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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html lang="en">
<head>
<meta content="text/html; charset=utf-8" http-equiv=Content-Type>
<title>CSS3 module: line</title>
<style type="text/css">
dt {font-weight: normal}
/*.issue, .note {font-style: italic}*/
.figure {font-size: smaller;}
/* Stolen from CSS2 Recommendation */
A.noxref:link, A.noxref:visited {color: black; /*color: inherit*/}
</style>
<style media="print" type="text/css">
img#edge { width: 80%; height: 70%;}
dt.label { display: run-in; }
</style>
<link href="default.css" rel="stylesheet" type="text/css">
<link href="http://www.w3.org/StyleSheets/TR/W3C-WD.css" rel="stylesheet"
type="text/css">
</head>
<body>
<div class="head">
<p><a href="http://www.w3.org/"><img alt="W3C" height="48"
src="http://www.w3.org/Icons/w3c_home" width="72"></a>
<h1 id="css3-module">CSS3 module: line</h1>
<h2 class="no-num no-toc" id="w3c-working">W3C Working Draft 10 February 2003</h2>
<dl>
<dt>This version:
<dd>TBD</dd>
<dt>Latest version:
<dd>TBD</dd>
<dt>Previous version:
<dd>none
<dt>Editors:
<dd><a href="mailto:michelsu@microsoft.com">Michel Suignard (Microsoft)</a>
<dd><a href="http://www.meyerweb.com/eric/">Eric A. Meyer</a>
</dl>
<dl>
<dt>Contributors:
<dd>Original CSS2 authors, and
<dd><a href="mailto:bert@w3.org">Bert Bos (W3C)</a>
<dd><a href="mailto:michelsu@microsoft.com">Michel Suignard (Microsoft)</a>
<dd><a href="mailto:szilles@adobe.com">Steve Zilles (Adobe)</a>
</dl>
<!--begin-include "../copyright.inc"-->
<p class="copyright"><a
href="http://www.w3.org/Consortium/Legal/ipr-notice-20000612#Copyright">
Copyright</a> ©2002 <a href="http://www.w3.org/"><abbr title="World Wide
Web Consortium">W3C</abbr></a><sup>®</sup> (<a
href="http://www.lcs.mit.edu/"><abbr title="Massachusetts Institute of
Technology">MIT</abbr></a>, <a href="http://www.inria.fr/"><abbr lang="fr"
title="Institut National de Recherche en Informatique et
Automatique">INRIA</abbr></a>, <a href="http://www.keio.ac.jp/">Keio</a>),
All Rights Reserved. W3C <a
href="http://www.w3.org/Consortium/Legal/ipr-notice-20000612#Legal_Disclaimer">liability</a>,
<a
href="http://www.w3.org/Consortium/Legal/ipr-notice-20000612#W3C_Trademarks">trademark</a>,
<a
href="http://www.w3.org/Consortium/Legal/copyright-documents-19990405">document
use</a> and <a
href="http://www.w3.org/Consortium/Legal/copyright-software-19980720">software
licensing</a> rules apply.
<!--end-include-->
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc" id="Abstract">Abstract</h2>
<p>This document presents a set of CSS line formatting properties. It also
includes baseline alignment features as well as related functions like initial
line and initial letter effect. It extends on the CSS 2 model <a href="#CSS2"
rel="biblioentry">[CSS2]</a>.
<h2 class="no-num no-toc" id="Status">Status of This Document</h2>
<p>This document is a working draft of the CSS working group which is part of
the <a href="/Style/">Style activity</a> (see <a
href="/Style/Activity">summary</a>). It contains a proposal for features
to be included in CSS level 3.
<p>Feedback is very much welcome. Comments can be sent directly to the
editor, but the mailing list <a
href="/Mail/Lists.html#www-style">www-style@w3.org</a> (see <a
href="/Mail/Request">instructions</a>) is also open and is preferred for
discussion of this and other drafts in the Style area. The mailing list is
archived.<p>This working draft may be updated, replaced or rendered obsolete by other
W3C documents at any time. It is inappropriate to use W3C Working Drafts as
reference material or to cite them as other than "work in progress". Its
publication does not imply endorsement by the W3C membership or the <a
href="/Style/Group/">CSS Working Group</a> (<a
href="http://cgi.w3.org/MemberAccess/AccessRequest">members only</a>).
<p>To find the latest version of this working draft, please follow the
"Latest version" link above, or visit the list of W3C <a
href="/TR/">Technical Reports</a>.
<h2 class="no-num no-toc" id="Contents">Contents</h2>
<!--begin-toc-->
<ul class="toc">
<li><a href="#dependencies"><span class="secno">1. </span>Dependencies on
other modules</a>
<li><a href="#introduction"><span class="secno">2. </span>Introduction</a>
<li><a href="#LineBox"><span class="secno">3. </span>Line box, Line
stacking and Content height</a>
<ul class="toc">
<li><a href="#InlineFormatting"><span class="secno">3.1. </span>Inline formatting
context</a>
<li><a href="#LineBoxWrapping"><span class="secno">3.2. Line box
wrapping</span></a>
<li><a href="#inline1"><span class="secno">3.3. </span>Inline box
progression dimension (height in horizontal flow), the 'text-height' property</a>
<li><a href="#InlineBoxHeight"><span class="secno">3.4. </span>Line height
adjustment: the 'line-height' property</a>
<li><a href="#LineStacking"><span class="secno">3.5. </span>Line Stacking:
the 'line-stacking-strategy', 'line-stacking-ruby', 'line-stacking-shift'
properties, and the 'line-stacking' shorthand property</a>
</ul>
<li><a href="#baseline">
<span class="secno">4. </span>Baseline alignment</a>
<ul class="toc">
<li><a href="#FontBaseline">
<span class="secno">4.1. </span>Baseline information provided by fonts</a>
<li><a href="#AlignmentBaselineType">
<span class="secno">4.2. </span>Baseline identifiers</a>
<li><a href="#BaselineAlignmentOverview">
<span class="secno">4.3. </span>Overview of the baseline alignment process</a>
<li><a href="#dominant-baseline-prop">
<span class="secno">4.4. </span>Dominant baseline: the <span
class="property">'dominant-baseline'</span> property</a>
<li><a href="#alignment-baseline-prop">
<span class="secno">4.5.
</span>Aligning the alignment point of an element: the <span
class="property">'alignment-baseline'</span> property</a>
<li><a href="#alignment-adjust-prop">
<span class="secno">4.6. </span>Setting the alignment point: the <span class="property">'alignment-adjust'</span>
property</a>
<li><a href="#baseline-shift-prop">
<span class="secno">4.7. </span>Repositioning the dominant baseline: the <span
class="property">'baseline-shift'</span> property</a>
<li><a href="#vertical-align-prop">
<span class="secno">4.8. </span>Vertical alignment: the <span class="property">'vertical-align'</span> shorthand
baseline alignment property</a>
<li><a href="#inline-box-align-prop">
<span class="secno">4.9. </span>Inline box alignment: the <span class="property">'inline-box-align'</span>
property</a>
</ul>
<li><a href="#Initial">
<span class="secno">5. </span>
Initial line and Drop initial</a>
<ul class="toc">
<li><a href="#InitialLine">
<span class="secno">5.1. </span>Initial line</a>
<li><a href="#DropInitial">
<span class="secno">5.2. </span>Drop Initial overview</a>
<li><a href="#DropInitialSize">
<span class="secno">5.3. </span>
Sizing drop initial, the <span class="property">'drop-initial-size'</span> and the <span class="property">'drop-initial-value'</span>
properties</a>
<li><a href="#DropInitialAlign">
<span class="secno">5.4. </span>Aligning drop initial: the <span
class="property">'drop-initial-before-align'</span>, <span
class="property">'drop-initial-before-adjust'</span>, <span
class="property">'drop-initial-after-align'</span> and <span
class="property">'drop-initial-after-adjust'</span> properties</a>
</ul>
<li><a href="#properties"><span class="secno">6. </span>Properties index</a>
<li><a href="#profiles"><span class="secno">7. </span>Profiles</a>
<li><a href="#glossary"><span class="secno">8. </span>Glossary</a>
<li><a href="#BaselineUsage">Appendix A: Usage of baseline alignment
(informative)</a>
<li><a href="#ack">Acknowledgments</a>
<li><a href="#ref">References</a>
<ul class="toc">
<li><a href="#normative">Normative references</a>
<li><a href="#other">Other references</a>
</ul>
</ul>
<!--end-toc-->
<hr>
<h2 id="dependencies"><span class="secno">1. </span>Dependencies on other
modules</h2>
<p>This CSS3 module depends on the following other CSS3 modules:
<ul>
<li>Fonts<li>Text
<li>Syntax and grammar
<li>Values and unit
</ul>
<p>It has non-normative (informative) references to the following other CSS3
modules:
<ul>
<li>Multi-column layout
<li>Ruby
</ul>
<h2 id="introduction"><span class="secno">2. </span>Introduction</h2>
<p>This modules specifies the presentation aspects of line within block elements
and inline elements. It also covers the design of baseline alignment within each
line and the placement of drop initial letter (also known as first letter or
drop caps). Most of the properties are new to CSS3.<p>All described properties, in addition to the noted values, take
'initial' and 'inherit'. These values are not repeated in each of the
property value enumeration.
<p>This module uses extensively the 'before', 'after', 'start' and
'end' notation to specify the four edges of a box relative to its text
advance direction, independently of its absolute positioning in terms of
'top', 'bottom', 'left' and 'right' (corresponding respectively to the
'before', 'after', 'start' and 'end' positions in a typical Western text
layout). This notation is also used extensively in <a href="#XSL1.0"
rel="biblioentry">[XSL1.0]</a> for the same purpose.
<p>Finally, in this document, requirements are expressed using the key words
"MUST", "MUST NOT", "REQUIRED",
"SHALL" and "SHALL NOT". Recommendations are expressed
using the key words "SHOULD", "SHOULD NOT" and
"RECOMMENDED". "MAY" and "OPTIONAL" are used to
indicate optional features or behavior. These keywords are used in accordance
with <a href="#RFC2119" rel="biblioentry">[RFC2119]</a>. For legibility these
keywords are used in lowercase form.
<hr>
<h2 id="LineBox"><span class="secno">3. </span>Line box, Line stacking and Content height </h2>
<p>This section describes inline boxes formatting, how lines are stacked
together and a mechanism to adjust the content height of inline elements. Two
terms: inline-progression dimension and block-progression dimension are used
frequently in the section and are defined as follows<p>The <b>inline-progression
dimension</b> is a length in the direction of the inline-progression of a box.
For an horizontal layout flow it can be perceived as related to the the width of
the box. However for a vertical layout flow it will be related to the height of
the box. The term inline-progression dimension is the neutral way to express
that dimension independently of the layout flow.
<p>The <b>block-progression dimension</b> is a length in the direction of the
block-progression of a box. For an horizontal layout flow it can be perceived as
related to the height of the box. However for a vertical layout flow it will be
related to the width of the box. The term block-progression dimension is the
neutral way to express that dimension independently of the layout flow.<h3 id="InlineFormatting">
<span class="secno">3.1. </span>Inline formatting context</h3>
<p>In an inline formatting context, boxes are laid out in the inline-progression
direction, one after
the other, following the block-progression within the containing block. Borders,
padding and inline-progression margins are respected between these boxes. The boxes may be aligned
within the inline-progression in different ways: their after-edges or
before-edges may be aligned, or the
baselines of text within them may be aligned. The rectangular area that contains
the boxes that form a line is called a <span class="index-def" title="line box">
<a id="line-box"><dfn>line box</dfn></a></span>.</p>
<p>The inline-progression dimension ('width' in horizontal flow) of a line box is
determined by its containing block. The block-progression dimension ('height' in
horizontal flow) of a line box is determined by the rules given
in the section on
<a href="#line-height">line height
calculations</a>. A line box is generally tall (relative) enough for all of the boxes it
contains. However, it may be taller than the tallest box it contains (if, for
example, boxes are aligned so that baselines line up). The alignment of boxes
within a line box is determined by the
<span class="propinst-vertical-align"><span style="background-position: 0% 0%">
<a href="#baseline">baseline alignment</a></span></span> properties.</p>
<p>In general, when several inline boxes cannot fit within a single line box,
they are distributed among two or more block-progression stacked line boxes. The
exact wrapping of inline boxes at the line ending edge is determined by several
text related property categories such as line-breaking, word-breaking, text
wrapping and white-space management. Thus, a
paragraph is a stack of line boxes.</p>
<p>Line boxes are stacked together following the strategy determined by the
<span class="property"><a href="#line-stacking-strategy">'line-stacking-strategy'</a></span> property. Depending on the set value, line boxes can be
stacked at constant spacing, in a grid manner or with enough space to
accommodate all the line boxes. Using a constant spacing may create a 'bleeding'
effect between line boxes.</p>
<p>A containing block defines a <b>root inline box</b> which wraps all the
inline children of the block element, including the anonymous inline boxes.
It inherits the inline behaviors that are set for the block
element (like <span class="property"><a href="#line-height">'line-height'</a></span>)
and play an important role in some line stacking strategies.</p>
<p>Although margins, borders, and padding of non-replaced elements do not enter
into inline box block-progression dimension calculation (and thus the line box
calculation), they are still rendered around inline boxes. This means that if
the block-progression dimension of a line box is shorter than the
<a href="http://www.w3.org/TR/REC-CSS2/box.html#outer-edge">outer edges</a> of
the boxes it contains, backgrounds and colors of padding and borders may "bleed"
into adjacent line boxes. However, in this case, some user agents may use the
line box to "clip" the border and padding areas (i.e., not render them). </p>
<h3 id="LineBoxWrapping"><span class="secno">3.2. </span>Line Box wrapping</h3>
<p>In general, the start edge of a line box touches the start edge of its
containing block and the end edge touches the end edge of its containing block.
However, floating boxes may come between the containing block edge and the line
box edge. Thus, although line boxes in the same inline formatting context
generally have the same inline-progression dimension (that of the
containing block), they may vary if available inline-progression space
is reduced due to <!-- a href="#floats"-->
floats<!--/a-->. Line boxes in the same inline formatting context may vary in
block-progression dimension or not, depending on the line stacking strategy.</p>
<p>When the total inline-progression dimension of the inline boxes on a line is less than the
inline-progression dimension of
the line box containing them, their inline-progression distribution within the line box
is determined by the
<a class="noxref" href="#text-align">
<span class="property">'text-align'</span></a> property. If that
property has the value 'justify', the user agent may stretch the inline boxes as
well. </p>
<p>When line-breaking opportunities are available within inline boxes and are
not pre-empted by the white-space properties, the inline boxes located at the
ending edge of the line box may be split into several boxes and these boxes
distributed across several line boxes. When an inline box is split, margins, borders, and padding have no visual
effect where the split occurs (or at any split, when they are several). Formatting of margins, borders, and padding may
not be fully defined if the split occurs within a bidirectional embedding. </p>
<p>Inline boxes may also be split into several boxes <em>within the same line
box</em> due to <a href="#direction">bidirectional text processing</a>. </p>
<div class="html-example">
Here is an example of inline box construction. The following paragraph
(created by the HTML block-level element P) contains anonymous text
interspersed with the elements EM and STRONG:
<pre><P>Several <EM>emphasized words</EM> appear
<STRONG>in this</STRONG> sentence, dear.</P>
</pre>
<p>The P element generates a block box that contains five inline boxes, three
of which are anonymous:</p>
<ul>
<li>Anonymous: "Several" </li>
<li>EM: "emphasized words" </li>
<li>Anonymous: "appear" </li>
<li>STRONG: "in this" </li>
<li>Anonymous: "sentence, dear." </li>
</ul>
<p>To format the paragraph, the user agent flows the five boxes into line
boxes. In this example, the box generated for the P element establishes the
containing block for the line boxes. If the containing block is sufficiently
wide (relative) , all the inline boxes will fit into a single line box: </p>
<pre> Several <em>emphasized words</em> appear <strong>in this</strong> sentence, dear.
</pre>
<p>If not, the inline boxes will be split up and distributed across several
line boxes. The previous paragraph might be split as follows: </p>
<pre>Several <em>emphasized words</em> appear
<strong>in this</strong> sentence, dear.
</pre>
<p>or like this: </p>
<pre>Several <em>emphasized</em>
<em>words</em> appear <strong>in this</strong>
sentence, dear.
</pre>
</div>
<p>In the previous example, the EM box was split into two EM boxes (call them
"split1" and "split2"). Margins, borders, padding, or text decorations have no
visible effect after split1 or before split2. </p>
<div class="html-example">
Consider the following example:
<pre><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN">
<HTML>
<HEAD>
<TITLE>Example of inline flow on several lines</TITLE>
<STYLE type="text/css">
EM {
padding: 2px;
margin: 1em;
border-width: medium;
border-style: dashed;
line-height: 2.4em;
}
</STYLE>
</HEAD>
<BODY>
<P>Several <EM>emphasized words</EM> appear here.</P>
</BODY>
</HTML>
</pre>
<p>Depending on the width of the P, the boxes may be distributed as follows:</p>
<div class="figure">
<img alt="Image illustrating the effect of line breaking on the
display of margins, borders, and padding." src="inline-layout.gif" width="260" height="99"><span class="dlink"> <a title="Long description for illustration of margin/border
behavior on split inline box" href="http://www.w3.org/TR/REC-CSS2/images/longdesc/inline-layout-desc.html" name="img-inline-layout">[D]</a></span></div>
<ul>
<li>The margin is inserted before "emphasized" and after "words". </li>
<li>The padding is inserted before, above, and below "emphasized" and after,
above, and below "words". A dashed border is rendered on three sides in each
case. </li>
</ul>
</div>
<h3 id="inline1"><span class="secno">3.3. </span>Inline box progression dimension (height in horizontal flow), the
<span class="property"><a href="#text-height">'text-height'</a></span> property</h3>
<p>Each inline box has a block-progression dimension which is derived from the
following parameters: the 'text-height' and 'font-size' properties for
non-replaced elements, the height or the width for replaced elements (depending
on the text flow being horizontal or vertical respectively) and the stacked
block-progression dimension for inline-block elements (identical to what is done
for block-level elements).</p>
<p>The block-progression dimension determines the position of the padding,
border and margin for the element but does not necessarily determine the line
stacking progression as this is also controlled by the 'line-stacking-strategy'.</p>
<table class="propdef" id="name-61">
<tr>
<td><em>Name:</em>
<td><dfn id="text-height">text-height</dfn><tr>
<td><em>Value:</em>
<td>auto | font-size | text-size | max-size | <number><tr>
<td><em>Initial:</em>
<td>auto<tr>
<td><em>Applies to:</em>
<td>inline elements and parents of element with display:ruby-text<tr>
<td><em>Inherited:</em>
<td>yes
<tr>
<td><em>Percentages:</em>
<td>N/A<tr>
<td><em>Media:</em>
<td><a class="noxref"
href="/TR/REC-CSS2/media.html#visual-media-group">visual</a>
<tr>
<td><em>Computed value:</em>
<
8D74
td>specified value (except for initial and inherit)</table>
<p>The 'text-height' property determine the block-progression dimension of the
text content area of an inline box (non-replaced elements) . Possible values:</p>
<dl>
<dt><strong>auto</strong>
<dd>The block-progression dimension is based either on the em square determined
by the computed element font-size property value or the cell-height (ascender + descender)
related to the computed element font-size as chosen by the user agent.
<dt>font-size</dt>
<dd>The block-progression dimension is based on the em square as determined by
the computed element font-size. </dd>
<dt>text-size</dt>
<dd>The block-progression dimension is based on the cell-height (ascender +
descender) related to the computed element font-size.</dd>
<dt>max-size</dt>
<dd>The block-progression dimension is based on the maximum extents toward the
before-edge and after-edge of the box obtained by considering all children
elements located on the same line, ruby annotations (elements with 'display:ruby-text')
and baseline shifted elements.</dd>
<dt><number></dt>
<dd>The block progression dimension is based on <number> times the em square as
determined by the computed font-size.</dd>
</dl>
<p>When more than one font-size is used (this could happen when glyphs are found
in different fonts), it is recommended that the largest font-size provides the em square and the cell-height.</p>
<p>Although the 'text-height' property does not apply directly to block
elements, it applies to their anonymous children inline boxes (if any).</p>
<p>For replaced elements, the block-progression dimension is determined by the
outer edges (i.e. margin edge).</p>
<h3 id="InlineBoxHeight"><span class="secno">3.4. </span>Line height adjustment: the
<span class="property"><a href="#line-height">'line-height'</a></span> property</h3>
<p>The 'line-height' property allows to control the amount of leading space
which is added before and after the block-progression dimension of either an
inline box, a line box or both. The 'line-stacking-strategy' property value
determines which effects are active. For example, there are line stacking
strategies for which leading is not applied to inline boxes, but only to the
line boxes. The sum of the possible leading space and the block-progression
dimension is called the <b>extended block-progression dimension</b>. That
extended value is not used for border, margin and padding placement but is used
for vertical alignment (relative) and line box block-progression dimension.</p>
<p>The <span class="index-def" title="leading"><em><a name="x15">leading</a></em></span><span title="leading">
for an inline element
is defined as the d</span>ifference between the block-progression dimension as
determined by the 'text-height' property and the computed value
of
<a class="noxref" href="http://www.w3.org/TR/REC-CSS2/visudet.html#propdef-line-height">
<span class="propinst-line-height">'line-height'</span></a>. Half the leading is
called the <span class="index-def" title="half-leading"><em><a name="x16">
half-leading</a></em></span><span title="half-leading">, each half-leading is
located before and after the block-progression dimension of the element.
Depending on the value of the 'line-stacking-strategy', the 'line-height' value
will specify the </span> <em>exact</em> extended block-progression dimension of each box
generated by the element or be ignored. (Except for inline
<a href="http://www.w3.org/TR/REC-CSS2/conform.html#replaced-element">replaced</a>
elements, where both the block-progression dimension and the extended
block-progression dimension of the box is given by the
<span class="propinst-height">outer edges (i.e. margin edge).)</span> When the line-height value is ignored for an inline
element, the extended block-progression dimension is identical to the
block-progression dimension. Anonymous inline boxes use the 'text-height' and
'line-height' property values specified for their parent.</p>
<p>Depending on the
value of the 'line-stacking-strategy', the 'line-height' value may provide a
minimum or exact extended block-progression dimension for each generated inline box and
the line boxes. How the leading space is distributed between the before-edge and
the after-edge of inline elements within the line box depends on their
vertical-align property value.</p>
<p>When applicable, the <b>minimum extended block-progression dimension</b> consists of a minimum
ascent above the block's baseline and a
minimum descent below it, exactly as if each line box starts with a zero-width
(relative) inline box with the blocks' font and line height properties (what T<sub>E</sub>X calls a
'strut').</p>
<p>Empty inline elements generate empty inline boxes, but these boxes still have
a line height, and thus may influence the line box block-progression dimension,
as if the empty box contained an infinitely narrow letter.</p>
<p>A inline box which otherwise would influence the line box extended
progression dimension may be removed from the computation by using a special
value of the line-height property: 'none'.</p>
<table class="propdef" id="name-62">
<tr>
<td><em>Name:</em>
<td><dfn id="line-height">line-height</dfn><tr>
<td><em>Value:</em>
<td>normal |
<a class="noxref" href="http://www.w3.org/TR/REC-CSS2/syndata.html#value-def-number">
<span class="value-inst-number"><number></span></a> |
<a class="noxref" href="http://www.w3.org/TR/REC-CSS2/syndata.html#value-def-length">
<span class="value-inst-length"><length></span></a> |
<a class="noxref" href="http://www.w3.org/TR/REC-CSS2/syndata.html#value-def-percentage">
<span class="value-inst-percentage"><percentage></span></a> | none
<tr>
<td><em>Initial:</em>
<td>normal<tr>
<td><em>Applies to:</em>
<td>all elements<tr>
<td><em>Inherited:</em>
<td>yes
<tr>
<td><em>Percentages:</em>
<td>refer to the font size of the element itself <tr>
<td><em>Media:</em>
<td><a class="noxref"
href="/TR/REC-CSS2/media.html#visual-media-group">visual</a>
<tr>
<td><em>Computed value:</em>
<td>see prose</table>
<p>Values for this property have the following meanings:</p>
<dl>
<dt><strong>normal</strong> </dt>
<dd>Tells user agents to set the
<a href="http://www.w3.org/TR/REC-CSS2/cascade.html#computed-value">computed
value</a> to a "reasonable" value based on the font size of the element. The
value has the same meaning as <span class="index-inst" title="<number>">
<a class="noxref" href="http://www.w3.org/TR/REC-CSS2/syndata.html#value-def-number" name="x18">
<span class="value-inst-number"><number></span></a></span>. We recommend a
computed value for 'normal' between 1.0 to 1.2. The user agent may allow the
<number> to vary depending on the metrics of the font(s) being used.</dd>
<dt><span class="index-inst" title="<length>">
<a class="noxref" href="http://www.w3.org/TR/REC-CSS2/syndata.html#value-def-length" name="x19">
<span class="value-inst-length"><strong><length></strong></span></a></span>
</dt>
<dd>The box height is set to this length. Negative values are illegal. The
length is the computed value.</dd>
<dt><span class="index-inst" title="<number>">
<a class="noxref" href="http://www.w3.org/TR/REC-CSS2/syndata.html#value-def-number" name="x20">
<span class="value-inst-number"><strong><number></strong></span></a></span>
</dt>
<dd>The <a href="http://www.w3.org/TR/REC-CSS2/cascade.html#computed-value">
computed value</a> of the property is this number multiplied by the element's
font size. Negative values are illegal. However, the number, not the
<a href="http://www.w3.org/TR/REC-CSS2/cascade.html#computed-value">computed
value</a>, is inherited. </dd>
<dt><span class="index-inst" title="<percentage>">
<a class="noxref" href="http://www.w3.org/TR/REC-CSS2/syndata.html#value-def-percentage" name="x21">
<span class="value-inst-percentage"><strong><percentage></strong></span></a></span>
</dt>
<dd>The <a href="http://www.w3.org/TR/REC-CSS2/cascade.html#computed-value">
computed value</a> of the property is this percentage multiplied by the
element's computed font size. Negative values are illegal.</dd>
<dt>none</dt>
<dd>The element does not influence the <i>extended block-progression dimension</i>
of the line. The computed value is the specified value ('none'). When set on a
block element where the <a href="#stack-height">stack-height</a> computation
is only based on the value or a multiple of the value of the 'line-height'
property, the 'none' value is ignored and 'normal' is used instead.</dd>
</dl>
<div class="example">
<p style="DISPLAY: none">Example(s):</p>
<p>The three rules in the example below have the same resultant line height:
</p>
<pre>DIV { line-height: 1.2; font-size: 10pt } /* number */
DIV { line-height: 1.2em; font-size: 10pt } /* length */
DIV { line-height: 120%; font-size: 10pt } /* percentage */
</pre>
</div>
<p>When an element contains text that is rendered in more than one font, user
agents should determine the
<a class="noxref" href="http://www.w3.org/TR/REC-CSS2/visudet.html#propdef-line-height">
<span class="propinst-line-height">'line-height'</span></a> value according to
the largest font size (when appropriate). </p>
<p>Note that replaced elements have a
<a class="noxref" href="http://www.w3.org/TR/REC-CSS2/fonts.html#propdef-font-size">
<span class="propinst-font-size">'font-size'</span></a> and a
<a class="noxref" href="http://www.w3.org/TR/REC-CSS2/visudet.html#propdef-line-height">
<span class="propinst-line-height">'line-height'</span></a> property, even if
they are not used directly to determine the extended block-progression dimension of the box: 'em' and 'ex'
values are relative to values of 'font-size and percentage values for
<a class="noxref" href="http://www.w3.org/TR/REC-CSS2/visudet.html#propdef-vertical-align">
<span class="propinst-vertical-align">'vertical-align'</span></a> are relative
to values of the extended block-progression dimension.</p>
<p>When the
<a class="noxref" href="http://www.w3.org/TR/REC-CSS2/visudet.html#propdef-line-height">
<span class="propinst-line-height">'line-height'</span></a> value is less than
the font size, the final inline box extended block-progression dimension will be less than the font size and
the rendered glyphs will "bleed" outside the box. If such a box touches the edge
of a line box, the rendered glyphs will also "bleed" into the adjacent line box.</p>
<p class="note">Editors' note: The effect of 'line-height: none' on block-level
elements needs to be specified (for all the values of 'line-stacking-strategy').</p>
<h3 id="LineStacking"><span class="secno">3.5. </span>Line Stacking: the
<span class="property"><a href="#line-stacking-strategy">'line-stacking-strategy'</a></span>,
<span class="property"><a href="#line-stacking-ruby">'line-stacking-ruby'</a></span>,
<span class="property"><a href="#line-stacking-shift">'line-stacking-shift'</a></span> properties, and the
<span class="property"><a href="#line-stacking">'line-stacking'</a></span> shorthand property</h3>
<p>Line stacking is the mechanism by which a line box is determined for each
line in a block and then these lines are stacked in the block-progression
direction resolving any spacing constraints between adjacent lines. The
line-stacking strategy covers both the determination of the block-progression
dimension (height in horizontal flow) of a line box and the rules for spacing
line boxes.</p>
<p>All line stacking strategies make use of the properties: 'font-size',
'text-height' and 'line-height'.</p>
<p>The line stacking properties are made of the following properties:</p>
<ol>
<li>The <span class="property"><a href="#line-stacking-strategy">'line-stacking-strategy'</a></span> property determines the overall stacking
method,</li>
<li>The <span class="property"><a href="#line-stacking-ruby">'line-stacking-ruby</a>'</span> property determines how elements with
'display=ruby' are stacked,</li>
<li>The <span class="property"><a href="#line-stacking-shift">'line-stacking-shift</a>'</span> property determines how elements which are
baseline-shifted are stacked,</li>
<li>Finally the <span class="property"><a href="#line-stacking">'line-stacking</a>'</span> property is a short-hand for the previous
properties.</li>
</ol>
<table class="propdef" id="name-162">
<tr>
<td><em>Name:</em>
<td><dfn id="line-stacking-strategy">line-stacking-strategy</dfn>
<tr>
<td><em>Value:</em>
<td>inline-line-height | block-line-height | max-height | grid-height
<tr>
<td><em>Initial:</em>
<td>inline-line-height<tr>
<td><em>Applies to:</em>
<td>block-level elements
<tr>
<td><em>Inherited:</em>
<td>yes
<tr>
<td><em>Percentages:</em>
<td>N/A<tr>
<td><em>Media:</em>
<td><a class="noxref"
href="/TR/REC-CSS2/media.html#visual-media-group">visual</a>
<tr>
<td><em>Computed value:</em>
<td>specified value (except for initial and inherit)</table>
<p>This property determines the line stacking strategy for stacked line boxes
within a containing block element. The term <b>stack-height</b> is used in the
context of this property description to indicate the block-progression dimension
for the line boxes. Possible values:<dl>
<dt><strong>inline-line-height</strong>
<dd>The <i id="stack-height">stack-height</i> is the smallest value that contains the <i>extended
block-progression dimension</i> of all the inline elements on that line when those
elements are properly aligned. Since the line spacing information is already
included in the computation of the line box, these line boxes are simply stacked
adjacent to one another in the formatted block to which they belong. The
'line-height' property value is taken into account for both the inline elements
and the block elements. For inline elements, it defines the extended
block-progression dimension. For block elements, it defines the <i>minimum
extended block-progression dimension</i>.<dt>block-line-height</dt>
<dd>The <i>stack-height</i> is determined by the block element computed 'line-height' property
value. The 'line-height' property value is ignored for inline elements. For
alignment purpose, this case is similar to the <i>minimum extended
block-progression dimension</i> case (strut model). This is the only line-stacking
strategy that may cause inline boxes within the line to bleed before and after
the line box because the line box is not constrained by its inline boxes. If the
block computed 'line-height' is 'none', the stack-height is determined as if
'line-height: normal'.</dd>
<dt>max-height</dt>
<dd>The <i>stack-height</i> is the smallest value that contains the
block-progression dimension of all the inline elements on that line when those
elements are properly aligned. The 'line-height' property value is taken into
account only for the block elements and it defines the <i>minimum
extended block-progression dimension</i>.</dd>
<dt>grid-height</dt>
<dd>The <i>stack-height</i> is the smallest multiple of the block element 'line-height'
computed value that can contain the block-progression of all the inline
elements on that line when those elements are properly aligned. The
'line-height' property value is ignored for inline elements. If the block
computed 'line-height' is 'none', the stack-height is determined as if
'line-height: normal'.</dd>
</dl>
<p>When the line-stack strategy dictates that the inline element line-height be
ignored, this means that for those elements only their block-progression
dimensions are considered for the <i>stack-height</i>, not their extended
block-progression dimensions.</p>
<p class="note"><b>Note.</b> XSL has a similar property with the same name which
use different but equivalent values: 'line-height' instead of
'inline-line-height', 'font-height' instead of 'block-line-height'. It also uses
'max-height'. The value 'grid-height' is new to the CSS3 property.<p> <table class="propdef" id="name-60">
<tr>
<td><em>Name:</em>
<td><dfn id="line-stacking-ruby">line-stacking-ruby</dfn><tr>
<td><em>Value:</em>
<td>exclude-ruby | include-ruby
<tr>
<td><em>Initial:</em>
<td>exclude-ruby<tr>
<td><em>Applies to:</em>
<td>block-level elements
<tr>
<td><em>Inherited:</em>
<td>yes
<tr>
<td><em>Percentages:</em>
<td>N/A<tr>
<td><em>Media:</em>
<td><a class="noxref"
href="/TR/REC-CSS2/media.html#visual-media-group">visual</a>
<tr>
<td><em>Computed value:</em>
<td>specified value (except for initial and inherit)</table>
<p>This property determines the line stacking method for block elements
containing ruby annotation elements (element with 'display: ruby-text' or
'display: ruby-text-container'). In all cases the ruby base elements (elements
with 'display: ruby-base' or display: ruby-base-container') are considered for
line stacking. Possible values:<dl>
<dt><strong>exclude-ruby</strong>
<dd>The ruby annotation elements are ignored for line stacking.<dt>include-ruby</dt>
<dd>The ruby annotation elements are considered for line stacking.</dd>
</dl>
<p>This property is ignored in two cases:<ol>
<li>The element text-height property is set to 'max-size'.</li>
<li>The line stacking strategy is set to 'block-line-height'.</li>
</ol>
<table class="propdef" id="name-160">
<tr>
<td><em>Name:</em>
<td><dfn id="line-stacking-shift">line-stacking-shift</dfn><tr>
<td><em>Value:</em>
<td>consider-shifts | disregard-shifts<tr>
<td><em>Initial:</em>
<td>consider-shifts<tr>
<td><em>Applies to:</em>
<td>block-level elements
<tr>
<td><em>Inherited:</em>
<td>yes
<tr>
<td><em>Percentages:</em>
<td>N/A<tr>
<td><em>Media:</em>
<td><a class="noxref"
href="/TR/REC-CSS2/media.html#visual-media-group">visual</a>
<tr>
<td><em>Computed value:</em>
<td>specified value (except for initial and inherit)</table>
<p>This property determines the line stacking method for block elements
containing elements with base-shift. Possible values:<dl>
<dt><strong>consider-shifts</strong>
<dd>In determining the <i>stack-height</i>, include the adjusted top-edge and
bottom-edge of any characters that have a baseline-shift.
<dt>disregard-shifts</dt>
<dd>In determining the <i>stack-height</i>, include the unshifted top-edge and
bottom-edge of any characters that have a baseline-shift. </dd>
</dl>
<p>This property is ignored in two cases:<ol>
<li>The element text-height property is set to 'max-size'.</li>
<li>The line stacking strategy is set to 'block-line-height'.</li>
</ol>
<p class="note"><b>Note.</b> XSL has a similar property with a different name:
'line-height-shift-adjustment' which use the same values.<p>Finally, the line
stacking strategy can be used using the following shorthand:</p>
<table class="propdef" id="name-260">
<tr>
<td><em>Name:</em>
<td><dfn id="line-stacking">line-stacking</dfn><tr>
<td><em>Value:</em>
<td><'line-stacking-strategy'> || <'line-stacking-ruby'> ||
<'line-stacking-shift'><tr>
<td><em>Initial:</em>
<td>see individual properties<tr>
<td><em>Applies to:</em>
<td>block-level elements
<tr>
<td><em>Inherited:</em>
<td>yes
<tr>
<td><em>Percentages:</em>
<td>N/A<tr>
<td><em>Media:</em>
<td><a class="noxref"
href="/TR/REC-CSS2/media.html#visual-media-group">visual</a>
<tr>
<td><em>Computed value:</em>
<td>see individual properties</table>
<hr>
<h2 id="baseline"><span class="secno">4. </span>Baseline alignment</h2>
<p>Baseline alignment describes the alignment of textual content and based on
information contained in font tables associated with font resources.
Additional descriptions for these font tables are provided in the <a
href="http://www.w3.org/Style/Group/css3-src/css3-fonts/Overview.html">CSS3
Fonts module</a>.
<h3 id="FontBaseline"><span class="secno">4.1. </span>Baseline information
provided by fonts</h3>
<p>The glyphs of a given script are positioned so that a particular point on
each glyph, the <b>alignment-point</b>, is aligned with the alignment-points of
the other glyphs in that script. The glyphs of different scripts are typically
aligned at different points on the glyph. For example, Western
glyphs are aligned on the bottoms of the capital letters, certain Indic
glyphs (including glyphs from the Devanagari, Gurmukhi and Bengali scripts)
are aligned at the top of a horizontal stroke near the top of the glyphs and
East Asian glyphs are aligned either at the bottom or center of the EM box of
the glyph. Within a script and within a line of text having a single
font-size, the sequence of alignment-points defines, in the
inline-progression-direction, a geometric line called a <b>baseline</b>.
Western and most other alphabetic and syllabic glyphs are aligned to an
"alphabetic" baseline, the above Indic glyphs are aligned to a "hanging"
baseline and the East Asian glyphs are aligned to an "ideographic" baseline.
<div class="figure">
<p><img alt="three alignment points" height="89"
src="AlignmentPointsMixedScripts2.gif" width="457">
<p>This figure shows the vertical position of the alignment-point for
alphabetic and many syllabic scripts, illustrated by a Roman "A"; for certain
Indic scripts, illustrated by a Gurmukhi syllable "ji"; and for ideographic
scripts, illustrated by the ideographic glyph meaning "country". The thin
black rectangle around the ideographic glyph illustrates the EM box for that
glyph and shows the typical positioning of the "black marks" of the glyph
within the EM box.
</div>
<p>A <b>baseline-table</b> specifies the position of one or more baselines in
the design space coordinate system. The function of the baseline table is to
facilitate the alignment of different scripts with respect to each other when
they are mixed on the same text line. Because the desired relative alignments
may depend on which script is dominant in a line (or block), there may be a
different baseline table for each script. In addition, different alignment
positions are needed for horizontal and vertical writing modes. Therefore,
the font may have a set of baseline tables: typically, one or more for
horizontal writing-modes and zero or more for vertical writing-modes.
<div class="figure">
<p><img alt="different baseline positions" height="473"
src="Baselines-HorizAndVert-ApCountry.gif" width="475">
<p>Examples of horizontal and vertical baseline positions. The thin lined box
in each example is the "EM box". For the Latin glyphs, only the EM box of the
first glyph is shown. Example 1 shows typical Latin text written