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<!doctype html>
<html lang="en">
<head>
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
<title>CSS Text Module Level 3</title>
<meta content="refining" name="csswg-work-status">
<meta content="ED" name="w3c-status">
<link href="../default.css" rel="stylesheet" type="text/css">
<link href="../csslogo.ico" rel="shortcut icon" type="image/x-icon">
<style>
body {
background: url("https://www.w3.org/StyleSheets/TR/logo-ED") top left no-repeat white;
background-attachment: fixed;
color: black;
font-family: sans-serif;
margin: 0 auto;
max-width: 50em;
padding: 2em 1em 2em 70px;
}
:link { color: #00C; background: transparent }
:visited { color: #609; background: transparent }
a[href]:active { color: #C00; background: transparent }
a[href]:hover { background: #ffa }
a[href] img { border-style: none }
h1, h2, h3, h4, h5, h6 { text-align: left }
h1, h2, h3 { color: #005A9C; }
h1 { font: 170% sans-serif }
h2 { font: 140% sans-serif }
h3 { font: 120% sans-serif }
h4 { font: bold 100% sans-serif }
h5 { font: italic 100% sans-serif }
h6 { font: small-caps 100% sans-serif }
.hide { display: none }
div.head { margin-bottom: 1em }
div.head h1 { margin-top: 2em; clear: both }
div.head table { margin-left: 2em; margin-top: 2em }
p.copyright { font-size: small }
p.copyright small { font-size: small }
pre { margin-left: 2em }
dt { font-weight: bold }
ul.toc, ol.toc {
list-style: none;
}
</style>
<meta content="Bikeshed 1.0.0" name="generator">
<script defer="" src="//test.csswg.org/harness/annotate.js#css-text-3_dev/css-text-3" type="text/javascript"></script>
<style type="text/css">
img { vertical-align: middle; }
span[lang] { font-size: 125%; line-height: 1; vertical-align: middle;}
/* Bidi & spaces example */
.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 }
.hyphens-ex {
border: thin solid black;
display: inline-block;
padding: 4pt;
}
/* Start Letter-spacing Tutorial */
.ls-ex {
font-size: 200%;
margin-left: 1em;
margin-right: 1em;
}
.ls-fixed-width {
width: 10em;
}
.color-box { background: rgb(224, 203, 82); }
.bad { color: red; }
.good { color: green; }
/* End Letter-spacing Tutorial */
.char { border: 1px dotted gray; }
.quarter { font-size: 25%; }
tt[lang="ja"] { font-family: "MS Gothic", "Osaka", monospace }
div.figure table {
margin :auto;
}
.feedback {
background: #FFEECC;
border-color: orange;
}
.feedback:before {
content: "Info Needed";
color: #FF8800;
}
</style>
</head>
<body class="h-entry">
<div class="head">
<p data-fill-with="logo"><a class="logo" href="http://www.w3.org/">
<img alt="W3C" height="48" src="https://www.w3.org/Icons/w3c_home" width="72">
</a>
</p>
<h1 class="p-name no-ref" id="title">CSS Text Module Level 3</h1>
<h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="content">Editor’s Draft,
<time class="dt-updated" datetime="2015-08-04">4 August 2015</time></span></h2>
<div data-fill-with="spec-metadata">
<dl>
<dt>This version:
<dd><a class="u-url" href="http://dev.w3.org/csswg/css-text-3/">http://dev.w3.org/csswg/css-text-3/</a>
<dt>Latest version:
<dd><a href="http://www.w3.org/TR/css-text-3/">http://www.w3.org/TR/css-text-3/</a>
<dt>Previous Versions:
<dd><a href="http://www.w3.org/TR/2012/WD-css3-text-20121113/" rel="previous">http://www.w3.org/TR/2012/WD-css3-text-20121113/</a>
<dt>Feedback:
<dd><span><a href="mailto:www-style@w3.org?subject=%5Bcss-text%5D%20YOUR%20TOPIC%20HERE">www-style@w3.org</a> with subject line “<kbd>[css-text] <var>… message topic …</var></kbd>” (<a href="http://lists.w3.org/Archives/Public/www-style/" rel="discussion">archives</a>)</span>
<dt>Test Suite:
<dd><a href="http://test.csswg.org/suites/css3-text/nightly-unstable/">http://test.csswg.org/suites/css3-text/nightly-unstable/</a>
<dt>Issue Tracking:
<dd><a href="https://github.com/w3c/csswg-drafts/issues/">GitHub</a>
<dd><a href="#issues-index">Inline In Spec</a>
<dd><span><a href="http://www.w3.org/Style/CSS/Tracker/products/10">http://www.w3.org/Style/CSS/Tracker/products/10</a></span>
<dt class="editor">Editors:
<dd class="editor p-author h-card vcard"><a class="p-name fn u-url url" href="http://fantasai.inkedblade.net/contact">fantasai</a> (<span class="p-org org">Invited Expert</span>)
<dd class="editor p-author h-card vcard"><a class="p-name fn u-email email" href="mailto:kojiishi@gluesoft.co.jp">Koji Ishii</a> (<span class="p-org org">Invited Expert</span>)
</dl>
</div>
<div data-fill-with="warning"></div>
<p class="copyright" data-fill-with="copyright"><a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a> © 2015 <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>, <a href="http://ev.buaa.edu.cn/">Beihang</a>). 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>
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc no-ref heading settled" id="abstract"><span class="content">Abstract</span></h2>
<div class="p-summary" data-fill-with="abstract">
<p>This CSS3 module defines properties for text manipulation and specifies their processing model. It covers line breaking, justification and alignment, white space handling, and text transformation.</p>
<a href="http://www.w3.org/TR/CSS/">CSS</a> is a language for describing the rendering of structured documents
(such as HTML and XML)
on screen, on paper, in speech, etc.</div>
<h2 class="no-num no-toc no-ref heading settled" id="status"><span class="content">Status of this document</span></h2>
<div data-fill-with="status">
<p>
This is a public copy of the editors’ draft.
It is provided for discussion only and may change at any moment.
Its publication here does not imply endorsement of its contents by W3C.
Don’t cite this document other than as work in progress.
</p>
<p>
The (<a href="http://lists.w3.org/Archives/Public/www-style/">archived</a>) public mailing list
<a href="mailto:www-style@w3.org?Subject=%5Bcss-text%5D%20PUT%20SUBJECT%20HERE">www-style@w3.org</a>
(see <a href="http://www.w3.org/Mail/Request">instructions</a>)
is preferred for discussion of this specification.
When sending e-mail,
please put the text “css-text” in the subject,
preferably like this:
“[css-text] <em>…summary of comment…</em>”
</p>
<p>
This document was produced by the <a href="http://www.w3.org/Style/CSS/members">CSS Working Group</a>
(part of the <a href="http://www.w3.org/Style/">Style Activity</a>).
</p>
<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>
This document is governed by the <a href="http://www.w3.org/2014/Process-20140801/" id="w3c_process_revision">1 August 2014 W3C Process Document</a>.
</p>
<p>
</p></div>
<div data-fill-with="at-risk">
<p>The following features are at-risk, and may be dropped during the CR period:
</p>
<ul>
<li>the <a class="css" data-link-type="maybe" href="#valdef-text-transform-full-width">full-width</a> value of <a class="property" data-link-type="propdesc" href="#propdef-text-transform">text-transform</a>
<li>the <length> values of the <a class="property" data-link-type="propdesc" href="#propdef-tab-size">tab-size</a> property
<li>the <a class="property" data-link-type="propdesc" href="#propdef-text-justify">text-justify</a> property
<li>the percentage values of <a class="property" data-link-type="propdesc" href="#propdef-word-spacing">word-spacing</a>
<li>the <a class="property" data-link-type="propdesc" href="#propdef-hanging-punctuation">hanging-punctuation</a> property
<li>the <a class="css" data-link-type="maybe" href="#valdef-white-space-pre-wrap-auto">pre-wrap-auto</a> value of the <a class="property" data-link-type="propdesc" href="#propdef-white-space">white-space</a> property
</ul></div>
<h2 class="no-num no-toc no-ref heading settled" id="contents"><span class="content">Table of Contents</span></h2>
<div data-fill-with="table-of-contents" role="navigation">
<ul class="toc" role="directory">
<li><a href="#intro"><span class="secno">1</span> <span class="content">
Introduction</span></a>
<ul class="toc">
<li><a href="#placement"><span class="secno">1.1</span> <span class="content">
Module Interactions</span></a>
<li><a href="#values"><span class="secno">1.2</span> <span class="content">
Values</span></a>
<li><a href="#terms"><span class="secno">1.3</span> <span class="content">
Terminology</span></a>
<ul class="toc">
<li><a href="#characters"><span class="secno">1.3.1</span> <span class="content">
Characters and Letters</span></a>
<li><a href="#languages"><span class="secno">1.3.2</span> <span class="content">
Languages and Typesetting</span></a>
</ul>
</ul>
<li><a href="#transforming"><span class="secno">2</span> <span class="content">
Transforming Text</span></a>
<ul class="toc">
<li><a href="#text-transform-property"><span class="secno">2.1</span> <span class="content">
<span></span>
<span></span>
Case Transforms: the <span class="property">text-transform</span> property</span></a>
</ul>
<li><a href="#white-space-property"><span class="secno">3</span> <span class="content">
<span></span><span></span>
White Space and Wrapping: the <span class="property">white-space</span> property</span></a>
<li><a href="#white-space-processing"><span class="secno">4</span> <span class="content">
White Space Processing Details</span></a>
<ul class="toc">
<li><a href="#white-space-rules"><span class="secno">4.1</span> <span class="content">
The White Space Processing Rules</span></a>
<ul class="toc">
<li><a href="#white-space-phase-1"><span class="secno">4.1.1</span> <span class="content">Phase I: Collapsing and Transformation</span></a>
<li><a href="#line-break-transform"><span class="secno">4.1.2</span> <span class="content">
Segment Break Transformation Rules</span></a>
<li><a href="#white-space-phase-2"><span class="secno">4.1.3</span> <span class="content">Phase II: Trimming and Positioning</span></a>
</ul>
<li><a href="#tab-size-property"><span class="secno">4.2</span> <span class="content">
Tab Character Size: the <span class="property">tab-size</span> property</span></a>
</ul>
<li><a href="#line-breaking"><span class="secno">5</span> <span class="content">
Line Breaking and Word Boundaries</span></a>
<ul class="toc">
<li><a href="#line-break-details"><span class="secno">5.1</span> <span class="content">
Line Breaking Details</span></a>
<li><a href="#word-break-property"><span class="secno">5.2</span> <span class="content">
Breaking Rules for Letters: the <span class="property">word-break</span> property</span></a>
<li><a href="#line-break-property"><span class="secno">5.3</span> <span class="content">
Breaking Rules for Punctuation: the <span class="property">line-break</span> property</span></a>
</ul>
<li><a href="#hyphenation"><span class="secno">6</span> <span class="content">Breaking Within Words</span></a>
<ul class="toc">
<li><a href="#hyphens-property"><span class="secno">6.1</span> <span class="content">Hyphenation Control: the <span class="property">hyphens</span> property</span></a>
<li><a href="#overflow-wrap-property"><span class="secno">6.2</span> <span class="content">
Overflow Wrapping: the <span class="property">overflow-wrap</span>/<span class="property">word-wrap</span> property</span></a>
</ul>
<li><a href="#justification"><span class="secno">7</span> <span class="content">
Alignment and Justification</span></a>
<ul class="toc">
<li><a href="#text-align-property"><span class="secno">7.1</span> <span class="content">
Text Alignment: the <span class="property">text-align</span> shorthand</span></a>
<li><a href="#text-align-all-property"><span class="secno">7.2</span> <span class="content">
Default Text Alignment: the <span class="property">text-align-all</span> property</span></a>
<li><a href="#text-align-last-property"><span class="secno">7.3</span> <span class="content">
Last Line Alignment: the <span class="property">text-align-last</span> property</span></a>
<li><a href="#text-justify-property"><span class="secno">7.4</span> <span class="content">
Justification Method: the <span class="property">text-justify</span> property</span></a>
<ul class="toc">
<li><a href="#expanding-text"><span class="secno">7.4.1</span> <span class="content">
Expanding and Compressing Text</span></a>
<li><a href="#justify-symbols"><span class="secno">7.4.2</span> <span class="content">
Handling Symbols and Punctuation</span></a>
<li><a href="#justify-limits"><span class="secno">7.4.3</span> <span class="content">
Unexpandable Text</span></a>
<li><a href="#justify-cursive"><span class="secno">7.4.4</span> <span class="content">
Cursive Scripts</span></a>
<li><a href="#justify-algos"><span class="secno">7.4.5</span> <span class="content">
Possible Algorithms</span></a>
</ul>
</ul>
<li><a href="#spacing"><span class="secno">8</span> <span class="content">
Spacing</span></a>
<ul class="toc">
<li><a href="#word-spacing-property"><span class="secno">8.1</span> <span class="content">
Word Spacing: the <span class="property">word-spacing</span> property</span></a>
<li><a href="#letter-spacing-property"><span class="secno">8.2</span> <span class="content">
Tracking: the <span class="property">letter-spacing</span> property</span></a>
</ul>
<li><a href="#edge-effects"><span class="secno">9</span> <span class="content">
Edge Effects</span></a>
<ul class="toc">
<li><a href="#text-indent-property"><span class="secno">9.1</span> <span class="content">
First Line Indentation: the <span class="property">text-indent</span> property</span></a>
<li><a href="#hanging-punctuation-property"><span class="secno">9.2</span> <span class="content">
Hanging Punctuation: the <span class="property">hanging-punctuation</span> property</span></a>
<li><a href="#bidi-linebox"><span class="secno">9.3</span> <span class="content">
Bidirectionality and Line Boxes</span></a>
</ul>
<li><a href="#order"><span class="secno"></span> <span class="content">Appendix A:
Text Processing Order of Operations</span></a>
<li><a href="#default-stylesheet"><span class="secno"></span> <span class="content">
Appendix B: Default UA Stylesheet</span></a>
<li><a href="#script-groups"><span class="secno"></span> <span class="content">
Appendix C: Scripts and Spacing</span></a>
<li><a href="#character-properties"><span class="secno"></span> <span class="content">Appendix D.
Characters and Properties</span></a>
<li><a href="#acknowledgements"><span class="secno"></span> <span class="content">
Acknowledgements</span></a>
<li><a href="#changes"><span class="secno"></span> <span class="content">
Changes</span></a>
<ul class="toc">
<li><a href="#recent-changes"><span class="secno"></span> <span class="content">
Changes from the <span>October
2013 CSS3 Text <abbr title="Last Call Working Draft">LCWD</abbr></span></span></a>
<li><a href="#changes-2013"><span class="secno"></span> <span class="content">
Changes from the <span>November
2012 CSS3 Text <abbr title="Working Draft">WD</abbr></span></span></a>
</ul>
<li><a href="#conformance"><span class="secno"></span> <span class="content">
Conformance</span></a>
<ul class="toc">
<li><a href="#conventions"><span class="secno"></span> <span class="content">
Document conventions</span></a>
<li><a href="#conformance-classes"><span class="secno"></span> <span class="content">
Conformance classes</span></a>
<li><a href="#partial"><span class="secno"></span> <span class="content">
Partial implementations</span></a>
<li><a href="#experimental"><span class="secno"></span> <span class="content">
Experimental implementations</span></a>
<li><a href="#testing"><span class="secno"></span> <span class="content">
Non-experimental implementations</span></a>
</ul>
<li><a href="#index"><span class="secno"></span> <span class="content">Index</span></a>
<ul class="toc">
<li><a href="#index-defined-here"><span class="secno"></span> <span class="content">Terms defined by this specification</span></a>
<li><a href="#index-defined-elsewhere"><span class="secno"></span> <span class="content">Terms defined by reference</span></a>
</ul>
<li><a href="#references"><span class="secno"></span> <span class="content">References</span></a>
<ul class="toc">
<li><a href="#normative"><span class="secno"></span> <span class="content">Normative References</span></a>
<li><a href="#informative"><span class="secno"></span> <span class="content">Informative References</span></a>
</ul>
<li><a href="#property-index"><span class="secno"></span> <span class="content">Property Index</span></a>
<li><a href="#issues-index"><span class="secno"></span> <span class="content">Issues Index</span></a>
</ul></div>
<main>
<h2 class="heading settled" data-level="1" id="intro"><span class="secno">1. </span><span class="content">
Introduction</span><a class="self-link" href="#intro"></a></h2>
<p>This module describes the typesetting controls of CSS;
that is, the features of CSS that control the translation of
source text to formatted, line-wrapped text.
Various CSS properties provide control over
<a href="#transforming">case transformation</a>,
<a href="#white-space">white space collapsing</a>,
<a href="#white-space">text wrapping</a>,
<a href="#line-breaking">line breaking rules</a>
and <a href="#hyphenation">hyphenation</a>,
<a href="#justification">alignment and justification</a>,
<a href="#spacing">spacing</a>,
and <a href="#edge-effects">indentation</a>.
</p>
<div class="note" role="note">
<p>Font selection is covered in <a href="http://www.w3.org/TR/css3-fonts/">CSS Fonts Level 3</a> <a data-link-type="biblio" href="#biblio-css3-fonts">[CSS3-FONTS]</a>.
</p>
<p>
<span id="decoration"></span>
<span id="text-decoration"></span>
<span id="line-decoration"></span>
<span id="text-decoration-line"></span>
<span id="text-decoration-color"></span>
<span id="text-decoration-style"></span>
<span id="text-decoration-skip"></span>
<span id="text-underline-position"></span>
<span id="emphasis-marks"></span>
<span id="text-emphasis-style"></span>
<span id="text-emphasis-color"></span>
<span id="text-emphasis"></span>
<span id="text-emphasis-position"></span>
<span id="text-shadow"></span>
Features for decorating text,
such as <a href="http://www.w3.org/TR/css-text-decor-3/#line-decoration">underlines</a>,
<a href="http://www.w3.org/TR/css-text-decor-3/#emphasis-marks">emphasis marks</a>,
and <a href="http://www.w3.org/TR/css-text-decor-3/#text-shadow-property">shadows</a>,
(previously part of this module)
are covered in
<a href="http://www.w3.org/TR/css-text-decor-3/">CSS Text Decoration Level 3</a> <a data-link-type="biblio" href="#biblio-css3-text-decor">[CSS3-TEXT-DECOR]</a>.
</p>
<p><a href="http://www.w3.org/TR/css3-writing-modes/#text-direction">Bidirectional</a> and
<a href="http://www.w3.org/TR/css3-writing-modes/#vertical-intro">vertical</a> text
are addressed in
<a href="http://www.w3.org/TR/css3-writing-modes/">CSS Writing Modes Level 3</a> <a data-link-type="biblio" href="#biblio-css3-writing-modes">[CSS3-WRITING-MODES]</a>.
</p>
</div>
<h3 class="heading settled" data-level="1.1" id="placement"><span class="secno">1.1. </span><span class="content">
Module Interactions</span><a class="self-link" href="#placement"></a></h3>
<p>This module, together with <a data-link-type="biblio" href="#biblio-css3-text-decor">[CSS3-TEXT-DECOR]</a>,
replaces and extends the text-level features defined in <a data-link-type="biblio" href="#biblio-css21">[CSS21]</a> chapter 16.
</p>
<h3 class="heading settled" data-level="1.2" id="values"><span class="secno">1.2. </span><span class="content">
Values</span><a class="self-link" href="#values"></a></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 data-link-type="biblio" href="#biblio-css21">[CSS21]</a>. Value types not defined in
this specification are defined in CSS Level 2 Revision 1 <a data-link-type="biblio" href="#biblio-css21">[CSS21]</a>.
Other CSS modules may expand the definitions of these value types: for
example <a data-link-type="biblio" href="#biblio-css3val">[CSS3VAL]</a>, when combined with this module, expands the
definition of the <var><length></var> 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.
</p>
<h3 class="heading settled" data-level="1.3" id="terms"><span class="secno">1.3. </span><span class="content">
Terminology</span><a class="self-link" href="#terms"></a></h3>
<p>In addition to the terms defined below,
other terminology and concepts used in this specification are defined
in <a data-link-type="biblio" href="#biblio-css21">[CSS21]</a> and <a data-link-type="biblio" href="#biblio-css3-writing-modes">[CSS3-WRITING-MODES]</a>.
</p>
<h4 class="heading settled" data-level="1.3.1" id="characters"><span class="secno">1.3.1. </span><span class="content">
Characters and Letters</span><a class="self-link" href="#characters"></a></h4>
<p>The basic unit of typesetting is the <dfn data-dfn-type="dfn" data-noexport="" id="character">character<a class="self-link" href="#character"></a></dfn>.
However, because writing systems are not always as simple as the basic English alphabet,
what a <a data-link-type="dfn" href="#character">character</a> actually is depends on the context in which the term is used.
For example, in Hangul (the Korean writing system),
each square representation of a syllable
(e.g. <span lang="ko-hang" title="Hangul syllable HAN">한</span>=<span lang="ko-Latn">Han</span>)
can be considered a <a data-link-type="dfn" href="#character">character</a>.
However, the square symbol is really composed of multiple letters each representing a phoneme
(e.g. <span lang="ko-hang" title="Hangul letter HIEUH">ㅎ</span>=<span lang="ko-Latn">h</span>,
<span lang="ko-hang" title="Hangul letter HIEUH">ㅏ</span>=<span lang="ko-Latn">a</span>,
<span lang="ko-hang" title="Hangul letter HIEUH">ㄴ</span>=<span lang="ko-Latn">n</span>)
and these also could each be considered a <a data-link-type="dfn" href="#character">character</a>.
</p>
<p>A basic unit of computer text encoding, for any given encoding,
is also called a <a data-link-type="dfn" href="#character">character</a>,
and depending on the encoding,
a single encoding <a data-link-type="dfn" href="#character">character</a> might correspond
to the entire pre-composed syllabic <a data-link-type="dfn" href="#character">character</a> (e.g. <span lang="ko-hang" title="Hangul syllable HAN">한</span>),
to the individual phonemic <a data-link-type="dfn" href="#character">character</a> (e.g. <span lang="ko-hang" title="Hangul letter HIEUH">ㅎ</span>),
or to smaller units such as
a base letterform (e.g. <span lang="ko-hang" title="Hangul letter IEUNG">ㅇ</span>)
and any combining marks that vary it (e.g. extra strokes that represent aspiration).
</p>
<p>In turn, a single encoding <a data-link-type="dfn" href="#character">character</a> can be represented in the data stream as one or more bytes;
and in programming environments one byte is sometimes also called a <a data-link-type="dfn" href="#character">character</a>.
</p>
<p>For text layout, we will refer to the <dfn data-dfn-type="dfn" data-export="" data-lt="typographic character unit|typographic character" id="typographic-character-unit">typographic character unit<a class="self-link" href="#typographic-character-unit"></a></dfn>
as the basic unit of text.
Even within the realm of text layout,
the relevant <a data-link-type="dfn" href="#character">character</a> unit depends on the operation.
For example, line-breaking and letter-spacing will segment
a sequence of Thai characters that include U+0E33 THAI CHARACTER SARA AM differently;
or the behaviour of a conjunct consonant in a script such as Devanagari
may depend on the font in use.
So the <a data-link-type="dfn" href="#typographic-character-unit">typographic character</a> represents a unit of the writing system—such as a Latin alphabetic letter (including its diacritics),
Hangul syllable,
Chinese ideographic character,
Myanmar syllable cluster—that is indivisible with respect to a particular typographic operation
(line-breaking, first-letter effects, tracking, justification, vertical arrangement, etc.).
</p>
<p><a href="http://www.unicode.org/reports/tr29/">Unicode Standard Annex #29: Text Segmentation</a>
defines a unit called the <dfn data-dfn-type="dfn" data-noexport="" id="grapheme-cluster">grapheme cluster<a class="self-link" href="#grapheme-cluster"></a></dfn>
which approximates the <a data-link-type="dfn" href="#typographic-character-unit">typographic character</a>.
A UA must use the <em>extended grapheme cluster</em>
(not <em>legacy grapheme cluster</em>), as defined in <a data-link-type="biblio" href="#biblio-uax29">[UAX29]</a>,
as the basis for its <a data-link-type="dfn" href="#typographic-character-unit">typographic character unit</a>.
However, the UA should tailor the definitions
as required by typographic tradition
since the default rules are not always appropriate or ideal,
and is expected to tailor them differently
depending on the operation as needed.</p>
<div class="example" id="example-645d2d72"><a class="self-link" href="#example-645d2d72"></a>
<p>For example,
in some scripts such as Myanmar or Devanagari,
the <a data-link-type="dfn" href="#typographic-character-unit">typographic character unit</a> for both justification and line-breaking
is an entire syllable,
which can include more than one <a data-link-type="biblio" href="#biblio-uax29">[UAX29]</a> <a data-link-type="dfn" href="#grapheme-cluster">grapheme cluster</a>.
</p>
<p>In other scripts such as Thai or Lao,
even though for line-breaking the <a data-link-type="dfn" href="#typographic-character-unit">typographic character</a>
matches Unicode’s default <a data-link-type="dfn" href="#grapheme-cluster">grapheme clusters</a>,
for letter-spacing the relevant unit
is <em>less</em> than a <a data-link-type="biblio" href="#biblio-uax29">[UAX29]</a> <a data-link-type="dfn" href="#grapheme-cluster">grapheme cluster</a>,
and may require decomposition or other substitutions
before spacing can be inserted.
</p>
<p>For instance,
to properly letter-space the Thai word คำ (U+0E04 + U+0E33),
the U+0E33 needs to be decomposed into U+0E4D + U+0E32,
and then the extra letter-space inserted before the U+0E32: คํ า.
</p>
<p>A slightly more complex example is น้ำ (U+0E19 + U+0E49 + U+0E33).
In this case, normal Thai shaping will first decompose the U+0E33 into U+0E4D + U+0E32
and then swap the U+0E4D with the U+0E49, giving U+0E19 + U+0E4D + U+0E49 + U+0E32.
As before the extra letter-space is then inserted before the U+0E32: นํ้ า.
</p>
</div>
<p>A <dfn data-dfn-type="dfn" data-export="" id="typographic-letter-unit">typographic letter unit<a class="self-link" href="#typographic-letter-unit"></a></dfn> or <dfn data-dfn-type="dfn" data-noexport="" id="letter">letter<a class="self-link" href="#letter"></a></dfn> for the purpose of this specification
is a <a data-link-type="dfn" href="#typographic-character-unit">typographic character unit</a> belonging to one of the Letter or Number general
categories in Unicode. <a data-link-type="biblio" href="#biblio-uax44">[UAX44]</a>
See <a href="#character-properties">Character Properties</a>
for how to determine the Unicode properties of a <a data-link-type="dfn" href="#typographic-character-unit">typographic character unit</a>.
</p>
<p>The rendering characteristics of a <a data-link-type="dfn" href="#typographic-character-unit">typographic character unit</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 <a data-link-type="dfn" href="#grapheme-cluster">grapheme clusters</a>
by element boundaries may give inconsistent or undesired results.
</p>
<h4 class="heading settled" data-level="1.3.2" id="languages"><span class="secno">1.3.2. </span><span class="content">
Languages and Typesetting</span><a class="self-link" href="#languages"></a></h4>
<p class="note" role="note">
Many typographic effects vary by linguistic context.
In CSS, language-specific typographic tailorings
are only applied when the content language is known (declared).
</p>
<p><strong class="advisement">
Authors should language-tag their content accurately for the best typographic behavior.
</strong>
</p>
<p>The <dfn data-dfn-type="dfn" data-noexport="" id="content-language">content language<a class="self-link" href="#content-language"></a></dfn> of an element is the (human) language
the element is declared to be in, according to the rules of the
<a href="http://www.w3.org/TR/CSS21/conform.html#doclanguage">document language</a>.
For example, the rules for determining the <a data-link-type="dfn" href="#content-language">content language</a> of an HTML
element use the <code>lang</code> attribute and are defined in <a data-link-type="biblio" href="#biblio-html5">[HTML5]</a>,
and the rules for determining the <a data-link-type="dfn" href="#content-language">content language</a> of an XML element use
the <code>xml:lang</code> attribute and are
<a href="http://www.w3.org/TR/REC-xml/#sec-lang-tag">defined</a> in <a data-link-type="biblio" href="#biblio-xml10">[XML10]</a>.
Note that it is possible for the <a data-link-type="dfn" href="#content-language">content language</a> of an element
to be unknown.
</p>
<h2 class="heading settled" data-level="2" id="transforming"><span class="secno">2. </span><span class="content">
Transforming Text</span><a class="self-link" href="#transforming"></a></h2>
<h3 class="heading settled" data-level="2.1" id="text-transform-property"><span class="secno">2.1. </span><span class="content">
<span id="caps-prop"></span>
<span id="text-transform"></span>
Case Transforms: the <a class="property" data-link-type="propdesc" href="#propdef-text-transform">text-transform</a> property</span><a class="self-link" href="#text-transform-property"></a></h3>
<table class="propdef">
<tbody>
<tr>
<th>Name:
<td><dfn class="css" data-dfn-type="property" data-export="" id="propdef-text-transform">text-transform<a class="self-link" href="#propdef-text-transform"></a></dfn>
<tr>
<th><a href="#values">Value</a>:
<td>none | capitalize | uppercase | lowercase | full-width
<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
<tr>
<th>Animatable:
<td>no
<tr>
<th>Canonical order:
<td>N/A
</table>
<p>This property transforms text for styling purposes.
(It has no effect on the underlying content.)
Values have the following meanings:</p>
<dl>
<dt><dfn class="css" data-dfn-for="text-transform" data-dfn-type="value" data-export="" id="valdef-text-transform-none">none<a class="self-link" href="#valdef-text-transform-none"></a></dfn>
<dd>No effects.
<dt><dfn class="css" data-dfn-for="text-transform" data-dfn-type="value" data-export="" id="valdef-text-transform-capitalize">capitalize<a class="self-link" href="#valdef-text-transform-capitalize"></a></dfn>
<dd>Puts the first <a data-link-type="dfn" href="#typographic-letter-unit">typographic letter unit</a> of each word in titlecase;
other characters are unaffected.
<dt><dfn class="css" data-dfn-for="text-transform" data-dfn-type="value" data-export="" id="valdef-text-transform-uppercase">uppercase<a class="self-link" href="#valdef-text-transform-uppercase"></a></dfn>
<dd>Puts all lettersin uppercase.
<dt><dfn class="css" data-dfn-for="text-transform" data-dfn-type="value" data-export="" id="valdef-text-transform-lowercase">lowercase<a class="self-link" href="#valdef-text-transform-lowercase"></a></dfn>
<dd>Puts all letters in lowercase.
<dt><dfn class="css" data-dfn-for="text-transform" data-dfn-type="value" data-export="" id="valdef-text-transform-full-width">full-width<a class="self-link" href="#valdef-text-transform-full-width"></a></dfn>
<dd>Puts all <a data-link-type="dfn" href="#typographic-character-unit">typographic character units</a> in fullwidth form.
If a character does not have a corresponding fullwidth form,
it is left as is.
This value is typically used to typeset Latin letters and digits
as if they were ideographic characters.
</dl>
<p>For <a class="css" data-link-type="maybe" href="#valdef-text-transform-capitalize">capitalize</a>, what constitutes a “word“ is UA-dependent;
<a data-link-type="biblio" href="#biblio-uax29">[UAX29]</a> is suggested (but not required) for determining such word
boundaries. Authors should not expect <a class="css" data-link-type="maybe" href="#valdef-text-transform-capitalize">capitalize</a> to follow
language-specific titlecasing conventions (such as skipping articles
in English).
</p>
<div class="example" id="example-7cb4bb58"><a class="self-link" href="#example-7cb4bb58"></a>
<p>The following example converts the ASCII characters
used in abbreviations in Japanese text to their fullwidth variants
so that they lay out and line break like ideographs:
</p>
<pre>abbr:lang(ja) { text-transform: full-width; }</pre>
</div>
<p class="note" role="note">
Note that, as defined in <a href="#order">Text Processing Order of Operations</a>,
transforming text affects line-breaking and other formatting operations.
</p>
<p>
The UA must use the full case mappings for Unicode
characters, including any conditional casing rules, as defined in
Default Case Algorithm section of The Unicode Standard <a data-link-type="biblio" href="#biblio-unicode">[UNICODE]</a>.
If (and only if) the <a data-link-type="dfn" href="#content-language">content language</a>
of the element is, according to the rules of the
<a href="http://www.w3.org/TR/CSS21/conform.html#doclanguage">document language</a>,
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>.
</p>
<div class="example" id="example-12e88f74"><a class="self-link" href="#example-12e88f74"></a>
<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 <a data-link-type="dfn" href="#content-language">content language</a> is Turkish
(or another Turkic language that uses Turkish casing rules);
in other languages, the usual mapping of “I”
and “i” is required. This rule is thus conditionally
defined in Unicode’s SpecialCasing.txt file.
</p>
</div>
<p>The definition of fullwidth and halfwidth forms can be found on the
Unicode consortium web site at <a data-link-type="biblio" href="#biblio-uax11">[UAX11]</a>.
The mapping to fullwidth form is defined by taking code points with
the <code><wide></code> or the <code><narrow></code> tag
in their <code>Decomposition_Mapping</code> in <a data-link-type="biblio" href="#biblio-uax44">[UAX44]</a>.
For the <code><narrow></code> tag,
the mapping is from the code point to the decomposition (minus <code><narrow></code> tag),
and for the <code><wide></code> tag,
the mapping is from the decomposition (minus the <code><wide></code> tag)
back to the original code point.
</p>
<p>Text transformation happens after <a href="#white-space-rules">white
space processing</a>, which means that <a class="css" data-link-type="maybe" href="#valdef-text-transform-full-width">full-width</a> only transforms
U+0020 spaces to U+3000 within <a data-link-type="dfn" href="#preserved">preserved</a> white space.
</p>
<p class="note" role="note">
A future level of CSS may introduce the ability to create custom mapping
tables for less common text transforms, such as by an <span class="css">@text-transform</span>
rule similar to <a class="css" data-link-type="maybe" href="https://drafts.csswg.org/css-counter-styles-3/#at-ruledef-counter-style">@counter-style</a> from <a data-link-type="biblio" href="#biblio-css-counter-styles-3">[CSS-COUNTER-STYLES-3]</a>.
</p>
<h2 class="heading settled" data-level="3" id="white-space-property"><span class="secno">3. </span><span class="content">
<span id="white-space-collapsing"></span><span id="text-wrap"></span>
White Space and Wrapping: the <a class="property" data-link-type="propdesc" href="#propdef-white-space">white-space</a> property</span><a class="self-link" href="#white-space-property"></a></h2>
<table class="propdef">
<tbody>
<tr>
<th>Name:
<td><dfn class="css" data-dfn-type="property" data-export="" id="propdef-white-space">white-space<a class="self-link" href="#propdef-white-space"></a></dfn>
<tr>
<th><a href="#values">Value</a>:
<td>normal | pre | nowrap | pre-wrap | pre-wrap-auto | pre-line
<tr>
<th>Initial:
<td>normal
<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
<tr>
<th>Animatable:
<td>no
<tr>
<th>Canonical order:
<td>N/A
</table>
<p>This property specifies two things:
</p>
<ul>
<li>whether and how <a data-link-type="dfn" href="#white-space">white space</a> inside the element is collapsed
<li>whether lines may <a data-link-type="dfn" href="#wrapping">wrap</a> at unforced <a data-link-type="dfn" href="#soft-wrap-opportunity">soft wrap opportunities</a>
</ul>
<p>Values have the following meanings, which must be interpreted
according to
the <a href="#white-space-rules">White Space Processing</a> and
<a href="#line-breaking">Line Breaking</a> rules:</p>
<dl>
<dt><dfn class="css" data-dfn-for="white-space" data-dfn-type="value" data-export="" id="valdef-white-space-normal">normal<a class="self-link" href="#valdef-white-space-normal"></a></dfn>
<dd>This value directs user agents to collapse sequences of <a data-link-type="dfn" href="#white-space">white space</a>
into a single character (or <a href="#line-break-transform">in some
cases</a>, no character).
Lines may wrap at allowed <a data-link-type="dfn" href="#soft-wrap-opportunity">soft wrap opportunities</a>,
as determined by the line-breaking rules in effect,
in order to minimize inline-axis overflow.
<dt><dfn class="css" data-dfn-for="white-space" data-dfn-type="value" data-export="" id="valdef-white-space-pre">pre<a class="self-link" href="#valdef-white-space-pre"></a></dfn>
<dd>This value prevents user agents from collapsing sequences of <a data-link-type="dfn" href="#white-space">white space</a>.
<a data-link-type="dfn" href="#segment-break">Segment breaks</a> such as line feeds and carriage returns are preserved as <a data-link-type="dfn" href="#forced-line-break">forced line breaks</a>.
Lines only break at <a data-link-type="dfn" href="#forced-line-break">forced line breaks</a>;
content that does not fit within the block container overflows it.
<dt><dfn class="css" data-dfn-for="white-space" data-dfn-type="value" data-export="" id="valdef-white-space-nowrap">nowrap<a class="self-link" href="#valdef-white-space-nowrap"></a></dfn>
<dd>Like <a class="css" data-link-type="maybe" href="#valdef-white-space-normal">normal</a>, this value collapses <a data-link-type="dfn" href="#white-space">white space</a>;
but like <a class="css" data-link-type="maybe" href="#valdef-white-space-pre">pre</a>, it does not allow wrapping.
<dt><dfn class="css" data-dfn-for="white-space" data-dfn-type="value" data-export="" id="valdef-white-space-pre-wrap">pre-wrap<a class="self-link" href="#valdef-white-space-pre-wrap"></a></dfn>
<dd>Like <a class="css" data-link-type="maybe" href="#valdef-white-space-pre">pre</a>, this value preserves <a data-link-type="dfn" href="#white-space">white space</a>;
but like <a class="css" data-link-type="maybe" href="#valdef-white-space-normal">normal</a>, it allows wrapping.