Label Generation Rules for Bulgarian

Overview

This document specifies a reference set of Label Generation Rules for Bulgarian using a language-specific repertoire appropriate for a second level domain.

Standalone LGR:This Reference LGR is designed to be used as is, or with suitable modifications in a zone that does not cater to IDNs other than those valid under this LGR. While it is anticipated that this LGR may be used in a zone that also supports LDH (ASCII) labels, 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.

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

All references converge on 30 Cyrillic code points (23 +9 as defined by RFC 5992 [130]). CLDR in its auxiliary list adds 7 code points of which 2 correspond to historic letters. These code points are U+0463 (ѣ) CYRILLIC SMALL LETTER YAT and U+046B (ѫ) CYRILLIC SMALL LETTER BIG YUS. They are also excluded from MSR-2 (see MSR-2 in the Table of References) as being obsolete. Of the other 5, 3 have no other sources and are not included. The last 2: U+0450 (ѐ) CYRILLIC SMALL LETTER IE WITH GRAVE and U+045D (ѝ) CYRILLIC SMALL LETTER I WITH GRAVE have additional sources and are part of the extended set.

Note: The article in [605] indicates that “In Bulgarian and Macedonian, the grave accent is sometimes, although not very often, used on the vowels а, о, у, е, и and ъ (ъ exists in Bulgarian only) to mark stress...In a few cases (mostly on the vowels е and и) the stress mark is orthographically required to distinguish words which are Homographs".

There is an IDN table published in the IANA Repository of IDN Practices for Bulgarian by .bg (Bulgaria cctld) in [700]

Excluded code points

Letters documented in some references but not included:

• U+044B (ы) CYRILLIC SMALL LETTER YERU

• U+044D (э) CYRILLIC SMALL LETTER E

• U+0451 (ё) CYRILLIC SMALL LETTER IO

• U+0463 (ѣ) CYRILLIC SMALL LETTER YAT

• U+046B (ѫ) CYRILLIC SMALL LETTER BIG YUS

• U+0463 (ѣ) CYRILLIC SMALL LETTER YAT

• U+0430 U+0300 (а̀) CYRILLIC SMALL LETTER A WITH GRAVE ACCENT

• U+043E U+0300 (о̀) CYRILLIC SMALL LETTER O WITH GRAVE ACCENT

• U+0443 U+0300 (у̀) CYRILLIC SMALL LETTER U WITH GRAVE ACCENT

• U+044A U+0300 (ъ̀) CYRILLIC SMALL LETTER HARD SIGN WITH GRAVE ACCENT

• U+044E U+0300 (ю̀) CYRILLIC SMALL LETTER YU WITH GRAVE ACCENT

• U+044F U+0300 (я̀) CYRILLIC SMALL LETTER YA WITH GRAVE ACCENT

Extended code points

A number of letters not considered essential to writing the core vocabulary of the language are nevertheless in common use. Where they have not been added to the core repertoire, they are flagged as “extended-cp” in the table of code points. A context rule is provided that by default will prohibit labels with such extended code points. To support extended single code points or code point sequences, delete the context “extended-cp” from their repertoire definition.

Variants

There are no variants defined between Cyrillic letters.

ASCII Variants: Because a common use case would be for a zone to also support LDH labels, the reference LGR contains definitions for “blocked” variants for letters that look indistinguishable from ASCII letters (homoglyphs). None of these variants has any effect when using the LGR in a standalone fashion, but if the zone also supports LDH labels, any label that consists entirely of Cyrillic letters that have ASCII counterparts could be “blocked” by a corresponding LDH variant label.

Character Classes

This LGR does not define named character classes.

Rules

Common Rules

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].

Actions

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].

Variant-related actions included to facilitate integration as appropriate.

Methodology and Contributors

This reference LGR for the Bulgarian language for the second level has been developed by Michel Suignard and Asmus Freytag, verified in expert reviews by Michael Everson, Nicholas Ostler, and Wil Tan, and based on multiple open public consultations.

Changes from Version 1

Language tag has been updated.

Changes from Version 2

Unicode Version has been updated.

Blocked variants have been added for homoglyphs of ASCII letters. These have no effect unless the LGR is used together with LDH labels in the same zone.

References

General reference for the language:

• Scatton, Ernest B. 1993. “Bulgarian”, in Bernard Comrie & Greville G. Corbett, eds. The Slavonic languages. London; New York: Routledge. ISBN 0-415-04755-2

Other reference cited in this document:

[RFC 7940]

Davies, K. and A. Freytag, “Representing Label Generation Rulesets Using XML”, RFC 7940, August 2016,
https://www.rfc-editor.org/info/rfc7940

[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/

In the listing of the repertoire by code point, references starting from [0] refer to the version of the Unicode Standard in which the corresponding code point was initially encoded. Other references (starting from [100]) document usage of 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. For more details, see the Table of References below.

Character Classes

Implict defined by script tag	3

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
implicit	Tag=sc:Cyrl	32	{0430-044A 044C 044E-0450 045D}		Any character tagged as Cyrillic
implicit	Tag=sc:Latn	8	{0061 0063 0065 006F-0070 0072 0078-0079}		Any character tagged as Latin
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).

Implicit

An anonymous class implicitly defined based on tag value and for which there is no named equivalent.

Whole label evaluation and context rules

Number of rules	3
Used to trigger actions	1
Used as context rule (C)	2
Anchored context rules	1

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}]]]	✔			[150]	RFC 5891 restrictions on placement of combining marks ⍟
hyphen-minus-disallowed	(((start))← ⚓︎)|(⚓︎ →((end)))|(((start)..\u002D)← ⚓︎)		✔	C	[150]	RFC 5891 restrictions on placement of U+002D (-) ⍟
extended-cp	(start)(end)			C		context to gate off code points from the extended range, matches no label ⍟

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.

( ) - 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 (...|...).

start or end

(start) matches the start of the label; (end) matches the end of the label.

. - any code point

. matches any code point.

[\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 (∪ = union, ∩ = intersection, ∖ = difference, ∆ = symmetric difference).

∅= - 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.

(^$) - empty label

The regex (^$) matches the empty label. Used as a context rule, it always fails to match, thus disallowing the affected code point in any label. By convention, it is used for context rules that disable code points that are not part of the repertoire, yet explicitly listed in the LGR as excluded or for optional future extension.

⍟ - 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		by default, labels with leading combining marks are invalid
2	if at least one variant is in	{out-of-repertoire-var}	→	invalid		any variant label with a code point out of repertoire is invalid ⍟
3	if at least one variant is in	{blocked}	→	blocked		any variant label containing blocked variants is blocked ⍟
4	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.