csswg-drafts/css3-regions/Overview.html at 8e2fbfefdc7473741c83cd7006e118ab5b154164 · w3c/csswg-drafts · GitHub

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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">

<html dir=ltr lang=en>
 <head profile="http://www.w3.org/2006/03/hcard"><meta content="IE=edge"
  http-equiv=X-UA-Compatible>
  <meta content="text/html; charset=utf-8" http-equiv=Content-Type>

  <title>CSS regions Module</title>
  <link href="http://dev.w3.org/csswg/default.css" rel=stylesheet
  type="text/css">
  <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="additional
  spec styles" type="text/css">
  <script src=style-toggle.js type="text/javascript">
</script>
  <!-- <script src='http://test.csswg.org/harness/annotate.js#CSS3-REGIONS_DEV' type=
    'text/javascript'> -->

 <body>
  <div class=head id=div-head> <!--begin-logo-->
   <p><a href="http://www.w3.org/"><img alt=W3C height=48
    src="http://www.w3.org/Icons/w3c_home" width=72></a> <!--end-logo--></p>

   <h1 id=css-regions-module>CSS regions Module</h1>

   <h2 class="no-num no-toc" id=longstatus-date>Editor's Draft 11 August 2011</h2>

   <dl>
    <dt>This version:

    <dd><a
     href="http://www.w3.org/TR/2011/ED-css3-regions-20110811/">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/csswg/css3-regions</a>

    <dt>Previous version:

    <dd>none

    <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>

    <dt>Authors and Former Editors:

    <dd class=vcard><span class=fn>Stephen Zilles</span>, <span
     class=org>Adobe Systems, Inc.</span>, <span
     class=email>szilles@adobe.com</span>

    <dd class=vcard><span class=fn>Alexandru Chiculita</span>, <span
     class=org>Adobe Systems, Inc.</span>, <span
     class=email>achicu@adobe.com</span>

    <dd class=vcard><span class=fn>Andrei Bucur</span>, <span class=org>Adobe
     Systems, Inc.</span>, <span class=email>abucur@adobe.com</span>

    <dd class=vcard><span class=fn>Mihnea Ovidenie</span>, <span
     class=org>Adobe Systems, Inc.</span>, <span
     class=email>mihnea@adobe.com</span>

    <dd class=vcard><span class=fn>Peter Sorotokin</span>, <span
     class=org>Adobe Systems, Inc.</span>, <span
     class=email>psorotok@adobe.com</span>

    <dd class=vcard><span class=fn>Virgil Palanciuc</span>, <span
     class=org>Adobe Systems, Inc.</span>, <span
     class=email>virgilp@adobe.com</span>

    <dd class=vcard><span class=fn>Arno Gourdol</span>, <span class=org>Adobe
     Systems, Inc.</span>, <span class=email>agourdol@adobe.com</span>
   </dl>
   <!--begin-copyright-->
   <p class=copyright><a
    href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
    rel=license>Copyright</a> &copy; 2011 <a
    href="http://www.w3.org/"><acronym title="World Wide Web
    Consortium">W3C</acronym></a><sup>&reg;</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
    use</a> rules apply.</p>
   <!--end-copyright-->
   <hr title="Separator for header">
  </div>

  <h2 class="no-num no-toc" id=abstract>Abstract</h2>

  <p><strong>CHANGES IN PROGRESS, NOT READY FOR REVIEW</strong>

  <p>The CSS regions module allows content to flow across multiple areas
   called regions. The regions do not necessarily follow 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>
  <!--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
   &#8220;css3-regions&#8221; in the subject, preferably like this:
   &#8220;[<!---->css3-regions<!---->] <em>&hellip;summary of
   comment&hellip;</em>&#8221;

  <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-->

  <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>

     <li><a href="#relation-to-document-events"><span class=secno>2.4.
      </span>Relation to document events</a>
    </ul>

   <li><a href="#properties-and-rules"><span class=secno>3. </span>Properties
    and rules</a>
    <ul class=toc>
     <li><a href="#the-flow-into-property"><span class=secno>3.1. </span>The
      &lsquo;<code class=property>flow-into</code>&rsquo; property</a>

     <li><a href="#the-content-property"><span class=secno>3.2. </span>The
      &lsquo;<code class=property>content</code>&rsquo; property</a>

     <li><a href="#the-content-order-property"><span class=secno>3.3.
      </span>The &lsquo;<code class=property>content-order</code>&rsquo;
      property</a>

     <li><a
      href="#region-flow-break-properties-break-before-break-after-break-inside"><span
      class=secno>3.4. </span>Region flow break properties: &lsquo;<code
      class=property>break-before</code>&rsquo;, &lsquo;<code
      class=property>break-after</code>&rsquo;, &lsquo;<code
      class=property>break-inside</code>&rsquo;</a>

     <li><a href="#the-region-overflow-property"><span class=secno>3.5.
      </span>The region-overflow property</a>

     <li><a href="#the-at-region-style-rule"><span class=secno>3.6.
      </span>The @region rule</a>
    </ul>

   <li><a href="#pseudo_elements"><span class=secno>4.
    </span>Pseudo-elements</a>
    <ul class=toc>
     <li><a href="#region-markers-processing-model"><span class=secno>4.1.
      </span>Region markers processing model</a>

     <li><a href="#the-region-before-and-region-after-pseudo-elements"><span
      class=secno>4.2. </span>The ::region-before and ::region-after
      pseudo-elements</a>
    </ul>

   <li><a href="#cssom_view_and_css_regions"><span class=secno>5.
    </span>CSSOM view and CSS regions</a>
    <ul class=toc>
     <li><a href="#the-namedflow-interface"><span class=secno>5.1. </span>The
      NamedFlow interface</a>

     <li><a href="#extension-to-the-element-interface"><span class=secno>5.2.
      </span>Extension to the Element interface</a>

     <li><a href="#region-flow-layout-events"><span class=secno>5.3.
      </span>Region flow layout events</a>
    </ul>

   <li><a href="#relation-to-other-specifications"><span class=secno>6.
    </span>Relation to other specifications</a>

   <li><a href="#conformance"><span class=secno>7. </span>Conformance</a>

   <li><a href="#changes"><span class=secno>8. </span>Changes</a>
    <ul class=toc>
     <li><a href="#changes_from_June_09_2011"><span class=secno>8.1.
      </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>&nbsp;

  <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>&nbsp;

  <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>&nbsp;

  <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 &lsquo;<code
   class=property>A</code>&rsquo; and to flow an article's text from region
   &lsquo;<code class=css>1</code>&rsquo;, to region &lsquo;<code
   class=css>2</code>&rsquo;, &lsquo;<code class=css>3</code>&rsquo; and
   &lsquo;<code class=css>4</code>&rsquo;.

  <p>The following code snippet shows the content to flow between the regions
   1, 2, 3 and 4.

  <pre>
&lt;div <em>id="article"</em>&gt;
  &lt;h1&gt;Introduction&lt;/h1&gt;
  &lt;p&gt;This is an example ...&lt;/p&gt;

  &lt;h1&gt;More Details&lt;/h1&gt;
  &lt;p&gt;This illustrates ...&lt;/p&gt;
  &lt;p&gt;Then, the example ...&lt;/p&gt;
  &lt;p&gt;Finally, this ...&lt;/p&gt;
&lt;/div&gt;

</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>Since the CSS regions module is independent of the layout of regions and
   the mechanism used to create them, the following assumes there is a CSS
   selector for the regions and, for the purpose of the example, the
   selectors for regions 1, 2, 3 and 4 show as &lsquo;<code
   class=css>&lt;region1_sel&gt;</code>&rsquo;, &lsquo;<code
   class=css>&lt;region2_sel&gt;</code>&rsquo;, &lsquo;<code
   class=css>&lt;region3_sel&gt;</code>&rsquo; and &lsquo;<code
   class=css>&lt;region4_sel&gt;</code>&rsquo; respectively.

  <div class=example>
   <pre>
&lt;style&gt;

#article {
    <strong>flow-into: article_flow;</strong>
}

&lt;region1_sel&gt;, &lt;region2_sel&gt;,
&lt;region3_sel&gt;, &lt;region4_sel&gt; {
    <strong>content: flow-from(article_flow);</strong>
}
&lt;/style&gt;
</pre>
  </div>

  <p>The &lsquo;<code class=css>article_flow</code>&rsquo; value on the
   &lsquo;<a href="#flow-into"><code
   class=property>flow-into</code></a>&rsquo; property directs the
   &lsquo;<code class=css>#article</code>&rsquo; element to the &lsquo;<code
   class=css>article_flow</code>&rsquo; named flow. Setting the regions'
   content property to &lsquo;<code
   class=css>flow-from(article_flow)</code>&rsquo; associates these regions
   with the named flow: the flow is &lsquo;<code
   class=css>poured</code>&rsquo; 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 <a
   href="#CSSMEDIAQUERIES">Media Queries</a> <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>&lt;h1&gt;</code> headers should be run-ins and crimson.

  <p>This design can be expressed with region styling as shown below.

  <div class=example>
   <pre>
&lt;style&gt;
/*
 * Default article styling.
 */
#article {
    color:#777;
    text-align: justify;
}

#article h1 {
    border-left: 1px solid #777;
    padding-left: 2ex;
}

/*
 * Additional styling to apply to content when it falls into
 * region1
 */
<strong>@region &lt;region1_sel&gt; {</strong>
    #article::region-lines {
        font-weight: bold;
        color: #0C3D5F;
        font-size: larger;
    }

    #article h1 {
        color: crimson;
        display: run-in;
        border: none;
        padding: 0px;
    }
<strong>}</strong>
&lt;/style&gt;
</pre>
  </div>

  <p>The &lsquo;<code class=css>@region</code>&rsquo; 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.

  <p>The &lsquo;<code class=css>::region-lines</code>&rsquo; pseudo-element
   is described later in this specification.

  <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>

  <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 <em>named flow</em> (see the
   &lsquo;<a href="#content-from"><code
   class=property>content</code></a>&rsquo; property).

  <p>A <span title=region>region</span>&lsquo;<code class=css>s intrinsic
   width is zero.</code>

  <div class="issue moved">
   <p>See <a
    href="http://wiki.csswg.org/spec/css3-regions#issue-2-auto-sizing-of-regions"></a></p>
   .
   <p>There was a recent discussion on intrinsic sizing of regions which <a
    href="http://lists.w3.org/Archives/Public/www-style/2011Jun/0629.html">has
    not been resolved</a></p>
   .</div>

  <h3 id=named-flow><span class=secno>2.2. </span>Named flow</h3>

  <p>A <def name=named-flow>named flow</def> 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 &rsquo;flow-into'
   property. The elements in a named flow are laid out in the chain of
   regions that are associated with this named flow. The &lsquo;<a
   href="#content-order"><code class=property>content-order</code></a>&rsquo;
   property defines how <span title=region>regions</span> are organized in to
   a <span title=region-cha
7DDD
in>region chain</span>.

  <p>Content from a named flow is broken up between regions according to the
   regions flow breaking rules.</p>
  <!--
    <p>In the <a href="http://www.w3.org/TR/CSS21/visuren.html">CSS formatting
    model</a>, elements and pseudo-elements can be in the <em>normal flow</em> or out of the
    <em>(normal) flow</em>. Boxes generated by elements in the normal flow are
    subject to their container box's normal layout scheme. Boxes generated by
    elements out of the normal flow are subject to a different layout scheme.
    For example, absolutely positioned elements are subject to absolute
    positioning into their <a href=
    "http://www.w3.org/TR/CSS21/visudet.html#containing-block-details">containing
    block</a>. This can be described by saying that the absolutely positioned
    elements are part of a special flow (called <span title=
    "positioned-flow">positioned flow</span>) which is subject to a special
    layout by its container box (i.e., its container box positions it into the
    containing block's box).</p>

    <p>&nbsp;</p>

    <p>In both cases, there is a notion of flow containing a sequence of
    elements and there is a notion of <a href=
    "http://www.w3.org/Style/Group/css2-src/visuren.html#block-boxes">(block)
    container box</a> into which the elements flow.</p>

    <p>&nbsp;</p>

    <p>The CSS regions module generalizes the concept of flow by adding the
    concept of a <em>named flow</em>. This module lets authors explicitly place
    elements into a <em>named flow</em>.</p>

    <p>&nbsp;</p>

    <p>With this model, all elements are moved to a flow as part of the visual
    formatting. That flow may be the normal flow, a named flow or a positioned
    flow, for example. A flow gets formatted visually when associated with one
    or several elements' container box(es). When an flow is associated with
    container boxes, the boxes generated by the flow's elements are laid out
    according to the container box's layout scheme and the flow is subject to
    the <a href='#flow-breaking-rules'>'flow breaking rules'</a> described
    below.</p>

    <p>A container's layout scheme is the strategy used by a container to
    position the boxes generated by its children and itself. Examples are the
    normal layout (block and inline formatting) ([[CSS21]]), table layout
    ([[CSS21]]), the multi-column layout ([[CSS3COL]]) or the grid layout
    ([[CSS3-GRID-LAYOUT]]).</p>
-->

  <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> (see the &lsquo;<a
   href="#content-order"><code class=property>content-order</code></a>&rsquo;
   property).

  <p>Each region in turn consumes content from its associated <span
   title=named-flow>named flow</span>. 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 is
   no more <span>region</span> in the region chain and there is still content
   in the flow, the positioning of the remaining content is controlled by the
   &lsquo;<a href="#region-overflow"><code
   class=property>region-overflow</code></a>&rsquo; property on the last
   <span>region</span> in the chain.</p>
  <!--
    <h3 id="the-visual-formatting-model-and-flows">The Visual Formatting Model
    and Flows</h3>

    <p>This section describes the flows to which elements formatted according
    to the CSS <a href="http://www.w3.org/TR/CSS21/visuren.html">Visual
    Formatting Model</a> and other layout modules (such as Multi-Column Layout
    [[CSS3COL]]) belong to.</p>

    <p>In particular, this section describes the 'generated flow' where
    generated content of pseudo-elements is placed and several <dfn id=
    "auto-flow" title="auto flows">'auto flows'</dfn> where children of content
    elements are automatically placed.</p>

    <h4 id="normal-flow">Normal flow</h4>

    <p>In the CSS formatting model, elements are by default placed in the
    <dfn id="normal-flow-def">normal flow</dfn> of their container. Also by
    default, a container element gets its content from its <em>normal
    flow</em>. This means that by default, a container element will visually
    format its children elements and will be the only container associated with
    its normal flow.</p>

    <p>Note that floats and relatively positioned elements, in this model, are
    part of the same flow of content and flow into the same container but are
    positioned in different ways.</p>

    <p>The <em>normal flow</em> is one of the <em>auto flows</em>.</p>

    <h4 id="positioned-flow">Positioned flow</h4>

    <p>An absolutely positioned element is placed into the <dfn title=
    "positioned-flow">positioned flow</dfn> of its container. The container
    positions this element into its <em>containing block</em>.</p>

    <p>If a container has children in the <em>normal flow</em> and in the
    <em>positioned flow</em>, it applies different positioning schemes to each
    flow.</p>

    <p>The <em>positioned flow</em> is one of the <em>auto flows</em>.</p>

    <h4 id="column-flow">Column flow</h4>

    <p>Children of the multi-column element are placed in the element's
    <dfn id="column-flow-def">column flow</dfn>. The column boxes are then
    implicitly associated with the element's 'column flow'. In this model,
    multiple regions (column boxes) get their content from a single flow (the
    element's 'column flow', which is the content of the element).</p>

    <p>The <em>column flow</em> is one of the <em>auto flows</em>.</p>

    <div class="issue">
        Need to add a <dfn id="grid-cell-flow">grid cell flow</dfn> section.
    </div>

    <div class="issue">
        Need to add examples for the different flow types.
    </div>

    <h4 id="generated-flow">Generated flow</h4>

    <p>In the CSS formatting model, when the ''::before'' or ''::after''
    pseudo-elements have their content property set to one of
    ''&lt;string&gt;'', ''&lt;uri&gt;'', ''&lt;counter&gt;'',
    ''attr(&lt;identifier&gt;)'', ''open-quote'', ''close-quote'',
    ''no-open-quote'' or ''no-close-quote'', they create a <dfn id=
    "generated-flow-def">generated flow</dfn> which they format visually.</p>
-->

  <h3 id=relation-to-document-events><span class=secno>2.4. </span>Relation
   to document events</h3>

  <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>3. </span>Properties and
   rules</h2>
  <!-- Commented out following section because it was redundant with the introduction -->
  <!--
    <p>The main CSS regions module properties are the ‘flow-into’ and 'content'
    properties. The ‘flow-into’ property may place an element into a specific named
    flow. The ‘content’ property binds a region with a particular named flow. When multiple
    regions are bound to the same flow, the 'content-order' property determines
    the order in which content flows into the sequence of regions. This
    sequences of regions is called a <dfn>region chain</dfn>.</p>

    <p>The “break-*” properties control how content is broken into segments which are
        then fitted in regions.</p>

    <p>Styling that is unique to the region can be specified by ‘@region’ rules.</p>
-->

  <h3 id=the-flow-into-property><span class=secno>3.1. </span>The &lsquo;<a
   href="#flow-into"><code class=property>flow-into</code></a>&rsquo;
   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>&lt;ident&gt; | auto

    <tr>
     <th>Initial:

     <td>auto

    <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&nbsp;value:

     <td>as specified
  </table>

  <dl>
   <dt>auto

   <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">&lt;ident&gt;</a>

   <dd>The element is placed into the flow with the name &lsquo;<code
    class=css>&lt;ident&gt;</code>&rsquo;. The element is said to have a <dfn
    id=specified-flow>specified flow</dfn>. The values &lsquo;<code
    class=property>none</code>&rsquo;, &lsquo;<code
    class=property>inherit</code>&rsquo;, &lsquo;<code
    class=property>default</code>&rsquo; and &lsquo;<code
    class=property>initial</code>&rsquo; 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 a the same specified flow value as one of its
   ancestors, it becomes a sibling of it's ancestor for the purpose of layout
   in the regions laying out content content from that flow.

  <p>The &lsquo;<a href="#flow-into"><code
   class=property>flow-into</code></a>&rsquo; property does not affect the
   CSS cascade and inheritance for the elements on which it is specified. The
   &lsquo;<a href="#flow-into"><code
   class=property>flow-into</code></a>&rsquo; 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>Elements in a named flow are sequenced in document order.

  <div class=note>
   <p><em>This note is informative.</em></p>

   <p>The &lsquo;<a href="#flow-into"><code
    class=property>flow-into</code></a>&rsquo; 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 &lsquo;<code
    class=property>table-content</code>&rsquo; named flow. However, the</p>

   <pre>table * {flow-into: table-content}</pre>

   <p>selector will move all the descendants of table elements in the
    &lsquo;<code class=property>table-content</code>&rsquo; 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&lsquo;<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 &rsquo;flow-into' property to avoid
    unintended results.</p>
  </div>

  <p> If the ‘flow-into’ property is specified on an <code
   class=html>&lt;iframe&gt;</code>, an <code
   class=html>&lt;object&gt;</code> or a <code
   class=html>&lt;embed&gt;</code> element, the ‘display’ property is
   computed to ‘none’ and the referenced document within the element is
   used as the named flow. In the case of the <code
   class=html>&lt;object&gt;</code> element if fallback occurs and the
   fallback element has a referenced document then that document is used as
   the named flow, otherwise the fallback element itself is added to the
   named flow.

  <p> Any properties set on the <code class=html>&lt;iframe&gt;</code>/<code
   class=html>&lt;object&gt;</code>/<code class=html>&lt;embed&gt;</code>
   elements (including margin, border, padding, background) have no effect.
   This redirection of content does not change representation of the elements
   in the document tree, just as for any other source of named flow; in this
   case the <code class=html>&lt;iframe&gt;</code> still provides security
   checks for script in content (and sandbox if required). Events and CSS
   cascading work the same way as in a documents hosted in regular <code
   class=html>&lt;iframe&gt;</code>s.

  <p> Region styling applies to content coming from <code
   class=html>&lt;iframe&gt;</code>/<code
   class=html>&lt;object&gt;</code>/<code class=html>&lt;embed&gt;</code>
   sources the same way it applies to other flow content.

  <h3 id=the-content-property><span class=secno>3.2. </span>The &lsquo;<a
   href="#content-from"><code class=property>content</code></a>&rsquo;
   property</h3>

  <p>This specification extends the definition of the &lsquo;<a
   href="#content-from"><code class=property>content</code></a>&rsquo;
   property.

  <table class=propdef summary="content property definition">
   <tbody>
    <tr>
     <th>Name:

     <td><dfn id=content-from>content</dfn>

    <tr>
     <th>Value:

     <td>normal | none | flow-from(&lt;ident&gt;)| [ &lt;string&gt; |
      &lt;uri&gt; | &lt;counter&gt; | attr(&lt;identifier&gt;) | open-quote |
      close-quote | no-open-quote | no-close-quote ]+ | inherit

    <tr>
     <th>Initial:

     <td>normal

    <tr>
     <th>Applies to:

     <td>non-replaced block elements and the ::before and ::after
      pseudo-elements

    <tr>
     <th>Inherited:

     <td>no

    <tr>
     <th>Percentages:

     <td>N/A

    <tr>
     <th>Media:

     <td>visual

    <tr>
     <th>Computed&nbsp;value:

     <td>as specified
  </table>

  <dl>
   <dt><a id=x9 name=x9><span class=index-inst id=none
    title=none><strong>none</strong></span></a>

   <dd>For &lsquo;<code class=css>::before</code>&rsquo; and &lsquo;<code
    class=css>::after</code>&rsquo; pseudo-elements, the pseudo-element is
    not generated. For other elements, the element will not get any content
    for its visual formatting

   <dt><strong>normal</strong>

   <dd>Computes to &lsquo;<code class=property>none</code>&rsquo; for the
    &lsquo;<code class=css>::before</code>&rsquo; and &lsquo;<code
    class=css>::after</code>&rsquo; pseudo-elements. For other elements, the
    element formats its children as defined by the CSS Visual Formatting
    Model <a href="#CSS21" rel=biblioentry>[CSS21]<!--{{CSS21}}--></a>.

   <dt><strong>&lt;string&gt;</strong>

   <dd>Text content (see the section on <a
    href="syndata.html#strings">strings</a>).

   <dt><strong>&lt;uri&gt;</strong>

   <dd>The value is a URI that designates an external resource (such as an
    image). If the user agent cannot display the resource it must either
    leave it out as if it were not specified or display some indication that
    the resource cannot be displayed.

   <dt><strong>&lt;counter&gt;</strong>

   <dd><a href="syndata.html#counter">Counters</a> may be specified with two
    different functions: &lsquo;<code class=css>counter()</code>&rsquo; or
    &lsquo;<code class=css>counters()</code>&rsquo;. The former has two
    forms: &lsquo;<code class=css>counter(<var>name</var>)</code>&rsquo; or
    &lsquo;<code class=css>counter(<var>name</var>,
    <var>style</var>)</code>&rsquo;. The generated text is the value of the
    innermost counter of the given name in scope at this pseudo-element; it
    is formatted in the indicated <a href="#counter-styles">style</a>
    (&lsquo;<code class=property>decimal</code>&rsquo; by default). The
    latter function also has two forms: &lsquo;<code
    class=css>counters(<var>name</var>, <var>string</var>)</code>&rsquo; or
    &lsquo;<code class=css>counters(<var>name</var>, <var>string</var>,
    <var>style</var>)</code>&rsquo;. The generated text is the value of all
    counters with the given name in scope at this pseudo-element, from
    outermost to innermost separated by the specified string. The counters
    are rendered in the indicated <a href="#counter-styles">style</a>
    (&lsquo;<code class=property>decimal</code>&rsquo; by default). See the
    section on <a href="#counters">automatic counters and numbering</a> for
    more information. The name must not be &lsquo;<code
    class=property>none</code>&rsquo;, &lsquo;<code
    class=property>inherit</code>&rsquo; or &lsquo;<code
    class=property>initial</code>&rsquo;. Such a name causes the declaration
    to be ignored.

   <dt><strong>open-quote</strong> and <strong>close-quote</strong>

   <dd>These values are replaced by the appropriate string from the <a
    class=noxref
    href="http://www.w3.org/TR/CSS21/generate.html#propdef-quotes"><span
    class=propinst-quotes><strong>&lsquo;<code
    class=property>quotes</code>&rsquo;</strong></span></a> property.

   <dt><strong>no-open-quote</strong> and <strong>no-close-quote</strong>

   <dd>Introduces no content, but increments (decrements) the level of
    nesting for quotes.

   <dt><strong>attr(X)</strong>

   <dd>This function returns as a string the value of attribute X for the
    subject of the selector. The string is not parsed by the CSS processor.
    If the subject of the selector does not have an attribute X, an empty
    string is returned. The case-sensitivity of attribute names depends on
    the document language.

   <dt><dfn id=flow-from-name>flow-from(&lt;ident&gt;)</dfn>

   <dd>If the element is not a <a
    href="http://www.w3.org/TR/CSS21/visuren.html#block-boxes">block
    container box</a>, the value evaluates to &lsquo;<code
    class=property>normal</code>&rsquo;. <br>
    Otherwise, the element becomes a <span>region</span> and is ordered in a
    <span>region chain</span> according to its document order and &lsquo;<a
    href="#content-order"><code
    class=property>content-order</code></a>&rsquo; property. The content from
    the flow with the <a
    href="http://www.w3.org/TR/2011/REC-CSS2-20110607/syndata.html#value-def-identifier">&lt;ident&gt;</a>
    name will be <a
    href="#region-flow-break-properties-break-before-break-after-break-inside">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 &lt;ident&gt;, then the element does not format any content
    visually. <br>
    This might be expanded in future versions of the specification to allow
    other types of containers to receive flow content.
  </dl>

  <p>When the &lsquo;<a href="#content-from"><code
   class=property>content</code></a>&rsquo; property is set to &lsquo;<code
   class=property>none</code>&rsquo;, &lsquo;<code
   class=property>from-flow</code>&rsquo;, &lt;string&gt;, &lt;uri&gt;,
   &lt;counter&gt;, &lsquo;<code
   class=css>attr(&lt;identifier&gt;)</code>&rsquo;, open-quote, close-quote,
   no-open-quote or no-close-quote, the document children of the element are
   not visually formatted unless they are directed to a named flow referenced
   by one or more regions.

  <div class=note>
   <p><em>This note is informative.</em></p>

   <p>The &lsquo;<a href="#content-from"><code
    class=property>content</code></a>&rsquo; property applies to block-level
    elements and the &lsquo;<code class=css>::before</code>&rsquo; and
    &lsquo;<code class=css>::after</code>&rsquo; pseudo elements. User agents
    may apply the content property to inline elements. The behavior is
    undefined in that case, but is generally expected to be similar to that
    of inline &lsquo;<code class=css>::before</code>&rsquo; and &lsquo;<code
    class=css>::after</code>&rsquo; pseudo-elements.</p>

   <p>In particular, note that the behavior of a &lsquo;<code
    class=css>::before</code>&rsquo; or &lsquo;<code
    class=css>::after</code>&rsquo; pseudo-element with a &lsquo;<code
    class=property>display</code>&rsquo; value that makes it an inline
    element combined with a &lsquo;<a href="#content-from"><code
    class=property>content</code></a>&rsquo; value set to &lsquo;<a
    href="#flow-from-name"><code
    class=css>flow-from(&lt;ident&gt;)</code></a>&rsquo; is undefined.</p>
  </div>

  <div class="issue resolved">
   <p><a
    href="http://lists.w3.org/Archives/Public/www-style/2011Aug/0069.html">Third
    resolution on Regions at the Seattle Face to Face meeting, July 2011</a>

   <p><strong>content: flow-from(&lt;flow-name&gt;) v.s. flow-from:
    &lt;flow-name&gt;</strong></p>

   <p><a
    href="http://lists.w3.org/Archives/Public/www-style/2011Jun/0413.html">WG
    Conference Call, CSSWG Minutes and Resolutions 2011-06-15</a>.</p>

   <p>See <a
    href="http://wiki.csswg.org/spec/css3-regions#contentflow-flow-from-name-vs-flow-fromflow-name">issue</a></p>
  </div>

  <div class="issue stale">
   <p>NOTE: stale issue because the spec. now contains a way to address these
    requirements.</p>

   <p>Should we consider adding the ability to do the following:</p>

   <ul>