csswg-drafts/css3-layout/new.html at eefa7de882f92aadef606c7510c2af36fe98476f · w3c/csswg-drafts · GitHub

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

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

  <title>CSS Grid Template Module</title>
  <link href="../default.css" rel=stylesheet type="text/css">
  <link href="http://www.w3.org/StyleSheets/TR/W3C-ED.css" rel=stylesheet
  type="text/css">

  <style type="text/css">
   .example .visible {border: thin dotted silver}

    /* delete this block when you've cleared out all the .replaceme elements */
    .replaceme {
      border: solid red;
      padding: 0 0.5em;
      margin: 0 0.1em;
      background: yellow;
      color: green;
    }
    .replaceme:before {
       content: "FIXME(";
       color: black;
    }
    .replaceme:after {
       content: ")";
       color: black;
    }
  </style>

 <body>
  <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>CSS Grid Template Module</h1>

   <h2 class="no-num no-toc" id=longstatus-date>Editor's Draft 23 February
    2012</h2>

   <dl>
    <dt>This version:

    <dd><a
     href="http://www.w3.org/TR/2012/ED-css3-grid-template-20120223/">http://www.w3.org/TR/2012/ED-css3-grid-template-20120223/</a>


    <dt>Latest version:

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


    <dt>Editor's draft:

    <dd><a
     href="http://dev.w3.org/csswg/css3-grid-template/">http://dev.w3.org/csswg/css3-grid-template/</a>


    <dt>Previous version:

    <dd><a href="http://www.w3.org/PreviousVersionURI">
     http://www.w3.org/PreviousVersionURI</a>

    <dt>Issues List:

    <dd><a
     href="http://www.w3.org/Style/CSS/Tracker/products/FIXME">http://www.w3.org/Style/CSS/Tracker/products/FIXME</a>


    <dt>Discussion:

    <dd><a
     href="http://lists.w3.org/Archives/Public/www-style/">www-style@w3.org</a>
     with subject line &ldquo;<kbd>[<!---->css3-grid-template] <var>&hellip;
     message topic &hellip;</var></kbd>&rdquo;

    <dt>Editors:

    <dd class=vcard><span class=fn>[editor1 name]</span>, <span
     class=org>[affiliation (opt.)]</span>, <span class=email>[email address
     (opt.)]</span>

    <dd class=vcard><span class=fn>[editor2 name]</span>, <span
     class=org>[affiliation (opt.)]</span>, <span class=email>[email address
     (opt.)]</span>
   </dl>
   <!--begin-copyright-->
   <p class=copyright><a
    href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
    rel=license>Copyright</a> &copy; 2012 <a
    href="http://www.w3.org/"><acronym
    title="World Wide Web Consortium">W3C</acronym></a><sup>&reg;</sup> (<a
    href="http://www.csail.mit.edu/"><acronym
    title="Massachusetts Institute of Technology">MIT</acronym></a>, <a
    href="http://www.ercim.eu/"><acronym
    title="European Research Consortium for Informatics and Mathematics">ERCIM</acronym></a>,
    <a href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. W3C <a
    href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
    <a
    href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a>
    and <a
    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>

  <p>CSS is a language for describing the rendering of structured documents
   (such as HTML and XML) on screen, on paper, in speech, etc. This module
   contains the features of CSS level&nbsp;3 relating to <var
   class=replaceme>DESCRIBE HERE</var>. It includes and extends the
   functionality of CSS level&nbsp;2 <a href="#CSS21"
   rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>, which builds on CSS
   level&nbsp;1 <a href="#CSS1" rel=biblioentry>[CSS1]<!--{{CSS1}}--></a>.
   The main extensions compared to level&nbsp;2 are <var
   class=replaceme>SUMMARIZE HERE</var>.

  <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-grid-template%5D%20PUT%20SUBJECT%20HERE">
   www-style@w3.org</a> (see <a
   href="http://www.w3.org/Mail/Request">instructions</a>) is preferred for
   discussion of this specification. When sending e-mail, please put the text
   &#8220;css3-grid-template&#8221; in the subject, preferably like this:
   &#8220;[<!---->css3-grid-template<!---->] <em>&hellip;summary of
   comment&hellip;</em>&#8221;

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

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

  <p>The following features are at risk: &hellip;

  <p class=issue>Leave for next level or different module: chaining regions,
   page templates, repeat (automatically add) columns and rows, style
   fragments of elements that are in a certain slot (region-based styling).

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

  <ul class=toc>
   <li><a href="#intro"><span class=secno>1. </span> Introduction</a>
    <ul class=toc>
     <li><a href="#grid-intro"><span class=secno>1.1. </span> Introduction to
      Grids</a>

     <li><a href="#background"><span class=secno>1.2. </span> Background</a>

     <li><a href="#space-adapt"><span class=secno>1.3. </span>Adapting
      Layouts to Available Space</a>

     <li><a href="#source-independence"><span class=secno>1.4. </span> Source
      Independence</a>

     <li><a href="#accessibility"><span class=secno>1.5. </span> A note on
      the accessibility of content reordering</a>

     <li><a href="#intro-layering"><span class=secno>1.6. </span> Grid
      Layering of Elements</a>

     <li><a href="#placement"><span class=secno>1.7. </span> Module
      interactions</a>

     <li><a href="#values"><span class=secno>1.8. </span> Values</a>
    </ul>

   <li><a href="#terminology"><span class=secno>2. </span> Core Concepts of
    the Grid</a>

   <li><a href="#display"><span class=secno>3. </span> Declaring a grid
    template</a>
    <ul class=toc>
     <li><a href="#grid-lines-tracks"><span class=secno>3.1. </span> Grid
      Lines and Tracks</a>

     <li><a href="#grid-templates"><span class=secno>3.2. </span> Declaring a
      template: &lsquo;<code class=property>grid-template</code>&rsquo;</a>

     <li><a href="#grid-column-sizes"><span class=secno>3.3. </span>
      Specifying the widths of columns: &lsquo;<code
      class=property>grid-columns</code>&rsquo;</a>

     <li><a href="#grid-row-sizes"><span class=secno>3.4. </span> Specifying
      the height of rows: &lsquo;<code
      class=property>grid-rows</code>&rsquo;</a>

     <li><a href="#grid-shorthand"><span class=secno>3.5. </span> The
      &lsquo;<code class=property>grid</code>&rsquo; shorthand property</a>

     <li><a href="#default-slots"><span class=secno>3.6. </span>Default
      slots</a>
      <ul class=toc>
       <li><a href="#fraction-values-fr"><span class=secno>3.6.1. </span>
        Fraction Values: &lsquo;<code class=property>fr</code>&rsquo;</a>

       <li><a href="#computed-values-grid-rows-and-columns"><span
        class=secno>3.6.2. </span> &lsquo;<code
        class=css>getComputedStyle()</code>&rsquo; values for &lsquo;<code
        class=property>grid-rows</code>&rsquo; and &lsquo;<code
        class=property>grid-columns</code>&rsquo;</a>
      </ul>

     <li><a href="#slot-sizes"><span class=secno>3.7. </span> Calculating the
      size of the grid</a>
    </ul>

   <li><a href="#positioning"><span class=secno>4. </span> Positioning
    content into a grid element</a>
    <ul class=toc>
     <li><a href="#flow"><span class=secno>4.1. </span> Flowing content into
      slots: &lsquo;<code class=property>flow</code>&rsquo;</a>

  
55E6
   <li><a href="#absolute-positioning-using-a-grid-grid-c"><span
      class=secno>4.2. </span> Absolute positioning using a grid:
      &lsquo;<code class=property>grid-column</code>&rsquo; and &lsquo;<code
      class=property>grid-row</code>&rsquo;</a>

     <li><a href="#grid-position"><span class=secno>4.3. </span> The
      &lsquo;<code class=property>grid-position</code>&rsquo; shorthand
      property</a>

     <li><a href="#float"><span class=secno>4.4. </span> Floating elements
      inside templates</a>
    </ul>

   <li><a href="#slot-pseudo"><span class=secno>5. </span>Styling named
    slots: the &lsquo;<code class=css>::slot()</code>&rsquo;
    pseudo-element</a>

   <li><a href="#slot-layout"><span class=secno>6. </span> Layout within a
    slot</a>
    <ul class=toc>
     <li><a href="#alignment"><span class=secno>6.1. </span> Alignment</a>

     <li><a href="#sizing"><span class=secno>6.2. </span> Calculating the
      Size of Grid Items</a>

     <li><a href="#vertical-alignment"><span class=secno>6.3. </span>
      Vertical alignment</a>
    </ul>

   <li><a href="#conformance"><span class=secno>7. </span> Conformance</a>
    <ul class=toc>
     <li><a href="#conventions"><span class=secno>7.1. </span> Document
      conventions</a>

     <li><a href="#conformance-classes"><span class=secno>7.2. </span>
      Conformance classes</a>

     <li><a href="#partial"><span class=secno>7.3. </span> Partial
      implementations</a>

     <li><a href="#experimental"><span class=secno>7.4. </span> Experimental
      implementations</a>

     <li><a href="#testing"><span class=secno>7.5. </span> Non-experimental
      implementations</a>

     <li><a href="#cr-exit-criteria"><span class=secno>7.6. </span> CR exit
      criteria</a>
    </ul>

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

   <li class=no-num><a href="#references"> References</a>
    <ul class=toc>
     <li class=no-num><a href="#normative-references"> Normative
      references</a>

     <li class=no-num><a href="#other-references"> Other references</a>
    </ul>

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

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

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

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

  <p class=issue>Merge introductory text, which right now is simply
   concatenated between Grid and Template.

  <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>Four slots, called a, b, c and d, each receive a part of
    a document
  </div>

  <p class=mtb>The styling of a Web page, a form or a graphical user
   interface can roughly be divided in 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 work by associating a <i>layout
   grid</i> with an element. Rather than letting an element lay out its
   descendants in their normal order as inline text or as blocks of text (the
   policies available in CSS level&nbsp;1), the policy defined in this module
   gives an element an invisible grid for aligning selected descendant
   elements.

  <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>The typical use cases for these properties include:

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

   <li>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>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.
  </ul>

  <p>Grid-based positioning is an alternative to absolute positioning, which,
   like absolute positioning, is 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 mapping them into slots in a table-like
   template. The relative size and alignment of elements is thus governed
   implicitly by the rows and columns of the template.

  <p>The mapping is done with the &lsquo;<code
   class=property>position</code>&rsquo; property, which specifies in this
   case into which slot of the template the element goes. The template itself
   is specified on the &lsquo;<a href="#grid-template"><code
   class=property>grid-template</code></a>&rsquo; property of some ancestor
   of the elements to remap.

  <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: "ab"
<!-- -->             "cd" }
<!-- -->  #sym1 { position: slot(a) }
<!-- -->  #lab1 { position: slot(b) }
<!-- -->  #sym2 { position: slot(c) }
<!-- -->  #lab2 { position: slot(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>
  </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: "aaa"
<!-- -->               "bcd" }
<!-- -->  #head { position: slot(a) }
<!-- -->  #nav  { position: slot(b) }
<!-- -->  #adv  { position: slot(c) }
<!-- -->  #body { position: slot(d) }
<!-- -->}
<!-- -->@media all and (max-width: 500px)
<!-- -->{
<!-- -->  body { grid: "a"
<!-- -->               "b"
<!-- -->               "c" }
<!-- -->  #head { position: slot(a) }
<!-- -->  #nav  { position: slot(b) }
<!-- -->  #adv  { display: none }
<!-- -->  #body { position: slot(c) }
<!-- -->}</pre>
  </div>

  <div class=example>
   <p>Elements can be positioned this way, but not made to 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 Zen Garden could be done:

   <pre>
<!-- -->#container { grid: "abc" }
<!-- -->#intro { position: (a); margin-right: -2em; box-shadow: 0.5em 0.5em 0.5em }
<!-- -->#supportingText { position: slot(b); box-shadow: 0.5em 0.5em 0.5em }
<!-- -->#linkList { position: slot(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 each other'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 class=menu>ccccc&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: "abc"}
<!-- -->.group > div {position: slot(a)}
<!-- -->.group > div + div {position: slot(b)}
<!-- -->.group > div + div + div {position: slot(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 containing block, we need to add

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

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

   <pre>.group {grid: "abc"; width: fit-content}</pre>

   <p>(See <a href="#CSS3BOX"
    rel=biblioentry>[CSS3BOX]<!--{{!CSS3BOX}}--></a> for the 
55E6
definition of
    the &lsquo;<code class=property>width</code>&rsquo; 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: "abc" * * 3em}</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 &lsquo;<code class=css>a</code>&rsquo;
    slot).

   <p>In both models, elements can have borders, but only in the table model
    can borders be collapsed, which makes setting borders a little 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 {position: slot(c)}
<!-- -->.group > div + div {position: slot(b)}
<!-- -->.group > div + div + div {position: slot(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>&hellip;
<!-- -->&lt;/div></pre>

   <p>with this style sheet

   <pre>
<!-- -->div.section {
<!-- -->    grid: "*" available
<!-- -->          "F" available}
<!-- -->.note {
<!-- -->    position: slot(F);
<!-- -->    content: counter(note) ".\A0" contents;
<!-- -->    counter-increment: note;
<!-- -->    font-size: smaller}
<!-- -->.note::before {
<!-- -->    content: counter(note);
<!-- -->    position: slot(*);
<!-- -->    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>
  </div>

  <h3 id=grid-intro><span class=secno>1.1. </span> Introduction to Grids</h3>

  <h3 id=background><span class=secno>1.2. </span> Background</h3>

  <div class=sidefigure> <img alt=FIXME class=figure
   src="images/basic-form.png">
   <p class=caption>Application layout example requiring horizontal and
    vertical alignment.</p>
  </div>

  <p>As websites evolved from simple documents into complex, interactive
   applications, tools for document layout, e.g. floats, were not necessarily
   well suited for application layout. By using a combination of tables,
   JavaScript, or careful measurements on floated elements, authors
   discovered workarounds to achieve desired layouts. Layouts that adapted to
   the available space were often brittle and resulted in counter-intuitive
   behavior as space became constrained. As an alternative, authors of many
   web applications opted for a fixed layout that cannot take advantage of
   changes in the available rendering space on a screen.

  <p>The layout capabilities of the Grid address these problems. The Grid
   provides a mechanism for authors to divide available space for layout into
   columns and rows using a set of predictable sizing behaviors. Authors can
   then precisely position and size the building block elements of their
   application by referencing the <a href="#grid-line">Grid Line</a>s between
   the columns and rows, or by defining and referencing a <a
   href="#grid-cell">Grid Slot</a>, which is a rectangular space covering an
   intersection of columns and rows. Figure 1 illustrates a basic layout
   which can be achieved with the Grid.

  <h3 id=space-adapt><span class=secno>1.3. </span>Adapting Layouts to
   Available Space</h3>

  <div class=sidefigure>
   <p><img alt=FIXME src="images/game-smaller.png">

   <p class=caption>Five grid items arranged according to content size and
    available space.</p>
  </div>

  <div class=sidefigure>
   <p><img alt=FIXME src="images/game-larger.png">

   <p class=caption>Growth in the grid due to an increase in available space.</p>
  </div>

  <p>The <a href="#grid-element1"><i>grid element</i></a> can be used to
   intelligently reflow elements within a webpage. Figure 2 represents a game
   with five major areas in the layout: the game title, stats area, game
   board, score area, and control area. The author's intent is to divide the
   space for the game such that:

  <ul>
   <li>The stats area always appears immediately under the game title.

   <li>The game board appears to the right of the stats and title.

   <li>The top of the game title and the game board should always align.

   <li>The bottom of the game board and the stats area align when the game
    has reached its minimum height, but otherwise the game board will stretch
    to take advantage of all the screen real-estate available to it.

   <li>The score area should align into the column created by the game and
    stats area, while the controls are centered under the board.
  </ul>

  <p>As an alternative to using script to control the absolute position,
   width, and height of all elements, the author can use the <a
   href="#grid-element1"><i>grid element</i></a>, as shown in Figure 3. The
   following example shows how an author might achieve all the sizing,
   placement, and alignment rules declaratively.

  <p>Note that there are multiple ways to specify the structure of the <a
   href="#grid-element">Grid</a> and to position and size <i>grid items</i>,
   each optimized for different scenarios. This example illustrates one that
   an author may use to define the position and space for each <i>grid
   item</i> using the &lsquo;<a href="#grid-rows"><code
   class=property>grid-rows</code></a>&rsquo; and &lsquo;<a
   href="#grid-columns"><code class=property>grid-columns</code></a>&rsquo;
   properties of the <a href="#grid-element1"><i>grid element</i></a>, and
   the &lsquo;<a href="#grid-row"><code
   class=property>grid-row</code></a>&rsquo; and &lsquo;<a
   href="#grid-column"><code class=property>grid-column</code></a>&rsquo;
   properties on each <i>grid item</i>.

  <pre class=example>&lt;style type="text/css"&gt;
    #grid {
        display: grid;

        /* Two columns: the first sized to content, the second receives the remaining space,   */
        /* but is never smaller than the minimum size of the board or the game controls, which */
        /* occupy this column. */
        grid-columns: auto minmax(min-content, 1fr);

        /* Three rows: the first and last sized to content, the middle row receives the remaining */
        /* space, but is never smaller than the minimum height of the board or stats areas.       */
        grid-rows: auto minmax(min-content, 1fr) auto
    }

    /* Each part of the game is positioned between grid lines by referencing the starting grid line and */
    /* then specifying, if more than one, the number of rows or columns spanned to determine the ending */
    /* grid line, which establishes bounds for the part. */
    #title    { grid-column: 1; grid-row: 1 }
    #score    { grid-column: 1; grid-row: 3 }
    #stats    { grid-column: 1; grid-row: 2; grid-row-align: start }
    #board    { grid-column: 2; grid-row: 1; grid-row-span: 2 }
    #controls { grid-column: 2; grid-row: 3; grid-column-align: center }
&lt;/style&gt;

&lt;div id="grid"&gt;
    &lt;div id="title"&gt;Game Title&lt;/div&gt;
    &lt;div id="score"&gt;Score&lt;/div&gt;
    &lt;div id="stats"&gt;Stats&lt;/div&gt;
    &lt;div id="board"&gt;Board&lt;/div&gt;
    &lt;div id="controls"&gt;Controls&lt;/div&gt;
&lt;/div&gt;</pre>

  <h3 id=source-independence><span class=secno>1.4. </span> Source
   Independence</h3>

  <div class=sidefigure>
   <p><img alt=FIXME src="images/game-portrait.png">

   <p class=caption>An arrangement suitable for "portrait" orientation.</p>
  </div>

  <div class=sidefigure>
   <p><img alt=FIXME src="images/game-landscape.png">

   <p class=caption>An arrangement suitable for "landscape" orientation.</p>
  </div>

  <p>Continuing the prior example, the author also wants the game to adapt to
   the space available on traditional computer monitors, handheld devices, or
   tablet computers. Also, the game should optimize the placement of the
   components when viewed either in landscape or portrait orientation
   (Figures 4 and 5). By combining the CSS markup for the <a
   href="#grid-element1"><i>grid element</i></a> with <a
   href="http://www.w3.org/TR/css3-mediaqueries/">media queries</a> <a
   href="#MEDIAQ" rel=biblioentry>[MEDIAQ]<!--{{MEDIAQ}}--></a>, the author
   is able to use the same semantic markup, but rearranged independent of its
   source order, to achieve the desired layout in both orientations.

  <p>The following example leverages the <a
   href="#grid-element">Grid</a>&lsquo;<code class=css>s ability to name the
   space which will be occupied by a <i>grid item</i>. This allows the author
   to avoid rewriting rules for <i>grid items</i> as the <a
   href="#grid-element">Grid</a></code>&rsquo;s definition changes.

  <pre class=example>&lt;style type="text/css"&gt;
    @media (orientation: portrait) {
        #grid {
            display: grid;

            /* The rows, columns and cells of the grid are defined visually using the grid-template property.        */
            /* Each string is a row, and each letter a cell.  The max number of letters in any one string determines */
            /* the number of columns. */
            grid-template: "ta"
                           "sa"
                           "bb"
                           "cc";

            /* Columns and rows created with the template property can be assigned a sizing function with the */
            /* grid-columns and grid-rows properties. */
            grid-columns: auto minmax(min-content, 1fr);
            grid-rows: auto auto minmax(min-content, 1fr) auto
        }
    }

    @media (orientation: landscape) {
        #grid {
            display: grid;

            /* Again the template property defines cells of the same name, but this time positioned differently */
            /* to better suit a landscape orientation. */
            grid-template: "tb"
                           "ab"
                           "sc";

            grid-columns: auto minmax(min-content, 1fr);
            grid-rows: auto minmax(min-content, 1fr) auto
        }
    }

    /* The grid-cell property places a grid item into named region (cell) of the grid. */
    #title    { grid-cell: "t" }
    #score    { grid-cell: "s" }
    #stats    { grid-cell: "a" }
    #board    { grid-cell: "b" }
    #controls { grid-cell: "c" }
&lt;/style&gt;

&lt;div id="grid"&gt;
    &lt;div id="title"&gt;Game Title&lt;/div&gt;
    &lt;div id="score"&gt;Score&lt;/div&gt;
    &lt;div id="stats"&gt;Stats&lt;/div&gt;
    &lt;div id="board"&gt;Board&lt;/div&gt;
    &lt;div id="controls"&gt;Controls&lt;/div&gt;
&lt;/div&gt;</pre>

  <h3 id=accessibility><span class=secno>1.5. </span> A note on the
   accessibility of content reordering</h3>

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

  <p>The facilities in this specification allow elements from a document to
   be displayed in a visual order that is to a large extent independent of
   the order in the document. That may have both positive and negative
   effects on accessibility. The positive aspect is that it allows the
   content in the document to be kept in logical order, so that the document
   is as functional as possible without the style sheet and on media where
   the style sheet doesn't apply. A negative aspect is that a document that
   has a defined tab order (the order in which elements get the focus when
   the tab-key is pressed) will show on the screen with a tab order unrelated
   to the visual order. It may be necessary to use the keyboard control
   features of the CSS Basic User Interface module <a href="#CSS3UI"
   rel=biblioentry>[CSS3UI]<!--{{CSS3UI}}--></a> to ensure that the tab
   navigation follows the visual order, or to refrain from positioning
   semantically related elements in different parts of a template.

  <p>The following two requirements from the Web Content Accessibility
   Guidelines (WCAG) 2.0 <a href="#WCAG20"
   rel=biblioentry>[WCAG20]<!--{{WCAG20}}--></a> are particularly relevant.
   See that specification for more information.

  <blockquote>
   <p><a
    href="http://www.w3.org/TR/2008/REC-WCAG20-20081211/#content-structure-separation-sequence"><strong>1.3.2
    Meaningful Sequence:</strong></a> When the sequence in which content is
    presented affects its meaning, a <a
    href="http://www.w3.org/TR/2008/REC-WCAG20-20081211/#correct-reading-sequencedef">correct
    reading sequence</a> can be <a
    href="http://www.w3.org/TR/2008/REC-WCAG20-20081211/#programmaticallydetermineddef     ">programmatically
    determined.</a> (Level A)
  </blockquote>

  <blockquote>
   <p><a
    href="http://www.w3.org/TR/2008/REC-WCAG20-20081211/#navigation-mechanisms-focus-order"><strong>2.4.3
    Focus Order:</strong></a> If a <a
    href="http://www.w3.org/TR/2008/REC-WCAG20-20081211/#webpagedef">Web
    page</a> can be <a
    href="http://www.w3.org/TR/2008/REC-WCAG20-20081211/#nav-seqdef">navigated
    sequentially</a> and the navigation sequences affect meaning or
    operation, focusable components receive focus in an order that preserves
    meaning and operability. (Level A)
  </blockquote>

  <h3 id=intro-layering><span class=secno>1.6. </span> Grid Layering of
   Elements</h3>

  <div class=sidefigure>
   <p><img alt=FIXME src="images/control-layering-and-alignment.png">

   <p class=caption>A control composed of layered HTML elements.</p>
  </div>

  <p>In the example shown in Figure 6, the author is creating a custom slider
   control. The control has six parts. The lower and upper labels align to
   the left and right edges of the control. The track of the slider spans the
   area between the labels. The lower and upper fill parts touch beneath the
   thumb, and the thumb is a fixed width and height that can be moved along
   the track by updating the two fraction-sized columns.

  <p>Prior to the <a href="#grid-element1"><i>grid element</i></a>, the
   author would have likely used absolute positioning to control the top and
   left coordinates, along with the width and height of each HTML element
   that comprises the control. By leveraging the <a
   href="#grid-element1"><i>grid element</i></a>, the author can instead
   limit script usage to handling mouse events on the thumb, which snaps to
   various positions along the track as the &lsquo;<a
   href="#grid-columns"><code class=property>grid-columns</code></a>&rsquo;
   property of the <a href="#grid-element1"><i>grid element</i></a> is
   updated.

  <pre class=example>&lt;style type="text/css"&gt;
    #grid {
        display: grid;

        /* The grid-columns and rows properties also support naming grid lines which can then be used */
        /* to position grid items.  The line names are assigned on either side of a column or row     */
        /* sizing function where the line would logically exist. */
        grid-columns:
            "start"        auto
            "track-start"  0.5fr
            "thumb-start"  auto
            "fill-split"   auto
            "thumb-end"    0.5fr
            "track-end"    auto
            "end";
    }

    /* Grid-column and grid-row accept a starting and optional endling line.  Below the lines are referred to by name. */
    /* Beyond any semantic advantage, the names also allow the author to avoid renumbering the grid-row and column     */
    /* properties of the grid items.  This is similar to the concept demonstrated in the prior example with the        */
    /* grid-template property during orientation changes, but grid lines can also work with layered grid items that    */
    /* have overlapping cells of different shapes like the thumb and track parts in this example. */
    #lower-label { grid-column: "start" }
    #track       { grid-column: "track-start" "track-end"; grid-row-align: center }
    #upper-label { grid-column: "track-end"; }

    /* Fill parts are drawn above the track so set z-index to 5. */
    #lower-fill  { grid-column: "track-start" "fill-split"; grid-row-align: center; z-index: 5 }
    #upper-fill  { grid-column: "fill-split" "track-end"; grid-row-align: center; z-index: 5 }

    /* Thumb is the topmost part; assign it the highest z-index value. */
    #thumb       { grid-column: "thumb-start" "thumb-end"; z-index: 10 }
&lt;/style&gt;

&lt;div id="grid"&gt;
    &lt;div id="lower-label"&gt;Lower Label&lt;/div&gt;
    &lt;div id="upper-label"&gt;Upper Label&lt;/div&gt;
    &lt;div id="track"&gt;Track&lt;/div&gt;
    &lt;div id="lower-fill"&gt;Lower Fill&lt;/div&gt;
    &lt;div id="upper-fill"&gt;Upper Fill&lt;/div&gt;
    &lt;div id="thumb"&gt;Thumb&lt;/div&gt;
&lt;/div&gt;</pre>

  <h3 id=placement><span class=secno>1.7. </span> Module interactions</h3>

  <p class=replaceme>Explain, normatively, how this module affects the
   definition of CSS.

  <p>This module replaces and extends the <var class=replaceme>SUMMARIZE
   HERE</var> features defined in <a href="#CSS21"
   rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a> sections <var
   class=replaceme>W.X and Y.Z</var>.

  <p>See <a href="#CSS3PAGE"
   rel=biblioentry>[CSS3PAGE]<!--{{!CSS3PAGE}}--></a> for the definition of
   <a href="http://www.w3.org/TR/css3-multicol/#multi-column-element"><dfn
   id=multi-column-element.>multi-column element.</dfn></a>

  <p><a href="#CSS3-WRITING-MODES"
   rel=biblioentry>[CSS3-WRITING-MODES]<!--{{!CSS3-WRITING-MODES}}--></a>
   defines the <dfn id=writing-mode>writing-mode</dfn> property, which
   defines when elements have a <dfn id=vertical-writing-mode>vertical
   writing mode</dfn> (text lines are vertical) or a <dfn
   id=horizontal-writing-mode>horizontal writing mode</dfn> (text lines are
   horizontal). For brevity, we refer to the former as a <dfn
   id=vertical-element title="vertical|vertical element">vertical
   element</dfn> and to the latter as a <dfn id=horizontal-element.
   title="horizontal|horizontal element">horizontal element.</dfn>

  <p><a href="#CSS3BOX" rel=biblioentry>[CSS3BOX]<!--{{!CSS3BOX}}--></a>
   defines the intrinsic sizes of boxes.

  <p>Following <a href="#CSS3-WRITING-MODES"
   rel=biblioentry>[CSS3-WRITING-MODES]<!--{{!CSS3-WRITING-MODES}}--></a> and
   <a href="#CSS3BOX" rel=biblioentry>[CSS3BOX]<!--{{!CSS3BOX}}--></a>, we
   define the <dfn id=inline-dimension>inline dimension</dfn> of a box,
   element or slot as meaning either its width or height, depending on
   whether it is <a href="#horizontal-element."><em>horizontal</em></a> or <a
   href="#vertical-element"><em>vertical,</em></a> respectively. And
   likewise: the <dfn id=block-dimension>block dimension</dfn> of a box,
   element or slot <em>at a given inline dimension</em> is its size in the
   perpendicular dimension.

  <p>&lsquo;<code class=property>Direction</code>&rsquo; is defined in <a
   href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>.

  <h3 id=values><span class=secno>1.8. </span> Values</h3>

  <p>This specification follows the <a
   href="http://www.w3.org/TR/CSS21/about.html#property-defs">CSS property
   definition conventions</a> from <a href="#CSS21"
   rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>. Value types not defined in
   this specification are defined in CSS Level 2 Revision 1 <a
   href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>. Other CSS
   modules may expand the definitions of these value types: for example <a
   href="#CSS3COLOR" rel=biblioentry>[CSS3COLOR]<!--{{CSS3COLOR}}--></a>,
   when combined with this module, expands the definition of the
   &lt;color&gt; value type as used in this specification.

  <p>In addition to the property-specific values listed in their definitions,
   all properties defined in this specification also accept the <a
   href="http://www.w3.org/TR/CSS21/cascade.html#value-def-inherit">inherit</a>
   keyword as their property value. For readability it has not been repeated
   explicitly.

  <h2 id=terminology><span class=secno>2. </span> Core Concepts of the Grid</h2>

  <div class=sidefigure> <img alt=FIXME class=figure
   src="images/grid-concepts.png">
   <p class=caption>A diagram illustrating the relationship between the <a
    href="#grid-element1"><i>grid element</i></a> and its Tracks, Lines,
    Cells and Items.</p>