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<!DOCTYPE html><html lang=en><head>
<meta content="text/html; charset=utf-8" http-equiv=Content-Type>
<title>CSS Regions Module Level 1</title>
<link href=../default.css rel=stylesheet type=text/css>
<link href=../csslogo.ico rel="shortcut icon" type=image/x-icon>
<style>
body {
background: url("https://www.w3.org/StyleSheets/TR/logo-ED") top left no-repeat white;
background-attachment: fixed;
color: black;
font-family: sans-serif;
margin: 0 auto;
max-width: 50em;
padding: 2em 1em 2em 70px;
}
:link { color: #00C; background: transparent }
:visited { color: #609; background: transparent }
a[href]:active { color: #C00; background: transparent }
a[href]:hover { background: #ffa }
a[href] img { border-style: none }
h1, h2, h3, h4, h5, h6 { text-align: left }
h1, h2, h3 { color: #005A9C; }
h1 { font: 170% sans-serif }
h2 { font: 140% sans-serif }
h3 { font: 120% sans-serif }
h4 { font: bold 100% sans-serif }
h5 { font: italic 100% sans-serif }
h6 { font: small-caps 100% sans-serif }
.hide { display: none }
div.head { margin-bottom: 1em }
div.head h1 { margin-top: 2em; clear: both }
div.head table { margin-left: 2em; margin-top: 2em }
p.copyright { font-size: small }
p.copyright small { font-size: small }
pre { margin-left: 2em }
dt { font-weight: bold }
ul.toc, ol.toc {
list-style: none;
}
</style>
<script defer src=//test.csswg.org/harness/annotate.js#css-regions-1_dev/css-regions-1 type=text/javascript></script>
</head>
<body class=h-entry>
<div class=head>
<p data-fill-with=logo><a class=logo href=http://www.w3.org/>
<img alt=W3C height=48 src=https://www.w3.org/Icons/w3c_home width=72>
</a>
</p>
<h1 class="p-name no-ref" id=title>CSS Regions Module Level 1</h1>
<h2 class="no-num no-toc no-ref heading settled" id=subtitle><span class=content>Editor’s Draft,
<span class=dt-updated><span class=value-title title=20141124>24 November 2014</span></span></span></h2>
<div data-fill-with=spec-metadata><dl><dt>This version:<dd><a class=u-url href=http://dev.w3.org/csswg/css-regions/>http://dev.w3.org/csswg/css-regions/</a><dt>Latest version:<dd><a href=http://www.w3.org/TR/css-regions-1/>http://www.w3.org/TR/css-regions-1/</a><dt>Previous Versions:<dd><a href=http://www.w3.org/TR/2014/WD-css3-regions-20140218/ rel=previous>http://www.w3.org/TR/2014/WD-css3-regions-20140218/</a><dt>Feedback:<dd><span><a href="mailto:www-style@w3.org?subject=%5Bcss-regions%5D%20feedback">www-style@w3.org</a> with subject line “<kbd>[css-regions] <var>… message topic …</var></kbd>” (<a href=http://lists.w3.org/Archives/Public/www-style/ rel=discussion>archives</a>)</span><dt>Test Suite:<dd><a href=http://test.csswg.org/suites/css-regions-1_dev/nightly-unstable/>http://test.csswg.org/suites/css-regions-1_dev/nightly-unstable/</a><dt class=editor>Editors:<dd class=editor><div class="p-author h-card vcard"><a class="p-name fn u-email email" href=mailto:ratan@microsoft.com>Rossen Atanassov</a> (<span class="p-org org">Microsoft Corporation</span>)</div><dd class=editor><div class="p-author h-card vcard"><a class="p-name fn u-email email" href=mailto:stearns@adobe.com>Alan Stearns</a> (<span class="p-org org">Adobe Systems, Inc.</span>)</div><dt>Former Editors:<dd><div class="p-author h-card vcard"><a class="p-name fn u-email email" href=mailto:vhardy@adobe.com>Vincent Hardy</a> (<span class="p-org org">Adobe Systems, Inc.</span>)</div><dt>Issues list:<dd><span><a href="https://www.w3.org/Bugs/Public/buglist.cgi?query_format=advanced&product=CSS&component=Regions&resolution=---&cmdtype=doit">In Bugzilla</a></span></dl></div>
<div data-fill-with=warning></div>
<p class=copyright data-fill-with=copyright><a href=http://www.w3.org/Consortium/Legal/ipr-notice#Copyright>Copyright</a> © 2014 <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>
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc no-ref heading settled" id=abstract><span class=content>Abstract</span></h2>
<div class=p-summary data-fill-with=abstract><p>The CSS Regions module allows content from one or more elements to flow through one or more boxes called CSS Regions, fragmented as defined in <a data-biblio-type=normative data-link-type=biblio href=#biblio-css3-break title=CSS3-BREAK>[CSS3-BREAK]</a>. This module also defines CSSOM to expose both the inputs and outputs of this fragmentation.</p>
<a href=http://www.w3.org/TR/CSS/>CSS</a> is a language for describing the rendering of structured documents
(such as HTML and XML)
on screen, on paper, in speech, etc.</div>
<h2 class="no-num no-toc no-ref heading settled" id=status><span class=content>Status of this document</span></h2>
<div data-fill-with=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-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 “css-regions” in the subject,
preferably like this:
“[css-regions] <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>
This document is governed by the <a href=http://www.w3.org/2014/Process-20140801/>1 August 2014 W3C Process Document</a>.
</div>
<div data-fill-with=at-risk></div>
<h2 class="no-num no-toc no-ref heading settled" id=contents><span class=content>Table of Contents</span></h2>
<div data-fill-with=table-of-contents role=navigation><ul class=toc role=directory><li><a href=#introduction><span class=secno>1</span> <span class=content>
Introduction</span></a><li><a href=#css-regions-concepts><span class=secno>2</span> <span class=content>
CSS Regions concepts</span></a><ul class=toc><li><a href=#regions><span class=secno>2.1</span> <span class=content>
Regions</span></a><li><a href=#region-chain-section><span class=secno>2.2</span> <span class=content>
Region chain</span></a><li><a href=#named-flow-section><span class=secno>2.3</span> <span class=content>
Named flows</span></a><li><a href=#regions-flow-breaking-rules><span class=secno>2.4</span> <span class=content>
Regions flow breaking rules</span></a></ul><li><a href=#properties><span class=secno>3</span> <span class=content>
Properties</span></a><ul class=toc><li><a href=#the-flow-into-property><span class=secno>3.1</span> <span class=content>
The <span class=property data-link-type=propdesc title=flow-into>flow-into</span> property</span></a><li><a href=#flow-from><span class=secno>3.2</span> <span class=content>
The <span class=property data-link-type=propdesc title=flow-from>flow-from</span> property</span></a><ul class=toc><li><a href=#circular-dependencies><span class=secno>3.2.1</span> <span class=content>
Cycle Detection</span></a><li><a href=#fragmenting-regions><span class=secno>3.2.2</span> <span class=content>
Nested fragmentation contexts</span></a></ul><li><a href=#region-flow-break><span class=secno>3.3</span> <span class=content>
Region flow break properties: <span class=property data-link-type=propdesc title=break-before>break-before</span>, <span class=property data-link-type=propdesc title=break-after>break-after</span>, <span class=property data-link-type=propdesc title=break-inside>break-inside</span></span></a><li><a href=#the-region-fragment-property><span class=secno>3.4</span> <span class=content>
The region-fragment property</span></a></ul><li><a href=#cssom_view_and_css_regions><span class=secno>4</span> <span class=content>
CSSOM</span></a><ul class=toc><li><a href=#the-namedflow-interface><span class=secno>4.1</span> <span class=content>
The NamedFlow interface</span></a><li><a href=#the-region-interface><span class=secno>4.2</span> <span class=content>
The Region interface</span></a><li><a href=#named-flow-events><span class=secno>4.3</span> <span class=content>
Named flow events</span></a><li><a href=#cssomview-and-regions><span class=secno>4.4</span> <span class=content>
Clarifications on pre-existing APIs</span></a><ul class=toc><li><a href=#cssomview-getclientrects-and-getboundingclientrect><span class=secno>4.4.1</span> <span class=content>
<code class=idl>getClientRects()</code> and <code>getBoundingClientRect()</code></span></a><li><a href=#cssomview-offset-attributes><span class=secno>4.4.2</span> <span class=content>
<code class=idl>offsetTop</code>, <code class=idl>offsetLeft</code>,
<code class=idl>offsetWidth</code>, <code class=idl>offsetHeight</code> and <code class=idl>offsetParent</code></span></a></ul></ul><li><a href=#multi-column-regions><span class=secno>5</span> <span class=content>
Multi-column regions</span></a><li><a href=#pseudo_elements><span class=secno>6</span> <span class=content>
Pseudo-elements</span></a><li><a href=#regions-visual-formatting-details><span class=secno>7</span> <span class=content>
Regions visual formatting details</span></a><ul class=toc><li><a href=#processing-model><span class=secno>7.1</span> <span class=content>
Processing model</span></a><li><a href=#regions-flow-content-box><span class=secno>7.2</span> <span class=content>
The Region Flow Content Box (RFCB)</span></a><ul class=toc><li><a href=#rfcb-width-resolution><span class=secno>7.2.1</span> <span class=content>
RFCB <span class=property data-link-type=propdesc title=width>width</span> resolution</span></a></ul><li><a href=#regions-visual-formatting-steps><span class=secno>7.3</span> <span class=content>
Regions visual formatting steps</span></a><ul class=toc><li><a href=#rfcb-flow-fragment-height-resolution><span class=secno>7.3.1</span> <span class=content>
Step 1: RFCB flow fragment height resolution</span></a><ul class=toc><li><a href=#rfcb-flow-fragment-height-resolution-phase-1><span class=secno>7.3.1.1</span> <span class=content>
RFCB flow fragment height resolution, Phase 1</span></a><li><a href=#rfcb-flow-fragment-height-resolution-phase-2><span class=secno>7.3.1.2</span> <span class=content>
RFCB flow fragment height resolution, Phase 2</span></a></ul><li><a href=#regions-boxes-layout><span class=secno>7.3.2</span> <span class=content>
Step 2: region boxes layout</span></a><li><a href=#named-flows-layout><span class=secno>7.3.3</span> <span class=content>
Step 3: named flows layout</span></a></ul><li><a href=#regions-visual-formatting-implementation-note><span class=secno>7.4</span> <span class=content>
Regions visual formatting: implementation note</span></a><li><a href=#regions-visual-formatting-examples><span class=secno>7.5</span> <span class=content>
Regions visual formatting example</span></a><ul class=toc><li><a href=#step1-phase1-example><span class=secno>7.5.1</span> <span class=content>
Step 1 - Phase 1: Laying out RFCBs with used height of zero</span></a><li><a href=#step1-phase2-example><span class=secno>7.5.2</span> <span class=content>
Step 1 - Phase 2: Layout flow to compute the RFCBs' flow fragments heights</span></a><li><a href=#step2-example><span class=secno>7.5.3</span> <span class=content>
Step 2: Layout document and regions without named flows</span></a><li><a href=#step3-example><span class=secno>7.5.4</span> <span class=content>
Step 3: named flows layout</span></a></ul></ul><li><a href=#relation-to-document-events><span class=secno>8</span> <span class=content>
Relation to document events</span></a><li><a href=#relation-to-other-specifications><span class=secno>9</span> <span class=content>
Relation to other specifications</span></a><li><a href=#usecases><span class=secno>10</span> <span class=content>
Use Cases</span></a><li><a href=#changes><span class=secno>11</span> <span class=content>
Changes</span></a><ul class=toc><li><a href=#changes_from_Feb_18_2014><span class=secno>11.1</span> <span class=content>
Changes from <span>February 18<sup>th</sup> 2014</span> version</span></a><li><a href=#changes_from_May_28_2013><span class=secno>11.2</span> <span class=content>
Changes from <span>May 28<sup>th</sup> 2013</span> version</span></a><li><a href=#changes_from_Aug_28_2012><span class=secno>11.3</span> <span class=content>
Changes from <span>August 28<sup>th</sup> 2012</span> version</span></a><li><a href=#changes_from_May_03_2012><span class=secno>11.4</span> <span class=content>
Changes from <span>May 3<sup>rd</sup> 2012</span> version</span></a><li><a href=#older_changes><span class=secno>11.5</span> <span class=content>Older Changes</span></a></ul><li><a href=#acknowledgments><span class=secno></span> <span class=content>
Acknowledgments</span></a><li><a href=#conformance><span class=secno></span> <span class=content>
Conformance</span></a><ul class=toc><li><a href=#conventions><span class=secno></span> <span class=content>
Document conventions</span></a><li><a href=#conformance-classes><span class=secno></span> <span class=content>
Conformance classes</span></a><li><a href=#partial><span class=secno></span> <span class=content>
Partial implementations</span></a><li><a href=#experimental><span class=secno></span> <span class=content>
Experimental implementations</span></a><li><a href=#testing><span class=secno></span> <span class=content>
Non-experimental implementations</span></a></ul><li><a href=#references><span class=secno></span> <span class=content>References</span></a><ul class=toc><li><a href=#normative><span class=secno></span> <span class=content>Normative References</span></a><li><a href=#informative><span class=secno></span> <span class=content>Informative References</span></a></ul><li><a href=#index><span class=secno></span> <span class=content>Index</span></a><li><a href=#property-index><span class=secno></span> <span class=content>Property Index</span></a><li><a href=#idl-index><span class=secno></span> <span class=content>IDL Index</span></a></ul></div>
<main>
<h2 class="heading settled" data-level=1 id=introduction><span class=secno>1. </span><span class=content>
Introduction</span><a class=self-link href=#introduction></a></h2>
<p><em>This section is non-normative.</em></p>
<p>The core concept behind CSS Regions
is the ability to say,
"Display <em>this</em> content (a <a data-link-type=dfn href=#named-flow>named flow</a>)
over <em>there</em> (a <a data-link-type=dfn href=#region-chain>region chain</a>)."
The simplest example is:</p>
<div class=example>
<pre><code>#this {
flow-into: my-flow;
}
#there {
flow-from: my-flow;
}
</code></pre>
</div>
<p>These two declarations will take
the element that matches <code>#this</code>,
put it into a flow named "my-flow",
and display the contents of "my-flow"
in the box from the element that matches <code>#there</code>.
This example has a single content source for the <a data-link-type=dfn href=#named-flow>named flow</a>,
and a single box for the <a data-link-type=dfn href=#region-chain>region chain</a>.
<a data-link-type=dfn href=#named-flow>Named flows</a> can also have multiple sources
and use multiple boxes for the <a data-link-type=dfn href=#region-chain>region chain</a>.</p>
<p>The <a data-link-type=dfn href=#named-flow>named flow</a> mechanism can be used
in several different ways -
some of which are
custom overflow handling,
aggregating content,
linked display boxes,
magazine-style layout,
and flowing content through areas in a paginated view.</p>
<div class=example>
Linked display boxes can be created
to display article content above and below
other content on a page.
Given markup like this:
<pre><code class=html><article> ...some content... </article>
<aside> ad or image content </aside>
</code></pre>
<p>The <aside> content will be displayed
below all of the article content.
On a large screen the page might display without scrolling,
but on a small screen the <aside> content
might not be visible until the view scrolls.
If it’s important to show at least some
of the <aside> content in the initial view,
CSS Regions can fragment the article content across two boxes -
one above the <aside> and one below.</p>
<p>In this example (for simplicity’s sake)
we create the boxes with additional elements:</p>
<pre><code class=html><article> ...some content... </article>
<div class="top region"></div>
<aside> ad or image content </aside>
<div class="region"></div>
</code></pre>
<pre><code>article {
flow-into: article-flow;
}
.region {
flow-from: article-flow;
}
.top {
max-height: 80vh;
}
</code></pre>
<p>So the top box in the <a data-link-type=dfn href=#region-chain>region chain</a>
is limited to 80% of the viewport height.
If the article content doesn’t fit in that box,
the article will continue
in the second box after the <aside> content.</p>
<figure style="float:left; margin:1em;">
<img alt="Article and aside rendering without CSS Regions" src=images/linked-boxes-before.png>
<figcaption>
Rendering without CSS Regions
</figcaption>
</figure>
<figure style="float:left; margin:1em;">
<img alt="Article and aside rendering with CSS Regions" src=images/linked-boxes-after.png>
<figcaption>
Rendering with CSS Regions
</figcaption>
</figure>
<p style=clear:left;>In the images above,
the gray area represents
the content below the screen edge
in the initial view.
<p>This example links just two boxes together,
but more boxes could be added to the <a data-link-type=dfn href=#region-chain>region chain</a>
to regularly interleave other content with the article.</p>
</div>
<div class=example>
<p>Custom overflow handling can be accomplished by linking a separate overflow box. In this example, the overflow box is nestled inside a menu in the markup, and only displays if the menu is toggled.</p>
<pre><code class=html><nav> ...some links... </nav>
<div class="menu">
<nav></nav>
...some more links...
</div>
</code></pre>
<p>If the links in the main nav element are placed in a <a data-link-type=dfn href=#named-flow>named flow</a>, that flow can be directed through both the main nav element and the overflow nav box in the menu:</p>
<pre><code>nav a {
flow-into: nav-link-flow;
}
nav {
flow-from: nav-link-flow;
}
</code></pre>
<p>Then the main nav element and the menu can be arranged with constraints such that when the screen is too narrow for the main nav element to display all of the navigation links, the overflow moves to the menu.</p>
<figure>
<img alt="Wide nav bar showing all of the links" src=images/menu-wide.png>
<figcaption>
Wide rendering with menu shown
</figcaption>
</figure>
<figure>
<img alt="Narrow nav bar with some of the links in the menu" src=images/menu-narrow.png>
<figcaption>
Narrow rendering with menu shown
</figcaption>
</figure>
</div>
<div class=example>
<p>Since content is assigned to a <a data-link-type=dfn href=#named-flow>named flow</a> using a CSS selector, the content can come from multiple sources. The resulting aggregation can be displayed in a single box or flowed through multiple boxes as above.</p>
<p>So given this markup:</p>
<pre><code class=html><div class="breaking-news"></div>
<article>News story</article>
<article class="breaking">Sports story</article>
<article>News story</article>
<article class="breaking">Entertainment story</article>
<article>Sports story</article>
</code></pre>
<p>You can take the "breaking" stories and display them above all the others using two lines of CSS:</p>
<pre><code>.breaking {
flow-into: breaking-news;
}
.breaking-news {
flow-from: breaking-news;
}
</code></pre>
<p>Given more data accessible to CSS selectors, you could rearrange the articles in other ways (sports on top, etc.) depending on the user’s preferences.</p>
</div>
<div class=note role=note><span class=note-prefix>Note </span>
<p><strong><a data-link-type=dfn href=#css-region>CSS Regions</a> are independent from layout</strong></p>
<p>Any of the CSS layout facilities can be used
to create, position and size boxes that can become <a data-link-type=dfn href=#css-region>CSS Regions</a>.</p>
<p>The CSS Regions module does not
define a layout mechanism
and is meant to integrate
with existing and future CSS layout facilities.</p>
</div>
<div class=note role=note><span class=note-prefix>Note </span>
<p><strong><a data-link-type=dfn href=#css-region>CSS Regions</a> do not have to be elements</strong></p>
<p>The CSS Regions module is independent
of the layout of boxes and
the mechanisms used to create them.</p>
<p>For simplicity,
our examples tend to
use elements to define the boxes.
Any other mechanism available
in markup or style
to create stylable boxes could be used instead,
such as pseudo-elements
or the @slot rule proposed
by the CSS Page Template Module <a data-biblio-type=informative data-link-type=biblio href=#biblio-css3-page-template title=CSS3-PAGE-TEMPLATE>[CSS3-PAGE-TEMPLATE]</a>.</p>
<p>The only requirement
for box to become a <a data-link-type=dfn href=#css-region>CSS Region</a>
is that the <a class=property data-link-type=propdesc href=#propdef-flow-from>flow-from</a> property applies to the box.</p>
</div>
<h2 class="heading settled" data-level=2 id=css-regions-concepts><span class=secno>2. </span><span class=content>
CSS Regions concepts</span><a class=self-link href=#css-regions-concepts></a></h2>
<h3 class="heading settled" data-level=2.1 id=regions><span class=secno>2.1. </span><span class=content>
Regions</span><a class=self-link href=#regions></a></h3>
<p>A <dfn data-dfn-type=dfn data-noexport="" id=css-region>CSS Region<a class=self-link href=#css-region></a></dfn>
is a block container
that has an associated
<em><a data-link-type=dfn href=#named-flow>named flow</a></em>
(see the <a class=property data-link-type=propdesc href=#propdef-flow-from>flow-from</a> property).</p>
<h3 class="heading settled" data-level=2.2 id=region-chain-section><span class=secno>2.2. </span><span class=content>
Region chain</span><a class=self-link href=#region-chain-section></a></h3>
<p>A <dfn data-dfn-type=dfn data-noexport="" id=region-chain>region chain<a class=self-link href=#region-chain></a></dfn>
is the sequence of regions
that are associated with
a <a data-link-type=dfn href=#named-flow>named flow</a>.
<a data-link-type=dfn href=#css-region>CSS Regions</a> in a
<a data-link-type=dfn href=#region-chain>region chain</a> receive content from the
<a data-link-type=dfn href=#named-flow>named flow</a> following their order in the chain.
<a data-link-type=dfn href=#css-region>CSS Regions</a> are organized
into a <a data-link-type=dfn href=#region-chain>region chain</a>
according to the document order.</p>
<h3 class="heading settled" data-level=2.3 id=named-flow-section><span class=secno>2.3. </span><span class=content>
Named flows</span><a class=self-link href=#named-flow-section></a></h3>
<p>A <dfn data-dfn-type=dfn data-noexport="" id=named-flow>named flow<a class=self-link href=#named-flow></a></dfn> is the ordered sequence of content
associated with a flow with a given identifier.
Contents in a <a data-link-type=dfn href=#named-flow>named flow</a> are ordered
according to the document order.</p>
<p>Content is placed into a <a data-link-type=dfn href=#named-flow>named flow</a>
with the <a class=property data-link-type=propdesc href=#propdef-flow-into>flow-into</a> property.
The content in a <a data-link-type=dfn href=#named-flow>named flow</a> is laid out
in the <a data-link-type=dfn href=#region-chain>region chain</a>
that is associated with this <a data-link-type=dfn href=#named-flow>named flow</a>
using the <a class=property data-link-type=propdesc href=#propdef-flow-from>flow-from</a> property.</p>
<p>Content from a <a data-link-type=dfn href=#named-flow>named flow</a>
is broken up between regions
according to the regions flow breaking rules.</p>
<p>A <a data-link-type=dfn href=#named-flow>named flow</a> is created when
some content is moved
into the flow with the given identifier
or when at least one <a data-link-type=dfn href=#css-region>CSS Region</a>
requests content from that flow.</p>
<h3 class="heading settled" data-level=2.4 id=regions-flow-breaking-rules><span class=secno>2.4. </span><span class=content>
Regions flow breaking rules</span><a class=self-link href=#regions-flow-breaking-rules></a></h3>
<p>Breaking a <a data-link-type=dfn href=#named-flow>named flow</a> across a <a data-link-type=dfn href=#region-chain>region chain</a>
is similar to breaking a document’s content across pages
(see <a data-biblio-type=informative data-link-type=biblio href=#biblio-css3page title=CSS3PAGE>[CSS3PAGE]</a>)
or a multi-column element’s content across column boxes
(see <a data-biblio-type=informative data-link-type=biblio href=#biblio-css3col title=CSS3COL>[CSS3COL]</a>).
One difference is that page boxes are generated
based on the available content
whereas a <a data-link-type=dfn href=#region-chain>region chain</a> is a set of recipient boxes
for the <a data-link-type=dfn href=#named-flow>named flow</a> content
whose dynamic generation is not in the scope
of this specification.</p>
<p>Each <a data-link-type=dfn href=#css-region>CSS Region</a> in turn
consumes content from its associated <a data-link-type=dfn href=#named-flow>named flow</a>.
The <a data-link-type=dfn href=#named-flow>named flow</a> content is positioned
in the current region
until a natural or forced region break occurs,
at which point the next region
in the <a data-link-type=dfn href=#region-chain>region chain</a>
becomes the current region.
If there are no more <a data-link-type=dfn href=#css-region>CSS Regions</a>
in the <a data-link-type=dfn href=#region-chain>region chain</a>
and there is still content in the flow,
the positioning of the remaining content
is controlled by the <a class=property data-link-type=propdesc href=#propdef-region-fragment>region-fragment</a> property
on the last <a data-link-type=dfn href=#css-region>CSS Region</a> in the chain.</p>
<p>The CSS regions module follows
the fragmentation rules defined
in the CSS Fragmentation Module Level 3
(see <a data-biblio-type=normative data-link-type=biblio href=#biblio-css3-break title=CSS3-BREAK>[CSS3-BREAK]</a>).</p>
<h2 class="heading settled" data-level=3 id=properties><span class=secno>3. </span><span class=content>
Properties</span><a class=self-link href=#properties></a></h2>
<h3 class="heading settled" data-level=3.1 id=the-flow-into-property><span class=secno>3.1. </span><span class=content>
The <a class=property data-link-type=propdesc href=#propdef-flow-into>flow-into</a> property</span><a class=self-link href=#the-flow-into-property></a></h3>
<div class="issue-marker wrapper">
<div class=issue-marker>
<a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=16527">Issue-16527</a>
<div class=issue-details>
<p class=short-desc>[Shadow]: getFlowByName and shadow DOM</p>
</div>
</div>
</div>
<p>The ‘flow-into’ property can place an element
or its contents
into a <a data-link-type=dfn href=#named-flow>named flow</a>.
Content that belongs to the same flow
is laid out in the <a data-link-type=dfn href=#region-chain>region chain</a>
associated with that flow.</p>
<table class="definition propdef"><tr><th>Name:<td><dfn class=css data-dfn-type=property data-export="" id=propdef-flow-into>flow-into<a class=self-link href=#propdef-flow-into></a></dfn><tr><th>Value:<td class=prod>none <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> <a class="production css" data-link-type=type href=http://dev.w3.org/csswg/mediaqueries-4/#typedef-ident><ident></a> [element<a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a>content]<a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#mult-opt>?</a><tr><th>Initial:<td>none<tr><th>Applies to:<td>All elements, but not <a href=http://www.w3.org/TR/selectors/#pseudo-elements>pseudo-elements</a> such as <code>::first-line</code>, <code>::first-letter</code>, <code>::before</code> or <code>::after</code>.<tr><th>Inherited:<td>no<tr><th>Percentages:<td>n/a<tr><th>Media:<td>visual<tr><th>Computed value:<td>as specified<tr><th>Animatable:<td>no</table>
<dl>
<dt>none</dt>
<dd>
The element is not moved
to a <a data-link-type=dfn href=#named-flow>named flow</a>
and normal CSS processing takes place.
</dd>
<dt><a href=http://www.w3.org/TR/2011/REC-CSS2-20110607/syndata.html#value-def-identifier><ident></a></dt>
<dd>
If the keyword <dfn data-dfn-type=dfn data-noexport="" id=element>element<a class=self-link href=#element></a></dfn> is present
or neither keyword is present,
then the element is taken out
of its parent’s flow
and placed into the flow
with the name '<a href=http://www.w3.org/TR/2011/REC-CSS2-20110607/syndata.html#value-def-identifier><ident></a>'.
If the keyword <dfn data-dfn-type=dfn data-noexport="" id=content>content<a class=self-link href=#content></a></dfn> is present,
then only the element’s contents
are placed into the named flow.
The element or content is said to have
a <dfn data-dfn-type=dfn data-noexport="" id=specified-flow>specified flow<a class=self-link href=#specified-flow></a></dfn>.
The values <span class=css>none</span>, <span class=css>inherit</span>, <span class=css>default</span>, <span class=css>auto</span> and <span class=css>initial</span>
are invalid flow names.
</dd>
</dl>
<p>The <a class=property data-link-type=propdesc href=#propdef-flow-into>flow-into</a> property affects
the visual formatting of elements or contents
placed into a <a data-link-type=dfn href=#named-flow>named flow</a>
and of the <a data-link-type=dfn href=#region-chain>region chain</a> laying out content
from a <a data-link-type=dfn href=#named-flow>named flow</a>.
The <a class=property data-link-type=propdesc href=#propdef-flow-into>flow-into</a> property does not affect
the CSS cascade and inheritance
for the elements on which it is specified.
The <a class=property data-link-type=propdesc href=#propdef-flow-into>flow-into</a> property does not affect the
<a href=http://www.w3.org/TR/2012/WD-dom-20120405/#introduction-to-the-dom>DOM</a>
<a data-biblio-type=normative data-link-type=biblio href=#biblio-dom title=DOM>[DOM]</a> position of an element or its contents.
The <a class=property data-link-type=propdesc href=#propdef-flow-into>flow-into</a> property does not affect ordering
in non-visual media
(such as <a href=http://www.w3.org/TR/css3-speech/>speech</a>).
Likewise, <a class=property data-link-type=propdesc href=#propdef-flow-into>flow-into</a> does not affect
the default traversal order
of sequential navigation modes
(such as cycling through links,
see e.g. <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css-ui-3/#propdef-nav-index>nav-index</a> <a data-biblio-type=informative data-link-type=biblio href=#biblio-css3ui title=CSS3UI>[CSS3UI]</a>
or <a href=http://www.whatwg.org/specs/web-apps/current-work/multipage/editing.html#sequential-focus-navigation-and-the-tabindex-attribute><code>tabindex</code></a> <a data-biblio-type=informative data-link-type=biblio href=#biblio-html40 title=HTML40>[HTML40]</a>).</p>
<p>A <a data-link-type=dfn href=#named-flow>named flow</a> needs to be associated
with a <a data-link-type=dfn href=#region-chain>region chain</a>
(one or more <a data-link-type=dfn href=#css-region>CSS Regions</a>)
for its content to be visually formatted.
If no <a data-link-type=dfn href=#region-chain>region chain</a> is associated
with a given <a data-link-type=dfn href=#named-flow>named flow</a>,
the content in the <a data-link-type=dfn href=#named-flow>named flow</a>
is not rendered:
it does not generate boxes
and is not displayed.</p>
<p>The children of an element or content
with a specified flow
may themselves have a specified flow,
in which case they become
the next sibling of the latest element
or content collected in that flow.
In some cases,
the child can become the next sibling
for one of its ancestors in the same flow.</p>
<p>Content in a <a data-link-type=dfn href=#named-flow>named flow</a>
is sequenced in document order.
The visual formatting model
uses the relationships between content
in the named flow as input,
rather than the contents’ position
in the DOM.</p>
<p>Each <a data-link-type=dfn href=#css-region>CSS Region</a> in a <a data-link-type=dfn href=#region-chain>region chain</a>
establishes a containing block for absolutely positioned
elements in the <a data-link-type=dfn href=#named-flow>named flow</a> (see <a data-biblio-type=normative data-link-type=biblio href=#biblio-css21 title=CSS21>[CSS21]</a>).
That first <a data-link-type=dfn href=#css-region>CSS Region</a> in a <a data-link-type=dfn href=#region-chain>region chain</a>
establishes the initial containing block for such absolutely
positioned elements.
<span>Regions</span> don’t establish a containing block for
fixed positioned elements in the <a data-link-type=dfn href=#named-flow>named flow</a>.
Such fixed positioned elements are still positioned relative
to the viewport or the page area even if they have been
redirected into a named flow</p>
<p>The first region defines the principal
<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>
<div class=note role=note><span class=note-prefix>Note </span>
<p>The <a class=property data-link-type=propdesc href=#propdef-flow-into>flow-into</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 "table-content"
<a data-link-type=dfn href=#named-flow>named flow</a>.
However, the</p>
<pre>table > * {flow-into: table-content} ...</pre>
<p>selector will move all immediate children
of all table elements
into the "table-content" <a data-link-type=dfn href=#named-flow>named flow</a>
(which may be useful as it will usually result,
if the immediate children are rows,
in merging rows of multiple tables),
but the</p>
<pre>table * {flow-into: table-content}</pre>
<p>selector will move all descendants
of table elements into the "table-content" <a data-link-type=dfn href=#named-flow>named flow</a>,
transforming the element tree
into a flat list in order of opening tags
(which is probably not intentional).
This will make all the descendants
of table elements siblings
in the <a data-link-type=dfn href=#named-flow>named flow</a>.
Having the descendants become siblings
in the <a data-link-type=dfn href=#named-flow>named flow</a>
results in a different processing
(see <a href=http://www.w3.org/TR/2011/REC-CSS2-20110607/tables.html#anonymous-boxes>CSS 2.1’s anonymous table objects</a>).
This note illustrates how authors must exercise caution
when choosing a particular selector
for setting the <a class=property data-link-type=propdesc href=#propdef-flow-into>flow-into</a> property
to avoid unintended results.</p>
</div>
<div class=note role=note><span class=note-prefix>Note </span>
<p>Another consequence of moving elements
into <a data-link-type=dfn href=#named-flow>named flows</a> is that surrounding whitespace
is not moved into the named flow.
If you have code like this:</p>
<pre>span {flow-into: span-content}
<span>one</span>
<span>two</span>
</pre>
<p>Then the "span-content" named flow contents
will contain this:</p>
<pre><span>one</span><span>two</span>
</pre>
<p>Which will change the display
from "one two" to "onetwo".
If whitespace is significant,
then moving the parent
that contains the whitespace
to the named flow
is required.</p>
</div>
<h3 class="heading settled" data-level=3.2 id=flow-from><span class=secno>3.2. </span><span class=content>
The <a class=property data-link-type=propdesc href=#propdef-flow-from>flow-from</a> property</span><a class=self-link href=#flow-from></a></h3>
<p>The <a class=property data-link-type=propdesc href=#propdef-flow-from>flow-from</a> property makes
a block container a region
and associates it with
a <a data-link-type=dfn href=#named-flow>named flow</a>.</p>
<table class="definition propdef"><tr><th>Name:<td><dfn class=css data-dfn-type=property data-export="" id=propdef-flow-from>flow-from<a class=self-link href=#propdef-flow-from></a></dfn><tr><th>Value:<td class=prod><a class="production css" data-link-type=type href=http://dev.w3.org/csswg/mediaqueries-4/#typedef-ident><ident></a> <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> none <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> inherit<tr><th>Initial:<td>none<tr><th>Applies to:<td>Non-replaced <a href=http://www.w3.org/TR/CSS21/visuren.html#block-boxes>block containers</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<tr><th>Animatable:<td>no</table>
<dl>
<dt><strong>none</strong></dt>
<dd>
The block container is not a <a data-link-type=dfn href=#css-region>CSS Region</a>.
</dd>
<dt><strong><a href=http://www.w3.org/TR/2011/REC-CSS2-20110607/syndata.html#value-def-identifier><ident></a></strong></dt>
<dd>
The block container becomes a <a data-link-type=dfn href=#css-region>CSS Region</a>
(except as detailed in the text below),
and is ordered in a <a data-link-type=dfn href=#region-chain>region chain</a>
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 fragments</a> and visually formatted in the
<a href=http://www.w3.org/TR/CSS21/visuren.html#principal-box>principal boxes</a>
of the <span>regions</span>
in the <a data-link-type=dfn href=#region-chain>region chain</a>.
<br>
If there is no flow with name
<a href=http://www.w3.org/TR/2011/REC-CSS2-20110607/syndata.html#value-def-identifier><ident></a>,
then the block container does not
format any content visually.
</dd>
</dl>
<p>If the <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css-content-3/#content>content</a> property computes
to something else than <span class=css>normal</span>
(or <span class=css>none</span> for a pseudo-element),
the block container does not become
a <a data-link-type=dfn href=#css-region>CSS Region</a>.
If the <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visuren.html#propdef-display>display</a> property
of the block container
or one of its ancestors
computes to <span class=css>none</span>,
the block container does not become
a <a data-link-type=dfn href=#css-region>CSS Region</a>.</p>
<p>A <a data-link-type=dfn href=#css-region>CSS Region</a>’s document children
are not visually formatted
unless they are directed
to a <a data-link-type=dfn href=#named-flow>named flow</a>
with an associated <a data-link-type=dfn href=#region-chain>region chain</a>.</p>
<p>Block container pseudo-elements where
the value of <a class=property data-link-type=propdesc href=#propdef-flow-from>flow-from</a> computes to an
<a href=http://www.w3.org/TR/2011/REC-CSS2-20110607/syndata.html#value-def-identifier><ident></a>
and the value of <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css-content-3/#content>content</a> computes to <span class=css>none</span>
are generated as <a data-link-type=dfn href=#css-region>CSS Regions</a>,
which is an update to the behavior
described in <a data-biblio-type=normative data-link-type=biblio href=#biblio-css21 title=CSS21>[CSS21]</a>.</p>
<div class=note role=note><span class=note-prefix>Note </span>
<p>A block container becomes a <a data-link-type=dfn href=#css-region>CSS Region</a>
when its <a class=property data-link-type=propdesc href=#propdef-flow-from>flow-from</a> property is set
to a valid <a href=http://www.w3.org/TR/2011/REC-CSS2-20110607/syndata.html#value-def-identifier><ident></a> 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>
<p>There is no element matching
the <code>.article</code> selector
and therefore no content
in the <code>thread</code> flow.
However, the block container matching
the <code>.region</code> selector
is still associated with
that empty <a data-link-type=dfn href=#named-flow>named flow</a>
and, consequently,
its children are not formatted visually.</p>
</div>
<div class=note role=note><span class=note-prefix>Note </span>
<p>At the time of this note-writing, the <code>display</code> values that
always result in a non-replaced block container include
<code>block</code>, <code>inline-block</code>, <code>table-cell</code>,
<code>table-caption</code>, and <code>list-item</code>. All of these
display values work as regions with non-replaced elements.</p>
<p>The <code>flex</code> and <code>grid</code> display values do not
result in block containers (they are defined as flex containers and grid
elements, respectively). So ‘<a href=#flow-from><code class=property>flow-from</code></a>’ combined with those display values
does not result in a <a data-link-type=dfn href=#css-region>CSS Region</a>.</p>
</div>
<p><a data-link-type=dfn href=#css-region>CSS Regions</a>
create a new
<a href=http://www.w3.org/TR/CSS2/visuren.html#z-index>stacking context</a>.
<a data-link-type=dfn href=#css-region>CSS Regions</a>
establish a new
<a href=http://www.w3.org/TR/CSS2/visuren.html#block-formatting>block formatting Context</a>.
Exclusions (see <a data-biblio-type=informative data-link-type=biblio href=#biblio-css3-exclusions title=CSS3-EXCLUSIONS>[CSS3-EXCLUSIONS]</a>)
potentially impact the content
laid out in <a data-link-type=dfn href=#region-chain>region chains</a>,
just as for non-regions.</p>
<div class=note role=note><span class=note-prefix>Note </span>
<p>With <a data-link-type=dfn href=#region-chain>region chains</a>,
an element may be split across multiple boxes
and these boxes 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 <a data-link-type=dfn href=#css-region>CSS Region</a> creates
a new stacking context,
it is clear that each fragment is rendered separately
and their rendering order follows
the regular CSS rendering model.</p>
<p>Fragments rendering separately
is also relevant to elements that might normally
be rendered as a unit
(for example,
an element with its own stacking context,
or with transparency).
Each fragment of these elements
is separately contained in the stacking context
created by the <a data-link-type=dfn href=#css-region>CSS Region</a>,
so each fragment of these elements
is rendered separately.</p>
</div>
<p>See the
<a href=#regions-visual-formatting-details>regions visual formatting details</a>
section for a description of how
<a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visudet.html#propdef-width>width</a> and <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css2/visudet.html#propdef-height>height</a> values are resolved
for <a data-link-type=dfn href=#css-region>CSS Region</a> boxes.</p>
<h4 class="heading settled" data-level=3.2.1 id=circular-dependencies><span class=secno>3.2.1. </span><span class=content>
Cycle Detection</span><a class=self-link href=#circular-dependencies></a></h4>
<p><a data-link-type=dfn href=#named-flow>named flows</a> containing elements
where the value of <a class=property data-link-type=propdesc href=#propdef-flow-from>flow-from</a> computes to an
<a href=http://www.w3.org/TR/2011/REC-CSS2-20110607/syndata.html#value-def-identifier><ident></a>
can produce nonsensical circular relationships,
such as a <a data-link-type=dfn href=#named-flow>named flow</a>
containing <a data-link-type=dfn href=#css-region>CSS Regions</a>
in its own <a data-link-type=dfn href=#region-chain>region chain</a>.
These relationships can be easily
and reliably detected and resolved, however,
by keeping track of a dependency graph
and using common cycle-detection algorithms.</p>
<p>The dependency graph consists of edges such that:</p>
<ul>
<li>
Every <a data-link-type=dfn href=#named-flow>named flow</a> depends on its elements
where the value of <a class=property data-link-type=propdesc href=#propdef-flow-from>flow-from</a> computes to an
<a href=http://www.w3.org/TR/2011/REC-CSS2-20110607/syndata.html#value-def-identifier><ident></a>.
</li>
<li>
Every element in a <a data-link-type=dfn href=#named-flow>named flow</a>
where the value of <a class=property data-link-type=propdesc href=#propdef-flow-from>flow-from</a> computes to an
<a href=http://www.w3.org/TR/2011/REC-CSS2-20110607/syndata.html#value-def-identifier><ident></a>
depends on the <a data-link-type=dfn href=#named-flow>named flow</a> with the
<a href=http://www.w3.org/TR/2011/REC-CSS2-20110607/syndata.html#value-def-identifier><ident></a>
name.
</li>
</ul>
<p>If the graph contains a cycle,
any elements where the value of <a class=property data-link-type=propdesc href=#propdef-flow-from>flow-from</a>
computes to an
<a href=http://www.w3.org/TR/2011/REC-CSS2-20110607/syndata.html#value-def-identifier><ident></a>
participating in the cycle
do not become <a data-link-type=dfn href=#css-region>CSS Regions</a>.</p>
<div class=note role=note><span class=note-prefix>Note </span>
<p>For example, styling like this:</p>
<pre>#id {
flow-into: foolish;
flow-from: foolish;
}
</pre>
<p>would move the <code>#id</code> element to a "foolish" <a data-link-type=dfn href=#named-flow>named flow</a>,
and try to make the <code>#id</code> element
a <a data-link-type=dfn href=#css-region>CSS Region</a> for the "foolish" <a data-link-type=dfn href=#named-flow>named flow</a>.
The "foolish" <a data-link-type=dfn href=#named-flow>named flow</a> would then contain its own region,
creating a cycle.
So the <code>#id</code> element does not become a <a data-link-type=dfn href=#css-region>CSS Region</a>.</p>
</div>
<div class=note role=note><span class=note-prefix>Note </span>
<p>The content keyword can be used to break cycles in some circumstances:</p>
<pre>#id {
flow-into: not-so-foolish content;
flow-from: not-so-foolish;
}
</pre>
<p>Here only the contents of the <code>#id</code> element are moved to the <a data-link-type=dfn href=#named-flow>named flow</a>, and the box for the <code>#id</code> element <em>does</em> become a <a data-link-type=dfn href=#css-region>CSS Region</a>. Since the <a data-link-type=dfn href=#named-flow>named flow</a> does not contain the element itself, there is no cycle. With this declaration the <code>#id</code> element becomes a single-box <a data-link-type=dfn href=#region-chain>region chain</a> for its contents, and other boxes could be added to the chain to customize overflow.</p>
</div>
<h4 class="heading settled" data-level=3.2.2 id=fragmenting-regions><span class=secno>3.2.2. </span><span class=content>
Nested fragmentation contexts</span><a class=self-link href=#fragmenting-regions></a></h4>
<p>A <a data-link-type=dfn href=#css-region>CSS Region</a> that contains
a fragment of a <a data-link-type=dfn href=#named-flow>named flow</a>
can itself be fragmented if it is nested
within a fragmentation context <a data-biblio-type=normative data-link-type=biblio href=#biblio-css3-break title=CSS3-BREAK>[CSS3-BREAK]</a>,
such as when a layout
using a <a data-link-type=dfn href=#region-chain>region chain</a> is printed.
In these cases break opportunities
in the named flow fragment
contained by the <a data-link-type=dfn href=#css-region>CSS Region</a>
are determined using the standard
<a href=http://www.w3.org/TR/css3-break/>fragmentation rules</a>.
In other words,
each region box and its associated fragment
should break as if it were a simple div
containing the fragment contents.
This can be controlled by using
an avoid break value on the <a data-link-type=dfn href=#css-region>CSS Region</a>,
if that is desired.</p>
<p>A <a data-link-type=dfn href=#css-region>CSS Region</a> can be part
of the contents of a separate named flow,
as long as there are no cycles broken
by the <a href=#circular-dependencies>Cycle Detection</a>
described above.
This case is a <dfn data-dfn-type=dfn data-noexport="" id=nested-region-context>nested region context<a class=self-link href=#nested-region-context></a></dfn>,
which has an effect
on the <a href=#regions-visual-formatting-steps>Visual Formatting Steps</a>
described below.</p>
<h3 class="heading settled" data-level=3.3 id=region-flow-break><span class=secno>3.3. </span><span class=content>
Region flow break properties: <a class=property data-link-type=propdesc href=#propdef-break-before>break-before</a>, <a class=property data-link-type=propdesc href=#propdef-break-after>break-after</a>, <a class=property data-link-type=propdesc href=#propdef-break-inside>break-inside</a></span><a class=self-link href=#region-flow-break></a></h3>
<div class=note role=note><span class=note-prefix>Note </span>
<p>This section is also defined in <a data-biblio-type=normative data-link-type=biblio href=#biblio-css3-break title=CSS3-BREAK>[CSS3-BREAK]</a>.
If that specification moves to last call
with the region values,
the section here can be replaced by a reference.</p>
</div>
<p>User agents laying out content in multiple regions
must determine where content breaks occur.
The problem of breaking content into fragments fitting in regions
is similar to breaking content into pages or columns.</p>
<p>Each break ends layout in the current region
and causes remaining pieces of content
from the <a data-link-type=dfn href=#named-flow>named flow</a> to be visually formatted
in the following region in the <a data-link-type=dfn href=#region-chain>region chain</a>,
if there is one.</p>
<p>The following extends
the <a class=property data-link-type=propdesc href=#propdef-break-before>break-before</a>, <a class=property data-link-type=propdesc href=#propdef-break-after>break-after</a> and <a class=property data-link-type=propdesc href=#propdef-break-inside>break-inside</a> properties
from the <a data-biblio-type=normative data-link-type=biblio href=#biblio-css3col title=CSS3COL>[CSS3COL]</a> specification to account for regions.
The additional values are described below.</p>
<table class="definition propdef"><tr><th>Name:<td><dfn class=css data-dfn-type=property data-export="" id=propdef-break-before>break-before<a class=self-link href=#propdef-break-before></a></dfn><tr><th>Value:<td class=prod>auto <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> always <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> avoid <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> left <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> right <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> page <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> column <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> region <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> avoid-page <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> avoid-column <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> avoid-region<tr><th>Initial:<td>auto<tr><th>Applies to:<td>block-level elements<tr><th>Inherited:<td>no<tr><th>Percentages:<td>n/a<tr><th>Media:<td>visual<tr><th>Computed value:<td>as specified<tr><th>Animatable:<td>no</table>
<table class="definition propdef"><tr><th>Name:<td><dfn class=css data-dfn-type=property data-export="" id=propdef-break-after>break-after<a class=self-link href=#propdef-break-after></a></dfn><tr><th>Value:<td class=prod>auto <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> always <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> avoid <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> left <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> right <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> page <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> column <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> region <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> avoid-page <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> avoid-column <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> avoid-region<tr><th>Initial:<td>auto<tr><th>Applies to:<td>block-level elements<tr><th>Inherited:<td>no<tr><th>Percentages:<td>n/a<tr><th>Media:<td>visual<tr><th>Computed value:<td>as specified<tr><th>Animatable:<td>no</table>
<table class="definition propdef"><tr><th>Name:<td><dfn class=css data-dfn-type=property data-export="" id=propdef-break-inside>break-inside<a class=self-link href=#propdef-break-inside></a></dfn><tr><th>Value:<td class=prod>auto <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> avoid <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> avoid-page <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> avoid-column <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> avoid-region<tr><th>Initial:<td>auto<tr><th>Applies to:<td>block-level elements<tr><th>Inherited:<td>no<tr><th>Percentages:<td>n/a<tr><th>Media:<td>visual<tr><th>Computed value:<td>as specified<tr><th>Animatable:<td>no</table>
<p>These properties describe page, column and region break behavior
before/after/inside the generated box. These values are normatively defined
in <a data-biblio-type=normative data-link-type=biblio href=#biblio-css3col title=CSS3COL>[CSS3COL]</a>:</p>
<p>This specification adds the following new values:</p>
<dl>
<dt>region</dt>
<dd>Always force a region break before (after) the generated box.</dd>
<dt>avoid-region</dt>
<dd>Avoid a region break before (after, inside) the generated box.</dd>
</dl>
<p>The behavior of region breaks with regards to regions
is identical to the behavior of page breaks with regards to pages,
as defined in the <a data-biblio-type=normative data-link-type=biblio href=#biblio-css21 title=CSS21>[CSS21]</a>.</p>
<h3 class="heading settled" data-level=3.4 id=the-region-fragment-property><span class=secno>3.4. </span><span class=content>
The region-fragment property</span><a class=self-link href=#the-region-fragment-property></a></h3>
<table class="definition propdef"><tr><th>Name:<td><dfn class=css data-dfn-type=property data-export="" id=propdef-region-fragment>region-fragment<a class=self-link href=#propdef-region-fragment></a></dfn><tr><th>Value:<td class=prod>auto <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> break<tr><th>Initial:<td>auto<tr><th>Applies to:<td><a data-link-type=dfn href=#css-region>CSS Regions</a><tr><th>Inherited:<td>no<tr><th>Percentages:<td>n/a<tr><th>Media:<td>visual<tr><th>Computed value:<td>as specified<tr><th>Animatable:<td>no</table>
<p>The <a class=property data-link-type=propdesc href=#propdef-region-fragment>region-fragment</a> property controls the behavior
of the <em id=last-region>last region</em>
associated with a <a data-link-type=dfn href=#named-flow>named flow</a>.</p>
<dl>
<dt>auto</dt>
<dd>
Content flows as it would in a regular content box.
If the content exceeds the container box,
it is subject to the
<a href=http://www.w3.org/TR/CSS21/visufx.html#propdef-overflow>overflow</a>