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

<!--=================================================================-->

<h2 class="no-num no-toc">[LONGSTATUS] [DATE: 3 August 2004]</h2>

<dl>
  <dt>This version:

  <dd><a href="[VERSION]"
  >https://www.w3.org/TR/[YEAR]/ED-[SHORTNAME]-[CDATE]/</a>

  <dt>Latest version:

  <dd> <a href="[LATEST]">https://www.w3.org/TR/css3-layout/</a>

  <dt>Previous version:

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

  <dt>Editors:

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

  <dd class=vcard><span class=fn>César Acebal</span> (<span
  class=org>University of Oviedo</span>)
</dl>
<!--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 absolutely position
elements on a grid.

<p>The 'grid' property sets up a matrix of rows and columns and
designates empty areas and areas for content (called “slots”). The
'flow' property specifies into which slot an element flows. A grid
templates is like a table in that the various slots are aligned in rows
and columns and can automatically adapt to each others 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 '::slot()' pseudo-element allows to style the slots
(backgrounds, borders, etc.)

<p>The 'grid-position' property can be used instead of the 'top',
'left', 'right' and 'bottom' properties from level 2 to position
absolutely positioned elements relative to a grid template, so that
they align with the content in the grid.

<p class=level4>Grid templates can also be associated with pages in
paged media, to create page templates.

<p class=level4>Slots can also 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 'break-*' properties from
[[CSS3-BREAK]]).

<p class=level4>The '::fragment()' pseudo-element 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>
<!--status-->

<p>This draft combines ideas from earlier drafts on Template Layout,
Grid Positioning [[CSS3GRID]] and Grid Layout [[CSS3-GRID-LAYOUT]].

<p>The section on <a href="#cr-exit-criteria">“CR exit criteria”</a>
lists some conditions for this specification to become a W3C
Recommendation.

<p>Issues on this draft are mentioned in the text itself
(<span class=issue>like this</span>) 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>
<!--toc-->

<!--=================================================================-->

<h2>Introduction</h2>

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

<h3>Summary and examples</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 'grid: "aaaaaaa" "bccccdd"'.
</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 layout
grid with an element. Rather than letting an element lay out its
descendants in a single flow, the policy defined in this module gives
an element a <span>grid template,</span> which is a set
of <span>slots</span> aligned to an invisible grid, where each slot is
a separate flow. The descendants are given a 'flow' 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>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 class=level4>Paged displays (e.g., printed media) where each page
is divided in fixed areas for different kinds of content.

<li><p class=level4>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.
</ul>

<p>Once a grid template has been defined, it can also be used as an
alternative coordinate system for absolutely positioned elements. Such
elements do not flow into slots, but, by using 'grid-position'
(instead of 'top', 'left' etc.) can be aligned to grid lines and thus
to the content in the grid.

<p>But for many applications, template-based positioning makes
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: "ab"
             "cd" }
  #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>
</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 { 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: "abc"}
#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 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 {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 containing 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: "abc"; width: auto}</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 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 ''a'' slot).

<p>(However, extra columns or rows <em>will</em> be created if
necessary to absolutely position elements. See the 'grid-position'
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>&hellip;
&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 [[CSS3GCPM]] is
expected to define specific features for footnotes that are both
easier and more powerful than this example.
</div>

<div class="example level4">
<p>This example shows the use of chained regions: 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 template 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 {
  grid: "A A c"
        "A A c"
        "* * c"
        "a b c";
  chains: * a b c }
</pre>

<p>The '*' is a special name. It indicates the <em>default slot,</em>
the slot where content goes if it doesn't have an explicit 'flow'
property. We could have used a normal letter and added an explicit
'flow' 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>
::slot(*) {
  font-weight: bold;
  color: #0C3D5F;
  font-size: larger }
h1::slot(*) {
  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 [[CSS3GCPM]] for some ideas), or we could allow a scrollbar
on slot c.
</div>

<!--=================================================================-->

<h3 id=dependencies>Dependencies on other modules</h3>

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

<ul>
<li><cite>CSS 2.1</cite> [[!CSS21]]
&ndash; <a href="https://www.w3.org/TR/CSS21/visuren.html#block-boxes"
><dfn>block container</dfn></a> and property <dfn>content</dfn>.

<li><cite>CSS syntax module</cite> [[!CSS3SYN]] &ndash;
<dfn>interactive</dfn> vs <dfn>non-interactive</dfn> media.

<li><cite>CSS values and Units module</cite> [[!CSS3VAL]] &ndash; <a
href="/TR/css3-values#strings">
<dfn><var>&lt;string&gt;</var></dfn></a> and <a
href="/TR/css3-values#length-value">
<dfn><var>&lt;length&gt;</var></dfn></a>.

<li><cite>CSS box module</cite> [[!CSS3BOX]] &ndash; properties
<dfn>margin</dfn>, <dfn>margin-right</dfn>, <dfn>margin-left</dfn>,
<dfn>width</dfn>, <dfn>height</dfn>, <dfn>float</dfn>,
<dfn>display</dfn> and <dfn>overflow</dfn>

<li><cite>CSS text layout</cite> [[!CSS3-WRITING-MODES]] &ndash;
defines <dfn>block flow direction</dfn> and the
properties <dfn>direction</dfn> and <dfn>writing-mode</dfn>. The
latter defines when an element has 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>

<li><cite>CSS positioning</cite> [[!CSS3POS]] &ndash; properties
<dfn>z-index</dfn>, <dfn>position</dfn>, <dfn>top</dfn>,
<dfn>right</dfn>, <dfn>bottom</dfn>, <dfn>left</dfn>.

<li><cite>CSS fragmentation</cite> [[CSS3-BREAK]] &ndash; properties
<dfn>break-before</dfn>, <dfn>break-after</dfn> and
<dfn>break-inside</dfn>; the definition of <dfn>fragmenter</dfn>.

<li><cite>CSS paged media</cite> [[CSS3PAGE]] &ndash; definition of
<dfn>page area</dfn> (in particular its width &amp; height).

<li><cite>CSS background and borders</cite> [[CSS3BG]] &ndash;
properties <dfn>background</dfn>, <dfn>background-image</dfn>,
<dfn>background-size</dfn>, <dfn>box-decoration-break</dfn>
<span class=issue>and <dfn>box-shadow</dfn>?</span>

<li><cite>CSS tables</cite> [[!CSS3TBL]] &ndash; property
<dfn>vertical-align</dfn>. <span class=issue>[or Box Module?]</span>

<li><cite>CSS Multi-column Layout Module</cite> [[CSS3COL]] &ndash;
property <dfn>columns</dfn>.

<li><cite>CSS Fragmentation Module</cite> [[!CSS3-BREAK]] &ndash;
properties <dfn>break-before</dfn>, <dfn>break-after</dfn> and
<dfn>break-inside</dfn>.
</ul>

<p class=issue>Add to the above all the properties that are allowed on
slots (see <a href="#slot-pseudo">“The '::slot()'
pseudo-element”</a>).

<p>It has non-normative (informative) references to the following other
CSS3 modules:

<ul>
<li><cite>Selectors</cite> [[SELECT]]
</ul>

<p>See <a
href="https://www.w3.org/TR/CSS21/about.html#property-defs" >section&nbsp;1.4.2
of CSS level&nbsp;2</a> [[CSS21]] for the grammar and other notations
that this specification uses in property definitions.

<!--=================================================================-->

<h3 id=values>Values</h3>

<p>This specification follows
the <a href="https://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="https://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.

<!--=================================================================-->

<h3 id=accessibility>A note about accessibility</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="https://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="https://www.w3.org/TR/2008/REC-WCAG20-20081211/#correct-reading-sequencedef"
>correct reading sequence</a> can
be <a
href="https://www.w3.org/TR/2008/REC-WCAG20-20081211/#programmaticallydetermineddef
" >programmatically determined.</a> (Level A)
</blockquote>

<blockquote>
<p><a
href="https://www.w3.org/TR/2008/REC-WCAG20-20081211/#navigation-mechanisms-focus-order"
><strong>2.4.3 Focus Order:</strong></a> If
a <a href="https://www.w3.org/TR/2008/REC-WCAG20-20081211/#webpagedef"
>Web page</a> can
be <a href="https://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>

<!--=================================================================-->

<h2>Declaring templates</h2>

<p>Grid templates are declared with the 'grid-template', 'grid-rows',
'grid-columns' and 'grid' properties, defined below.

<p>An element that has a grid template is called a <dfn>grid
element.</dfn> More precisely: an element is a grid element if (1) it
generates a <span>block container box</span> [[!CSS21]] and (2) at
least one of 'grid-template', 'grid-rows' or 'grid-columns' has a
value other than the initial value.

<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>An element's <dfn>grid ancestor</dfn> is the nearest ancestor that
is a <span>grid element.</span>

<p class=note>Note that not all elements have a grid ancestor. E.g.,
the root element has none.

<p>The <dfn>number of columns</dfn> of a grid element is the number
of <var>&lt;col-width&gt;</var> values in 'grid-columns' or the number
of columns in 'grid-template', whichever is larger.

<p>The <dfn>number of rows</dfn> is the number
of <var>&lt;row-height&gt;</var> values in 'grid-rows' or the number
of rows in 'grid-template', whichever is larger.

<p class=note>Note that a grid element always has at least one row and one
column. Those may, however, have zero size.

<!--=================================================================-->


<h3 id=grid-template> Declaring a template: 'grid-template'</h3>

<p>The 'grid-template' property implicitly assigns a grid to an
element and defines named slots in the grid. It can also designate a
slot as the <em>default slot</em> for content without an explicit
flow.

<table class=propdef>
<tbody>
<tr>
<th>Name:
<td><dfn>grid-template</dfn>

<tr>
<th><a href="#values" >Value</a>:
<td>none | <var>&lt;string&gt;</var>+

<tr>
<th>Initial:
<td>none

<tr>
<th>Applies to:
<td><a href="https://www.w3.org/TR/CSS21/visuren.html#block-boxes"
>block container elements</a> [[!CSS21]]

<tr>
<th>Inherited:
<td>no

<tr>
<th>Animatable:
<td>no

<tr>
<th>Percentages:
<td>N/A

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

<tr>
<th>Canonical order:
<td><abbr title="follows order of property value definition">per
grammar</abbr>
</table>

<p>Each string consist of one or more asterisks (“*”), letters,
periods (“.”), spaces and tabs. Each string represents one row in the
template, each symbol other than a space or tab represents one column
in that row. Spaces and tabs have no meaning. They may be added for
readability.

<p>The symbols in the template have the following meaning

<dl>
<dt>&lt;letter&gt;
<dd>
Named slot for content.

<p class=issue>CSS doesn't yet have a type corresponding to single
letter. The letters in this module are also used outside of strings
(on 'flow', e.g.), so they should be a subset of identifiers. There is
a “nmstart” macro in the grammar, but it is not exactly what we want
here. E.g., U+0300 (“combining grave accent”) is a valid first
character for an identifier, but may not be desirable as a slot in a
template. We probably want a definition based on the principle that it
is a single letter if it <em>looks</em> like a single letter. This may
correspond to the notion of <em>character cluster.</em> (There may
also be a connection with the open issue against the CSS syntax about
Unicode normalization. We want é to match é, no matter if the author
typed U+0301 U+0065 or U+00C9.)

<dt>*
<dd>
(Asterisk.) Default slot for content (explained below).

<dt>.
<dd>
(Period.) Blank space.
</dl>

<p>Multiple identical letters in adjacent rows or columns form a
single <dfn>slot</dfn> that spans those rows and columns. Ditto for
multiple “*”s. Slot names are case-sensitive, so uppercase and
lowercase letters are considered to be different letters.

<p>Non-rectangular slots and multiple slots with the same letter are
illegal. A template without any letter or “*” is illegal. A template
with more than one “*” slot is illegal. These errors cause the
declaration to be ignored.

<p class=note>Note: non-rectangular and disconnected regions may be
permitted in a future update of CSS.

<p>Rows with fewer columns than other rows are implicitly padded with
periods (“.”).

<p>Each slot (letter or “*”) acts as a block element for its contents.

<p>If the value is ''none'', then no explicit slots are defined. If
the element is a <em>grid element,</em> then the element instead has
an <dfn>implicit template</dfn> consisting of a single '*' slot.

<p class=note>Note that an element is a grid element in this case if
'grid-columns' and 'grid-rows' are not both ''auto''.

<div class=example>
<p>For example, the following two sets of style rules are equivalent:

<pre>DIV {
  grid-template: none;
  grid-rows: 10em 10em 10em;
  grid=columns: * * * * }
</pre>

<p>and

<pre>DIV {
  grid-template: "****" "****" "****";
  grid-rows: 10em 10em 10em;
  grid=columns: * * * * }
</pre>
</div>


<h3 id=grid-column-sizes> Specifying the widths of columns:
'grid-columns'</h3>

<table class=propdef>
<tbody>
<tr>
<th>Name:
<td><dfn>grid-columns</dfn>

<tr>
<th><a href="#values" >Value</a>:
<td>auto | <var>&lt;col-width&gt;</var>+

<tr>
<th>Initial:
<td>auto

<tr>
<th>Applies to:
<td><span>block container</span> elements

<tr>
<th>Inherited:
<td>no

<tr>
<th>Animatable:
<td>yes, between grids with the same number of tracks

<tr>
<th>Percentages:
<td>N/A

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

<tr>
<th>Canonical order:
<td><abbr title="follows order of property value definition">per
grammar</abbr>
</table>

<p>The 'grid-columns' property specifies the sizes of the columns of
a grid.

<p>Where

<pre class=prod>
<dfn>&lt;col-width&gt;</dfn> = <var>&lt;length&gt;</var> | <var>&lt;percentage&gt;</var> | * | <var>&lt;fraction&gt;</var> |
  <var>&lt;minmax&gt;</var> | min-content | max-content | auto
<dfn>&lt;minmax&gt;</dfn> = minmax( <var>&lt;col-width&gt;</var> , <var>&lt;col-width&gt;</var> )</pre>

<p class=issue>The definition of minmax isn't correct, it should only
accepts certain values.

<p>Each <var>&lt;col-width&gt;</var> sets the width of a column, the
first value for the first column, the second for the second columns,
etc.

<p>If there are fewer <var>&lt;col-width&gt;</var> values than
the <span>number of columns</span> in the element, or if the value is
''auto'', the missing columns widths are all '*'.

<p>Each <var>&lt;col-width&gt;</var> can be one of the following:

<dl>
<dt><var>&lt;length&gt;</var>
<dd>
An explicit width for that column. Negative values are illegal.

<dt><var>&lt;fraction&gt;</var>
<dd>
(A non-negative number followed by ''fr''.) A fraction of the
remaining space, see <a href="#fraction-values-fr" >Fraction
values</a> below.

<dt>*
<dd>
(Asterisk.) All columns with a width of '*' have the same width.

<dt><var>&lt;percentage&gt;</var>
<dd>
Expresses a size as a percentage of the element's a-priori
content width. <span class=issue>When the width of the <span>grid
element</span> is dependent on content, the result is
undefined.</span>

<dt>max-content
<dt>min-content
<dd>
The column's width is determined by its contents. See
the <a href="#slot-sizes" >algorithm</a> below.

<dt>minmax(<var>p</var>,<var>q</var>)
<dd>
The column's width is constrained to be greater than or equal
to <var>p</var> and less than or equal to <var>q</var>. <var>p</var>
and <var>q</var> stand for [ <var>&lt;length&gt;</var> | max-content |
min-content | * ]. There may be white space around the <var>p</var>
and <var>q</var>. If <var>q</var> &lt; <var>p</var>, then <var>q</var>
is ignored and ''minmax(<var>p</var>,<var>q</var>)'' is treated as
'minmax(<var>p</var>,<var>p</var>)'.

<dt>auto
<dd>
Equivalent to 'minmax(min-content, max-content)'.
</dl>

<!--=================================================================-->

<h3 id=grid-row-sizes> Specifying the height of rows: 'grid-rows'</h3>

<table class=propdef>
<tbody>
<tr>
<th>Name:
<td><dfn>grid-rows</dfn>

<tr>
<th><a href="#values" >Value</a>:
<td>auto | <var>&lt;row-height&gt;</var>+

<tr>
<th>Initial:
<td>auto

<tr>
<th>Applies to:
<td><span>block container</span> elements

<tr>
<th>Inherited:
<td>no

<tr>
<th>Animatable:
<td>yes, between grids with the same number of tracks

<tr>
<th>Percentages:
<td>N/A

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

<tr>
<th>Canonical order:
<td><abbr title="follows order of property value definition">per
grammar</abbr>
</table>

<p>The 'grid-rows' property specifies the heights of the rows of a
grid.

<pre class=prod>
<dfn>&lt;row-height&gt;</dfn> = <var>&lt;length&gt;</var> | <var>&lt;percentage&gt;</var> | * | <var>&lt;fraction&gt;</var> |
  <var>&lt;minmax&gt;</var> | min-content | max-content | auto
<dfn>&lt;minmax&gt;</dfn> = minmax( <var>&lt;row-height&gt;</var> , <var>&lt;row-height&gt;</var> )
</pre>

<p class=issue>The definition of minmax isn't correct, it should only
accepts certain values.

<p class=note>Note that the syntax is the same syntax as for
'grid-columns'

<p>If there are fewer <var>&lt;row-height&gt;</var> values than
the <span>number of rows</span> in the element, or if the value is
''auto'', the missing row heights are all ''auto''.

<p>Each <var>&lt;row-height&gt;</var> can be one of the following:

<dl>
<dt><var>&lt;length&gt;</var>
<dd>
An explicit height for that row. Negative values are illegal.

<dt><var>&lt;fraction&gt;</var>
<dd>
(A non-negative number followed by ''fr''.) A fraction of the
remaining space, see <a href="#fraction-values-fr" >Fraction
values</a> below.

<dt>* (asterisk)
<dd>
All rows with a height of '*' have the same height.

<dt><var>&lt;percentage&gt;</var>
<dd>
Expresses a size as a percentage of the element's a-priori
content height.

<p class=issue>When the height of the <span>grid element</span> is
dependent on content, the result is undefined.

<dt>max-content
<dt>min-content
<dd>
The row's height is determined by its contents. See
the <a href="#slot-sizes" >algorithm</a> below.

<dt>minmax(<var>p</var>,<var>q</var>)
<dd>
The row's height is constrained to be greater than or equal
to <var>p</var> and less than or equal to <var>q</var>. <var>p</var>
and <var>q</var> stand for [ <var>&lt;length&gt;</var> | max-content |
min-content | * ]. There may be white space around the <var>p</var>
and <var>q</var>. If <var>q</var> &lt; <var>p</var>, then <var>q</var>
is ignored and ''minmax(<var>p</var>,<var>q</var>)'' is treated as
'minmax(<var>p</var>,<var>p</var>)'.

<dt>auto
<dd>
Equivalent to 'minmax(min-content, max-content)'.
</dl>

<!--=================================================================-->

<h3 id=grid-shorthand> The 'grid' shorthand property</h3>

<table class=propdef>
<tbody>
<tr>
<th>Name:
<td><dfn>grid</dfn>

<tr>
<th><a href="#values" >Value</a>:
<td>none | [ [ <var>&lt;string&gt;</var> [
/ <var>&lt;row-height&gt;</var> ]? ]+ ] <var>&lt;col-width&gt;</var>*

<tr>
<th>Initial:
<td>none

<tr>
<th>Applies to:
<td><span>block container</span> elements

<tr>
<th>Inherited:
<td>no

<tr>
<th>Animatable:
<td>see individual properties

<tr>
<th>Percentages:
<td>see individual properties

<tr>
<th>Computed&nbsp;value:
<td>see individual properties

<tr>
<th>Canonical order:
<td>N/A
</table>

<p>The 'grid' property is a shorthand for 'grid-template',
'grid-columns' and 'grid-rows' and is equivalent to setting those
properties as follows:

<ul>
<li>'grid-template' is set to the list of <var>&lt;string&gt;</var>
values.

<li>'grid-rows' is set to the list of <var>&lt;row-height&gt;</var>
values, with any omitted ones set to ''auto''.

<li>'grid-columns' is set to the list of <var>&lt;col-width&gt;</var>
values, or to ''auto'' if there are none.
</ul>

<div class=example>
<p>For example, the rule

<pre>grid: "abc" "abd"/4em * 10em</pre>

<p>is the same as

<pre>
grid-template: "abc" "abd";
grid-rows: auto 4em;
grid-columns: * 10em;
</pre>

<p>Note the ''auto'' keyword that was implied in the shorthand,
but must be made explicit in the 'grid-rows' property.
</div>

<div class=issue>
<!-- The idea to put column sizes first is due to Fantasai:
http://www.w3.org/mid/4F4FF423.1000205@inkedblade.net -->
<p>Does it look better with the column sizes first instead of last?
There would be no need for a slash:

<blockquote>
<p>none |  <var>&lt;col-width&gt;</var>* [ <var>&lt;string&gt;</var>
<var>&lt;row-height&gt;</var>? ]+
</blockquote>

<p>E.g.:

<pre>
grid: 5em 1em  *  1em 10em
      "a   .   b   .   c"  2em
      ".   .   .   .   ."  1em
      "d   .   e   .   f"
      ".   .   .   .   ."  1em
      "g   .   h   .   i"  2em
</pre>
</div>

<!--=================================================================-->

<h3 id=default>Default slots</h3>

<p>Every <span>grid element</span> has a <dfn>default slot.</dfn> If
there is an asterisk (“*”) in the template, then that slot is the
default. If there is no asterisk, then the first letter in the
template defines the default slot. If there is no letter either,
then&hellip;

<p class=issue>&hellip; define where a grid element's content goes if it
doesn't have any slots at all.

<div class=example>
<p>For example, if the template is defined by 'grid-template: "..."
"..c" "abb" "abb"', then “c” is the default slot.
</div>

<p class=note>If the grid has an <em>implicit template</em> (i.e.,
'grid-template' is ''none''), then its single slot is the default
slot.

<p>All content of a grid element that is not inside another flow
(i.e., not inside a float, not absolutely positioned, etc.) is flowed
into the default slot. In particular, any text content of the grid
element itself is in that default flow.

<div class=example>
<p>For example, in this document fragment

<pre>
&lt;DIV STYLE="grid: 'ab*'">
 &lt;IMG STYLE="flow: a" SRC="image.png" ALT="Foo">
 This is an
 &lt;EM STYLE="flow: *">emphasized&lt;/EM>
 &lt;EM STYLE="flow: b">(note well!)&lt;/EM>
 sentence.
 &lt;
&lt;/DIV>
</pre>

<p>The three slots of the grid contain:

<dl>
<dt>Slot a <dd>The image

<dt>Slot b <dd>The text “(note well!)”

<dt>Default slot <dd>The text “This is an <em>emphasized</em>
sentence.”
</dl>

<p>(The 'flow' property is defined below.)
</div>

<!--=================================================================-->

<h3 id=slot-sizes>Calculating the size of the grid</h3>

<p>For the purpose of the calculations below, each slot (letter or
“*”) in a grid has four dimensions associated with it,
called <var>MINW</var> (“minimum width”), <var>PREFW</var> (“preferred
width”), <var>MINH</var> (“minimum height”) and <var>PREFH</var>
(“preferred height”). We can think of them as the minimum and
preferred dimensions of the slot in isolation, i.e., if it wasn't
constrained by other slots in the same row or column. They are defined
as follows:

<dl>
<dt><var>MINW</var>
<dd>
<ul>
<li>If the slot spans only columns whose width does not depend on the
contents of the column (i.e., the column widths are specified with
only <var>&lt;length&gt;</var> values,
'*', <var>&lt;fraction&gt;</var> values, or any combination of those),
then <var>MINW</var> is 0. <span class=note>(Note
that <var>&lt;length&gt;</var> values can be specified with 'calc()'
as well, see [CSS3VALUES]].)</span>

<li>Otherwise, if the slot is <em>vertical,</em> then <var>MINW</var>
is the <em>block dimension</em> of the slot, plus its horizontal
padding, border and margin (i.e., any 'margin-left', 'margin-right',
etc., that is set on it by means of the '::slot()' pseudo-element).
Any ''auto'' margins are counted as 0 in this case.

<li>Otherwise, if the slot spans at least one column whose width is
specified as ''max-content'' (or 'minmax()' with a first argument of
''max-content''), then <var>MINW</var> is the intrinsic preferred
width (see [[!CSS3BOX]]) of the slot plus its horizontal margin,
border and padding. Any ''auto'' margins are counted as 0 in this
case.

<li>Otherwise (i.e., the slot spans at least one column whose width is
specified as ''min-content'' or ''minmax()'' with a first argument of
''min-content'', but no ''max-content'') <var>MINW</var> is the
intrinsic minimum width (see [[!CSS3BOX]] of the slot, plus its
horizontal padding, border and margin.
</ul>

<dt><var>PREFW</var>
<dd>
<ul>
<li>If the slot spans only columns whose width does not depend on the
contents of the column (i.e., the column widths are specified with
only <var>&lt;length&gt;</var> values,
'*', <var>&lt;fraction&gt;</var> values, or any combination of those),
then <var>PREFW</var> is infinite.

<li>Otherwise, if the slot is <em>vertical,</em> then <var>PREFW</var>
is the <em>block dimension</em> of the slot, plus its horizontal
padding, border and margin.

<li>Otherwise, if the slot spans at least one column whose width is
specified as ''max-content'' (or 'minmax()' with a first argument of
''max-content''), then <var>PREFW</var> is the intrinsic preferred
width (see [[!CSS3BOX]]) of the slot plus its horizontal margin,
border and padding.

<li>Otherwise <var>PREFW</var> is the intrinsic minimum width (see
[[!CSS3BOX]] of the slot, plus its horizontal padding, border and
margin.
</ul>

<dt><var>MINH</var>
<dd>
<ul>
<li>If the slot spans only rows whose height does not depend on the
contents of the column (i.e., the row heights are specified with
only <var>&lt;length&gt;</var> values,
'*', <var>&lt;fraction&gt;</var> values, or any combination of those),
then <var>MINH</var> is 0.

<li>Otherwise, if the slot is <em>horizontal,</em>
then <var>MINH</var> is the <em>block dimension</em> of the slot, plus
its vertical padding, border and margin

<li>Otherwise, if the slot spans at least one row whose height is
specified as ''max-content'' (or 'minmax()' with a first argument of
''max-content''), then <var>MINH</var> is the intrinsic preferred
height (see [[!CSS3BOX]]) of the slot plus its vertical margin, border
and padding.

<li>Otherwise <var>MINH</var> is the intrinsic minimum height (see
[[!CSS3BOX]] of the slot, plus its vertical padding, border and
margin.
</ul>

<dt><var>PREFH</var>
<dd>
<ul>
<li>If the slot spans only rows whose height does not depend on the
contents of the column (i.e., the row heights are specified with
only <var>&lt;length&gt;</var> values,
'*', <var>&lt;fraction&gt;</var> values, or any combination of those),
then <var>PREFH</var> is infinite.

<li>Otherwise, if the slot is <em>horizontal,</em>
then <var>PREFH</var> is the <em>block dimension</em> of the slot,
plus its vertical padding, border and margin.

<li>Otherwise, if the slot spans at least one row whose height is
specified as ''max-content'' (or 'minmax()' with a first argument of
''max-content''), then <var>PREFH</var> is the intrinsic preferred
height (see [[!CSS3BOX]]) of the slot plus its vertical margin, border
and padding.

<li>Otherwise <var>PREFH</var> is the intrinsic minimum height (see
[[!CSS3BOX]] of the slot, plus its vertical padding, border and
margin.
</ul>
</dl>

<div class=example>
<p>For example, the <var>MINW</var> values of the slots in this grid

<pre>
grid: "  a  a  .  "
      "  b  .  c  "
       auto * 10em
</pre>

<p>are as follows:

<dl>
<dt>a
<dd>
''min-content'' (because the slot spans at least one column with a
width specified as ''min-content'' or ''auto'').

<dt>b
<dd>
''min-content'' (ditto).

<dt>c
<dd>
0 (because the slot spans only columns with a width that is
independent of the content).
</dl>
</div>

<p>The UA must choose the widths and heights of all columns and rows
such that the following constraints are satisfied.

<ol>
<!-- Constraints relating to the element's own width and
   height. These constraints may be dropped if overconstrained -->

<li>
<p>If the element has an a-priori known content height, then the sum
of the heights of all rows must be equal to the element's height.

<div class=example>
<p>For example, the two rows in this grid must be 8em each so that the
total height matches the height of the element:

<pre>
div {
  height: 16em;
  grid: "a.b"/*<!--*/-->
        "ac."/*<!--*/--> }
</pre>
</div>

<li>
<p>If the grid element has an a-priori known content width, then the
sum of the widths of all columns must be equal to the element's width.

<div class=example>
<p>For example, the three columns in this grid must be 20em each:

<pre>div {width: 60em; grid: "abc"}</pre>
</div>
<!-- Constraints relating to fixed-size rows and columns -->

<li>Each row with a height specified as a <var>&lt;length&gt;</var>
must have exactly that height.

<li>Each column with a width specified as a <var>&lt;length&gt;</var>
must have exactly that width.
<!-- Constraints on rows and column with fractional sizes. -->

<li>All rows with a height specified as '*' must have the same height.

<p class=issue>If we have both '*' and ''fr'', then '*' will be defined
as '1fr' and we can drop this rule and the next. Otherwise either
these two rules or the next two must be removed.

<li>All columns with a width specified as '*' must have the same
width.

<li>For any pair (<var>i</var>,<var>j</var>) of rows
whose <var>&lt;row-height&gt;</var> values h<sub>i</sub> and
h<sub>j</sub> are both specified in ''fr'', the computed heights
H<sub>i</sub> and H<sub>j</sub> must be such that H<sub>i</sub> *
h<sub>j</sub> = H<sub>j</sub> * h<sub>i</sub>. (I.e., their heights
are proportional to their number of ''fr'' units.)

<li>For any pair (<var>i</var>,<var>j</var>) of columns
whose <var>&lt;col-width&gt;</var> values w<sub>i</sub> and
w<sub>j</sub> are both specified in ''fr'', the computed width
W<sub>i</sub> and W<sub>j</sub> must be such that W<sub>i</sub> *
w<sub>j</sub> = W<sub>j</sub> * W<sub>i</sub>. (I.e., their widths are
proportional to their number of ''fr'' units.)
<!-- Constraints relating to rows and columns without slots that span
   into other rows or columns, i.e., cases where the size of a slot
   can put an upper limits on the size of a row or column -->

<li>
<p>Each row that contains slots that span only one row and no slots
that span more than one row, must not be higher than the
largest <var>PREFH</var> of all slots in the row plus the amount
needed to vertically align the <span>horizontal</span> slots that have
a 'vertical-align' of ''baseline''.

<div class=example>
<p>For example, the second row in this grid

<pre>
grid: "a.c.." / 5em
      "....b" / auto
</pre>

<p>must not be taller than the height (<span>block dimension</span>)
of slot b. The first row contains a slot that spans two rows (slot a),
so this rule does not apply to that row.
</div>

<li>
<p>Each column that contains slots that span only one column and no
slots that span more than one column, must not be wider than the
largest <var>PREFW</var> of all slots in the column plus the amount
needed to align the <span>vertical</span> slots that have a
'vertical-align' of ''baseline''.

<div class=example>
<p>For example, in this grid

<pre>
grid: "ac"
      "ab"
      auto *
</pre>

<p>the first column must not be wider than the <var>PREFW</var> of
slot a. Both slots in the second column have an
infinite <var>PREFW</var>, so this rule effectively puts no constraint
on that column.
</div>
<!-- Constraints on slots, only to set lower limits.  -->

<li>Each slot must be at least as wide as its <var>MINW</var>.

<li>Each slot must be at least as high as its <var>MINH</var>.
</ol>

<p>If it is impossible to choose such widths and heights, then try
without constraint 1. If it is still impossible, try without
constraint 2 instead. And, finally, try with both 1 and 2 dropped.

<div class=example>
<p>For example, the sum of the row heights in this example can never
be the same as the height of the element:

<pre>
div {
  height: 20em;
  grid: "a b c" / 7em
        "a . c" / 7em }
</pre>

<p>The first constraint is therefore ignored, the rows are 7em each
and 6em of space below the grid remains empty.
</div>

<p>If there are multiple solutions, and constraint 1 was dropped or
did not apply, then the sizes must additionally be chosen such that
the sum of the heights of the rows is minimized.

<p>If there are still multiple solutions, and constraint 2 was dropped
or did not apply, then the sizes must additionally be chosen such that
the sum of the widths of the columns is minimized.

<p class=note>The calculation is intended to be symmetric in width and
height (except for the case when both width and height are fixed and
the grid is over-constrained, when a solution that ignores the height
is tried before trying one that ignores the width).

<div class=example>
<p>For example, there would be multiple solutions for this grid:

<pre>
&lt;DIV STYLE="float: left; grid: 'a.b'">
 &lt;P STYLE="flow: a">Two words
 &lt;P STYLE="flow: b">Only three words
&lt;/DIV>
</pre>

<p>The columns must have equal width, but there is no other constraint
on the width. They could be narrow:

<blockquote>
<p><code class=visible style="display: inline-block">Two  <br>
words<br>
     </code><code class=visible style="display:
inline-block">     <br>
     <br>
     </code><code class=visible style="display:
inline-block">Only <br>
three<br>
words</code>
</blockquote>

<p>or wider:

<blockquote>
<p><code class=visible style="display:
inline-block">Two words       </code><code class=visible
style="display:
inline-block">                </code><code class=visible
style="display: inline-block">Only three words</code>
</blockquote>

<p>or even wider still, e.g.:

<blockquote>
<p><code class=visible style="display:
inline-block">Two words          </code><code class=visible
style="display:
inline-block">                   </code><code class=visible
style="display: inline-block">Only three words   </code>
</blockquote>

<p>The rule to minimize height excludes the first, narrow solution.
The rule to minimize width excludes the third and all wider solutions.
So the second layout, the narrowest that has all words on one line, is
the correct one.

<p>(This example assumes the width of the floating DIV's containing
block is large enough. The default width of a float is actually
''fit-content'', and thus if the containing block is too narrow, the
result will be narrower, too, because the calculation will have to be
redone using that width as the a-priori width for the DIV.)
</div>

<p class=note>The width isn't known a-priori, if, e.g., 'width' is
''auto'' and the element is floating, absolutely positioned,
inline-block or a child of a block with vertical writing mode.

<p>An extra step may be necessary in paged media if a page break
occurs inside a template (only in the case of an <em>element-based
template,</em> see <a href="#element-based-page-break" >below</a>). If
the template, after computing the width and height, is too big to fit
on the current page, and if a suitable break point exists, the part of
the template after that break point is put on the next page. The width
of the containing block on that page may be different if that page has
different margins from the current page (see [[!CSS3PAGE]]) and thus
the width and height of that part of the template must be recalculated
in the new context.

<p class=note>Note that the widths of the columns can be completely
determined before laying out any of the contents as long as there are
no columns with a <var>&lt;col-width&gt;</var> of ''min-content'' or
''max-content''.

<p class=issue>Do we define restrictions or approximations for slots
that are part of a <em>chain</em> to avoid complicated optimization
algorithms?

<p class=note>Note: In a future update of CSS, rows might get a
property to specify how the height of that row is adjusted in case the
above calculation yields a template that is less tall than the element
itself.

<p>The height of a slot is measured as if the slot had
one <dfn title="anonymous block of a slot">anonymous block</dfn> as a
child that contains all the slot's contents and the anonymous block is
a <em>flow root</em> (see [[!CSS3BOX]]).

<div class=example>
<p>This example divides the window in three rows and three columns,
separated by 1em of white space. The middle row and the middle column
are flexible, the others are fixed at a specific size. The first
column is 5em wide, the last one 10em.

<pre>
&lt;style type="text/css"&gt;
  body {
    height: 100%;
    grid: "a   .   b   .   c"  /2em
          ".   .   .   .   ."  /1em
          "d   .   e   .   f"
          ".   .   .   .   ."  /1em
          "g   .   h   .   i"  /2em
          5em 1em  *  1em 10em}
  #logo {flow: a}
  #motto {flow: b}
  #date {flow: c}
  #main {flow: e}
  #adv {flow: f}
  #copy {flow: g}
  #about {flow: h}
&lt;/style&gt;
&lt;p id=logo&gt;&lt;img src=...
&lt;p id=motto&gt;Making Web pages since 1862
&lt;p id=date&gt;August 2, 2004
...
</pre>
</div>

<p class=issue>[Add example with three columns, first two as narrow as
possible, third one taking up all remaining space.]

<!--=================================================================-->

<h2 id=positioning>Putting content into a grid element</h2>

<p><em>This section until the next subsection is not normative.</em>

<p>Grids can be used in two different ways to position content. The
first way is to flow content into slots (either into explicit slots
identified by letters, or the default slot “*”). Each slot is an
individual flow root (“establishes a block formatting context” in the
terminology of CSS level 2), very much like a table cell.

<p>The second way is to absolutely position elements using
four <em>grid lines</em> to specify the positions of the four margin
edges of the element. Like other positioned elements [[!CSS21]], these
elements can overlap each other and the 'z-index' property applies to
them.

<!--=================================================================-->

<h3 id=flow>Flowing content into slots: 'flow'</h3>

<p>The 'flow' property adds an element to a slot.

<table class=propdef>
<tbody>
<tr>
<th>Name:
<td><dfn>flow</dfn>

<tr>
<th><a href="#values" >Value</a>:
<td>auto | <var>&lt;identifier&gt;</var> | '*' | same

<tr>
<th>Initial:
<td>auto

<tr>
<th>Applies to:
<td>elements with 'position' equal to ''static'' or ''relative''

<tr>
<th>Inherited:
<td>no

<tr>
<th>Animatable:
<td>no

<tr>
<th>Percentages:
<td>N/A

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

<tr>
<th>Canonical order:
<td><abbr title="follows order of property value definition">per
grammar</abbr>
</table>

<p>If the value is not ''auto'', the element is added to the flow of
the given slot, instead of to the flow of its parent.

<p>If the element has no <span>grid ancestor</span>, or that grid
ancestor has no slot of the given name, the property is treated as if
it were ''auto''.

<p>A value of ''same'' means the element is put into the same slot as
the nearest preceding element in document order that (1) has the
same <span>grid ancestor</span>, (2) to which the 'flow' property
applies and (3) whose 'flow' property is not ''auto''.

<div class=issue>
<p>If the letter refers to a slot that doesn't exist in the
element's <em>grid ancestor</em> (or there is no grid ancestor) there
are several possibilities:

<ol>
<li>The element is not positioned (i.e., it is positioned in the
current flow).

<li>The letter is looked for in the grid ancestor's own grid ancestor,
etc., recursively. If no slot of that name is found in any of them,
then the element is not positioned.

<li>The element is positioned in the default slot (i.e., as if 'flow:
*' had been specified); or not positioned at all, in case there is no
grid ancestor.

<li>The letter is looked for in the grid ancestor's own grid ancestor,
etc., recursively. If no slot of that name is found in any of them,
then the element is positioned in the default slot.
</ol>
</div>

<p>All content flowed into the same slot, whether explicitly with
'flow' or implicitly by flowing into the default slot, forms a single
flow, with content in document order. The slot establishes a block
formatting context and becomes the <dfn>containing block</dfn> of the
resulting content flow. The boxes of elements flowed into the same
slot explicitly (by means of 'flow') are each others siblings in the
slot.

<p>The content flowed into a slot does not inherit properties from the
slot.

<div class=example>
<p>For example, the style sheet

<pre>
BODY {grid: "a." ".b"}
.paris {flow: a}
.london {flow: b}
</pre>

<p>with this document

<pre>
&lt;DIV CLASS=london>
 &lt;P>The...
 &lt;DIV CLASS=paris>
  &lt;P>The...
  &lt;DIV CLASS=london>
   &lt;P>The...
  &lt;/DIV>
 &lt;/DIV>
&lt;/DIV>
</pre>

<p>causes the second and third DIVs to be taken out of their parents.
The second DIV becomes the first child of slot a (i.e., of the
pseudo-element called '::slot(a)'). The third DIV becomes the sibling
of the first DIV, because both are added to slot b independently.
</div>

<p class=note>Note that 'flow' applies to floating elements: they are
floated relative to their containing block, and if their 'flow'
property indicates a slot in a grid, that slot is their containing
block. See also <a href="#float" >“Floating elements inside
templates”</a> below.

<div class=example>
<p>A common markup in HTML for illustrations with captions is as
follows:

<pre>
&lt;div class=figure>
 &lt;p>&lt;img src="paul.jpg" alt="...">
 &lt;p class=caption>A pond in a playground in Amsterdam
&lt;/div>
</pre>

<p>The caption can be put above the image by using a template as
follows:

<pre>
div.figure {grid: "aaa"
                  ".b."
                  * min-content *}
div.figure p {flow: b}
div.figure p.caption {flow: a; text-align: center}
</pre>

<p>The caption can be wider than the image and the image will be
centered.

<p>When the figure is floating, it is probably better to not let the
caption become wider than the image (unless the caption cannot be made
narrow enough):

<pre>
div.figure {float: right; grid: "a" "b" min-content}
div.figure p {flow: b}
div.figure p.caption {flow: a; text-align: center}
</pre>
</div>

<div class=example>
<p>In this example, a form is laid out on a grid, with two labels and
two input boxes and a submit and a reset button:

<pre>
form {
  border: thin solid;
  grid: "aaaa.bbbb"
        "........."/1em
        "cccc.dddd"
        "........."/1em
        "...ee..ff" }
label[for=minv] { flow: a }
input#minv { flow: b; display: block }
label[for=maxv] { flow: c }
input#maxv { flow: d; display: block }
input[type=submit] { flow: e; display: block }
input[type=reset] { flow: f; display: block }
</pre>

<p>Here is the fragment of HTML that the style is applied to:

<pre>
&lt;form action="./"&gt;
  &lt;label for=minv&gt;Enter minimum value:&lt;/label&gt;
  &lt;input id=minv name=minv&gt;
  &lt;label for=maxv&gt;Enter maximum value:&lt;/label&gt;
  &lt;input id=maxv name=maxv&gt;
  &lt;input type=submit value="OK"&gt;
  &lt;input type=reset value="Reset"&gt;
&lt;/form&gt;
</pre>

<p>The addition of 'display: block' causes the form controls to use
the width computation of blocks, in other words: they will be as wide
as their containing block, which in this case means that they will be
as wide as the slot they are assigned to. Without it, they would be
inline elements and just be left-aligned in their slots.

<div class=figure>
<p><img alt="Image simulating the layout of the example"
longdesc=form.desc src=form.png>

<p class=caption>Possible rendering of the example.
</div>
</div>

<div class=example>
<p>This example shows that templates can be nested. The body has two
columns. The #content element that goes into the second column has
itself another template, into which the various “modules” are placed.

<div class=figure>
<p><img alt="[Screendump with nested templates]" longdesc=table5.desc
src=table5.png>

<p class=caption>Possible rendering of the nested templates. (The
borders are added for clarity, they don't occur in the style rules
below. The red border is the inner template.)
</div>

<p>For clarity, the inner template uses different letters for the
slots than the outer template. This is not required.

<pre>
&lt;style type="text/css">
body {
     grid: "a   b"
           10em *;
}
#nav {
     flow: a;
}
#content {
     flow: b;
     grid: "c   .   d   .   e   "
           ".   .   .   .   .   "/1em
           ".   .   f   .   .   "
            *  1em  *  1em  *;
}
.module.news {
     flow: c;
}
.module.sports {
     flow: d;
}
.module.personal {
     flow: e;
}
#foot {
     flow: f;
}
&lt;/style>
&lt;body>
&lt;ul id="nav">
     &lt;li>navigation&lt;/li>
&lt;/ul>
&lt;div id="content">
    &lt;div class="module news">
         &lt;h3>Weather&lt;/h3>
         &lt;p>There will be weather&lt;/p>
    &lt;/div>
    &lt;div class="module sports">
         &lt;h3>Football&lt;/h3>
         &lt;p>People like football.&lt;/p>
    &lt;/div>
    &lt;div class="module sports">
         &lt;h3>Chess&lt;/h3>
         &lt;p>There was a brawl at the chess tournament&lt;/p>
    &lt;/div>
    &lt;div class="module personal">
         &lt;h3>Your Horoscope&lt;/h3>
         &lt;p>You're going to die (eventually).&lt;/p>
    &lt;/div>
    &lt;p id="foot">Copyright some folks&lt;/p>
&lt;/div>

&lt;/body>
</pre>
</div>

<div class=example>
<p>This example shows the use of ''same'' to put <code>DD</code>
elements in the same slot as the preceding <code>DT</code>.

<pre>
...
DL {grid: "a.b.c"  * 2em * 2em *}
DT.mineral {flow: a}
DT.animal {flow: b}
DT.plant {flow: c}
DD {flow: same; margin-left: 1em}
...
<b>&lt;DL></b>
 <b>&lt;DT class=animal></b>falcon
 <b>&lt;DD></b>This bird of prey...
 <b>&lt;DT class=animal></b>rabbit
 <b>&lt;DD></b>Local restaurants...
 <b>&lt;DT class=mineral></b>granite
 <b>&lt;DD></b>This rock occurs...
 <b>&lt;DT class=plant></b>olive
 <b>&lt;DD></b>The fruit of...
 <b>&lt;DT class=mineral></b>limestone
 <b>&lt;DD></b>A rock composed of...
 <b>&lt;DT class=plant></b>pine
 <b>&lt;DD></b>The western half...
<b>&lt;/DL></b>
</pre>

<div class=figure>
<p><img alt=screendump longdesc=granite.desc src=granite.png>

<p class=caption>Possible rendering of the <code>DL</code> list, with
items sorted into three columns.
</div>
</div>

<p class=issue>An alternative to ''same'' may be to create selectors
with regular-expression-like capabilities: 'DT.plant + DD* + DD {flow:
c}' selects a DD that follows zero or more DDs that follow DT.plant.

<p class=issue>Does a percentage 'height' work on an element that is
flowed into a slot? If the grid template assigns a fixed height to the
slot, it is obvious what a percentage means, but if the slot's height
is ''max-content' and an element in the slot has 'height: 110%', there
is a conflict&hellip;

<!--=================================================================-->

<h3>Absolute positioning using a grid: 'grid-position-x' and
'grid-position-y'</h3>

<p class=issue>Trying to combine 'grid-row/column' and
'grid-row/column-span', because they should not cascade independently.
(If one style rule tries to place by start/end lines, and another
tries to place by span, the result of the cascade will be a mess.)

<p>The 'grid-position-x' and 'grid-position-y' properties can
absolutely position an element relative to a grid.

<table class=propdef>
<tbody>
<tr>
<th>Name:
<td><dfn>grid-position-x</dfn>, <dfn>grid-position-y</dfn>

<tr>
<th><a href="#values" >Value</a>:
<td>auto | [ <var>&lt;identifier&gt;</var> |
<var>&lt;grid-line&gt;</var> ] [ + <var>&lt;span&gt;</var> | - [
<var>&lt;identifier&gt;</var> | <var>&lt;grid-line&gt;</var> ] ]?

<tr>
<th>Initial:
<td>auto

<tr>
<th>Applies to:
<td>elements with 'position: absolute'

<tr>
<th>Inherited:
<td>no

<tr>
<th>Animatable:
<td>no

<tr>
<th>Percentages:
<td>N/A

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

<tr>
<th>Canonical order:
<td><abbr title="follows order of property value definition">per
grammar</abbr>
</table>

<p>Where

<pre class=prod>
<var>&lt;grid-line&gt;</var> = <var>&lt;integer&gt;</var> | same | next
<var>&lt;span&gt;</var> = <var>&lt;integer&gt;</var>
</pre>

<p>If the value is ''auto'', the element is positioned with 'top' and
'bottom' (for 'grid-position-y') or 'left' and 'right' (for
'grid-position-x', see [[!CSS21]]. The other values mean that the
computed values of 'top'/'bottom' or 'left'/'right' are ignored and
their used values are set as defined below.

<p>If the element has no <span>grid ancestor,</span> the value is
interpreted as if it were ''auto''.

<p>An <var>&lt;identifier&gt;</var> refers to a <span>slot</span> in
the <span>grid ancestor.</span>

<p>If an <var>&lt;identifier&gt;</var> refers to a non-existent slot,
the whole value is interpreted as if it were ''auto''.

<p>If <var>&lt;grid-line&gt;</var> is an integer, it refers to
a <dfn>grid line,</dfn> i.e., the horizontal line at the edge of a row
or the vertical line at the edge of a column. The top of the first row
of a grid template is the horizontal grid line with number 1, the top
of the second row is 2, etc. up to <var>N</var>+1 for a grid template
with <var>N</var> rows. Similarly, the vertical grid lines are
numbered 1 to <var>M</var>+1 for a grid template with <var>M</var>
columns.

<p>It is an error if the integer is &le; 0.

<p>The keyword ''same'' stands for the grid line specified by the
nearest preceding element in document order with the same <span>grid
ancestor</span> to which 'grid-position-x' or 'grid-position-y'
applied. If there is no such element, or if it specified ''auto'',
then ''same'' stands for '1'.

<p>The keyword ''next'' stands for next the grid line after the one
specified by the nearest preceding element in document order with the
same <span>grid ancestor</span> to which 'grid-position-x' or
'grid-position-y' applied. If there is no such element, or if it
specified ''auto'', then ''next'' stands for '1'.

<p>A <var>&lt;span&gt;</var> is a non-negative integer. It indicates
the number of rows or columns the element spans, as defined below.

<p>It is an error if the span is &lt; 0.

<p>The values are of the following forms:

<dl>
<dt><var>&lt;identifier&gt;</var>
<dd>
Equivalent to '<var>&lt;identifier&gt;</var> -
<var>&lt;identifier&gt;</var>' (twice the same identifier).

<dt><var>&lt;grid-line&gt;</var>
<dd>
Equivalent to '<var>&lt;grid-line&gt;</var> + 1' (i.e., a position and
a span of 1).

<dt><var>&lt;identifier&gt;</var> - <var>&lt;identifier&gt;</var>
<dd>
'Top' (or 'left') is set to the top (or left) margin edge of
the first slot. 'Bottom' (or 'right') is set to the bottom (or
right) margin edge of the second slot.

<dt><var>&lt;identifier&gt;</var> - <var>&lt;grid-line&gt;</var>
<dd>
'Top' (or 'left') is set to the top (or left) margin edge of
the first slot. 'Bottom' (or 'right') is set to the given grid
line.

<dt><var>&lt;grid-line&gt;</var> - <var>&lt;identifier&gt;</var>
<dd>
'Top' (or 'left') is set to the indicated grid line. 'Bottom'
(or 'right') is set to the bottom (or right) margin edge of the
second slot.

<dt><var>&lt;grid-line&gt;</var> - <var>&lt;grid-line&gt;</var>
<dd>
'Top' (or 'left') is set to the grid line indicated by the
first number. 'Bottom' (or 'right') is set to grid line given by
the second number.

<dt><var>&lt;identifier&gt;</var> + <var>&lt;span&gt;</var>
<dd>
'Top' (or 'left') is set to the top (or left) margin edge of
the first slot. The <var>&lt;span&gt;</var> specifies the number of
rows (or columns) spanned, i.e., 'bottom' (or 'right') is set to
the grid line <var>&lt;span&gt;</var> rows below (or columns to the
right) of that edge.

<dt><var>&lt;grid-line&gt;</var> + <var>&lt;span&gt;</var>
<dd>
'Top' (or 'left') is set to the grid line given by the first
number The second number specifies the number of rows (or columns)
spanned, i.e., 'bottom' (or 'right') is set to the grid line
<var>&lt;span&gt;</var> rows below (or columns to the right) of the
first.
</dl>

<div class=example>
<p>For example, these rules

<pre>
DIV {grid: "ab"
           "cd"}
P {position: absolute; grid-position-x: d; grid-position-y: a}
</pre>

<p>mean that any P spans the same rows as slot a and spans the same
columns as slot d. In this case, that means it coincides with slot b.
All of the following are thus equivalent:

<pre>
P {position: absolute; grid-position-x: b; grid-position-y: b}
P {position: absolute; grid-position-x: b + 1; grid-position-y: b + 1}
P {position: absolute; grid-position-x: b - b; grid-position-y: a - a}
P {position: absolute; grid-position-x: 2 + 1; grid-position-y: 1 - 2}
P {position: absolute; grid-position-x: 2; grid-position-y: 1}
</pre>
</div>

<p class=issue>Use negative number to count from the right/bottom?

<p class=issue>This needs to be worked into the constraints for the
calculation of the grid size, so that these absolutely positioned
elements also contribute to the calculation of ''min-content'' and
''max-content''.

<p>When using <var>&lt;grid-line&gt;</var> or <var>&lt;span&gt;</var>
(but not when using <var>&lt;identifier&gt;</var>), it is possible to
refer to grid lines that do not exist in the grid declared with
'grid-columns'/'grid-rows'. In such a case, the grid is automatically
extended with the necessary rows or columns. The sequence of sizes
given by 'grid-columns'/'grid-rows' is repeated as often as necessary
to create exactly the required number of rows and column.

<div class=example>
<p>For example, you can transpose a table such as

<pre>
&lt;TABLE>
 &lt;TR>&lt;TD>A1 &lt;TD>A2 &lt;TD>A3
 &lt;TR>&lt;TD>B1 &lt;TD>B2 &lt;TD>B3
 ...
 &lt;TR>&lt;TD>K1 &lt;TD>K2 &lt;TD>K3
 ...
&lt;/TABLE>
</pre>

<p>to display it somewhat like this

<pre>
A1 B1... K1...
A2 B2... K2...
A3 B3... K3...
</pre>

<p>with style rules like this:

<pre>
TABLE {grid-columns: auto; grid-rows: auto}
TD:first-child {grid-position-x: next; grid-position-y: 1}
TD {grid-position-x: same; grid-position-y: next}
</pre>
</div>

<p
class=issue><a href="http://www.w3.org/Style/CSS/Tracker/issues/201"
>ISSUE-201:</a> Terra
Informatica's <a href="http://www.terrainformatica.com/htmlayout/"
>HTMLayout</a> program proposes an interesting shortcut: if a slot's
name is a number (instead of a letter), it refers directly to the
child with that number. That child is absolutely positioned on top of
that slot and doesn't need 'position', 'grid-position-x' or
'grid-position-y' to be set.
See <a
href="http://www.terrainformatica.com/w3/flex-layout/flex-layout.htm"
>the documentation by Andrew Fedoniouk and Ivan Goroun.</a>
E.g., <code>&lt;ul style="grid: '2 1'">&lt;li>one &lt;li>two
&lt;/ul></code> puts “two” on the left and “one” on the right. (Note
that this requires that the names of slots are separated by spaces.)
It is thus also a shortcut for some applications
of <a href="https://www.w3.org/TR/css3-flexbox/#flex-order"
>'flex-order'.</a>

<!--=================================================================-->

<h3 id=grid-position> The 'grid-position' shorthand property</h3>

<table class=propdef>
<tbody>
<tr>
<th>Name:
<td><dfn>grid-position</dfn>

<tr>
<th><a href="#values" >Value</a>:
<td><var>&lt;grid-position-x&gt;</var> [ /
<var>&lt;grid-position-y&gt;</var> ]?

<tr>
<th>Initial:
<td>auto

<tr>
<th>Applies to:
<td>elements with 'position: absolute'

<tr>
<th>Inherited:
<td>no

<tr>
<th>Animatable:
<td>no

<tr>
<th>Percentages:
<td>N/A

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

<tr>
<th>Canonical order:
<td><abbr title="follows order of property value definition">per
grammar</abbr>
</table>

<p>This is a shorthand for 'grid-position-x' and 'grid-position-y'.
If <var>&lt;grid-position-y&gt;</var> is omitted, it is the same
as <var>&lt;grid-position-x&gt;</var>.

<div class=example>
<p>For example, these rules

<pre>
DIV {grid: "ab"
           "cd"}
P {position: absolute; grid-position: d / a}
</pre>

<p>position any P to coincide with slot b. All of the following are
thus equivalent:

<pre>
P {position: absolute; grid-position: b / b}
P {position: absolute; grid-position: b + 1 / b + 1}
P {position: absolute; grid-position: b - b / a - a}
P {position: absolute; grid-position: 2 + 1 / 1 - 2}
P {position: absolute; grid-position: 2 / 1}
P {position: absolute; grid-position: b}
</pre>
</div>

<!--=================================================================-->

<h2 id=slot-pseudo>Styling slots: the ''::slot()'' pseudo-element</h2>

<p>The slots of a <em>grid element</em> can be individually addressed
with the <dfn>''::slot()'' pseudo-element.</dfn>

<div class=example>
<p>For example, the following sets the background and vertical
alignment of some of the slots in a template:

<pre>
body { grid: "aaa"
             "bcd" }
body::slot(b) { background: #FF0 }
body::slot(c), body::slot(d) { vertical-align: bottom }
</pre>
</div>

<p>Only the following properties apply to the ''slot()''
pseudo-element.

<ul>
<li>background properties

<li>'vertical-align' (see <a href="#vertical-alignment" >“vertical
alignment”</a> below)

<li>'overflow' (see the sections on <a href="#vertical-alignment"
>vertical alignment</a> and <a href="#paged" >paged media</a> below)

<li>'writing-mode'

<li>'direction'

<li>'box-shadow'

<li>border properties

<li>padding properties

<li>margin properties

<li>'box-decoration-break'

<li>column properties
</ul>

<p class=issue>Should 'content' be allowed? or should instead
'::slot(a)::before' be possible (and ditto with '::after')?  The
content would be at the start of the flow, before any elements flowed
into the slot and even before the <span title="grid element" >grid
element's</span> '':before'' pseudo-element, if the slot is the
<span>default slot.</span> If content applies, then most other
properties apply, too, to set the style of that content: color, font,
text-decoration&hellip;

<p class=issue>Should the 'content' property allow 'element()' from
GCPM? You could then repeat the heading of an article at the top of
each slot in case the article is split over several chained slots or
several pages. (See also the <a href="#see-page" >issue about
“continued on.”)</a>

<p class=issue><a href="http://www.w3.org/Style/CSS/Tracker/issues/37"
>ISSUE-37:</a> Can a slot have a border and if so, where is it drawn?

<p>The background of a slot is drawn immediately on top of the
background of the element itself. E.g., the background set on
''P::slot(a)'' is immediately in front of the background set on ''P''.

<p>Margins on slots do not collapse, neither with other slots, nor
with elements inside the slot.

<p class=issue>Margins aren't really necessary on slots. You can add
'.' cells in the grid template to make empty space.

<!--=================================================================-->

<div class=level4>
<h2>Styling the contents of slots: '::fragment()'</h2>

<p>The ':fragment(a)' pseudo-element selects the part of an element
that is inside slot a (similar to how '::first-line' selects the part
of an element that is on the first line).

<p>Inherited properties&hellip;

<p>Non-inherited properties&hellip;
</div>

<!--=================================================================-->

<h2>Rendering of grid elements</h2>

<p>Grid elements influence the stacking order, page breaks, the
position of floats, etc. of the content inside them.

<!--=================================================================-->

<h3 id=vertical-alignment>Vertical alignment of the contents of slots</h3>

<p>The 'vertical-align' property of a '::slot()' pseudo-element can be
used to align elements vertically in a slot (or horizontally, if the
slot is <span>vertical</span>). The effect is as if the
<em title="anonymous block of a slot">hypothetical anonymous block</em>
that contains the slot's contents is positioned as defined below.

<p>For the purpose of this section we define the <dfn>tail edge</dfn>
and <dfn>head edge</dfn> of a box as a writing-mode-dependent edge as
follows:

<table class=equiv-table>
<thead>
<tr><th>Value of 'writing-mode' <th>Meaning of “head” <th>Meaning of “tail”
<tbody>
<tr><th>''horizontal-tb'' <td>top <td>bottom
<tr><th>''vertical-rl'' <td>right <td>left
<tr><th>''vertical-lr'' <td>left <td>right
</table>

<p>E.g., if a box is <span>horizontal,</span> “head edge” means the
top edge.

<dl>
<dt>bottom
<dd>
The content of the slot is aligned to the <span>tail edge</span> of
the slot: the tail margin edge of the anonymous block coincides with
the tail margin edge of the slot.

<dt>middle
<dd>
The content of the slot is centered in the slot: the distance between
the <span title="head edge">head</span> margin edge of the anonymous
block and the <span title="head edge">head</span> margin edge of the
slot is equal to the distance between the <span title="tail
edge">tail</span> margin edge of the anonymous block and
the <span title="tail edge">tail</span> margin edge of the
slot.

<p class=note>(Note that if the content overflows the slot, it will
overflow at both edges.)

<dt>baseline
<dd>
The anonymous block that encloses the content is placed as far as
possible in the direction against the <em>block flow direction</em>
under two constraints:

<ol>
<li>The <span title="head edge">head</span> margin edge of the
anonymous block may not be beyond the <span title="head edge">head</span>
margin edge of the slot.

<li>If the content has a relevant first line (see below), then the
baseline of that line must align with the baselines of the relevant
first lines in all other slots with the same 'writing-mode' and the
same 'vertical-align' in the same row (if the slot
is <span>horizontal</span>) or the same column (if the slot
is <span>vertical</span>). A slot has a relevant first line, if the
content has a first line (ignoring any lines inside floats) and that
first line has the same 'writing-mode' as the slot itself.
</ol>

<p class=note>For example, for a <span>horizontal</span> slot, this
means that the first baseline must be aligned with the first baselines
of all other horizontal slots in the row that also have
'vertical-align: baseline'.

<dt><var>&lt;percentage&gt;</var>
<dd>
''0%'' means the same as ''bottom'', ''100%'' means the same as
''top'', other values are linear interpolations of these. Negative
values and values over 100% are interpreted as 0% and 100%
respectively.

<p class=note>Note that 100% minus the percentage corresponds to the
initial position of the scrolling mechanism (if any) in case the
content overflows.
</dl>

<p>For all other values, the content is aligned as for ''baseline''.

<!--=================================================================-->

<h3 id=paged>Breaking grid elements across pages or columns</h3>

<p><span>Grid elements</span> may be broken across pages, columns or
similar regions (including chained slots of another grid element),
subject to the 'break-before', 'break-after' and 'break-inside'
properties. In addition to the break points listed in the Fragmentation
module [[!CSS3-BREAK]], a page break may occur between two rows in a
template, if there is a possible break point at the same height or
higher in all slots that span those two rows; and a page break may
occur inside a row if there is a possible break point in all slots in
that row.

<p class=issue>Try to be more precise?

<p>In the terminology of [[CSS3-BREAK]], a slot is a
<em>fragmenter</em> of type ''region''.

<p>A forced break on an element in a slot causes the rest of the flow
of that slot to continue in another page, column or slot (depending on
the type of break). The following cases are special:

<ul>
<li>
<p>A forced page break causes all elements after the break (in document
order) to be on a new page. On which subsequent page they fall depends
on any page templates: there may not be a slot with the right name on
the next page.

<li>
<p>A forced column break only has effect if the element's multicol
ancestor is a descendant (is “inside”) the element's grid ancestor.
</ul>

<div class=example>
<p>For example, this document fragment has a column element inside a
grid element. Column breaks affect the content of a single slot, but do
not affect the other slots of the grid element:

<pre>
&lt;DIV STYLE="grid: 'ab' 'cd'">
 &lt;DIV STYLE="flow: a">
  I'm in slot a.
 &lt;/DIV>
 &lt;DIV STYLE="flow: b; columns: 20em">
  &lt;P>This text is in columns.
  &lt;H2 STYLE="break-before: column">Heading at top of column&lt;/H2>
  &lt;P>...
 &lt;/DIV
&lt;/DIV></pre>
</div>

<div class=example>
<p>For example, this document fragment has a grid element inside a
column element and thus the column break on the H2 is ignored:

<pre>
&lt;DIV STYLE="columns: 20em">
 &lt;DIV STYLE="grid: 'ab' 'cd'">
  &lt;P>I'm inside slot a inside some columns.
  &lt;H2 STYLE="break-before: column">No break&lt;/H2>
  &lt;P>...
 &lt;/DIV>
&lt;/DIV></pre>
</div>

<div class="example level4">
<p>A slide presentation can be made with a template for each page
(i.e., slide) and forced page break between the slides:

<pre>
@page	{ grid: "a" / 5em
	        "@" / *
	        "b" / auto }
h1	{ page-break-before: always;
	  flow: a }
p.note	{ flow: b }
</pre>

<p>With a document similar to this: (fragment)

<pre>
<b>&lt;h1></b>Slide 1 title<b>&lt;/h1></b>
<b>&lt;ul></b>
 <b>&lt;li></b>Topic one
<b>&lt;/ul></b>
<b>&lt;h1></b>Slide 2 title<b>&lt;/h1></b>
<b>&lt;ul></b>
 <b>&lt;li></b>More topics
<b>&lt;/ul></b>
<b>&lt;p class=note></b>Note the note
</pre>
</div>

<div class=example>
<p>The document in the example above doesn't have an element that
corresponds to a slide; a slide simply starts at an H1 and ends before
the next H1. But if there is a DIV around each slide (as is the case in
many slide formats in practice), the same effect can also be achieved
without page-based templates, by using the ''vh'' unit [[!CSS3VAL]]:

<pre>
div.slide {height: 100vh; grid: "a"/5em "*" "b"/intrinsic;
    page-break-before: always}
h1 {flow: a}
p.note {flow: b}
</pre>

<p>With a document similar to this: (fragment)

<pre>
<b>&lt;div class=slide></b>
 <b>&lt;h1></b>Slide 1 title<b>&lt;/h1></b>
 <b>&lt;ul></b>
  <b>&lt;li></b>Topic one
 <b>&lt;/ul></b>
<b>&lt;/div></b>
<b>&lt;div class=slide></b>
 <b>&lt;h1></b>Slide 2 title<b>&lt;/h1></b>
 <b>&lt;ul></b>
  <b>&lt;li></b>More topics
 <b>&lt;/ul></b>
 <b>&lt;p class=note></b>Note the note
<b>&lt;/div></b>
</pre>
</div>

<!--=================================================================-->

<h3 id=stacking-order>Stacking order</h3>

<p class=issue>Slots are stacked in the order they are listed in
'grid-template' (order of their top left corners). 'z-index' applies.
The general rules for <a href="/TR/CSS21/zindex" >stacking contexts</a>
<span class=issue>[ref in CSS3?]</span> apply.

<div class=example>
<p>This example uses 'z-index' and negative margins to make the middle
slot partly overlap the other slots:

<pre>
body { grid: "a.b"
             ".c."
             "d.e";
       height: 240px;
       width: 240px }
::slot(a) { background: #0C0 }
::slot(b) { background: #C00 }
::slot(c) { background: #FD0; margin: -20px; z-index: 1 }
::slot(d) { background: #00C }
::slot(e) { background: #A0A }
</pre>

<div class=figure>
<p><img alt="Five colored rectangles" longdesc=overlap.desc
src=overlap.png>

<p class=caption>Rendering of the above example.
</div>
</div>

<!--=================================================================-->

<h3>Floating elements inside templates</h3>

<p>An element may be flowed into a slot and be a floating element at
the same time. The following cases must be distinguished:

<ul>
<li>Page-based floats &ndash; In paged media (see [[!CSS3PAGE]]), if
the value of 'float' specifies that the element floats to the top or
bottom of the page (in a horizontal writing mode) or the left or right
of the page (in a vertical writing mode), the slot act as the page.
(I.e., the element floats to the top, bottom, etc. of the slot, not of
the page.

<li>Footnotes &ndash; Likewise, the footnote area for elements with
'float: footnote' is at the bottom of the slot, not of the page. The
@footnote at-rule can position the footnote area at other places, such
as the top, but always inside the slot.

<li>Normal floats &ndash; In other cases, the element floats normally
within its <span>containing block,</span> which in this case is its
slot in the template.
</ul>

<p class=issue>The '@footnote' at-rule from [[CSS3GCPM]] needs to be
extended to apply to slots: '@footnote :first::slot(a)' is the footnote
area of slot a on the first page.

<div class=level4>

<!--=================================================================-->

<h2 id=page-templates> Page-based grid templates</h2>

<p>A template can also be attached to a page, rather than an element.
Such a template is called a <dfn>page-based template</dfn> as opposed
to an <dfn>element-based template.</dfn>

<p>The syntax of a page-based template is the same as that of an
element-based one, but the declaration appears in an '@page' rule.

<p>In a page-based template, the height and width are typically known
(defined by the output media and the margin boxes, see [[CSS3PAGE]]).
And content that overflows a slot typically is not clipped (or hidden
behind a scrolling mechanism), but is continued on a subsequent page.

<p>Because the grid template is not attached to an element but to a
page, it is not scoped. The slot names are global, although they can be
hidden to elements that have a grid ancestor that uses the same slot
names.

<p>This modifies the rules for 'flow' and 'grid-position': if these
properties refer to a slot that is not found in a <span>grid
ancestor,</span> they refer instead to a slot in a page template (if
there is one and it has a slot of that name).

<p>Similarly, a 'grid-position' that refers to grid lines by number,
when set on an element that has no <span>grid ancestor,</span> refers
to grid lines of the page template instead, if it exists. But unlike an
element-based template, a page-based template is not automatically
grown if 'grid-position' refers to a grid line that was not declared in
the 'grid' property. Instead, 'grid-position' is ignored.

<p class=issue>Should we simplify page-based templates to only allow
<var>&lt;length&gt;</var> and * as row heights and column widths? (And
treat illegal sizes as '*'?)

<div class=example>
<pre>
@page :first {grid: "abc" "def"}
@page {grid: "def"}

body {flow: e}
h1 {flow: b}
</pre>
</div>

<p>A page that has a grid template does not have a footnote area
[[CSS3GCPM]]. Instead each slot in the grid template has its own
footnote area.

<p id=page-break>If a slot of a page-based template on
<em>non-interactive</em> media has an 'overflow' property of
''visible'', then content that overflows that slot in the block
progression direction (i.e., below the slot in the case of horizontal
text) causes a page break and is continued on the next page.

<p class=issue>What happens in non-interactive media with an 'overflow'
of ''scroll'' or ''auto''?

<p>For page breaking purposes, each slot is considered as a page and
the page break properties on the elements in that slot determine where
the content for that slot is broken [[!CSS3-BREAK]]. Content after the
page break is put in the slot of the same name on the next page that
has such a slot. If there is no such page, the UA should display the
content on a separate page.

<p class=issue>Or: the content after the page break is not displayed?
displayed in the default slot?

<p class=note>Note that this may happen if the template for the first
page ('@page :first') uses a letter that occurs in no other @page rule.
Possibly also if a page template is bound to a “named page”
[[CSS3GCPM]] and that named page is not allowed to repeat. (At the time
of writing, this is only a proposal in the GCPM Module.)

<p class=note>Note that an element <var>A</var> that appears later in
the document than an element <var>B</var> may thus be displayed on an
earlier page than element <var>B</var>, because their respective slots
are broken across pages in different ways.

<p>Because of limitations of a device (e.g., limited memory), it may be
that a UA has to print a page (force page breaks) even though some
slots aren't filled yet.

<div class=example>
<p>This example shows how the first page may have a different layout
from the other pages. The slot ''a'' only occurs on the first page. If
the content for that slot (in this case: all H1 elements) is too long,
the remaining content of that slot <span class=issue>will not be
displayed.</span> The slot ''@'' occurs on normal pages and all its
content can thus be displayed by adding additional pages.

<pre>
@page :first {grid: "a" "*"}
@page {grid: "*"}
h1 {flow: a}
</pre>
</div>

<p class=note>Note that “page masters” (sequences of different
templates for sequences of pages) can be made with the selectors
defined in <span class=issue>[not yet decided].</span>

<div class=example>
<p>Both page-based and element-based templates can be used in the same
document.

<pre>
@page {grid: "a*"}
:lang(fr} {flow: a}
div.special {grid: "abc" "abd"}
</pre>
</div>

<div class=example>
<p>Here is a page as one might find in a newspaper. It combines a
layout template with multicolumn layout.

<div class=figure>
<p><img
alt="5-column newspaper page with some   blocks of text that span several columns"
longdesc=newspaper.desc src=newspaper.png>

<p class=caption>The front page of a newspaper, with the first parts of
several stories that are continued on other pages and headings and
images that span several columns.
</div>

<pre>
@page :first {
  grid: "A  A  A  A  A  A  A  A  A" / 5cm
	".  .  .  .  .  .  .  .  ." / 0.25cm
	"B  .  C  C  C  C  C  C  C" / *
	"B  .  C  C  C  C  C  C  C" / *
	"B  .  C  C  C  C  C  C  C" / *
	"B  .  C  C  C  C  C  C  C" / *
	"B  .  C  C  C  C  C  C  C" / *
	"B  .  D  D  D  D  D  D  D" / *
	"B  .  D  D  D  D  D  D  D" / *
	"B  .  E  E  E  .  F  F  F" / *
	"B  .  E  E  E  .  F  F  F" / *
	"B  .  E  E  E  .  F  F  F" / *
	 * 3em * 3em * 3em * 3em *
}
h1 {flow: a; border-bottom: thick; margin-bottom: 1.5em}
#toc {flow: b; margin-right: -1.5em; border-right: thin;
  padding-right: 1.5em}
#leader {flow: c; columns: 4; column-gap: 3em}
#art1 {flow: d; columns: 4; column-gap: 3em; border-top: thin}
#art2 {flow: e; columns: 2; column-gap: 3em}
#art3 {flow: f; columns: 2; column-gap: 3em}
</pre>
</div>

<p class=issue id=see-page>If a slot on a page is full and the content
continues on the next page, it may be useful to insert something like
“continued on page X.” This is useful at any page break, but more
important if there are multiple “flows” of content on each page.
Maybe a break-content property? 'break-content: "▶
continued on p. " targetcounter(???, page)' or extend text-overflow
from [[!CSS3TEXT]]?

<p class=issue>How do you set the 'vertical-align' property of a slot
in a page? Does the '::slot()' pseudo-element apply? '@page :first
:slot(A) {vertical-align: bottom}'
</div>

<!--=================================================================-->

<div class=level4>
<h2 id=chains>Chaining slots: the 'chains' property</h2>

<p>Slots must be rectangular, but the appearance of non-rectangular
slots can be achieved to some extent by chaining slots together.
Content that is positioned in the first slot of a chain is
automatically continued in the second slot if the first slot is full,
and then the third, etc.

<table class=propdef>
  <tbody>
  <tr>
  <td>Name:
  <td><dfn>chains</dfn>

  <tr>
  <td>Value:
  <td>none | <var>&lt;letter&gt;</var>+ [ , <var>&lt;letter&gt;</var>+ ]*

  <tr>
  <td>Initial:
  <td>none

  <tr>
  <td>Applies to:
  <td><span title="template element">template elements</span>

  <tr>
  <td>Inherited:
  <td>no

  <tr>
  <td>Percentages:
  <td>N/A

  <tr>
  <td>Computed&nbsp;value:
  <td>specified value
</table>

<p>A value of ''none'' means the element's template has no chains.
Otherwise the value consists of one or more comma-separated lists of
letters. No letter may appear more than once in the value. Letters that
do not occur in the <em>template</em> are ignored, but do not make the
value invalid. A list with only ignored letters is itself ignored.

<p>All the non-ignored letters in a list, except for the last one, must
refer to slots whose size does not depend on their contents, otherwise
the list is ignored. The size of a slot does not depend on its content
if all the columns and all the rows that the slot spans have a width,
respectively height, that is a <var>&lt;length&gt;</var> or '*'.

<p>Each non-ignored list defines one <dfn>chain.</dfn>

<p>Each chain is filled with content in an analogous way to the pages
in paged media: all the content that is positioned to the first slot in
the chain is flowed, in document order, into the first slot in the
chain until the slot is full, the rest is flowed into the second slot
until it is full, etc.

<p>Content must only be split between slots at an allowed page break
[[!CSS3PAGE]]. As for page breaks, if a break occurs in the margin
between blocks, all adjoining margins are set to zero.

<p>CSS3 does not define what is the best break point to split content
over slots. However, it is recommended to use the last possible break
point that does not cause overflow. (If such a break point exists.)

<p class=note>Note: It is the author's responsibility to make the
height of relevant slots an integral number of lines if he wants to
ensure that the lines in chained slots are aligned. The height does not
automatically “snap” to a multiple of the line height.

<div class=example>
<p>The following template creates a double-staircase layout. In case
the content is too long for the staircase, a slot of flexible height is
added at the bottom.

<pre>
div { display: "@@..ff...." / 3.6em
               ".aa..gg..." / 3.6em
               "..bb..hh.." / 3.6em
               "...cc..ii." / 3.6em
               "....dd..jj" / 3.6em
               ".........." / 0.6em
               "eeee..kkkk" / auto;
   chains: @ a b c d e, f g h i j k}
#first { position: @ }
#second { position: f }
</pre>

<p>This could be applied to a document fragment such as

<pre>
&lt;DIV&gt;
  &lt;P ID=first&gt;...
  &lt;P ID=second&gt;...
&lt;/DIV&gt;
</pre>
</div>

<div class=example>
<p>Here is a paragraph shaped as a circle:

<pre>
p { width: 12em;
    grid: ". . . . @ @ . . . ." / 1.2em
	  ". . a a a a a a . ." / 1.2em
	  ". b b b b b b b b ." / 1.2em
	  ". b b b b b b b b ." / 1.2em
	  "c c c c c c c c c c" / 1.2em
	  "c c c c c c c c c c" / 1.2em
	  ". d d d d d d d d ." / 1.2em
	  ". d d d d d d d d ." / 1.2em
	  ". . e e e e e e . ." / 1.2em
	  ". . . . f f . . . ." / 1.2em
	  "g g g g g g g g g g" / auto;
   chains: @ a b c d e f g }
</pre>
</div>

<div class=example>
<p>Here is a page-based template that creates a two-column layout with
a “hole” in the center:

<pre>
@page:first {
    grid:
    "aaaaaaa.ddddddd"
    "aaaaaaa.ddddddd"
    "aaaaaaa.ddddddd"
    "aaaaaaa.ddddddd"
    "bbbb.......eeee"
    "bbbb.ggggg.eeee"
    "bbbb.ggggg.eeee"
    "bbbb.ggggg.eeee"
    "bbbb.......eeee"
    "ccccccc.fffffff"
    "ccccccc.fffffff"
    "ccccccc.fffffff"
    "ccccccc.fffffff";
    chains: a b c d e f }
@page::slot(g) {
    vertical-align: middle }

body { flow: a }
h1 { flow: g }
</pre>
</div>

<p class=note>Note: For more analysis of the possibilities and limits
of non-rectangular slots, see the PhD thesis of César Acebal
[[ACEBAL2010]].

<div class=issue>
<p>Chaining of rectangular slots is not enough to create layouts with
holes, e.g., an image in the middle of a text. Allowing
non-rectangular, <em>connected</em> regions (in addition to chaining)
would allow an example such as this:

<pre>
grid: "A A A . . ."
      "A . A . . ."
      "A A A . . ."
      ". . . B B B"
      ". . . B . B"
      ". . . B B B";
chains: a b;
</pre>

<p>Such cutouts in the middle of text usually create text that is
difficult to read, and that is why there is no 'float: center', e.g.
But the CSS WG is considering a new property 'wrap-flow' for absolutely
positioned elements that would allow, e.g.: 'p {position: absolute;
top: 1fr; left: 1fr; width: 1fr; height: 1fr; wrap-flow: both}' to
absolutely position a P element on top of a template element and cause
the content of the element under it to wrap around it as if it were a
float [[CSS3-EXCLUSIONS]].
</div>

<p class=note>Note that a slot can have overflowing content even if it
is part of a <span>chain</span>: it can have content that is too wide
but cannot be broken.

<p>The 'break-before', 'break-after' and 'break-inside' properties
have values that control breaking of content between slots in a chain
(in particular ''region'' and ''avoid-region'', see
[[!CSS3-BREAK]]).

<p class=note>Note that, as defined in <a href="#paged" >“Breaking
grid elements across pages or columns”</a> above, a slot is a
<em>fragmenter</em> of type <em>region</em> in the terminology of
[[!CSS3-BREAK]].
</div>

<!--=================================================================-->

<h2 id=cr-exit-criteria>CR exit criteria</h2>

<p>For this specification to be advanced to Proposed Recommendation,
there must be at least two independent, interoperable implementations
of each feature. Each feature may be implemented by a different set of
products, there is no requirement that all features be implemented by a
single product. For the purposes of this criterion, we define the
following terms:

<dl>
<dt>independent
<dd>
each implementation must be developed by a different party and
cannot share, reuse, or derive from code used by another qualifying
implementation. Sections of code that have no bearing on the
implementation of this specification are exempt from this requirement.

<dt>interoperable
<dd>
passing the respective test case(s) in the official CSS test suite,
or, if the implementation is not a Web browser, an equivalent test.
Every relevant test in the test suite should have an equivalent test
created if such a user agent (UA) is to be used to claim
interoperability. In addition if such a UA is to be used to claim
interoperability, then there must one or more additional UAs which can
also pass those equivalent tests in the same way for the purpose of
interoperability. The equivalent tests must be made publicly available
for the purposes of peer review.

<dt>implementation
<dd>
a user agent which:

<ol class=inline>
<li>implements the specification.

<li>is available to the general public. The implementation may be a
shipping product or other publicly available version (i.e., beta
version, preview release, or “nightly build”). Non-shipping product
releases must have implemented the feature(s) for a period of at least
one month in order to demonstrate stability.

<li>is not experimental (i.e., a version specifically designed to pass
the test suite and is not intended for normal usage going forward).
</ol>
</dl>

<p>The specification will remain Candidate Recommendation for at least
six months.

<p>A <a href="/Style/CSS/Test/" >test suite</a> will be developed during
the Candidate Recommendation phase of this specification.

<!--=================================================================-->

<h2 id=history>History</h2>

<p>The following sections contain some of the use cases and design
decision that led to this module and influenced its evolution.

<!--=================================================================-->

<h3>Developing a model of declaring, using, styling and resizing grids</h3>

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

<p class=mtb>The following types of use cases were considered for
template-based layout.

<ol>
<li>
<p>Standard Web pages.

<li>
<p>Grids and other table-like layouts. This includes grid layouts,
frame layouts and table-like subdivision of a rectangular area.

<li>
<p>A layout structure with “flex”ing information. The flexing is
represented by constraints that specify how the cells are to relate to
one another: which cells are to be allowed to grow or shrink and how
much. There may also be a priority ordering, which determines, based on
the size of the allowed display window, which cells shrink, which grow
and under which conditions.

<li>
<p>Layout structures with absolutely positioned (fixed-size) elements;
for example a block of text into which several illustrations intrude at
fixed positions within the block. This is like a float with respect to
tightly wrapping the text around the intrusion, but the position of the
intrusion is determined by the layout structure, not the content flowed
into that structure.

<p>An example of this is a multicolumn layout with one or more
“absolutely positioned floats” that intrude on the columns (see <a
href="#intrusion" >figure</a>).

<div class=figure id=intrusion>
<p><img
alt="An image that partially overlaps two columns makes the text wrap around it on both sides."
longdesc=cutout.desc src=cutout.svg>

<p class=caption>An image (or a “pull quote”) is placed centered on
the page and intrudes on two areas.
</div>

<li>
<p>Multiple, disconnected, fixed-size areas on a page that are chained
together, each one receiving the content that doesn't fit in the
previous slot. In combination with page breaks, this may give a layout
as often seen in newspapers: the first few lines of each story on the
first page, the rest of the story in other areas on subsequent pages.
(It will probably need a way to conditionally insert “continued on
page&nbsp;7” or similar text.)
</ol>

<p>For comparing proposals for template-based layouts, the working
group identified four important aspects of each proposal:

<ol>
<li>
<p>the physical layout structures &ndash; the way of structuring the
“cells” (slots) into which content is flowed. This includes a way
to identify the various layout containers.

<li>
<p>the binding mechanism &ndash; the way to specify that a given
element (and its descendants) are to be placed in a given layout cell.

<li>
<p>the property distribution mechanism &ndash; the way to put
properties onto the layout structure and the cells within it.

<li>
<p>the flexing mechanism &ndash; the way to describe how the layout
structure should adapt itself to the higher level container (window) in
which it is placed. This includes statements about which cells should
grow and when they should grow.
</ol>

<p>In this specification, these aspects are as follows:

<ol>
<li>
<p>A character matrix is used to show the layout structure and the
cells are named by the character used to show where they are
positioned.

<li>
<p>The binding of content to cells is handled by the 'position'
property which identifies a cell to which the content is bound.

<li>
<p>The shape, size and flexibility of the layout are specified with the
character matrix. Some properties (background, border and vertical
alignment) are attached to individual slots.

<li>
<p>There is limited “flexing” information. The choice is between
fixed size, a fraction of the available size or the content's intrinsic
size. (The latter is further subject to min/max sizes specified on that
content.) It is not possible to say, e.g., that some column can only
become wider if all other columns are at their maximum size.
</ol>

<!--=================================================================-->

<h3>Syntax, features and levels</h3>

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

<p>The following is a partial list of design decisions and some
arguments for and against each choice:

<!--=================================================================-->

<h4>Named vs numbered slots</h4>

<p>Named slots are very easy to understand and use. Experience with
the draft showed that everybody who sees an example immediately
understands what it means. Moreover, there is no need to use numbers
or to count.

<p>But it is different for absolutely positioned elements that use the
grid. Those elements do not belong to a slot, they are merely placed
on top of it, overlapping what is already there and each other.

<p>Also, if grids are <a href="#auto-add" >automatically extended with
extra rows and columns (see below)</a> based on content, then those
extra rows and columns cannot have names and must (probably, see below)
be referred to by number.

<p>In this specification, named slots are used to create flows of
content, while numbers are used for absolute positioning, although
names can be used there too, if the author prefers.

<!--=================================================================-->

<h4>Single letter names vs identifiers</h4>

<p>The set of single letters is finite. And even if Unicode has many
symbols, typing them may not be easy. Letters also do not permit to
give a hint as to a slot's function (“heading,” “footer,”
“advertisement”&hellip;).

<p>On the other hand, any Unicode character can be typed as an escape,
so if you run out of letters on the keyboard, you can always make a
template like this:

<pre>DIV {grid: "\1001\1002\1003"
           "\1001\1004\1005\1006"}
DIV H1 {flow: \1001}</pre>

<p>In practice, it is also hard to come up with meaningful identifiers
and so single letters require less thinking. And if you always have single
letters, you don't need spaces between them either, which makes big
templates easier to read.

<p>This specification therefore uses single letters (i.e., on
'grid-template'; the syntaxes of 'flow' and 'grid-position' are the
same either way).

<!--=================================================================-->

<h4 id=display>Extend 'display' or add a grid property</h4>

<p>Grids can be defined on elements such as table cells, blocks,
inline blocks or list items, but not on elements such as tables or,
inline elements. That can be expressed in the syntax by adding the
grid to the 'display' property: 'display: inline-block "abc" "abd"' is
valid, but 'display: inline "abc" "abd"' would not be. Or it can be
expressed by an implicit dependency between properties: 'display:
inline-block; grid: "abc" "abd"' has a grid, but 'display: inline;
grid: "abc" "abd"' ignores the grid. (In this case it is actually the
computed value of 'display' that applies, so, e.g., if the element
floats, it would be a block and thus have a grid.)

<p>The Multicol specification uses the latter model: 'columns' is a
separate property and only applies if the element is a <em>block
container.</em> Given that precedent, it seemed reasonable to do the
same here.

<!--=================================================================-->

<h4>Combining columns and grids</h4>

<p>Style rules can specify both a grid and columns for the same
element:

<pre>DIV {columns: 20em; grid: "aabccc"}</pre>

<p>The specification could say that grids don't apply to column
elements, or vice versa, or it could say that the columns apply to
contents of the DIV, after it has been flowed into the <em>default
slot.</em> This last option seemed the most useful. It is consistent
with other elements that flow into a slots: they, too, can have
columns.

<!--=================================================================-->

<h4>Shorthand vs single property</h4>

<p>It is convenient to specify the grid as the value of a single
property. It puts the column and row sizes immediately next to the rows
and columns they apply to. The typical column widths can either be
omitted or are short values like '*' and '1em', and they fit easily in
one line.

<p>But if a grid has very many columns, or their sizes are complex
(with many ''minmax()'' and ''calc()'' values, e.g.), it may be more
readable to separate the slot names from the column sizes.

<p>Also, separable properties for row and column sizes makes is easier
to specify a transition/animation on them,, because you don't have to
repeat the slot names (which cannot animate).

<p>For those reasons, this specification defines the 'grid' property
as a shorthand, at the cost for authors of having to learn four new
properties instead of one (or zero, if the grid had been added to <a
href="#display" >display (see above).</a>

<!--=================================================================-->

<h4>The number of rows and columns</h4>

<p>If the grid template can also be specified with individual
properties, how many columns &amp; rows does it have if those
properties contradict each other? Does the template (if not ''none'')
determine the number of columns or the maximum of the template and the
list of sizes? E.g.:

<table class=equiv-table>
<thead>
<tr>
<th>Specified values
<th>Meaning if the template prevails
<th>Meaning if the maximum value is used

<tbody>
<tr>
<td>
<pre>grid-template: "a b c";
grid-columns: * * * * *</pre>
<td>
<pre>grid-template: "a b c";
grid-columns: * * *</pre>
<td>
<pre>grid-template: "a b c . .";
grid-columns: * * * *</pre>
</table>

<p>The former is consistent with the model for 'background-image' and
'background-size'. However, unlike for backgrounds, where a size
without an image makes no sense, in this case a size without a slot
name <em>can</em> make sense: it can represent empty space ('.') of
the given size.

<p>What is more likely: that people consciously specify empty rows and
columns without putting dots in the template (to save typing or to
avoid typing too many dots), or that people mistakenly add a size too
many?

<p>The specification currently sets the number of rows and columns to
the maximum of the three properties.

<!--=================================================================-->

<h4 id=need-fr>'*' vs ''fr''</h4>

<p><a href="http://www.w3.org/Style/CSS/Tracker/issues/127"
>ISSUE-127:</a> It is very common for the columns of a grid to have
all the same width. That is because the slots in a grid, although of
different widths themselves, typically are multiples of some
fundamental measure. And thus equal columns is the default in the
current syntax. And if it needs to be specified explicitly which
columns have the same width (e.g., because there are also other
columns in the grid) then the symbol for it is short: '*'. This is
ideal for slots whose widths are small multiples of the fundamental
measure. E.g., the widths of slots a, b and c in the following grid
relate to each other as 1:3:2:

<pre>
grid: "a b b b c c"
      "a . . . c c"
</pre>

<p>However, if the ratios of the slots are ratios of larger numbers,
the notation may become long. E.g., to make slots a and b with ratio
10:11, you would have to make 21 columns:

<pre>grid: "aaaaaaaaaabbbbbbbbbbb"</pre>

<p>It needs to be investigated if such ratios are frequent. (They
don't seem to occur in printed magazines.) And if among the ratios
that do occur, even if infrequently, there are some would be
impractical to write in this way.

<p>Assuming another notation is needed, it could be made by prefixing
a number (e.g., '7* 10*') or, to make the notation look more like a
dimension, by creating a special unit ''fr'' ('e.g., '3.5fr 5fr',
which is the same as 7 + 10 stars).

<p>If ''fr'' is added, it could either be in addition to '*' or instead
of '*'. In the former case, '*' = '1fr'.

<p>Unless it is shown that the notation with only '*' is not practical
in real cases, it seems better to neither introduce numbers ('7*') nor
units ('3.5fr'). It would give too many different ways to write the
same grid, causing authors and readers of style sheets to have to
think longer about each grid. (E.g., 'grid: "abbbcc"' could then also
be written as 'grid: "abc" 1* 3* 2*' or 'grid: "abbbc" 0.5fr 0.5fr
0.5fr 0.5fr 1fr', etc.)

<p>For the moment, the specification allows both the 'fr' and *
notations.

<!--=================================================================-->

<h4 id=auto-add>Automatically add rows and columns</h4>

<p>The main purpose of grids is to improve on absolute positioning for
displaying elements in a different visual order. You typically know
how many positions you need in advance.

<p>If you don't need to change the visual order, then table layout can
often align the elements sufficiently.

<p>However, if table layout isn't possible (there are not enough
elements in the source to create the necessary table rows, the control
over the size of table cells is too limited, or you want a
column-major table), it may be useful to use a grid in a similar
manner to a table: the number of rows and columns is not specified in
the style, but depends on the number of elements that are put in the
grid.

<p>E.g., you could transpose a table with an unknown number or rows
like this:

<pre>
&lt;TABLE>
 &lt;TR>&lt;TD>A1 &lt;TD>A2 &lt;TD>A3
 &lt;TR>&lt;TD>B1 &lt;TD>B2 &lt;TD>B3
 ...
 &lt;TR>&lt;TD>K1 &lt;TD>K2 &lt;TD>K3
 ...
&lt;/TABLE>
</pre>

<p>into a tabular display with an unknown number of columns somewhat
like this:

<pre>
A1 B1... K1...
A2 B2... K2...
A3 B3... K3...
</pre>

<p>with style rules like this:

<pre>
TABLE {grid-columns: auto; grid-rows: auto}
TD:first-child {grid-position: next / 1}
TD {grid-position: same / next}
</pre>

<p>This uses keywords instead of numbers, as described in <a
href="#next-same" >“Automatic placement of elements”</a> below.

<p>What is the size of the added rows and columns? The example above
assumes the size of the single, specified grid cell is simply
repeated. There could also be a marker in the list of sizes to
indicate which set of sizes is repeated. Or there could be a separate
property with the list of sizes that is repeated for all added rows
and columns.

<p>It would probably be difficult to specify that any number of
columns of size A can be added, but that the last column must have
size B&hellip;

<p>The current specification specifies that extra rows and columns are
added when needed for absolute positioning ('grid-position'). It is
not possible to automatically create new, anonymous flows. (But
sometimes you can use multi-column elements to do that, and possibly
grid templates can be attached to columns, via a '::column')
pseudo-element, see [[CSS3GCPM]].)

<!--=================================================================-->

<h4>Rectangular slots vs non-rectangular slots</h4>

<p>Non-rectangular slots, such as

<pre>
grid: "a a a"
      "a a ."
      "a . ."
</pre>

<p>are probably something for level 4. Or maybe the Exclusions module
can be used instead.

<!--=================================================================-->

<h4 id=chained>Chained slots</h4>

<p>Many layouts found in magazines can be handled with multi-columns
[[CSS3COL]] (possibly extended with ideas in GCPM [[CSS3GCPM]]) or with
multi-column elements inside a grid, but some more complicated designs
appear to require chained slots (and some would be easier to specify
that way than with columns).

<pre>
grid: "A A E"
      "A A E"
      "B B E"
      "C D E";
chains: B C D E
</pre>

<p>Also, when grids are applied to pages (see <a href="#page-grid"
>“Page grids”</a> below), it is essential that slots are connected to
slots on the next or some subsequent page, so that the overflow can
find a place.

<p>But this could be a feature for level 4.

<!--=================================================================-->

<h4 id=page-grid>Page grids</h4>

<p>Typically in magazines, each page has a slightly different layout
of slots, although they are all based on the same set of columns,
usually between 3 and 6. It is difficult to specify the grids of all
pages as a single long grid on the BODY element; and indeed impossible
if you don't know how many pages use each kind of layout.

<p>Applying grids to '@page' is an alternative. It has a few issues:

<ul>
<li>We need named paged ('@page news {&hellip;}'), a way for an
element to say it needs to start on a specific kind of page
('break-before: page(news)' or 'break-before; always; page: news'),
and a way to say which style follows which ('@page news-odd {next:
news-even}').

<li>What happens to footnotes [[CSS3GCPM]]? Each slot probably has its
own footnote area.

<li>How are slots on different pages connected? Probably by having the
same name.
</ul>

<p>This is probably for level 4.

<!--=================================================================-->

<h4>Style the slots (pseudo-elements)</h4>

<p>Slots can have properties of their own: background, overflow,
writing-mode, direction, box-shadow, margin, border, padding. What
else?

<p>For 'vertical-align', see <a href="#vert-align" >“Vertical
alignment inside slots”</a> below.

<p>This specification also allows 'z-index', because then you can give
a slot negative margins and have it partially overlap some other slot.

<p>'Wrap-flow' (from <a href="https://www.w3.org/TR/css3-exclusions/"
>CSS Exclusions and Shapes</a>) could be useful for slots with
negative margins, too.

<p>'Content' might be useful, but is maybe too powerful: you could
write a whole document, with proper styling, in a style sheet and
would only need an empty source document.

<!--=================================================================-->

<h4>Style the contents of slots (region-based styling)</h4>

<p>By means of a new pseudo-element, style could be applied to only
the part of an element that is inside a certain slot (similar to how
''::first-line'' applies style only to the part of an element in the
first line of a paragraph):

<pre>P::fragment(a) {font-size: large}</pre>

<p>This looks like a level 4 feature.

<!--=================================================================-->

<h4>Orient the grid with writing mode vs orient the slots</h4>

<p>A grid can contain vertical text, but the grid itself probably
doesn't need to be rotated or flipped. Indeed, it would be confusing
if it did. In other words, the following element has vertical text in
the top right slot and an image in the bottom right slot:

<pre>
&lt;DIV STYLE="grid: "a*" "ab"; writing-mode: vertical-rl">
 Some text here...
 &lt;IMG STYLE="flow: b"...>
 ...
&lt;/DIV>
</pre>

<p>In this specification, a grid template is always laid out with the
first row at the top and the first column on the left. But the slots
themselves can have a writing mode (by default the one “inherited”
from the grid element).

<!--=================================================================-->

<h4>Indicating the default slot ('*' vs '@')</h4>

<p>The symbol '*' seems a good choice, as the concept of default is
somewhat similar to the concept of wildcard. The '*' is also used to
set the size of rows and columns, but the context is probably enough
to avoid confusion.

<!--=================================================================-->

<h4 id=abspos>Flowing vs absolutely positioning content in a grid</h4>

<p>The most flexible model for positioning content in a grid is to
consider the slot as a flow, which can contain zero, one or more
elements and even anonymous content. This is the same concept as a
table cell: the cell also is a separate flow that can contain several
elements as well as anonymous content.

<p>An element inside a slot thus has its size determined as an element
in normal flow. E.g., if you set a background on it, the background
covers the element only, not the whole slot. (But the slot has its own
background property for that.)

<p>But you may also want to use the grid as a coordinate system for
absolutely positioned elements, which then overlap with the contents
of the grid (above or below it, depending on 'z-index').

<p>And, as <a href="#auto-add" >“Automatically add rows and
columns”</a> above explains, you may want a table-like display of
elements that are neither absolutely positioned nor flowed, but the
table properties aren't powerful enough.

<p>Those two ideas can be added to the grid template model: the
declaration of the grid is reused, but instead of using 'flow' to
position an element into it, the element is absolutely positioned on
top of it. But unlike the absolute positioning in level 2, this
positioning is allowed to influence the size of the grid element on
which it is positioned.

<p>There are two ideas for how to do this. One idea is to define a
special kind of unit, ''gr'', which is only defined for elements that
have a <em>grid ancestor,</em> and which can be used on the 'top',
'right', 'bottom' and 'left', properties of absolutely positioned
elements. ''left: 2.25gr'' means the position is in the third column,
one quarter of the way towards the fourth column.

<p>Another way is to define a new property 'grid-position' (shorthand
for 'grid-position-x' and 'grid-position-y'), which, if set, overrides 'top',
'left', etc. and which takes numbers or names of slots (up to four
of them, to set the four sides).

<p>Yet another way is to extend 'top', 'left', etc., with unitless
values (meaning the n'th grid column or row) and letters (meaning the
appropriate edge of the slot of that name).

<p>This specification adds a 'grid-position' property, which overrides
'top', 'right', etc. When it is used, it also indicates that the
element takes part in the size calculations of the rows and columns it
is put on top of.

<!--=================================================================-->

<h4>Use the pseudo-class to create additional slots</h4>

<p>If you want a flow that overlaps with a grid element (i.e.,
absolutely positioned on top of it), but that flow doesn't correspond
to an element in the document you could create a pseudo-element that
is like an “absolutely positioned slot:”

<pre>DIV::slot(z) {position: absolute; grid-position: 2 / 2}</pre>

<p>Like other '::slot()' pseudo-elements, it applies to <span>grid
elements</span> only (the DIV in this example must be a grid element),
but unlike other '::slot()' pseudo-elements it doesn't style an
existing slot, but implicitly creates a new one. (It is some kind of
error if the name ''z'' already exists in the grid template.)

<p>Then you can flow other elements into this slot:

<pre>.note {flow: z}</pre>

<p>This mechanism is pretty difficult to understand. Experience shows
it is also difficult to explain and in a style sheet it is difficult
to recognize. What are the use cases (that can't be done with negative
margins, absolute positioning, etc.)? This specification does not
allow the creation of arbitrary, absolutely positioned
pseudo-elements. If needed, it could be added in level 4.

<!--=================================================================-->

<h4>Names for edges</h4>

<p>If you position elements absolutely (with 'top', 'left', etc. or
with 'grid-position', see <a href="#abspos" >“Flowing vs absolutely
positioning content in a grid”</a> above), you can use numbers to
refer to grid lines: from '1' (the left edge of the first column) to
<var>N</var>+1 (the right edge of the last column) and ditto for
rows. You can also refer to the edges of slots, for an extra level of
indirection and to avoid the need for numbers.

<p>It has been suggested to create a mechanism to assign arbitrary
names to grid lines, even multiple aliases for the same grid line. You
could then absolutely position an element at grid line ''foo'' (e.g.,
'grid-position: foo / 1') and later assign that alias ''foo'' to a
different grid line without having to change the style rules that use
it. E.g., the following could make the name ''a-line'' an alias for
the number 2 and ''b-line'' an alias for the number 4:

<pre>
/* Create a 7x2 grid template */
DIV {grid-columns: * a-line * * b-line * *; grid-rows: * *}
/* Put H2 at cell x=4, y=2 */
DIV H2 {position: absolute; grid-position: b-line / 2}
</pre>

<p>(This could also use strings instead of identifiers, for even more
flexible names.)

<p>This turns out to be very difficult to explain to users, partly
because of the syntax, partly because of the indirection, which comes
on top of the inherent indirection that CSS already requires (the
style rules are in a style sheet, not on the elements they apply to)
and the indirection of specifying a position indirectly by referring
to an abstract grid.

<p>Also, the number of usages of 'grid-position' (for a given grid) is
not likely to be so big that a symbolic name for a grid line is
necessary. Moreover, this is easy to handle with a macro processor.

<p>This specification does not include a mechanism to assign aliases
to grid lines.

<!--=================================================================-->

<h4>Position from the right and bottom</h4>

<p>If elements are absolutely positioned relative to a grid (with
'top', 'left' or 'grid-position', see <a href="#abspos" >“Flowing vs
absolutely positioning content in a grid”</a> above), and especially
if the grid can automatically grow (see <a href="#auto-add"
>“Automatically add rows and columns”</a>) it might be useful to
position elements relative to the last row or column, independent of
how many rows or columns the grid element has. That could be done with
negative numbers:

<pre>grid-position-x: -1</pre>

<p>This specification does not allow positioning from the end. If uses
cases are found, it could be added in level 4.

<!--=================================================================-->

<h4>Syntax features to shorten long grid specifications</h4>

<p>Grids are typically very regular (see also <a href="#need-fr" >'*'
vs ''fr''</a> above). E.g., if you specify the margins between slots
in the template (rather then with a 'margin' property on the slots),
you often end up with a grid similar to this:

<pre>grid-template: "a.b.c.d.e.f";
grid-columns: * 1em * 1em * 1em * 1em * 1em *</pre>

<p>Even for the columns of broadsheet newspapers (6&ndash;8 columns),
that still fits easily on one line, even with margins between the
columns. But if the grid gets even longer, there may be a need for
abbreviations, e.g.:

<pre>grid-columns: * repeat(1em *, 5)</pre>

<p>or

<pre>grid-columns: * (1em *)[5]</pre>

<p>or

<pre>grid-columns: * 5//1em *//</pre>

<p>This makes the syntax harder to learn and read, though. So it needs
some good use cases first. This can be postponed to level 4.

<!--=================================================================-->

<h4>''fit-content'' vs ''auto'' vs&hellip;</h4>

<p>Column sizes can have an exact size or a minimum and maximum size,
by means of ''minmax()''. A common case is probably
''minmax(min-content, max-content)''. (Is that really true?) Should
that common case have its own keyword? If so, should that keyword be
''fit-content''?

<p>''fit-content'' in the Box Module is defined as something else, viz.,
min(max(available width, ''min-content''), ''max-content'')).

<p>In this specification, ''auto'' (not ''fit-content'') is allowed
for column and row sizes and has the meaning of ''minmax(min-content,
max-content)''.

<!--=================================================================-->

<h4 id=vert-align>Vertical alignment inside slots</h4>

<p>The content of a slot can be vertically aligned with
'vertical-align', exactly like the content in table cells. (Despite
the name, it would, of course, be horizontal alignment if the slot's
writing mode was vertical.)

<p>There could also be a property that applies exclusively to grids
(grid-slot-align?), just like Flexbox proposes an alignment property
that applies exclusively to flex items ('flex-item-align'). But why
should users learn a new property when 'vertical-align' fits so well?

<p>Looking beyond tables, flex boxes and grids, there is also a need
for vertical alignment of content in normal blocks (when those blocks
have a height that does not depend on their contents). There might
thus also be a new property that applies uniformly to all cases. E.g.:
''block-align: top | bottom | middle | baseline |
<var>&lt;percentage&gt;</var> | <var>&lt;length&gt;</var>'', where
''baseline'' simply means ''top'' everywhere outside grids and
tables. (A separate question is if it would override 'vertical-align'
in tables). Or 'vertical-align' itself could be generalized to apply
to all <em>block container</em> boxes (although the meaning would be
ambiguous on ''inline-block'').

<p>Given how little progress has been made on this generally
applicable property, the present specification just reuses
'vertical-align'. If a differently named property is developed after
the grid template module becomes a REC, then whatever interaction it
has with 'vertical-align' would apply to slots, too.

<!--=================================================================-->

<h4>Horizontal alignment inside slots</h4>

<p>Elements can be centered in, or aligned to a side of, their parent
with ''auto'' margins. But this doesn't always work: for many
combinations of 'width' and 'direction', the auto margins are
ignored. There may thus be a new property ('block-align: center'?) or
value ('margin: any'?) in the future for correct alignment and
centering.

<p>Or should there be an alignment property that only applies to grid
slots? 'grid-slot-align'?

<p>This specification defines nothing, in the expectation of a general
solution in the future.

<!--=================================================================-->

<h4>Auto margins on slots</h4>

<p>Do ''auto'' margins on slots (e.g., ''::slot(a) {margin: auto}'')
do anything? Or are they simply 0?

<!--=================================================================-->

<h4>Page floats</h4>

<p>[[CSS3GCPM]] defines “page floats” (which are slightly misnamed,
because they cause floats to float not just to the top or bottom of a
page, but also to the top or bottom of a column in certain
contexts). What do they do in slots?

<p>This specification treats a slot similar to a column, e.g.,
''float: top'' means the top of the slot, not of the page. Similarly,
if slots are <a href="#chained" >chained,</a> then the float modifiers
select the next slot, not the next page.

<!--=================================================================-->

<h4>Break-* properties</h4>

<p>The 'break-before', 'break-after' and 'break-inside' properties in
the draft of February 2012 (see [[CSS3-BREAK]]) have keywords
''region'' and ''avoid-region''. Should they be called ''slot'' and
''avoid-slot'' instead?

<!--=================================================================-->

<h4 id=next-same>Automatic placement of elements</h4>

<p>There may be cases where elements are to be placed based on where
the previous elements was placed, which isn't always expressible with
a clever selector. An example is placing DD elements in the same slot
as the preceding DT element. (Note that there may be more than one DD
associated with a single DT, so a selector such as ''DT + DD'' doesn't
work. The selector ''DT ~ DD'' doesn't work either, because it selects
DDs that belong to the next DT, too.).

<p>A keyword may help: 'flow: same'.

<p>In some cases, elements may need to be placed in the next column or
row after the previous element. If there are cases where rows or
columns need to be <a href="#auto-add" >added automatically based on
content,</a> those are probably also the cases where element are to
be placed in the “next” row or column w.r.t. to the preceding element.

<p>E.g., with a keyword: 'grid-position: next/same' (for “next
column, same row”).

<p>This specification defines ''same'' on 'flow' and 'grid-position'
and ''next'' on 'grid-position' only, because so far there are no use
case for ''next'' on 'flow'.

<!--=================================================================-->

<h2 id=changes>Changes</h2>

<p>Summary of major changes since the <a
href="/TR/2011/WD-css3-layout-20111129/" >29 November 2011 draft:</a>

<ul>
<li>Added a <a href="#accessibility" >note about accessibility.</a>

<li>Instead of directly on 'display', the grid template is now
specified with a new property, 'grid', to be consistent with 'columns'
in the multi-column specification [[CSS3COL]], and also to allow the
grid to be a shorthand for more primitive properties: 'grid-template',
'grid-rows' and 'grid-columns', which makes animations easier to
specify.

<li>Replaced @ by * to indicate the default slot. The asterisk looks
better and may also be easier to remember, because of its association
with the notion of “wild card.”

<li>Added dimensions with the ''fr'' unit as an alternative to * on
row and column sizes (and an issue about whether these units are
useful enough).

<li>Removed the ''gr'' unit as a means to absolutely position elements
on a grid and instead added a special property, 'grid-position'
(shorthand for 'grid-position-x' and 'grid-position-y').

<li>Absolutely positioned elements, if positioned relative to a grid,
are now taken into account when calculating the size of the grid.

<li>Because of the above, it is now possible to automatically add rows
and columns to a grid element if elements are absolutely positioned
relative to grid lines beyond those declared in the grid template.

<li>Moved the 'chains' property to level 4 of this module. (In theory,
it shouldn't be more difficult for a UA to balance content in a chain
of slots than in a chain of columns, but it requires some new code,
nevertheless.)

<li>Moved page-based templates ('@page') to level 4. The scope of slot
names, automatic chaining of slots on different pages, and especially
the question of how to create more than three page templates
(':first', ':left' and ':right') need more investigation.

<li>Moved region-based styling (i.e., pseudo-element selectors for
styling elements differently based on which slots they fall into) to
level 4. It is only useful in combination with chaining of slots (the
'chains' property) or page-based templates.

<li>Renamed the keyword ''fit-content'' to ''auto''. The former has a
specific meaning in [[CSS3BOX]], which is related, but not the same.

<li>The margin properties are now allowed on slots. Even though this
is redundant with the possibility to create empty slots in the grid
template, it seems more consistent, because slots also have borders
(which, unlike in tables, do not collapse).

<li>Different set of constraints and a different function to optimize
when calculating the size of rows and columns: the row heights and
column widths are now considered together, which should guarantee that
the overall size of the grid element is as small as possible in all
cases and also makes the handling of width and height symmetric.

<li>References to 'page-break-*' properties and to [[CSS3PAGE]] have
been replaced with references to 'break-*' properties and the new
[[CSS3-BREAK]] module.

<li>Now allows <var>&lt;percentage&gt;</var> on 'vertical-align'.

<li>Generalized the text for 'vertical-align' to apply to all writing
modes.
</ul>

<!--=================================================================-->

<h2 class="no-num" id="acknowledgments">Acknowledgments</h2>

<p>The first ideas for describing a template in CSS date from 1996 and
are described in <a href="/TR/NOTE-layout" ><cite>Frame-based layout
via Style Sheets</cite></a> by Bert Bos, Dave Raggett and Håkon Wium
Lie. The idea was revived in 2005 on the request of W3C's Device
Independence Working Group and benefited especially from discussions
with Rhys Lewis and Rotan Hanrahan from that group.

<p>This specification was further influenced by ideas about form
layout by <a
href="https://lists.w3.org/Archives/Member/w3c-css-wg/2002JulSep/0077.html" >
Dave Raggett [member-only link]</a> and an early write-up of the
features of <a href="http://www.mozilla.org/projects/xul/xul.html" >
XUL</a> by <a
href="https://lists.w3.org/Archives/Member/w3c-css-wg/2002JanMar/0432.html" >
Ian Hickson [member-only link].</a>

<p><a href="http://transcendingcss.com/support/" >Andy
Clarke,</a> <a href="http://sushiandrobots.com/about" >Jina Bolton</a>
and <a href="http://lawver.net/" >Kevin Lawver</a> provided use cases,
examples and requirements. The analysis in the <a href="#history"
>History</a> section is a slightly shortened version of work by Steve
Zilles.

<p>César Acebal built the
first <a href="http://transcendingcss.com/support/almcss.zip" >
prototype.</a> Andrew Fedoniouk
built <a
href="http://lists.w3.org/Archives/Public/www-style/2009Mar/0278.html"
> the second.</a>
A <a
href="http://lists.w3.org/Archives/Public/www-style/2009Apr/0383.html"
> third prototype</a> was made by Alexis Deveria.

<!--=================================================================-->

<h2 class="no-num" id="references">References</h2>

<p id="normative-references">Normative references:
<!--begin-normative-->

<p>[Here will be inserted the file “normative.inc”]
<!--end-normative-->

<p id="other-references">Other references:
<!--begin-informative-->

<p>[Here will be inserted the file “informative.inc”]
<!--end-informative-->

<!--=================================================================-->

<h2 class="no-num" id="index">Index</h2>
<!--index-->

<!--=================================================================-->

<h2 class="no-num" id="property-index">Property index</h2>
<!-- properties -->

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