Label Generation Rules for Belarusian

Overview

This document specifies a reference set of Label Generation Rules for Belarusian using a limited repertoire as appropriate for a second level domain.

Repertoire

All references converge on 32 Cyrillic code points (23 +9 as defined by RFC 5992 [130]). One source [302], lists U+0449 (щ) CYRILLIC SMALL LETTER SHCHA and U+044A (ъ) CYRILLIC SMALL LETTER HARD SIGN as rare in Belarusian; these appear to be used in Russian words or names, not in Belarusian words and names themselves. In Russian, the hard sign indicates the non-palatalization of a consonant preceding a morpheme beginning with a iotated vowel; in Belarusian this function is met by the use of an apostrophe or of U+02BC (ʼ) MODIFIER LETTER APOSTROPHE.

Note that, while U+02BC (ʼ) MODIFIER LETTER APOSTROPHE is protocol valid (PVALID) in IDNA2008; other forms of apostrophes such as U+0027 (') APOSTROPHE or U+2019 (’) RIGHT SINGLE QUOTATION MARK are DISALLOWED. As [RFC6912] points out, in a public zone, many users may read U+02BC (ʼ) as indistinguishable from the regular apostrophe. Therefore, following the principle of conservatism, and in response to a comment made by the IAB during public Comments, the code point U+02BC (ʼ) is not included here.

There is an IDN table published in the IANA Repository of IDN Practices for Belarus, not under '.by' (Belarus cctld) but in a new TLD .бел also administered by Belarus, see [700]. The following text is excerpted from clause 7 from its General Provisions:

"A domain name in domain ".бел" must contain not less than two and no more than sixty three letters of Belarusian or Russian alphabet, numbers, symbols, "hyphen" ("-") and "apostrophe" (" ' "), it must not begin (end) with the symbol "hyphen" ("-") and (or) "apostrophe" (" ' "). When choosing a domain name one should consider writing of the domains on Russian and Belarusian."

This apparently allows for support of a combination of both Belarusian and Russian and, contrary to the postition taken here, it also caters for support of U+02BC (ʼ) , albeit with a rule concerning the position of apostrophe within a label: neither leading nor ending.

The Acute accent may also be used as a stress mark on the vowel of a syllable or to disambiguate between minimal pairs. However, this is rare. See Stress and Disambiguation in [ACUTE].

There is some attested use of U+0438 (и) CYRILLIC SMALL LETTER I, U+0449 (щ) CYRILLIC SMALL LETTER SHCHA, U+044A (ъ) CYRILLIC SMALL LETTER HARD SIGN, and U+0491 (ґ) CYRILLIC SMALL LETTER GHE WITH UPTURN, but they seem to be only used as borrowed letters from Russian and/or Ukrainian. These 4 letters are part of the extended set.

Excluded code points

All letters in some references but not included:

• U+02BC (ʼ) MODIFIER LETTER APOSTROPHE

• U+0430 U+0301 (а́) CYRILLIC SMALL LETTER A WITH ACUTE ACCENT

• U+0435 U+0301 (е́) CYRILLIC SMALL LETTER IE WITH ACUTE ACCENT

• U+043E U+0301 (о́) CYRILLIC SMALL LETTER O WITH ACUTE ACCENT

• U+0443 U+0301 (у́) CYRILLIC SMALL LETTER U WITH ACUTE ACCENT

• U+044B U+0301 (ы́) CYRILLIC SMALL LETTER YERU WITH ACUTE ACCENT

• U+044D U+0301 (э́) CYRILLIC SMALL LETTER E WITH ACUTE ACCENT

• U+044E U+0301 (ю́) CYRILLIC SMALL LETTER YU WITH ACUTE ACCENT

• U+044F U+0301 (я́) CYRILLIC SMALL LETTER YA WITH ACUTE ACCENT

• U+0451 U+0301 (ё́) CYRILLIC SMALL LETTER IO WITH ACUTE ACCENT

• U+0456 U+0301 (і́) CYRILLIC SMALL LETTER BYELORUSSIAN-UKRAINIAN I WITH ACUTE 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 extended code points. To support extended single code points or code point sequences, delete the context "extended-cp" from their repertoire definition.

Variants

None.

Character Classes

This LGR defines no named character classes.

Rules

Common rules:

• 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 RFC5891 [120]. 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 RFC5891 [120].

Actions

Actions included are the default actions for LGRs as well as those needed to invalidate labels with misplaced combining marks and apostrophe modifiers.

Methodology and Contributors

This reference LGR for Belarusian for the 2nd 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.

References

General references for the language:

• Mayo, Peter. 1993. "Belorussian", in Bernard Comrie & Greville G. Corbett, eds. The Slavonic languages. London; New York: Routledge. ISBN 0-415-04755-2

• Ushkevich, Alexander, & Alexandra Zezulin. 1992. Byelorussian-English English Byelorussian dictionary with compete phonetics. New York: Hippocrene Books. ISBN 0-87052-114-4

Other references cited in this document:

[ACUTE]

Wikipedia, "Acute accent"
https://en.wikipedia.org/wiki/Acute_accent

[HARD-SIGN]

Wikipedia, "Hard sign",
http://en.wikipedia.org/wiki/Hard_sign

[RFC6912]

RFC6912, "Principles for Unicode Code Point Inclusion in Labels in the DNS",
http://www.rfc-base.org/txt/rfc-6912.txt

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. For more details, see the Table of References below.

Character Classes

The following table lists all named 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:Zyyy	11 Elements:	{002D 0030-0039}
implicit	Tag=sc:Cyrl	36 Elements:	{0430-044F 0451 0456 045E 0491}

Whole label evaluation and context rules

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. (Any use of context rules for variants is not indicated).

Name	Used as Trigger	Used as Context	Anchor	Regular Expression	Ref	Comment
leading-combining-mark	✔			(^[∅=[[∅=\p{gc=Mn}][∅=\p{gc=Mc}]]])	[120]	RFC5891 restrictions on placement of combining marks
hyphen-minus-disallowed		✔	✔	((((?<=^)⚓)|(⚓(?=$))|((?<=^..\u002D)⚓)))	[120]	RFC5891 restrictions on placement of U+002D
extended-cp		✔		(^$)		code points from the extended range

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 any label (catch-all)		→	valid		catch all (default action)