drafts: css3-regions/Overview.src.html@2e04f2d16ef5 (annotated)

css3-regions/Overview.src.html@2e04f2d16ef5 (annotated)

css3-regions/Overview.src.html

Mon, 23 Apr 2012 22:27:12 -0700

author: Alan Stearns <stearns@adobe.com>
date: Mon, 23 Apr 2012 22:27:12 -0700
changeset 5598: 2e04f2d16ef5
parent 5579: afb867e7b4ae
child 5599: c76a4ff42fc3
permissions: -rw-r--r--

added CSSRegionStyleRule to OM section

 <!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">
        <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>
             <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>
     <!--begin-status-->
     <p><em>This section describes the status of this document at the time of
     its publication. Other documents may supersede this document. A list of
     current W3C publications and the latest revision of this technical report
     can be found in the <a href="http://www.w3.org/TR/">W3C technical reports
     index at http://www.w3.org/TR/.</a></em></p>
     <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>
     <p>The archived public mailing list www-style@w3.org is preferred for
     discussion of this specification. When sending e-mail, please put the text
     "css3-regions" in the subject, preferably like this: "[css3-regions]
     …summary of comment…"</p>
     <!--end-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">Bug-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>&lt;article&gt;</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>
 &lt;style&gt;
   article {
     <strong>flow-into: article_flow;</strong>
   }
   #region1, #region2, #region3, #region4 {
     <strong>flow-from: article_flow;</strong>
   }
 &lt;/style&gt;
       </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="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>
     <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>
 &lt;style&gt;
   @region #region1 {
       p {
           color: #0C3D5F;
           font-weight: bold;
       }
 &lt;/style&gt;</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">Bug-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">Bug-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>
     <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">Bug-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">Bug-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">Bug-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>&lt;ident&gt; | 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&nbsp;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">&lt;ident&gt;</a></dt>
         <dd>The element is taken out
           of its parent's flow
           and placed into the flow
           with the name '&lt;ident&gt;'.
           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>
     <div class="issue-marker wrapper">
     <div class="issue-marker" data-bug_id="15870" data-bug_status="NEW">
         <a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=15870">Bug-15870</a>
         <div class="issue-details">
             <p class="short-desc">Describe how containing blocks are used for element fragments</p>
         </div>
     </div>
     </div>
     <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.</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 &gt; * {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>&lt;ident&gt; | 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&nbsp;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>&lt;ident&gt;</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">&lt;ident&gt;</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 &lt;ident&gt;,
             then the block container does not
             format any content visually.
             <br/>
             Likewise, if the block container is part
             of the flow with name &lt;ident&gt;,
             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">Bug-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 &lt;ident&gt; value,
         even if there is no content contributing
         to the referenced flow.
         For example:</p>
         <pre>
 &lt;style&gt;
   .article{
     flow-into: thread;
   }
   .region{
     flow-from: thread;
   }
 &lt;/style&gt;
 &lt;html&gt;
   &lt;body&gt;
     &lt;div class=region&gt;div content&lt;/div&gt;
   &lt;/body&gt;
 &lt;/html&gt;
         </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="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">Bug-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">Bug-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">Bug-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">Bug-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&nbsp;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&nbsp;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>
             <td>N/A</td>
         </tr>
         <tr>
             <td><em>Media:</em></td>
             <td>visual</td>
         </tr>
         <tr>
             <td><em>Computed&nbsp;value:</em></td>
             <td>specified value</td>
         </tr>
     </table>
     <p>These properties describe page, column and region break behavior
     before/after/inside the generated box. These values are normatively defined
     in [[!CSS3COL]]:</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 [[!CSS21]].</p>
     <h3 id="the-region-overflow-property">The region-overflow property</h3>
     <div class="issue-marker" data-bug_id="15878" data-bug_status="NEW">
         <a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=15878">Bug-15878</a>
         <div class="issue-details">
             <p class="short-desc">region-overflow:nobreak</p>
         </div>
     </div>
     <table class="propdef" summary="break-after property definition">
         <tr>
             <td><em>Name:</em></td>
             <td><dfn>region-overflow</dfn></td>
         </tr>
         <tr>
             <td><em>Value:</em></td>
             <td>auto | break</td>
         </tr>
         <tr>
             <td><em>Initial:</em></td>
             <td>auto</td>
         </tr>
         <tr>
             <td><em>Applies to:</em></td>
             <td><em title="region element">CSS Regions</em></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&nbsp;value:</em></td>
             <td>specified value</td>
         </tr>
     </table>
     <div class="issue-marker wrapper">
     <div class="issue-marker" data-bug_id="15832" data-bug_status="NEW">
         <a href=
         "https://www.w3.org/Bugs/Public/show_bug.cgi?id=15832">Bug-15832</a>
         <div class="issue-details">
             <p class="short-desc">Should we have region-overflow:nobreak and have 'region-overflow' apply to all regions, not just the last?</p>
         </div>
     </div>
     <div class="issue-marker" data-bug_id="16622" data-bug_status="NEW">
     <a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=16622">Bug-16622</a>
     <div class="issue-details">
         <p class="short-desc">Should we rename region-overflow to flow-overset?</p>
     </div>
     </div>
   </div>
     <p>The 'region-overflow' property controls the behavior of the <em id=
     "last-region">last region</em> associated with a <span>named
     flow</span>.</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>
         property's computed value on the CSS Region. Region breaks must be
         ignored on the last region.</dd>
         <dt>break</dt>
         <dd><p>If the content fits within the <em>CSS Region</em>, then this
         property has no effect. If the content does not fit within the
         <em>CSS Region</em>, the content breaks as if flow was going to
         continue in a subsequent region. See the <a href=
         "#regions-flow-breaking-rules">breaking rules</a> section. A forced region break takes precedence over
         a natural break point.</p>
         <p>Flow content that follows the last break in the last region, if any is not rendered.</p>
         </dd>
     </dl>
     <p>The 'region-overflow' property does not influence
       the size of the region it applies to.</p>
     <p>The following code sample illustrates
       the usage of the 'region-overflow' property.</p>
     <div class="example">
       <pre>
 &lt;style&gt;
 article {
   flow-into: "article";
 }
 #region_1, #region_2 {
   flow-from: article;
   <strong>region-overflow: break;</strong> /* or none */
   <strong>overflow: visible;</strong> /* or hidden */
 }
 &lt;/style&gt;
 &lt;article&gt;...&lt;/article&gt;
 &lt;div id="region_1"&gt;&lt;/div&gt;
 &lt;div id="region_2"&gt;&lt;/div&gt;
       </pre>
     </div>
     <div class="figure">
         <table style="border: 1px solid gray;width: 100%;" summary=
         "Different values for the region-overflow property - Illustration.">
             <tr>
                 <td>''flow-into: "article"''</td>
                 <td><code class="html">region_1</code> and <code class=
                 "html">region_2</code></td>
                 <td>''region-overflow: auto''<br>
                 ''overflow:visible''</td>
             </tr>
             <tr>
                 <td rowspan="3" style="vertical-align: top;"><img src=
                 "images/region-overflow-flow.png" alt=
                 "regions receiving the flow content"></td>
                 <td><img src="images/region-overflow-regions.png" alt=
                 "result if region-overflow is set to 'break'"></td>
                 <td><img src="images/region-overflow-auto-overflow-visible.png"
                 alt="regions receiving the flow content"></td>
             </tr>
             <tr>
                 <td>''region-overflow: break''</td>
                 <td>''region-overflow: auto''<br>
                 ''overflow:hidden''</td>
             </tr>
             <tr>
                 <td><img src="images/region-overflow-break.png" alt=
                 "result if region-overflow is set to 'break'"></td>
                 <td><img src="images/region-overflow-auto-overflow-hidden.png"
                 alt="regions receiving the flow content"></td>
             </tr>
         </table>
         <p class="caption">Different values for the region-overflow
         property</p>
     </div>
     <div class="note"><span class="note-prefix">Note </span>
         <p>The 'overflow' property is honored on a region: if region content overflows,
         such as the borders of elements on the
         last line, the 'overflow' property controls the visibility of the overflowing
         content. See the 'overflow' property definition
         ([[CSS21]]).</p>
     </div>
     <h3 id="the-at-region-style-rule">The @region rule</h3>
     <p>An '@region' rule contains style declarations specific to particular
     regions.</p>
         <pre>
 @region &lt;selector&gt; {
     ... CSS styling rules ...
 }
     </pre>
     <p>The '@region' rule consists of the keyword '@region' followed by a
     <a href="http://www.w3.org/TR/css3-selectors/#selector-syntax">selector</a>
     and a block of style rules. The '@region' rule and the selector constitute
     the region's 'flow fragment' selector. The region's flow fragment selector
     specifies which range of elements in the flow are subject to the style rules in the
     following block: it applies to the range (see
     [[!DOM]]) from the region's flow that flows in the
     selected region(s).</p>
     <div class="issue-marker" data-bug_id="15713" data-bug_status="NEW">
         <a href=
         "https://www.w3.org/Bugs/Public/show_bug.cgi?id=15713">Bug-15713</a>
         <div class="issue-details">
             <p class="short-desc">Model for styling element fragments</p>
         </div>
     </div>
     <p>Elements that are fully or partially in the 'flow fragment' may match any of the
     selectors found in the style rule. However, the style rules only apply to the
     portion of the element that falls into the corresponding region.</p>
     <p>Only a limited list of properties can be set in a region style rule:</p>
     <div class="issue-marker" data-bug_id="15190" data-bug_status="NEW">
         <a href=
         "https://www.w3.org/Bugs/Public/show_bug.cgi?id=15190">Bug-15190</a>
         <div class="issue-details">
             <p class="short-desc">List of region style properties</p>
         </div>
     </div>
     <ol>
         <li><a href="http://www.w3.org/TR/CSS2/fonts.html">font properties</a></li>
         <li><a href="http://www.w3.org/TR/CSS2/colors.html">color property</a></li>
         <li><a href="http://www.w3.org/TR/css3-color/#transparency">opacity property</a></li>
         <li><a href="http://www.w3.org/TR/css3-background/#backgrounds">background property</a></li>
         <li><a href="http://www.w3.org/TR/CSS2/text.html#propdef-word-spacing">'word-spacing'</a></li>
         <li><a href="http://www.w3.org/TR/CSS2/text.html#propdef-letter-spacing">'letter-spacing'</a></li>
         <li><a href="http://www.w3.org/TR/CSS2/text.html#propdef-text-decoration">'text-decoration'</a></li>
         <li><a href="http://www.w3.org/TR/CSS2/text.html#propdef-text-transform">'text-transform'</a></li>
         <li><a href="http://www.w3.org/TR/CSS2/visudet.html#propdef-line-height">'line-height'</a></li>
         <li><a href="http://www.w3.org/TR/css3-background/#borders">border properties</a></li>
         <li><a href="http://www.w3.org/TR/css3-background/#corners">rounded corner properties</a></li>
         <li><a href="http://www.w3.org/TR/css3-background/#border-images">border images properties</a></li>
         <li><a href="http://www.w3.org/TR/CSS2/box.html#margin-properties">margin properties</a></li>
         <li><a href="http://www.w3.org/TR/CSS2/box.html#padding-properties">padding properties</a></li>
         <li><a href="http://www.w3.org/TR/css3-text/#text-shadow">'text-shadow' property</a></li>
         <li><a href="http://www.w3.org/TR/css3-background/#the-box-shadow">'box-shadow' property</a></li>
         <li><a href="http://www.w3.org/TR/css3-background/#the-box-decoration-break">'box-decoration-break' property</a></li>
         <li><a href="http://www.w3.org/TR/CSS2/visudet.html#the-width-property">'width' property</a></li>
     </ol>
     <div class="example" id="region-style-example">
         <p>In the following example, the <span>named flow</span> 'article_flow' flows
         through 'region_1' and 'region_2'.</p>
         <pre>
 &lt;style&gt;
     #div_1 {
         <strong>flow-into: article_flow;</strong>
     }
     #region1, #region2 {
         <strong>flow-from: article_flow;</strong>
     }
     /* region style "RSA" */
     <strong>@region #region1, #region2</strong> {
         div {...}
         p {...}
     }
     /* region style "RSB" */
     <strong>@region #region1</strong> {
         p {...}
     }
 &lt;/style&gt;
 &lt;div id="div_1"&gt;
     &lt;p id="p_1"&gt;...&lt;/p&gt;
     &lt;p id="p_2"&gt;...&lt;/p&gt;
 &lt;/div&gt;
 &lt;div id="region1"&gt;&lt;/div&gt;
 &lt;div id="region2"&gt;&lt;/div&gt;
 </pre>
         <div id="region_styling_illustration">
             <img id="region_styling_img_2" src="images/region-styling-2.png"
             alt=
             "Illustration showing how a named flow content fits into regions to illustrate the @region styling."
             name="region_styling_img_2">
             <ul class="swatch-list">
                 <li><span class="swatch" style=
                 "background:#1C75BC">&nbsp;</span>div div_1</li>
                 <li><span class="swatch" style=
                 "background:crimson">&nbsp;</span>paragraph p_1</li>
                 <li><span class="swatch" style=
                 "background:white">&nbsp;</span>paragraph p_2</li>
                 <li><span class="swatch" style=
                 "background:#E6E7E8">&nbsp;</span>range of flow that fits into
                 region_1</li>
                 <li><span class="swatch" style=
                 "background:#BCBEC0">&nbsp;</span>range of flow that fits into
                 region_2</li>
             </ul>
         </div>
         <p>The region style ''RSA'' applies to flow content that is laid out in either
         'region_1' or 'region_2'.</p>
         <p>The first rule set ''div {...}'' applies to all <code class=
         "html">&lt;div&gt;</code> elements that fit partially or fully into 'region_1' or
         'region_2'. <code class="html">div_1</code> is split between 'region_1' and
         'region_2' and gets the style from this style rule.</p>
         <p>The second rule set ''p {...}'' applies to all <code class=
         "html">&lt;p&gt;</code> elements that fit into 'region_1' or
         'region_2'. In our example, both <code class="html">p_1</code>
         and <code class="html">p_2</code> are selected.</p>
         <p>The region style ''RSB'' applies to flow content that fits in
         'region_1'.</p>
         <p>The first rule set ''p {...}'' matches <code class="html">p_1</code>
         and <code class="html">p_2</code>
         because these paragraphs flow into 'region_1'. Only the fragment of
         <code class="html">p_2</code> that flows into <code class="html">region_1</code>
         is styled with this rule.</p>
     </div>
     <div class="issue-marker" data-bug_id="15734" data-bug_status="NEW">
         <a href=
         "https://www.w3.org/Bugs/Public/show_bug.cgi?id=15734">Bug-15734</a>
         <div class="issue-details">
             <p class="short-desc">@region and specificity</p>
         </div>
     </div>
     <p>The specificity of the selectors in a '@region' rule is calculated as
     <a href="http://www.w3.org/TR/css3-selectors/#specificity">defined</a> in
     the CSS Selectors module (see [[SELECT]]). In other words, the '@region'
     rule adds an extra condition to the selector's matching, but does not
     change the selector's specificity. This is the same behavior as selectors
     appearing in '@media' rules declaration blocks (see [[MEDIAQ]]), where the
     rule does not influence the selectors' specificity.</p>
     <p>Consequently, selectors that match a given element (as describe above),
     participate in the <a href="http://www.w3.org/TR/2011/REC-CSS2-20110607/cascade.html#cascading-order">CSS Cascading
     order</a> as defined in [[!CSS21]].</p>
     <div>
         Region styling does not apply to nested regions. For example, if a region
         'A' receives content from a flow that contains region 'B', the content that
         flows into 'B' does not receive the region styling specified for region 'A'.
     </div>
     <h2 id="multi-column-regions">Multi-column regions</h2>
     <p>A
       <a href="http://dev.w3.org/csswg/css3-multicol/#multi-column-element">multi-column</a>
       [[CSS3COL]]
       element can have
       an assigned <em><span>named flow</span></em>.
       The element becomes part
       of the region chain
       for that named flow,
       and flows its content fragments
       through columns according to
       the multi-column specification
       [[!CSS3COL]].
       In particular,
       when computing the
       <a href="#flow-fragment-height-resolution">flow fragment height</a>
       of a multi-column element
       that is associated with a <em><span>named flow</span></em>,
       the <a href="http://dev.w3.org/csswg/css3-multicol/#column-fill">'column-fill'</a>
       [[!CSS3COL]]
       property is honored
       to balance the fragments of content
       that would flow through
       its columns.</p>
     <div class="example">
         <p>The following example:</p>
         <pre>
 &lt;style&gt;
    #multi-col {
        column-count: 2;
        flow-from: article;
        height: 6em;
        column-gap: 1em;
    }
    #remainder {
        flow-from: article;
        height: auto;
    }
 &lt;/style&gt;
 &lt;article&gt;...&lt;/article&gt;
 &lt;div id="multicol"&gt&lt;/div&gt;
 &lt;div id="remainder"&gt;&lt;/div&gt;</pre>
         <p>is equivalent in rendering to, for example:</p>
                 <pre>
 &lt;style&gt;
    #flex {
        display: flex;
        flex-pack: justify;
        height: 6em;
    }
    #flex > div {
        flow-from: article;
        width: calc(50% - 0.5em);
    }
    #remainder {
        flow-from: article;
        height: auto;
    }
 &lt;/style&gt;
 &lt;article&gt;...&lt;/article&gt;
 &lt;div id="flex"&gt;
    &lt;div /&gt;
    &lt;div /&gt;
 &lt;/div&gt;
 &lt;div id="remainder"&gt;&lt;/div&gt;</pre>
     </div>
     <p>Overflow of multicol regions
       is mostly handled
       according to the same rules
       as other CSS Regions.
       If the remainder of the named flow
       does not fit
       in the multicol region,
       then the rest
       of the content flows into
       the remaining region chain.
       However,
       if a multicol region
       is the last region
       in a <span>region chain</a>,
       then the multicol region must follow the
       <a href="http://dev.w3.org/csswg/css3-multicol/#overflow-columns">overflow column rules</a>
       [[!CSS3COL]].</p>
     <h2 id="pseudo_elements">Pseudo-elements</h2>
     <div class="issue-marker" data-bug_id="15188" data-bug_status="NEW">
         <a href=
         "https://www.w3.org/Bugs/Public/show_bug.cgi?id=15188">Bug-15188</a>
         <div class="issue-details">
             <p class="short-desc">add functionality for having textual description like "continued here" or "continued on page x" to regions.</p>
         </div>
     </div>
     <p>It can be useful
       to visually mark the content
       to highlight that a content thread
       is flowing through the region chain.
       For example, a marker
       such as <em>'continued below'</em> clearly indicates,
       at the end of a CSS Region,
       that there is more content in the flow
       which can be found by scrolling past
       whatever content interrupts the region chain.</p>
     <p>The '::before' and '::after' pseudo-elements (see [[!SELECT]])
       let content authors mark the beginning
       and end of a region with such markers.</p>
     <h3 id="processing-model">Processing model</h3>
     <p>The '::before' content is laid out
       in the region prior to
       any other content coming from the flow.
       Note that it is possible
       to set the '::before' pseudo-element's 'display' property
       to 'run-in' to align it
       with the content's inline boxes.</p>
     <p>The '::after' content is laid out
       in the region after laying out
       the flow fragment content.
       Then, flow content is removed from the fragment
       to accommodate the '::after' content.
       Accommodating means that the '::after' content
       is laid out without overflowing the region.
       The 'display' property of the '::after' content
       can be set to 'run-in' to align
       with the region's content's inline boxes.
       In that case, the '::after' content becomes
       the last inline box of the previous element
       in the flow that has some visual rendering
       in the region and can accommodate for the '::after' box.</p>
     <p>If there is not enough room to accommodate
       the ::before content,
       the '::after' content after removing all flow fragment content,
       or a combination of the two,
       then the ::before and/or ::after content overflows.</p>
     <h2 id="cssom_view_and_css_regions">CSSOM</h2>
     <div class="issue-marker-wrapper">
     <div class="issue-marker" data-bug_id="15679" data-bug_status="NEW">
         <a href=
         "https://www.w3.org/Bugs/Public/show_bug.cgi?id=15679">Bug-15679</a>
         <div class="issue-details">
             <p class="short-desc">elementFromPoint and CSS regions</p>
         </div>
     </div>
     <div class="issue-marker" data-bug_id="15933" data-bug_status="ASSIGNED">
     <a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=15933">Bug-15933</a>
     <div class="issue-details">
         <p class="short-desc">Terms in WebIDL snippets inconsistently linked</p>
     </div>
     </div>
     </div>
     <p>Since content may flow into multiple regions, authors need a way to
     determine if there are enough regions to flow all the content from a named
     flow. This is especially important considering that the size of regions or
     the size of the content may change depending on the display context. For
     example, flowing the same content on a mobile phone with a small screen may
     require more regions than on a large desktop display. Another example is the
     user changing the font size of text flowing through regions. Depending on
     the change, new regions may be needed to accommodate for the additional
     space required to fit the larger text or some regions may need to be removed
     for smaller text.
     </p>
     <h3 id="the-namedflow-interface">The NamedFlow interface</h3>
     <p>A <span>named flow</span> is created when it becomes referenced by the
         'flow-into' and/or 'flow-from' computed values. The following APIs allow
         scripts to reference a <code class="idl">NamedFlow</code> object representation
         of a <span>named flow</span>.</p>
     <p>An additional method and an additional attribute on the <a href=
     "http://www.w3.org/TR/dom/#interface-document"><code class=
     "idl">Document</code></a> interface provide access to <span>named flows</span>.</p>
     <pre class="idl">
 partial interface <a href=
 "http://www.w3.org/TR/dom/#interface-document">Document</a> {
   readonly attribute <a href="#dom-named-flow-collection">NamedFlowCollection</a> <a href="#document-namedflows">namedFlows</a>;
   <a href="#dom-named-flow">NamedFlow?</a> <a href="#document-getflowbyname">getFlowByName(DOMString name)</a>;
 };
 </pre>
     <p>The <dfn id="document-namedflows"><code class="idl">namedFlows</code></dfn> attribute on the <a href=
     "http://www.w3.org/TR/dom/#interface-document"><code class=
     "idl">Document</code></a> interface returns the live list of all the current <span>named
     flows</span> in the document. </p>
     <p>The <code class="idl">namedFlows</code> collection must include all <span>named flows</span>
     that are currently in the <code>CREATED</code> state.
     The list must not include <span>named flows</span> that are in the <code>NULL</code> state. </p>
     <p>The <dfn id="document-getflowbyname"><code class="idl">getFlowByName</code></dfn> method on the <a href=
     "http://www.w3.org/TR/dom/#interface-document"><code class=
     "idl">Document</code></a> interface provides access to the document's <code class="idl">NamedFlow</code>
          instances. The return value depends on the <span>named flow</span>
     state:</p>
     <ul>
         <li><code class="idl">NULL</code>: the user agent must return <code>null</code>.</li>
         <li><code class="idl">CREATED</code>: the user agent must return a valid
             <code class="idl">NamedFlow</code> instance.</li>
     </ul>
     <p>The <dfn id="dom-named-flow-collection"><code class="idl">NamedFlowCollection</code></dfn>
     interface provides a list of current <code class="idl">NamedFlow</code> instances in the
     document. The collection is live and methods operate on the underlying data, not a snapshot of
     the data.</p>
     <pre class="idl">
 interface NamedFlowCollection {
   readonly attribute unsigned long <a href="#dom-named-flow-collection-length">length</a>;
   getter <a href="#dom-named-flow">NamedFlow?</a> <a href="#named-flow-collection-item">item (unsigned long index)</a>;
 };</pre>
     <p>The <dfn id="dom-named-flow-collection-length"><code class="idl">length</code></dfn>
         attribute returns the number of items in the collection.</p>
     <p>The <dfn id="dom-named-flow-collection-item"><code class="idl">item(index)</code></dfn>
         method returns the item at index <em>index</em>
         in the collection or <code class="idl">null</code> if <em>index</em> is out of range.
         An object <code>collection</code> implementing <code>NamedFlowCollection</code> supports
         indices in the range <code>0 ≤ index < collection.length</code>.</p>
     <p>The <dfn id="dom-named-flow"><code class="idl">NamedFlow</code></dfn>
     interface offers a representation of a <span>named flow</span> instance.</p>
             <p>The <code class="idl">NamedFlow</code> interface
       can be used for different purposes.
       For example, the <code>getRegionsByContent()</code> method
       can help navigate by bookmark:
       a script can find the <span>region</span>s
       that display a particular anchor
       and bring them to view.</p>
     <p>Likewise, the interface allows authors
       to check if all content has been fitted
       into existing regions.
       If it has, the <code>overset</code> attribute
       would be false.</p>
     <pre class="idl">
 interface <a href="#dom-named-flow">NamedFlow</a> implements <a href="http://www.w3.org/TR/dom/#interface-eventtarget">EventTarget</a> {
   readonly attribute DOMString <a href="#dom-named-flow-name">name</a>;
   readonly attribute boolean <a href="#dom-named-flow-overset">overset</a>;
   sequence&lt;<a href="#region-interface">Region</a>&gt; <a href="#dom-named-flow-get-regions">getRegions()</a>;
   readonly attribute integer <a href="#dom-named-flow-first-empty-region-index">firstEmptyRegionIndex</a>;
   <a href="http://www.w3.org/TR/dom/#interface-nodelist">NodeList</a> <a href="#dom-named-flow-get-content">getContent()</a>;
   sequence&lt;<a href="#region-interface">Region</a>&gt; <a href="#dom-named-flow-get-regions-by-content">getRegionsByContent</a>(<a href="http://www.w3.org/TR/dom/#interface-node">Node</a> node)</a>;
 };</pre>
     <p>The <dfn id="dom-named-flow-name"><code class="idl">name</code></dfn> attribute
      returns the name of the <code class="idl">NamedFlow</code> instance.</p>
     <p>The <dfn id="dom-named-flow-overset"><code class= "idl">overset</code></dfn>
       attribute returns true
       if there are <span>named flow</span> fragments
       that do not fit in the associated region chain.
       The attribute also returns true
       if there is no associated region chain.
       Otherwise, it returns false. </p>
     <p>The <dfn id="dom-named-flow-get-regions"><code class="idl">getRegions()</code></dfn>
       method returns the sequence
       of regions in the <span>region chain</span>
       associated with the <span>named flow</span>.
       Note that the returned values
       is a static sequence
       in document order.</p>
     <p>The <dfn id="dom-named-flow-first-empty-region-index">firstEmptyRegionIndex</dfn>
       is the index of the first region
       in the region chain with the <code>regionOverset</code> attribute
       set to <code>empty</code>.
       If all regions have the <code>regionOverset</code> attribute
       set to <code>fit</code> or <code>overset</code>,
       the value for <code>firstEmptyRegionIndex</code> is <code>-1</code>.
       If there are no regions in the <span>region chain</span>,
       the value is <code>-1</code> as well. </p>
     <p>The <dfn id="dom-named-flow-get-content">getContent()</dfn>
       method returns an ordered collection
       of nodes that constitute the <span>named flow</span>.
       The returned list is a static snapshot
       of the <span>named flow</span> content
       at the time the method is invoked.
       This list contains the elements
       that were moved to the <span>named flow</span>
       but not their descendants
       (unless the descendants are themselves
       moved to the <span>named flow</span>).
     </p>
     <p>The <dfn id="dom-named-flow-get-regions-by-content">getRegionsByContent()</dfn>
       method returns the sequence of regions
       that contain at least part
       of the target content node.
       Note that the returned values
       is a static sequence
       in document order.</p>
     <p>The <span>named flow</span> states are :</p>
     <ul>
         <li><code class="idl">NULL</code>: the <span>named flow</span> is not referenced
             by any 'flow-into' or 'flow-from' computed value.</li>
         <li><code class="idl">CREATED</code>: the <span>named flow</span> is referenced by
             at least one 'flow-into' or 'flow-from' computed value.</li>
     </ul>
     <p>A <code class="idl">NamedFlow</code>
     object is live: it always represents the <span>named flow</span> with the corresponding
     name even if that <span>named flow</span> has transitioned to the <code>NULL</code> state.</p>
     <p>If a script holds a reference to a <code class="idl">NamedFlow</code> instance that
         has entered the <code>NULL</code> state, its attributes and methods should behave
         as follows:</p>
     <ul>
         <li>the <code class="idl">name</code> attribute returns its value as normal.</li>
         <li>the <code class="idl">overset</code> attribute returns <code class="idl">true</code>.</li>
         <li>the <code class="idl">getRegions</code> method returns an empty sequence.</li>
         <li>the <code class="idl">firstEmptyRegionIndex</code> attribute returns <code class="idl">-1</code>.</li>
         <li>the <code class="idl">getContent()</code> method returns an empty <code class="idl">NodeList</code> instance.</li>
         <li>the <code class="idl">getRegionsByContentNode()</code> method retuns an empty sequence.</li>
     </ul>
     <div class="issue-marker" data-bug_id="16382" data-bug_status="ASSIGNED">
     <a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=16382">Bug-16382</a>
     <div class="issue-details">
         <p class="short-desc">Should we have a NamedFlow.getRegionsByFlowRanges?</p>
     </div>
     </div>
     <h3 id="the-region-interface">The Region interface</h3>
     <p>The <dfn id='region-interface'><code class="idl">Region</code> interface</dfn>
         provides an abstraction for <a href=
         "http://www.w3.org/TR/dom/#interface-element"><code class=
         "idl">Element</code>s</a>, pseudo-elements or other CSS constructs (such as
         <a href="http://dev.w3.org/csswg/css3-page-template/#templates-and-slots">slots</a>
         [[!CSS3-PAGE-TEMPLATE]]) which can be regions.</p>
         <pre class="idl">
 interface Region {
   readonly attribute DOMString <a href="#dom-region-regionoverset">regionOverset</a>;
   readonly attribute DOMString <a href="#dom-region-flowfrom">flowFrom</a>;
   sequence&lt;<a href="#">Range</a>&gt;? <a href=
 "#dom-region-getregionflowranges">getRegionFlowRanges()</a>;
 };</pre>
         <p>The <dfn id="dom-region-regionoverset"><code class=
         "idl">regionOverset</code></dfn> attribute returns one of the following
         values:</p>
         <dl>
             <dt>'overset'</dt>
             <dd>The region is the last one in the
             <span title="region-chain">region chain</span> and
             not able to fit the remaining content from the <span>named flow</span>.
             Note that the region's <a href=
             "http://www.w3.org/TR/CSS21/visufx.html#overflow"><code class=
             "idl">overflow</code></a> property value can be used to control the
             visibility of the overflowing content and the
             'region-overflow' property controls whether or not fragmentation happens
             on the content that overflows the last region.</dd>
             <dt>'fit'</dt>
             <dd>The region's flow fragment content fits into the region's <a href=
             "http://www.w3.org/TR/CSS21/box.html#box-dimensions">content box</a>.
             If the region is the last one in the <span title=
             "region-chain">region chain</span>, it means that the content fits
             without overflowing. If the region is not the last one in the region
             chain, that means the <span>named flow</span>
             content is further fitted in subsequent regions. In this
             last case, note that the <span>named flow</span> fragment may be
             empty (for example if the region is too small to accommodate any content).</dd>
             <dt>'empty'</dt>
             <dd>All content from the <span>named flow</span> was fitted in prior regions.</dd>
         </dl>
         <p>Note that if there is no content in the <span>named flow</span>, all regions associated
             with that <span>named flow</span> should have their <code class="idl">regionOverset</code>
             attribute return 'empty'.
             If there is content in the flow but that content does not generate any box
             for visual formatting, the 'overset' attribute on the first region in the
             region chain associated with the flow will return 'fit'.</p>
         <p>The <dfn id="dom-region-flowfrom">flowFrom</dfn> attribute returns the name of the
             <span>named flow</span> this region is associated with.</p>
         <p>The <dfn id="dom-region-getregionflowranges">getRegionFlowRanges</dfn> method
           returns an array of <a href= "http://www.w3.org/TR/dom/#interface-range">Range</a>
           instances corresponding to fragment
           from the <span>named flow</span>
           that is laid out in the region.
           If the region has not received a fragment
           because it is too small to accommodate any,
           the method returns a single <code class="idl">Range</code>
           where the <code>startContainer</code>
           and <code>startOffset</code>
           have the same values as
           the <code>endContainer</code>
           and <code>endOffset</code>
           and therefore the collapsed attribute
           on the <code class="idl">Range</code> is true.
           In that situation,
           if the region is the first
           in the <span>region chain</span>,
           the <code>startContainer</code>
           is the first <code>Node</code>
           in the <span>named flow</span>
           and the <code>startOffset</code> is zero.
           If the region is the last region
           in the region chain
           (but not the first and only one),
           the <code>startContainer</code>
           and <code>startOffset</code>
           are the same values as
           the <code>endContainer</code>
           and <code>endOffset</code>
           on the previous region
           in the <span>region chain</span>.
           The method returns null
           if the <span>region</span> object
           is not (or no longer) a region.</p>
         <div class="note">
             <p>A <code class="idl">Region</code> instance may represent and
             object that is no longer a <span>region</span>. This may happen, for example if the
             'flow-from' property on the corresponding pseudo-element, element or other construct
             becomes 'none' but a script is still holding a reference to the <code class="idl">Region</code> object.</p>
         </div>
         <p>If a <code class="idl">Region</code> instance is no longer a <span>region</span>,
             accessing its attributes (<code class="idl">regionOverset</code> and <code class="idl">flowFrom</code>) or
             invoking its <code class=
         "idl"><span title="#document-element-getregionflowranges">getRegionFlowRanges</span></code>
         method throws a <a href="http://www.w3.org/TR/dom/#interface-domexception"><code class="idl">DOMException</code></a> with the
         <a href="http://www.w3.org/TR/dom/#dom-domexception-invalid_access_err"><code class="idl">INVALID_ACCESS_ERR</code></a> error code.</p>
         </div>
     <h3 id="region-style-rule-interface">The CSSRegionStyleRule interface</h3>
     <p>The CSSRegionStyleRule interface represents
       an '@region' rule
       in a CSS style sheet.
       This rule type is added
       to the <a href="http://dev.w3.org/csswg/cssom/#cssrule"><code>CSSRule</code></a> [[!CSSOM]] interface.</p>
     <pre class="idl">
 partial interface CSSRule {
   const unsigned short REGION_STYLE_RULE = 1001;
 }
 </pre>
     <dt>REGION_STYLE_RULE</dt>
     <dd>The rule is a CSSRegionStyleRule</dd>
     <pre class="idl">
 interface CSSRegionStyleRule : CSSRule {
   attribute DOMString selectorText;
   readonly attribute CSSRuleList cssRules;
   unsigned long insertRule(DOMString rule,  unsigned long index)
       raises(DOMException);
   void deleteRule(unsigned long index)
       raises(DOMException);
 };
 </pre>
     <p>The <dfn id="region-style-rule-selectorText">
       <code class="idl">selectorText</code></dfn>
       attribute gets and sets
       the associated selector
       as defined in section <a href="http://dev.w3.org/csswg/cssom/#dom-cssstylerule-selectortext">6.4.3</a> of [[!CSSOM]].
     <p>The <dfn id="region-style-rule-cssRules">
       <code class="idl">cssRules</code></dfn>
       attribute must return a
       <a href="http://dev.w3.org/csswg/cssom/#cssrulelist"><code>CSSRuleList</code></a> [[!CSSOM]]
       object for the list of
       <a href="http://www.w3.org/TR/DOM-Level-2-Style/css.html#CSS-CSSStyleRule"><code class="idl">CSSStyleRules</code></a>
       specified in the region style block.</p>
     <p>The <dfn id="region-style-rule-insertRule">
       <code class="idl">insertRule(rule, index)</code></dfn>
       method inserts a
       <a href="http://www.w3.org/TR/DOM-Level-2-Style/css.html#CSS-CSSStyleRule"><code class="idl">CSSStyleRule</code></a>
       into the region style block
       before the specified index.
       If the index is equal to the length
       of the <a href="http://dev.w3.org/csswg/cssom/#cssrulelist"><code>CSSRuleList</code></a> the
       <a href="http://www.w3.org/TR/DOM-Level-2-Style/css.html#CSS-CSSStyleRule"><code class="idl">CSSStyleRule</code></a>
       is inserted at the end of the list.</p>
     <p>Possible exceptions:</p>
     <ul>
       <li>HIERARCHY_REQUEST_ERR:
         Raised if the rule to insert is not a
         <a href="http://www.w3.org/TR/DOM-Level-2-Style/css.html#CSS-CSSStyleRule"><code class="idl">CSSStyleRule</code></a>.</li>
       <li>INDEX_SIZE_ERR:
         Raised if the specified index
         is not a valid insertion point.</li>
       <li>SYNTAX_ERR:
         Raised if the specified rule
         has a syntax error
         and is unparsable.</li>
     </ul>
     <p>The <dfn id="region-style-rule-deleteRule">
       <code class="idl">deleteRule(index)</code></dfn>
       method deletes the <a href="http://www.w3.org/TR/DOM-Level-2-Style/css.html#CSS-CSSStyleRule"><code class="idl">CSSStyleRule</code></a> in the CSSRuleList
       at the specified index.</p>
     <p>Possible exceptions:</p>
     <ul>
       <li>INDEX_SIZE_ERR:
         Raised if the specified index
         does not correspond to a rule
         in the region style block.</li>
     </ul>
     <h3 id="region-flow-layout-events">Region flow layout events</h3>
     <p><a href="#dom-named-flow"><code class="idl">NamedFlow</code></a> objects are
      <a href="">Event Targets</a> which
     dispatch <code class="idl">regionLayoutUpdate</code> events when there is a
     possible layout change of their <span>named flow</span> fragment. Note that the event is asynchronous.</p>
     <div class="issue-marker" data-bug_id="16391" data-bug_status="ASSIGNED">
     <a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=16391">Bug-16391</a>
     <div class="issue-details">
         <p class="short-desc">regionLayoutUpdate needs to be async</p>
     </div>
     </div>
     <div class="note">The remaining issue in this bug is when the event gets fired.</div>
     <table class="event-desc" border="0" summary="This table contains information about the semantics of the given event type" cellpadding="2" cellspacing="0">
                 <tbody><tr class="assert must"><th>Type</th>
                 <td class="eventname"><strong><code>regionLayoutUpdate</code></strong></td></tr>
                 <tr class="assert must"><th>Interface</th> <td><code><a href="http://www.w3.org/TR/DOM-Level-3-Events/#webidl-events-UIEvent">UIEvent</a></code> (see [[!DOM-LEVEL-3-EVENTS]])</td></tr>
                 <tr class="assert must"><th>Sync / Async</th> <td>Async</td></tr>
                 <tr class="assert must"><th>Bubbles</th> <td>Yes</td></tr>
                 <tr class="assert must"><th>Target</th> <td><a href="#dom-named-flow"><code class="idl">NamedFlow</code></a></td></tr>
                 <tr class="assert must"><th>Cancelable</th> <td>Yes</td></tr>
                 <tr class="assert must"><th>Default action</th> <td>none</td></tr>
                 <tr class="assert must"><th>Context info</th>
                   <td>
                     <ul>
                       <li><code class="attribute-name">Event.target</code>:
                           <a href="#dom-named-flow"><code class="idl">NamedFlow</code></a> whose layout may have changed</li>
                     </ul>
                    </td>
                  </tr>
               </tbody></table>
     <h3 id="cssomview-and-regions">Clarifications on pre-existing APIs</h3>
     <h4 id="cssomview-getclientrects-and-getboundingclientrect"><code class="idl">getClientRects()</code> and <code>getBoundingClientRects()</code></h4>
     <p>The <a href="http://www.w3.org/TR/cssom-view/">CSSOM View Module</a>
       defines how user agents compute
       the bounding client rectangle
       for an element (<code class="idl">getBoundingClientRect()</code>)
       and its generated boxes (<code class="idl">getClientRects()</code>).</p>
     <p>This definition applies to
       the (possibly) multiple boxes
       generated for an element in a named flow
       flowing through a region chain.
       The <code class="idl">getClientRects()</code> method
       returns the list of boxes generated
       for each of the element fragments
       laid out in different regions.
       The <code>getBoundingClientRect()</code> method
       operates as specified in the
       <a href="http://www.w3.org/TR/cssom-view/">CSSOM View Module</a>
       as well and is computed
       from the set of rectangles
       returned by <code class="idl">getClientRects()</code>.</p>
     <h4 id="cssomview-offset-attributes"><code class="idl">offsetTop</code>, <code class="idl">offsetLeft</code>,
         <code class="idl">offsetWidth</code> and <code class="idl">offsetWidth</code></h4>
     <p>The computation of the <a href="http://dev.w3.org/csswg/cssom-view/#offset-attributes">offset attributes</a>
         for elements laid out in a <span>named flow</code> follow the <a href="http://dev.w3.org/csswg/cssom-view/#offset-attribute">specification</a>. For the purpose of the
             algorithm, the <em>first CSS layout box</em> associated
             with an element laid out in a <span>named flow</span> is the box generated for the first region
             the element is laid out into.</p>
     <h2 id="regions-visual-formatting-details">Regions visual formatting details</h2>
     <p>Regions are laid out by CSS and take part in the normal box model and other layout models
         offered by CSS modules such as flexible boxes ([[CSS3-FLEXBOX]]). However, <span>regions</span>
         lay out a fragment of their <span>named flow</span> instead of laying out descendant content as happens with other
         boxes.</p>
     <p>This section describes the model for laying out <span>regions</span>
       and for laying out <span>named flow</span> content into regions.
       The descriptions in this section are biased towards a horizontal writing mode,
       using <span>width</span> for logical width (or measure)
       and <span>height</span> for logical height (or extent)
       as <a href="http://www.w3.org/TR/css3-writing-modes/#abstract-dimensions">defined</a>
       in the CSS Writing Modes Module [[!CSS3-WRITING-MODES]]).
       To use this model in a vertical writing mode apply the principles
       <a href="http://www.w3.org/TR/css3-writing-modes/#vertical-layout">described</a>
       in that specification.</p>
     <h3 id="regions-flow-content-box">The Region Flow Content Box (RFBC)</h3>
     <p>A region box lays out the following boxes:</p>
     <ul>
         <li>The boxes generated by its <code class="css">::before</code> and
             <code class="css">::after</code> pseudo-elements, if any.</code>
         <li>The anonymous <def>region flow content box</dev> (called <def>RFCB</def> in this document) which
             contains the fragment of the <span>named flow</span> that the region receives.</li>
     </ul>
     <div class="figure">
         <img src="images/RFCB.svg" width="600px" />
         <p class="caption">The Region Flow Content Box (RFCB)</p>
     </div>
     <p>Laying out a <span>region</span> box follows the same processing rules as for any other
         <a href="http://www.w3.org/TR/CSS2/visuren.html#block-boxes">block container box</a>.</p>
     <p>The <span>RFCB</span> is a <a href="http://www.w3.org/TR/CSS21/visuren.html#block-boxes">block container box</a>
         with a <a href="">computed</a> 'width' of 'auto' and a whose <a href="">used</a> 'height' is
         resolved as detailed below.</li>
     <h4 id="rfbc-width-resolution">RFCB 'width' resolution</h4>
     <p>At various points in the visual formatting of documents containing regions, the
         used 'width' of RFCBs and regions need to be resolved. In all cases, the resolution is done following the
       rules for <a href="http://www.w3.org/TR/CSS2/visudet.html#Computing_widths_and_margins">calculating
             widths and margins</a> (see [[!CSS21]]). Sometimes, resolving the used 'width' value
             requires measuring the content's
             <code class="css">min-content</code> and <code class="css">max-content</code> values (as
             <a href="http://www.w3.org/TR/css3-writing-modes/#intrinsic-sizing">defined</a> in the CSS Writing Modes Module [[!CSS3-WRITING-MODES]]). For an RFCB, <strong>these measures are
         made on the <em>entire</em> associated <span>named flow</span> content</strong>.</p>
         <p>As a consequence, all <span>RFCBs</span> of <span>regions</span> associated with a given
             <span>named flow</span> share the
             same <code class="css">min-content</code> and <code class="css">max-content</code> measures.</p>
     <p>This approach is consistent with the <a href="http://www.w3.org/TR/css3-break/#varying-size-boxes">box model for breaking</a> ([[!CSS3-BREAK]]).</p>
     <h3 id="regions-visual-formatting-steps">Regions visual formatting steps</h3>
     <p>Formatting documents that contain <span>named flows</span> laid out in regions is a three-step
         process:</p>
     <ul>
         <li><em>Step 1: RFCB <def>flow fragment height</def> resolution</em>. In this step, the heights of fragments
             fitting in the regions' RFCBs are resolved.</li>
         <li><em>Step 2: document and regions layout</em>. In this step, the document content and regions are
             laid out. However, <span>named flow</span> content is not laid out in regions yet.</li>
         <li><em>Step 3: <span>named flow</span> layout</em>. In this step, the content of <span>named flows</span> is laid
             out in their respective <span>region chains</span>.</li>
     </ul>
     <div class="figure">
         <img src="images/regions-layout-three-steps.svg" width="600px" />
         <p class="caption">Regions visual formatting steps</p>
     </div>
     <h4 id="rfcb-flow-fragment-height-resolution">Step 1: RFCB flow fragment height resolution</h4>
     <p>Conceptually, resolving the flow fragment height is a two phase process.</p>
     <h5 id="rfcb-flow-fragment-height-resolution-phase-1">RFCB flow fragment height resolution, Phase 1</h5>
     <p>The document is laid out with a
         <a href="http://www.w3.org/TR/CSS2/cascade.html#used-value">used</a> height of zero
         for all <span>RFCB</span>s. In this phase, the content of <span>named flows</span> is not laid out in
         <span>regions</span>. This phase yields resolved position and sizes for all regions and
         their RFCBs in the document.</p>
     <h5 id="rfcb-flow-fragment-height-resolution-phase-2">RFCB flow fragment height resolution, Phase 2</h5>
     <p><span>Named flows</span> are laid out in <span>regions</span>. The
         user agent resolves the <em><span>flow fragment height</span></em> for
         the <span>RFCB</span>s using the remainder of the flow and accounting for
         <a href="http://www.w3.org/TR/css3-break/">fragmentation rules</a>.
         This process accounts for constraints such as the 'height' or 'max-height' values, as described
         in the CSS 2.1 section on
         <a href="http://www.w3.org/TR/CSS2/visudet.html#Computing_heights_and_margins">calculating heights
             and margins</a> (see the <a href="http://www.w3.org/TR/CSS2/visudet.html#normal-block">Block-level
                 non-replaced elements in normal flow when 'overflow' computes to 'visible'</a> section and the
         <a href="http://www.w3.org/TR/CSS2/visudet.html#block-root-margin">complicated cases</a> section).
         During this phase, generated content is laid out according to the
         <a href="#processing-model">rules</a> described earlier in this document.
         </p>
     <h4 id="regions-boxes-layout">Step 2: region boxes layout</h4>
     <p>In this step, the document is laid out according to the normal CSS layout rules.</p>
     <p>If a measure of the content is required to resolve the used 'width' of the region box, the value
         is resolved as described in the
         <a href="#rfbc-width-resolution">RFCB width resolution</a> section.</p>
     <p>If a measure of the content
         is required to resolve the used height of the RFCB (for example if the region box is absolutely positioned),
         the <span>flow fragment height</span> resolved in Step 1 is used for the vertical content measure of the
         RFCB.</p>
     <p>At the end of this step, regions are laid out and ready to receive
     content from their associated <span>named flows</span>.</p>
     <h4 id="named-flows-layout">Step 3: named flows layout</h4>
     <p>In this final step, the content of <span>named flows</span> is laid out in the <span>regions</span>' RFCBs
         along with the generated content boxes.</p>
     <p>The used 'width' for RFCBs is resolved <a href="#rfbc-width-resolution">as described before</a>.</p>
     <p>The used 'height' of RFCBs is resolved such that none of the boxes in the region box's normal flow
         overflow the region's box. In other words, the RFCB boxes are stretched vertically
         to accommodate as much of the flow as possible without overflowing the region box and
         accounting for <a href="http://www.w3.org/TR/css3-break/">fragmentation rules</a> and
         generated content boxes.</p>
     <p>During this phase, generated content is laid out according to the
         <a href="#processing-model">rules</a>
         described earlier in this document.</p>
     <div class="note">
         <p>The model for resolving auto sized regions will cause, under certain circumstances,
             the flow content to be overset or underset. In other words, it will not fit tightly.
             The model prevents having circular dependencies in the layout model. Implementations
             may decide to apply further layout steps to ensure that the whole flow content is
             displayed to the user, even in edge cases.</p>
     </div>
     <h3 id="regions-visual-formatting-implementation-note">Regions visual formatting: implementation note</h3>
     <p>The process for resolving an RFCB's 'height' and the three-step process used to
         lay out documents containing regions and <span>named flows</span> are
         <em>conceptual</em> descriptions of what the layout
         should yield and implementations should optimize to reduce the number of
         steps and phases necessary wherever possible.</p>
     <h3 id="regions-visual-formatting-examples">Regions visual formatting example</h3>
     <p>This section is non-normative.</p>
     <p>This example considers a document where content flows between three regions,
         and region boxes are intermixed with the normal document content.</p>
     <div class="example">
         <pre>
 &lt;style&gt;
 article {
     flow-into: article;
 }
 #rA, #rB, #rC {
     flow-from: article;
     height: auto;
     margin: 1em 1em 0em 1em;
     padding: 1em;
     border: 3px solid #46A4E9;
 }
 #rA {
     width: auto;
     height: auto;
 }
 #rB {
     float: left;
     width: 15em;
     height: auto;
     max-height: 150px;
 }
 #rC {
     float: right;
     width: 12em;
     height: auto;
 }
 #main-flow {
     padding: 0em 1em 0em 1em;
 }
 &lt;/style&gt;
 &lt;body&gt;
     &lt;article&gt;
         &lt;p style="region-break-after:always;"&gt;I am not a ... &lt;/p&gt;
         &lt;p&gt;...&lt;/p&gt;
     &lt;/article&gt;
     &lt;div id="rA"&gt;&lt;/div&gt;
     &lt;div id="rB"&gt;&lt;/div&gt;
     &lt;div id="rC"&gt;&lt;/div&gt;
     &lt;div id="main-flow"&gt;
         &lt;p&gt;Lorem ipsum dolor ...&lt;/p&gt;
     &lt;/div&gt;
 &lt;/body&gt;
         </pre>
     </div>
     <p>The following sections and figures illustrate the intermediate results for the visual formatting process.
         In the following, we call RFCB-A, RFCB-B and RFCB-C the <span>RFCBs</span> for
         regions rA, rB and rC respectively. </p>
     <h4>Step 1 - Phase 1: Laying out RFCBs with used height of zero</h4>
     <p>Applying the rules for Step 1, Phase 1, the computed 'auto' 'width' values for the RFCBs are resolved
         to used values according to the normal
         <a href="http://www.w3.org/TR/CSS2/visudet.html#Computing_widths_and_margins">CSS layout rules</a> meaning they
         stretch to the width of their containing block's content box.</p>
     <ol>
         <li>RFCB-A: stretches to fit the rA content box.</li>
             Since rA also has an 'auto' 'width', its own used 'width' is stretched to fit the
             <code>&lt;body&gt;</code> content box.</p>
         <li>RFCB-B: stretches to fit the <code>rB</code> content box.</li>
         <li>RFCB-C: stretches to fit the <code>rC</code> content box.</li>
     </ol>
     <p>Also applying the rules for Step 1, Phase 1, the used values for the RFCBs 'height' properties are all zero.</p>
     <p>Conceptually, this produces the layout illustrated below.</p>
     <div class="figure">
         <img src="images/flow-fragment-height-phase-1.png" width="500px" alt="Step 1 - Phase 1: Layout RFBCs with used heights of 0"/>
         <p class="caption">Step 1 - Phase 1: Layout RFBCs with used heights of 0</p>
     </div>
     <h4>Step 1 - Phase 2: Layout flow to compute the RFCBs' flow fragments heights</h4>
     <p>In this second phase of Step 1, the named flow is laid out in <span>regions</span>
         and the height of each fragment falling in each RFCB is computed.</p>
     <p>The user agent lays out as much of the flow into an area
         with RFCB-A's used 'width'. rA's 'height' computes to 'auto' and there is no vertical maximum
         height for RFCA's 'height'. However, because there is a break after the
         first paragraph in the 'article' <code>named flow</code>, only this first paragraph is
         laid out in RFCB-A and FH-A (the flow fragment height for RFCB-A) is resolved by laying out
         this first paragraph in the used 'width'.</p>
     <p>At this point, the user agent lays out as much of the remaining flow as possible in RFCB-B.
         Because rB's 'max-height' computed value is '150px', the user agent only lays out
         the 'article' named flow using RFCB-B's used 'width' until the point where
         laying out additional content would cause RFCB-B to overflow rB's box.
         The fragment height for RFCB-B is resolved: FH-B (<code class="css">150px</code>).</p>
     <p>Finally, the user agent lays out the remainder of the flow in RFCB-C.
         Because rC has no other constraints and no region breaks, the remaining content is
         laid out in RFCB-C's used 'width'. This results in a resolved flow fragment height: FH-C.</p>
     <div class="figure">
         <img src="images/flow-fragment-height-phase-2.png" width="370px" alt="Step 1 - Phase 2: Measure flow fragments heights"/>
         <p class="caption">Step 1 - Phase 2: Measure flow fragments heights</p>
     </div>
     <h4>Step 2: Layout document and regions without named flows</h4>
     <p>The used 'width' of RFCB-A, RFCB-B and RFCB-C are resolved as in the previous step. However, the
         'height' is resolved differently.</p>
     <p>Resolving the 'height' of rA <a href="http://www.w3.org/TR/CSS2/visudet.html#normal-block">requires a content measure</a>
         which is FH-A (the flow fragment height for RFCB-A).</p>
     <p>The 'height' of rB results from first computing its
         <a href="http://www.w3.org/TR/CSS2/visudet.html#block-root-margin">content measure</a> and then applying the
         <a href="http://www.w3.org/TR/CSS2/visudet.html#min-max-heights">rules for 'max-height'</a>. Here, the
             vertical content measure evaluates to FH-B. After applying the
             rules for 'max-height' and accounting for margins, padding and borders, the used 'height' of rB
             is resolved to LH-B (<code class="css">150px</code>).</a>.
     <p>The 'height' of rC's box results from
         <a href="http://www.w3.org/TR/CSS2/visudet.html#block-root-margin">calculating
             its content measure</a>: FH-C becomes rC's used 'height'.</a>
     <div class="figure">
         <img src="images/regions-visual-formatting-step-2.png" width="370px" alt="Step 2: Layout document and regions without named flows"/>
         <p class="caption">Step 2: Layout document and regions without <span>named flows</span></p>
     </div>
     <h4>Step 3: named flows layout</h4>
     <p>In this final step, the <code class="css">article</code> <span>named flow</span> is laid out in its
         <span>region chain</span>. The used 'width' for each of the RFCB is resolved as in step 1 above.</p>
     <p>The used 'height' for the RFCB is a result of laying out the as much of the content in the
         <span>region</span> without overflowing its content box and following the
         <a href="http://www.w3.org/TR/css3-break/">fragmentation rules</a>.</p>
     <p>Because the computed 'width' of the RFCB has not changed and the fragmentation rules applied are
         the same as in Phase 1, Step 2, the used 'height' for RFCB-A, RFCB-B and RFCB-C are
         LH-A, LH-B and LH-C, respectively.</p>
     <p>There may be situations where the used 'height' of RFCBs resolved in Step 3 are different from the
         <span>flow fragment height</span> computed in Step 1 Phase 2.</p>
     <div class="figure">
         <img src="images/regions-visual-formatting-step-3.png" width="370px" alt="Step 3: Final result after laying out named flows in regions"/>
         <p class="caption">Step 3: Final result after laying out named flows in regions</p>
     </div>
     <h2 id="relation-to-document-events">Relation to document events</h2>
     <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 <span>named flow</span>, the <a href=
     "http://www.w3.org/TR/dom/#events">event's
     bubble and capture phases</a> happen following the document tree order.</p>
     <h2 id="relation-to-other-specifications">Relation to other
     specifications</h2>
     <p>This specification is related to other specifications as described in
     the <a href='#references'>references</a> section. In addition, it is
     related to the following specifications:</p>
     <ol>
         <li>CSS Fragmentation Module Level 3 [[CSS3-BREAK]]. This module defines the
             rules for fragmenting content over multiple containers and applies to
             CSS regions in addition to applying to multi-column and paged media.</li>
         <li>CSS Pagination Templates Module Level 3 [[CSS3-PAGE-TEMPLATE]]. This module
             defines a syntax to define layout templates which can be used
             when paginating content. The page templates use regions.</li>
         <li>CSS Exclusions Module [[CSS3-EXCLUSIONS]]. This module defines a
         generic way to define arbitrarily shaped exclusions into which content
         can flow or around which content can flow. This can be seen as an
         extension to the way CSS floats provide rectangular areas into which
         content flows and around which content flows. In advanced layout
         designs, it is expected that the CSS Exclusions module will be commonly
         combined with the CSS regions module.</li>
         <li>CSS Line Grid Module [[CSS3-LINE-GRID]]. This module defines a
         concept of line grid to align the position of lines in different
         elements. The line grid functionality is related and needed for
         aligning content flowing in separate regions.</li>
     </ol>
     <h2 id="usecases">Use Cases</h2>
     <p>Use cases are described on <a href="http://wiki.csswg.org/spec/css3-regions/regions-use-cases">this
             page</a>.</p>
     <h2 id="conformance">Conformance</h2>
     <h2 id="changes">Changes</h2>
     <h3 id="changes_from_November_29_2011">Changes from <a href="http://www.w3.org/TR/2011/WD-css3-regions-20111129/">November 29<sup>th</sup> 2011</a> version</h3>
     <ul>
         <li>Modified region styling examples to use element selector instead of of pseudo-code selectors (this had been omitted in the
             previous pass at removing pseudo-code from the examples).</li>
         <li>Removed divs with class set to "issue moved", "issue stale" and "issue resolved" since these divs where not displayed.
         <li>Minor updates to the alternate stylesheet.</li>
         <li>Removed "This section is normative" paragraphs since in CSS specifications, sections are normative unless
             otherwise specified.</li>
         <li>Removed "This section is informative" paragraphs since in CSS specifications notes are always informative.</li>
         <li>Reworded the text about flow-into: &lt;ident&gt; and removed obsolete text about the interaction with the
             'content' property.</li>
         <li>Removed "this section is non-normative" from the "Regions Concepts" section.</li>
         <li>In the section on region breaks, removed descriptions of break values normatively defined in external specifications.
             Removed the section about split boxes and replaced with paragraph referencing the page breaking behavior.
             Removed the discussion about how the 'overflow' property applies to content flown in regions from the
             break section, since this is covered in the section on 'region-overflow' already. See <a href="http://lists.w3.org/Archives/Public/www-style/2011Dec/0477.html">mailing list feedback.</a></li>
         <li>Clarified that @region style rules only apply to the 'portion' of an element that falls into
             the corresponding region and added an issue that the model for 'partial' styling needs to
             be defined. See <a href="http://lists.w3.org/Archives/Public/www-style/2011Dec/0480.html">mailing list feedback</a>.</li>
         <li>Clarified that the <code>NodeList</code> returned by <code>getRegionsByContentNode</code> is live.</li>
         <li>Added a name property to the <code>NamedFlow</code> interface. Added a <code>NamedFlowCollection</code>
             interface and added a <code>getNamedFlows</code> method on the <code>Document</code> interface, as
             per <a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=15828">Bug 15828</a>.</li>
         <li>Modified wording about containing block resolution for absolutely positioned elements in a
             named flow.</li>
         <li>Modified initial examples as per <a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=15131">Bug 15131</a></li>
         <li>Multiple editorial changes following
             <a href="http://lists.w3.org/Archives/Public/www-style/2012Feb/0001.html">mailing list review comments</a></li>
         <li>Fixed DOM references to now point to the DOM TR</li>
         <li>Fixed Web IDL issues as reported in <a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=15931">Issue 15931</a></li>
         <li>Added text to explain support for multi-column elements as required by <a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=15191">Issue 15191</a> and <a href="http://www.w3.org/Style/CSS/Tracker/actions/375">Action 375</a>.</li>
         <li>Renamed 'regionOverflow' to 'regionOverset' to avoid confusion between fitting a flow in
             regions and the concept of visual overflow that the word 'overflow' (and the property) carry.</li>
         <li>Reworked the partial document interface following the <a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=14948">Issue 14948</a> on <code>getFlowByName</code>.</li>
         <li>Updated the object model section as proposed on the <a href="http://wiki.csswg.org/spec/css3-regions/css-om">wiki</a> and in particular:
             <ul>
                 <li>introduced a <code>Region</code> interface to replace the supplemental Element interface</li>
                 <li>Added a 'flowFrom' attribute on the Region interface</li>
                 <li>NamedFlow.getRegions() was added</li>
                 <li>Renamed getContentNode to getContent and getRegionsByContentNode to getRegionsByContent as
                     per <a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=15879">Isseu 15879</a></li>
                 <li>NamedFlow now returns static lists (see <a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=16286">Issue 16286</a>)</li>
             </ul>
         </li>
         <li>Modified region layout event to be dispatched on <code>NamedFlow</code> instead of region
             as before. Was requested by <a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=15938">Issue 15938</a>
             and required in the general effort to have the DOM APIs work with non-element regions.</li>
         <li>Changed paragraph on pseudo-elements to disallow 'flow-into' on all pseudo-elements because
             moving a '::before' element (for a example) to a named flow does not seem useful and causes specification
             and implementation complexity.</li>
         <li>Added section about getClientRects(), getBoundingClientRect(), offsetWidth, offsetHeight, offsetTop and
             offsetLeft.</li>
         <li>Added 'Regions visual formatting details' section to better describe the model for
             resolving auto sizing on regions.</li>
         <li>Reworked the initial specification example.</li>
         <li>Changed break and region-overflow properties to apply to visual media instead of paged.</li>
         <li>Added opacity to region styling.</li>
         <li>Added possibility of ::before content contributing to overflow.</li>
         <li>Added CSSRegionStyleRule</li>
     </ul>
     <h3 id="changes_from_June_09_2011">Changes from <a href="http://www.w3.org/TR/2011/WD-css3-regions-20110609/">June 09<sup>th</sup> 2011</a> version</h3>
     <ul>
         <li>Editorial changes (typos, rephrasings).</li>
         <li>Made 'content-order' a &lt;integer&gt; and not a &lt;float&gt; following a working group
             <a href="http://lists.w3.org/Archives/Public/www-style/2011Jun/0329.html">resolution</a></li>
         <li>Added Alex Mogilevsky as an editor</li>
         <li>Flow names became &lt;ident&gt; instead of &lt;string&gt; following a working group
             <a href="http://lists.w3.org/Archives/Public/www-style/2011Jun/0413.html">resolution</a></li>
         <li>Removed issue about possibly altering the DOM Events model for region events following
             a working group
             <a href="http://lists.w3.org/Archives/Public/www-style/2011Jun/0413.html">resolution</a></li>
         <li>Made the "relation to document events" section informative following a     working group
             <a href="http://lists.w3.org/Archives/Public/www-style/2011Jun/0413.html">resolution</a></li>
         <li>Removed issue in section "The NamedFlow interface" following the working group's
             <a href="http://lists.w3.org/Archives/Public/www-style/2011Jun/0413.html">resolution</a> to
             have both NamedFlow and the Element interface extension</li>
         <li>Following a working group <a href="http://lists.w3.org/Archives/Public/www-style/2011Jun/0413.html">resolution</a>:
         	<ul>
             	<li>Turned the first issue in the "Extensions to the Element interface" into a note
             explaining that the NamedFlow interface can be used when regions are pseudo-elements.</li>
             	<li>Added NamedFlowUpdate</li>
                 </ul>
         </li>
         <li>Excluded 'none', 'inherit' and 'initial' from the possible identifier names on
         	the flow property following <a href="http://lists.w3.org/Archives/Public/www-style/2011Jun/0583.html">discussion</a> on the mailing list.</li>
         <li>Simplified integration discussion on multi-column layout and just state that since
         column boxes are not addressable by selectors, they cannot be regions.</li>
         <li>Added specification of how the 'flow-into' property interacts with object, embed and iframe
         elements.</li>
         <li>Excluded 'default' from the possible identifier names on the flow property because it
             <a href="http://www.w3.org/TR/2006/WD-css3-values-20060919/#keywords">may get reserved</a>.</li>
         <li>Added to the definition of 'auto' on 'region-overflow' specifying that region breaks must
             be ignored.</li>
         <li>Renamed 'Document.flowWithName' to 'Document.getFlowByName' since it is not a property.</li>
         <li>Added a note that a 'NamedFlow' instance is live.</li>
         <li>Added an 'undefined' string value to the regionOverflow property on the Element interface
             extension.</li>
         <li>Renamed NamedFlowEvent to regionLayoutUpdate to avoid having 'Event' in the event name.</li>
 		<li>Added description for special behavior of iframe/object/embed as
 		flow source</li>
 		<li>Removed issue on copying content to a named flow instead of moving elements to named
 		    flow following working group <a href="http://lists.w3.org/Archives/Public/www-style/2011Aug/0069.html">resolution</a>.</li>
     	<li>Removed issue on content:flow-from v.s., flow-from property following working group <a href="http://lists.w3.org/Archives/Public/www-style/2011Aug/0069.html">resolution</a>.</li>
     	<li>Renamed 'flow' to 'flow-into' following working group <a href="http://lists.w3.org/Archives/Public/www-style/2011Aug/0069.html">resolution</a>.</li>
     	<li>Updated the css3-grid-align example following working group <a href="http://lists.w3.org/Archives/Public/www-style/2011Aug/0069.html">resolution</a> that
     	    it should use &lt;div&gt; instead of grid-cell pseudo elements that were removed
     	    from the CSS Grid Layout specification.</li>
         <li>Renamed 'from-flow' to 'flow-from' following a working group <a href="http://lists.w3.org/Archives/Public/www-style/2011Aug/0069.html">resolution</a>.</li>
         <li>Limited the applicability of 'content: flow-from()' to block container box and added
             a note that this might be expanded in the future, following a working group <a href="http://lists.w3.org/Archives/Public/www-style/2011Aug/0069.html">resolution</a>.</li>
         <li>Removed issue about API to find which region displays an element in a named flow
             since <a href="http://www.w3.org/Style/CSS/Tracker/actions/350">ACTION-350</a> was
             created to add this API.</li>
         <li>In the 'flow' property description, removed the required wrapper anonymous
             block as agreed on <a href="http://lists.w3.org/Archives/Public/www-style/2011Aug/0161.html">mailing list discussion</a>.</li>
         <li>Reworded the paragraph on how regions create a new stacking context, as
             per the <a href="http://lists.w3.org/Archives/Public/www-style/2011Aug/0025.html">mailing list discussion</a>.</li>
         <li>Reworked the "CSS regions Model" section to now be "CSS regions Layout". Moved the
             definition of a region as the first sub-section.</li>
         <li>Removed the "Visual Formatting Model and Flows" section to match the new Regions Model
             (now CSS regions Layout) section.</li>
         <li>Moved the sections on allowed region breaks, forced region breaks and "best" regions
             breaks to follow the property definitions to follow the formatting of the paged
             media section in CSS 2.1.</li>
         <li>Added note about why regions create a new stacking context following the discussion
             on the <a href="http://lists.w3.org/Archives/Public/www-style/2011Jul/0158.html">mailing list</a>.</li>
         <li>Removed sentence about content:none making elements disconnected following the
                 discussion on the <a href="http://lists.w3.org/Archives/Public/www-style/2011Jul/0158.html">mailing list</a>.</li>
         <li>Removed sentence about content:none making elements disconnected following the
                     discussion on the <a href="http://lists.w3.org/Archives/Public/www-style/2011Jul/0158.html">mailing list</a>.</li>
         <li>Added the ::region-before and a ::region-after pseudo-elements.</li>
         <li>Added note of caution when using selectors and the 'flow-into' property following
             a <a href="http://lists.w3.org/Archives/Public/www-style/2011Jul/0191.html">mailing list discussion</a>.</li>
         <li>Removed sections about allowed, forced and best region breaks to align with the
             multi-column specification approach and until the group agrees on where and how the
             general issue of breaks (regions/pages/columns) should be addressed.</li>
         <li>Removed the section on Integration with other specifications since specifications that
             was superfluous especially since there is no specific integration with multi column,
             grid or template layout.</li>
         <li>Added a note that regions establish a new block formatting context.</li>
         <li>Renamed content-order to region-order.</li>
         <li>Added a note about overflowing content in regions (e.g., for content with borders).</li>
         <li>Added a note that a region cannot layout content it is part of (to avoid creating a
             circular dependency) in the flow-from description, specifying that if flow-from
             references the flow an element is part of, then the element does not format
             anything visually.</li>
         <li>Replaced 'content:flow-from(&lt;ident&gt;)' with 'flow-from: &lt;ident&gt;' following a
             <a href="http://krijnhoetmer.nl/irc-logs/css/20110824">working group resolution</a>.</li>
         <li>Added more specific wording about auto width and auto height, following
             <a href="http://www.w3.org/Style/CSS/Tracker/actions/351">ACTION 351</a>.</li>
         <li>Reworked section on region markers to now use '::before' and '::after' and explain
             how 'display:run-in' works with regions.</li>
         <li>Modified the @region style rule to remove the ::region-lines pseudo-selector.</li>
         <li>Removed the 'region-order' property following implementation feedback.</li>
         <li>Specified that region-overflow does not influence a region's size.</li>
         <li>Specified that the flow's writing mode is defined by the first region's writing mode
             following <a href="http://lists.w3.org/Archives/Public/www-style/2011Aug/0306.html">mailing list discussion</a>.</li>
         <li>Made iframe, object and embed support of flow-into optional following
             <a href="http://lists.w3.org/Archives/Public/www-style/2011Sep/0073.html">mailing list discussion</a>.</li>
         <li>Clarified that flow content following the last break in the last region is not rendered,
             following <a href="http://lists.w3.org/Archives/Public/www-style/2011Oct/0167.html">mailing list
                 discussions.</a></li>
         <li>Modified the rule for computing the width and height of a region when they are set to auto,
             following <a href="http://lists.w3.org/Archives/Public/www-style/2011Oct/0216.html">a mailing list
                 discussion.</a></li>
         <li>Added 'auto' to the list of invalid flow identifiers.</li>
         <li>Made 'none' the initial value for 'flow-into' and aligned with 'flow-from', as
             explained in this <a href="http://lists.w3.org/Archives/Public/www-style/2011Oct/0576.html">email</a>.
             Also allowed the 'inherit' value on 'flow-from' and 'flow-into' (same email).</li>
         <li>Added note about nested region styling following <a href="http://lists.w3.org/Archives/Public/www-style/2011Oct/0650.html">a mailing list discussion</a>.</li>
         <li>Added additional DOM interface following <a href="http://www.w3.org/Style/CSS/Tracker/actions/350">Action 350</a>.</li>
         <li>Clarified that a region becomes a region only if its 'content' property computes to
             normal, following the resolution of <a href="http://wiki.csswg.org/spec/css3-regions#issue-22content-vs-flow-from-precedence">Issue 22</a>.</li>
         <li>Removed text about special iframe behavior as a result of
             <a href="http://www.w3.org/Style/CSS/Tracker/actions/376">ACTION 376</a>.</li>
         <li>Made the selectors explicit in the initial section code examples, following
             discussion in <a href="http://krijnhoetmer.nl/irc-logs/css/20111030">San Jose, October 2011</a> face to face meeting.</li>
         <li>Added section on use cases following <a href="http://www.w3.org/Style/CSS/Tracker/actions/377">ACTION-377</a>.</li>
     </ul>
     <h2 class="no-num" id="acknowledgments">Acknowledgments</h2>
     <p>The editors are grateful to the CSS working group for their feedback and help with
         the genesis of this specification.</p>
     <p>In addition, the editors would like to thank the following individuals for their contributions,
         either during the conception of CSS regions or during its development and specification review
         process:</p>
     <ul>
         <li>Rossen Atanassov</li>
         <li>Tab Atkins</li>
         <li>Andrei Bucur</li>
         <li>Alexandru Chiculita</li>
         <li>Phil Cupp</li>
         <li>Arron Eicholz</li>
         <li>John Jansen</li>
         <li>Daniel Glazman</li>
         <li>Arno Gourdol</li>
         <li>David Hyatt</li>
         <li>Brian Heuston</li>
         <li>Ian Hickson</li>
         <li>Jonathan Hoersch</li>
         <li>Michael Jolson</li>
         <li>Brad Kemper</li>
         <li>Håkon Wium Lie</li>
         <li>Markus Mielke</li>
         <li>Robert O'Callahan</li>
         <li>Edward O'Connor</li>
         <li>Mihnea Ovidenie</li>
         <li>Virgil Palanciuc</li>
         <li>Olga Popiv</li>
         <li>Christoph Päper</li>
         <li>Anton Prowse</li>
         <li>Peter Sorotokin</li>
         <li>Alan Stearns</li>
         <li>Christian Stockwell</li>
         <li>Eugene Veselov</li>
         <li>Boris Zbarsky</li>
         <li>Stephen Zilles</li>
     </ul>
     <h2 id="intro-example-code" class="no-num">Appendix A. Example Code for Introduction</h2>
       <p>The following is one possible way
         to code the example from
         the <a href="#introduction">introduction</a>.
         This code uses grid cells
         to define, size and position the region areas
         but table layout, absolute positioning,
         or any other CSS layout facility could be used.</p>
     <div class="example"><pre>
 &lt;style&gt;
   #grid {
     width: 80vw;
     height: 60vw;
     grid-template: "aaa.d"
                    "....d"
                    "bbb.d"
                    "....d"
                    "ccc.d";
     grid-rows: 52% 4% 20% 4% 20%;
     grid-columns: 30% 5% 30% 5% 30%;
   }
   #region1 { grid-cell: a; }
   #region2 { grid-cell: b; }
   #boxA    { grid-cell: c; }
   #region3 { grid-cell: d; }
   #region4 {
     width: 80vw;
   }
   #region2 {
     column-count: 2;
   }
   <span class="highlight">/*
    * Creates the named flow
    */</span>
   article {
     <strong>flow-into: article_flow;</strong>
   }
   <span class="highlight">/*
    * Associate it with the intended CSS Regions.
    * This creates a region chain for the named flow.
    */</span>
   #region1, #region2, #region3, #region4 {
     <strong>flow-from: article_flow;</strong>
   }
 &lt;/style&gt;
 <span class="highlight">&lt;!--
      The following code element is the content to flow
      through the region chain.
 --&gt;</span>
 &lt;article</em>&gt;
   &lt;h1&gt;Introduction&lt;/h1&gt;
   &lt;p&gt;This is an example ...&lt;/p&gt;
   &lt;h2&gt;More Details&lt;/h2&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;/article&gt;
 <span class="highlight">&lt;!--
      For this example, we layout the regions with a grid.
      Regions could be pseudo-elements and could be laid out
      with another layout module (e.g., flexible boxes)
 --&gt;</span>
 &lt;div id="grid"&gt;
   &lt;div id="region1"&gt;&lt;/div&gt;
   &lt;div id="region2"&gt;&lt;/div&gt;
   &lt;div id="boxA"&gt;&lt;/div&gt;
   &lt;div id="region3"&gt;&lt;/div&gt;
 &lt;/div&gt;
 &lt;div id="region4"&gt;&lt;/div&gt;
     </pre></div>
     <div class="note"><span class="note-prefix">Note </span>
       <p>
       Note that a multi-column element is used for #region2,
       which is a bit gratuitous here
       (because grid cells could be used).
       The reason to use a multi-column element
       is to illustrate that
       regions can be multi-column.</p>
     </div>
     <h2 class="no-num" id="references">References</h2>
     <div class="issue-marker" data-bug_id="16404" data-bug_status="ASSIGNED">
     <a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=16404">Bug-16404</a>
     <div class="issue-details">
         <p class="short-desc">Fix specification dependencies</p>
     </div>
     </div>
     <h3 class="no-num" id="normative-references">Normative references</h3>
     <!--begin-normative--><!--end-normative-->
     <h3 class="no-num" id="other-references">Other references</h3>
     <!--begin-informative--><!--end-informative-->
     <h2 class="no-num" id="index">Index</h2><!--index-->
     <h2 class="no-num" id="property-index">Property index</h2>
     <!-- template markup for issues pulled from Bugzilla -->
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 <div class="issue-marker" style="display:none" data-bug_id="{{bug_id}}" data-bug_status="{{bug_status}}">
     <a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id={{bug_id}}">Bug-{{bug_id}}</a>
     <div class="issue-details">
         <p class="short-desc">{{short_desc}}</p>
     </div>
 </div>
     </script>
     <script type="text/javascript" src="../shared/scripts/BugzillaTrackerUtil.js"></script>
     <script type="text/javascript" src="../shared/scripts/BugzillaTracker.js"></script>
     <script type="text/javascript">
 checkSpecificationIssues('CSS', 'Regions');
     </script>
     <div id="issue-manager">
         <h2>Issue manager</h2>
         <form action="#">
             <label>
                 <input type="radio" name="issue-filter" value="all" checked/>
                 All issues
             </label>
             <label>
                 <input type="radio" name="issue-filter" value="updated" />
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             </label>
             <label>
                 <input type="radio" name="issue-filter" value="new" />
                 New issues
             </label>
         </form>
         <!-- all the bugs are dumped the #issue-list after being retreived and matched to the ones in the page -->
         <div id="issue-list">
         </div>
     </div>
 </body>
 </html>
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