Root Zone LGR for script und-Thai (Thai) lgr-3-thai-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-Thai
Scope domain: "." (Root)
Unicode Version 6.3.0

Table of Contents

1 Description

Root Zone Label Generation Rules for the Thai Script


This file contains Label Generation Rules (LGR) for the Thai script for the Root zone. For more details on this LGR and its development, see "Proposal for a Thai Script Root Zone 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].


In addition to the 68 code points according to Section 5 “Repertoire” in [Proposal], 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 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 it brings the total of distinct code points to 69.

The repertoire only includes code points used by languages that are actively written in the Thai script. The repertoire is based on [MSR-4], which is a subset of [Unicode 6.3].

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.


According to Section 6, "Variants" in [Proposal], this LGR defines no variants.

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].

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 tag "fv1","fv2","fv3","av","bv","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].

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].

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].

The Thai GP decided to exclude a fourth above diacritic, U+0E4E (YAMAKKAN), from the 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.

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 ⍟.

Thai-specific Rules

The rules provided in this LGR as described in Section 7 of [Proposal] 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

For methodology and contributors, see Sections 4 and 8 in [Proposal], as well as [RZ-LGR-3-Overview].


The following general references are cited in this document:

Integration Panel, "Maximal Starting Repertoire — MSR-4 Overview and Rationale", 7 February 2019,
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-3: Overview and Summary", 10 July 2019 (PDF),
Integration Panel, "Label Generation Rules for the Root Zone — LGR-3", 10 July 2019 (XML),
non-normative HTML presentation:
[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 Root Zone 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] for justifying the inclusion of for the corresponding code points. Single code point or ranges may have multiple source reference values.

2 Repertoire

Repertoire Summary

Number of elements in Repertoire 71
Number of code points 68
Number of sequences 3
Longest code point sequence 2
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.

See also the legend provided below the table.

Glyph Script Name Ref Tags Required Context Comment
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]     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]     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+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+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]   follows-consonant-tone = sara am sequence; Thai


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.
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 “+”.
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.
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.
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.
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.

3 Variant Sets

This LGR does not specify any variants.

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
sara-aa Tag=sara-aa 1 {0E32}   Thai SARA AA
tone Tag=tone 4 {0E48-0E4B}   Any Thai tone mark
c-av-bv combined =
51 {0E01-0E23 0E25 0E27-0E2E 0E31 0E34-0E39}   Any Thai consonant, vowel-above or vowel-below
ct combined =
48 {0E01-0E23 0E25 0E27-0E2E 0E48-0E4B}   Any Thai consonant or tone mark
ctaa combined =
49 {0E01-0E23 0E25 0E27-0E2E 0E32 0E48-0E4B}   Any Thai consonant, tone or sara-aa
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=lv 5 {0E40-0E44}   Any character tagged as lv
implicit Tag=sc:Thai 68 {0E01-0E2E 0E30-0E32 0E34-0E3A 0E40-0E44 0E47-0E4D}   Any character tagged as Thai


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.
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}]]       Default WLE rule matching labels with leading combining marks ⍟
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


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.
start or end
(start) matches the start of the label; (end) matches the end of the label.
[: :] - 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 at least one variant is in {blocked} blocked   any variant label containing blocked variants is blocked ⍟
4 if each variant is in {allocatable} allocatable   variant labels with all variants allocatable are allocatable ⍟
5 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

[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