WD-css3-linebox-20020515
146 KB
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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>
<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 15 May 2002</h2>
<dl>
<dt>This version:
<dd><a
href="http://www.w3.org/TR/2002/WD-css3-linebox-20020515">http://www.w3.org/TR/2002/WD-css3-linebox-20020515</a>
<dt>Latest version:
<dd><a
href="http://www.w3.org/TR/css3-linebox">http://www.w3.org/TR/css3-linebox</a>
<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>Authors:
<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.
<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>
<li><a href="#changes">Changes from Previous Working Draft</a>
</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.
<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). When the block
progression dimension of a box
B is less than the similar dimension of the line box containing it, the alignment
of B within the 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>When several inline boxes cannot fit within a single line box,
they are distributed among two or more block-progression stacked line boxes. 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 element</b> which wraps all the
inline children of the block element, including the anonymous inline elements.
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 advance (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 advance or not, depending on the line stacking strategy.</p>
<p>When the total inline-progression advance 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>Since an inline box may not exceed the inline-progression width of a line box, long inline boxes
are 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. 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 advance 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 determines 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
<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>
<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. Possible values:</p>
<dl>
<dt><strong>auto</strong>
<dd>The block-progression dimension is based either on the em square determined
by the element font-size property value or the cell-height (ascender + descender)
related to the 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 element font-size. </dd>
<dt>text-size</dt>
<dd>The block-progression dimension is based on the cell-height (ascender +
descender) related to the 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>
</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 elements (if any).</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 the block-progression dimension of the box is given by the
<a class="noxref" href="http://www.w3.org/TR/REC-CSS2/visudet.html#propdef-height">
<span class="propinst-height">'height'</span></a> or the 'width' property
depending on the text flow.) 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 elements 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 minimum extended block-progression dimension 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'. This is equivalent to setting its line-height to
the font-size of its ancestor block element.</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. </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 computed value of the property is the ancestor block element
font-size.</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>
<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 'stack-height' is used in the
context of this property description to indicate the block-progression advance
for the line boxes. Possible values:<dl>
<dt><strong>inline-line-height</strong>
<dd>The stack-height is the smallest value that contains the <i>extended</i>
block progression dimension 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</i>
extended block progression dimension.<dt>block-line-height</dt>
<dd>The stack-height is determined by the block element 'line-height' property
value. The 'line-height' property value is ignored for inline elements. For
alignment purpose, this case is similar to the minimum extended block
progression dimension 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.</dd>
<dt>max-height</dt>
<dd>The stack-height 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.</dd>
<dt>grid-height</dt>
<dd>The stack-height 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.</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 stack-height, 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 stack-height, include the adjusted top-edge and
bottom-edge of any characters that have a baseline-shift.
<dt>disregard-shifts</dt>
<dd>In determining the stack-height, 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
horizontally. This text is positioned relative to the alphabetic baseline,
shown in blue. Example 2 shows a typical ideographic glyph positioned on the
horizontal ideographic baseline. Note that the EM Box is positioned
differently for these two cases. Examples 3 and 4 show the same set of
baselines used in vertical writing. The Latin text, example 3, is shown with
a glyph-orientation of 90 degrees which is typical for proportionally space
Latin glyphs in vertical writing. Even though the ideographic glyph in
Example 4 is positioned on the vertical ideographic baseline, because it is
centered in the EM box, all glyphs with the same EM Box are centered,
vertically, with respect to one another.
</div>
<p>The font tables for a font include font characteristics for the individual
glyphs in the font. CSS assumes that the font tables include, for each glyph
in the font, one width value, one alignment-baseline and one alignment-point
for the horizontal writing-modes. If vertical writing-modes are supported,
then each glyph must have another width value, alignment-baseline and
alignment-point for the vertical writing-modes. (Even though it is specified
as a width, for vertical writing-modes the width is used in the vertical
direction.)
<p>The script to which a glyph belongs determines an alignment-baseline to
which the glyph is to be aligned. The position of this baseline in the design
space coordinate system determines the default block progression direction
position of the alignment-point. The inline progression direction position of
the alignment-point is on the start-edge of the glyph.
<div class="figure">
<p><img alt="alignment in em box" height="110"
src="AlignmentPointsMixedScriptsOnBaselines.gif" width="458">
<p>This figure shows glyphs from three different scripts, each with its EM
box and within the EM box, the baseline table applicable to that glyph. The
alignment-point of each glyph is shown by an "X" on the start edge of the EM
box and by making alignment-baseline blue. The baseline-table of the parent
element of the characters that mapped to these glyphs is shown as a set of
dashed lines.
</div>
<h3 id="AlignmentBaselineType"><span class="secno">4.2. </span>Baseline
identifiers</h3>
<p>The baseline alignment properties control the alignment of child element
with respect to their parent. The positions of these baselines are
illustrated in the following figure:
<div class="figure">
<p><img alt="different baselines" height="102" src="Baselines-rev.gif"
width="587">
<p>This figure shows samples of Gurmukhi (a hanging Indic script), Latin and
ideographic scripts together with most of the baselines defined below. The
thin line around the ideographic glyphs symbolizes the EM box in which these
glyphs are centered. In this figure, the position of the "text-before-edge"
and "text-after-edge" baselines is computed assuming that the "alphabetic"
baseline is the dominant-baseline. The "central" baseline has been omitted
from the figure, but it lies halfway between the "text-before-edge" and
"text-after-edge" baselines, just about where the "math" baseline is shown.
</div>
<p>The baseline-identifiers below are used in this specification. Some of
these are determined by baseline-tables contained in a font as described in
the section describing the <a href="#FontBaseline">baseline information
provided by fonts</a>. Others are computed from other font characteristics as
described below. Whether determined by the font or computed, a derived
baseline-table is constructed with positions of each of the baselines below.
<dl>
<dt><b>alphabetic</b>
<dd>
<p>This identifies the baseline used by most alphabetic and syllabic scripts.
These include, but are not limited to, many Western, Southern Indic,
Southeast Asian (non-ideographic) scripts.
<dt><b>ideographic</b>
<dd>
<p>This identifies the baseline used by ideographic scripts. For historical
reasons, this baseline is at the bottom of the ideographic EM box and not in
the center of the ideographic EM box. See the "central" baseline. The
ideographic scripts include Chinese, Japanese, Korean, and Vietnamese Chu
Nom.
<dt><b>hanging</b>
<dd>
<p>This identifies the baseline used by certain Indic scripts. These scripts
include Devanagari, Gurmukhi and Bengali.
<dt><b>mathematical</b>
<dd>
<p>This identifies the baseline used by mathematical symbols.
<dt><b>central</b>
<dd>
<p>This identifies a computed baseline that is at the center of the EM box.
This baseline lies halfway between the text-before-edge and text-after-edge
baselines.
<p class="note">Note. For ideographic fonts, this baseline is often used to
align the glyphs; it is an alternative to the ideographic baseline.
<dt><b>middle</b>
<dd>
<p>This identifies a baseline that is offset from the alphabetic baseline in
the <b>shift-direction</b> by 1/2 the value of the x-height font
characteristic. The position of this baseline may be obtained from the font
data or, for fonts that have a font characteristic for "x-height", it may be
computed using 1/2 the "x-height". Lacking either of these pieces of
information, the position of this baseline may be approximated by the
"central" baseline.
<dt><b>text-before-edge</b>
<dd>
<p>This identifies the before-edge of the EM box. The position of this
baseline may be specified in the baseline-table or it may be calculated.
<p class="note">Note. The position of this baseline is normally around or at
the top of the ascenders, but it may not encompass all accents that can
appear above a glyph. For fonts with ascenders, the value of the "ascent"
font characteristic is used. For ideographic fonts, the position of this
baseline is normally 1 EM in the <b>shift-direction</b> from the
"ideographic" baseline. However, some ideographic fonts have a reduced width
in the inline-progression-direction to allow tighter setting. When such a
font, designed only for vertical writing-modes, is used in a horizontal
writing-mode, the "text-before-edge" baseline may be less than 1 EM from the
text-after-edge.
<dt><b>text-after-edge</b>
<dd>
<p>This identifies the after-edge of the EM box. The position of this
baseline may be specified in the baseline-table or it may be calculated.
<p class="note">Note. For fonts with descenders, the position of this
baseline is normally around or at the bottom of the descenders. For these
fonts the value of the "descent" font characteristic is used. For ideographic
fonts, the position of this baseline is normally at the "ideographic"
baseline.
</dl>
<p>There are, in addition, two computed baselines that are only defined for line
boxes: 'before-edge' and 'after-edge'. For each line box, there is a
dominant-baseline, a baseline-table and a baseline-table font-size which are
those of the nearest block-level ancestor element and are applied to its root
inline element. Depending on the 'line-stacking-strategy' being used, the line
stacking progression (also called stack-height) can be different from the line
block progression dimension. The 'before-edge' and 'after-edge' baselines are
always based on the block progression dimension and are in fact part of its
determination.<p>For an inline element, the <b>extended inline box</b> includes
the maximum extent of their static or relative positioned children located in
the same line box and <i>may</i> include leading specified by their line-height
value. Depending on the line-stacking-strategy value, the extended line box may
have a different block progression dimension. For replaced elements the margin
extents are always added.<p>The following text explains the interaction between
the line-stacking-strategy and the various baseline alignment parameters.<ul>
<li>For 'line-stacking-strategy: inline-line-height', all 'line-height' values
(set for both inline elements and ancestor block element) participate on
the evaluation of the line block progression dimension. The position of the
dominant-baseline on the start edge of the line box is determined after all
vertical (relative) alignments have been performed on the line. The extended
inline boxes of all inline elements include the leading introduced by their
line-height value.</li>
<li>For 'line-stacking-strategy: block-line-height', the ancestor block
'line-height' value participates on the evaluation of the line block
progression dimension. The inline element line-height values are ignored. The
position of the dominant-baseline on the start edge of the line box is
determined by using a virtual 'zero-width' inline box with the block font and
line height properties located on the start edge of the line box. The extended
inline boxes of all inline elements do not include any extra leading.</li>
<li>For 'line-stacking-strategy: max-height' and 'line-stacking-strategy:
grid-height', only the ancestor block 'line-height' value participates on the
evaluation of the line block progression dimension. The inline element
line-height values are ignored. The position of the dominant-baseline on the
start edge of the line box is determined after all vertical (relative)
alignments have been performed on the line. The extended inline boxes of all
inline elements do not include any extra leading.</li>
</ul>
<p>The "before-edge" and "after-edge" baselines are
defined as follows.
<dl>
<dt><b>before-edge</b>
<dd>
<p>The offset of the "before-edge" baseline of the line from the
dominant-baseline of the line is determined by ignoring all extended inline boxes
whose alignment-baseline is either "before-edge" or "after-edge". For the
"before-edge", extents are measured from the dominant-baseline in the
direction toward the top (relative) of the extended inline box. The "before-edge" baseline
offset is set to the maximum extent of the "before-edges" of the extended inline boxes of the remaining areas. If all the
extended inline
boxes in a line box are aligned either to the "before-edge" or to the "after-edge",
then use the offset of the "text-before-edge" baseline of the line as the
offset of the "before-edge" baseline of the line.
<dt><b>after-edge</b>
<dd>
<p>The offset of the "after-edge" baseline of the line from the
dominant-baseline of the line is determined by ignoring all extended inline boxes
whose alignment-baseline is <code>after-edge</code>. For the "after-edge",
extents are measured from the dominant-baseline in the direction toward the
bottom (relative) of the extended inline box. The "after-edge" baseline offset is
set to the negative of the maximum of (1) the maximum extent of the
"after-edges" of the remaining extended inline boxes and (2) the
maximum height of the extended inline boxes that are ignored
minus the offset of the "before-edge" baseline of the line.
<p class="note">Note. If all the extended inline boxes in a line box are aligned to
the "after-edge" then the specification for the "before-edge" will set the
"before-edge" baseline to coincide with the "text-before-baseline" of the
line. Then, case (2) above will determine an offset to the "bottom-edge"
baseline that will align the "before-edge" of the box with the greatest
height to its allocation-rectangle to "before-edge" baseline.
<p class="note">Note. The above specifications for "before-edge" and
"after-edge" have the following three properties: (1) all extended inline boxes
are below the "before-edge", (2) all extended inline boxes are above the "after-edge", and (3)
the distance between the "before-edge" and the "after-edge" cannot be
decreased without violating (1) or (2). The specified placement of the
"before-edge" and "after-edge" is not the only way that (1)-(3) can be
satisfied, but it is the only way they can be satisfied with the smallest
possible offset to the "before-edge".
</dl>
<p dir="ltr">For the purpose of before-edge and after-edge baseline
computation, inline boxes include the maximum extent of their static or
relative positioned children located in the same line box. Maximum alignment
extents are measured by including the half leading extent in the appropriate
direction for non replaced elements and by using the margin extents for
replaced elements.
<p dir="ltr">Examples showing "before-edge" and "after-edge" alignment:
<div class="figure">
<p><img alt="aligning text and images" id="edge" src="ArrowsInText.gif">
<p>The rectangles with lines or arrows are images with an intrinsic size as
shown. The rectangles with no arrows represent images that receive the
default, dominant baseline, alignment. The alignment of the other rectangles
is at the furthest point from the arrow head (which is in the middle when
there are two arrowheads). Examples 1 and 2 show the "before-edge" alignment
is determined by the tallest non-"before-edge" aligned objects: in example 1
this is the default aligned, arrowhead free rectangular image and in example
2 this is the double headed arrow rectangle. Examples 3 and 4 show defaulting
to the "text-before-edge" when all the boxes have either "before-edge" or
"after-edge" alignment. In example 3, the images with "before-edge" alignment
has a taller member than do the "after-edge" aligned images. In example 4,
the tallest image is in the "after-edge" aligned set. Example 5 is a
repetition of example 2 with largest image being an "after-edge" aligned
image.
</div>
<p>There are also four baselines that are defined only for horizontal
writing-modes.
<dl>
<dt><b>top</b>
<dd>
<p>This baseline is the same as the "before-edge" baseline in a horizontal
writing-mode and is undefined in a vertical writing mode.
<dt><b>text-top</b>
<dd>
<p>This baseline is the same as the "text-before-edge" baseline in a
horizontal writing-mode and is undefined in a vertical writing mode.
<dt><b>bottom</b>
<dd>
<p>This baseline is the same as the "after-edge" baseline in a horizontal
writing-mode and is undefined in a vertical writing mode.
<dt><b>text-bottom</b>
<dd>
<p>This baseline is the same as the "text-after-edge" baseline in a
horizontal writing-mode and is undefined in a vertical writing mode.
</dl>
<h3 id="BaselineAlignmentOverview"><span class="secno">4.3. </span>Overview
of the baseline alignment process</h3>
<p>The alignment of an element with respect to its parent is determined by
three things: the scaled-baseline-table of the parent and the
alignment-baseline and alignment-point of the element being aligned. Prior to
alignment, the scaled-baseline-table of the parent may be shifted. The
property specifications below provide the information necessary to align the
parent and child elements.
<p>There are four properties that control alignment of elements to the above
set of baselines: <span class="property"><a
href="#dominant-baseline">'dominant-baseline'</a></span>, <span
class="property"><a
href="#alignment-baseline">'alignment-baseline'</a></span>, <span
class="property"><a href="#baseline-shift">'baseline-shift'</a></span> and
<span class="property"><a
href="#alignment-adjust">'alignment-adjust'</a></span>. These properties are
all independent and are designed so that typically only the specification of
one of the properties is needed to achieve a particular alignment goal.
<p>The primary baseline alignment property is the <span class="property"><a
href="#dominant-baseline">'dominant-baseline'</a></span> property. This
property sets the <b>scaled-baseline-table</b> as a compound value with the
three following components:
<ol>
<li>The dominant-baseline-identifier component is the default <span
class="property"><a
href="#alignment-baseline">'alignment-baseline'</a></span> to be used when
aligning two inline areas.
<li>The baseline-table component specifies the positions of the baselines in
the font design space coordinates. The baseline-table acts something like a
musical staff; it defines particular points along the
<b>block-progression-direction</b> to which glyphs and inline elements can be
aligned.
<li>The baseline-table <span class="property"><a
href="#font-size">'font-size'</a></span> component is used to scale the
positions of the baselines in that baseline table. In a
scaled-baseline-table, the positions of the baselines can be adjusted by
multiplying the design-space coordinate values by the baseline-table
font-size.
</ol>
<p>Because the value of the <a
href="/TR/REC-CSS2/fonts.html#font-family-prop"><span
class="property">'font-family'</span></a> property is a list of fonts, to
insure a consistent choice of baseline-table we define the <em>nominal
font</em> in a font list as the first font in the list for which a glyph data
is available. This is the first that could contain a glyph for each character
encountered. (For this definition, glyph data is assumed to be present if a
font substitution is made or if the font is synthesized.) This definition
insures a content independent determination of the font and baseline table
that is to be used.
<p>For convenience, the specification will sometimes refer to the baseline
identified by the dominant-baseline-identifier component of the
"dominant-baseline" property as the "dominant baseline" (in an abuse of
terminology).
<p>The model also assumes that each glyph has an <span class="property"><a
href="#alignment-baseline">'alignment-baseline'</a></span> value which
specifies the baseline with which the glyph is to be aligned. (The
'alignment-baseline' is called the "Baseline Tag" in the OpenType
baseline-table description.) The initial value of the 'alignment-baseline'
property uses the baseline identifier associated with the given glyph.
Alternate values for 'alignment-baseline' can be useful for glyphs such as a
"*" which are ambiguous with respect to script membership.
<p>The model assumes that the font from which the glyph is drawn also has a
baseline table, the <span class="SVG-Term">font baseline-table</span>. This
baseline table has offsets in units-per-em from the (0,0) point to each of
the baselines the font knows about. In particular, it has the offset from the
glyph's (0,0) point to the baseline identified by the 'alignment-baseline'.
<p>The offset values in the baseline-table are in "design units" which means
fractional units of the EM. CSS calls these <a
href="/TR/REC-CSS2/fonts.html#descdef-units-per-em">"units-per-em"</a>. Thus,
the current <span class="property"><a
href="#font-size">'font-size'</a></span> is used to determine the actual
offset from the dominant baseline to the alternate baselines.
<p>The glyph is aligned so that its baseline identified by its
'alignment-baseline' is aligned with the baseline with the same name from the
dominant baseline-table.
<p>The offset from the dominant baseline of the parent to the baseline
identified by the 'alignment-baseline' is computed using the dominant
baseline-table and dominant baseline-table font-size. The font baseline-table
and font-size applicable to the glyph are used to compute the offset from the
identified baseline to the (0,0) point of the glyph. This second offset is
subtracted from the first offset to get the position of the (0,0) point in
the shift direction. Both offsets are computed by multiplying the baseline
value from the baseline-table times the appropriate font-size value.
<p>If the 'alignment-baseline' identifies the dominant baseline, then the
first offset is zero and the glyph is aligned with the dominant baseline;
otherwise, the glyph is aligned with the chosen alternate baseline.
<p>The third baseline alignment property is the <span class="property"><a
href="#baseline-shift">'baseline-shift'</a></span> property. Like the
properties other than the "dominant-baseline" property, this property does
not change the baseline-table or the baseline-table font-size. It does shift
the whole baseline table of the parent element so that when an inner inline
element is aligned to one of the parents baselines, the position of the inner
inline element is shifted.
<p>The fourth alignment property is the <span class="property"><a
href="#alignment-adjust">'alignment-adjust'</a></span> property. This
property is primarily used for replaced elements. The "alignment-adjust"
property allows the author to assign where, on the start-edge of the object,
the alignment point for that element lies.
<p>For alignment purposes, the margins are added to the replaced elements
dimensions.
<p>In addition to the following definition of these properties, an
informative <a href="#BaselineUsage">appendix: B</a> provides usage examples
of these properties.
<h3 id="dominant-baseline-prop"><span class="secno">4.4. </span>Dominant
baseline: the <span class="property"><a
href="#dominant-baseline">'dominant-baseline'</a></span> property</h3>
<table class="propdef" id="name-12">
<tbody>
<tr>
<td><em>Name:</em>
<td><dfn id="dominant-baseline">dominant-baseline</dfn>
<tr>
<td><em>Value:</em>
<td>auto | use-script | no-change | reset-size | alphabetic | hanging |
ideographic |<br>
mathematical | central | middle | text-after-edge | text-before-edge
<tr>
<td><em>Initial:</em>
<td>auto
<tr>
<td><em>Applies to:</em>
<td>inline-level elements (but see prose)
<tr>
<td><em>Inherited:</em>
<td>no
<tr>
<td><em>Percentages:</em>
<td>N/A
<tr>
<td><em>Media:</em>
<td>visual
<tr>
<td><em>Computed value:</em>
<td>specified value (except for initial and inherit)
</table>
<p>The <span class="property"><a
href="#dominant-baseline">'dominant-baseline'</a></span> property is used to
determine or re-determine a scaled-baseline-table. A scaled-baseline-table is
a compound value with three components:
<ul>
<li>a baseline-identifier for the dominant baseline; it can be qualified as
the 'dominant' baseline-identifier (or 'dominant baseline' in short); the
baseline-identifier is basically an <span class="property"><a
href="#alignment-baseline">'alignment-baseline'</a></span> value.
<li>a derived baseline-table which contains definition for additional
baseline-identifiers related to various scripts,
<li>and a baseline-table font-size.
</ul>
<p>Some values of the property re-determine all three values; other only
reestablish the baseline-table font-size. Values for the property have the
following meaning:
<dl>
<dt><span class="attr-value">auto</span>
<dd>If this property occurs on a block or inline-block element, then the user
agent behavior depends on the value of the <span class="property"><a
href="#script">'script'</a></span> property. If the value of the script
property is 'auto, the 'auto' value is equivalent to 'alphabetic' for
horizontal <span class="property"><a
href="#writing-mode">'writing-mode'</a></span> values and 'central' for
vertical <span class="property"><a
href="#writing-mode">'writing-mode'</a></span> values. If the value of the
script property is other than 'auto', the 'auto' value is equivalent to
'use-script'
<dd> Otherwise, if this property occurs on an inline-level element, then the
baseline-identifier and the baseline-table components remain the same as
those of the parent element. The baseline-table font-size also remains the
same as the parent's one, unless the computed 'baseline-shift' value actually
shifts the baseline; then the baseline-table font-size is set to the value of
the 'font-size' property on this element. If there is no parent element, the
dominant-baseline components are set as for the block elements.
<dt><span class="attr-value">use-script</span>
<dd>The dominant baseline-identifier is set using the computed value of the
<span class="property"><a href="#script">'script'</a></span> property. The
<span class="property"><a href="#writing-mode">'writing-mode'</a></span>
value, whether horizontal or vertical is used to select the baseline-table
that correspond to that baseline-identifier. The baseline-table font-size
component is set to the value of the 'font-size' property on this element.
<dt><span class="attr-value">no-change</span>
<dd>The dominant baseline-identifier, the baseline-table and the
baseline-table font-size remain the same as that of the parent.
<dt><span class="attr-value">reset-size</span>
<dd>The dominant baseline-identifier and the baseline table remain the same,
but the baseline-table font-size is changed to the value of the <a
href="/TR/REC-CSS2/fonts.html#font-size-props"><span
class="property">'font-size'</span></a> property on this element. This
re-scales the baseline table for the current 'font-size'.
<dt><span class="attr-value">alphabetic</span>
<dd>The dominant baseline-identifier is set to the 'alphabetic' baseline, the
derived baseline-table is constructed using the 'alphabetic' baseline-table
in the nominal font, and the baseline-table font-size is changed to the value
of the 'font-size' property on this element. (The 'alphabetic' baseline is
the standard baseline for Roman scripts.)
<dt><span class="attr-value">hanging</span>
<dd>The dominant baseline-identifier is set to the 'hanging' baseline, the
derived baseline- table is constructed using the 'hanging' baseline-table in
the nominal font, and the baseline-table font-size is changed to the value of
the 'font-size' property on this element.
<dt><span class="attr-value">ideographic</span>
<dd>The dominant baseline-identifier is set to the 'ideographic' baseline,
the derived baseline- table is constructed using the 'ideographic'
baseline-table in the nominal font, and the baseline-table font-size is
changed to the value of the 'font-size' property on this element.
<dt><span class="attr-value">mathematical</span>
<dd>The dominant baseline-identifier is set to the 'mathematical' baseline,
the derived baseline- table is constructed using the 'mathematical'
baseline-table in the nominal font, and the baseline-table font-size is
changed to the value of the 'font-size' property on this element.
<dt>central
<dd>The dominant baseline-identifier is set to be 'central'. The derived
baseline-table is constructed from the defined baselines in a baseline-table
in the nominal font. That font baseline-table is chosen using the following
priority order of baseline-table names: 'ideographic', 'alphabetic',
'hanging' and 'mathematical'. The baseline-table is changed to the value of
the 'font-size' property on this element.
<dt>middle
<dd>The dominant baseline-identifier is set to be 'middle'. The derived
baseline-table is constructed from the defined baselines in a baseline-table
in the nominal font. That font baseline-table is chosen using the following
priority order of baseline-table names: 'alphabetic', 'ideographic',
'hanging' and 'mathematical'. The baseline-table is changed to the value of
the 'font-size' property on this element.
<dt>text-after-edge
<dd>The dominant baseline-identifier is set to be 'text-after-edge'. The
derived baseline-table is constructed from the defined baselines in a
baseline-table in the nominal font. That font baseline-table is chosen using
the following priority order of baseline-table names: 'alphabetic',
'ideographic', 'hanging' and 'mathematical'. The baseline-table is changed to
the value of the 'font-size' property on this element.
<dt>text-before-edge
<dd>The dominant baseline-identifier is set to be 'text-before-edge'. The
derived baseline-table is constructed from the defined baselines in a
baseline-table in the nominal font. That font baseline-table is chosen using
the following priority order of baseline-table names: 'alphabetic',
'ideographic', 'hanging' and 'mathematical'. The baseline-table is changed to
the value of the 'font-size' property on this element.
</dl>
<p class="note">Note: Computed baselines do not (necessarily) choose a
defining baseline table from the nominal font. The expected baseline-tables
that a font would have are those that correspond to the defined baselines.
The catch is that the positions of the defined baselines -- the 'hanging',
'alphabetic', 'mathematical' and 'ideograph' baselines -- can be specified
differently for different choices of which of these baselines is dominant.
That is, the absolute value of the offset of an alphabetic baseline from the
ideographic baseline in ideographic text may be different from the offset of
the ideographic baseline from the alphabetic baseline in alphabetic text.
Therefore, it matters which baseline-table from the nominal font is used for
the defined baselines.
<p>If there is no baseline-table in the nominal font or if the baseline-table
lacks an entry for the desired baseline, then the user agent may use
heuristics to determine the position of the desired baseline.
<h3 id="alignment-baseline-prop"><span class="secno">4.5. </span>Aligning the
alignment point of an element: the <span class="property"><a
href="#alignment-baseline">'alignment-baseline'</a></span> property</h3>
<table class="propdef" id="name-13">
<tbody>
<tr>
<td><em>Name:</em>
<td><dfn id="alignment-baseline">alignment-baseline</dfn>
<tr>
<td><em>Value:</em>
<td>baseline | use-script | before-edge | text-before-edge | after-edge |
text-after-edge |<br>
central | middle | ideographic | alphabetic | hanging | mathematical
<tr>
<td><em>Initial:</em>
<td>baseline
<tr>
<td><em>Applies to:</em>
<td>inline-level elements
<tr>
<td><em>Inherited:</em>
<td>no
<tr>
<td><em>Percentages:</em>
<td>N/A
<tr>
<td><em>Media:</em>
<td>visual
<tr>
<td><em>Computed value:</em>
<td>specified value (except for initial and inherit)
</table>
<p>This property specifies how an inline-level element is aligned with
respect to its parent. That is, to which of the parent's baselines the
alignment point of this element is aligned. Unlike the 'dominant-baseline'
property the 'alignment-baseline' property has no effect on its children
dominant-baselines.
<p class="note">Note: The <span class="property"><a
href="#alignment-adjust">'alignment-adjust'</a></span> property specifies how
the alignment point is determined and defaults to the baseline with the same
name as the computed value of the alignment-baseline property.
<p>Except for 'use-script', all baseline values refer to the respective
baseline-identifier components of the dominant-baseline of the parent, and
glyphs within the element are aligned similarly to the element itself. The
description for 'use-script' covers these points specifically. The property
values have the following meanings:
<dl>
<dt><strong>baseline</strong>
<dd>The alignment-point of the element being aligned is aligned with the
dominant baseline of the parent.
<dt><strong>use-script</strong>
<dd>If the element <span class="property"><a
href="#script">'script'</a></span> property value is 'auto', the alignment
point of each glyph is aligned with the baseline-identifier of the script to
which the glyph belongs. If the element <span class="property"><a
href="#script">'script'</a></span> property value is other than 'auto', the
alignment point of each glyph is aligned with the baseline-identifier
specified by the <span class="property"><a href="#script">'script'</a></span>
property. The baseline-identifier position is determined by using the
relevant information related to the parent element dominant-baseline set. The
alignment point of the element itself is aligned as for the 'baseline' value.
<dt><strong>before-edge</strong>
<dd>The alignment point of the box is aligned with the 'before-edge' baseline
of the line box.
<dt><strong>text-before-edge</strong>
<dd>The alignment-point of the element being aligned is aligned with the
<span class="css">'text-before-edge'</span> baseline of the parent.
<dt><strong>after-edge</strong>
<dd>The alignment point of the box is aligned with the 'after-edge' baseline
of the line box.
<dt><strong>text-after-edge</strong>
<dd>The alignment-point of the element being aligned is aligned with the
<span class="css">'text-after-edge'</span> baseline of the parent.
<dt><strong>central</strong>
<dd>The alignment point of the box is aligned with the 'central' baseline of
the parent.
<dt><strong>middle</strong>
<dd>The alignment point of the box is aligned with the 'middle' baseline of
the parent.
<dt><strong>ideographic</strong>
<dd>The alignment-point of the element being aligned is aligned with the
'ideographic' baseline of the parent.
<dt><strong>alphabetic</strong>
<dd>The alignment-point of the element being aligned is aligned with the
lower baseline of the parent.
<dt><strong>hanging</strong>
<dd>The alignment-point of the element being aligned is aligned with the
hanging baseline of the parent.
<dt><strong>mathematical</strong>
<dd>The alignment-point of the element being aligned is aligned with the
mathematical baseline of the parent.
</dl>
<p>The values: before-edge, text-before-edge, after-edge and text-after-edge
all work relatively to the writing-mode property values. For example
'before-edge' means 'top' in an horizontal writing mode and 'right' in a
vertical writing mode.
<p class="note"><b>Note.</b> The reason why 'baseline' is the initial value
instead of 'use-script' (called 'auto' in the similar XSL property) has to do
with the fact that most fonts today are designed with an alignment point
located at the 'alphabetical' level, even for glyphs belonging to non Latin
scripts. User agents have to deal with that constraint, and therefore they
use the 'baseline' value as initial.
<h3 id="alignment-adjust-prop"><span class="secno">4.6. </span>Setting the
alignment point: the <span class="property"><a
href="#alignment-adjust">'alignment-adjust'</a></span> property</h3>
<table class="propdef" id="name-14">
<tbody>
<tr>
<td><em>Name:</em>
<td><dfn id="alignment-adjust">alignment-adjust</dfn>
<tr>
<td><em>Value:</em>
<td>auto | baseline | before-edge | text-before-edge | middle | central |
after-edge | text-after-edge | ideographic | alphabetic | hanging |
mathematical | <a
href="/TR/REC-CSS2/syndata.html#percentage-units"><percentage></a> | <a
href="/TR/REC-CSS2/syndata.html#length-units"><length></a>
<tr>
<td><em>Initial:</em>
<td>auto
<tr>
<td><em>Applies to:</em>
<td>inline-level elements
<tr>
<td><em>Inherited:</em>
<td>no
<tr>
<td><em>Percentages:</em>
<td>refers to the 'line-height' of the element
<tr>
<td><em>Media:</em>
<td>visual
<tr>
<td><em>Computed value:</em>
<td>see text
</table>
<p>The <span class="property"><a
href="#alignment-adjust">'alignment-adjust'</a></span> property allows more
precise alignment of elements, such as graphics, that do not have a
baseline-table or lack the desired baseline in their baseline-table. With the
<span class="property"><a
href="#alignment-adjust">'alignment-adjust'</a></span> property, the position
of the baseline identified by the <span class="property"><a
href="#alignment-baseline">'alignment-baseline'</a></span> can be explicitly
determined. It also determines precisely the alignment point for each glyph
within a textual element. The user agent should use heuristics to determine
the position of a non existing baseline for a given element.
<p>Values for the property have the following meaning:
<dl>
<dt><strong>auto</strong>
<dd>For each glyph corresponding to textual information within the element,
the alignment-point is the intersection of the start-edge of the glyph box
and the block-progression-direction position of the alignment point from the
font. Padding, border or margin do not affect that alignment point. The
alignment point of the inline-level element itself is at the intersection of
the start-edge of the first inline box and the baseline identified by the
<span class="property"><a
href="#alignment-baseline">'alignment-baseline'</a></span> property if this
baseline exists in the baseline-table for the element dominant-baseline. If
that specific baseline does not exist, the user agent may use heuristics to
determine where that missing baseline would be. For other inline box content
like images, the user agent will use heuristics to determine the position of
the alignment point. For example when the resulting baseline is 'alphabetic'
or 'ideographic', it is expected that the alignment point will be at the
intersection of the start-edge and the after-edge of the inline box,
including its respective margin. If the resulting baseline is 'hanging', the
intersection of the start-edge and the before-edge of the inline box,
including its respective margin should be used instead.<dd>When the
'alignment-baseline' property is set to either 'after-edge' or 'before-edge',
the 'alignment-adjust: auto' value is equivalent to 'after-edge' or
'before-edge' respectively.<dt><strong>baseline</strong>
<dd>The alignment point is at the intersection of the start-edge of the
element and the dominant-baseline of the element.
<dt><strong>before-edge</strong>
<dd>The alignment point is at the intersection of the start-edge of the
element and the before-edge of the extended inline box of the element. This may
include or not the line-height of the element, depending on the
line-stacking-strategy.<dt><strong>text-before-edge</strong>
<dd>The alignment point is at the intersection of the start-edge of the
element and the <span class="css">'text-before-edge'</span> baseline of the
element.
<dt><strong>central</strong>
<dd>The alignment point is at the intersection of the start-edge of the
element and the 'central' baseline of the element.
<dt><strong>middle</strong>
<dd>The alignment point is at the intersection of the start-edge of the
element and the 'middle' baseline of the element.
<dt><strong>after-edge</strong>
<dd>The alignment point is at the intersection of the start-edge of the
element and the after-edge of the extended inline box of the element. This may
include or not the line-height of the element, depending on the
line-stacking-strategy.<dt><strong>text-after-edge</strong>
<dd>The alignment point is at the intersection of the start-edge of the
element and the <span class="css">'text-after-edge'</span> baseline of the
element.
<dt><strong>ideographic</strong>
<dd>The alignment point is at the intersection of the start-edge of the
element and the 'ideographic' baseline of the element.
<dt><strong>alphabetic</strong>
<dd>The alignment point is at the intersection of the start-edge of the
element and the 'alphabetic' baseline of the element.
<dt><strong>hanging</strong>
<dd>The alignment point is at the intersection of the start-edge of the
element and the 'hanging' baseline of the element.
<dt><strong>mathematical</strong>
<dd>The alignment point is at the intersection of the start-edge of the
element and the 'mathematical' baseline of the element.
<dt><strong><percentage></strong>
<dd>The computed value of the property is this percentage multiplied by the
computed 'line-height' of the element. The alignment point is on the
start-edge of the inline box. Its position along the start-edge relative to
the intersection of the dominant-baseline and the start-edge is offset by the
computed value. The offset is opposite to the shift-direction (positive
value) or in the shift-direction (negative value). A value of '0%' makes the
dominant-baseline the alignment point.
<dt><strong><length></strong>
<dd>The alignment-point is on the start-edge of the inline box. Its position
along the start-edge relative to the intersection of the dominant-baseline
and the start-edge is offset by the <length> value. The offset is
opposite to the shift-direction (positive value) or in the shift-direction
(negative value). A value of '0cm' makes the dominant-baseline the alignment
point.
</dl>
<h3 id="baseline-shift-prop"><span class="secno">4.7. </span>Repositioning
the dominant baseline: the <span class="property"><a
href="#baseline-shift">'baseline-shift'</a></span> property</h3>
<table class="propdef" id="name-15">
<tbody>
<tr>
<td><em>Name:</em>
<td><dfn id="baseline-shift">baseline-shift</dfn>
<tr>
<td><em>Value:</em>
<td>baseline | sub | super | <a
href="/TR/REC-CSS2/syndata.html#percentage-units"><percentage></a> | <a
href="/TR/REC-CSS2/syndata.html#length-units"><length></a>
<tr>
<td><em>Initial:</em>
<td>baseline
<tr>
<td><em>Applies to:</em>
<td>inline-level elements
<tr>
<td><em>Inherited:</em>
<td>no
<tr>
<td><em>Percentages:</em>
<td>refers to the 'line-height' of the parent element
<tr>
<td><em>Media:</em>
<td>visual
<tr>
<td><em>Computed value:</em>
<td>see text
</table>
<p>The <span class="property"><a
href="#baseline-shift">'baseline-shift'</a></span> property allows
repositioning of the dominant-baseline relative to the dominant-baseline. The
shifted object might be a sub- or superscript. Within the shifted element,
the whole baseline table is offset; not just a single baseline. For sub- and
superscript, the amount of offset is determined from the nominal font of the
parent.
<p>Values for the property have the following meaning:
<dl>
<dt><strong>baseline</strong>
<dd>There is no baseline shift; the dominant baseline remains in its original
position.
<dt><strong>sub</strong>
<dd>The dominant baseline is shifted to the default position for subscripts.
The offset for this position is determined by the font data for the parent
nominal font as adjusted by the dominant baseline-table font-size of the
parent element. If there is no applicable font data the User Agent may use
heuristic to determine the offset.
<dt><strong>super</strong>
<dd>The dominant baseline is shifted to the default position for
superscripts. The offset for this position is determined by the font data for
the parent nominal font as adjusted by the dominant baseline-table font-size
of the parent element. If there is no applicable font data the User Agent may
use heuristic to determine the offset.
<dt><strong><percentage></strong>
<dd>The computed value of the property is this percentage multiplied by the
computed 'line-height' of the parent element. The dominant-baseline is
shifted in the shift-direction (positive value) or opposite to the
shift-direction (negative value) of the parent area by the computed value. A
value of '0%' is equivalent to 'baseline'.
<dt><strong><length></strong>
<dd>The dominant-baseline is shifted in the shift-direction (positive value)
or opposite to the shift-direction (negative value) of the parent area by the
<length> value. A value of '0cm' is equivalent to 'baseline'.
</dl>
<p class="note"><b>Note.</b> Although it may seem that 'baseline-shift' and
<span class="property"><a
href="#alignment-adjust">'alignment-adjust'</a></span> properties are doing
the same thing, there are important differences. For <span
class="property"><a href="#alignment-adjust">'alignment-adjust'</a></span>
the percentage values refer to the 'line-height' of the element being
aligned. For 'baseline-shift the percentage values refer to the 'line-height'
of the parent element. Similarly, it is the 'sub' and 'super' offsets of the
parent that are used to align the shifted baseline rather than the 'sub' and
'super' offsets of the element being positioned. To ensure a consistent sub-
or superscript position, it makes more sense to use the parent as the
reference rather than the subscript element which may have a changed
"line-height" due to "font-size" changes in the sub- or superscript
element.<br>
Using the "alignment-adjust" property is more suitable for positioning
elements, such as graphics, that have no internal textual structure. Using
the "baseline-shift" property is intended for sub- and superscripts where the
positioned element may itself be textual. The baseline-shift provides a way
to define a specific baseline offset other than the named offsets that are
defined relative to the dominant-baseline. In addition, having
"baseline-shift" makes it easier for a tool to generate the relevant
properties; many formatting programs already have a notion of baseline shift.
<h3 id="vertical-align-prop"><span class="secno">4.8. </span>Vertical
alignment: the <span class="property"><a
href="#vertical-align">'vertical-align'</a></span> shorthand baseline
alignment property</h3>
<table class="propdef" id="name-16">
<tbody>
<tr>
<td><em>Name:</em>
<td><dfn id="vertical-align">vertical-align</dfn>
<tr>
<td><em>Value:</em>
<td>auto | use-script | baseline | sub | super | top | text-top | central |
middle | bottom | text-bottom | <a
href="/TR/REC-CSS2/syndata.html#percentage-units"><percentage></a> | <a
href="/TR/REC-CSS2/syndata.html#length-units"><length></a>
<tr>
<td><em>Initial:</em>
<td>not defined for shorthand properties
<tr>
<td><em>Applies to:</em>
<td>inline-level and 'table-cell' elements
<tr>
<td><em>Inherited:</em>
<td>no
<tr>
<td><em>Percentages:</em>
<td>refers to the 'line-height' of the element itself
<tr>
<td><em>Media:</em>
<td>visual
<tr>
<td><em>Computed value:</em>
<td>see text
</table>
<p>This property affects the vertical positioning of the inline boxes generated
by an inline-level element inside a line box. The following values only have
meaning with respect to a parent inline-level element, or to a parent
block-level element, if that element generates <a
href="/TR/REC-CSS2/visuren.html#anonymous">anonymous inline boxes</a>; they
have no effect if no such parent exists.
<div class="note">
<p><em><strong>Note.</strong> Values of this property have slightly different
meanings in the context of tables. Please consult the section on <a
href="/TR/REC-CSS2/tables.html#height-layout">table height algorithms</a> for
details.</em>
</div>
<dl>
<dt><strong>auto</strong>
<dd>Align the dominant baseline of the parent box with the equivalent, or
heuristically reconstructed, baseline of the element inline box. If the element doesn't have
a baseline, align the bottom of the inline box, including its margin with the
parent's dominant baseline. If there is no parent or if there is a change of
flow orientation between this element and its parent, the dominant baseline
is set to 'alphabetic' for horizontal flow and 'central' for vertical flow.
<dt><strong>use-script</strong>
<dd>Align the script preferred baseline of the element (determined by the
computed script value) with the equivalent baseline of the parent element.
<dt><strong>baseline</strong>
<dd>Align the 'alphabetic' baseline of the element with the 'alphabetic' baseline
of the parent element. If the inline element doesn't have an 'alphabetic' baseline, align
the bottom of the box, including its margin for replaced elements, with the
parent's 'alphabetic' baseline. The dominant baseline is set to 'alphabetic'
if there is no parent or if there is a flow orientation change between this
element and its parent, otherwise it is set to 'no-change'.
<dt><strong>central</strong>
<dd>Align the 'central' baseline of the inline element with the central baseline
of the parent.
<dt><strong>middle</strong>
<dd>Align the 'middle' baseline of the inline element with the middle baseline of the parent.
<dt><strong>sub</strong>
<dd>Lower the baseline of the box to the proper position for subscripts of
the parent's box. (This value has no effect on the font size of the element's
text.)
<dt><strong>super</strong>
<dd>Raise the baseline of the box to the proper position for superscripts of
the parent's box. (This value has no effect on the font size of the element's
text.)
<dt><strong>text-top</strong>
<dd>Align the top of the box with the before-edge of the parent element's
font.
<dt><strong>text-bottom</strong>
<dd>Align the bottom of the box with the after-edge of the parent element's
font.
<dt><span class="index-inst" id="ltpercentagegt"
title="<percentage>"><a class="noxref"
href="/TR/REC-CSS2/syndata.html#value-def-percentage" name="x23"><span
class="value-inst-percentage"><strong><percentage></strong></span></a></span>
<dd>Raise (positive value) or lower (negative value) the box by this distance
(a percentage of the computed <a class="noxref"
href="/TR/REC-CSS2/visudet.html#propdef-line-height"><span
class="propinst-line-height">'line-height'</span></a> of the element). The
value '0%' means the same as 'baseline'.
<dt><span class="index-inst" id="ltlengthgt" title="<length>"><a
class="noxref" href="/TR/REC-CSS2/syndata.html#value-def-length"
name="x24"><span
class="value-inst-length"><strong><length></strong></span></a></span>
<dd>Raise (positive value) or lower (negative value) the box by this
distance. The value '0cm' means the same as 'baseline'.
</dl>
<p>The remaining values refer to the line box in which the generated box
appears:
<dl>
<dt><strong>top</strong>
<dd>Align the before edge of the extended inline box with the before-edge of the line box.
<dt><strong>bottom</strong>
<dd>Align the after edge of the extended inline box with the after-edge of the line box.
</dl>
<p>The 'vertical-align' property values affect the baseline alignment
properties for which it is a shorthand in the following manner:
<table border="1">
<tbody>
<tr>
<th>vertical-align value
<th>alignment-baseline
<th>alignment-adjust
<th>baseline-shift
<th>dominant-baseline
<tr>
<th>auto
<td>baseline
<td>auto
<td>baseline
<td>auto
<tr>
<th>use-script
<td>use-script
<td>auto
<td>auto
<td>auto
<tr>
<th>baseline
<td>baseline
<td>auto
<td>baseline
<td><span class="propinst-vertical-align">alphabetic <i>(if no parent or
different flow from parent)</i></span><br>
no-change <i>(otherwise)</i>
<tr>
<th>sub
<td>baseline
<td>auto
<td>sub
<td>auto
<tr>
<th>super
<td>baseline
<td>auto
<td>super
<td>auto
<tr>
<th>top
<td>before-edge
<td>auto
<td>baseline
<td>auto
<tr>
<th>text-top
<td>text-before-edge
<td>auto
<td>baseline
<td>auto
<tr>
<th>central<td>central<td>auto<td>baseline<td>auto<tr>
<th>middle
<td>middle
<td>auto
<td>baseline
<td>auto
<tr>
<th>bottom
<td>after-edge
<td>auto
<td>baseline
<td>auto
<tr>
<th>text-bottom
<td>text-after-edge
<td>auto
<td>baseline
<td>auto
<tr>
<th><percentage>
<td>baseline
<td><percentage>
<td>baseline
<td>auto
<tr>
<th><length>
<td>baseline
<td><length>
<td>baseline
<td>auto
</table>
<h3 id="inline-box-align-prop"><span class="secno">4.9. </span>Inline box
alignment: the <span class="property"><a
href="#inline-box-align">'inline-box-align'</a></span> property</h3>
<table class="propdef" id="name-17">
<tbody>
<tr>
<td><em>Name:</em>
<td><dfn id="inline-box-align">inline-box-align</dfn>
<tr>
<td><em>Value:</em>
<td>initial | last | <a
href="/TR/REC-CSS2/syndata.html#percentage-units"><integer></a>
<tr>
<td><em>Initial:</em>
<td>last
<tr>
<td><em>Applies to:</em>
<td>inline-block-level elements
<tr>
<td><em>Inherited:</em>
<td>no
<tr>
<td><em>Percentages:</em>
<td>N/A
<tr>
<td><em>Media:</em>
<td>visual
<tr>
<td><em>Computed value:</em>
<td>specified value (except for initial and inherit)
</table>
<p>The <span class="property"><a
href="#inline-box-align">'inline-box-align'</a></span> property determines
which line of a multi-line inline block align with the previous and next
inline elements within a line. The alignment strategy for the inline lock
itself (i.e. the definition of it alignment point and which parent baseline
should be used for the alignment) is determined by the inline block element
baseline alignment properties applicable to the line being used for the
alignment. This property has no effect for single line inline block. Possible
values:
<dl>
<dt>initial
<dd>Use the initial line of the inline block element for alignment purpose.
<dt>last
<dd>Use the last line of the inline block element for alignment purpose.
<dt><integer>
<dd>Use nth line (as determined by the integer value) of the inline block
element for alignment purpose.
</dl>
<hr>
<h2 id="Initial"><span class="secno">5. Initial line and Drop initial</span></h2>
<h3 id="InitialLine"><span class="secno">5.1. </span>Initial line</h3>
<p>On a block element containing inline elements, the initial line is very often
presented differently. For example it may use a difference typeface, a color,
font-size or even casing (like all uppercase). The presentation of that initial
line can be controlled by applying a limited set of style properties to the
::first-line pseudo element. Only the following properties can be applied to the
::first-line pseudo elements:<ul>
<li>font properties</li>
<li>color properties</li>
<li>background properties</li>
<li>text decoration properties</li>
<li>baseline alignment properties</li>
<li>'word-spacing'</li>
<li>'letter-spacing'</li>
<li>'line-height' (may be ignored depending on the block line-stacking strategy)</li>
<li>'text-shadow'</li>
<li>'clear'</li>
</ul>
<p>Although there is no properties only applicable to ::first-line pseudo
elements, in essence the 'text-indent' property which is applied to
'block-level' elements is in fact only effective on the first line of the block
element.</p>
<h3 id="DropInitial"><span class="secno">5.2. </span>Drop Initial overview</h3>
<p>Drop initial is a typographic effect emphasizing the initial letter(s) of a block
element with a presentation similar to a 'floated' element. It can be described as the combination of the following effects:
<ul>
<li>
<p>For the purpose of drop initial, an initial letter has two alignment points: an
'after' alignment point and a 'before' alignment point. (For
writing-mode:lr-tb, 'after' corresponds to bottom and 'before' to 'top').
<li>
<p>The 'after' alignment point connects with one of the alignment point of
the n<sup>th</sup> line of the block element of which the initial letter is
part of. The value 'n' is the number of lines by which the initial letter is
dropped. That connection point is called the primary connection point. The
union of the two alignment lines makes a connection line.
<li>
<p>If no drop initial size is explicitly provided, there is a secondary connection
point where the 'before' alignment points connects with one of the alignment
point of the initial line. In that case the initial letter is totally sunken.
<li>
<p>If a drop initial size is provided, there is no secondary connection point as
it would result otherwise in an over constraint situation. In that case the
initial letter may not be totally sunken, especially if the size is provided in
'line' unit with a number larger than the drop.
<li>
<p>The values provided above result in the creation of an 'ink box' which is
filled by the initial letter. Depending on the selected alignment points, part
of the glyphs may bleed beyond the ink box.
<li>
<p>The character content of the drop initial influences greatly how the drop
initial
letters are best aligned with the rest of the block element content.
</ul>
<p>The CSS mechanism to 'select' the drop initial content is the ::first-letter
pseudo element. The first letter is defined as including all starting
punctuation characters (defined in Unicode as 'open' (Ps), 'close' (Pe) and
'other' (Po), if any, followed by the first non-punctuation character cluster. A
character cluster may be a single character, a combining sequences (base
character followed by combining characters) or a stacked set of characters (like
in Thai).
<p>Only the following properties can be applied to the ::first-letter pseudo
elements:<ul>
<li>font properties</li>
<li>color properties</li>
<li>background properties</li>
<li>text decoration properties</li>
<li>baseline alignment properties (only if 'float' is 'none')</li>
<li>'text-transform'</li>
<li>'letter-spacing'</li>
<li>'line-height' (may be ignored depending on the block line-stacking strategy)</li>
<li>margin properties</li>
<li>padding properties</li>
<li>border properties</li>
<li>'float'</li>
<li>text-shadow</li>
<li>'clear'</li>
<li>all properties described in this section (drop-initial-...)</li>
</ul>
<p>In addition, one property: 'text-indent' although applying to block-level
elements is in fact effective on its first line of text and has therefore an
influence on the indentation of the first-letter versus the start edge of the
containing block. Using the 'text-indent' allows the correction of optical
effect (like uppercase 'O') or even pushing the starting piece of the initial
letter in a 'virtual' margin.</p>
<p class="note">Editor's note: Additional drop initial features are desirable
but are not described in this specification:<ul>
<li>
<p class="note">bleeding between the drop initial and its related block content,</li>
<li>
<p class="note">tight wrap between the drop initial and its related block
content</li>
<li>
<p class="note">multiple letter with author control (not possible with
::first-letter)</li>
<li>
<p class="note">multiple size and alignment within the drop initial (required
for French opening guillemet)</li>
</ul>
<p class="note">Some of these features (multiple letter and size) could be
achieved by introducing a new display value, like 'display: drop-initial' which
when applied to an inline element part of the first line could make it behave
like a drop initial inline element.<p>The following figure shows first a simple case of a
three line drop initial, and
second a case of a two line drop initial but with a three line size initial letter.
<div class="figure">
<p> <img alt="simple drop caps" height="121" src="dc-simple.gif" width="376">
<p>Typical drop initial cases: sunken cap and partially raised
cap
</div>
<p>The bottom horizontal line in the first example shows the alignment
between the baseline of the initial letter and the baseline of the third line
of its block element. The primary connection point occurs at the intersection
of these baselines between the two boxes (the third line box and the initial
letter box). The top horizontal line shows a connection point between the top
of the ink of the initial letter and the text-before-edge baseline of the
initial
line. Alternatively, instead of the text-before-edge baseline, a new computed
alignment could be used which correspond loosely to the maximum caps-height
of the initial line.
<p>Typically the ink of drop initial characters 'fills' the space between the
baseline and the text-before-edge, therefore 'taller' characters are
processed accordingly. This is shown in the first two pictures of the
following figure, using first an accentuated letter, and then a letter
without accent.
<div class="figure">
<p> <img alt="drop caps showing case with and without accent" height="148"
src="dc-accents.gif" width="599">
<p>Drop initial with accent and without accent
</div>
<p>The third picture shows a more correct effect with the acute accent drawn
in the upper padding area. This effect is realized by having the secondary
connection point between the initial letter caps height and the maximum caps
height of the initial line.
<p>Typically characters are stretched in both direction to fill the space
between the primary and secondary connection lines (in the absence of an
explicit drop initial size). Even if the character has no 'ink' at the primary
connection line, the stretching is performed as if there were a 'virtual'
point at that level. The following figure demonstrates the effect for the
hyphen-minus character. The other two characters demonstrate the variable
stretching made by the drop initial effect.
<div class="figure">
<p> <img alt="drop cap with period, hyphen and exclamation point"
height="122" src="dc-symbols.gif" width="625">
<p>Drop initial with period, hyphen and exclamation point
</div>
<p>For characters that have only ink 'after' (below) their baseline there is
really no good strategy. It may be better to use the font EM square as
reference for symbols that have no ink at the primary connection line.
<p>Some characters are always expected to be shown as if using their full EM
square, even in drop initial situation. For example, this is the case for all
ideograms and related characters like the Japanese Kana characters. The
following figure shows how the ink of the character representing the number
one in CJK (middle picture) is not stretched to hit the top of the
text-before-edge of the initial line, but is instead stretched following the
same ratio as the character in the left picture. The picture on the right
shows that drop initial can also be used in vertical flow.
<div class="figure">
<p> <img alt="drop cap with ideographs" height="140" src="dc-ideo.gif"
width="521">
<p>Drop initial with ideographic characters
</div>
<p>Drop initial characters can be aligned using a variety of baselines for the
drop initial alignment point used for the primary connection point. The examples
above used the alphabetic and the ideographic baselines. The following
figures compares the usage of the text-after-edge baseline (picture on the
left) and the alphabetic baseline (picture on the right). Note that when the
alphabetic baseline is used for characters that have ink below the baseline,
the actual drop initial effect may occur through many more lines to accommodate
the text-after-edge constraint.
<div class="figure">
<p> <img alt="drop cap with lowercase letters" height="144"
src="dc-lowercase.gif" width="474">
<p>Drop initial with lowercase characters
</div>
<div class="figure">
<p> <img alt="drop cap with uppercase q" height="137" src="dc-upperq.gif"
width="463">
<p>Drop initial with uppercase character with descender
</div>
<p>The drop initial effect may also be used for writing systems which use
different alignment strategies. For example, in Devanagari the hanging
baseline may be preferred. In that case the primary connection point connects the text-after-edge of the
initial letter with the text-after-edge
of the nth line, but the secondary connection point connects the hanging
baselines of the initial letter and the initial line. This is shown in the
following figure:
<div class="figure">
<p> <img alt="drop cap with devanagari" height="129" src="dc-devanagari.gif"
width="225">
<p>Drop initial with hanging devanagari characters
</div>
<p>The drop initial effect is typically based on a number of lines, i.e. the
combined line-height adjusted by the alignment strategies for the connection
lines is used to determine the default size of the drop initial character.
However there is a potential circular issue as the activation of the effect
modifies the content of the lines and therefore may affect their line-height.
The recommended strategy is to determine the drop initial character size using
the initial combined line height and to possibly stretch the character along
the new baseline if the combined line height is modified by the drop initial
effect. The following figure shows the initial text on the left, an incorrect
drop initial effect in the middle (no stretch applied) and a correct effect on
the right (stretch applied).
<div class="figure">
<p> <img alt="drop cap with variable line heights" height="192"
src="dc-variable.gif" width="565">
<p>Drop initial with variable line heights
</div>
<h3 id="DropInitialSize"><span class="secno">5.3. </span>Sizing drop initial, the <span class="property"><a
href="#drop-initial-size">'drop-initial-size'</a></span> and the <span
class="property"><a href="#drop-initial-value">'drop-initial-value'</a> properties</span></h3>
<table cellpadding="0" cellspacing="0" class="propdef" id="name-19">
<tbody>
<tr valign="baseline">
<td><em>Name:</em>
<td><dfn id="drop-initial-value">drop-initial-value</dfn>
<tr valign="baseline">
<td><em>Value:</em>
<td><span class="value-inst-length">initial | <a class="noxref"
href="/TR/REC-CSS2/syndata.html#value-def-integer"><integer></a></span>
<tr valign="baseline">
<td><em>Initial:</em>
<td>initial
<tr valign="baseline">
<td><em>Applies to:</em>
<td>::first-letter pseudo element
<tr valign="baseline">
<td><em>Inherited:</em>
<td>no
<tr valign="baseline">
<td><em>Percentages:</em>
<td>N/A
<tr valign="baseline">
<td><em>Media:</em>
<td><a class="noxref"
href="/TR/REC-CSS2/media.html#visual-media-group">visual</a>
<tr valign="baseline">
<td><em>Computed value:</em>
<td>specified values (except for initial and inherit)
</table>
<p>The <span class="property"><a
href="#drop-initial-value">'drop-initial-value'</a></span> property is the basic
property that activates a drop-initial effect. By providing a value different than
'initial or '1', the primary connection point is moved after the initial line.
Possible values:
<dl>
<dt>initial
<dd>The drop initial letter is aligned on the initial line
<dt><span class="value-inst-integer"><strong><integer></strong></span>
<dd>The drop initial letter is sunken to the nth line (as determined by the
integer value).
</dl>
<table cellpadding="0" cellspacing="0" class="propdef" id="name-20">
<tbody>
<tr valign="baseline">
<td><em>Name:</em>
<td><dfn id="drop-initial-size">drop-initial-size</dfn>
<tr valign="baseline">
<td><em>Value:</em>
<td>auto | <line> | <length> | <percentage>
<tr valign="baseline">
<td><em>Initial:</em>
<td>auto
<tr valign="baseline">
<td><em>Applies to:</em>
<td>::first-letter pseudo element
<tr valign="baseline">
<td><em>Inherited:</em>
<td>no
<tr valign="baseline">
<td><em>Percentages:</em>
<td>refer to combined line height size as provided by drop-initial-value
<tr valign="baseline">
<td><em>Media:</em>
<td><a class="noxref"
href="/TR/REC-CSS2/media.html#visual-media-group">visual</a>
<tr valign="baseline">
<td><em>Computed value:</em>
<td>specified values (except for initial and inherit)
</table>
<p>The <span class="property"><a
href="#drop-initial-size">'drop-initial-size'</a></span> property controls the partial
sinking of the initial letter. Using any other value than 'auto' removes the
secondary connection line constraint. Possible values:
<dl>
<dt>auto
<dd>The drop initial letter is sized according to the constraints created by the
the ink filling strategy and the two connection lines.
<dt> <strong><line></strong>
<dd>The drop initial letter is sized using the combined line height of the nth
lines (as determined by the line value). The letter may be stretched on one
dimension if the line height of each line is variable to avoid circular
issues.
<dt><length>
<dd>The drop initial letter is sized using the length value.
<dt><percentage>
<dd>The drop initial letter is sized relatively to the combined line height of
the n lines determined by the <span class="property"><a
href="#drop-initial-value">'drop-initial-value'</a></span> property value.
</dl>
<h3 id="DropInitialAlign"><span class="secno">5.4. </span>Aligning drop initial: the <span
class="property"><a
href="#drop-initial-before-align">'drop-initial-before-align'</a></span>, <span
class="property"><a
href="#drop-initial-before-adjust">'drop-initial-before-adjust'</a></span>, <span
class="property"><a
href="#drop-initial-after-align">'drop-initial-after-align'</a></span> and <span
class="property"><a
href="#drop-initial-after-adjust">'drop-initial-after-adjust'</a></span> properties</h3>
<table cellpadding="0" cellspacing="0" class="propdef" id="name-21">
<tbody>
<tr valign="baseline">
<td><em>Name:</em>
<td><dfn id="drop-initial-after-align">drop-initial-after-align</dfn>
<tr valign="baseline">
<td><em>Value:</em>
<td><'alignment-baseline'>
<tr valign="baseline">
<td><em>Initial:</em>
<td>baseline
<tr valign="baseline">
<td><em>Applies to:</em>
<td>::first-letter pseudo element
<tr valign="baseline">
<td><em>Inherited:</em>
<td>no
<tr valign="baseline">
<td><em>Percentages:</em>
<td>N/A
<tr valign="baseline">
<td><em>Media:</em>
<td><a class="noxref"
href="/TR/REC-CSS2/media.html#visual-media-group">visual</a>
<tr valign="baseline">
<td><em>Computed value:</em>
<td>specified values (except for initial and inherit)
</table>
<p>The <span class="property"><a
href="#drop-initial-after-align">'drop-initial-after-align'</a></span> property
determines which alignment line within the nth line box (n being defined by
the <span class="property"><a
href="#drop-initial-value">'drop-initial-value'</a></span> property) is used at the
primary connection point with the initial letter box. The values are the same
as the 'alignment-baseline' property values.
<table cellpadding="0" cellspacing="0" class="propdef" id="name-22">
<tbody>
<tr valign="baseline">
<td><em>Name:</em>
<td><dfn id="drop-initial-after-adjust">drop-initial-after-adjust</dfn>
<tr valign="baseline">
<td><em>Value:</em>
<td>central | middle | after-edge | text-after-edge | ideographic |
alphabetic | mathematical | <percentage> | <length>
<tr valign="baseline">
<td><em>Initial:</em>
<td>text-after-edge
<tr valign="baseline">
<td><em>Applies to:</em>
<td>::first-letter pseudo element
<tr valign="baseline">
<td><em>Inherited:</em>
<td>no
<tr valign="baseline">
<td><em>Percentages:</em>
<td>refer to combined line height size as provided by drop-initial-value
<tr valign="baseline">
<td><em>Media:</em>
<td><a class="noxref"
href="/TR/REC-CSS2/media.html#visual-media-group">visual</a>
<tr valign="baseline">
<td><em>Computed value:</em>
<td>specified values (except for initial and inherit)
</table>
<p>The <span class="property"><a
href="#drop-initial-after-adjust">'drop-initial-after-adjust'</a></span> property sets
the alignment point of the drop initial for the primary connection point.
Possible values:
<dl>
<dt><strong>central</strong>
<dd>The alignment point is at the intersection of the end-edge of the element
and the 'central' baseline of the element.
<dt><strong>middle</strong>
<dd>The alignment point is at the intersection of the end-edge of the element
and the 'middle' baseline of the element.
<dt><strong>after-edge</strong>
<dd>The alignment point is at the intersection of the end-edge of the element
and the 'after-edge' of the extended inline box of the element. This may include
or not the line-height of the element, depending on the line-stacking-strategy.
<dt><strong>text-after-edge</strong>
<dd>The alignment point is at the intersection of the end-edge of the element
and the <span class="css">'text-after-edge'</span> baseline of the element.
<dt><strong>ideographic</strong>
<dd>The alignment point is at the intersection of the end-edge of the element
and the 'ideographic' baseline of the element.
<dt><strong>alphabetic</strong>
<dd>The alignment point is at the intersection of the end-edge of the element
and the 'alphabetic' baseline of the element.
<dt><strong>hanging</strong>
<dd>The alignment point is at the intersection of the end-edge of the element
and the 'hanging' baseline of the element.
<dt><strong>mathematical</strong>
<dd>The alignment point is at the intersection of the end-edge of the element
and the 'mathematical' baseline of the element.
<dt><strong><percentage></strong>
<dd>The computed value of the property is this percentage multiplied by the
computed 'line-height' of the element. The alignment point is on the end-edge
of the inline box and is offset from the after-edge by the computed value. A
value of '0%' makes the text-after-edge the alignment point.
<dt><strong><length></strong>
<dd>The alignment-point is on the end-edge of the inline box. Its position
along the end-edge is offset from the after-edge by the <length> value.
A value of '0cm' makes the text-after-edge the alignment point.
</dl>
<table cellpadding="0" cellspacing="0" class="propdef" id="name-23">
<tbody>
<tr valign="baseline">
<td><em>Name:</em>
<td><dfn id="drop-initial-before-align">drop-initial-before-align</dfn>
<tr valign="baseline">
<td><em>Value:</em>
<td>caps-height | <'alignment-baseline'>
<tr valign="baseline">
<td><em>Initial:</em>
<td>caps-height
<tr valign="baseline">
<td><em>Applies to:</em>
<td>::first-letter pseudo element
<tr valign="baseline">
<td><em>Inherited:</em>
<td>no
<tr valign="baseline">
<td><em>Percentages:</em>
<td>N/A
<tr valign="baseline">
<td><em>Media:</em>
<td><a class="noxref"
href="/TR/REC-CSS2/media.html#visual-media-group">visual</a>
<tr valign="baseline">
<td><em>Computed value:</em>
<td>specified values (except for initial and inherit)
</table>
<p>The <span class="property"><a
href="#drop-initial-before-align">'drop-initial-before-align'</a></span> property
determines which alignment line within the initial line box is used at
the secondary connection point with the initial letter box. This property is
only effective is the value of the <span class="property"><a
href="#drop-initial-size">'drop-initial-size'</a></span> property is 'auto'. Possible
values:
<dl>
<dt>caps-height
<dd>The caps-height alignment line is used.
<dt> <strong><'alignment-baseline'></strong>
<dd>The values are the same as the 'alignment-baseline' property values.
</dl>
<table cellpadding="0" cellspacing="0" class="propdef" id="name-24">
<tbody>
<tr valign="baseline">
<td><em>Name:</em>
<td><dfn id="drop-initial-before-adjust">drop-initial-before-adjust</dfn>
<tr valign="baseline">
<td><em>Value:</em>
<td>before-edge | text-before-edge | central | middle | hanging |
mathematical | <percentage> | <length>
<tr valign="baseline">
<td><em>Initial:</em>
<td>text-before-edge
<tr valign="baseline">
<td><em>Applies to:</em>
<td>::first-letter pseudo element
<tr valign="baseline">
<td><em>Inherited:</em>
<td>no
<tr valign="baseline">
<td><em>Percentages:</em>
<td>refer to combined line height size as provided by drop-initial-value
<tr valign="baseline">
<td><em>Media:</em>
<td><a class="noxref"
href="/TR/REC-CSS2/media.html#visual-media-group">visual</a>
<tr valign="baseline">
<td><em>Computed value:</em>
<td>specified values (except for initial and inherit)
</table>
<p>The <span class="property"><a
href="#drop-initial-before-adjust">'drop-initial-before-adjust'</a></span> property
sets the alignment point of the drop initial for the secondary connection point.
This property is only effective is the value of the <span class="property"><a
href="#drop-initial-size">'drop-initial-size'</a></span> property is 'auto'. Possible
values:
<dl>
<dt><strong>before-edge</strong>
<dd>The alignment point is at the intersection of the end-edge of the element
and the 'before-edge' of the extended inline box of the element. This may
include or not the line-height of the element, depending on the
line-stacking-strategy.
<dt><strong>text-before-edge</strong>
<dd>The alignment point is at the intersection of the end-edge of the element
and the <span class="css">'text-before-edge'</span> baseline of the element.
<dt><strong>central</strong>
<dd>The alignment point is at the intersection of the end-edge of the element
and the 'central' baseline of the element.
<dt><strong>middle</strong>
<dd>The alignment point is at the intersection of the end-edge of the element
and the 'middle' baseline of the element.
<dt><strong>hanging</strong>
<dd>The alignment point is at the intersection of the end-edge of the element
and the 'hanging' baseline of the element.
<dt><strong>mathematical</strong>
<dd>The alignment point is at the intersection of the end-edge of the element
and the 'mathematical' baseline of the element.
<dt><strong><percentage></strong>
<dd>The computed value of the property is this percentage multiplied by the
computed 'line-height' of the element. The alignment point is on the end-edge
of the inline box and is offset from the text-before-edge by the computed
value. A value of '0%' makes the text-before-edge the alignment point.
<dt><strong><length></strong>
<dd>The alignment-point is on the end-edge of the inline box. Its position
along the end-edge is offset from the text-before-edge by the <length>
value. A value of '0cm' makes the text-before-edge the alignment point.
</dl>
<hr>
<h2 id="properties"><span class="secno">6. </span>Properties index</h2>
<p>In addition to the specified values, all properties take the
<!--begin properties-->
initial and inherit values<table class="proptable">
<thead>
<tr>
<th>Property
<th>Values
<th>Initial
<th>Applies to
<th>Inh.
<th>Percentages
<th>Media
<tbody>
<tr valign="baseline">
<td><span class="property"><a
href="#alignment-adjust">alignment-adjust</a></span>
<td>auto | baseline | before-edge | text-before-edge | middle | central |
after-edge | text-after-edge | ideographic | alphabetic | hanging |
mathematical | <percentage> | <length>
<td>auto
<td>inline-level elements
<td>no
<td>refers to the 'line-height' of the element
<td>visual
<tr valign="baseline">
<td><span class="property"><a
href="#alignment-baseline">alignment-baseline</a></span>
<td>baseline | use-script | before-edge | text-before-edge | after-edge |
text-after-edge | central | middle | ideographic | alphabetic | hanging |
mathematical
<td>baseline
<td>inline-level elements
<td>no
<td>N/A
<td>visual
<tr valign="baseline">
<td><span class="property"><a
href="#baseline-shift">baseline-shift</a></span>
<td>baseline | sub | super | <percentage> | <length>
<td>baseline
<td>inline-level elements
<td>no
<td>refers to the 'line-height' of the parent element
<td>visual
<tr valign="baseline">
<td><span class="property"><a
href="#dominant-baseline">dominant-baseline</a></span>
<td>auto | use-script | no-change | reset-size | alphabetic | hanging |
ideographic | mathematical | central | middle | text-after-edge |
text-before-edge
<td>auto
<td>inline-level elements (but see prose)
<td>no
<td>N/A
<td>visual
<tr>
<td><span class="property"><a href="#drop-initial-after-adjust">drop-initial-after-adjust</a></span>
<td>central | middle |
after-edge | text-after-edge | ideographic | alphabetic | hanging |
mathematical | <percentage> | <length>
<td>text-after-edge<td>::first-letter pseudo element<td>no
<td>N/A
<td>visual
</tr>
<tr>
<td><span class="property"><a href="#drop-initial-after-align">drop-initial-after-align</a></span>
<td><'alignment-baseline'><td>baseline<td>::first-letter pseudo element<td>no
<td>N/A
<td>visual
</tr>
<tr>
<td><span class="property"><a href="#drop-initial-before-adjust">drop-initial-before-adjust</a></span>
<td>before-edge | text-before-edge | middle | central |
after-edge | text-after-edge | ideographic | hanging |
mathematical | <percentage> | <length>
<td>text-before-edge<td>::first-letter pseudo element<td>no
<td>N/A
<td>visual
</tr>
<tr>
<td><span class="property"><a href="#drop-initial-before-align">drop-initial-before-align</a></span>
<td>caps-height | <'alignment-baseline'><td>caps-height<td>::first-letter pseudo
element<td>no
<td>N/A
<td>visual
</tr>
<tr>
<td><span class="property"><a href="#drop-initial-size">drop-initial-size</a></span>
<td>auto | <line> | <length> | <percentage><td>auto
<td>::first-letter pseudo element<td>no
<td>refers to combined line height size as provided by drop-initial-value<td>visual
</tr>
<tr valign="baseline">
<td><span class="property"><a href="#drop-initial-value">drop-initial-value</a></span>
<td>initial | <integer>
<td>initial<td>::first-letter pseudo element<td>no
<td>N/A
<td>visual
<tr valign="baseline">
<td><span class="property"><a
href="#inline-box-align">inline-box-align</a></span>
<td>initial | last | <integer>
<td>last
<td>inline-block-level elements
<td>no
<td>N/A
<td>visual
<tr valign="baseline">
<td><span class="property"><a href="#line-height">line-height</a></span>
<td>normal | number | <length> <percentage> | none<td>normal
<td>all elements and generated content
<td>yes
<td>refer to the font size of the element itself<td>visual
<tr>
<td><span class="property"><a href="#line-stacking">line-stacking</a></span>
<td><'line-stacking-strategy'> || <'line-stacking-ruby'> ||
<'line-stacking-shift'>
<td>see individual properties
<td>block-level elements
<td>yes
<td>N/A
<td>visual
</tr>
<tr>
<td><span class="property"><a href="#line-stacking-ruby">line-stacking-ruby</a></span>
<td>exclude-ruby | include-ruby<td>exclude-ruby<td>block-level elements
<td>yes
<td>N/A<td>visual
</tr>
<tr>
<td><span class="property"><a href="#line-stacking-shift">line-stacking-shift</a></span>
<td>consider-shifts | disregard-shifts
<td>consider-shifts<td>block-level elements
<td>yes
<td>N/A<td>visual
</tr>
<tr valign="baseline">
<td><span class="property"><a
href="#line-stacking-strategy">line-stacking-strategy</a></span>
<td>inline-line-height | block-line-height | max-height | grid-height<td>
inline-line-height<td>block-level elements
<td>yes
<td>N/A
<td>visual
<tr valign="baseline">
<td><span class="property"><a href="#text-height">text-height</a></span>
<td>auto | font-size | text-size | max-size<td>auto<td>inline elements and
parents of element with display:ruby-text<td>yes
<td>N/A
<td>visual
<tr valign="baseline">
<td><span class="property"><a
href="#vertical-align">vertical-align</a></span>
<td>auto | use-script | baseline | sub | super | top | text-top | central |
middle | bottom | text-bottom | <percentage> | <length>
<td>not defined for shorthand properties
<td>inline-level and 'table-cell' elements
<td>no
<td>refers to the 'line-height' of the element itself
<td>visual
</table>
<!--end properties-->
<p>The following properties are mentioned in this module, but are defined
elsewhere:</p>
<ul>
<li><dfn id="script">script</dfn>,
<dfn id="direction">direction</dfn>,
<dfn id="text-align">text-align</dfn>,
<dfn id="writing-mode">writing-mode</dfn>,
see the Text module.
<li><dfn id="font-size">font-size</dfn>,
see the Fonts module.
</ul>
<h2 id="profiles"><span class="secno">7. </span>Profiles</h2>
<p>There are 3 modules defined by this chapter:
<p>CSS1 line model:
<p>CSS2 line model:
<p>CSS3 line model:
<p>The CSS1 line module is made of the following properties/values:
<table class="proptable">
<tbody>
<tr>
<th>Name
<th>Values
<th>Initial
<th>Applies to
<th>Inherited
<th>Percentages
<th>Media groups
<tr>
<td><span class="property"><a
href="#line-height">'line-height'</a></span>
<td>normal | <number> | <a class="noxref"
href="/TR/REC-CSS2/syndata.html#value-def-length"><span
class="value-inst-length"><length></span></a> | <a class="noxref"
href="/TR/REC-CSS2/syndata.html#value-def-percentage"><span
class="value-inst-percentage"><percentage></span></a><td>normal
<td> all elements
<td>yes
<td> relative to the font-size of the element itself<td>N/A
<tr>
<td><span class="property"><a
href="#vertical-align">'vertical-align'</a></span>
<td>baseline | sub | super | top | text-top | middle | bottom | text-bottom |
<a href="/TR/REC-CSS2/syndata.html#percentage-units"><percentage></a>
<td>baseline
<td>inline-level elements
<td>no
<td> N/A
<td>N/A
</table>
<p>The following table describes the CSS2 text module. Because all properties
have added the 'inherit' value and have a media type, all CSS1 properties have
been specified below as well. In
addition, the <span class="property"><a
href="#vertical-align">'vertical-align'</a></span> has a new value:
<length>. Properties that applies to all
elements also applies to generated content. Finally, <span
class="property"><a href="#vertical-align">'vertical-align'</a></span> also
applies to table-cell elements.
<table class="proptable">
<tbody>
<tr>
<th>.Name
<th>Values
<th>Initial
<th>Applies to
<th>Inherited
<th>Percentages
<th>Media groups
<tr>
<td><span class="property"><a
href="#line-height">'line-height'</a></span>
<td>normal | <number> | <a class="noxref"
href="/TR/REC-CSS2/syndata.html#value-def-length"><span
class="value-inst-length"><length></span></a> | <a class="noxref"
href="/TR/REC-CSS2/syndata.html#value-def-percentage"><span
class="value-inst-percentage"><percentage></span></a><td>normal
<td> all elements and generated content<td>yes
<td> relative to the font-size of the element itself<td>N/A
</tr>
<tr>
<td><span class="property"><a
href="#vertical-align">'vertical-align'</a></span>
<td>baseline | sub | super | top | text-top | central | middle | bottom |
text-bottom | <a
href="/TR/REC-CSS2/syndata.html#percentage-units"><percentage></a> | <a
href="/TR/REC-CSS2/syndata.html#length-units"><length></a> | inherit
<td>baseline
<td>inline-level and table-cell elements
<td>no
<td> N/A
<td><a class="noxref"
href="/TR/REC-CSS2/media.html#visual-media-group">visual</a>
</table>
<p>The CSS3 module adds the following properties:
<ul>
<li>Line stacking and content height: <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>, <span
class="property"><a href="#line-stacking">'line-stacking'</a></span>, <span
class="property"><a href="#text-height">'text-height'</a></span>,
<li>Baseline alignment: <span class="property"><a
href="#alignment-adjust">'alignment-adjust'</a></span>, <span
class="property"><a
href="#alignment-baseline">'alignment-baseline'</a></span>, <span
class="property"><a href="#baseline-shift">'baseline-shift'</a></span>, <span
class="property"><a href="#dominant-baseline">'dominant-baseline'</a></span>,
'inline-box-align',<li>Drop initial letter: <span class="property"><a
href="#drop-initial-size">'drop-initial-size'</a></span>, <span
class="property"><a
href="#drop-initial-value">'drop-initial-value'</a></span>, <span
class="property"><a
href="#drop-initial-after-adjust">'drop-initial-after-adjust'</a></span>, <span
class="property"><a
href="#drop-initial-after-align">'drop-initial-after-align'</a></span>, <span
class="property"><a href="#drop-initial-before-adjust">'drop-initial-before-adjust'</a></span>, <span
class="property"><a
href="#drop-initial-before-align">'drop-initial-before-align'</a></span>,</ul>
<p>It also modifies the following properties as described:
<ul>
<li><span class="property"><a
href="#vertical-align">'vertical-align'</a></span> has three new value: <span
class="css">'auto', middle</span> and <span class="css">'use-script'</span> and has its
initial value changed to <span class="css">'auto'</span>.
<li>all properties take the value 'initial'.
</ul>
<hr>
<h2 id="glossary"><span class="secno">8. </span>Glossary</h2>
<dl>
<dt><a id="g-hiragana"><strong><span lang="ja">Hiragana</span></strong></a>
<dd>Japanese syllabic script, or character of that script. Rounded and cursive
in appearance. Subset of the Japanese writing system, used together with kanji
and katakana. In recent times, mostly used to write Japanese words when kanji
are not available or appropriate, and word endings and particles. Also see <a href="#g-katakana"><span lang="ja">
Katakana</span></a>.
<dt><a id="g-ideogram"><strong>Ideograph</strong></a>
<dd>A character that is used to represent an idea, word, or word component,
in contrast to a character from an alphabetic or syllabic script. The most
well-known ideographic script is used (with some variation) in East Asia
(China, Japan, Korea,...).
<dt><a id="g-kana"><strong><span lang="ja">Kana</span></strong></a>
<dd>Collective term for hiragana and katakana.
<dt><a id="g-katakana"><strong><span lang="ja">Katakana</span></strong></a>
<dd>Subset of the Japanese writing system consisting of phonetic characters
used to represent Roman words. Also see <a href="#g-hiragana"><span
lang="ja">Hiragana</span></a>.
<dt><a id="g-ruby"><strong>Ruby</strong></a>
<dd>A run of text that appears in the vicinity of another run of text and
serves as an annotation or a pronunciation guide for that text.
</dl>
<p>
<hr>
<h2 class="no-num" id="BaselineUsage">Appendix A: Usage of baseline alignment
(informative)</h2>
<p>The following appendix shows some examples of baseline alignment,
exercising the related properties .
<p>A simple example of alignment is shown in the following figure. The figure
shows the presentation of two inline elements, one inside the other. These
inline elements make up the content of a line in a block where the
writing-mode is "lr-tb" and the font is "Helvetica". The structure of the
example is as follows:
<pre><p><span class="outer">Apex <span class="inner">Top</span></span></p></pre>
<p>with the style being defined as:
<pre>p { writing-mode: lr-tb; font: Helvetica; }
span { alignment-baseline: use-script; }</pre>
<p>The other baseline alignment initial values apply. Since a horizontal
writing-mode is in use, the dominant-baseline-identifier is set to
"alphabetic" and the baseline-table is taken from the nominal-font for the
block in which the line appears, which, in this case, is Helvetica.
<p>In the figure, the positions of the baselines relative to the current font
size are shown as red (staff) lines. These lines are labeled with
abbreviations of the names of the baselines (e.g., TBE for
"text-before-edge"). The baseline identified by the
dominant-baseline-identifier (A) is shown in blue. There is a break in the
staff lines to separately show the inner inline element. This is not
necessary for this example, but this distinction will become important in
subsequent examples.
<p>The "alignment-baseline" property is the primary control on the
positioning of an inner element with respect to its parent. The initial value
of the "alignment-baseline" property is "baseline". This aligns the
dominant-baseline of the inner inline element with the dominant baseline of
the outer inline element. This is shown by the short blue line that connects
the two separated staffs (A) in the figure.
<p>The glyphs that are in the content of the two elements are aligned based
on the script to which the glyph belongs. Since this example only has Latin
glyphs, they are aligned to the "alphabetic" baseline.
<div class="figure">
<p><img alt="alphabetic baseline" height="98" src="AlignIntro-1.gif"
width="385">
<p>An inner inline element containing Latin characters aligned to an outer
inline element also containing Latin characters.
</div>
<p>In the next figure, the content of the inner inline element is in
Gurmukhi, the script of the Punjabi language. The Gurmukhi syllables are read
as "guru". Rather than use Unicode values for these characters, they are
symbolized by placing the Latin transliteration in italic type. The structure
of the example becomes (assuming the same style):
<pre><p><span class="outer">Apex <span class="inner"><i>guru</i></span></span></p></pre>
<p>The only change from the previous example is that the glyphs of the
Gurmukhi script are aligned to the "hanging" baseline of the inner inline
element. The alignment of that element itself, with respect to the outer
inline element, is unchanged. The "hanging" baseline position is computed
from the font-table part of the dominant-baseline set of the parent element
(in this case the outer inline element which is getting itself the set from
its parent, the block element).
<div class="figure">
<p><img alt="alphabetic alignment" height="98" src="AlignIntro-2.gif"
width="387">
<p>An inner inline element containing Gurmukhi characters aligned to an outer
inline element containing Latin characters.
</div>
<p>In the next figure, fragments of the text of the previous examples make up
the content of the outer inline element. The inner inline element has a
change of font-size, however. The structure is:
<pre><p><span class="outer">Ap<i>guru</i> <span class="inner">Ex<i>ji</i></span></span></p></pre>
<p>with the following style:
<pre>p { writing-mode: lr-tb; font: Helvetica; }
span { alignment-baseline: use-script; }
span.inner { font-size: .75em; }</pre>
<p>In this example, the alignment of the inner inline element itself does not
change, nor does the alignment of the smaller glyphs inside the inner
element. The Latin glyphs are still aligned to the "alphabetic" baseline and
the Gurmukhi glyphs, which are pronounced "ji" are aligned to the "hanging"
baseline. Note also that just changing the "font-size" property did not
change the baseline-table in effect in the inner inline element.
<div class="figure">
<p><img alt="baselines and font size" height="98" src="AlignIntroB-2FS.gif"
width="391">
<p>The inner inline element has a reduced font-size.
</div>
<p>The next figure is equivalent to the previous example with the Gurmukhi
character replaced by ideographic characters. These are aligned to the
"ideographic" baseline.
<div class="figure">
<p><img alt="baselines and font size" height="98" src="AlignIntroB-4FS.gif"
width="391">
<p>The previous figure redone with ideographic glyphs instead of Gurmukhi
glyphs. The EM boxes are shown for the ideograms to clarify the alignment of
these glyphs.
</div>
<p>To change the scaling of the lines of the baseline table, it is necessary
to use the "dominant-baseline" property on the inner inline element. The
value of "reset-size" causes the baseline-table font-size to be reset from
the font-size of the element on which the "dominant-baseline" property
appears. The next figure shows the effect of this, using the structure:
<pre><p><span class="outer">Ap<i>guru</i> <span class="inner">Ex<i>ji</i></span></span></p></pre>
<p>with the following style:
<pre>p { writing-mode: lr-tb; font: Helvetica; }
span { alignment-baseline: use-script; }
span.inner { font-size: .75em; dominant-baseline: reset-size; }</pre>
<p>The alignment of the inner inline element, with respect to the outer
inline element, is still determined by aligning the dominant baselines
(alphabetic). But, the baseline-table of the inner inline element has been
rescaled to the font-size of the inner inline element. Hence the smaller
glyphs align with each other.
<div class="figure">
<p><img alt="baseline tables" height="98" src="AlignIntroB-3RS.gif"
width="351">
<p>The baseline-table of the inner inline element has been resized to match
the font-size of the inner inline element.
</div>
<p>But, what if it is more important that the small Gurmukhi glyphs align
with the large Gurmukhi glyphs than having the Latin glyphs align. There are
at least two ways to achieve this. The structure:
<pre><p><span class="outer">Ap<i>guru</i> <span class="inner">Ex<i>ji</i></span></span></p></pre>
<p>with the following style:
<pre>p { writing-mode: lr-tb; font: Helvetica; }
span { alignment-baseline: use-script; }
span.outer {dominant-baseline: hanging }
span.inner { font-size: .75em; dominant-baseline: reset-size; }</pre>
<p>is illustrated in the next figure. The "hanging" baseline becomes the
dominant baseline and the initial value of the "alignment-baseline" property
causes the (newly) dominant "hanging" baselines to be aligned as is shown by
the connection of the blue baselines.
<div class="figure">
<p><img alt="dominant baseline" height="98" src="AlignIntroB-3DH.gif"
width="351">
<p>Changing the dominant baseline to the "hanging" baseline causes the inner
inline element to be aligned on its parent's "hanging" baseline.
</div>
<p>It is also possible to achieve the effect of the above figure without
changing the dominant baseline. Instead it is sufficient to explicitly
specify that the inner inline element is aligned on its "hanging" baseline.
This is done by:
<pre><p><span class="outer">Ap<i>guru</i> <span class="inner">Ex<i>ji</i></span></span></p></pre>
<p>with the following style:
<pre>p { writing-mode: lr-tb; font: Helvetica; }
span { alignment-baseline: use-script; }
span.inner { font-size: .75em; dominant-baseline: reset-size; alignment-baseline: hanging; }</pre>
<p>The only change this approach would make in the above figure is to color
the "hanging" baseline red and keep the "alphabetic" baseline as the (blue)
dominant baseline. This baseline in the inner inline element would not (as it
does not in the above figure) align with the "alphabetic" baseline in the
outer inline element.
<p>Another baseline alignment property is the "baseline-shift" property. Like
the properties other than the "dominant-baseline" property, this property
does not change the baseline-table or the baseline-table font-size. It does
shift the whole baseline table of the parent element so that when an inner
inline element is aligned to one of the parents baselines, the position of
the inner inline element is shifted. This is illustrated in the next figure.
The structure which creates this figure is:
<pre><p><span class="outer">Apex <span class="inner">1<i>ji</i></span></span></p></pre>
<p>with the following style:
<pre>p { writing-mode: lr-tb; font: Helvetica; }
span { alignment-baseline: use-script; }
span.inner { baseline-shift: super; }</pre>
<p>Because the whole set of baseline-table staff lines are shifted to the
position of the superscript baseline: it does not matter to which baseline
the glyphs in the superscript are aligned. The European number "1" is aligned
to the "alphabetic" baseline and the Gurmukhi syllable "ji" is aligned to the
"hanging" baseline.
<div class="figure">
<p><img alt="baseline shift" height="120" src="AlignIntroB-5.gif"
width="385">
<p>Using a "baseline-shift" for a superscript (or a subscript).
</div>
<p>It is more common for the font-size of the superscript text to be smaller
than the font-size of the text to which it is appended. Consider:
<pre><p><span class="outer">Apex <span class="inner">1<i>ji</i></span></span></p></pre>
<p>with the following style:
<pre>p { writing-mode: lr-tb; font: Helvetica; }
span { alignment-baseline: use-script; }
span.inner { baseline-shift: super; font-size: .75em; }</pre>
<p>Because changing the font-size on a superscript (or subscript) is common,
this is the one case where changing the font-size does cause the
baseline-table font-size to be reset when the "dominant-baseline" property
has its initial value. After the rescaling, the default alignment to the
dominant baseline positions the inline element for the superscript to the
dominant baseline position in the shifted baseline-table of the parent
element.
<div class="figure">
<p><img alt="baseline shift" height="114" src="AlignIntroB-5FS.gif"
width="372">
<p>Reducing the font-size of the superscript automatically resets the
baseline-table size so that mixed languages in the superscript stay mutually
aligned.
</div>
<hr>
<h2 class="no-num" id="ack">Acknowledgments</h2>
<p>In additions to the authors, this specification would not have been possible without the help from:
<p>Stephen Deach, Sujal Parikh, Grzegorz Zygmunt, Chris Wilson, David M Brown.
<p>
<hr>
<h2 class="no-num" id="ref">References</h2>
<h3 class="no-num" id="normative">Normative references</h3>
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<h3 class="no-num" id="other">Other references</h3>
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<dt id="CSS2">[CSS2]
<dd>Bert Bos; Håkon Wium Lie; Chris Lilley; Ian Jacobs. <cite>Cascading Style
Sheets, level 2.</cite> 1998. W3C Recommendation. URL: <a
href="http://www.w3.org/TR/REC-CSS2">http://www.w3.org/TR/REC-CSS2</a>
<!---->
<dt id="CSS3-background">[CSS3-background]
<dd>Tim Boland; Bert Bos. <cite>CSS3 module: backgrounds.</cite> 19 February
2002. W3C working draft. (Work in progress.) URL: <a
href="http://www.w3.org/TR/2002/WD-css3-background-20020219">http://www.w3.org/TR/2002/WD-css3-background-20020219</a>
<!---->
<dt id="CSS3-color">[CSS3-color]
<dd>Tantek Çelik; Chris Lilley. <cite>CSS3 module: color.</cite> 5 March
2001. W3C working draft. (Work in progress.) URL: <a
href="http://www.w3.org/TR/2001/WD-css3-color-20010305">http://www.w3.org/TR/2001/WD-css3-color-20010305</a>
<!---->
<dt id="CSS3-fonts">[CSS3-fonts]
<dd>Michel Suignard; Chris Lilley. <cite>CSS3 module: fonts.</cite> 31 July
2001. W3C working draft. (Work in progress.) URL: <a
href="http://www.w3.org/TR/2001/WD-css3-fonts-20010731">http://www.w3.org/TR/2001/WD-css3-fonts-20010731</a>
<!---->
<dt id="HTML40">[HTML40]
<dd>Raggett, D.; Le Hors, A.; Jacobs, I.. <cite>HTML 4.0 Specification
(revised).</cite> Apr 1998. W3C Recommendation. URL: <a
href="http://www.w3.org/TR/1998/REC-html40-19980424">http://www.w3.org/TR/1998/REC-html40-19980424</a>
<!---->
<dt id="HTML401">[HTML401]
<dd>Raggett, D.; Le Hors, A.; Jacobs, I.. <cite>HTML 4.01
Specification.</cite> Dec 1999. W3C Recommendation. URL: <a
href="http://www.w3.org/TR/1999/REC-html401-19991224">http://www.w3.org/TR/1999/REC-html401-19991224</a>
<!---->
<dt id="ISO15924">[ISO15924]
<dd><cite>Code for the representation of names of scripts.</cite>
International Organization for Standardization.. 1998. ISO 15924:1998. Draft
International Standard
<!---->
<dt id="RFC2119">[RFC2119]
<dd>S. Bradner. <cite>Key words for use in RFCs to Indicate Requirement
Levels.</cite> Internet RFC 2119. URL: <a
href="http://www.ietf.org/rfc/rfc2119.txt">http://www.ietf.org/rfc/rfc2119.txt</a>
<!---->
<dt id="SVG1.0">[SVG1.0]
<dd>Various. <cite>Scalable Vector Graphics (SVG) 1.0 Specification.</cite>
Sep 2001. W3C Recommendation. URL: <a
href="http://www.w3.org/TR/2001/REC-SVG-20010904">http://www.w3.org/TR/2001/REC-SVG-20010904</a>
<!---->
<dt id="UNICODE">[UNICODE]
<dd>The Unicode Consortium. <cite>The Unicode Standard: Version 3.1.0.</cite>
Addison Wesley Longman. 2000. ISBN 0-201-61633-5. The latest version of
Unicode. For more information, consult the Unicode Consortium's home page at
<a
href="http://www.unicode.org/">http://www.unicode.org/</a>
URL: <a
href="http://www.unicode.org/unicode/standard/versions/enumeratedversions.html#Unicode_3_1_0">http://www.unicode.org/unicode/standard/versions/enumeratedversions.html#Unicode_3_1_0</a>
<!---->
<dt id="UTR-24">[UTR-24]
<dd>Mark Davis. <cite>Script Names.</cite> 27 September 2001. Unicode
Technical Report #24. URL: <a
href="http://www.unicode.org/unicode/reports/tr24/tr24-3.html">http://www.unicode.org/unicode/reports/tr24/tr24-3.html</a>
<!---->
<dt id="XHTML1.0">[XHTML1.0]
<dd>Steven Pemberton; et al. <cite>XHTML 1.0: The Extensible HyperText Markup
Language.</cite> Jan 2000. W3C Recommendation. URL: <a
href="http://www.w3.org/TR/2000/REC-xhtml1-20000126">http://www.w3.org/TR/2000/REC-xhtml1-20000126</a>
<!---->
<dt id="XHTMLMOD">[XHTMLMOD]
<dd>Adams, Robert; Altheim, Murray; et al. <cite>Modularization of
XHTML.</cite> Apr 2001. W3C Recommendation. URL: <a
href="http://www.w3.org/TR/2001/REC-xhtml-modularization-20010410">http://www.w3.org/TR/2001/REC-xhtml-modularization-20010410</a>
<!---->
<dt id="XML1.0">[XML1.0]
<dd>Tim Bray; Jean Paoli; C. M. Sperberg-McQueen; Eve Maler. <cite>Extensible
Markup Language (XML) 1.0 (Second Edition).</cite> Oct 2000. W3C
Recommendation. URL: <a
href="http://www.w3.org/TR/2000/REC-xml-20001006">http://www.w3.org/TR/2000/REC-xml-20001006</a>
<!---->
<dt id="XSL1.0">[XSL1.0]
<dd>Adler, Sharon; Berglund, Anders; et al. <cite>Extensible Stylesheet
Language (XSL) Version 1.0.</cite> Oct 2001. W3C Recommendation. URL: <a
href="http://www.w3.org/TR/2001/REC-xsl-20011015">http://www.w3.org/TR/2001/REC-xsl-20011015</a>
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<hr>
<h2 class="no-num" id="changes">Changes from Previous Working Draft</h2>
<p>New draft, but with a large piece taken out from former versions of CSS3 text
and CSS2</p>
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