Reference Label Generation Rules for the Malayalam script

Overview

This document specifies a reference set of Label Generation Rules (LGR) for the Malayalam script for the second level. The starting point for the development of this LGR can be found in the related Root Zone LGR [RZ-LGR-3-Mlym]. For details and additional background on the script, see "Proposal for a Malayalam Script Root Zone Label Generation Ruleset (LGR) [Proposal-Malayalam]". The format of this file follows [RFC 7940].

This is a DRAFT document released for public comments and not final. Please see the announcement on the ICANN website for public comments on the Second Level Reference LGRs for details on how to submit comments.

Repertoire

The repertoire contains 70 code points for letters used in the Malayalam language in addition to ten sequences used in defining variants. The repertoire is a subset of [Unicode 6.3]. For more detail, see Section 5, "Repertoire" in [Proposal-Malayalam]. (The proposal cited has been adopted for the Malayalam 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), and U+002D (-) HYPHEN-MINUS for a total of 91 repertoire elements.

Code points outside the Malayalam 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 or range is tagged with the script or scripts that the code point is used with, one or more tag values denoting character category, and one or more references documenting sufficient justification for inclusion in the repertoire, see "References" below.

Variants

This reference LGR is designed for use in zones shared by more than one script. Where appropriate, cross-script variants have been defined to mutually exclude labels from different scripts that could otherwise be substituted by the users. Once a label has been delegated for one script, any variant labels from other scripts consisting of cross-script variants would be blocked. Any label containing at least one code point that is not a cross-script variant would be considered distinct. Because of that, even large numbers of defined cross-script variants generally do not lead to a high percentage of labels experiencing a collision.

This LGR defines in-script variants and cross-script variants as described in Section 6, "Variants", in "[Proposal-Malayalam]". One in-script variant is due to the multiple ways to write the conjunct “nta" in Malayalam. Cross-script variants are mainly defined for Tamil code points.

Digit Variants: The Malayalam reference LGR does not include native digits, so there are no variants defined. By transitivity, all ASCII digits are semantic variants of any cross-script native digits. Any Malayalam label that is otherwise a cross-script variant of a label in another script, will remain a variant if both labels add digits of the same value in the same position, irrespective of whether they are ASCII or (in the case of the other script) native digits. However, some Malayalam letters are homoglyphs of Malayalam native digits. For example, U+0D6A (൪) MALAYALAM DIGIT FOUR and U+0D6F (൯) MALAYALAM DIGIT NINE are homoglyphs of U+0D7C (ർ) MALAYALAM CHILLU RR and U+0D7D (ൽ) MALAYALAM CHILLU N respectively. Should an extension be contemplated that adds native digits, these might require variant relations. At the same time, however, the native digits would normally also be semantic variants of the European digits. In any zone containing multiple scripts, these two types of variant relation for digits may lead to complication once transitivity is applied.

Variant Disposition: All 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, the other one equivalent variant label should be blocked. There is no preference among these variants.

The specification of variants in this reference LGR follows the guidelines in [RFC 8228].

Context Rules for Variants: some of the variants defined in this LGR are "effective null variants", that is, some code points in the source map to "nothing" in the target with all other code points unchanged. (Because mappings are symmetric, it does not matter whether it is the forward or reverse mapping that maps to "null"). Such variants require a context rule to keep the variant set well-behaved. Symmetry requires the same context rule for both forward and reverse mappings.

In other cases, the sequences or code points making up source and target are constrained by context rules on the code points. In such a case, any variants require context rules that match the intersection between the contexts for both source and target; otherwise a sequence might be considered valid in some variant label when it would not be valid in an equivalent context in an original label.

Character Classes

The basic characters in Malayalam are classified here into the following categories: Consonants, Vowels, Matra and Reordrant Vowel Diacritics, Halant, Visargam, Anusvaram and Chillu letters.

Consonant: Malayalam is written in an abugida script derived ultimately from Brahmi in which every consonant carries an inherent /a/. More details in Section 3.8, "The Structure of Malayalam Script" of [Proposal-Malayalam].

Vowels: Like consonants, the independent vowels can follow any other class of code points in a label.

Matra: Vowels other than the inherent vowel are written as vowel diacritics. They are referred to as Matras, when they follow consonants. More details in Section 3.8, "The Structure of Malayalam Script" of [Proposal-Malayalam].

Halant: A consonant can be combined with another consonant or conjunct using the halant encoded as U+0D4D (്) MALAYALAM SIGN VIRAMA. This strips off the implicit vowel. More details in Section 3.8, "The Structure of Malayalam Script" of [Proposal-Malayalam].

Anusvaram: In Malayalam, anusvara represented as U+0D02 (ം), simply represents a consonant /m/ after a vowel, though this /m/ may be assimilated to another nasal consonant. More details in Section 3.8, "The Structure of Malayalam Script" of [Proposal-Malayalam].

Visargam: The visarga represents a consonant /h/ after a vowel, and is transliterated as ḥ. Like the anusvara, it is a special symbol, and is never followed by an inherent vowel or another vowel. More details in Section 3.8, "The Structure of Malayalam Script" of [Proposal-Malayalam].

Chillu: Chillu letters, aka "Chillaksharam", represent pure consonants without any vowel sound. More details in Section 3.8, "The Structure of Malayalam Script" of [Proposal-Malayalam].

Reordrant: Vowel diacritics, part of which reorder around the preceding character or conjunct. More details in Sections 6.1 "In-script Variants" and 7.1.1 "Variables or definitions" of [Proposal-Malayalam].

Whole Label Evaluation (WLE) and Context Rules

Common Rules

• Hyphen Restrictions — restrictions on the allowable placement of hyphens (no leading/ending hyphen and no hyphen in positions 3 and 4). These restrictions are described in section 4.2.3.1 of RFC 5891 [150]. They are implemented here as context rule on U+002D (-) HYPHEN-MINUS.
• Leading Combining Marks — restrictions on the allowable placement of combining marks (no leading combining mark). This rule is described in section 4.2.3.2 of RFC 5891 [150].
• One non-ASCII code point — An IDN label must contain one non-ASCII code point, as described in Section 4.2.4 of RFC 5891 [150].

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].

Malayalam-specific Rules

There are constraints on the context for many of the character classes in Malayalam. A corresponding set of context and whole label rules has been formulated for LGR specification, as described in Section 7, "Whole Label Evaluation (WLE) Rules" in [Proposal-Malayalam].

The following symbols are used in the WLE rules:
C → Consonant
M → Matra
V → Vowel
B → Anusvara
X → Visarga
D → Chandrabindu
H → Halant
L → Chillu
R → Reordrant Matra

Note: the Reordrant Matras include one sequence. That requires an auxiliary rule R in addition to class R.

The rules are:

• 1. H: must be preceded by C or U+0D41 (ു) VOWEL SIGN U
• 2. M: must be preceded by C
• 3. B: must be preceded by C, V or M
• 4. X: must be preceded by C, V or M
• 5. L: cannot be preceded by B, X or H
• 6. A label does not begin with L

The following context rules apply to Consonants U+0D33 (ള) RRA and U+0D31 (റ) LLA as well as to sequences ending in these code points:

• 7. The character U+0D33 (ള) cannot immediately follow U+0D33 (ള), except as part of a defined sequence
• 8. The character U+0D31 (റ) cannot immediately follow U+0D31 (റ), except as part of a defined sequence

Note: the implementation of Rules 7 & 8 relies on the fact that a context rule is not evaluated between code points in the same sequence. For example, if a label contains two adjacent U+0D33 U+0D33 (ളള) surrounded by other code points , the two code points can only be interpreted as the sequence U+0D33 U+0D33 (ളള) because a singleton U+0D33 (ള) is not allowed to be followed by another U+0D33 (ള).

The following context rule applies to the sequence Chillu N + Halant (U+0D7B U+0D4D):

• 9. The sequence U+0D7B U+0D4D (ൻ്) must be preceded by C, L, M, V and must be followed by U+0D31 (റ) RRA

The following context rules apply to variants:

• V1: A variant is defined when followed by U+0D31 (റ)
• V2: A variant preceded by 0D33+Halant or followed by R or Halant+0D33 is not defined
• V3: A variant preceded by 0D31+Halant or followed by R or Halant+0D31 is not defined

These rules ensure that the variant label sets are well-behaved in cases where variant sequences overlap.

Note: any sequences ending with 0D31 would overlap with the various variant sequences beginning with 0D31, therefore this LGR drops the 0D31 from the end of these sequences, but adds context rule V1, when="followed-by-0D31" instead. Because all the variants also end in 0D31, this results in the same generated variants as if the sequences had been defined with trailing U+0D31 (റ), but now the variants are well-behaved in all contexts.

More details in Section 6.1, "In-script Variants" and Section 7, "Whole Label Evaluation Rules (WLE)" of [Proposal-Malayalam].

There are a number of cross-script homoglyphs to U+0D31 (റ) RRA, which would interact with the definition of in-script sequences and variants, leading to unacceptable complexity. These variants would affect only labels made solely of letters RRA, and no other labels. Rule 8 already restricts labels consisting solely of copies of the letter RRA to either "റ" or "ററ", thus allowing only two such labels. The following rule disallows the remaining two possible labels, obviating any need to define these cross-script variants.

• 10. A label cannot consist solely of letters U+0D31 (റ) RRA

Malayalam-specific actions

WLE rules 6 and 10 trigger Malayalam-specific actions to invalidate any original and variant labels not satisfying the constraints. See Section 7, "Whole Label Evaluation (WLE) Rules" in [Proposal-Malayalam].

Methodology and Contributors

This reference LGR for Malayalam for the 2nd Level has been developed by Michel Suignard and Asmus Freytag, based on the latest available Root Zone LGR for Malayalam and information contained or referenced therein, see [RZ-LGR-3-Mlym]. Suitable extensions for the second level have been applied according to the [Guidelines]. The original proposal for a Root Zone LGR for the Malayalam script, that this reference LGR is based on, was developed by the Neo-Brahmi Generation Panel (NBGP). For more information on methodology and contributors to the underlying Root Zone LGR, see [Proposal-Malayalam].

References

The following general references are cited in this document:

[Guidelines]

ICANN, "Guidelines for Developing Reference LGRs for the Second Level, (Los Angeles, California: ICANN, 27 May 2020),
https://www.icann.org/en/system/files/files/lgr-guidelines-second-level-06jan16-en.pdf

[Proposal-Malayalam]

Neo-Brahmi Generation Panel, "Proposal for a Malayalam Script Root Zone Label Generation Ruleset (LGR)", 7 May 2020,
https://www.icann.org/en/system/files/files/proposal-malayalam-lgr-07may19-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-Mlym]

ICANN, Root Zone Label Generation Rules for the Malayalam Script (und-Mlym) , 10 July 2019 (XML)
https://www.icann.org/sites/default/files/lgr/lgr-3-malayalam-script-10jul19-en.xml

[RZ-LGR-Overview]

Integration Panel, "Root Zone Label Generation Rules - LGR-3: Overview and Summary", 01 March 2020 (PDF),
https://www.icann.org/sites/default/files/lgr/lgr-3-overview-10jul19-en.pdf

[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 references consulted particularly in designing the repertoire for the Malayalam script for the Root Zone please see details in the Table of References below. References [0] to [9] refer to the Unicode Standard versions in which the corresponding code points were initially encoded. Reference [106] corresponds to a source given in [Proposal-Malayalam] justifying the inclusion of the corresponding code points. Entries in the table may have multiple source reference values.

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	36	{0D15-0D28 0D2A-0D39}		Any Malayalam consonant
V	Tag=Vowel	13	{0D05-0D0B 0D0E-0D10 0D12-0D14}		Any Malayalam independent vowel
M	Tag=Matra	12	{0D3E-0D43 0D46-0D48 0D4A-0D4B 0D57}		Any Malayalam vowel sign (matra)
H	Tag=Halant	1	{0D4D}		The Malayalam Halant/Virama
B	Tag=Anusvaram	1	{0D02}		The Malayalam Anusvaram
X	Tag=Visargam	1	{0D03}		The Malayalam Visargam
L	Tag=Chillu	6	{0D7A-0D7F}		Any Malayalam chillu (consonant without any vowel sound)
R	Tag=R	5	{0D46-0D48 0D4A-0D4B}		Any Malayalam reordrant vowel sign
hyphen	Tag=Hyphen	1	{002D}		The Hyphen-minus character ⍟
implicit	Tag=Common-digit	10	{0030-0039}		Any character tagged as Common-digit
implicit	Tag=sc:Mlym	70	{0D02-0D03 0D05-0D0B 0D0E-0D10 0D12-0D28 0D2A-0D39 0D3E-0D43 0D46-0D48 0D4A-0D4B 0D4D 0D57 0D7A-0D7F}		Any character tagged as Malayalam
implicit	Tag=sc:Orya	1	{0B20}		Any character tagged as Oriya
implicit	Tag=sc:Taml	6	{0B9C 0BAE 0BB5 0BBF 0BC6-0BC7}		Any character tagged as Tamil
implicit	Tag=sc:Zyyy	11	{002D 0030-0039}		Any character tagged as Common

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}]]	✔				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 (-) ⍟
follows-C-or-0D41	([:C:]|\u0D41)← ⚓		✔	C		Section 7, WLE 1: Rule 1: H must be preceded by C or 0D41
follows-C	([:C:])← ⚓		✔	C		Section 7, WLE 2: M must be preceded by C
follows-C-V-or-M	([:C:]|[:V:]|[:M:])← ⚓		✔	C		Section 7, WLE 3: B must be preceded by C, V or M and WLE 4: X must be preceded by C, V or M
follows-B-X-or-H	([:B:]|[:X:]|[:H:])← ⚓		✔	C		Section 7, WLE 5: L cannot be preceded by B, X or H
begins-with-L	(start)[:L:]	✔				Section 7, WLE 6: Label does not begin with L
follows-0D33	(\u0D33)← ⚓		✔	C		Section 7, WLE 7. The character ള (0D33) cannot immediately follow ള (0D33), except as part of a defined sequence
follows-0D31	(\u0D31)← ⚓		✔	C		Section 7, WLE 8. The character റ (0D31) cannot immediately follow റ (0D31), except as part of a defined sequence
follows-C-L-M-V-and-followed-by-03D1	([:C:]|[:L:]|[:M:]|[:V:])← ⚓ →(\u0D31)		✔	C		Section 7, WLE 9: Sequence 0D7B 0D4D must be preceded by C, L, M, V and must be followed by റ (0D31)
reordrant-matra	[:R:]|\u0D4D\u0D30					Reordrant matras, including sequence U+0D4D U+0D30 (്ര)
followed-by-R	⚓ →((:reordrant-matra:))		✔	V		variant not defined if followed by reordrant matra
followed-by-0D31	⚓ →(\u0D31)		✔	V		Section 6.1, V1: A variant is defined when followed by 0D31
follows-0D33-0D4D-or-followed-by-0D4D-0D33-or-R	((\u0D33\u0D4D)← ⚓)|(⚓ →(\u0D4D\u0D33|(:reordrant-matra:)))		✔	V		Section 6.1, V2: variant not defined if preceded by 0D33+Halant or followed by Halant+0D33 or R
follows-0D31-0D4D-or-followed-by-0D4D-0D31-or-R	((\u0D31\u0D4D)← ⚓)|(⚓ →(\u0D4D\u0D31|(:reordrant-matra:)))		✔	V		Section 6.1, V3: variant not defined if preceded by 0D31+Halant or followed by Halant+0D31 or R
only-RRA	(start)\u0D31+(end)	✔				Section 7, WLE 10: Labels consisting solely of the letter RRA are disallowed to limit cross-script interaction
ascii-only-label	(start)[\u002D\u0030-\u0039]+(end)	✔			[150]	RFC 5891 restriction requiring at least one non-ASCII code point ⍟

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	ascii-only-label	→	invalid	[150]	ascii-only labels invalid (not IDNs) ⍟
3	if label matches	begins-with-L	→	invalid		Section 7, WLE 6: Label does not begin with L
4	if label matches	only-RRA	→	invalid		Section 7, WLE 10: Label cannot contain only RRA
5	if at least one variant is in	{out-of-repertoire-var}	→	invalid		any variant label with a code point out of repertoire is invalid ⍟
6	if at least one variant is in	{blocked}	→	blocked		any variant label containing blocked variants is blocked ⍟
7	if each variant is in	{allocatable}	→	allocatable		variant labels with all variants allocatable are allocatable ⍟
8	if any label (catch-all)		→	valid		catch all; default action ⍟