Root Zone LGR for script und-Thai (Thai)

This document is mechanically formatted from the 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 2017-07-26
LGR Version 2
Language und-Thai
Scope domain: "." (Root)
Unicode Version 6.3.0


Label Generation Rules for the Thai Script


This file contains Label Generation Rules (LGR) for the Thai script as would be appropriate for the Root zone. For more details on this LGR see "Proposal for a Thai Script Root Zone LGR [Proposal]". 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 (THAI CHARACTER 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 (THAI CHARACTER 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-2], which is a subset of Unicode 6.3 [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.

There are 44 characters that are classified as consonants, code points from this subset have been given the tag "cons".

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).

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"

There are 3 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 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). 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

The LGR includes the set of required default WLE rules and actions applicable to the Root Zone and defined in [MSR-2]. 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 of [Proposal].


Reference [0] refers to the Unicode Standard version in which corresponding code points were initially encoded. Reference [100] corresponds to a source given in [Proposal] for justifying the inclusion of for the corresponding code points. Single code point or ranges may have multiple source reference values.

In addition the following references are cited in this document:

Integration Panel, "Maximal Starting Repertoire — MSR-2 Overview and Rationale", 14 April 2015
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,
[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 more details for references [100] and up and [0] and up refer to the Table of References below.



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

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.

See also the legend provided below the table.

Glyph Script Name References 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 [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 [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 [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.
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 not annotated with a script value.
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 the rule defining the required context a code point or sequence must satisfy. If prefixed by "not:", identifies a context that must not occur.
If the comment in this row consists only of the code point or sequence name, it is suppressed in this view.

Variant Sets

This LGR does not specify any variants.

Classes, Rules and Actions

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 Elements: {0E31 0E34-0E37}   Any above vowel
below-vowel Tag=bv 2 Elements: {0E38-0E39}   Any below vowel
consonant Tag=cons 44 Elements: {0E01-0E23 0E25 0E27-0E2E}   Any Consonant
sara-aa Tag=sara-aa 1 Elements: {0E32}   SARA AA
tone Tag=tone 4 Elements: {0E48-0E4B}   Any tone mark
c-av-bv combined =
51 Elements: {0E01-0E23 0E25 0E27-0E2E 0E31 0E34-0E39}   Any consonant, vowel-above or vowel-below
ct combined =
48 Elements: {0E01-0E23 0E25 0E27-0E2E 0E48-0E4B}   Any consonant or tone
ctaa combined =
49 Elements: {0E01-0E23 0E25 0E27-0E2E 0E32 0E48-0E4B}   Any consonant, tone or sara-aa
implicit Tag=fv3 2 Elements: {0E24 0E26}    
implicit Tag=fv1 2 Elements: {0E30 0E32}    
implicit Tag=bd 1 Elements: {0E3A}    
implicit Tag=lv 5 Elements: {0E40-0E44}    
implicit Tag=ad 3 Elements: {0E47 0E4C-0E4D}    
implicit Tag=sc:Thai 68 Elements: {0E01-0E2E 0E30-0E32 0E34-0E3A 0E40-0E44 0E47-0E4D}    


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 (&& = intersection, - = difference, ^ = symmetric difference) or concatenated (union).

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. (Any use of context rules for variants is not indicated).

Name Used as
Used as
Anchor Regular Expression Ref Comment
leading-combining-mark     (^[[\p{gc=Mn}][∅=\p{gc=Mc}]])   Default WLE rule from MSR-2 matching labels with leading combining marks ⍟
precedes-consonant   (⚓(?=[:consonant:]))   WLE 7.2: check if current cp is preceding a consonant
follows-consonant   ((?<=[:consonant:])⚓)   WLE 7.3: check if current cp is following a consonant
between-consonant-and-ct   ((?<=[:consonant:])⚓(?=[:ct:]))   WLE 7.4: check if current cp is in between a consonant and either tone or consonant
follow-consonant-tone-sara-aa   ((?<=[:ctaa:])⚓)   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:])⚓)   WLE 7.6, 7.9: check if current cp is following a consonant or a tone
follows-consonant-av-bv   ((?<=[:c-av-bv:])⚓)   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 context for a code point.
This has a placeholder for the code point for which it is evaluated.
Regular Expression
A regular expression equivalent to the rule, shown in the standard notation with some extensions 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.
[: :] - 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
A character set defined by reference to a value for a given Unicode property [\p{prop=val}]. A set defined via "\P" indicates the set complement.
[&&,-,^] - set operators
Sets may be combined by set operators (&& = intersection, - = difference, ^ = symmetric difference) or concatenated (union).
⍟ - default rule
Rules marked with ⍟ are included by default and may or may not be triggered by any possible label under this LGR.


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.

Note: The following variant types are used in one or more actions, but are not defined in this LGR: out-of-repertoire-var, blocked, allocatable. This is not necessarily an error.

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