UAX #14: Unicode Line Breaking Algorithm

UAX #14: Unicode Line Breaking Algorithm
Technical Reports
Unicode® Standard Annex #14
Unicode Line Breaking Algorithm
Version
Unicode 17.0.0
Editors
Robin Leroy (
eggrobin@unicode.org
Date
2025-09-05
This Version
Previous Version
Latest Version
Latest Proposed Update
Revision
55
Summary
This annex presents the Unicode 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 suitable for wrapping lines
when preparing text for display.
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 used as reference
material or cited as a normative reference by other specifications.
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 require conformance to normative content in a 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 to
the version of the Unicode Standard of which it forms a part.
Please submit corrigenda and other comments with the online reporting
form [
Feedback
].
Related information that is useful in understanding this annex is found in Unicode Standard Annex #41,
Common References for Unicode Standard Annexes
.”
For the latest version of the Unicode Standard, see [
Unicode
].
For a list of current Unicode Technical Reports, see [
Reports
].
For more information about versions of the Unicode Standard, see [
Versions
].
For any errata which may apply to this annex, see [
Errata
].
Contents
Overview and Scope
Definitions
Introduction
3.1
Determining Line Break Opportunities
Conformance
4.1
Conformance Requirements
Line Breaking Properties
5.1
Description of Line Breaking Properties
5.2
Dictionary Usage
5.3
Use of Hyphen
5.4
Use of Soft Hyphen
5.5
Use of Double Hyphen
5.6
Tibetan Line Breaking
5.7
Word Separator Characters
Line Breaking Algorithm
6.1
Non-tailorable Line Breaking Rules
6.2
Tailorable Line Breaking Rules
Deleted.
(Formerly was: Pair Table-Based Implementation)
Customization
8.1
Types of Tailoring
8.2
Examples of Customization
Implementation Notes
9.1
Combining Marks in Regular Expression-Based Implementations
9.2
Legacy Support for Space Character as Base for Combining Marks
10
Testing
11
History
References
Acknowledgments
Modifications
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.
The text of the Unicode Standard [
Unicode
] presents
a limited description of some of the characters with specific functions in
line breaking, but does not give a complete specification of line breaking behavior. This annex
provides more detailed information about default line breaking behavior, reflecting best
practices for the support of multilingual texts.
For most Unicode characters, considerable variation in line breaking
behavior can be expected, including variation based on local or stylistic
preferences. For that reason, the line breaking properties provided for
these characters 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 breaking properties in context to determine line break
opportunities.
This annex opens with formal definitions, a 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.
Two main sections follow:
Section 5,
Line Breaking Properties
, contains a narrative description of the
line breaking behavior of the characters in the Unicode Standard, grouping them in alphabetical
order by line breaking class.
Section 6,
Line Breaking Algorithm
provides a set of rules listed in order of precedence that
constitute a line breaking algorithm.
The next sections discuss issues of customization and implementation.
Section 8,
Customization
, provides a discussion of how to 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,
History
, provides references to additional
documentation for investigating changes to the algorithm across Unicode
versions.
Definitions
The notation defined in this annex differs somewhat from the
notation defined elsewhere 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:
The process of determining 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 position in the text where one line ends and the
next one starts.
LD3
Line Break Opportunity:
A place where a line is allowed to end.
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 process of selecting one among several line
break opportunities such that the resulting line is optimal or ends at a
user-requested explicit line break.
LD5
Line Breaking Property:
A character property with enumerated
values, as listed in
Table 1
, and separated into normative and informative
values.
Line breaking property values are used to classify characters and, taken in context,
determine the type of line break opportunity.
LD6
Line Breaking Class:
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 Properties
LD7
Mandatory Break:
A line must break following a character that has the mandatory break property.
Such a break is also known as a
forced
break and is
indicated in the rules as
B !
, where
is the character with the
mandatory break property.
LD8
Direct Break:
A line break opportunity exists between two
adjacent characters of the given line breaking classes.
A direct break is indicated in
the rules below as
, where
is the character class
of the character
before
and
is the character class of the
character
after
the break. If they are separated by one or more space
characters, a break opportunity exists instead after the last space.
LD9
Indirect Break:
A line break opportunity exists between two
characters of the given line breaking classes
only
if they are
separated by one or more spaces.
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
an indirect break is represented as two
rules:
and
SP
+ ÷ A
where the “+” sign means one or more occurrences.
LD10
Prohibited Break:
No line break opportunity exists between two
characters of the given line breaking classes, even if they are separated
by one or more space characters.
In the notation of the rules in
Section 6,
Line Breaking Algorithm
a prohibited break is expressed as a rule of the form:
SP
* × A
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 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 each line breaking class, including
detailed overview of the line breaking behavior for characters of that
class.
Table 1.
Line Breaking Classes
Class
Descriptive Name
Examples
Behavior
Non-tailorable Line Breaking Classes
BK
Mandatory Break
NL, PARAGRAPH SEPARATOR
Cause a line break (after)
CR
Carriage Return
CR
Cause a line break (after), except between CR and LF
LF
Line Feed
LF
Cause a line break (after)
CM
Combining Mark
Combining marks, control codes
Prohibit a line break between the character and the preceding character
NL
Next Line
NEL
Cause a line break (after)
SG
Surrogate
Surrogates
Do not occur in well-formed text
WJ
Word Joiner
WJ
Prohibit line breaks before and after
ZW
Zero Width Space
ZWSP
Provide a break opportunity
GL
Non-breaking (“Glue”)
CGJ, NBSP, ZWNBSP
Prohibit line breaks before and after
SP
Space
SPACE
Enable indirect line breaks
ZWJ
Zero Width Joiner
Zero Width Joiner
Prohibit line breaks within joiner sequences
Break Opportunities
B2
Break Opportunity Before and After
Em dash
Provide a line break opportunity before and after the character
BA
Break After
Spaces, most sentence-terminal punctuation
Generally provide a line break opportunity after the character
BB
Break Before
Punctuation used in dictionaries
Generally provide a line break opportunity before the character
HY
Hyphen
HYPHEN-MINUS
Provide a line break opportunity after the character, except in numeric context
HH
Unambiguous Hyphen
HYPHEN
Generally provide a line break opportunity after the character, except word-initially.
CB
Contingent Break Opportunity
Inline objects
Provide a line break opportunity contingent on additional information
Characters Prohibiting Certain Breaks
CL
Close Punctuation
“}”, “❳”, “⟫” etc.
Prohibit line breaks before
CP
Close Parenthesis
“)”, “]”
Prohibit line breaks before
EX
Exclamation/
Interrogation
“!”, “?”, etc.
Prohibit line breaks before
IN
Inseparable
Leaders
Allow only indirect line breaks between pairs
NS
Nonstarter
“‼”, “‽”, “⁇”, “⁉”, etc.
Allow only indirect line breaks before
OP
Open Punctuation
“(“, “[“, “{“, etc.
Prohibit line breaks after
QU
Quotation
Quotation marks
Act like they are opening, closing, or both
Numeric Context
IS
Infix Numeric Separator
. ,
Prevent breaks after any and before numeric
NU
Numeric
Digits
Form numeric expressions for line breaking purposes
PO
Postfix Numeric
%, ¢
Do not break following a numeric expression
PR
Prefix Numeric
$, £, ¥, etc.
Do not break in front of a numeric expression
SY
Symbols Allowing Break After
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 as
ID
AK
Aksara
Consonants
Form orthographic syllables in Brahmic scripts
AL
Alphabetic
Alphabets and regular symbols
Are 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
Form Korean syllable blocks
H3
Hangul LVT Syllable
Hangul
Form Korean syllable blocks
HL
Hebrew Letter
Hebrew
Special rules around hyphens and SOLIDUS; otherwise act as Alphabetic
ID
Ideographic
Ideographs
Break before or after, except in some numeric context
JL
Hangul L Jamo
Conjoining jamo
Form Korean syllable blocks
JV
Hangul V Jamo
Conjoining jamo
Form Korean syllable blocks
JT
Hangul T Jamo
Conjoining jamo
Form Korean syllable blocks
RI
Regional Indicator
REGIONAL INDICATOR SYMBOL LETTER A .. Z
Keep pairs
together. For pairs, break before and after
other classes
SA
Complex Context Dependent (South East Asian)
South East Asian: Thai, Lao, Khmer
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, private-use
Have as yet unknown line breaking behavior or unassigned code positions
Introduction
Lines are broken as the result of two conditions.
The first is the presence of a mandatory line breaking character. The second
condition results from a formatting algorithm having selected among available
line break opportunities; ideally the chosen line break results in the optimal
layout of the text.
Different formatting algorithms may use different methods to determine an
optimal line break. For example, simple implementations consider a single line at a
time, trying to find a
locally optimal
line break. A basic, yet widely
used approach is to
allow no compression or expansion of the intercharacter and interword 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
] implements an
example of such a
globally
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
].
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 interword space according to common
typographical practice, only the spaces marked by
U+0020 SPACE and U+00A0 NO-BREAK SPACE are 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 intercharacter space, the presence
of U+200B ZERO WIDTH SPACE or U+2060 WORD JOINER is always ignored.
Local custom or document style determines whether and to what degree expansion of
intercharacter space
is allowed in justifying a line. In languages, such as German, where
intercharacter space is commonly used to mark e m p h a s i s
(like this), allowing variable intercharacter spacing would
have the unintended effect of adding random emphasis, and is therefore best
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.
In line breaking it is necessary to distinguish
between three 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, text layout systems may support an emergency mode that
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 such an emergency mode are outside
the scope of this annex, however, it is recommended that grapheme clusters
be kept together.
3.1
Determining Line Break Opportunities
Four principal styles of context analysis determine line break
opportunities.
Western:
spaces and hyphens are used to determine breaks
East Asian:
lines can break anywhere, unless prohibited
South East Asian:
line breaks require morphological analysis
Brahmic:
line breaks can occur at the boundaries of any orthographic syllable
The Western style is commonly used for scripts employing the space character.
Hyphenation is often used with space-based line breaking to provide additional
line break opportunities—however, it requires knowledge of the language and
it may need user interaction or overrides.
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. When Korean text is justified, the second style is
commonly used, even for interspersed Latin letters. But when ragged margins
are used, the Western style (relying on spaces) is commonly used instead, even
for ideographs.
The third style is used for scripts such as Thai, which allow
line breaks only at word boundaries, but
do not mark word boundaries in any way, so that the determination of line
break opportunities requires language dependent text analysis. Algorithms
and data for such analysis are beyond the scope of the Unicode
Standard.
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, East Asian, and Brahmic styles can be unified into a single set
of specifications, based on the information in this annex. Unicode characters have explicit line breaking properties assigned to them.
These properties can be utilized to implement the effect of both of 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, line breaks are determined before applying rule L1 of the Unicode Bidirectional
Algorithm [
UAX9
].
However, line breaking is strictly independent of directional properties of
the characters or of any auxiliary information determined by the application
of rules of that algorithm.
Conformance
There is no single method for determining line breaks; the rules may
differ based on user preference and document layout. The information
in this annex, including the specification of the line breaking algorithm,
allows for the necessary flexibility in determining line breaks according to
different conventions. However, some characters
have been encoded explicitly for their effect on line breaking.

Because users adding such characters to a text expect that they will have
the desired effect, these characters have been given required line breaking behavior.
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 not use
spaces, such as Thai; recognition of the language
of the text in order to choose among different punctuation conventions;
using 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, 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 subconditions shall be met:
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
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
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 a higher-level protocol, that fact must be disclosed
and any behavior that differs from that specified by the rules of Section 6.1,
Non-tailorable Line Breaking Rules
must be documented.
Example: An XML 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.
Line Breaking Properties
This section provides 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
effect in line breaking.
This section also summarizes the membership of character
classes corresponding to each value of the line breaking property. Note
that the mnemonic names for 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 broadly mnemonic labels. In other words,
as long as their line breaking behavior is identical, otherwise unrelated
characters will be grouped together in the same line break class.
The classification
by property values defined in this section and in the data file is used as input
into the algorithm defined in
Section 6,
Line Breaking Algorithm
That section describes
a workable default line breaking method.
Section 8,
Customization
discusses how the default line breaking behavior can be tailored to the
needs of specific languages or for particular document styles and user preferences.
Permitted customizations can include changing the classification
of characters for certain classes.
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
],
as well as the General_Category and Extended_Pictographic properties.
Note that for purposes of the line breaking algorithm, those property
values are tailorable, as are the rules of the line breaking algorithm which use them.
(See rules
LB15a
LB15b
LB19
LB19a
LB21a
LB30
and
LB30b
.)
Data File
The full classification of all Unicode characters by their line breaking
properties is available in
the file LineBreak.txt [
Data14
] in the Unicode
Character Database [
UCD
].
This is a semicolon-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.
The same data, but with a more explicit listing of
code point ranges with complex default values, is available in the file
DerivedLineBreak.txt [
Data14Derived
].
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 be 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 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.)
5.1
Description of Line Breaking Properties
Line breaking classes are listed alphabetically.
For each line breaking class, the rules that explicitly reference that class
are listed in italics above the description of the class.
Note that characters in these classes may be involved in other rules;
for instance, rule
LB31
can apply to characters with
almost any line breaking class,
but it does not list any line breaking class explicitly.
AI
: Ambiguous (Alphabetic or Ideograph)
LB1
Some characters that ordinarily act like
alphabetic characters are treated like ideographs (line breaking class
ID
) in certain East Asian legacy contexts.
Their line breaking behavior
therefore depends on the context. In the absence of appropriate context information,
they are treated as class
AL
; see
the note at the end of this description.
As originally defined until Unicode Version
3.1.0, the line break class
AI
contained
all
characters with East_Asian_Width value A (ambiguous width) that
would otherwise be
AL
in this
classification. For more information on East_Asian_Width and how to
resolve it, see Unicode Standard Annex #11,
East Asian Width
UAX11
].
The original definition included many Latin, Greek, and Cyrillic
characters. Since Unicode Version 4.0.1, these characters are classified by default as
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 these
characters need 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.
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.
In Unicode Version 4.0.1, the
AI
line breaking
class therefore included all characters with East Asian Width A that are outside the range U+0000..U+1FFF, plus the following
characters:
24EA
CIRCLED DIGIT ZERO
2780..2793
DINGBAT CIRCLED SANS-SERIF DIGIT ONE..DINGBAT NEGATIVE CIRCLED SANS-SERIF NUMBER TEN
Since that time,
the East_Asian_Width and Line_Break properties have been maintained
independently, with the latter being based on the need for language-specific
line-breaking behavior rather than compatibility with legacy encodings.
In particular, all vulgar fractions have Line_Break=AI.
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
merely require that all ambiguous characters be 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 classes 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
LB28a
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
1132A..11330
GRANTHA LETTER PA..GRANTHA LETTER RA
11332..11333
GRANTHA LETTER LA..GRANTHA LETTER LLA
11335..11339
GRANTHA LETTER VA..GRANTHA LETTER HA
11360..11361
GRANTHA LETTER VOCALIC RR..GRANTHA LETTER VOCALIC LL
11F04..11F10
KAWI LETTER A..KAWI LETTER O
11F12..11F33
KAWI LETTER KA..KAWI LETTER JNYA
AL
: Ordinary Alphabetic and Symbol Characters
LB1
LB10
LB20a
LB23
LB24
LB28
LB29
LB30
Ordinary characters require other characters to provide break opportunities; otherwise, no
line breaks are allowed between pairs of them. However, this behavior is tailorable. In
some Far Eastern documents, it may be desirable to allow breaking between
pairs of ordinary characters—particularly Latin characters and symbols.
Note:
Use ZWSP as a manual override to provide break
opportunities around alphabetic or symbol characters.
This class contains alphabetic or symbolic characters not explicitly assigned to another line breaking class. These are primarily characters of the following categories:
Category
General_Category Values
Alphabetic
Lu, Ll, Lt, Lm, and Lo
Symbols
Sm, Sk, and So
Non-decimal Numbers
Nl and No
Punctuation
Pc, Pd, and Po
Line break class
AL
also contains several format characters, including:
0600..0604
ARABIC NUMBER SIGN..ARABIC SIGN SAMVAT
06DD
ARABIC END OF AYAH
070F
SYRIAC ABBREVIATION MARK
2061..2064
FUNCTION APPLICATION..INVISIBLE PLUS
110BD
KAITHI NUMBER SIGN
These format characters occur in the middle or at the beginning of words or alphanumeric or symbol sequences. However, when alphabetic characters are tailored to allow breaks, these characters should not allow breaks after.
Major exceptions to the general pattern of alphabetic and symbolic characters having line break class
AL
include:
HL for Hebrew letters
AI or ID, based on the East Asian Width property of the character
ID for certain pictographic symbols
CJ for small hiragana and katakana
SA for complex context scripts
JL, JV, JT, H2 or H3 for Hangul characters
AP
: Aksara Pre-Base
LB28a
The
AP
line break class is only used for scripts that use the Brahmic style of context analysis.
It contains the characters of such scripts that are part of an orthographic syllable but in logical order precede the base or any half-forms.
This includes characters with the Indic syllabic categories Consonant_Preceding_Repha, Consonant_With_Stacker, and Consonant_Prefixed.
11003..11004
BRAHMI SIGN JIHVAMULIYA..BRAHMI SIGN UPADHMANIYA
11F02
KAWI SIGN REPHA
AS
: Aksara Start
LB28a
The
AS
line break class is only used for scripts that use the Brahmic style of context analysis.
It contains characters that can occur as the bases of orthographic syllables, but cannot 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,, and several others.
This class also contains all digits of scripts that use the Brahmic
style of line breaking; in some of these scripts, such as Brahmi or
Kawi, digits can occur as bases of orthographic syllables.
1B50..1B59
BALINESE DIGIT ZERO..BALINESE DIGIT NINE
1BC0..1BE5
BATAK LETTER A..BATAK LETTER U
A9D0..A9D9
JAVANESE DIGIT ZERO..JAVANESE DIGIT NINE
AA00..AA28
CHAM LETTER A..CHAM LETTER HA
AA50..AA59
CHAM DIGIT ZERO..CHAM DIGIT NINE
11066..1106F
BRAHMI DIGIT ZERO..BRAHMI DIGIT NINE
11350
GRANTHA OM
1135E..1135F
GRANTHA LETTER VEDIC ANUSVARA..GRANTHA LETTER VEDIC DOUBLE ANUSVARA
11950..11959
DIVES AKURU DIGIT ZERO..DIVES AKURU DIGIT NINE
11EE0..11EF1
MAKASAR LETTER KA..MAKASAR LETTER A
11F50..11F59
KAWI DIGIT ZERO..KAWI DIGIT NINE
BA
: Break After
LB12a
LB21
Like SPACE, the characters in this class provide a break opportunity; unlike
SPACE, they do not take part in determining indirect breaks.
They can be subdivided into several categories.
Breaking Spaces
Breaking spaces are a subset of characters with General_Category Zs. Examples include:
1680
OGHAM SPACE MARK
2000
EN QUAD
2001
EM QUAD
2002
EN SPACE
2003
EM SPACE
2004
THREE-PER-EM SPACE
2005
FOUR-PER-EM SPACE
2006
SIX-PER-EM SPACE
2008
PUNCTUATION SPACE
2009
THIN SPACE
200A
HAIR SPACE
205F
MEDIUM MATHEMATICAL SPACE
3000
IDEOGRAPHIC SPACE
All of these space characters have a specific width, but
otherwise behave as breaking spaces. In setting a justified line, none of these spaces
normally changes in width, except for THIN SPACE
when used in mathematical notation. See also the
SP
property.
The OGHAM SPACE MARK may be rendered visibly between words but it is
recommended that it be elided at the end of a line. For more information,
see
Section 5.7,
Word Separator Characters
For a list of all space characters in the Unicode Standard, see
Section 6.2, General Punctuation
in [
Unicode
].
Tabs
0009
TAB
Except for the effect of the location of the tab stops, the tab character
acts similarly to a space for the purpose of line breaking.
Conditional Hyphens
00AD
SOFT HYPHEN (SHY)
SHY is an invisible format character with no width. It marks
the place where an optional line break may occur inside a word.
It can be used with all scripts. If a line is broken at an optional
line break position marked by a SHY, the text at that line break
position often has a modified appearance as described in
Section 5.4,
Use of Soft Hyphen
Visible Word Dividers
The following are examples of other forms of visible word dividers that
provide break opportunities:
0F0B
TIBETAN MARK INTERSYLLABIC TSHEG
1361
ETHIOPIC WORDSPACE
17D8
KHMER SIGN BEYYAL
17DA
KHMER SIGN KOOMUUT
The Tibetan
tsheg
is a visible mark, but it functions effectively
like a space to separate words (or other units) in Tibetan. It provides a
break opportunity after itself. For additional
information, see
Section 5.6,
Tibetan Line Breaking
The ETHIOPIC WORDSPACE is a visible word delimiter and is kept on the
previous line. In contrast, U+1360 ETHIOPIC SECTION MARK is typically
used in a sequence of several such marks on a separate line, and separated by spaces. As such
lines are typically marked with separate hard line breaks (
BK
),
the section mark is treated like an ordinary symbol and given line break
class
AL
2027
HYPHENATION POINT
A hyphenation point is a raised dot, which is mainly used in dictionaries
and similar works to visibly indicate syllabification of words. Syllable
breaks frequently also are potential line break opportunities in the middle of words.
When an actual line break falls inside a word containing hyphenation
point characters, the hyphenation point is usually rendered as a regular hyphen at the
end of the line.
007C
VERTICAL LINE
In some dictionaries, a vertical bar is used instead of a hyphenation
point. In this usage, U+0323 COMBINING DOT BELOW is
used to mark stressed syllables, so all breaks are marked by the vertical
bar. For an actual line break
the vertical bar is rendered as a hyphen at the end of the line.
Historic Word Separators
Historic texts, especially ancient ones, often do not use spaces, even
for scripts where modern use of spaces is standard. Special punctuation was
used to mark word boundaries in such texts. For modern text processing it is
recommended to treat these as line break opportunities by default.
WJ
can
be used to override this default, where necessary.
Examples of Historic Word Separators include:
16EB
RUNIC SINGLE PUNCTUATION
16EC
RUNIC MULTIPLE PUNCTUATION
16ED
RUNIC CROSS PUNCTUATION
2056
THREE DOT PUNCTUATION
2058
FOUR DOT PUNCTUATION
2059
FIVE DOT PUNCTUATION
205A
TWO DOT PUNCTUATION
205B
FOUR DOT MARK
205D
TRICOLON
205E
VERTICAL FOUR DOTS
2E19
PALM BRANCH
2E2A
TWO DOTS OVER ONE DOT PUNCTUATION
2E2B
ONE DOT OVER TWO DOTS PUNCTUATION
2E2C
SQUARED FOUR DOT PUNCTUATION
2E2D
FIVE DOT MARK
2E30
RING POINT
10100
AEGEAN WORD SEPARATOR LINE
10101
AEGEAN WORD SEPARATOR DOT
10102
AEGEAN CHECK MARK
1039F
UGARITIC WORD DIVIDER
103D0
OLD PERSIAN WORD DIVIDER
1091F
PHOENICIAN WORD SEPARATOR
12470
CUNEIFORM PUNCTUATION SIGN OLD ASSYRIAN WORD DIVIDER
Dandas
DEVANAGARI DANDA is similar to a
full stop. The
danda
or historically related symbols are used with several other
Indic scripts. Unlike a full stop, the
danda
is not used in number
formatting. DEVANAGARI DOUBLE DANDA marks the end of a verse. It also has
analogues in other scripts.
Examples of dandas include:
0964
DEVANAGARI DANDA
0965
DEVANAGARI DOUBLE DANDA
0E5A
THAI CHARACTER ANGKHANKHU
0E5B
THAI CHARACTER KHOMUT
104A
MYANMAR SIGN LITTLE SECTION
104B
MYANMAR SIGN SECTION
1735
PHILIPPINE SINGLE PUNCTUATION
1736
PHILIPPINE DOUBLE PUNCTUATION
17D4
KHMER SIGN KHAN
17D5
KHMER SIGN BARIYOOSAN
1B5E
BALINESE CARIK SIKI
1B5F
BALINESE CARIK PAREREN
A8CE
SAURASHTRA DANDA
A8CF
SAURASHTRA DOUBLE DANDA
AA5D
CHAM PUNCTUATION DANDA
AA5E
CHAM PUNCTUATION DOUBLE DANDA
AA5F
CHAM PUNCTUATION TRIPLE DANDA
10A56
KHAROSHTHI PUNCTUATION DANDA
10A57
KHAROSHTHI PUNCTUATION DOUBLE DANDA
Tibetan
0F34
TIBETAN MARK BSDUS RTAGS
0F7F
TIBETAN SIGN RNAM BCAD
0F85
TIBETAN MARK PALUTA
0FBE
TIBETAN KU RU KHA
0FBF
TIBETAN KU RU KHA BZHI MIG CAN
0FD2
TIBETAN MARK NYIS TSHEG
For additional information, see
Section 5.6,
Tibetan Line Breaking
Other Terminating Punctuation
Termination punctuation stays with the line, but otherwise allows a break after
it. This is similar to
EX
, except that
the latter may be separated by a space from the preceding word without
allowing a break, whereas these marks are used without spaces.
Terminating punctuation includes:
1804
MONGOLIAN COLON
1805
MONGOLIAN FOUR DOTS
1B5A
BALINESE PANTI
1B5B
BALINESE PAMADA
1B5D
BALINESE CARIK PAMUNGKAH
1B60
BALINESE PAMENENG
1C3B
LEPCHA PUNCTUATION TA-ROL
1C3C
LEPCHA PUNCTUATION NYET THYOOM TA-ROL
1C3D
LEPCHA PUNCTUATION CER-WA
1C3E
LEPCHA PUNCTUATION TSHOOK CER-WA
1C3F
LEPCHA PUNCTUATION TSHOOK
1C7E
OL CHIKI PUNCTUATION MUCAAD
1C7F
OL CHIKI PUNCTUATION DOUBLE MUCAAD
2CFA
COPTIC OLD NUBIAN DIRECT QUESTION MARK
2CFB
COPTIC OLD NUBIAN INDIRECT QUESTION MARK
2CFC
COPTIC OLD NUBIAN VERSE DIVIDER
2CFF
COPTIC MORPHOLOGICAL DIVIDER
2E0E..2E15
EDITORIAL CORONIS..UPWARDS ANCORA
A60D
VAI COMMA
A60F
VAI QUESTION MARK
A92E
KAYAH LI SIGN CWI
A92F
KAYAH LI SIGN SHYA
10A50
KHAROSHTHI PUNCTUATION DOT
10A51
KHAROSHTHI PUNCTUATION SMALL CIRCLE
10A52
KHAROSHTHI PUNCTUATION CIRCLE
10A53
KHAROSHTHI PUNCTUATION CRESCENT BAR
10A54
KHAROSHTHI PUNCTUATION MANGALAM
10A55
KHAROSHTHI PUNCTUATION LOTUS
11EF7..11EF8
MAKASAR PASSIMBANG..MAKASAR END OF SECTION
Letters Attached to Orthographic Syllables
In scripts that use the Brahmic style of line breaking, most characters that attach to the initial consonant cluster of an orthographic syllable and are part of that syllable are encoded as combining marks.
These have line break class
CM
Sometimes, however, additional characters with general category Lo or Lm, such as final consonants or vowel lengtheners, should remain attached to the preceding orthographic syllable.
They are then assigned line break class
BA
A9CF
JAVANESE PANGRANGKEP
AA40..AA42
CHAM LETTER FINAL K..CHAM LETTER FINAL NG
AA44..AA4B
CHAM LETTER FINAL CH..CHAM LETTER FINAL SS
1133D
GRANTHA SIGN AVAGRAHA
1135D
GRANTHA SIGN PLUTA
11EF2
MAKASAR ANGKA
BB
: Break Before
LB21
Characters of this line break class move to the next line at a line break
and thus provide a line break opportunity before.
Examples of
BB
characters are described
in the following sections.
Dictionary Use
00B4
ACUTE ACCENT
1FFD
GREEK OXIA
In some dictionaries, stressed syllables are indicated with a spacing acute
accent instead of the hyphenation point. In this case the accent moves to
the next line, and the preceding line ends with a hyphen.
The oxia is canonically equivalent to the acute accent.
02DF
MODIFIER LETTER CROSS ACCENT
A cross accent also appears in some dictionaries to mark the stress of the following
syllable, and should be handled in the same way as the other stress marking
characters in this section. The accent should not be separated from the
syllable it marks by a break.
02C8
MODIFIER LETTER VERTICAL LINE
02CC
MODIFIER LETTER LOW VERTICAL LINE
These characters are used in dictionaries to indicate stress and secondary
stress when IPA is used. Both are prefixes to the stressed syllable in IPA.
Breaking before them keeps them with the
syllable.
Note:
It is hard to find actual examples in most dictionaries
because the pronunciation fields usually occur right after the headword, and
the columns are wide enough to prevent line breaks in most pronunciations.
Tibetan and Phags-Pa Head Letters
0F01
TIBETAN MARK GTER YIG MGO TRUNCATED A
0F02
TIBETAN MARK GTER YIG MGO -UM RNAM BCAD MA
0F03
TIBETAN MARK GTER YIG MGO -UM GTER TSHEG MA
0F04
TIBETAN MARK INITIAL YIG MGO MDUN MA
0F06
TIBETAN MARK CARET YIG MGO PHUR SHAD MA
0F07
TIBETAN MARK YIG MGO TSHEG SHAD MA
0F09
TIBETAN MARK BSKUR YIG MGO
0F0A
TIBETAN MARK BKA- SHOG YIG MGO
0FD0
TIBETAN MARK BSKA- SHOG GI MGO RGYAN
0FD1
TIBETAN MARK MNYAM YIG GI MGO RGYAN
0FD3
TIBETAN MARK INITIAL BRDA RNYING YIG MGO MDUN MA
A874
PHAGS-PA SINGLE HEAD MARK
A875
PHAGS-PA DOUBLE HEAD MARK
Tibetan head letters allow a break before. For more information,
see
Section 5.6,
Tibetan Line Breaking
Mongolian
1806
MONGOLIAN TODO SOFT HYPHEN
Despite its name, this Mongolian character is not an invisible control like
SOFT HYPHEN,
but rather a visible character like a regular hyphen. Unlike the hyphen, MONGOLIAN TODO SOFT HYPHEN stays with the following line. Whenever optional line breaks are to be marked invisibly,
SOFT HYPHEN should be used instead.
B2
: Break Opportunity Before and After
LB17
2014
EM DASH
The EM DASH is used to set off
parenthetical text. Normally, it is used without spaces. However, this is language dependent.
For example, in Swedish, spaces are used around
the EM DASH. Line breaks can occur
before and after an EM DASH. Because EM DASHes
are sometimes used in pairs instead of a single quotation dash, the default
behavior is not to break the line between even though not all
fonts use connecting glyphs for the
EM DASH.
Some languages, including Spanish, use EM DASH to set off
a parenthetical, and the surrounding dashes should not be broken from the contained text.
In this usage there is space on the side where it can be broken. This does not conflict with
symmetrical usages, either with spaces on both sides of the em-dash or with no spaces.
BK
: Mandatory Break (Non-tailorable)
LB4
LB6
LB9
LB15a
LB15b
LB20a
Explicit breaks act independently of the surrounding characters.
No characters can be added to the
BK
class as
part of tailoring, but implementations are not required to support the VT
character.
000B
LINE TABULATION (VT)
000C
FORM FEED (FF)
FORM FEED separates pages. The text on the new page starts at the beginning
of the line. In some layout modes there may be no
visible advance to a new “page”.
2028
LINE SEPARATOR
The text after the LINE SEPARATOR starts at the beginning of the line.
This is similar to HTML
.
2029
PARAGRAPH SEPARATOR
The text of the new paragraph starts at the beginning of the line.
This character defines a paragraph break, causing suitable formatting to be
applied, for example, interparagraph spacing or first line indentation.
LINE SEPARATOR, FF, VT as well as
CR
LF
and
NL
do not define a paragraph break.
Newline Function (NLF)
Newline Functions are defined in the Unicode
Standard as providing additional mandatory breaks. They are not
individual characters, but are encoded as sequences of the control characters
NEL, LF, and CR. If a character sequence for a
Newline Function contains more than one character, it is kept together.
The particular sequences that form an NLF
depend on the implementation and other circumstances as described in
Section 5.8,
Newline Guidelines
, of [
Unicode
].
This specification defines the NLF implicitly. It
defines the three character
classes
CR
LF
, and
NL
. Their line
break behavior, defined in rule
LB5
in
Section 6.1,
Non-tailorable Line Breaking Rules
, is to
break after
NL
LF
or
CR
, but not between
CR
and
LF
CB
: Contingent Break Opportunity
LB1
LB20
LB20a
By default, there is a break opportunity both
before
and
after
any inline object. Object-specific line breaking behavior is implemented in
the associated object itself, and where available can override the default
to prevent either or both of the default break opportunities. Using U+FFFC
OBJECT REPLACEMENT CHARACTER allows the object
anchor to take a character position in the string.
FFFC
OBJECT REPLACEMENT CHARACTER
Object-specific line break behavior is best implemented by
querying the object itself, not by replacing the
CB
line breaking class by
another class.
CJ
: Conditional Japanese Starter
LB1
This character class contains Japanese small hiragana and katakana. Characters of this class may be treated
as either
NS
or
ID
CSS Text Level 3 (which supports Japanese line layout) defines three distinct values
for its line-break behavior:
strict, typically used for long lines
normal, the behavior typically used for books and documents
loose, typically used for short lines such as in newspapers
These have different sets of “kinsoku” characters which cannot be at the beginning or end of
a line; strict has the largest set, while loose has the smallest. The motivation for the smaller
number of kinsoku characters is to avoid triggering justification that puts characters off the grid
position.
Treating characters of class
CJ
as class
NS
will give CSS strict line breaking;
treating them as class
ID
will give CSS normal breaking.
The
CJ
line break class includes
3041, 3043, 3045, etc.
Small hiragana
30A1, 30A3, 30A5, etc.
Small katakana
30FC
KATAKANA-HIRAGANA PROLONGED SOUND MARK
FF67..FF70
Halfwidth variants
CL
: Close Punctuation
LB13
LB15b
LB16
LB25
The closing character of any set of paired punctuation should be kept with
the preceding character, and the same applies to all forms of wide comma and
full stop. This is desirable, even when there are
intervening space characters, to prevent the appearance of a bare
closing punctuation mark at the head of a line.
The class
CL
is closely related to the class
CP
(Close Parenthesis). They differ only in that
CP
will not introduce a break when followed
by a letter or number, which prevents breaks within constructs like “(s)he”.
The
CL
line break class contains characters
of General_Category Pe in the Unicode Character Database, but
excludes any characters included in the class
CP
It also contains certain non-paired punctuation characters, including:
3001..3002
IDEOGRAPHIC COMMA..IDEOGRAPHIC FULL STOP
FE10
PRESENTATION FORM FOR VERTICAL COMMA
FE11
PRESENTATION FORM FOR VERTICAL IDEOGRAPHIC COMMA
FE12
PRESENTATION FORM FOR VERTICAL IDEOGRAPHIC FULL STOP
FE50
SMALL COMMA
FE52
SMALL FULL STOP
FF0C
FULLWIDTH COMMA
FF0E
FULLWIDTH FULL STOP
FF61
HALFWIDTH IDEOGRAPHIC FULL STOP
FF64
HALFWIDTH IDEOGRAPHIC COMMA
CM
: Combining Mark (Non-tailorable)
LB1
LB9
LB10
Combining Characters
Combining character sequences are treated as units for the purpose of line
breaking. The line breaking behavior of the sequence is that of the base
character.
The preferred base character for showing combining
marks in isolation is U+00A0 NO-BREAK SPACE.
If a line break before or after the combining sequence is desired, U+200B
ZERO WIDTH SPACE
can be used. The use of U+0020 SPACE as a base character
is deprecated.
For most purposes, combining characters take on
the properties of their base characters, and that is how the
CM
class is
treated in rule
LB9
of this specification.
As a result, if the sequence <0021, 20E4> is
used to represent a triangle enclosing an exclamation point, it
is effectively treated as
EX
, the line
break class of the exclamation mark. If U+26A0 WARNING SIGN
had been used, which also looks like an exclamation point inside a triangle,
it would have the line break class of
AL
Only the latter corresponds to the line breaking behavior expected by
users for this symbol. To
avoid surprising behavior, always use a base character that is a symbol
or letter (Line Break
AL
) when
using enclosing combining marks (General_Category Me).
The
CM
line break class includes all
combining characters with General_Category Mc, Me, and Mn, unless listed
explicitly elsewhere. This includes
viramas
that don’t have line break class
VI
or
VF
In particular, line breaking class
CM
includes the character U+034F COMBINING GRAPHEME JOINER.
This character is used for specialized collation or display; see
Unicode Technical Standard #10, “Unicode Collation Algorithm” [
UTS10
], and
Unicode Standard Annex #53, “Unicode Arabic Mark Rendering” [
UAX53
].
It functions as an invisible combining mark; it should be ignored outside of the few
processes that ascribe meaning to it.
Assigning it class
CM
means the line
breaking algorithm ignores it.
Control and Formatting Characters
Most control and formatting characters are ignored in line breaking and do
not contribute to the line width. By giving them class
CM
, the line breaking
behavior of the last preceding character that is not of class
CM
affects the
line breaking behavior.
Note:
When control codes and format characters
are rendered visibly during editing, more graceful layout might be achieved
by treating them as if they had the line break
class of the visible symbols instead, that is
AL
or
ID
Such visible modes do not violate
the constraint on tailorability, because they are logically equivalent to
having temporarily substituted symbol
characters
, such as the
characters from the Control Pictures block, or in some cases, character
sequences, for the actual control characters.
The
CM
line break class includes all characters
of General_Category Cc and Cf, unless listed explicitly elsewhere.
The
CM
class also includes
U+3035 VERTICAL KANA REPEAT MARK LOWER HALF. This character is
normally preceded by either U+3033 VERTICAL KANA REPEAT MARK UPPER HALF
or U+3034 VERTICAL KANA REPEAT WITH VOICED SOUND MARK UPPER HALF,
and should not be separated from them.
CP
: Closing Parenthesis
LB13
LB15b
LB16
LB25
LB30
This class contains two common characters, U+0029 RIGHT PARENTHESIS
and U+005D RIGHT SQUARE BRACKET. It also contains
closing brackets used in phonetic notations.
Characters of class
CP
differ from those of the
CL
(Close Punctuation) class
in that they will not cause a break opportunity when appearing in contexts like “(s)he.”
In all other respects the breaking behavior of
CP
and
CL
are the same.
0029
RIGHT PARENTHESIS
005D
RIGHT SQUARE BRACKET
2E56
RIGHT SQUARE BRACKET WITH STROKE
2E58
RIGHT SQUARE BRACKET WITH DOUBLE STROKE
2E5A
TOP HALF RIGHT PARENTHESIS
2E5C
BOTTOM HALF RIGHT PARENTHESIS
CR
: Carriage Return (Non-tailorable)
LB5
LB6
LB9
LB15a
LB15b
LB20a
000D
CARRIAGE RETURN (CR)
CR
indicates a mandatory break after, unless followed by
LF
. See also the discussion
under
BK
Note:
On some platforms the character sequence
is used to indicate
the location of actual line breaks, whereas is treated like a hard line
break. As soon as a user edits the text, the location of all the
sequences may change as the new text breaks differently, while the relative
position of any to the surrounding text stays the same. This
convention allows an editor to return a buffer and the client to tell which text is displayed on
which line by counting the number of and sequences.
This convention is essentially equivalent to
markup that captures the result of applying the line break algorithm, not a
tailoring of the CR character. The sequences are thus not
considered part of
the plain text content.
EB
: Emoji Base
LB23a
LB30b
This class includes characters whose appearance can be modified by a subsequent emoji modifier
in an emoji modifier sequence. This class directly corresponds to the
Emoji_Modifier_Base property as defined in
Section 1.4.4 Emoji Modifiers
of
UTS51
].
Examples include:
1F466
BOY
1F478
PRINCESS
1F6B4
BICYCLIST
Breaks within emoji modifier sequences are prevented by rule
LB30b
In other contexts, characters of class EB behave similarly to ideographs of class
ID
, with break opportunities before and after.
EM
: Emoji Modifier
LB23a
LB30b
This class includes characters that can be used to modify
the appearance of a preceding emoji in an emoji modifier sequence.
This class directly corresponds to the Emoji_Modifier property
as defined in
Section 1.4.4 Emoji Modifiers
of [
UTS51
].
Breaks within emoji modifier sequences are prevented by rule
LB30b
Emoji modifiers include:
1F3FB..1F3FF
EMOJI MODIFIER FITZPATRICK TYPE-1-2..EMOJI MODIFIER FITZPATRICK TYPE-6
EX
: Exclamation/Interrogation
LB13
LB15b
Characters in this line break class behave like closing characters, except in relation to postfix
PO
) and
non-starter characters (
NS
).
Examples include:
0021
EXCLAMATION MARK
003F
QUESTION MARK
05C6
HEBREW PUNCTUATION NUN HAFUKHA
061B
ARABIC SEMICOLON
061E
ARABIC TRIPLE DOT PUNCTUATION MARK
061F
ARABIC QUESTION MARK
06D4
ARABIC FULL STOP
07F9
NKO EXCLAMATION MARK
0F0D
TIBETAN MARK SHAD
FF01
FULLWIDTH EXCLAMATION MARK
FF1F
FULLWIDTH QUESTION MARK
GL
: Non-breaking (“Glue”) (Non-tailorable)
LB12
LB12a
LB15a
LB15b
LB20a
Non-breaking characters prohibit breaks on either
side, but that prohibition can be overridden by
SP
or
ZW
In particular, when NO-BREAK SPACE
follows SPACE, there is a break opportunity after
the SPACE and the NO-BREAK SPACE
will go as visible space onto the next line.
See also
WJ
. The following are examples of characters of line break
class
GL
00A0
NO-BREAK SPACE (NBSP)
202F
NARROW NO-BREAK SPACE (NNBSP)
180E
MONGOLIAN VOWEL SEPARATOR (MVS)
NO-BREAK SPACE is the preferred character to use where two words
are to be visually separated but kept on the same line, as in the case of a title and a
name “Dr.Joseph Becker”. When SPACE follows NO-BREAK SPACE,
there is no break, because there never is a break in front of SPACE.
NARROW NO-BREAK SPACE has exactly the same line breaking behavior
as NO-BREAK SPACE,
but with a narrow display width.
The MONGOLIAN VOWEL SEPARATOR
acts like a NARROW NO-BREAK SPACE
in its line breaking behavior. Both of these characters are regularly used in
Mongolian text, where they participate in special shaping behavior,
as described in
Section 13.5, Mongolian
of [
Unicode
].
When NARROW NO-BREAK SPACE
occurs in French text, it should be interpreted as an “espace fine
insécable”.
1107F
BRAHMI NUMBER JOINER
13430..13436
EGYPTIAN HIEROGLYPH VERTICAL JOINER..EGYPTIAN HIEROGLYPH OVERLAY MIDDLE
13439..1343B
EGYPTIAN HIEROGLYPH INSERT AT MIDDLE..EGYPTIAN HIEROGLYPH INSERT AT BOTTOM
16FE4
KHITAN SMALL SCRIPT FILLER
These characters participate in shaping behavior.
Together with the characters on either side, they form a ligature, quadrat,
or cluster, within which there can be no line break.
See
Section 14.1, Brahmi
Section 11.4, Egyptian Hieroglyphs
, and
Section 18.12, Khitan Small Script
, respectively, of
Unicode
].
2007
FIGURE SPACE
This is the preferred space to use in numbers. It has the same width as a
digit and keeps the number together for the purpose of line breaking.
2011
NON-BREAKING HYPHEN
This is the preferred character to use where words need to be hyphenated but
may not be broken at the hyphen. Because of its use
as a substitute for ordinary hyphen, the appearance of this character should
match that of U+2010 HYPHEN.
0F08
TIBETAN MARK SBRUL SHAD
0F0C
TIBETAN MARK DELIMITER TSHEG BSTAR
0F12
TIBETAN MARK RGYA GRAM SHAD
The TSHEG BSTAR looks exactly like a Tibetan
tsheg
, but can be used to prevent
a break like
no-break space
. It inhibits breaking on either side. For
more information, see
Section 5.6,
Tibetan Line Breaking
035C..0362
COMBINING DOUBLE BREVE BELOW..COMBINING DOUBLE RIGHTWARDS ARROW BELOW
These diacritics span two characters, so no word or line breaks are
possible on either side.
FE20
COMBINING LIGATURE LEFT HALF
FE22
COMBINING DOUBLE TILDE LEFT HALF
FE24
COMBINING MACRON LEFT HALF
FE27
COMBINING LIGATURE LEFT HALF BELOW
FE29
COMBINING TILDE LEFT HALF BELOW
FE2B
COMBINING MACRON LEFT HALF BELOW
FE2E
COMBINING CYRILLIC TITLO LEFT HALF
FE26
COMBINING CONJOINING MACRON
FE2D
COMBINING CONJOINING MACRON BELOW
The left half diacritics are part of a legacy representation of the
double diacritics; they occur between the two characters spanned by the double
diacritic. Preventing breaks on either side therefore achieves the same
line breaking behavior as when using the preferred representation
U+035C..U+0362.
In addition, the conjoining macrons above and below, together with left and
right half marks, form marks spanning more than two characters; likewise no
line break occurs within such spans.
H2
: Hangul LV Syllable
LB26
LB27
This class includes all characters of Hangul Syllable Type LV.
Together with conjoining jamos, Hangul syllables form Korean Syllable Blocks, which are kept together; see
Unicode Standard Annex #29, “Unicode Text Segmentation” [
UAX29
].
Korean uses space-based line breaking in many styles of documents. To
support these, Hangul syllables and conjoining jamos need to be tailored
to use class
AL
. The default in this specification is
class
ID
, which supports the case of Korean documents not using
space-based line breaking. See
Section 8.1,
Types of Tailoring
. See also
JL
JT
JV
, and
H3
H3
: Hangul LVT Syllable
LB26
LB27
This class includes all characters of Hangul Syllable Type LVT. See also
JL
JT
JV
, and
H2
HH
: Unambiguous Hyphen
LB12a
LB20a
LB21
LB21a
This class consists of breaking hyphens.
These characters
establish explicit break opportunities immediately after
each occurrence, unless they occur word-initally, as
when referring to a suffix such as
-ing
The hyphens become non-breaking between Hebrew and non-Hebrew.
058A
ARMENIAN HYPHEN
05BE
HEBREW PUNCTUATION MAQAF
1400
CANADIAN SYLLABICS HYPHEN
2010
HYPHEN
2012
FIGURE DASH
2013
EN DASH
2E17
DOUBLE OBLIQUE HYPHEN
2E40
DOUBLE HYPHEN
2E5D
OBLIQUE HYPHEN
10D6E
GARAY HYPHEN
10EAD
YEZIDI HYPHENATION MARK
Hyphens are graphic characters with width. Because, unlike spaces, they
are visible, they are included in the measured part of the preceding line, except
where the layout style allows hyphens to hang into the margins.
For additional
information about how to format line breaks resulting from the presence of hyphens, see
Section 5.3,
Use of Hyphen
HY
: Hyphen
LB12a
LB20a
LB21
LB21a
LB25
002D
HYPHEN-MINUS
Some additional context analysis is required to distinguish usage of this
character as a hyphen from its usage as a minus sign (or indicator of numerical
range). If used as hyphen, it acts like U+2010 HYPHEN,
which has line break class
HH
Note:
Some typescript conventions use runs of
HYPHEN-MINUS to stand in
for longer dashes or horizontal rules. If actual character code conversion
is not performed and it is desired to treat them like the characters or
layout elements they stand for, line breaking needs to support these
runs explicitly.
ID
: Ideographic
LB23a
Characters with this property do not require other characters to provide break opportunities;
lines can ordinarily break before and after and between pairs of ideographic characters.
Examples of characters with the
ID
line break class include most assigned characters in the ranges listed below.
Note that this class also includes characters other than Han ideographs.
2E80..2FFF
CJK, Kangxi Radicals, Ideographic Description Symbols
3040..309F
Hiragana (except small characters)
30A2..30FA
Katakana (except small characters)
3400..4DBF
CJK Unified Ideographs Extension A
4E00..9FFF
CJK Unified Ideographs
F900..FAFF
CJK Compatibility Ideographs
See the data file LineBreak.txt [
Data14
or the data file
DerivedLineBreak.txt [
Data14Derived
for the complete list of characters with the
ID
line break class.
Note:
Use U+2060 WORD JOINER
as a manual override to prevent
break opportunities around characters of class
ID
Unassigned code points in blocks or regions of the Unicode codespace
that have been reserved for CJK scripts are also assigned this line break class.
These assignments anticipate that future characters assigned in these ranges will have
the class
ID
. Once a character is assigned to one
of these code points, the property value could change.
For example,
all of the undesignated code points in Planes 2 (20000..2FFFD) and 3 (30000..3FFFD)
default to
ID
See the data file DerivedLineBreak.txt for
the complete list of code point ranges which default to
the
ID
line break class.
Korean
Korean is encoded with conjoining jamos, Hangul syllables, or both. See also
JL
JT
JV
H2
, and
H3
The following set of compatibility jamo is treated as
ID
by default.
3130..318F
HANGUL COMPATIBILITY JAMO
Symbols
Certain pictographic symbols of General Category So
are also included in this line break class.
HL
: Hebrew Letter
LB20a
LB21a
LB21b
LB23
LB24
LB28
LB29
LB30
This class includes all Hebrew letters.
When a Hebrew letter is separated from following non-Hebrew text by a hyphen, there is no break on either side of the hyphen.
In this context a hyphen is any character of class
HY
or class
BA
There is also no break between a solidus and a Hebrew letter.
In other respects, Hebrew letters behave the same as characters of class
AL
Included in this class are all characters of General Category Letter that have Script=Hebrew.
IN
: Inseparable Characters
LB22
Leaders
These characters are intended to be used consecutively.
There is never a line break between two characters of this class.
Examples include:
2024
ONE DOT LEADER
2025
TWO DOT LEADER
2026
HORIZONTAL ELLIPSIS
FE19
PRESENTATION FORM FOR VERTICAL HORIZONTAL ELLIPSIS
HORIZONTAL ELLIPSIS can be used as a three-dot leader.
IS
: Infix Numeric Separator
LB15b
LB15c
LB15d
LB25
LB29
Characters that usually occur inside a numerical expression may not be
separated from the numeric characters that follow, unless a space character
intervenes. For example, there is no break in “100.00” or “10,000”, nor in “12:59”.
Examples include:
002C
COMMA
002E
FULL STOP
003A
COLON
003B
SEMICOLON
037E
GREEK QUESTION MARK (canonically equivalent to 003B)
0589
ARMENIAN FULL STOP
060C
ARABIC COMMA
060D
ARABIC DATE SEPARATOR
07F8
NKO COMMA
2044
FRACTION SLASH
When not used in a numeric context, infix separators are sentence-ending punctuation.
Therefore they always prevent breaks before.
Note:
FIGURE SPACE, not being a punctuation mark, has
been given the line break class
GL
JL
: Hangul L Jamo
LB26
LB27
The
JL
line break class consists of all characters of Hangul Syllable Type L.
Conjoining jamos form Korean Syllable Blocks, which are kept together; see
Unicode Standard Annex #29, “Unicode Text Segmentation” [
UAX29
].
Korean uses space-based line breaking in many styles of documents. To support
these, Hangul syllables and conjoining jamos need to be tailored
to use class
AL
. The default in this specification is
class
ID
, which supports the case of Korean documents not using space-based
line breaking. See
Section 8.1,
Types of Tailoring
. See also
JT
JV
H2
, and
H3
JT
: Hangul T Jamo
LB26
LB27
The
JT
line break class consists of all characters of Hangul Syllable Type T. See also
JL
JV
H2
, and
H3
JV
: Hangul V Jamo
LB26
LB27
The
JV
line break class consists of all characters of Hangul Syllable Type V. See also
JL
JT
H2
, and
H3
LF
: Line Feed (Non-tailorable)
LB5
LB6
LB9
LB15a
LB15b
LB20a
000A
LINE FEED (LF)
There is a mandatory break after any LF character, but see the discussion
under
BK
NL
: Next Line (Non-tailorable)
LB5
LB6
LB9
LB15a
LB15b
LB20a
0085
NEXT LINE (NEL)
The
NL
class acts like
BK
in all respects (there is a mandatory break after any NEL character).
It cannot be tailored, but implementations are not required to support the
NEL character; see the discussion
under
BK
NS
: Nonstarters
LB1
LB16
LB21
Nonstarter characters cannot start a line, but unlike
CL
they may allow a
break in some contexts when they follow one or more space characters.
Nonstarters include:
17D6
KHMER SIGN CAMNUC PII KUUH
203C
DOUBLE EXCLAMATION MARK
203D
INTERROBANG
2047
DOUBLE QUESTION MARK
2048
QUESTION EXCLAMATION MARK
2049
EXCLAMATION QUESTION MARK
3005
IDEOGRAPHIC ITERATION MARK
301C
WAVE DASH
303C
MASU MARK
303B
VERTICAL IDEOGRAPHIC ITERATION MARK
309B.. 309E
KATAKANA-HIRAGANA VOICED SOUND MARK..HIRAGANA VOICED ITERATION MARK
30A0
KATAKANA-HIRAGANA DOUBLE HYPHEN
30FB
KATAKANA MIDDLE DOT
30FD..30FE
KATAKANA ITERATION MARK..KATAKANA VOICED ITERATION MARK
FE13
PRESENTATION FORM FOR VERTICAL COLON
FE54..FE55
SMALL SEMICOLON..SMALL COLON
FF1A..FF1B
FULLWIDTH COLON.. FULLWIDTH SEMICOLON
FF65
HALFWIDTH KATAKANA MIDDLE DOT
FF9E..FF9F
HALFWIDTH KATAKANA VOICED SOUND MARK..HALFWIDTH KATAKANA SEMI-VOICED SOUND MARK
Note:
Optionally, the
NS
restriction may be relaxed by tailoring, with some or all
characters treated like
ID
to achieve a more permissive style of
line breaking, especially in some East Asian document styles.
Alternatively, line breaking can be tightened by moving characters that are
ID
into
NS
For additional information about U+30A0
KATAKANA-HIRAGANA DOUBLE HYPHEN, see
Section 5.5,
Use of Double Hyphen
NU
Numeric
LB15c
LB23
LB25
LB30
These characters behave like ordinary characters (
AL
) in the context of
most characters
but activate the prefix and postfix behavior of prefix and postfix characters.
Numeric characters consist of decimal digits (all characters of General_Category Nd), except:
those with East_Asian_Width F (Fullwidth)
those from scripts that use the Brahmic style of context analysis
plus these characters:
066B
ARABIC DECIMAL SEPARATOR
066C
ARABIC THOUSANDS SEPARATOR
Unlike
IS
characters, the Arabic numeric
punctuation does not occur as sentence terminal punctuation outside numbers.
OP
: Open Punctuation
LB14
LB15a
LB25
LB30
The opening character of any set of paired punctuation
should be kept with the character that follows. This is desirable,
even if there are intervening space characters, as it prevents the
appearance of a bare opening punctuation mark at the end of a line.
The
OP
line break
class consists of all characters of General_Category Ps in the Unicode
Character Database, plus
00A1
INVERTED EXCLAMATION MARK
00BF
INVERTED QUESTION MARK
2E18
INVERTED INTERROBANG
Note:
The first two of these characters used to be
in the class
AI
based on their East_Asian_Width assignment of A. Such characters are
normally resolved to either
ID
or
AL
However, the characters listed above are used as punctuation marks in
Spanish, where they would behave more like a character of class
OP
PO
Postfix Numeric
LB23a
LB24
LB25
LB27
Characters that usually follow a numerical expression may not be separated
from preceding numeric characters or preceding closing characters. For example, there is no break opportunity in “(12.00)%”.
Some of these characters—in
particular,
degree sign
and
percent sign
—can appear on both sides of a numeric
expression. Therefore the line breaking algorithm by default does not break
between
PO
and
numbers or letters on either side.
Examples of Postfix characters include
0025
PERCENT SIGN
00A2
CENT SIGN
00B0
DEGREE SIGN
060B
AFGHANI SIGN
066A
ARABIC PERCENT SIGN
2030
PER MILLE SIGN
2031
PER TEN THOUSAND SIGN
2032..2037
PRIME..REVERSED TRIPLE PRIME
20A7
PESETA SIGN
2103
DEGREE CELSIUS
2109
DEGREE FAHRENHEIT
FDFC
RIAL SIGN
FE6A
SMALL PERCENT SIGN
FF05
FULLWIDTH PERCENT SIGN
FFE0
FULLWIDTH CENT SIGN
Alphabetic characters are also widely used as unit designators in a postfix position. For purposes of
line breaking, their classification as
alphabetic is sufficient to keep them together with the preceding number.
PR
: Prefix Numeric
LB23a
LB24
LB25
LB27
Characters that usually precede a numerical expression may not be separated
from following numeric characters or following opening characters. For example, there is no break opportunity in “$(100.00)”.
Many currency signs can appear on
both sides, or even the middle, of a numeric expression. Therefore the
line breaking algorithm, by default, does not break between
PR
and
numbers or letters on either side.
All currency symbols
(General_Category Sc) except those in class
PO
have been assigned line breaking class
PR
This class also contains all unassigned code points in the Currency Symbols block,
and additional characters, including:
002B
PLUS SIGN
005C
REVERSE SOLIDUS
00B1
PLUS-MINUS SIGN
2116
NUMERO SIGN
2212
MINUS SIGN
2213
MINUS-OR-PLUS SIGN
Note:
Many currency symbols may be used either as prefix or as
postfix, depending on local convention. For details on the conventions used,
see [
CLDR
].
QU
Quotation
LB15a
LB15b
LB19
LB19a
Some quotation characters can be opening or closing,
or even both, depending on usage.
The default is to use the General_Category values Initial_Punctation
and Final_Punctation as a hint, together with context, but to err on the side
of treating them as both opening and closing,
thus preventing breaks on either side.
This will prevent some breaks that might have been
legal for a particular language or usage, such as
outside a Simplified Chinese quotation of Latin text, or before a German
quotation of text starting with a full stop.
Note:
If language information is available, it can be used to
determine which character is used as the opening quote and which as the closing quote. See
the information in
Section 6.2, General Punctuation
, in
Unicode
].
In such a case, the quotation marks could be tailored to either
OP
or
CL
depending on their actual usage.
The
QU
line break class consists of characters of
General_Category Pf or Pi in the Unicode Character Database
and additional characters, including:
0022
QUOTATION MARK
0027
APOSTROPHE
275B
HEAVY SINGLE TURNED COMMA QUOTATION MARK ORNAMENT
275C
HEAVY SINGLE COMMA QUOTATION MARK ORNAMENT
275D
HEAVY DOUBLE TURNED COMMA QUOTATION MARK ORNAMENT
275E
HEAVY DOUBLE COMMA QUOTATION MARK ORNAMENT
2E00..2E01
RIGHT ANGLE SUBSTITUTION MARKER..RIGHT ANGLE DOTTED SUBSTITUTION MARKER
2E06..2E08
RAISED INTERPOLATION MARKER..DOTTED TRANSPOSITION MARKER
2E0B
RAISED SQUARE
RI
: Regional Indicator
LB30a
For line Breaking, the Regional Indicator characters are
all those with the Unicode character property of
Regional_Indicator. This includes:
1F1E6..1F1FF
REGIONAL INDICATOR SYMBOL LETTER A .. REGIONAL INDICATOR SYMBOL LETTER Z
Pairs of RI characters are used to represent a two-letter ISO 3166 region code.
Runs of adjacent RI characters are grouped into pairs, beginning at the start of the run.
No break opportunity occurs within a pair; breaks can occur between adjacent pairs.
When RI characters are adjacent to characters of other classes, breaks can occur before and after,
except where forbidden by other rules.
SA
: Complex-Context Dependent (South East Asian)
LB1
Runs of these characters require morphological analysis to determine break
opportunities. This is similar to, for example, a hyphenation algorithm. For the
characters that have this property,
no
break opportunities will be
found otherwise. Therefore complex context analysis, often involving
dictionary lookup of some form, is required to determine non-emergency line
breaks. If such analysis is not available, it is recommended to treat them as
AL
Note:
These characters can be mapped into their equivalent line breaking classes
by using dictionary lookup, thus permitting a logical
separation of this algorithm from the morphological analysis.
The class
SA
consists of all characters of General_Category Cf, Lo, Lm, Mn,
or Mc in the following blocks that are not members of another line break class.
0E00..0E7F
Thai
0E80..0EFF
Lao
1000..109F
Myanmar
1780..17FF
Khmer
1950..197F
Tai Le
1980..19DF
New Tai Lue
1A20..1AAF
Tai Tham
A9E0..A9FF
Myanmar Extended-B
AA60..AA7F
Myanmar Extended-A
AA80..AADF
Tai Viet
11700..1173F
Ahom
SG
Surrogate (Non-tailorable)
LB1
Line break class
SG
comprises all code points with General_Category Cs. The line breaking behavior of
isolated surrogates is undefined. In UTF-16,
paired surrogates represent non-BMP code points. Such code points must be
resolved before assigning line break properties. In UTF-8 and UTF-32
surrogate code points represent corrupted data and their line break behavior
is undefined.
Note:
The use of this line breaking class is deprecated. It was of
limited usefulness for UTF-16 implementations that did not support characters beyond the BMP. The
correct implementation is to resolve a
pair
of surrogates into a
supplementary character before line breaking.
SP
: Space (Non-tailorable)
LB7
LB8
LB9
LB12a
LB14
LB15a
LB15b
LB15c
LB16
LB17
LB18
LB20a
The space characters are used as explicit break opportunities;
they allow line breaks before most other characters. However, spaces at the
end of a line are ordinarily not measured for fit. If there is a sequence of space
characters, and breaking after any of the space characters would result in the
same visible line, then the line breaking position after the last space character
in the sequence is the locally most optimal one. In other words, when the
last character measured for fit is
before
the space character, any number of
space characters are kept together invisibly on the previous line and the
first non-space character starts the next line.
0020
SPACE (SP)
Note:
By default, SPACE,
but none of the other breaking spaces, is used in
determining an indirect break. For other breaking space characters, see
BA
SY
: Symbols Allowing Break After
LB13
LB15b
LB21b
LB25
The
SY
line breaking property is intended to provide a break opportunity after, except in front of
digits, so as to not break “1/2” or “06/07/99”.
002F
SOLIDUS
URLs are now so common in regular plain text that they need to be taken
into account when assigning general-purpose line breaking properties. Slash (
solidus
is allowed as an additional, limited break opportunity to improve layout of Web addresses.
As a side effect, some common abbreviations
such as “w/o” or “A/S”, which normally would not be broken,
acquire a line
break opportunity. The recommendation in this case is for the layout system
not to utilize a line break opportunity allowed by
SY
unless the distance
between it and the next line break opportunity exceeds an implementation-defined minimal distance.
Note:
Normally, symbols are treated as
AL
However, symbols can be added to this line breaking
class or classes
BA
BB
and
B2
by tailoring.
This can be used to allow additional line breaks—for example,
after “=”. Mathematics requires additional specifications for line
breaking, which are outside the scope of this annex.
VF
: Virama Final
LB28a
The
VF
line break class is only used for scripts that use the Brahmic style of context analysis.
It contains the viramas of Indic syllabic category Pure_Killer in scripts where the final consonant of a phonological syllable is expressed as a sequence of a consonant and such a virama, and the final consonant needs to be kept together with the preceding orthographic syllable.
This includes:
1BF2..1BF3
BATAK PANGOLAT..BATAK PANONGONAN
Viramas of Indic syllabic category Pure_Killer that don’t meet the conditions for line break class
VF
use the line break class
CM
VI
: Virama
LB28a
The
VI
line break class is only used for scripts that use the Brahmic style of context analysis.
It contains the viramas of Indic syllabic categories Virama and Invisible_Stacker of such scripts.
1B44
BALINESE ADEG ADEG
A9C0
JAVANESE PANGKON
11046
BRAHMI VIRAMA
1134D
GRANTHA SIGN VIRAMA
11F42
KAWI CONJOINER
WJ
: Word Joiner (Non-tailorable)
LB11
LB15b
These characters glue together left and right neighbor characters such
that they are kept on the same line.
2060
WORD JOINER (WJ)
FEFF
ZERO WIDTH NO-BREAK SPACE (ZWNBSP)
The word joiner character is the preferred choice for an invisible
character to keep other characters together that would otherwise be split
across the line at a direct break. The character FEFF has the same effect, but
because it is also used in an unrelated way as a
byte order mark,
the use
of the WJ as the preferred interword glue simplifies the handling of FEFF.
By definition, WJ and ZWNBSP take precedence over the action
of
SP
, but not
ZW
XX
: Unknown
LB1
The
XX
line break class consists of all characters with
General_Category Co as well as those unassigned code points that are not within a CJK block.
Unassigned characters in blocks or ranges of the Unicode codespace
that have been reserved for CJK scripts default to the class
ID
and are listed in the description of that class.
Unassigned code positions, private-use characters, and characters for which
reliable line breaking information is not available are assigned this
line breaking property. The default behavior for this class is identical to
class
AL
Users can manually insert ZWSP or WORD JOINER around
characters of class
XX
to allow or prevent breaks as needed.
In addition, implementations can override or tailor this default behavior—for example,
by assigning characters the property
ID
or another class.
Doing so may give better default behavior for their users. There are
other possible means of determining the desired behavior of private-use
characters. For example, one implementation
might treat any private-use character in ideographic context as
ID
while another implementation might support a method for assigning specific
properties to specific definitions of private-use characters. The details of
such use of private-use characters are outside the scope of this standard.
For supplementary characters, a useful default is to treat characters in the
range 10000..1FFFD as
AL
and characters in the ranges
20000..2FFFD and 30000..3FFFD as
ID
until the implementation can be revised to take into
account the actual line breaking properties for these characters.
For more information on handling default property values for unassigned
characters, see the discussion on default property values in
Section
5.3, Unknown and Missing Characters
, of
Unicode
].
The line breaking rules in
Section 6,
Line Breaking Algorithm
assume that all unknown characters have
been assigned one of the other line breaking classes,
such as
AL
as part of assigning line breaking classes to the
input characters.
Implementations that do not support a given character should also treat it as unknown
XX
).
ZW
: Zero Width Space (Non-tailorable)
LB7
LB8
LB9
LB15a
LB15b
LB20a
200B
ZERO WIDTH SPACE (ZWSP)
This character is used to enable additional
(invisible) break opportunities wherever SPACE
cannot be used. As its name implies, it normally has no width. However,
its presence between two characters does not prevent increased letter
spacing in justification.
ZWJ
: Zero Width Joiner (Non-tailorable)
LB8a
LB9
LB10
200D
ZERO WIDTH JOINER (ZWJ)
A ZWJ prevents breaks between most pairs of characters that would otherwise break. It
has various uses, including as a connector in emoji zwj sequences
and as a joiner in complex scripts.
Emoji zwj sequences are defined by
ED-16, emoji zwj sequence
, in [
UTS51
and implemented for line breaking by rule
LB8a
In other respects, the line breaking behavior of ZWJ is that of a combining character of class
CM
5.2
Dictionary Usage
Dictionaries follow specific conventions that guide their use of special characters to
indicate features of the terms they list. Marks used for some of these
conventions may occur near line break opportunities and therefore interact
with line breaking. For example, in one dictionary a natural hyphen in a
word becomes a tilde dash when the word is split.
Section 6.2.8,
Hyphenation Point and Dictionary Syllabification
of [
Unicode
] illustrates the use
of marks whose line breaking classes have been assigned to accomodate various
dictionary usages.
5.3
Use of Hyphen
The rules for treating hyphens in line breaking
vary by language. In many instances, these rules are not supported as such in the
algorithm, but the correct appearance can be realized by using a
non-breaking hyphen.
Some languages and some transliteration systems
use a hyphen at the first position in a word. For example, the Finnish
orthography uses a hyphen at the start of a word in certain types of
compounds of the form xxx yyy -zzz (where xxx yyy is a two-word expression
that acts as the first part of a compound noun, with zzz as the second
part). Line break after the hyphen is not allowed here by
rule
LB20a
There are line breaking conventions that
modify the appearance of a line break when the line break opportunity is
based on an explicit hyphen. In
standard Polish orthography, explicit hyphens are always promoted to the
next line if a line break occurs at that location in the text. For example,
if, given the sentence "Tam wisi czerwono-niebieska flaga" ("There
hangs a red-blue flag"), the optimal line break occurs at the location of
the explicit hyphen, an additional hyphen
will be displayed at the beginning of the next line like this:
Tam wisi czerwono-
-niebieska flaga.
The same convention is used in Portuguese, where the use
of hyphens is common, because they are mandatory for verb forms that include a
pronoun. Homographs or ambiguity may arise if hyphens are treated
incorrectly: for example, "disparate" means "folly" while "dispara-te" means "fire
yourself" (or "fires onto you"). Therefore the former needs to be line
broken as
dispara-
te
and the latter as
dispara-
-te.
A recommended practice is to type NON-BREAKING HYPHEN> instead of to achieve promotion of the hyphen to the next
line. This practice is reportedly already common and supported by major text
layout applications. See also
Section 5.4,
Use of Soft Hyphen
5.4
Use of Soft Hyphen
Unlike U+2010 HYPHEN, which always has a visible rendition, the character
U+00AD SOFT HYPHEN (SHY) is an invisible format character that merely indicates a
preferred intraword line break position. If the line is broken at that point,
then whatever mechanism is appropriate for intraword line breaks should be
invoked, just as if the line break had been triggered by another hyphenation mechanism,
such as a dictionary lookup. Depending on the language and the word, that
may produce different visible results, for example:
Simply inserting a hyphen glyph
Inserting a hyphen glyph and changing spelling in the divided word
parts
Not showing any visible change and simply breaking at that point
Inserting a hyphen glyph at the beginning of the new line
The following are a few examples of spelling changes. Each example shows the line
break as “ / ” and any inserted hyphens. There are many other cases.
In pre-reform German orthography, a “c” before the
hyphenation point can change into a “k”: “Drucker”
hyphenates into “Druk- / ker”.
In modern Dutch, an
e-diaeresis
after the hyphenation point can
change into a simple “e”: “geërfde” hyphenates
into “ge- / erfde”, and “geëerd” into “ge-/ eerd”.
In Swedish, a consonant is sometimes doubled: “tuggummi”;
hyphenates into “tugg- / gummi”.
In Dutch, a letter can disappear: “opaatje” hyphenates into
“opa- / tje”.
The inserted hyphen glyph can take a wide variety of shapes, as appropriate for the situation. Examples
include shapes like U+2010 HYPHEN, U+058A ARMENIAN HYPHEN, U+180A MONGOLIAN
NIRUGU, or U+1806 MONGOLIAN TODO SOFT HYPHEN.
When a SHY is used to represent a possible hyphenation
location, the spelling is that of the word without hyphenation:
“tuggummi”. It is up to the line breaking
implementation to make any necessary spelling changes when such a possible
hyphenation is actually used.
Sometimes it is desirable to encode text that includes line breaking
decisions and will not be further broken into lines. If
such text includes hyphenations, the spelling needs to reflect the changes due to
hyphenation: “tugg/ gummi”, including the appropriate
character for any inserted hyphen. For a list of dash-like characters in
Unicode, see
Section 6.2, General Punctuation
, in
Unicode
].
Hyphenation, and therefore the SHY, can be used
with the Arabic script. If the rendering
system breaks at that point, the display—including shaping—should be what
is appropriate for the given language. For
example, sometimes a hyphen-like mark is placed
on the end of the line. This mark looks like a
kashida
, but is not
connected to the letter preceding it. Instead, the
appearance of the mark is as if it had been placed—and the line
divided—after the contextual shapes for the line have been determined. For
more information on shaping, see [
UAX9
] and
Section 9.2, Arabic
, of [
Unicode
].
There are three types of hyphens: explicit hyphens, conditional hyphens,
and dictionary-inserted hyphens resulting from a hyphenation process. There
is no character code for the third kind of hyphen. If a
distinction is desired, the fact that a hyphen is dictionary-inserted and
not user-supplied can only be
represented out of band or by using another control code instead
of SHY.
The action of a hyphenation algorithm is equivalent to the insertion of a
SHY. However, when a word contains an explicit SHY, it is customarily treated
as overriding the action of the hyphenator for that word.
The sequence
is given a particular interpretation, see
Section 5.3,
Use of Hyphen
5.5
Use of Double Hyphen
In some fonts, notably Fraktur fonts, it is customary to use a double-stroke form
of the hyphen, usually oblique. Such use is a font-based
glyph variation and does not affect line breaking in any way. In texts using
such a font, automatic hyphenation or SHY would also result in the display
of a double-stroke, oblique hyphen.
Some modern editions of older German publications use a horizontal double
hyphen to transcribe the original Fraktur hyphens, but a single hyphen for
modern automatic hyphenation. Such editions can be represented using
U+2E40 ⹀ DOUBLE HYPHEN for the double hyphens.
In some dictionaries, such as
Webster’s 3rd New International Dictionary
double-stroke, oblique hyphens are used to indicate
an explicit hyphen at the end of the line; in other words, a hyphen that
would be retained when the term shown is not line wrapped.
It is not necessary to store a special character in the data to support
this option; one merely needs to substitute the glyph of any ordinary hyphen that winds up
at the end of a line. In this example, if the shape of the special hyphen matches an existing
character, such as U+2E17 DOUBLE OBLIQUE HYPHEN,
that character can be substituted temporarily for display purposes by the line formatter.
With such a convention, automatic hyphenation or
SHY would result in the display of an ordinary hyphen without further
substitution. (See also
Section 5.3,
Use of Hyphen
).
Certain linguistic notations make use of a double-stroke, oblique hyphen
to indicate specific features, often contrasting with the
ordinary hyphen. The U+2E17 ⸗ DOUBLE OBLIQUE HYPHEN
character is used in this case.
U+30A0 ゠ KATAKANA-HIRAGANA DOUBLE HYPHEN is used in scientific
notation, for example, to mark the presence of a space that would otherwise
have been lost in transcribing text, such as the name of a chemical
compound, into Katakana. In such notation, ordinary hyphens are retained.
5.6
Tibetan Line Breaking
The Tibetan script uses spaces sparingly,
relying instead on the
tsheg
. There is no punctuation equivalent to a
period in Tibetan; Tibetan
shad
characters indicate the end of a
phrase, not a sentence. Phrases are often metrical—that is, written
after every
syllables—and a new sentence can often start within the
middle of a phrase. Sentence boundaries need to be determined
grammatically rather than by punctuation.
Traditionally there is nothing akin to a
paragraph in Tibetan text. It is typical to have many pages of text
without a paragraph break—that is, without an explicit line break.
The closest thing to a paragraph in Tibetan is a
new section or topic starting with U+0F12 or U+0F08. However, these occur
inline: one section ends and a new one starts on the same line, and the new
section is marked only by the presence of one of these characters.
Some modern books, newspapers, and magazines
format text more like English with a break before each section or topic—and (often)
the title of the section on a separate line. Where this is done,
authors insert an explicit line break. Western punctuation (full stop,
question mark, exclamation mark, comma, colon, semicolon, quotes) is
starting to appear in Tibetan documents, particularly those published in
India, Bhutan, and Nepal. Because there are no formal rules for their use in
Tibetan, they get treated generically by default. In Tibetan documents
published in China, CJK bracket and punctuation characters occur frequently;
it is recommended to treat these as in horizontally written Chinese.
Note:
The detailed rules for formatting Tibetan texts are
complex, and the original assignment of line break classes was found to be insufficient.
In [
Unicode4.1
], the assignment of line
break classes for Tibetan was revised significantly in an attempt to
better model Tibetan line breaking behavior. No new rules or line break
classes were added.
The set of line break classes for Tibetan is expected to provide a good starting
point, even though there is limited practical experience in their
implementation. As more experience is gained, some modifications, possibly
including new rules or additional line break classes, can be expected.
5.7
Word Separator Characters
Visible word separator
characters may behave in one of three ways at line breaks. As an example,
consider the text “The:quick:brown:fox:jumped.”, where the colon (:)
represents a visible word separator, with a break between “brown” and “fox”.
The desired visual appearance could be one of the following:
1. suppress the visible word separator
The:quick:brown
fox:jumped.
2. break before the visible word separator
The:quick:brown
:fox:jumped.
3. break after the visible word separator
The:quick:brown:
fox:jumped.
Both (2) and (3) can be
expressed with the Unicode Line Breaking Algorithm by tailoring the Line
Break property value for the word separator character to be
Break Before
or
Break After
, respectively.
For case (1), the line break
opportunity is positioned after the word separator character, as in case
(3), but the visual display of the character is suppressed. The means
by which a line layout and display process inhibits the visible display of
the separator character are outside of the scope of the Line Break
algorithm. U+1680 OGHAM SPACE MARK is an example of a character which may
exhibit this behavior.
Line Breaking Algorithm
Unicode Standard Annex #29, “Unicode Text Segmentation” [
UAX29
],
describes a particular method for
boundary detection, based on a set of hierarchical rules
and character classifications. That method is well suited for
implementation of some of the advanced heuristics for line breaking.
The line breaking algorithm presented in this section can be expressed in a
series of rules that take line breaking classes defined in
Section 5.1,
Description of Line Breaking Properties
, as input.
The title of each rule contains a mnemonic summary of the main effect of the
rule. The formal statement of each line breaking rules consists either of a
remap rule or of one or more regular expressions containing one or more
line breaking classes and one of three special symbols indicating the type
of line break opportunity:
! Mandatory break at the indicated position
× No break allowed at the indicated position
÷ Break allowed at the indicated position
In the regular expressions, parentheses may be used for grouping,
and square brackets, &, -, and \p{...} may be used to compose sets of characters,
as in UAX #29,
Unicode Text Segmentation
UAX29
] and in
UTS #18,
Unicode Regular Expressions
UTS18
].
Use of a line break class such as
BK
is short
for the property expression \p{lb=
BK
}. The
symbol $EastAsian stands for the set [\p{ea=F}\p{ea=W}\p{ea=H}] of characters with
Fullwidth, Wide, or Halfwidth East Asian Width.
The rules are applied in order. That is, there is an implicit “otherwise”
at the front of each rule following the first. It is possible to construct
alternate sets of such rules that are fully equivalent. To be equivalent, an
alternate set of rules must have the same effect.
The distinction between a direct break and an indirect break as defined in
Section 2,
Definitions
, is handled in rule
LB18
which explicitly considers the effect of
SP
Because rules are applied in order, allowing breaks following
SP
in rule
LB18
implies that any prohibited break in rules
LB19
LB30
is equivalent to an indirect break.
The examples for each rule use representative characters, where ‘H’ stands for an ideographs,
‘h’ for small kana, and ‘9’ for digits.
Except where a rule contains no expressions, the italicized text of the rule
is intended merely as a handy summary.
The algorithm consists of a part for which
tailoring is prohibited and a freely tailorable part.
6.1
Non-tailorable Line Breaking Rules
The rules in this subsection and the membership
in the classes
BK
CM
CR
GL
LF
NL
SP
WJ
ZW
and
ZWJ
define behavior that is required of all line break
implementations; see
Section 4,
Conformance
Resolve line breaking classes:
LB1
Assign a line breaking class to each code point of the input.
Resolve
AI
CB
CJ
SA
SG
and
XX
into other line
breaking classes depending on criteria outside the scope of this algorithm.
In the absence of such criteria all characters with a specific
combination of original class and
General_Category property value are resolved as follows:
Resolved
Original
General_Category
AL
AI
SG
XX
Any
CM
SA
Only Mn or Mc
AL
SA
Any except Mn and Mc
NS
CJ
Any
Start and end of text:
There are two special logical positions:
sot
, which occurs before the first character in the text, and
eot,
which occurs after the last character in the text. Thus an
empty string would consist of
sot
followed immediately by
eot
. With these
two definitions, the line break rules for start and end of text can be
specified as follows:
LB2
Never break at the start of text.
sot ×
LB3
Always break at the end of text.
! eot
These two rules are designed to deal with degenerate cases, so that there
is at least one character on each line, and at least one line break for
the whole text. Emergency line breaking behavior usually also allows line
breaks anywhere on the line if a legal line break cannot be found. This has
the effect of preventing text from running into the margins.
Mandatory breaks:
A hard line break can consist of
BK
or a Newline
Function (NLF) as described in
Section 5.8, Newline Guidelines
of [
Unicode
]. These three rules are
designed to handle the line ending and line separating characters as
described there.
LB4
Always break after hard line
breaks.
BK !
LB5
Treat
CR
followed by
LF
, as well as
CR
LF
, and
NL
as hard line breaks.
CR × LF
CR !
LF !
NL !
Note:
When displaying source code, failing to support all forms of the new line function
can have security implications; for instance, executable code can appear commented out.
It is therefore strongly recommended that source code editors support the VT character
within the BK class, and support the NEL character within the NL class, even though that support is
not required for conformance.
See
Unicode Technical Standard #55,
Unicode Source Code Handling
UTS55
].
LB6
Do not break before hard line breaks.
× ( BK | CR | LF | NL )
Explicit breaks and non-breaks:
LB7
Do not break before spaces or zero
width space.
× SP
× ZW
LB8
Break before any character following a zero-width space,
even if one or more spaces intervene.
ZW SP* ÷
LB8a
Do not break after a
zero width joiner
ZWJ ×
ZWJ
will prevent breaks between most pairs of characters.
This behavior is used to prevent breaks within emoji zwj sequences.
Combining marks:
See also
Section 9.2,
Legacy Support for Space Character as Base for Combining Marks
LB9
Do not break a combining character sequence; treat it as
if it has the line breaking class of the base character in all of the following rules.
Treat
ZWJ
as if it were
CM
Treat X (CM | ZWJ)* as if it were X.
where X is any line break class except
BK
CR
LF
NL
SP
, or
ZW
In subsequent rules, any
CM
or
ZWJ
characters affected by this rule are ignored.
Note that despite the summary title, this rule is not limited to
standard combining character sequences. For the purposes
of line breaking, sequences containing most of the control codes or layout
control characters are treated like combining sequences.
LB10
Treat any remaining
combining mark
or
ZWJ
as
AL
Treat any remaining CM or ZWJ as if it had the properties of U+0041 A LATIN CAPITAL LETTER A, that is, Line_Break=AL, General_Category=Lu, East_Asian_Width=Na, Extended_Pictographic=N.
This catches the case where a
CM
is the first character on the line or
follows
SP
BK
CR
LF
NL
, or
ZW
Word joiner:
LB11
Do not break before or after
Word joiner and related
characters.
× WJ
WJ ×
Non-breaking characters:
LB12
Do not break after NBSP and related characters.
GL ×
6.2
Tailorable Line Breaking Rules
The following rules and the classes referenced in them provide a reasonable
default set of line break opportunities. Implementations should implement them
unless alternate approaches produce better results for some classes of
text or applications. When using alternative rules or algorithms, implementations
must ensure that the mandatory breaks, break opportunities and non-break positions
determined by the algorithm and rules of
Section 6.1,
Non-tailorable Line Breaking Rules
are preserved. See
Section 4,
Conformance
Non-breaking characters:
LB12a
Do not break before NBSP and related characters,
except after spaces and hyphens.
[^SP BA HY HH] × GL
The expression [^SP
BA HY HH] designates any line break class other than
SP
BA
HY
, or
HH
. The symbol ^ is used, instead of !,
to avoid confusion with the use of ! to indicate an explicit break. Unlike the case for
WJ
, inserting a
SP
overrides the non-breaking nature of
GL
. Allowing
a break after
BA
or
HY
matches widespread implementation practice
and supports a common way of handling special line breaking of
explicit hyphens, such as in Polish and Portuguese. See
Section 5.3,
Use of Hyphen
Opening and closing:
These have special behavior with respect to spaces, and therefore come before rule
LB18.
LB13
Do not break before ‘]’ or ‘!’ or ‘/’, even after spaces.
× CL
× CP
× EX
× SY
LB14
Do not break after ‘[’, even after spaces.
OP SP* ×
LB15a
Do not break after an unresolved initial punctuation that lies at the start of
the line, after a space, after opening punctuation, or after an unresolved
quotation mark, even after spaces.
(sot | BK | CR | LF | NL | OP | QU | GL | SP | ZW) [\p{Pi}&QU] SP* ×
LB15b
Do not break before an unresolved final punctuation that lies at the end
of the line, before a space, before a prohibited break, or before an unresolved
quotation mark, even after spaces.
× [\p{Pf}&QU] ( SP | GL | WJ | CL | QU | CP | EX | IS | SY | BK | CR | LF | NL | ZW | eot)
LB15c
Break before a decimal mark that follows a space, for instance, in ‘subtract .5’.
SP ÷ IS NU
LB15d
Otherwise, do not break before ‘;’, ‘,’, or ‘.’, even after spaces.
× IS
LB16
Do not break
between closing punctuation and a nonstarter (lb=
NS
),
even with intervening spaces.
(CL | CP) SP* × NS
LB17
Do not break within ‘——’, even with intervening
spaces.
B2 SP* × B2
Spaces:
LB18
Break after spaces.
SP ÷
Special case rules:
LB19
Do not break before non-initial unresolved quotation marks, such as ‘ ” ’ or ‘ " ’, nor after non-final unresolved quotation marks, such as ‘ “ ’ or ‘ " ’.
× [ QU - \p{Pi} ]
[ QU - \p{Pf} ] ×
LB19a
Unless surrounded by East Asian characters, do not break either side of any unresolved quotation marks.
[^$EastAsian] × QU
× QU ( [^$EastAsian] | eot )
QU × [^$EastAsian]
( sot | [^$EastAsian] ) QU ×
LB20
Break before and after unresolved
CB
÷ CB
CB ÷
Conditional breaks should be resolved external to the line breaking rules.
However, the default action is to treat unresolved
CB
as breaking before and
after.
LB20a
Do not break after a word-initial hyphen.
( sot | BK | CR | LF | NL | SP | ZW | CB | GL ) ( HY | HH ) × ( AL | HL )
LB21
Do not break before hyphen-minus, other hyphens,
fixed-width spaces, small kana, and other non-starters, or after acute
accents.
× BA
× HH
× HY
× NS
BB ×
LB21a
Do not break after the hyphen in Hebrew + Hyphen + non-Hebrew.
HL (HY | HH) × [^HL]
LB21b
Do not break between Solidus and Hebrew letters.
SY × HL
LB22
Do not break before ellipses.
× IN
Examples:
‘9...’, ‘a...’, ‘H...’
Numbers:
Do not break alphanumerics.
LB23
Do not break between digits and letters.
(AL | HL) × NU
NU × (AL | HL)
LB23a
Do not break between numeric prefixes and ideographs, or between
ideographs and numeric postfixes.
PR × (ID | EB | EM)
(ID | EB | EM) × PO
LB24
Do not break between
numeric prefix/postfix and letters, or between letters and prefix/postfix.
(PR | PO) × (AL | HL)
(AL | HL) × (PR | PO)
In general, it is recommended to not break lines inside numbers of the form described
by the following regular expression:
PR
PO
) ?
OP
HY
) ?
IS
NU
NU
SY
IS
) *
CL
CP
) ?
PR
PO
) ?
Examples:
$(12.35)    2,1234
(12)¢    12.54¢
.50
₹1,00,000.00
-1/12
The default line breaking algorithm implements this with the following
rule. Note that some cases have already been handled, such as ‘9,’, ‘[9’.
LB25
Do not break numbers:
NU ( SY | IS )* CL × PO
NU ( SY | IS )* CP × PO
NU ( SY | IS )* CL × PR
NU ( SY | IS )* CP × PR
NU ( SY | IS )* × PO
NU ( SY | IS )* × PR
PO × OP NU
PO × OP IS NU
PO × NU
PR × OP NU
PR × OP IS NU
PR × NU
HY × NU
IS × NU
NU ( SY | IS )* × NU
Korean syllable blocks
Conjoining jamos, Hangul syllables, or combinations of both form Korean
Syllable Blocks. Such blocks are effectively treated as if they were Hangul
syllables; no breaks can occur in the middle of a syllable block. See
Unicode Standard Annex #29, “Unicode Text Segmentation”
UAX29
],
for more information on Korean Syllable Blocks.
LB26
Do not break a Korean
syllable.
JL × (JL | JV | H2 | H3)
(JV | H2) × (JV | JT)
(JT | H3) × JT
where the notation (JT | H3) means JT or H3.
The effective line breaking class for the syllable block matches the
line breaking class for Hangul syllables, which is
ID
by default. This is achieved by
the following rule:
LB27
Treat a Korean Syllable Block the
same as
ID
(JL | JV | JT | H2 | H3) × PO
PR × (JL | JV | JT | H2 | H3)
When Korean uses SPACE for line breaking, the classes in rule
LB26
, as well as characters of
class
ID
are often tailored to
AL
; see
Section 8,
Customization
Finally, join alphabetic letters into words and break everything else.
LB28
Do not break between alphabetics (“at”).
(AL | HL) × (AL | HL)
LB28a
Do not break inside the orthographic syllables of Brahmic scripts.
AP × (AK | [◌] | AS)
(AK | [◌] | AS) × (VF | VI)
(AK | [◌] | AS) VI × (AK | [◌])
(AK | [◌] | AS) × (AK | [◌] | AS) VF
Note:
In the above regular expressions,
the class [◌] contains the single character U+25CC DOTTED CIRCLE.
LB29
Do not break between numeric punctuation
and alphabetics (“e.g.”).
IS × (AL | HL)
LB30
Do not break between
letters, numbers, or ordinary symbols and opening or closing parentheses.
(AL | HL | NU) × [OP-$EastAsian]
[CP-$EastAsian] × (AL | HL | NU)
The purpose of this rule is to prevent breaks in common cases where a part of a word
appears between delimiters—for example, in “person(s)”.
The excluded set ($EastAsian) refines the behavior of this rule, to enable
a break before an East Asian OP or after an East Asian CP. Those cases are identified by
excluding East_Asian_Width values of Fullwidth, Wide, or Halfwidth.
This is illustrated by the following
example, which shows East Asian corner brackets immediately following a Latin letter
in Japanese text. In such a case, the preferred line break is between the Latin letter and
the opening angle bracket.
Preferred
Bad Break
日中韓統合漢字拡張G
「ユニコード」
日中韓統合漢字拡張
G「ユニコード」
LB30a
Break between two regional indicator symbols if and only if there are an even number of
regional indicators preceding the position of the break.
sot (RI RI)* RI × RI
[^RI] (RI RI)* RI × RI
LB30b
Do not break between an
emoji base
(or potential emoji) and an
emoji modifier
EB × EM
[\p{Extended_Pictographic}&\p{Cn}] × EM
LB31
Break everywhere else.
ALL ÷
÷ ALL
Deleted
Formerly was: Pair Table-Based Implementation.
Customization
A real-world line breaking algorithm has to be tailorable to some degree to meet
user or document requirements.
In Korean, for example, two distinct line breaking modes occur,
which can be summarized as breaking after each character or breaking after spaces
(as in Latin text). The former tends to occur when text is set justified; the latter, when
ragged margins are used. In that case, even ideographs are broken only at space
characters. In Japanese, for example, tighter and looser specifications of prohibited line breaks
may be used.
Specialized text or specialized text constructs may need specific line
breaking behavior that differs from the default line breaking rules given in
this annex. This may require additional tailorings beyond those considered
in this section. For example, the rules given here are insufficient for
mathematical equations, whether inline or in display format. Likewise, text
that commonly contains lengthy URLs might benefit from special tailoring that suppresses
SY
NU
from rule
LB25
within the scope of a
URL to allow breaks after a “/” separated segment in the URL regardless of
whether the next segment starts with a digit.
Notes:
Locale-sensitive line break specifications can be expressed in LDML [
UTS35
].
Tailorings are available in the Common Locale Data Repository [
CLDR
].
Some changes to rules and data are needed for the best segmentation
behavior of emoji zwj sequences [
UTS51
].
Implementations are strongly encouraged to use the line break rules in
the latest version of CLDR (Version 35 or later)
CLDR
and the latest emoji properties (Version 12.0 or later)
UTS51
].
The remainder of this section gives an overview of common types of tailorings.
8.1
Types of Tailoring
There are two principal ways of tailoring
the line breaking algorithm:
Changing the line breaking class assignment for some characters
This is useful in cases where the line breaking properties of one class of
characters are occasionally lumped together with the properties of another
class to achieve a less restrictive line breaking behavior.
Changing the line breaking rules
Adding new rules, or altering or removing existing rules, provides more flexibility in
changing the line breaking behavior. This can also include introducing new character classes
for use by the new or altered rules.
For example, specialized
rules could be added to recognize and break common constructs, such as URLs, numeric
expressions, and so on. Such open-ended customizations place no limits on possible changes, other than the
requirement that non-tailorable line breaking rules be
correctly implemented. This means that whatever changes are made must
be equivalent to changes to the line breaking assignments of tailorable line breaking rules, and to alteration,
removal, or addition of rules applied after rule LB12.
8.2
Examples of Customization
Example 1.
The exact method of resolving the line break class for
characters with class
SA
is not
specified in the default algorithm. One method of implementing line breaks for complex
scripts is to invoke context-based classification for all runs of characters
with class
SA
. For example, a dictionary-based algorithm could return
different classes for Thai letters depending on their context: letters at the
start of Thai words would become
BB
and other Thai letters would become
AL
. Alternatively, for text consisting of,
or predominantly containing characters with line breaking class
SA
it may be useful to instead defer the determination of line breaks to a
different algorithm.
Example 2.
To implement terminal style line breaks, it would be necessary to allow
breaks at fixed positions. These could occur
inside a run of spaces or in the middle of words without regard to
hyphenation. Such a modification essentially disregards the output of
the line breaking algorithm, and is therefore not a conformant tailoring. For
a system that supports both regular line breaking and terminal style line
breaks, only some of its line break modes would be conformant.
Example 3.
Depending on the nature of the document, Korean either uses implicit breaking around characters
(type 2 as defined in
Section 3,
Introduction
) or uses spaces (type 1).
Space-based layout is common in magazines and other informal documents with ragged margins,
while books, with both margins justified, use the other type, as
it affords more line break opportunities and therefore leads to better
justification.
Example 4.
In a Far Eastern context it is sometimes necessary to allow alphabetic characters and digit strings to break anywhere.
According to reference [
Suign98
],
this can again be done in the same way as Korean.
This can be implemented by adjusting rules
LB23
LB25
and
LB28
to allow breaks between all permutations of the character classes
AL
and
NU
Example 5.
Some users prefer to relax the requirement that Kana syllables be kept
together. For example, the syllable
kyu,
spelled with the two kanas
KI
and “small
yu
”, would no longer be kept together as if
KI
and
yu
were atomic. This customization can be handled by
mapping class
CJ
to be handled as class
ID
in rule
LB1
Example 6.
Tailor to prevent line breaks from falling within default grapheme
clusters, as defined by Unicode Standard Annex #29, “Unicode Text Segmentation”
UAX29
]. The tailoring can be accomplished by
first segmenting the text into grapheme clusters according to the rules defined
in UAX #29, and then finding line breaks according to the default line break rules,
as follows: After applying the mandatory line break rules,
give each grapheme cluster the line breaking class of its first code point.
An example of a grapheme cluster that would be split by the default line break
rules is U+0020 SPACE followed by a combining mark.
Example 7 (deleted).
Versions 4.1.0 through 15.1.0 of The Unicode Standard
defined a tailoring of the line breaking of numeric expressions as Example 7.
This tailoring was used in the test files provided with Unicode 5.1.0 and later.
Since Unicode version 16.0, that behavior has been incorporated into the default;
it no longer constitutes a tailoring.
Example 8.
Some scripts that traditionally follow the Brahmic style of context analysis are nowadays occasionally written with spaces, and word-based line breaking might be desired in that case.
This can be accomplished by remapping the line break classes
AK
AP
, and
AS
to
AL
; and
VI
or
VF
to
CM
In some cases other word-forming characters, such as U+A9CF JAVANESE PANGRANGKEP, also need to be remapped to
AL
Digits, which may have line break class
AS
or
ID
in such scripts, need to be remapped to
NU
Punctuation, which may have line break class
ID
in such scripts, need to be remapped to
AL
or
BA
Implementation Notes
This section provides additional notes on implementation issues.
9.1
Combining Marks in Regular Expression-Based Implementations
Implementations that use regular expressions cannot directly
express rules
LB9
and
LB10
However, it is possible to make these rules unnecessary by rewriting
all
the rules from
LB11
on down so that the
overall result of the algorithm is unchanged. This restatement of the rules is
therefore not a tailoring, but rather an equivalent statement of the algorithm
that can be directly expressed as regular expressions.
To replace rule
LB9
, terms of
the form
SP* #
SP* #
are replaced by terms of the form
CM* #
CM* SP* #
CM* #
CM* SP* #
where
and
are any line break class or set of
alternate line break classes, such as (X |Y), and where # is any of the three
operators !, ÷, or ×.
Note that because
sot
BK
CR
LF
NL
, and
ZW
are all handled by rules
above
LB9
, these classes cannot occur in
position
in any rule that is rewritten as shown here.
Replace
LB10
by the following rule:
× CM
For each rule containing AL on its left side,
add a rule that is identical except for the replacement of AL by CM, but taking
care of correctly handling sets of alternate line break classes. For example,
for rule
(AL | NU) × OP
add another rule
CM × OP.
These prescriptions for rewriting the rules are, in
principle, valid
even where the rules have been tailored as permitted in
Section 4,
Conformance
. However, for extended context rules
such as in
LB25
, additional
considerations apply. These are described in
Section 6.2, Replacing Ignore Rules
, of
Unicode Standard Annex #29, “Unicode Text Segmentation” [
UAX29
].
9.2
Legacy Support for Space Character as Base for Combining Marks
As stated in
Section 7.9, Combining Marks
of [
Unicode
],
combining characters are shown in isolation by applying them to U+00A0 NO-BREAK SPACE (NBSP).
In earlier versions, this recommendation included the use of U+0020 SPACE.
The use of SPACE for this purpose has been deprecated
because it leads to many complications in text processing. The visual appearance is the same with
both NO-BREAK SPACE and SPACE,
but the line breaking behavior is different.
Under the current rules,
SP
CM*
will allow a break between
SP
and
CM*
, which could result in a new line starting with a combining mark. Previously,
whenever the base character was
SP
, the sequences
CM*
and
SP
CM*
were defined to act like indivisible clusters,
allowing breaks on either side like
ID
Where backward compatibility with documents created under the prior
practice is desired, the following tailoring should be applied to those
CM
characters that have a General_Category value of Combining_Mark (M):
Legacy-CM: In all of the rules following rule
LB8
if a space is the base character for a
combining mark, the space is changed to type
ID
In other words, break before
SP
in the same cases as one would break before an
ID
Treat
SP
CM*
as if it were
ID
While this tailoring changes the location of the line break
opportunities in the string, it is ordinarily not expected to affect the display of
the text. That is because spaces at the end of the line are normally
invisible and the recommended display for isolated combining marks is the
same as if they were applied to a preceding SPACE
or NBSP.
10
Testing
As with the other default specifications,
implementations are free to override (tailor) the results to meet the
requirements of different environments or particular languages as described in
Section 4,
Conformance
. For those
who do implement the default breaks as specified in this annex and wish
to check that their implementation matches that specification, a
test file has been made available in [
Tests14
].
These tests cannot be exhaustive, because of the large number of possible
combinations; but they do provide samples that test all pairs of property
values, using a representative character for each value, plus certain other
sequences.
A sample HTML file is also available for each that shows various
combinations in chart form, in [
Charts14
].
The header cells of the chart
consist of a property value, followed by a representative code point number.
The body cells in the chart show the break status: whether a break occurs
between the row property value and the column property value. If the browser
supports tool-tips, then hovering the mouse over the code point number will
show the character name, General_Category and Script property
values. Hovering over the break status will display the number of the rule
responsible for that status.
Note:
To determine a break it is generally not sufficient to
just test the two adjacent characters.
The chart is followed by some test cases. These test cases consist of
various strings with the break status between each pair of characters shown
by blue lines for breaks and by whitespace for non-breaks. Hovering over
each character (with tool-tips enabled) shows the character name and
property value; hovering over the break status shows the number of the rule
responsible for that status.
Due to the way they have been mechanically processed for generation, the
test rules do not match the rules in this annex precisely. In particular:
The rules are cast into a more regex-style.
The rules “sot”, “eot”, and “Any” are added
mechanically and have artificial numbers.
The rules are given decimal numbers without prefixes,
so rules such as LB14 are given a number using tenths, such as 14.0.
Where a rule has multiple parts (lines), each one is numbered using
hundredths, such as
13.01) [^NU] × CL
13.02) × EX
...
The mapping from the rule numbering in this annex to the numbering for
the test rules is summarized in
Table 4
Table 4.
Numbering of Test Rules
Rule in This Annex
Test Rule
Comment
LB2
0.2
start of text
LB3
0.3
end of text
LB12a
12.0
GL ×
LB12b
12.1
[^SP, BA, HY] × GL
LB31
999
÷ any
11
History
Since its publication in 1999 as part of Unicode
Version 3.0.0, the line breaking algorithm has undergone many changes. It
started as a set of 29 line breaking classes involved in 23 rules which were
representable as a pair table with some special handling for combining marks
and spaces.
It now encompasses 48 line breaking classes involved in more than 40 rules,
many of which rely on extended context which may be several characters removed
from the position they govern.
As the algorithm grew, rules were split, reordered, added, and removed.
In Unicode Version 5.0, the rules were renumbered to reduce the number of
alphabetic suffixes on the rule numbers.
Please refer to Unicode Technical Note #54, “Annotated Line Breaking
Algorithm” [
UTN54
], for a
complete history of the changes to the text of this document since
Unicode Version 3.0.0, and for additonal background on these changes.
Of particular note is the history of the line breaking
assignment of U+034F COMBINING GRAPHEME JOINER.
This character was originally meant to merge adjoining characters into a
graphemic unit, and the character was accordingly originally documented in
Version 3.2 of this annex as having line breaking class
GL
However, this behavior of the combining grapheme joiner was made obsolete in
Unicode Version 4.0, and the character was repurposed for uses where the line
breaking algorithm should ignore it.
From that point on, retaining the line breaking assignment
GL
was
a mistake, and changing it to
CM
would have
been appropriate. This was only corrected in Unicode Version 17.0, more than
twenty years later. For more on the history of U+034F COMBINING GRAPHEME JOINER,
including a mistake in the data files in the other direction between
Unicode Version 3.2 and Unicode Version 4.1, see Section 6.3 of UTC document
L2/24-224
References
For references for this annex, see Unicode Standard Annex #41,
“Common References for Unicode Standard Annexes”
UAX41
].
Acknowledgments
Asmus Freytag created the initial version of this
annex and maintained the text for many years. Andy Heninger
maintained the
text from 2008 through 2019. Christopher Chapman maintained the text from 2020 through 2022.
Robin Leroy has maintained the text since September 2022.
The initial assignments of properties are based on input by Michel
Suignard. Mark Davis provided algorithmic verification and formulation of the
rules, and detailed suggestions on the algorithm and text. Ken Whistler, Rick McGowan,
Deborah Anderson, Lorna Evans, and other members of the editorial committee
provided valuable feedback. Tim Partridge enlarged the information on
dictionary usage. Sun Gi Hong reviewed the information on Korean and provided
copious printed samples. Eric Muller reanalyzed the behavior of the soft hyphen
and collected the samples. Adam Twardoch provided the Polish example.
António Martins-Tuválkin supplied information about Portuguese. Tomoyuki
Sadahiro provided information on use of U+30A0. Christopher Fynn provided the background
information on Tibetan line breaking. Andrew West, Kamal Mansour, Andrew Glass,
Daniel Yacob, and Peter Kirk suggested improvements for Mongolian, Arabic,
Kharoshthi, Ethiopic, and Hebrew punctuation characters, respectively.
Kent Karlsson reviewed the line break properties for consistency.
Jerry Hall reviewed the sample code. Elika J. Etemad (fantasai)
reviewed the entire document in an effort to make it easier to reference from
external standards. Norbert Lindenberg added the Brahmic style of line breaking and provided clarifications
on the South East Asian style of line breaking.
Charlotte Buff and David Corbett provided ample feedback on property
assignments and ramifications of the rules. Many
others provided additional review of the rules and property assignments.
Modifications
The following summarizes modifications from the previous revision of this
annex.
Revision 55:
Reissued
for Unicode 17.0.
Updated the test files to more closely match the rules.
Split part of class
BA
into a new class Unambiguous_Hyphen
HH
) and updated rules
LB20a
and
LB21a
to use it.
Rules
LB12a
and
LB21
treat HH like
BA, preserving their old behavior.
181-C53
Updated rule
LB20a
to treat Hebrew letters (HL) like
other alphabetic characters (AL).
181-C53
Updated the descriptions of classes
CM
and
GL
to reflect the change to the Line_Break property of U+034F COMBINING GRAPHEME JOINER.
Added a discussion of this long-standing mistaken assignment in Section 11,
History
181-C54
Section 5.3,
Use of Hyphen
: updated for
LB20a
added in Unicode 16.0. [
179-C32
Section 5.5,
Use of Double Hyphen
Add a discussion of the actual DOUBLE HYPHEN, based on
L2/11-038
Section 5.5,
Use of Double Hyphen
Corrected confusing statements about U+2E17 DOUBLE OBLIQUE HYPHEN.
Modifications for previous versions are listed in those respective versions.
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