Label Generation Rules for Khmer

Overview

This file contains Label Generation Rules (LGR) for the Khmer script as would be appropriate for the Root zone. For more details on this LGR see "Proposal for a Khmer Script Root Zone LGR [Proposal]". The format of this file follows [RFC 7940].

Repertoire

In addition to the 71 code points according to Section 5 "Repertoire", in [Proposal], two Khmer subscript consonant sequences have been defined. The repertoire only includes code points used by languages that are actively written in the Khmer 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.

Variants

According to Section 6 "Variants", in [Proposal], two Khmer consonants are variants of each other in their subscript form only. This is captured by a variant relation between the two subscript sequences, which are listed explicitly in the repertoire.

Character Classes

Some consonants have been given the tag "base-only"; these do not take subscript form.

The character U+17C9 (៉) KHMER SIGN MUUSIKATOAN is used with a subset of first series consonants, code points from this subset have been given the tag "series-one".

The character U+17CA (៊) KHMER SIGN TRIISAP is used with subset of second series consonants and with U+1794 (ប) KHMER LETTER BA. Code points from this subset have been given the tag "series-two". The series, and the sets of code points used with these two signs are defined in [210]. The character U+17CB (់) KHMER SIGN BANTOC is used with a subset of consonants, that subset has been given the tag "series-three" [205]. The characters U+17C9 (៉) KHMER SIGN MUUSIKATOAN and U+17CA (៊) KHMER SIGN TRIISAP are collectively known as consonant shifters and have been given the tag "shifter".

The character U+17CC (៌) KHMER SIGN ROBAT has been given the tag "robat".

The character U+17C6 (ំ) KHMER SIGN NIKAHIT is used with consonants and some dependent vowels. These dependent vowels have been given a tag "dependent-vowel-1" (see Section 5.3 in [Proposal]). The character U+17C7 (ះ) KHMER SIGN REAHMUK is used with consonants and some dependent vowels. These dependent vowels have been given a tag "dependent-vowel-2" (see Section 5.3 in [Proposal]). The code point U+17B7 (ិ) KHMER VOWEL SIGN I has been given a tag "dependent-vowel-3".

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 ⍟. The default prohibition on leading combining marks is equivalent to ensuring that a label only starts with a consonant or independent-vowel.

Khmer-specific Rules

Rules provided in the LGR as described in Section 7 of [Proposal] reasonably restrict labels so that they conform to Khmer syllable structure. These constraints are presented as context rules, except for the limit on the number of consecutive subscripted consonants.

The rules are:

• Subscript-consonant — A rule that specifies allowable consonant sequence. See Section 7.2 in [Proposal]
• Subscript-consonant-limit — It limits the occurrence of subscript-consonant to two. In case of three, label is stated as invalid. See Section 7.3 in [Proposal]
• Coeng-context — A context rule for 17D2 that must have a consonant or base-only before it and a consonant after it. See Section 7.4 in [Proposal]
• Follows-consonant-robat-shifter — A context rule for those code points that must follow a consonant, robat or shifter. See Section 7.5 in [Proposal]
• Follows-series-two — A context rule for those code points that must follow series-two consonants. See Section 7.6 in [Proposal]
• Follows-series-one — A context rule for those code points that must follow series-one consonants. See Section 7.7 in [Proposal]
• Follows-consonant — A context rule for those code points that must always follow a consonant. See Section 7.8 in [Proposal]
• Follows-consonant-shifter A context rule for those code points that must always follow a consonant or shifter. See Section 7.9 in [Proposal]
• Follows-consonant-depvowel-1-shifter — A context rule for those code points that must follow consonant, shifter or dependent-vowel-1. See Section 7.10 in [Proposal]
• Follows-consonant-depvowel-2-shifter — A context rule for those code points that must follow consonant, shifter or dependent-vowel-2. See Section 7.11 in [Proposal]
• Follows-series-three — A context rule for those code points that must follow series-three consonants. See Section 7.12 in [Proposal]
• Follows-consonant-or-vowel-i — A context rule for those code points that must follow a consonant or 17B7 KHMER VOWEL SIGN I. See Section 7.13 in [Proposal]

Methodology and Contributors

For methodology and contributors, see Sections 4 and 8 of [Proposal].

References

Reference [3] refers to Unicode Standard versions in which corresponding code points were initially encoded. References [100], [203], [204], [205], [206], [207], [208], [209] & [210] correspond to sources justifying the inclusion of or classification 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:

[MSR-2]

Integration Panel, "Maximal Starting Repertoire — MSR-2 Overview and Rationale", 14 April 2015
https://www.icann.org/en/system/files/files/msr-2-overview-14apr15-en.pdf

[Proposal]

Proposal for Khmer Script Root Zone LGR, 15 August 2016,
https://www.icann.org/en/system/files/files/proposal-khmer-lgr-15aug16-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.

[Unicode 6.3]

The Unicode Consortium. The Unicode Standard, Version 6.3.0, (Mountain View, CA: The Unicode Consortium, 2013. ISBN 978-1-936213-08-5)
http://www.unicode.org/versions/Unicode6.3.0/

For more details for references [100] and up and [3] and up refer to the Table of References below.

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
consonant	Tag=consonant	33 Elements:	{1780-179C 179F-17A2}		Any consonant
consonant-but-not-base-only	combined = [[:consonant:]-[:base-only:]]	32 Elements:	{1780-179C 179F-17A0 17A2}		Any consonant that is not base-only
dependent-vowel-1	Tag=dependent-vowel-1	2 Elements:	{17B6 17BB}
dependent-vowel-2	Tag=dependent-vowel-2	5 Elements:	{17B7 17B9 17BB 17C1 17C4}
dependent-vowel-3	Tag=dependent-vowel-3	1 Elements:	{17B7}
robat	Tag=robat	1 Elements:	{17CC}
series-one	Tag=series-one	4 Elements:	{1794 179F-17A0 17A2}
series-three	Tag=series-three	9 Elements:	{1780 1784-1785 1789 178F 1793-1794 179B 179F}
series-two	Tag=series-two	7 Elements:	{1784 1789 1794 1798-179A 179C}
shifter	Tag=shifter	2 Elements:	{17C9-17CA}
implicit	Tag=base-only	1 Elements:	{17A1}
implicit	Tag=independent-vowel	12 Elements:	{17A5-17A7 17AA-17B1 17B3}
implicit	Tag=dependent-vowel	16 Elements:	{17B6-17C5}
implicit	Tag=sign	6 Elements:	{17C6-17C8 17CB 17CD 17D0}
implicit	Tag=coeng	1 Elements:	{17D2}
implicit	Tag=sc:Khmr	71 Elements:	{1780-179C 179F-17A2 17A5-17A7 17AA-17B1 17B3 17B6-17CD 17D0 17D2}

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 Trigger	Used as Context	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 ⍟
subscript-consonant				(\u17D2[:consonant-but-not-base-only:])		WLE Rule 2: allowable subscript consonant sequence
subscript-consonant-limit	✔			((:subscript-consonant:){3,3})		WLE Rule 3: more than two subscript consonants
coeng-context		✔	✔	((?<=[:consonant:])⚓(?=[:consonant-but-not-base-only:]))		WLE Rule 4: checks for 17D2 and its surrounding code points
follows-consonant-robat-shifter		✔	✔	((?<=([:shifter:]|[:consonant:]|[:robat:]))⚓)		WLE Rule 5: makes sure that dependent vowel follows a consonant or a shifter or a robat
follows-series-two		✔	✔	((?<=[:series-two:])⚓)		WLE Rule 6: checks sequence for shifter 17C9 MUUSIKATOAN
follows-series-one		✔	✔	((?<=[:series-one:])⚓)		WLE Rule 7: checks sequence for shifter 17CA TRIISAP
follows-consonant		✔	✔	((?<=[:consonant:])⚓)		WLE Rule 8: checks if sign code point or subscript consonant follows a consonant
follows-consonant-shifter		✔	✔	((?<=([:consonant:]|[:shifter:]))⚓)		WLE Rule 9: checks if 17D0 KHMER SIGN SAMYOKSANNYA follows a consonant or a shifter
follows-consonant-depvowel-1-shifter		✔	✔	((?<=([:consonant:]|[:dependent-vowel-1:]|[:shifter:]))⚓)		WLE Rule 10: checks if 17C6 KHMER SIGN NIKAHIT follows a consonant or a dependent vowel-1 or a shifter
follows-consonant-depvowel-2-shifter		✔	✔	((?<=([:consonant:]|[:dependent-vowel-2:]|[:shifter:]))⚓)		WLE Rule 11: checks if 17C7 KHMER SIGN REAHMUK follows a consonant or a dependent vowel-2 or a shifter
follows-series-three		✔	✔	((?<=[:series-three:])⚓)		WLE Rule 12: checks if 17CB KHMER SIGN BANTOC code point follows a series-three consonant
follows-consonant-or-vowel-i		✔	✔	((?<=[:consonant:][:dependent-vowel-3:]?)⚓)		WLE Rule 13: checks if 17CD KHMER SIGN TOANDAKHIAT follows a consonant or 17B7 KHMER VOWEL SIGN I (Dependent-vowel-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	subscript-consonant-limit	→	invalid		any label with more than two subscript consonants in a row 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) ⍟

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