csswg-drafts/css-template/Overview.html at 62f40eb5637177cd5f5a92934afa033791abe10b · w3c/csswg-drafts · GitHub

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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN">

<html lang=en>
 <head
  profile="http://dublincore.org/documents/2008/08/04/dc-html/ http://microformats.org/profile/hcard http://microformats.org/wiki/rel-license">
  <meta content="text/html; charset=utf-8" http-equiv=content-type>
  <title>CSS Grid Template Layout Module</title>

  <link href="http://purl.org/dc/terms/" rel=schema.dcterms>
  <link href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
   rel=dcterms.rights>
  <meta content="CSS Grid Template Layout Module" name=dcterms.title>
  <meta content=text name=dcterms.type>
  <meta content=2013-06-10 name=dcterms.date>
  <meta content="Bert Bos" name=dcterms.creator>
  <meta content="César Acebal" name=dcterms.creator>
  <meta content=W3C name=dcterms.publisher>
  <meta content="http://dev.w3.org/csswg/css3-layout/"
   name=dcterms.identifier>
  <link href="../default.css" rel=stylesheet type="text/css">
  <style type="text/css">
  /* Just in case an incorrect max-width occurs in default.css */
  body {max-width: none !important}

  .prod { font-family: inherit; font-size: inherit }
  pre.prod { white-space: pre-wrap; margin: 1em 0 1em 2em }
  code { font-size: inherit; }

  .example .visible {border: thin dotted silver}
</style>
  <link href="http://www.w3.org/StyleSheets/TR/W3C-ED.css" rel=stylesheet>

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

   <h1 class=p-name>CSS Grid Template Layout Module</h1>

   <h2 class="no-num no-toc" id=longstatus-date-3-august-2004>Editor's Draft
    10 June 2013</h2>

   <dl>
    <dt>This version:

    <dd><a class=u-url
     href="http://dev.w3.org/csswg/css3-layout/">http://dev.w3.org/csswg/css3-layout/</a>

    <dt>Latest version:

    <dd><a
     href="http://www.w3.org/TR/css3-layout/">http://www.w3.org/TR/css3-layout/</a>

    <dt>Previous version:

    <dd><a
     href="http://www.w3.org/TR/2011/WD-css3-layout-20111129/">http://www.w3.org/TR/2011/WD-css3-layout-20111129/</a>

    <dt>Feedback:

    <dd><a
     href="mailto:www-style@w3.org?subject=%5Bcss3-layout%5D%20feedback">www-style@w3.org</a>
     with subject line “[css3-layout] <var>… message topic …</var>”
     (<a href="http://lists.w3.org/Archives/Public/www-style/"
     rel=discussion>archives</a>)

    <dt>Editors:

    <dd class="p-author h-card vcard"><span class="p-name fn">Bert Bos</span>
     (<span class="p-org org h-org">W3C</span>) <a class="u-email email"
     href="mailto:bert@w3.org" rel=author>bert@w3.org</a>

    <dd class="p-author h-card vcard"><span class="p-name fn">César
     Acebal</span> (<span class="p-org org h-org">University of
     Oviedo</span>)
   </dl>
   <!--begin-copyright-->
   <p class=copyright><a
    href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
    rel=license>Copyright</a> © 2013 <a href="http://www.w3.org/"><abbr
    title="World Wide Web Consortium">W3C</abbr></a><sup>®</sup> (<a
    href="http://www.csail.mit.edu/"><abbr
    title="Massachusetts Institute of Technology">MIT</abbr></a>, <a
    href="http://www.ercim.eu/"><abbr
    title="European Research Consortium for Informatics and Mathematics">ERCIM</abbr></a>,
    <a href="http://www.keio.ac.jp/">Keio</a>, <a
    href="http://ev.buaa.edu.cn/">Beihang</a>), All Rights Reserved. W3C <a
    href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
    <a
    href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a>
    and <a
    href="http://www.w3.org/Consortium/Legal/copyright-documents">document
    use</a> rules apply.</p>
   <!--end-copyright-->
   <hr title="Separator for header">
  </div>
  <!--=================================================================-->

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

  <div class=sidefigure>
   <p><img alt="Image: four elements move to four slots in a template"
    longdesc=diagram.desc src=diagram.png>

   <p class=caption>Above: a typical Web page. Below: the underlying grid
    template.
  </div>

  <p>CSS is a simple, declarative language for creating style sheets that
   specify the rendering of HTML and other structured documents. This module
   defines a typographic grid for CSS. It has features to set up a grid
   template, to flow content into it, and to position overlapping elements on
   a grid.

  <p>The ‘<a href="#grid"><code class=property>grid</code></a>’ property
   sets up a matrix of rows and columns and designates empty areas and areas
   for content (called “slots”). The ‘<a href="#flow0"><code
   class=property>flow</code></a>’ property specifies into which slot an
   element flows. A grid template is like a table in that the various slots
   are aligned in rows and columns and can automatically adapt to each
   other's size, and it is like absolute positioning in that elements can be
   put in arbitrary slots so that the visual order becomes independent of the
   document order.

  <p>The <a href="#slot-pseudo-element.">‘<code
   class=css>::slot()</code>’ pseudo-element</a> allows to style the slots
   (backgrounds, borders, etc.)

  <p>Use ‘<a href="#grid-area"><code class=property>grid-area</code></a>’
   instead of ‘<a href="#flow0"><code class=property>flow</code></a>’ to
   put multiple elements on top of one another in the same slot.

  <p>Grid templates can also be associated with pages in paged media, to
   create page templates.

  <p>Slots can form “chains” to create non-rectangular regions. A chain
   of slots is like a series of pages or columns: content is distributed over
   the slots by breaking it at possible break points (see the ‘<code
   class=css>break-*</code>’ properties from <a href="#CSS3-BREAK"
   rel=biblioentry>[CSS3-BREAK]<!--{{CSS3-BREAK}}--></a>).

  <p>The <a href="#region-based">‘<code class=css>@region</code>’
   rule</a> <a href="#CSS3-REGIONS"
   rel=biblioentry>[CSS3-REGIONS]<!--{{!CSS3-REGIONS}}--></a> allows to
   select (parts of) elements based on whether they fall in a certain slot or
   not, and thus style content differently in different slots (region-based
   styling).
   <!--=================================================================-->

  <h2 class="no-num no-toc" id=status>Status of this document</h2>
  <!--begin-status-->

  <p>This is a public copy of the editors' draft. It is provided for
   discussion only and may change at any moment. Its publication here does
   not imply endorsement of its contents by W3C. Don't cite this document
   other than as work in progress.

  <p>The (<a
   href="http://lists.w3.org/Archives/Public/www-style/">archived</a>) public
   mailing list <a
   href="mailto:www-style@w3.org?Subject=%5Bcss3-layout%5D%20PUT%20SUBJECT%20HERE">
   www-style@w3.org</a> (see <a
   href="http://www.w3.org/Mail/Request">instructions</a>) is preferred for
   discussion of this specification. When sending e-mail, please put the text
   “css3-layout” in the subject, preferably like this:
   “[<!---->css3-layout<!---->] <em>…summary of comment…</em>”

  <p>This document was produced by the <a
   href="http://www.w3.org/Style/CSS/members">CSS Working Group</a> (part of
   the <a href="http://www.w3.org/Style/">Style Activity</a>).

  <p>This document was produced by a group operating under the <a
   href="http://www.w3.org/Consortium/Patent-Policy-20040205/">5 February
   2004 W3C Patent Policy</a>. W3C maintains a <a
   href="http://www.w3.org/2004/01/pp-impl/32061/status"
   rel=disclosure>public list of any patent disclosures</a> made in
   connection with the deliverables of the group; that page also includes
   instructions for disclosing a patent. An individual who has actual
   knowledge of a patent which the individual believes contains <a
   href="http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">Essential
   Claim(s)</a> must disclose the information in accordance with <a
   href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">section
   6 of the W3C Patent Policy</a>.</p>
  <!--end-status-->

  <p>This draft combines ideas from earlier drafts on Template Layout, Grid
   Positioning <a href="#CSS3GRID"
   rel=biblioentry>[CSS3GRID]<!--{{CSS3GRID}}--></a> and Grid Layout <a
   href="#CSS3-GRID-LAYOUT"
   rel=biblioentry>[CSS3-GRID-LAYOUT]<!--{{CSS3-GRID-LAYOUT}}--></a>.

  <p>Issues on this draft are mentioned in the text itself and/or in the
   on-line Tracker under <a
   href="http://www.w3.org/Style/CSS/Tracker/products/15">“Details on
   Product CSS3 Template Layout.”</a>
   <!--=================================================================-->

  <h2 class="no-num no-toc" id=contents>Table of contents</h2>
  <!--begin-toc-->

  <ul class=toc>
   <li><a href="#introduction"><span class=secno>1. </span>Introduction</a>
    <ul class=toc>
     <li><a href="#summary-and-use-cases"><span class=secno>1.1.
      </span>Summary and use cases</a>

     <li><a href="#dependencies"><span class=secno>1.2. </span>Dependencies
      on other modules</a>

     <li><a href="#values"><span class=secno>1.3. </span>Values</a>

     <li><a href="#accessibility"><span class=secno>1.4. </span>A note about
      accessibility</a>
    </ul>

   <li><a href="#declaring-templates"><span class=secno>2. </span>Declaring
    templates</a>
    <ul class=toc>
     <li><a href="#grid-template"><span class=secno>2.1. </span>Declaring a
      template: ‘<code class=property>grid-template</code>’</a>

     <li><a href="#grid-column-sizes"><span class=secno>2.2.
      </span>Specifying the widths of columns: ‘<code
      class=property>grid-columns</code>’</a>

     <li><a href="#grid-row-sizes"><span class=secno>2.3. </span>Specifying
      the height of rows: ‘<code class=property>grid-rows</code>’</a>

     <li><a href="#grid-shorthand"><span class=secno>2.4. </span>The ‘<code
      class=property>grid</code>’ shorthand property</a>

     <li><a href="#default"><span class=secno>2.5. </span>Default slots</a>

     <li><a href="#columns"><span class=secno>2.6. </span>Interaction of
      ‘<code class=property>grid</code>’ and ‘<code
      class=property>columns</code>’</a>

     <li><a href="#slot-sizes"><span class=secno>2.7. </span>Calculating the
      size of the grid</a>
    </ul>

   <li><a href="#flow"><span class=secno>3. </span>Flowing content into
    slots: ‘<code class=property>flow</code>’</a>

   <li><a href="#absolute"><span class=secno>4. </span>Absolute positioning
    on top of a grid</a>
    <ul class=toc>
     <li><a href="#taking-elements-out-of-the-flow-with-pos"><span
      class=secno>4.1. </span>Taking elements out of the flow with ‘<code
      class=css>position: grid</code>’ or ‘<code class=css>display:
      grid</code>’</a>

     <li><a href="#stacking-elements-on-top-of-a-grid-grid-"><span
      class=secno>4.2. </span>Stacking elements on top of a grid: ‘<code
      class=property>grid-area</code>’ and ‘<code
      class=property>grid-auto</code>’</a>
    </ul>

   <li><a href="#styling-slots"><span class=secno>5. </span>Styling slots</a>

    <ul class=toc>
     <li><a href="#slot-pseudo"><span class=secno>5.1. </span>The ‘<code
      class=css>::slot()</code>’ pseudo-element</a>

     <li><a href="#the-blank-pseudo-element"><span class=secno>5.2.
      </span>The ‘<code class=css>::blank()</code>’ pseudo-element</a>

     <li><a href="#content"><span class=secno>5.3. </span>Slots and the
      ‘<code class=property>content</code>’ property</a>
    </ul>

   <li><a href="#region-based"><span class=secno>6. </span>Styling the
    contents of slots with ‘<code class=css>@region</code>’</a>

   <li><a href="#rendering-of-grid-elements"><span class=secno>7.
    </span>Rendering of grid elements</a>
    <ul class=toc>
     <li><a href="#vertical-alignment"><span class=secno>7.1. </span>Vertical
      alignment of the contents of slots</a>

     <li><a href="#paged"><span class=secno>7.2. </span>Breaking grid
      elements across pages or columns</a>

     <li><a href="#stacking-order"><span class=secno>7.3. </span>Stacking
      order</a>

     <li><a href="#floating-elements-inside-templates"><span class=secno>7.4.
      </span>Floating elements inside templates</a>
    </ul>

   <li><a href="#page-templates"><span class=secno>8. </span>Page-based grid
    templates</a>

   <li><a href="#chains"><span class=secno>9. </span>Chaining slots: the
    ‘<code class=property>chains</code>’ property</a>

   <li><a href="#history"><span class=secno>10. </span>History</a>
    <ul class=toc>
     <li><a href="#developing-a-model-of-declaring-using-st"><span
      class=secno>10.1. </span>Developing a model of declaring, using,
      styling and resizing grids</a>

     <li><a href="#syntax-features-and-levels"><span class=secno>10.2.
      </span>Syntax, features and levels</a>
      <ul class=toc>
       <li><a href="#named-vs-numbered-slots"><span class=secno>10.2.1.
        </span>Named vs numbered slots</a>

       <li><a href="#single-letter-names-vs-identifiers"><span
        class=secno>10.2.2. </span>Single letter names vs identifiers</a>

       <li><a href="#display"><span class=secno>10.2.3. </span>Extend
        ‘<code class=property>display</code>’ or add a grid property</a>

       <li><a href="#combining-columns-and-grids"><span class=secno>10.2.4.
        </span>Combining columns and grids</a>

       <li><a href="#shorthand-vs-single-property"><span class=secno>10.2.5.
        </span>Shorthand vs single property</a>

       <li><a href="#the-number-of-rows-and-columns"><span
        class=secno>10.2.6. </span>The number of rows and columns</a>

       <li><a href="#need-fr"><span class=secno>10.2.7. </span>‘<code
        class=css>*</code>’ vs ‘<code class=css>fr</code>’</a>

       <li><a href="#auto-add"><span class=secno>10.2.8. </span>Automatically
        add rows and columns</a>

       <li><a href="#rectangular-slots-vs-non-rectangular-slo"><span
        class=secno>10.2.9. </span>Rectangular slots vs non-rectangular
        slots</a>

       <li><a href="#chained"><span class=secno>10.2.10. </span>Chained
        slots</a>

       <li><a href="#page-grid"><span class=secno>10.2.11. </span>Page
        grids</a>

       <li><a href="#style-the-slots-pseudo-elements"><span
        class=secno>10.2.12. </span>Style the slots (pseudo-elements)</a>

       <li><a href="#select-after-pseudo"><span class=secno>10.2.13.
        </span>Style the contents of slots (region-based styling)</a>

       <li><a href="#orient-the-grid-with-writing-mode-vs-ori"><span
        class=secno>10.2.14. </span>Orient the grid with writing mode vs
        orient the slots</a>

       <li><a href="#indicating-the-default-slot-vs-at"><span
        class=secno>10.2.15. </span>Indicating the default slot (‘<code
        class=css>*</code>’ vs ‘<code class=css>@</code>’)</a>

       <li><a href="#abspos"><span class=secno>10.2.16. </span>Flowing vs
        absolutely positioning content in a grid</a>

       <li><a href="#use-the-pseudo-class-to-create-additiona"><span
        class=secno>10.2.17. </span>Use the pseudo-class to create additional
        slots</a>

       <li><a href="#names-for-edges"><span class=secno>10.2.18. </span>Names
        for edges</a>

       <li><a href="#position-from-the-right-and-bottom"><span
        class=secno>10.2.19. </span>Position from the right and bottom</a>

       <li><a href="#syntax-features-to-shorten-long-grid-spe"><span
        class=secno>10.2.20. </span>Syntax features to shorten long grid
        specifications</a>

       <li><a href="#fit-content-vs-auto-vshellip"><span class=secno>10.2.21.
        </span>‘<code class=css>fit-content</code>’ vs ‘<code
        class=css>auto</code>’ vs…</a>

       <li><a href="#vert-align"><span class=secno>10.2.22. </span>Vertical
        alignment inside slots</a>

       <li><a href="#horizontal-alignment-inside-slots"><span
        class=secno>10.2.23. </span>Horizontal alignment inside slots</a>

       <li><a href="#auto-margins-on-slots"><span class=secno>10.2.24.
        </span>Auto margins on slots</a>

       <li><a href="#page-floats"><span class=secno>10.2.25. </span>Page
        floats</a>

       <li><a href="#break-properties"><span class=secno>10.2.26.
        </span>Break-* properties</a>

       <li><a href="#next-same"><span class=secno>10.2.27. </span>Automatic
        placement of elements</a>

       <li><a href="#the-names-of-the-properties"><span class=secno>10.2.28.
        </span>The names of the properties</a>
      </ul>
    </ul>

   <li><a href="#conformance"><span class=secno>11. </span>Conformance</a>

   <li><a href="#changes"><span class=secno>12. </span>Changes</a>

   <li class=no-num><a href="#acknowledgments">Acknowledgments</a>

   <li class=no-num><a href="#references">References</a>

   <li class=no-num><a href="#index">Index</a>

   <li class=no-num><a href="#property-index">Property index</a>
  </ul>
  <!--end-toc-->
  <!--=================================================================-->

  <h2 id=introduction><span class=secno>1. </span>Introduction</h2>

  <p><em>(This section is not normative.)</em>

  <h3 id=summary-and-use-cases><span class=secno>1.1. </span>Summary and use
   cases</h3>

  <div class=sidefigure>
   <p><img alt="Image: four elements move to four slots in a template"
    longdesc=diagram.desc src=diagram.png>

   <p class=caption>Above: a typical Web page. Below: the underlying grid
    template. It has four slots, a, b, c and d and the grid template is
    defined by ‘<code class=css>grid: "a a a a a a a" "b c c c c d
    d"</code>’.
  </div>

  <p class=mtb>The styling of a Web page, a form or a graphical user
   interface can roughly be divided into two parts: (1) defining the overall
   “grid” of the page or window and (2) specifying the fonts, indents,
   colors, etc., of the text and other objects. The two are not completely
   separate, of course, because indenting or coloring a text influences the
   perceived grid as well. Nevertheless, when one separates the parts of a
   style that should change when the window gets bigger from the parts that
   stay the same, one often finds that the grid changes (room for a sidebar,
   extra navigation bar, big margins, larger images…), while fonts, colors,
   indents, numbering styles, and many other things don't have to change,
   until the size of the window becomes extreme.

  <p>The properties in this specification associate a layout grid with an
   element. Rather than rendering all descendants of an element in a single
   flow, they give an element multiple flows, called <a
   href="#slot">slots,</a> placed on an invisible grid by means of a
   <span>grid template.</span> The descendants are given a ‘<a
   href="#flow0"><code class=property>flow</code></a>’ property to
   designate the slot into which they flow.

  <p>Because layouts on the Web have to adapt to different window and paper
   sizes, the rows and columns of the grid can be made fixed or flexible in
   size.

  <p class=note>In some typographical traditions, the slots are called
   “<span class=index id=fields
   title="field (of a typographical grid)">fields</span>” or “<span
   class=index id=spatial-zones. title="spatial zone">spatial
   zones.</span>” Traditionally, also, all columns have the same width,
   called the “<span class=index id=module
   title="module (of a typographical grid)">module</span>” or “<span
   class=index id=unit title="unit (of a typographical grid)">unit</span>.”
   The horizontal lines of a grid that define the rows are sometimes called
   “<span class=index id=flow-lines. title="flow line">flow
   lines.</span>” Some traditions make the space between pieces of content
   an explicit part of the grid, some consider the space part of the content:
   Both styles are possible in CSS, the latter by using the ‘<a
   href="#margin"><code class=property>margin</code></a>’ property, the
   former by using the ‘<code class=css>.</code>’ symbol in a grid
   template.

  <p>The typical use cases for these properties include:

  <ul>
   <li>
    <p>Complex Web pages, with multiple navigation bars in fixed positions,
     areas for advertisements, etc.

   <li>
    <p>Complex forms, where the alignment of labels and form fields may be
     easier with the properties of this module than with the properties for
     tables and margins.

   <li>
    <p>GUIs, where buttons, toolbars, labels, icons, etc., are aligned in
     complex ways and have to stay aligned (and not wrap, for example) when
     the window is resized.

   <li>
    <p>Paged displays (e.g., printed media) where each page is divided in
     fixed areas for different kinds of content.

   <li>
    <p>Complex pages with multiple regions, where the style of the text does
     not only depend on the type of element it comes from, but also on the
     region it is displayed in.

   <li>Paged displays with complex running headers and footers, e.g., running
    headers that are in between parts of the page content, rather than at the
    edge of the page.
  </ul>

  <p>Once a grid template has been defined, it can also be used to position
   elements without adding them to a flow, typically for the purpose of
   making them overlap (somewhat similar to absolute positioning). For those
   elements, ‘<a href="#grid-area"><code
   class=property>grid-area</code></a>’, instead of ‘<a
   href="#flow0"><code class=property>flow</code></a>’, specifies the
   position; and ‘<a href="#z-index"><code
   class=property>z-index</code></a>’ determines the stacking order.

  <p>Template-based positioning makes many traditional uses of absolute
   positioning unnecessary. Like absolute positioning, grid templates are
   especially useful for aligning elements that don't have simple
   relationships in the source (parent-child, ancestor-descendant, immediate
   sibling). But in contrast to absolute positioning, the elements are not
   positioned with the help of horizontal and vertical coordinates, but by
   flowing them into a template that is very much like a table: The size and
   alignment of elements are governed implicitly by the rows and columns of
   the template, and can automatically adapt to the overall size of the
   element and to the content in each row and column.

  <div class=example>
   <p>In this example, the four children of an element are assigned to four
    slots (called a, b, c and d) in a 2×2 template. (All mark-up examples in
    this specification are HTML fragments, unless otherwise stated.)

   <div class=sidefigure>
    <p><img alt="Image: sample rendering" longdesc=aapje.desc src=aapje.png>

    <p class=caption>Each element occupies one slot. In this template, all
     slots have the same size.
   </div>

   <pre>
&lt;style type="text/css"&gt;
  dl { grid: "a b"
             "c d" }
  #sym1 { flow: a }
  #lab1 { flow: b }
  #sym2 { flow: c }
  #lab2 { flow: d }
&lt;/style&gt;
&lt;dl&gt;
  &lt;dt id=sym1&gt;A
  &lt;dd id=lab1&gt;A is een aapje
  &lt;dt id=sym2&gt;B
  &lt;dd id=lab2&gt;B is de bakker
&lt;/dl&gt;
</pre>

   <p><a href=ex-aapje.html>Try it out!</a> (Uses a JavaScript emulation in
    browsers that do not implement grid templates natively.)
  </div>

  <div class=example>
   <p>Templates can also help with device-independence. This example uses
    Media Queries <a href="#MEDIAQ"
    rel=biblioentry>[MEDIAQ]<!--{{MEDIAQ}}--></a> to change the overall
    layout of a page from 3-column layout for a wide screen to a 1-column
    layout for a narrow screen. It assumes the page has been marked-up with
    logical sections with IDs.

   <pre>
@media all
{
  body { grid: "a a a"
               "b c d" }
  #head { flow: a }
  #nav { flow: b }
  #adv { flow: c }
  #body { flow: d }
}
@media all and (max-width: 500px)
{
  body { grid: "a"
               "b"
               "c" }
  #head { flow: a }
  #nav { flow: b }
  #adv { display: none }
  #body { flow: c }
}
</pre>
  </div>

  <div class=example>
   <p>The slots in a grid do not overlap, unless with negative margins. Here
    is how the <a
    href="http://www.csszengarden.com/?cssfile=/026/026.css&amp;page=0">
    “zunflower” design</a> of the CSS Zen Garden could be done:

   <pre>
#container {grid: "A B C"}
#container::slot(A) {box-shadow: 0.5em 0.5em 0.5em; z-index: 1}
#container::slot(B) {box-shadow: 0.5em 0.5em 0.5em; margin-left: -2em}
#intro {flow: A}
#supportingText {flow: B}
#linkList {flow: C}
</pre>
  </div>

  <div class=example>
   <p>Template-based positioning borrows some concepts from table layout, in
    particular the idea of aligning elements in rows and columns, so that
    they constrain one another's size. But there are also differences. This
    example shows some of them. Assume this document fragment:

   <pre>
&lt;div class=group>
 &lt;div>aa aa aa aa aa aa&lt;/div>
 &lt;div>bbb&lt;/div>
&lt;/div>
</pre>

   <p>We can lay it out as three columns, as the following illustrations
    show. The style sheet would contain the following.

   <pre>
.group {display: table}
.group > div {display: table-cell}
</pre>

   <div class=figure>
    <p><img alt="[Three unequal cells]" longdesc=table1.desc src=table1.png>

    <p class=caption>Example of rendering with a table.
   </div>

   <p>We can also use a template, in which case the style sheet would contain
    this:

   <pre>
.group {grid: "a b c"}
.group > div {flow: a}
.group > div + div {flow: b}
.group > div + div + div {flow: c}
</pre>

   <p>By default, the table is as wide as needed to fit its contents. To make
    sure it is as wide as its cont
EE5A
aining block, we need to add

   <pre>.group {display: table; width: 100%}</pre>

   <p>That is not needed for the grid template, but, on the other hand, if we
    want the template to fit its contents, we would need to say so:

   <pre>.group {grid: "a b c"; width: auto}</pre>

   <p>(See <a href="#CSS3BOX"
    rel=biblioentry>[CSS3BOX]<!--{{!CSS3BOX}}--></a> for the definition of
    the ‘<a href="#width"><code class=property>width</code></a>’
    property.) The columns of the template are by default all the same size.
    The columns of the table satisfy certain constraints, but the exact size
    is not defined. We can make them all the same by adding a rule (see <a
    href="#CSS3TBL" rel=biblioentry>[CSS3TBL]<!--{{!CSS3TBL}}--></a>):

   <pre>.group {display: table; width: 100%; table-layout: fixed}</pre>

   <div class=figure>
    <p><img alt="[Three equal cells]" longdesc=table2.desc src=table2.png>

    <p class=caption>Example of rendering with equal columns.
   </div>

   <p>In both styles, we can set a column to a certain size:

   <pre>div.menu {width: 3em}</pre>

   <p>resp.,

   <pre>.group {grid: * * 3em  "a b c"}</pre>

   <div class=figure>
    <p><img alt="[Two equal cells, third is 3em wide]" longdesc=table3.desc
     src=table3.png>

    <p class=caption>Example of rendering with a fixed third column and the
     other two columns of equal width.
   </div>

   <p>If there is an unknown number of columns (children of the div.group
    element), the style sheet for the table model will automatically take
    them into account. The style sheet for the template model, however,
    creates a template of exactly three columns and can't handle tables with
    an unknown number of columns. The extra elements will be added into the
    default slot (in this case the ‘<code class=css>a</code>’ slot).

   <p>(However, extra columns or rows <em>will</em> be created if necessary
    to absolutely position elements. See the ‘<a href="#grid-area"><code
    class=property>grid-area</code></a>’ property.)

   <p>In both models, elements can have borders, but only in the table model
    can borders be collapsed, which makes setting borders easier in the table
    model:

   <pre>
.group {display: table; border-collapse: collapse}
.group > div {border: solid}
</pre>

   <p>resp.,

   <pre>
.group > div {border: solid; border-left: none}
.group > div:first-child {border-left: solid}
</pre>

   <p>In the template model, the order of the elements is explicit, and thus
    it is possible to reverse the order of the columns:

   <pre>
.group > div {flow: c}
.group > div + div {flow: b}
.group > div + div + div {flow: a}
</pre>

   <div class=figure>
    <p><img alt="[Different contents for the cells]" longdesc=table4.desc
     src=table4.png>

    <p class=caption>Example of rendering with the contents of the three
     columns reversed: the third element is shown in the first slot and the
     first element in the third slot.
   </div>

   <p>In the table model, the order of the rows and columns is given by the
    document source and thus can't be changed.
  </div>

  <div class=example>
   <p>This example shows a way to move notes to the end of a section.
    “Notes” in this example refers to elements in HTML with a class of
    “note”. A fragment of HTML such as

   <pre>
&lt;div class=section>
  &lt;p>The balubious coster of the fifth secter&lt;span
    class=note> The sixth secter coster is a difter
    manon.&lt;/span> of The Rollow Carpug mentizes a costernica.
  &lt;p>…
&lt;/div>
</pre>

   <p>with this style sheet

   <pre>
div.section {
    grid: "*"
          "F"}
.note {
    flow: F;
    content: counter(note) ".\A0" contents;
    counter-increment: note;
    font-size: smaller}
.note::before {
    content: counter(note);
    vertical-align: super;
    font-size: larger}
</pre>

   <p>results in a rendering similar to this:

   <div class=figure>
    <p><img
     alt="Same text, with the SPAN replaced by “(1)” and its content moved to the end."
     longdesc=footnotes.desc src=footnotes.png>

    <p class=caption>Rendering of a text with footnotes.
   </div>

   <p>The “Generated content for paged media” module <a href="#CSS3GCPM"
    rel=biblioentry>[CSS3GCPM]<!--{{CSS3GCPM}}--></a> is expected to define
    specific features for footnotes that are both easier and more powerful
    than this example.
  </div>

  <div class=example>
   <p>This example shows the use of <a class=index href="#chain."
    id=chained-regions title=chain>chained regions:</a> text from region 1
    continues in region 2, 3 and 4. And it shows how to use pseudo-elements
    to style text in a particular region: text in region 1 is bigger than in
    other regions.

   <div class=figure>
    <p><img alt="Image of a complex, 3-column layout"
     longdesc=regions-intro-rendering.desc src=regions-intro-rendering.png>

    <p class=caption>Example rendering
   </div>

   <p>We assume a document fragment similar to this:

   <pre>
&lt;div id=article>
  &lt;h1>Introduction&lt;/h1>
  &lt;p>&lt;img src="sunset" alt="">
  &lt;p>This is an example…

  &lt;h1>More Details&lt;/h1>
  &lt;p>This illustrates…
  &lt;p>Then, the example…
  &lt;p>Finally, this…
&lt;/div>
</pre>

   <p>The style sheet makes the DIV into a grid element with five regions,
    called A, *, b, c and d. The regions are grouped into two chains: region
    A on its own, and the chain consisting of *, b, c and d.

   <pre>
#article {
  <a class=index href="#grid" id=grid0>grid</a>: "A A c"
        "A A c"
        "* * c"
        "a b c";
  <a
    class=index href="#chains0" id=chains1>chains</a>: * a b c }
</pre>

   <p>The ‘<code class=css>*</code>’ is a special name. It indicates the
    <a href="#default-slot."><em>default slot,</em></a> the slot where
    content goes if it doesn't have an explicit ‘<a href="#flow0"><code
    class=property>flow</code></a>’ property. We could have used a normal
    letter and added an explicit ‘<a href="#flow0"><code
    class=property>flow</code></a>’ property to the children of the DIV,
    but by using * we don't have to. All children thus go into region * (and
    continue in a, b and c as needed). The IMG element goes into region A. We
    assume for simplicity that there is only one IMG element:

   <pre>#article img { flow: A }</pre>

   <p>The text in region * is bolder, larger and a different color than in
    the other regions. Also, an H1 that falls into this region is rendered
    differently from other H1s:

   <pre>
<a class=index href="#atregion" id=atregion0>@region</a> ::slot(*)
{
  * {
    font-weight: bold;
    color: #0C3D5F;
    font-size: larger }
  h1 {
    color: crimson;
    display: run-in }
}
</pre>

   <p>(For brevity, the example doesn't show the style rules to set the color
    and background, to make the text justified, add the left border to the
    second H1, etc.)

   <p>As the image shows, the text of the last paragraph isn't complete and
    presumably continues somewhere else, but that part is outside the scope
    of this example. In paged media, we could attach the grid template to a
    page instead of an element and let the text continue on the next page; we
    could also make slot c into a multi-column element so that the text forms
    additional columns to the right of current image (see <a href="#CSS3GCPM"
    rel=biblioentry>[CSS3GCPM]<!--{{CSS3GCPM}}--></a> for some ideas), or we
    could allow a scrollbar on slot c.
  </div>

  <div class=example>
   <p>This example shows two [three] ways to align the contents of a
    fixed-height paragraph to the bottom of the box:

   <dl>
    <dt>Method 1

    <dd>
     <pre>P {height: 20em; grid: "." "*" fit-content}</pre>

    <dt>Method 2

    <dd>
     <pre>P {height: 20em; grid: "*"}
P::slot(*) {vertical-align: bottom}</pre>

    <dt>[Method 3]

    <dd class=issue>[If <a class=index href="#vertical-align"
     id=vertical-align0>vertical-align</a> is generalized to apply to all
     blocks, rather than only to table cells, margin boxes and slots:]
     <pre>P {height: 20em; vertical-align: bottom}</pre>
   </dl>

   <p>However, the styles differ in case the content is taller than 20 em
    and overflows: the first style has a baseline-aligned content which will
    thus overflow <em>below</em> the element's box; the second example has
    bottom-aligned content, which will thus overflow <em>above</em> the
    element's box.
  </div>

  <div class=example>
   <p>This example (based on a challenge by Andrew Fedoniouk) shows how a
    grid template can be used to display six items in two rows of three.
    Assume the following document:

   <pre>
&lt;p&gt;
  &lt;span&gt;...&lt;/span&gt;
  &lt;span&gt;...&lt;/span&gt;
  &lt;span&gt;...&lt;/span&gt;
  &lt;span&gt;...&lt;/span&gt;
  &lt;span&gt;...&lt;/span&gt;
  &lt;span&gt;...&lt;/span&gt;
&lt;/p&gt;
</pre>

   <p>The simplest way to break this into two lines (or more) is to add a
    hard line break after the third SPAN: ‘<code
    class=css>span:nth-child(3)::after {content: "\A"; white-space:
    pre}</code>’. That works fine, unless the SPANs are inline blocks
    (‘<code class=css>span {display: inline-block}</code>’). Another way
    is to float all SPANs and add a ‘<code class=property>clear</code>’
    property on the fourth: ‘<code class=css>span {float: left}
    span:nth-child(4) {clear: left}</code>’. But if the SPANs have
    different heights or baselines, their vertical alignment will be
    different than if they were on the same line.

   <p>With a grid template, we can say that the P has not one, but two flows,
    a and b, the second one positioned below the first; and then we assign
    the fourth and subsequent SPANs to the “b” flow. (The others
    automatically go into the default, first flow.)

   <pre>
p {grid: "a" "b"}
span:nth-child(n+4) {flow: b}
</pre>

   <p>This almost works. There is just a subtle issue with the spaces between
    the SPANs. We moved the last three SPANs to flow b, but we have no way to
    move the spaces between them. They remain in the default (first) slot.
    (They collapse, as there is nothing left between them, so we don't
    actually see them anymore.) To get spaces between the SPANs in slot b, we
    need to generate new spaces:

   <pre>span:nth-child(n+4)::after {content: " "}</pre>

   <p class=issue>This space handling is not very intuitive. One might expect
    there to be a way to say “select everything from this element onward”
    or maybe a pseudo-element selector for the text between elements. Or a
    new property to specify different ways to handle the anonymous text
    inside a grid element. For the moment, there is no such thing.
    Suggestions are welcome.
  </div>

  <div class=example>
   <p>This example uses a <a href="#page-based-template"><em>page-based
    template</em></a> to create a running header that is not at the top of
    the page, but exactly in the middle. We need to define our own page
    template for this, because the predefined page template of <a
    href="#CSS3PAGE" rel=biblioentry>[CSS3PAGE]<!--{{CSS3PAGE}}--></a> only
    has margin boxes along the edge of the page.

   <pre>
@page {
  grid:
    "top-half"
    "running-header" 3em
    "bottom-half";
  chains: top-half bottom-half
}
::slot(running-header) {
  content: "My Magazine - page " counter(page) " - February 2013";
  text-align: center;
  <a
    class=index href="#vertical-align"
    id=vertical-align1>vertical-align</a>: middle;
  border: solid;
  margin: 1em 0;
}
</pre>

   <div class=figure>
    <p><img alt="Image: Example rendering" longdesc=page.desc src=page.png>

    <p class=caption>An example of a page rendered with the above page
     template. It has the “running header” with the page number right in
     the middle of the page.
   </div>
  </div>
  <!--=================================================================-->

  <h3 id=dependencies><span class=secno>1.2. </span>Dependencies on other
   modules</h3>

  <p>This CSS3 module depends on the following other CSS3 modules:

  <ul>
   <li><cite>CSS 2.1</cite> <a href="#CSS21"
    rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a> – <a
    href="http://www.w3.org/TR/CSS21/visuren.html#block-boxes"><dfn
    id=block-container>block container,</dfn></a> the property <dfn
    id=content0>content,</dfn> and the concept of <dfn
    id=stacking-context.>stacking context.</dfn>

   <li><cite>CSS syntax module</cite> <a href="#CSS3SYN"
    rel=biblioentry>[CSS3SYN]<!--{{!CSS3SYN}}--></a> – <dfn