CSS Text Level 3

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 https://www.w3.org/TR/.

This Text module and a separate (upcoming) Text Layout module replace and obsolete the May 2003 CSS3 Text Module Candidate Recommendation. Since this is a thorough overhaul of the previous version, a list of changes has been provided instead of a diff.

This document is a Working Draft, and it is still very incomplete. In fact, many of its sections have not been added in.

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.

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. I will do my best to respond to all feedback.

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

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.

The following features are at risk and may be cut from the spec during its CR period: multiple text shadows, the tibetan text justification mode, the 'text-outline' property, the 'break-strict' value of 'word-break'

Table of Contents

• 1. Introduction
• 2. Conformance
  • 2.1. Partial and Experimental Implementations
• 3. White Space Processing
  • 3.1. White Space Collapsing: the 'white-space-collapse' property
  • 3.2. The White Space Processing Rules
    • 3.2.1. Example of bidirectionality with white space collapsing
    • 3.2.2. Line Break Transformation Rules
    • 3.2.3. Informative Summary of White Space Collapsing Effects
  • 3.3. White Space and Text Wrapping Shorthand: the 'white-space' property
• 4. Line Breaking and Word Boundaries
  • 4.1. Line Breaking Restrictions: the 'word-break' property
  • 4.2. Hyphenation
• 5. Text Wrapping
  • 5.1. Text Wrap Settings: the 'text-wrap' property
    • 5.1.1. Example of using 'text-wrap: suppress' in presenting a footer
  • 5.2. Force Wrapping: the 'word-wrap' property
• 6. Alignment and Justification
  • 6.1. Text Alignment: the 'text-align' property
  • 6.2. Last Line Alignment: the 'text-align-last' property
  • 6.3. Justification Method: the 'text-justify' property
• 7. Spacing
  • 7.1. Word Spacing: the 'word-spacing' property
  • 7.2. Tracking: the 'letter-spacing' property
  • 7.3. Fullwidth Punctuation Kerning: the 'punctuation-trim' property
• 8. Text Decoration
  • 8.2. Emphasis Marks: the 'text-emphasis' property
  • 8.3. Text Shadows: the 'text-shadow' property
  • 8.4. Text Outlines: the 'text-outline' property
• 9. Edge Effects
  • 9.1 First Line Indentation: the 'text-indent' property
  • 9.2 Hanging Punctuation: the 'hanging-punctuation' property
• 10 Changes from the May 2003 CSS3 Text CR
• 11 Changes from the June 2005 CSS3 Text WD
• 12 Acknowledgements
• 13. References
  • 13.1. Normative References
  • 13.2. Informative References

1. Introduction

[document here]

2. Conformance

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 (see [RFC2119]). However, for readability, these words do not typically appear in all uppercase letters in this specification.

Additional key words, e.g. "User agent (UA)", are defined by CSS 2.1 ([CSS21], section 3.1).

2.1. Partial and Experimental Implementations

UAs must treat as invalid any properties or values they do not support. Experimental implementations of a feature should support only a vendor-prefixed syntax for the property/value.

3. White Space Processing

White space processing in CSS interprets white space characters for rendering: it has no effect on the underlying document data. In the context of CSS, the document white space set is defined to be any space characters (Unicode value U+0020), tab characters (U+0009), or line break characters (defined by the document format: typically line feed, U+000A). Control characters besides the white space characters and the bidi formatting characters (U+202x) are treated as normal characters and rendered according to the same rules.

The document parser must normalize line break character sequences according to its own format rules before CSS processing takes effect. However, in generated content strings the line feed character (U+000A) and only the line feed character is considered a line break sequence. For CSS white space processing all line breaks must be normalized to a single character representation—usually the line feed character (U+000A)—here called a "line break". This way, all recognized line breaks are treated the same and style rules behave consistently across systems.

Note that the document parser may have not only normalized line break characters, 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.

3.1. White Space Collapsing: the 'white-space-collapse' property

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

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 breaks are preserved.

preserve-breaks

This value collapses white space as for 'collapse', but preserves line breaks.

discard

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

3.2. The White Space Processing Rules

Any text that is directly contained inside a block (not inside an inline) is treated as being inside an anonymous inline element.

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

• If 'white-space-collapse' is set to 'collapse' or 'preserve-breaks', white space characters are considered collapsible and are processed by performing the following steps:

  1. All non-line-break white space characters immediately following a line break character are removed. (This has the effect of discarding all white space at the start of a line but preserving a trailing space if one exists at the end.)
  2. If 'white-space-collapse' is not 'preserve-breaks', line break characters are transformed for rendering according to the line break transformation rules.
  3. Every tab (U+0009) is converted to a space (U+0020)
  4. Any space (U+0020) following another space (U+0020)—even a space before the inline, if that space is also collapsible—is removed.

• If 'white-space-collapse' is set to 'preserve', any sequence of spaces (U+0020) unbroken by an element boundary is treated as a sequence of non-breaking spaces. However, a line breaking opportunity exists at the end of the sequence.

• If 'white-space-collapse' is set to 'discard', the first white space character in every white space sequence is converted to a zero width non-joiner (U+200C) and the rest of the sequence is removed.

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 (U+0020) at the beginning of a line is removed.
2. A tab (U+0009) 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 8 times the width of a space (U+0020) rendered in the block's font from the block's starting content edge.
3. A sequence of collapsible spaces (U+0020) at the end of a line is removed.

<ltr>A <rtl> B </rtl> C</ltr>

A  BC

3.2.2. Line Break Transformation Rules

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

The script context is determined by the Unicode-given script value [UAX24] of the first character that side of the line break. However, characters such as punctuation that belong to the COMMON and INHERITED scripts are ignored in this check; the next character is examined instead. The UA must not examine characters outside the block and may limit its examination to as few as four characters on each side of the line break. If the check fails to find an acceptable script value (i.e. it has hit the check limits), then the script context is neutral.

• If the character immediately before or immediately after the line break is the zero width space character (U+200B), then the line break is removed.
• Otherwise, if the script context on one side of the line break is Han, Yi, Hiragana, or Katakana and the context on the other side is Han, Yi, Hiragana, Katakana, or neutral, then the line break is removed.
• Otherwise, the line break is converted to a space (U+0020).

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

3.2.3. Informative Summary of White Space Collapsing Effects

• Consecutive white space collapses into a single space.
• A sequence of line breaks and other white space between two ideographic characters collapses into nothing unless there is a space before the first line break in the sequence.
• A zero width space immediately before or anywhere after a line break causes the entire sequence of white space beginning with the line break to collapse into a zero width space.

3.3. White Space and Text Wrapping Shorthand: the 'white-space' property

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

normal

Sets 'white-space-collapse' to 'collapse' and 'text-wrap' to 'normal'

pre

Sets 'white-space-collapse' to 'preserve' and 'text-wrap' to 'none'

nowrap

Sets 'white-space-collapse' to 'collapse' and 'text-wrap' to 'none'

pre-wrap

Sets 'white-space-collapse' to 'preserve' and 'text-wrap' to 'normal'

pre-line

Sets 'white-space-collapse' to 'preserve-breaks' and 'text-wrap' to 'normal'

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

4. Line Breaking and Word Boundaries

For most scripts, 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 opportunities are based on syllable boundaries, not words. 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.

4.1. Line Breaking Restrictions: the 'word-break' property

CSS distinguishes between two levels of strictness in the rules for implicit line breaking in CJK text. The precise set of rules in effect for the strict and loose levels is up to the UA and should follow language conventions. However, this specification does recommend that the following breaks be forbidden in strict line breaking and allowed in loose:

• breaks before Japanese small kana
• breaks before Japanese iteration marks (U+3005, U+303B, U+309D, U+309E, U+30FD, U+30FE)
• breaks before the katakana lengthening mark (U+30FC)
• ???

Breaks between Hangul syllable blocks are allowed in both strict and loose rules: to restrict breaks in Korean to spaces, the 'keep-all' value of 'word-break' can be specified.

Information on line breaking conventions can be found in [JIS4051] for Japanese, [标点符号] for Chinese, and [?] for Korean, and in [UAX14] for all scripts in Unicode.

Any guidance for appropriate references here would be much appreciated.

This property specifies what set of line breaking restrictions are in effect within the element. Values have the following meanings:

normal

Breaks non-CJK scripts according to their own rules while using a strict set of line breaking restrictions for CJK scripts (Hangul, Japanese Kana, and CJK ideographs).

keep-all

Same as 'normal' for all non-CJK scripts. However, sequences of CJK characters can no longer break on implied break points. This option should only be used where the presence of white space characters still creates line-breaking opportunities, as in Korean.

loose

As for 'normal', but CJK scripts use a less restrictive set of line-breaking restrictions.

break-strict

Same as 'normal' for CJK scripts, but non-CJK scripts can break anywhere. This option is used mostly when the text is predominantly CJK characters with few non-CJK excerpts and it is desired that the text be more evenly distributed on each line.

break-all

As for 'break-strict', except CJK scripts break according to the rules for 'loose'.

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

4.2. Hyphenation

insert value name here

Words may be broken at an appropriate hyphenation point. This requires that the user agent have an hyphenation resource appropriate to the language of the text being broken.

If hyphenation is applied to a shaped script such as Arabic then the shaping process must ignore the hyphenation break and shape as if the word were still whole and unhyphenated.

5. Text Wrapping

Text wrapping is controlled by the 'text-wrap' and 'word-wrap' properties:

5.1. Text Wrap Settings: the 'text-wrap' property

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 box overflows it.

unrestricted

Lines may break between any two grapheme clusters. Line-breaking restrictions have no effect and hyphenation does not take place. Character shaping is performed on each side of the break as if the break had not occurred.

suppress

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'.

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 'suppress', UAs that allow breaks at punctutation 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.

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

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

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

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

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

5.2. Force Wrapping: the 'word-wrap' property

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 'suppress'. Possible values:

normal

Lines may break only at allowed break points.

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.

6. Alignment and Justification

6.1. Text Alignment: the 'text-align' property

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>

When applied to a table cell, specifies a character on which all cells in its table column that also have a character value for 'text-align' will align (see the section on horizontal alignment in a column for details and an example). When applied to any other element, it is treated as 'start'. The string must be a single character; otherwise the declaration must be ignored.

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 boxes within each line box align within the line box: alignment is not with respect to the viewport or containing block. In the case of 'justify', the UA may stretch the inline boxes in addition to adjusting their positions. (See also the 'text-justify', 'text-justify-trim', 'text-kashida-space', 'letter-spacing' and 'word-spacing'.)

6.2. Last Line Alignment: the 'text-align-last' property

This property describes how the last line of a block or a line right before a forced line break is aligned when 'text-align' is set to 'justify'. Values have the same meaning as for 'text-align'.

6.3. Justification Method: the 'text-justify' property

This property selects the justification method used when 'text-align' is set to 'justify'. It takes the following values:

auto

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

inter-word

Justification primarily changes spacing at word separators

inter-ideograph

Justification primarily changes spacing at word separators and at inter-graphemic boundaries in scripts that use no word spaces

inter-cluster

Justification primarily changes spacing at word separators and at grapheme cluster boundaries in cluster scripts.

distribute

Justification primarily changes spacing both at word separators and at grapheme cluster boundaries in all scripts except those in the connected and cursive groups.

kashida

Justification primarily stretches Arabic and related scripts through the use of kashida or other calligraphic elongation.

tibetan

Justification primarily stretches spaces after shad if the line contains any and/or pads the end of the line with tsek marks if the line already ends in one.

The 'tibetan' value of 'text-justify' will most likely be removed in the next draft, as inter-word justification is preferred in modern typesetting.

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.

Justification affects different types of writing systems in different ways. For justification purposes, writing systems are grouped as follows:

block

CJK (including Hangul and half-width kana) and by extension all "wide" characters. (See [UAX11])

clustered

South-East Asian scripts that have discrete units but do not use space between words (such as Thai, Lao, Khmer, Myanmar)

connected

Devanagari and other scripts such as such as Bengali and Gurmukhi, that use spaces between words and baseline connectors within words. The Ogham script also falls into this category.

cursive

Arabic and similar cursive scripts

discrete

Scripts that use spaces between words and have discrete, unconnected (in print) units within words, such as Latin, Greek, Cyrillic, Hebrew; this category also includes symbols and punctuation.

tibetan

Tibetan has clusters similar to South and South Asian scripts but also has its own punctuation system. Its traditional justification does not match any of the other scripts, so this category represents the Tibetan script.

Where do scripts like Tamil fit in?

The UA may enable or break optional ligatures or use other font features such as alternate glyphs to help justify the text under any method. This behavior is not defined by CSS.

CSS defines expansion opportunities as points where the justification algorithm may alter spacing within the text. Expansion opportunities occur at word separators and between grapheme clusters. These expansion opportunities fall into priority levels as defined by the justification method. Within a line, higher priority expansion opportunities must be expanded or compressed to their limits before lower priority expansion opportunities may be adjusted. These 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 (or as 'start' if 'text-align-last' is 'justify').

The expansion opportunity priorities for values of 'text-justify' are given in the table below. Space must be distributed evenly among all types of expansion opportunities in a given prioritization group, but may vary within a line due to changes in the font or letter-spacing and word-spacing values. The different types of expansion opportunities are defined as follows:

spaces

An expansion opportunity exists at spaces and other word separators. Expand as for 'word-spacing'.

block

clustered

connected

discrete

tibetan

An expansion opportunity exists between two grapheme clusters, when at least one of them belongs to the affected script group and the spacing that point has not already been altered at a higher priority.

I'm not sure grapheme clusters are the right unit to use for some of these complex scripts...

cursive

If the UA is capable of extending the graphical connection between cursively connected grapheme clusters, an expansion opportunity exists between any two cursively connected grapheme clusters belonging to cursive scripts, but not between disjoint grapheme clusters. The UA must not break the graphical connection when changing the spacing between cursively connected grapheme clusters.

The two values kashida and tibetan trigger special justification behavior as specified below. This special behavior takes priority over the expansion opportunity adjustments described above.

kashida

apply kashida elongation. This may be done in discrete kashida units, 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 ruleset. The UA should limit elongation so that in multi-script lines a short stretch of Arabic will not be forced to soak up too much of the extra space by itself.

tibetan

apply Tibetan justification. Tibetan justification stretches the spaces after shads (TIBETAN MARK SHAD U+0F0D, TIBETAN MARK NYIS SHAD U+0F0E, TIBETAN MARK TSHEG SHAD U+0F0F, TIBETAN MARK NYIS TSHEG SHAD U+0F10, TIBETAN MARK RIN CHEN SPUNGS SHAD U+0F11, TIBETAN MARK RGYA GRAM SHAD U+0F12) and spaces after the letters KA (U+0F40) and GA (U+0F42)—with or without combining vowels—if the line contains any. Otherwise, if the line ends in a tsek mark (TIBETAN MARK INTERSYLLABIC TSHEG U+0F0B, TIBETAN MARK DELIMITER TSHEG BSTAR U+0F0C) it pads the end of the line with tsek (U+0F0B) to fill the remaining space. The UA may use a more sophisticated algorithm than the simple two-step one above, but must still prioritize flexing a space after a shad over padding the line with tseks. For example, one possible algorithm stretches spaces up to twice their width, then falls back to padding the line with up to six tseks. If there is still more space to soak up, it goes back to stretching the spaces beyond that limit, or, if there are none, adding tseks past the six-tsek limit. Balancing the two methods in such a way results in more even-looking justified text. Note that this method was used to justify text in hand-written documents and primitive typesetting systems. Modern practice prefers inter-word justification, and therefore this method is only useful for recreating historical layouts.

7. Spacing

The next two properties refer to the <spacing-limit> value type, which is defined as follows:

<spacing-limit>

[ normal | <length> | <percentage> ]

normal

Specifies the normal optimum/minimum/maximum spacing, as defined by the current font and/or the user agent. Normal spacing should be percentage-based. Normal minimum and maximum spacing must be based on the optimum spacing so that the minimum and maximum limits increase and decrease with changes to the optimum spacing. Normal minimum and maximum spacing may also vary according to some measure of the amount of text on a line (e.g. block width divided by font size): larger measures can accomodate 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.

<length> or <percentage>

Specifies extra spacing in addition to the normal spacing. Percentages are with respect to the width of a space (U+0020). Values may be negative, but there may be implementation-dependent limits.

7.1. Word Spacing: the 'word-spacing' property

This property specifies the minimum, maximum, and optimal spacing between words. If only one value is specified, then it represents the optimal spacing and the minimum and maximum are both 'normal'. If two values are specified, then the first represents both the optimal spacing and the minimum spacing, and the second represents the maximum spacing. If three values are specified, they represent the optimum, minimum, and maximum respectively.

If the value of the optimum or maximum spacing is less than the value of the minimum spacing, then its used value is the minimum spacing. If the optimum spacing is greater than the maximum spacing then its used value is the maximum spacing. (This substitution occurs after inheritance.)

In the absence of justification the optimal 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.

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. This is correct for Ethiopian and doesn't matter for invisible spaces, but is it correct for Tibetan? Most publications seem to add space after the tsek mark during justification. Word-separator characters include the space (U+0020), the no-break space (U+00A0), the Ethiopic word space (U+1361), the ideographic space (U+3000), the Aegean word separators (U+10100,U+10101), the Ugaritic word divider (U+1039F), and the Tibetan tsek (U+0F0B, U+0F0C). Is this list correct? 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+2000 through U+200A) are not considered word-separators.

7.2. Tracking: the 'letter-spacing' property

This property specifies the minimum, maximum, and optimal spacing between grapheme clusters. If only one value is specified, then it represents all three values. If two values are specified, then the first represents both the optimal spacing and the minimum spacing, and the second represents the maximum spacing. If three values are specified, they represent the optimum, minimum, and maximum respectively.

If the value of the optimum or maximum spacing is less than the value of the minimum spacing, then its used value is the minimum spacing. If the optimum spacing is greater than the maximum spacing then its used value is the maximum spacing. (This substitution occurs after inheritance.)

In the absence of justification the optimal 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. Letter-spacing is applied in addition to any word-spacing. 'normal' optimum letter-spacing is typically zero.

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 relies on the default (not tailored) rules only.

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.

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

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

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 graphemes as specified above and extend the visible connection between cursively connected graphemes 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 grapheme clusters 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.

7.3. Fullwidth Punctuation Kerning: the 'punctuation-trim' property

This property determines whether or not a fullwidth punctuation character should be trimmed (kerned) if it appears at the start or end of a line, or adjacent to another fullwidth punctuation character. Values are defined as follows:

none

Do not trim or kern the blank half of fullwidth opening or closing punctuation glyphs.

start

Trim (kern) the blank half of fullwidth opening punctuation at the beginning of each line.

end

Trim (kern) the blank half of fullwidth closing punctuation at the end of each line.

adjacent

Trim (kern) the blank half of fullwidth opening punctuation if its previous adjacent character is a fullwidth opening punctuation, fullwidth middle dot punctuation, fullwidth closing punctuation, or ideographic space (U+3000). Trim (kern) the blank half of fullwidth closing punctuation if its next adjacent character is a fullwidth closing punctuation, fullwidth middle dot punctuation, or ideographic space (U+3000).

In the context of this property the following definitions apply:

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).

Fullwidth opening and closing punctuation must not be trimmed if the glyph is not actually fullwidth. A fullwidth glyph is one that has the same advance width as a typical Han character in the same font.

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 layout orientation (horizontal vs. vertical), and/or font information to determine this categorization. The UA may also add additional characters to any category as appropriate.

8. Text Decoration

8.1 Line Decoration

8.2 Emphasis Marks: the 'text-emphasis' property

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

This property applies emphasis formatting applied to text. Unlike 'text-decoration', emphasis marks can affect the line height. Values have the following meanings:

none

No emphasis marks.

accent

Draw calligraphic accent strokes as marks.

dot

Draw calligraphic dots as marks.

circle

Draw hollow circles as marks.

disc

Draw filled circles as marks.

before

Draw marks above the text in horizontal layout, to the right in vertical layout. This is the default position.

after

Draw marks below the text in horizontal layout, to the left in vertical layout.

The list of shapes here is copied from the CSS3 Fonts module drafts, and it is not correct or at least not complete. Any input on what shapes are needed, what usage patterns are found in real texts, etc. would be much appreciated. Send them off to www-style@w3.org or www-international@w3.org with [CSS3 Text] in the subject line.

Note, the preferred position of emphasis marks depends on the language. In Japanese for example, the preferred position is 'before'. In Chinese used in the PRC, on the other hand, the preferred position is 'after'. The informative table below summarizes the preferred emphasis mark position for Chinese and Japanese:

Preferred emphasis mark and ruby position

Language	Preferred mark position	Illustration
Japanese	before
Chinese (Traditional)	before
Chinese (Simplified)	after

8.3 Text Shadows: the 'text-shadow' property

This property accepts a comma-separated list of shadow effects to be applied to the text of the element. <shadow> is defined as [ <color>? <length> <length> <length>? | <length> <length> <length>? <color>? ], where the first two lengths represent the offset and the third an optional blur radius. The shadow is applied to all of the element's text as well as any text decoration applied to it. Would it be better to apply shadows together with text decoration: i.e. a descendent of an underlined element doesn't apply shadow to its underline, but the underlining element, if it has shadows, would apply it to the underline of all text it underlines. When a text outline is specified, the shadow shadows the outlined shape rather than the glyph shape.

The shadow offset is specified with two <length> values that indicate an offset from direct alignment with the text. The first length value specifies the horizontal distance to the right of the text. A negative horizontal length value places the shadow to the left of the text. The second length value specifies the vertical distance below the text. A negative vertical length value places the shadow above the text.

A blur radius may optionally be specified after the shadow offset. The blur radius is a length value that indicates the boundaries of the blur effect. The exact algorithm for computing the blur effect is not specified. If the blur radius is not specified, it is equal to zero.

A color value may optionally be specified before or after the length values of the shadow effect. The color value will be used as the color of the shadow effect. If the color is not specified, a UA-chosen color will be used.

The shadow effects are applied in the order specified should this be changed to layer the same way multiple backgrounds do (earlier on top)? and may thus overlay each other, but they will never overlay the text itself. Shadow effects do not alter the size of a box, but may extend beyond its boundaries. The stack level of the shadow effects is the same as for the element itself. Does this definition cause problems with the shadow of one element painting over the text of the previous element? How would we solve that?

8.4 Text Outlines: the 'text-outline' property

This property specifies a text outline where the first length represents the outline's thickness and the second represents an optional blur radius. The outline never overlays the text itself. Its effect is the same as that obtained by applying text shadows in every radial direction, i.e. all text shadows whose offsets satisfy the equation x2 + y2 = thickness2.

The Timed-Text WG had suggestions for some keywords (text-outline: normal|heavy|light;) as well as a <length> thickness. Should these be added? How would they be defined? (Maybe use (thin|medium|thick) as in border-width?)

The blur radius is a length value that indicates the boundaries of the blur effect. The exact algorithm for computing the blur effect is not specified, but it is only applied to the outer edge of the outline. If the blur radius is not specified, it is equal to zero. Is a second blur radius needed for the inner edge? Or should the blur apply to both edges? Implementations may choose to ignore the blur radius when text outline is combined with a text shadow.

A color value must be specified before or after the length values of the outline effect. The color value will be used as the color of the outline.

9. Edge Effects

9.1 First Line Indentation: the 'text-indent' property

This property specifies the indentation applied to lines of inline content in a block. The indendation only affects the first line of inline content in the block unless the 'hanging' keyword is specified, in which case it affects all lines except the first.

The indent is treated as a margin applied to the start edge of the line box. The amount of indentation is given by the length or percentage value. Percentages are relative to the containing block, even in the presence of floats. They are inherited as percentages, not as absolute lengths.

     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 descendent 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

This property determines whether a punctuation mark, if one is present, may be placed outside the line box at the start or at the end of a full line of text. If a justified line can fit the punctuation will it expand to push it outside the content area? No. What if the line ends in multiple punctuation marks? Which punctuation marks are affected? Values have the following meanings:

start

Punctuation may hang outside the start edge of the first line.

end

Punctuation may hang outside the end edge of the last line.

end-edge

Punctuation may hang outside the end edge of all lines.

Need to work on the description. Cover indentation as well.

To be continued...

10. Changes from the May 2003 CSS3 Text CR

Much of the text has been rewritten or severely revised, so all changes will not be listed here. Highlights include:

• The 'line-break' and 'word-break-cjk' properties have been replaced by the 'word-break' property.
• The 'word-break-inside' property has been replaced by the 'hyphenate' property.
• The 'wrap-option' property has been replaced by the 'text-wrap' and 'word-break' property.
• The 'linefeed-treatment', 'white-space-treatment', and 'all-space-treatment' properties have been replaced by the 'white-space-collapse' property.
• The 'min-font-size' and 'max-font-size' properties have been delegated to the next revision of the CSS3 Fonts module.
• Change 'text-align's vertical text behavior for the 'left' and 'right' values to be relative to LTR text rather than relative to the beginning of the line stack.
• The 'size' value has been removed from the 'text-align-last' property.
• The 'newspaper' value for 'text-justify' has been dropped in favor of using minimum and maximum limits set on the 'word-spacing' and 'letter-spacing' properties to guide justification.
• The 'word-spacing' and 'letter-spacing' now take percentage values.
• The new 'text-wrap' property's 'suppress' value allows authors to suppress text wrapping within an element with respect to its surrounding text without forbidding correctly-restricted breaks when they are needed.
• The automatic line break conversions specified in the white space processing rules have been changed to try not to break existing East and Southeast Asian content. Explicit control of these rules through the 'linefeed-treatment' property has been removed because style sheets should not be expected to adapt to the source code formatting style.
• The 'size' value for text-align-last has been removed.
• Text justification has been much more explicitly specified with prioritized expansion opportunities.
• The 'tibetan' value for 'text-justify' has been added to specify traditional Tibetan justification (which is still in use in modern books and newspapers) and details have been added for handling Tibetan text in other justification schemes.
• An 'end' value has been added to 'punctuation-trim'.
• 'kerning-mode: contextual' has been replaced with 'punctuation-trim: adjacent'. Any further controls for kerning will likely be delegated to the Fonts module.
• The 'text-shadow' property now inherits, which makes more sense and is consistent with recent implementation. The default color is now UA-specified, which is more reasonable than defaulting to the current text color. The definition now also mentions that it applies to text decoration and makes a few minor clarifications.
• The 'text-outline' property has been added in response to feedback from the Timed-Text WG and Ada Chan. Its design derives from a discussion of requirements within the CSS Working Group.
• The 'text-emphasis' property has been added to replace the 'font-emphasis' property from the CSS3 Fonts module.
• The definition for 'text-indent' has been replaced with the precise text sent in by Ian Hickson and fantasai on 8 March 2003 (minus the 'text-align' dependence rules).
• The 'hanging-punctuation' property has been redesigned with the combinable values 'start', 'end', and 'end-edge' instead of 'start' 'end' and 'both' to eliminate the script and language dependencies.

Many sections intended for this module are not yet represented in this draft. In particular, the 'text-justify-trim', 'text-overflow', 'text-decoration', 'text-transformation', 'text-autospace', other properties have not yet been evaulated.

Sections relating to text layout (vertical text, grids, 'text-combine') will be moved to a separate Text Layout module. These features may change greatly from the last revision, but they have not been dropped. The vertical text feature, for example, will likely be based on the methods described in Unicode Technical Note #22.

11. Changes from the June 2005 CSS3 Text WD

• Update references
• Add an at-risk section
• Add Yi to the Line Break Transformation rules
• Rewrite line-breaking intro
• Put reference to UAX14 et al. in a note and add note of caution about UAX14
• Define shaping behavior for hyphenated words
• Allow only a single character, not a string, as a value of 'text-align'
• Fix syntax definition for <spacing-limit> and adjust min/max wording
• Define letter-spacing behavior at element boundaries.
• Allow and specify letter-spacing expansion for cursive scripts
• Recommend that 'normal' min/max limits for letter-spacing and word-spacing vary based on the line length; also allow them to change based on text-justify.
• Re-add definition for 'white-space' shorthand property
• Change 'text-align's vertical text behavior for the 'left' and 'right' values to be relative to LTR text rather than relative to the beginning of the line stack.
• Add Tibetan justification definition
• Remove 'size' justification value
• Rename 'inter-character' justification value back to 'distribute'
• Improve justification text
• Add back 'white-space' shorthand
• Add back text-decoration section as an open issue.
• Add 'text-emphasis' property to replace 'font-emphasis' from CSS3 Fonts drafts
• Add back definition for 'text-indent', with more precise (and concise) text
• Add back definition for 'text-shadow', make it inherit and let UA pick default color.
• Add 'text-outline' property.
• Add back 'punctuation-trim' with new value 'adjacent' (which replaces 'kerning-mode: contextual').
• Add back 'hanging-punctuation'.
• Various minor clarifications.

12. Acknowledgements

This specification would not have been possible without the help from: Ayman Aldahleh, Bert Bos, Tantek Çelik, Stephen Deach, Martin Dürst, Laurie Anna Edlund, Ben Errez, Yaniv Feinberg, Arye Gittelman, Ian Hickson, Martin Heijdra, Richard Ishida, Koji Ishii, Masayasu Ishikawa, Michael Jochimsen, Eric LeVine, Chris Lilley, Shinyu Murakami, Paul Nelson, Chris Pratley, Martin Sawicki, Rahul Sonnad, Frank Tang, Chris Thrasher, Etan Wexler, Chris Wilson, Masafumi Yabe and Steve Zilles.

13. References

13.1. Normative References

[CSS21]

Bert Bos; et al. Cascading Style Sheets, level 2 revision 1. 06 November 2006. W3C Working Draft. (Work in progress.) URL: https://www.w3.org/TR/2006/WD-CSS21-20061106/

[RFC2119]

S. Bradner. Key words for use in RFCs to Indicate Requirement Levels. Internet RFC 2119.URL: https://www.ietf.org/rfc/rfc2119.txt

[UAX11]

Asmus Freytag. East Asian Width. 15 September 2006. Unicode Standard Annex #11. URL: https://www.unicode.org/unicode/reports/tr11/tr11-15.html

[UAX14]

Asmus Freytag. Line Breaking Properties. 29 March 2005. Unicode Standard Annex #14. URL: https://www.unicode.org/unicode/reports/tr14/tr14-17.html

[UAX24]

Mark Davis. Script Names. 15 September 2006. Unicode Standard Annex #24. URL: https://www.unicode.org/unicode/reports/tr24/tr24-9.html

[UAX29]

Mark Davis. Text Boundaries. 12 October 2006. Unicode Standard Annex #29. URL: https://www.unicode.org/unicode/reports/tr29/tr29-11.html

13.2. Informative References

[标点符号]

标点符号用法 (Punctuation Mark Usage). 中华人民共和国国家标准. 1995.

[JIS4051]

JIS X 4051:2004. Formatting rules for Japanese documents. (『日本語文書の組版方法』) Japanese Standards Association. 2004.

[UAX14]

Asmus Freytag. Line Breaking Properties. 29 March 2005. Unicode Standard Annex #14. URL: https://www.unicode.org/unicode/reports/tr14/tr14-17.html