Reference LGR for script: Thaana (Thaa) lgr-second-level-thaana-script-25oct24-en

This document is mechanically formatted from the above XML file for the LGR. It provides additional summary data and explanatory text. The XML file remains the sole normative specification of the LGR.

Date 2024-10-25
LGR Version 1 (Second Level Reference LGR)
Language und-Thaa (Thaana Script)
Unicode Version 11.0.0

Description

INSTRUCTIONS

  • These instructions cover how to adopt an LGR based on this reference LGR for a given zone and how to prepare the file for deposit in the IANA Repository of IDN Practices.
  • As described the IANA procedure
    (https://www.iana.org/help/idn-repository-procedure)
    an LGR MUST contain the following elements in its header:
    • Script or Language Designator (see below for guidance)
    • Version Number (this must increase with each amendment to the LGR, even if the updates are limited to the header itself)
    • Effective Date (the date at which the policy becomes applicable in operational use)
    • Registry Contact Details (contact name, email address, and/or phone number)
  • The following information is optional:
    • Document creation date
    • Applicable Domain(s)
    • Changes made to the Reference LGR before adopting

Please add or modify the following items in the XML source code for this file before depositing the document in the IANA Repository.
(https://www.iana.org/domains/idn-tables)

Meta Data

Note: version numbers start at 1. RFC 7940 recommends using simple integers. The version comment is optional, please replace or delete the default comment. Version comments may be used by some tools as part of the page header.

<version comment="[Please replace (or delete) the optional comment]">[Please fill in version number, starting at 1]</version>

<date>[Please fill in with publication date, in YYYY-MM-DD format]</date>

<validity-start>[Please fill in effective date, in YYYY-MM-DD format]</validity-start>

Note: the scope element may be repeated, so that the same document can serve for multiple domains.

<scope type="domain">[Please provide, in ".domain" format]</scope>

Registry Contact Information:

Please fill in the Registry Contact Details.

Change History

If you made technical modifications to the LGR, please summarize them in the Change History (and also note the details in the appropriate section of the description).

PLEASE DELETE THESE INSTRUCTIONS BEFORE DEPOSITING THE DOCUMENT

Registry Contact Details

Reference Label Generation Rules for the Thaana Script

Overview

This document specifies a set of Label Generation Rules (LGR) for the Thaana script using a script-specific repertoire for the second level domain or domains identified above. The format of this file follows [RFC 7940]. This LGR is adapted from the “Reference LGR for the Second Level for the Thaana Script” [Ref-LGR-und-Thaa], for details, see Change History below.

Standalone LGR: This LGR is designed to be used in a zone that does not cater to IDNs other than those valid under this LGR. This LGR lacks features that would allow its use in the context of another LGR in the same zone, and it may contain other features incompatible with such use.

For details and additional background on the Thaana script, see "Thaana Script Reference Label Generation Rules for Second-Level Domain Names" [Proposal-Thaana].

Repertoire

The repertoire includes the 49 letters and diacritics of the Thaana script in everyday use as defined in Section 5.1 “Included Code Points” in [Proposal-Thaana].

U+07B1 ޱ THAANA LETTER NAA (baru nūnu) is a dialect specific consonant. Given the resurgence of the use of the consonant in online writing and social media, a decision was made to include it in the repertoire at this time, despite it not being officially recognized as part of the base consonants.

For the second level, the repertoire has been augmented with the ASCII digits, U+0030 0 to U+0039 9, plus U+002D - HYPHEN-MINUS, for a total of 61 repertoire elements.

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 a number 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. However, if used in the context of an LGR for any other zone, variants may be required for the digits.

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].

Character Classes

Thaana has 25 consonants and 11 vowels. The first nine letters of Thaana are derived from the Arabic/Persian numerals (see below). The vowels are written above/below the letters.

  • Common-digits — ASCII digits: U+0030 0 to U+0039 9.
  • Consonants — in the Thaana script, consonants are base characters and all but one must be followed by a vowel. Additional restrictions apply to the two consonants Noonu and Raa.
  • Consonants for Arabic — additions in the script for transcribing Arabic and other loan words. For the purposes of this LGR, there is no distinction between these and other consonants.
  • Vowels — vowels are combining marks that always follow a consonant.

Whole Label Evaluation (WLE) and Context Rules

Common Rules

By default, the LGR includes the rules and actions to implement the following restrictions mandated by the IDNA protocol. They are marked with ⍟.

  • 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].

Script-specific rules in this LGR already prevent combining marks in leading position making the "leading-combining-mark" rule technically redundant. It is retained here for consistency.

Right-to-Left Rules

  • leading-digit — restrictions on the allowable placement of digits in a right-to-left context (no leading digit), (see section 2.1 of RFC 5893 [160]); implemented here as a context rule on each digit.

Default Actions

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.

Script-specific Rules

The LGR defines the following script-specific rules concerning the placement of vowels and preventing some combinations from starting a word.

  • follows-C-or-N — WLE 1: a vowel always follows a consonant or including Noonu and Raa.
  • followed-by-V — WLE 2: a consonant, except Noonu or Raa is always followed by a vowel.
  • start-of-word-followed-by-C — WLE 3: N followed by C cannot start a word, that is, it cannot be the start of a label, or follow a hyphen or digit.
  • followed-by-NC-or-NN= — WLE 4: N cannot be follwoed by NC or NN.

Methodology

This Second Level Reference LGR for the Thaana Script was developed by the Thaana community and edited by Asmus Freytag and Michel Suignard, based on community feedback and public review.

Changes from Version Dated 25 October 2024

Adopted from the Second Level Reference LGR for the Thaana Script [Ref-LGR-und-Thaa] without normative changes.

References

This document cites the following general references.

[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-27may20-en.pdf
[Level-2-Overview]
Internet Corporation for Assigned Names and Numbers, (ICANN),“Reference Label Generation Rules (LGR) for the Second Level: Overview and Summary” (PDF), (Los Angeles, California: ICANN, 25 October 2024),
https://www.icann.org/en/system/files/files/level2-lgr-overview-summary-25oct24-en.pdf
[Proposal-Thaana]
"Thaana Script Reference Label Generation Rules for Second-Level Domain Names", 12 September 2024,
https://www.icann.org/en/system/files/files/proposal-thaana-second-level-12Sep24-en.pdf
[Ref-LGR-und-Thaa]
ICANN, Second Level Reference Label Generation Rules for the Thaana Script (und-Thaa), 25 October 2024 (XML)
https://www.icann.org/sites/default/files/packages/lgr/lgr-second-level-thaana-script-25oct24-en.xml
non-normative HTML presentation:
https://www.icann.org/sites/default/files/packages/lgr/lgr-second-level-thaana-script-25oct24-en.html
[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
[UNICODE 11.0.0]
The Unicode Consortium. The Unicode Standard, Version 11.0.0, (Mountain View, CA: The Unicode Consortium, 2018. ISBN 978-1-936213-19-1)
https://www.unicode.org/versions/Unicode11.0.0/

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 cod5 points. Entries in the table may have multiple source reference values. In the listing of whole label evaluation and context rules, references [150] and [160] indicate the source for common rules.

Repertoire

Repertoire Summary

Number of elements in repertoire 61
Number of code points
for each script
Thaana 50
Common 11
Longest code point sequence 1

Repertoire by Code Point

The following table lists the repertoire by code point (or code point sequence). The data in the Script and Name column are extracted from the Unicode character database. Where a comment in the original LGR is equal to the character name, it has been suppressed.

For any code point or sequence for which a variant is defined, additional information is provided in the Variants column. See also the legend provided below the table.

Code
Point		 Glyph Script Name Ref Tags Required Context Variants Comment
U+002D - Common HYPHEN-MINUS [0]   not: hyphen-minus-disallowed    
U+0030 0 Common DIGIT ZERO [0] Common-digit not: leading-digit    
U+0031 1 Common DIGIT ONE [0] Common-digit not: leading-digit    
U+0032 2 Common DIGIT TWO [0] Common-digit not: leading-digit    
U+0033 3 Common DIGIT THREE [0] Common-digit not: leading-digit    
U+0034 4 Common DIGIT FOUR [0] Common-digit not: leading-digit    
U+0035 5 Common DIGIT FIVE [0] Common-digit not: leading-digit    
U+0036 6 Common DIGIT SIX [0] Common-digit not: leading-digit    
U+0037 7 Common DIGIT SEVEN [0] Common-digit not: leading-digit    
U+0038 8 Common DIGIT EIGHT [0] Common-digit not: leading-digit    
U+0039 9 Common DIGIT NINE [0] Common-digit not: leading-digit    
U+0780 ހ Thaana THAANA LETTER HAA [3], [401] consonant followed-by-V set 1  
U+0781 ށ Thaana THAANA LETTER SHAVIYANI [3], [401] consonant followed-by-V set 2  
U+0782 ނ Thaana THAANA LETTER NOONU [3], [401] consonant not: disallowed-for-N set 3  
U+0783 ރ Thaana THAANA LETTER RAA [3], [401] consonant not: disallowed-for-N set 4  
U+0784 ބ Thaana THAANA LETTER BAA [3], [401] consonant followed-by-V    
U+0785 ޅ Thaana THAANA LETTER LHAVIYANI [3], [401] consonant followed-by-V    
U+0786 ކ Thaana THAANA LETTER KAAFU [3], [401] consonant followed-by-V    
U+0787 އ Thaana THAANA LETTER ALIFU [3], [401] consonant followed-by-V set 5  
U+0788 ވ Thaana THAANA LETTER VAAVU [3], [401] consonant followed-by-V set 6  
U+0789 މ Thaana THAANA LETTER MEEMU [3], [401] consonant followed-by-V    
U+078A ފ Thaana THAANA LETTER FAAFU [3], [401] consonant followed-by-V    
U+078B ދ Thaana THAANA LETTER DHAALU [3], [401] consonant followed-by-V set 7  
U+078C ތ Thaana THAANA LETTER THAA [3], [401] consonant followed-by-V set 8  
U+078D ލ Thaana THAANA LETTER LAAMU [3], [401] consonant followed-by-V    
U+078E ގ Thaana THAANA LETTER GAAFU [3], [401] consonant followed-by-V set 9  
U+078F ޏ Thaana THAANA LETTER GNAVIYANI [3], [401] consonant followed-by-V    
U+0790 ސ Thaana THAANA LETTER SEENU [3], [401] consonant followed-by-V set 10  
U+0791 ޑ Thaana THAANA LETTER DAVIYANI [3], [401] consonant followed-by-V    
U+0792 ޒ Thaana THAANA LETTER ZAVIYANI [3], [401] consonant followed-by-V    
U+0793 ޓ Thaana THAANA LETTER TAVIYANI [3], [401] consonant followed-by-V    
U+0794 ޔ Thaana THAANA LETTER YAA [3], [401] consonant followed-by-V    
U+0795 ޕ Thaana THAANA LETTER PAVIYANI [3], [401] consonant followed-by-V    
U+0796 ޖ Thaana THAANA LETTER JAVIYANI [3], [401] consonant followed-by-V    
U+0797 ޗ Thaana THAANA LETTER CHAVIYANI [3], [401] consonant followed-by-V    
U+0798 ޘ Thaana THAANA LETTER TTAA [3], [401] consonant, thaana-arabic followed-by-V set 8  
U+0799 ޙ Thaana THAANA LETTER HHAA [3], [401] consonant, thaana-arabic followed-by-V set 1  
U+079A ޚ Thaana THAANA LETTER KHAA [3], [401] consonant, thaana-arabic followed-by-V set 1  
U+079B ޛ Thaana THAANA LETTER THAALU [3], [401] consonant, thaana-arabic followed-by-V set 7  
U+079C ޜ Thaana THAANA LETTER ZAA [3], [401] consonant, thaana-arabic followed-by-V set 4  
U+079D ޝ Thaana THAANA LETTER SHEENU [3], [401] consonant, thaana-arabic followed-by-V set 2  
U+079E ޞ Thaana THAANA LETTER SAADHU [3], [401] consonant, thaana-arabic followed-by-V set 10  
U+079F ޟ Thaana THAANA LETTER DAADHU [3], [401] consonant, thaana-arabic followed-by-V set 10  
U+07A0 ޠ Thaana THAANA LETTER TO [3], [401] consonant, thaana-arabic followed-by-V set 8  
U+07A1 ޡ Thaana THAANA LETTER ZO [3], [401] consonant, thaana-arabic followed-by-V set 8  
U+07A2 ޢ Thaana THAANA LETTER AINU [3], [401] consonant, thaana-arabic followed-by-V set 5  
U+07A3 ޣ Thaana THAANA LETTER GHAINU [3], [401] consonant, thaana-arabic followed-by-V set 5  
U+07A4 ޤ Thaana THAANA LETTER QAAFU [3], [401] consonant, thaana-arabic followed-by-V set 9  
U+07A5 ޥ Thaana THAANA LETTER WAAVU [3], [401] consonant, thaana-arabic followed-by-V set 6  
U+07A6  ަ Thaana THAANA ABAFILI [3], [401] vowel follows-C-or-N    
U+07A7  ާ Thaana THAANA AABAAFILI [3], [401] vowel follows-C-or-N    
U+07A8  ި Thaana THAANA IBIFILI [3], [401] vowel follows-C-or-N    
U+07A9  ީ Thaana THAANA EEBEEFILI [3], [401] vowel follows-C-or-N    
U+07AA  ު Thaana THAANA UBUFILI [3], [401] vowel follows-C-or-N    
U+07AB  ޫ Thaana THAANA OOBOOFILI [3], [401] vowel follows-C-or-N    
U+07AC  ެ Thaana THAANA EBEFILI [3], [401] vowel follows-C-or-N    
U+07AD  ޭ Thaana THAANA EYBEYFILI [3], [401] vowel follows-C-or-N    
U+07AE  ޮ Thaana THAANA OBOFILI [3], [401] vowel follows-C-or-N    
U+07AF  ޯ Thaana THAANA OABOAFILI [3], [401] vowel follows-C-or-N    
U+07B0  ް Thaana THAANA SUKUN [3], [401] vowel follows-C-or-N    
U+07B1 ޱ Thaana THAANA LETTER NAA [5], [401] consonant followed-by-V set 3  

Legend

Code Point
A code point or code point sequence.
Glyph
The shape displayed depends on the fonts available to your browser.
Script
Shows the script property value from the Unicode Character Database. Combining marks may have the value Inherited and code points used with more than one script may have the value Common.
Name
Shows the character or sequence name from the Unicode Character Database.
Ref
Links to the references associated with the code point or sequence, if any.
Tags
LGR-defined tag values. Any tags matching the Unicode script property are suppressed in this view.
Required Context
Link to a rule defining the required context a code point or sequence must satisfy. If prefixed by “not:” identifies a context that must not occur.
Variants
Link to the variant set the code point or sequence is a member of, except where a coded point or sequence maps only to itself, in which case the type of that mapping is listed.
Comment
The comment as given in the XML file. However, if the comment for this row consists only of the code point or sequence name, it is suppressed in this view. By convention, comments starting with “=” denote an alias. If present, the symbol ⍟ marks a default item shared among a set of LGRs.

Variants

Variant Set Summary

Number of variant sets 10
Largest variant set 4
Variants by Type
blocked 42

Variant Sets

The following tables list all variant sets defined in this LGR, except for singleton sets. Each table lists all variant mapping pairs of the set; one per row. Mappings are assumed to be symmetric: each row documents both forward (→) and reverse (←) mapping directions. In each table, the mappings are sorted by Source value in ascending code point order; shading is used to group mappings from the same source code point or sequence.

Where the type of both forward and reverse mappings are the same, a single value is given in the Type column; otherwise the types for forward and reverse mappings, as well as comments and references, are listed above one another. For summary counts, both forward and reverse mappings are always counted separately.

In any LGR with variant specifications that are well behaved, all members within each variant set are defined as variants of each other; the mappings in each set are symmetric and transitive; and all variant sets are disjoint.

Common Legend

Source
By convention, the smaller of the two code points in a variant mapping pair.
Target
By convention, the larger of the two code points in a variant mapping pair.
Glyph
The shape displayed for source or target depends on the fonts available to your browser.
→ - forward
Indicates that Type, Ref and Comment apply to the mapping from source to target.
← - reverse
Indicates that Type, Ref and Comment apply to the reverse mapping from target to source.
↔ - both
Indicates that Type, Ref and Comment apply to both forward and reverse mapping.
Type
The type of the variant mapping, including predefined variant types such as “allocatable” and “blocked”; or any that are defined specifically for this LGR.
Ref
One or more reference IDs (optional). A “/” separates references for reverse / forward mappings, if different.
Comment
A descriptive comment (optional). A “/” separates comments for reverse / forward mappings, if different.

Variant Set 1 — 3 Members

Source Glyph Target Glyph   Type Ref Comment
0780 ހ 0799 ޙ ↔ blocked    
0780 ހ 079A ޚ ↔ blocked    
0799 ޙ 079A ޚ ↔ blocked    

Variant Set 2 — 2 Members

Source Glyph Target Glyph   Type Ref Comment
0781 ށ 079D ޝ ↔ blocked    

Variant Set 3 — 2 Members

Source Glyph Target Glyph   Type Ref Comment
0782 ނ 07B1 ޱ ↔ blocked    

Variant Set 4 — 2 Members

Source Glyph Target Glyph   Type Ref Comment
0783 ރ 079C ޜ ↔ blocked    

Variant Set 5 — 3 Members

Source Glyph Target Glyph   Type Ref Comment
0787 އ 07A2 ޢ ↔ blocked    
0787 އ 07A3 ޣ ↔ blocked    
07A2 ޢ 07A3 ޣ ↔ blocked    

Variant Set 6 — 2 Members

Source Glyph Target Glyph   Type Ref Comment
0788 ވ 07A5 ޥ ↔ blocked    

Variant Set 7 — 2 Members

Source Glyph Target Glyph   Type Ref Comment
078B ދ 079B ޛ ↔ blocked    

Variant Set 8 — 4 Members

Source Glyph Target Glyph   Type Ref Comment
078C ތ 0798 ޘ ↔ blocked    
078C ތ 07A0 ޠ ↔ blocked    
078C ތ 07A1 ޡ ↔ blocked    
0798 ޘ 07A0 ޠ ↔ blocked    
0798 ޘ 07A1 ޡ ↔ blocked    
07A0 ޠ 07A1 ޡ ↔ blocked    

Variant Set 9 — 2 Members

Source Glyph Target Glyph   Type Ref Comment
078E ގ 07A4 ޤ ↔ blocked    

Variant Set 10 — 3 Members

Source Glyph Target Glyph   Type Ref Comment
0790 ސ 079E ޞ ↔ blocked    
0790 ސ 079F ޟ ↔ blocked    
079E ޞ 079F ޟ ↔ blocked    

Classes, Rules and Actions

Character Classes

Number of named classes 4
Implicit (except script) 2
Implicit defined by script tag 2

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
Common-digits Tag=Common-digit 10 {0030-0039}   Digits from the ASCII range ⍟
N explicit 2 {0782-0783}   Thaana NoonNu and Thana Raa
C combined =
[[:consonant:] ∖ [:N:]]		 37 {0780-0781 0784-07A5 07B1}   Any Thaana consonant other than NoonNu or Raa
V Tag=vowel 11 {07A6-07B0}   Any Thaana vowel
implicit Tag=consonant 39 {0780-07A5 07B1}   Any character tagged as consonant
implicit Tag=thaana-arabic 14 {0798-07A5}   Any character tagged as thaana-arabic
implicit Tag=sc:Thaa 50 {0780-07B1}   Any character tagged as Thaana
implicit Tag=sc:Zyyy 11 {002D 0030-0039}   Any character tagged as Common

Legend

Members or Ranges
Lists the members of the class as code points (xxx) or as ranges of code points (xxx-yyy). Any class too numerous to list in full is elided with "...".
Tag=ttt
A named or implicit class defined by all code points that share the given tag value (ttt).
Explicit
A named class defined by explicitly listing all its members.
Implicit
An anonymous class implicitly defined based on tag value and for which there is no named equivalent.
Combined
A named class defined by set operations on other classes using the following syntax:
[: :] - named or implicit character set
Reference to a named character set [:name:] or an implicit character set [:tag:]. A leading “^” before name or tag indicates the set complement.
[&&, -, ^] - set operators
Sets may be combined by set operators (&& = intersection, - = difference, ^ = symmetric difference) or concatenated (union).

Whole label evaluation and context rules

Number of rules 9
Used to trigger actions 1
Used as context rule (C) 5
Anchored context rules 7
Used only in another rule 3

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
hyphen-minus-disallowed ((((start))← ⚓︎)|(⚓︎ →((end)))|(((start)..\u002D)← ⚓︎))   ✔ C   RFC 5891 restrictions on placement of U+002D - HYPHEN-MINUS ⍟
leading-combining-mark (start)[\p{gc=Mn}][∅=\p{gc=Mc}] ✔     [150] RFC 5891 restrictions on placement of combining marks ⍟
leading-digit ((start))← ⚓︎   ✔ C [160] RFC 5893 RTL labels cannot start with a digit ⍟
start-of-word ((start)|\u002D|[:Common-digits:])         A context describing the start of a word, used in the formuation of WLE 3
start-of-word-followed-by-C ((:start-of-word:))← ⚓︎ →([:C:])   ✔     WLE 3: N followed by C cannot start a word, that is, it cannot be the start of a label, or follow a hyphen or digit.
followed-by-NC-or-NN ⚓︎ →([:N:]([:C:]|[:N:]))   ✔     WLE 4: N cannot be followed by NC or NN
disallowed-for-N ((:start-of-word-followed-by-C:)|(:followed-by-NC-or-NN:))   ✔ C   Prohibited context for N, combines WLE 3 and WLE 4
follows-C-or-N ([:C:]|[:N:])← ⚓︎   ✔ C   WLE1: a vowel always follows a consonant or Noonnu or Raa.
followed-by-V ⚓︎ →([:V:])   ✔ C   WLE2: a consonant is always follwed by a vowel.

Legend

Used as Trigger
This rule triggers one of the actions listed below.
Used as Context
This rule defines a required or prohibited context for a code point C or variant V.
Anchor
This rule has a placeholder for the code point for which it is evaluated.
Regular Expression
A regular expression equivalent to the rule, shown in a modified notation as noted:
⚓︎ - context anchor
Placeholder for the actual code point when a context is evaluated. The code point must occur at the position corresponding to the anchor. Rules containing an anchor cannot be used as triggers.
(?<=...) - look-behind
If present encloses required context preceding the anchor.
(?=...) - look-ahead
If present encloses required context following the anchor.
(: :) - rule reference
Non-recursive reference to a named rule.
( ) - group
An anonymous nested rule is used to group match operators.
(... | ...) - choice
When there is more than one alternative in a rule, the choices are separated by the alternation operator (...|...).
^ or $ - start or end
^ matches the start of the label; $ matches the end of the label.
. - any code point
. matches any code point.
[: :] - named or implicit character set
Reference to a named character set [:name:] or an implicit character set [:tag:]. A leading “^” before name or tag indicates the set complement.
[\p{ }] - property
Set of all characters matching a given value for a Unicode property [\p{prop=val}]. Note: uppercase “\P” defines the complement of a property set.
[&&, -, ^] - set operators
Sets may be combined by set operators (&& = intersection, - = difference, ^ = symmetric difference) or concatenated (union).
∅= - empty set
Indicates that the following set is empty because of the result of set operations, or because none of its elements is part of the repertoire defined here. A rule with a non-optional empty set never matches.
⍟ - default rule
Rules marked with ⍟ are included by default and may or may not be triggered by any possible label under this LGR.

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   RFC 5891 restrictions on placement of combining marks ⍟
2 if at least one variant is in {blocked} → blocked   any variant label containing blocked variants is blocked ⍟
3 if any label (catch-all)   → valid   catch all; default action ⍟

Legend

{...} - variant type set
In the “Rule/Variant Set” column, the notation {...} means a set of variant types.
⍟ - default action
Actions marked with ⍟ are included by default and may or may not be triggered by any possible label under this LGR.

Table of References

The following lists the references cited for specific code points, variants, classes, rules or actions in this LGR. For General references refer to the References section in the Description.

[0] The Unicode Standard, Version 1.1
Code points cited were originally encoded in Unicode Version 1.1
[3] The Unicode Standard, Version 3.0
Code points cited were originally encoded in Unicode Version 3.0
[5] The Unicode Standard, Version 3.2
Code points cited were originally encoded in Unicode Version 3.2
[150] RFC 5891, Internationalized Domain Names in Applications(IDNA): Protocol
https://tools.ietf.org/html/rfc5891
[160] RFC 5893, Right - to - Left Scripts for Internationalized Domain Names for Applications (IDNA)
https://tools.ietf.org/html/rfc5893
[401] Dhivehi Writing Systems by Naseema Mohamed, page 7-8, NCLHR, 1999.