This document specifies a set of Label Generation Rules (LGR) for the Tamil 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: Malayalam. The starting point for the development of this LGR can be found in the related Root Zone LGR [RZ-LGR-Taml]. The format of this file follows [RFC 7940]. This LGR is adapted from the “Reference LGR for the Second Level for the Tamil Script” [Ref-LGR-und-Taml], for details, see Change History below.
For details and additional background on the Tamil script, see “Proposal for a Tamil Script Root Zone Label Generation Rule-Set (LGR)” [Proposal-Tamil].
The repertoire contains 48 code points for letters and 4 sequences used to write the Tamil language. The repertoire is a subset of [Unicode 11.0.0]. For details, see Section 5, “Repertoire” in [Proposal-Tamil]. (The proposal cited has been adopted for the Tamil script portion of the Root Zone LGR.)
For the second level, the repertoire has been augmented with the ASCII digits, U+0030 to U+0039, plus U+002D HYPHEN-MINUS, for a total of 63 repertoire elements.
Any code points outside the Tamil 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. Comments provide alternate names for some code points.
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].
This LGR defines four sequences as in-script variants. Two of them are variants to single code points; the other two are variants of each other; all defined variants look exactly alike and can cause confusion even to a careful observer. For detais, see Section 6, “Variants” in [Proposal-Tamil].
In addition to these, this LGR defines 6 cross-script variants with the Malayalam script.
Digit Variants: The Tamil reference LGR does not include native digits, so there are no semantic variants defined.
However, some Tamil letters are homoglyphs of native digits. For example, U+0BE7 TAMIL DIGIT ONE and U+0BED TAMIL DIGIT SEVEN are homoglyphs of U+0B95 TAMIL LETTER KA and U+0B8E TAMIL LETTER E respectively.
Should an extension be contemplated that adds native digits, these might require variant relations. At the same time, however, any native digits would normally be semantic variants of the ASCII 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 would be delegated, while any other equivalent labels should be blocked. There is no preference among these labels.
This LGR does not define allocatable variants.
The specification of variants in this LGR follows the guidelines in [RFC 8228].
For historical reasons, there are two sequences that both represent the same akshar (Shri) with exactly the same rendered form. These two sequences are thus semantically identical and users may choose either one, except that a single label must use one of these forms consistently. This variant pair is thus being defined as “allocatable” variant. (For more details see Section 6.1 in [Proposal-Tamil].)
Tamil is an alphasyllabary and the heart of the writing system is the akshar. This is the unit which is instinctively recognized by users of the script. As encoded, the writing system of Tamil is composed of Consonants, the Implicit Vowel Killer: Halant, Vowels and Visarga/Aytham.
Consonants: More details in Section 3.3.1, “The Consonants” in [Proposal-Tamil].
Halant / Virama: All consonants contain an implicit vowel /a/. A special sign is needed to denote that this implicit vowel is stripped off. This is known as the Pulli and encoded as U+0BCD TAMIL SIGN VIRAMA. The virama thus joins two adjacent consonants. In Tamil, there are only two cases where this forms conjuncts. More details in Section 3.3.2, “Virama/Pulli” of the [Proposal-Tamil].
Vowels and Matras: Separate symbols exist for all Vowels that are pronounced independently either at the beginning or after another vowel sound. To indicate a Vowel sound other than the implicit one following a consonant, a Vowel sign (matra) is attached to the consonant. Since the consonant has a built-in /a/, there are equivalent Matras for all vowels excepting the அ. More details in Section 3.3.3, “Vowels” in [Proposal-Tamil].
Visarga: The Visarga (or Aytham) is used in Tamil to represent a sound very close to /ḵ/. More details in Section 3.3.4, “Visarga/Aytham” in [Proposal-Tamil].
Common Digits: U+0030 to U+0039 are the set of digits from the ASCII range.
By default, the LGR includes the rules and actions to implement the following restrictions mandated by the IDNA protocol. They are marked with ⍟.
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].
These rules have been drafted to ensure that the prospective Tamil label conforms to akshar formation norms as desired in Tamil script. These norms are exclusively presented as context rules.
The following symbols are used in the WLE rules:
C → Consonant
M → Matra
H → Haleant / Virama =Pulli
X → Visarga = Aytham
The rules are:
The following whole-label rule and associated action prevent the mixing of two allocatable variants of the same sequence within the same label. This reduces overproduction of variant labels.
More details in Section 7, “Whole Label Evaluation Rules (WLE)” in [Proposal-Tamil].
The LGR in this document has been adapted from the corresponding Reference LGR for the Second Level. The Second Level Reference LGR for the Tamil Script was developed by Michel Suignard and Asmus Freytag, based on the Root Zone LGR for the Tamil script and information contained or referenced therein; see [RZ-LGR-Taml]. 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 Tamil 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 Sections 4 and 8 in [Proposal-Tamil], as well as [RZ-LGR-Overview].
Unicode Version has been updated.
This version modifies the Second Level Reference LGR for the Tamil Script [Ref-LGR-und-Taml] by injecting the complete (maximal) set of cross-repertoire variants, including any imposed by transitivity. Injected variants are marked by special comments. Any character classes, context and WLE rules required for testing are also imported. In all other respects, description or annotations have not been updated to reflect the injected variants. Any LGR elements that might pose a possible conflict when the LGR is used with the Common LGR for cross-repertoire variant resolution are clearly marked. All modifications are carried out mechanically; there may be an occasional context rule or similar that is injected because its definition relates to some repertoire element even though it can never be triggered by any label valid under the modified LGR.
The following general references are cited in this document:
For references consulted particularly in designing the repertoire for the Tamil Script for the second level please see details in the Table of References below.
References [0] and [7] refer to the Unicode Standard versions in which the corresponding code points were initially encoded. References [101] and above correspond to sources given in [Proposal-Tamil] justifying the inclusion of the corresponding code points. Entries in the table may have multiple source reference values. In the listing of whole label evaluation and context rules, reference [150] indicates the source for common rules.
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