleant /V irama =Pulli
X → Visarga = Aytham

The rules are:

1. H: must be preceded by C
2. M: must be preceded by C
3. X: cannot be preceded by X

The following whole-label rule and associated action prevent the mixing of two allocatable variants of the same sequence within the same label. This reduces overproduction of variant labels.

4. Two representations of 'Shri' cannot be mixed in the same label

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

## Methodology and Contributors

The LGR for the Tamil script was developed by the Neo-Brahmi Generation Panel (NBGP) the members of which have experience in linguistics and computational linguistics in a wide variety of languages written with Neo-Brahmi scripts. Under the Neo-Brahmi Generation Panel, there are nine scripts belonging to separate Unicode blocks. Each of these scripts has been assigned a separate LGR, with the Neo-Brahmi GP ensuring that the fundamental philosophy behind building each LGR is in sync with all other Brahmi derived scripts. For further details on methodology and contributors, see Sections 4 and 8 in [Proposal], as well as [RZ-LGR-3-Overview].

## References

The following general references are cited in this document:

[MSR-4]
  Integration Panel, "Maximal Starting Repertoire — MSR-4 Overview and Rationale", 7 February 2019,
  https://www.icann.org/en/system/files/files/msr-4-overview-25jan19-en.pdf
[Proposal]
  Neo-Brahmi Generation Panel, "Proposal for a Tamil Script Root Zone Label Generation Rule-Set (LGR)", 6 March 2019,
  https://www.icann.org/en/system/files/files/proposal-tamil-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-3-Overview]
  Integration Panel, "Root Zone Label Generation Rules - LGR-3: Overview and Summary", 10 July 2019 (PDF),
  https://www.icann.org/sites/default/files/lgr/lgr-3-overview-10jul19-en.pdf
[RZ-LGR-3]
  Integration Panel, "Label Generation Rules for the Root Zone — LGR-3", 10 July 2019 (XML),
  https://www.icann.org/sites/default/files/lgr/lgr-3-common-10jul19-en.xml
  non-normative HTML presentation:
  https://www.icann.org/sites/default/files/lgr/lgr-3-common-10jul19-en.html
[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/

# 2 Repertoire

## Repertoire Summary

Number of elements in Repertoire | 52
Out of repertoire variants | 6
Total entries in table | 58
Number of code points for each script |
Malayalam | 6
Tamil | 48
Number of code points | 54
Number of sequences | 4
Longest code point sequence | 4

## Repertoire by Code Point

The following table lists the repertoire by code point (or code point sequence). The data in the Script and Name column are extracted from the Unicode character database. Where a comment in the original LGR is equal to the character name, it has been suppressed.

For any code point or sequence for which a variant is defined, additional information is provided in the Variants column. Some code points or sequences listed in the following table are not part of the repertoire itself; they document targets for out-of-repertoire variant mappings as indicated. See also the legend provided below the table.

Code Point | Glyph | Script | Name | Ref | Tags | Required Context | Part of Repertoire | Variants | Comment
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
U+0B83 | ஃ | Tamil | TAMIL SIGN VISARGA | [1003] | Visarga | not: preceded-by-X | ✔ |  | = aytham
U+0B85 | அ | Tamil | TAMIL LETTER A | [1001] | Vowel |  | ✔ |  |
U+0B86 | ஆ | Tamil | TAMIL LETTER AA | [1001] | Vowel |  | ✔ |  |
U+0B87 | இ | Tamil | TAMIL LETTER I | [1001] | Vowel |  | ✔ |  |
U+0B88 | ஈ | Tamil | TAMIL LETTER II | [1001] | Vowel |  | ✔ |  |
U+0B89 | உ | Tamil | TAMIL LETTER U | [1001] | Vowel |  | ✔ |  |
U+0B8A | ஊ | Tamil | TAMIL LETTER UU | [1001] | Vowel |  | ✔ |  |
U+0B8E | எ | Tamil | TAMIL LETTER E | [1001] | Vowel |  | ✔ |  |
U+0B8F | ஏ | Tamil | TAMIL LETTER EE | [1001] | Vowel |  | ✔ |  |
U+0B90 | ஐ | Tamil | TAMIL LETTER AI | [1001] | Vowel |  | ✔ |  |
U+0B92 | ஒ | Tamil | TAMIL LETTER O | [1001] | Vowel |  | ✔ |  |
U+0B92 U+0BB3 | ஒள | [Tamil] | TAMIL LETTER O + TAMIL LETTER LLA |  |  |  | ✔ | set 1 | homoglyph of U+0B94 (ஔ)
U+0B93 | ஓ | Tamil | TAMIL LETTER OO | [1001] | Vowel |  | ✔ |  |
U+0B94 | ஔ | Tamil | TAMIL LETTER AU | [1001] | Vowel |  | ✔ | set 1 |
U+0B95 | க | Tamil | TAMIL LETTER KA | [1002] | Consonant |  | ✔ |  |
U+0B99 | ங | Tamil | TAMIL LETTER NGA | [1002] | Consonant |  | ✔ |  |
U+0B9A | ச | Tamil | TAMIL LETTER CA | [1002] | Consonant |  | ✔ |  |
U+0B9C | ஜ | Tamil | TAMIL LETTER JA | [1002] | Consonant |  | ✔ | set 2 |
U+0B9E | ஞ | Tamil | TAMIL LETTER NYA | [1002] | Consonant |  | ✔ |  |
U+0B9F | ட | Tamil | TAMIL LETTER TTA | [1002] | Consonant |  | ✔ |  |
U+0BA3 | ண | Tamil | TAMIL LETTER NNA | [1002] | Consonant |  | ✔ |  |
U+0BA4 | த | Tamil | TAMIL LETTER TA | [1002] | Consonant |  | ✔ |  |
U+0BA8 | ந | Tamil | TAMIL LETTER NA | [1002] | Consonant |  | ✔ |  |
U+0BA9 | ன | Tamil | TAMIL LETTER NNNA | [1002] | Consonant |  | ✔ |  |
U+0BAA | ப | Tamil | TAMIL LETTER PA | [1002] | Consonant |  | ✔ |  |
U+0BAE | ம | Tamil | TAMIL LETTER MA | [1002] | Consonant |  | ✔ | set 3 |
U+0BAF | ய | Tamil | TAMIL LETTER YA | [1002] | Consonant |  | ✔ |  |
U+0BB0 | ர | Tamil | TAMIL LETTER RA | [1002] | Consonant |  | ✔ |  |
U+0BB1 | ற | Tamil | TAMIL LETTER RRA | [1002] | Consonant |  | ✔ |  |
U+0BB2 | ல | Tamil | TAMIL LETTER LA | [1002] | Consonant |  | ✔ |  |
U+0BB3 | ள | Tamil | TAMIL LETTER LLA | [1002] | Consonant |  | ✔ |  |
U+0BB4 | ழ | Tamil | TAMIL LETTER LLLA | [1002] | Consonant |  | ✔ |  |
U+0BB5 | வ | Tamil | TAMIL LETTER VA | [1002] | Consonant |  | ✔ | set 4 |
U+0BB6 | ஶ | Tamil | TAMIL LETTER SHA | [1002] | Consonant |  | ✔ |  |
U+0BB6 U+0BCD U+0BB0 U+0BC0 | ஶ்ரீ | [Tamil] | TAMIL SYLLABLE SHRII |  |  |  | ✔ | set 5 |
U+0BB7 | ஷ | Tamil | TAMIL LETTER SSA | [1002] | Consonant |  | ✔ |  |
U+0BB8 | ஸ | Tamil | TAMIL LETTER SA | [1002] | Consonant |  | ✔ |  |
U+0BB8 U+0BCD U+0BB0 U+0BC0 | ஸ்ரீ | [Tamil] | TAMIL LETTER SA + TAMIL SIGN VIRAMA + TAMIL LETTER RA + TAMIL VOWEL SIGN II |  |  |  | ✔ | set 5 | Alternate for Tamil SHRII
U+0BB9 | ஹ | Tamil | TAMIL LETTER HA | [1002] | Consonant |  | ✔ |  |
U+0BBE | ா | Tamil | TAMIL VOWEL SIGN AA | [1002] | Matra | follows-C | ✔ |  |
U+0BBF | ி | Tamil | TAMIL VOWEL SIGN I | [1002] | Matra | follows-C | ✔ | set 6 |
U+0BC0 | ீ | Tamil | TAMIL VOWEL SIGN II | [1002] | Matra | follows-C | ✔ |  |
U+0BC1 | ு | Tamil | TAMIL VOWEL SIGN U | [1002] | Matra | follows-C | ✔ |  |
U+0BC2 | ூ | Tamil | TAMIL VOWEL SIGN UU | [1002] | Matra | follows-C | ✔ |  |
U+0BC6 | ெ | Tamil | TAMIL VOWEL SIGN E | [1002] | Matra | follows-C | ✔ | set 7 |
U+0BC6 U+0BB3 | ெள | [Tamil] | TAMIL VOWEL SIGN E + TAMIL LETTER LLA |  |  | follows-C | ✔ | set 8 | homoglyph of U+0BCC (ௌ)
U+0BC7 | ே | Tamil | TAMIL VOWEL SIGN EE | [1002] | Matra | follows-C | ✔ | set 9 |
U+0BC8 | ை | Tamil | TAMIL VOWEL SIGN AI | [1002] | Matra | follows-C | ✔ |  |
U+0BCA | ொ | Tamil | TAMIL VOWEL SIGN O | [1002] | Matra | follows-C | ✔ |  |
U+0BCB | ோ | Tamil | TAMIL VOWEL SIGN OO | [1002] | Matra | follows-C | ✔ |  |
U+0BCC | ௌ | Tamil | TAMIL VOWEL SIGN AU | [1002] | Matra | follows-C | ✔ | set 8 |
U+0BCD | ் | Tamil | TAMIL SIGN VIRAMA | [1002] | Halant | follows-C | ✔ |  | = pulli
U+0D16 | ഖ | Malayalam | MALAYALAM LETTER KHA |  |  |  | ✗ | set 4 | Not part of repertoire
U+0D1C | ജ | Malayalam | MALAYALAM LETTER JA |  |  |  | ✗ | set 2 | Not part of repertoire
U+0D25 | ഥ | Malayalam | MALAYALAM LETTER THA |  |  |  | ✗ | set 3 | Not part of repertoire
U+0D3F | ി | Malayalam | MALAYALAM VOWEL SIGN I |  |  |  | ✗ | set 6 | Not part of repertoire
U+0D46 | െ | Malayalam | MALAYALAM VOWEL SIGN E |  |  |  | ✗ | set 7 | Not part of repertoire
U+0D47 | േ | Malayalam | MALAYALAM VOWEL SIGN EE |  |  |  | ✗ | set 9 | Not part of repertoire

Legend

Throughout this LGR, a code point sequence may be annotated with a string in ALL CAPS that is constructed on the same principle as a name for a Unicode Named Sequence. No claim is made that a sequence thus annotated is in fact a named sequence, nor that the annotation in such case actually corresponds to the formal name of a named sequence.

Code Point
  A code point or code point sequence.
Name
  Shows the character or sequence name from the Unicode Character Database. Named sequences are listed with their normative names, for ad-hoc sequences the individual names are shown separated by “+”.
Glyph
  The shape displayed depends on the fonts available to your browser.
Script
  Shows the script property value from the Unicode Character Database. Combining marks may have the value Inherited and code points used with more than one script may have the value Common. Sequences are annotated with a set of all distinct script values.
Ref
  Links to the references associated with the code point or sequence, if any.
Tags
  LGR-defined tag values. Any tags matching the Unicode script property are suppressed in this view.
Required Context
  Link to a rule defining the required context a code point or sequence must satisfy. If prefixed by “not:ℍ identifies a context that must not occur.
Variants
  Link to the variant set the code point or sequence is a member of, except where a coded point or sequence maps only to itself, in which case the type of that mapping is listed.
Comment
  The comment as given in the XML file. However, if the comment for this row consists only of the code point or sequence name, it is suppressed in this view. By convention, comments starting with “=” denote an alias.
✔ - core repertoire
  A check mark in the Part-of-Repertoire column indicates a code point is part of the core repertoire.
✗ - out-of-repertoire
  A code point shown with ✗ is not part of the repertoire. It is listed only because it is the target of an out-of-repertoire-var variant mapping.

# 3 Variant Sets

## Variant Set Summary

Number of variant sets | 9
Largest variant set | 2
Ordinary Variants by Type |
allocatable | 2
blocked | 16
Reflexive Variants by Type |
out-of-repertoire-var | 6

The following tables list all variant sets defined in this LGR, except for singleton sets. Each table lists all variant mapping pairs of the set; one per row. Mappings are assumed to be symmetric: each row documents both forward (→) and reverse (←) mapping directions. In each table, the mappings are sorted by Source value in ascending code point order; shading is used to group mappings from the same source code point or sequence.

Where the type of both forward and reverse mappings are the same, a single value is given in the Type column, otherwise the types for forward and reverse mappings, as well as comments and references are listed above one another. For summary counts, both forward and reverse mappings are always counted separately.

A mapping where source and target are the same is reflexive. Variant sets consisting of only a single reflexive mapping are not shown as a set. Instead, the variant type of the mapping is listed in the Variants column of the Repertoire by Code Point table. Reflexive mappings that are part of a larger set are indicated with a “≡” and are counted once per entry.

In any LGR with variant specifications that are well behaved, all members within each variant set are defined as variants of each other; the mappings in each set are symmetric and transitive; and all variant sets are disjoint.

Common Legend

Source
  By convention, the smaller of the two code points in a variant mapping pair.
Target
  By convention, the larger of the two code points in a variant mapping pair.
Glyph
  The shape displayed for source or target depends on the fonts available to your browser.
→ - forward
  Indicates that Type, Ref and Comment apply to the mapping from source to target.
← - reverse
  Indicates that Type, Ref and Comment apply to the reverse mapping from target to source.
↔ - both
  Indicates that Type, Ref and Comment apply to both forward and reverse mapping.
≡ - reflexive
  Indicates that Type, Ref and Comment are for a reflexive mapping where source equals target.
Type
  The type of the variant mapping. There are some predefined variant types such as “allocatable” and “blocked”, while others are defined specifically for each LGR. A reflexive variant type “out-of-repertoire-var” designates the target as not part of the repertoire; it is required as target for one or more variant mappings that cross repertoire boundaries.
Ref
  One or more reference IDs (optional). A “/” separates references for reverse / forward mappings, if different.
Comment
  A descriptive comment (optional). A “/” separates comments for reverse / forward mappings, if different.

### Variant Set 1 — 2 Members

Source | Glyph | Target | Glyph |  | Type | Ref | Comment
--- | --- | --- | --- | --- | --- | --- | ---
0B92 0BB3 | ஒள | 0B94 | ஔ | ↔ | blocked |  | Tamil homoglyph / homoglyph

### Variant Set 2 — 2 Members

Source | Glyph | Target | Glyph |  | Type | Ref | Comment
--- | --- | --- | --- | --- | --- | --- | ---
0B9C | ஜ | 0D1C | ജ | ↔ | blocked |  | Cross-script homoglyph
0D1C | ജ | 0D1C | ജ | ≡ | out-of-repertoire-var |  | Out-of-repertoire

### Variant Set 3 — 2 Members

Source | Glyph | Target | Glyph |  | Type | Ref | Comment
--- | --- | --- | --- | --- | --- | --- | ---
0BAE | ம | 0D25 | ഥ | ↔ | blocked |  | Cross-script homoglyph
0D25 | ഥ | 0D25 | ഥ | ≡ | out-of-repertoire-var |  | Out-of-repertoire

### Variant Set 4 — 2 Members

Source | Glyph | Target | Glyph |  | Type | Ref | Comment
--- | --- | --- | --- | --- | --- | --- | ---
0BB5 | வ | 0D16 | ഖ | ↔ | blocked |  | Cross-script homoglyph
0D16 | ഖ | 0D16 | ഖ | ≡ | out-of-repertoire-var |  | Out-of-repertoire

### Variant Set 5 — 2 Members

Source | Glyph | Target | Glyph |  | Type | Ref | Comment
--- | --- | --- | --- | --- | --- | --- | ---
0BB6 0BCD 0BB0 0BC0 | ஶ்ரீ | 0BB8 0BCD 0BB0 0BC0 | ஸ்ரீ | ↔ | allocatable |  | Alternate for Tamil SHRII

### Variant Set 6 — 2 Members

Source | Glyph | Target | Glyph |  | Type | Ref | Comment
--- | --- | --- | --- | --- | --- | --- | ---
0BBF | ி | 0D3F | ി | ↔ | blocked |  | Cross-script homoglyph
0D3F | ി | 0D3F | ി | ≡ | out-of-repertoire-var |  | Out-of-repertoire

### Variant Set 7 — 2 Members

Source | Glyph | Target | Glyph |  | Type | Ref | Comment
--- | --- | --- | --- | --- | --- | --- | ---
0BC6 | ெ | 0D46 | െ | ↔ | blocked |  | Cross-script homoglyph
0D46 | െ | 0D46 | െ | ≡ | out-of-repertoire-var |  | Out-of-repertoire

### Variant Set 8 — 2 Members

Source | Glyph | Target | Glyph |  | Type | Ref | Comment
--- | --- | --- | --- | --- | --- | --- | ---
0BC6 0BB3 | ெள | 0BCC | ௌ | ↔ | blocked |  | homoglyph / Tamil Homoglyph

### Variant Set 9 — 2 Members

Source | Glyph | Target | Glyph |  | Type | Ref | Comment
--- | --- | --- | --- | --- | --- | --- | ---
0BC7 | ே | 0D47 | േ | ↔ | blocked |  | Cross-script homoglyph
0D47 | േ | 0D47 | േ | ≡ | out-of-repertoire-var |  | Out-of-repertoire

# 4 Classes, Rules and Actions

## 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).

Name | Definition | Count | Members or Ranges | Ref | Comment
--- | --- | --- | --- | --- | ---
C | Tag=Consonant | 23 | {0B95 0B99-0B9A 0B9C 0B9E-0B9F 0BA3-0BA4 0BA8-0BAA 0BAE-0BB9} |  | Any Tamil consonant
X | Tag=Visarga | 1 | {0B83} |  | The Tamil Visarga (aytham)
implicit | Tag=Halant | 1 | {0BCD} |  | The character tagged as Halant
implicit | Tag=Matra | 11 | {0BBE-0BC2 0BC6-0BC8 0BCA-0BCC} |  | Any character tagged as Matra
implicit | Tag=Vowel | 12 | {0B85-0B8A 0B8E-0B90 0B92-0B94} |  | Any character tagged as Vowel
implicit | Tag=sc:Mlym | 6 | {0D16 0D1C 0D25 0D3F 0D46-0D47} |  | Any character tagged as Malayalam
implicit | Tag=sc:Taml | 48 | {0B83 0B85-0B8A 0B8E-0B90 0B92-0B95 0B99-0B9A 0B9C 0B9E-0B9F 0BA3-0BA4 0BA8-0BAA 0BAE-0BB9 0BBE-0BC2 0BC6-0BC8 0BCA-0BCD} |  | Any character tagged as Tamil

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.

## 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.

Name | Regular Expression | Used as Trigger | Anchor | Used as Context | Ref | Comment
--- | --- | --- | --- | --- | --- | ---
leading-combining-mark | `(start)[[\p{gc=Mn}]∪[\p{gc=Mc}]]` | ✔ |  |  |  | Default WLE rule matching labels with leading combining marks ⍟
follows-C | `([:C:])← ⚓` |  | ✔ | C |  | Section 7, WLE 1, 2: H and M must be preceded by C
preceded-by-X | `⚓ →([:X:])` |  | ✔ | C |  | Section 7, WLE 3 , X cannot be preceded by X
no-mix-sri-shri | `(\u0BB6\u0BCD\u0BB0\u0BC0.*\u0BB8\u0BCD\u0BB0\u0BC0)|(\u0BB8\u0BCD\u0BB0\u0BC0.*\u0BB6\u0BCD\u0BB0\u0BC0)` | ✔ |  |  |  | Section 7: WLE 4: Two representations of 'Shri' cannot be mixed in the same label

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.
(... | ...) - 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 character set
  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.

## 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.

# | Condition | Rule / Variant Set |  | Disposition | Ref | Comment
--- | --- | --- | --- | --- | --- | ---
1 | if label matches | leading-combining-mark | → | invalid |  | labels with leading combining marks are invalid ⍟
2 | if at least one variant is in | {out-of-repertoire-var} | → | invalid |  | any variant label with a code point out of repertoire is invalid ⍟
3 | if label matches | no-mix-sri-shri | → | invalid |  | do not mix two representations of 'Shri' in the same label
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.

# 5 Table of References

[1001] | Omniglot, Tamil, http://www.omniglot.com/writing/tamil.htm (Accessed on 21 Nov. 2017)
[1002] | Unicode 11.0.0, South and Central Asia-I, Page 488-493, R5 and R5a, https://www.unicode.org/versions/Unicode11.0.0/ch12.pdf (Accessed on 5 July. 2018)
[1003] | Tamil Sign Visarga, https://www.charbase.com/0b83-unicode-tamil-sign-visarga (Accessed on 27 Nov. 2017)