Reference LGR for language: Thai (th) lgr-second-level-thai-language-18may21-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 2021-05-18
LGR Version 2 (Second Level Reference LGR)
Language th (Thai Language)
Unicode Version 6.3.0

Table of Contents

1 Description

Reference Label Generation Rules for the Thai Language


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


The repertoire contains 68 code points for letters used in the Thai language. In addition, three sequences have been defined. The sequence U+0E4D U+0E32 (ํา) was defined to replace the disallowed U+0E33 (SARA AM) and to facilitate implementation of the WLE rule follows-consonant-tone as a context rule. The other two sequences were defined to restrict U+0E45 (LAKKHANGYAO) from appearing in any context other than these sequences. Accordingly, while U+0E45 (ๅ) is not listed by itself this brings the total of code points avaliable for letters to 69.

The repertoire is a subset of [Unicode 6.3]. For more detail, see Section 5, "Repertoire" in [Proposal-Thai]. (The proposal cited has been adopted for the Thai 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); Thai digits, U+0E50 (๐) to U+0E59 (๙); U+002D (-) HYPHEN-MINUS; the abbreviation mark U+0E2F (ฯ) THAI CHARACTER PAIYANNOI; and the repetition mark U+0E46 (ๆ) THAI CHARACTER MAIYAMOK. Also, a special sequence using the abbreviation mark has been added for a total of 95 repertoire elements.

Each code point or range is tagged with the script or scripts that the code point is used with, and one or more references documenting sufficient justification for inclusion in the repertoire, see "References" below.


This LGR defines no variants for letters, see Section 6, "Variants" in [Proposal-Thai].

Digit Variants: All Thai 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 strong resemblance between Thai and Khmer digits, and certain Lao digits. In addition, Thai 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.

Character Classes

The Thai Script is an abugida in which consonant–vowel sequences are written as a unit: each unit is based on a consonant letter, and vowel, tone mark or diacritic notation are secondary. It is written with the combining marks stacked above or below the base consonant, like diacritics in European languages. However, although the concepts are quite similar, the implementations are significantly different.

Consonants: There are 44 characters that are classified as consonants; code points from this subset have been given the tag "cons". See Section 5.1, "Consonants" in [Proposal-Thai].

Vowels: The 18 vowel symbols pronounced after a consonant are non-sequential: they can be located before (lv) , after (fv), above (av) or below (bv) the consonant, or in a combination of these positions, code points from this subset have been given the tags "fv1","fv2", "fv3", "av", "bv", or "lv". There are three code point sequences defined that include vowels. (Code point sequences do not carry tag values; instead, for code point sequences the subset values are identified in comments). See Section 5.2, "Vowels" in [Proposal-Thai].

Tones: There are 5 phonemic tones: mid, low, falling, high, and rising. These 5 tones are represented by 4 tone marks plus the absence of a mark. Code points from this subset have been given the tag "tone". See section 5.3, "Tone Marks" in [Proposal-Thai].

Diacritical Marks: There are 3 above diacritic symbols that have been included here and given the tag "ad". They differ in their frequency and purpose of usage. See also the discussion in Section 5.,4 "Diacritics" in [Proposal-Thai].

A fourth above diacritic, U+0E4E (YAMAKKAN), has been excluded from the Root Zone LGR repertoire because it is rarely used in Modern Thai or even in older Pali manuscripts; it is more common to replace it with U+0E3A (PHINTHU), a below diacritic, which has been given the tag "bd". Moreover, excluding U+0E4E (YAMAKKAN) also eliminates the chance of confusion between U+0E4E (YAMAKKAN) and U+0E4C (THANTHAKHAT). Both look similar, are always placed at the same position in the word cell, and they are normally displayed in a small size.

Abbreviation Mark: The abbreviation mark (or ellipsis) U+0E2F (PAIYANNOI) should not be at the beginning position and must end the label. An exception to this rule has been provided for by a special sequence.

Repetition Mark: The repetition mark U+0E46 (MAIYAMOK) repeats anything before it. Therefore, it should not be at the beginning position. The repetition mark must not be followed by any combining mark, or follow a leading vowel to prevent unstable rendering. A repetition mark may be repeated. A context rule has been defined to limit the repetition mark to acceptable context, however, some of the restrictions are taken care of by other rules, for example, the rule that leading vowel must be followed by a consonant.

Thai Digits: U+0E50 (๐) to U+0E59 (๙) are a set of Thai-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

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].

Thai-specific Rules

The rules provided in this LGR as described in Section 7 of [Proposal-Thai] reasonably restrict labels so that they conform to Thai syllable structure. These constraints are exclusively presented as context rules.

The rules are:

Methodology and Contributors

This reference LGR for Thai for the 2nd Level has been developed by Michel Suignard and Asmus Freytag, based on the Root Zone LGR for Thai and information contained or referenced therein, see [RZ-LGR-4-Thai]. 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 Thai script, that this reference LGR is based on, was developed by the Thai Generation Panel. For more information on methodology and contributors to the underlying Root Zone LGR, see Sections 4 and 8 in [Proposal-Thai], as well as [RZ-LGR-Overview].

Changes from Version 1

Language tag has been updated.


The following general references are cited in this document:

ICANN, "Guidelines for Developing Reference LGRs for the Second Level, (Los Angeles, California: ICANN, 27 May 2020),
Proposal for a Thai Script Root Zone LGR, 25 May 2017,
[RFC 7940]
Davies, K. and A. Freytag, "Representing Label Generation Rulesets Using XML", RFC 7940, August 2016,
Integration Panel, "Root Zone Label Generation Rules - LGR-4: Overview and Summary", 5 November 2020 (PDF),
ICANN, Root Zone Label Generation Rules for the Thai Script (und-Thai) , 5 November 2020 (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)

For references consulted particularly in designing the repertoire for the Thai script for the second level. please see details in the Table of References below. Reference [0] refers to the Unicode Standard version in which corresponding code points were initially encoded. References [100] and [101] correspond to sources given in [Proposal-Thai] for justifying the inclusion of for the corresponding code points. Entries in the table may have multiple source reference values. Reference [150] indicates the source for common rules.

2 Repertoire

Repertoire Summary

Number of elements in repertoire 95
Number of code points
for each script
Thai 80
Common 11
Number of code points 91
Number of sequences 4
Longest code point sequence 3
Code points defined via sequence 1

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.

Some code points that may be part of a valid label under this LGR only occur as part of one or more sequences. Such code points are not listed individually in the table.

For any code point or sequence for which a variant is defined, additional information is provided in the Variants column. See also the legend provided below the table.

Glyph Script Name Ref Tags Required Context Variants Comment
U+002D - Common HYPHEN-MINUS [0] Hyphen not: hyphen-minus-disallowed  
U+0030 0 Common DIGIT ZERO [0] Common-digit   set 1
U+0031 1 Common DIGIT ONE [0] Common-digit   set 2
U+0032 2 Common DIGIT TWO [0] Common-digit   set 3
U+0033 3 Common DIGIT THREE [0] Common-digit   set 4
U+0034 4 Common DIGIT FOUR [0] Common-digit   set 5
U+0035 5 Common DIGIT FIVE [0] Common-digit   set 6
U+0036 6 Common DIGIT SIX [0] Common-digit   set 7
U+0037 7 Common DIGIT SEVEN [0] Common-digit   set 8
U+0038 8 Common DIGIT EIGHT [0] Common-digit   set 9
U+0039 9 Common DIGIT NINE [0] Common-digit   set 10
U+0E01 Thai THAI CHARACTER KO KAI [0], [100], [101] cons     Thai
U+0E02 Thai THAI CHARACTER KHO KHAI [0], [100], [101] cons     Thai
U+0E03 Thai THAI CHARACTER KHO KHUAT [0], [100], [101] cons     Thai
U+0E04 Thai THAI CHARACTER KHO KHWAI [0], [100], [101] cons     Thai
U+0E05 Thai THAI CHARACTER KHO KHON [0], [100], [101] cons     Thai
U+0E06 Thai THAI CHARACTER KHO RAKHANG [0], [100], [101] cons     Thai
U+0E07 Thai THAI CHARACTER NGO NGU [0], [100], [101] cons     Thai
U+0E08 Thai THAI CHARACTER CHO CHAN [0], [100], [101] cons     Thai
U+0E09 Thai THAI CHARACTER CHO CHING [0], [100], [101] cons     Thai
U+0E0A Thai THAI CHARACTER CHO CHANG [0], [100], [101] cons     Thai
U+0E0B Thai THAI CHARACTER SO SO [0], [100], [101] cons     Thai
U+0E0C Thai THAI CHARACTER CHO CHOE [0], [100], [101] cons     Thai
U+0E0D Thai THAI CHARACTER YO YING [0], [100], [101] cons     Thai
U+0E0E Thai THAI CHARACTER DO CHADA [0], [100], [101] cons     Thai
U+0E0F Thai THAI CHARACTER TO PATAK [0], [100], [101] cons     Thai
U+0E10 Thai THAI CHARACTER THO THAN [0], [100], [101] cons     Thai
U+0E11 Thai THAI CHARACTER THO NANGMONTHO [0], [100], [101] cons     Thai
U+0E12 Thai THAI CHARACTER THO PHUTHAO [0], [100], [101] cons     Thai
U+0E13 Thai THAI CHARACTER NO NEN [0], [100], [101] cons     Thai
U+0E14 Thai THAI CHARACTER DO DEK [0], [100], [101] cons     Thai
U+0E15 Thai THAI CHARACTER TO TAO [0], [100], [101] cons     Thai
U+0E16 Thai THAI CHARACTER THO THUNG [0], [100], [101] cons     Thai
U+0E17 Thai THAI CHARACTER THO THAHAN [0], [100], [101] cons     Thai
U+0E18 Thai THAI CHARACTER THO THONG [0], [100], [101] cons     Thai
U+0E19 Thai THAI CHARACTER NO NU [0], [100], [101] cons     Thai
U+0E1A Thai THAI CHARACTER BO BAIMAI [0], [100], [101] cons     Thai
U+0E1B Thai THAI CHARACTER PO PLA [0], [100], [101] cons     Thai
U+0E1C Thai THAI CHARACTER PHO PHUNG [0], [100], [101] cons     Thai
U+0E1D Thai THAI CHARACTER FO FA [0], [100], [101] cons     Thai
U+0E1E Thai THAI CHARACTER PHO PHAN [0], [100], [101] cons     Thai
U+0E1F Thai THAI CHARACTER FO FAN [0], [100], [101] cons     Thai
U+0E20 Thai THAI CHARACTER PHO SAMPHAO [0], [100], [101] cons     Thai
U+0E21 Thai THAI CHARACTER MO MA [0], [100], [101] cons     Thai
U+0E22 Thai THAI CHARACTER YO YAK [0], [100], [101] cons     Thai
U+0E23 Thai THAI CHARACTER RO RUA [0], [100], [101] cons     Thai
U+0E24 Thai THAI CHARACTER RU [0], [100], [101] fv3     Thai
U+0E24 U+0E45 ฤๅ {Thai} THAI CHARACTER RU + THAI CHARACTER LAKKHANGYAO [0], [100], [101] [fv3] + U+0E45     fv2, Thai
U+0E25 Thai THAI CHARACTER LO LING [0], [100], [101] cons     Thai
U+0E26 Thai THAI CHARACTER LU [0], [100], [101] fv3     Thai
U+0E26 U+0E45 ฦๅ {Thai} THAI CHARACTER LU + THAI CHARACTER LAKKHANGYAO [0], [100], [101] [fv3] + U+0E45     fv2, Thai
U+0E27 Thai THAI CHARACTER WO WAEN [0], [100], [101] cons     Thai
U+0E28 Thai THAI CHARACTER SO SALA [0], [100], [101] cons     Thai
U+0E29 Thai THAI CHARACTER SO RUSI [0], [100], [101] cons     Thai
U+0E2A Thai THAI CHARACTER SO SUA [0], [100], [101] cons     Thai
U+0E2B Thai THAI CHARACTER HO HIP [0], [100], [101] cons     Thai
U+0E2C Thai THAI CHARACTER LO CHULA [0], [100], [101] cons     Thai
U+0E2D Thai THAI CHARACTER O ANG [0], [100], [101] cons     Thai
U+0E2E Thai THAI CHARACTER HO NOKHUK [0], [100], [101] cons     Thai
U+0E2F Thai THAI CHARACTER PAIYANNOI [0], [100], [101] abbr follows-any-precedes-end   Thai
U+0E2F U+0E25 U+0E2F ฯลฯ {Thai} THAI CHARACTER PAIYANNOI + THAI CHARACTER LO LING + THAI CHARACTER PAIYANNOI [0], [100], [101] [abbr] + [cons] + [abbr] follows-any-precedes-end   Thai
U+0E30 Thai THAI CHARACTER SARA A [0], [100], [101] fv1 follow-consonant-tone-sara-aa   Thai
U+0E31 Thai THAI CHARACTER MAI HAN-AKAT [0], [100], [101] av between-consonant-and-ct   Thai
U+0E32 Thai THAI CHARACTER SARA AA [0], [100], [101] fv1, sara-aa follows-consonant-tone   Thai
U+0E34 Thai THAI CHARACTER SARA I [0], [100], [101] av follows-consonant   Thai
U+0E35 Thai THAI CHARACTER SARA II [0], [100], [101] av follows-consonant   Thai
U+0E36 Thai THAI CHARACTER SARA UE [0], [100], [101] av follows-consonant   Thai
U+0E37 Thai THAI CHARACTER SARA UEE [0], [100], [101] av follows-consonant   Thai
U+0E38 Thai THAI CHARACTER SARA U [0], [100], [101] bv follows-consonant   Thai
U+0E39 Thai THAI CHARACTER SARA UU [0], [100], [101] bv follows-consonant   Thai
U+0E3A Thai THAI CHARACTER PHINTHU [0], [100], [101] bd follows-consonant   = phinthu; Thai
U+0E40 Thai THAI CHARACTER SARA E [0], [100], [101] lv precedes-consonant   Thai
U+0E41 Thai THAI CHARACTER SARA AE [0], [100], [101] lv precedes-consonant   Thai
U+0E42 Thai THAI CHARACTER SARA O [0], [100], [101] lv precedes-consonant   Thai
U+0E43 Thai THAI CHARACTER SARA AI MAIMUAN [0], [100], [101] lv precedes-consonant   Thai
U+0E44 Thai THAI CHARACTER SARA AI MAIMALAI [0], [100], [101] lv precedes-consonant   Thai
U+0E46 Thai THAI CHARACTER MAIYAMOK [0], [100], [101] rep follows-any-precedes-rep-cons-lv-end   Thai
U+0E47 Thai THAI CHARACTER MAITAIKHU [0], [100], [101] ad follows-consonant   = maitaikhu; Thai
U+0E48 Thai THAI CHARACTER MAI EK [0], [100], [101] tone follows-consonant-av-bv   Thai
U+0E49 Thai THAI CHARACTER MAI THO [0], [100], [101] tone follows-consonant-av-bv   Thai
U+0E4A Thai THAI CHARACTER MAI TRI [0], [100], [101] tone follows-consonant-av-bv   Thai
U+0E4B Thai THAI CHARACTER MAI CHATTAWA [0], [100], [101] tone follows-consonant-av-bv   Thai
U+0E4C Thai THAI CHARACTER THANTHAKHAT [0], [100], [101] ad follows-consonant-av-bv   = thanthakhat; Thai
U+0E4D Thai THAI CHARACTER NIKHAHIT [0], [100], [101] ad follows-consonant-av-bv   = nikhahit; Thai
U+0E4D U+0E32 ํา {Thai} THAI CHARACTER NIKHAHIT + THAI CHARACTER SARA AA [0], [100], [101] [ad] + [fv1, sara-aa] follows-consonant-tone   = sara am sequence; Thai
U+0E50 Thai THAI DIGIT ZERO [0] Thai-digit   set 1  
U+0E51 Thai THAI DIGIT ONE [0] Thai-digit   set 2  
U+0E52 Thai THAI DIGIT TWO [0] Thai-digit   set 3  
U+0E53 Thai THAI DIGIT THREE [0] Thai-digit   set 4  
U+0E54 Thai THAI DIGIT FOUR [0] Thai-digit   set 5  
U+0E55 Thai THAI DIGIT FIVE [0] Thai-digit   set 6  
U+0E56 Thai THAI DIGIT SIX [0] Thai-digit   set 7  
U+0E57 Thai THAI DIGIT SEVEN [0] Thai-digit   set 8  
U+0E58 Thai THAI DIGIT EIGHT [0] Thai-digit   set 9  
U+0E59 Thai THAI DIGIT NINE [0] Thai-digit   set 10  


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.
The shape displayed depends on the fonts available to your browser.
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.
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 “+”.
Links to the references associated with the code point or sequence, if any.
LGR-defined tag values. Any tags matching the Unicode script property are suppressed in this view. For sequences, the tags for all member code points are shown in [] for information; sequences as such do not have tags.
Required Context
Link to a rule defining the required context a code point or sequence must satisfy. If prefixed by “not:” identifies a context that must not occur.
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.
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. If present, the symbol ⍟ marks a default item shared among a set of LGRs.

3 Variant Sets

Variant Set Summary

Number of variant sets 10
Largest variant set 2
Variants by Type
blocked 20

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.

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

By convention, the smaller of the two code points in a variant mapping pair.
By convention, the larger of the two code points in a variant mapping pair.
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.
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.
One or more reference IDs (optional). A “/” separates references for reverse / forward mappings, if different.
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
0030 0 0E50 blocked   ASCII digit variant / Thai digit variant

Variant Set 2 — 2 Members

Source Glyph Target Glyph   Type Ref Comment
0031 1 0E51 blocked   ASCII digit variant / Thai digit variant

Variant Set 3 — 2 Members

Source Glyph Target Glyph   Type Ref Comment
0032 2 0E52 blocked   ASCII digit variant / Thai digit variant

Variant Set 4 — 2 Members

Source Glyph Target Glyph   Type Ref Comment
0033 3 0E53 blocked   ASCII digit variant / Thai digit variant

Variant Set 5 — 2 Members

Source Glyph Target Glyph   Type Ref Comment
0034 4 0E54 blocked   ASCII digit variant / Thai digit variant

Variant Set 6 — 2 Members

Source Glyph Target Glyph   Type Ref Comment
0035 5 0E55 blocked   ASCII digit variant / Thai digit variant

Variant Set 7 — 2 Members

Source Glyph Target Glyph   Type Ref Comment
0036 6 0E56 blocked   ASCII digit variant / Thai digit variant

Variant Set 8 — 2 Members

Source Glyph Target Glyph   Type Ref Comment
0037 7 0E57 blocked   ASCII digit variant / Thai digit variant

Variant Set 9 — 2 Members

Source Glyph Target Glyph   Type Ref Comment
0038 8 0E58 blocked   ASCII digit variant / Thai digit variant

Variant Set 10 — 2 Members

Source Glyph Target Glyph   Type Ref Comment
0039 9 0E59 blocked   ASCII digit variant / Thai digit variant

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
above-vowel Tag=av 5 {0E31 0E34-0E37}   Any Thai above vowel
below-vowel Tag=bv 2 {0E38-0E39}   Any Thai below vowel
consonant Tag=cons 44 {0E01-0E23 0E25 0E27-0E2E}   Any Thai consonant
leading-vowel Tag=lv 5 {0E40-0E44}   Any Thai leading vowel
repetition Tag=rep 1 {0E46}   The Thai repetition mark, MAIYAMOK
sara-aa Tag=sara-aa 1 {0E32}   Thai SARA AA
tone Tag=tone 4 {0E48-0E4B}   Any Thai tone mark
c-av-bv combined =
[[:consonant:] ∪ [:above-vowel:] ∪ [:below-vowel:]]
51 {0E01-0E23 0E25 0E27-0E2E 0E31 0E34-0E39}   Any Thai consonant, vowel-above or vowel-below
ct combined =
[[:consonant:] ∪ [:tone:]]
48 {0E01-0E23 0E25 0E27-0E2E 0E48-0E4B}   Any Thai consonant or tone mark
ctaa combined =
[[:consonant:] ∪ [:tone:] ∪ [:sara-aa:]]
49 {0E01-0E23 0E25 0E27-0E2E 0E32 0E48-0E4B}   Any Thai consonant, tone or sara-aa
common-digits Tag=Common-digit 10 {0030-0039}   Digits from the ASCII range; ⍟
thai-digits Tag=Thai-digit 10 {0E50-0E59}   Thai digits
hyphen Tag=Hyphen 1 {002D}   The Hyphen-minus character ⍟
implicit Tag=abbr 1 {0E2F}   The character tagged as abbr
implicit Tag=ad 3 {0E47 0E4C-0E4D}   Any character tagged as ad
implicit Tag=bd 1 {0E3A}   The character tagged as bd
implicit Tag=fv1 2 {0E30 0E32}   Any character tagged as fv1
implicit Tag=fv3 2 {0E24 0E26}   Any character tagged as fv3
implicit Tag=sc:Thai 80 {0E01-0E32 0E34-0E3A 0E40-0E44 0E46-0E4D 0E50-0E59}   Any character tagged as Thai
implicit Tag=sc:Zyyy 11 {002D 0030-0039}   Any character tagged as Common


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 "...".
A named or implicit class defined by all code points that share the given tag value (ttt).
An anonymous class implicitly defined based on tag value and for which there is no named equivalent.
A named class defined by set operations on other classes using the following syntax:
[: :] - 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.
∪, ∩, ∖, ∆ - set operators
Sets may be combined by set operators ( = union, = intersection, = difference, = symmetric difference).

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
Anchor Used as
Ref Comment
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)..[:hyphen:])← ⚓︎)   C [150] RFC 5891 restrictions on placement of U+002D (-) ⍟
precedes-consonant ⚓︎ →([:consonant:])   C   WLE 7.2: check if current cp is preceding a consonant
follows-consonant ([:consonant:])← ⚓︎   C   WLE 7.3: check if current cp is following a consonant
between-consonant-and-ct ([:consonant:])← ⚓︎ →([:ct:])   C   WLE 7.4: check if current cp is in between a consonant and either tone or consonant
follow-consonant-tone-sara-aa ([:ctaa:])← ⚓︎   C   WLE 7.5: U+0E30 (THAI CHARACTER SARA A, ะ) can follow a consonant, a tone or U+0E32 (THAI CHARACTER SARA AA, า)
follows-consonant-tone ([:ct:])← ⚓︎   C   WLE 7.6, 7.9: check if current cp is following a consonant or a tone
follows-consonant-av-bv ([:c-av-bv:])← ⚓︎   C   WLE 7.7, 7.8: A tone-mark, THANTHAKHAT, NIKAHIT can only follow a consonant, above-vowel or below-vowel
follows-any-precedes-end (.)← ⚓︎ →((end))   C [102] WLE SL1: An abbreviation mark, PAIYANNOI cannot be at the beginning of the label and must end it
follows-any-precedes-rep-cons-lv-end (.)← ⚓︎ →([:consonant:]|[:repetition:]|[:leading-vowel:]|(end))   C [102] WLE SL2: A repetition mark, MAIYAMOK cannot be at the beginning of the label and must be followed by itself, a consonat or a leading vowel
digit-mixing ([:common-digits:].*[:thai-digits:])|([:thai-digits:].*[:common-digits:])       restrictions on mixing digits


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.
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).
∅= - empty set
Indicates that the following set is empty because of the result of set operations, or because none of its elements is part of the repertoire defined here. A rule with a non-optional empty set never matches.
⍟ - 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 [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 at least one variant is in {out-of-repertoire-var} invalid   any variant label with a code point out of repertoire is invalid ⍟
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) ⍟


{...} - 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

The following lists the references cited for specific code points, variants, classes, rules or actions in this LGR. For General references refer to the "References" section in the Description.

[0] The Unicode Standard 1.1
Any code point originally encoded in Unicode 1.1
[100] Thai Industrial Standard (TIS) 1566-2541(1988)
[101] Computers and the Thai Language
[102] Thai Generation Panel experts, private communication during review for second level
[150] RFC 5891, Internationalized Domain Names in Applications (IDNA): Protocol