csswg-drafts/css-template/new.src.html at 7a88b495173d16e8b2a0ad41924099aeb957f70c · 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 http-equiv="Content-Type" content="text/html; charset=utf-8">
  <title>CSS Grid Template Module</title>
  <link rel="stylesheet" type="text/css" href="../default.css">
  <link rel="stylesheet" type="text/css"
        href="http://www.w3.org/StyleSheets/TR/W3C-[STATUS].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>
</head>

<div class="head">
<!--logo-->

<h1>CSS Grid Template Module</h1>

<h2 class="no-num no-toc">[LONGSTATUS] [DATE]</h2>
<dl>
  <dt>This version:
    <dd><a href="[VERSION]">http://www.w3.org/TR/[YEAR]/ED-css3-grid-template-[CDATE]/</a>

  <dt>Latest version:
    <dd><a href="http://www.w3.org/TR/[SHORTNAME]/">http://www.w3.org/TR/[SHORTNAME]/</a>

  <dt>Editor's draft:
    <dd><a href="http://dev.w3.org/csswg/[SHORTNAME]/">http://dev.w3.org/csswg/[SHORTNAME]/</a>

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

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

  <dt>Discussion:</dt>
    <dd><a href="http://lists.w3.org/Archives/Public/www-style/">www-style@w3.org</a> with subject line &ldquo;<kbd>[<!---->[SHORTNAME]] <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=email>[email address (opt.)]</span>
</dl>

<!--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 [[!CSS21]],
  which builds on CSS level&nbsp;1 [[CSS1]].
  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>

<!--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>

<!--toc-->


<h2 id="intro">
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.</p>
  
  <div class=sidefigure>
    <p><img src="diagram.png" alt="Image: four elements move to four slots
    in a template" longdesc="diagram.desc">
    
    <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 'position' property, which specifies
  in this case into which slot of the template the element goes. The
  template itself is specified on the 'grid-template' 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 src="aapje.png" alt="Image: sample rendering" longdesc="aapje.desc">
      <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 [[MEDIAQ]] 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 src="table1.png" alt="[Three unequal cells]" longdesc="table1.desc">
      <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 [[!CSS3BOX]] for the definition of the 'width' 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
    [[!CSS3TBL]]):
    
    <pre>.group {display: table; width: 100%; table-layout: fixed}</pre>

    <div class=figure>
      <p><img src="table2.png" alt="[Three equal cells]" longdesc="table2.desc">
      <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 src="table3.png" alt="[Two equal cells, third is 3em wide]"
      longdesc="table3.desc">
    
      <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 ''a'' 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 src="table4.png" alt="[Different contents for the cells]"
      longdesc="table4.desc">
    
      <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 src="footnotes.png" alt="Same text, with the SPAN replaced by
      “(1)” and its content moved to the end." longdesc="footnotes.desc">
      <p class=caption>Rendering of a text with footnotes.
    </div>
  </div>

<h3 id="grid-intro">
Introduction to Grids</h3>
    
<h3 id="background">
Background</h3>
            
  <div class="sidefigure">
    <img class="figure" alt="FIXME" 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">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 <i>grid element</i> 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>
    <li>The game board appears to the right of the stats and title.</li>
    <li>The top of the game title and the game board should always align.</li>
    <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>
    <li>The score area should align into the column created by the game and stats area, while the controls are centered under the board.</li>
  </ul> 
  
  <p>As an alternative to using script to control the absolute position,
  width, and height of all elements, the author can use the
  <i>grid element</i>, 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
  'grid-rows' and 'grid-columns' properties of the
  <i>grid element</i>, 
  and the 'grid-row' and 'grid-column' properties on each
  <i>grid item</i>.
  </p>
  
  <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">
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
  <i>grid element</i> with
  <a href="http://www.w3.org/TR/css3-mediaqueries/">media queries</a>
  [[MEDIAQ]], 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>'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>'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>
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 [[CSS3UI]] 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 [[WCAG20]] 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">
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 <i>grid element</i>, 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 <i>grid element</i>,
  the author can instead limit script usage to handling mouse events on the
  thumb,  which snaps to various positions along the track as the
  'grid-columns' property of the <i>grid element</i> 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">
Module interactions</h3>

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

  <p>This module replaces and extends the <var class="replaceme">SUMMARIZE HERE</var>
  features defined in [[!CSS21]] sections <var class="replaceme">W.X and Y.Z</var>.


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

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

  <p>[[!CSS3BOX]] defines the intrinsic sizes of boxes.

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

  <p>'Direction' is defined in [[!CSS21]].


<h3 id="values">
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 [[!CSS21]]. Value types not defined in
  this specification are defined in CSS Level 2 Revision 1 [[!CSS21]].
  Other CSS modules may expand the definitions of these value types: for
  example [[CSS3COLOR]], when combined with this module, expands the
  definition of the &lt;color&gt; value type as used in this specification.</p>
  
  <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">
Core Concepts of the Grid</h2>

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

  <p>A <dfn id="grid-element">grid element</dfn> is declared in markup by
  setting the display property of an element to ''grid'' or ''inline-grid''.
  <!--
  Child elements of the Grid are termed <a href="#grid-item">grid items</a>
  and may be positioned and sized by the <i>grid element</i>
  by leveraging the following logical concepts:

  <ul>
      <li><a href="#grid-track">Grid Track</a>s</li>
      <li><a href="#grid-line">Grid Line</a>s</li>
      <li><a href="#slot">Slot</a>s</li>
  </ul>
  -->
  
  <p>
  Figure 7 illustrates the relationship between these concepts and the markup
  in the subsections that follow produce the result shown in the figure.
  </p>

  <p><dfn>Grid track</dfn> is the generic name in this specification
  for a row or column in a grid. Grid tracks are defined with the
  properties 'grid-rows' (to define rows) and 'grid-columns' (to
  define columns) on the <i>grid element</i>. Each track is defined by
  declaring a list of sizes, one size for each track. <!-- Tracks
  define the space between <a href="#grid-line">Grid Line</a>s. -->

  <pre class="example">&lt;style type="text/css"&gt;
#grid { 
    grid-columns: 150px 1fr; /* two columns */
    grid-rows: 50px 1fr 50px /* three rows  */
}
&lt;/style&gt;</pre>

  <p><dfn>Grid line</dfn> is the term in this specification for the
  vertical edges of columns and the horizontal edges of rows. If there
  are <var>N</var> columns, their edges are numbered from 1 (the
  leftmost edge of the first column) to <var>N</var>+1 (the rightmost
  edge of the last column. Analogously for the edges of the rows.

  <!--
  <p>The following two examples create three column <i>Grid Lines</i>
  and four row <i>Grid Lines</i>.  The first example demonstrates how
  an author would refer to the <a href="#grid-line">Grid Line</a>s
  using <a href="#grid-line">Grid Line</a> numbers.  The second example
  uses explicitly named <a href="#grid-line">Grid Line</a>s.

  <pre class="example">&lt;style type="text/css"&gt;
  #grid { 
      display: grid; 
      grid-columns: 150px 1fr;
      grid-rows: 50px 1fr 50px
  }

  #item1 { grid-column: 2; grid-row: 1 4 }
&lt;/style&gt;</pre>

  <pre class="example">&lt;style type="text/css"&gt;
  /* equivalent layout to the prior example, but using named lines */
  #grid { 
      display: grid; 
      grid-columns: 150px "item1-start" 1fr "item1-end";
      grid-rows: "item1-start" 50px 1fr 50px "item1-end"
  }

  #item1 { 
      grid-column: "item1-start" "item1-end"; 
      grid-row: "item1-start" "item1-end" 
  }
&lt;/style&gt;</pre>
  -->

  <p>A <dfn>grid cell</dfn> is the intersection of a row and a
  column. A grid with <var>N</var> columns and <var>M</var> rows has
  <var>N</var>*<var>M</var> cells.

  <!-- The term “slot” is defined under 'grid-template' -->

  <!--
  are the logical space used to lay out
  one or more <i>grid items</i>.
  <i>slots</i> can be defined explicitly using the 'grid-template'
  property, or anonymously by referencing a region of the Grid using the
  'grid-row' and 'grid-column' properties on a <i>grid item</i>.

  <p>Whether a <i>slot</i> is created explicitly or implicitly, there
  is no difference in the layout or drawing order of the
  <i>grid items</i> which are associated with that
  <i>slot</i>.
  <pre class="example">&lt;style type="text/css"&gt;
/* using the template syntax */
#grid  { 
    display: grid; 
    grid-template: "ad"
                   "bd"
                   "cd";
    grid-columns: 150px 1fr;
    grid-rows: 50px 1fr 50px
}

#item2 { position: slot(b) }
#item3 { position: slot(b) }

/* Align items 2 and 3 at different points in the slot "b".  */
/* By default, Grid Items are stretched to fit their slot    */
/* and these items would layer one over the other. */
#item2 { grid-row-align: start }
#item3 { grid-column-align: end; grid-row-align: end }&lt;/style&gt;</pre>
  -->

<h2 id=display>
Declaring a grid template</h2>

  <p>An element is a <dfn>grid element</dfn> (i.e., it defines a grid
  for its descendants) if its 'display' value is ''grid'' or ''inline-grid''.

  <p>The <dfn>grid ancestor</dfn> of an element is the nearest
  ancestor that is a grid element.

  <table class="propdef">
    <tr>
      <th>Name:
      <td><dfn>display</dfn>
    <tr>
      <th><a href="#values">Value</a>:
      <td>&hellip; | grid | inline-grid
  </table>
  
  <p>This module adds the ''grid'' and ''inline-grid'' values to the 'display'
  property [[CSS21]], as defined below:
  
  <dl>
    <dt><dfn id="value-def-display--grid">''grid''</dfn></dt>
    <dd>A value of grid causes an element to display as a block-level
    <i>grid element</i>.</dd>
  
    <dt><dfn id="value-def-display-inline-grid">''inline-grid''</dfn></dt>
    <dd>A value of inline-grid causes an element to display as an
    inline-level <i>grid element</i>.</dd>
  </dl>
  
<div class="issue">
  <p>Should grid elements be created automatically without using
  'display'? On the one hand, this (a) is not consistent with how flex
  boxes are created and (b) could create some confusing dynamics
  (e.g., setting ''display: table'' or 'display: flexbox' removes any
  grid, but setting 'display: table-cell' or 'display: list-item'
  keeps the grid); but (1) requires only one instead of two properties
  to create a grid element, (2) allows other block container elements
  (such as table cells, table captions, list items, flex
  items&hellip;) to contain a grid, without extra keywords for
  'display' ('table-cell-grid', 'list-item-grid'&hellip;), and (3) is
  consistent with how <a
  href="http://www.w3.org/TR/css3-multicol/#multi-column-element"
  >multicolumn elements</a> are created.

  <p>Proposed text:
  
  <p>An element is a <dfn>grid element</dfn> (i.e., it defines a grid
  for its descendants) if it generates a
  a <a href="http://www.w3.org/TR/CSS21/visuren.html#block-boxes" >block
  container box</a> [[!CSS21]] and one or more of the following is true:
  
  <ul>
  <li>The element's 'grid-template' is not ''none''.
  <li>The element's 'grid-rows' is not ''auto''.
  <li>The element's 'grid-columns' is not ''auto''.
  </ul>
  
  <p>These properties are defined below.
</div>

  <p class=note>Block containers are, informally, elements that can have
  block elements as children, such as blocks, inline blocks or table
  cells, but not inline elements or replaced elements.
  
  <p>The <dfn>number of columns</dfn> of a <span>grid element</span>
  is defined as follows:

  <ol>
    <li>If 'grid-template' is not 'none', it determines the number of
    columns.

    <li>Otherwise, if 'grid-columns' is not 'auto', the number of
    columns is equal to the number of <var>&lt;track-size&gt;</var>
    values in 'grid-columns'.

    <li>Otherwise, the grid has one column.
  </ol>

  <p>The <dfn>number of rows</dfn> of a <span>grid element</span> is
  defined as follows:

  <ol>
    <li>If 'grid-template' is not 'none', it determines the number of
    rows.

    <li>Otherwise, if 'grid-rows' is not 'auto', the number of rows is
    equal to the number of <var>&lt;track-size&gt;</var> values in
    'grid-rows'.

    <li>Otherwise, the grid has one row.
  </ol>

  <div class=issue>
  <p>Alternative definition:

  <p>The number of columns is the number of
  <var>&lt;track-size&gt;</var> values in 'grid-columns' or the number
  of columns in 'grid-template', whichever is larger. (A value of
  ''none'' in this case means zero columns.)

  <p>The number of rows is the number of <var>&lt;track-size&gt;</var>
  values in 'grid-rows' or the number of rows in 'grid-template',
  whichever is larger.  (A value of ''none'' in this case means zero
  rows.)
  </div>

  <p class=issue>What if an element has both 'columns' and
  'grid-template', is it a grid element or a column element? (or do the
  columns apply to the default slot?)
  
  <p class=issue>Use 'fr' unit (as in css3-grid-align) instead of '*' (as
  in css3-layout).


<h3 id="grid-lines-tracks">
Grid Lines and Tracks</h3>

  <div class="sidefigure">
      <img class="figure" alt="Image: Grid Lines." src="images/grid-lines.png">
      <p class="caption">Grid Lines.</p>
  </div>

  <p><i>grid element</i>s use
  <a href="#grid-line">Grid Line</a>s to divide their space.
  There are two sets of <a href="#grid-line">Grid Line</a>s: one set
  defined by the columns parallel to the
  <a href="http://www.w3.org/TR/css3-writing-modes/#block-flow-dimensions">block flow dimension</a>,