Annotated Unicode® Standard AnnexTechnical Report #14

Annotated Unicode Line Breaking AlgorithmProperties

VersionRevision

Unicode 151413121110987654Unicode 36.21.1.21.321.1.0.0.0.0.10.1

EditorsAuthors

Robin LeroyChristopher ChapmanAsmus Freytag (asmus@unicode.org), Andy Heninger (eggrobincchapmanandy.heninger@unicode.orgadobegmail.com)

Date	2023202220212020201920182017201620152014201320122010200920082006200520042003200220001999-0802050609010903080304030811-1516231715211201052014172718312229301715233115

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Summary

This annexreport presents the Unicodespecification of line breaking algorithm along with detailed descriptions of each of the character classes established by the Unicode line breaking property. The line breaking algorithm produces a set of "break opportunities", or positions that would be suitableproperties for wrapping lines when preparing textUnicode characters as well as a default algorithm for displaydetermining line break opportunities. A model implementation using pair tables is also provided.algorithm for determining line break opportunities..

Discussion: This Annotated Line Breaking Algorithm contains the entire text of Unicode Standard Annex #14, Unicode Line Breaking Algorithm, plus certain annotations. The annotations give a more in-depth analysis of the algorithm. They describe the reason for each nonobvious rule, and point out interesting ramifications of the rules and interactions among the rules (interesting to Unicode maintainers, that is). (The text you are reading now is an annotation.)

The structure of this document is heavily inspired by that of the Annotated Ada Reference Manual. For a description of the various kinds of annotations, see paragraphs 1(2.dd) through 1(2.ll) in that document.

A version number of the form /v[.v[.v]] follows the paragraph number for any paragraph that has been modified from the original Unicode Line Breaking Algorithm (Unicode Version 3.0.0). Paragraph numbers are of the form pp{.nn}, where pp is a sequential numbering of the paragraphs of Version 3.0.0, and the nn are insertion numbers. For instance, the first paragraph inserted after paragraph 3 is numbered 3.1, the second is numbered 3.2, etc. A paragraph inserted between paragraphs 3.1 and 3.2 is numbered 3.1.1, a paragraph inserted between paragraphs 3 and 3.1 is numbered 3.0.1. Inserted text is indicated by highlighting, and deleted text is indicated by strikethroughs. Colour is used to indicate the version of the change. Deleted paragraphs are indicated by the text “This paragraph was deleted.”, or by a description of the new location of any text retained. Compare the Annotated Ada 2012 Reference Manual, Introduction (77.5).

Annotations are numbered similarly, except that the first insertion number is alphabetic rather than numeric.

Discussion: This document is available as an interactive web page; the bar on the right-hand side of the document allows for the selection of the base version from which changes are shown and the “head” version which determines the most recent changes shown. Paragraph deleted by the base version or by earlier versions may be suppressed. Clicking on a version number sets the head to that version and the base to the preceding version, thus showing the changes from that version. These settings are reflected as URL parameters.

Status

This document has been reviewed by Unicode members and other interested parties, and has been approved for publication by the Unicode Consortium. This is a stable document and may be usedTechnical Committee as reference material or cited as a normativeUnicode Standard Annex. ThisIt is a stable document and may be used as referencecontains informative material or cited as aand normative specifications which have been considered and approved by the Unicode Technical Committee for publication as a Technical Report and as part of the Unicode Standard, Version 3.0. Any reference by other specifications.from another document.to version 3.0 of the Unicode Standard automatically includes this technical report. Please mail corrigenda and other comments to the author.

To be honest: The document that has been reviewed by the UTC is the actual UAX #14, available at https://www.unicode.org/unicode/reports/tr14/. While the text outside of the annotations comes from that UAX, it has been processed in a way that is not stable and may alter its meaning; in particular, most formatting is lost.

The annotations have not been considered, reviewed, nor approved by the UTC nor by any other Technical Committee.

This Annotated UAX is not a stable document. It has not been approved by any of the Unicode Technical Committees, nor is it part of the Unicode Standard or any other Unicode specification.

A Unicode Standard Annex (UAX) forms an integral part of the Unicode Standard, but is published online as a separate document. The Unicode Standard may requireNote that conformance to normative content in acarrying the same Unicode Standard Annex, if so specified in the Conformance chapter of that version of the Unicode Standard. The version number of a UAX document corresponds includes conformance to the version number of theits Unicode Standard of which it forms a part.at the last point that theAnnexes. The version number of, but is published as a UAXseparate document corresponds. Note that conformance to thea version number of the Unicode Standard at the last point that the UAX document was updated.includes conformance to its Unicode Standard Annexes.

Please submit corrigenda and other comments with the online reporting form [Feedback]. Related information that is useful in understanding this annexdocument is found in Unicode Standard Annex #41, “Commonthe References for Unicode Standard Annexes.”section. For the latest version of the Unicode Standard, see [Unicode]. For a list of current Unicode Technical Reports, seeSee [Reports]. For more information about versions of the for aA list of currentThe content of all technical reports must be understood in the context of the appropriate version of the Unicode Technical Reports is found onStandard. References in this technical report to sections of the Unicode Standard refer to the Unicode Standard, Version 3.0. See http://www.unicode.org/unicode/reports/. For more information about versions of the Unicode Standard, see [Versions]. For any errata which may apply to this annex, see [Errata].http://www.unicode.org/unicode/standard/versions/. for more information.

Contents

• 1. Overview and Scope

• 2. Definitions

• 3. IntroductionDescription

3.1 Determining Line Break Opportunities

• 4. Conformance

4.1 Conformance Requirements

• 5. Line Breaking Properties

• 5.1 Description of Line Breaking Properties

• 5.2 Additional Details on Dictionary Usage

5.3 Use of Hyphen

5.43 Additional Details on the Use of Soft Hyphen

5.54 Additional Details on the Use of Double Hyphen

5.65 Tibetan Line Breaking

5.7 Word Separator Characters

• 6. Line Breaking Algorithm

6.1 Non-tailorable Line Breaking Rules

6.2 Tailorable Line Breaking Rules

• 7. Deleted. (Formerly was: Pair Table-BasedbasedTabletable Based Implementation)

• 8.• 7.6 Customization

8.1 Types of Tailoring

8.2• 7.7 Examples of Customization

9 Implementation Notes

9.1 Combining Marks in Regular Expression-Based Implementations

9.28.3 Legacy Support for Space Character as Base for Combining Marks

10 Testing

11 Rule Numbering Across Versions

• 8 References

• 9 Acknowledgments

• Modifications10 Changes from Previous Revisions

1 Overview and Scope

Line breaking, also known as word wrapping, is the process of breaking a section of text into lines such that it will fit in the available width of a page, window or other display area. The Unicode Line Breaking Algorithm performs part of this process. Given an input text, it produces a set of positions called "break opportunities" that are appropriate points to begin a new line. The selection of actual line break positions from the set of break opportunities is not covered by the Unicode Line Breaking Algorithm, but is in the domain of higher level software with knowledge of the available width and the display size of the text.

TheAlthough the text of theThe Unicode Standard [UnicodeU3.0] presents a limited description of some of the characters with specific functionsfunction ina summary of basic line -breaking behavior, butitbut does not give a complete specification of line breaking behavior. This annexUnicode Standard Annextechnical report provides more detailedthe needed information about default line breaking behavior, reflectingin a way that reflects best practices. The Unicode Standard assigns normativeNormative line-breaking properties to those characters that are intendedassigned to explicitly influencethose characters whose line breaking behavior must be identical across all implementations. For all other classes of characters informative, line-breaking and for the support of multilingual texts.which the line-breaking behavior is therefore expected to be identical across all implementations.properties are provided.

For most Unicode characters, considerable variation in line breaking behavior can be expected, including variation based on local or stylistic preferences. For that reasonTherefore, the line breaking properties provided for these charactersthat are informative. Some characters are intended to explicitly influence line breaking. Their line breaking behavior is therefore expected to be identical across all implementations. As described in this annex, the Unicode Standard assigns normative line breaking properties to those characters. The Unicode Line Breaking Algorithm is a tailorable set of rules that uses these line breakStandard assigns normative line breaking properties to those characters. The Unicode Line Breaking Algorithm is a tailorable set of rules that usesprovided for these line breaking properties in contextcharacters are informative. Some characters are intended to determineexplicitly influence line break opportunities.ing. Their line breaking behavior is therefore expected to be identical across all implementations. The Unicode Standard assigns normative line breaking properties to thoseother characters. informative line-breaking properties are provided. For these characters, considerable variation in line-breaking behavior can be expected, including variation based on local or stylistic preferences.

This annexdocument opens withFollowing the formal definitions, a and summary of the line - breaking task and the context in which it occurs in overall text layout, followed by a brief section on conformance requirements. TwoThreeFourproperties, there are fourthree main sections follow::

•1. Section 5, Line Breaking Properties, contains a narrativetextual description of the line breaking behavior of the characters inof the Unicode Standard, and their grouping them in alphabetical order by line breaking class.property. These descriptions do not take account of the order of precedence. Section 6 provides a set of rules listed in order of precedence that constitute a line breaking algorithm. Section 7 provides the detailed description of an efficient pair table based implementation of the algorithm.

•2. Section 6, Line Breaking Algorithm, provides a set of rules listed in order of precedence that constitute a line breaking algorithm.

The nextfinal two sections discuss issues of customization and implementation.

• Section 8, Customization, provides a discussion of howon ways to customize or tailor the algorithm.

• Section 9, Implementation Notes, provides additional information to implementers using regular expression-based techniques or requiring legacy support for combining marks.

• Section 10, Testing, describes the test data file that is available for checking implementations of the line breaking algorithm.

• Section 11, Rule Numbering Across Versions, documents changes in the numbering of the line breaking rules across Unicode versions.

2 Definitions

The notationAll terms not defined in this annex differs somewhat from the notationhere shall be as defined elsewhere in the Unicode Standard. [UnicodeUnicode5.20]. The notation defined in this annex differs somewhat from the notation defined elsewhere in the Unicode Standard. All other]. The notation used here without an explicit definition shall be as defined elsewhere in this technical report differs somewhat from the notation defined elsewhere in the Unicode Standard. All other notation used here without an explicit definition shall be as defined in the Unicode Standard. ..

All other notation used here without an explicit definition shall be as defined elsewhere in the Unicode Standard [Unicode].

LD1. Line Fitting: Thefitting —- the process of determining the how much text will fit on a line of text, given the available space between the margins and the actual display width of the text.

LD2. Line Break: The —- the position in the text where one line ends and the next one starts.

LD3. Line Break Opportunity: A place where —- a place where a line is allowed to end. Whether a given position in the text is a valid line break opportunity depends on context as well as the line breaking rules in force., as well as on context.

• Whether a given position in the text is a valid line break opportunity depends on the context as well as the line breaking rules in force.

LD4. Line Breaking: The —- the process of selecting one among several line break opportunities such that the resulting line is optimal or ends atthat part of a text that can be displayed on a line. In other words, selecting one among several line breaking opportunities such that the resulting line is optimal or ends at a(unless the user- requested an explicit line break.).

LD5. Line Breaking Property: —- A character property with enumeratedmutually exclusive values, as listedset out in Table 1, and separated into normative and informative values.. Line breaking property values are used to classify characters, and takenarranged in context, determine the type ofapproximate order of precedence. Line break.ing properties are used to determine the type of break.

• Line breaking property values are used to classify characters and, taken in context, determine the type of line break opportunity..

Discussion: While many rules depend only on the code points either side of the break (those of the form A # B or simply A # or # B, where # is either ÷, ×, or !), others depend on context further away. Such rules are said to require extended context.

Rules requiring extended context used to be a concern for pair table-based implementations, and were listed in Section 7. As more rules of this kind have been added, pair table-based implementations have become intractable, and this section has been removed.

However, extended context can lead to unexpected interactions between the rules, so they are called out in this annotated version with the annotation “Ramification: This rule requires extended context.” in order to facilitate the analysis of the algorithm.

Implementations based on state machines may require special treatment for rules of the form A # B C or similar that require more than one character of lookahead beyond the break. These are annotated with “Ramification: This rule requires extended context after the break.”.

LD6. Line Breaking Class: A —- a class of characters with the same line breaking property value.

• The line breaking classes are described in Section 5.1, Description of Line Breaking Classes are described in Section 5.1, Description of Line Breaking Properties.

LD7. Mandatory Break: A line must break following -— a character that has the mandatoryline must break following a character that has the mandatory break property. Such a break is alsoAlso known as a forced break and. This is indicated in the rules as B !, where B is the character with the mandatory break property. (In the notation of the Unicode Standard, Version 3.0 [U3.0], this would be: B ×, although the standard doesn't specify whether or not a break is forced or just an opportunity.)

• Such a break is also known as a forced break and is indicated in the rules as B !, where B is the character with the mandatory break property.

LD8. Direct Break: A —- a line breaking opportunity exists between two adjacent characters of the given line breaking classesproperties. This is indicated in the rules below as B ÷ A, where B is the character class of the character before and A is the character class of the character after the break. (If they are separated by one or more space characters, a break opportunity also exists after the last space. In) This indicated in the pair table, below as B ÷ A, where B is the character class of the character before and A is the character class of the character after the break and the optional space characters are not shown.

• A direct break is indicated in the rules below as B ÷ A, where B is the character class of the character before and A is the character class of the character after the break. If they are separated by one or more space characters, a break opportunity also exists instead after the last space. In the pair table, the optional space characters are not shown.

LD9. Indirect Break: A —- a line breaking opportunity exists between two characters of the given line breaking classesproperties only if they are separated by one or more spaces. In this case, a break opportunity exists after the last space. No break opportunity exists if the characters are immediately adjacent. This is indicated in the pair table below as B % A, where B is the character class of the character before and A is the character class of the character after the break. Even though no and the optional space characters are not shown in the pair table, an indirect break can only occur if one or more spaces follow B. In the notation of the rules in Section 6, Line Breaking AlgorithmUnicode Standard, this would be represented as two rules: B × A and B SP+ ÷ A.

• For an indirect break, a break opportunity exists after the last space. No break opportunity exists if the characters are immediately adjacent.

• In the notation of the rules in Section 6, Line Breaking Algorithm, anAn indirect break is representedindicated in the pair table in Table 2 as two rules: B ×% A and, where B is the character class of the character before and A is the character class of the character after the break. Even though space characters are not shown in the pair table, an indirect break can occur only if one or more spaces follow B. In the notation of the rules in Section 6, Line Breaking Algorithm, this would be represented as two rules: B × A and B SP+ ÷ A where the “+” sign means one or more occurrences..

Discussion: Indirect breaks can be represented with such a rule requiring extended context, but within the algorithm, they are instead expressed as × SP, SP ÷, B × A, which does not require extended context.

LD10. Prohibited Break: No —- no line breaking opportunity exists between two characters of the given line breaking classesproperties, even if they are separated by one or more space characters. This is indicated in the pair table below as B ^ A, where B is the character class of the character before and A is the character class of the character after the break and the optional space characters are not shown. In the notation of the the rules in Section 6, Line Breaking AlgorithmUnicode Standard, this would be expressed as athe rule of the form: B SP* × A.

• In the notation of the rules in Section 6, Line Breaking Algorithm, aA prohibiteddirect break is expressedindicated in the pair table in Table 2 as a rule of the form: B ^ A, where B is the character class of the character before and A is the character class of the character after the break, and the optional space characters are not shown. In the notation of the rules in Section 6, Line Breaking Algorithm, this would be expressed as a rule of the form: B SP* × A.

Discussion: Not all prohibited breaks involve a rule requiring extended context: a rule × A before the rule SP ÷ is a prohibited break before A. However, prohibited breaks with context before spaces require extended context.

LD11. Hyphenation: — Hyphenation uses language-specific rules to provide additional line break opportunities within a word. Hyphenation improves the layout of narrow columns, especially for languages with many longer words, such as German or Finnish. For the purpose of this document, it is assumed that hyphenation is equivalentuses language specific rules to insertinginsertion of soft hyphen characters. All other aspects of hyphenation are outside the scopeprovide additional line breaking opportunities within a word. Hyphenation improves the layout of narrow columns, especially for languages with many longer words, such as German or Finnish. For the purpose of this document., it is assumed that hyphenation is equivalent to insertion of soft hyphen characters. All other aspects of hyphenation are outside the scope of this document.

• Hyphenation improves the layout of narrow columns, especially for languages with many longer words, such as German or Finnish. For the purpose of this annex, it is assumed that hyphenation is equivalent to inserting soft hyphen characters. All other aspects of hyphenation are outside the scope of this annex.

Table 1 lists all of line breaking classes by name, also giving their class abbreviation and their status as tailorable or not. The examples and brief indication of line breaking behavior in this table are merely typical, not exhaustive. Section 5.1, Description of Line Breaking Properties, provides a detailed description of eachsummary listing of all line breaking class, includingclasses while Section 5.1, Description of Line Breaking Properties, provides a detailed overview of thedescription of each line breaking behavior for characters of that class., including detailed overview of the line breaking behavior for characters of that class.

Table 1.: Line Breaking ClassesProperties (* = non-tailorablenormative)

ClassValue

Descriptive NameLine Breaking Property

Examples

Behavior

Characters with This Property...this property...

Non-tailorableNormative Line Breaking ClassesProperties

BK *

Mandatory Break

NL, PARAGRAPH SEPARATORPS

Cause

cause a line break (after).

CR *

Carriage Return

CR

Cause

cause a line break (after), except between CR and LF

LF *

Line Feed

LF

Cause

cause a line break (after), except between CR and LF

CM *

Attached Characters and Combining Marks

Combining Mark

Combining marksMarks, control codes, Conjoining Jamo (non-initial)

Prohibitprohibit a line break between the character and the preceding character

NL *

Next Line

NEL

Cause

cause a line break (after)

SG *

SurrogateSurrogates

High Surrogates

DoShould

should not occur in well-formed textprohibit a break betweenfrom a high and a following low surrogate

WJ *

Word Joiner

WJ

Prohibit

prohibit line breaks before andor after

ZW *

Zero Width Space

ZWSP

Provide

provide aoptional break opportunity

GL *

Non-breaking (“Glue”)

CGJ,

NBSP, ZWNBSP, WJ, CGJZWNSP

Prohibit

prohibit line breaks before andor after.

SP *

Space

SPACE

Space

Enable indirectGenerally

generally provide a line break opportunity after the character, enableenables indirect breaks

ZWJ

Zero Width Joiner

Zero Width Joiner

Prohibit line breaks within joiner sequences

Break Opportunities

B2

Break Opportunity Before and After

Em dash

EM Dash

Provide

provide a line break opportunity before and after the character

BA

Break Opportunity After

Spaces, hyphensHyphens

Generally

generally provide a line break opportunity after the character

BB

Break Opportunity Before

Punctuation used in dictionaries

Generally

generally provide a line break opportunity before the character.

HY

Hyphen

HYPHENHyphen-MINUSMinus

Provide

provide a line break opportunity after the character, except in numeric context

CB

Contingent Break Opportunity

Inline objects

Provide a line break opportunity contingent on additional information

Characters Prohibiting Certain Breaks

CL

CloseClosing Punctuation

“)”, “]”, “}”, “❳”, “⟫” etc.

Prohibitprohibit a line breaksbreak before

CP

Close Parenthesis

“)”, “]”

Prohibit line breaks before

EX

Exclamation/ Interrogation

“!”, “?”, etc.

Prohibitprohibit line breaksbreak before

IN

Inseparable

Leaders

Allow

allow only indirect line breaks between pairs.

NS

NonstarterNon Starter

“‼”, “‽”, “⁇”, “⁉”, etc.

small kana

Allow

allow only indirect line breaksbreak before

OP

Opening Punctuation

“(“, “[“, “{“, etc.

Prohibitprohibit a line breaksbreak after

QU

Ambiguous Quotation

Quotation marks

Act

act like they are both opening and closing

Numeric ContextID

Ideographic

Ideographs

break before or after

IS

Infix Numeric Separator (Numeric)

. ,

. ,

Preventprevent breaks after any and before numeric

NU

Numeric

Digits

Form

form numeric expressions for line breaking purposes

PO

Postfix (Numeric)

%, ¢

Do

do not break following a numeric expression

PR

Prefix (Numeric)

$, £, ¥, etc.

Dodo notdon't break in front of a numeric expression

SY

Symbols Allowing Break AfterBreaks

/

Prevent

prevent a break before, and allow a break after

Other Characters

AI

Ambiguous (Alphabetic or Ideographic)

Characters with Ambiguous East Asian Width

Act like AL when the resolved EAW is N; otherwise,

act like AL when the resolved EAW is N otherwise act as ID

AK

Aksara

Consonants

Form orthographic syllables in Brahmic scripts

AL

Ordinary Alphabetic and Symbol Characters

Alphabets and regular symbols

Are alphabetic characters or symbols that

are used with alphabetic characters or symbols that are used with alphabetic characters

AP

Aksara Pre-Base

Pre-base repha

Form orthographic syllables in Brahmic scripts

AS

Aksara Start

Independent vowels

Form orthographic syllables in Brahmic scripts

CJ

Conditional Japanese Starter

Small kana

Treat as NS or ID for strict or normal breaking.

EB

Emoji Base

All emoji allowing modifiers

Do not break from following Emoji Modifier

EM

Emoji Modifier

Skin tone modifiers

Do not break from preceding Emoji Base

H2

Hangul LV Syllable

Hangul

Formform Korean syllable blocks

H3

Hangul LVT Syllable

Hangul

Formform Korean syllable blocks

HL

Hebrew Letter

Hebrew

Do not break around a following hyphen; otherwise act as Alphabetic

ID

Ideographic

Ideographs

Breakbreak before or after, except in some numeric context

JL

Hangul L Jamo

Conjoining jamoJamo

Formform Korean syllable blocks

JV

Hangul V Jamo

Conjoining jamoJamo

Formform Korean syllable blocks

JT

Hangul T Jamo

Conjoining jamoJamo

Formform Korean syllable blocks

RI

Regional Indicator

REGIONAL INDICATOR SYMBOL LETTER A .. Z

Keep pairs together. For pairs, break before and after other classesfrom others

SA

Complex Context Dependent (South East Asian)

South East Asian: Thai, Lao, Khmer

Provide

provide a line break opportunity contingent on additional, language- specific context analysis

VF

Virama Final

Viramas for final consonants

Form orthographic syllables in Brahmic scripts

VI

Virama

Conjoining viramas

Form orthographic syllables in Brahmic scripts

XX

Unknown

Most unassigned

Unassigned, private-usePrivate Use

Havehave

are all characters with (as yet) unknown line breaking behavior or unassigned code positions

3 IntroductionDescription

Lines are broken as the result of oneeither of two conditions. The first is the presence of a mandatory line breaking character. The second condition results fromis the presence of a formatting algorithm having selected among availablemandatoryan explicit line break opportunities; ideally the chosen line breaking character. The second condition results from a formatting algorithm having selected among available line breaking opportunities; ideally the chosen line break the particular one that results in the optimal layout of the text.

Different formatting algorithms may use different methods to determineof determining anThe definition of optimal line break. For example, simple implementations just consider a single line at a time, trying to find a locally is outside the scope of this document. Different formatting algorithms may use different methods of determining an optimal line break. A basic, yet widely used approach isFor example, simple implementations just consider a line at a time, trying to find a locally optimal line break. A common approach is to allow no compression or expansion of the intercharacter and interwordinter-character and inter-word spaces and consider the longest line that fits. More complex formatting algorithms often take into account the interaction of line breaking decisions for the whole paragraph. The well-known text layout system [TEX] implements an example of such a globallyWhen compression or expansion is allowed, a locally optimal strategy that may make complex tradeoffs across an entire paragraph to avoid unnecessary hyphenation and other legal, but inferior breaks. For a description of this strategy, see [Knuth78].line break seeks to balance the relative merits of the resulting amounts of compression and expansion for different line break candidates.

When compression or expansion is allowed, a locally optimal line break seeks to balance the relative merits of the resulting amounts of compression and expansion for different line break candidates. When expanding or compressing interwordinter-word space according to common typographical practice, only the spacesspace marked by U+0020 SPACE and, U+00A0 NO-BREAK SPACE, and U+3000 IDEOGRAPHIC SPACE are normally subject to compression, and only spaces marked by U+0020 SPACE, U+00A0 NO-BREAK SPACE, and occasionally spaces marked by U+2009 THIN SPACE are subject to expansion. All other space characters normally have fixed width. When expanding or compressing intercharacterinter-character space, the presence of U+200B ZERO WIDTH SPACE or U+2060 WORD JOINER isare always ignored.

Local custom or document style determines whether andWhether to what degreeallow expansion of intercharacterinter-character space is allowed into justifying a line, and how much, depends on local custom. In thosesome languages, such asfor example, German, where intercharacterinter-character space is commonly used to mark e m p h a s i s (like this). In such languages, allowing variable intercharacterinter-character spacing would have the unintended effect of adding random emphasis, and isshould therefore bestbe avoided. In table headings that use Han ideographs, even extreme amounts of intercharacter space commonly occur as short texts are spread out across the entire available space to distribute the characters evenly from end to end. altogether..

In line breaklinebreaking it is necessary to distinguish between threetwo related tasks. The first is the determination of all legal line break opportunities, given a string of text. This is the scope of the Unicode Line Breaking Algorithm. The second task is the selection of the actual location for breaking a given line of text. This selection not only takes into account the width of the line compared to the width of the text, but may also apply an additional prioritization of line breaks based on aesthetic and other criteria. What defines an optimal choice for a given line break is outside the scope of this annex, as are methods for its selection. The third is the possible justification of lines, once actual locations for line breaking have been determined, and is also out of scope for the Unicode Line Breaking Algorithm.

Finally, most text layout systems maywill support an emergency mode thatwhich handles the case of an unusual line that contains no otherwise permitted line break opportunities. In such line layout emergencies, line breaks may be placed with no regard to the ordinary line breaking behavior of the characters involved. The details of opportunities. In such an emergency modeline layout emergencies, line breaks are outside the scope of this annex, however, it is recommended that grapheme clusters be kept together.placed with no regard to the ordinary line breaking behavior of the characters involved.

3.1 Determining Line Break Opportunitiesline breaking opportunities

FourThree principal styles of context analysis determine line -breaking opportunities.

1. Western: — (spaces and hyphens are used to determine breaks)

2. East Asian: — (lines can break anywhere, unless prohibited)

3. South East Asian: — line breaks (require morphological analysis)

4. Brahmic: line breaks can occur at the boundaries of any orthographic syllable

The first, or Western style is commonly used for scripts employing the space character. Hyphenation is oftenThe second is used with spaceEast Asian ideographic scripts. The third is used for scripts such as Thai, which do not use spaces, but which restrict word-based line breakingbreaks to provide additional line break opportunities— - however, itsyllable boundaries, the determination of which requires knowledge of the language and in addition, it may needpotentially user interaction or overrides.comparable to that required by a hyphenation algorithm.

The second style of context analysis is used with East Asian ideographic and syllabic scripts. In these scripts, lines can break anywhere, except before or after certain characters. The precise set of prohibited line breaks may depend on user preference or local custom and is commonly tailorable..

Korean makes use of both styles of line break.NOTE: WhenNote: Korean text is laid out justified, the second style is commonly used, even for interspersed Latin letters. But when ragged margins are used, the Westernfirst stylemay alternately use a space-based (relying on spacesstyle 1) is commonly used instead, even for ideographs.. of the style 2 context analysis.

The third style is used for scripts such as Thai, which allow line breaks only at word boundaries, but do not markuse spaces, but which restrict word -breaks to syllable boundaries in any way, so that the, whosethe determination of line break opportunities of which requires knowledge of the language dependent text analysis. Algorithms and data for such analysis arecomparable to that required by a hyphenation algorithm. Such anand algorithm is beyond the scope of the Unicode Standard.this report.

The fourth style is used in some Brahmic scripts, such as Brahmi, Balinese, or Javanese, which allow line breaks to occur at the boundaries of any orthographic syllable, without restricting them to word boundaries. This style is only supported for scripts that encode orthographic syllables in primarily phonetic order.

For multilingual text, the Western, and East Asian, and Brahmic styles can be unified into a single set of specifications, based on the information in this annexreport. Unicode characters have explicit line breaking properties assigned to them. These properties can be utilized to implement the effect of both ofwith theseone and two styles of context analysis for line break opportunities. Customization for user preferences or document style can then be unified into a single set of specifications, based on the information provided in this report. Some Unicode characters have explicit line breaking properties assigned to them. These can be utilized with these two styles of context analysis for line break opportunities. Customization for user preferences or document style can then be achieved by tailoring that specification.

In bidirectional text,Determining the line breaks in bidirectional text takes are determinedplace before applying rule L1 of the Unicode Bidirectional Algorithm [UAX9Bidi]. However, line breakingit is strictly independent of directional properties of the characters or of any auxiliary information determined by the application of rules of that algorithm.

4 Conformance

There is no single method for determining line breaks; the rules may differchange based on user preference and document layout. TheTherefore the information, in this annex, including the specification of the line breaking algorithm, allowsmust allow for the necessary flexibility in determining line breaks according to different conventionsis informative, rather than normative. However, some characters have been encoded explicitly for their effectfact, the rules may change based on user preference and document layout. Therefore the information in this annex, including the specification of the line breaking. Because usersUsers adding such characters to a text expect that they will have the desired effect. For that reason, these characters have been given algorithm, is informative, rather than requirednon-tailorable linenormative. However, there are some characters which have been encoded explicitly for the purpose of their effect on line breaking. Users adding such characters to a text must be able to expect that they will have the desired effect. For that reason, these characters have been given normative line breaking behavior. The conformance requirements are spelled out in the following subsections.

To handle certain situations, some line breaking implementations use techniques that cannot be expressed within the framework of the Unicode Line Breaking Algorithm. Examples include using dictionaries of words for languages that do notthe use spaces, such as Thai; recognition of the language of the text in order to choose among different punctuation conventions; usingof dictionaries of common abbreviations or contractions to resolve ambiguities with periods or apostrophes; or a deeper analysis of common syntaxeswords for numberslanguages that do not use spaces, such as Thai; recognition of the language of the text in order to choose among different punctuation conventions; the use of dictionaries of common abbreviations or contractions to resolve ambiguities with periods or apostrophes; or a deeper analysis of common syntaxes for numbers or dates, and so on. The conformance requirements permit variations of this kind.

Processes which support multiple modes for determining line breaks are also accommodated. This situation can arise with marked-up text, rich text, style sheets, or other environments in which a higher-level protocol can carry formatting instructions that prevent or force line breaks in positions that differ from those specified by the Unicode Line Breaking Algorithm. The approach taken here requires that such processes have a conforming default line break behavior, andis to disclose that they also include overrides or optional behaviors that are invoked viarequire that such processes have a conforming default line break behavior, and to disclose that they also include overrides or optional behaviors that are invoked via a higher-level protocol.

The methods by which a line layout process chooses optimal line breaks from among the available break opportunities is outside the scope of this specification. The behavior of a line layout process in situations where there are no suitable break opportunities is also outside of the scope of this specification.

Note: Locale-sensitive line break specifications can be expressed in LDML [UTS35]. Tailorings are available in the Common Locale Data Repository [CLDR].

4.1 Conformance Requirements

UAX14-C1. A process that determines line breaks in Unicode text, and that purports to implement the Unicode Line Breaking Algorithm, shall do so in accordance with the specifications in this annex. In particular, the following three subconditionsthe absence of a permissible higher-level protocol, a process that determines line breaks in Unicode text, and that purports to implement the Unicode Line Breaking Algorithm, shall be met:do so in accordance with the specifications in this annex.

1. The sets of mandatory break positions and of break opportunities which the implementation produces include all of those specified by the rules in Section 6.1, Non-tailorable Line Breaking Rules.

2. There exist no break opportunities or mandatory breaks produced by the implementation that fall on a "non-break" position specified by the rules in Section 6.1, Non-tailorable Line Breaking Rules.

3. If the implementation tailors the behavior of Section 6.2, Tailorable Line Breaking Rules, that fact must be disclosed.

UAX14-C2. If an implementation has a default line breaking operation which conforms to UAX14-C1, but also has overrides based on aThe permissible higher-level protocol, that fact must be disclosed and any behavior that differs from that specified by the rules ofprotocols are described in Section 6.1, Non4.3, Higher-tailorable Line Breaking Rules, must be documented.Level Protocols.

Example: An XMLxml format provides markup which disables all line breaking over some span of text. When the markup is not in place, the default behavior is in conformance according to UAX14-C1. As long as the existence of the option is disclosed, that format can be said to conform to the Unicode Line Breaking Algorithm according to UAX14-C2.

As is the case for all other Unicode algorithms, this specification is a logical description—particular implementations can have more efficient mechanisms as long as they produce the same results. See C18 in Chapter 3, Conformance, of [Unicode]. While only disclosure of tailorings is required in the conformance clauses, documentation of the differences in behaviors is strongly encouraged.

5 Line Breaking Properties

ThisThe main emphasis in this section providesis to provide detailed narrative descriptions of the line breaking behavior of many Unicode characters. Many descriptions in this section provide additional informative detail about handling a given character at the end of a line, or during line layout, which goes beyond the simple determination of line breaks. In some cases, the text also gives guidance as to preferred characters for achieving a particular effectmany instances, the descriptions in this section provide additional informative detail about handling a given character at the end of a line, or during line layout, which goes beyond the simple determination of line breaks. In some cases, the text also gives guidance as to preferred characters for achieving a particular effectfew instances, the descriptions in this section provide additional detail about handling a given character at the end of adescription of the line breaking., which goes beyond the simple determination of breaking behavior and summarizesto summarize the membership of character classes for each value of the line breaks.breaking property. The full classification of all Unicode characters by their line breaking properties is available as the file LineBreaking.txt in the Unicode Character Database. This is a tab-delimited, three column plain text file, with code position, line breaking class and character name (for reference purpose only). The abbreviated way of listing the Ideographic, Hangul, Surrogate, and Private Use ranges is the same as in UnicodeData.txt.

This section also summarizes the membership of character classes corresponding to each value of the line breaking property. Note that the mnemonic names for each value of the line break classes are intended neither as exhaustive descriptions of their membership nor as indicators of their entire range of behaviors in the line breaking process. Instead, their main purpose is to serve as unique, yet broadlying property. Note that the mnemonic labels. In other words, as long as theirnames for the line breaking behavior is identical, otherwise unrelated characters will be grouped together classes are intended neither as exhaustive descriptions of their membership nor as indicators of their entire range of behaviors in the same line breaking process. Instead, their main purpose is to serve as unique, yet broadly mnemonic labels. In other words, as long as their line break behavior is identical, otherwise unrelated characters will be found grouped together in the same line break class.

The classification by property valuesproperties defined in this section and in the data filehere is used as input into the algorithmtwo algorithms defined in Section 6, Line Breaking Algorithm. ThatThis section describes a workable default line breaking method., and Section 8, Customization, discusses how the7, Pair -Table-Basedbased Implementation. These sections describebelow that implement workable default line breaking methods. Section 8, Customization, discusses how the defaultIn a few instances, the descriptions in this section provide additional detail about handling a given character at the end of a line breaking behavior can be tailored to the needs of specific languages or for particular languages for particular document styles and user preferences. Permitted customizations can include changing the classification of characters for certain classes., and which goes beyond the simple determination of line breaks.

In addition to the line breaking properties defined in this section, the algorithm defined in Section 6, Line Breaking Algorithm also makes use of East_Asian_Width property values, defined in Unicode Standard Annex #11, East Asian Width [UAX11]. Note that for purposes of the line breaking algorithm, those East_Asian_Width property values are tailorable, as are the rules of the line breaking algorithm which use them. (See rule LB30.)

Data File

The full classification of all Unicode characters by their line breaking properties, as of the time of publication of this document, is available in the current version of the file LineBreak.txt [Data14Data] in the Unicode Character Database [UCD]. This is a semicolontab-delimited, two- column, plain text file, with code position, and line breaking class. A comment at the end of each line indicates the character name. Ideographic, Hangul, Surrogate, and Private Use ranges are collapsed by giving a range in the first column.

The line break property assignments from the data file are normative. The descriptions of the line break classes in this UAX include examples of representative or interesting characters for each class, but for the complete list always refer to the data file.

Future Updates

As scripts are added to the Unicode Standard and become more widely implemented, line breaking classes may bescripts are added or the assignment of line breaking class may be changed for some characters. Implementers must not make any assumptions to the contrary. Any future updates willUnicode Standard and become, and more widely implemented and used on computers,scripts become more widely implemented and used on computers, more line breaking classes may be added, or the assignment of line breakinglinebreak class may be changed for some characters. Implementers mustImplementations should not make any assumptions to the contrary. Any future updates will be reflected in the latest version of the data file. (See the Unicode Character Database [UCD] for any specific version of the data file.datafile).

5.1 Description of Line Breaking Properties

Line breaking classesproperties are listed alphabetically. Each line breaking classproperty is marked with an annotation in parentheses with the following meanings:parenthesis for easy reference showing that...

Label

Meaning for the Class

(A)	It —- the classproperty allows a break opportunity after in specified contexts.

(XA)	It —- the classproperty prevents a break opportunity after in specified contexts.

(B)	It —- the classproperty allows a break opportunity before in specified contexts.

(XB)	It —- the classproperty prevents a break opportunity before in specified contexts.

(P)	It —- the classproperty allows a break opportunity for a pair of same characters.

(XP)	It —- the classproperty prevents a break opportunity for a pair of same characters.

NoteNOTE: The use of the letters B and A in these annotations marks the position of the break opportunity relative to the character. It is not to be confused with the use of the same letters in the other parts of this annexdocument, where they indicate the positionsposition of the characters relative to the break opportunity.

AI: —- Ambiguous (Alphabetic or Ideograph)

SomeAmbiguous characters that ordinarily act either like alphabetic or symbol characters (which havethat is,are those that can act either like alphabetic characters (i.e. those with the AL line breaking class) are treatedor like ideographs (that isor characters with line breaking class ID) in certain East Asian legacy contexts. Their line breaking behavior therefore depends, depending on the context. In the absence of appropriate context information, they are treated as class AL;, but see the note at the end of this description..

As originally defined, the line breakthis class AI contained all charactersCharacters with East_Asian_Width valueEast Asian Width property A (ambiguous width) that, and which would otherwise be AL in this classification. They, take on the AL line breaking class only when their resolved width is N (narrow) and take the line breaking class ID line breaking class, when their resolved width is W (wide). For more information on East_Asian_WidthEast Asian Width, and how to resolve it, see Unicode Standard AnnexTechnical Report #11, East Asian Width [UAX11EAW]. In the absence of information needed to resolve their East Asian Width, they are treated as class AL..

The original definition included many Latin, Greek, and Cyrillic characters. These characters are now classified by for which a default asassignment of the AL because use of the AL line breaking class better corresponds to modern practice. Where strict compatibility with older legacy implementations is desired, some of theseAt the same time, the set of ambiguous characters needhas been extended to be treated as ID in certain contexts. This can be done by always tailoring them to ID or by continuing to classify them as AI and resolving them to ID where required.completely encompass the enclosed alphanumeric characters used for numbering of bullets.

As part of the same revision, the set of ambiguous characters has been extended to completely encompass the enclosed alphanumeric characters used for numbering of bullets.

As updated, the AI line breaking class includes all characters with East Asian Width A that are outsidethe exception ofthis line breaking class includes all characters with East Asian Width W, except those in the range U+0000..U+1FFF, plus the followingthis line breaking class includes all characters: with East Asian Width A, plus the following characters:

24EA	CIRCLED DIGIT ZERO

2780..2793

DINGBAT CIRCLED SANS-SERIF DIGIT ONE..DINGBAT NEGATIVE CIRCLED SANS-SERIF NUMBER TEN

Characters with the line break class AI with East_Asian_Width value A typically take the AL line breaking class when their resolved East_Asian_Width is N (narrow) and take the line breaking class ID when their resolved width is W (wide). The remaining characters are then resolved to AL or ID in a consistent fashion. The details of this resolution are not specified in this annex. The line breaking rules in Section 6, Line Breaking Algorithm, and the pair table in Section 7, Pair Table-Based Implementation, merely require that all ambiguous characters be resolvedhave been resolved appropriately as part of assigning line breaking classes to the input characters.

Note: The canonical decompositions of characters of class AI are not necessarily of class AI themselves. The East_Asian_Width property A on which the definition of AI is largely based, does not preserve canonical equivalence. In the context of line breaking, the fact that a character has been assigned class AI means that the line break implementation must resolve it to either AL, or ID, in the absence of further tailoring. If preserving canonical equivalence is desired, an implementation is free to make sure that the resolved line break classesconversely. The East_Asian_Width property A on which the definition of AI is largely based, does not preserve canonical equivalence. Unless compatibility with particular legacy behavior is important, it may be sufficient to map all such characters to AL. This achievesIn the context of line breaking, the fact that a canonically equivalent resolution of line breakingcharacter has been assigned class AI means that the line break implementation must resolve it to either AL or ID, in the absence of further tailoring. If preserving canonical equivalence is desired, an implementation is free to make sure that the resolved line break classes, and is compatible preserve canonical equivalence. Unless compatibility with particular legacy behavior is important, it may be sufficient to map all such characters to AL. This achieves a canonically equivalent resolution of line breaking classes, and is compatible with emerging modern practice that treats these characters increasingly like regular alphabetic characters.

AK: Aksara (XB/XA)

The AK line break class is used for scripts that use the Brahmic style of context analysis and have a virama of Indic syllabic category Virama or Invisible_Stacker. It contains characters that can occur as the bases of orthographic syllables and can also follow a virama of Indic syllabic category Virama or Invisible_Stacker within the same orthographic syllable. Depending on the script, this may include characters with the Indic syllabic categories Consonant, Vowel_Independent, or Number.

1B05..1B33

BALINESE LETTER AKARA..BALINESE LETTER HA

1B45..1B4C

BALINESE LETTER KAF SASAK..BALINESE LETTER ARCHAIC JNYA

A984..A9B2

JAVANESE LETTER A..JAVANESE LETTER HA

11005..11037

BRAHMI LETTER A..BRAHMI LETTER OLD TAMIL NNNA

11071..11072

BRAHMI LETTER OLD TAMIL SHORT E..BRAHMI LETTER OLD TAMIL SHORT O

11075

BRAHMI LETTER OLD TAMIL LLA

11305..1130C

GRANTHA LETTER A..GRANTHA LETTER VOCALIC L

1130F..11310

GRANTHA LETTER EE..GRANTHA LETTER AI

11313..11328

GRANTHA LETTER OO..GRANTHA LETTER NA