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<!doctype html>
<html lang="en">
<head>
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
<title>CSS Ruby Layout Module Level 1</title>
<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">
</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 Ruby Layout Module Level 1</h1>
<h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="content">Editor’s Draft,
<time class="dt-updated" datetime="2015-02-07">7 February 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-ruby-1/">http://dev.w3.org/csswg/css-ruby-1/</a>
<dt>Latest version:
<dd><a href="http://www.w3.org/TR/css-ruby-1/">http://www.w3.org/TR/css-ruby-1/</a>
<dt>Previous Versions:
<dd><a href="http://www.w3.org/TR/2013/WD-css3-ruby-20130919/" rel="previous">http://www.w3.org/TR/2013/WD-css3-ruby-20130919/</a>
<dt>Feedback:
<dd><span><a href="mailto:www-style@w3.org?subject=%5Bcss-ruby%5D%20feedback">www-style@w3.org</a> with subject line “<kbd>[css-ruby] <var>… message topic …</var></kbd>” (<a href="http://lists.w3.org/Archives/Public/www-style/" rel="discussion">archives</a>)</span>
<dt>Issue Tracking:
<dd><a href="#issues-index">Inline In Spec</a>
<dt class="editor">Editors:
<dd class="editor">
<div class="p-author h-card vcard"><a class="p-name fn u-url url" href="http://fantasai.inkedblade.net/contact">Elika J. Etemad</a> (<span class="p-org org">Invited Expert</span>)</div>
<dd class="editor">
<div class="p-author h-card vcard"><a class="p-name fn u-email email" href="mailto:kojiishi@gmail.com">Koji Ishii</a> (<span class="p-org org">Google</span>)</div>
</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/">
<acronym title="World Wide Web Consortium">W3C</acronym>
</a><sup>®</sup> (<a href="http://www.csail.mit.edu/">
<acronym title="Massachusetts Institute of Technology">MIT</acronym>
</a>, <a href="http://www.ercim.eu/">
<acronym title="European Research Consortium for Informatics and Mathematics">ERCIM</acronym>
</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>“Ruby”, a form of interlinear annotation, are short runs of text alongside the base text.
They are typically used in East Asian documents to indicate pronunciation or to provide a short annotation.
This module describes the rendering model and formatting controls related to displaying ruby annotations in CSS.</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-ruby%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-ruby” in the subject,
preferably like this:
“[css-ruby] <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"></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="#diagram-conventions"><span class="secno">1.3</span> <span class="content">
Diagram conventions</span></a>
<li><a href="#ruby-def"><span class="secno">1.4</span> <span class="content">
What is ruby?</span></a>
</ul>
<li><a href="#ruby-model"><span class="secno">2</span> <span class="content">
Ruby Box Model</span></a>
<ul class="toc">
<li><a href="#ruby-display"><span class="secno">2.1</span> <span class="content">
Ruby-specific <span class="property" data-lt="display">display</span> Values</span></a>
<ul class="toc">
<li><a href="#formatting-context"><span class="secno">2.1.1</span> <span class="content">
The Ruby Formatting Context</span></a>
<li><a href="#display-inside-outside"><span class="secno">2.1.2</span> <span class="content">
Ruby-specific <span class="property" data-lt="display-inside">display-inside</span> and <span class="property" data-lt="display-outside">display-outside</span> values</span></a>
<li><a href="#block-ruby"><span class="secno">2.1.3</span> <span class="content">
Non-Inline Ruby</span></a>
</ul>
<li><a href="#box-fixup"><span class="secno">2.2</span> <span class="content">
Anonymous Ruby Box Generation</span></a>
<li><a href="#ruby-pairing"><span class="secno">2.3</span> <span class="content">
Annotation Pairing</span></a>
<ul class="toc">
<li><a href="#segment-pairing"><span class="secno">2.3.1</span> <span class="content">
Segment Pairing and Annotation Levels</span></a>
<li><a href="#base-annotation-pairing"><span class="secno">2.3.2</span> <span class="content">
Unit Pairing and Spanning Annotations</span></a>
<li><a href="#nested-pairing"><span class="secno">2.3.3</span> <span class="content">
Complex Spanning with Nested Ruby</span></a>
</ul>
<li><a href="#autohide"><span class="secno">2.4</span> <span class="content">
Autohiding Base-identical Annotations</span></a>
<li><a href="#white-space"><span class="secno">2.5</span> <span class="content">
White Space Collapsing</span></a>
</ul>
<li><a href="#ruby-layout"><span class="secno">3</span> <span class="content">
Ruby Layout</span></a>
<ul class="toc">
<li><a href="#inter-character-layout"><span class="secno">3.1</span> <span class="content">
Inter-character Ruby Layout</span></a>
<li><a href="#box-style"><span class="secno">3.2</span> <span class="content">
Styling Ruby Boxes</span></a>
<li><a href="#line-breaks"><span class="secno">3.3</span> <span class="content">
Breaking Across Lines</span></a>
<ul class="toc">
<li><a href="#break-between"><span class="secno">3.3.1</span> <span class="content">
Breaking Between Bases</span></a>
<li><a href="#break-within"><span class="secno">3.3.2</span> <span class="content">
Breaking Within Bases</span></a>
</ul>
<li><a href="#bidi"><span class="secno">3.4</span> <span class="content">
Bidi Reordering</span></a>
<li><a href="#line-height"><span class="secno">3.5</span> <span class="content">
Line Spacing</span></a>
</ul>
<li><a href="#ruby-props"><span class="secno">4</span> <span class="content">
Ruby Formatting Properties</span></a>
<ul class="toc">
<li><a href="#rubypos"><span class="secno">4.1</span> <span class="content">
Ruby Positioning: the <span class="property" data-lt="ruby-position">ruby-position</span> property</span></a>
<li><a href="#collapsed-ruby"><span class="secno">4.2</span> <span class="content">
Sharing Annotation Space: the <span class="property" data-lt="ruby-merge">ruby-merge</span> property</span></a>
<li><a href="#ruby-align-property"><span class="secno">4.3</span> <span class="content"><span></span>
Ruby Text Distribution: the <span class="property" data-lt="ruby-align">ruby-align</span> property</span></a>
<li><a href="#ruby-text-decoration"><span class="secno">4.4</span> <span class="content">
Ruby Text Decoration</span></a>
</ul>
<li><a href="#edge-effects"><span class="secno">5</span> <span class="content">
Edge Effects</span></a>
<ul class="toc">
<li><a href="#ruby-overhang"><span class="secno">5.1</span> <span class="content">
Overhanging Ruby</span></a>
<li><a href="#line-edge"><span class="secno">5.2</span> <span class="content">
Line-edge Alignment</span></a>
</ul>
<li><a href="#default-stylesheet"><span class="secno"></span> <span class="content">
Appendix A: Default Style Sheet</span></a>
<ul class="toc">
<li><a href="#default-ua-ruby"><span class="secno"></span> <span class="content">
<span class="secno">A.1</span> Supporting Ruby Layout</span></a>
<li><a href="#default-inline"><span class="secno"></span> <span class="content">
<span class="secno">A.2</span> Inlining Ruby Annotations</span></a>
<li><a href="#default-parens"><span class="secno"></span> <span class="content">
<span class="secno">A.3</span> Generating Parentheses</span></a>
</ul>
<li><a href="#glossary"><span class="secno">6</span> <span class="content">
Glossary</span></a>
<li><a href="#acknowledgments"><span class="secno"></span> <span class="content">
Acknowledgments</span></a>
<li><a href="#changes"><span class="secno"></span> <span class="content">
Changes</span></a>
<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="#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="#index"><span class="secno"></span> <span class="content">Index</span></a>
<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>
<p></p>
<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><em>This section is not normative.</em>
</p>
<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 extends the inline box model of CSS Level 2 <a data-link-type="biblio" href="#biblio-css21">[CSS21]</a>
to support ruby.
</p>
<p>None of the properties in this module apply to the <code>::first-line</code> or
<code>::first-letter</code> pseudo-elements.
</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="diagram-conventions"><span class="secno">1.3. </span><span class="content">
Diagram conventions</span><a class="self-link" href="#diagram-conventions"></a></h3>
<p>Many typographical conventions in East Asian typography depend
on whether the character rendered is wide (CJK) or narrow (non-CJK).
There are a number of illustrations in this document
for which the following legend is used:
</p>
<dl>
<dt><img alt="Symbolic wide-cell glyph representation" height="39" src="images/fullwidth.gif" width="39">
<dd>Wide-cell glyph (e.g. Han) that is the <var>n</var>th character in the text run.
They are typically sized to 50% when used as annotations.
<dt><img alt="Symbolic narrow-cell glyph representation" height="39" src="images/halfwidth.gif" width="19">
<dd>Narrow-cell glyph (e.g. Roman) which is the <var>n</var>th glyph in the text run.
</dl>
<p>The orientation which the above symbols assume in the diagrams
corresponds to the orientation that the glyphs they represent
are intended to assume when rendered by the user agent.
Spacing between these characters in the diagrams is incidental,
unless intentionally changed to make a point.
</p>
<h3 class="heading settled" data-level="1.4" id="ruby-def"><span class="secno">1.4. </span><span class="content">
What is ruby?</span><a class="self-link" href="#ruby-def"></a></h3>
<p><dfn data-dfn-type="dfn" data-noexport="" id="ruby">Ruby<a class="self-link" href="#ruby"></a></dfn> is the commonly-used name for a run of text
that appears alongside another run of text (referred to as the “base”)
and serves as an annotation or a pronunciation guide associated with that run of text.
</p>
<p>The following figures show two examples of Ruby,
a simple case and one with more complicated structure.
</p>
<div class="example">
<p>In this first example, a single annotation is used to annotate the base text.
</p>
<div class="figure">
<p><img alt="Example of ruby applied on top of a Japanese expression" src="images/licence.png">
</p>
<p class="caption">Example of ruby used in Japanese (simple case)
</p>
</div>
<p>In Japanese typography, this case is sometimes called
<span lang="ja">taigo</span> ruby or group-ruby (per-word ruby),
because the annotation as a whole is associated
with multi-character word (as a whole).
</p>
</div>
<div class="example">
<p>In this second example,
two levels of annotations are attached to a base sequence:
the hiragana characters on top refer to the pronunciation of each of the base kanji characters,
while the words “Keio” and “University” on the bottom are annotations describing the English translation.
</p>
<div class="figure">
<p><img alt="Example showing complex ruby with annotation text over and under the base characters" src="images/ruby-univ.gif">
</p>
<p class="caption">Complex ruby with annotation text over and under the base characters
</p>
</div>
<p>
</p>
<p>Notice that to allow correct association between the hiragana characters and
their corresponding Kanji base characters,
the spacing between these Kanji characters is adjusted.
(This happens around the fourth Kanji character in the figure above.)
To avoid variable spacing between the Kanji characters in the example above
the hiragana annotations can be styled as a <i>collapsed annotation</i>,
which will look more like the group-ruby example earlier.
However because the base-annotation pairings are recorded in the ruby structure,
if the text breaks across lines, the annotation characters will stay
correctly paired with their respective base characters.
</p>
</div>
<p><i>Ruby</i> formatting as used in Japanese is described in JIS X-4051 <a data-link-type="biblio" href="#biblio-jis4051">[JIS4051]</a> (in Japanese)
and in Requirements for Japanese Text Layout <a data-link-type="biblio" href="#biblio-jlreq">[JLREQ]</a> (in English and Japanese)].
In HTML, ruby structure and markup to represent it is described
in the Ruby Markup Extension specification.
This module describes the CSS rendering model
and formatting controls relevant to ruby layout of such markup.
</p>
<h2 class="heading settled" data-level="2" id="ruby-model"><span class="secno">2. </span><span class="content">
Ruby Box Model</span><a class="self-link" href="#ruby-model"></a></h2>
<p>The CSS ruby model is based on
the <a href="http://www.w3.org/TR/html5/text-level-semantics.html#the-ruby-element">W3C HTML5 Ruby Markup</a> model
and the <a href="http://www.w3.org/TR/ruby/">XHTML Ruby Annotation Recommendation</a> <a data-link-type="biblio" href="#biblio-ruby">[RUBY]</a>.
In this model, a ruby structure consists of
one or more <i>ruby base</i> elements representing the base (annotated) text,
associated with one or more levels of <i>ruby annotation</i> elements representing the annotations.
The structure of ruby is similar to that of a table:
there are “rows” (the <i data-lt="base level">base text level</i>, each <i>annotation level</i>)
and “columns” (each <i>ruby base</i> and its corresponding <i>ruby annotations</i>).
</p>
<p>Consecutive bases and annotations are grouped together into <i>ruby segments</i>.
Within a <i>ruby segment</i>, a <i>ruby annotation</i> may span multiple <i>ruby bases</i>.
</p>
<p class="note" role="note">In HTML, a single <code><ruby></code> element may contain multiple <i>ruby segments</i>.
(In the XHTML Ruby model, a single <code><ruby></code> element can only contain one <i>ruby segment</i>.)
</p>
<h3 class="heading settled" data-level="2.1" id="ruby-display"><span class="secno">2.1. </span><span class="content">
Ruby-specific <a class="property" data-link-type="propdesc" href="#propdef-display">display</a> Values</span><a class="self-link" href="#ruby-display"></a></h3>
<p>For document languages (such as XML applications) that do not have pre-defined ruby elements,
authors must map document language elements to ruby elements;
this is done with the <a class="property" data-link-type="propdesc" href="#propdef-display">display</a> property.
</p>
<table class="propdef">
<tbody>
<tr>
<th>Name:
<td><dfn class="css" data-dfn-type="property" data-export="" id="propdef-display">display<a class="self-link" href="#propdef-display"></a></dfn>
<tr>
<th><a href="#values">New Values</a>:
<td>ruby | ruby-base | ruby-text | ruby-base-container | ruby-text-container
</table>
<p>The following new <a class="property" data-link-type="propdesc" href="#propdef-display">display</a> values assign ruby layout roles to an arbitrary element:
</p>
<dl>
<dt><dfn class="css" data-dfn-for="display" data-dfn-type="value" data-export="" id="valdef-display-ruby"><a class="css" data-link-type="maybe" href="#valdef-display-ruby">ruby</a><a class="self-link" href="#valdef-display-ruby"></a></dfn>
<dd>Specifies that an element generates a <dfn data-dfn-for="" data-dfn-type="dfn" data-export="" data-lt="ruby container | ruby container box" id="ruby-container">ruby container box<a class="self-link" href="#ruby-container"></a></dfn>.
(Corresponds to HTML/XHTML <code><ruby></code> elements.)
<dt><dfn class="css" data-dfn-for="display" data-dfn-type="value" data-export="" id="valdef-display-ruby-base"><a class="css" data-link-type="maybe" href="#valdef-display-ruby-base">ruby-base</a><a class="self-link" href="#valdef-display-ruby-base"></a></dfn>
<dd>Specifies that an element generates a <dfn data-dfn-for="" data-dfn-type="dfn" data-export="" data-lt="ruby base box | ruby base" id="ruby-base-box">ruby base box<a class="self-link" href="#ruby-base-box"></a></dfn>.
(Corresponds to HTML/XHTML <code><rb></code> elements.)
<dt><dfn class="css" data-dfn-for="display" data-dfn-type="value" data-export="" id="valdef-display-ruby-text"><a class="css" data-link-type="maybe" href="#valdef-display-ruby-text">ruby-text</a><a class="self-link" href="#valdef-display-ruby-text"></a></dfn>
<dd>Specifies that an element generates a <dfn data-dfn-for="" data-dfn-type="dfn" data-export="" data-lt="ruby annotation box | ruby annotation | annotation" id="ruby-annotation-box">ruby annotation box<a class="self-link" href="#ruby-annotation-box"></a></dfn>.
(Corresponds to HTML/XHTML <code><rt></code> elements.)
<dt><dfn class="css" data-dfn-for="display" data-dfn-type="value" data-export="" id="valdef-display-ruby-base-container"><a class="css" data-link-type="maybe" href="#valdef-display-ruby-base-container">ruby-base-container</a><a class="self-link" href="#valdef-display-ruby-base-container"></a></dfn>
<dd>Specifies that an element generates a <dfn data-dfn-for="" data-dfn-type="dfn" data-export="" data-lt="ruby base container box | ruby base container" id="ruby-base-container-box">ruby base container box<a class="self-link" href="#ruby-base-container-box"></a></dfn>.
(Corresponds to XHTML <code><rbc></code> elements; generated as an anonymous box in HTML.)
<dt><dfn class="css" data-dfn-for="display" data-dfn-type="value" data-export="" id="valdef-display-ruby-text-container"><a class="css" data-link-type="maybe" href="#valdef-display-ruby-text-container">ruby-text-container</a><a class="self-link" href="#valdef-display-ruby-text-container"></a></dfn>
<dd>Specifies that an element generates a <dfn data-dfn-for="" data-dfn-type="dfn" data-export="" data-lt="ruby annotation container box | ruby annotation container" id="ruby-annotation-container-box">ruby annotation container box<a class="self-link" href="#ruby-annotation-container-box"></a></dfn>.
(Corresponds to HTML/XHTML <code><rtc></code> elements.)
</dl>
<p class="advisement">Authors using a language (such as HTML)
that supports dedicated ruby markup
should use that markup rather than
styling arbitrary elements (like <code><span></code>)
with ruby <a class="property" data-link-type="propdesc" href="#propdef-display">display</a> values.
Using the correct markup ensures that screen readers
and non-CSS renderers can interpret the ruby structures.
</p>
<h4 class="heading settled" data-level="2.1.1" id="formatting-context"><span class="secno">2.1.1. </span><span class="content">
The Ruby Formatting Context</span><a class="self-link" href="#formatting-context"></a></h4>
<p><i>Ruby containers</i> are non-atomic inline-level boxes.
Like inline boxes, they break across lines,
and their containing block is the nearest block container ancestor.
And just as the contents of an inline box
participate in the same inline formatting context that contains the inline box itself,
a <i>ruby container</i> and its base-level contents
participate in the same inline formatting context that contains the <i>ruby container</i> itself.
</p>
<p>However <i>ruby containers</i> also establish a <dfn data-dfn-type="dfn" data-noexport="" id="ruby-formatting-context">ruby formatting context<a class="self-link" href="#ruby-formatting-context"></a></dfn>
that builds further structure around their segment of the inline formatting context.
<i>Ruby bases</i>, <i>ruby annotations</i>, <i>ruby base containers</i>, and <i>ruby annotation containers</i>
are <dfn data-dfn-type="dfn" data-lt="internal ruby boxes|internal ruby display types" data-noexport="" id="internal-ruby-boxes">internal ruby boxes<a class="self-link" href="#internal-ruby-boxes"></a></dfn>:
like <i>internal table elements</i>,
they have specific roles in ruby layout,
and participate in their <i>ruby container</i>’s <i>ruby formatting context</i>.
</p>
<p>As with the contents of inline boxes,
the containing block for the contents of a <i>ruby container</i> (and all its <i>internal ruby boxes</i>)
is the containing block of the <i>ruby container</i>.
So floats, for example, are trapped by the <i>ruby container</i>’s containing block,
not any of the ruby box types.
</p>
<p class="issue" id="issue-ca88244c"><a class="self-link" href="#issue-ca88244c"></a>Are internal ruby boxes inline-level?
</p>
<h4 class="heading settled" data-level="2.1.2" id="display-inside-outside"><span class="secno">2.1.2. </span><span class="content">
Ruby-specific <a class="property" data-link-type="propdesc" href="http://dev.w3.org/csswg/css-display-3/#propdef-display-inside">display-inside</a> and <a class="property" data-link-type="propdesc" href="http://dev.w3.org/csswg/css-display-3/#propdef-display-outside">display-outside</a> values</span><a class="self-link" href="#display-inside-outside"></a></h4>
<p>The ruby-specific <a class="property" data-link-type="propdesc" href="#propdef-display">display</a> values map to <a class="property" data-link-type="propdesc" href="http://dev.w3.org/csswg/css-display-3/#propdef-display-inside">display-inside</a> and <a class="property" data-link-type="propdesc" href="http://dev.w3.org/csswg/css-display-3/#propdef-display-outside">display-outside</a> as follows:
</p>
<table class="data">
<thead>
<tr>
<th><a class="property" data-link-type="propdesc" href="#propdef-display">display</a>
<th><a class="property" data-link-type="propdesc" href="http://dev.w3.org/csswg/css-display-3/#propdef-display-outside">display-outside</a>
<th><a class="property" data-link-type="propdesc" href="http://dev.w3.org/csswg/css-display-3/#propdef-display-inside">display-inside</a>
<tbody>
<tr>
<td><a class="css" data-link-type="maybe" href="#valdef-display-ruby">ruby</a>
<td><a class="css" data-link-type="maybe" href="http://dev.w3.org/csswg/css-display-3/#valdef-display-outside-inline-level">inline-level</a>
<td><a class="css" data-link-type="maybe" href="http://dev.w3.org/csswg/css-display-3/#valdef-display-inside-ruby">ruby</a>
<tr>
<td><a class="css" data-link-type="maybe" href="#valdef-display-ruby-base">ruby-base</a>
<td><a class="css" data-link-type="maybe" href="http://dev.w3.org/csswg/css-display-3/#valdef-display-outside-ruby-base">ruby-base</a>
<td><a class="css" data-link-type="maybe" href="http://dev.w3.org/csswg/css-display-3/#valdef-display-inside-auto">auto</a>
<tr>
<td><a class="css" data-link-type="maybe" href="#valdef-display-ruby-text">ruby-text</a>
<td><a class="css" data-link-type="maybe" href="http://dev.w3.org/csswg/css-display-3/#valdef-display-outside-ruby-text">ruby-text</a>
<td><a class="css" data-link-type="maybe" href="http://dev.w3.org/csswg/css-display-3/#valdef-display-inside-auto">auto</a>
<tr>
<td><a class="css" data-link-type="maybe" href="#valdef-display-ruby-base-container">ruby-base-container</a>
<td><a class="css" data-link-type="maybe" href="http://dev.w3.org/csswg/css-display-3/#valdef-display-outside-ruby-base-container">ruby-base-container</a>
<td><a class="css" data-link-type="maybe" href="http://dev.w3.org/csswg/css-display-3/#valdef-display-inside-auto">auto</a>
<tr>
<td><a class="css" data-link-type="maybe" href="#valdef-display-ruby-text-container">ruby-text-container</a>
<td><a class="css" data-link-type="maybe" href="http://dev.w3.org/csswg/css-display-3/#valdef-display-outside-ruby-text-container">ruby-text-container</a>
<td><a class="css" data-link-type="maybe" href="http://dev.w3.org/csswg/css-display-3/#valdef-display-inside-auto">auto</a>
</table>
<p>See the <a href="http://www.w3.org/TR/css-display/">CSS Display Module</a>
for more information on <a class="property" data-link-type="propdesc" href="http://dev.w3.org/csswg/css-display-3/#propdef-display-inside">display-inside</a> and <a class="property" data-link-type="propdesc" href="http://dev.w3.org/csswg/css-display-3/#propdef-display-outside">display-outside</a>. <a data-link-type="biblio" href="#biblio-css3-display">[CSS3-DISPLAY]</a>
</p>
<h4 class="heading settled" data-level="2.1.3" id="block-ruby"><span class="secno">2.1.3. </span><span class="content">
Non-Inline Ruby</span><a class="self-link" href="#block-ruby"></a></h4>
<p>If an element has a computed <i>inner display type</i> of <a class="css" data-link-type="maybe" href="#valdef-display-ruby">ruby</a>
and a computed computed <i>outer display type</i> other than <a class="css" data-link-type="maybe" href="http://dev.w3.org/csswg/css-display-3/#valdef-display-outside-inline-level">inline-level</a>,
then it generates two boxes:
a principal block container box of the required <a class="property" data-link-type="propdesc" href="http://dev.w3.org/csswg/css-display-3/#propdef-display-outside">display-outside</a> type,
and an inline-level <i>ruby container</i>.
All properties specified on the element apply to the principal box
(and if inheritable, inherit to the <i>ruby container box</i>).
This allows styling the element as a block,
while correctly maintaining the internal ruby structure.
</p>
<p class="note" role="note">
Note: There is no dedicated block-level <a class="property" data-link-type="propdesc" href="#propdef-display">display</a> shorthand keyword
because ruby is fundamentally an inline layout feature.
</p>
<p class="note" role="note">
Note that absolute positioning or floating an element causes its <a class="property" data-link-type="propdesc" href="#propdef-display">display</a> value
to compute to a block-level equivalent. (See <a data-link-type="biblio" href="#biblio-css3-display">[CSS3-DISPLAY]</a> or <a data-link-type="biblio" href="#biblio-css21">[CSS21]</a> section 9.7.)
For the <i>internal ruby display types</i>,
this causes their <a class="property" data-link-type="propdesc" href="#propdef-display">display</a> value to compute to <a class="css" data-link-type="maybe" href="http://dev.w3.org/csswg/css-display-3/#valdef-display-block">block</a>.
</p>
<h3 class="heading settled" data-level="2.2" id="box-fixup"><span class="secno">2.2. </span><span class="content">
Anonymous Ruby Box Generation</span><a class="self-link" href="#box-fixup"></a></h3>
<p>The CSS model does not require that the document language
include elements that correspond to each of these components.
Missing parts of the structure are implied through the anonymous box generation rules
<a href="http://www.w3.org/TR/CSS21/tables.html#anonymous-boxes">similar to those used to normalize tables</a>. <a data-link-type="biblio" href="#biblio-css21">[CSS21]</a>
</p>
<ol>
<li id="anon-gen-anon-ruby"><a class="self-link" href="#anon-gen-anon-ruby"></a><strong>Generate anonymous ruby containers</strong>:
Any <a href="http://www.w3.org/TR/CSS21/tables.html#anonymous-boxes">consecutive</a> sequence of
improperly-contained
<i>ruby base containers</i>,
<i>ruby annotation containers</i>,
<i>ruby bases</i>,
and/or
<i>ruby annotations</i>
(and any intervening <i>white space</i>)
is wrapped in an anonymous <i>ruby container</i>.
For the purpose of this step:
<ul>
<li>an improperly-contained <i>ruby base</i> is one not parented by a <i>ruby base container</i> or <i>ruby container</i>
<li>an improperly-contained <i>ruby annotation</i> is one not parented by a <i>ruby annotation container</i> or <i>ruby container</i>
<li>an improperly-contained <i>ruby base container</i> or <i>ruby annotation container</i>
is one not parented by a <i>ruby container</i>
</ul>
<li id="anon-gen-inlinize"><a class="self-link" href="#anon-gen-inlinize"></a><strong>Inlinize block-level boxes:</strong>
Any in-flow block-level boxes directly contained by a
<i>ruby container</i>,
<i>ruby base container</i>,
<i>ruby annotation container</i>,
<i>ruby base box</i>,
or <i>ruby annotation box</i>
are forced to be inline-level boxes,
and their <a class="property" data-link-type="propdesc" href="#propdef-display">display</a> value computed accordingly.
For example,
the <a class="property" data-link-type="propdesc" href="#propdef-display">display</a> property of an in-flow element with <a class="css" data-link-type="propdesc" href="#propdef-display">display: block</a>
parented by an element with <a class="css" data-link-type="propdesc" href="#propdef-display">display: ruby-text</a>
computes to <a class="css" data-link-type="maybe" href="http://dev.w3.org/csswg/css-display-3/#valdef-display-inline-block">inline-block</a>.
This computation occurs after any intermediary anonymous-box fixup
(such as that required by internal table elements).
<li id="anon-gen-bare-inlines"><a class="self-link" href="#anon-gen-bare-inlines"></a><strong>Wrap misparented inline-level content:</strong>
Any consecutive sequence of text and inline-level boxes
directly parented by a <i>ruby container</i> or <i>ruby base container</i>
is wrapped in an anonymous <i>ruby base</i>.
Similarly, any consecutive sequence of text and inline-level boxes
directly parented by a <i>ruby annotation container</i>
is wrapped in an anonymous <i>ruby annotation</i>.
<p>However, if an anonymous box so constructed contains only <i>white space</i>,
it is considered <dfn data-dfn-type="dfn" data-noexport="" id="intra_ruby-white-space">intra-ruby white space<a class="self-link" href="#intra_ruby-white-space"></a></dfn>
and is either discarded
or preserved
as described below.</p>
<li id="anony-gen-trim-space"><a class="self-link" href="#anony-gen-trim-space"></a><strong>Trim leading/trailing white space:</strong>
Any <i>intra-ruby white space</i>
that is not the sole child of its parent
and occurs at the beginning or end of
a <i>ruby container</i>, <i>ruby annotation container</i>, or <i>ruby base container</i>
is removed, as if it had <a class="css" data-link-type="propdesc" href="#propdef-display">display: none</a>
<li id="anon-gen-discard-space"><a class="self-link" href="#anon-gen-discard-space"></a><strong>Remove inter-level white space:</strong>
Any <i>intra-ruby white space</i>
whose immediately adjacent siblings match one of the patterns below
is <dfn data-dfn-type="dfn" data-noexport="" id="inter_level-white-space">inter-level white space<a class="self-link" href="#inter_level-white-space"></a></dfn>
and is removed, as if it had <a class="css" data-link-type="propdesc" href="#propdef-display">display: none</a>.
<table class="data">
<thead>
<tr>
<th>Previous box
<th>Next box
<tbody>
<tr>
<td><var>any</var>
<td><i>ruby annotation container</i>
<tr>
<td>not <i>ruby annotation</i>
<td><i>ruby annotation</i>
</table>
<li id="anon-gen-interpret-space"><a class="self-link" href="#anon-gen-interpret-space"></a><strong>Interpret intra-level white space:</strong>
Any <i>intra-ruby white space</i> box
whose immediately adjacent siblings match one of the patterns below
is assigned the box type and subtype defined in the table below:
<table class="data">
<colgroup span="2"></colgroup>
<colgroup span="2"></colgroup>
<thead>
<tr>
<th>Previous box
<th>Next box
<th>Box type
<th>Subtype
<tbody>
<tr>
<td><i>ruby base</i>
<td><i>ruby base</i>
<td><i>ruby base</i>
<td><dfn data-dfn-type="dfn" data-noexport="" id="inter_base-white-space">inter-base white space<a class="self-link" href="#inter_base-white-space"></a></dfn>
<tr>
<td><i>ruby annotation</i>
<td><i>ruby annotation</i>
<td><i>ruby annotation</i>
<td><dfn data-dfn-type="dfn" data-noexport="" id="inter_annotation-white-space">inter-annotation white space<a class="self-link" href="#inter_annotation-white-space"></a></dfn>
<tr>
<td><i>ruby annotation</i> or <i>ruby annotation container</i>
<td><i>ruby base</i> or <i>ruby base container</i>
<td rowspan="3"><i>ruby base</i>
<td rowspan="3"><dfn data-dfn-type="dfn" data-noexport="" id="inter_segment-white-space">inter-segment white space<a class="self-link" href="#inter_segment-white-space"></a></dfn>
<tr>
<td><i>ruby base</i> or <i>ruby base container</i>
<td><i>ruby base container</i>
<tr>
<td><i>ruby base container</i>
<td><i>ruby base</i> or <i>ruby base container</i>
</table>
The <dfn data-dfn-type="dfn" data-noexport="" id="intra_level-white-space">intra-level white space<a class="self-link" href="#intra_level-white-space"></a></dfn> boxes defined above are
treated specially for pairing and layout. See below.
<li id="anon-gen-unbreak"><a class="self-link" href="#anon-gen-unbreak"></a><strong>Suppress line breaks:</strong>
Convert all forced line breaks inside <i>ruby annotations</i> (regardless of <a class="property" data-link-type="propdesc" href="http://dev.w3.org/csswg/css-text-3/#propdef-white-space">white-space</a> value)
as defined for <i>collapsible</i> segment breaks in <a href="http://www.w3.org/TR/css-text-3/#line-break-transform">CSS Text Level 3 § 4.1.2</a>.
<p class="issue" id="issue-8af70305"><a class="self-link" href="#issue-8af70305"></a>The goal of this is to simplify the layout model by suppressing any line breaks within ruby annotations.
Alternatively we could try to define some kind of acceptable behavior for them.
</p>
<li id="anon-gen-anon-containers"><a class="self-link" href="#anon-gen-anon-containers"></a><strong>Generate anonymous level containers:</strong>
Any consecutive sequence of <i>ruby bases</i> and <i>inter-base white space</i>
(and not <i>inter-segment white space</i>)
not parented by a <i>ruby base container</i>
is wrapped in an anonymous <i>ruby base container</i>.
Similarly, any consecutive sequence of <i>ruby annotations</i> and <i>inter-annotation white space</i>
not parented by a <i>ruby annotation container</i>
is wrapped in an anonymous <i>ruby annotation container</i>.
</ol>
<p class="issue" id="issue-778a7acd"><a class="self-link" href="#issue-778a7acd"></a>Make <a href="http://lists.w3.org/Archives/Public/www-archive/2014Jun/att-0027/PastedGraphic-1.png">this diagram</a> into an example.
</p>
<p>Once all ruby layout structures are properly parented,
the UA can start to associate bases with their annotations.
</p>
<p class="note" role="note">
Note that the UA is not required to create any of these anonymous boxes
(or the anonymous empty <i>intra-level white space</i> boxes in the pairing section)
in its internal structures,
as long as pairing and layout behaves as if they existed.
</p>
<h3 class="heading settled" data-level="2.3" id="ruby-pairing"><span class="secno">2.3. </span><span class="content">
Annotation Pairing</span><a class="self-link" href="#ruby-pairing"></a></h3>
<p>Annotation <dfn data-dfn-type="dfn" data-noexport="" id="pairing">pairing<a class="self-link" href="#pairing"></a></dfn> is the process of associating
<i>ruby annotations</i> with <i>ruby bases</i>.
Each <i>ruby annotation</i> is associated with one or more <i>ruby bases</i>,
and is said to <dfn data-dfn-type="dfn" data-noexport="" id="span">span<a class="self-link" href="#span"></a></dfn> those bases.
(A <i>ruby annotation</i> that <i>spans</i> multiple bases is called
a <dfn data-dfn-type="dfn" data-noexport="" id="spanning-annotation">spanning annotation<a class="self-link" href="#spanning-annotation"></a></dfn>.)
</p>
<p>A <i>ruby base</i> is can be associated with
only one <i>ruby annotation</i> per <i>annotation level</i>.
However, if there are multiple <i>annotation levels</i>,
it can be associated with multiple <i>ruby annotations</i>.</p>
<p>Once pairing is complete, ruby “column” units are defined,
each represented by a single <i>ruby base</i>
and one <i>ruby annotation</i> (possibly an empty, anonymous one)
from each <i>annotation level</i> in its <i>ruby segment</i>.</p>
<h4 class="heading settled" data-level="2.3.1" id="segment-pairing"><span class="secno">2.3.1. </span><span class="content">
Segment Pairing and Annotation Levels</span><a class="self-link" href="#segment-pairing"></a></h4>
<p>A ruby structure is divided into <dfn data-dfn-type="dfn" data-noexport="" id="ruby-segments">ruby segments<a class="self-link" href="#ruby-segments"></a></dfn>,
each consisting of a single <i>ruby base container</i>
followed by one or more <i>ruby annotation containers</i>.
Each <i>ruby annotation container</i> in a <i>ruby segment</i>
represents one <dfn data-dfn-type="dfn" data-lt="annotation level | level" data-noexport="" id="annotation-level">level<a class="self-link" href="#annotation-level"></a></dfn> of annotation for the base text:
the first one represents the first level of annotation,
the second one represents the second level of annotation,
and so on.
The <i>ruby base container</i> represents the <dfn data-dfn-type="dfn" data-noexport="" id="base-level">base level<a class="self-link" href="#base-level"></a></dfn>.
The <i>ruby base container</i> in each segment is thus paired
with each of the <i>ruby annotation containers</i> in that segment.
</p>
<p>In order to handle degenerate cases, some empty anonymous containers are assumed:
</p>
<ul>
<li>If the first child of a <i>ruby container</i> is a <i>ruby annotation container</i>,
an anonymous, empty <i>ruby base container</i> is assumed to exist before it.
<li>Similarly, if the <i>ruby container</i> contains consecutive <i>ruby base containers</i>,
anonymous, empty <i>ruby annotation containers</i> are assumed to exist between them.
</ul>
<p><i>Inter-segment white space</i> is effectively a <i>ruby segment</i> of its own.
</p>
<h4 class="heading settled" data-level="2.3.2" id="base-annotation-pairing"><span class="secno">2.3.2. </span><span class="content">
Unit Pairing and Spanning Annotations</span><a class="self-link" href="#base-annotation-pairing"></a></h4>
<p>Within a <i>ruby segment</i>,
each <i>ruby base</i> in the <i>ruby base container</i>
is paired with one <i>ruby annotation</i>
from each <i>ruby annotation container</i> in its <i>ruby segment</i>.
</p>
<p>If a <i>ruby annotation container</i> contains only
a single, anonymous <i>ruby annotation</i>,
then that <i>ruby annotation</i> is paired with (i.e. <i>spans</i> across)
all of the <i>ruby bases</i> in its <i>ruby segment</i>.
</p>
<p>Otherwise, each <i>ruby annotation</i> is paired,
in order, with the corresponding <i>ruby base</i> in that segment.
If there are not enough <i>ruby annotations</i> in a <i>ruby annotation container</i>,
the remaining <i>ruby bases</i> are paired with anonymous empty annotations
inserted at the end of the <i>ruby annotation container</i>.
If there are not enough <i>ruby bases</i>,
any remaining <i>ruby annotations</i> pair with empty, anonymous bases
inserted at the end of the <i>ruby base container</i>.
</p>
<p>If an implementation supports ruby markup with explicit spanning
(e.g. XHTML Complex Ruby Annotations),
it must adjust the pairing rules to pair <i>spanning annotations</i>
to their bases appropriately.
</p>
<p><i>Intra-level white space</i> does not participate in standard annotation <i>pairing</i>.
However, if the immediately-adjacent <i>ruby bases</i> or <i>ruby annotations</i>
are paired
</p>
<ul>
<li>with two <i>ruby bases</i> or <i data-lt="ruby annotations">annotations</i>
that surround corresponding <i>intra-level white space</i> in another level,
then the so-corresponding <i>intra-level white space</i> boxes are also paired.
<li>with a single spanning <i>ruby annotation</i>,
then the <i>intra-level white space</i> is also paired to that <i>ruby annotation</i>
<li>with two <i>ruby bases</i> or <i data-lt="ruby annotations">annotations</i>
with no intervening <i>intra-level white space</i>,
then the <i>intra-level white space</i> box pairs with
an anonymous empty <i>intra-level white space</i> box assumed to exist between them.
</ul>
<p class="issue" id="issue-0230a91a"><a class="self-link" href="#issue-0230a91a"></a>Insert diagram</p>
<h4 class="heading settled" data-level="2.3.3" id="nested-pairing"><span class="secno">2.3.3. </span><span class="content">
Complex Spanning with Nested Ruby</span><a class="self-link" href="#nested-pairing"></a></h4>
<p>When <i>ruby containers</i> are <dfn data-dfn-type="dfn" data-lt="nested ruby" data-noexport="" id="nested-ruby">nested<a class="self-link" href="#nested-ruby"></a></dfn>,
pairing begins with the deepest <i>ruby container</i>,
then expands out.
From the pairing perspective of the outer <i>ruby container</i>,
each <i>ruby container</i> nested within another <i>ruby container</i>