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<!DOCTYPE html>
<html lang=en>
<head>
<meta content="text/html; charset=utf-8" http-equiv=Content-Type>
<title>CSS Box Alignment Module Level 3</title>
<!--
<link href="http://purl.org/dc/terms/" rel="schema.dcterms">
<link href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright" rel="dcterms.rights">
-->
<meta content="CSS Box Alignment Module Level 3" name=dcterms.title>
<meta content=text name=dcterms.type>
<meta content=2013-05-13 name=dcterms.date>
<meta content="Elika J. Etemad" name=dcterms.creator>
<meta content="Tab Atkins Jr." name=dcterms.creator>
<meta content=W3C name=dcterms.publisher>
<meta content="http://dev.w3.org/c
7292
sswg/css-align/" name=dcterms.identifier>
<link href="#contents" rel=contents>
<link href="#index" rel=index>
<link href="../default.css" rel=stylesheet type="text/css">
<link href="../csslogo.ico" rel="shortcut icon" type="image/x-icon">
<link href="http://www.w3.org/StyleSheets/TR/W3C-ED.css" rel=stylesheet
type="text/css">
<style type="text/css">
.issue th:first-child { text-align: left !important; }
[rowspan] > img { float: right; }
[rowspan] { vertical-align: middle; }
small { display: block; }
</style>
<body>
<div class=head> <!--begin-logo-->
<p><a href="http://www.w3.org/"><img alt=W3C height=48
src="http://www.w3.org/Icons/w3c_home" width=72></a> <!--end-logo-->
<h1>CSS Box Alignment Module Level 3</h1>
<h2 class="no-num no-toc" id=longstatus-date>Editor's Draft 13 May 2013</h2>
<dl>
<dt>This version:
<!--<dd><a href="http://dev.w3.org/csswg/css-align/">http://www.w3.org/TR/2013/WD-css-align-20130513/</a>-->
<dd><a
href="http://dev.w3.org/csswg/css-align/">http://dev.w3.org/csswg/css-align</a>
<dt>Latest version:
<dd><a
href="http://www.w3.org/TR/css3-align/">http://www.w3.org/TR/css3-align/</a>
<dt>Editor's draft:
<dd><a
href="http://dev.w3.org/csswg/css-align/">http://dev.w3.org/csswg/css-align/</a>
<dt>Previous version:
<dd><a
href="http://www.w3.org/TR/2012/WD-css3-align-20120612/">http://www.w3.org/TR/2012/WD-css3-align-20120612/</a>
<dt>Issue Tracking:
<dd><a
href="http://www.w3.org/Style/CSS/Tracker/products/39">http://www.w3.org/Style/CSS/Tracker/products/39</a>
<dt>Feedback:
<dd><a
href="mailto:www-style@w3.org?subject=%5Bcss-align%5D%20feedback">www-style@w3.org</a>
with subject line “<kbd>[css-align] <var>… message topic
…</var></kbd>” (<a
href="http://lists.w3.org/Archives/Public/www-style/"
rel=discussion>archives</a>)
<dt>Editors:
<dd class="h-card vcard"> <a class="p-name fn u-url url"
href="http://fantasai.inkedblade.net/contact" rel=author>Elika J.
Etemad</a>, <span class="p-org org">Mozilla</span>
<dd class="p-author h-card vcard"> <a class="p-name fn u-url url"
href="http://www.xanthir.com/contact" rel=author>Tab Atkins Jr.</a>,
<span class="p-org org">Google Inc.</span>
</dl>
<!--begin-copyright-->
<p class=copyright><a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
rel=license>Copyright</a> © 2013 <a href="http://www.w3.org/"><abbr
title="World Wide Web Consortium">W3C</abbr></a><sup>®</sup> (<a
href="http://www.csail.mit.edu/"><abbr
title="Massachusetts Institute of Technology">MIT</abbr></a>, <a
href="http://www.ercim.eu/"><abbr
title="European Research Consortium for Informatics and Mathematics">ERCIM</abbr></a>,
<a href="http://www.keio.ac.jp/">Keio</a>, <a
href="http://ev.buaa.edu.cn/">Beihang</a>), All Rights Reserved. W3C <a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
<a
href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a>
and <a
href="http://www.w3.org/Consortium/Legal/copyright-documents">document
use</a> rules apply.</p>
<!--end-copyright-->
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc" id=abstract>Abstract</h2>
<p>This module contains the features of <a
href="http://www.w3.org/TR/CSS/">CSS</a> relating to the alignment of
boxes within their containers in the various CSS box layout models: block
layout, table layout, flex layout, and grid layout. (The alignment of text
and inline-level content is defined in <a href="#CSS3TEXT"
rel=biblioentry>[CSS3TEXT]<!--{{CSS3TEXT}}--></a> and <a href="#CSS3LINE"
rel=biblioentry>[CSS3LINE]<!--{{CSS3LINE}}--></a>.) CSS is a language for
describing the rendering of structured documents (such as HTML and XML) on
screen, on paper, in speech, etc.
<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?Subject=%5Bcss-align%5D%20PUT%20SUBJECT%20HERE">
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
“css-align” in the subject, preferably like this:
“[<!---->css-align<!---->] <em>…summary of comment…</em>”
<p>This document was produced by the <a
href="http://www.w3.org/Style/CSS/members">CSS Working Group</a> (part of
the <a href="http://www.w3.org/Style/">Style Activity</a>).
<p>This document was produced by a group operating under the <a
href="http://www.w3.org/Consortium/Patent-Policy-20040205/">5 February
2004 W3C Patent Policy</a>. W3C maintains a <a
href="http://www.w3.org/2004/01/pp-impl/32061/status"
rel=disclosure>public list of any patent disclosures</a> made in
connection with the deliverables of the group; that page also includes
instructions for disclosing a patent. An individual who has actual
knowledge of a patent which the individual believes contains <a
href="http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">Essential
Claim(s)</a> must disclose the information in accordance with <a
href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">section
6 of the W3C Patent Policy</a>.</p>
<!--end-status-->
<p>The following features are at risk: …
<h2 class="no-num no-toc" id=contents> Table of contents</h2>
<!--begin-toc-->
<ul class=toc>
<li><a href="#intro"><span class=secno>1. </span> Introduction</a>
<ul class=toc>
<li><a href="#placement"><span class=secno>1.1. </span> Module
interactions</a>
<li><a href="#values"><span class=secno>1.2. </span> Values</a>
</ul>
<li><a href="#overview"><span class=secno>2. </span> Overview of Alignment
Properties</a>
<li><a href="#alignment-values"><span class=secno>3. </span> Alignment
Values</a>
<ul class=toc>
<li><a href="#positional-values"><span class=secno>3.1. </span>
Positional Alignment: the ‘<code class=css>center</code>’, ‘<code
class=css>stretch</code>’, ‘<code class=css>start</code>’,
‘<code class=css>end</code>’, ‘<code
class=css>self-start</code>’, ‘<code class=css>self-end</code>’,
‘<code class=css>flex-start</code>’, ‘<code
class=css>flex-end</code>’, ‘<code class=css>left</code>’, and
‘<code class=css>right</code>’ keywords</a>
<li><a href="#baseline"><span class=secno>3.2. </span> Baseline
Alignment: the ‘<code class=css>baseline</code>’ keyword</a>
<ul class=toc>
<li><a href="#baseline-rules"><span class=secno>3.2.1. </span>
Determining the Baseline of a Box</a>
</ul>
<li><a href="#distribution-values"><span class=secno>3.3. </span>
Distributed Alignment: the ‘<code class=css>space-between</code>’,
‘<code class=css>space-around</code>’, and ‘<code
class=css>space-evenly</code>’ keywords</a>
<li><a href="#overflow-values"><span class=secno>3.4. </span> Overflow
Alignment: the ‘<code class=css>safe</code>’ and ‘<code
class=css>true</code>’ keywords</a>
</ul>
<li><a href="#content-distribution"><span class=secno>4. </span> Content
Distribution: the ‘<code class=property>justify-content</code>’ and
‘<code class=property>align-content</code>’ properties</a>
<ul class=toc>
<li><a href="#baseline-align-content"><span class=secno>4.1. </span>
Baseline Content-Alignment</a>
</ul>
<li><a href="#self-alignment"><span class=secno>5. </span> Self-Alignment:
Aligning the Box within its Parent</a>
<ul class=toc>
<li><a href="#justify-self-property"><span class=secno>5.1. </span>
Inline/Main-Axis Alignment: the ‘<code
class=property>justify-self</code>’ property</a>
<li><a href="#align-self-property"><span class=secno>5.2. </span>
Block/Cross-Axis Alignment: the ‘<code
class=property>align-self</code>’ property</a>
<li><a href="#baseline-align-self"><span class=secno>5.3. </span>
Baseline Self-Alignment</a>
</ul>
<li><a href="#default-alignment"><span class=secno>6. </span> Default
Alignment</a>
<ul class=toc>
<li><a href="#justify-items-property"><span class=secno>6.1. </span>
Inline/Main-Axis Alignment: the ‘<code
class=property>justify-items</code>’ property</a>
<li><a href="#align-items-property"><span class=secno>6.2. </span>
Block/Cross-Axis Alignment: the ‘<code
class=property>align-items</code>’ property</a>
</ul>
<li><a href="#changes"><span class=secno>7. </span> Changes</a>
<li><a href="#conformance"><span class=secno>8. </span> Conformance</a>
<ul class=toc>
<li><a href="#conventions"><span class=secno>8.1. </span> Document
conventions</a>
<li><a href=&q
1898
uot;#conformance-classes"><span class=secno>8.2. </span>
Conformance classes</a>
<li><a href="#partial"><span class=secno>8.3. </span> Partial
implementations</a>
<li><a href="#experimental"><span class=secno>8.4. </span> Experimental
implementations</a>
<li><a href="#testing"><span class=secno>8.5. </span> Non-experimental
implementations</a>
<li><a href="#cr-exit-criteria"><span class=secno>8.6. </span> CR exit
criteria</a>
</ul>
<li class=no-num><a href="#acknowledgments"> Acknowledgments</a>
<li class=no-num><a href="#references"> References</a>
<ul class=toc>
<li class=no-num><a href="#normative-references"> Normative
references</a>
<li class=no-num><a href="#other-references"> Other references</a>
</ul>
<li class=no-num><a href="#index"> Index</a>
<li class=no-num><a href="#property-index"> Property index</a>
</ul>
<!--end-toc-->
<h2 id=intro><span class=secno>1. </span> Introduction</h2>
<p><em>This section is not normative.</em>
<p>CSS Levels 1 and 2 allowed for the alignment of text via ‘<code
class=property>text-align</code>’ and the alignment of blocks by
balancing ‘<code class=css>auto</code>’ margins. However, except in
table cells, vertical alignment was not possible. As CSS3 adds further
capabilities, the ability to align boxes in various dimensions becomes
more critical. This module attempts to create a cohesive and common box
alignment model to share among all of CSS.
<p class=note>The alignment of text and inline-level content is defined in
<a href="#CSS3TEXT" rel=biblioentry>[CSS3TEXT]<!--{{CSS3TEXT}}--></a> and
<a href="#CSS3LINE" rel=biblioentry>[CSS3LINE]<!--{{CSS3LINE}}--></a>.
<p>Inspiration for this document:
<ul>
<li><a
href="http://wiki.csswg.org/ideas/centering#alignment-property">summary
of a discussion for implementing <CENTER></a>
<li><a
href="https://lists.w3.org/Archives/Member/w3c-css-wg/2008AprJun/0015.html">Minutes
from March 2008 F2F</a>
<li><a
href="http://lists.w3.org/Archives/Public/www-style/2012Feb/0743.html">fantasai's
attempt to merge all alignment properties</a>
</ul>
<h3 id=placement><span class=secno>1.1. </span> Module interactions</h3>
<p>This module adds some new alignment capabilities to the block layout
model described in <a href="#CSS21"
rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a> chapters 9 and 10 and defines
the interaction of these properties with the alignment of table cell
content using ‘<code class=property>vertical-align</code>’, as defined
in <a href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a> chapter
17. The interaction of these properties with Grid Layout <a
href="#CSS3-GRID-LAYOUT"
rel=biblioentry>[CSS3-GRID-LAYOUT]<!--{{!CSS3-GRID-LAYOUT}}--></a> and
Flexible Box Layout <a href="#CSS3-FLEXBOX"
rel=biblioentry>[CSS3-FLEXBOX]<!--{{!CSS3-FLEXBOX}}--></a> is defined in
their respective modules.
<p>No properties in this module apply to the <code>::first-line</code> or
<code>::first-letter</code> pseudo-elements.
<h3 id=values><span class=secno>1.2. </span> Values</h3>
<p>This specification follows the <a
href="http://www.w3.org/TR/CSS21/about.html#property-defs">CSS property
definition conventions</a> from <a href="#CSS21"
rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>. Value types not defined in
this specification are defined in CSS Level 2 Revision 1 <a
href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>. Other CSS
modules may expand the definitions of these value types: for example <a
href="#CSS3VAL" rel=biblioentry>[CSS3VAL]<!--{{CSS3VAL}}--></a>, when
combined with this module, adds the ‘<code class=css>initial</code>’
keyword as a possible property value.
<p>In addition to the property-specific values listed in their definitions,
all properties defined in this specification also accept the <a
href="http://www.w3.org/TR/CSS21/cascade.html#value-def-inherit">inherit</a>
keyword as their property value. For readability it has not been repeated
explicitly.
<h2 id=overview><span class=secno>2. </span> Overview of Alignment
Properties</h2>
<p>The alignment properties in CSS can be described along two axes:
<ul>
<li>which dimension they apply to (inline vs. stacking), and
<li>whether they control the position of the box within its parent, or the
box's content within itself.
</ul>
<p class=note>This proposal uses the terms ‘<code
class=property>justify</code>’ and ‘<code
class=property>align</code>’ to distinguish between alignment in the
inline and stacking dimensions, respectively. The choice is somewhat
arbitrary, but having the two terms allows for a consistent naming scheme
that works across all of CSS's layout models.
<p>The following table summarizes the proposed alignment properties and the
display types they can apply to.
<table class=data>
<colgroup span=1></colgroup>
<colgroup span=2></colgroup>
<colgroup span=1></colgroup>
<thead>
<tr>
<th>Common
<th>Axis
<th>Aligns
<th>Applies to
<tbody>
<tr>
<th>‘<a href="#justify-content"><code
class=property>justify-content</code></a>’
<td>inline
<td rowspan=2><img alt="" height=106 src="images/content-example.svg"
width=106>content within element <small>(effectively adjusts
padding)</small>
<td>block containers and flex containers
<tr>
<th>‘<a href="#align-content"><code
class=property>align-content</code></a>’
<td>stacking
<td>block containers and flex containers
<tbody>
<tr>
<th>‘<a href="#justify-self"><code
class=property>justify-self</code></a>’
<td>inline
<td rowspan=2><img alt="" height=106 src="images/self-example.svg"
width=106> element within parent <small>(effectively adjusts
margins)</small>
<td>block-level elements and grid items
<tr>
<th>‘<a href="#align-self"><code
class=property>align-self</code></a>’
<td>stacking
<td>flex items and grid items
<tbody>
<tr>
<th>‘<a href="#justify-items"><code
class=property>justify-items</code></a>’
<td>inline
<td rowspan=2><img alt="" height=106 src="images/items-example.svg"
width=106> items inside element <small>(controls child items’
‘<code class=css>align/justify-self: auto</code>’)</small>
<td>grid containers
<tr>
<th>‘<a href="#align-items"><code
class=property>align-items</code></a>’
<td>stacking
<td>flex containers and grid containers
</table>
<p class=issue> The exact definition of these properties outside what's <a
href="http://www.w3.org/TR/css3-flexbox">what's defined in Flexbox</a> is
still <strong>being worked out</strong>. This is a <strong>second Working
Draft</strong> and is <strong>NOT STABLE</strong>.
<p class=note> The ‘<code class=property>-items</code>’ values don't
affect the element itself. When set on a flex container or grid container,
they specify the interpretation of any ‘<code
class=css>align/justify-self: auto</code>’ used on the items in the
container element.
<h2 id=alignment-values><span class=secno>3. </span> Alignment Values</h2>
<p>All of the alignment properties use a common set of values, defined
below.
<dl>
<dt><dfn id=alignment-subject>alignment subject</dfn>
<dd> The <a href="#alignment-subject"><i>alignment subject</i></a> is the
thing or things being aligned by the property. For ‘<a
href="#justify-self"><code class=property>justify-self</code></a>’ and
‘<a href="#align-self"><code class=property>align-self</code></a>’,
the <a href="#alignment-subject"><i>alignment subject</i></a> is the
margin box of the box the property is set on. For ‘<a
href="#justify-content"><code
class=property>justify-content</code></a>’ and ‘<a
href="#align-content"><code class=property>align-content</code></a>’,
the <a href="#alignment-subject"><i>alignment subject</i></a> is defined
by the layout mode.
<dt><dfn id=alignment-container>alignment container</dfn>
<dd> The <a href="#alignment-container"><i>alignment container</i></a> is
the rectangle that the <a href="#alignment-subject"><i>alignment
subject</i></a> is aligned within. This is defined by the layout mode,
but is usually the <a href="#alignment-subject"><i>alignment
subject</i></a>’s containing block.
</dl>
<h3 id=positional-values><span class=secno>3.1. </span> Positional
Alignment: the ‘<a href="#center"><code class=css>center</code></a>’,
‘<a href="#stretch0"><code class=css>stretch</code></a>’, ‘<a
href="#start"><code class=css>start</code></a>’, ‘<a href="#end"><code
class=css>end</code></a>’, ‘<a href="#self-start"><code
class=css>self-start</code></a>’, ‘<a href="#self-end"><code
class=css>self-end</code></a>’, ‘<a href="#flex-start"><code
class=css>flex-start</code></a>’, ‘<a href="#flex-end"><code
class=css>flex-end</code></a>’, ‘<a href="#left"><code
class=css>left</code></a>’, and ‘<a href="#right"><code
class=css>right</code></a>’ keywords</h3>
<p> The positional alignment keywords specify a position for an <a
href="#alignment-subject"><i>alignment subject</i></a> with respect to its
<a href="#alignment-container"><i>alignment container</i></a>.
<p> The <a href="#ltitem-position"><var><item-position></var></a> set of
values is used by ‘<a href="#justify-self"><code
class=property>justify-self</code></a>’ and ‘<a
href="#align-self"><code class=property>align-self</code></a>’ to align
the box within its <a href="#alignment-container"><i>alignment
container</i></a>, and also by ‘<code
class=css>justify/align-items</code>’ (to specify default values for
‘<code class=css>justify/align-self</code>’). The <a
href="#ltcontent-position"><var><content-position></var></a> set of
values is used by ‘<a href="#justify-content"><code
class=property>justify-content</code></a>’ and ‘<a
href="#align-content"><code class=property>align-content</code></a>’ to
align the box's contents within itself.
<pre class=prod>
<dfn
id=ltitem-position><item-
67F6
position></dfn> = center | start | end | self-start | self-end |
flex-start | flex-end | left | right;
<dfn
id=ltcontent-position><content-position></dfn> = center | start | end | flex-start | flex-end | left | right;</pre>
<p> Values have the following meanings:
<dl>
<dt><dfn id=center>‘<code class=css>center</code>’</dfn>
<dd>Centers the <a href="#alignment-subject"><i>alignment subject</i></a>
within its <a href="#alignment-container"><i>alignment container</i></a>.
<dt><dfn id=stretch>‘<code class=css>stretch</code>’</dfn>
<dd>If the ‘<code class=property>width</code>’ or ‘<code
class=property>height</code>’ (as appropriate) of the <a
href="#alignment-subject"><i>alignment subject</i></a> is ‘<code
class=css>auto</code>’, its used value is the length necessary to make
the <a href="#alignment-subject"><i>alignment subject</i></a>’s outer
size as close to the size of the <a
href="#alignment-container"><i>alignment container</i></a> as possible,
while still respecting the constraints imposed by ‘<code
class=css>min/max-width/height</code>’. Otherwise, this is equivalent
to ‘<a href="#start"><code class=css>start</code></a>’.
<dt><dfn id=start>‘<code class=css>start</code>’</dfn>
<dd>Aligns the <a href="#alignment-subject"><i>alignment subject</i></a>
to be flush with the <a href="#alignment-container"><i>alignment
container</i></a>’s start edge.
<dt><dfn id=end>‘<code class=css>end</code>’</dfn>
<dd>Aligns the <a href="#alignment-subject"><i>alignment subject</i></a>
to be flush with the <a href="#alignment-container"><i>alignment
container</i></a>’s end edge.
<dt><dfn id=self-start>‘<code class=css>self-start</code>’</dfn>
<dd>Aligns the <a href="#alignment-subject"><i>alignment subject</i></a>
to be flush with the edge of the <a
href="#alignment-container"><i>alignment container</i></a> corresponding
to the <a href="#alignment-subject"><i>alignment subject</i></a>’s
start side.
<dt><dfn id=self-end>‘<code class=css>self-end</code>’</dfn>
<dd>Aligns the <a href="#alignment-subject"><i>alignment subject</i></a>
to be flush with the edge of the <a
href="#alignment-container"><i>alignment container</i></a> corresponding
to the <a href="#alignment-subject"><i>alignment subject</i></a>’s end
side.
<dt><dfn id=flex-start>‘<code class=css>flex-start</code>’</dfn>
<dd><strong>Only used in flex layout.</strong> <a href="#CSS3-FLEXBOX"
rel=biblioentry>[CSS3-FLEXBOX]<!--{{!CSS3-FLEXBOX}}--></a> Aligns the <a
href="#alignment-subject"><i>alignment subject</i></a> to be flush with
the edge of the <a href="#alignment-container"><i>alignment
container</i></a> corresponding to the <i>flex container</i>’s
main-start or cross-start side, as appropriate. When used in layout modes
other than Flexbox, this is equivalent to ‘<a href="#start"><code
class=css>start</code></a>’.
<dt><dfn id=flex-end>‘<code class=css>flex-end</code>’</dfn>
<dd><strong>Only used in flex layout.</strong> Aligns the <a
href="#alignment-subject"><i>alignment subject</i></a> to be flush with
the edge of the <a href="#alignment-container"><i>alignment
container</i></a> corresponding to the <i>flex container</i>’s main-end
or cross-end side, as appropriate. When used in layout modes other than
Flexbox, this is equivalent to ‘<a href="#start"><code
class=css>start</code></a>’.
<dt><dfn id=left>‘<code class=css>left</code>’</dfn>
<dd>Aligns the <a href="#alignment-subject"><i>alignment subject</i></a>
to be flush with the <a href="#alignment-container"><i>alignment
container</i></a>’s <a
href="http://www.w3.org/TR/css3-writing-modes/#line-left">line-left</a>
edge. If the property's axis is not parallel with the inline axis, this
is equivalent to ‘<a href="#start"><code class=css>start</code></a>’.
<dt><dfn id=right>‘<code class=css>right</code>’</dfn>
<dd>Aligns the <a href="#alignment-subject"><i>alignment subject</i></a>
to be flush with the <a href="#alignment-container"><i>alignment
container</i></a>’s <a
href="http://www.w3.org/TR/css3-writing-modes/#line-right">line-right</a>
edge. If the property's axis is not parallel with the inline axis, this
is equivalent to ‘<a href="#start"><code class=css>start</code></a>’.
</dl>
<p class=issue>Add example images.
<h3 id=baseline><span class=secno>3.2. </span> Baseline Alignment: the
‘<a href="#baseline0"><code class=css>baseline</code></a>’ keyword</h3>
<p>Baseline alignment is a form of positional alignment that relies on
aligning the baselines of related <a
href="#alignment-subject"><i>alignment subjects</i></a> to each other.
<dl>
<dt><dfn id=baseline0>‘<code class=css>baseline</code>’</dfn>
<dd>
<p> For table cells, grid items, and flex items, aligns the cell/item's
<i>first formatted line</i>'s baseline, if any, with the same
baseline in other ‘<a href="#baseline0"><code
class=css>baseline</code></a>’-aligned cells/items in the row/column
(as appropriate for the axis).
<p> In the case of ‘<a href="#align-content"><code
class=property>align-content</code></a>’/‘<a
href="#justify-content"><code
class=property>justify-content</code></a>’, this shifts the content of
the box within it, and may also affect its sizing. In the case of ‘<a
href="#align-self"><code class=property>align-self</code></a>’/‘<a
href="#justify-self"><code class=property>justify-self</code></a>’
this shifts the entire box within its container, and may affect the
sizing of its container.
<p> If the <a href="#alignment-subject"><i>alignment subject</i></a>’s
position is not fully determined by baseline alignment, the content is
start-aligned insofar as possible while preserving the baseline
alignment. (Content that has no first-line baseline is thus
start-aligned.)
</dl>
<p class=issue>Add example images.
<h4 id=baseline-rules><span class=secno>3.2.1. </span> Determining the
Baseline of a Box</h4>
<p> The baseline of a box is determined differently based on the layout
model, as follow:
<dl>
<dt>‘<code class=css>block</code>’
<dt>‘<code class=css>list-item</code>’
<dd>
<p> The inline-axis baseline of a block is the baseline of the first
in-flow line box in the block, or the first in-flow block-level child in
the block that has a baseline, whichever comes first. If there is no
such line box or child, then the block has no baseline. For the purposes
of finding a baseline, in-flow boxes with a scrolling mechanisms (see
the ‘<code class=property>overflow</code>’ property) must be
considered as if scrolled to their origin position.
<p> A block has no block-axis baseline.
<dt>‘<code class=css>table</code>’
<dd>
<p> The inline-axis baseline of a table box is the baseline of its first
row. However, when calculating the baseline of an inline-block, table
boxes must be skipped.
<p> The block-axis baseline of a table is undefined.
<p class=issue> Or does it have no baseline? Or is it based on its first
column?
<dt>‘<code class=css>table-row</code>’
<dd>
<p> If any cells in the row participate in its baseline alignment, the
inline-axis baseline of the row is their baseline, after baseline
alignment has been performed. Otherwise, the inline-axis baseline of the
row is the bottom content edge of the lowest cell in the row. <a
href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>
<p> A table row has no block-axis baseline.
<dt>‘<code class=css>table-cell</code>’
<dd>
<p> The inline-axis baseline of a table cell is the baseline of the first
in-flow line box in the cell, or the first in-flow element that
contributes a baseline in that axis, whichever comes first.
<p> A table cell has no block-axis baseline.
<dt>‘<code class=css>flex</code>’
<dd> See <a href="http://www.w3.org/TR/css3-flexbox/#flex-baselines">Flex
Baselines</a> in <a href="#CSS3-FLEXBOX"
rel=biblioentry>[CSS3-FLEXBOX]<!--{{!CSS3-FLEXBOX}}--></a>.
<dt>‘<code class=css>grid</code>’
<dd> See <a
href="http://www.w3.org/TR/css3-grid-layout/#grid-baselines">Grid
Baselines</a> in <a href="#CSS3-GRID-LAYOUT"
rel=biblioentry>[CSS3-GRID-LAYOUT]<!--{{!CSS3-GRID-LAYOUT}}--></a>.
</dl>
<p class=issue> Maybe these things are wrong? CSS 2.1 is really weird about
baseline alignment. This whole section needs to be better defined and
reviewed.
<h3 id=distribution-values><span class=secno>3.3. </span> Distributed
Alignment: the ‘<a href="#space-between"><code
class=css>space-between</code></a>’, ‘<a href="#space-around"><code
class=css>space-around</code></a>’, and ‘<a href="#space-evenly"><code
class=css>space-evenly</code></a>’ keywords</h3>
<p>The distribution values are used by ‘<a href="#justify-content"><code
class=property>justify-content</code></a>’ and ‘<a
href="#align-content"><code class=property>align-content</code></a>’ to
distribute the items in the <a href="#alignment-subject"><i>alignment
subject</i></a> evenly between the start and end edges of the <a
href="#alignment-container"><i>alignment container</i></a>. When the <a
href="#alignment-subject"><i>alignment subject</i></a> cannot be
distributed in this way, they behave as their <dfn
id=fallback-alignment>fallback alignment</dfn>. Each distribution value
has an associated <a
href="#ltcontent-position"><var><content-position></var></a> as a <a
href="#fallback-alignment"><i>fallback alignment</i></a>, but one can
alternatively be explicitly specified in the property.
<pre class=prod>
<dfn
id=ltcontent-distribution><content-distribution></dfn> = space-between | space-around | space-evenly | stretch</pre>
<dl>
<dt><dfn id=space-between>‘<code class=css>space-between</code>’</dfn>
<dd>The items are evenly distributed in the <a
href="#alignment-container"><i>alignment container</i></a>. The first
item is placed flush with the start edge of the <a
href="#alignment-container"><i>alignment container</i></a>, the last item
is placed flush with the end edge of the <a
href="#alignment-container"><i>alignment container</i></a>, and the
remaining items are distributed so that the spacing between any two
adjacent items is the same. Unless otherwise specified, this value falls
back to ‘<a href="#start"><code class=css>start</code></a>’.
<dt><dfn id=space-around>‘<code class=css>space-around</code>’</dfn>
<dd>The items are evenly distributed in the <a
href="#alignment-container"><i>alignment container</i></a>, with a
half-size space on either end. The items are distributed so that the
spacing between any two adjacent items is the same, and the spacing
before the first and after the last item is half the size of the other
spacing. Unless otherwise specified, this value falls back to ‘<a
href="#center"><code class=css>center</code></a>’.
<dt><dfn id=space-evenly>‘<code class=css>space-evenly</code>’</dfn>
<dd>The items are evenly distributed in the <a
href="#alignment-container"><i>alignment container</i></a>, with a
full-size space on either end. The items are distributed so that the
spacing between any two adjacent items, before the first item, and after
the last item is the same. Unless otherwise specified, this value falls
back to ‘<a href="#center"><code class=css>center</code></a>’.
<dt><dfn id=stretch0>‘<code class=css>stretch</code>’</dfn>
<dd>If the combined size of the items is less than the size of the <a
href="#alignment-container"><i>alignment container</i></a>, any ‘<code
class=css>auto</code>’-sized items have their size increased equally so
that the combined size exactly fills the <a
href="#alignment-container"><i>alignment container</i></a>. Otherwise, or
if there are no ‘<code class=css>auto</code>’-sized items, this value
is identical to ‘<a href="#flex-start"><code
class=css>flex-start</code></a>’. <span class=note>(For layout modes
other than flex layout, ‘<a href="#flex-start"><code
class=css>flex-start</code></a>’ is identical to ‘<a
href="#start"><code class=css>start</code></a>’.)</span>
</dl>
<p class=issue>Add example images.
<h3 id=overflow-values><span class=secno>3.4. </span> Overflow Alignment:
the ‘<a href="#safe"><code class=css>safe</code></a>’ and ‘<a
href="#true"><code class=css>true</code></a>’ keywords</h3>
<p>When the <a href="#alignment-subject"><i>alignment subject</i></a> is
larger than the <a href="#alignment-container"><i>alignment
container</i></a>, it will overflow. Some alignment modes, if honored in
this situation, may cause data loss: for example, if the contents of a
sidebar are centered, when they overflow they may send part of their boxes
past the viewport's start edge, which can't be scrolled to.
<p>To help combat this problem, an <dfn id=overflow-alignment>overflow
alignment</dfn> mode can be explicitly specified. "True" alignment honors
the specified alignment mode in overflow situations, even if it causes
data loss, while "safe" alignment changes the alignment mode in overflow
situations in an attempt to avoid data loss.
<p>If the <a href="#overflow-alignment"><i>overflow alignment</i></a> isn't
explicitly specified, the default <a
href="#overflow-alignment"><i>overflow alignment</i></a> is determined by
the layout mode. Document-centric layout modes, such as block layout,
default to "safe" <a href="#overflow-alignment"><i>overflow
alignment</i></a>, while design-centric layout modes, such as flex layout,
default to "true" <a href="#overflow-alignment"><i>overflow
alignment</i></a>.
<pre class=prod>
<dfn
id=ltoverflow-position><overflow-position></dfn> = true | safe</pre>
<dl>
<dt><dfn id=safe>‘<code class=css>safe</code>’</dfn>
<dd>If the size of the <a href="#alignment-subject"><i>alignment
subject</i></a> overflows the <a href="#alignment-container"><i>alignment
container</i></a>, the <a href="#alignment-subject"><i>alignment
subject</i></a> is instead aligned as if the alignment mode were ‘<a
href="#start"><code class=css>start</code></a>’.
<dt><dfn id=true>‘<code class=css>true</code>’</dfn>
<dd>Regardless of the relative sizes of the <a
href="#alignment-subject"><i>alignment subject</i></a> and <a
href="#alignment-container"><i>alignment container</i></a>, the given
alignment value is honored.
</dl>
<p class=issue>Transplant example 10 from flexbox.
<h2 id=content-distribution><span class=secno>4. </span> Content
Distribution: the ‘<a href="#justify-content"><code
class=property>justify-content</code></a>’ and ‘<a
href="#align-content"><code class=property>align-content</code></a>’
properties</h2>
<p>The ‘<a href="#justify-content"><code
class=property>justify-content</code></a>’ and ‘<a
href="#align-content"><code class=property>align-content</code></a>’
properties control alignment of the box's content within the box.
<div class=figure>
<p><img
alt="Diagram showing that the alignment of the content within the element is affected."
height=212 src="images/content-example.svg" width=212>
</div>
<table class=propdef>
<tbody>
<tr>
<th>Name:
<td><dfn id=justify-content>justify-content</dfn>, <dfn
id=align-content>align-content</dfn>
<tr>
<th><a href="#values">Value</a>:
<td>auto | <a href="#baseline">baseline</a> | [ <a
href="#ltcontent-distribution"><var><content-distribution></var></a>
<a href="#ltcontent-position"><var><content-position></var></a>? |
<a href="#ltcontent-position"><var><content-position></var></a> ] &&
<a href="#ltoverflow-position"><var><overflow-position></var></a>?
<tr>
<th>Initial:
<td>auto
<tr>
<th>Applies to:
<td>block containers, flex containers, and grid containers
<tr>
<th>Inherited:
<td>no
<tr>
<th>Percentages:
<td>N/A
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>specified value
<tr>
<th>Animatable:
<td>no
<tr>
<th>Canonical order:
<td><abbr title="follows order of property value definition">per
grammar</abbr>
</table>
<p> Aligns the contents of the box as a whole along the box's
inline/row/main axis. Values other than ‘<code class=css>auto</code>’
are <a href="#alignment-values">defined above</a>. If both a <a
href="#ltcontent-distribution"><var><content-distribution></var></a>
and <a href="#ltcontent-position"><var><content-position></var></a> are
given, the second value represents an explicit <a
href="#fallback-alignment"><i>fallback alignment</i></a>.
<dl>
<dt>Block Containers:
<dd>
<p>The <a href="#alignment-container"><i>alignment container</i></a> is
the <i>block container</i>’s content box. The <a
href="#alignment-subject"><i>alignment subject</i></a> is the entire
contents of the block.
<p>The ‘<a href="#align-content"><code
class=property>align-content</code></a>’ property applies along the
<i>block axis</i>, but if a <a
href="#ltcontent-distribution"><var><content-distribution></var></a>
is specified the <a href="#fallback-alignment"><i>fallback
alignment</i></a> is used instead. The ‘<a
href="#justify-content"><code
class=property>justify-content</code></a>’ property does not apply to
and has no effect on block containers.
<p>All values other than ‘<code class=css>auto</code>’ force the
block container to establish a new formatting context. For table cells,
the behavior of the ‘<code class=css>auto</code>’ depends on the
computed value of ‘<code class=property>vertical-align</code>’:
‘<code class=css>top</code>’ makes it behave as ‘<a
href="#start"><code class=css>start</code></a>’, ‘<code
class=css>middle</code>’ makes it behave as ‘<a href="#center"><code
class=css>center</code></a>’, ‘<code class=css>bottom</code>’
makes it behave as ‘<a href="#end"><code class=css>end</code></a>’,
and all other values make it behave as ‘<a href="#baseline0"><code
class=css>baseline</code></a>’. ‘<code class=css>auto</code>’
otherwise behaves as ‘<a href="#start"><code
class=css>start</code></a>’.
<dt>Multicol Layout:
<dd>
<p>The <a href="#alignment-container"><i>alignment container</i></a> is
the <i>multi-column element</i>’s content box. The <a
href="#alignment-subject"><i>alignment subject</i></a> is the column
boxes, as a unit.
<p>The ‘<a href="#align-content"><code
class=property>align-content</code></a>’ property applies along the
<i>block axis</i>, but if a <a
href="#ltcontent-distribution"><var><content-distribution></var></a>
is specified the <a href="#fallback-alignment"><i>fallback
alignment</i></a> is used instead. The ‘<a
href="#justify-content"><code
class=property>justify-content</code></a>’ property does not apply to
and has no effect on multi-column elements.
<p>‘<code class=css>auto</code>’ behaves as ‘<a href="#start"><code
class=css>start</code></a>’.
<dt>Flex Containers:
<dd>
<p>‘<code class=css>auto</code>’ computes to ‘<a
href="#stretch0"><code class=css>stretch</code></a>’.
<p>The <a href="#alignment-container"><i>alignment container</i></a> is
the <i>flex container</i>’s content box. For ‘<a
href="#justify-content"><code
class=property>justify-content</code></a>’, the <a
href="#alignment-subject"><i>alignment subject</i></a> is the <i>flex
items</i> in each <i>flex line</i>; for ‘<a
href="#align-content"><code class=property>align-content</code></a>’,
the <a href="#alignment-subject"><i>alignment subject</i></a> is the
<i>flex lines</i>.
<p>The ‘<a href="#align-content"><code