Thaana

The Thaana script contains a series of consonants used for writing Arabic loan words. Their occurrence is relatively rare and omitting them here avoids some complications that might make their use problematic for the Root Zone. The primary issue is that they are used inconsistently and alternation with the equivalent ordinary consonants is common. Their inclusion would thus have necessitated the definition of in-script variants. See also Section 5.2 “Excluded Code Points” in [Proposal-Thaana]

As part of the Root Zone, this LGR includes neither decimal digits nor the HYPHEN-MINUS.

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.

Variants

This LGR defines one set of in-script variants as described in Section 6.1 “In-script Variants”of [Proposal-Thaana]. No cross-script variants have been identified based on any discernable similarity with another script or otherwise required for the security of the Thaana LGR. In particular, the structure of the Thaana script, requiring a vowel after each consonant, removes similarity between Arabic and Thaana labels.

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 the Root Zone LGR follows the guidelines in [RFC 8228].

Character Classes

Thaana has 25 consonants and 11 vowels. The vowels are written above/below the letters.

• Consonants — in the Thaana script, consonants are base characters and must be followed by a vowel.
• Vowels — vowels are combining marks that always follow a consonant.

Whole Label Evaluation (WLE) and Context Rules

Default Whole Label Evaluation Rules and Actions

The LGR includes the set of required default WLE rules and actions applicable to the Root Zone and defined in [MSR-6]. They are marked with ⍟. The actions compute a label disposition based on WLE rules or variant mapping types.

Script-specific Rules

The LGR defines the following script-specific rules concerning the placement of consonants and vowels.

• follows-C — WLE 1: a vowel always follows a consonant including Noonu and Raa.
• followed-by-V — WLE 2: a consonant, including Noonu or Raa is always followed by a vowel.

Note that in writing Thaana, U+0782 THAANA LETTER NOONU and U+0783 THAANA LETTER RAA can either appear with or without a vowel, depending on the context. For the purpose of the Root Zone, these special contexts have been disallowed and they behave like all other consonants for the purpose of the RZ-LGR. Because the exceptions to their behavior as ordinary consonants are statistically rare, this more conservative approach was chosen even though it restricts a small number of labels that might be valid in other zones.

Methodology and Contributors

The Root Zone LGR for the Thaana Script was developed by the Thaana Generation Panel. For details on methodology and contributors, see Sections 4 and 8 in [Proposal-Thaana], as well as [RZ-LGR-6-Overview].

References

This document cites the following general references.

[MSR-6]

Integration Panel, “Maximal Starting Repertoire — MSR-6 Overview and Rationale”, 23 September 2025, https://www.icann.org/en/system/files/files/msr-6-overview-23sep25-en.pdf

[Proposal-Thaana]

“Thaana Script Label Generation Rules for the Root Zone” , 23 May 2025, https://www.icann.org/en/system/files/files/proposal-thaana-lgr-23may25-en.pdf

[RFC 7940]

Davies, K. and A. Freytag, “Representing Label Generation Rulesets Using XML”, RFC 7940, August 2016, https://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-6-Overview]

Integration Panel, “Root Zone Label Generation Rules (RZ LGR-6): Overview and Summary”, 23 September 2025, https://www.icann.org/sites/default/files/lgr/rz-lgr-6-overview-23sep25-en.pdf

[RZ-LGR-6]

Integration Panel, “Root Zone Label Generation Rules (RZ-LGR-6)”, 23 September 2025 (XML), https://www.icann.org/sites/default/files/lgr/rz-lgr-6-common-23sep25-en.xml
non-normative HTML presentation: https://www.icann.org/sites/default/files/lgr/rz-lgr-6-common-23sep25-en.html

[Unicode 16.0.0]

The Unicode Consortium. The Unicode Standard, Version 16.0.0, (South San Francisco: The Unicode Consortium, 2024. ISBN 978-1-936213-34-4) https://www.unicode.org/versions/Unicode16.0.0/

References [0] to [3] refer to the Unicode Standard versions in which the corresponding code points were initially encoded. References [401] and above correspond to sources given in [Proposal-Thaana] justifying the inclusion of the corresponding code points.