![[Unicode]](http://www.unicode.org/webscripts/logo60s2.gif){kind=small}
Technical
Reports| Technical
Reports |
| Version | 4.1.0 |
| Authors | Asmus Freytag (asmus@unicode.org) |
| Date | 2005-08-29 |
| This Version | http://www.unicode.org/reports/tr14/tr14-17.html |
| Previous Version | http://www.unicode.org/reports/tr14/tr14-15.html |
| Latest Version | http://www.unicode.org/reports/tr14/ |
| Revision | 17 |
This report presents the specification of line breaking properties for Unicode characters as well as a model algorithm for determining line break opportunities.
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 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 number of the Unicode Standard at the last point that the UAX document was updated.
Please submit corrigenda and other comments with the online reporting form [Feedback]. Related information that is useful in understanding this document is found in the References section. For the latest version of the Unicode Standard see [Unicode]. See [Reports] for a list of current Unicode Technical Reports. For more information about versions of the Unicode Standard, see [Versions].
The text of The Unicode Standard [Unicode] presents a limited description of some of the characters with specific function in line breaking, but does not give a complete specification of line breaking behavior. This Unicode Standard 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. Therefore, 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. 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 document opens with formal definitions, a summary of the line breaking task and a brief section on conformance requirements. Four main sections follow:
All terms not defined here shall be as defined in the Unicode Standard [Unicode]. The notation defined in this technical report differs somewhat from the notation defined elsewhere in the Unicode Standard. All other notation used here without an explicit definition shall be as defined in the Unicode Standard.
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.
Line Break — the position in the text where one line ends and the next one starts.
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 context as well as the line breaking rules in force.
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.
Line Breaking Property — A character property with enumerated values, as listed in Table 1 and separated into normative and informative. Line breaking property values are used to classify characters, and taken in context, determine the type of break.
Line Breaking Class — a class of characters with the line breaking property value.
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 B is the character with the mandatory break property.
Direct Break — a line break opportunity exists between two adjacent characters of the given line breaking classes. This is indicated in the rules below as B ÷ A, where B is the character class of the character before and A is the character class of the character after the break. If they are separated by one or more space characters, a break opportunity also exists after the last space. In the pair table, the optional space characters are not shown.
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. In this case, a break opportunity exists after the last space. No break opportunity exists if the characters are immediately adjacent. This is indicated in the pair table below as B % A, where B is the character class of the character before and A is the character class of the character after the break. Even though space characters are not shown in the pair table, an indirect break can only occur if one or more spaces follow B. In the notation of the rules in Section 6, Line Breaking Algorithm this would be represented as two rules: B × A and B SP+ ÷ A.
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. This is indicated in the pair table below as B ^ A, where B is the character class of the character before and A is the character class of the character after the break and the optional space characters are not shown. In the notation of the rules in Section 6, Line Breaking Algorithm this would be expressed as a rule of the form: B SP* × A.
Hyphenation — Hyphenation uses language-specific rules to provide additional line break opportunities within a word. Hyphenation improves the layout of narrow columns, especially for languages with many longer words, such as German or Finnish. For the purpose of this document, it is assumed that hyphenation is equivalent to inserting soft hyphen characters. All other aspects of hyphenation are outside the scope of this document.
Table 1: Line Breaking Classes (* = normative)
|
Class |
Descriptive Name |
Examples |
Characters with this property... |
|
Normative Line Breaking Classes |
|||
|
Mandatory Break |
NL, PS |
cause a line break (after) |
|
|
Carriage Return |
CR |
cause a line break (after), except between CR and LF |
|
|
Line Feed |
LF |
cause a line break (after) |
|
|
Attached Characters and Combining Marks |
Combining Marks, control codes |
prohibit a line break between the character and the preceding character |
|
| NL * | Next Line | NEL | cause a line break (after) |
|
Surrogates |
Surrogates |
should not occur in well-formed text |
|
| WJ * | Word Joiner | WJ | prohibit line breaks before or after |
|
Zero Width Space |
ZWSP |
provide a break opportunity |
|
|
Non-breaking (“Glue”) |
NBSP, ZWNBSP, CGJ |
prohibit line breaks before or after |
|
|
Contingent Break Opportunity |
Inline Objects |
provide a line break opportunity contingent on additional information. |
|
|
Space |
Space |
generally provide a line break opportunity after the character, enable indirect breaks |
|
|
Break Opportunities |
|||
|
Break Opportunity Before and After |
EM Dash |
provide a line break opportunity before and after the character |
|
|
Break Opportunity After |
Spaces, Hyphens |
generally provide a line break opportunity after the character |
|
|
Break Opportunity Before |
Punctuation used in dictionaries |
generally provide a line break opportunity before the character |
|
|
Hyphen |
Hyphen-Minus |
provide a line break opportunity after the character, except in numeric context |
|
|
Characters Prohibiting Certain Breaks |
|||
|
Closing Punctuation |
“)”, “]”, “}”, etc. |
prohibit a line break before |
|
|
Exclamation/Interrogation |
“!”, “?” etc. |
prohibit line break before |
|
|
Inseparable |
Leaders |
allow only indirect line breaks between pairs. |
|
|
Non Starter |
small kana |
allow only indirect line break before |
|
|
Opening Punctuation |
“(“, “[“, “{“, etc. |
prohibit a line break after |
|
|
Ambiguous Quotation |
Quotation marks |
act like they are both opening and closing |
|
|
Numeric Context |
|||
|
Infix Separator (Numeric) |
. , |
prevent breaks after any and before numeric |
|
|
Numeric |
Digits |
form numeric expressions for line breaking purposes |
|
|
Postfix (Numeric) |
%, ¢ |
do not break following a numeric expression |
|
|
Prefix (Numeric) |
$, £, ¥, etc. |
do not break in front of a numeric expression |
|
|
Symbols Allowing Breaks |
/ |
prevent a break before, and allow a break after |
|
|
Other Characters |
|||
|
Ambiguous (Alphabetic or Ideographic) |
Characters with Ambiguous East Asian Width |
||
|
Ordinary Alphabetic and Symbol Characters |
Alphabets and regular symbols |
are alphabetic characters or symbols that are used with alphabetic characters |
|
| H2 | Hangul LV Syllable | Hangul | form Korean syllable blocks |
| H3 | Hangul LVT Syllable | Hangul | form Korean syllable blocks |
|
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 |
|
Complex Context (South East Asian) |
South East Asian: Thai, Lao, Khmer |
provide a line break opportunity contingent on additional, language specific context analysis |
|
|
Unknown |
Unassigned, Private Use |
have as yet unknown line breaking behavior or unassigned code positions |
|
Lines are broken as result of one of two conditions. The first condition is the presence of an explicit 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 inter-character and inter-word spaces and consider the longest line that fits. 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 inter-word space according to common typographical practice, only the spaces marked by U+0020 SPACE, U+00A0 NO-BREAK SPACE, and U+3000 IDEOGRAPHIC 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 inter-character 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 inter-character space is allowed in justifying a line. In languages, such as German, where inter-character space is commonly used to mark e m p h a s i s (like this), allowing variable inter-character spacing would have the unintended effect of adding random emphasis, and should therefore be avoided.
In table headings that use Han ideographs, on the other hand, even extreme amounts of inter-character space commonly occur as short texts are spread out across the entire available space to distribute the characters evenly from end to end.
More complex formatting algorithms may take into account the interaction of line breaking decisions for the whole paragraph. The well known text layout system [TEX] implements an example of such a 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].
The definition of optimal line breaks is outside the scope of this document, as are methods for their selection. For the purpose of this document, what is important is not so much what defines the optimal amount of text on the line, but how to determine all legal line break opportunities. Whether and how any given line break opportunity is actually used is up to the full layout system. Some layout systems will further evaluate the raw line break opportunities returned from the line breaking algorithm and apply additional rules. [TEX] for example, uses line break opportunities based on hyphens only as a last resort.
Finally, most text layout systems will support an emergency mode which handles the case of an unusual line that contains no ordinary line break opportunities. In such line layout emergencies line breaks are placed with no regard to the ordinary line breaking behavior of the characters involved.
Three principal styles of context analysis determine line break opportunities.
The first, or 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 in addition, 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 do not use spaces, but which restrict word-breaks to syllable boundaries, the determination of which requires knowledge of the language comparable to that required by a hyphenation algorithm. Such an algorithm is beyond the scope of the Unicode Standard.
For multilingual text, the Western and East Asian styles can be unified into a single set of specifications, based on the information in this report. Unicode characters have explicit line breaking properties assigned to them. These can be utilized with these two styles of context analysis for line break opportunities. Customization for user preferences or document style can then be achieved by tailoring that specification.
In bidirectional text, line breaks takes are determined before applying rule L1 of the Unicode Bidirectional Algorithm [Bidi]. 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.
There is no single method for determining line breaks; the rules may change based on user preference and document layout. Therefore the information in this annex, including the specification of the line breaking algorithm, is informative, rather than normative. However, some characters have been encoded explicitly for their effect on line breaking. Users adding such characters to a text expect that they will have the desired effect. For that reason, these characters have been given normative line breaking behavior.
Conformant implementations must not tailor characters with normative line breaking classes to any of the informative line breaking classes, but may tailor characters with informative line breaking classes to one of the normative line breaking classes.
Higher-level protocols may further restrict, override, or extend the line breaking classes of certain characters in some contexts.
The specification of the Line Breaking Algorithm in this annex is informative. As stated in [Unicode] Section 3.2, Conformance Requirements, conformant implementations are not required to implement the Unicode Line Breaking Algorithm. The relationship between conformance to the Unicode Standard, and conformance to an individual Unicode Standard Annex (UAX) is described in more detail in the Unicode Standard in Section 3.2 Conformance Requirements.
There are many different ways to break lines of text, and the Unicode Standard does not restrict the ways in which implementations can do this. However, any Unicode-conformant implementation that purports to implement this specification must do so as described in the following clause. Implementations are free to deviate from this, as long as they do not purport to conform to this specification.
| C1 | An implementation that claims conformance
to the default Unicode Line Breaking Algorithm shall produce the same results as the
algorithm published in this specification.
|
| C2 | This specification defines default
behavior, which is to be used in the absence of tailoring
for particular languages and environments.
|
| C3 | If tailoring is used by an implementation that
claims conformance to the default Unicode Line Breaking Algorithm,
the existence of such tailoring must be documented.
|
At times, this specification recommends best practice. These recommendations are not normative and conformance with this specification does not depend on their realization. These recommendations contain the expression "This specification recommends ...", or some similar wording.
This section provides detailed narrative descriptions of the line breaking behavior of many Unicode characters. In a few instances, the descriptions in this section provide additional detail about handling a given character at the end of a line, which goes beyond the simple determination of line breaks.
This section also summarizes the membership of character classes for 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 break behavior is identical, otherwise unrelated characters will be found 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 two algorithms defined in Section 6, Line Breaking Algorithm and Section 7, Pair-Table-based Implementation. These sections describe workable default line breaking methods. Section 8, Customization discusses how the default line breaking behavior can be tailored to the needs of particular languages for particular document styles and user preferences.
The full classification of all Unicode characters by their line breaking properties, is available in the file LineBreak.txt [Data] in the Unicode Character Database [UCD]. This is a tab-delimited, two column plain text file, with code position, and line breaking class. A comment at the end of each line indicates the character name. Ideographic, Hangul, Surrogate, and Private Use ranges are collapsed by giving a range in the first column.
As more scripts are added to the Unicode Standard and become more widely implemented and used on computers, more line breaking classes may be added, or the assignment of line breaking class may be changed for some characters. Implementations should not make any assumptions to the contrary. Any future updates will be reflected in the latest version of the data file. (See the Unicode Character Database [UCD] for any specific version of the datafile).
Line breaking classes are listed alphabetically. Each line breaking class is marked with an annotation in parentheses with the following meanings:
(A) — the class allows a break opportunity after in specified contexts
(XA) — the class prevents a break opportunity after in specified contexts
(B) — the class allows a break opportunity before in specified contexts
(XB) — the class prevents a break opportunity before in specified contexts
(P) — the class allows a break opportunity for a pair of same characters
(XP) — the class prevents a break opportunity for a pair of same characters
NOTE: The use of the letters B and A in these annotations marks the position of the break opportunity relative to the character. It is not to be confused with the use of the same letters in the other parts of this document, where they indicate position of the characters relative to the break opportunity.
Ambiguous characters act either like alphabetic characters (that is, those with the AL line breaking class) or like ideographs (that is characters with line breaking class ID), depending on context. In the absence of appropriate context information, they are treated as class AL.
As originally defined, this class contained all characters with East Asian Width property A (ambiguous width), and which would otherwise be AL in this classification. They take the AL line breaking class only when their resolved width is N (narrow) and take the line breaking class ID when their resolved width is W (wide). For more information on East Asian Width, and how to resolve it, see Unicode Standard Annex #11, East Asian Width [EAW].
The original definition included many Latin, Greek and Cyrillic characters for which a default assignment of the AL line breaking class better corresponds to modern practice. At the same time, the set of ambiguous characters has been extended to completely encompass the enclosed alphanumeric characters used for numbering of bullets.
As updated, with the exception of characters in the range U+0000..U+1FFF, this line breaking class includes all characters with East Asian Width A, plus the following characters:
| 24EA | CIRCLED DIGIT ZERO |
| 2780..2793 | DINGBAT CIRCLED SANS-SERIF DIGIT ONE..DINGBAT NEGATIVE CIRCLED SANS-SERIF NUMBER TEN |
The line breaking rules in Section 6, Line Breaking Algorithm and the pair table in Section 7, Pair Table-based Implementation, assume that all ambiguous characters have been resolved appropriately as part of assigning line breaking classes to the input characters.
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.
Except as listed explicitly below as part of another line breaking class, and except as assigned class AI or ID based on East Asian Width, this class contains the following characters:
ALPHABETIC — all characters of General Categories Lu, Ll, Lt, Lm, Lo
SYMBOLS — all characters of General Categories Sm, Sk, So
NON-DECIMAL NUMBERS — all characters of General Categories Nl and No
PUNCTUATION — all characters of General Categories Pc, Pd and Po
plus these characters:
| 0600..0603 | ARABIC NUMBER SIGN..ARABIC SIGN SAFHA |
| 06DD | ARABIC END OF AYAH |
| 070F | SYRIAC ABBREVIATION MARK |
| 2061..2063 | FUNCTION APPLICATION..INVISIBLE SEPARATOR |
These 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.
Like the SPACE the characters in this class provide a break opportunity, but unlike SPACE they do not take part in determining indirect breaks. They can be subdivided into several categories.
Breaking spaces are the following subset of characters with General Category Zs:
| 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 |
The preceding list of space characters all 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 is rendered visibly between words but should be elided at the end of a line.
See the ID property for U+3000 IDEOGRAPHIC SPACE. For a list of all space characters in the Unicode Standard, see Section 6.2, General Punctuation in [Unicode].
|
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.
|
00AD |
SOFT HYPHEN (SHY) |
SHY marks an optional place where a line break may occur inside a word. It can be used with all scripts. SHY is rendered invisibly and has no width: it merely indicates an optional line break. The rendering of the optional line break depends on the script. For the Latin script, rendering the line break typically means displaying a hyphen at the end of the line, however, some languages require a change in spelling surrounding a line break. For examples, see Section 5.3 Use of Soft Hyphen.
Breaking hyphens establish explicit break opportunities immediately after each occurrence.
|
058A |
ARMENIAN HYPHEN |
|
2010 |
HYPHEN |
| 2012 | FIGURE DASH |
| 2013 | EN DASH |
Hyphens are graphic characters with width. Because, unlike spaces, they print, they are included in the measured part of the preceding line, except where the layout style allows hyphens to hang into the margins.
The following are other forms of visible word dividers that provide break opportunities:
|
0F0B |
TIBETAN MARK INTERSYLLABIC TSHEG |
|
1361 |
ETHIOPIC WORDSPACE |
|
17D5 |
KHMER SIGN BARIYOOSAN |
| 10100 | AEGEAN WORD SEPARATOR LINE |
| 10101 | AEGEAN WORD SEPARATOR DOT |
| 10102 | AEGEAN CHECK MARK |
| 1039F | UGARITIC WORD DIVIDER |
The Tibetan thseg 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, like space. For additional information, see Section 5.4 Tibetan Line Breaking.
The Ethiopian word space 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 primarily used to visibly indicate syllabification of words. Syllable breaks are potential line break opportunities in the middle of words. It is mainly used in dictionaries and similar works. When an actual line break falls inside a word containing hyphenation point characters, the hyphenation point is 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 break opportunity, the vertical bar is rendered as a hyphen.
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 these should be treated as linebreak opportunities by default. WJ can be used to override this default, where necessary.
| 16EB | RUNIC SINGLE DOT PUNCTUATION |
| 16EC | RUNIC MULTIPLE DOT 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 |
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.
| 0964 | DEVANAGARI DANDA |
| 0965 | DEVANAGARI DOUBLE DANDA |
| 0E5A | THAI CHARACTER ANGKHANKHU |
| 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 |
| 17D8 | KHMER SIGN BEYYAL |
| 17DA | KHMER SIGN KOOMUUT |
| 10A56 | KHAROSHTHI PUNCTUATION DANDA |
| 10A57 | KHAROSHTHI PUNCTUATION DOUBLE DANDA |
| 0F85 | TIBETAN MARK PALUTA |
| 0F34 | TIBETAN MARK BSDUS RTAGS |
| 0F7F | TIBETAN SIGN RNAM BCAD |
| 0FBE | TIBETAN KU RU KHA |
| 0FBF | TIBETAN KU RU KHA BZHI MIG CAN |
For additional information, see Section 5.5 Tibetan Line Breaking.
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.
| 1802 | MONGOLIAN COMMA |
| 1803 | MONGOLIAN FULL STOP |
| 1804 | MONGOLIAN COLON |
| 1805 | MONGOLIAN FOUR DOTS |
| 1808 | MONGOLIAN MANCHU COMMA |
| 1809 | MONGOLIAN MANCHU FULL STOP |
| 1A1E | BUGINESE PALLAWA |
| 2CF9 | COPTIC OLD NUBIAN FULL STOP |
| 2CFA | COPTIC OLD NUBIAN DIRECT QUESTION MARK |
| 2CFB | COPTIC OLD NUBIAN INDIRECT QUESTION MARK |
| 2CFC | COPTIC OLD NUBIAN VERSE DIVIDER |
| 2CFE | COPTIC FULL STOP |
| 2CFF | COPTIC MORPHOLOGICAL DIVIDER |
| 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 |
|
00B4 |
ACUTE ACCENT |
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.
|
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.
| 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 |
These characters are Tibetan head letters which allow a break before. For more information, see Section 5.5 Tibetan Line Breaking.
|
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, SOFT HYPHEN should be used instead.
|
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, but not between a pair of them. Such pairs are sometimes used instead of a single quotation dash. For that reason, the line should not be broken between EM DASHes even though not all fonts use connecting glyphs for the EM DASH.
Explicit breaks act independently of the surrounding characters.
|
000C |
FORM FEED |
FORM FEED separates pages. The text on the new page starts at the beginning of the line. No paragraph formatting is applied.
|
2028 |
LINE SEPARATOR |
The text after the Line Separator starts at the beginning of the line. No paragraph formatting is applied.
This is similar to HTML <BR>
|
2029 |
PARAGRAPH SEPARATOR |
The text of the new paragraph starts at the beginning of the line. Paragraph formatting is applied.
“NEW LINE FUNCTION (NLF)”
New line functions provide additional explicit breaks. They are not individual characters, but are expressed as sequences of the control characters NEL, LF, and CR. What particular sequence(s) form a NLF depends on the implementation and other circumstances as described in [Unicode] Section 5.8, Newline Guidelines.
If a character sequence for a new line function contains more than one character, it is kept together. The default behavior is to break after LF or CR, but not between CR and LF. Two additional line breaking classes have been added for convenience in this operation.
|
FFFC |
OBJECT REPLACEMENT CHARACTER |
By default there is a break opportunity both before and after the 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 break opportunities. Note that this is best implemented by querying the object itself, not by replacing the CB line breaking class by another class.
The closing character of any set of paired punctuation must be kept with the preceding character, and the same applies to all forms of wide comma and full stop. This line break class contains the following characters:
|
3001..3002 |
IDEOGRAPHIC COMMA..IDEOGRAPHIC FULL STOP |
| 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 |
plus any characters of General Category Pe in the Unicode Character Database.
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.
The CM line break class includes all combining characters with General Category Mc, Me, and Mn, unless listed explicitly elsewhere. This includes viramas.
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 assigning them the AL or ID class instead.
The CM line break class includes all characters of General Category Cc and Cf, unless listed explicitly elsewhere.
|
000D |
CARRIAGE RETURN (CR) |
A CR indicates a mandatory break after, unless followed by a LF. See also the discussion under BK.
NOTE: On some platforms the sequence CR, CR, LF is used to indicate the location of actual line breaks, whereas CR LF is treated like a hard line break. As soon as a user edits the text, the location of all the CR CR LF may change as the new text breaks differently, while the relative position of the CR LF to the surrounding text stays the same. This convention allows an editor to return a buffer and the client is able to tell which text is displayed on which line, by counting CR CR LFs and CR LFs.
Characters in this line break class behave like closing characters, except in relation to postfix and ‘non-starter’ characters. They include:
|
0021 |
EXCLAMATION MARK |
|
003F |
QUESTION MARK |
| 05C6 | HEBREW PUNCTUATION NUN HAFUKHA |
| 060C | ARABIC COMMA |
| 061B | ARABIC SEMICOLON |
| 061E | ARABIC TRIPLE DOT PUNCTUATION MARK |
| 061F | ARABIC QUESTION MARK |
| 066A | ARABIC PERCENT SIGN |
| 06D4 | ARABIC FULL STOP |
| 0F0D | TIBETAN MARK SHAD |
| 0F0E | TIBETAN MARK NYIS SHAD |
| 0F0F | TIBETAN MARK TSHEG SHAD |
| 0F10 | TIBETAN MARK NYIS TSHEG SHAD |
| 0F11 | TIBETAN MARK RIN CHEN SPUNGS SHAD |
| 0F14 | TIBETAN MARK GTER TSHEG |
| 1944 | LIMBU EXCLAMATION MARK |
| 1945 | LIMBU QUESTION MARK |
| 2762 | HEAVY EXCLAMATION MARK ORNAMENT |
| 2763 | HEAVY HEART EXCLAMATION MARK ORNAMENT |
|
FE56..FE57 |
SMALL QUESTION MARK..SMALL EXCLAMATION MARK |
|
FF01 |
FULLWIDTH EXCLAMATION MARK |
|
FF1F |
FULLWIDTH QUESTION MARK |
| FE15 | PRESENTATION FORM FOR VERTICAL EXCLAMATION MARK |
| FE16 | PRESENTATION FORM FOR VERTICAL QUESTION MARK |
Non-breaking characters prohibit breaks on either side, but that prohibition can be overridden by SP or ZW. In particular, when NBSP follows SPACE, there is a break opportunity after the SPACE and NBSP will go as visible space onto the next line. See also WJ. The following lists the characters of line break class GL with additional description.
|
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 should be visually separated but kept on the same line, as in the case of a title and a name “Dr.<NBSP>Joseph Becker”. When SPACE follows NBSP, there is no break, because there never is a break in front of SPACE. NARROW NO-BREAK SPACE is used in Mongolian. The mongolian vowel separator acts like a NNBSP in its line breaking behavior. It additionally affects the shaping of certain vowel characters as described in [Unicode] Section 12.3, Mongolian.
|
034F |
COMBINING GRAPHEME JOINER |
This character has no visible glyph and its presence indicates that adjoining characters are to be treated as a graphemic unit, therefore preventing line breaks between them.
|
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 (NBHY) |
This is the preferred character to use where words must be hyphenated but may not be broken at the 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 5.5 Tibetan Line Breaking.
| 035D..0362 | COMBINING DOUBLE BREVE..COMBINING DOUBLE RIGHTWARDS ARROW BELOW |
These diacritics span two characters, thus no word or line breaks are possible on either side.
Some dictionaries use a character that looks like a vertical series of four dots to indicate places where there is a syllable, but no allowable break. This can be represented by a sequence of 205E VERTICAL FOUR DOTS followed by 2060 WORD JOINER.
All characters of Hangul Syllable Type LV.
Together with conjoining jamos, Hangul syllables form Korean Syllable Blocks which are kept together; see [Boundaries. Korean uses space-based line breaking in many styles of documents. In that case Hangul syllables and conjoining jamo are tailored to use class AL but the default is class ID. See also JL, JT, JV and H3.
All characters of Hangul Syllable Type LVT. See also JL, JT, JV and H2.
|
002D |
HYPHEN-MINUS |
Some additional context analysis is required to distinguish usage of this character as a hyphen from the use as minus sign (or indicator of numerical range). If used as hyphen, it acts like hyphen.
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.
NOTE: The actual set of characters in this class includes characters other than Han ideographs.
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. The ID line break class consists of:
|
2E80..2FFF |
CJK, KANGXI RADICALS, DESCRIPTION SYMBOLS |
|
3000 |
IDEOGRAPHIC SPACE |
|
|
Hiragana (except small characters) |
|
|
Katakana (except small characters) |
|
3400..4DBF |
CJK UNIFIED IDEOGRAPHS EXTENSION A |
|
4E00..9FAF |
CJK UNIFIED IDEOGRAPHS |
|
F900..FAFF |
CJK COMPATIBILITY IDEOGRAPHS |
|
A000..A48F |
YI SYLLABLES |
|
A490..A4CF |
YI RADICALS |
|
FE62..FE66 |
SMALL PLUS SIGN to SMALL EQUALS SIGN |
|
FF10..FF19 |
WIDE DIGITS |
| 20000..2A6D6 | CJK UNIFIED IDEOGRAPHS EXTENSION B |
| 2F800..2FA1D | CJK COMPATIBILITY IDEOGRAPHS SUPPLEMENT |
plus all of the FULLWIDTH LATIN letters and all of the 3000-33FF blocks not covered elsewhere.
NOTE: Use 2060 WORD JOINER as a manual override to prevent break opportunities around characters of class ID.
U+3000 IDEOGRAPHIC SPACE may be subject to expansion or compression during line justification.
Korean is encoded with conjoining jamo, Hangul syllables or both. See also JL, JT, JV, H2 and H3. The following set of compatibility jamo are treated as ID by default.
|
3130..318F |
HANGUL COMPATIBILITY JAMO |
These characters are intended to be used in consecutive sequence. There is never a line break between two character of this class.
| 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.
| 002C | COMMA |
| 002E | FULL STOP |
| 003A | COLON |
| 003B | SEMICOLON |
| 037E | GREEK QUESTION MARK (canonically equivalent to 003B) |
| 0589 | ARMENIAN FULL STOP |
| 060D | ARABIC DATE SEPARATOR |
| 2044 | FRACTION SLASH |
| FE10 | PRESENTATION FORM FOR VERTICAL COMMA |
| FE13 | PRESENTATION FORM FOR VERTICAL COLON |
| FE14 | PRESENTATION FORM FOR VERTICAL SEMICOLON |
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”.
Infix separators are sentence ending punctuation when not used in a numeric context. Therefore they always prevent breaks before.
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 [Boundaries]. Korean uses space-based line breaking in many styles of documents. In that case Hangul Syllables and Conjoining Jamo are tailored to use class AL but the default is class ID. See Section 8.1, Types of Tailoring. See also JT, JV, H2 and H3.
The JT line break class consists of all characters of Hangul Syllable Type T. See also JL, JV, H2 and H3.
The JV line break class consists of all characters of Hangul Syllable Type V. See also JL, JT, H2 and H3.
|
000A |
LINE FEED (LF) |
There is a mandatory break after any LF character, but see the discussion under BK.
|
0085 |
NEXT LINE (NEL) |
There is a mandatory break after any NEL character, but see the discussion under BK.
Non-starter characters cannot start a line, but unlike CL they may allow a break in some context when they follow one or more space characters. Non-starters include:
|
0E5A..0E5B |
THAI CHARACTER ANGKHANKHU..THAI CHARACTER KHOMUT |
|
17D4 |
KHMER SIGN KHAN |
|
17D6..17DA |
KHMER SIGN CAMNUC PII KUUH..KHMER SIGN KOOMUUT |
|
203C |
DOUBLE EXCLAMATION MARK |
|
3005 |
IDEOGRAPHIC ITERATION MARK |
|
301C |
WAVE DASH |
| 303C | MASU MARK |
| 303B | VERTICAL IDEOGRAPHIC ITERATION MARK |
|
309B.. 309E |
KATAKANA-HIRAGANA VOICED SOUND MARK to HIRAGANA VOICED ITERATION MARK |
| 30A0 | KATAKANA-HIRAGANA DOUBLE HYPHEN |
|
30FB..30FE |
KATAKANA MIDDLE DOT..KATAKANA VOICED ITERATION MARK |
| A015 | YI SYLLABLE WU |
|
FE54..FE55 |
SMALL SEMICOLON..SMALL COLON |
|
FF1A..FF1B |
FULLWIDTH COLON.. FULLWIDTH SEMICOLON |
|
FF65 |
HALFWIDTH KATAKANA MIDDLE DOT |
|
FF70 |
HALFWIDTH KATAKANA-HIRAGANA PROLONGED SOUND MARK |
| FF9E..FF9F | HALFWIDTH KATAKANA VOICED SOUND MARK..HALFWIDTH KATAKANA SEMI-VOICED SOUND MARK |
plus all Hiragana, Katakana, and Halfwidth Katakana “small” characters
NOTE: Optionally, the NS restriction may be relaxed and characters treated like ID, to achieve a more permissive style of line breaking, particular in some East Asian document styles.
These characters behave like ordinary characters in the context of ordinary 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 FULL WIDTH) plus these characters:
| 066B | ARABIC DECIMAL SEPARATOR |
| 066C | ARABIC THOUSANDS SEPARATOR |
Unlike IS, the Arabic numeric punctuation does not occur as sentence terminal punctuation outside numbers.
The opening character of any set of paired punctuation must be kept with the following character.
The OP line break class consists of all characters of General Category Ps in the Unicode Character Database.
Characters that usually follow a numerical expression may not be separated from preceding numeric characters or preceding closing characters, even if one or more space characters intervene. For example, there is no break in “(12.00) %”
The list of post-fix characters is:
|
0025 |
PERCENT SIGN |
|
00A2 |
CENT SIGN |
|
00B0 |
DEGREE SIGN |
| 060B |
AFGHANI SIGN |
|
20300 |
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 post-fix position. For purposes of line breaking, their classification as alphabetic is sufficient to keep them together with the preceding number.
Characters that usually precede a numerical expression may not be separated from following numeric characters or following opening characters, even if space character intervenes. For example, there is no break in “$ (100.00)”
The PR line break class consists of all currency symbols (General Category Sc) except as listed explicitly in PO as well as the following:
|
002B |
PLUS SIGN |
|
005C |
REVERSE SOLIDUS |
|
00B1 |
PLUS-MINUS |
|
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. When used in that way, these currency symbols should be treated as if they have line breaking class PO.
Some paired characters can be either opening or closing depending on usage. The default is to treat them as both opening and closing.
NOTE: If language information is available, it can be used to determine which character is used as opening and which as closing quote. See the information in [Unicode] Section 6.2, General Punctuation.
The QU line break class consists of characters of General Category Pf or Pi in the Unicode Character Database as well as:
|
0022 |
QUOTATION MARK |
|
0027 |
APOSTROPHE |
| 23B6 | BOTTOM SQUARE BRACKET OVER TOP SQUARE BRACKET |
| 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 |
U+23B6 BOTTOM SQUARE BRACKET OVER TOP SQUARE BRACKET is subtly different from the others in this class, in that it is both an opening and a closing punctuation character at the same time. However, its use is limited to certain vertical text modes in terminal emulation. Instead of creating a one of a kind class for this rarely used character, assigning it to the QU class approximates the intended behavior.
Runs of these characters require morphological analysis to determine break opportunities. This is similar to e.g. a hyphenation algorithm. For the characters that have this property, no line breaks will be found otherwise, therefore complex context analysis is mandatory.
NOTE: These characters can be mapped into their equivalent line breaking classes as result of dictionary lookup, thus permitting a logical separation of this algorithm from the morphological analysis.
If dictionary lookup is not available they should be treated as XX.
All characters of General Category Cf, Lo or Lm in these ranges:
|
0E00..0EFF |
THAI / LAO |
|
1000..109F |
MYANMAR |
|
1780..17FF |
KHMER |
Line break class SG comprises all code points with General Category Cs. The line breaking behavior of isolated surrogates is undefined.
NOTE: The use of this line breaking class is deprecated. It was of limited usefulness for UTF-16 implementations that are not supporting characters beyond the BMP. The correct implementation is to resolve a pair of surrogates into a supplementary character before line breaking.
|
0020 |
SPACE (SP) |
The space characters are explicit break opportunities, however spaces at the end of a line are 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, the line breaking position after the last space character in the sequence is the locally most optimal one. In other words, because 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.
NOTE: SPACE, but none of the other breaking spaces, is used in determining an indirect break.
URLs are now so common in regular plain text, that they must be taken into account when assigning general-purpose line breaking properties. The SY line breaking property is intended to provide a break after, but not in front of digits so as to not break “1/2” or “06/07/99”.
|
002F |
SOLIDUS |
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, additional symbols can be added to this line breaking class, or classes BA, BB, 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 document.
These characters glue together both left and right neighbor character 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.
The XX line break class consists of all characters with General Category Co and all code points with General Category Cn.
Unassigned code positions, private use characters and characters for which reliable line breaking information is not available are assigned this default 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 0x10000 to 0x1FFFD as AL and characters in the range 0x20000 to 0x2FFFD, and 0x30000 to 0x3FFFD 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 and the pair table in Section 7, Pair Table-based Implementation, 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.
|
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.
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.
Examples of conventions used in several dictionaries are briefly described in this subsection. Where possible, the default line breaking properties for characters commonly used in dictionaries have been assigned so as to accommodate these and similar conventions. However, implementing the full conventions in dictionaries requires special support.
Looking up the noun “syllable” in eight dictionaries yields eight different conventions:
Dictionary of the English Language, Samuel Johnson, 1843 SY´LLABLE where ´ is an oversized U+02B9 and follows the vowel of the main syllable (not the syllable itself).
Oxford English Dictionary (1st Edition) si·lă'bl where · is a slightly raised middle dot indicating the vowel of the stressed syllable (similar to Johnson's acute). The letter ă is U+0103. The ' is an apostrophe.
Oxford English Dictionary (2nd Edition) has gone to IPA 'sIləb(ə)l where ' is U+02C8, I is U+026A, ə is U+0259 (both times). The ' comes before the stressed syllable. The () indicate the schwa may be omitted.
Chambers English Dictionary (7th Edition) sil´ə-bl where the stressed syllable is followed by ´ U+02B9, ə is U+0259, and - is a hyphen. When splitting a word like abate´- ment the stress mark ´ goes after stressed syllable followed by the hyphen. No special convention is used, when splitting at hyphen.
BBC English Dictionary sIləbl where I is <U+026A, U+0332>, ə is U+0259. The vowel of the stressed syllable is underlined.
Collins Cobuild English Language Dictionary sIləbə°l where I is <U+026A, U+0332> and has the same meaning as in the BBC English dictionary. The ə is U+0259 (both times). The ° is a U+2070 and indicates the schwa may be omitted.
Readers Digest Great Illustrated Dictionary. syl·la·ble (sílləb'l) The spelling of the word has hyphenation points (· is a U+2027) followed by phonetic spelling. The vowel of the stressed syllable is given an accent, rather than being followed by an accent. The ' is an apostrophe.
Webster's 3rd New International Dictionary. syl·la·ble /'siləbəl/ The spelling of the word has hyphenation points (· is a U+2027) and is followed by phonetic spelling. The stressed syllable is preceded by ' U+02C8. The ə's are schwas as usual. Webster splits words at the end of a line with a normal hyphen. A U+2E17 DOUBLE OBLIQUE HYPHEN indicates that a hyphenated word is split at the 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 intra-word line-break position. If the line is broken at that point, then whatever mechanism is appropriate for intra-word line-breaks should be invoked, just as if the line break had been triggered by another mechanism, such as a dictionary lookup. Depending on the language and the word, that may produce different visible results, such as:
Here are a few