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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html lang=en>
<head><meta content="text/html;utf-8" http-equiv=Content-Type>
<title>CSS Text Layout Module Level 3</title>
<link href="../default.css" rel=stylesheet type="text/css">
<link href="http://www.w3.org/StyleSheets/tr/W3C-ED.css" rel=stylesheet
type="text/css">
<style type="text/css">
.data, .proptable {
margin: 1em auto;
border-collapse: collapse;
border: solid #005A9B;
}
.data caption {
width: 100%;
text-align: center;
}
.data td, .data th,
.proptable td, .proptable th {
border: thin solid;
padding: 0.2em;
text-align: center;
}
.data thead th[scope="row"],
.proptable thead th[scope="row"] {
text-align: right;
background: #A4C8E2;
color: inherit;
}
.data thead,
.proptable thead {
background: #EEEEEE;
color: inherit;
}
.data tbody th:first-child,
.proptable tbody th:first-child {
text-align: right;
background: #EEEEEE;
color: inherit;
}
.data thead,
.data tbody,
.data tfoot,
.data colgroup {
border: solid;
}
table.propdef {
table-layout: auto;
}
.propdef th {
font-style: italic;
font-weight: normal;
text-align: left;
width: 3em;
}
dt dfn code {
font-size: inherit;
}
.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 }
</style>
<body>
<div class=head> <!--begin-logo-->
<p><a href="http://www.w3.org/"><img alt=W3C height=48
src="http://www.w3.org/Icons/w3c_home" width=72></a> <!--end-logo-->
<h1 id=css-text>CSS Text Layout Module Level 3</h1>
<h2 class="no-num no-toc" id=longstatus>Editor's Draft 8 October 2008</h2>
<dl>
<dt>This version:
<dd><a
href="http://dev.w3.org/csswg/css3-text-layout/">http://dev.w3.org/csswg/css3-text-layout/</a>
<dt>Latest version:
<dd><a
href="http://www.w3.org/TR/css3-text-layout/">http://www.w3.org/TR/css3-text-layout/</a>
<dt>Previous version:
<dd><a
href="http://www.w3.org/tr/2003/CR-css3-text-20030514/">http://www.w3.org/tr/2003/CR-css3-text-20030514/</a>
<dt>Editors:
<dd><a href="mailto:paulnel@microsoft.com">Paul Nelson</a> (<a
href="http://www.microsoft.com/">Microsoft</a>)
<dd><a href="http://fantasai.inkedblade.net/contact">Elika J. Etemad</a>
<dt>Previous Editor:
<dd><a href="mailto:michelsu@microsoft.com">Michel Suignard</a> (<a
href="http://www.microsoft.com/">Microsoft</a>)
</dl>
<!--begin-copyright-->
<p class=copyright><a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
rel=license>Copyright</a> © 2008 <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.org/"><acronym title="European Research Consortium
for Informatics and Mathematics">ERCIM</acronym></a>, <a
href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. W3C <a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
<a
href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a>
and <a
href="http://www.w3.org/Consortium/Legal/copyright-documents">document
use</a> rules apply.</p>
<!--end-copyright-->
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc" id=abstract>Abstract</h2>
<p>This module specifies the text layout model in CSS and the properties
that control it. It covers bidirectionality, vertical text, grid layout,
and other special inline text layout effects.
<h2 class="no-num no-toc" id=status>Status of this document</h2>
<!--begin-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>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> (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 “css3-text” in the subject, preferably like this:
“[<!---->css3-text<!---->] <em>…summary of
comment…</em>”
<p>This document was produced by the <a href="/Style/CSS/members">CSS
Working Group</a> (part of the <a href="/Style/">Style Activity</a>).
<p>This document was produced by a group operating under the <a
href="/Consortium/Patent-Policy-20040205/">5 February 2004 W3C Patent
Policy</a>. W3C maintains a <a href="/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="/Consortium/Patent-Policy-20040205/#def-essential">Essential
Claim(s)</a> must disclose the information in accordance with <a
href="/Consortium/Patent-Policy-20040205/#sec-Disclosure">section 6 of the
W3C Patent Policy</a>.</p>
<!--end-status-->
<h2 class="no-num no-toc" id=Contents>Contents</h2>
<!--begin-toc-->
<ul class=toc>
<li><a href="#intro"><span class=secno>1. </span>Text layout
introduction</a>
<li><a href="#text-flow"><span class=secno>2. </span>Text flow</a>
<ul class=toc>
<li><a href="#text-direction"><span class=secno>2.1
</span>Bidirectionality</a>
<li><a href="#direction"><span class=secno>2.2 </span>Specifying
Directionality: the ‘<code class=property>direction</code>’
property</a>
<li><a href="#unicode-bidi"><span class=secno>2.3 </span>Embeddings and
Overrides: the ‘<code class=property>uncode-bidi</code>’
property</a>
<li><a href="#bidi-example"><span class=secno>2.4 </span>Example of
Bidirectional Text</a>
<li><a href="#block-progression"><span class=secno>2.5 </span>Block
progression direction: the ‘<code
class=property>block-flow</code>’ property</a>
<li><a href="#details"><span class=secno>2.6 </span>Details</a>
<li><a href="#example"><span class=secno>2.7 </span>Example</a>
<li><a href="#writing-mode"><span class=secno>2.8 </span>Text flow short
cut: the ‘<code class=property>writing-mode</code>’
property</a>
<li><a href="#writing-mode-mixed"><span class=secno>2.9 </span> Mixing
the ‘<code class=property>writing-mode</code>’ in normal
usage</a>
</ul>
<li><a href="#document-grid"><span class=secno>3. </span>Document grid</a>
<ul class=toc>
<li><a href="#grid-introduction"><span class=secno>3.1 </span>Document
grid introduction</a>
<li><a href="#line-grid-mode"><span class=secno>3.2 </span>Line grid
mode: the ‘<code class=property>line-grid-mode</code>’
property</a>
<li><a href="#line-grid-progression"><span class=secno>3.3 </span>Line
grid progression: the ‘<code
class=property>line-grid-progression</code>’ property</a>
<li><a href="#line-grid"><span class=secno>3.4 </span>Line grid: the
‘<code class=property>line-grid</code>’ shorthand
property</a>
</ul>
</ul>
<!--end-toc-->
<h2 id=intro><span class=secno>1. </span>Text layout introduction</h2>
<p>This section describes the text layout features supported by CSS, which
includes support for various international writing directions, such as
left-to-right (e.g., Latin scripts), right-to-left (e.g., Hebrew or
Arabic), bidirectional (e.g., mixing Latin with Arabic) and vertical
(e.g., Asian scripts). In addition, this section defines a set of
properties that provide for a document grid layout system that is commonly
used with East Asian text layout.
<h2 id=text-flow><span class=secno>2. </span>Text flow</h2>
<p>Text flow is defined in terms of inline progression and block
progression. Inline progression is the way elements flow on the line and
defines on which end of the line the "start" and "end" are located. The
<span class=property> <a href="#direction">‘<code
class=property>direction</code>’</a></span> and <span
class=property> <a href="#unicode-bidi">‘<code
class=property>unicode-bidi</code>’</a></span> properties determine
the inline-progression and bidirectional layout. The <span class=property>
<a href="#block-progression">‘<code
class=property>block-progression</code>’</a></span> property
determines the line progression, or way lines stack, in a block. The <span
class=property><a href="#writing-mode">‘<code
class=property>writing-mode</code>’</a></span> shorthand combines
inline and block progression together.
<p>Some examples of text flow are:
<ul>
<li>Latin scripts are typically written using a left to right inline
progression with a top to bottom block progression.
<li>Mongolian script languages are typically written using a top to bottom
inline progression with a left to right block progression.
<li>Japanese is commonly written using both a left to right inline
progression with a top to bottom block progression, <strong>and</strong>
a top to bottom inline progression with a right to left block
progression. Many magazines and newspapers will mix these two text flows
on the same page.
</ul>
<h3 id=text-direction><span class=secno>2.1 </span>Bidirectionality</h3>
<p><a href="conform.html#conformance">Conforming</a> user agents that do
not support bidirectional text may ignore the <span
class=propinst-direction>‘<code class=property><a
href="#direction0">direction</a></code>’</span> and <span
class=propinst-unicode-bidi>‘<code class=property><a
href="#unicode-bidi0">unicode-bidi</a></code>’</span> properties
described in this section. This exception includes UAs that render
right-to-left characters simply because a font on the system contains them
but do not support the concept of right-to-left text direction.
<p>The characters in certain scripts are written from right to left. In
some documents, in particular those written with the Arabic or Hebrew
script, and in some mixed-language contexts, text in a single (visually
displayed) block may appear with mixed directionality. This phenomenon is
called <span class=index-def id=bidirectionality title="bidirectionality
(bidi)"><dfn id=bidirectionality0>bidirectionality</dfn></span>, or "bidi"
for short.
<p>The Unicode standard (<a
href="http://www.unicode.org/reports/tr9/">Unicode Standard Annex #9</a>)
defines a complex algorithm for determining the proper directionality of
text. The algorithm consists of an implicit part based on character
properties, as well as explicit controls for embeddings and overrides. CSS
relies on this algorithm to achieve proper bidirectional rendering. The
<span class=propinst-direction>‘<code class=property><a
href="#direction0">direction</a></code>’</span> and <span
class=propinst-unicode-bidi>‘<code class=property><a
href="#unicode-bidi0">unicode-bidi</a></code>’</span> properties
allow authors to specify how the elements and attributes of a document
language map to this algorithm.
<p>User agents that support bidirectional text must apply the Unicode
bidirectional algorithm to every sequence of inline boxes uninterrupted by
a forced line break or block boundary. This sequence forms the "paragraph"
unit in the bidirectional algorithm. The paragraph embedding level is set
according to the value of the <span class=propinst-direction>‘<code
class=property><a href="#direction0">direction</a></code>’</span>
property of the containing block rather than by the heuristic given in
steps P2 and P3 of the Unicode algorithm.
<p>Because the directionality of a text depends on the structure and
semantics of the document language, these properties should in most cases
be used only by designers of document type descriptions (Dtds), or authors
of special documents. If a default style sheet specifies these properties,
authors and users should not specify rules to override them.
<p>The HTML 4 specification ([HTML4], section 8.2) defines bidirectionality
behavior for HTML elements. The style sheet rules that would achieve the
bidi behaviors specified in [[HTML4]] are given below. The HTML 4
specification also contains more information on bidirectionality issues.
<pre>
*[dir="ltr"] { direction: ltr; unicode-bidi: embed; }
*[dir="rtl"] { direction: rtl; unicode-bidi: embed; }
bdo[dir="ltr"] { direction: ltr; unicode-bidi: bidi-override; }
bdo[dir="rtl"] { direction: rtl; unicode-bidi: bidi-override; }
</pre>
<p class=note>Because HTML UAs can turn off CSS styling, we advise HTML
authors to use the HTML ‘<code class=property>dir</code>’
property and <bdo> element to ensure correct bidirectional layout in
the absence of a style sheet.
<h3 id=direction><span class=secno>2.2 </span>Specifying Directionality:
the ‘<code class=property><a
href="#direction0">direction</a></code>’ property</h3>
<table class=propdef id=namedirection>
<tbody>
<tr>
<th>Name:
<td><dfn id=direction0>direction</dfn>
<tr>
<th>Value:
<td>ltr | rtl
<tr>
<th>Initial:
<td>ltr
<tr>
<th>Applies to:
<td>all elements
<tr>
<th>Inherited:
<td>yes
<tr>
<th>Percentages:
<td>N/A
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>specified value
</table>
<p>This property specifies the inline progression of text and elements on a
line, and the direction of embeddings and overrides (see <span
class=propinst-unicode-bidi>‘<code class=property><a
href="#unicode-bidi0">unicode-bidi</a></code>’</span>) for the
Unicode bidirectional algorithm. In addition, it specifies the direction
of <a
href="http://www.w3.org/TR/2006/WD-CSS21-20060411/tables.html">table</a>
column layout, the direction of horizontal <a
href="http://www.w3.org/TR/2006/WD-CSS21-20060411/visufx.html#overflow">overflow</a>,
and the position of an incomplete last line in a block in case of
‘<code class=css>text-align: justify</code>’.
<p>Values for this property have the following meanings:
<dl>
<dt><strong>ltr</strong>
<dd>Left-to-right direction.
<dt><strong>rtl</strong>
<dd> Right-to-left direction.
</dl>
<p>For the <span class=propinst-direction>‘<code class=property><a
href="#direction0">direction</a></code>’</span> property to affect
reordering in inline-level elements, the <span
class=propinst-unicode-bidi>‘<code class=property><a
href="#unicode-bidi0">unicode-bidi</a></code>’</span> property's
value must be ‘<code class=property>embed</code>’ or
‘<code class=property>override</code>’.
<p class=note>The <span class=propinst-direction>‘<code
class=property><a href="#direction0">direction</a></code>’</span>
property, when specified for table column elements, is not inherited by
cells in the column since columns are not the ancestors of the cells in
the document tree. Thus, CSS cannot easily capture the "dir" attribute
inheritance rules described in [[HTML4]], section 11.3.2.1.
<h3 id=unicode-bidi><span class=secno>2.3 </span>Embeddings and Overrides:
the ‘<code class=property>uncode-bidi</code>’ property</h3>
<table class=propdef id=nameunicode-bidi>
<tbody>
<tr>
<th>Name:
<td><dfn id=unicode-bidi0>unicode-bidi</dfn>
<tr>
<th>Value:
<td>normal | embed | bidi-override
<tr>
<th>Initial:
<td>normal
<tr>
<th>Applies to:
<td>all elements, but see prose
<tr>
<th>Inherited:
<td>no
<tr>
<th>Percentages:
<td>N/A
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>specified value
</table>
<p>Values for this property have the following meanings:
<dl>
<dt><strong>normal</strong>
<dd>The element does not open an additional level of embedding with
respect to the bidirectional algorithm. For inline-level elements,
implicit reordering works across element boundaries.
<dt><strong>embed</strong>
<dd>If the element is inline-level, this value opens an additional level
of embedding with respect to the bidirectional algorithm. The direction
of this embedding level is given by the <span
class=propinst-direction>‘<code class=property><a
href="#direction0">direction</a></code>’</span> property. Inside
the element, reordering is done implicitly. This corresponds to adding a
LRE (U+202A; for ‘<code class=css>direction: ltr</code>’) or
RLE (U+202B; for ‘<code class=css>direction: rtl</code>’) at
the start of the element and a PDF (U+202C) at the end of the element.
<dt><strong>bidi-override</strong>
<dd>For inline-level elements this creates an override. For block-level,
table-cell, table-caption, or inline-block elements this creates an
override for inline-level descendents not within another block-level,
table-cell, table-caption, or inline-block element. This means that
inside the element, reordering is strictly in sequence according to the
<span class=propinst-direction>‘<code class=property><a
href="#direction0">direction</a></code>’</span> property; the
implicit part of the bidirectional algorithm is ignored. This corresponds
to adding a LRO (U+202D; for ‘<code class=css>direction:
ltr</code>’) or RLO (U+202E; for ‘<code class=css>direction:
rtl</code>’) at the start of the element and a PDF (U+202C) at the
end of the element.
</dl>
<p>The final order of characters in each block-level element is the same as
if the bidi control codes had been added as described above, markup had
been stripped, and the resulting character sequence had been passed to an
implementation of the Unicode bidirectional algorithm for plain text that
produced the same line-breaks as the styled text. In this process,
non-textual entities such as images are treated as neutral characters,
unless their <span class=propinst-unicode-bidi>‘<code
class=property><a
href="#unicode-bidi0">unicode-bidi</a></code>’</span> property has a
value other than ‘<code class=property>normal</code>’, in
which case they are treated as strong characters in the <span
class=propinst-direction>‘<code class=property><a
href="#direction0">direction</a></code>’</span> specified for the
element.
<p>Please note that in order to be able to flow inline boxes in a uniform
direction (either entirely left-to-right or entirely right-to-left), more
inline boxes (including anonymous inline boxes) may have to be created,
and some inline boxes may have to be split up and reordered before
flowing.
<p>Because the Unicode algorithm has a limit of <em title="According to
unicode 3.0, chapter 3, section 12, definition BD2. Specifically, page 58
here: http://www.unicode.org/unicode/uni2book/ch03.pdf"> 61 levels</em> of
embedding, care should be taken not to use <span
class=propinst-unicode-bidi>‘<code class=property><a
href="#unicode-bidi0">unicode-bidi</a></code>’</span> with a value
other than ‘<code class=property>normal</code>’ unless
appropriate. In particular, a value of ‘<code
class=property>inherit</code>’ should be used with extreme caution.
However, for elements that are, in general, intended to be displayed as
blocks, a setting of ‘<code class=css>unicode-bidi:
embed</code>’ is preferred to keep the element together in case
display is changed to inline (see example below).
<p>The following example shows an XML document with bidirectional text. It
illustrates an important design principle: <span class=index-inst id=dtd
title=Dtd>Dtd</span> designers should take bidi into account both in the
language proper (elements and attributes) and in any accompanying style
sheets. The style sheets should be designed so that bidi rules are
separate from other style rules. The bidi rules should not be overridden
by other style sheets so that the document language's or Dtd's bidi
behavior is preserved.
<h3 id=bidi-example><span class=secno>2.4 </span>Example of Bidirectional
Text</h3>
<div class=example>
<p>In this example, lowercase letters stand for inherently left-to-right
characters and uppercase letters represent inherently right-to-left
characters. The text stream is shown in logical backing store order.</p>
<pre class=xml-example><code class=xml>
<HEBREW>
<PAR>HEBREW1 HEBREW2 english3 HEBREW4 HEBREW5</PAR>
<PAR>HEBREW6 <EMPH>HEBREW7</EMPH> HEBREW8</PAR>
</HEBREW>
<ENGLISH>
<PAR>english9 english10 english11 HEBREW12 HEBREW13</PAR>
<PAR>english14 english15 english16</PAR>
<PAR>english17 <HE-QUO>HEBREW18 english19 HEBREW20</HE-QUO></PAR>
</ENGLISH>
</code></pre>
<p>Since this is XML, the style sheet is responsible for setting the
writing direction. This is the style sheet:</p>
<pre class=example>
/* Rules for bidi */
HEBREW, HE-QUO {direction: rtl; unicode-bidi: embed;}
ENGLISH {direction: ltr; unicode-bidi: embed;}
/* Rules for presentation */
HEBREW, ENGLISH, PAR {display: block;}
EMPH {font-weight: bold;}
</pre>
<p>The HEBREW element is a block with a right-to-left base direction, the
ENGLISH element is a block with a left-to-right base direction. The PARs
are blocks that inherit the base direction from their parents. Thus, the
first two PARs are read starting at the top right, the final three are
read starting at the top left. Please note that HEBREW and ENGLISH are
chosen as element names for explicitness only; in general, element names
should convey structure without reference to language.</p>
<p>The EMPH element is inline-level, and since its value for <span
class=propinst-unicode-bidi>‘<code class=property><a
href="#unicode-bidi0">unicode-bidi</a></code>’</span> is
‘<code class=property>normal</code>’ (the initial value), it
has no effect on the ordering of the text. The HE-QUO element, on the
other hand, creates an embedding.</p>
<p>The formatting of this text might look like this if the line length is
long:</p>
<pre class=ascii-art>
5WERBEH 4WERBEH english3 2WERBEH 1WERBEH
8WERBEH <b>7WERBEH</b> 6WERBEH
english9 english10 english11 13WERBEH 12WERBEH
english14 english15 english16
english17 20WERBEH english19 18WERBEH
</pre>
<p>Note that the HE-QUO embedding causes HEBREW18 to be to the right of
english19.</p>
<p>If lines have to be broken, it might be more like this:</p>
<pre class=ascii-art>
2WERBEH 1WERBEH
-EH 4WERBEH english3
5WERB
-EH <b>7WERBEH</b> 6WERBEH
8WERB
english9 english10 en-
glish11 12WERBEH
13WERBEH
english14 english15
english16
english17 18WERBEH
20WERBEH english19
</pre>
<p>Because HEBREW18 must be read before english19, it is on the line above
english19. Just breaking the long line from the earlier formatting would
not have worked. Note also that the first syllable from english19 might
have fit on the previous line, but hyphenation of left-to-right words in
a right-to-left context, and vice versa, is usually suppressed to avoid
having to display a hyphen in the middle of a line.</p>
</div>
<!-- example -->
<h3 id=block-progression><span class=secno>2.5 </span>Block progression
direction: the ‘<code class=property><a
href="#block-flow">block-flow</a></code>’ property</h3>
<table class=propdef id=nameblock-flow>
<tbody>
<tr>
<th>Name:
<td><dfn id=block-flow>block-flow</dfn>
<tr>
<th>Value:
<td>tb | rl | lr
<tr>
<th>Initial:
<td>tb
<tr>
<th>Applies to:
<td><span class=issue>??</span>
<tr>
<th>Inherited:
<td>yes
<tr>
<th>Percentages:
<td>N/A
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>specified value
</table>
<p class=issue>Should we change the name to something more understandable?
"block-flow"? "block-direction"? We need to make sure terminology for
inline progression and block progression ("layout" vs "flow" vs
"orientation" vs "direction", "horizontal" vs "vertical") is consistent
throughout the document as well.)
<p>This property sets the block-progression value and the layout
orientation. Possible values:
<dl>
<dt>tb
<dd>Top-to-bottom block flow. The layout orientation is horizontal.
<dt>rl
<dd>Right-to-left block flow. The layout orientation is vertical.
<dt>lr
<dd>Left-to-right block flow. The layout orientation is vertical.
</dl>
<p>An inline-level element that has a different ‘<code
class=property><a href="#block-flow">block-flow</a></code>’ from its
containing block becomes an ‘<code
class=property>inline-block</code>’ element <a href="#CSS3-box"
rel=biblioentry>[CSS3-box]</a>. <span class=issue>switch to CSS2.1</span>
<h3 id=details><span class=secno>2.6 </span>Details</h3>
<p>Box layout in vertical orientations is exactly analogous to layout in
the horizontal orientation.
<ul>
<li>Calculations that refer to ‘<code
class=property>width</code>’ use ‘<code
class=property>height</code>’ instead, and vice versa.
<li>Calculations that refer to the ‘<code
class=css>*-left</code>’ and ‘<code
class=css>*-right</code>’ box properties (border, margin, padding,
outline) use ‘<code class=css>*-top</code>’ and ‘<code
class=css>*-bottom</code>’ instead, and vice versa. In RL layout
‘<code class=css>*-right</code>’ is analogous to TB's
‘<code class=css>*-top</code>’; in LR layout ‘<code
class=css>*-left</code>’ is analogous to TB's ‘<code
class=css>*-top</code>’. The logic for this is clear if you lock an
arrow representing the TB block flow to a compass of the four directions
and rotate it to represent RL and LR flow.
<li>Layout effects that depend on the directionality to choose between
left and right (e.g. overflow, overconstraint resolution, ‘<code
class=property>start</code>’ values for ‘<code
class=property>text-align</code>’ and other properties, table
column ordering) depend instead on the effective physical directionality
(top-to-bottom or bottom-to-top) to choose between top and bottom.
</ul>
<p>When an element has a different ‘<code
class=property>block-progression</code>’ from its containing block
two cases are possible:
<p><em class=issue>These descriptions need work</em>
<ul>
<li>The two block-progressions are perpendicular to each other. (For
example, ‘<code class=property>tb</code>’ and ‘<code
class=property>lr</code>’). In such cases, <span class=issue>detail
calculation of width/height and determination of containing block
dim</span>
CDD
<li>The two block-progressions are parallel to each other. (For example,
‘<code class=property>rl</code>’ and ‘<code
class=property>lr</code>’).
</ul>
<h3 id=example><span class=secno>2.7 </span>Example</h3>
<div class=example>
<p>In the following example, two blocks elements (1 and 3) separated by an
image (2) are presented in various flow orientations.</p>
<p>Here is a diagram of horizontal layout (<code>block-progression:
tb</code>):</p>
<p><img alt="Diagram of horizontal layout: blocks 1, 2, and 3 are stacked
top-to-bottom" height=300 src=horizontal.png width=219></p>
<p>Here is a diagram for the right-to-left vertical layout commonly used
in East Asia (<code>block-progression: rl</code>):</p>
<p><img alt="Diagram of a right-to-left vertical layout: blocks 1, 2, and
3 are arranged side by side from right to left" height=191
src=vertical-rl.png width=297></p>
<p>And finally, here is a diagram for the left-to-right vertical layout
used for Uighur and Mongolian (<code>block-progression: lr</code>):</p>
<p><img alt="Diagram of left-to-right vertical layout: blocks 1, 2, and 3
are arranged side by side from left to right" height=191
src=vertical-lr.png width=300></p>
</div>
<h3 id=writing-mode><span class=secno>2.8 </span>Text flow short cut: the
‘<code class=property><a
href="#writing-mode">writing-mode</a></code>’ property</h3>
<table class=propdef id=name->
<tbody>
<tr>
<td><em>Name:</em>
<td><dfn id=writing-mode>writing-mode</dfn>
<tr>
<td><em>Value:</em>
<td>lr-tb | rl-tb | tb-rl | bt-rl | tb-lr | bt-lr
<tr>
<td><em>Initial:</em>
<td>not defined for shorthand properties
<tr>
<td><em>Applies to:</em>
<td>all elements and generated content
<tr>
<td><em>Inherited:</em>
<td>yes
<tr>
<td><em>Percentages:</em>
<td>N/A
<tr>
<td><em>Media:</em>
<td>visual
<tr>
<td><em>Computed value:</em>
<td>see individual properties
</table>
<p>The <span class=property><a href="#writing-mode">‘<code
class=property>writing-mode</code>’</a></span> property is a
shorthand property for the <span class=property><a
href="#direction">‘<code
class=property>direction</code>’</a></span> property and the <span
class=property> <a href="#block-progression">‘<code
class=property>block-progression</code>’</a></span> property.
Although strictly speaking, the property has no initial value, it is
equivalent to ‘<code class=property>lr-tb</code>’. The
definition of the property values are established by the following table,
which shows the setting of the constituent properties and example of
common usage.
<div class=figure>
<table border=1 cellpadding=0 cellspacing=0 style="border-collapse:
collapse" width="100%">
<tbody>
<tr>
<th>writing-mode:
<th>direction:
<th>block-progression:
<th>Common Usage:
<tr>
<td>lr-tb
<td>ltr
<td>tb
<td>Latin-based, Greek, Cyrillic writing systems (and many others)
<tr>
<td>rl-tb
<td>rtl
<td>tb
<td>Arabic, Hebrew writing systems
<tr>
<td>tb-rl
<td>ltr
<td>rl
<td>East Asian writing systems in vertical mode
<tr>
<td>bt-rl
<td>ltr
<td>rl
<td>Arabic script block quote embedded in East Asian vertical text
<tr>
<td>tb-lr
<td>ltr
<td>lr
<td>Mongolian script writing system
<tr>
<td>bt-lr
<td>rtl
<td>lr
<td>Arabic script block quote embedded in Mongolian script document
</table>
</div>
<h3 id=writing-mode-mixed><span class=secno>2.9 </span> Mixing the
‘<code class=property><a
href="#writing-mode">writing-mode</a></code>’ in normal usage</h3>
<p>In East Asian documents, it is often preferred to display certain
Latin-based strings, such as numerals in a year, always in a horizontal
layout orientation regardless of the flow orientation of the line of text
these strings appear in, as in:
<div class=figure>
<p><img alt="Diagram of Tate Naka Yoko, showing a group of glyphs
appearing horizontally in a vertical column of text" class=example
height=170 src=lf-tny.gif width=90> <img alt="Example of Tate Naka Yoko,
showing the year 1996 appearing horizontally in a column of vertical
text" class=example height=132 src=tny.gif width=37>
<p>Horizontal in vertical ("<span lang=ja>Tate-chu-yoko</span>")
</div>
<p>In Japanese, this effect is known as <a href="#tatechuyoko"
lang=ja>"Tate-chu-yoko"</a>. In order to achieve it in a CSS document, the
Latin string should be enclosed in an inline element with a horizontal
layout orientation, as in:
<pre>.date {block-progression: tb;}
<!-- --><span class="date">1996</span></pre>
<h2 id=document-grid><span class=secno>3. </span>Document grid</h2>
<h3 id=grid-introduction><span class=secno>3.1 </span>Document grid
introduction</h3>
<p>Documents written in East Asian languages, such as Chinese or Japanese,
are commonly laid out on the page according to a specified one- or
two-dimensional grid. The concept of grid can also be used with other
non-ideographic contexts such as Braille script or monospaced layout.
<p>The diagram below represents a fragment of horizontal text on a page
with mixed wide-cell and narrow-cell glyphs that a Japanese content author
intended to be laid out on a grid system that has 9 glyphs per line. Gray
grid lines are shown for clarity):
<div class=figure>
<p><img alt="Example of strict grid layout (genko) applied to mixed
Japanese and English in horizontal layout." class=example height=89
src=lg-s-ex.gif width=274> <br>
'<span lang=ja>Genko</span>' grid applied to mixed text</p>
</div>
<p>The grid behavior can be set on the inline-progression, on the
block-progression or both. The grid on the block-progression dimension is
determined by the following properties:
<ul>
<li>‘<code class=property>line-stacking-strategy</code>’ <a
href="http://www.w3.org/tr/2003/CR-css3-text-20030514/#CSS3-line"
rel=biblioentry>[CSS3-line]</a> set to the ‘<code
class=property>grid-height</code>’ value,
<li>‘<code class=property>line-height</code>’ <a
href="http://www.w3.org/tr/2003/CR-css3-text-20030514/#CSS3-line"
rel=biblioentry>[CSS3-line]</a> of the block element set to the desired
grid block-progression value,
<li>‘<code class=property>text-height</code>’ <a
href="http://www.w3.org/tr/2003/CR-css3-text-20030514/#CSS3-line"
rel=biblioentry>[CSS3-line]</a> which defines the block-progression value
for inline boxes. Depending on the content size, one or a multiple of
‘<code class=property>line-height</code>’ will be necessary
to accommodate a given inline box.
</ul>
<p>The block-progression grid is not described in this section as it can be
You can’t perform that action at this time.