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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 profile="http://www.w3.org/2006/03/hcard"><meta
content="text/html; charset=utf-8" http-equiv=Content-Type>
<title>CSS Regions Module Level 3</title>
<link href=default.css rel=stylesheet type="text/css">
<style type="text/css">
/* Alternate stylesheet fonts are here because in some browsers (Opera 11.5) */
/* The fonts are not applied if only loaded from the alternate stylesheet */
/* License font the following two fonts: fonts/Droid-Serif-fontfacekit/Google Android License.txt */
@import url(fonts/Droid-Serif-fontfacekit/stylesheet.css);
@import url(fonts/Droid-Sans-Mono-fontfacekit/stylesheet.css);
/*
@import url(http://fonts.googleapis.com/css?family=Droid+Serif:700,400,400italic,700italic);
@import url(http://fonts.googleapis.com/css?family=Droid+Sans+Mono);
*/
a.toggle {
position: fixed;
top: 0.5em;
right: 0.5em;
font-size: smaller;
color: gray;
opacity: 0.2;
}
a.toggle:hover {
opacity: 1;
color: #46A4E9;
}
.issue.resolved, .issue.stale, .issue.moved {
display: none;
}
#region-style-example p, #region-style-example pre {
clear: both;
}
#region_styling_illustration {
margin: 0px auto;
width: 70ex;
}
.big.note {
font-size: 1.2em;
line-height: 1.3em;
color: #2f2f2f;
}
.big.note:before {
content: "NOTE";
display: block;
color: rgba(0, 0, 0, 0.15);
font-weight: bold;
margin-bottom: 0.5em;
}
#mobile-logo {
display: none;
}
</style>
<link href="http://www.w3.org/StyleSheets/TR/W3C-ED.css" rel=stylesheet
type="text/css">
<link href=alternate-spec-style.css id=st rel=stylesheet
title="alternate spec style" type="text/css">
<body>
<div class=head id=div-head>
<p><a href="http://www.w3.org/"><img alt=W3C height=53 id=mobile-logo
src="http://www.w3.org/2008/site/images/logo-w3c-mobile-lg" width=90></a>
<!--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--></p>
<h1 id=css-regions-module>CSS Regions Module Level 3</h1>
<h2 class="no-num no-toc" id=longstatus-date>Editor's Draft 16 December
2011</h2>
<dl>
<dt>This version:
<dd><a
href="http://www.w3.org/TR/2011/ED-css3-regions-20111216/">http://www.w3.org/csswg/css3-regions</a>
<dt>Latest version:
<dd><a
href="http://www.w3.org/TR/css3-regions/">http://www.w3.org/TR/css3-regions/</a>
<dt>Previous version:
<dd><a
href="http://www.w3.org/TR/2011/WD-css3-regions-20111129/">http://www.w3.org/TR/2011/WD-css3-regions-20111129/</a>
<dt>Editors:
<dd class=vcard><span class=fn>Vincent Hardy</span>, <span
class=org>Adobe Systems, Inc.</span>, <span
class=email>vhardy@adobe.com</span>
<dd class=vcard><span class=fn>Alex Mogilevsky</span>, <span
class=org>Microsoft</span>, <span
class=email>alexmog@microsoft.com</span>
</dl>
<!--begin-copyright-->
<p class=copyright><a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
rel=license>Copyright</a> © 2011 <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.eu/"><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 regions module allows content to flow across multiple areas
called regions. The regions are not necessarily contiguous in the document
order. The CSS regions module provides an advanced content flow mechanism,
which can be combined with positioning schemes as defined by other CSS
modules such as the Multi-Column Module <a href="#CSS3COL"
rel=biblioentry>[CSS3COL]<!--{{CSS3COL}}--></a> or the Grid Layout Module
<a href="#CSS3-GRID-LAYOUT"
rel=biblioentry>[CSS3-GRID-LAYOUT]<!--{{CSS3-GRID-LAYOUT}}--></a> to
position the regions where content flows.
<h2 class="no-num no-toc" id=status-of-this-document>Status of this
document</h2>
<p class="big note">This document uses an experimental style sheet. We
welcome your feedback on the styles at <a
href="mailto:site-comments@w3.org">site-comments@w3.org</a>.</p>
<!--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=%5Bcss3-regions%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
“css3-regions” in the subject, preferably like this:
“[<!---->css3-regions<!---->] <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. An individual who has actual
knowledge of a patent which the individual believes contains <a
href="/Consortium/Patent-Policy-20040205/#def-essential">Essential
Claim(s)</a> must disclose the information in accordance with <a
href="/Consortium/Patent-Policy-20040205/#sec-Disclosure">section 6 of the
W3C Patent Policy</a>.</p>
<!--end-status-->
<p>This draft is related to the drafts about Multi-column Layout <a
href="#CSS3COL" rel=biblioentry>[CSS3COL]<!--{{CSS3COL}}--></a>, Grid
Layout <a href="#CSS3GRID"
rel=biblioentry>[CSS3GRID]<!--{{CSS3GRID}}--></a>, Flexible Box La
A0B3
yout <a
href="#CSS3-FLEXBOX"
rel=biblioentry>[CSS3-FLEXBOX]<!--{{CSS3-FLEXBOX}}--></a>, and Template
Layout <a href="#CSS3LAYOUT"
rel=biblioentry>[CSS3LAYOUT]<!--{{CSS3LAYOUT}}--></a>.
<h2 class="no-num no-toc" id=table-of-contents>Table of contents</h2>
<!--begin-toc-->
<ul class=toc>
<li><a href="#introduction"><span class=secno>1. </span>Introduction</a>
<ul class=toc>
<li><a href="#named-flows-and-regions"><span class=secno>1.1.
</span>Named flows and regions</a>
<li><a href="#region-styling"><span class=secno>1.2. </span>Regions
styling</a>
</ul>
<li><a href="#css-regions-concepts"><span class=secno>2. </span>CSS
regions concepts</a>
<ul class=toc>
<li><a href="#regions"><span class=secno>2.1. </span>Regions</a>
<li><a href="#named-flow"><span class=secno>2.2. </span>Named flow</a>
<li><a href="#regions-flow-breaking-rules"><span class=secno>2.3.
</span>Regions flow breaking rules</a>
</ul>
<li><a href="#relation-to-document-events"><span class=secno>3.
</span>Relation to document events</a>
<li><a href="#properties-and-rules"><span class=secno>4. </span>Properties
and rules</a>
<ul class=toc>
<li><a href="#the-flow-into-property"><span class=secno>4.1. </span>The
‘<code class=property>flow-into</code>’ property</a>
<li><a href="#the-flow-from-property"><span class=secno>4.2. </span>The
‘<code class=property>flow-from</code>’ property</a>
<ul class=toc>
<li><a href="#auto-width-on-regions"><span class=secno>4.2.1.
</span>Auto width on regions</a>
<li><a href="#auto-height-on-regions"><span class=secno>4.2.2.
</span>Auto height on regions</a>
</ul>
<li><a href="#region-flow-break"><span class=secno>4.3. </span>Region
flow break properties: ‘<code
class=property>break-before</code>’, ‘<code
class=property>break-after</code>’, ‘<code
class=property>break-inside</code>’</a>
<li><a href="#the-region-overflow-property"><span class=secno>4.4.
</span>The region-overflow property</a>
<li><a href="#the-at-region-style-rule"><span class=secno>4.5.
</span>The @region rule</a>
</ul>
<li><a href="#pseudo_elements"><span class=secno>5.
</span>Pseudo-elements</a>
<ul class=toc>
<li><a href="#processing-model"><span class=secno>5.1. </span>Processing
model</a>
</ul>
<li><a href="#cssom_view_and_css_regions"><span class=secno>6.
</span>CSSOM view and CSS regions</a>
<ul class=toc>
<li><a href="#the-namedflow-interface"><span class=secno>6.1. </span>The
NamedFlow interface</a>
<li><a href="#extension-to-the-element-interface"><span class=secno>6.2.
</span>Extension to the Element interface</a>
<li><a href="#region-flow-layout-events"><span class=secno>6.3.
</span>Region flow layout events</a>
</ul>
<li><a href="#relation-to-other-specifications"><span class=secno>7.
</span>Relation to other specifications</a>
<li><a href="#usecases"><span class=secno>8. </span>Use Cases</a>
<li><a href="#conformance"><span class=secno>9. </span>Conformance</a>
<li><a href="#changes"><span class=secno>10. </span>Changes</a>
<ul class=toc>
<li><a href="#changes_from_June_09_2011"><span class=secno>10.1.
</span>Changes from November 29<sup>th</sup> 2011 version</a>
<li><a href="#changes_from_June_09_2011"><span class=secno>10.2.
</span>Changes from June 09<sup>th</sup> 2011 version</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=introduction><span class=secno>1. </span>Introduction</h2>
<p><em>This section is non-normative.</em>
<p>Capturing the complex layouts of a typical magazine, newspaper, or
textbook requires capabilities beyond those available in existing CSS
modules. This is the purpose of the CSS regions module.
<p>The CSS regions module can be seen as an extension of the concept of
multi-column elements. With CSS Multi-column layout <a href="#CSS3COL"
rel=biblioentry>[CSS3COL]<!--{{CSS3COL}}--></a>, columns share the same
dimensions and define column boxes organized in rows. Content flows from
one column to the next.
<p>The multi-column model is an example of flowing content from one area to
another, where the areas are the multi-column element's column boxes and
the flow is made of the multi-column element's children.
<p>However, for more complex layouts, content needs to flow from one area
of the page to the next without limitation of the areas' sizes and
positions. These arbitrary areas are the target of specific content flows.
In this document these areas are called regions, and the content flows are
called named flows. Regions are based on the rectangular geometry of the
CSS box model. Elements in a named flow are taken out of the normal visual
formatting and rendered in a chain of regions.
<h3 id=named-flows-and-regions><span class=secno>1.1. </span>Named flows
and regions</h3>
<p>Consider the layout illustrated in figure 1.
<div class=figure> <img
alt="multiple chained regions which should receive content from a flow"
src="images/regions-intro.svg" width=400>
<p class=caption>Layout requiring sophisticated content flow</p>
</div>
<p>The designer's intent is to position an image in region ‘<code
class=property>A</code>’ and to flow an article's text from region
‘<code class=css>1</code>’, to region ‘<code
class=css>2</code>’, ‘<code class=css>3</code>’ and
‘<code class=css>4</code>’.
<p>The following code snippet shows the content to flow between the regions
1, 2, 3 and 4.
<pre>
<div <em>id="article"</em>>
<h1>Introduction</h1>
<p>This is an example ...</p>
<h1>More Details</h1>
<p>This illustrates ...</p>
<p>Then, the example ...</p>
<p>Finally, this ...</p>
</div>
</pre>
<p>And the following snippet shows an example of elements that will be used
as regions.
<pre>
<div id="region1"></div>
<div id="region2"></div>
<div id="region3"></div>
<div id="region4"></div>
</pre>
<p>CSS layout facilities can position and size regions as needed. However,
there is no existing mechanism to associate the content with the regions
so that content flows as intended. Figure 2 shows an example of the
intended visual rendering of the content.
<div class=figure> <img
alt="Sample rendering showing a single thread of text flowing through a chain of regions"
src="images/regions-intro-rendering.png" width=450>
<p class=caption>Sample rendering for desired layout</p>
</div>
<p>The CSS regions module is independent of the layout of regions and the
mechanism used to create them. However, for simplicity, our example uses
elements as regions as shown in the previous code snippet.
<p>The following code example illustrates how the content of the
<code>article</code> element becomes a flow and how the areas ‘<code
class=css>region1</code>’, ‘<code
class=css>region2</code>’, ‘<code
class=css>region3</code>’ and ‘<code
class=css>region4</code>’ become regions that consume the
‘<code class=css>article_flow</code>’ content.
<div class=example>
<pre>
<style>
#article {
<strong>flow-into: article_flow;</strong>
}
#region1, #region2, #region3, #region4 {
<strong>flow-from: article_flow;</strong>
}
</style>
</pre>
</div>
<p>The ‘<code class=css>article_flow</code>’ value on the
‘<a href="#flow-into"><code
class=property>flow-into</code></a>’ property directs the
‘<code class=css>#article</code>’ element to the ‘<code
class=css>article_flow</code>’ named flow. Setting the elements'
‘<a href="#flow-from"><code
class=property>flow-from</code></a>’ property to ‘<code
class=css>article_flow</code>’ on elements makes them regions and
associates these regions with the named flow: the flow is ‘<code
class=css>poured</code>’ into the desired regions.
<h3 id=region-styling><span class=secno>1.2. </span>Regions styling</h3>
<p>Region styling allows content to be styled depending on the region it
flows into. It is a form of context-based styling, similar to Media
Queries <a href="#MEDIAQ" rel=biblioentry>[MEDIAQ]<!--{{MEDIAQ}}--></a>
which enable or disable selectors depending on the rendering context. With
region styling, additional selectors may apply depending on the region
into which content flows.
<p>In our example, the designer wants to make text flowing into region 1
larger, bold and dark blue. In addition, <code
class=html><h1></code> headers should be crimson.
<p>This design can be expressed with region styling as shown below.
<div class=example>
<pre>
<style>
/*
* Default article styling.
*/
#article {
color:#777;
text-align: justify;
}
#article h1 {
border-left: 1px solid #777;
padding-left: 2ex;
display: run-in;
}
/*
* Additional styling to apply to content when it falls into
* region1
*/
<strong>@region #region1 {</strong>
#article {
font-weight: bold;
color: #0C3D5F;
font-size: larger;
}
#article h1 {
color: crimson;
border: none;
padding: 0px;
}
<strong>}</strong>
</style>
</pre>
</div>
<p>The ‘<code class=css>@region</code>’ rule for region 1
limits its selectors to content flowing into region 1. The following
figure shows how the rendering changes if we do not increase the font size
nor make it bold for content flowing into region 1. As more content can be
fitted, more content is subject to the contextual selectors, resulting in
more dark blue text into region 1.
<div class=figure> <img
alt="Illustrate how changing region styling affects the flow of content."
src="images/region-styling.png" width=450>
<p class=caption>Different rendering with a different region styling</p>
</div>
<h2 id=css-regions-concepts><span class=secno>2. </span>CSS regions
concepts</h2>
<p><em>This section is non-normative.</em>
<h3 id=regions><span class=secno>2.1. </span>Regions</h3>
<p class=index id=region title=region>A region is an element that generates
a <a href="http://www.w3.org/TR/CSS21/visuren.html#block-boxes">block
container box</a> and has an associated <a href="#named-flow0"><em>named
flow</em></a> (see the ‘<a href="#flow-from"><code
class=property>flow-from</code></a>’ property).
<h3 id=named-flow><span class=secno>2.2. </span>Named flow</h3>
<p>A <dfn id=named-flow0>named flow</dfn> is the ordered sequence of
elements associated with a flow with a given identifier. Elements in a
named flow are ordered according to the document order.
<p>Elements are placed into a named flow with the ‘<a
href="#flow-into"><code class=property>flow-into</code></a>’
property. The elements in a named flow are laid out in the chain of
regions that are associated with this named flow. <span
title=region>Regions</span> are organized in to a <span
title=region-chain>region chain</span> according to the document order.
<p>Content from a named flow is broken up between regions according to the
regions flow breaking rules.
<h3 id=regions-flow-breaking-rules><span class=secno>2.3. </span>Regions
flow breaking rules</h3>
<p>Breaking a named flow across multiple regions is similar to breaking a
document's content across multiple pages (see <a href="#CSS3PAGE"
rel=biblioentry>[CSS3PAGE]<!--{{CSS3PAGE}}--></a>) or a multi-column
element's content across column boxes (see <a href="#CSS3COL"
rel=biblioentry>[CSS3COL]<!--{{CSS3COL}}--></a>). One difference is that
page boxes are generated based on the available content whereas regions
are a predefined set of recipient boxes for the named flow content.
<p><span title=region>Regions</span> are organized in to a <span
title=region-chain>region chain</span>.
<p>Each region in turn consumes content from its associated <a
href="#named-flow0">named flow</a>. The named flow content is positioned
in the <dfn id=current-region title=current-region>current region</dfn>
until a natural or forced region break occurs, at which point the <a
href="#current-region" title=current-region>current region</a> becomes the
next one in the <span title=region-chain>region chain</span>. If there are
no more <span>region</span>s in the region chain and there is still
content in the flow, the positioning of the remaining content is
controlled by the ‘<a href="#region-overflow"><code
class=property>region-overflow</code></a>’ property on the last
<span>region</span> in the chain.
<h2 id=relation-to-document-events><span class=secno>3. </span>Relation to
document events</h2>
<p><em>This section is normative.</em>
<p>The CSS regions module does not alter the normal processing of events in
the document tree. In particular, if an event occurs on an element that is
part of a named flow, the <a
href="http://www.w3.org/TR/DOM-Level-3-Events/#dom-event-architecture">event's
bubble and capture phases</a> happen following the document tree order.
<h2 id=properties-and-rules><span class=secno>4. </span>Properties and
rules</h2>
<p><em>This section is normative.</em>
<h3 id=the-flow-into-property><span class=secno>4.1. </span>The ‘<a
href="#flow-into"><code class=property>flow-into</code></a>’
property</h3>
<p>The ‘flow-into’ property can place an element into a named flow.
Elements that belong to the same flow are laid out in the regions
associated with that flow.
<table class=propdef summary="flow property definition">
<tbody>
<tr>
<th>Name:
<td><dfn id=flow-into>flow-into</dfn>
<tr>
<th>Value:
<td><ident> | none | inherit
<tr>
<th>Initial:
<td>none
<tr>
<th>Applies to:
<td>any element
<tr>
<th>Inherited:
<td>no
<tr>
<th>Percentages:
<td>N/A
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>as specified
</table>
<dl>
<dt>none
<dd>The element is not moved to a named flow and normal CSS processing
takes place.
<dt><a
href="http://www.w3.org/TR/2011/REC-CSS2-20110607/syndata.html#value-def-identifier"><ident></a>
<dd>The element is placed into the flow with the name ‘<code
class=css><ident></code>’. The element is said to have a <dfn
id=specified-flow>specified flow</dfn>. The values ‘<code
class=property>none</code>’, ‘<code
class=property>inherit</code>’, ‘<code
class=property>default</code>’, ‘<code
class=property>auto</code>’ and ‘<code
class=property>initial</code>’ are invalid flow names.
</dl>
<p>A named flow needs to be associated with one or more regions for its
elements to be visually formatted. If no region is associated with a given
named flow, the elements in the named flow are not rendered: they do not
generate boxes and are not displayed.
<p>The children of an element with a specified flow may themselves have a
specified flow.
<p>If an element has the same specified flow as one of its ancestors, it
becomes a sibling of it's ancestor for the purpose of layout in the
regions laying out content from that flow.
<p>The ‘<a href="#flow-into"><code
class=property>flow-into</code></a>’ property does not affect the
CSS cascade and inheritance for the elements on which it is specified. The
‘<a href="#flow-into"><code
class=property>flow-into</code></a>’ property affects the visual
formatting of elements placed into a named flow and of regions laying out
content from a named flow.
<p>The edges of the first region in a region chain associated with a named
flow establish the rectangle that is the initial containing block of the
named flow.
<p>The first region defines the <a
href="http://www.w3.org/TR/css3-writing-modes/#writing-mode">writing
mode</a> for the entire flow. The writing mode on subsequent regions is
ignored.
<p>Elements in a named flow are sequenced in document order.
<div class=note>
<p><em>This note is informative.</em></p>
<p>The ‘<a href="#flow-into"><code
class=property>flow-into</code></a>’ property moves an element into
the flow and the interplay with selectors should be considered carefully.</p>
<p>For example,</p>
<pre>table {flow-into: table-content}</pre>
<p>will move all tables in the ‘<code
class=property>table-content</code>’ named flow. However, the</p>
<pre>table * {flow-into: table-content}</pre>
<p>selector will move all the descendants of table elements in the
‘<code class=property>table-content</code>’ named flow. This
will make all the descendants of table elements siblings in the named
flow. Having the descendants become siblings in the named flow results in
a different processing (see the <a
href="http://www.w3.org/TR/2011/REC-CSS2-20110607/tables.html#anonymous-boxes">CSS
2.1‘<code class=css>s anonymous table objects</code></a>). This
note illustrates how authors must exercise caution when choosing a
particular selector for setting the ’flow-into' property to avoid
unintended results.</p>
</div>
<p>The ‘<a href="#flow-into"><code
class=property>flow-into</code></a>’ property does not apply to the
<code class=css>::first-line</code> and <code
class=css>::first-character</code>.
<p>The effect of ‘<a href="#flow-into"><code
class=property>flow-into</code></a>’ on generated content such as
<code class=css>::marker</code>, <code class=css>::before</code> and <code
class=css>::after</code> is undefined. This may change depending on
implementation feedback.
<h3 id=the-flow-from-property><span class=secno>4.2. </span>The ‘<a
href="#flow-from"><code class=property>flow-from</code></a>’
property</h3>
<p>The ‘<a href="#flow-from"><code
class=property>flow-from</code></a>’ property makes an element a
region and associates it with a named flow.
<div class=issue-marker><a
href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=15191">Bug-15191</a></div>
<table class=propdef summary="flow-from property definition">
<tbody>
<tr>
<th>Name:
<td><dfn id=flow-from>flow-from</dfn>
<tr>
<th>Value:
<td><ident> | none | inherit
<tr>
<th>Initial:
<td>none
<tr>
<th>Applies to:
<td>Elements that generate a <a
href="http://www.w3.org/TR/CSS21/visuren.html#block-boxes">block
container box</a>. <br>
This might be expanded in future versions of the specification to allow
other types of containers to receive flow content.
<tr>
<th>Inherited:
<td>no
<tr>
<th>Percentages:
<td>N/A
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>as specified
</table>
<dl>
<dt><strong>none</strong>
<dd>The element is not a <span title=region>region</span>.
<dt><strong><ident></strong>
<dd> If the ‘<code class=property>content</code>’ property
computes to something else than ‘<code
class=property>normal</code>’, the element does not become a
region. If the ‘<code class=property>content</code>’ property
computes to ‘<code class=property>normal</code>’, then the
element becomes a <span>region</span> and is ordered in a <span>region
chain</span> according to its document order. The content from the flow
with the <a
href="http://www.w3.org/TR/2011/REC-CSS2-20110607/syndata.html#value-def-identifier"><ident></a>
name will be <a href="#region-flow-break">broken into segments</a> and
visually formatted in the <a
href="http://www.w3.org/TR/CSS21/visuren.html#principal-box">principal
boxes</a> of the regions in the region chain. If there is no flow with
name <ident>, then the element does not format any content
visually. <br>
Likewise, if the element is part of the flow with name <ident>,
then the element does not format any content visually.
</dl>
<p class=note>A region's document children are not visually formatted
unless they are directed to a named flow referenced by one or more
regions.
<div class=note>
<p>An element becomes a region when its ‘<a href="#flow-from"><code
class=property>flow-from</code></a>’ property is set to a valid
<ident> value, even if there is no content contributing to the
referenced flow. For example:</p>
<pre>
<style>
.article{
flow-into: thread;
}
.region{
flow-from: thread;
}
</style>
<html>
<body>
<div class=region>div content</div>
</body>
</html>
</pre>
There is no element matching the <code>.article</code> selector and
therefore no content in the <code>thread</code> flow. However, the element
matching the <code>.region</code> selector is still associated with that
empty named flow and, consequently, its children are not formatted
visually.</div>
<div class=issue-marker><a
href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=15189">Bug-15189</a></div>
<p><span title=region>Regions</span> create a new <a
href="http://www.w3.org/TR/CSS2/visuren.html#z-index">stacking
context</a>. <span title=region>Regions</span> establish a new <a
href="http://www.w3.org/TR/CSS2/visuren.html#block-formatting">block
formatting Context</a>.
<p>If the ‘<code class=property>content</code>’ property is
defined on a region, it has no effect on the region's visual formatting.
<div class=note>
<p><em>This note is informative.</em></p>
<p>With regions, an element may be split across multiple regions and these
regions may overlap (for example if they are absolutely positioned). So
fragments of the same element can overlap each other. Since each element
has a single z-index, it would be required to find another mechanism to
decide in which order the fragments are rendered. Since each region
creates a new stacking context, it is clear that each region is rendered
separately and their rendering order follows the regular CSS rendering
model.</p>
</div>
<p> Floats or other exclusions (see <a href="#CSS3-EXCLUSIONS"
rel=biblioentry>[CSS3-EXCLUSIONS]<!--{{CSS3-EXCLUSIONS}}--></a>)
potentially impact the content laid out in regions, just as for
non-regions.
<div class=example>
<p>In the following example, the inline content coming from the <code
class=html>body_text</code> <a href="#named-flow0">named flow</a> wraps
around the <code class=html>#float</code> box.</p>
<pre>
<style>
#float {
float: left;
width: 100px;
height: 300px;
}
#region1, #region2 {
width: 200px;
height: 200px;
flow-from: body_text;
}
#content {
flow-into: body_text;
}
</style>
<div id="float"></div>
<div id="region1"></div>
<div id="region2"></div>
<div id="content"></div>
</pre>
</div>
<h4 id=auto-width-on-regions><span class=secno>4.2.1. </span>Auto width on
regions</h4>
<p>If a region's ‘<code class=property>width</code>’ property
is computed to ‘<code class=property>auto</code>’, its
resolved value is computed based on the region's <em>::before</em> and
<em>::after</em> generated content only.
<h4 id=auto-height-on-regions><span class=secno>4.2.2. </span>Auto height
on regions</h4>
<p>If a region's ‘<code class=property>height</code>’ property
is computed to ‘<code class=property>auto</code>’, its
resolved value is computed based on the region's <em>::before</em> and
<em>::after</em> generated content only.
<h3 id=region-flow-break><span class=secno>4.3. </span>Region flow break
properties: ‘<a href="#break-before"><code
class=property>break-before</code></a>’, ‘<a
href="#break-after"><code class=property>break-after</code></a>’,
‘<a href="#break-inside"><code
class=property>break-inside</code></a>’</h3>
<p>User agents laying out content in multiple regions must determine where
content breaks occur. The problem of breaking content into segments
fitting in regions is similar to breaking content into pages or columns.
<p>Each break ends layout in the current region and causes remaining pieces
of content from the named flow to be visually formatted in the following
region in the region chain. Note that there is no region break in the last
region associated with a named flow.
<p>The following extends the ‘<a href="#break-before"><code
class=property>break-before</code></a>’, ‘<a
href="#break-after"><code class=property>break-after</code></a>’ and
‘<a href="#break-inside"><code
class=property>break-inside</code></a>’ properties from the <a
href="#CSS3COL" rel=biblioentry>[CSS3COL]<!--{{!CSS3COL}}--></a>
specification to account for regions. The additional values are described
below.
<table class=propdef summary="break-before property definition">
<tbody>
<tr>
<td><em>Name:</em>
<td><dfn id=break-before>break-before</dfn>
<tr>
<td><em>Value:</em>
<td>auto | always | avoid | left | right | page | column | region |
avoid-page | avoid-column | avoid-region
<tr>
<td><em>Initial:</em>
<td>auto
<tr>
<td><em>Applies to:</em>
<td>block-level elements
<tr>
<td><em>Inherited:</em>
<td>no
<tr>
<td><em>Percentages:</em>
<td>N/A
<tr>
<td><em>Media:</em>
<td>paged
<tr>
<td><em>Computed value:</em>
<td>specified value
</table>
<table class=propdef summary="break-after property definition">
<tbody>
<tr>
<td><em>Name:</em>
<td><dfn id=break-after>break-after</dfn>
<tr>
<td><em>Value:</em>
<td>auto | always | avoid | left | right | page | column | region |
avoid-page | avoid-column | avoid-region
<tr>
<td><em>Initial:</em>
<td>auto
<tr>
<td><em>Applies to:</em>
<td>block-level elements
<tr>
<td><em>Inherited:</em>
<td>no
<tr>
<td><em>Percentages:</em>
<td>N/A
<tr>
<td><em>Media:</em>