W3C

CSS Text Level 4

Editor's Draft 3 February 2014

This version:
$Date: 2014/02/03 23:56:22 $ (CVS $Revision: 28aab46acf1a $)
Latest version:
http://www.w3.org/TR/css3-text
Latest editor's draft:
http://dev.w3.org/csswg/css3-text/
Previous version:
http://www.w3.org/TR/2011/WD-css3-text-20110901/
Feedback:
www-style@w3.org with subject line “[css-text] … message topic …” (archives)
Editors:
Elika J. Etemad (Mozilla)
Koji Ishii (Invited Expert)

Not Ready For Implementation

This spec is not yet ready for implementation. It exists in this repository to record the ideas and promote discussion.

Before attempting to implement this spec, please contact the CSSWG at www-style@w3.org.

Abstract

This CSS3 module defines properties for text manipulation and specifies their processing model. It covers line breaking, justification and alignment, white space handling, text decoration and text transformation.

Status of This Document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.

Publication as a Working Draft does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

This CSS module has been produced as a combined effort of the W3C Internationalization Activity, and the Style Activity and is maintained by the CSS Working Group. It also includes contributions made by participants in the XSL Working Group (members only).

This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

Feedback on this draft should be posted to the (archived) public mailing list www-style@w3.org (see instructions) with [css3-text] in the subject line. You are strongly encouraged to complain if you see something stupid in this draft. The editors will do their best to respond to all feedback.

If you have implemented properties from the May 2003 CSS3 Text CR please let us know so we can take that into account as we redraft the spec. You can post to www-style (public), post to the CSS WG mailing list (Member-restricted), or email fantasai directly (personal).

The following features are at risk and may be cut from the spec during its CR period if there are no (correct) implementations:

Table of Contents

1. Introduction

[document here]

This draft describes features that are specific to certain scripts. There is an ongoing discussion about where these features belong: in existing CSS properties, in new CSS properties, or perhaps in other specifications.

1.1. Module Interactions

This module replaces and extends the text-level features defined in [CSS21] chapter 16.

1.2. Values

This specification follows the CSS property definition conventions from [CSS21]. Value types not defined in this specification are defined in CSS Level 2 Revision 1 [CSS21]. Other CSS modules may expand the definitions of these value types: for example [CSS3COLOR], when combined with this module, expands the definition of the <color> value type as used in this specification.

In addition to the property-specific values listed in their definitions, all properties defined in this specification also accept the inherit keyword as their property value. For readability it has not been repeated explicitly.

1.3. Terminology

A grapheme cluster is what a language user considers to be a character or a basic unit of the script. The term is described in detail in the Unicode Technical Report: Text Boundaries [UAX29]. This specification uses the extended grapheme cluster definition in [UAX29] (not the legacy grapheme cluster definition). The UA may further tailor the definition as allowed by Unicode. Within this specification, the ambiguous term character is used as a friendlier synonym for grapheme cluster. See Characters and Properties for how to determine the Unicode properties of a character.

A letter for the purpose of this specification is a character belonging to one of the Letter or Number general categories in Unicode. [UAX44]

2. Transforming Text

2.1. Transforming Text: the ‘text-transform’ property

Name: text-transform
Value: none | [ [ capitalize | uppercase | lowercase ] || full-width || full-size-kana ]
Initial: none
Applies to: all elements
Inherited: yes
Percentages: N/A
Media: visual
Computed value: as specified

This property transforms text for styling purposes. Values have the following meanings:

none
No effects.
capitalize
Puts the first letter of each word in titlecase; other characters are unaffected.
uppercase
Puts all characters in uppercase.
lowercase
Puts all characters in lowercase.
full-width
Puts all characters in fullwidth form. If the character does not have a corresponding fullwidth form, it is left as is. This value is typically used to typeset Latin characters and digits like ideographic characters.
full-size-kana
Converts all small Kana characters to normal Kana. This value is typically used for ruby annotation text, where all small Kana should be drawn as large Kana.

The case mapping rules for the character repertoire specified by the Unicode Standard can be found on the Unicode Consortium Web site [UNICODE]. The UA must use the full case mappings for Unicode characters, including any conditional casing rules, as defined in Default Case Algorithm section. 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.

For example, in Turkish there are two “i”s, one with a dot—“İ” and “i”— and one without—“I” and “ı”. Thus the usual case mappings between “I” and “i” are replaced with a different set of mappings to their respective undotted/dotted counterparts, which do not exist in English. This mapping must only take effect if the language is known to be Turkish or Azeri; in other languages, the usual mapping of “I” and “i” is required. This rule is thus conditionally defined in Unicode's SpecialCasing.txt file.

The definition of "word" used for ‘capitalize’ is UA-dependent; [UAX29] is suggested (but not required) for determining such word boundaries. Authors should not expect ‘capitalize’ to follow language-specific titlecasing conventions (such as skipping articles in English).

The definition of fullwidth and halfwidth forms can be found on the Unicode consortium web site at [UAX11]. The mapping to fullwidth form is defined by taking code points with the <wide> or the <narrow> tag in their Decomposition_Mapping in [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 normal Kana are defined in Small Kana Mappings.

When multiple values are specified and therefore multiple transformations need to be applied, they are applied in the following order:

  1. capitalize’, ‘uppercase’, and ‘lowercase
  2. full-width
  3. full-size-kana

Text transformation happens after white space processing, which means that ‘full-width’ transforms only preserved U+0020 spaces to U+3000.

The following example converts the ASCII characters in abbreviations in Japanese to their fullwidth variants so that they lay out and line break like ideographs:

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

All-caps text sometimes has special typographic considerations. For example: Punctuation and number glyphs might be adjusted for the higher "center of gravity" (see the case feature in OpenType). Should we turn that on by default, as they suggest?

CSS may introduce the ability to create custom mapping tables for less common text transforms, such as by an ‘@text-transform’ rule similar to ‘@counter-style’ from [CSS3LIST], and this mechanism may be used to replace ‘full-size-kana’.

3. White Space Processing

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.

In the document source, segments can be delimited by carriage returns (U+000D), linefeeds (U+000A) or a combination (U+000D U+000A), or by some other mechanism, such as the SGML RECORD-START and RECORD-END tokens. If no segmentation rules are specified for the document language, each line feed (U+000A), carriage return (U+000D) and CRLF sequence (U+000D U+000A) in the text is considered a segment break. (This default rule also applies to generated content.) In CSS, each such segment break is treated as a single line feed character (U+000A).

White space processing in CSS interprets white space characters only for rendering: it has no effect on the underlying document data.

Note that the document parser may have not only normalized segment breaks, but also collapsed other space characters or otherwise processed 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.

Control characters (Unicode class Cc) other than tab (U+0009), line feed (U+000A), space (U+0020), and the bidi formatting characters (U+202x) should be rendered as invisible zero-width characters. UAs may instead treat them as visible characters. (Note, however, that this will usually result in them being rendered as missing glyphs.) What's the line-breaking behavior? Effects on joining? Can we just copy the behavior of some zero-width Unicode character?

3.1. White Space Collapsing: the ‘text-space-collapse’ property

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

Name: text-space-collapse
Value: collapse | discard | [ [preserve | preserve-breaks] && [ trim-inner || consume-before || consume-after ]
Initial: collapse
Applies to: all elements
Inherited: yes
Percentages: N/A
Media: visual
Computed value: specified value

Need a property name

This property declares whether and how white space inside the element 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. Line feeds are preserved as forced line breaks.
preserve-breaks
This value collapses white space as for ‘collapse’, but preserves line feeds as forced line breaks.
discard
This value directs user agents to "discard" all white space in the element.
trim-inner
For block containers this value directs UAs to discard all whitespace at the beginning of the element up to and including the last line feed 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 line feed 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.
consume-before
This value directs the UA to collapse all collapsible whitespace immediately before the start of the element.
consume-after
This value directs the UA to collapse all collapsible whitespace immediately after the end of the element.

The following style rules implement MathML's white space processing:

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

The following style rules render DT elements as a comma-separated list:

dt { display: inline; }
dt + dt:before { content: ", "; text-space-collapse: consume-before; }

It's been pointed out that ‘trim-inner’, ‘consume-before’, and ‘consume-after’ won't work well because ‘text-space-collapse’ is inherited, meaning that inserting a <span> or >div> would cause more white space to be removed than otherwise.

3.2. Tab Character Size: the ‘tab-size’ property

Name: tab-size
Value: <integer> | <length>
Initial: 8
Applies to: block containers
Inherited: yes
Percentages: N/A
Media: visual
Computed value: specified value

This property determines the measure of the tab character (U+0009) when rendered. Integers represent the measure in space characters (U+0020). Negative integers are not allowed.

3.3. The White Space Processing Rules

White space processing affects only spaces (U+0020), tabs (U+0009), and (post-normalization) line feeds (U+00A0).

For each inline (including anonymous inlines) within an inline formatting context, white space characters are handled as follows, ignoring bidi formatting characters as if they were not there:

Then, the entire block is rendered. Inlines are laid out, taking bidi reordering into account, and wrapping as specified by the ‘text-wrap’ property.

As each line is laid out,

  1. A sequence of collapsible spaces at the beginning of a line is removed.
  2. Each tab is rendered as a horizontal shift that lines up the start edge of the next glyph with the next tab stop. Tab stops occur at points that are multiples of the width of a space (U+0020) rendered in the block's font from the block's starting content edge. How many spaces is given by the ‘tab-size’ property.
  3. A sequence of collapsible spaces at the end of a line is removed.
  4. If spaces or tabs at the end of a line are non-collapsible but have ‘text-wrap’ set to ‘normal’ or ‘avoid’ the UA may visually collapse their character advance widths.

White space that was not removed during the white space processing steps is called preserved white space.

3.3.1. Example of bidirectionality with white space collapsing

Consider the following markup fragment, taking special note of spaces (with varied backgrounds and borders for emphasis and identification):

<ltr>A <rtl> B </rtl> C</ltr>

where the <ltr> element represents a left-to-right embedding and the <rtl> element represents a right-to-left embedding. If the ‘text-space-collapse’ property is set to ‘collapse’, the above processing model would result in the following:

This would leave two spaces, one after the A in the left-to-right embedding level, and one after the B in the right-to-left embedding level. This is then ordered according to the Unicode bidirectional algorithm, with the end result being:

A  BC

Note that there are two spaces between A and B, and none between B and C. This is best avoided by putting spaces outside the element instead of just inside the opening and closing tags and, where practical, by relying on implicit bidirectionality instead of explicit embedding levels.

3.3.2. Line Feed Transformation Rules

When line feeds are collapsible, they are either transformed into a space (U+0020) or removed depending on the context before and after the line break.

Note that the white space processing rules have already removed any tabs and spaces after the line feed before these checks take place.

Comments on how well this would work in practice would be very much appreciated, particularly from people who work with Thai and similar scripts.

3.3.3. Informative Summary of White Space Collapsing Effects

3.4. White Space and Text Wrapping Shorthand: the ‘white-space’ property

Name: white-space
Value: normal | pre | nowrap | pre-wrap | pre-line
Initial: not defined for shorthand properties
Applies to: all elements
Inherited: yes
Percentages: N/A
Media: visual
Computed value: see individual properties

The ‘white-space’ property is a shorthand for the ‘text-space-collapse’ and ‘text-wrap’ properties. Not all combinations are represented. Values have the following meanings:

normal
Sets ‘text-space-collapse’ to ‘collapse’ and ‘text-wrap’ to ‘normal
pre
Sets ‘text-space-collapse’ to ‘preserve’ and ‘text-wrap’ to ‘none
nowrap
Sets ‘text-space-collapse’ to ‘collapse’ and ‘text-wrap’ to ‘none
pre-wrap
Sets ‘text-space-collapse’ to ‘preserve’ and ‘text-wrap’ to ‘normal
pre-line
Sets ‘text-space-collapse’ to ‘preserve-breaks’ and ‘text-wrap’ to ‘normal

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

New Lines Spaces and Tabs Text Wrapping
normal Collapse Collapse Wrap
pre Preserve Preserve No wrap
nowrap Collapse Collapse No wrap
pre-wrap Preserve Preserve Wrap
pre-line Preserve Collapse Wrap

4. Line Breaking and Word Boundaries

In most writing systems, in the absence of hyphenation a line break occurs only at word boundaries. Many writing systems use spaces or punctuation to explicitly separate words, and line break 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 break points in such texts.

In several other writing systems, (including Chinese, Japanese, Yi, and sometimes also Korean) a line break opportunity is based on character boundaries, not word boundaries. In these systems a line can break anywhere except between certain character combinations. Additionally the level of strictness in these restrictions can vary with the typesetting style.

CSS does not fully define where line breaking opportunities occur, however some controls are provided to distinguish common variations.

Further information on line breaking conventions can be found in [JLREQ] and [JIS4051] for Japanese, [ZHMARK] for Chinese, and in [UAX14] for all scripts in Unicode.

Any guidance for appropriate references here would be much appreciated.

Information on line-breaking in the absence of dictionaries: for Thai

Floated and absolutely-positioned elements do not introduce a line breaking opportunity. The line breaking behavior of a replaced element is equivalent to that of a Latin character.

It is not clear whether this section handles Southeast Asian scripts well. Additionally, some guidance should be provided on how to break or not break Southeast Asian in the absence of a dictionary.

4.1. Line Breaking Strictness: the ‘line-break’ property

Name: line-break
Value: auto | loose | normal | strict
Initial: auto
Applies to: all elements
Inherited: yes
Percentages: N/A
Media: visual
Computed value: specified value

This property specifies the strictness of line-breaking rules applied within an element: particularly how line-breaking interacts with punctuation. 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.

CSS distinguishes between three levels of strictness in the rules for implicit line breaking. The precise set of rules in effect for each level is up to the UA and should follow language conventions. However, this specification does recommend that:

In CSS3 no distinction is made among the levels of strictness in non-CJK text: only CJK codepoints are affected, unless the text is marked as Chinese or Japanese, in which case some additional common codepoints are affected. However a future level of CSS may add behaviors affecting non-CJK text.

Support for this property is optional. It is recommended for UAs that wish to support CJK typography and strongly recommended for UAs in the Japanese market.

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.

4.2. Word Breaking Rules: the ‘word-break’ property

Name: word-break
Value: normal | keep-all | break-all
Initial: normal
Applies to: all elements
Inherited: yes
Percentages: N/A
Media: visual
Computed value: specified value

This property specifies line break opportunities within words. Values have the following meanings:

normal
Break lines according to their usual rules.
break-all
Lines may break between any two characters within words. Hyphenation is not applied. This option is used mostly in a context where the text is predominantly using CJK characters with few non-CJK excerpts and it is desired that the text be better distributed on each line.
keep-all
Lines may break only at word separators and other explicit break opportunities. Otherwise this option is equivalent to ‘normal’. This option is mostly used where the presence of word separator characters still creates line-breaking opportunities, as in Korean.

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.

5. Hyphenation

Hyphenation allows the controlled splitting of words to improve the layout of paragraphs. CSS3 Text does not define the exact rules for hyphenation, but defines six properties and an at-rule that influence hyphenation.

Whether hyphenation is applied can controlled with the ‘hyphens’ property.

The following author controls are not required to be supported for the UA to claim conformance to CSS Text Level 4:

Nonetheless, UAs are strongly encouraged to optimize their line-breaking implementation to choose good break points and appropriate hyphenation points.

These controls are optional because for a low-end implementation of hyphenation, they are not critical enough; and for a high-end implementation of paragraph breaking (such as in Teχ) they are not considered especially useful.

Hyphenation opportunities are not considered when calculating ‘min-content’ intrinsic sizes.

5.1. Hyphenation Control: the ‘hyphens’ property

Name: hyphens
Value: none | manual | auto
Initial: manual
Applies to: all elements
Inherited: yes
Percentages: N/A
Media: visual
Computed value: specified value

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

none
Words are not broken at line breaks, even if characters inside the word suggest line break points.
manual
Words are only broken at line breaks where there are characters inside the word that suggest line break opportunities. Characters can be explicit or conditional.

In Unicode, U+00AD is a conditional "soft hyphen" and U+2010 is an explicit 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 line break opportunity.

ex&shy;ample
auto
Words can be broken at appropriate hyphenation points either as determined by hyphenation characters inside the word or as determined automatically by a language-appropriate hyphenation resource. Conditional hyphenation characters inside a word, if present, take priority over automatic resources when determining hyphenation points within the word.

Correct automatic hyphenation requires a hyphenation resource appropriate to the language of the text being broken. The UA is therefore only required to automatically hyphenate text for which the author has declared a language (e.g. via HTML lang or XML xml:lang) and for which it has an appropriate hyphenation resource.

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.

5.2. Hyphens: the ‘hyphenate-character’ property

Name: hyphenate-character
Value: auto | <string>
Initial: auto
Applies to: all elements
Inherited: yes
Percentages: N/A
Media: visual
Computed value: specified value

This property specifies strings that are shown between parts of hyphenated words. The ‘auto’ value means that the user agent should find an appropriate value, preferably from the same source as the hyphenation dictionary. If a string is specified, it appears at the end of the line before a hyphenation break.

In Latin scripts, the hyphen character (U+2010) is often used to indicate that a word has been split. Normally, it will not be necessary to set it explicitly. However, this can easily be done:

article { hyphenate-character: "\2010" }

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

5.3. Hyphenation Size Limit: the ‘hyphenate-limit-zone’ property

Name: hyphenate-limit-zone
Value: <percentage> | <length>
Initial: 0
Applies to: block containers
Inherited: yes
Percentages: refers to width of the line box
Media: visual
Computed value: specified value

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.

5.4. Hyphenation Character Limits: the ‘hyphenate-limit-chars’ property

Name: hyphenate-limit-chars
Value: [auto | <integer>]{1,3}
Initial: auto
Applies to: all elements
Inherited: yes
Percentages: N/A
Media: visual
Computed value: specified value

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 class) and intra-word punctuation (Unicode classes 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.

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.

In the example below, the minimum size of a hyphenated word is left to the UA (which means it may vary depending on the language, the length of the line, or other factors), but the minimum number of characters before and after the hyphenation point is set to 3.

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

5.5. Hyphenation Line Limits: the ‘hyphenate-limit-lines’ and ‘hyphenate-limit-last’ properties

Name: hyphenate-limit-lines
Value: no-limit | <integer>
Initial: no-limit
Applies to: block containers
Inherited: yes
Percentages: N/A
Media: visual
Computed value: specified value

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.

Name: hyphenate-limit-last
Value: none | always | column | page | spread
Initial: none
Applies to: block containers
Inherited: yes
Percentages: N/A
Media: visual
Computed value: specified value

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 are:

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 }

A paragraph may be formatted like this when ‘hyphenate-limit-last: none’ is set:

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

With ‘hyphenate-limit-last: always’ one would get:

This is just a
simple example
to        show
Antarctica.
      

6. Text Wrapping

Text wrapping is controlled by the ‘text-wrap’ and ‘overflow-wrap’ properties:

6.1. Text Wrap Settings: the ‘text-wrap’ property

Name: text-wrap
Value: normal | none | avoid
Initial: normal
Applies to: all elements
Inherited: yes
Percentages: N/A
Media: visual
Computed value: specified value

This property specifies the mode for text wrapping. Possible values:

normal
Lines may break at allowed break points, as determined by the line-breaking rules in effect. Line breaking behavior defined for the WJ, ZW, and GL line-breaking classes in [UAX14] must be honored.
none
Lines may not break; text that does not fit within the block container overflows it.
avoid
Line breaking is suppressed within the element: the UA may only break within the element if there are no other valid break points in the line. If the text breaks, line-breaking restrictions are honored as for ‘normal’.

Regardless of the ‘text-wrap’ value, lines always break at forced breaks: for all values, line-breaking behavior defined for the BK, CR, LF, CM NL, and SG line breaking classes in [UAX14] must be honored.

When text-wrap is set to ‘normal’ or ‘avoid’, UAs that allow breaks at punctuation other than spaces should prioritize breakpoints. For example, if breaks after slashes have a lower priority than spaces, the sequence "check /etc" will never break between the ‘/’ and the ‘e’. The UA may use the width of the containing block, the text's language, and other factors in assigning priorities. As long as care is taken to avoid such awkward breaks, allowing breaks at appropriate punctuation other than spaces is recommended, as it results in more even-looking margins, particularly in narrow measures.

6.1.1. Example of using ‘text-wrap: avoid’ in presenting a footer

The priority of breakpoints can be set to reflect the intended grouping of text.

Given the rules

footer { text-wrap: avoid; /* inherits to all descendants */ }
      

and the following markup:

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

In a narrow window the footer could be broken as

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

or in a narrower window as

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

but not as

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

6.2. Emergency Wrapping: the ‘overflow-wrap’ property

Name: overflow-wrap
Value: normal | [ break-word || hyphenate ]
Initial: normal
Applies to: all elements
Inherited: yes
Percentages: N/A
Media: visual
Computed value: specified value

This property specifies whether the UA may break within a word to prevent overflow when an otherwise-unbreakable string is too long to fit within the line box. It only has an effect when ‘text-wrap’ is either ‘normal’ or ‘avoid’. 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’ and the various hyphenation limit properties may be ignored if there are no otherwise-acceptable break points in the line.
hyphenate
An unbreakable "word" may be hyphenated if there are no otherwise-acceptable break points in the line even if hyphenation is turned off or otherwise restricted. Hyphenation controls may influence where the word breaks, but cannot forbid the word from hyphenating to prevent overflow.
break-word
An unbreakable "word" 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 together stay as one unit. If specified together with ‘hyphenate’, valid hyphenation takes precedence over ‘break-word’ breaking.

Break opportunities not part of ‘overflow-wrap: normal’ line breaking are not considered when calculating ‘min-content’ intrinsic sizes.

For legacy reasons, UAs may also accept ‘word-wrap’ as an alternate name for the ‘overflow-wrap’ property. However this syntax not valid.

7. Alignment and Justification

7.1. Text Alignment: the ‘text-align’ property

Name: text-align
Value: start end | match-parent | <string>? [ start | end | left | right | center | justify ]
Initial: start
Applies to: block containers
Inherited: yes
Percentages: N/A
Media: visual
Computed value: specified value, except for ‘match-parent’ (see prose)

This property describes how inline contents of a block are horizontally aligned if the contents do not completely fill the line box. Values have the following meanings:

start
The inline contents are aligned to the start edge of the line box.
end
The inline contents are aligned to the end edge of the line box.
left
The inline contents are aligned to the left edge of the line box. In vertical text, ‘left’ aligns to the edge of the line box that would be the start edge for left-to-right text.
right
The inline contents are aligned to the right edge of the line box. In vertical text, ‘right’ aligns to the edge of the line box that would be the end edge for left-to-right text.
center
The inline contents are centered within the line box.
justify
The text is justified according to the method specified by the text-justify property.
<string>
The string must be a single character; otherwise the declaration 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.
match-parent
This value behaves the same as ‘inherit’ except that an inherited ‘start’ or ‘end’ keyword is calculated against its parent's ‘direction’ value and results in a computed value of either ‘left’ or ‘right’.
start end
Specifies ‘start’‘ alignment of the first line and any line immediately after a forced line break; and ’‘end’‘ alignment of any remaining lines not affected by ’text-align-last'.

A block of text is a stack of line boxes. In the case of ‘start’, ‘end’, ‘left’, ‘right’ and ‘center’, 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 in addition to shifting their positions. (See also ‘text-justify’, ‘letter-spacing’, and ‘word-spacing’.) If an element's white space is set to be 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 expansion 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.

7.1.1. 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.)

The following style sheet:
TD { text-align: "." center }
will cause the column of dollar figures in the following HTML table:
<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>

to align along the decimal point. The table might be rendered as follows:

+---------------------+
| Long distance calls |
+---------------------+
|        $11.30       |
|        $22.50       |
|         $0.80       |
|    $200567.01       |
|        $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:

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.

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.

7.2. Last Line Alignment: the ‘text-align-last’ property

Name: text-align-last
Value: auto | start | end | left | right | center | justify
Initial: auto
Applies to: block containers
Inherited: yes
Percentages: N/A
Media: visual
Computed value: specified value

This property describes how the last line of a block or a line right before a forced line break is aligned. If a line is also the first line of the block or the first line after a forced line break, then ‘text-align-last’ takes precedence over ‘text-alignexcept when two keywords are given for ‘text-align’ (i.e. when ‘text-align’ assigns an explicit first line alignment).

auto’ is equivalent to the value of the ‘text-align’ property except when ‘text-align’ is set to ‘justify’, in which case it is ‘justify’ when ‘text-justify’ is ‘distribute’ and ‘start’ otherwise. All other values have the same meanings as in ‘text-align’.

7.3. Justification Method: the ‘text-justify’ property

Name: text-justify
Value: auto | none | inter-word | inter-ideograph | inter-cluster | distribute | kashida
Initial: auto
Applies to: block containers and, optionally, inline elements
Inherited: yes
Percentages: N/A
Media: visual
Computed value: specified value

This property selects the justification method used when a line's alignment is set to ‘justify’ (see ‘text-align’), primarily by controlling which scripts' characters are adjusted together or separately. The property applies to block containers, but the UA may (but is not required to) also support it on inline elements. It takes the following values:

auto
The UA determines the justification algorithm to follow, based on a balance between performance and adequate presentation quality.

One possible algorithm is to determine the behavior based on the language of the paragraph: the UA can then choose appropriate value for the language, like ‘inter-ideograph’ for CJK, or ‘inter-word’ for English. Another possibility is to use a justification method that is a universal compromise for all scripts, e.g. the ‘inter-cluster’ method with block scripts raised to first priority.

none
Justification is disabled. This value is intended for use in user stylesheets to improve readability or for accessibility purposes.
inter-word
Justification primarily changes spacing at word separators. This value is typically used for languages that separate words using spaces, like English or Korean.
inter-ideograph
Justification primarily changes spacing at word separators and between characters in block scripts. This value is typically used for CJK languages.
inter-cluster
Justification primarily changes spacing at word separators and between characters in clustered scripts. This value is typically used for Southeast Asian scripts such as Thai.
distribute
Justification primarily changes spacing both at word separators and between characters in all scripts equally (except those in the connected and cursive categories). This value is sometimes used in e.g. Japanese.
kashida
Justification primarily stretches cursive scripts through the use of kashida or other calligraphic elongation. This value is optional for conformance to CSS3 Text. (UAs that do not support cursive elongation must treat the value as invalid.)

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 contents so that the contents exactly fill the line box. If the ‘letter-spacing’ and ‘word-spacing’ property values allow it, the user agent may also distribute negative space, putting more content on the line than would otherwise fit under normal spacing conditions. The exact justification algorithm is UA-dependent; however, CSS provides some general guidelines which should be followed when any justification method other than ‘auto’ is specified.

CSS defines expansion opportunities as points where the justification algorithm may alter spacing within the text. These expansion opportunities fall into priority levels as defined by the justification method. Within a line, expansion and compression should primarily target the first-priority expansion opportunities; lower priority expansion opportunities are adjusted at a lower priority as needed.

Expansion and compression limits are given by the letter-spacing and word-spacing properties. How any remaining space is distributed once all expansion opportunities reach their limits is up to the UA. 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’ if ‘text-justify’ is ‘distribute’ and as ‘start’ otherwise.)

The expansion opportunity priorities for values of ‘text-justify’ are given in the table below. Since justification behavior varies by writing system, expansion opportunities are organized by script categories. An expansion opportunity exists between two letters at a priority level when at least one of them belongs to a script category at that level and the other does not belong to a higher priority level. All scripts in the same priority level must be treated exactly the same. Word separators (spaces) and other symbols and punctuation are treated specially, see below.

Prioritization of Expansion Points
inter-wordinter-ideographdistributeinter-clusterkashidaauto
block 2 1 2 2 3 1*
clustered 2 2 1 1 3 1*
cursive 2 2 2 2 1 2*
discrete 2 2 1 2 3 2*
connected never never never never never never
spaces 1 1 1 1 2 1*
symbols 2 1 1 1 3 *

* The ‘auto’ column defined above is informative; it suggests a prioritization that presents a universal compromise among justification methods.

The spaces category represents expansion opportunities at word separators. (See word-spacing.) The UA may treat spaces differently than other expansion points in the same priority, but must not change their priority with respect to expansion points in other priority levels. For example, in Japanese ‘inter-ideograph’ justification (which treats CJK characters at a higher priority than Latin characters), word spaces traditionally have a higher priority than inter-CJK spacing, and the UA may split the 1st-priority level to implement that. However the UA is not allowed to drop spaces to the same priority as Latin characters.

The symbols category represents the expansion opportunities existing at or between any pair of characters from the Unicode Symbols (S*) and Punctuation (P*) classes and at enabled autospace points. The default justification priority of these points is given above. However, there may be additional rules controlling their justification behavior due to typographic tradition. Therefore, the UA may reassign specific characters or introduce additional levels of prioritization to handle expansion opportunities involving symbols and punctuation. For example, there are traditionally no expansion opportunities between consecutive EM DASH U+2014, HORIZONTAL BAR U+2015, HORIZONTAL ELLIPSIS U+2026, or TWO DOT LEADER U+2025 characters [JLREQ]; thus a UA might assign these characters to the "never" prioritization level. As another example, certain fullwidth punctuation characters are considered to contain an expansion opportunity (see ‘text-spacing’). The UA might therefore assign these characters to a higher prioritization level than the opportunities between ideographic characters.

For justification of cursive scripts, words may be expanded through kashida elongation or other cursive expansion processes. Kashida may be applied in discrete units or continuously, and the prioritization of kashida points is UA-dependent: for example, the UA may apply more at the end of the line. The UA should not apply kashida to fonts for which it is inappropriate. It may instead rely on other justification methods that lengthen or shorten Arabic segments (e.g. by substituting in swash forms or optional ligatures). Because elongation rules depend on the typeface style, the UA should rely on on the font whenever possible rather than inserting kashida based on a font-independent style rule. The UA should limit elongation so that, e.g. in multi-script lines a short stretch of Arabic will not be forced to soak up too much of the extra space by itself. If the UA does not support cursive elongation, then, as with connected scripts, no expansion points exist between characters of these scripts.

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.

Add example of using ‘text-justify’ with the TeX algorithm.

3.8 Line Adjustment in [JLREQ] gives an example of a set of rules for how a text formatter can justify Japanese text. It describes rules for cases where the ‘text-justify’ property is ‘inter-ideograph’ and the ‘text-spacing’ property does not specify ‘no-compress’.

It produces an effect similar to cases where the computed value of ‘text-spacing’ property does not specify ‘trim-end’ or ‘space-end’. If the UA wants to prohibit this behavior, rule b. of 3.8.3 should be omitted.

Note that the rules described in the document specifically target Japanese. Therefore they may produce non-optimal results when used to justify other languages such as English. To make the rules more applicable to other scripts, the UA could, for instance, omit the rule to compress half-width spaces (rule a. of 3.8.3).

8. Spacing

The <spacing-limit> value type, which is to represent an optimum, minimum, and maximum for ‘word-spacing’ and ‘letter-spacing’, is defined as

<spacing-limit> = [ normal | <length> | <percentage>]{1,3}

  

If three values are specified, they represent the optimum, minimum, and maximum respectively. If only two values are specified, then the first represents both the optimum and the minimum, and the second represents the maximum. If just one value is specified, then it represents the optimum, minimum, and maximum. The values are interpreted as defined below:

normal
Specifies the normal optimum/minimum/maximum spacing, as defined by the current font and/or the user agent. Normal minimum and maximum spacing must be defined relative to the optimum spacing so that the minimum and maximum limits increase and decrease with changes to the optimum spacing. These limits may also vary according to some measure of the amount of text on a line (e.g. block width divided by font size), as larger measures can accommodate tighter spacing constraints. Normal optimum/minimum/maximum spacing may also vary based on the value of the text-justify property, the element's language, and other factors. Normal spacing between a pair of connected or cursive characters is always zero.
<length>
Specifies extra spacing in addition to the normal spacing. Values may be negative, but there may be implementation-dependent limits.
<percentage>
Specifies the spacing as a percentage of the affected character. Only valid on ‘word-spacing’. Negative values are not allowed.

In the absence of justification the optimum spacing must be used. The text justification process may alter the spacing from its optimum (see the text-justify property, above) but must not violate the minimum spacing limit and should also avoid exceeding the maximum.

If the minimum is more than the maxmimum, then the used maximum is set to the minimum. Likewise for the optimum. If the maximum is less than the optimum, then the used optimum is set to the used maximum.

8.1. Word Spacing: the ‘word-spacing’ property

Name: word-spacing
Value: <spacing-limit>
Initial: normal
Applies to: all elements
Inherited: yes
Percentages: refers to width of the affected glyph
Media: visual
Computed value: as specified, except with <length> values computed to absolute lengths

This property specifies the minimum, maximum, and optimal spacing between “words”, as follows:

Spacing is applied to each word-separator character left in the text after the white space processing rules have been applied, and should be applied half on each side of the character. Word-separator characters include 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 Tibetan tsek (U+0F0B, U+0F0C). If there are no word-separator characters, or if the word-separating character has a zero advance width (such as the zero width space U+200B) then the user agent must not create an additional spacing between words. General punctuation and fixed-width spaces (such as U+3000 and U+2000 through U+200A) are not considered word-separator characters.

The following example will make all the spaces between words in Arabic be rendered as zero-width, and double the width of each space in English:

:lang(ar) { word-spacing:   0%; }
:lang(en) { word-spacing: 200%; }

The following example will add half the the width of the “0” glyph to word spacing character [CSS3VAL]:

p { word-spacing: 0.5ch; }

8.2. Tracking: the ‘letter-spacing’ property

Name: letter-spacing
Value: <spacing-limit>
Initial: normal
Applies to: all elements
Inherited: yes
Percentages: N/A
Media: visual
Computed value: as specified, except with <length> values computed to absolute lengths

This property specifies the minimum, maximum, and optimal spacing between characters. Letter-spacing is applied in addition to any word-spacing. ‘normal’ optimum letter-spacing is typically zero.

Letter-spacing must not be applied at the beginning or at the end of a line. At element boundaries, the letter spacing is given by and rendered within the innermost element that contains the boundary.

For the purpose of letter-spacing, each atomic inline (such as an image or inline block) is treated as a single character.

For example, given the markup

<P>a<LS>b<Z>cd</Z><Y>ef</Y></LS>g</P>

and the style sheet

LS { letter-spacing: 1em; }
Z { letter-spacing: 0.3em; }
Y { letter-spacing: 0.4em; }

the spacing would be

a[0]b[1em]c[0.3em]d[1em]e[0.4em]f[0]g

UAs may apply letter-spacing to cursive scripts. In this case, UAs should extend the space between disjoint characters as specified above and extend the visible connection between cursively connected characters by the same amount (rather than leaving a gap). The UA may use glyph substitution or other font capabilities to spread out the letters. If the UA cannot expand a cursive script without breaking the cursive connections, it should not apply letter-spacing between characters of that script at all.

When the resulting space between two characters is not the same as the default space, user agents should not use optional ligatures.

8.3. Character Class Spacing: the ‘text-spacing’ property

Name: text-spacing
Value: normal | none | [ trim-start | space-start ] || [ trim-end | space-end | allow-end ] || [ trim-adjacent | space-adjacent ] || no-compress || ideograph-alpha || ideograph-numeric || punctuation
Initial: normal
Applies to: block containers
Inherited: yes
Percentages: N/A
Media: visual
Computed value: specified value

This property controls spacing between adjacent characters on the same line within the same inline formatting context using a set of character-class-based rules. Such spacing can either be created between or trimmed from the affected glyphs. Values are defined as follows:

normal
Specifies the baseline behavior, equivalent to ‘space-start allow-end trim-adjacent’.
none
Turns off all text-spacing features. All fullwidth characters are set with full-width glyphs.
ideograph-alpha
Creates 1/4em extra spacing between runs of ideographs and non-ideographic letters. A commonly used algorithm for determining this behavior is specified in [JLREQ]
ideograph-numeric
Creates 1/4em extra spacing between runs of ideographs and non-ideographic numerals glyphs. A commonly used algorithm for determining this behavior is specified in [JLREQ]
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 be inserted where required by French typographic guidelines. Otherwise this value has no effect. However future specifications may add automatic spacing behavior for other languages.
space-start
Set fullwidth opening punctuation with full-width glyphs (spaced) at the start of each line.
trim-start
Set fullwidth opening punctuation with half-width glyphs (flush) at the start of each line.
allow-end
Set fullwidth closing punctuation with half-width glyphs (flush) at the end of each line if it does not otherwise fit prior to justification, otherwise sets the punctuation with full-width glyphs.
space-end
Set fullwidth opening punctuation with full-width glyphs (spaced) at the start of each line.
trim-end
Set fullwidth closing punctuation with half-width glyphs (flush) at the end of each line.
space-adjacent
Set fullwidth opening punctuation with full-width glyphs (spaced) when not at the start of the line. Set fullwidth closing punctuation with full-width glyphs (spaced) when not at the end of the line.
trim-adjacent
Collapse spacing between punctuation glyphs as described below.
no-compress
Justification may not compress text-spacing. (If this value is not specified, the justification process may reduce autospacing except when the spacing is at the start or end of the line.) An example of compression rules is given for Japanese in 3.8 Line Adjustment in [JLREQ].

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-spacing’. 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. If the extra spacing is applied to a particular glyph, then the spacing is determined by the innermost element containing that glyph.

Values other than ‘normal’, ‘none’, ‘trim-start’, ‘trim-end’, and ‘space-end’ are at-risk and may be dropped from this level of CSS. They are defined here currently to help work out a complete design of this feature.

Support for this property is optional. It is strongly recommended for UAs that wish to support CJK typography.

It was requested to add a value for doubling the space after periods.

8.3.1. 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’ 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 may need to either

Some fonts use proportional glyphs for fullwidth punctuation characters. For such proportional glyphs, the given advance width is considered simultaneously full-width and half-width: no space is added or removed.

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.

Unless ‘text-spacing’ is set to ‘space-adjacent’ or ‘none’ (or the font has proportional fullwidth punctuation glyphs), the UA must collapse the space typically associated with such full width glyphs as follows:

The following example table lists the punctuation pairs affected by adjancent-pairs trimming. It uses halfwidth equivalents to approximate the trimming effect.

Demonstration of adjacent-pairs punctuation trimming
Combination Sample Pair Looks Like
Opening—Opening + (
Middle Dot—Opening + (
Closing—Opening + )  (
Ideographic Space—Opening  +  (
Closing—Closing + )
Closing—Middle Dot + )
Closing—Ideographic Space +  ) 

8.3.2. Text Spacing Character Classes

In the context of this property the following definitions apply:

classes and Unicode code point should be reviewed.

Ideographs
Includes all characters listed below:
Non-ideographic letters
Includes all characters that belongs to Unicode Letters [L*] and Mark [M*] category, except any of the following conditions are met:
Non-ideographic numerals
Includes all characters that belongs to Unicode Number, Decimal Digit [Nd] category, except any of the following conditions are met:
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.

The following informative table summarizes language conventions for classifying fullwidth colon and dot punctuation:

colon punctuation dot punctuation
Simplified Chinese (horizontal) closing closing
Simplified Chinese (vertical) closing closing
Traditional Chinese middle dot middle dot
Korean middle dot closing
Japanese middle dot closing

Note, that for Chinese fonts at least, the author observes that the standard convention is often not followed.

9. Edge Effects

Edge effects control the indentation of lines with respect to other lines in the block (‘text-indent’) and how content is aligned to the start and end edges of a line (‘hanging-punctuation’, see also ‘text-spacing’).

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

The first scheme aligns opening brackets flush with the indent              edge on the first line and with the start edge of other lines.              The second scheme gives the opening bracket its full width, so              that it is effectively indented half an em from the indent edge              and from the start edge of other lines.              The third scheme aligns the opening brackets flush with the              start edge of lines, but hangs them inside the indent on the              first line (resulting in an effective half-em indent instead              of the full em for paragraphs that begin with an opening bracket).

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:

9.1. First Line Indentation: the ‘text-indent’ property

Name: text-indent
Value: [ <length> | <percentage> ] && [ hanging || each-line ]?
Initial: 0
Applies to: block containers
Inherited: yes
Percentages: refers to width of containing block
Media: visual
Computed value: the percentage as specified or the absolute length

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 via the ‘each-line’ and/or ‘hanging’ keywords, only lines that are the first formatted line of an element are affected. 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 containing block's logical width.
each-line
Indentation affects the first line of the block container as well as each line after a forced line break, but does not affect lines after a text wrap break.
hanging
Inverts which lines are affected.

If ‘text-align’ is ‘start’ and ‘text-indent’ is ‘5em’ in left-to-right text with no floats present, then first line of text will start 5em into the block:

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

Note that 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 Punctuation: the ‘hanging-punctuation’ property

Name: hanging-punctuation
Value: none | [ first || [ force-end | allow-end ] || last ]
Initial: none
Applies to: inline elements
Inherited: yes
Percentages: N/A
Media: visual
Computed value: as specified

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

Note that if there is not sufficient padding on the block container, hanging punctuation can trigger overflow.

Values have the following meanings:

none
No characters can hang.
first
An opening bracket or quote at the start of the first formatted line of an element hangs. This applies to all characters in the Unicode categories Ps, Pf, Pi.
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.
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 hangs if it does not otherwise fit prior to justification.

When a punctuation mark hangs, it is not considered when measuring the line's contents for fit, alignment, or justification. Depending on the line's alignment, this can push the mark outside the line box. At most one punctuation character may hang outside each edge of the line.

A hanging punctuation mark is still enclosed inside its inline box and participates in text justification: its character advance width 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.

Non-zero start and end borders or padding on an inline box are not allowed to hang. This can prevent a hangable punctuation mark from hanging: for example, a period at the end of an inline box with end padding cannot hang outside the end edge of a line.

Stops and commas allowed to hang include:

U+002C , COMMA
U+002E . FULL STOP
U+060C ، ARABIC COMMA
U+06D4 ۔ ARABIC FULL STOP
U+3001 IDEOGRAPHIC COMMA
U+3002 IDEOGRAPHIC FULL STOP
U+FF0C FULLWIDTH COMMA
U+FF0E FULLWIDTH FULL STOP
U+FE50 SMALL COMMA
U+FE51 SMALL IDEOGRAPHIC COMMA
U+FE52 SMALL FULL STOP
U+FF61 HALFWIDTH IDEOGRAPHIC FULL STOP
U+FF64 HALFWIDTH IDEOGRAPHIC COMMA

The UA may include other characters as appropriate. Should other characters be included?

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

Support for this property is optional. It is recommended for UAs that wish to support CJK typography, particularly those in the Japanese market.

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

hanging-punctuation: allow-end
p {
   hanging-punctuation: allow-end;
}
hanging-punctuation: force-end
p {
   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 the line is expanded.

10. Text Decoration

10.1. Line Decoration: Underline, Overline, and Strike-Through

The following properties describe line decorations that are added to the content of an element. When specified on or propagated to an inline box, such decoration affects all the boxes generated by that element, and is further propagated to any in-flow block-level boxes that split the inline (see CSS2.1 section 9.2.1.1) When specified on or propagated to a ruby box, the decorations are further propagated only to the ruby base. When specified on or propagated to a a block container that establishes an inline formatting context, the decorations are propagated to an anonymous inline element that wraps all the in-flow inline-level children of the block container. For all other elements, the decorations are propagated to any in-flow children.

Note that text decorations are not propagated to any out-of-flow descendants, nor to the contents of atomic inline-level descendants such as inline blocks and inline tables.

By default underlines, overlines, and line-throughs are applied only to text (including white space, letter spacing, and word spacing): margins, borders, and padding are skipped. Elements containing no text, such as images, are likewise not decorated. The ‘text-decoration-skip’ property can be used to modify this behavior, for example allowing inline replaced elements to be underlined or requiring that white space be skipped.

In determining the position and thickness of text decoration lines, user agents may consider the font sizes and dominant baselines of descendants, but for a given element's decoration must use the same position and thickness throughout each line box. The color and line style of decorations must remain the same on all decorations applied by a given element, even if descendant elements have different color or line style values.

One use case we would like to support is to change color and/or style of descendants while keeping the same position and thickness.

The following figure shows the averaging for underline:

In the first rendering of the underlined text '1st a'                    with 'st' as a superscript, both the '1st' and the 'a'                    are rendered in a small font. In the second rendering,                    the 'a' is rendered in a larger font. In the third, both                    '1st' and 'a' are large.

In the three fragments of underlined text, the underline is drawn consecutively lower and thicker as the ratio of large text to small text increases.

Relatively positioning a descendant moves all text decorations affecting it along with the descendant's text; it does not affect calculation of the decoration's initial position on that line. The ‘visibility’ property, filters, and other graphical transformations likewise affect text decorations as part of the text they're drawn on, even if the decorations were specified on an ancestor element. Does this include ‘text-shadow’? What about text-fill etc.?

In the following style sheet and document fragment:


   blockquote { text-decoration: underline; color: blue; }
   em { display: block; }
   cite { color: fuchsia; }

   <blockquote>
    <p>
     <span>
      Help, help!
      <em> I am under a hat! </em>

      <cite> —GwieF </cite>
     </span>
    </p>
   </blockquote>

...the underlining for the blockquote element is propagated to an anonymous inline element that surrounds the span element, causing the text "Help, help!" to be blue, with the blue underlining from the anonymous inline underneath it, the color being taken from the blockquote element. The <em>text</em> in the em block is also underlined, as it is in an in-flow block to which the underline is propagated. The final line of text is fuchsia, but the underline underneath it is still the blue underline from the anonymous inline element.

Sample rendering of the above underline example

This diagram shows the boxes involved in the example above. The rounded aqua line represents the anonymous inline element wrapping the inline contents of the paragraph element, the rounded blue line represents the span element, and the orange lines represent the blocks.

10.1.1. Text Decoration Lines: the ‘text-decoration-line’ property

Name: text-decoration-line
Value: none | [ underline | no-underline | replace-underline ] || [ overline | no-overline | replace-overline ] || [ line-through | no-line-through | replace-line-through ] | remove-all
Initial: none
Applies to: all elements
Inherited: no (but see prose)
Percentages: N/A
Media: visual
Computed value: as specified

Specifies what line decorations, if any, are added to the element. Values have the following meanings:

none
Neither produces nor inhibits text decoration.
underline
Each line of text is underlined.
no-underline
Inhibits propagated underlines.
replace-underline
Inhibits propagated underlines and produces an underline.
overline
Each line of text has a line above it (i.e. on the opposite side from an underline).
no-overline
Inhibits propagated overlines.
replace-overline
Inhibits propagated overlines and produces an overline.
line-through
Each line of text has a line through the middle.
no-line-through
Inhibits propagated line-throughs.
replace-line-through
Inhibits propagated line-throughs and produces an line-through.
remove-all
Inhibits all propagated text decorations.

10.1.2. Text Decoration Color: the ‘text-decoration-color’ property

Name: text-decoration-color
Value: <color>
Initial: currentColor
Applies to: all elements
Inherited: no
Percentages: N/A
Media: visual
Computed value: the computed color

This property specifies the color of text decoration (underlines overlines, and line-throughs) set on the element with ‘text-decoration-line’.

10.1.3. Text Decoration Style: the ‘text-decoration-style’ property

Name: text-decoration-style
Value: solid | double | dotted | dashed | wavy
Initial: solid
Applies to: all elements
Inherited: no
Percentages: N/A
Media: visual
Computed value: as specified

This property specifies the style of the line(s) drawn for text decoration specified on the element. Values have the same meaning as for the border-style properties [CSS3BG]. ‘wavy’ indicates a wavy line.

10.1.4. Text Decoration Shorthand: the ‘text-decoration’ property

Name: text-decoration
Value: <text-decoration-line> || <text-decoration-style> || <text-decoration-color> || blink
Initial: none
Applies to: all elements
Inherited: no
Percentages: N/A
Media: visual
Computed value: as specified

This property is a shorthand for setting ‘text-decoration-line’, ‘text-decoration-color’, and ‘text-decoration-style’ in one declaration. Omitted values are set to their initial values. A ‘text-decoration’ declaration that omits both the ‘text-decoration-color’ and ‘text-decoration-style’ values is backwards-compatible with CSS Levels 1 and 2.

If the ‘blink’ keyword is specified the text blinks (alternates between visible and invisible). Conforming user agents may simply not blink the text. Note that not blinking the text is one technique to satisfy checkpoint 3.3 of WAI-UAAG.

The following example underlines unvisited links with a solid blue underline in CSS1 and CSS2 UAs and a navy dotted underline in CSS3 UAs.


:link {
    color: blue;
    text-decoration: underline;
    text-decoration: navy dotted underline; /* Ignored in CSS1/CSS2 UAs */
}

10.1.5. Text Decoration Line Continuity: the ‘text-decoration-skip’ property

Name: text-decoration-skip
Value: none | [ objects || spaces || ink || edges ]
Initial: objects
Applies to: all elements
Inherited: yes
Percentages: N/A
Media: visual
Computed value: as specified

This property specifies what parts of the element's content any text decoration affecting the element must skip over. It controls all text decoration lines drawn by the element and also any text decoration lines drawn by its ancestors. Values have the following meanings:

none
Skip nothing: text-decoration is drawn for all text content and for inline replaced elements.
objects
Skip this element if it is an atomic inline (such as an image or inline-block).
spaces
Skip white space: this includes regular spaces (U+0020) and tabs (U+0009), as well as nbsp (U+00A0), ideographic space (U+3000), all fixed width spaces (such as U+2000–U+200A, U+202F and U+205F), and any adjacent letter-spacing or word-spacing.
ink
Skip over where glyphs are drawn: interrupt the decoration line to let text show through where the text decoration would otherwise cross over a glyph. The UA may also skip a small distance to either side of the glyph outline.
edges
The UA should place the start and end of the line inwards from the content edge of the decorating element so that, e.g. two underlined elements side-by-side do not appear to have a single underline. (This is important in Chinese, where underlining is a form of punctuation.)

Do we need a value that doesn't skip margins and padding?

Note that this property inherits and that descendant elements can have a different setting.

10.1.6. Text Underline Position: the ‘text-underline-position’ property

Name: text-underline-position
Value: auto | alphabetic | below left | below right
Initial: auto
Applies to: all elements
Inherited: yes
Percentages: N/A
Media: visual
Computed value: as specified

This property sets the position of an underline specified on the same element: it does not affect underlines specified by ancestor elements. Values have the following meanings:

auto
The user agent may use any algorithm to determine the underline's position.

It is suggested that the underline position be ‘alphabetic’ unless it crosses either subscripted (or otherwise lowered) text, or it affects characters from Asian scripts such as Han or Tibetan, for which an alphabetic underline is too high: in such cases, aligning to the em box edge as described for ‘below left’ is more appropriate.

alphabetic
The underline is positioned relative to the alphabetic baseline. In this case the underline is likely to cross some descenders.
below left
The underline is positioned relative to the under edge of the element's content box. In this case the underline usually does not cross the descenders. (This is sometimes called "accounting" underline.) If the underline affects descendants with a lower content edge, the user agent should shift the underline down further to the lowest underlined content box edge. The user agent may ignore elements with ‘vertical-align’ values given as lengths, percentages, ‘top’, or ‘bottom’ when making this adjustment. (Note that images that are not affected by the underline per ‘text-decoration-skip’ will not affect the position of the underline.)
below right
In horizontal typographic mode, this value is equivalent to ‘below left’. In vertical typographic mode, the underline is aligned as for ‘below left’, except it is aligned to the right edge of the text. If this causes the underline to be drawn on the "over" side of the text, then an overline also switches sides and is drawn on the "under" side.

In some cases (such as in OpenType) the font format can offer information about the appropriate position of an underline. Typically this information gives the position of an ‘alphabetic’ underline; in some cases (especially in CJK fonts), it gives the position of a ‘below left’ underline. (In this case, the font's underline metrics typically touch the bottom edge of the em box). The UA is encouraged to use information (such as the underline thickness, or appropriate alphabetic alignment) from the font wherever appropriate.

10.2. Emphasis Marks

East Asian documents traditionally use small symbols next to each glyph to emphasize a run of text. For example:

Example of emphasis in Japanese appearing above the text

Accent emphasis (shown in blue for clarity) applied to Japanese text

10.2.1. Emphasis Mark Style: the ‘text-emphasis-style’ property

Name: text-emphasis-style
Value: none | [ [ filled | open ] || [ dot | circle | double-circle | triangle | sesame ] ] | <string>
Initial: none
Applies to: all elements
Inherited: yes
Percentages: N/A
Media: visual
Computed value: none’, a pair of keywords representing the shape and fill, or a string

This property applies emphasis marks to the element's text. Values have the following meanings:

none
No emphasis marks.
filled
The shape is filled with solid color.
open
The shape is hollow.
dot
Display small circles as marks. The filled dot is U+2022 ‘’, and the open dot is U+25E6 ‘’.
circle
Display large circles as marks. The filled circle is U+25CF ‘’, and the open circle is U+25CB ‘’.
double-circle
Display double circles as marks. The filled double-circle is U+25C9 ‘’, and the open double-circle is U+25CE ‘’.
triangle
Display triangles as marks. The filled triangle is U+25B2 ‘’, and the open triangle is U+25B3 ‘’.
sesame
Display sesames as marks. The filled sesame is U+FE45 ‘’, and the open sesame is U+FE46 ‘’.
<string>
Display the given string as marks. Authors should not specify more than one character in <string>. The UA may truncate or ignore strings consisting of more than one grapheme cluster.

If a shape keyword is specified but neither of ‘filled’ nor ‘open’ is specified, ‘filled’ is assumed. If only ‘filled’ or ‘open’ is specified, the shape keyword computes to ‘circle’ in horizontal writing mode and ‘sesame’ in vertical writing mode.

The marks should be drawn using the element's font settings with its size scaled down to 50%. However, not all fonts have all these glyphs, and some fonts use inappropriate sizes for emphasis marks in these code points. The UA may opt to use a font known to be good for emphasis marks, or the marks may instead be synthesized by the UA. Marks must remain upright in vertical typographic modes: like CJK characters, they do not rotate to match the writing mode.

One example of good fonts for emphasis marks is Adobe's opensource project, Kenten Generic OpenType Font, which is specially designed for the emphasis marks.

The marks are drawn once for each character. However, emphasis marks are not drawn for characters that are:

If emphasis marks are drawn for characters for which ruby is drawn in the same position as the emphasis mark, the ruby should be stacked between the emphasis marks and the base text. In this case, the position of the emphasis marks for a given element should be determined as if all characters have ruby boxes of the same height as the highest ruby box in the element. If the UA is not capable of drawing ruby and emphasis marks on the same side, the UA may hide ruby and draw only emphasis marks.

Example of emphasis marks applied to 4 characters, and ruby to 2 of them

Emphasis marks applied to 4 characters, and ruby to 2 of them

A future level of CSS may define controls to specify what to do when emphasis marks and ruby text coincide.

10.2.2. Emphasis Mark Color: the ‘text-emphasis-color’ property

Name: text-emphasis-color
Value: <color>
Initial: currentcolor
Applies to: all elements
Inherited: yes
Percentages: N/A
Media: visual
Computed value: as specified

This property describes the foreground color of the emphasis marks.

10.2.3. Emphasis Mark Shorthand: the ‘text-emphasis’ property

Name: text-emphasis
Value: <text-emphasis-style>’ || ‘<text-emphasis-color>
Initial: see individual properties
Applies to: all elements
Inherited: yes
Percentages: N/A
Media: visual
Computed value: see individual properties

This property is a shorthand for setting ‘text-emphasis-style’ and ‘text-emphasis-color’ in one declaration. Omitted values are set to their initial values.

Note that ‘text-emphasis-position’ is not reset in this shorthand. This is because typically the shape and color vary, but the position is consistent for a particular language throughout the document. Therefore the position should inherit independently.

10.2.4. Emphasis Mark Position: the ‘text-emphasis-position’ property

Name: text-emphasis-position
Value: [ above | below ] && [ right | left ]
Initial: above right
Applies to: all elements
Inherited: yes
Percentages: N/A
Media: visual
Computed value: as specified

This property describes where emphasis marks are drawn at. The values have following meanings:

above
Draw marks over the text in horizontal typographic mode.
below
Draw marks under the text in horizontal typographic mode.
right
Draw marks to the right of the text in vertical typographic mode.
left
Draw marks to the left of the text in vertical typographic mode.

Emphasis marks are drawn exactly as if each character was assigned the mark as its ruby annotation text with the ruby position given by ‘text-emphasis-position’ and the ruby alignment as centered.

The effect of emphasis marks on the line height is the same as for ruby text.

Note, the preferred position of emphasis marks depends on the language. In Japanese for example, the preferred position is ‘above right’. In Chinese, on the other hand, the preferred position is ‘below right’. The informative table below summarizes the preferred emphasis mark positions for Chinese and Japanese:

Preferred emphasis mark and ruby position
Language Preferred mark position Illustration
Horizontal Vertical
Japanese above right Emphasis marks appear above each emphasized character in horizontal Japanese text. Emphasis marks appear on the right of each emphasized character in vertical Japanese text.
Chinese below right Emphasis marks appear below each emphasized character in horizontal Simplified Chinese text.

10.2.5. Emphasis Mark Skip: the ‘text-emphasis-skip’ property

This section is under brainstorming.

Name: text-emphasis-skip
Value: spaces || punctuation || symbols || narrow
Initial: spaces
Applies to: all elements
Inherited: yes
Percentages: N/A
Media: visual
Computed value: as specified

This property describes for which characters marks are drawn. The values have following meanings:

spaces
Skip Word separators or characters belonging to the Unicode separator category (Z*). (But note that emphasis marks are drawn for a space that combines with any combining characters.)
punctuation
Skip punctuation. Punctuation in this definition includes characters belonging to the Unicode Pc, Pd, Ps, Pe, Pi, or Pf categories. It also includes characters where the Unicode category is Po and the Sentence_Break property [UAX29] of the Unicode database [UAX44] is ATerm, Close, SContinue, or STerm.
symbols
Skip symbols. Symbols in this definition includes characters belonging to the Unicode S* category. It also includes the Unicode Po category that are not defined as ‘punctuation’ above.
narrow
Skip characters where the East_Asian_Width property [UAX11] of the Unicode database [UAX44] is not F (Fullwidth) or W (Wide).

Characters belonging to the Unicode classes for control codes and unassigned characters (Cc, Cf, Cn) are skipped regardless of the value of this property.

This syntax requires UA to implement drawing marks for spaces. Is there any use case for doing so? If not, should we modify the syntax not to allow drawing marks for spaces?

10.3. Text Shadows: the ‘text-shadow’ property

Name: text-shadow
Value: none | [<shadow>, ] * <shadow>
Initial: none
Applies to: all elements
Inherited: yes
Percentages: N/A
Media: visual
Computed value: a color plus three absolute <length>s

This property accepts a comma-separated list of shadow effects to be applied to the text of the element. <shadow> is the same as defined for the ‘box-shadow’ property except that the ‘inset’ keyword is not allowed. The shadow is applied to all of the element's text as well as any text decorations it specifies.

The shadow effects are applied front-to-back: the first shadow is on top. The shadows may thus overlay each other, but they never overlay the text itself. The shadow must be painted at a stack level between the element's border and/or background, if present, and the elements text and text decoration. UAs should avoid painting text shadows over text in adjacent elements belonging to the same stack level and stacking context. (This may mean that the exact stack level of the shadows depends on whether the element has a border or background: the exact stacking behavior of text shadows is thus UA-defined.)

Unlike ‘box-shadow’, text shadows are not clipped to the shadowed shape and may show through if the text is partially-transparent. Like ‘box-shadow’, text shadows do not influence layout, and do not trigger scrolling or increase the size of the scrollable area.

The painting order of shadows defined here is the opposite of that defined in the 1998 CSS2 Recommendation.

The ‘text-shadow’ property applies to both the ::first-line and ::first-letter pseudo-elements.

11. Conformance

11.1. Document Conventions

Conformance requirements are expressed with a combination of descriptive assertions and RFC 2119 terminology. The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in the normative parts of this document are to be interpreted as described in RFC 2119. However, for readability, these words do not appear in all uppercase letters in this specification.

All of the text of this specification is normative except sections explicitly marked as non-normative, examples, and notes. [RFC2119]

Examples in this specification are introduced with the words “for example” or are set apart from the normative text with class="example", like this:

This is an example of an informative example.

Informative notes begin with the word “Note” and are set apart from the normative text with class="note", like this:

Note, this is an informative note.

11.2. Conformance Classes

Conformance to CSS Text Level 4 is defined for three conformance classes:

style sheet
A CSS style sheet.
renderer
A UA that interprets the semantics of a style sheet and renders documents that use them.
authoring tool
A UA that writes a style sheet.

A style sheet is conformant to CSS Text Level 4 if all of its declarations that use properties defined in this module have values that are valid according to the generic CSS grammar and the individual grammars of each property as given in this module.

A renderer is conformant to CSS Text Level 4 if, in addition to interpreting the style sheet as defined by the appropriate specifications, it supports all the features defined by CSS Text Level 4 by parsing them correctly and rendering the document accordingly. However, the inability of a UA to correctly render a document due to limitations of the device does not make the UA non-conformant. (For example, a UA is not required to render color on a monochrome monitor.)

An authoring tool is conformant to CSS Text Level 4 if it writes style sheets that are syntactically correct according to the generic CSS grammar and the individual grammars of each feature in this module, and meet all other conformance requirements of style sheets as described in this module.

11.3. Partial Implementations

So that authors can exploit the forward-compatible parsing rules to assign fallback values, CSS renderers must treat as invalid (and ignore as appropriate) any at-rules, properties, property values, keywords, and other syntactic constructs for which they have no usable level of support. In particular, user agents must not selectively ignore unsupported component values and honor supported values in a single multi-value property declaration: if any value is considered invalid (as unsupported values must be), CSS requires that the entire declaration be ignored.

11.4. Experimental Implementations

To avoid clashes with future CSS features, the CSS2.1 specification reserves a prefixed syntax for proprietary and experimental extensions to CSS.

Prior to a specification reaching the Candidate Recommendation stage in the W3C process, all implementations of a CSS feature are considered experimental. The CSS Working Group recommends that implementations use a vendor-prefixed syntax for such features, including those in W3C Working Drafts. This avoids incompatibilities with future changes in the draft.

11.5. Non-Experimental Implementations

Once a specification reaches the Candidate Recommendation stage, non-experimental implementations are possible, and implementors should release an unprefixed implementation of any CR-level feature they can demonstrate to be correctly implemented according to spec.

To establish and maintain the interoperability of CSS across implementations, the CSS Working Group requests that non-experimental CSS renderers submit an implementation report (and, if necessary, the testcases used for that implementation report) to the W3C before releasing an unprefixed implementation of any CSS features. Testcases submitted to W3C are subject to review and correction by the CSS Working Group.

Further information on submitting testcases and implementation reports can be found from on the CSS Working Group's website at http://www.w3.org/Style/CSS/Test/. Questions should be directed to the public-css-testsuite@w3.org mailing list.

11.6. CR Exit Criteria

For this specification to be advanced to Proposed Recommendation, there must be at least two independent, interoperable implementations of each feature. Each feature may be implemented by a different set of products, there is no requirement that all features be implemented by a single product. For the purposes of this criterion, we define the following terms:

independent
each implementation must be developed by a different party and cannot share, reuse, or derive from code used by another qualifying implementation. Sections of code that have no bearing on the implementation of this specification are exempt from this requirement.
interoperable
passing the respective test case(s) in the official CSS test suite, or, if the implementation is not a Web browser, an equivalent test. Every relevant test in the test suite should have an equivalent test created if such a user agent (UA) is to be used to claim interoperability. In addition if such a UA is to be used to claim interoperability, then there must one or more additional UAs which can also pass those equivalent tests in the same way for the purpose of interoperability. The equivalent tests must be made publicly available for the purposes of peer review.
implementation
a user agent which:
  1. implements the specification.
  2. is available to the general public. The implementation may be a shipping product or other publicly available version (i.e., beta version, preview release, or “nightly build”). Non-shipping product releases must have implemented the feature(s) for a period of at least one month in order to demonstrate stability.
  3. is not experimental (i.e., a version specifically designed to pass the test suite and is not intended for normal usage going forward).

The specification will remain Candidate Recommendation for at least six months.

Appendix A: Acknowledgements

This specification would not have been possible without the help from: Ayman Aldahleh, Bert Bos, Tantek Çelik, Stephen Deach, John Daggett, Martin Dürst, Laurie Anna Edlund, Ben Errez, Yaniv Feinberg, Arye Gittelman, Ian Hickson, Martin Heijdra, Richard Ishida, Masayasu Ishikawa, Michael Jochimsen, Eric LeVine, Ambrose Li, Håkon Wium Lie, Chris Lilley, Ken Lunde, Nat McCully, Shinyu Murakami, Paul Nelson, Chris Pratley, Marcin Sawicki, Arnold Schrijver, Rahul Sonnad, Michel Suignard, Takao Suzuki, Frank Tang, Chris Thrasher, Etan Wexler, Chris Wilson, Masafumi Yabe and Steve Zilles.

Appendix B: References

Normative references

[CSS21]
Bert Bos; et al. Cascading Style Sheets Level 2 Revision 1 (CSS 2.1) Specification. 7 June 2011. W3C Recommendation. URL: http://www.w3.org/TR/2011/REC-CSS2-20110607
[CSS3-FONTS]
John Daggett. CSS Fonts Module Level 3. 3 October 2013. W3C Candidate Recommendation. (Work in progress.) URL: http://www.w3.org/TR/2013/CR-css-fonts-3-20131003/
[CSS3-WRITING-MODES]
Elika J. Etemad; Koji Ishii. CSS Writing Modes Module Level 3. 15 November 2012. W3C Working Draft. (Work in progress.) URL: http://www.w3.org/TR/2012/WD-css3-writing-modes-20121115/
[CSS3BG]
Bert Bos; Elika J. Etemad; Brad Kemper. CSS Backgrounds and Borders Module Level 3. 24 July 2012. W3C Candidate Recommendation. (Work in progress.) URL: http://www.w3.org/TR/2012/CR-css3-background-20120724/
[RFC2119]
S. Bradner. Key words for use in RFCs to Indicate Requirement Levels. Internet RFC 2119. URL: http://www.ietf.org/rfc/rfc2119.txt
[UAX11]
Asmus Freytag. East Asian Width. 17 January 2012. Unicode Standard Annex #11. URL: http://www.unicode.org/reports/tr11/
[UAX14]
Asmus Freytag. Line Breaking Properties. 17 January 2012. Unicode Standard Annex #14. URL: http://www.unicode.org/unicode/reports/tr14/
[UAX24]
Mark Davis; Ken Whistler. Unicode Script Property. 13 January 2012. Unicode Standard Annex #24. URL: http://www.unicode.org/reports/tr24/
[UAX29]
Mark Davis. Unicode Text Segmentation. 12 September 2012. Unicode Standard Annex #29. URL: http://www.unicode.org/reports/tr29/
[UAX44]
Mark Davis; Ken Whistler. Unicode Character Database. 23 January 2012. Unicode Standard Annex #44. URL: http://www.unicode.org/reports/tr44/
[UNICODE]
The Unicode Consortium. The Unicode Standard. 2012. Defined by: The Unicode Standard, Version 6.2.0 (Mountain View, CA: The Unicode Consortium, 2012. ISBN 978-1-936213-07-8), as updated from time to time by the publication of new versions URL: http://www.unicode.org/standard/versions/enumeratedversions.html

Informative references

[CSS3COLOR]
Tantek Çelik; Chris Lilley; L. David Baron. CSS Color Module Level 3. 7 June 2011. W3C Recommendation. URL: http://www.w3.org/TR/2011/REC-css3-color-20110607
[CSS3LIST]
Tab Atkins Jr. CSS Lists and Counters Module Level 3. 24 May 2011. W3C Working Draft. (Work in progress.) URL: http://www.w3.org/TR/2011/WD-css3-lists-20110524
[CSS3VAL]
Håkon Wium Lie; Tab Atkins; Elika J. Etemad. CSS Values and Units Module Level 3. 30 July 2013. W3C Candidate Recommendation. (Work in progress.) URL: http://www.w3.org/TR/2013/CR-css3-values-20130730/
[JIS4051]
Formatting rules for Japanese documents (『日本語文書の組版方法』). Japanese Standards Association. 2004. JIS X 4051:2004. In Japanese
[JLREQ]
Yasuhiro Anan (阿南 康宏); et al. Requirements for Japanese Text Layout. 3 April 2012. W3C Working Group Note. URL: http://www.w3.org/TR/2012/NOTE-jlreq-20120403/
[ZHMARK]
标点符号用法 (Punctuation Mark Usage). 1995. 中华人民共和国国家标准

Appendix C: Changes

Appendix D: Default UA Stylesheet

This appendix is informative, and is to help UA developers to implement default stylesheet, but UA developers are free to ignore or change.


/* make list items align together */
li { text-align: match-parent; }
/* disable inheritance of text-emphasis marks to ruby text:
  emphasis marks should only apply to base text */
rt { text-emphasis: none; }

:root:lang(zh), [lang|=zh] {
/* default emphasis mark position is 'below right' for Chinese */
  text-emphasis-position: below right;
}

If you find any issues, recommendations to add, or corrections, please send the information to www-style@w3.org with [css3-text] in the subject line.

Appendix E: Scripts and Spacing

This appendix is informative (non-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 expansion opportunities.

block scripts
CJK and by extension all Wide characters. (See [UAX11]) The following scripts are included: Bopomofo, Han, Hangul, Hiragana, Katakana, Yi
clustered scripts
Scripts that have discrete units but do not use spaces between words, such as many Southeast Asian systems. The following scripts are included: Khmer, Lao, Myanmar, Thai, This list is likely incomplete. What else fits here?
connected scripts
Devanagari, Ogham, and other scripts that use spaces between words and baseline connectors within words. By extension this category also includes any other Indic scripts whose typographic behavior is similar to Devanagari. The following scripts are included: Bengali, Brahmi, Devanagari, Gujarati, Gurmukhi, Kannada, Malayalam, Oriya?, Ogham, Tamil?, Telugu
cursive scripts
Arabic and similar inherently cursive scripts. The following scripts are included: Arabic, Mongolian, N'Ko?, Phags Pa?, Syriac
discrete scripts
Scripts that use spaces or visible word-separating punctuation between words and have discrete, unconnected (in print) units within words. The following scripts are included: Armenian, Bamum?, Braille, Canadian Aboriginal, Cherokee, Coptic, Cyrillic, Deseret, Ethiopic Greek, Hebrew, Kharoshthi, Latin, Lisu, Osmanya, Shavian, Tifinagh, Vai?

UAs should treat unrecognized scripts as discrete.

This listing should ideally be exhaustive wrt Unicode. Please send suggestions and corrections to the CSS Working Group.

Guidelines for classification consider letter-spacing and justification:

  1. If the script is cursive and may expand cursively but must not space between letters, it is cursive.
  2. If the script primarily flexes word separators, it is either discrete or connected. Discrete scripts can space between letters. Connected scripts must not space between letters (typically because that would break the connections or otherwise look bad).
  3. If the script primarily expands equally between its "letters" in native typesettings, it is either block or clustered. The exact classification depends on whether it always spaces when mixed with CJK and sometimes stays together when mixed with Thai and related scripts (block) or sometimes spaces when mixed with CJK and always spaces with Thai (clustered).

Appendix F: Small Kana Mappings

Small Kana Map to Normal Kana
A I U E O
small normal small normal small normal small normal small normal
ぁ U+3041 あ U+3042 ぃ U+3043 い U+3044 ぅ U+3045 う U+3046 ぇ U+3047 え U+3048 ぉ U+3049 お U+304A
ゕ U+3095 か U+304B ゖ U+3096 け U+3051
っ U+3063 つ U+3064
ゃ U+3083 や U+3084 ゅ U+3085 ゆ U+3086 ょ U+3087 よ U+3088
ゎ U+308E わ U+308F
ァ U+30A1 ア U+30A2 ィ U+30A3 イ U+30A4 ゥ U+30A5 ウ U+30A6 ェ U+30A7 エ U+30A8 ォ U+30A9 オ U+30AA
ヵ U+30F5 カ U+30AB ㇰ U+31F0 ク U+30AF ヶ U+30F6 ケ U+30B1
ㇱ U+31F1 シ U+30B7 ㇲ U+31F2 ス U+30B9
ッ U+30C3 ツ U+30C4 ㇳ U+31F3 ト U+30C8
ㇴ U+31F4 ヌ U+30CC
ㇵ U+31F5 ハ U+30CF ㇶ U+31F6 ヒ U+30D2 ㇷ U+31F7 フ U+30D5 ㇸ U+31F8 ヘ U+30D8 ㇹ U+31F9 ホ U+30DB
ㇺ U+31FA ム U+30E0
ャ U+30E3 ヤ U+30E4 ュ U+30E5 ユ U+30E6 ョ U+30E7 ヨ U+30E8
ㇻ U+31FB ラ U+30E9 ㇼ U+31FC リ U+30EA ㇽ U+31FD ル U+30EB ㇾ U+31FE レ U+30EC ㇿ U+31FF ロ U+30ED
ヮ U+30EE ワ U+30EF
ァ U+FF67 ア U+FF71 ィ U+FF68 イ U+FF72 ゥ U+FF69 ウ U+FF73 ェ U+FF6A エ U+FF74 ォ U+FF6B オ U+FF75
ッ U+FF6F ツ U+FF82
ャ U+FF6C ヤ U+FF94 ュ U+FF6D ユ U+FF95 ョ U+FF6E ヨ U+FF96

Appendix G: Text Processing Order of Operations

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. text combination [CSS3-WRITING-MODES]
  2. white space processing part I (pre-wrapping)
  3. text transformation
  4. default spacing
  5. text wrapping while applying per line:
    1. white space processing part II
    2. indentation
    3. bidirectional reordering [CSS21] / [CSS3-WRITING-MODES]
    4. text orientation [CSS3-WRITING-MODES]
    5. font/glyph selection and kerning [CSS21] / [CSS3-FONTS]
    6. hanging punctuation
  6. justification (which may affect glyph selection and/or text wrapping, looping back into that step)
  7. text alignment
  8. text decoration

Appendix H: Full Property Index

Property Values Initial Applies to Inh. Percentages Media
hanging-punctuation none | [ first || [ force-end | allow-end ] || last ] none inline elements yes N/A visual
hyphenate-character auto | <string> auto all elements yes N/A visual
hyphenate-limit-chars [auto | <integer>]{1,3} auto all elements yes N/A visual
hyphenate-limit-last none | always | column | page | spread none block containers yes N/A visual
hyphenate-limit-lines no-limit | <integer> no-limit block containers yes N/A visual
hyphenate-limit-zone <percentage> | <length> 0 block containers yes refers to width of the line box visual
hyphens none | manual | auto manual all elements yes N/A visual
letter-spacing <spacing-limit> normal all elements yes N/A visual
line-break auto | loose | normal | strict auto all elements yes N/A visual
overflow-wrap normal | [ break-word || hyphenate ] normal all elements yes N/A visual
tab-size <integer> | <length> 8 block containers yes N/A visual
text-align start end | match-parent | <string>? [ start | end | left | right | center | justify ] start block containers yes N/A visual
text-align-last auto | start | end | left | right | center | justify auto block containers yes N/A visual
text-decoration <text-decoration-line> || <text-decoration-style> || <text-decoration-color> || blink none all elements no N/A visual
text-decoration-color <color> currentColor all elements no N/A visual
text-decoration-line none | [ underline | no-underline | replace-underline ] || [ overline | no-overline | replace-overline ] || [ line-through | no-line-through | replace-line-through ] | remove-all none all elements no (but see prose) N/A visual
text-decoration-skip none | [ objects || spaces || ink || edges ] objects all elements yes N/A visual
text-decoration-style solid | double | dotted | dashed | wavy solid all elements no N/A visual
text-emphasis ‘<text-emphasis-style>’ || ‘<text-emphasis-color>’ see individual properties all elements yes N/A visual
text-emphasis-color <color> currentcolor all elements yes N/A visual
text-emphasis-position [ above | below ] && [ right | left ] above right all elements yes N/A visual
text-emphasis-skip spaces || punctuation || symbols || narrow spaces all elements yes N/A visual
text-emphasis-style none | [ [ filled | open ] || [ dot | circle | double-circle | triangle | sesame ] ] | <string> none all elements yes N/A visual
text-indent [ <length> | <percentage> ] && [ hanging || each-line ]? 0 block containers yes refers to width of containing block visual
text-justify auto | none | inter-word | inter-ideograph | inter-cluster | distribute | kashida auto block containers and, optionally, inline elements yes N/A visual
text-shadow none | [<shadow>, ] * <shadow> none all elements yes N/A visual
text-space-collapse collapse | discard | [ [preserve | preserve-breaks] && [ trim-inner || consume-before || consume-after ] collapse all elements yes N/A visual
text-spacing normal | none | [ trim-start | space-start ] || [ trim-end | space-end | allow-end ] || [ trim-adjacent | space-adjacent ] || no-compress || ideograph-alpha || ideograph-numeric || punctuation normal block containers yes N/A visual
text-transform none | [ [ capitalize | uppercase | lowercase ] || full-width || full-size-kana ] none all elements yes N/A visual
text-underline-position auto | alphabetic | below left | below right auto all elements yes N/A visual
text-wrap normal | none | avoid normal all elements yes N/A visual
white-space normal | pre | nowrap | pre-wrap | pre-line not defined for shorthand properties all elements yes N/A visual
word-break normal | keep-all | break-all normal all elements yes N/A visual
word-spacing <spacing-limit> normal all elements yes refers to width of the affected glyph visual

Appendix J: Cultural Correlations

This section is non-normative.

Some features are more important in some typographic traditions than in others. This table summarizes which typographic traditions these features were designed for. Parentheses indicates traditions for which the feature is particularly significant. This table should be considered incomplete and non-exhaustive.

Feature Typographic Tradition
hanging-punctuationCJK
hyphensWestern, South Asian
hyphenate-characterWestern, South Asian
hyphenate-limit-charsWestern, South Asian
hyphenate-limit-lastWestern, South Asian
hyphenate-limit-linesWestern, South Asian
hyphenate-limit-zoneWestern, South Asian
line-breakCJK (Japanese)
text-decoration-skip’: ‘edgesCJK
text-justify’: ‘inter-clusterSoutheast Asian
text-justify’: ‘inter-ideograph’, ‘distributeCJK
text-justify’: ‘inter-wordWestern, African, Middle-Eastern, Indic
text-justify’: ‘kashidaArabic
text-emphasis-styleCJK
text-emphasis-colorCJK
text-emphasis-positionCJK
text-emphasis-skipCJK
text-spacingCJK
text-spacing’: ‘punctuationEuropean (French)
text-transform’: ‘capitalize’, ‘uppercase’, ‘lowercaseWestern
text-transform’: ‘full-width’, ‘full-size-kanaCJK
text-underline-position’: ‘autoCJK
word-breakCJK (Korean)
word-spacingWestern, African, Middle-Eastern, Indic

Additional information / corrections on this table are welcome.