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This document specifies a set of Label Generation Rules (LGR) for the Myanmar script for the second level domain or domains identified above. This LGR contains the full set of cross-script variants required for use with the following scripts: Georgian, Latin, Oriya and Malayalam. The starting point for the development of this LGR can be found in the related Root Zone LGR [RZ-LGR-Mymr]. The format of this file follows [RFC 7940]. This LGR is adapted from the “Reference LGR for the Second Level for the Myanmar Script” [Ref-LGR-und-Mymr], for details, see Change History below.
For details and additional background on the Myanmar script, see “Proposal for a Myanmar Script Root Zone Label Generation Rule-Set (LGR)”; [Proposal-Myanmar].
The repertoire consists of 98 Myanmar script unique code points and 65 sequences. The code point U+1063 Myanmar Tone Mark Sgaw Karen Hathi is not listed separately, but is available as part of a defined sequence, bringing the total to 99 distinct code points.
The repertoire is a subset of [Unicode 11.0.0]. For details, see Section 5, “Repertoire” in [Proposal-Myanmar]. (The proposal cited has been adopted for the Myanmar script portion of the Root Zone LGR.)
The repertoire includes code points used by languages written in Myanmar script that fall within levels 1 to 4 on the [EGIDS] scale, as well as EGIDS 5 languages which have more than 500,000 users are included in the analysis. They are Burmese, Shan, Rakhine, S’gaw Karen, Mon, Pa’O Karen. (See also [Ethnologue].) A non-exhaustive list of languages using each code point can be found in the comments. For more details, see Section 5 “Repertoire” in [Proposal-Myanmar].
Note: In this document, to avoid confusion, the term ‘Myanmar’ is used for the Myanmar script and the term ‘Burmese’ is used for the Myanmar language.
For the second level, the repertoire has been augmented with the Myanmar digits, U+1040 to U+1049, the ASCII digits, U+0030 to U+0039, and U+002D HYPHEN-MINUS, for a total of 184 repertoire elements.
Note that some languages, such as Burmese, commonly use the Myanmar digits while others, such as Shan, use the ASCII digits. Therefore, both sets of digits included, albeit with mutual exclusion. However, see the discussion under Digit Variants below as to why this necessitates some restrictions on U+1040 MYANMAR DIGIT ZERO.
Any code points outside the Myanmar Script repertoire that are targets for out-of-repertoire variants would be included here only if the variant is listed in this file. In this case they are identified as a reflexive (identity) variant of type “out-of-repertoire-var”. Whether or not they are listed, they do not form part of the repertoire.
Repertoire Listing: Each code point or range is tagged with the script or scripts with which the code point is used and one or more other character categories. For each repertoire element, one or more references document sufficient justification for inclusion in the repertoire; see the “References” below. For code points that are part of the repertoire, comments identify the languages using the code point along with their [EGIDS] level.
Unlike other LGRs for this script, which only incude the variant definitions needed when used as standalone in their zone, this LGR contains the full set of variants needed for 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. To meet the requirement for variant transitivity, additional in-script variants may be defined as needed. Once a label has been delegated for one script, any of its variant labels consisting entirely 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 across scripts.
The definition of variants included in this LGR contributes to the definition of variants in the Common LGR. Even though this LGR contains the full set of variants affecting this script, use of the Common LGR is required for actual mitigation of issues caused by using multiple languages or scripts in the same zone. For details, see Section 3, "Use of Multiple Reference LGRs in the Same Zone" in [Level-2-Overview].
In-script variants: this LGR defines in-script variants because they have identical appearance, constitute language-based variants, or are otherwise analogues of the same code point or sequence (semantic variants). For details, Section 6, “Variants”, in [Proposal-Myanmar].
There are two pairs of in-script variants where a naive implementation would interact with cross-script variants in undesirable ways. They, and the required mitigations are discussed in more detail below.
Variant Dispositions: The disposition for some variants is “blocked” : only a single version of the label should be delegated at one time, while all other variants are excluded. The disposition for the remaining in-script variants is “allocatable”, allowing more than one variant to be delegated to the same entity. See Section 6.1 in [Proposal-Myanmar].
Variants that have the same meaning, pronunciation and property should not appear both in the same string. Based on the language, only one variant should be chosen and written consistently. The LGR contains rules and other constraints on variants that prohibit mixed-language labels and arbitrary mixture of variants. See Section 7 in [Proposal-Myanmar].
Some additional code point combinations could create visual variants; however the WLE rules disallow these combinations. They are therefore not normatively defined as variants, but listed in Appendix A of [Proposal-Myanmar].
Cross-script variants:; Some Myanmar characters look the same as characters in Malayalam, Oriya, and Georgian scripts. See Section 6.2 in [Proposal-Myanmar]. The letters U+101D and U+1004 look like their counterparts in one or more of the Latin, Greek, Cyrillic and Armenian scripts among others. Not all these variants are listed here explicitly.
Digit Variants: All Myanmar 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 variant relations are deemed to exist implicitly by transitivity but are not listed explicitly in each reference LGR. Instead, if needed, they are applied by using the Common LGR in label processing.
U+1040 MYANMAR DIGIT ZERO is an in-script homoglyph of U+101D MYANMAR LETTER WA and thus must be a blocked variant of it. At the same time, Myanmar letter WA is a homoglyph of Latin letter ‘o’ and in zones that support ASCII letters, it is a cross-script variant to WA. The policy stated above treats digits as semantic variants of each other across sets, making Myanmar digit ZERO an in-repertoire variant of ASCII digit ZERO ‘0’ as well. In zones that support Latin letter ‘o’ transitivity would then lead to an additional variant definition between ASCII digit ‘0’ and Latin letter ‘o’.
However, variants inside the ASCII set are strictly excluded because LDH labels have never had variants. The easiest work-around is to not allow Myanmar digit ZERO to be part of labels for which a homograph variant with an ASCII label is possible and to only define variants between U+101D and U+1040 for allowed labels. This restriction affects only a small fraction of labels. While this work-around is not strictly necessary in zones that do not support Latin letter ‘o’, it is required for consistency with the Common LGR.
Additional Variants: When integrated to be used with another script LGR in the same zone, this LGR may inherit additional blocked cross-script variants by integration; they may not be listed here unless they reflect resulting in-script variants. Always use an applicable merged, or Common LGR created by integration for determining cross-script collisions of labels. For consistency with other reference LGRs, cross-script variants to ASCII code points are listed explicitly as well.
The specification of variants in this LGR follows the guidelines in [RFC 8228].
The syllable principle is at the heart of the Myanmar script writing system. The general order of elements in a syllable is Consonant > (Medials) > Vowels > (Consonant) > Tone. Overall, the Myanmar script is composed of:
Consonants: Consonants usually stay at the head of each syllable. A consonant can be stand-alone or be followed by Medials, Dependent Vowels, other Signs or Tone Mark. A Consonant cannot be between Viramas to prevent the invalid case of c+v+c+v+c. See Section 3.3.1, “The Consonants” in [Proposal-Myanmar].
Independent Vowels: Only Burmese, Mon and Pa’O languages use Independent Vowels. An Independent Vowel can be at any position in a label. See Section 3.3.2, “The Independent Vowels” in [Proposal-Myanmar].
Dependent Vowels: Dependent vowel signs add vowel property to consonants. These signs appear in top/below/left/right positions of a center consonant or consonant+medial. The dotted-circle indicates where the centre character would be. Dependent vowel signs cannot be repeated and Dependent vowels cannot be adjacent to each other unless within sequences defined in Table 8-A. Dependent vowels also cannot be followed by Asat (U+1038) unless within sequences defined in Table 8-A. See Section 3.3.3, “The Diacritic - Dependent Vowels” of [Proposal-Myanmar].
Medials: Medials are used to enhance the sound of Consonants. They are also noted as Dependent Consonants as they need a leading Consonant to attach to. All five languages in this proposal use Medials. See Section 3.3.4, “Diacritic - Medials” of [Proposal-Myanmar].
Virama: U+1039 MYANMAR SIGN VIRAMA is used in Burmese and Mon. Virama has two properties, as killer (devoweliser) and joiner of syllable chaining. This virama brings the consonant after it to be rendered below the consonant before. Pattern of syllable chaining : Consonant + Virama + Consonant. However. a repetition of Consonant + Virama + Consonant is not allowed to prevent rendering issues. See Section 3.3.5, “Diacritic - Tone Marks and Other Signs” in [Proposal-Myanmar].
Killer or Asat: U+103A MYANMAR SIGN ASAT is used in Burmese and Mon. This sign is used to remove the consonant sound of a letter and take only the vowel property to create more vowel sounds out of consonants. Except for defined sequences, Asat cannot follow other Diacritics. See Section 3.3.5, “Diacritic - Tone Marks and Other Signs” in [Proposal-Myanmar].
Long Tone (t_long): U+1038 MYANMAR SIGN VISARGA appears at the end of the syllable. It creates a vowel sound with the higher tone. It follows a Consonant, Medial, Long vowel or the sequence U+102D U+102F. See Section 3.3.5.1, “Burmese Tone Marks and Other Signs” in [Proposal-Myanmar].
Short Tone (t_short): MYANMAR SIGN DOT BELOW (U+1037) appears at the end of the syllable. It creates a vowel sound with the higher tone. It follows a Consonant, Medial, Long vowel or the sequence U+102D U+102F. See Section 3.3.5.1, “Burmese Tone Marks and Other Signs” in [Proposal-Myanmar].
Other classes defined for use in WLE and context rules
Additional classes defined for extensions for the second level:
The LGR includes the rules and actions to implement the following restrictions, some of which are mandated by the IDNA protocol. They are marked with ⍟ and included here by default.
This LGR includes the complete set default actions for LGRs as well as the action needed to invalidate labels with misplaced combining marks. They are marked with ⍟. For a description see [RFC 7940] and [150]. An additional action is triggered by mixed digit labels.
There are constraints on the context for many of the character classes in Myanmar. These constraints enforce the syllable structure to the degree needed for stability of rendering (which affects both security and usability) without enforcing other linguistic constraints or spellings. These constraints are implemented via a set of context and whole label rules formulated for LGR specification, as described in Section 7, “Whole Label Evaluation (WLE) Rules” in [Proposal-Myanmar].
The following shorthand names for sequences are used in the description or definition of these rules:
The rules are:
These rules are implemented as required or prohibited contexts for the respective repertoire elements.
According to Table 10 of [Proposal-Myanmar], there are code points which cannot occur both in the same label. The following WLE rules enforce these constraints:
These rules are implemented as WLE rules which trigger a corresponding action.
As described under Digit Variants above, a small restriction on U+1040 MYANMAR DIGIT ZERO is required to side-step unwanted interactions among in-script and cross-script variants. The effect is to require at least one digit other than U+1040 and/or at least one letter that is not U+101D or U+1004. The number of possible labels thus restricted is very limited, a small price to pay for being able to support the much larger set of critical variants among homoglyph labels. The rule is the same as described below in Context Rules for Variants.
The following prohibited context applies to certain variants:
In addition to preventing a variant in contexts where the two code point do not look the same, this means that unlike U+1004, U+105A can never inherit a cross-script variant to Latin U+0063, because it only takes on that appearance when followed by some other Myanmar-unique code point.
This context rule also applies to U+1040 MYANMAR DIGIT 0. The combined effect is to support the in-script variant between U+101D and U+1040 in all contexts where ASCII variants can be ignored.
This LGR includes the default actions for LGRs as well as the action needed to invalidate labels with misplaced combining marks. They are marked with ⍟. For a description see [RFC 7940].
The no-mix rules trigger Myanmar-specific actions that invalidate any original and variant labels not satisfying the constraints. See Section 7, “Whole Label Evaluation (WLE) Rules” in [Proposal-Myanmar].
In addition, to limit the number of allocatable variant labels, further constraints on variants are included. These allow allocatable variant labels to either contain members of Grapheme-set-1 (left column in Table 10) or Grapheme-set-2 (right column in Table 10) but not a mixture of members from both sets. The code points on the left column are either the simpler forms (shorter sequence) or the lower Unicode code point values. The mixture of code points from different sets, however, is possible in the original, applied-for label. See Section 6.1 “In-script Variants” in [Proposal-Myanmar].
Each code point or sequence in grapheme-set 1 has been given the reflexive variant type “r-set1” and each code point or sequence in grapheme-set 2 has been given the reflexive variant of type “r-set2”. (By convention, the prefix “r-” marks a type used in a reflexive variant mapping, that is, it represents an instance of the original code point at that location in a variant label, see Section 5.3.4 in [RFC 7940].)
A variant mapping from a member of grapheme-set 1 to a member of grapheme-set 2 is of type “set1-to- set2”, while the variant type for mapping from grapheme-set 2 to grapheme-set 1 is of type “set2-to-set1”.
Script-specific actions evaluate these variant types to ensure the following constraints:
See Section 6.1 “In-script Variants” and Section 7, “Whole Label Evaluation (WLE) Rules” in [Proposal-Myanmar].
The LGR in this document has been adapted from the corresponding Reference LGR for the Second Level. The Second Level Reference LGR for the Myanmar Script was developed by Michel Suignard and Asmus Freytag, based on the Root Zone LGR for the Myanmar script and information contained or referenced therein; see [RZ-LGR-Mymr]. 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 Myanmar script, that this LGR is based on, was developed by the Myanmar Generation Panel. For more information on methodology and contributors to the underlying Root Zone LGR, see Sections 4 and 8 in [Proposal-Myanmar], as well as [RZ-LGR-Overview].
Removed an erroneous variant mapping. This correction does not affect processing of Myanmar labels.
Adopted from the Second Level Reference LGR for the Myanmar Script [Ref-LGR-und-Mymr] without normative changes.
For references consulted particularly in designing the repertoire for the Myanmar Script for the second level 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 [101] and above correspond to sources given in [Proposal-Myanmar] justifying the inclusion of the corresponding code points. Entries in the table may have multiple source reference values. Reference [150] indicates the source for common rules. ]]>