CSS Text Module Level 4

Unofficial Proposal Draft,

This version:
http://dev.w3.org/csswg/css-text-4/
Feedback:
www-style@w3.org with subject line “[css-text] … message topic …” (archives)
Issue Tracking:
Inline In Spec
Editors:
fantasai (Invited Expert)
(Invited Expert)
(Adobe Systems)

Abstract

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

CSS is a language for describing the rendering of structured documents (such as HTML and XML) on screen, on paper, in speech, etc.

Status of this document

Table of Contents

1. Introduction

Add final level 3 content

2. Transforming Text

Add final level 3 content

3. White Space Processing

Add final level 3 tab-size and processing details

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
Initial: collapse
Applies to: all elements
Inherited: yes
Percentages: n/a
Media: visual
Computed value: as specified
Animatable: no

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. Issue: Does this preserve line break opportunities or no? Do we need a "hide" value?

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;
}

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

3.2. White Space Trimming: the text-space-trim property

Name: text-space-trim
Value: none | trim-inner || consume-before || consume-after
Initial: collapse
Applies to: all elements
Inherited: no
Percentages: n/a
Media: visual
Computed value: as specified
Animatable: no

This property allows authors to specify trimming behavior at the beginning and end of a box. Values have the following meanings, which must be interpreted according to the white space processing rules:

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 render DT elements as a comma-separated list:

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

4. Line Breaking and Word Boundaries

Add final level 3 content

5. Text Wrapping

Text wrapping is controlled by the text-wrap, wrap-before, wrap-after, wrap-inside, and overflow-wrap properties:

Add final level 3 overflow-wrap

5.1. Text Wrap Settings: the text-wrap property

Name: text-wrap
Value: normal | nowrap | balance
Initial: normal
Applies to: all elements
Inherited: yes
Percentages: n/a
Media: visual
Computed value: as specified
Animatable: no

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.
nowrap
Lines may not break; text that does not fit within the block container overflows it.
balance
Same as normal for inline-level elements. For block-level elements that contain line boxes as direct children, line breaks are chosen to balance the inline-size those line boxes consume, if better balance than normal is possible. This must not change the number of line boxes the block would contain if text-wrap were set to normal.

For balancing purposes, the inline-size to consider includes any length taken up by floats that shorten the line box. The inline-size to consider comes before any adjustments for justification. Line boxes are balanced when the standard deviation from the average inline-size consumed is reduced over the block (including lines that end in a forced break).

The exact algorithm is UA-defined.

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

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.

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.

5.2. Inline breaks between boxes: the wrap-before/wrap-after properties

Name: wrap-before, wrap-after
Value: auto | avoid | avoid-line | avoid-flex | line | flex
Initial: auto
Applies to: all elements
Inherited: no
Percentages: n/a
Media: visual
Computed value: as specified
Animatable: no

These properties specify modifications to break opportunities in line and flex line breaking Possible values:

auto
Lines may break at allowed break points before and after the element, as determined by the line-breaking rules in effect.
avoid
Flex and line breaking is suppressed before/after the element: the UA may only break before/after the element if there are no other valid break points in the line. If the text breaks, line-breaking restrictions are honored as for auto.
avoid-line
Same as avoid, but only for line breaks.
avoid-flex
Same as avoid, but only for flex line breaks.
line
Force a line break before/after the element if this is a valid line break point.
flex
Force a flex line break before/after the element if this is a valid flex line break point and the element is a flex item in a multi-line flex container.

5.3. Line breaks within boxes: the wrap-inside property

Name: wrap-inside
Value: auto | avoid
Initial: auto
Applies to: all elements
Inherited: no
Percentages: n/a
Media: visual
Computed value: as specified
Animatable: no
auto
Lines may break at allowed break points within the element, as determined by the line-breaking rules in effect.
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 auto.

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

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

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

Given the rules

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

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. Last Line Minimum Length

See thread. Issue is about requiring a minimum length for lines. Common measures seem to be

Suggestion for value space is ''match-indent | <length> | <percentage>'' (with Xch given as an example to make that use case clear). Alternately <integer> could actually count the characters.

It’s unclear how this would interact with text balancing (above); one earlier proposal had them be the same property (with 100% meaning full balancing).

People have requested word-based limits, but since this is really dependent on the length of the word, character-based is better.

7. Shorthand for White Space and Wrapping: the white-space property

Diff needs to have the shorthand details

8. Breaking Within Words

Add final level 3 content

8.1. 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: as specified
Animatable: no

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.

8.2. 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: as specified
Animatable: no

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.

8.3. 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: as specified
Animatable: no

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; }

8.4. 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: as specified
Animatable: no

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: as specified
Animatable: no

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.

9. Alignment and Justification

Add final level 3 content

Add this value to text-align

<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.

9.1. 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.

10. Spacing

Add final level 3 word-spacing, letter-spacing

10.1. 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.

Note: 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.

Note: 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 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 set 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.)

Note: 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.

Note: 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.

10.1.1. 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 will 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 +   )  

10.1.2. Text Spacing Character Classes

In the context of this property the following definitions apply:

Classes and Unicode code points need to be reviewed.

ideographs
Includes all typographic character units [CSS3TEXT] whose base character is listed below:
  • All characters in the range of U+3041 to U+30FF, except those that belong to Unicode Punctuation [P*] category.
  • CJK Strokes (U+31C0 to U+31EF).
  • Katakana Phonetic Extensions (U+31F0 to U+31FF).
  • All characters that belongs to Han Unicode Script Property [UAX24].
non-ideographic letters
Includes all typographic character units that belong to Unicode Letters [L*] and Mark [M*] category, except when any of the following conditions are met:
non-ideographic numerals
Includes all typographic character units that belong to the Unicode Decimal Digit Number [Nd] category, except when 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.

10.1.3. Japanese Paragraph-start Conventions in CSS

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:

11. Edge Effects

Add final level 3 content

Acknowledgements

Add final level 3 list, with Randy Edmunds and Florian Rivoal added

Conformance

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.

Advisements are normative sections styled to evoke special attention and are set apart from other normative text with <strong class="advisement">, like this: UAs MUST provide an accessible alternative.

Conformance classes

Conformance to this specification 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 this specification if all of its statements that use syntax defined in this module are valid according to the generic CSS grammar and the individual grammars of each feature defined in this module.

A renderer is conformant to this specification if, in addition to interpreting the style sheet as defined by the appropriate specifications, it supports all the features defined by this specification 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 this specification 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.

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.

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.

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.

Index

Terms defined by this specification

Terms defined by reference

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
[UAX11]
Asmus Freytag. East Asian Width. 23 March 2001. Unicode Standard Annex #11. URL: http://www.unicode.org/unicode/reports/tr11/tr11-8.html
[UAX14]
Asmus Freytag. Line Breaking Properties. 29 March 2005. Unicode Standard Annex #14. URL: http://www.unicode.org/unicode/reports/tr14/tr14-17.html
[UAX24]
Mark Davis. Script Names. 28 March 2005. Unicode Standard Annex #24. URL: http://www.unicode.org/unicode/reports/tr24/tr24-7.html
[CSS-VALUES-3]
CSS Values and Units Module Level 3 URL: http://www.w3.org/TR/css3-values/
[CSS-WRITING-MODES-3]
Elika Etemad; Koji Ishii. CSS Writing Modes Level 3. 20 March 2014. CR. URL: http://www.w3.org/TR/css-writing-modes-3/
[RFC2119]
S. Bradner. Key words for use in RFCs to Indicate Requirement Levels. March 1997. Best Current Practice. URL: https://tools.ietf.org/html/rfc2119

Informative References

[CSS3TEXT]
Elika J. Etemad; Koji Ishii. CSS Text Module Level 3. 13 November 2012. W3C Working Draft. (Work in progress.) URL: http://www.w3.org/TR/2012/WD-css3-text-20121113/
[JLREQ]
Yasuhiro Anan; et al. Requirements for Japanese Text Layout. 3 April 2012. NOTE. URL: http://www.w3.org/TR/jlreq/

Property Index

Name Value Initial Applies to Inh. %ages Media Animatable Computed value Computed value
text-space-collapse collapse | discard | preserve | preserve-breaks collapse all elements yes n/a visual no as specified
text-space-trim none | trim-inner || consume-before || consume-after collapse all elements no n/a visual no as specified
text-wrap normal | nowrap | balance normal all elements yes n/a visual no as specified
wrap-before auto | avoid | avoid-line | avoid-flex | line | flex auto all elements no n/a visual no as specified
wrap-after auto | avoid | avoid-line | avoid-flex | line | flex auto all elements no n/a visual no as specified
wrap-inside auto | avoid auto all elements no n/a visual no as specified
hyphenate-character auto | <string> auto all elements yes n/a visual no as specified
hyphenate-limit-zone <percentage> | <length> 0 block containers yes refers to width of the line box visual no as specified
hyphenate-limit-chars [ auto | <integer> ]{1,3} auto all elements yes n/a visual no as specified
hyphenate-limit-lines no-limit | <integer> no-limit block containers yes n/a visual no as specified
hyphenate-limit-last none | always | column | page | spread none block containers yes n/a visual no as specified
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 specified value

Issues Index

Add final level 3 content
Add final level 3 content
Add final level 3 tab-size and processing details
This section is still under discussion and may change in future drafts.
Need a property name
This section is still under discussion and may change in future drafts.
Add final level 3 content
Add final level 3 overflow-wrap
See thread. Issue is about requiring a minimum length for lines. Common measures seem to be

Suggestion for value space is ''match-indent | <length> | <percentage>'' (with Xch given as an example to make that use case clear). Alternately <integer> could actually count the characters.

It’s unclear how this would interact with text balancing (above); one earlier proposal had them be the same property (with 100% meaning full balancing).

People have requested word-based limits, but since this is really dependent on the length of the word, character-based is better.

Add final level 3 content
Is hyphenate-limit-zone a good name? Comments/suggestions?
Unicode class
Add final level 3 content
Add final level 3 word-spacing, letter-spacing
It was requested to add a value for doubling the space after periods.
Classes and Unicode code points need to be reviewed.