CSS Text Module Level 4

1. Introduction

This module describes the typesetting controls of CSS; that is, the features of CSS that control the translation of source text to formatted, line-wrapped text. Various CSS properties provide control over case transformation, white space collapsing, text wrapping, line breaking rules and hyphenation, alignment and justification, spacing, and indentation. See Additions Since Level 3 for additions since Level 3.

Further information about the typesetting requirements of various languages and writing systems around the world can be found in the Internationalization Working Group’s Language Enablement Index. [TYPOGRAPHY]

1.1. Module Interactions

This module, together with the CSS Text Decoration Module, replaces and extends the text-level features defined in Cascading Style Sheets Level 2 chapter 16. [CSS-TEXT-DECOR-3] [CSS2]

In addition to the terms defined below, other terminology and concepts used in this specification are defined in Cascading Style Sheets Level 2 and the CSS Writing Modes Module. [CSS2] and [CSS-WRITING-MODES-4].

1.2. Value Definitions

This specification follows the CSS property definition conventions from [CSS2] using the value definition syntax from [CSS-VALUES-3]. Value types not defined in this specification are defined in CSS Values & Units [CSS-VALUES-3]. Combination with other CSS modules may expand the definitions of these value types.

In addition to the property-specific values listed in their definitions, all properties defined in this specification also accept the CSS-wide keywords as their property value. For readability they have not been repeated explicitly.

1.3. Languages and Typesetting

Authors should accurately language-tag their content for the best typographic behavior.

Many typographic effects vary by linguistic context. Language and writing system conventions can affect line breaking, hyphenation, justification, glyph selection, and many other typographic effects. In CSS, language-specific typographic tailorings are only applied when the content language is known (declared). Therefore, higher quality typography requires authors to communicate to the UA the correct linguistic context of the text in the document.

The content language of an element is the (human) language the element is declared to be in, according to the rules of the document language. Note that it is possible for the content language of an element to be unknown—​e.g. untagged content, or content in a document language that does not have a language-tagging facility, is considered to have an unknown content language.

Note: Authors can declare the content language using the global lang attribute in HTML or the universal xml:lang attribute in XML. See the rules for determining the content language of an HTML element in HTML, and the rules for determining the content language of an XML element in XML 1.0. [HTML] [XML10]

The content language an element is declared to be in also identifies the specific written form of that language used in that element, known as the content writing system. Depending on the document language’s facilities for identifying the content language, this information can be explicit or implied. See the normative Appendix F: Identifying the Content Writing System.

Note: Some languages have more than one writing system tradition; in other cases a language can be transliterated into a foreign writing system. Authors should subtag such cases so that the UA can adapt appropriately.

1.4. Characters and Letters

The basic unit of typesetting is the character. However, because writing systems are not always as simple as the basic English alphabet, what a character actually is depends on the context in which the term is used. For example, in Hangul (the Korean writing system), each square representation of a syllable (e.g. 한=Han) can be considered a character. However, the square symbol is really composed of multiple letters each representing a phoneme (e.g. ㅎ=h, ㅏ=a, ㄴ=n) and these also could each be considered a character.

A basic unit of computer text encoding, for any given encoding, is also called a character, and depending on the encoding, a single encoding character might correspond to the entire pre-composed syllabic character (e.g. 한), to the individual phonemic character (e.g. ㅎ), or to smaller units such as a base letterform (e.g. ㅇ) and any combining marks that vary it (e.g. extra strokes that represent aspiration).

In turn, a single encoding character can be represented in the data stream as one or more bytes; and in programming environments one byte is sometimes also called a character.

Therefore the term character is fairly ambiguous where technical precision is required.

For text layout, we will refer to the typographic character unit as the basic unit of text. Even within the realm of text layout, the relevant character unit depends on the operation. For example, line-breaking and letter-spacing will segment a sequence of Thai characters that include U+0E33  ำ THAI CHARACTER SARA AM differently; or the behavior of a conjunct consonant in a script such as Devanagari may depend on the font in use. So the typographic character represents a unit of the writing system—​such as a Latin alphabetic letter (including its diacritics), Hangul syllable, Chinese ideographic character, Myanmar syllable cluster—​that is indivisible with respect to a particular typographic operation (line-breaking, first-letter effects, tracking, justification, vertical arrangement, etc.).

Unicode Standard Annex #29: Text Segmentation defines a unit called the grapheme cluster which approximates the typographic character. [UAX29] A UA must use the extended grapheme cluster (not legacy grapheme cluster), as defined in UAX29, as the basis for its typographic character unit. However, the UA should tailor the definitions as required by typographic tradition since the default rules are not always appropriate or ideal—​and is expected to tailor them differently depending on the operation as needed.

Note: The rules for such tailorings are out of scope for CSS.

A typographic letter unit (or letter for the purpose of this specification) is a typographic character unit belonging to one of the Letter or Number general categories. See Appendix E: Characters and Properties for how to determine the Unicode properties of a typographic character unit.

The rendering characteristics of a typographic character unit divided by an element boundary is undefined. Ideally each component should be rendered according to the formatting requirements of its respective element’s properties while maintaining correct shaping and positioning of the typographic character unit as a whole. However, depending on the nature of the formatting differences between its parts and the capabilities of the font technology in use, this is not always possible. Therefore such a typographic character unit may be rendered as belonging to either side of the boundary, or as some approximation of belonging to both. Authors are forewarned that dividing grapheme clusters or ligatures by element boundaries may give inconsistent or undesired results.

1.5. Text Processing

CSS is built on Unicode. [UNICODE] UAs that support Unicode must adhere to all normative requirements of the Unicode Core Standard, except where explicitly overridden by CSS. UAs implemented on the basis of a non-Unicode text encoding model are still expected to fulfill the same text handling requirements by assuming an appropriate mapping and analogous behavior.

For the purpose of determining adjacency for text processing (such as white space processing, text transformation, line-breaking, etc.), and thus in general within this specification, intervening inline box boundaries and out-of-flow elements must be ignored. With respect to text shaping, however, see § 8.7 Shaping Across Element Boundaries.

2. Transforming Text

2.1. Case Transforms: the text-transform property

This property transforms text for styling purposes. It has no effect on the underlying content, and must not affect the content of a plain text copy & paste operation.

Authors must not rely on text-transform for semantic purposes; rather the correct casing and semantics should be encoded in the source document text and markup.

Values have the following meanings:

none

No effects.

capitalize

Puts the first typographic letter unit of each word, if lowercase, in titlecase; other characters are unaffected.

uppercase

Puts all letters in uppercase.

lowercase

Puts all letters in lowercase.

full-width

Puts all typographic character units in full-width form. If a character does not have a corresponding full-width form, it is left as is. This value is typically used to typeset Latin letters and digits as if they were ideographic characters.

full-size-kana

Converts all small Kana characters to the equivalent full-size Kana. This value is typically used for ruby annotation text, where authors may want all small Kana to be drawn as large Kana to compensate for legibility issues at the small font sizes typically used in ruby.

math-auto

See MathML Core § 4.2 New text-transform value.

abbr:lang(ja) { text-transform: full-width; }

Note: The purpose of text-transform is to allow for presentational casing transformations without affecting the semantics of the document. Note in particular that text-transform casing operations are lossy, and can distort the meaning of a text. While accessibility interfaces may wish to convey the apparent casing of the rendered text to the user, the transformed text cannot be relied on to accurately represent the underlying meaning of the document.

section > p:first-of-type::first-line {
  text-transform: uppercase;
}

rt { font-size: 50%; text-transform: full-size-kana; }
:is(h1, h2, h3, h4) rt { text-transform: none; /* unset for large text*/ }

<ruby>十<rt>じゅう</ruby>

2.1.1. Mapping Rules

For capitalize, what constitutes a “word“ is UA-dependent; [UAX29] is suggested (but not required) for determining such word boundaries. Out-of-flow elements and inline element boundaries must not introduce a text-transform word boundary and must be ignored when determining such word boundaries.

Note: Authors cannot depend on capitalize to follow language-specific titlecasing conventions (such as skipping articles in English).

The UA must use the full case mappings for Unicode characters, including any conditional casing rules, as defined in the Default Case Algorithms section of The Unicode Standard. [UNICODE] If (and only if) the content language of the element is, according to the rules of the document language, known, then any appropriate language-specific rules must be applied as well. These minimally include, but are not limited to, the language-specific rules in Unicode’s SpecialCasing.txt.

The definition of full-width and half-width forms can be found in Unicode Standard Annex #11: East Asian Width. [UAX11] The mapping to full-width form is defined by taking code points with the <wide> or the <narrow> tag in their Decomposition_Mapping in Unicode Standard Annex #44: Unicode Character Database. [UAX44] For the <narrow> tag, the mapping is from the code point to the decomposition (minus <narrow> tag), and for the <wide> tag, the mapping is from the decomposition (minus the <wide> tag) back to the original code point.

The mappings for small Kana to full-size Kana are defined in Appendix G: Small Kana Mappings.

2.2. Expanding Between Words: the word-space-transform property

Some languages and writing systems have alternative ways of delimiting words, either using different separating characters, or sometimes no visible character at all. This property allows authors to change the rendering from one style to another without needing to change the markup.

none

This property has no effect.

space

Expandable separators within the child text of this element are replaced by U+0020 SPACE.

ideographic-space

Expandable separators within the child text of this element are replaced by U+3000 IDEOGRAPHIC SPACE.

auto-phrase

If the content language is known and the user agent supports linguistic analysis for this language, the user agent must detect phrase boundaries. If a word-separator character, other space separator, or U+200B ZERO WIDTH SPACE character does not already occur at that boundary, then the UA must insert a virtual expandable separator.

If this value is omitted, or if the content language is unknown, or if the user agent does not support detecting phrase boundaries for that language, there are no virtual expandable separator.

For the purpose of this property, expandable separators are any of:

• U+200B ZERO WIDTH SPACE characters

• wbr elements

• virtual expandable separators

A virtual expandable separator is a UA-detected syntactic boundary in the text that represents an expandable separator not otherwise occuring in the source document. It has no effect other than for this property.

The user agent must not replace expandable separators immediately preceding or following a forced line break (ignoring any intervening inline box boundaries, and associated margin/border/padding).

Note: Because virtual expandable separators are placed in the outermost element that participates in an inline box boundary, if one would coincide with boundary of an inline box whose parent box has a used value of word-space-transform: none, that particular virtual expandable separator is not expanded, since it would be placed in the parent box.

Like text-transform, this property transforms text for styling purposes only. It has no effect on the underlying content, and must not affect the content of a plain text copy & paste operation.

<p>むかしむかし、<wbr>あるところに、<wbr>おじいさんと<wbr>おばあさんが<wbr>すんでいました。

p {
  word-space-transform: ideographic-space;
}

p {
  word-break: keep-all;
  word-space-transform: ideographic-space;
}

<p>らいしゅう<wbr>の<wbr>じゅぎょう<wbr>に<wbr class=p
>たいこ<wbr>と<wbr>ばち<wbr>を<wbr class=p
>もって<wbr>きて<wbr>ください。

p wbr.p {
  word-space-transform: ideographic-space;
}

p wbr {
  word-space-transform: ideographic-space;
}

p {
  word-break: keep-all;
}
p wbr.p {
  word-space-transform: ideographic-space;
}

p {
  word-break: keep-all;
}
p wbr {
  word-space-transform: ideographic-space;
}

2.3. Order of Operations

When multiple transformations need to be applied, they are applied in the following order:

1. word-space-transform
2. capitalize, uppercase, and lowercase
3. full-width
4. full-size-kana

Word space transformation and text transformation happen after § 4.3.1 Phase I: Collapsing and Transformation but before § 4.3.2 Phase II: Trimming and Positioning. This means for instance that full-width only transforms spaces (U+0020) to U+3000 IDEOGRAPHIC SPACE within preserved white space.

Note: As defined in Appendix A: Text Processing Order of Operations, transforming affects line-breaking and other formatting operations.

3. White Space and Wrapping: the white-space property

This property is a shorthand for white-space-collapse, text-wrap-mode, and white-space-trim. It specifies two things:

• whether and how white space is collapsed; see White Space Processing
• whether lines may wrap at unforced soft wrap opportunities; see § 5 Text Wrapping and Line Breaking

Note: This shorthand combines both inheritable and non-inheritable properties. If this is a problem, please inform the CSSWG.

Unless otherwise specified, any omitted longhand is set to its initial value.

The following table gives the normative mapping of the values of the shorthand’s special keywords to their equivalent longhand values.

Note: In some cases, preserved white space and other space separators can hang when at the end of the line; this can affect whether they are measured for intrinsic sizing.

The following informative table summarizes the behavior of various white-space values:

4. White Space Processing & Control Characters

The source text of a document often contains formatting that is not relevant to the final rendering: for example, breaking the source into segments (lines) for ease of editing or adding white space characters such as tabs and spaces to indent the source code. CSS white space processing allows the author to control interpretation of such formatting: to preserve or collapse it away when rendering the document. White space processing in CSS (which is controlled with the white-space-collapse and white-space-trim properties) interprets white space characters only for rendering: it has no effect on the underlying document data.

Note: Depending on the document language, segments can be separated by a particular newline sequence (such as a line feed or CRLF pair), or delimited by some other mechanism, such as the SGML RECORD-START and RECORD-END tokens.

For CSS processing, each document language–defined “segment break” or “newline sequence”—​or if none are defined, each line feed (U+000A)—​in the text is treated as a segment break, which is then interpreted for rendering as specified by the white-space property.

In the case of HTML, newlines are normalized to line feed characters (U+000A) for representation in the DOM, so when an HTML document is represented as a DOM tree each line feed (U+000A) is treated as a segment break. [HTML] [DOM]

Note: In most common CSS implementations, HTML does not get styled directly. Instead, it is processed into a DOM tree, which is then styled. Unlike HTML, the DOM does not give any particular meaning to carriage returns (U+000D), so they are not treated as segment breaks. If carriage returns (U+000D) are inserted into the DOM by means other than HTML parsing, they then get treated as defined below.

Note: A document parser might not only normalize any segment breaks, but also collapse other space characters or otherwise process white space according to markup rules. Because CSS processing occurs after the parsing stage, it is not possible to restore these characters for styling. Therefore, some of the behavior specified below can be affected by these limitations and may be user agent dependent.

Note: Anonymous blocks consisting entirely of collapsible white space are removed from the rendering tree. Thus any such white space surrounding a block-level element is collapsed away. See CSS 2.1 § 9.2.2.1 Anonymous inline boxes. [CSS2]

Control characters (Unicode category Cc)—​other than tabs (U+0009), line feeds (U+000A), carriage returns (U+000D) and sequences that form a segment break—​must be rendered as a visible glyph which the UA must synthesize if the glyphs found in the font are not visible, and must be otherwise treated as any other character of the Other Symbols (So) general category and Common script. The UA may use a glyph provided by a font specifically for the control character, substitute the glyphs provided for the corresponding symbol in the Control Pictures block, generate a visual representation of its code point value, or use some other method to provide an appropriate visible glyph. As required by Unicode, unsupported Default_ignorable characters must be ignored for text rendering. [UNICODE]

Carriage returns (U+000D) are treated identically to spaces (U+0020) in all respects.

Note: For HTML documents, carriage returns present in the source code are converted to line feeds at the parsing stage (see HTML § 13.2.3.5 Preprocessing the input stream and the definition of normalize newlines in Infra and therefore do no appear as U+000D CARRIAGE RETURN to CSS. [HTML] [INFRA]) However, the character is preserved—​and the above rule observable—​when encoded using an escape sequence (
).

4.1. White Space Collapsing: the white-space-collapse property

This section is still under discussion and may change in future drafts.

This property specifies whether and how white space is collapsed. Values have the following meanings, which must be interpreted according to the White Space Processing Rules:

collapse

This value directs user agents to collapse sequences of white space into a single character (or in some cases, no character).

preserve

This value prevents user agents from collapsing sequences of white space. Segment breaks such as line feeds are preserved as forced line breaks.

preserve-breaks

Like collapse, this value collapses consecutive white space characters, but preserves segment breaks in the source as forced line breaks.

preserve-spaces

This value prevents user agents from collapsing sequences of white space, and converts tabs and segment breaks to spaces. (This value is intended to represent the behavior of xml:space="preserve" in SVG.)

break-spaces

The behavior is identical to that of preserve, except that:

• Any sequence of preserved white space or other space separators always takes up space, including at the end of the line.
• A soft wrap opportunity exists after every preserved white space character and after every other space separator (including between adjacent spaces).

Note: This value does not guarantee that there will never be any overflow due to white space: for example, if the line length is so short that even a single white space character does not fit, overflow is unavoidable.

discard

This value directs user agents to “discard” all white space in the element.

Does this preserve line break opportunities or no? Do we need a distinct "hide" value? If it preserves line break opportunities, maybe it should be replaced with a word-space-transform value?

White space that was not removed or collapsed due to white space processing is called preserved white space.

@namespace m "http://www.w3.org/1998/Math/MathML";
m|* {
  white-space-collapse: discard;
}
m|mi, m|mn, m|mo, m|ms, m|mtext {
  white-space-trim: discard-inner;
}

4.2. White Space Trimming: the white-space-trim property

This property allows authors to specify trimming behavior at the beginning and end of a box. Values have the following meanings:

discard-before

This value directs the UA to collapse all collapsible whitespace immediately before the start of the element.

discard-after

This value directs the UA to collapse all collapsible whitespace immediately after the end of the element.

discard-inner

For block containers this value directs UAs to discard all whitespace at the beginning of the element up to and including the last segment break before the first non-white-space character in the element as well as to discard all white space at the end of the element starting with the first segment break after the last non-white-space character in the element. For other elements this value directs UAs to discard all whitespace at the beginning and end of the element.

Note: Discarding document white space using white-space-trim can change where soft wrap opportunities occur in the text.

dt { display: inline; }
dt + dt:before { content: ", "; white-space-trim: discard-before; }

pre { white-space: pre; white-space-trim: discard-inner; }

<pre>

  some
preformatted

  text

</pre>

<pre>  some
preformatted

  text</pre>

  some
preformatted

  text

span { white-space: normal; white-space-trim: discard-inner; }

start[<span>

  some
inline
  text

</span>]end

start[<span>  some
inline
  text</span>]end

start[some inline text]end

White space processing for white-space-trim takes place before § 4.3.1 Phase I: Collapsing and Transformation.

4.3. The White Space Processing Rules

Except where specified otherwise, white space processing in CSS affects only the document white space characters: spaces (U+0020), tabs (U+0009), and segment breaks.

Note: The set of characters considered document white space (part of the document content) and those considered syntactic white space (part of the CSS syntax) are not necessarily identical. However, since both include spaces (U+0020), tabs (U+0009), and line feeds (U+000A) most authors won’t notice any differences.

Besides space (U+0020) and no-break space (U+00A0), Unicode defines a number of additional space separator characters. [UNICODE] In this specification all characters in the Unicode general category Zs except space (U+0020) and no-break space (U+00A0) are collectively referred to as other space separators.

4.3.1. Phase I: Collapsing and Transformation

Note: white-space-trim is taken into account prior to this phase.

For each inline (including anonymous inlines; see CSS 2.1 § 9.2.2.1 Anonymous inline boxes [CSS2]) within an inline formatting context, white space characters are processed as follows prior to line breaking and bidi reordering, ignoring bidi formatting characters (characters with the Bidi_Control property [UAX9]) as if they were not there:

• If white-space-collapse is set to collapse or preserve-breaks, white space characters are considered collapsible and are processed by performing the following steps:
  1. Any sequence of collapsible spaces and tabs immediately preceding or following a segment break is removed.
  2. Collapsible segment breaks are transformed for rendering according to the segment break transformation rules.
  3. Every collapsible tab is converted to a collapsible space (U+0020).
  4. Any collapsible space immediately following another collapsible space—​even one outside the boundary of the inline containing that space, provided both spaces are within the same inline formatting context—​is collapsed to have zero advance width. (It is invisible, but retains its soft wrap opportunity, if any.)
• If white-space-collapse is set to preserve-spaces, each tab and segment break is converted to a space.
• If white-space-collapse is set to preserve or preserve-spaces, any sequence of spaces is treated as a sequence of non-breaking spaces except that a soft wrap opportunity exists at the end of each maximal sequence of spaces and/or tabs. For break-spaces, a soft wrap opportunity exists after every space and every tab.

<ltr>A <rtl> B </rtl> C</ltr>

A  BC

4.3.2. Phase II: Trimming and Positioning

Then, the entire block is rendered. Inlines are laid out, taking bidi reordering into account, and wrapping as specified by the text-wrap-mode and text-wrap-style property. As each line is laid out,

1. A sequence of collapsible spaces at the beginning of a line is removed.
2. If the tab size is zero, preserved tabs are not rendered. Otherwise, each preserved tab is rendered as a horizontal shift that lines up the start edge of the next glyph with the next tab stop. If this distance is less than 0.5ch, then the subsequent tab stop is used instead. Tab stops occur at points that are multiples of the tab size from the starting content edge of the preserved tab’s nearest block container ancestor. The tab size is given by the tab-size property.

   Note: See the Unicode rules on how tabulation (U+0009) interacts with bidi. [UAX9]

3. A sequence of collapsible spaces at the end of a line is removed, as well as any trailing U+1680   OGHAM SPACE MARK whose white-space-collapse property is collapse or preserve-breaks.

   Note: Due to Unicode Bidirectional Algorithm rule L1, a sequence of collapsible spaces located at the end of the line prior to bidi reordering will also be at the end of the line after reordering. [UAX9] [CSS-WRITING-MODES-4]

4. If there remains any sequence of white space, other space separators, and/or preserved tabs at the end of a line (after bidi reordering [CSS-WRITING-MODES-4]):
   • If white-space-collapse is collapse or preserve-breaks, the UA must hang this sequence (unconditionally).
   • If white-space-collapse is preserve and text-wrap-mode is not nowrap, the UA must (unconditionally) hang this sequence, unless the sequence is followed by a forced line break, in which case it must conditionally hang the sequence instead. It may also visually collapse the character advance widths of any that would otherwise overflow.

     Note: Hanging the white space rather than collapsing it allows users to see the space when selecting or editing text.

   • If white-space-collapse is set to break-spaces, spaces, tabs, and other space separators are treated the same as other visible characters: they cannot hang nor have their advance width collapsed.

     Note: Such characters therefore take up space, and depending on the available space and applicable line breaking controls will either overflow or cause the line to wrap.

   What should happen here for white-space-collapse: preserve-spaces?

p {
  white-space: pre-wrap;
  width: 5ch;
  border: solid 1px;
  font-family: monospace;
  text-align: center;
}

<p> 0 </p>

p {
  white-space: pre-wrap;
  width: 3ch;
  border: solid 1px;
  font-family: monospace;
}

<p> 0 0 0 0 </p>

p {
  white-space: pre-wrap;
  width: 3ch;
  border: solid 1px;
  font-family: monospace;
}

<p>0 0 0 0 </p>

4.3.3. Segment Break Transformation Rules

When white-space-collapse is not collapse, segment breaks are not collapsible. For values other than collapse or preserve-spaces (which transforms them into spaces), segment breaks are instead transformed into a preserved line feed (U+000A).

When white-space-collapse is collapse, segment breaks are collapsible, and are collapsed as follows:

1. First, any collapsible segment break immediately following another collapsible segment break is removed.
2. Then any remaining segment break is either transformed into a space (U+0020) or removed depending on the context before and after the break. The rules for this operation are UA-defined in this level.

   Should we define this for Level 4?

   Note: The white space processing rules have already removed any tabs and spaces around the segment break before this context is evaluated.

Here is an English paragraph
that is broken into multiple lines
in the source code so that it can
be more easily read and edited
in a text editor.

這個段落是那麼長，
在一行寫不行。最好
用三行寫。

Note: Historically, HTML and CSS have unconditionally converted segment breaks to spaces, which has prevented content authored in languages such as Chinese from being able to break lines within the source. Thus UA heuristics need to be conservative about where they discard segment breaks even as they strive to improve support for such languages.

4.4. Tab Character Size: the tab-size property

This property determines the tab size used to render preserved tab characters (U+0009). A <number> represents the measure as a multiple of the advance width of the space character (U+0020) of the nearest block container ancestor of the preserved tab, including its associated letter-spacing and word-spacing. Negative values are not allowed.

5. Text Wrapping

When inline-level content is laid out into lines, it is broken across line boxes. Such a break is called a line break. When a line is broken due to explicit line-breaking controls (such as a preserved newline character), or due to the start or end of a block, it is a forced line break. When a line is broken due to content wrapping (i.e. when the UA creates unforced line breaks in order to fit the content within the measure), it is a soft wrap break. The process of breaking inline-level content into lines is called line breaking.

Wrapping is only performed at an allowed break point, called a soft wrap opportunity. When wrapping is enabled (see white-space), the UA must minimize the amount of content overflowing a line by wrapping the line at a soft wrap opportunity, if one exists.

Where text is allowed to wrap is controlled by the line-breaking rules and controls; whether it is allowed to wrap and how multiple soft wrap opportunities within a line are prioritized is controlled by the text-wrap-mode, text-wrap-style, wrap-before, wrap-after, and wrap-inside properties.

5.1. Deciding Whether to Wrap: the text-wrap-mode property

The name of this property is a placeholder, pending the CSSWG finding a better name.

Note: This property is a longhand of both white-space and text-wrap.

This property specifies whether lines may wrap at unforced soft wrap opportunities. Possible values:

wrap

Content may break across lines at allowed soft wrap opportunities, as determined by the line-breaking rules in effect, in order to minimize inline-axis overflow.

Note: See § 5.6 Line Breaking Details for more information about rules and constrains on soft wrap opportunities.

nowrap

Inline-level content does not break across lines; content that does not fit within the block container overflows it.

Regardless of the text-wrap-mode value, preserved segment breaks, and any Unicode character with the BK, CR, LF, and NL line breaking class, must be treated as forced line breaks. [UAX14]

Note: The bidi implications of such forced line breaks are defined by the Unicode Bidirectional Algorithm. [UAX9]

5.2. Controlling Breaks Within Boxes: the wrap-inside property

auto

Lines may break at allowed break points within the box, as determined by the line-breaking rules in effect.

avoid

Line breaking is suppressed within the box: the UA may only break within the box if there are no other valid break points in the line. If the text breaks, line-breaking restrictions are honored as for auto.

If boxes with avoid are nested and the UA must break within these boxes, a break in an outer box must be used before a break within an inner box may be used.

5.2.1. Example of using 'wrap-inside: avoid' in presenting a footer

footer { wrap-inside: avoid; }
venue { wrap-inside: avoid; }
date { wrap-inside: avoid; }
place { wrap-inside: avoid; }

<footer>
<venue>27th Internationalization and Unicode Conference</venue>
&#8226; <date>April 7, 2005</date> &#8226;
<place>Berlin, Germany</place>
</footer>

27th Internationalization and Unicode Conference •
April 7, 2005 • Berlin, Germany

27th Internationalization and Unicode
Conference • April 7, 2005 •
Berlin, Germany

27th Internationalization and Unicode Conference • April
7, 2005 • Berlin, Germany

5.3. Controlling Breaks Between Boxes: the wrap-before/wrap-after properties

These properties specify modifications to break opportunities in line breaking (and flex line breaking [CSS3-FLEXBOX]). Possible values:

auto

Lines may break at allowed break points before and after the box, as determined by the line-breaking rules in effect.

avoid

Line breaking is suppressed immediately before/after the box: the UA may only break there if there are no other valid break points in the line. If the text breaks, line-breaking restrictions are honored as for auto.

avoid-line

Same as avoid, but only for line breaks.

avoid-flex

Same as avoid, but only for flex line breaks.

line

Force a line break immediately before/after the box if the box is an inline-level box.

flex

Force a flex line break immediately before/after the box if the box is a flex item in a multi-line flex container.

Forced line breaks on inline-level boxes propagate upward through any parent inline boxes the same way forced breaks on block-level boxes propagate upward through any parent block boxes in the same fragmentation context. [CSS3-BREAK]

5.4. Selecting How to Wrap: the text-wrap-style property

When wrapping is allowed (see text-wrap-mode), this property selects between several approaches for wrapping lines, trading off between speed, quality and style of layout, or stability. It does not change which soft wrap opportunity exist, but changes how the user agent selects among them. Possible values:

auto

The exact algorithm for selecting which soft wrap opportunity to break at is UA-defined. The algorithm may consider multiple lines when making break decisions. The UA may bias for speed over best layout. The UA must not attempt to even out all lines (including the last) as for balance. This value selects the UA’s preferred (or most Web-compatible) wrapping algorithm.

balance

Line breaks are chosen to balance the remaining (empty) space in each line box, if better balance than auto is possible. This should avoid changing—​and in the case of 5 or fewer lines must not change—​the number of line boxes the block would contain if text-wrap were set to auto.

Note: The height of the line boxes may nevertheless change, due to changes in which content appears together on one line.

The remaining space to consider is that which remains after placing floats and inline content, but before any adjustments due to text justification. Line boxes are balanced when the standard deviation from the average inline-size of the remaining space in each line box is reduced over the block (including lines that end in a forced break).

Groups of lines separated by a forced line break are processed separately. If the element is affected by line-clamp, the claming effect is applied first, then the remaining lines are balanced.

The exact algorithm is UA-defined.

UAs may treat this value as auto if there are more than ten lines to balance.

stable

Specifies that content on subsequent lines should not be considered when making break decisions so that when editing text any content before the cursor remains stable; otherwise equivalent to auto,

pretty

Specifies the UA should bias for better layout over speed, and is expected to consider multiple lines, when making break decisions. Otherwise equivalent to auto,

Note: The auto value will typically map to Web browsers’ speedy legacy line breaking, which has so far used first-fit/greedy algorithms that can often give sub-optimal results. UAs can experiment with better line breaking algorithms with this default value, but as optimal results often take more time, pretty is offered as an opt-in to take more time for better results. The pretty value is intended for body text, where the last line is expected to be a bit shorter than the average line; the balance value is intended for titles and captions, where equal-length lines of text tend to be preferred; and the stable is intended for sections that are, or are likely become toggled as, editable.

5.5. Joint Wrapping Control: the text-wrap shorthand property

This property is a shorthand for the text-wrap-mode and text-wrap-style properties. Any omitted longhand is set to its initial value.

5.6. Line Breaking Details

When determining line breaks:

• The interaction of line breaking and bidirectional text is defined by CSS Writing Modes 4 § 2.4 Applying the Bidirectional Reordering Algorithm and the Unicode Bidirectional Algorithm (UAX9§3.4 Reordering Resolved Levels in particular). [CSS-WRITING-MODES-4] [UAX9]
• Except where explicitly defined otherwise (e.g. for line-break: anywhere or overflow-wrap: anywhere) line breaking behavior defined for the CM, and SG, WJ, ZW, GL, and ZWJ Unicode line breaking classes must be honored. [UAX14]
• UAs that allow wrapping at punctuation other than word separators in writing systems that use them should prioritize breakpoints. (For example, if breaks after slashes are given a lower priority than spaces, the sequence “check /etc” will never break between the "/" and the "e".) As long as care is taken to avoid such awkward breaks, allowing breaks at appropriate punctuation other than word separators is recommended, as it results in more even-looking margins, particularly in narrow measures. The UA may use the width of the containing block, the text’s language, the line-break value, and other factors in assigning priorities: CSS does not define prioritization of soft wrap opportunities. Prioritization of word separators is not expected, however, if word-break: break-all is specified (since this value explicitly requests line breaking behavior not based on breaking at word separators)—​and is forbidden under line-break: anywhere.
• Out-of-flow elements and inline element boundaries do not introduce a forced line break or soft wrap opportunity in the flow.
• For Web-compatibility there is a soft wrap opportunity before and after each replaced element or other atomic inline, even when adjacent to a character that would normally suppress them, including U+00A0 NO-BREAK SPACE. However, with the exception of U+00A0 NO-BREAK SPACE, there must be no soft wrap opportunity between atomic inlines and adjacent characters belonging to the Unicode GL, WJ, or ZWJ line breaking classes. [UAX14]
• For soft wrap opportunities created by characters that disappear at the line break (e.g. U+0020 SPACE), properties on the box directly containing that character control the line breaking at that opportunity. For soft wrap opportunities defined by the boundary between two characters or atomic inlines, the white-space property on the nearest common ancestor of the two characters controls breaking; which elements’ line-break, word-break, and overflow-wrap properties control the determination of soft wrap opportunities at such boundaries is undefined in this level.
• For soft wrap opportunities before the first or after the last character of a box, the break occurs immediately before/after the box (at its margin edge) rather than breaking the box between its content edge and the content.
• Line breaking in/around Ruby is defined in CSS Ruby Annotation Layout 1 § 3.4 Breaking Across Lines. [CSS-RUBY-1]
• When shaping scripts such as Arabic wrap at unforced soft wrap opportunities within words (such as when breaking due to word-break: break-all, line-break: anywhere, overflow-wrap: break-word, overflow-wrap: anywhere, or when hyphenating) the characters must still be shaped (their joining forms chosen) as if the word were still whole.
  For example, if the word “نوشتن” is broken between the “ش” and “ت”, the “ش” still takes its initial form (“ﺷ”), and the “ت” its medial form (“ﺘ”)—​forming as in “ﻧﻮﺷ | ﺘﻦ”, not as in “نوش | تن”.

6. Line Breaking and Word Boundaries

In most writing systems, in the absence of hyphenation a soft wrap opportunity occurs only at word boundaries. Many such systems use spaces or punctuation to explicitly separate words, and soft wrap opportunities can be identified by these characters.

Scripts such as Thai, Lao, and Khmer, however, do not use spaces or punctuation to separate words. Although the zero width space (U+200B) can be used as an explicit word delimiter in these scripts, this practice is not common. As a result, a lexical resource is needed to correctly identify soft wrap opportunities in such texts.

In some other writing systems, soft wrap opportunities are based on orthographic syllable boundaries, not word boundaries. Some of these systems, notably Brahmic scripts such as Javanese and Balinese, require analysis of the text to find breaking opportunities. Unlike languages that use characters from the SA line breaking class, this analysis does not depend on the content language nor requires (language specific) word boundary detection or a lexical resource.

In others such as Chinese (as well as Japanese, Yi, and sometimes also Korean), each syllable tends to correspond to a single typographic letter unit, and thus line breaking conventions allow the line to break anywhere except between certain character combinations. Additionally the level of strictness in these restrictions varies with the typesetting style.

While CSS does not fully define where soft wrap opportunities occur, some controls are provided to distinguish common variations:

• The line-break property allows choosing various levels of “strictness” for line breaking restrictions.
• The word-break property controls what types of letters are glommed together to form unbreakable “words”, causing CJK characters to behave like non-CJK text or vice versa, enabling control over word detection in South East Asian Languages, or allowing words to be grouped into phrases…
• The hyphens property controls whether automatic hyphenation is allowed to break words in scripts that hyphenate.
• The overflow-wrap property allows the UA to take a break anywhere in otherwise-unbreakable strings that would otherwise overflow.

Note: Unicode Standard Annex #14: Unicode Line Breaking Algorithm defines a baseline behavior for line breaking for all scripts in Unicode, which is expected to be further tailored. [UAX14] More information on line breaking conventions can be found in Requirements for Japanese Text Layout [JLREQ] and Formatting Rules for Japanese Documents [JIS4051] for Japanese, Requirements for Chinese Text Layout [CLREQ] and General Rules for Punctuation [ZHMARK] for Chinese. See also the Internationalization Working Group’s Language Enablement Index which includes more information on additional languages. [TYPOGRAPHY] Any guidance on additional appropriate references would be much appreciated.

6.1. Breaking Rules for Letters: the word-break property

This property specifies soft wrap opportunities between and within “words”, i.e. where it is “normal” and permissible to break lines of text. It focuses on breaks between letters, and does not define whether and how soft wrap opportunities are created by white space and other space separators (though auto-phrase may suppress some), nor around punctuation. (See line-break for controls affecting punctuation and small kana.)

In particular, word-break controls whether a soft wrap opportunity generally exists between adjacent typographic letter units, treating non-letter typographic character units belonging to the NU, AL, AI, or ID Unicode line breaking classes as typographic letter units for this purpose (only). [UAX14]

For example, in some styles of CJK typesetting, English words are allowed to break between any two letters, rather than only at spaces or hyphenation points; this can be enabled with word-break:break-all.

As another example, Korean has two styles of line-breaking: between any two Korean syllables (word-break: normal) or, like English, mainly at spaces (word-break: keep-all).

각 줄의 마지막에 한글이 올 때 줄 나눔 기
준을 “글자” 또는 “어절” 단위로 한다.

각 줄의 마지막에 한글이 올 때 줄 나눔
기준을 “글자” 또는 “어절” 단위로 한다.

Ethiopic similarly has two styles of line-breaking, either only breaking at word separators (word-break: normal), or also allowing breaks between letters within a word (word-break: break-all).

ተወልዱ፡ኵሉ፡ሰብእ፡ግዑዛን፡ወዕሩያን፡
በማዕረግ፡ወብሕግ።ቦሙ፡ኅሊና፡ወዐቅል፡
ወይትጌበሩ፡አሐዱ፡ምስለ፡አሀዱ፡
በመንፈሰ፡እኍና።

ተወልዱ፡ኵሉ፡ሰብእ፡ግዑዛን፡ወዕሩያን፡በማ
ዕረግ፡ወብሕግ።ቦሙ፡ኅሊና፡ወዐቅል፡ወይትጌ
በሩ፡አሐዱ፡ምስለ፡አሀዱ፡በመንፈሰ፡እኍና።

Values have the following meanings:

normal

Words break according to their customary rules, as described above. Korean, which commonly exhibits two different behaviors, allows breaks between any two consecutive Hangul/Hanja. For Ethiopic, which also exhibits two different behaviors, such breaks within words are not allowed.

Some writing systems require specific processing to obtain the customarily expected soft wrap opportunities, as described in § 6.1.1 Analytical Word Breaking.

break-all

Breaking is allowed within “words”: specifically, in addition to soft wrap opportunities allowed for normal, any typographic letter units (and any typographic character units resolving to the NU (“numeric”), AL (“alphabetic”), or SA (“Southeast Asian”) line breaking classes [UAX14]) are instead treated as ID (“ideographic characters”) for the purpose of line-breaking. Hyphenation is not applied.

Note: This value does not affect whether there are soft wrap opportunities around punctuation characters. To allow breaks anywhere, see line-break: anywhere.

Note: This option enables the other common behavior for Ethiopic. It is also often used in a context where the text consists predominantly of CJK characters with only short non-CJK excerpts, and it is desired that the text be better distributed on each line.

keep-all

Breaking is forbidden within “words”: implicit soft wrap opportunities between typographic letter units (or other typographic character units belonging to the NU, AL, AI, or ID Unicode line breaking classes [UAX14]) are suppressed, i.e. breaks are prohibited between pairs of such characters (regardless of line-break settings other than anywhere) except where opportunities exist due to § 6.1.1.1 Lexical Word Breaking. Otherwise this option is equivalent to normal. In this style, sequences of CJK characters do not break.

Note: This is the other common behavior for Korean (which uses spaces between words), and is also useful for mixed-script text where CJK snippets are mixed into another language that uses spaces for separation.

manual

Behaves the same as normal, except that § 6.1.1.1 Lexical Word Breaking must not be performed. Specifically, typographic character units with class SA in [UAX14] must be treated as if they had class AL (i.e. assuming a value of line-break other than anywhere, there is no soft wrap opportunity between pairs of such characters).

Note: This value does not affect syllable-based soft wrap opportunities within words in languages such as Balinese. (See § 6.1.1.2 Orthographic Breaking for some discussion of such writing systems.)

alternatively, this value could be based on keep-all rather than normal. Yet another variant is to merge this behavior with keep-all.

Note: Some Southeast Asian languages are commonly misdetected by user agents. With word-break: normal, they would then apply inappropriate language-specific logic to find wrapping opportunities, and place them inappropriately.

For instance, many languages other than Thai are written using the Thai script, and line-breaking them as if they were Thai will generally produce inadequate—​and possibly confusing—​results.

When this occurs, this value enables authors to turn off the word boundary detection built into user agents for word-break: normal, so that they can manually mark up the text to indicate wrapping opportunities and obtain sensible results.

Authors using this value are expected to manually indicate word boundaries for Southeast Asian languages, using wbr or U+200B. Otherwise, there will be no soft wrap opportunity and the text may overflow.

auto-phrase

Behaves the same as normal, except that this value directs the user agent to perform language-specific content analysis to prioritize keeping natural phrases (of multiple words) together.

If the content language of the element is unknown, or if the user agent does not know how to detect phrase boundaries for that particular language, this value must behave as normal. Otherwise, the user agent should detect phrase boundaries and suppress soft wrap opportunities within each phrase.

Regardless of the content language and support for phrase boundary detection, hyphenation opportunities are suppressed as if hyphens: none had been specified.

Note: Whether a word boundary detection system designed for one language is suitable for some or all dialects of that language is somewhat subjective, and this specifications leaves it at the discretion of the user agent. Even if a detection system is not able to cope with all nuances of a particular dialect, it may be reasonable to claim support if the detection correctly recognizes word boundaries most of the time. However, the user agent would do a disservice to authors and users if it claimed support for languages where it fails to detect most word boundaries or has a high error rate.

If a user agent has a word-boundary detection system for Cantonese that is not suitable for the broader set of Chinese languages, auto-phrase should have an effect on content marked as lang=yue, lang=zh-yue, or lang=zh-HK, but not lang=zh or lang=zh-Hant.

However, if the user agent supports a generic word-boundary detection system that is suitable for Chinese in general, auto-phrase should have an effect on content marked with the broad lang=zh characterization, as well as any more specific ones, such as lang=zh-yue, lang=zh-Hant-HK, lang=zh-Hans-SG, or lang=zh-hak.

Symbols that line-break the same way as letters of a particular category are affected the same way as those letters.

User agents must not, in response to any value of this property, suppress soft wrap opportunities which are:

• introduced by the wbr HTML element or U+200B ZERO WIDTH SPACE

• required by the line-break property

• surrounding atomic inlines

Note: To control additional break opportunities available only in the case of overflow, see overflow-wrap.

The effects of word-break are taken into account when computing intrinsic sizes.

这是一些汉字 and some Latin و کمی خط عربی และตัวอย่างการเขียนภาษาไทย በጽሑፍ፡ማራዘሙን፡አንዳንድ፡

<h1>
窓ぎわの<wbr>トットちゃん
</h1>

h1 {
  word-break: normal;
}

窓ぎわのトッ
トちゃん

<h1>
窓ぎわの<wbr>トットちゃん
</h1>

h1 {
  word-break: keep-all;
}

窓ぎわの
トットちゃん

<h1 lang=ja>
窓ぎわのトットちゃん
</h1>

h1 {
  word-break: auto-phrase;
}

窓ぎわの
トットちゃん

When shaping scripts such as Arabic are allowed to break within words due to break-all the characters must still be shaped as if the word were not broken.

For compatibility with legacy content, the word-break property also supports a deprecated break-word keyword. When specified, this has the same effect as word-break: normal and overflow-wrap: anywhere, regardless of the actual value of the overflow-wrap property.

6.1.1. Analytical Word Breaking

6.1.1.1. Lexical Word Breaking

To provide the expected normal behavior for Southeast Asian languages, typographic character units with line breaking class SA in [UAX14] must be treated as if they had class AL. However, the user agent must additionally analyze the content of a run of such characters to detect word boundaries and treat each boundary as a soft wrap opportunities.

As various languages can be written in scripts which use the characters with class SA, if the content language is known, the user agent should use this information to tailor its analysis.

6.1.1.2. Orthographic Breaking

For scripts (such as Balinese) that use line breaking based on orthographic syllables, the UA must analyze the content to find the correct points to insert soft wrap opportunities.

Note: At the time of writing, Unicode does not define how to perform this analysis, and treats all characters in these writing systems as having line breaking class AL. However, a proposal has been made to solve that issue. Even though it is not final, it can be informative to consult. [L2-22-080R]

6.1.1.3. Fallback Breaking

In order to avoid unexpected overflow, if the user agent is unable to perform the requisite lexical or orthographic analysis for line breaking any content language that requires it—​for example due to lacking a dictionary for languages written in characters with class SA—​it must assume a soft wrap opportunity between pairs of typographic letter units in that writing system.

Note: This provision is not triggered merely when the UA fails to find a word boundary in a particular text run; the text run may well be a single unbreakable word. It applies for example when a text run is composed of Khmer characters (U+1780 to U+17FF) if the user agent does not know how to determine word boundaries in Khmer.

6.1.2. Expressing User Preferences for Phrase-based Line Breaking

User agents may activate language-specific content analysis described in auto-phrase in response to user preferences. User agents with this behavior must do this by setting the declared value of word-break to auto-phrase in the user origin.

Note: This allows authors to detect whether or not this feature is enabled by calling getComputedStyle(), or to override it in the author origin where appropriate.

6.2. Line Breaking Strictness: the line-break property

This property specifies the strictness of line-breaking rules applied within an element: especially how wrapping interacts with punctuation and symbols. Values have the following meanings:

auto

The UA determines the set of line-breaking restrictions to use, and it may vary the restrictions based on the length of the line; e.g., use a less restrictive set of line-break rules for short lines.

loose

Breaks text using the least restrictive set of line-breaking rules. Typically used for short lines, such as in newspapers.

normal

Breaks text using the most common set of line-breaking rules.

strict

Breaks text using the most stringent set of line-breaking rules.

anywhere

There is a soft wrap opportunity around every typographic character unit, including around any punctuation character or preserved white spaces, or in the middle of words, disregarding any prohibition against line breaks, even those introduced by characters with the GL, WJ, or ZWJ line breaking classes or mandated by the word-break property. [UAX14] The different wrapping opportunities must not be prioritized. Hyphenation is not applied.

Note: This value triggers the line breaking rules typically seen in terminals.

Note: This values only creates soft wrap opportunities between typographic character units, not within them. Consequently, the CM and SG Unicode line breaking classes must be honored. [UAX14]

Note: anywhere only allows preserved white spaces at the end of the line to be wrapped to the next line when white-space is set to break-spaces, because in other cases:

• preserved white space at the end/start of the line is discarded (normal, pre-line)
• wrapping is forbidden altogether (nowrap, pre)
• the preserved white space hang (pre-wrap).

When it does have an effect on preserved white space, with white-space: break-spaces, it allows breaking before the first space of a sequence, which break-spaces on its own does not.

CSS distinguishes between four levels of strictness in the rules for text wrapping. The precise set of rules in effect for each of loose, normal, and strict is up to the UA and should follow language conventions. However, this specification does require that:

• The following breaks are forbidden in strict line breaking and allowed in normal and loose:
  • breaks before Japanese small kana or the Katakana-Hiragana prolonged sound mark, i.e. characters from the Unicode line breaking class CJ. [UAX14]
• The following breaks are allowed for normal and loose line breaking if the writing system is Chinese or Japanese, and are otherwise forbidden:
  • breaks before certain CJK hyphen-like characters:
    〜 U+301C, ゠ U+30A0
• The following breaks are allowed for loose line breaking if the preceding character belongs to the Unicode line breaking class ID [UAX14] (including when the preceding character is treated as ID due to word-break: break-all), and are otherwise forbidden:
  • breaks before hyphens:
    ‐ U+2010, – U+2013
• The following breaks are forbidden for normal and strict line breaking and allowed in loose:
  • breaks before iteration marks:
    々 U+3005, 〻 U+303B, ゝ U+309D, ゞ U+309E, ヽ U+30FD, ヾ U+30FE
  • breaks between inseparable characters (such as ‥ U+2025, … U+2026) i.e. characters from the Unicode line breaking class IN. [UAX14]
• The following breaks are allowed for loose if the writing system is Chinese or Japanese and are otherwise forbidden:
  • breaks before certain centered punctuation marks:
    ・ U+30FB, ： U+FF1A, ； U+FF1B, ･ U+FF65, ‼ U+203C, ⁇ U+2047, ⁈ U+2048, ⁉ U+2049, ！ U+FF01, ？ U+FF1F
  • breaks before suffixes:
    Characters with the Unicode line breaking class PO [UAX14] and the East Asian Width property [UAX11] Ambiguous, Fullwidth, or Wide.
  • breaks after prefixes:
    Characters with the Unicode line breaking class PR [UAX14] and the East Asian Width property [UAX11] Ambiguous, Fullwidth, or Wide.

Note: The requirements listed above only create distinctions in CJK text. In an implementation that matches only the rules above, and no additional rules, line-break would only affect CJK code points unless the writing system is tagged as Chinese or Japanese. Future levels may add additional specific rules for other writing systems and languages as their requirements become known.

Note: The CSSWG recognizes that in a future edition of the specification finer control over line breaking may be necessary to satisfy high-end publishing requirements.

6.3. Hyphenation: Morphological Breaking Within Words

6.3.1. Hyphenation Control: the hyphens property

Hyphenation is the controlled splitting of words where they usually would not be allowed to break to improve the layout of paragraphs, typically splitting words at syllabic or morphemic boundaries and often visually indicating the split (usually by inserting a hyphen, U+2010). In some cases, hyphenation may also alter the spelling of a word. Regardless, hyphenation is a rendering effect only: it must have no effect on the underlying document content or on text selection or searching.

Hyphenation practices vary across languages, and can involve not just inserting a hyphen before the line break, but inserting a hyphen after the break (or both), inserting a different character than U+2010, or changing the spelling of the word.

Language	Unbroken	Before	After
English	Unbroken	Un‐	broken
Dutch	cafeetje	café‐	tje
Hungarian	Összeg	Ösz‐	szeg
Mandarin	tú’àn	tú‐	àn
	àizēng‐fēnmíng	àizēng‐	‐fēnmíng
Uyghur
Cree

Hyphenation occurs when the line breaks at a valid hyphenation opportunity, which is a type of soft wrap opportunity that exists within a word where hyphenation is allowed. In CSS hyphenation opportunities are controlled with the hyphens property. CSS Text Level 3 does not define the exact rules for hyphenation; however UAs are strongly encouraged to optimize their choice of break points and to chose language-appropriate hyphenation points.

Note: The soft wrap opportunity introduced by the U+002D - HYPHEN-MINUS character or the U+2010 ‐ HYPHEN character is not a hyphenation opportunity, as no visual indication of the split is created when wrapping: these characters are visible whether the line is wrapped at that point or not.

Hyphenation opportunities are considered when calculating min-content intrinsic sizes.

Note: This allows tables to hyphenate their contents instead of overflowing their containing block, which is particularly important in long-word languages like German.

This property controls whether hyphenation is allowed to create more soft wrap opportunities within a line of text. Values have the following meanings:

none

Words are not hyphenated, even if characters inside the word explicitly define hyphenation opportunities.

Note: This does not suppress the existing soft wrap opportunities introduced by always visible characters such as U+002D - HYPHEN-MINUS or U+2010 ‐ HYPHEN.

manual

Words are only hyphenated where there are characters inside the word that explicitly suggest hyphenation opportunities. The UA must use the appropriate language-specific hyphenation character(s) and should apply any appropriate spelling changes just as for automatic hyphenation at the same point.

In Unicode, U+00AD is a conditional "soft hyphen" and U+2010 is an unconditional hyphen. Unicode Standard Annex #14 describes the role of soft hyphens in Unicode line breaking. [UAX14] In HTML, &shy; represents the soft hyphen character, which suggests a hyphenation opportunity.

ex­ample

auto

Words may be broken at hyphenation opportunities determined automatically by a language-appropriate hyphenation resource in addition to those indicated explicitly by a conditional hyphen. Automatic hyphenation opportunities elsewhere within a word must be ignored if the word contains a conditional hyphen (&shy; or U+00AD SOFT HYPHEN), in favor of the conditional hyphen(s). However, if, even after breaking at such opportunities, a portion of that word is still too long to fit on one line, an automatic hyphenation opportunity may be used.

Correct automatic hyphenation requires a hyphenation resource appropriate to the language of the text being broken. The UA must therefore only automatically hyphenate text for which the content language is known and for which it has an appropriate hyphenation resource.

The UA may use language-tailored heuristics to exclude certain words from automatic hyphenation. For example, a UA might try to avoid hyphenation in proper nouns by excluding words matching certain capitalization and punctuation patterns. Such heuristics are not defined by this specification. (Note that such heuristics will need to vary by language: English and German, for example, have very different capitalization conventions.)

For the purpose of the hyphens property, what constitutes a “word” is UA-dependent. However, inline element boundaries and out-of-flow elements must be ignored when determining word boundaries.

Any glyphs shown due to hyphenation at a hyphenation opportunity created by a conditional hyphen character (such as U+00AD SOFT HYPHEN) are represented by that character and are styled according to the properties applied to it.

When shaping scripts such as Arabic are allowed to break within words due to hyphenation, the characters must still be shaped as if the word were not broken.

For example, if the Uyghur word “داميدى” were hyphenated, it would appear as not as .

6.3.2. Hyphens: the hyphenate-character property

This property specifies the string that is shown between parts of hyphenated words. Values have the following meanings:

auto

Specifies that the user agent should find an appropriate string based on the content language’s typographic conventions, possibly from the same source as the hyphenation dictionary.

<string>

Specifies the string that appears at the hyphenation break when hyphenating. (The position of this string is not affected: the UA must insert the string according to the typographic conventions of the content language, defaulting to immediately before the hyphenation break.) The UA may truncate the used value to a limited number of typographic character units; it must not truncate only part of a typographic character unit.

Note: Specifying the empty string "" is valid, and causes the UA to break at hyphenation opportunities without inserting a visible hyphenation character.

[lang]:lang(ojs) { hyphenate-character: "᐀" /* CANADIAN SYLLABICS HYPHEN (U+1400) */ }

Note: Both hyphens triggered by automatic hyphenation and hyphens triggered by soft hyphens are rendered according to hyphenate-character.

6.3.3. Hyphenation Size Limit: the hyphenate-limit-zone property

Is hyphenate-limit-zone a good name? Comments/suggestions?

This property specifies the maximum amount of unfilled space (before justification) that may be left in the line box before hyphenation is triggered to pull part of a word from the next line back up into the current line.

6.3.4. Hyphenation Character Limits: the hyphenate-limit-chars property

This property specifies the minimum number of characters in a hyphenated word. If the word does not meet the required minimum number of characters in the word / before the hyphen / after the hyphen, then the word must not be hyphenated. Nonspacing combining marks (Unicode General Category Mn) and intra-word punctuation (Unicode General Category P*) do not count towards the minimum.

If three values are specified, the first value is the required minimum for the total characters in a word, the second value is the minimum for characters before the hyphenation point, and the third value is the minimum for characters after the hyphenation point. If the third value is missing, it is the same as the second. If the second value is missing, then it is auto. The auto value means that the UA chooses a value that adapts to the current layout.

Note: Unless the UA is able to calculate a better value, it is suggested that auto means 2 for before and after, and 5 for the word total.

p { hyphenate-limit-chars: auto 3; }

6.3.5. Hyphenation Line Limits: the hyphenate-limit-lines and hyphenate-limit-last properties

This property indicates the maximum number of successive hyphenated lines in an element. The no-limit value means that there is no limit.

In some cases, user agents may not be able to honor the specified value. (See overflow-wrap.) It is not defined whether hyphenation introduced by such emergency breaking influences nearby hyphenation points.

This property indicates hyphenation behavior at the end of elements, column, pages, and spreads. A spread is a set of two pages that are visible to the reader at the same time. Values have the following meanings:

none

No restrictions imposed.

always

The last full line of the element, or the last line before any column, page, or spread break inside the element should not be hyphenated.

column

The last line before any column, page, or spread break inside the element should not be hyphenated.

page

The last line before page or spread break inside the element should not be hyphenated.

spread

The last line before any spread break inside the element should not be hyphenated.

p { hyphenate-limit-last: always }
div.chapter {  hyphenate-limit-last: spread }

This is just a
simple example
to show Antarc-
tica.

This is just a
simple example
to        show
Antarctica.

6.4. Overflow Wrapping: the overflow-wrap/word-wrap property

This property specifies whether the UA may break at otherwise disallowed points within a line to prevent overflow, when an otherwise-unbreakable string is too long to fit within the line box. It only has an effect when white-space allows wrapping. Possible values:

normal

Lines may break only at allowed break points. However, the restrictions introduced by word-break: keep-all may be relaxed to match word-break: normal if there are no otherwise-acceptable break points in the line.

Also, the restrictions introduced by word-break: auto-phrase are relaxed if there are no otherwise-acceptable break points in the line:

• If suppressing soft wrap opportunities within a particular phrase would cause that phrase to overflow even when placed on an otherwise empty line, the user agent must fall back to the same soft wrap opportunities as normal within that phrase.
• If that is not enough to prevent overflow, suppression of hyphenation opportunities must also be abandoned within each line that would overflow.
• As an intermediary measure, user agents may also detect multiple levels of phrases, choosing to shorter ones (possibly down to individual words) when longer ones would lead to overflow.

The soft wrap opportunities obtained by relaxing the restrictions introduced by word-break: keep-all and word-break: auto-phrase are not considered when calculating min-content intrinsic sizes.

anywhere

An otherwise unbreakable sequence of characters may be broken at an arbitrary point if there are no otherwise-acceptable break points in the line. Shaping characters are still shaped as if the word were not broken, and grapheme clusters must stay together as one unit. No hyphenation character is inserted at the break point. Soft wrap opportunities introduced by anywhere are considered when calculating min-content intrinsic sizes.

In the case of word-break: auto-phrase, these additional soft wrap opportunities are only introduced if relaxing the restrictions introduced by word-break: auto-phrase as described in overflow-wrap: normal is insufficient to prevent overflow.

break-word

As for anywhere except that soft wrap opportunities introduced by break-word are not considered when calculating min-content intrinsic sizes.

Do we need to add a none value to overflow-wrap to opt out of relaxing the keep-all' and auto-phrase'' restrictions as allowed by overflow-wrap: normal?

For legacy reasons, UAs must treat word-wrap as a legacy name alias of the overflow-wrap property.

7. Alignment and Justification

Alignment and justification controls how inline content is distributed within a line box.

7.1. Text Alignment: the text-align shorthand

This shorthand property sets the text-align-all and text-align-last properties and describes how the inline-level content of a block is aligned along the inline axis if the content does not completely fill the line box. Values other than justify-all or match-parent are assigned to text-align-all and reset text-align-last to auto.

Values have the following meanings:

start

Inline-level content is aligned to the start edge of the line box.

end

Inline-level content is aligned to the end edge of the line box.

left

Inline-level content is aligned to the line-left edge of the line box. (In vertical writing modes, this can be either the physical top or bottom, depending on writing-mode.) [CSS-WRITING-MODES-4]

right

Inline-level content is aligned to the line-right edge of the line box. (In vertical writing modes, this can be either the physical top or bottom, depending on writing-mode.) [CSS-WRITING-MODES-4]

center

Inline-level content is centered within the line box.

<string>

The string must be a single character; otherwise the declaration is invalid and must be ignored. When applied to a table cell, specifies the alignment character around which the cell’s contents will align. See below for further details and how this value combines with keywords.

justify

Text is justified according to the method specified by the text-justify property, in order to exactly fill the line box. Unless otherwise specified by text-align-last, the last line before a forced break or the end of the block is start-aligned.

justify-all

Sets both text-align-all and text-align-last to justify, forcing the last line to justify as well.

match-parent

This value behaves the same as inherit (computes to its parent’s computed value) except that an inherited value of start or end is interpreted against the parent’s direction value and results in a computed value of either left or right. Computes to start when specified on the root element.

When specified on the text-align shorthand, sets both text-align-all and text-align-last to match-parent.

A block of text is a stack of line boxes. This property specifies how the inline-level boxes within each line box align with respect to the start and end sides of the line box. Alignment is not with respect to the viewport or containing block.

In the case of justify, the UA may stretch or shrink any inline boxes by adjusting their text. (See text-justify.) If an element’s white space is not collapsible, then the UA is not required to adjust its text for the purpose of justification and may instead treat the text as having no justification opportunities. If the UA chooses to adjust the text, then it must ensure that tab stops continue to line up as required by the white space processing rules.

If (after justification, if any) the inline contents of a line box are too long to fit within it, then the contents are start-aligned: any content that doesn’t fit overflows the line box’s end edge.

See § 9.3 Bidirectionality and Line Boxes for details on how to determine the start and end edges of a line box.

7.2. Character-based Alignment in a Table Column

When multiple cells in a column have an alignment character specified, the alignment character of each such cell in the column is centered along a single column-parallel axis and the rest of the text in the column shifted accordingly. (Note that the strings do not have to be the same for each cell, although they usually are.)

Is this intended to say that it’s the centers of the alignment characters that should be aligned? It’s not clear that’s what it says, but that (or a different behavior) needs to be specified, to describe what happens when different occurrences of the alignment character are in different fonts. (Further, is that the intended behavior? Probably the most significant use case to consider is bold vs. non-bold text, which only varies slightly in width.) [feedback] [minutes face-to-face 2016-02-02 10:00 AM]

TD { text-align: "." center }

<TABLE>
<COL width="40">
<TR> <TH>Long distance calls
<TR> <TD> $1.30
<TR> <TD> $2.50
<TR> <TD> $10.80
<TR> <TD> $111.01
<TR> <TD> $85.
<TR> <TD> N/A
<TR> <TD> $.05
<TR> <TD> $.06
</TABLE>

+---------------------+
| Long distance calls |
+---------------------+
|         $1.30       |
|         $2.50       |
|        $10.80       |
|       $111.01       |
|        $85.         |
|        N/A          |
|          $.05       |
|          $.06       |
+---------------------+

A keyword value may be specified in conjunction with the <string> value; if it is not given, it defaults to right. This value is used:

• when character-based alignment is applied to boxes that are not table cells.
• when the text wraps to multiple lines (at unforced break points).
• when a character-aligned cell spans more than one column. In this case the keyword alignment value is used to determine which column’s axis to align with: the leftmost column for left, the rightmost column for right and center, the startmost column for start, the endmost column for end.
• when the column is wide enough that the character alignment alone does not determine the positions of its character-aligned contents. In this case the keyword alignment of the first cell in the column with a specified alignment character is used to slide the position of the character-aligned contents to match the keyword alignment insofar as possible without changing the width of the column. For center, the UA may center the aligned contents using its extremes, center the alignment axis itself (insofar as possible), or optically center the aligned contents some other way (such as by taking a weighted average of the extent of the cells' contents to either side of the axis).

Note: Right alignment is used by default for character-based alignment because numbering systems are almost all left-to-right even in right-to-left writing systems, and the primary use case of character-based alignment is for numerical alignment.

If the alignment character appears more than once in the text, the first instance is used for alignment. If the alignment character does not appear in a cell at all, the string is aligned as if the alignment character had been inserted at the end of its contents.

This needs to specify what text is searched for the alignment character. Is it only in-flow text whose containing block is the cell? Or is text within any in-flow descendants in the block formatting context established by the cell considered? If so, is it considered only as long as its text-align property is consistent with the cell’s? (Consistent in the alignment character, or fully consistent?)

This behavior of aligning as though the alignment character had been inserted at the end of the contents of the cell, combined with center-of-character alignment, will produce gaps on the end-side of lines that are alone on a line with <string> text-alignment, when none of the lines of the column has the alignment character, or, more importantly, when some of the lines do have the alignment character, but the column is not laid out at its max-content width. This is probably undesirable.

When the alignment character is inserted at the end of the contents, which font is used? (In particular, if the alignment character might be within a descendant block, is it the font of the block or the font of the table cell? Or if the insertion is at a forced break within an inline, does it use the font of the inline or the font of the block or cell?)

Character-based alignment occurs before table cell width computation so that auto width computations can leave enough space for alignment. Whether column-spanning cells participate in the alignment prior to or after width computation is undefined. If width constraints on the cell contents prevent full alignment throughout the column, the resulting alignment is undefined.

This should have a formal definition of how character alignment affects the min-content and max-content intrinsic widths (of table columns and all content that can be inside table columns). Max-content intrinsic widths need to be split into three numbers (assuming that it’s the centers of the alignment character that are aligned): one for widths without alignment characters, one for widths on the inline-start side of the center of the alignment character, one for widths on the inline-end side of the center of the alignment character. This operates based on all segments of text between forced breaks for max-content widths. For min-content widths, segments of text between forced breaks that contain optional breaks within them should clearly contribute only to the without-alignment-character width. However, it’s less clear whether all min-content widths should work this way, or whether segments between forced breaks that do not have optional breaks (and perhaps only those that actually contain the alignment character) should contribute to start-side-of-alignment-character and end-side-of-alignment-character min-content widths instead; this choice is a tradeoff between the meaning of min-content sizing of a table meaning the narrowest reasonable size versus honoring alignment characters in more cases. Another option might be to use whether line-breaking of optional breaks is allowed as a control for which behavior to use.

Formally defining the intrinsic width contributions of column-spanning cells with <string> values of text-align is a complicated (although straightforward) extension of the decisions made for intrinsic width contributions of non-column-spanning cells; this should also be formally defined. Contributions end up being made to the split intrinsic widths of the startmost or endmost column (whichever is used for alignment), and to the without-alignment-character intrinsic widths of the other spanned columns.

7.3. Default Text Alignment: the text-align-all property

This longhand of the text-align shorthand property specifies the inline alignment of all lines of inline content in the block container, except for last lines overridden by a non-auto value of text-align-last. See text-align for a full description of values.

Authors should use the text-align shorthand instead of this property.

7.4. Last Line Alignment: the text-align-last property

This property describes how the last line of a block or a line right before a forced line break is aligned.

If auto is specified, content on the affected line is aligned per text-align-all unless text-align-all is set to justify, in which case it is start-aligned. All other values are interpreted as described for text-align.

7.5. Justification Method: the text-justify property

This property selects the justification method used when a line’s alignment is set to justify (see text-align). The property applies to text, but is inherited from block containers to the root inline box containing their inline-level contents. It takes the following values:

auto

The UA determines the justification algorithm to follow, based on a balance between performance and adequate presentation quality. Since justification rules vary by writing system and language, UAs should, where possible, use a justification algorithm appropriate to the text.

For example, the UA could use by default a justification method that is a simple universal compromise for all writing systems—​such as primarily expanding word separators and between CJK typographic letter units along with secondarily expanding between Southeast Asian typographic letter units. Then, in cases where the content language of the paragraph is known, it could choose a more language-tailored justification behavior e.g. following the Requirements for Japanese Text Layout for Japanese [JLREQ], using cursive elongation for Arabic, using inter-word for German, etc.

none

Justification is disabled: there are no justification opportunities within the text.

Note: This value is intended for use in user stylesheets to improve readability or for accessibility purposes.

inter-word

Justification adjusts spacing at word separators only (effectively varying the used word-spacing on the line). This behavior is typical for languages that separate words using spaces, like English or Korean.

inter-character

Justification adjusts spacing between each pair of adjacent typographic character units (effectively varying the used letter-spacing on the line). This value is sometimes used in East Asian systems such as Japanese.

For legacy reasons, UAs must also support the alternate keyword distribute which must compute to inter-character, thus having the exact same meaning and behavior. UAs may treat this as a legacy value alias.

ruby

Justification adjusts spacing as for auto except:

• Justification opportunities are disabled at word separators.

• Justification opportunities are disabled between Bopomofo characters

Note: This value is intended for use in ruby annotations, providing a reasonable default alignment. See [CSS-RUBY-1].

no-compress

Justification must not compress spacing controlled by text-spacing-trim or text-autospace. (If this value is not specified, the justification process may reduce such spacing except when the spacing is at the start or end of the line.)

Note: An example of compression rules is given for Japanese in 3.8 Line Adjustment in [JLREQ].

This keyword used to be part of text-spacing; it might need renaming to be more specific now that it’s here, as it implies that e.g. U+0020 cannot be compressed. [Issue #7079]

Since optimal justification is language-sensitive, authors should correctly language-tag their content for the best results.

Note: The guidelines in this level of CSS do not describe a complete justification algorithm. They are merely a minimum set of requirements that a complete algorithm should meet. Limiting the set of requirements gives UAs some latitude in choosing a justification algorithm that meets their needs and desired balance of quality, speed, and complexity.

7.5.1. Expanding and Compressing Text

When justifying text, the user agent takes the remaining space between the ends of a line’s contents and the edges of its line box, and distributes that space throughout its content so that the contents exactly fill the line box. The user agent may alternatively distribute negative space, putting more content on the line than would otherwise fit under normal spacing conditions.

A justification opportunity is a point where the justification algorithm may alter spacing within the text. A justification opportunity can be provided by a single typographic character unit (such as a word separator), or by the juxtaposition of two typographic character units. As with controls for soft wrap opportunities, whether a typographic character unit provides a justification opportunity is controlled by the text-justify value of its parent; similarly, whether a justification opportunity exists between two consecutive typographic character units is determined by the text-justify value of their nearest common ancestor.

Space distributed by justification is in addition to the spacing defined by the letter-spacing or word-spacing properties. When such additional space is distributed to a word separator justification opportunity, it is applied under the same rules as for word-spacing. Similarly, when space is distributed to a justification opportunity between two typographic character units, should be applied under the same rules as for letter-spacing.

A justification algorithm may divide justification opportunities into different priority levels. All justification opportunities within a given level are expanded or compressed at the same priority, regardless of which typographic character units created that opportunity. For example, if justification opportunities between two Han characters and between two Latin letters are defined to be at the same level (as they are in the inter-character justification style), they are not treated differently because they originate from different typographic character units. It is not defined in this level whether or how other factors (such as font size, letter-spacing, glyph shape, position within the line, etc.) may influence the distribution of space to justification opportunities within the line.

The UA may enable or break optional ligatures or use other font features such as alternate glyphs or glyph compression to help justify the text under any method. This behavior is not controlled by this level of CSS. However, UAs must not break required ligatures or otherwise disable features required to correctly shape complex scripts.

If a justification opportunity exists within a line, and text alignment specifies full justification (justify) for that line, it must be justified.

7.5.2. Handling Symbols and Punctuation

When determining justification opportunities, a typographic character unit from the Unicode Symbols (S*) and Punctuation (P*) classes is generally treated the same as a typographic letter unit of the same script (or, if the character’s script property is Common, then as a typographic letter unit of the dominant script).

However, by typographic tradition there may be additional rules controlling the justification of symbols and punctuation. Therefore, the UA may reassign specific characters or introduce additional levels of prioritization to handle justification opportunities involving symbols and punctuation.

7.5.3. Unexpandable Text

If the inline contents of a line cannot be stretched to the full width of the line box, then they must be aligned as specified by the text-align-last property. (If text-align-last is justify, then they must be aligned as for center.)

7.5.4. Cursive Scripts

Justification must not introduce gaps between the joined typographic letter units of cursive scripts such as Arabic. If it is able, the UA may translate space distributed to justification opportunities within a run of such typographic letter units into some form of cursive elongation for that run. It otherwise must assume that no justification opportunity exists between any pair of typographic letter units in cursive script (regardless of whether they join).

The following are examples of unacceptable justification:

Some font designs allow for the use of the tatweel character for justification. A UA that performs tatweel-based justification must properly handle the rules for its use. Note that correct insertion of tatweel characters depends on context, including the letter-combinations involved, location within the word, and location of the word within the line.

7.5.5. Minimum Requirements for auto Justification

For auto justification, this specification does not define what all of the justification opportunities are, how they are prioritized, or when and how multiple levels of justification opportunities interact. However, it does require that:

• Unless contraindicated by the typographic traditions of the content language or adjacent symbols/punctuation, each of the following provides a justification opportunity:
  • Word separators
  • The boundary between a typographic character unit of any block scripts and any other typographic character unit
  • The boundary between a typographic character unit of any clustered scripts and any other typographic character unit
• All letters belonging to all block scripts are treated the same, and all letters belonging to all clustered scripts are treated the same. For example, no distinction is made between the justification opportunity between a Han letter followed by another Han letter, vs. the justification opportunity between a Han letter followed by a Hangul letter.

Further information on text justification can be found in (or submitted to) “Approaches to Full Justification”, which indexes by writing system and language, and is maintained by the W3C Internationalization Working Group. [JUSTIFY]

7.6. Aligning a block of text within its container: the text-group-align property

This property aligns the contents of the line boxes as a group while maintaining their text alignment.

Group alignment is performed by finding the line box with the shortest remaining space and adding that amount of space as padding to one or both sides of the line box, reducing the amount of space available for its contents; text alignment is then applied to its contents within the remaining space. All descendant in-flow line boxes within the same block formatting context are considered both when searching for the shortest remaining space and when adding the padding; the contents of descendants that establish independent formatting contexts are skipped.

A variant of this property is inherited, and applies on each block container individually, only affecting the line boxes that are direct children of that block. This is less useful, but probably easier to implement.

Somehow also moving the floats that originate in the same block container by the same amount would make things line up more nicely, which would be especially valuable in CJK layout. Exactly how that works, and how it interacts with intruding floats from ancestor elements is left as an exercise for the reader.

Values have the following meanings:

none

Text alignment happens normally: group alignment is not performed.

start

Inline-level content is group-aligned to the inline start side, by padding the inline end side of each line box.

end

Inline-level content is group-aligned to the inline end side, by padding the inline start side of each line box.

left

Inline-level content is group-aligned to the line-left side, by padding the line-right side of each line box.

right

Inline-level content is group-aligned to the line-right side, by padding the line-left side of each line box.

center

Inline-level content is group-aligned to the center, by padding both sides of each line box, half the spacing to each side.

8. Spacing

CSS offers control over regular text spacing via the word-spacing, letter-spacing, and line-padding properties, which specify additional space around word separators between typographic character units, or at the start/end of the line, respectively. It also provides contextual control over spacing via the text-spacing-trim property, which allows for contextual fullwidth vs halfwidth setting of CJK punctuation; and the text-autospace property, which allows automatic insertion of extra space at script changes or around punctuation.

8.1. Word Spacing: the word-spacing property

This property specifies additional spacing between “words”. Values are interpreted as defined below:

normal

No additional spacing is applied. Computes to zero.

<length-percentage>

Specifies extra spacing in addition to the intrinsic inter-word spacing defined by the font.

Note: Percentages inherit intact, and are resolved against the computed font-size of the current element (and thus represent a size relative to the size of the text to which they apply), unlike em units which are resolved against the computed font-size of the element from which they inherit, as an absolute length.

Additional spacing is applied to each word separator left in the text after the white space processing rules have been applied, and should be applied half on each side of the character unless otherwise dictated by typographic tradition. Values may be negative, but there may be implementation-dependent limits.

Word-separator characters are typographic character units whose primary purpose and general usage is to separate words. In Unicode this includes (but is not exhaustively defined as) the space (U+0020), the no-break space (U+00A0), the Ethiopic word space (U+1361), the Aegean word separators (U+10100,U+10101), the Ugaritic word divider (U+1039F), and the Phoenician word separator (U+1091F). [UNICODE]

Note: Neither punctuation in general, nor fixed-width spaces (such as U+3000 and U+2000 through U+200A), are considered word-separator characters, because even though they frequently happen to separate words, their primary purpose is not to separate words.

If there are no word-separator characters, or if a word-separating character has a zero advance width (such as U+200B ZERO WIDTH SPACE) then the user agent must not create an additional spacing between words.

8.2. Tracking: the letter-spacing property

This property specifies additional spacing (commonly called tracking) between adjacent typographic character units. Letter-spacing is applied after bidi reordering and is in addition to kerning and word-spacing. [CSS-WRITING-MODES-4] [CSS-FONTS-3] Depending on the justification rules in effect, user agents may further increase or decrease the space between typographic character units in order to justify text.

Values have the following meanings:

normal

No additional spacing is applied. Computes to zero.

<length-percentage>

Specifies additional spacing between typographic character units. Values may be negative, but there may be implementation-dependent limits.

Note: Percentages inherit intact, and are resolved against the computed font-size of the current element (and thus represent a size relative to the size of the text to which they apply), unlike em units which are resolved against the computed font-size of the element from which they inherit, as an absolute length.

For legacy reasons, a computed letter-spacing of zero yields a resolved value (getComputedStyle() return value) of normal.

For the purpose of letter-spacing, each consecutive run of atomic inlines (such as images and inline blocks) is treated as a single typographic character unit.

Letter-spacing must not be applied at the beginning of a line. Whether letter-spacing is applied at the end of a line is undefined in this level.

p { letter-spacing: 1em; }

<p>abc</p>

Letter spacing between two typographic character units effectively “belongs” to the innermost element that contains the two typographic character units: the total letter spacing between two adjacent typographic character units (after bidi reordering) is specified by and rendered within the innermost element that contains the boundary between the two typographic character units. However, the UA may instead attach letter-spacing at element boundaries to one or the other typographic character unit using the letter-spacing value pertaining to its containing element.

Note: This secondary behavior is permitted in this level due to Web-compat concerns.

p { letter-spacing: 1em; }

<p>a<span>bb</span>c</p>

p    { letter-spacing: 1em; }
span { letter-spacing: 2em; }

<p>a<span>bb</span>c</p>

p    { letter-spacing: 1em; }
span { letter-spacing: 2em; }

<p>a<span>b</span>c</p>

p    { letter-spacing: 1em; }
span { letter-spacing: 2em; }

<!-- abc followed by Hebrew letters alef (א), bet (ב) and gimel (ג) -->
<!-- Reordering will display these in reverse order. -->
<p>ab<span>cא</span>בג</p>

Letter spacing ignores invisible zero-width formatting characters (such as those from the Unicode Cf category). Spacing must be added as if those characters did not exist in the document.

When the effective spacing between two characters is not zero (due to either justification or a non-zero value of letter-spacing), user agents should not apply optional ligatures, i.e. those that are not defined as required for fundamentally correct glyph shaping. However, ligatures and other font features specified via the low-level font-feature-settings property take precedence over this rule. See CSS Fonts Module Level 3 § feature-precedence.

Note: In OpenType, required ligatures are expected to be associated to the rlig feature. All other ligatures are therefore considered optional. In some cases, however, UA or platform heuristics apply additional ligatures in order to handle broken fonts; this specification does not define or override such exceptional handling.

8.2.1. Cursive Scripts

If it is able, the UA may apply letter spacing to cursive scripts by translating the total extra space to be distributed to a run of such letters into some form of cursive elongation (or compression, for negative tracking values) for that run that results in an equivalent total expansion (or compression) of the run. Otherwise, if the UA cannot expand text from a cursive script without breaking its cursive connections, it must not apply spacing between any pair of that script’s typographic letter units at all (effectively treating each word as a single typographic letter unit for the purpose of letter-spacing). Both cases will result in an effective spacing of zero between such letters; however the former will preserve the sense of stretching out the text.

Below are some appropriate and inappropriate examples of spacing out Arabic text.

	—	Original text
	BAD	Even distribution of space between each letter. Notice this breaks cursive joins!
	OK	Distributing ∑letter-spacing by typographically-appropriate cursive elongation. The resulting text is as long as the previous evenly-spaced example.
	OK	Suppressing letter-spacing between Arabic letters. Notice letter-spacing is nonetheless applied to non-Arabic characters (like spaces).
	BAD	Applying letter-spacing only between non-joined letters. This distorts typographic color and obfuscates word boundaries.

Note: Proper cursive elongation or compression of a text can vary depending on the script, typeface, language, location within a word, location within a line, implementation complexity, font capabilities, and calligraphic preferences, and may not be possible in certain cases at all. It may involve the use of shortening ligatures, swash variants, contextual forms, elongation glyphs such as U+0640 ـ ARABIC TATWEEL, or other microtypography. It is outside the scope of CSS to define rules for these effects. Authors should avoid applying letter-spacing to cursive scripts unless they are prepared to accept non-interoperable results.

8.3. Line Start/End Padding: the line-padding property

Whereas letter-spacing adjusts spacing between typographic character units and does not apply at the start or end of a line, this property adjusts spacing only at the start/end of a line. The extra spacing is applied only by the innermost inline box at the start/end of the line box, and is inserted between that inline box’s content edge and the adjacent inline-level content (text or atomic inline). This extra space is not a justification opportunity.

p    { line-padding: 0.5em; line-height: 1; text-align: center }
span { background: black; color: white; }
em   { background: green; color: white; }

<p><span>Here is <em>some text</em></span>

Here is some
text

8.4. Automatic Contextual Spacing: the text-autospace property

Controls spacing between adjacent characters on the same line within the same inline formatting context using a set of character-class-based rules, allowing for automatic control over inter-script spacing and for spacing around punctuation.

Values are defined as follows:

<autospace> = no-autospace |
              [ ideograph-alpha || ideograph-numeric || punctuation ]
              || [ insert | replace ]

normal

Same behavior as ideograph-alpha ideograph-numeric.

no-autospace

No automatic space is inserted.

insert

The specified spacing is automatically inserted if there are no space characters of any kind (Unicode general category Z) already there.

If neither insert nor replace are specified, the behavior is the same as insert.

replace

The specified spacing is automatically inserted even if there is already a space (U+0020) at that point; additionally, the space (U+0020) is removed. Other types of space characters (Unicode general category Z) suppress automatic spacing, as for insert.

Note: This is for correcting text which is using the easy-to-type U+0020 instead of proper spacing.

ideograph-alpha

Creates extra spacing between runs of ideographs and non-ideographic letters, see § 8.4.1 Inter-script Spacing.

ideograph-numeric

Creates extra spacing between runs of ideographs and non-ideographic numerals, see § 8.4.1 Inter-script Spacing.

punctuation

Creates extra non-breaking spacing around punctuation as required by language-specific typographic conventions.

In this level, if the element’s content language is French, narrow no-break space (U+202F) and no-break space (U+00A0) is inserted where required by French typographic guidelines. Otherwise this value has no effect. However future specifications may add automatic spacing behavior for other languages.

auto

The user agent chooses a set of typographically high quality spacing values. Different user agents running on different platforms may pick different values.

Note: These spacing values may or may not match OS platform conventions.

This property is additive with the word-spacing and letter-spacing properties. That is, the amount of spacing contributed by the letter-spacing setting (if any) is added to the spacing created by text-autospace. The same applies to word-spacing.

At element boundaries, the amount of extra spacing introduced between characters is determined by and rendered within the innermost element that contains the boundary.

8.4.1. Inter-script Spacing

The ideograph-alpha and ideograph-numeric values introduce spacing at the boundary between particular classes of characters when they are directly adjoining on a line, i.e. without any intervening non-zero margin, border, or padding or intervening characters (such as a quotation mark or a space). The amount of space introduced by these keywords is 1/8 of the CJK advance measure, i.e 0.125ic.

Note: Spacing conventions vary, but values typically range from 1/4ic to as low as 1/8ic, with 1/4ic being more common in historical contexts due to metal type limitations and 1/6ic or thinner being more common in proportional typesetting. Because these spaces are inserted by default (through the initial value, normal), CSS uses 1/8ic in order to be conservative in its interference. A future level of this module may introduce control over the amount of spacing.

8.5. CJK Punctuation Spacing: the text-spacing-trim property

Controls spacing around CJK punctuation characters on the same line within the same inline formatting context using a set of character-class-based rules, allowing them to be set halfwidth or fullwidth based on their position and neighbors within the line.

Values are defined as follows:

<spacing-trim> = space-all | normal | space-first | trim-start | trim-both | trim-all

space-all

All fullwidth punctuation characters are set with full-width glyphs (spaced).

normal

Set fullwidth opening punctuation with full-width glyphs (spaced) at the start of each line; set fullwidth closing punctuation with half-width glyphs (flush) at the end of each line if it does not otherwise fit prior to justification, else set the punctuation with full-width glyphs; and collapse spacing between punctuation glyphs as described below.

trim-both

Set fullwidth opening punctuation with half-width glyphs (flush) at the start of each line; set fullwidth closing punctuation with half-width glyphs (flush) at the end of each line; and collapse spacing between punctuation glyphs as described below.

space-first

Set fullwidth opening punctuation with full-width glyphs (spaced) on the first line of the block container and each line after a forced line break. Otherwise as normal.

This value exists for compat requirements.

This value exists to manage formatting of some existing Chinese and Japanese content, for which trim-both would have been appropriate typographically, except that they are already written to expect the first line to be set as for space-all.

Specifically, due to the lack of reliable hanging-punctuation support across UAs, existing content (especially ePub content) uses U+3000 ideographic space in place of text-indent, but omits it when the paragraph begins with punctuation that is desired to hang in the indent in order to create the hanging punctuation effect. Using trim-both on the first line would thus trim away the effective indent in such content and thus obscure that line’s distinction as the first line of a new paragraph.

Note that this typesetting practice of using ideographic spaces for indentation (sometimes and not always) is contrary to the separation of content and style offered by HTML and CSS. Using hanging-punctuation and text-indent to control paragraph formatting rather than tweaking the text content of the document preserves the text’s true semantics in the document source and allows the style sheet designer to freely switch among the various spacing/indentation styles without needing to alter the content. See § 8.5.3 Japanese Paragraph-start Conventions in CSS for examples.

Additionally, the behavior at the end of lines is aligned with the normal and trim-start values rather than trim-both, in that it only trims the glyphs if they do not otherwise fit prior to justification. While improving the typography in fewer cases, it is closer to the legacy behavior of space-all which reduces compatibility concerns.

trim-start

Set fullwidth opening punctuation with half-width glyphs (flush) at the start of each line. Otherwise as normal.

trim-all

Set fullwidth opening punctuation, fullwidth closing punctuation, and fullwidth middle dot punctuation with half-width glyphs, without regards for the position within the line nor for adjacent characters.

auto

The user agent chooses a set of typographically high quality spacing values. Different user agents running on different platforms may pick different values.

Note: These spacing values may or may not match OS platform conventions.

Do we need auto? It would be weird for the author to choose platform-dependent behavior at the start of the first line, and it should otherwise use trim-both.

8.5.1. Fullwidth Punctuation Collapsing

Typically, fullwidth characters have glyphs with the same advance width as a standard Han character (e.g. 水 U+6C34). However, many fullwidth punctuation glyphs only take up part of the fullwidth design space. Thus such punctuation are not always set fullwidth. Several values of text-spacing-trim allow the author to control when such characters are set half-width (typically half the width of an ideograph) and when they are set full-width.

In order to set the text as specified, the UA will need to either

• trim (kern) the blank half of the glyphs, if they are given full-width and must be set half-width, or
• add space to the glyphs, if they are given half-width and must be set full-width.

The UA may use the OpenType halt and vhal features if implemented by a font in order to perform the requisite trimming of a particular glyph. The UA must not use the hwid feature or otherwise substitute halfwidth forms as switching to halfwidth glyphs can change the glyph shape which is not acceptable here.

Some fonts use proportional glyphs for fullwidth punctuation characters. If there is no support in the font for distinguishing fullwidth vs halfwidth glyph shapes (e.g. through font features), then for such proportional glyphs, the given advance width is considered simultaneously full-width and half-width: the UA must not add or remove space to these glyphs.

Note: The advance width of a standard Han character can be determined either from font metrics such as the OpenType ideo and idtp baselines for the opposite writing mode, or by taking the advance width of a Han character such as 水 U+6C34. (The opposite writing mode must be used because some fonts are compressed so that the characters are not square.) More information on OpenType metrics can be found in the OpenType spec. Note that if 水 U+6C34, 卜 U+535C, and 一 U+4E00 do not all have the same advance width, the font has proportional ideographs and the fullwidth advance width cannot be reliably determined by measuring glyphs.

Some fonts have fullwidth punctuation characters whose blank are too small to trim (kern.) UA may choose not to trim (kern) when the UA determined the trimming (kerning) may cause glyph cut-offs, collisions, or excessive kerning through glyph bounding box, glyph metrics, or font features.

If text-spacing-trim is trim-all, the UA must collapse the space typically associated with such full width glyphs regardless of the context in which they appear. Otherwise, unless text-spacing-trim is set to space-all (or the font has proportional fullwidth punctuation glyphs), the UA must collapse the space typically associated with such full width glyphs when placed adjacently on a line as follows:

• Set fullwidth opening punctuation half-width if the previous character is any of:

  • a fullwidth opening punctuation

  • a fullwidth middle dot punctuation

  • an ideographic space (U+3000)

  • a fullwidth closing punctuation of an equivalent or larger font-size

  • a character belonging to Unicode general category Ps

  Otherwise set it full-width.

• Set fullwidth closing punctuation half-width if the next character is any of:

  • a fullwidth closing punctuation

  • a fullwidth middle dot punctuation

  • an ideographic space (U+3000)

  • a fullwidth opening punctuation of a larger font-size

  • a character belonging to Unicode general category Pe

  Otherwise set it full-width.

8.5.2. Text Spacing Character Classes

In the context of this property the following definitions apply:

Classes and Unicode code points are under review, and at least some changes are needed to accommodate more recent additions to Unicode. [Issue #9503]

ideographs

Includes all typographic character units [CSS-TEXT-3] whose base character is listed below:

• All characters in the range of U+3041 to U+30FF, except those that belong to Unicode Punctuation [P*] general category.
• CJK Strokes (U+31C0 to U+31EF).
• Katakana Phonetic Extensions (U+31F0 to U+31FF).
• All characters that have the Han script property.

non-ideographic letters

Includes all typographic character units that belong to Unicode Letters [L*] and Mark [M*] general category, except when any of the following conditions are met:

• is defined as ideograph.
• is categorized as East Asian Fullwidth (F) by [UAX11].
• is upright in vertical text flow using the text-orientation property or the text-combine-upright property.

non-ideographic numerals

Includes all typographic character units that belong to the Unicode Decimal Digit Number [Nd] general category, except when any of the following conditions are met:

• is categorized as East Asian Fullwidth (F) by [UAX11].
• is upright in vertical text flow using the text-orientation property or the text-combine-upright property.

fullwidth opening punctuation

Includes any opening punctuation character (Unicode category Ps) that belongs to the CJK Symbols and Punctuation block (U+3000–U+303F) or is categorized as East Asian Fullwidth (F) by [UAX11]. Also includes LEFT SINGLE QUOTATION MARK (U+2018) and LEFT DOUBLE QUOTATION MARK (U+201C). When trimmed, the left (for horizontal text) or top (for vertical text) half is kerned.

fullwidth closing punctuation

Includes any closing punctuation character (Unicode category Pe) that belongs to the CJK Symbols and Punctuation block (U+3000–U+303F) or is categorized as East Asian Fullwidth (F) by [UAX11]. Also includes RIGHT SINGLE QUOTATION MARK (U+2019) and RIGHT DOUBLE QUOTATION MARK (U+201D). May also include fullwidth colon punctuation and/or fullwidth dot punctuation (see below). When trimmed, the right (for horizontal text) or bottom (for vertical text) half is kerned.

fullwidth middle dot punctuation

Includes MIDDLE DOT (U+00B7), HYPHENATION POINT (U+2027), and KATAKANA MIDDLE DOT (U+30FB). May also include fullwidth colon punctuation and/or fullwidth dot punctuation (see below).

fullwidth colon punctuation

Includes FULLWIDTH COLON (U+FF1A) and FULLWIDTH SEMICOLON (U+FF1B).

fullwidth dot punctuation

Includes IDEOGRAPHIC COMMA (U+3001), IDEOGRAPHIC FULL STOP (U+3002), FULLWIDTH COMMA (U+FF0C), FULLWIDTH FULL STOP (U+FF0E).

Whether fullwidth colon punctuation and fullwidth dot punctuation should be considered fullwidth closing punctuation or fullwidth middle dot punctuation depends on where in the glyph’s box the punctuation is drawn. If the punctuation is centered, then it should be considered middle dot punctuation. If the punctuation is drawn to one side (left in horizontal text, top in vertical text) and the other half is therefore blank then the punctuation should be considered closing punctuation and trimmed accordingly.

The UA must classify fullwidth colon punctuation and fullwidth dot punctuation under either the fullwidth closing punctuation category or the fullwidth middle dot punctuation category as appropriate. The UA may rely on language conventions and the writing mode (horizontal vs. vertical), and/or font information to determine this categorization. The UA may also add additional characters to any category as appropriate.

8.5.3. Japanese Paragraph-start Conventions in CSS

Japanese has three common start-edge typesetting schemes, which are distinguished by their handling of opening brackets.

Positioning of opening brackets at line head [JLREQ]

Assuming a UA style sheet of p { margin: 1em 0; }, CSS can achieve the Japanese typesetting styles with the following rules:

• Brackets flush with indent, flush with other lines (first scheme):

  p { /* Flush alignment */
    margin: 0;
    text-indent: 1em;
    text-spacing-trim: trim-both;
  }
  

• Brackets preserve fullwidth spacing on all lines (second scheme):

  p { /* Fullwidth alignment */
    margin: 0;
    text-indent: 1em;
    text-spacing-trim: space-all;
  }
  

• Brackets hang in indent, flush with other lines (third scheme):

  p { /* Hanging alignment */
    margin: 0;
    text-indent: 1em;
    text-spacing-trim: trim-both;
    hanging-punctuation: first;
  }
  

8.6. Character Class Spacing Shorthand: the text-spacing property

This property is a shorthand for setting text-spacing-trim and text-autospace in a single declaration. Values are defined as follows:

none

Turns off all text-spacing features: sets text-spacing-trim to space-all and text-autospace to no-autospace.

auto

Sets both text-spacing-trim and text-autospace to auto.

<spacing-trim>

Sets text-spacing-trim to the specified value. If no <autospace> value is given, text-autospace is set to its initial value.

<autospace>

Sets text-autospace to the specified value. If no <spacing-trim> value is given, text-spacing-trim is set to its initial value.

Note: As normal is the initial value of both text-spacing-trim and text-autospace, text-spacing: normal resets both to their initial values.

8.7. Shaping Across Element Boundaries

Text shaping must be broken at inline box boundaries when any of the following are true for any box whose boundary separates the two typographic character units:

• Any of margin/border/padding separating the two typographic character units in the inline axis is non-zero.
• vertical-align is not baseline.
• The boundary is a bidi isolation boundary.

Text shaping must not be broken across inline box boundaries when there is no effective change in formatting, or if the only formatting changes do not affect the glyphs (as in applying text decoration).

Text shaping should not be broken across inline box boundaries otherwise, if it is reasonable and possible for that case given the limitations of the font technology.

9. Edge Effects

Edge effects control the indentation of lines with respect to other lines in the block (text-indent) and how content is measured at the start and end edges of a line (hanging-punctuation).

9.1. First Line Indentation: the text-indent property

This property specifies the indentation applied to lines of inline content in a block. The indent is treated as a margin applied to the start edge of the line box.

Unless otherwise specified by the each-line and/or hanging keywords, only lines that are the first formatted line of an element are affected. [CSS-PSEUDO-4] For example, the first line of an anonymous block box is only affected if it is the first child of its parent element.

Values have the following meanings:

<length>

Gives the amount of the indent as an absolute length.

<percentage>

Gives the amount of the indent as a percentage of the block container’s own logical width.

Percentages must be treated as 0 for the purpose of calculating intrinsic size contributions, but are always resolved normally when performing layout.

Note: This can lead to the element overflowing. It is not recommended to use percentage indents and intrinsic sizing together.

each-line

Indentation affects the first line of each block container and each line after a forced line break (but not lines after a soft wrap break).

hanging

Inverts which lines are affected.

     Since CSS1 it has been possible to
indent the first line of a block element
5em by setting the 'text-indent' property 
to '5em'.

In CSS3 we can instead indent all other
     lines of the block element by 5em
     by setting the 'text-indent' property
     to 'hanging 5em'.

   For example, in the middle of
this paragraph is an equation,
which is centered:
             x + y = z
The first line after the equation
is flush (else it would look like
we started a new paragraph).

In a short line of text
There need be no wrapping,
But when we go on and on and on  
   and on,
Sometimes a soft break
Can help us stay on the page.

Note: Since the text-indent property inherits, when specified on a block element, it will affect descendant inline-block elements. For this reason, it is often wise to specify text-indent: 0 on elements that are specified display: inline-block.

9.2. Hanging Glyphs

When a glyph at the start or end edge of a line hangs, it is not considered when measuring the line’s contents for fit, alignment, or justification. Depending on the line’s alignment/justification, this can result in the mark being placed outside the line box. The hanging glyph is also not taken into account when computing intrinsic sizes (min-content size and max-content size), and any sizes derived thereof. (The interaction of this measurement and kerning is currently UA-defined; the CSSWG welcomes advice on this point.)

A hanging glyph is still enclosed inside its parent inline box and still participates in text justification: its character advance is just not measured when determining how much content fits on the line, how much the line’s contents need to be expanded or compressed for justification, or how to position the content within the line box for text alignment. Effectively, the hanging glyph character advance is re-interpreted as an additional negative margin on the affected edge of its parent inline box; the line is otherwise laid out as usual. An overflowing hanging glyph should typically be considered ink overflow so as to avoid creating unnecessary scrollbars, but the UA may treat it as scrollable overflow when the content is editable or in other circumstances where treating it as scrollable overflow would be useful to the user. [CSS-OVERFLOW-3]

In some cases, a glyph at the end of a line can conditionally hang: it hangs only if it does not otherwise fit in the line prior to justification. It is not considered when measuring the line’s contents for fit; however, any part of it that does not fit is considered to hang. Glyphs that conditionally hang are not taken into account when computing min-content sizes and any sizes derived thereof, but they are taken into account for max-content sizes and any sizes derived thereof.

Non-zero inline-axis borders or padding between a hangable glyph and the edge of the line prevent the glyph from hanging. For example, a period at the end of an inline box with end padding does not hang at the end edge of a line.

Multiple adjacent glyphs can hang together, however specific limits on how many are allowed to hang may be specified (e.g. at most one punctuation character may hang at each edge of the line).

9.2.1. Hanging Punctuation: the hanging-punctuation property

This property determines whether a punctuation mark, if one is present, hangs and may be placed outside the line box (or in the indent) at the start or at the end of a line of text.

Note: If there is not sufficient padding on the block container, hanging-punctuation can trigger overflow.

Values have the following meanings:

none

No punctuation character is made to hang.

first

An opening bracket, quote, or ideographic space at the start of the first formatted line of an element hangs. This applies to all characters in the Unicode categories Ps, Pf, Pi plus the ASCII quote marks U+0027 ' APOSTROPHE and U+0022 " QUOTATION MARK and the IDEOGRAPHIC SPACE U+3000.

last

A closing bracket or quote at the end of the last formatted line of an element hangs. This applies to all characters in the Unicode categories Pe, Pf, Pi plus the ASCII quote marks U+0027 ' APOSTROPHE and U+0022 " QUOTATION MARK.

force-end

A stop or comma at the end of a line hangs.

allow-end

A stop or comma at the end of a line conditionally hangs.

At most one punctuation character may hang at each edge of the line.

Stops and commas allowed to hang include:

The UA may include other characters as appropriate.

Note: The CSS Working Group would appreciate if UAs including other characters would inform the working group of such additions.

The allow-end and force-end are two variations of hanging punctuation used in East Asia.

p {
  text-align: justify;
  hanging-punctuation: allow-end;
}

p {
  text-align: justify;
  hanging-punctuation: force-end;
}

The punctuation at the end of the first line for allow-end does not hang, because it fits without hanging. However, if force-end is used, it is forced to hang. The justification measures the line without the hanging punctuation. Therefore when the line is expanded, the punctuation is pushed outside the line.

9.3. Bidirectionality and Line Boxes

The start and end sides of a line box are determined by the inline base direction of the line box. Although they usually match, the inline base direction of a line box is distinct from the inline base direction of the containing block or the bidi paragraph. The line box’s inline base direction affects text-align-all, text-align-last, text-indent, and hanging-punctuation—​i.e. the position and alignment of its contents with respect to its edges. It does not affect the formatting or ordering of inline content (which is controlled by the Unicode Bidirectional Algorithm as applied by CSS Writing Modes [UAX9] [CSS-WRITING-MODES-4]).

In most cases, a line box’s inline base direction is given by its containing block’s computed direction. However, if its containing block has unicode-bidi: plaintext [CSS-WRITING-MODES-4]:

• If the bidi paragraph to which the line box belongs (that is, the bidi paragraph for which the line box holds content) has strong directionality, the line box’s inline base direction is that direction.
• If the line box is empty (i.e. contains no atomic inlines or characters other than the newline character, if any) or otherwise has no strong directionality (contains only weak or neutral characters), its inline base direction is taken from the preceding line box (if any), or, if this is the first line box in the containing block, from the direction property of the containing block. (This can result in an RTL line box whose contents have an LTR base direction.)

<block style="unicode-bidi: plaintext">
français
فارسی
français
فارسی
français
فارسی
</block>

<para style="display: block; direction: rtl; unicode-bidi:plaintext">
“<quote style="unicode-bidi:plaintext">שלום!</quote>”, they said.
</para>

<textarea style="direction: rtl; unicode-bidi:plaintext">

Hello!

</textarea>

Appendix A: Text Processing Order of Operations

This appendix is normative.

The following list defines the order of text operations. (Implementations are not bound to this order as long as the resulting layout is the same.)

1. § 4.2 White Space Trimming: the white-space-trim property
2. white space processing part I (pre-wrapping)
3. § 2.2 Expanding Between Words: the word-space-transform property and text transformation
4. text combination [CSS-WRITING-MODES-4]
5. text orientation [CSS-WRITING-MODES-4]
6. text wrapping while applying per line:

   • indentation

   • bidirectional reordering [CSS2] / [CSS-WRITING-MODES-4]

   • white space processing part II

   • font/glyph selection and positioning [CSS-FONTS-3]

   • letter-spacing, word-spacing, text-spacing, and line-padding

   • hanging punctuation

7. justification (which may affect glyph selection and/or text wrapping, looping back into that step)
8. text alignment
9. text group alignment

Appendix B: Conversion to Plaintext

This appendix is normative for the purpose of plaintext copy-paste operations.

When a CSS-rendered document is converted to a plaintext format, it is expected that:

• The text-transform property has no effect.
• white-space-trim and § 4.3.1 Phase I: Collapsing and Transformation is applied and any sequence of collapsible white space at the beginning of a block or immediately following a forced line break is removed.

Appendix C: Default UA Stylesheet

This appendix is informative, and is to help UA developers to implement a default stylesheet for HTML, but UA developers are free to ignore or modify as appropriate.

/* make option elements align together */
option { text-align: match-parent; }

/* do not allow white space to collapse in textarea */
textarea { white-space-collapse: preserve !important; }

/* preserve character grid in preformatted text */
pre, code, kbd, samp, tt { text-spacing: none; }

/* Avoid hanging punctuation inheriting into preformatted blocks */
pre { hanging-punctuation: none; }

Appendix D: Scripts and Spacing

This appendix is normative.

Typographic behavior varies somewhat by language, but varies drastically by writing system. This appendix categorizes some common scripts in Unicode 6.0 according to their justification and spacing behavior. Category descriptions are descriptive, not prescriptive; the determining factor is the prioritization of justification opportunities.

block scripts

CJK and by extension all Wide characters (see East Asian Width [UAX11]). The following Unicode scripts are included: Bopomofo, Han, Hangul, Hiragana, Katakana, and Yi. Characters of the East Asian Width property Wide and Fullwidth are also included, but Ambiguous characters are included only if the writing system is Chinese, Korean, or Japanese.

clustered scripts

Clustered scripts have discrete units and break only at word boundaries, but do not use visible word separators. They prioritize stretching spaces, but comfortably admit inter-character spacing for justification. The clustered scripts include, but are not limited to, the following Unicode scripts: Khmer, Lao, Myanmar, New Tai Lue, Tai Le, Tai Tham, Tai Viet, Thai

cursive scripts

Cursive scripts do not admit gaps between their letters for either justification or letter-spacing. The following Unicode scripts are included: Arabic, Hanifi Rohingya, Mandaic, Mongolian, N’Ko, Phags Pa, Syriac

Note: Indic scripts with baseline connectors (such as Devanagari and Gujarati) are not considered cursive scripts, and do admit such gaps between typographic character units. See Indic Layout Requirements. [ILREQ]

User agents should update this list as they update their Unicode support to handle as-yet-unencoded cursive scripts in future versions of Unicode, and are encouraged to ask the CSSWG to update this spec accordingly.

Appendix E: Characters and Properties

This appendix is normative.

Unicode defines four code point-level properties that are referenced in CSS typesetting:

East Asian width property

Defined in Unicode Standard Annex #11 [UAX11] and given as the East_Asian_Width property in the Unicode Character Database [UAX44].

general category

Defined in Unicode Standard Annex #44 [UAX44] and given as the General_Category property in the Unicode Character Database [UAX44].

script property

Defined in Unicode Standard Annex #24 [UAX24] and given as the Script property in the Unicode Character Database [UAX44]. (UAs must include any ScriptExtensions.txt assignments in this mapping.)

Vertical Orientation

Defined in Unicode Standard Annex #50 [UAX50] as the Vertical_Orientation property in the Unicode Character Database [UAX44].

Unicode defines properties for individual code points, but sometimes it is necessary to determine the properties of a typographic character unit. For the purposes of CSS Text, the properties of a typographic character unit are given by the base character of its first grapheme cluster—​except in two cases:

• Grapheme clusters formed with an Enclosing Mark (Me) of the Common script are considered to be Other Symbols (So) in the Common script. They are assumed to have the same Unicode properties as the replacement character (U+FFFD).
• Grapheme clusters formed with a Space Separator (Zs) as the base are considered to be Modifier Symbols (Sk). They are assumed to have the same East Asian Width property as the base, but take their other properties from the first combining character in the sequence.

Appendix F: Identifying the Content Writing System

This appendix is normative.

While most languages have a preferred writing system, some have multiple, and most can also be transcribed into one or more foreign writing systems. As a common example, most languages have at least one Latin transcription, and can thus be written in the Latin writing system. Transcribed texts typically adopt the typographic conventions of the writing system: for example Japanese “romaji” and Chinese Pinyin use Latin letters and word spaces, and follow Latin line-breaking and justification practices accordingly. As another example, historical ideographic Korean (ko-Hani) does not use word spaces, and should therefore be typeset similar to Chinese rather than modern Korean.

In HTML or any other document language using BCP47 tags for identifying languages to declare the content language, authors can disambiguate or indicate the use of an atypical writing system with script subtags. [BCP47] For example, to indicate use of the Latin writing system for languages which don’t natively use it, the -Latn script subtag can be added, e.g. ja-Latn for Japanese romaji. Other subtags exist for other writing systems, see ISO’s Code for the Representation of Names of Scripts and the ISO15924 script tag registry. [ISO15924]

However, BCP47 script subtags are not typically used (and are in fact discouraged) for languages strongly associated with a single writing system: instead that writing system is expected to be implied when no other is specified. [BCP47] IANA maintains a database of various languages’ most common writing system via the Suppress-Script field in its language subtag registry for this purpose.

Note: More advice on language tagging can be found in the Internationalization Working Group’s “Language tags in HTML and XML” and “Choosing a Language Tag”.

When no writing system is explicitly indicated, UAs should assume the most common writing system of the declared content language for language-sensitive typographic behaviors such as line-breaking or justification. However, UAs must not assume that writing system if the author has explicitly declared a different one. If the UA has no language-specific knowledge of a particular language and writing system combination, it must use the typographic conventions of the declared writing system (assuming the conventions of a different language if necessary), not the conventions of the declared language in an assumed writing system, which would be inappropriate to the declared writing system.

The full correspondence between languages and their most common writing systems is out of scope for this document. However, user agents must assume at least the following:

• If the content language is Chinese and the writing system is unspecified, or for any content language if the writing system to specified to be one of the Hant, Hans, Hani, Hanb, or Bopo ISO script codes, then the writing system is Chinese.
• If the content language is Japanese and the writing system is unspecified, or for any content language if the writing system to specified to be one of the Jpan, Hrkt, Hira, or Kana ISO script codes, then the writing system is Japanese.
• If the content language is Korean and the writing system is unspecified, or for any content language if the writing system to specified to be one of the Kore, Hang, or Jamo ISO script codes, then the writing system is Korean.
• The writing system is only considered to be unknown if the content language itself is unknown, or if it explicitly indicates an unknown writing system.

  Note: Mere omission of the writing system information when the content language is declared means the that the writing system is implied, not unknown.

Appendix G: Small Kana Mappings

This appendix is normative.

Appendix H: Word and Phrase Detection

This appendix is normative.

A few operations in this specification depend on automated word boundary detection or phrase boundary detection.

Both operations are similar: the user agent performs linguistic analysis of the text to identify language-specific meaningful sequences of characters. They differ only targetting different units of text: either words or phrases.

While easily understood in a broad sense, both concepts of word and phrase are difficult to precisely define, especially in a way that works accross multiple languages. Nonetheless, in this context:

• A word is a recognizable semantic unit which may comprise one or more characters or syllables.

  Note: See What is a word? for some discussion of this concept.

• A phrase is a short grouping of one or several words standing together as a conceptual or grammatical unit, forming a component of a clause or sentence.

  Note: This is not to be confused with the French word phrase which means sentence rather than phrase in the English sense used here. In Japanese, this corresponds to the concept of 文節.

  A phrase could be a noun with its article and prepositions or postpositions, a phrasal verb, a compound verb tense…

The start and end position of each detected word or phrase is called a word boundary or phrase boundary. By themselves, word and phrase boundaries are not observable, but properties like word-space-transform or word-break can cause visible effects at those positions.

The specific algorithm to detect word or phrases and to place their boundaries is UA-dependent, and may take into account a variety of factors or approaches, such as dictionary-based lexical analysis, identification of punctuation or other delimiting characters, morphological analysis, machine learning methods…

The following constraints must nevertheless be respected:

• The user agent must not place a word or phrase boundary between characters that compose a single typographic character unit.
• The user agent must not place a word or phrase boundary adjacent to any characters with the line breaking class GL, WJ, or ZWJ; when two would-be words or phrases are separated by such characters, they must be treated as a single one. [UAX14]
• If a word or phrase is immediately followed by one or more of the following characters, the user agent must consider them to be part of the preceeding word or phrase:
  • word-separator characters
  • other space separators
  • U+200B ZERO WIDTH SPACE characters

• Punctuation is not a phrase by itself: it should to be attached to the relevant side of an adjacent linguistic word or phrase. For example, enclosing punctuation such as brackets and quotes are part of the phrase they enclose; commas and semicolons are suffixed to the preceding phrase; U+00BF INVERTED QUESTION MARK is attached to the subsequent word; etc.

  However, unconventional use of punctuation, such as smileys, kaomoji, or Perl snippets, may cause the user agent to need to deviate from this principle.

• Inline box boundaries and out-of-flow elements must be ignored when determining word or phrase boundaries. However, if a word or phrase boundary is found at the same position as one or more inline box boundaries, the word or phrase boundary must be inserted in the outermost element that participates in this inline box boundary.
  In the following example, the red “|” indicates reasonable positions for a user agent detecting word boundaries to place them:

  กรุงเทพ|คือ|สวยงาม

  If that sentence had contained some inline markup, the following example shows the correct position to place the word boundaries:

  กรุงเทพ|คือ|<em>สวยงาม</em>

  The following example shows incorrect positions:

  กรุงเทพ|คือ<em>|สวยงาม</em>

  The following shows the correct positions in a more contrived situation:

  กรุงเทพ|<b><u>คือ</u>|<em>สวยงาม</em></b>

Security Considerations

This specification introduces no new security considerations.

Privacy Considerations

This specification leaks the user’s installed hyphenation and line-breaking dictionaries.

Acknowledgements

This specification would not have been possible without the help from: Addison Phillips, Aharon Lanin, Alan Stearns, Ambrose Li, Arnold Schrijver, Arye Gittelman, Ayman Aldahleh, Ben Errez, Bert Bos, Chris Lilley, Chris Pratley, Chris Thrasher, Chris Wilson, Dave Hyatt, David Baron, Emilio Cobos Álvarez, Eric LeVine, Etan Wexler, Frank Tang, Håkon Wium Lie, IM Mincheol, Ian Hickson, James Clark, Javier Fernandez, John Daggett, Jonathan Kew, Ken Lunde, Laurie Anna Edlund, Marcin Sawicki, Martin Dürst, Martin Heijdra, Masafumi Yabe, Masayasu Ishikawa, Michael Jochimsen, Michel Suignard, Mike Bemford, Myles Maxfield, Nat McCully, Paul Nelson, Pierre-Anthony Lemieux, Rahul Sonnad, Randy Edmunds, Richard Ishida, Shinyu Murakami, Stephen Deach, Steve Zilles, Takao Suzuki, Tantek Çelik, Xidorn Quan, Yaniv Feinberg.

Changes

This draft is kept in sync with [CSS-TEXT-3], see CSS Text 3 §  Changes.
Changes specific to Level 4 are listed below.

Significant changes since the 19 February 2024 Working Draft include:

• Renamed the text-spacing-trim value trim-auto to trim-both. (Issue 10161)

• Loosened requirement about not changing lines for text-wrap-style: balance for cases with large numbers of lines. (Issue 10186)

• Define interraction between text-wrap-style: balance and line-clamp (Issue 9310)

• Add the math-auto value for text-transform. (Issue 5386)

Significant changes since the 20 October 2023 Working Draft include:

• Restored accidentally deleted “and each line after a forced line break” from definition of text-spacing-trim: space-first. (Issue 9532)

• Make normal the initial value of text-spacing-trim. (Issue 9511)

• Change the end-of-line behavior of space-first. (Issue 9736)

• space-first applies after line-breaks. (Issue 9532)

• Clarify details of fullwidth punctuation collapsing. (Issue 9225)

• Prevent pre from inheriting hanging-punctuation by default with a user-agent style rule. (Issue 9689)

Significant changes since the 29 March 2023 Working Draft include:

• Recast the text-wrap property as a shorthand of two new properties, text-wrap-mode and text-wrap-style, and making text-wrap-mode rather than text-wrap a longhand of the white-space property.

• Updated Appendix G: Small Kana Mappings to Unicode 15.0. (Issue 8442)

• Redesign of the word-break: auto-phrase word-break: manual features (from an earlier attempt as a standalone word-boundary-detection property), and add an auto-phrase value to word-space-transform (since it can no longer depend on word-boundary-detection). and update supporting related mechanics.

• Rename word-boundary-expansion to word-space-transform

• Add trim-all to text-spacing-trim. (Issue 8482)

• Non-tailorable Unicode line breaking controls other than NBSP take precedence over our rule about atomic inlines. (Issue 8972)

Significant changes since the 1 March 2023 Working Draft include:

• Completed the translation of white-space to multiple longhands by

  • adding break-spaces to white-space-collapse so that all shorthand values can be represented in the longhands (Issue 8256)

  • integrating all longhand keywords into the white-space shorthand

  • updating prose accordingly

• Renamed text-space-collapse and text-space-trim to white-space-collapse and white-space-trim. (Issue 8273)

Significant changes since the 31 December 2022 Working Draft include:

• Redesigned text-spacing by:

  • Removing non-useful keyword combinations (Issues 4246, 8288)

  • Making space-first the initial value (Issue 2462)

  • Splitting into longhands (Issues 4246, 7183, 8288)

  • Ensuring the ability to turn each feature “off”. (Issues 6950, 8288)

  • Add keywords to allow replacing incorrect space characters in the source. (Issues 318, 7183, 8263)

  • Allow hanging-punctuation to hang leading ideographic spaces to compensate for plaintext-derived source text practices. (Issue 2462)

  • Move no-compress to text-justify since it controls justification more than spacing. (Issue 7079)

• Extended contextual characters evaluated in text-spacing to include characters from the Pe and Ps categories. (Issue 6091)

• Renamed text-space-collapse back to white-space-collapse. (Issue 8273)

Significant changes since the 5 May 2022 Working Draft include:

• Added ruby value to text-justify. (Issue 771 Issue 779)
• Switched text-spacing: normal to use trim-end instead of allow-end. (Issue 7055)
• Switched text-spacing: normal to also apply ideograph-alpha and ideograph-numeric, updated UA default stylesheet to exclude these from monospace contexts, specified that non-zero margin/border/padding inhibits space insertion, and defined the amount of inserted space as 0.125ic. (Issue 6950)
• Defined text-align: match-parent to compute to start on the root element for simplicity of implementation. (Issue 6542)
• Allow distribute keyword to be a legacy value alias or to simply compute to inter-character; this allows UAs to do whichever is easier, since the distinction does not matter for backwards-compatibility. (Issue 7322)
• Renamed trim-inner value of white-space-trim to discard-inner for consistency with other values. (Issue 448)

Significant changes since the 2019 Working Draft include:

• Integrating the full text of [CSS-TEXT-3].
• Adding percentages to word-spacing and letter-spacing to represent sizes relative to the current font-size. (Issue 2165)
• Suggesting a UA rule to prevent spaces in textarea from collapsing. (Issue 6309)

Additions Since Level 3

New features in Level 4:

• word-break: auto-phrase, for automaticly determining phrases to keep together while line breaking

• word-space-transform, for transforming word separators

• breaking up of the white-space property into multiple longhands:

  • white-space-collapse and its preserve-spaces and discard values

  • white-space-trim, for trimming excess white space at the boundaries of an element

  • text-wrap-mode to control whether wrapping occurs or not

• text-wrap-style and its balance, stable, and pretty values

• wrap-before, wrap-after, and wrap-inside, to avoid or force wrapping (similar to the break-* properties for pagination)

• hyphenate-character, to explicitly control the hyphenation character

• hyphenate-limit-zone, hyphenate-limit-chars, hyphenate-limit-lines, hyphenate-limit-last, for better control over automatic hyphenation

• <string> values for text-align for aligning on, e.g., a decimal point

• text-group-align for group-aligning a set of line boxes whose contents are aligned by text-align

• line-padding for inserting spaces within the inline box at the start/end of lines

• text-spacing for automatic spacing around punctuation and script changes