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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html lang=en>
<head><meta content="text/html; charset=utf-8" http-equiv=Content-Type>
<title>CSS3 module: line</title>
<style type="text/css">
dt {font-weight: normal}
/*.issue, .note {font-style: italic}*/
.figure {font-size: smaller;}
/* Stolen from CSS2 Recommendation */
A.noxref:link, A.noxref:visited {color: black; /*color: inherit*/}
</style>
<style media=print type="text/css">
img#edge { width: 80%; height: 70%;}
dt.label { display: run-in; }
</style>
<link href="../default.css" rel=stylesheet type="text/css">
<link href="http://www.w3.org/StyleSheets/TR/W3C-ED.css" rel=stylesheet
type="text/css">
<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>Editor's Draft 23 February 2008</h2>
<dl>
<dt>This version:
<!--<dd><a href="http://www.w3.org/TR/2008/ED-css3-linebox-20080223/">http://www.w3.org/TR/2008/ED-css3-linebox-20080223/</a></dd>-->
<dd>[no permanent URL]
<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><a
href="http://www.w3.org/TR/2002/WD-css3-linebox-20020515/">http://www.w3.org/TR/2002/WD-css3-linebox-20020515/</a>
<dt>Editors:<
1898
/div>
<dd><a href="mailto:michelsu@microsoft.com">Michel Suignard
(Microsoft)</a> (until February 2003)
<dd><a href="http://www.meyerweb.com/eric/">Eric A. Meyer</a> (until
February 2003)
<dd><a href="http://dbaron.org/">L. David Baron</a> (Mozilla Corporation)
(from March 2003)
</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>
<dd><a href="http://dbaron.org/">L. David Baron (Mozilla Corporation)</a>
</dl>
<!--begin-copyright-->
<p class=copyright><a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
rel=license>Copyright</a> © 2008 <a
href="http://www.w3.org/"><acronym title="World Wide Web
Consortium">W3C</acronym></a><sup>®</sup> (<a
href="http://www.csail.mit.edu/"><acronym title="Massachusetts Institute
of Technology">MIT</acronym></a>, <a
href="http://www.ercim.org/"><acronym title="European Research Consortium
for Informatics and Mathematics">ERCIM</acronym></a>, <a
href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. W3C <a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
<a
href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a>
and <a
href="http://www.w3.org/Consortium/Legal/copyright-documents">document
use</a> rules apply.</p>
<!--end-copyright-->
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc" id=Abstract>Abstract</h2>
<p>The CSS formatting model provides for a flow of elements and text inside
of a container to be wrapped into lines. The formatting of elements and
text within a line, its positioning in the inline progression direction,
and the breaking of lines are described in <a href="#CSS3TEXT"
rel=biblioentry>[CSS3TEXT]<!--{{CSS3TEXT}}--></a>. This module describes
the positioning in the block progression direction both of elements and
text within lines and of the lines themselves. This positioning is often
relative to a baseline. It also describes special features for formatting
of first lines and drop caps. It extends on the model in <a href="#CSS2"
rel=biblioentry>[CSS2]<!--{{CSS2}}--></a>.
<h2 class="no-num no-toc" id=Status>Status of This Document</h2>
<!--begin-status-->
<p>This is a public copy of the editors' draft. It is provided for
discussion only and may change at any moment. Its publication here does
not imply endorsement of its contents by W3C. Don't cite this document
other than as work in progress.
<p>The (<a
href="http://lists.w3.org/Archives/Public/www-style/">archived</a>) public
mailing list <a href="mailto:www-style@w3.org">www-style@w3.org</a> (see
<a href="http://www.w3.org/Mail/Request">instructions</a>) is preferred
for discussion of this specification. When sending e-mail, please put the
text “css3-linebox” in the subject, preferably like this:
“[<!---->css3-linebox<!---->] <em>…summary of
comment…</em>”
<p>This document was produced by the <a href="/Style/CSS/members">CSS
Working Group</a> (part of the <a href="/Style/">Style Activity</a>).
<p>This document was produced by a group operating under the <a
href="/Consortium/Patent-Policy-20040205/">5 February 2004 W3C Patent
Policy</a>. W3C maintains a <a href="/2004/01/pp-impl/32061/status"
rel=disclosure>public list of any patent disclosures</a> made in
connection with the deliverables of the group; that page also includes
instructions for disclosing a patent.</p>
<!--end-status-->
<p>This document may be available in translations in the future. The
English version of this specification is the only normative version.
<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="#conformance"><span class=secno>2. </span>Conformance</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
</span>Inline-progression: Line Box wrapping</a>
<li><a href="#inline1"><span class=secno>3.3 </span>Block-progression
dimensions: the <span class=property>‘text-height’</span>
property</a>
<li><a href="#LineBoxHeight"><span class=secno>3.4 </span>Block
progression positioning and spacing</a>
<ul class=toc>
<li><a href="#InlineBoxHeight"><span class=secno>3.4.1 </span>Line
height adjustment: the <span
class=property>‘line-height’</span> property</a>
<li><a href="#LineStacking"><span class=secno>3.4.2 </span>Line
Stacking: the <span
class=property>‘line-box-contain’</span> property</a>
</ul>
</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 class=no-num><a href="#BaselineUsage">Appendix A: Usage of baseline
alignment (informative)</a>
<li class=no-num><a href="#ack">Acknowledgments</a>
<li class=no-num><a href="#ref">References</a>
<ul class=toc>
<li class=no-num><a href="#normative">Normative references</a>
<li class=no-num><a href="#other">Other references</a>
</ul>
<li class=no-num><a href="#index">Index</a>
</ul>
<!--end-toc-->
<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 <a href="#CSS3FONT"
rel=biblioentry>[CSS3FONT]<!--{{!CSS3FONT}}--></a>
<li>Text <a href="#CSS3TEXT"
rel=biblioentry>[CSS3TEXT]<!--{{!CSS3TEXT}}--></a>
<li>Syntax and grammar <a href="#CSS3SYN"
rel=biblioentry>[CSS3SYN]<!--{{!CSS3SYN}}--></a>
<li>Values and units <a href="#CSS3VAL"
rel=biblioentry>[CSS3VAL]<!--{{!CSS3VAL}}--></a>
<li>Cascade <a href="#CSS3CASCADE"
rel=biblioentry>[CSS3CASCADE]<!--{{!CSS3CASCADE}}--></a>
</ul>
<p>It has non-normative (informative) references to the following other
CSS3 modules:
<ul>
<li>Multi-column layout <a href="#CSS3COL"
rel=biblioentry>[CSS3COL]<!--{{CSS3COL}}--></a>
<li>Ruby <a href="#CSS3RUBY"
rel=biblioentry>[CSS3RUBY]<!--{{CSS3RUBY}}--></a>
</ul>
<h2 id=conformance><span class=secno>2. </span>Conformance</h2>
<p class=issue>[Add some real conformance text here.]
<p>All described properties, in addition to the noted values, take
‘<span class=property>initial</span>’ and ‘<span
class=property>inherit</span>’. These values are not repeated in
each of the property value enumeration.
<p>This module uses extensively the ‘<span
class=property>before</span>’, ‘<span
class=property>after</span>’, ‘<span
class=property>start</span>’ and ‘<span
class=property>end</span>’ notation to specify the four edges of a
box relative to its text advance direction, independently of its absolute
positioning in terms of ‘<span class=property>top</span>’,
‘<span class=property>bottom</span>’, ‘<span
class=property>left</span>’ and ‘<span
class=property>right</span>’ (corresponding respectively to the
‘<span class=property>before</span>’, ‘<span
class=property>after</span>’, ‘<span
class=property>start</span>’ and ‘<span
class=property>end</span>’ positions in a typical Western text
layout). This notation is also used extensively in <a href="#XSL10"
rel=biblioentry>[XSL10]<!--{{XSL10}}--></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 "OPTIONA
67F6
L" are used
to indicate optional features or behavior. These keywords are used in
accordance with <a href="#RFC2119"
rel=biblioentry>[RFC2119]<!--{{!RFC2119}}--></a>. For legibility these
keywords are used in lowercase form.
<h2 id=LineBox><span class=secno>3. </span>Line box, Line stacking and
Content height</h2>
<p>This section describes inline boxes formatting, how lines are stacked
together and a mechanism to adjust the content height of inline elements.
Two terms: inline-progression dimension and block-progression dimension
are used frequently in the section and are defined as follows
<p>The <b>inline-progression dimension</b> is a length in the direction of
the inline-progression of a box. For an horizontal layout flow it can be
perceived as related to the the width of the box. However for a vertical
layout flow it will be related to the height of the box. The term
inline-progression dimension is the neutral way to express that dimension
independently of the layout flow.
<p>The <b>block-progression dimension</b> is a length in the direction of
the block-progression of a box. For an horizontal layout flow it can be
perceived as related to the height of the box. However for a vertical
layout flow it will be related to the width of the box. The term
block-progression dimension is the neutral way to express that dimension
independently of the layout flow.
<h3 id=InlineFormatting><span class=secno>3.1 </span>Inline formatting
context</h3>
<p>In an inline formatting context, boxes are laid out in the
inline-progression direction, one after the other, following the
block-progression within the containing block. Borders, padding and
inline-progression margins are respected between these boxes. The boxes
may be aligned within the inline-progression in different ways: their
after-edges or before-edges may be aligned, or the baselines of text
within them may be aligned. The rectangular area that contains the boxes
that form a line is called a <a class=index-def href="#line-box0" id=x
title="line box"> </a><a id=line-box><dfn id=line-box0>line box</dfn></a>.
<p>The inline-progression dimension (‘<span
class=property>width</span>’ in horizontal flow) of a line box is
determined by its containing block. The block-progression dimension
(‘<span class=property>height</span>’ in horizontal flow) of a
line box is determined by the rules given in the section on <a
href="#line-height">line height calculations</a>. A line box is generally
tall (relative) enough for all of the boxes it contains. However, it may
be taller than the tallest box it contains (if, for example, boxes are
aligned so that baselines line up). The alignment of boxes within a line
box is determined by the <a href="#baseline">baseline alignment</a>
properties.
<p>In general, when several inline boxes cannot fit within a single line
box, they are distributed among two or more block-progression stacked line
boxes. The exact wrapping of inline boxes at the line ending edge is
determined by several text related property categories such as
line-breaking, word-breaking, text wrapping and white-space management.
Thus, a paragraph is a stack of line boxes.
<p>Line boxes are stacked together in the block-progression direction
without any separation. The block-progression dimension of the line box is
determined by the contents of the line box (including the root inline box)
and the <span class=property>‘<a class=property
href="#line-box-contain">line-box-contain</a>’</span> property.
<p>A containing block defines a <b>root inline box</b> which wraps all the
inline children of the block element, including the anonymous inline
boxes. It inherits inheritable properties from the parent block box (like
<span class=property>‘<a class=property
href="#line-height">line-height</a>’</span>), while non-inherited
properties have their default values. The root inline box establishes a
baseline for vertical alignment and may affect the height of the line
boxes.
<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).
<h3 id=LineBoxWrapping><span class=secno>3.2 </span>Inline-progression:
Line Box wrapping</h3>
<p>In general, the start edge of a line box touches the start edge of its
containing block and the end edge touches the end edge of its containing
block. However, floating boxes may come between the containing block edge
and the line box edge. Thus, although line boxes in the same inline
formatting context generally have the same inline-progression dimension
(that of the containing block), they may vary if available
inline-progression space is reduced due to <!-- a href="#floats"-->
floats<!--/a-->. Line boxes in the same inline formatting context may vary
in block-progression dimension.
<p>When the total inline-progression dimension of the inline boxes on a
line is less than the inline-progression dimension of the line box
containing them, their inline-progression distribution within the line box
is determined by the <span class=property>‘<a class=property
href="#text-align">text-align</a>’</span> property. If that property
has the value ‘<span class=property>justify</span>’, the user
agent may stretch the inline boxes as well.
<p>When line-breaking opportunities are available within inline boxes and
are not pre-empted by the white-space properties, the inline boxes located
at the ending edge of the line box may be split into several boxes and
these boxes distributed across several line boxes. When an inline box is
split, margins, borders, and padding have no visual effect where the split
occurs (or at any split, when they are several). Formatting of margins,
borders, and padding may not be fully defined if the split occurs within a
bidirectional embedding.
<p>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>.
<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>EM: "emphasized words"
<li>Anonymous: "appear"
<li>STRONG: "in this"
<li>Anonymous: "sentence, dear."
</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.
<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." height=99
src=inline-layout.gif width=260><span class=dlink> <a
href="http://www.w3.org/TR/REC-CSS2/images/longdesc/inline-layout-desc.html"
name=img-inline-layout title="Long description for illustration of
margin/border behavior on split inline box">[D]</a></span></div>
<ul>
<li>The margin is inserted before "emphasized" and after
"words".
<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.
</ul>
</div>
<h3 id=inline1><span class=secno>3.3 </span>Block-progression dimensions:
the <span class=property>‘<a class=property
href="#text-height">text-height</a>’</span> property</h3>
<p>Each inline bo
2334
x has a block-progression dimension which is derived from
the following parameters: the ‘<a class=property
href="#text-height">text-height</a>’ and ‘<a class=property
href="#font-size">font-size</a>’ properties for non-replaced
elements, the height or the width for replaced elements (depending on the
text flow being horizontal or vertical respectively) and the stacked
block-progression dimension for inline-block elements (identical to what
is done for block-level elements).
<p>The block-progression dimension determines the position of the padding,
border and margin for the element but does not necessarily determine the
line stacking progression as this is also affected by the ‘<a
class=property href="#line-box-contain">line-box-contain</a>’
property.
<table class=propdef id=nametext-height>
<tbody>
<tr>
<td><em>Name:</em>
<td><dfn id=text-height>text-height</dfn>
<tr>
<td><em>Value:</em>
<td>auto | font-size | text-size | max-size | <number>
<tr>
<td><em>Initial:</em>
<td>auto
<tr>
<td><em>Applies to:</em>
<td>inline elements and parents of element with display:ruby-text
<tr>
<td><em>Inherited:</em>
<td>yes
<tr>
<td><em>Percentages:</em>
<td>N/A
<tr>
<td><em>Media:</em>
<td>visual
<tr>
<td><em>Computed value:</em>
<td>specified value (except for initial and inherit)
</table>
<p>The ‘<a class=property href="#text-height">text-height</a>’
property determine the block-progression dimension of the text content
area of an inline box (non-replaced elements) . Possible values:
<dl>
<dt><strong>auto</strong>
<dd>The block-progression dimension is based either on the em square
determined by the computed element font-size property value or the
cell-height (ascender + descender) related to the computed element
font-size as chosen by the user agent.
<dt>font-size
<dd>The block-progression dimension is based on the em square as
determined by the computed element font-size.
<dt>text-size
<dd>The block-progression dimension is based on the cell-height (ascender
+ descender) related to the computed element font-size.
<dt>max-size
<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 ‘<code class=css>display:ruby-text</code>’) and baseline
shifted elements.
<dt><number>
<dd>The block progression dimension is based on <number> times the
em square as determined by the computed font-size.
</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>Although the ‘<a class=property
href="#text-height">text-height</a>’ property does not apply
directly to block elements, it applies to their anonymous children inline
boxes (if any).
<p>For replaced elements, the block-progression dimension is determined by
the outer edges (i.e. margin edge).
<h3 id=LineBoxHeight><span class=secno>3.4 </span>Block progression
positioning and spacing</h3>
<h4 id=InlineBoxHeight><span class=secno>3.4.1 </span>Line height
adjustment: the <span class=property>‘<a class=property
href="#line-height">line-height</a>’</span> property</h4>
<p>The ‘<a class=property href="#line-height">line-height</a>’
property controls the amount of leading space which is added before and
after the block-progression dimension of an inline box (not including
replaced inline boxes, but including the root inline box) to determine the
extended block-progression dimension of the inline box. The value of the
‘<a class=property
href="#line-box-contain">line-box-contain</a>’ property determines
how the block-progression dimension and the extended block-progression
dimension affect the height of the line box. 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>The <span class=index-def id=leading title=leading><em><a
name=x15>leading</a></em></span><span title=leading> for an inline
non-replaced element is defined as the d</span>ifference between the
block-progression dimension as determined by the ‘<a class=property
href="#text-height">text-height</a>’ property and the computed value
of <span class=property>‘<a class=property
href="#line-height">line-height</a>’</span>. Half the leading is
called the <a class=index-def href="#half-leading" id=half-leading0
title=half-leading><em><a name=x16> half-leading</a></em></a>, each
half-leading is located before and after the block-progression dimension
of the element. The ‘<a class=property
href="#line-height">line-height</a>’ value will specify the
<em>exact</em> extended block-progression dimension of each box generated
by the element. (Depending on the value of ‘<a class=property
href="#line-box-contain">line-box-contain</a>’, the extended
block-progression dimension may be ignored.) (For inline <a
href="http://www.w3.org/TR/REC-CSS2/conform.html#replaced-element">replaced</a>
elements, both the block-progression dimension and the extended
block-progression dimension of the box are given by the outer edges (i.e.
margin edge).) Anonymous inline boxes use the ‘<a class=property
href="#text-height">text-height</a>’ and ‘<a class=property
href="#line-height">line-height</a>’ property values specified for
their parent.
<p>Depending on the value of the ‘<a class=property
href="#line-stacking-strategy">line-stacking-strategy</a>’, the
‘<a class=property href="#line-height">line-height</a>’ 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. <span
class=issue>[LDB: I don't understand this paragraph.]</span>
<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>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: ‘<span
class=property>none</span>’.
<table class=propdef id=name-62>
<tbody>
<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:
<dl>
<dt><strong>normal</strong>
<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
id=ltnumbergt 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 ‘<span
class=property>normal</span>’ between 1.0 to 1.2. The user agent
may allow the <number> to vary depending on the metrics of the
font(s) being used.
<dt><span class=index-inst id=ltlengthgt0 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>
<dd>The box height is set to this length. Negative values are illegal. The
length is the computed value.
<dt><span class=index-inst id=ltnumbergt0 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>
<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.
<dt><span class=index-inst id=ltpercentagegt0 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>
<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.
<dt>none
<dd>For inline-level elements, the element does not influence the
<i>extended block-progression dimension</i> of the line. The computed
value is the specified value (‘<span
class=property>none</span>’). For block-level elements, equivalent
to ‘<span class=property>normal</span>’ (and the computed
value is ‘<span class=property>normal</span>’). <span
class=issue>This definition should be briefer, and should refer to the
next section.</span>
</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 <span class=property>‘<a
class=property href="#line-height">line-height</a>’</span> value
according to the largest font size (when appropriate).
<p>Note that replaced elements have a <span class=property>‘<a
class=property href="#font-size">font-size</a>’</span> and a <span
class=property>‘<a class=property
href="#line-height">line-height</a>’</span> property, even if they
are not used directly to determine the extended block-progression
dimension of the box: ‘<span class=property>em</span>’ and
‘<span class=property>ex</span>’ values are relative to values
of ‘<a class=property href="#font-size">font-size</a>’ and
percentage values for <span class=property>‘<a class=property
href="#vertical-align">vertical-align</a>’</span> are relative to
values of the extended block-progression dimension. <span
class=issue>[LDB: The second part of this sentence is a significant change
from CSS2, and also doesn't mauke senes in the context of the
sentence.]</span>
<p>When the <span class=property>‘<a class=property
href="#line-height">line-height</a>’</span> 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.
<h4 id=LineStacking><span class=secno>3.4.2 </span>Line Stacking: the <span
class=property>‘<a class=property
href="#line-box-contain">line-box-contain</a>’</span> property</h4>
<table class=propdef id=name-30>
<tbody>
<tr>
<td><em>Name:</em>
<td><dfn id=line-box-contain>line-box-contain</dfn>
<tr>
<td><em>Value:</em>
<td>[ block || inline || font || text || replaced || inline-box ] | none
| inherit | initial
<tr>
<td><em>Initial:</em>
<td>block inline replaced
<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>visual
<tr>
<td><em>Computed value:</em>
<td>specified value (except for ‘<span
class=property>inherit</span>’ and ‘<span
class=property>initial</span>’)
</table>
<p>This property enumerates which aspects of the elements in a line box
contribute to the height height of that line box.
<dl>
<dt>block
<dd>The extended block progression dimension of the root inline box must
fit within the line box.
<dt>inline
<dd>The extended block progression dimension of all non-replaced inline
boxes whose ‘<a class=property
href="#line-height">line-height</a>’ is not ‘<span
class=property>none</span>’ in the line box must fit within the
line box.
<dt>font
<dd>The block progression dimension of all non-replaced inline boxes in
the line whose ‘<a class=property
href="#line-height">line-height</a>’ is not ‘<span
class=property>none</span>’ that directly (i.e., within the box but
not within one of its descendants) contain non-removed text must fit
within the line box, where non-removed text is any characters not removed
based on the values of the ‘<span
class=property>linefeed-treatment</span>’, ‘<span
class=property>white-space-treatment</span>’, and ‘<span
class=property>all-space-treatment</span>’ properties. <span
class=issue>[LDB: This isn't quite right. What about zwnj, etc.?</span>
<dt>replaced
<dd>The margin box of all <span title="replaced element"><a
href="#replaced">replaced elements</a></span> within the line must fit
within the line box.
<dt>inline-box
<dd>The margin-box of all non-replaced inline elements in the line whose
‘<a class=property href="#line-height">line-height</a>’ is
not ‘<span class=property>none</span>’ must fit within the
line box. <span class=issue>Should this split into ‘<span
class=property>inline-border</span>’ and ‘<span
class=property>inline-margin</span>’?</span>
</dl>
<p>If the property has no value for all elements within a line, then the
line box has 0 height, and the line within the anonymous inline
established by the block that coincides with the line block is the
baseline of that anonymous inline block (or should it be determined by the
‘<a class=property href="#vertical-align">vertical-align</a>’
property of the block?). <span class=issue>[This is arbitrary. Does anyone
have better ideas?]</span>
<p class=note>Note that the CSS2 model is equivalent to ‘<code
class=css>block inline replaced</code>’ but the backwards-compatible
HTML model is similar to (but not exactly) ‘<code class=css>font
replaced</code>’ [1].
<p class=issue>Concerns: * How does this work with the cascade? * What
about determining the visual size of inline boxes?
<p class=issue>[1] I believe the differences are restricted to the first
line of LI elements, the last line of LI, DD, and DT elements, and issues
concerning whitespace around images. [DB]
<p>The height of each line box is established as follows (we describe the
case for <em><a href="#horizontal">horizontal flow</a></em>, but vertical
flow is analogous). First align all the boxes on the line relative to each
other according to the rules for <span class=property>‘<a
class=property href="#vertical-align">vertical-align</a>’</span>.
The line box must satisfy all of the following constraints:
<ol>
<li>For each box on the line that has <span class=css>‘<span
class=property>font</span>’</span> in its value of <span
class=property>‘<a class=property
href="#line-box-contain">line-box-contain</a>’</span>, the line box
must be high enough to contain the <a href="#top-of" title="top of the
text"></a><a href="#top-of">top and bottom of that box's text</a>.
<li>For each box that has <span class=css><a href="#inline">‘<span
class=property>inline</span>’</a></span> in <span