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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html lang=en>
<head><meta content="text/html; charset=utf-8" http-equiv=Content-Type>
<title>CSS Text Level 3</title>
<link href="../default.css" rel=stylesheet type="text/css">
<style type="text/css">
.egbidiwsaA,.egbidiwsbB,.egbidiwsaB,.egbidiwsbC
{ white-space:pre;font-size:80%;font-family:monospace; vertical-align:2px; margin:1px }
.egbidiwsaA { background:lime;padding:2px; }
.egbidiwsbB { border:2px solid blue }
.egbidiwsaB { background:yellow;border:2px dotted white }
.egbidiwsbC { border:2px dotted red }
.char { border: 1px dotted gray; }
.quarter { font-size: 25%; }
tt[lang="ja"] { font-family: "MS Gothic", "Osaka", monospace }
div.figure table {
margin :auto;
}
</style>
<link href="http://www.w3.org/StyleSheets/TR/W3C-ED.css" rel=stylesheet
type="text/css">
<body>
<div class=head> <!--begin-logo-->
<p><a href="http://www.w3.org/"><img alt=W3C height=48
src="http://www.w3.org/Icons/w3c_home" width=72></a> <!--end-logo-->
<h1>CSS Text Level 3</h1>
<h2 class="no-num no-toc" id=longstatus-date>Editor's Draft 27 March 2012</h2>
<dl>
<dt>This version:
<dd><a href="http://dev.w3.org/csswg/css3-text/">$Date$ (CVS
$Revision$)</a> <!--
<dd><a href="http://www.w3.org/TR/2012/WD-css3-text-20120327/">http://www.w3.org/TR/2012/WD-css3-text-20120327/</a></dd>
-->
<dt>Latest version:
<dd><a
href="http://www.w3.org/TR/css3-text/">http://www.w3.org/TR/css3-text/</a>
<dt>Latest editor's draft:
<dd><a
href="http://dev.w3.org/csswg/css3-text/">http://dev.w3.org/csswg/css3-text/</a>
<dt>Previous version:
<dd><a
href="http://www.w3.org/TR/2011/WD-css3-text-20110901/">http://www.w3.org/TR/2011/WD-css3-text-20110901/</a>
<dt>Issues List:
<dd><a
href="http://www.w3.org/Style/CSS/Tracker/products/10">http://www.w3.org/Style/CSS/Tracker/products/10</a>
<dt>Discussion:
<dd><a
href="http://lists.w3.org/Archives/Public/www-style/">www-style@w3.org</a>
with subject line “<kbd>[css3-text] <var>… message topic
…</var></kbd>”
<dt>Editors:
<dd><a href="http://fantasai.inkedblade.net/contact">Elika J. Etemad</a>
(Mozilla)
<dd><a href="mailto:kojiishi@gluesoft.co.jp">Koji Ishii</a> (Invited
Expert)
</dl>
<!--begin-copyright-->
<p class=copyright><a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
rel=license>Copyright</a> © 2012 <a href="http://www.w3.org/"><abbr
title="World Wide Web Consortium">W3C</abbr></a><sup>®</sup> (<a
href="http://www.csail.mit.edu/"><abbr
title="Massachusetts Institute of Technology">MIT</abbr></a>, <a
href="http://www.ercim.eu/"><abbr
title="European Research Consortium for Informatics and Mathematics">ERCIM</abbr></a>,
<a href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. W3C <a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
<a
href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a>
and <a
href="http://www.w3.org/Consortium/Legal/copyright-documents">document
use</a> rules apply.</p>
<!--end-copyright-->
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc" id=abstract>Abstract</h2>
<p>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.
<h2 class="no-num no-toc" id=status>Status of This Document</h2>
<p><em>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 <a href="http://www.w3.org/TR/">W3C technical reports
index at http://www.w3.org/TR/.</a></em>
<p>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.
<p>This CSS module has been produced as a combined effort of the <a
href="http://www.w3.org/International/Activity">W3C Internationalization
Activity</a>, and the <a href="http://www.w3.org/Style/Activity">Style
Activity</a> and is maintained by the <a
href="http://www.w3.org/Style/CSS/members">CSS Working Group</a>. It also
includes contributions made by participants in the <a
href="http://www.w3.org/Style/XSL/Group/">XSL Working Group</a> (<a
href="http://cgi.w3.org/MemberAccess/AccessRequest">members only</a>).
<p>This document was produced by a group operating under the <a
href="http://www.w3.org/Consortium/Patent-Policy-20040205/">5 February
2004 W3C Patent Policy</a>. W3C maintains a <a
href="http://www.w3.org/2004/01/pp-impl/32061/status"
rel=disclosure>public list of any patent disclosures</a> 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 <a
href="http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">Essential
Claim(s)</a> must disclose the information in accordance with <a
href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">section
6 of the W3C Patent Policy</a>.
<p><strong>Feedback on this draft should be posted to the (<a
href="http://lists.w3.org/Archives/Public/www-style/">archived</a>) public
mailing list <a
href="mailto:www-style@w3.org">www-style@w3.org</a></strong> (see <a
href="http://www.w3.org/Mail/Request">instructions</a>) <strong>with
<kbd>[css3-text]</kbd> in the subject line.</strong> 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.
<p>The following features are at risk and may be cut from the spec during
its CR period if there are no (correct) implementations:
<ul>
<li>the <length> values of the ‘<a href="#tab-size0"><code
class=property>tab-size</code></a>’ property
<li>the ‘<code class=css>start end</code>’ and ‘<code
class=css><string></code>’ values of ‘<a
href="#text-align0"><code class=property>text-align</code></a>’
<li>the ‘<a href="#hanging-punctuation0"><code
class=property>hanging-punctuation</code></a>’ property
<li>the percentage values of ‘<a href="#word-spacing0"><code
class=property>word-spacing</code></a>’
<li>the ‘<a href="#text-decoration-skip0"><code
class=property>text-decoration-skip</code></a>’ property /
‘<code class=css>ink</code>’ value
<li><span class=issue>audit draft and add more here</span>
</ul>
<h2 class="no-num no-toc" id=contents> Table of Contents</h2>
<!--begin-toc-->
<ul class=toc>
<li><a href="#intro"><span class=secno>1. </span> Introduction</a>
<ul class=toc>
<li><a href="#placement"><span class=secno>1.1. </span> Module
Interactions</a>
<li><a href="#values"><span class=secno>1.2. </span> Values</a>
<li><a href="#terms"><span class=secno>1.3. </span> Terminology</a>
</ul>
<li><a href="#transforming"><span class=secno>2. </span> Transforming
Text</a>
<ul class=toc>
<li><a href="#text-transform"><span class=secno>2.1. </span>
Transforming Text: the ‘<code
class=property>text-transform</code>’ property</a>
</ul>
<li><a href="#white-space-processing"><span class=secno>3. </span> White
Space Processing</a>
<ul class=toc>
<li><a href="#white-space-collapsing"><span class=secno>3.1. </span>
White Space Collapsing: the ‘<code
class=property>text-space-collapse</code>’ property</a>
<li><a href="#tab-size"><span class=secno>3.2. </span> Tab Character
Size: the ‘<code class=property>tab-size</code>’
property</a>
<li><a href="#white-space-rules"><span class=secno>3.3. </span> The
White Space Processing Rules</a>
<ul class=toc>
<li><a href="#egbidiwscollapse"><span class=secno>3.3.1. </span>
Example of bidirectionality with white space collapsing</a>
<li><a href="#line-break-transform"><span class=secno>3.3.2. </span>
Line Break Transformation Rules</a>
</ul>
<li><a href="#white-space"><span class=secno>3.4. </span> White Space
and Text Wrapping Shorthand: the ‘<code
class=property>white-space</code>’ property</a>
</ul>
<li><a href="#line-breaking"><span class=secno>4. </span> Line Breaking
and Word Boundaries</a>
<ul class=toc>
<li><a href="#line-break"><span class=secno>4.1. </span> Line Breaking
Strictness: the ‘<code class=property>line-break</code>’
property</a>
<li><a href="#word-break"><span class=secno>4.2. </span> Word Breaking
Rules: the ‘<code class=property>word-break</code>’
property</a>
</ul>
<li><a href="#hyphenation"><span class=secno>5. </span>Hyphenation</a>
<ul class=toc>
<li><a href="#hyphens"><span class=secno>5.1. </span>Hyphenation
Control: the ‘<code class=property>hyphens</code>’
property</a>
</ul>
<li><a href="#wrapping"><span class=secno>6. </span> Text Wrapping</a>
<ul class=toc>
<li><a href="#text-wrap"><span class=secno>6.1. </span> Text Wrap
Settings: the ‘<code class=property>text-wrap</code>’
property</a>
<ul class=toc>
<li><a href="#example-avoid"><span class=secno>6.1.1. </span>
Phrase-controlled Breaking</a>
</ul>
<li><a href="#overflow-wrap"><span class=secno>6.2. </span> Emergency
Wrapping: the ‘<code class=property>overflow-wrap</code>’
property</a>
</ul>
<li><a href="#justification"><span class=secno>7. </span> Alignment and
Justification</a>
<ul class=toc>
<li><a href="#text-align"><span class=secno>7.1. </span> Text Alignment:
the ‘<code class=property>text-align</code>’ property</a>
<ul class=toc>
<li><a href="#character-alignment"><span class=secno>7.1.1.
</span>Character-based Alignment in a Table Column</a>
</ul>
<li><a href="#text-align-last"><span class=secno>7.2. </span> Last Line
Alignment: the ‘<code
class=property>text-align-last</code>’ property</a>
<li><a href="#text-justify"><span class=secno>7.3. </span> Justification
Method: the ‘<code class=property>text-justify</code>’
property</a>
</ul>
<li><a href="#spacing"><span class=secno>8. </span> Spacing</a>
<ul class=toc>
<li><a href="#word-spacing"><span class=secno>8.1. </span> Word Spacing:
the ‘<code class=property>word-spacing</code>’ property</a>
<li><a href="#letter-spacing"><span class=secno>8.2. </span> Tracking:
the ‘<code class=property>letter-spacing</code>’
property</a>
</ul>
<li><a href="#edge-effects"><span class=secno>9. </span> Edge Effects</a>
<ul class=toc>
<li><a href="#text-indent"><span class=secno>9.1. </span> First Line
Indentation: the ‘<code class=property>text-indent</code>’
property</a>
<li><a href="#hanging-punctuation"><span class=secno>9.2. </span>
Hanging Punctuation: the ‘<code
class=property>hanging-punctuation</code>’ property</a>
</ul>
<li><a href="#decoration"><span class=secno>10. </span> Text
Decoration</a>
<ul class=toc>
<li><a href="#line-decoration"><span class=secno>10.1. </span> Line
Decoration: Underline, Overline, and Strike-Through</a>
<ul class=toc>
<li><a href="#text-decoration-line"><span class=secno>10.1.1. </span>
Text Decoration Lines: the ‘<code
class=property>text-decoration-line</code>’ property</a>
<li><a href="#text-decoration-color"><span class=secno>10.1.2. </span>
Text Decoration Color: the ‘<code
class=property>text-decoration-color</code>’ property</a>
<li><a href="#text-decoration-style"><span class=secno>10.1.3. </span>
Text Decoration Style: the ‘<code
class=property>text-decoration-style</code>’ property</a>
<li><a href="#text-decoration"><span class=secno>10.1.4. </span> Text
Decoration Shorthand: the ‘<code
class=property>text-decoration</code>’ property</a>
<li><a href="#text-decoration-skip"><span class=secno>10.1.5. </span>
Text Decoration Line Continuity: the ‘<code
class=property>text-decoration-skip</code>’ property</a>
<li><a href="#text-underline-position"><span class=secno>10.1.6.
</span> Text Underline Position: the ‘<code
class=property>text-underline-position</code>’ property</a>
</ul>
<li><a href="#emphasis-marks"><span class=secno>10.2. </span> Emphasis
Marks</a>
<ul class=toc>
<li><a href="#text-emphasis-style"><span class=secno>10.2.1. </span>
Emphasis Mark Style: the ‘<code
class=property>text-emphasis-style</code>’ property</a>
<li><a href="#text-emphasis-color"><span class=secno>10.2.2. </span>
Emphasis Mark Color: the ‘<code
class=property>text-emphasis-color</code>’ property</a>
<li><a href="#text-emphasis"><span class=secno>10.2.3. </span>
Emphasis Mark Shorthand: the ‘<code
class=property>text-emphasis</code>’ property</a>
<li><a href="#text-emphasis-position"><span class=secno>10.2.4.
</span> Emphasis Mark Position: the ‘<code
class=property>text-emphasis-position</code>’ property</a>
</ul>
<li><a href="#text-shadow"><span class=secno>10.3. </span> Text Shadows:
the ‘<code class=property>text-shadow</code>’ property</a>
</ul>
<li><a href="#conformance"><span class=secno>11. </span> Conformance</a>
<ul class=toc>
<li><a href="#conventions"><span class=secno>11.1. </span> Document
Conventions</a>
<li><a href="#conformance-classes"><span class=secno>11.2. </span>
Conformance Classes</a>
<li><a href="#partial"><span class=secno>11.3. </span> Partial
Implementations</a>
<li><a href="#experimental"><span class=secno>11.4. </span> Experimental
Implementations</a>
<li><a href="#testing"><span class=secno>11.5. </span>Non-Experimental
Implementations</a>
<li><a href="#cr-exit-criteria"><span class=secno>11.6. </span> CR Exit
Criteria</a>
</ul>
<li class=no-num><a href="#acknowledgements"> Appendix A:
Acknowledgements</a>
<li class=no-num><a href="#appendix-b-references">Appendix B:
References</a>
<ul class=toc>
<li class=no-num><a href="#normative-ref">Normative references</a>
<li class=no-num><a href="#informative-ref">Informative references</a>
</ul>
<li class=no-num><a href="#changes">Appendix C: Changes</a>
<ul class=toc>
<li class=no-num><a href="#recent-changes"> Changes from the September
2011 CSS3 Text <abbr title="Working Draft">WD</abbr></a>
</ul>
<li class=no-num><a href="#default-stylesheet">Appendix D: Default UA
Stylesheet</a>
<li class=no-num><a href="#script-groups">Appendix E: Scripts and
Spacing</a>
<li class=no-num><a href="#small-kana">Appendix F: Small Kana Mappings</a>
<li class=no-num><a
href="#appendix-g-text-processing-order-of-oper">Appendix G: Text
Processing Order of Operations</a>
<li class=no-num><a href="#appendix-h-full-property-index">Appendix H:
Full Property Index</a>
</ul>
<!--end-toc-->
<h2 id=intro><span class=secno>1. </span> Introduction</h2>
<p>[document here]
<p class=issue>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.
<h3 id=placement><span class=secno>1.1. </span> Module Interactions</h3>
<p>This module replaces and extends the text-level features defined in <a
href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a> chapter 16.
<h3 id=values><span class=secno>1.2. </span> Values</h3>
<p>This specification follows the <a
href="http://www.w3.org/TR/CSS21/about.html#property-defs">CSS property
definition conventions</a> from <a href="#CSS21"
rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>. Value types not defined in
this specification are defined in CSS Level 2 Revision 1 <a
href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>. Other CSS
modules may expand the definitions of these value types: for example <a
href="#CSS3COLOR" rel=biblioentry>[CSS3COLOR]<!--{{CSS3COLOR}}--></a>,
when combined with this module, expands the definition of the
<color> value type as used in this specification.
<p>In addition to the property-specific values listed in their definitions,
all properties defined in this specification also accept the <a
href="http://www.w3.org/TR/CSS21/cascade.html#value-def-inherit">inherit</a>
keyword as their property value. For readability it has not been repeated
explicitly.
<h3 id=terms><span class=secno>1.3. </span> Terminology</h3>
<p id=grapheme-cluster>A <dfn id=grapheme-cluster0>grapheme cluster</dfn>
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 <a href="#UAX29"
rel=biblioentry>[UAX29]<!--{{!UAX29}}--></a>. This specification uses the
<em>extended grapheme cluster</em> definition in <a href="#UAX29"
rel=biblioentry>[UAX29]<!--{{!UAX29}}--></a> (not the <em>legacy grapheme
cluster</em> definition). The UA may further tailor the definition as
allowed by Unicode. Within this specification, the ambiguous term <dfn
id=character>character</dfn> is used as a friendlier synonym for <a
href="#grapheme-cluster0"><i>grapheme cluster</i></a>. See <a
href="http://dev.w3.org/csswg/css3-writing-modes/#character-properties">Characters
and Properties</a> for how to determine the Unicode properties of a
character.
<p id=letter>A <dfn id=letter0>letter</dfn> for the purpose of this
specification is a <a href="#character"><i>character</i></a> belonging to
one of the Letter or Number general categories in Unicode. <a
href="#UAX44" rel=biblioentry>[UAX44]<!--{{!UAX44}}--></a>
<p>The rendering characteristics of a <a
href="#character"><i>character</i></a> divided by an element boundary is
undefined: it may be rendered as belonging to either side of the boundary,
or as some approximation of belonging to both. Authors are forewarned that
dividing grapheme clusters by element boundaries may give inconsistent or
undesired results.
<h2 id=transforming><span class=secno>2. </span> Transforming Text</h2>
<h3 id=text-transform><span class=secno>2.1. </span> <a name=caps-prop></a>
Transforming Text: the ‘<a href="#text-transform0"><code
class=property>text-transform</code></a>’ property</h3>
<table class=propdef>
<tbody>
<tr>
<th>Name:
<td><dfn id=text-transform0>text-transform</dfn>
<tr>
<th><a href="#values">Value</a>:
<td>none | [ [ capitalize | uppercase | lowercase ] || full-width ||
full-size-kana ]
<tr>
<th>Initial:
<td>none
<tr>
<th>Applies to:
<td>all elements
<tr>
<th>Inherited:
<td>yes
<tr>
<th>Percentages:
<td>N/A
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>as specified
</table>
<p>This property transforms text for styling purposes. Values have the
following meanings:
<dl>
<dt><dfn id=none title="text-transform:none">‘<code
class=css>none</code>’</dfn>
<dd>No effects.
<dt><dfn id=capitalize title="text-transform:capitalize">‘<code
class=css>capitalize</code>’</dfn>
<dd>Puts the first <a href="#letter0"><i>letter</i></a> of each word in
titlecase; other characters are unaffected.
<dt><dfn id=uppercase title="text-transform:uppercase">‘<code
class=css>uppercase</code>’</dfn>
<dd>Puts all characters in uppercase.
<dt><dfn id=lowercase title="text-transform:lowercase">‘<code
class=css>lowercase</code>’</dfn>
<dd>Puts all characters in lowercase.
<dt><dfn id=full-width title="text-transform:full-width">‘<code
class=css>full-width</code>’</dfn>
<dd>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.
<dt><dfn id=full-size-kana
title="text-transform:full-size-kana">‘<code
class=css>full-size-kana</code>’</dfn>
<dd>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.
</dl>
<p>The case mapping rules for the character repertoire specified by the
Unicode Standard can be found on the Unicode Consortium Web site <a
href="#UNICODE" rel=biblioentry>[UNICODE]<!--{{!UNICODE}}--></a>. 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 <a
href="http://www.unicode.org/Public/UNIDATA/SpecialCasing.txt">SpecialCasing.txt</a>.
<div class=example>
<p>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.
</div>
<!--
<div class="example">
<p>An example where the UA may choose to include rules beyond those
in Unicode is Greek. In Greek, if the entire word is in upper case,
accents are dropped or transformed
http://blogs.msdn.com/b/michkap/archive/2006/08/18/706383.aspx
</div>
-->
<p>The definition of "word" used for ‘<code
class=css>capitalize</code>’ is UA-dependent; <a href="#UAX29"
rel=biblioentry>[UAX29]<!--{{!UAX29}}--></a> is suggested (but not
required) for determining such word boundaries. Authors should not expect
‘<code class=css>capitalize</code>’ to follow
language-specific titlecasing conventions (such as skipping articles in
English).
<p>The definition of fullwidth and halfwidth forms can be found on the
Unicode consortium web site at <a href="#UAX11"
rel=biblioentry>[UAX11]<!--{{!UAX11}}--></a>. The mapping to fullwidth
form is defined by taking code points with the <wide> or the
<narrow> tag in their Decomposition_Mapping in <a href="#UAX44"
rel=biblioentry>[UAX44]<!--{{!UAX44}}--></a>. 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.
<p>The mappings for small Kana to normal Kana are defined in <a
href="#small-kana">Small Kana Mappings</a>.
<p>When multiple values are specified and therefore multiple
transformations need to be applied, they are applied in the following
order:
<ol>
<li>‘<code class=css>capitalize</code>’, ‘<code
class=css>uppercase</code>’, and ‘<code
class=css>lowercase</code>’
<li>‘<code class=css>full-width</code>’
<li>‘<code class=css>full-size-kana</code>’
</ol>
<p>Text transformation happens after <a href="#white-space-rules">white
space processing</a>, which means that ‘<code
class=css>full-width</code>’ transforms only preserved U+0020 spaces
to U+3000.
<div class=example>
<p>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:
<pre>abbr:lang(ja) { text-transform: full-width; }</pre>
</div>
<p class=issue>CSS may introduce the ability to create custom mapping
tables for less common text transforms, such as by an ‘<a
href="#text-transform0"><code class=css>@text-transform</code></a>’
rule similar to ‘<code class=css>@counter-style</code>’ from
<a href="#CSS3LIST" rel=biblioentry>[CSS3LIST]<!--{{CSS3LIST}}--></a>, and
this mechanism may be used to replace ‘<code
class=css>full-size-kana</code>’.
<h2 id=white-space-processing><span class=secno>3. </span> White Space
Processing</h2>
<p>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. Note that white
space processing in CSS interprets white space characters only for
rendering: it has no effect on the underlying document data.
<p id=segment-normalization> CSS does not define document segmentation
rules. Segments could be separated by a particular newline seqence (such
as a line feed or CRLF pair), or delimited by some other mechanism, such
as the SGML RECORD-START and RECORD-END tokens. For CSS processing, each
document-defined segment break, CRLF sequence (U+000D U+000A), carriage
return (U+000D), and line feed (U+000A) in the text is treated as a
segment break, which is then interpreted for rendering as defined below.
<p class=note>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 <em>after</em> 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.
<p class=note>Note that anonymous inlines consisting entirely of <a
href="#collapsible"><i>collapsible</i></a> white space are removed from
the rendering tree. See <a href="#CSS21"
rel=biblioentry>[CSS21]<!--{{CSS21}}--></a> section <a
href="http://www.w3.org/TR/CSS21/visuren.html#anonymous">9.2.2.1</a>
<p>Control characters (Unicode class Cc) other than tab (U+0009), line feed
(U+000A), and carriage return (U+000D) are ignored for the purpose of
rendering.
<h3 id=white-space-collapsing><span class=secno>3.1. </span> White Space
Collapsing: the ‘<a href="#text-space-collapse"><code
class=property>text-space-collapse</code></a>’ property</h3>
<table class=propdef>
<tbody>
<tr>
<th>Name:
<td><dfn id=text-space-collapse>text-space-collapse</dfn>
<tr>
<th><a href="#values">Value</a>:
<td>collapse | preserve | preserve-breaks
<tr>
<th>Initial:
<td>collapse
<tr>
<th>Applies to:
<td>all elements
<tr>
<th>Inherited:
<td>yes
<tr>
<th>Percentages:
<td>N/A
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>specified value
</table>
<p>This property declares whether and how <a
href="#white-space-processing">white space</a> inside the element is
collapsed. Values have the following meanings, which must be interpreted
according to the <a href="#white-space-rules">white space processing
rules</a>:
<dl>
<dt><dfn id=collapse0 title="white-space:collapse">‘<code
class=css>collapse</code>’</dfn>
<dd>This value directs user agents to collapse sequences of white space
into a single character (or <a href="#line-break-transform">in some
cases</a>, no character).
<dt><dfn id=preserve title="white-space:preserve">‘<code
class=css>preserve</code>’</dfn>
<dd>This value prevents user agents from collapsing sequences of white
space. Segment breaks such as line feeds and carriage returns are
preserved as forced line breaks.
<dt><dfn id=preserve-breaks
title="white-space:preserve-breaks">‘<code
class=css>preserve-breaks</code>’</dfn>
<dd>This value collapses consecutive spaces, but renders segment breaks as
forced line breaks.
</dl>
<p>See <a href="#white-space-processing">White Space Processing Rules</a>
for details on how white space collapses. An informative summary of
‘<code class=css>collapse</code>’ is presented below:
<ul>
<li>A sequence of segment breaks and other white space between two
Chinese, Japanese, or Yi characters collapses into nothing.
<li>A zero width space before or after a white space sequence containing a
segment break causes the entire sequence of white space to collapse into
a zero width space.
<li>Otherwise, consecutive white space collapses into a single space.
</ul>
<h3 id=tab-size><span class=secno>3.2. </span> Tab Character Size: the
‘<a href="#tab-size0"><code
class=property>tab-size</code></a>’ property</h3>
<table class=propdef>
<tbody>
<tr>
<th>Name:
<td><dfn id=tab-size0>tab-size</dfn>
<tr>
<th><a href="#values">Value</a>:
<td><integer> | <length>
<tr>
<th>Initial:
<td>8
<tr>
<th>Applies to:
<td>block containers
<tr>
<th>Inherited:
<td>yes
<tr>
<th>Percentages:
<td>N/A
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>specified value
</table>
<p>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.
<h3 id=white-space-rules><span class=secno>3.3. </span> The White Space
Processing Rules</h3>
<p>White space processing affects only spaces (U+0020), tabs (U+0009), and
<a href="#segment-normalization">segment breaks</a>.
<p>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:
<ul>
<li id=collapse>
<p>If ‘<a href="#text-space-collapse"><code
class=property>text-space-collapse</code></a>’ is set to
‘<code class=css>collapse</code>’ or ‘<code
class=css>preserve-breaks</code>’, white space characters are
considered <dfn id=collapsible>collapsible</dfn> and are processed by
performing the following steps:</p>
<ol>
<li>All spaces and tabs immediately preceding or following a segment
break are removed.
<li>Segment breaks are transformed for rendering according to the <a
href="#line-break-transform">line break transformation rules</a>.
<li>Every tab is converted to a space (U+0020).
<li>Any space immediately following another collapsible space
—even one outside the boundary of the inline containing the
space, provided they are within the same inline formatting
context—is collapsed to have zero advance width. (It is
invisible, but retains its line-breaking opportunity, if any.)
</ol>
<li>
<p>If ‘<a href="#text-space-collapse"><code
class=property>text-space-collapse</code></a>’ is set to
‘<code class=css>preserve</code>’, any sequence of spaces is
treated as a sequence of non-breaking spaces. However, a line breaking
opportunity exists at the end of the sequence.
</ul>
<p>Then, the entire block is rendered. Inlines are laid out, taking bidi
reordering into account, and wrapping as specified by the ‘<a
href="#text-wrap0"><code class=property>text-wrap</code></a>’
property.
<p>As each line is laid out,
<ol>
<li>A sequence of collapsible spaces at the beginning of a line is
removed.
<li>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 ‘<a href="#tab-size0"><code
class=property>tab-size</code></a>’ property.
<li>A sequence of collapsible spaces at the end of a line is removed.
<li>If spaces or tabs at the end of a line are non-collapsible but have
‘<a href="#text-wrap0"><code
class=property>text-wrap</code></a>’ set to ‘<code
class=property>normal</code>’ or ‘<code
class=property>avoid</code>’ the UA may visually collapse their
character advance widths.
</ol>
<p>White space that was not removed or collapsed during the white space
processing steps is called <dfn id=preserved>preserved</dfn> white space.
<div class=example>
<h4 id=egbidiwscollapse><span class=secno>3.3.1. </span> Example of
bidirectionality with white space collapsing</h4>
<p>Consider the following markup fragment, taking special note of spaces
(with varied backgrounds and borders for emphasis and identification):</p>
<pre><code><ltr>A<span
class=egbidiwsaA> </span><rtl><span
class=egbidiwsbB> </span>B<span
class=egbidiwsaB> </span></rtl><span
class=egbidiwsbC> </span>C</ltr></code></pre>
<p>where the <code><ltr></code> element represents a left-to-right
embedding and the <code><rtl></code> element represents a
right-to-left embedding. If the ‘<a
href="#text-space-collapse"><code
class=property>text-space-collapse</code></a>’ property is set to
‘<code class=css>collapse</code>’, the above processing model
would result in the following:</p>
<ul style="line-height:1.3">
<li>The space before the B (<span class=egbidiwsbB> </span>) would
collapse with the space after the A (<span
class=egbidiwsaA> </span>).
<li>The space before the C (<span class=egbidiwsbC> </span>) would
collapse with the space after the B (<span
class=egbidiwsaB> </span>).
</ul>
<p>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:</p>
<pre>A<span class=egbidiwsaA> </span><span
class=egbidiwsaB> </span>BC</pre>
<p>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.</p>
</div>
<h4 id=line-break-transform><span class=secno>3.3.2. </span> Line Break
Transformation Rules</h4>
<p>When ‘<a href="#text-space-collapse"><code
class=property>text-space-collapse</code></a>’ is ‘<code
class=css>preserve-breaks</code>’, segment breaks are not <a
href="#collapsible"><i>collapsible</i></a> and are transformed into a
preserved line feed (U+000A).
<p>When segment breaks are <a href="#collapsible"><i>collapsible</i></a>,
they are either transformed into a space (U+0020) or removed depending on
the context before and after the break.
<p class=note>Note that the white space processing rules have already
removed any tabs and spaces after the segment break before these checks
take place.
<ul>
<li>If the character immediately before or immediately after the segment
break is the zero-width space character (U+200B), then the break is
removed, leaving behind the zero-width space.
<li>Otherwise, if the East Asian Width property <a href="#UAX11"
rel=biblioentry>[UAX11]<!--{{!UAX11}}--></a> of both the character before
and after the line feed is F, W, or H (not A), and neither side is
Hangul, then the segment break is removed.
<li>Otherwise, the segment break is converted to a space (U+0020).
</ul>
<p class=issue>Comments on how well this would work in practice would be
very much appreciated, particularly from people who work with Thai and
similar scripts.
<h3 id=white-space><span class=secno>3.4. </span> White Space and Text
Wrapping Shorthand: the ‘<a href="#white-space0"><code
class=property>white-space</code></a>’ property</h3>
<table class=propdef>
<tbody>
<tr>
<th>Name:
<td><dfn id=white-space0>white-space</dfn>
<tr>
<th><a href="#values">Value</a>:
<td>normal | pre | nowrap | pre-wrap | pre-line