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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 http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>CSS Regions Module Level 3</title>
<link rel="stylesheet" type="text/css" href="../shared/style/default.css">
<script src='http://test.csswg.org/harness/annotate.js#CSS3-REGIONS_DEV' type='text/javascript' defer></script>
<style type="text/css">
#region-style-example p, #region-style-example pre {
clear: both;
}
#region_styling_illustration {
margin: 0px auto;
width: 70ex;
}
</style>
<link rel="stylesheet" type="text/css"
href="http://www.w3.org/StyleSheets/TR/W3C-ED.css">
<link rel="stylesheet" type="text/css"
href="../shared/style/issues.css">
<link id="st" href="../shared/style/alternate-spec-style.css" rel="stylesheet"
type="text/css" title="alternate spec style">
</head>
<body>
<div class="head" id="div-head">
<p><a href="http://www.w3.org/"><img id="mobile-logo" alt="W3C" height="53" 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 id="logo" 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">[LONGSTATUS]
[DATE]</h2>
<dl>
<dt>This version:</dt>
<dd><a href=
"[VERSION]">http://www.w3.org/csswg/css3-regions</a></dd>
<dt>Latest version:</dt>
<dd><a href=
"http://www.w3.org/TR/css3-regions/">http://www.w3.org/TR/css3-regions/</a></dd>
<dt>Previous version:</dt>
<dd><a href="http://www.w3.org/TR/2011/WD-css3-regions-20111129/">http://www.w3.org/TR/2011/WD-css3-regions-20111129/</a></dd>
<dt>Editors:</dt>
<dd class="vcard"><span class="fn">Vincent Hardy</span>,
<span class="org">Adobe Systems, Inc.</span>, <span class=
"email">vhardy@adobe.com</span></dd>
<dd class="vcard"><span class="fn">Alex Mogilevsky</span>,
<span class="org">Microsoft</span>, <span class=
"email">alexmog@microsoft.com</span></dd>
<dd class="vcard"><span class="fn">Alan Stearns</span>,
<span class="org">Adobe Systems, Inc.</span>, <span class=
"email">stearns@adobe.com</span></dd>
<dt>Issues List:</dt>
<dd><a href="https://www.w3.org/Bugs/Public/buglist.cgi?product=CSS&component=Regions&resolution=---">Bugzilla Bugs for CSS regions</a></dd>
<dt>Discussion:</dt>
<dd><a href="http://lists.w3.org/Archives/Public/www-style/">www-style@w3.org</a> with subject line "<code>[css3-regions] message topic</code>"</dd>
</dl><!--begin-copyright--><!--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 [[CSS3COL]] or the Grid Layout Module
[[CSS3-GRID-LAYOUT]] to position the regions where content flows.</p>
<h2 class="no-num no-toc" id="status-of-this-document">Status of this
document</h2>
<p class="big note"><span class="note-prefix">Note </span>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>
<!--status-->
<p>This draft is related to the drafts about Multi-column Layout
[[CSS3COL]], Grid Layout [[CSS3GRID]], Flexible Box Layout
[[CSS3-FLEXBOX]], and Template Layout [[CSS3LAYOUT]].</p>
<h2 class="no-num no-toc" id="table-of-contents">Table of contents</h2>
<!--begin-toc--><!--end-toc-->
<h2 id="introduction">Introduction</h2>
<p><em>This section is non-normative.</em></p>
<p>Displaying the complex layouts
of a typical magazine, newspaper, or textbook on the web
requires capabilities beyond those available in existing CSS modules.
Dynamic magazine layout in particular requires flexibility
in placement of boxes for content flows.
This is the purpose of the CSS regions module.</p>
<div class="issue-marker" data-bug_id="15733" data-bug_status="NEW">
<a href=
"https://www.w3.org/Bugs/Public/show_bug.cgi?id=15733">Issue-15733</a>
<div class="issue-details">
<p class="short-desc">Should the region specification define a
mechanism to create blocks that can be regions with CSS
syntax?</p>
</div>
</div>
<p>For more complex layouts,
content needs to flow from one area of the page to the next
without limitation on the areas' sizes and positions.
These arbitrary areas are the target of specific content flows
which this document calls <span>named flows</span>.
Each <span>named flow</span> can be associated
with a set of CSS Regions called a region chain.
CSS Regions are based on the rectangular geometry
of the CSS box model.
Elements in a <span>named flow</span>
are taken out of the normal visual formatting
and rendered in a chain of CSS Regions.</p>
<h3 id="named-flows-and-regions">Named flows and region chains</h3>
<p>Consider the layout illustrated in figure 1.</p>
<div class="figure">
<img src="images/intro-example-layout.svg" width="400" alt=
"multiple chained regions which should receive content from a flow">
<p class="caption">Layout requiring sophisticated content flow</p>
</div>
<p>The designer's intent is
to position an image in box 'A'
and to flow an article's content
from box '1' through boxes '2', '3' and '4'.
Note that the second box should have two columns,
and the image is not contained in the article.
Box '4' should auto-size to render
the remainder of the article content
that did not fit in the earlier boxes.</p>
<p>Figure 2 shows an example
of the intended visual rendering
of the content.</p>
<div class="figure">
<img src="images/regions-intro-rendering.png" width="450" alt=
"Sample rendering showing a single thread of text flowing through a chain of regions">
<p class="caption">Sample rendering for desired layout</p>
</div>
<p>There is no existing mechanism in CSS
to associate the content with these boxes
arranged in this manner
so that content flows as intended.
The CSS regions module properties provide that mechanism.</p>
<p>The following example illustrates
how the content of an <code><article></code> element
becomes a <span>named flow</span>
and how boxes marked with 'region1', 'region2', 'region3' and 'region4' IDs
become CSS Regions that consume the 'article_flow' content.</p>
<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 'article_flow' value on the 'flow-into' property
directs the <code>article</code> element
to the 'article_flow' <span>named flow</span>.
Setting the 'flow-from' property on block containers
to 'article_flow' makes them CSS Regions
and associates the resulting region chain
with the <span>named flow</span>:
the flow is ''poured''
into the region chain.</p>
<p>See <a href="#intro-example-code">Appendix A</a>
for sample code using grid layout
that implements this example</p>
<div class="issue-marker" data-bug_id="16858" data-bug_status="ASSIGNED">
<a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=16858">Issue-16858</a>
<div class="issue-details">
<p class="short-desc">Should creation of regions from elements be disallowed?</p>
</div>
</div>
<div class="note"><span class="note-prefix">Note </span>
<p><strong>CSS Regions 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 CSS Regions.
Using a grid layout [[CSS3-GRID-LAYOUT]] is just an example.
The example could use
a flexible box layout [[CSS3-FLEXBOX]] instead.</p>
<p>The CSS regions specification does not
define a layout mechanism
and is meant to integrate
with existing and future CSS layout facilities.</p>
<p><strong>CSS Regions do not have to be elements</strong></p>
<p>The CSS regions module is independent
of the layout of boxes and
the mechanism used to create them.
For simplicity,
our example code in <a href="#intro-example-code">Appendix A</a>
uses elements to define the boxes.</p>
<p>While the example uses elements for CSS Regions
(since [[CSS3-GRID-LAYOUT]] requires elements to create grid items)
it is important to note that
this is not required.
CSS Regions can be pseudo-elements,
such as '::before' and '::after'.
The only requirement
for an element or pseudo-element
to become a CSS Region
is that it needs to be subject
to CSS styling
to receive the 'flow-from' property.
The CSS page template module
(see [[CSS3-PAGE-TEMPLATE]])
proposes another mechanism
to create stylable boxes that can become CSS Regions
with the <code class="css">@slot</code> syntax.</p>
</div>
<h3 id="region-styling">CSS Region names and styling</h3>
<div class="issue-marker" data-bug_id="16859" data-bug_status="NEW">
<a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=16859">Issue-16859</a>
<div class="issue-details">
<p class="short-desc">Reconsider using @rule for region styling</p>
</div>
</div>
<p>Content can be styled depending on
the CSS Region it flows into.
It is an extension
of pseudo-element styling such as
<a href="http://www.w3.org/TR/css3-selectors/#first-line">
<code class="css">::first-line</code>
</a>
which applies a particular style
to a fragment of content.
With CSS Region styling,
additional selectors may apply
depending on the CSS Region
into which content flows.</p>
<p>In our example,
the designer wants to make
text flowing into #region1
dark blue and bold.</p>
<p>This design can be expressed as shown below.</p>
<div class="example">
<pre>
<style>
@region #region1 {
p {
color: #0C3D5F;
font-weight: bold;
}
</style></pre>
</div>
<p>The <code class="css">@region #region1</code> rule
limits its selectors to content
flowing into <code class="css">#region1</code>.
The following figure shows how
the rendering changes
if we apply styling specific to <code>#region1</code>.
Note how less text fits into this box
now that the 'font-weight' is
bold instead of normal.</p>
<div class="figure">
<img src="images/region-styling.png" width="450" alt=
"Illustrate how changing region styling affects the flow of content.">
<p class="caption">Different rendering with a different region
styling</p>
</div>
<h2 id="css-regions-concepts">CSS regions concepts</h2>
<h3 id="regions">Regions</h3>
<div class="issue-marker wrapper">
<div class="issue-marker" data-bug_id="15186" data-bug_status="NEW">
<a href=
"https://www.w3.org/Bugs/Public/show_bug.cgi?id=15186">Issue-15186</a>
<div class="issue-details">
<p class="short-desc">Is a mechanism to auto-generate regions
necessary in order to support reusable style sheets?</p>
</div>
</div>
<div class="issue-marker" data-bug_id="15187" data-bug_status="NEW">
<a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=15187">Issue-15187</a>
<div class="issue-details">
<p class="short-desc">Explain how regions and pages interact. How can regions be placed onto certain pages, and how can they be positiond wrt. pages.</p>
</div>
</div>
</div>
<p id="region">
A <dfn title="region">CSS Region</dfn>
is a block container
that has an associated
<em><span>named flow</span></em>
(see the 'flow-from' property).</p>
<h3 id="region-chain">Region chain</h3>
<p>A <dfn>region chain</dfn> is the sequence of regions that are associated with
a <span>named flow</span>. <span title="region">CSS Regions</span> in a
region chain receive content from the
named flow following their order in the chain. <span title="region">CSS Regions</span> are organized
into a <span title="region-chain">region chain</span>
according to the document order.</p>
<h3 id="named-flow">Named flows</h3>
<p>A <dfn>named flow</dfn> is the ordered sequence of elements
associated with a flow with a given identifier.
Elements in a <span>named flow</span> are ordered
according to the document order.</p>
<p>Elements are placed into a <span>named flow</span>
with the 'flow-into' property.
The elements in a <span>named flow</span> are laid out
in the <span title="region-chain">region chain</span>
that is associated with this <span>named flow</span>.
</p>
<p>Content from a <span>named flow</span>
is broken up between regions
according to the regions flow breaking rules.</p>
<p>A <span>named flow</span> is created when
at least one element is moved
into the flow with the given identifier
or when at least one CSS Region
requests content from that flow.</p>
<h3 id="regions-flow-breaking-rules">Regions flow breaking rules</h3>
<p>Breaking a <span>named flow</span> across a region chain
is similar to breaking a document's content across pages
(see [[CSS3PAGE]])
or a multi-column element's content across column boxes
(see [[CSS3COL]]).
One difference is that page boxes are generated
based on the available content
whereas a region chain is a set of recipient boxes
for the <span>named flow</span> content
whose dynamic generation is not in the scope
of this specification.</p>
<p>Each CSS Region in turn
consumes content from its associated <span>named flow</span>.
The <span>named flow</span> content is positioned
in the <dfn title="current-region">current region</dfn>
until a natural or forced region break occurs,
at which point the next region
in the <span title="region-chain">region chain</span>
becomes the <span title="current-region">current region</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 'region-overflow' property
on the last <span>region</span> in the chain.</p>
<p>The CSS regions module follows
the fragmentation rules defined
in the CSS Fragmentation Module Level 3
(see [[!CSS3-BREAK]]).</p>
<h2 id="properties-and-rules">Properties and rules</h2>
<h3 id="the-flow-into-property">The 'flow-into' property</h3>
<div class="issue-marker wrapper">
<div class="issue-marker" data-bug_id="15811" data-bug_status="NEW">
<a href=
"https://www.w3.org/Bugs/Public/show_bug.cgi?id=15811">Issue-15811</a>
<div class="issue-details">
<p class="short-desc">Creating a named flow from external resource</p>
</div>
</div>
<div class="issue-marker" data-bug_id="16002" data-bug_status="NEW">
<a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=16002">Issue-16002</a>
<div class="issue-details">
<p class="short-desc">flow-into and anonymous blocks or fix-ups</p>
</div>
</div>
<div class="issue-marker" data-bug_id="16527" data-bug_status="ASSIGNED">
<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
into a <span>named flow</span>.
Elements that belong to the same flow
are laid out in the region chain
associated with that flow.</p>
<table class="propdef" summary="flow property definition">
<tr>
<th>Name:</th>
<td><dfn id="flow-into">flow-into</dfn></td>
</tr>
<tr>
<th>Value:</th>
<td><ident> | none | inherit</td>
</tr>
<tr>
<th>Initial:</th>
<td>none</td>
</tr>
<tr>
<th>Applies to:</th>
<td>any element. <p>The 'flow-into' property does not apply to any <a href="http://www.w3.org/TR/selectors/#pseudo-elements">pseudo-element</a> such as
<code class="css">::first-line</code>, <code class="css">::first-letter</code>,
<code class="css">::before</code> or <code class="css">::after</code>.</p></td>
</tr>
<tr>
<th>Inherited:</th>
<td>no</td>
</tr>
<tr>
<th>Percentages:</th>
<td>N/A</td>
</tr>
<tr>
<th>Media:</th>
<td>visual</td>
</tr>
<tr>
<th>Computed value:</th>
<td>as specified</td>
</tr>
</table>
<dl>
<dt>none</dt>
<dd>The element is not moved to a <span>named flow</span> 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>The element is taken out
of its parent's flow
and placed into the flow
with the name '<ident>'.
The element is said to have
a <dfn id="specified-flow">specified flow</dfn>.
The values 'none', 'inherit', 'default', 'auto' and 'initial'
are invalid flow names.</dd>
</dl>
<p>A <span>named flow</span> needs to be associated
with a region chain
(one or more CSS regions)
for its elements to be visually formatted.
If no region chain is associated
with a given <span>named flow</span>,
the elements in the <span>named flow</span>
are not rendered:
they do not generate boxes
and are not displayed.</p>
<p>The children of an element
with a specified flow
may themselves have a specified flow.</p>
<p>If an element has the same specified flow
as one of its ancestors,
it becomes a sibling of its ancestor
for the purpose of layout
in the region chain
laying out content
from that flow.</p>
<p>The 'flow-into' property does not affect
the CSS cascade and inheritance
for the elements on which it is specified.
The 'flow-into' property affects
the visual formatting of elements
placed into a <span>named flow</span>
and of the region chain laying out content
from a <span>named flow</span>.</p>
<p>The edges of the first CSS region in a region chain
associated with a <span>named flow</span>
establish the rectangle that is the
<a href="http://www.w3.org/TR/CSS2/visudet.html#containing-block-details">containing block</a>
used for absolutely positioned elements
in the <span>named flow</span>
which do not have an ancestor
with a 'position' of 'absolute', 'relative' or 'fixed'
(see [[!CSS21]]).
That first CSS region rectangle is used
as the containing block
instead of the initial containing block.
This does not affect
fixed position elements
in the <span>named flow</span> -
they are still positioned relative
to the viewport or page area even if
they have been redirected
to a named flow.</p>
<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>
<p>Elements in a <span>named flow</span>
are sequenced in document order.</p>
<div class="note"><span class="note-prefix">Note </span>
<p>The 'flow-into' 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'
<span>named flow</span>.
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’ <span>named flow</span>
(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’ <span>named flow</span>,
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 <span>named flow</span>.
Having the descendants become siblings
in the <span>named flow</span>
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 'flow-into' property
to avoid unintended results.</p>
</div>
<h3 id="the-flow-from-property">The 'flow-from' property</h3>
<p>The 'flow-from' property makes
a block container a region
and associates it with
a <span>named flow</span>.</p>
<table class="propdef" summary="flow-from property definition">
<tr>
<th>Name:</th>
<td><dfn id="flow-from">flow-from</dfn></td>
</tr>
<tr>
<th>Value:</th>
<td><ident> | none | inherit</td>
</tr>
<tr>
<th>Initial:</th>
<td>none</td>
</tr>
<tr>
<th>Applies to:</th>
<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.</td>
</tr>
<tr>
<th>Inherited:</th>
<td>no</td>
</tr>
<tr>
<th>Percentages:</th>
<td>N/A</td>
</tr>
<tr>
<th>Media:</th>
<td>visual</td>
</tr>
<tr>
<th>Computed value:</th>
<td>as specified</td>
</tr>
</table>
<dl>
<dt><strong>none</strong></dt>
<dd>The block container is not a <span title="region">region</span>.</dd>
<dt><strong><ident></strong></dt>
<dd>
If the 'content' property computes
to something else than 'normal',
the block container does not become a <span>CSS Region</span>.
If the 'content' property computes to 'normal',
then the block container becomes a <span>CSS 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 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 <span>region chain</span>.
<br/>
If there is no flow with name <ident>,
then the block container does not
format any content visually.
<br/>
Likewise, if the block container is part
of the flow with name <ident>,
then the block container does not
format any content visually.
</dd>
</dl>
<div class="issue-marker" data-bug_id="16819" data-bug_status="ASSIGNED">
<a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=16819">Issue-16819</a>
<div class="issue-details">
<p class="short-desc">No display when combining flow-from and flow-into is bad</p>
</div>
</div>
<p>A <span>CSS Region</span>'s document children
are not visually formatted
unless they are directed
to a <span>named flow</span>
with an associated <span>region chain</span>.</p>
<div class="note"><span class="note-prefix">Note </span>
<p>An block container becomes a <span>CSS Region</span>
when its 'flow-from' 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 block container matching
the <code>.region</code> selector
is still associated with
that empty <span>named flow</span>
and, consequently,
its children are not formatted visually.
</div>
<div class="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.
</div>
<div class="issue-marker wrapper">
<div class="issue-marker" data-bug_id="15189" data-bug_status="NEW">
<a href=
"https://www.w3.org/Bugs/Public/show_bug.cgi?id=15189">Issue-15189</a>
<div class="issue-details">
<p class="short-desc">Should regions be non-breakable?</p>
</div>
</div>
<div class="issue-marker" data-bug_id="15824" data-bug_status="NEW">
<a href=
"https://www.w3.org/Bugs/Public/show_bug.cgi?id=15824">Issue-15824</a>
<div class="issue-details">
<p class="short-desc">Should regions not create a new stacking context?</p>
</div>
</div>
<div class="issue-marker" data-bug_id="15827" data-bug_status="NEW">
<a href=
"https://www.w3.org/Bugs/Public/show_bug.cgi?id=15824">Issue-15827</a>
<div class="issue-details">
<p class="short-desc">Specify behavior of stacking contexts that are split between regions</p>
</div>
</div>
<div class="issue-marker" data-bug_id="16636" data-bug_status="NEW">
<a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=16636">Issue-16636</a>
<div class="issue-details">
<p class="short-desc">Should re-introduce region order</p>
</div>
</div>
</div>
<p><span title="region">CSS Regions</span> create a new <a href="http://www.w3.org/TR/CSS2/visuren.html#z-index">stacking context</a>. <span title="region">CSS Regions</span> establish a new <a href="http://www.w3.org/TR/CSS2/visuren.html#block-formatting">block formatting Context</a>.</p>
<div class="note"><span class="note-prefix">Note </span>
<p>With <span>region chains</span>,
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 <span>CSS Region</span> 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>
</div>
<p>Floats or other exclusions
(see [[CSS3-EXCLUSIONS]])
potentially impact the content
laid out in region chains,
just as for non-regions.</p>
<p>See the
<a href="#regions-visual-formatting-details">regions visual formatting details</a>
section for a description of how
'width' and 'height' values are resolved
for <span>CSS Region</span> boxes.</p>
<h3 id=
"region-flow-break">Region
flow break properties: 'break-before', 'break-after', 'break-inside'</h3>
<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 <span>named flow</span> to be visually formatted in the following
region in the region chain, if there is one.</p>
<p>The following extends the 'break-before', 'break-after' and
'break-inside' properties from the [[!CSS3COL]] specification to account
for regions. The additional values are described below.</p>
<table class="propdef" summary="break-before property definition">
<tr>
<td><em>Name:</em></td>
<td><dfn>break-before</dfn></td>
</tr>
<tr>
<td><em>Value:</em></td>
<td>auto | always | avoid | left | right | page | column | region |
avoid-page | avoid-column | avoid-region</td>
</tr>
<tr>
<td><em>Initial:</em></td>
<td>auto</td>
</tr>
<tr>
<td><em>Applies to:</em></td>
<td>block-level elements</td>
</tr>
<tr>
<td><em>Inherited:</em></td>
<td>no</td>
</tr>
<tr>
<td><em>Percentages:</em></td>
<td>N/A</td>
</tr>
<tr>
<td><em>Media:</em></td>
<td>visual</td>
</tr>
<tr>
<td><em>Computed value:</em></td>
<td>specified value</td>
</tr>
</table>
<table class="propdef" summary="break-after property definition">
<tr>
<td><em>Name:</em></td>
<td><dfn>break-after</dfn></td>
</tr>
<tr>
<td><em>Value:</em></td>
<td>auto | always | avoid | left | right | page | column | region |
avoid-page | avoid-column | avoid-region</td>
</tr>
<tr>
<td><em>Initial:</em></td>
<td>auto</td>
</tr>
<tr>
<td><em>Applies to:</em></td>
<td>block-level elements</td>
</tr>
<tr>
<td><em>Inherited:</em></td>
<td>no</td>
</tr>
<tr>
<td><em>Percentages:</em></td>
<td>N/A</td>
</tr>
<tr>
<td><em>Media:</em></td>
<td>visual</td>
</tr>
<tr>
<td><em>Computed value:</em></td>
<td>specified value</td>
</tr>
</table>
<table class="propdef" summary="break-inside property definition">
<tr>
<td><em>Name:</em></td>
<td><dfn>break-inside</dfn></td>
</tr>
<tr>
<td><em>Value:</em></td>
<td>auto | avoid | avoid-page | avoid-column | avoid-region</td>
</tr>
<tr>
<td><em>Initial:</em></td>
<td>auto</td>
</tr>
<tr>
<td><em>Applies to:</em></td>
<td>block-level elements</td>
</tr>
<tr>
<td><em>Inherited:</em></td>
<td>no</td>
</tr>
<tr>
<td><em>Percentages:</em></td>