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F328
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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 http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>CSS Text Level 4</title>
<link rel="stylesheet" type="text/css" href="../default.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 }
</style>
<link rel="stylesheet" type="text/css" href="http://www.w3.org/StyleSheets/TR/W3C-ED.css">
</head>
<body>
<div class="head">
<!--logo-->
<h1>CSS Text Level 4</h1>
<h2 class="no-num no-toc">[LONGSTATUS] [DATE]</h2>
<dl>
<dt>This version:</dt>
<dd><a href="http://dev.w3.org/csswg/css3-text/">$Date$ (CVS $Revision$)</a>
<!--
<dd><a href="http://www.w3.org/TR/[YEAR]/WD-css3-text-[CDATE]/">http://www.w3.org/TR/[YEAR]/WD-css3-text-[CDATE]/</a></dd>
-->
<dt>Latest version:</dt>
<dd><a href="http://www.w3.org/TR/css3-text">http://www.w3.org/TR/css3-text</a></dd>
<dt>Latest editor's draft:</dt>
<dd><a href="http://dev.w3.org/csswg/css3-text/">http://dev.w3.org/csswg/css3-text/</a></dd>
<dt>Previous version:</dt>
<dd><a
href="http://www.w3.org/TR/2011/WD-css3-text-20110901/">http://www.w3.org/TR/2011/WD-css3-text-20110901/</a></dd>
<dt>Feedback:</dt>
<dd><a href="mailto:www-style@w3.org?subject=%5Bcss-text%5D%20feedback">www-style@w3.org</a>
with subject line “<kbd>[css-text] <var>… message topic …</var></kbd>”
(<a rel="discussion" href="http://lists.w3.org/Archives/Public/www-style/">archives</a>)
<dt>Editors:</dt>
<dd><a href="http://fantasai.inkedblade.net/contact">Elika J. Etemad</a> (Mozilla)</dd>
<dd><a href="mailto:kojiishi@gluesoft.co.jp">Koji Ishii</a> (Invited Expert)</dd>
</dl>
<!--begin-copyright-->
<p>[Here will be included the file "../copyright.inc"]</p>
<!--end-copyright-->
<hr title="Separator for header">
</div>
<details class=obsolete open>
<summary>Not Ready For Implementation</summary>
<p>
This spec is not yet ready for implementation.
It exists in this repository to record the ideas and promote discussion.
<p>
Before attempting to implement this spec,
please contact the CSSWG at www-style@w3.org.
</details>
<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.</p>
<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>
<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>
<p><strong>If you have implemented properties from the
<a href="http://www.w3.org/TR/2003/CR-css3-text-20030514/">May 2003
CSS3 Text CR</a></strong>
<em>please</em> let us know so we can take that into account as
we redraft the spec. You can post to
<a href="http://lists.w3.org/Archives/Public/www-style/">www-style</a> (public),
post to the <a href="http://lists.w3.org/Archives/Member/w3c-css-wg/">CSS WG mailing list</a>
(<a href="http://cgi.w3.org/MemberAccess/AccessRequest">Member-restricted</a>),
or <a href="http://fantasai.inkedblade.net/contact">email fantasai directly</a> (personal).</p>
<p>The following features are at risk and may be cut from the spec during
its CR period if there are no (correct) implementations:</p>
<ul>
<li>the <length> values of the 'tab-size' property
<li>the 'hanging-punctuation' property
<li>the percentage values of 'letter-spacing' and 'word-spacing'
<li>the 'hyphenate-limit-*' properties
<li>the 'text-spacing' property
<li>the 'text-decoration-skip' property / ''ink'' value
<li>the 'text-emphasis-skip' property
<li><span class="issue">audit draft and add more here</span>
</ul>
<h2 class="no-num no-toc" id="contents">
Table of Contents</h2>
<!--toc-->
<h2 id="intro">
Introduction</h2>
<p>[document here]</p>
<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">
Module Interactions</h3>
<p>This module replaces and extends the text-level
features defined in [[!CSS21]] chapter 16.
<h3 id="values">
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 [[!CSS21]]. Value types not defined in
this specification are defined in CSS Level 2 Revision 1 [[!CSS21]].
Other CSS modules may expand the definitions of these value types: for
example [[CSS3COLOR]], when combined with this module, expands the
definition of the <color> value type as used in this specification.</p>
<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">
Terminology</h3>
<p id="grapheme-cluster">A <dfn>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 [[!UAX29]]. This specification uses the
<em>extended grapheme cluster</em> definition in [[!UAX29]] (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>character</dfn> is used as a friendlier synonym
for <i>grapheme cluster</i>.
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>letter</dfn> for the purpose of this specification
is a <i>character</i> belonging to one of the Letter or Number general
categories in Unicode. [[!UAX44]]
<h2 id="transforming">
Transforming Text</h2>
<h3 id="text-transform">
<a name="caps-prop"></a>
Transforming Text: the 'text-transform' property</h3>
<table class="propdef">
<tbody>
<tr>
<th>Name:</th>
<td><dfn>text-transform</dfn></td>
</tr>
<tr>
<th>Value:</th>
<td>none |
[ [ capitalize | uppercase | lowercase ] || full-width || full-size-kana ]
</td>
</tr>
<tr>
<th>Initial:</th>
<td>none</td>
</tr>
<tr>
<th>Applies to:</th>
<td>all elements</td>
</tr>
<tr>
<th>Inherited:</th>
<td>yes</td>
</tr>
<tr>
<th>Percentages:</th>
<td>N/A</td>
</tr>
<tr>
<th>Media:</th>
<td>visual</td>
</tr>
<tr>
<th>Computed value:</th>
<td>as specified</td>
</tr>
</tbody>
</table>
<p>This property transforms text for styling purposes.
Values have the following meanings:</p>
<dl>
<dt><dfn title="text-transform:none">''none''</dfn></dt>
<dd>No effects.</dd>
<dt><dfn title="text-transform:capitalize">''capitalize''</dfn></dt>
<dd>Puts the first <i>letter</i> of each word in titlecase; other characters
are unaffected.</dd>
<dt><dfn title="text-transform:uppercase">''uppercase''</dfn></dt>
<dd>Puts all characters in uppercase.
<dt><dfn title="text-transform:lowercase">''lowercase''</dfn></dt>
<dd>Puts all characters in lowercase.</dd>
<dt><dfn title="text-transform:full-width">''full-width''</dfn></dt>
<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 title="text-transform:full-size-kana">''full-size-kana''</dfn></dt>
<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
[[!UNICODE]]. The UA must use the full case mappings for Unicode
characters, including any conditional casing rules, as defined in
Default Case Algorithm section. If (and only if) the content language
of the element is, according to the rules of the document language,
known, then any appropriate language-specific rules must be applied
as well.
These minimally include, but are not limited to, the language-specific
rules in Unicode's
<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 ''capitalize'' is UA-dependent;
[[!UAX29]] is suggested (but not required) for determining such word
boundaries. Authors should not expect ''capitalize'' to follow
language-specific titlecasing conventions (such as skipping articles
in English).
<p>The definition of fullwidth and halfwidth forms can be found on the
Unicode consortium web site at [[!UAX11]].
The mapping to fullwidth form is defined by taking code points with
the <wide> or the <narrow> tag in their Decomposition_Mapping
in [[!UAX44]]. For the <narrow> tag, the mapping is from the code
point to the decomposition (minus <narrow> tag), and for the
<wide> tag, the mapping is from the decomposition (minus the
<wide> tag) back to the original code point.</p>
<p>The mappings for small Kana to normal Kana are defined in
<a href="#small-kana">Small Kana Mappings</a>.</p>
<p>When multiple values are specified and therefore multiple
transformations need to be applied, they are applied in the following
order:</p>
<ol>
<li>''capitalize'', ''uppercase'', and ''lowercase''</li>
<li>''full-width''</li>
<li>''full-size-kana''</li>
</ol>
<p>Text transformation happens after <a href="#white-space-rules">white
space processing</a>, which means that ''full-width'' 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">All-caps text sometimes has special typographic considerations.
For example: Punctuation and number glyphs might be adjusted for the
higher "center of gravity" (see the
<a href="http://www.microsoft.com/typography/otspec/features_ae.htm#case">case</a>
feature in OpenType). Should we turn that on by default, as they suggest?</p>
<p class="issue">CSS may introduce the ability to create custom mapping
tables for less common text transforms, such as by an ''@text-transform''
rule similar to ''@counter-style'' from [[CSS3LIST]], and this mechanism
may be used to replace ''full-size-kana''.
<h2 id="white-space-processing">
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.
<p id="segment-normalization">
In the document source, segments can be delimited by carriage
returns (U+000D), linefeeds (U+000A) or a combination (U+000D U+000A),
or by some other mechanism, such as the SGML RECORD-START
and RECORD-END tokens.
If no segmentation rules are specified for the document language,
each line feed (U+000A), carriage return (U+000D) and CRLF sequence
(U+000D U+000A) in the text is considered a segment break. (This
default rule also applies to generated content.)
In CSS, each such segment break is treated as a single line feed
character (U+000A).
<p>White space processing in CSS interprets white space characters
only for rendering: it has no effect on the underlying document data.
<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>
<p>Control characters (Unicode class Cc) other than tab (U+0009), line feed
(U+000A), space (U+0020), and the bidi formatting characters (U+202<var>x</var>)
should be rendered as invisible zero-width characters. UAs may instead treat
them as visible characters. (Note, however, that this will usually result in
them being rendered as missing glyphs.)
<span class="issue">What's the line-breaking behavior? Effects on joining?
Can we just copy the behavior of some zero-width Unicode character?</span>
<h3 id="white-space-collapsing">
White Space Collapsing: the 'text-space-collapse' property</h3>
<p class="issue">This section is still under discussion and may change in future drafts.</p>
<table class="propdef">
<tbody>
<tr>
<th>Name:</th>
<td><dfn>text-space-collapse</dfn></td>
</tr>
<tr>
<th>Value:</th>
<td>collapse | discard | [ [preserve | preserve-breaks] && [ trim-inner || consume-before || consume-after ]</td>
</tr>
<tr>
<th>Initial:</th>
<td>collapse</td>
</tr>
<tr>
<th>Applies to:</th>
<td>all elements</td>
</tr>
<tr>
<th>Inherited:</th>
<td>yes</td>
</tr>
<tr>
<th>Percentages:</th>
<td>N/A</td>
</tr>
<tr>
<th>Media:</th>
<td>visual</td>
</tr>
<tr>
<th>Computed value:</th>
<td>specified value</td>
</tr>
</tbody>
</table>
<p class="issue">Need a property name</p>
<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>:</p>
<dl>
<dt><dfn title="white-space:collapse">''collapse''</dfn></dt>
<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).</dd>
<dt><dfn title="white-space:preserve">''preserve''</dfn></dt>
<dd>This value prevents user agents from collapsing sequences
of white space. Line feeds are preserved as forced line breaks.</dd>
<dt><dfn title="white-space:preserve-breaks">''preserve-breaks''</dfn></dt>
<dd>This value collapses white space as for ''collapse'', but preserves
line feeds as forced line breaks.</dd>
<dt><dfn title="white-space:discard">''discard''</dfn></dt>
<dd>This value directs user agents to "discard" all white space in the
element.
<dt><dfn title="white-space:trim-inner">''trim-inner''</dfn></dt>
<dd>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.</dd>
<dt><dfn title="white-space:consume-before">''consume-before''</dfn></dt>
<dd>This value directs the UA to collapse all collapsible whitespace
immediately before the start of the element.
<dt><dfn title="white-space:consume-after">''consume-after''</dfn></dt>
<dd>This value directs the UA to collapse all collapsible whitespace
immediately after the end of the element.
</dl>
<div class="example">
<p>The following style rules implement MathML's white space processing:
<pre>
<!-- -->@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;
<!-- -->}</pre>
</div>
<div class="example">
<p>The following style rules render DT elements as a comma-separated list:
<pre>
<!-- -->dt { display: inline; }
<!-- -->dt + dt:before { content: ", "; text-space-collapse: consume-before; }</pre>
</div>
<p class="issue">It's been pointed out that ''trim-inner'', ''consume-before'',
and ''consume-after'' won't work well because 'text-space-collapse' is
inherited, meaning that inserting a <span> or >div> would cause more
white space to be removed than otherwise.
<h3 id="tab-size">
Tab Character Size: the 'tab-size' property</h3>
<table class="propdef">
<tbody>
<tr>
<th>Name:</th>
<td><dfn>tab-size</dfn></td>
</tr>
<tr>
<th>Value:</th>
<td><integer> | <length></td>
</tr>
<tr>
<th>Initial:</th>
<td>8</td>
</tr>
<tr>
<th>Applies to:</th>
<td>block containers</td>
</tr>
<tr>
<th>Inherited:</th>
<td>yes</td>
</tr>
<tr>
<th>Percentages:</th>
<td>N/A</td>
</tr>
<tr>
<th>Media:</th>
<td>visual</td>
</tr>
<tr>
<th>Computed value:</th>
<td>specified value</td>
</tr>
</tbody>
</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">
The White Space Processing Rules</h3>
<p>White space processing affects only spaces (U+0020), tabs (U+0009),
and (<a href="#segment-normalization">post-normalization</a>)
line feeds (U+00A0).
<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:</p>
<ul>
<li id="collapse"><p>If 'text-space-collapse'
is set to ''collapse'' or ''preserve-breaks'', white space characters
are considered <dfn>collapsible</dfn> and are processed by
performing the following steps:</p>
<ol>
<li>All spaces and tabs immediately preceding or following a line
feed character are removed.</li>
<li>If 'text-space-collapse' is not
''preserve-breaks'', line feed characters are transformed for
rendering according to the <a href="#line-break-transform">line
feed transformation rules</a>.
</li>
<li>Every tab is converted to a space (U+0020).</li>
<li>Any space immediately following another collapsible space
—even one outside the boundary of the inline—is
removed.
However, if removing this space would eliminate a line breaking
opportunity in the text, that opportunity is still considered
to exist.</li>
<li>A collapsible space immediately preceding an element with
''consume-before'' is removed. Such removed spaces do not indicate
a line breaking opportunity in the text.
<li>Any collapsible spaces after the end of an element with
''consume-after'' are removed. Such removed spaces do not indicate
a line breaking opportunity in the text.
</ol>
</li>
<li><p>If 'text-space-collapse' is set to
''preserve'', any sequence of spaces 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.</p></li>
<li><p>If 'text-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.</p>
</ul>
<p>Then, the entire block is rendered. Inlines are laid out, taking bidi
reordering into account, and wrapping as specified by the
'text-wrap' property.</p>
<p>As each line is laid out,</p>
<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 'tab-size'
property.</li>
<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 'text-wrap' set to 'normal' or 'avoid' the UA may visually
collapse their character advance widths.
</ol>
<p>White space that was not removed during the white space processing
steps is called <dfn>preserved</dfn> white space.</p>
<div class="example">
<h4 id="egbidiwscollapse">
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 'text-space-collapse' property is set
to ''collapse'', 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>
<li>The space before the C (<span class="egbidiwsbC"> </span>)
would collapse with the space after the B (<span
class="egbidiwsaB"> </span>).</li>
</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">
Line Feed Transformation Rules</h4>
<p>When line feeds are <a href="#collapse">collapsible</a>, they are
either transformed into a space (U+0020) or removed depending on the
context before and after the line break.</p>
<p class="note">Note that the white space processing rules have already
removed any tabs and spaces after the line feed before these checks
take place.</p>
<ul>
<li>If the character immediately before or immediately after the line
feed is the zero width space character (U+200B), then the line feed
is removed.
<li>Otherwise, if the East Asian Width property [[!UAX11]] of both
the character before and after the line feed is F, W, or H (not A),
and neither side is Hangul,
then the line feed is removed.
<li>Otherwise, the line feed 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.</p>
<h4 id="white-space-summary">
Informative Summary of White Space Collapsing Effects</h4>
<ul>
<li>Consecutive white space collapses into a single space.
<li>A sequence of newlines 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 newline causes the entire sequence of white space
to collapse into a zero width space.
</ul>
<h3 id="white-space">
White Space and Text Wrapping Shorthand: the 'white-space' property</h3>
<table class="propdef">
<tbody>
<tr>
<th>Name:</th>
<td><dfn>white-space</dfn></td>
</tr>
<tr>
<th>Value:</th>
<td>normal | pre | nowrap | pre-wrap | pre-line</td>
</tr>
<tr>
<th>Initial:</th>
<td>not defined for shorthand properties</td>
</tr>
<tr>
<th>Applies to:</th>
<td>all elements</td>
</tr>
<tr>
<th>Inherited:</th>
<td>yes</td>
</tr>
<tr>
<th>Percentages:</th>
<td>N/A</td>
</tr>
<tr>
<th>Media:</th>
<td>visual</td>
</tr>
<tr>
<th>Computed value:</th>
<td>see individual properties</td>
</tr>
</tbody>
</table>
<p>The 'white-space' property is a shorthand for the
'text-space-collapse' and 'text-wrap' properties.
Not all combinations are represented.
Values have the following meanings:</p>
<dl>
<dt><dfn title="white-space:normal">''normal''</dfn></dt>
<dd>Sets 'text-space-collapse' to ''collapse'' and
'text-wrap' to ''normal''</dd>
<dt><dfn title="white-space:pre">''pre''</dfn></dt>
<dd>Sets 'text-space-collapse' to ''preserve'' and
'text-wrap' to ''none''</dd>
<dt><dfn title="white-space:nowrap">''nowrap''</dfn></dt>
<dd>Sets 'text-space-collapse' to ''collapse'' and
'text-wrap' to ''none''</dd>
<dt><dfn title="white-space:pre-wrap">''pre-wrap''</dfn></dt>
<dd>Sets 'text-space-collapse' to ''preserve'' and
'text-wrap' to ''normal''</dd>
<dt><dfn title="white-space:pre-line">''pre-line''</dfn></dt>
<dd>Sets 'text-space-collapse' to ''preserve-breaks'' and
'text-wrap' to ''normal''</dd>
</dl>
<p>The following informative table summarizes the behavior of various
'white-space' values:</p>
<table class="data">
<colgroup class="header"></colgroup>
<colgroup span=3></colgroup>
<thead>
<tr>
<th></th>
<th>New Lines</th>
<th>Spaces and Tabs</th>
<th>Text Wrapping</th>
</tr>
</thead>
<tbody>
<tr>
<th>normal</th>
<td>Collapse</td>
<td>Collapse</td>
<td>Wrap</td>
</tr>
<tr>
<th>pre</th>
<td>Preserve</td>
<td>Preserve</td>
<td>No wrap</td>
</tr>
<tr>
<th>nowrap</th>
<td>Collapse</td>
<td>Collapse</td>
<td>No wrap</td>
</tr>
<tr>
<th>pre-wrap</th>
<td>Preserve</td>
<td>Preserve</td>
<td>Wrap</td>
</tr>
<tr>
<th>pre-line</th>
<td>Preserve</td>
<td>Collapse</td>
<td>Wrap</td>
</tbody>
</table>
<h2 id="line-breaking">
Line Breaking and Word Boundaries</h2>
<p>In most writing systems, in the absence of hyphenation a line break occurs
only at word boundaries. Many writing systems use spaces or
punctuation to explicitly separate words, and line break opportunities
can be identified by these characters. Scripts such as Thai, Lao, and
Khmer, however, do not use spaces or punctuation to separate words.
Although the zero width space (U+200B) can be used as an explicit word
delimiter in these scripts, this practice is not common. As a result,
a lexical resource is needed to correctly identify break points in such
texts.
<p>In several other writing systems, (including Chinese, Japanese, Yi,
and sometimes also Korean) a line break opportunity is based on
character boundaries, not word boundaries. In these systems a line can break
anywhere <em>except</em> between certain character combinations.
Additionally the level of strictness in these restrictions can vary
with the typesetting style.</p>
<p>CSS does not fully define where line breaking opportunities occur,
however some controls are provided to distinguish common variations.
<p class="note">Further information on line breaking conventions can be
found in
[[JLREQ]] and [[JIS4051]] for Japanese,
[[ZHMARK]] for Chinese, and
in [[!UAX14]] for all scripts in Unicode.
<!-- The CSS Working Group notes that although UAX 14 contains a wealth of
information about line breaking conventions, a literal implementation
of its algorithm has been found to be inadequate in multiple situations. --></p>
<p class="issue">Any guidance for appropriate references here would be
much appreciated.</p>
<p class="issue">Information on line-breaking in the absence of dictionaries:
<a href="http://lists.w3.org/Archives/Public/www-style/2011Feb/0126.html">for Thai</a>
<p>Floated and absolutely-positioned elements do not introduce a line
breaking opportunity. The line breaking behavior of a replaced element
is equivalent to that of a Latin character.</p>
<p class="issue">It is not clear whether this section handles Southeast Asian
scripts well. Additionally, some guidance should be provided on how to
break or not break Southeast Asian in the absence of a dictionary.</p>
<h3 id="line-break">
Line Breaking Strictness: the 'line-break' property</h3>
<table class="propdef">
<tbody>
<tr>
<th>Name:</th>
<td><dfn>line-break</dfn></td>
</tr>
<tr>
<th>Value:</th>
<td>auto | loose | normal | strict</td>
</tr>
<tr>
<th>Initial:</th>
<td>auto</td>
</tr>
<tr>
<th>Applies to:</th>
<td>all elements</td>
</tr>
<tr>
<th>Inherited:</th>
<td>yes</td>
</tr>
<tr>
<th>Percentages:</th>
<td>N/A</td>
</tr>
<tr>
<th>Media:</th>
<td>visual</td>
</tr>
<tr>
<th>Computed value:</th>
<td>specified value</td>
</tr>
</tbody>
</table>
<p>This property specifies the strictness of line-breaking rules applied
within an element: particularly how line-breaking interacts with
punctuation. Values have the following meanings:</p>
<dl>
<dt><dfn title="line-break:auto">''auto''</dfn></dt>
<dd>The UA determines the set of line-breaking restrictions to use,
and it may vary the restrictions based on the length of the line; e.g.,
use a less restrictive set of line-break rules for short lines.</dd>
<dt><dfn title="line-break:loose">''loose''</dfn></dt>
<dd>Breaks text using the least restrictive set of line-breaking
rules. Typically used for short lines, such as in newspapers.</dd>
<dt><dfn title="line-break:normal">''normal''</dfn></dt>
<dd>Breaks text using the most common set of line-breaking rules.</dd>
<dt><dfn title="line-break:strict">''strict''</dfn></dt>
<dd>Breaks text using the most stringent set of line-breaking
rules.</dd>
</dl>
<p>CSS distinguishes between three levels of strictness in the rules for
implicit line breaking. The precise set of rules in effect for each
level is up to the UA and should follow language conventions. However,
this specification does recommend that:</p>
<ul>
<li>Following breaks be forbidden in ''strict'' line breaking and
allowed in ''normal'' and ''loose'':
<ul>
<li>breaks before Japanese <a href="#small-kana">small kana</a>
<li>breaks before the Katakana-Hiragana prolonged sound mark:
ー U+30FC
</ul>
If the language is known to be Chinese or Japanese, then additionally:
<ul>
<li>breaks before before hyphens:<br>
‐ U+2010, – U+2013, 〜 U+301C,
゠ U+30A0
</ul>
<li>Following breaks be forbidden in ''normal'' and ''strict'' line
breaking and allowed in ''loose'':
<ul>
<li>breaks before iteration marks:<br>
々 U+3005, 〻 U+303B, ゝ U+309D,
ゞ U+309E, ヽ U+30FD, ヾ U+30FE
<li>breaks between some inseparable characters:<br>
‥ U+2025, … U+2026
</ul>
If the language is known to be Chinese or Japanese, then additionally:
<ul>
<li>breaks before certain centered punctuation marks:<br>
: U+003A, ; U+003B, ・ U+30FB,
： U+FF1A, ； U+FF1B, ･ U+FF65,
! U+0021, ? U+003F, ‼ U+203C,
⁇ U+2047, ⁈ U+2048, ⁉ U+2049,
！ U+FF01, ？ U+FF1F
<li>breaks before postfixes:<br>
% U+0025, ¢ U+00A2, ° U+00B0,
‰ U+2030, ′ U+2032, ″ U+2033,
℃ U+2103, ％ U+FF05, ￠ U+FFE0
<li>breaks after prefixes:<br>
$ U+0024, £ U+00A3, ¥ U+00A5,
€ U+20AC, № U+2116, ＄ U+FF04,
￡ U+FFE1, ￥ U+FFE5
</ul>
</ul>
<p class="note">In CSS3 no distinction is made among the levels of
strictness in non-CJK text: only CJK codepoints are affected, unless
the text is marked as Chinese or Japanese, in which case some additional
common codepoints are affected. However a future level of CSS may add
behaviors affecting non-CJK text.
<p>Support for this property is <em>optional</em>. It is recommended
for UAs that wish to support CJK typography and strongly recommended
for UAs in the Japanese market.</p>
<p class="note">The CSSWG recognizes that in a future edition of the
specification finer control over line breaking may be necessary to
satisfy high-end publishing requirements.
<h3 id="word-break">
Word Breaking Rules: the 'word-break' property</h3>
<table class="propdef">
<tbody>
<tr>
<th>Name:</th>
<td><dfn>word-break</dfn></td>
</tr>
<tr>
<th>Value:</th>
<td>normal | keep-all | break-all</td>
</tr>
<tr>
<th>Initial:</th>
<td>normal</td>
</tr>
<tr>
<th>Applies to:</th>
<td>all elements</td>
</tr>
<tr>
<th>Inherited:</th>
<td>yes</td>