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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>CSS Text Layout Module Level 3</title>
<link rel="stylesheet" type="text/css" href="../default.css">
<link rel="stylesheet" type="text/css" href="http://www.w3.org/StyleSheets/tr/W3C-ED.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>
</head>
<body>
<div class="head">
<!--logo-->
<h1>CSS Text Layout Module Level 3</h1>
<h2 class="no-num no-toc">[LONGSTATUS] [DATE]</h2>
<dl>
<dt>This version:</dt>
<dd><a href="http://dev.w3.org/csswg/css3-text-layout/">http://dev.w3.org/csswg/css3-text-layout/</a>
<dt>Latest version:</dt>
<dd><a
href="http://www.w3.org/TR/css3-text-layout/">http://www.w3.org/TR/css3-text-layout/</a></dd>
<dt>Previous version:</dt>
<dd><a
href="http://www.w3.org/tr/2003/CR-css3-text-20030514/">http://www.w3.org/tr/2003/CR-css3-text-20030514/</a></dd>
<dt>Editors:</dt>
<dd><a href="http://fantasai.inkedblade.net/contact">Elika J. Etemad</a></dd>
<dd><a href="mailto:murakami@antenna.co.jp">Shinyu Murakami</a> (<a href="http://www.antennahouse.com/">Antenna House</a>)</dd>
<dt>Previous Editors:</dt>
<dd><a href="mailto:paulnel@microsoft.com">Paul Nelson</a> (<a href="http://www.microsoft.com/">Microsoft</a>)</dd>
<dd><a href="mailto:michelsu@microsoft.com">Michel Suignard</a> (<a href="http://www.microsoft.com/">Microsoft</a>)</dd>
</dl>
<!--begin-copyright-->
<p>[Here will be included the file "../copyright.inc"]</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 and vertical text.</p>
<h2 class="no-num no-toc" id="status">Status of this document</h2>
<!--status-->
<h2 class="no-num no-toc" id="Contents">Contents</h2>
<!--toc-->
<h2 id="intro">Introduction</h2>
<p>This module 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 module defines a set of writing-mode relative
(logical) properties, such as margin-before/after/start/end.</p>
<h2 id="text-flow">Writing Modes and Terminology</h2>
<p>A <dfn>writing mode</dfn> is defined in terms of its <dfn>inline direction</dfn>
(<dfn>inline progression</dfn>) and its block flow (<dfn>block progression</dfn>).
The <dfn>inline direction</dfn> is the primary direction in which content
is ordered on a line and defines on which sides of a box the "start" and
"end" are. The 'direction' and 'unicode-bidi' properties determine the
direction of inline flow. The <dfn>block flow</dfn> direction is the
direction in which block-level boxes stack and the direction in which line
boxes stack within a block box. The 'block-flow' property determines the
block flow direction. The term "writing mode" is chosen because these
properties are strongly associated with the layout of text.</p>
<p>Writing systems typically have one or two standard writing modes. Some
examples are:
<ul>
<li>Latin scripts are typically written using a left-to-right inline
direction with a downward (top-to-bottom) block flow.</li>
<li>Mongolian script languages are typically written using a top-to-bottom
inline direction with a rightward (left-to-right) block flow.</li>
<li>Japanese is commonly written using both a left-to-right inline direction
with a downard (top-to-bottom) block flow, <strong>and</strong> a
top-to-bottom inline progression with a leftward (right-to-left) block
flow. Many magazines and newspapers will mix these two writing modes
on the same page.</li>
</ul>
<p>A <dfn>horizontal writing mode</dfn> is one with horizontal lines of
text, i.e. a downward or upward block flow. A <dfn>vertical writing
mode</dfn> is one with vertical lines of text, i.e. a leftward or
rightward block flow. <span class="note">These terms should not be
confused with <dfn>vertical block flow</dfn> (which is a downard or
upward block flow) and <dfn>horizontal block flow</dfn> (which is
leftward or rightward block flow). To avoid confusion, this
specification avoids the latter set.</span></p>
<h2 id="text-direction">Inline Direction and Bidirectionality</h2>
<p>While the characters in most scripts are written from left to right,
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" title="bidirectionality (bidi)"><dfn>bidirectionality</dfn></span>, or
"bidi" for short.</p>
<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">'direction'</span> and <span
class="propinst-unicode-bidi">'unicode-bidi'</span> properties allow
authors to specify how the elements and attributes of a document
language map to this algorithm.</p>
<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">'direction'</span> property of the containing
block rather than by the heuristic given in steps P2 and P3 of the Unicode
algorithm.</p>
<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>
<p>The HTML 4 specification ([[HTML401]], section 8.2) defines
bidirectionality behavior for HTML elements. The style sheet
rules that would achieve the bidi behaviors specified in [[HTML401]] are
given below. The HTML 4 specification also contains more information on
bidirectionality issues.</p>
<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 'dir' property and <bdo> element to
ensure correct bidirectional layout in the absence of a style sheet.</p>
<h3 id="direction">Specifying Directionality: the 'direction' property</h3>
<table class="propdef">
<tbody>
<tr>
<th>Name:</th>
<td><dfn>direction</dfn></td>
</tr>
<tr>
<th>Value:</th>
<td>ltr | rtl </td>
</tr>
<tr>
<th>Initial:</th>
<td>ltr</td>
</tr>
<tr>
<th>Applies to:</th>
<td>all elements</td>
</tr>
<tr>
<th>Inherited:</th>
<td>yes</td>
</tr>
<tr>
<th>Percentages:</th>
<td>N/A</td>
</tr>
<tr>
<th>Media:</th>
<td>visual</td>
</tr>
<tr>
<th>Computed value:</th>
<td>specified value</td>
</tr>
</tbody>
</table>
<p>This property specifies the inline progression of text and elements
on a line, and the direction of embeddings and overrides (see <span
class="propinst-unicode-bidi">'unicode-bidi'</span>) for the Unicode
bidirectional algorithm. In addition, it specifies the direction of <a
href="http://www.w3.org/TR/CSS21/tables.html">table</a> column layout, the direction of
horizontal <a href="http://www.w3.org/TR/CSS21/visufx.html#overflow">overflow</a>, and the
position of an incomplete last line in a block in case of 'text-align:
justify'.</p>
<p>Values for this property have the following meanings:</p>
<dl>
<dt><strong>ltr</strong></dt>
<dd>Left-to-right direction.</dd>
<dt><strong>rtl</strong></dt>
<dd> Right-to-left direction.</dd>
</dl>
<p>For the <span class="propinst-direction">'direction'</span>
property to affect reordering in inline-level elements, the <span
class="propinst-unicode-bidi">'unicode-bidi'</span> property's value
must be 'embed' or 'override'.</p>
<p class="note">The <span class="propinst-direction">'direction'</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 [[HTML401]], section 11.3.2.1.
<h3 id="unicode-bidi">Embeddings and Overrides: the 'uncode-bidi' property</h3>
<table class="propdef">
<tbody>
<tr>
<th>Name:</th>
<td><dfn>unicode-bidi</dfn></td>
</tr>
<tr>
<th>Value:</th>
<td>normal | embed | ( isolate || ( plaintext | override )</td>
</tr>
<tr>
<th>Initial:</th>
<td>normal</td>
</tr>
<tr>
<th>Applies to:</th>
<td>all elements, but see prose</td>
</tr>
<tr>
<th>Inherited:</th>
<td>no</td>
</tr>
<tr>
<th>Percentages:</th>
<td>N/A</td>
</tr>
<tr>
<th>Media:</th>
<td>visual</td>
</tr>
<tr>
<th>Computed value:</th>
<td>specified value</td>
</tr>
</tbody>
</table>
<p>Values for this property have the following meanings:</p>
<dl>
<dt><strong>normal</strong></dt>
<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.</dd>
<dt><strong>embed</strong></dt>
<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">'direction'</span>
property. Inside the element, reordering is done implicitly. This
corresponds to adding a LRE (U+202A; for 'direction: ltr') or RLE
(U+202B; for 'direction: rtl') at the start of the element and a PDF
(U+202C) at the end of the element.</dd>
<dt><strong>bidi-override</strong></dt>
<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 descendants 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">'direction'</span>
property; the implicit part of the bidirectional algorithm is
ignored. This corresponds to adding a LRO (U+202D; for 'direction:
ltr') or RLO (U+202E; for 'direction: rtl') at the start of the
element and a PDF (U+202C) at the end of the element.</dd>
<dt><strong>isolate</strong></dt>
<dd>For the purposes of the Unicode bidirectional algorithm, the
contents of the element are considered to be inside a separate,
independent paragraph, and for the purpose of bidi resolution
in its containing paragraph (if any), the element itself is
treated as if it were an Object Replacement Character (U+FFFC).
(If the element is broken across multiple lines, then each box
of the element is treated as an Object Replacement Character.)</dd>
<dt><strong>plaintext</strong></dt>
<dd>For the purposes of the Unicode bidirectional algorithm, the
base directionality of each "paragraph" for which the element
is the containing block element is determined not by the element's
computed 'direction' as usual, but by following rules P1, P2,
and P3 of the Unicode bidirectional algorithm.
</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">'unicode-bidi'</span> property has a
value other than 'normal', in which case they are treated as strong
characters in the <span class="propinst-direction">'direction'</span>
specified for the element.</p>
<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>
<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">'unicode-bidi'</span> with a value other
than 'normal' unless appropriate. In particular, a value of 'inherit'
should be used with extreme caution. However, for elements that are,
in general, intended to be displayed as blocks, a setting of
'unicode-bidi: embed' is preferred to keep the element together in
case display is changed to inline (see example below).</p>
<p>The following example shows an XML document with bidirectional
text. It illustrates an important design principle: <span
class="index-inst" 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.</p>
<h3 id="bidi-example">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">'unicode-bidi'</span> is 'normal' (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 -->
<h2 id="block-flow">Block Flow Direction: the 'block-flow' property</h2>
<table class="propdef">
<tbody>
<tr>
<th>Name:</th>
<td><dfn>block-flow</dfn></td>
</tr>
<tr>
<th>Value:</th>
<td>tb | rl | lr | bt</td>
</tr>
<tr>
<th>Initial:</th>
<td>tb</td>
</tr>
<tr>
<th>Applies to:</th>
<td><span class="issue">??</span></td>
</tr>
<tr>
<th>Inherited:</th>
<td>yes</td>
</tr>
<tr>
<th>Percentages:</th>
<td>N/A</td>
</tr>
<tr>
<th>Media:</th>
<td>visual</td>
</tr>
<tr>
<th>Computed value:</th>
<td>specified value</td>
</tr>
</tbody>
</table>
<!--<p class="issue">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>-->
<p>This property sets the block-flow direction. Possible values:</p>
<dl>
<dt>tb</dt>
<dd>Top-to-bottom block flow. The writing mode is horizontal.</dd>
<dt>rl</dt>
<dd>Right-to-left block flow. The writing mode is vertical.</dd>
<dt>lr</dt>
<dd>Left-to-right block flow. The writing mode is vertical.</dd>
<dt>bt</dt>
<dd>Bottom-to-top block flow. The writing mode is horizontal.</dd>
</dl>
<p class="issue">Would <code>downward</code>/<code>leftward</code>/<code>rightward</code>/<code>upward</code>
be better value names?</p>
<p>An inline element that has a different 'block-flow' from
its containing block becomes an 'inline-block' element <a href="#CSS3-box" rel="biblioentry">[CSS3-box]</a>.
<span class="issue">switch to CSS2.1</span></p>
<h3>Details</h3>
<p>Box layout in vertical writing modes is exactly analogous to layout in
the horizontal writing modes.</p>
<ul>
<li>Calculations that refer to 'width' use 'height' instead, and vice
versa.</li>
<li>Calculations that refer to the '*-left' and '*-right' box properties
(border, margin, padding, outline) use '*-top' and '*-bottom'
instead, and vice versa. In RL layout '*-right' is analogous to
TB's '*-top'; in LR layout '*-left' is analogous to TB's '*-top'.
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>
<li>Layout effects that depend on the directionality to choose between
left and right (e.g. overflow, overconstraint resolution, 'start'
values for 'text-align' 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.</li>
</ul>
<p>When an element has a different 'block-flow' from its
containing block two cases are possible:
<em class="issue">These descriptions need work</em>
<ul>
<li>The two block flows are perpendicular to each other. (For
example, 'tb' and 'lr'). In such cases, <span class="issue">detail
calculation of width/height and determination of containing block dim</span></li>
<li>The two block-flows are parallel to each other. (For example,
'rl' and 'lr').</li>
</ul>
<h3>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 writing modes.</p>
<p>Here is a diagram of horizontal writing mode (<code>block-flow: tb</code>):</p>
<p><img alt="Diagram of horizontal layout: blocks 1, 2, and 3 are stacked top-to-bottom"
src="horizontal.png" width="219" height="300" /></p>
<p>Here is a diagram for the right-to-left vertical writing mode commonly
used in East Asia (<code>block-flow: 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"
src="vertical-rl.png" height="191" width="297" /></p>
<p>And finally, here is a diagram for the left-to-right vertical
writing mode used for Uighur and Mongolian (<code>block-flow: 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"
src="vertical-lr.png" height="191" width="300" /></p>
</div>
<h3 id="writing-mode">The 'writing-mode' shorthand property</h3>
<table class="propdef" id="name-">
<tr>
<td><em>Name:</em></td>
<td><dfn>writing-mode</dfn></td>
</tr>
<tr>
<td><em>Value:</em></td>
<td>lr-tb | rl-tb | tb-rl | bt-rl | tb-lr | bt-lr</td>
</tr>
<tr>
<td><em>Initial:</em></td>
<td>not defined for shorthand properties</td>
</tr>
<tr>
<td><em>Applies to:</em></td>
<td>all elements and generated content</td>
</tr>
<tr>
<td><em>Inherited:</em></td>
<td>yes</td>
</tr>
<tr>
<td><em>Percentages:</em></td>
<td>N/A</td>
</tr>
<tr>
<td><em>Media:</em></td>
<td>visual</td>
</tr>
<tr>
<td><em>Computed value:</em></td>
<td>see individual properties</td>
</tr>
</table>
<p>The <span class="property"><a
href="#writing-mode">'writing-mode'</a></span> property is a shorthand
property for the <span class="property"><a
href="#direction">'direction'</a></span> property and the <span class="property"> <a
href="#block-flow">'block-flow'</a></span> property. Although
strictly speaking, the property has no initial value, it is equivalent to 'lr-tb'.
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.</p>
<div class="figure">
<table border="1" style="border-collapse: collapse" cellpadding="0" cellspacing="0" width="100%">
<tr>
<th>writing-mode:</th>
<th>direction:</th>
<th>block-flow:</th>
<th>Common Usage:</th>
</tr>
<tr>
<td>lr-tb</td>
<td>ltr</td>
<td>tb</td>
<td>Latin-based, Greek, Cyrillic writing systems (and many others)</td>
</tr>
<tr>
<td>rl-tb</td>
<td>rtl</td>
<td>tb</td>
<td>Arabic, Hebrew writing systems</td>
</tr>
<tr>
<td>tb-rl</td>
<td>ltr</td>
<td>rl</td>
<td>East Asian writing systems in vertical mode</td>
</tr>
<tr>
<td>bt-rl</td>
<td>rtl</td>
<td>rl</td>
<td>Arabic script block quote embedded in East Asian vertical text</td>
</tr>
<tr>
<td>tb-lr</td>
<td>ltr</td>
<td>lr</td>
<td>Mongolian script writing system</td>
</tr>
<tr>
<td>bt-lr</td>
<td>rtl</td>
<td>lr</td>
<td>Arabic script block quote embedded in Mongolian script document</td>
</tr>
</table>
</div>
<h3 id="writing-mode-mixed">Mixing the 'writing-mode' 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:</p>
<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" src="lf-tny.gif" height="170" width="90">
<img alt="Example of Tate Naka Yoko, showing the year 1996
appearing horizontally in a column of vertical text"
class="example" src="tny.gif" height="132" 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 writing mode, as in:
<pre>.date {block-flow: tb;}
<!-- --><span class="date">1996</span></pre>
<h2 id="writing-mode-switching">Proposals for Dealing with Writing Mode Switching</h2>
<p class="issue">NOTE: These are only proposals for dealing with writing mode switching. The CSS Working Group has not endorsed any of them yet, and that they are very likely to be removed at any time.</p>
<h3 id="logical-directional">Logical directional properties and values</h3>
<p class="issue">NOTE: This is only a proposal under discussion.</p>
<h4 id="logical-terminology">Terminology</h4>
<p>In this section we use the following terminology about directional properties:</p>
<dl>
<dt>logical properties</dt><dd>the properties regarding the direction relative to the writing-mode (e.g., margin-before)</dd>
<dt>physical properties</dt><dd>the properties regarding the physical direction (e.g., margin-top)</dd>
<dt>corresponding properties</dt><dd>the pair of a logical property and its corresponding physical property.</dd>
</dl>
<p>The sides of a box are designated as follows:</p>
<dl>
<dt>before side</dt><dd>the side occurring first in the block direction (=top side in lr-tb writing-mode)</dd>
<dt>after side</dt><dd>the side opposite the before side (=bottom side in lr-tb writing-mode)</dd>
<dt>start side</dt><dd>the side occurring first in the inline direction (=left side in lr-tb writing-mode)</dd>
<dt>end side</dt><dd>the side opposite the start side (=right side in lr-tb writing-mode)</dd>
</dl>
<p>The dimensions of a box are designated as follows:</p>
<dl>
<dt>logical width<dt><dd>the dimension in the inline direction
(=width in horizontal writing-mode; height in vertical writing-mode)</dd>
<dt>logical height<dt><dd>the dimension in the block direction
(=height in horizontal writing-mode; width in vertical writing-mode)</dd>
</dl>
<div class="example">
<p>An English (LTR-TB) block:</p>
<pre class="ascii-art">
<---- width / logical width --->
top side/
before side
+------------------------------+ A
left side/ | ---inline direction ---> | right side/ |
start side | | | end side |
| | block * horizontal * | height/
| | direction *writing mode* | logical height
| V | |
+------------------------------+ V
bottom side/
after side
</pre>
</div>
<div class="example">
<p>A vertical Japanese block (TTB-RL):</p>
<pre class="ascii-art">
<--- width / logical height --->
top side/
start side
+------------------------------+ A
left side/ | <---block direction--- | right side/ |
after side | | | before side |
| * vertical * inline| | height/
| *writing mode* direction| | logical width
| V | |
+------------------------------+ V
bottom side/
end side
</pre>
</div>
<h4 id="logical-prop">Logical properties: 'margin-before', 'logical-width', etc.</h4>
<table class="propdef">
<tbody>
<tr>
<th>Name:</th>
<td><dfn>margin-before</dfn>, <dfn>margin-after</dfn>, <dfn>margin-start</dfn>, <dfn>margin-end</dfn></td>
</tr>
<tr>
<th>Value:</th>
<td><var><length></var> | <var><percentage></var> | auto</td>
</tr>
<tr>
<th>Initial:</th>
<td>0</td>
</tr>
<tr>
<th>Applies to:</th>
<td>same as 'margin'</td>
</tr>
<tr>
<th>Inherited:</th>
<td>no</td>
</tr>
<tr>
<th>Percentages:</th>
<td>logical-width of containing block</td>
</tr>
<tr>
<th>Media:</th>
<td>visual</td>
</tr>
<tr>
<th>Computed value:</th>
<td>the percentage as specified or the absolute length or 'auto' (see text)</td>
</tr>
</tbody>
</table>
<table class="propdef">
<tbody>
<tr>
<th>Name:</th>
<td><dfn>padding-before</dfn>, <dfn>padding-after</dfn>, <dfn>padding-start</dfn>, <dfn>padding-end</dfn></td>
</tr>
<tr>
<th>Value:</th>
<td><var><length></var> | <var><percentage></var></td>
</tr>
<tr>
<th>Initial:</th>
<td>0</td>
</tr>
<tr>
<th>Applies to:</th>
<td>all elements </td>
</tr>
<tr>
<th>Inherited:</th>
<td>no</td>
</tr>
<tr>
<th>Percentages:</th>
<td>logical-width of containing block</td>
</tr>
<tr>
<th>Media:</th>
<td>visual</td>
</tr>
<tr>
<th>Computed value:</th>
<td><length> (see text)</td>
</tr>
</tbody>
</table>
<table class="propdef">
<tbody>
<tr>
<th>Name:</th>
<td><dfn>border-before-width</dfn>, <dfn>border-after-width</dfn>, <dfn>border-start-width</dfn>, <dfn>border-end-width</dfn></td>
</tr>
<tr>
<th>Value:</th>
<td><var><border-width></var></td>
</tr>
<tr>
<th>Initial:</th>
<td>medium</td>
</tr>
<tr>
<th>Applies to:</th>
<td>all elements</td>
</tr>
<tr>
<th>Inherited:</th>
<td>no</td>
</tr>
<tr>
<th>Percentages:</th>
<td>logical-width of containing block</td>
</tr>
<tr>
<th>Media:</th>
<td>visual</td>
</tr>
<tr>
<th>Computed value:</th>
<td>absolute length; '0' if the border style is 'none' or 'hidden' (see text)</td>
</tr>
</tbody>
</table>
<table class="propdef">
<tbody>
<tr>
<th>Name:</th>
<td><dfn>border-before-style</dfn>, <dfn>border-after-style</dfn>, <dfn>border-start-style</dfn>, <dfn>border-end-style</dfn></td>
</tr>
<tr>
<th>Value:</th>
<td><var><border-style></var></td>
</tr>
<tr>
<th>Initial:</th>
<td>none</td>
</tr>
<tr>
<th>Applies to:</th>
<td>all elements</td>
</tr>
<tr>
<th>Inherited:</th>
<td>no</td>
</tr>
<tr>
<th>Percentages:</th>
<td>N/A</td>
</tr>
<tr>
<th>Media:</th>
<td>visual</td>
</tr>
<tr>
<th>Computed value:</th>
<td>specified value (see text)</td>
</tr>
</tbody>
</table>
<table class="propdef">
<tbody>
<tr>
<th>Name:</th>
<td><dfn>border-before-color</dfn>, <dfn>border-after-color</dfn>, <dfn>border-start-color</dfn>, <dfn>border-end-color</dfn></td>
</tr>
<tr>
<th>Value:</th>
<td><var><color></var></td>
</tr>
<tr>
<th>Initial:</th>
<td>currentcolor</td>
</tr>
<tr>
<th>Applies to:</th>
<td>all elements</td>
</tr>
<tr>
<th>Inherited:</th>
<td>no</td>
</tr>
<tr>
<th>Percentages:</th>
<td>N/A</td>
</tr>
<tr>
<th>Media:</th>
<td>visual</td>
</tr>
<tr>
<th>Computed value:</th>
<td>the computed color (see text)</td>
</tr>
</tbody>
</table>