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<!DOCTYPE html public '-//W3C//DTD HTML 4.01//EN'>
<html lang=en>
<head profile="http://microformats.org/profile/hcard
http://microformats.org/wiki/rel-license">
<meta http-equiv=content-type content="text/html; charset=utf-8">
<title>CSS Template Layout Module</title>
<link rel=stylesheet type="text/css" href="../default.css">
<link rel=stylesheet type="text/css"
href="http://www.w3.org/StyleSheets/TR/W3C-MO.css">
<div class=head>
<!--logo-->
<h1>CSS Template Layout Module</h1>
<h2 class="no-num no-toc">[LONGSTATUS] [DATE: 3 August 2004]</h2>
<dl>
<dt>This version: </dt>
<dd><a href="[VERSION]">
http://www.w3.org/TR/[YEAR]/WD-[SHORTNAME]-[CDATE]/</a>
<dt>Latest version:</dt>
<dd><a
href="[LATEST]">
http://www.w3.org/TR/css3-layout/</a>
<dt>Previous version:</dt>
<dd><a href="http://www.w3.org/TR/2011/WD-css3-layout-20111129/">
http://www.w3.org/TR/2011/WD-css3-layout-20111129/</a>
<dt>Editors:</dt>
<dd class=vcard><span class=fn>Bert Bos</span>
(<span class=org>W3C</span>) <a class=email
href="mailto:bert@w3.org">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 src="diagram.png" alt="Image: four elements move to four
slots in a template" longdesc="diagram.desc">
<p class=caption>A grid with four slots defined by 'display:
"aaaaaaa" "bccccdd"'.
</div>
<p>CSS is a simple, declarative language for creating style sheets
that specify the rendering of HTML and other structured documents.
This module contains CSS features to describe layouts at a high level,
meant for tasks such as the positioning and alignment of “widgets” in
a graphical user interface or the layout grid for a page or a window.
<p>A layout grid or “template” defines one or more “slots” that an
element's content can flow into. This allows elements to have
complex shapes and it allows the visual order to be different from the
order of the elements in the source document.
<p>A '::slot' selector allows elements to be styled differently based
on which slot they appear in.
<h2 class="no-num no-toc" id=status>Status of this document</h2>
<!--status-->
<p>This draft is related to the drafts about positoning with grid
units ('gr'), creating and naming grids and regions
[[CSS3-GRID-LAYOUT]], flexible <abbr title="Graphical User
Interfaces">GUIs</abbr> [[CSS3-FLEXBOX]], and tables [[!CSS3TBL]]. The
CSS Working Group is considering combining some or all of these into a
single specification with all matrix-based layouts.
<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 id=dependencies>Dependencies on other modules</h2>
<p>This CSS3 module depends on the following other CSS3 modules:
<ul>
<li><cite>CSS syntax module</cite> [[!CSS3SYN]] –
<dfn>interactive</dfn> vs <dfn>non-interactive</dfn> media.
<li><cite>CSS values and Units module</cite> [[!CSS3VAL]] – <a
href="/TR/css3-values#strings">
<dfn><var><string></var></dfn></a> and <a
href="/TR/css3-values#length-value">
<dfn><var><length></var></dfn></a>.
<li><cite>CSS box module</cite> [[!CSS3BOX]] – properties
<dfn>width</dfn>, <dfn>height</dfn>, <dfn>float</dfn>,
<dfn>display</dfn> and <dfn>overflow</dfn>
<li><cite>CSS text layout</cite> [[!CSS3TEXTLAYOUT]] –
properties <dfn>direction</dfn> and <dfn>block-flow</dfn>
<li><cite>CSS positioning</cite> [[!CSS3POS]] – property
<dfn>z-index</dfn>
<li><cite>CSS paged media</cite> [[!CSS3PAGE]] – properties
<dfn>page-break-before</dfn>, <dfn>page-break-after</dfn> and
<dfn>page</dfn>; <a href="/TR/css3-page#page-area0"><dfn>page
area</dfn></a> (in particular its width & height).
<li><cite>CSS background and borders</cite> [[!CSS3BG]] –
property <dfn>background</dfn> <span
class=issue>and <dfn>box-shadow</dfn>?</span>
<li><cite>CSS tables</cite> [[!CSS3TBL]] – property
<dfn>vertical-align</dfn>. <span class=issue>[or Box Module?]</span>
<li><cite>CSS Multi-column Layout Module</cite> [[!CSS3COL]] –
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="http://www.w3.org/TR/CSS21/about.html#property-defs">section 1.4.2
of CSS level 2</a> [[CSS21]] for the grammar and other notations
that this specification uses in property definitions.
<h2>Introduction</h2>
<p><em>(This section is not normative.)</em>
<div class=sidefigure>
<p><img src="diagram.png" alt="Image: four elements move to four
slots in a template" longdesc="diagram.desc">
<p class=caption>Four regions, called a, b, c and d, each receive a
part of a document
</div>
<p class=mtb>The styling of a Web page, a form or a graphical user
interface can roughly be divided in two parts: (1) defining the
overall “grid” of the page or window and (2) specifying the fonts,
indents, colors, etc., of the text and other objects. The two are not
completely separate, of course, because indenting or coloring a text
influences the perceived grid as well. Nevertheless, when one
separates the parts of a style that should change when the window gets
bigger from the parts that stay the same, one often finds that the
grid changes (room for a sidebar, extra navigation bar, big margins,
larger images…), while fonts, colors, indents, numbering styles, and
many other things don't have to change, until the size of the window
becomes extreme.
<p>The properties in this specification work by associating a
<em>layout policy</em> with an element. Rather than letting an element
lay out its descendants in their normal order as inline text or as
blocks of text (the policies available in CSS level 1), the
policy defined in this module, called <em>template-based
positioning,</em> gives an element an invisible grid for aligning
descendant elements.
<p>Because layouts on the Web have to adapt to different window and
paper sizes, the rows and columns of the grid can be made fixed or
flexible in size.
<p>The typical use cases for these properties include:
<ul>
<li>Complex Web pages, with multiple navigation bars in fixed
positions, areas for advertisements, etc.
<li>Complex forms, where the alignment of labels and form fields may
be easier with the properties of this module than with the
properties for tables and margins.
<li>GUIs, where buttons, toolbars, labels, icons, etc., are aligned
in complex ways and have to stay aligned (and not wrap, for example)
when the window is resized.
<li>Paged displays (e.g., printed media) where each page is divided
in fixed areas for different kinds of content.
<li>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>Template-based positioning is an alternative to absolute
positioning, which, like absolute positioning, is especially useful
for aligning elements that don't have simple relationships in the
source (parent-child, ancestor-descendant, immediate sibling). But in
contrast to absolute positioning, the elements are not positioned with
the help of horizontal and vertical coordinates, but by mapping them
into slots in a table-like template. The relative size and alignment
of elements is thus governed implicitly by the rows and columns of the
template. A template doesn't allow elements to overlap, but it provides
layouts that adapt better to different widths.
<p class=issue>Call it a “slot” or rather a “region”?
<p>The mapping is done with the 'position' property, which specifies
in this case into which slot of the template the element goes. The
template itself is specified on the 'display' property of some
ancestor of the elements to remap.
<div class=example>
<p>In this example, the four children of an element are assigned to
four slots (called a, b, c and d) in a 2×2 template. (All mark-up
examples in this specification are HTML fragments, unless otherwise
stated.)
<div class=sidefigure>
<p><img src="aapje.png" alt="Image: sample rendering" longdesc="aapje.desc">
<p class=caption>Each element occupies one slot. In this template,
all slots have the same size.
</div>
<pre>
<style type="text/css">
dl { display: "ab"
"cd" }
#sym1 { position: a }
#lab1 { position: b }
#sym2 { position: c }
#lab2 { position: d }
</style>
<dl>
<dt id=sym1>A
<dd id=lab1>A is een aapje
<dt id=sym2>B
<dd id=lab2>B is de bakker
</dl>
</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 { display: "aaa"
"bcd" }
#head { position: a }
#nav { position: b }
#adv { position: c }
#body { position: d }
}
@media all and (max-width: 500px)
{
body { display: "a"
"b"
"c" }
#head { position: a }
#nav { position: b }
#adv { display: none }
#body { position: c }
}</pre>
</div>
<div class=example>
<p>Elements can be positioned this way, but not made to overlap,
unless with negative margins. Here is how the <a
href="http://www.csszengarden.com/?cssfile=/026/026.css&page=0">
“zunflower” design</a> of the Zen Garden could be done:
<pre>
#container { display: "abc" }
#intro { position: a; margin-right: -2em; box-shadow: 0.5em 0.5em 0.5em }
#supportingText { position: b; box-shadow: 0.5em 0.5em 0.5em }
#linkList { position: c }
</pre>
</div>
<div class=example>
<p>Template-based positioning borrows some concepts from table layout,
in particular the idea of aligning elements in rows and columns, so
that they constrain each other's size. But there are also differences.
This example shows some of them. Assume this document fragment:
<pre>
<div class=group>
<div>aa aa aa aa aa aa</div>
<div>bbb</div>
<div class=menu>ccccc</div>
</div>
</pre>
<p>We can lay it out as three columns, as the following illustrations
show. The style sheet would contain the following.
<pre>
.group {display: table}
.group > div {display: table-cell}
</pre>
<div class=figure>
<p><img src="table1.png" alt="[Three unequal cells]" longdesc="table1.desc">
<p class=caption>Example of rendering with a table.
</div>
<p>We can also use a template, in which case the style sheet would
contain this:
<pre>
.group {display: "abc"}
.group > div {position: a}
.group > div + div {position: b}
.group > div + div + div {position: c}
</pre>
<p>By default, the table is as wide as needed to fit its contents. To
make sure it is as wide as its containing block, we need to add
<pre>.group {display: table; width: 100%}</pre>
<p>That is not needed for the template, but, on the other hand, if we
want the template to fit its contents, we would need to say so:
<pre>.group {display: "abc"; width: fit-content}</pre>
<p>(See [[!CSS3BOX]] for the definition of the 'width' property.) The
columns of the template are by default all the same size. The columns
of the table satisfy certain constraints, but the exact size is not
defined. We can make them all the same by adding a rule (see
[[!CSS3TBL]]):
<pre>.group {display: table; width: 100%; table-layout: fixed}</pre>
<div class=figure>
<p><img src="table2.png" alt="[Three equal cells]" longdesc="table2.desc">
<p class=caption>Example of rendering with equal columns.
</div>
<p>In both styles, we can set a column to a certain size:
<pre>div.menu {width: 3em}</pre>
<p>resp.,
<pre>.group {display: "abc" * * 3em}</pre>
<div class=figure>
<p><img src="table3.png" alt="[Two equal cells, third is 3em wide]"
longdesc="table3.desc">
<p class=caption>Example of rendering with a fixed third column and
the other two columns of equal width.
</div>
<p>If there is an unknown number of columns (children of the div.group
element), the style sheet for the table model will automatically take
them into account. The style sheet for the template model, however,
creates a template of exactly three columns and can't handle tables
with an unknown number of columns. The extra elements will be added
into the default slot (in this case the ''a'' slot).
<p>In both models, elements can have borders, but only in the table
model can borders be collapsed, which makes setting borders a little
easier in the table model:
<pre>
.group {display: table; border-collapse: collapse}
.group > div {border: solid}
</pre>
<p>resp.,
<pre>
.group > div {border: solid; border-left: none}
.group > div:first-child {border-left: solid}
</pre>
<p>In the template model, the order of the elements is explicit, and
thus it is possible to reverse the order of the columns:
<pre>
.group > div {position: c}
.group > div + div {position: b}
.group > div + div + div {position: a}
</pre>
<div class=figure>
<p><img src="table4.png" alt="[Different contents for the cells]"
longdesc="table4.desc">
<p class=caption>Example of rendering with the contents of the three
columns reversed: the third element is shown in the first slot and
the first element in the third slot.
</div>
<p>In the table model, the order of the rows and columns is given by
the document source and thus can't be changed.
</div>
<div class=example>
<p>This example shows a way to move notes to the end of a section.
“Notes” in this example refers to elements in HTML with a class of
“note”. A fragment of HTML such as
<pre>
<div class=section>
<p>The balubious coster of the fifth secter<span
class=note> The sixth secter coster is a difter
manon.</span> of The Rollow Carpug mentizes a costernica.
<p>…
</div>
</pre>
<p>with this style sheet
<pre>
div.section {
display: "@" available
"F" available}
.note {
position: F;
content: counter(note) ".\A0" contents;
counter-increment: note;
font-size: smaller}
.note::before {
content: counter(note);
position: @;
vertical-align: super;
font-size: larger}
</pre>
<p>results in a rendering similar to this:
<div class=figure>
<p><img src="footnotes.png" alt="Same text, with the SPAN replaced by
“(1)” and its content moved to the end." longdesc="footnotes.desc">
<p class=caption>Rendering of a text with footnotes.
</div>
</div>
<div class=example>
<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 src="regions-intro-rendering.png" alt="Image of a complex,
3-column layout" longdesc="regions-intro-rendering.desc">
<p class=caption>Example rendering
</div>
<p>We assume a document fragment similar to this:
<pre>
<div id=article>
<p><img src="sunset" alt="">
<h1>Introduction</h1>
<p>This is an example…
<h1>More Details</h1>
<p>This illustrates…
<p>Then, the example…
<p>Finally, this…
</div>
</pre>
<p>The style sheet makes the DIV into a template element with five
regions, called A, 1, 2, 3 and 4. The regions are grouped into two
chains: region A on its own, and the chain consisting of 1, 2, 3 and 4.
<pre>
#article {
display: "A A 4"
"A A 4"
"1 1 4"
"2 3 4";
chains: 1 2 3 4 }
</pre>
<p>All children go into region 1 (and continue in 2, 3 and 4 as
needed). The IMG element goes into region A. We assume for simplicity
that there is only one IMG element:
<pre>
#article > * { position: 1 }
#article img { position: A }
</pre>
<p>The text in region 1 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(1) {
font-weight: bold;
color: #0C3D5F;
font-size: larger }
h1::slot(1) {
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.)
</div>
<h2 id=accessibility>A note about accessibility</h2>
<p><em>(This section is not normative.)</em>
<p>The facilities in this specification allow elements from a document
to be displayed in a visual order that is to a large extent
independent of the order in the document. That may have both positive
and negative effects on accessibility. The positive aspect is that it
allows the content in the document to be kept in logical order, so
that the document is as functional as possible without the style sheet
and on media where the style sheet doesn't apply. A negative aspect is
that a document that has a defined tab order (the order in which
elements get the focus when the tab-key is pressed) will show on the
screen with a tab order unrelated to the visual order. It may be
necessary to use the keyboard control features of the CSS Basic User
Interface module [[CSS3UI]] to ensure that the tab navigation follows
the visual order, or to refrain from positioning semantically related
elements in different parts of a template.
<p>The following two requirements from the Web Content Accessibility
Guidelines (WCAG) 2.0 [[WCAG20]] are particularly relevant. See that
specification for more information.
<blockquote>
<p><a
href="http://www.w3.org/TR/2008/REC-WCAG20-20081211/#content-structure-separation-sequence"
><strong>1.3.2 Meaningful Sequence:</strong></a> When the sequence in
which content is presented affects its meaning, a <a
href="http://www.w3.org/TR/2008/REC-WCAG20-20081211/#correct-reading-sequencedef"
>correct reading sequence</a> can be <a
href="http://www.w3.org/TR/2008/REC-WCAG20-20081211/#programmaticallydetermineddef
">programmatically determined.</a> (Level A)
</blockquote>
<blockquote>
<p><a
href="http://www.w3.org/TR/2008/REC-WCAG20-20081211/#navigation-mechanisms-focus-order"
><strong>2.4.3 Focus Order:</strong></a> If a <a
href="http://www.w3.org/TR/2008/REC-WCAG20-20081211/#webpagedef" >Web
page</a> can be <a
href="http://www.w3.org/TR/2008/REC-WCAG20-20081211/#nav-seqdef"
>navigated sequentially</a> and the navigation sequences affect
meaning or operation, focusable components receive focus in an order
that preserves meaning and operability. (Level A)
</blockquote>
<h2>Features out of scope</h2>
<p>A number of features that are related to grid layouts are not
handled in this module. Some of them are in other modules.
<h3>Repeating templates</h3>
<p>The templates defined by this specification have a fixed number of
slots, independent of the amount of content or the number of child
elements. In some situations it may be useful to define a template and
then, in the case there is more content than fits, automatically
create new copies of the template, to the side of or below the first
one, just like new pages are created in paged media or new columns in
multi-column layouts.
<p>In some cases it may be possible to simulate that behavior by
putting the template element inside a column layout.
<h3>Non-rectangular shapes and wrap-arounds</h3>
<p>This specification allows to chain multiple slots together to form
complex shapes, but each of the slots is itself still rectangular.
<p>Another module, <cite>CSS exclusions and shapes</cite>
[[CSS3-EXCLUSIONS]], is expected to allow floating elements to have
non-rectangular shapes and allow positioned elements to cause
wrap-around.
<h2>Declaring templates: the 'display' property</h2>
<p class=issue><a href="http://www.w3.org/Style/CSS/Tracker/issues/123"
>ISSUE-123:</a> One way to experiment safely with implementations
before the specification reaches Candidate Recommendation status is to
add an identifier with a vendor prefix somewhere in the value, e.g.,
'display: -my-product "aa" "bc"' or 'display: -my-product("aa"
"bc")'.
<table class=propdef-extra>
<tr>
<td><em>Name:</em>
<td>'display'
<tr>
<td><em>New value:</em>
<td><var><display-type></var>? && [ [ <var><string></var> [ /
<var><row-height></var> ]? ]+ ]
<var><col-width></var>*
<tr>
<td><em>Percentages:</em>
<td>N/A
<tr>
<td><em>Computed value:</em>
<td>specified value
</table>
<p>A value of this form is called a <dfn>template.</dfn>
<p>An element with such a 'display' value is
similar to a table element, in that its content is laid out in rows and
columns. The two main differences are that the number of rows and
columns doesn't depend on the content, but is fixed by the value of
the property; and that the order of the descendants in the source
document may be different from the order in which they appear in the
rendered template.
<p>The <dfn><var><display-type></var></dfn> is one of the
following keywords. An omitted keyword is equivalent to ''block''.
<pre class=prod><dfn><var><display-type></var></dfn> = inline |
block | list-item | inline-block | table | inline-table |
table-row-group | table-header-group | table-footer-group | table-row
| table-column-group | table-column | table-cell | table-caption |
none</pre>
<dl>
<dt>''inline''
<dt>''inline-block''
<dt>''inline-table''
<dd>These three values are equivalent. The element is
an <em>inline-level</em> element.
<dt>''list-item''
<dd>The element is formatted as a list item. If the element has the
value ''inside'' for its 'list-style-position', that ''inside'' is
treated as if it were ''outside''.
<dt>''block''
<dt>''table''
<dd>These two values are equivalent.
<dt>''table-row-group''
<dt>''table-header-group''
<dt>''table-footer-group''
<dd>This creates a principal block-level box that is the template,
with around it an anonymous ''table-row'' box and around it a box of
the indicated type. Around it may be more anonymous boxes according to
the rules for <a href="/TR/CSS2/tables.html#anonymous-boxes"
>Anonymous table objects</a> [[!CSS21]].
<dt>''table-row''
<dd>This creates a principal block-level box that is the template and
around it a ''table-row'' box. Around it may be zero or more anonymous
boxes according to the rules
for <a href="/TR/CSS2/tables.html#anonymous-boxes" >Anonymous table
objects</a> [[!CSS21]].
<dt>''table-column-group''
<dt>''table-column''
<dd>The template is ignored and the element is treated as an element
of the indicated type.
<dt>''table-cell''
<dd>The element is a table cell with a template.
<dt>''table-caption''
<dd>The element is a table caption with a template.
<dt>''none''
<dd>The template is ignored and the element is treated as for
'display: none'.
</dl>
<p class=issue>Future display types added in other modules?
<p class=note>Note that 'display' is extended to apply to '@page'
rules as well and that it has a different default there, viz.,
''"@"''. See <a href="#paged">“Templates in paged media”</a> below.
<!-- If display becomes a shorthand for display-model and
display-role, explain that the former gets the template (and the
latter is inline or block depending on whether the inline
keyword is present). -->
<p>Each string consist of one or more at signs (“@”), letters (or
digits, see
<var><letter></var> below), periods
(“.”) and spaces. Each string represents
one row in the template, each character other than a space represents
one column in that row. Spaces have no meaning. They may be added for
readability.
<p>The symbols in the template have the following meaning
<dl>
<dt>a letter
<dd>slot for content.
<dt>@
<dd>(at sign) default slot for content.
<dt>.
<dd>(period) white-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. Uppercase and lowercase are considered to be
the same letter (i.e., the template is case-insensitive).
<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 (“.”) (that will thus not contain any elements).
<p>Each slot (letter or “@”) acts as a block element for its
contents.
<p>Each <dfn><var><row-height></var></dfn> sets the
height of the preceding row. The default is ''auto''. The values can
be as follows:
<dl>
<dt><var><length></var>
<dd>An explicit height for that row. Negative values make the
template illegal. If the length is expressed in ''gr'' units, these
refer to the inherited grid, not the grid defined by the template
itself (see <a href="#gr-unit" >“Definition of the ''gr'' unit in a
template element”</a>).
<dt>auto
<dd>The row's height is determined by its contents. See the <a
href="#rowheight">algorithm</a> below.
<dt>*
<dd>(asterisk) All rows with an
asterisk will be of equal height. See the <a
href="#rowheight">algorithm</a> below.
</dl>
<p>Each <dfn><var><col-width></var></dfn> sets the width of a
column. If there are more <var><col-width></var>s then columns,
the last ones are ignored. If there are fewer, the missing ones are
assumed to be '*'. Each <var><col-width></var> can be one of the
following:
<dl>
<dt><var><length></var>
<dd>An explicit width for that column. Negative values make the
template illegal.
<dt>*
<dd>(asterisk.) All columns with a '*' have
the same width. See the <a href="#colwidth">algorithm</a> below.
<dt>max-content,
<dt>min-content
<dd>The column's width is determined by its contents. See the
<a href="#colwidth">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><length></var> | max-content
| min-content | * ]. There may be white space around the <var>p</var>
and <var>q</var>. If <var>q</var> < <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>fit-content
<dd>Equivalent to 'minmax(min-content, max-content)'.
</dl>
<p class=note>Note that it is legal to specify no widths at all. In
that case, all columns have the same width.
<div class=issue>
<p><a href="http://www.w3.org/Style/CSS/Tracker/issues/127"
>ISSUE-127:</a>
It has been suggested that the template may become too verbose in
the case of column widths that are very small factions, e.g., a column
of 1/40th of the width:
<pre>display: "abbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb"</pre>
<p>Abbreviating this with percentages ('2.5% 97.5%') introduces an
opportunity for errors (e.g., '3% 98%' causes the template to be
rejected). Abbreviating with numbers,
<pre>display: "ab" * 39*</pre>
<p>(or even just '1 39') is safer. On the other hand, those 39
identical letters make it immediately clear what the intention
is…
<p>Percentages that do no sum to 100% need not be rejected, however:
they could be used to force overflow.
</div>
<p>The orientation of the template is independent of the writing mode
('direction' and 'block-flow' properties): the first string is the
topmost row and the first symbol in each string is the leftmost
column.
<div class=example>
<pre><style type="text/css">
div { display: ".aa..bb." }
p.left { position: a }
p.right { position: b }
</style>
<div>
<p class=left>Left column
<p class=right>Right column
</div></pre>
</div>
<p>An element with a template value for its 'display' property
is called a <dfn>template element</dfn>. An element's <dfn>template
ancestor</dfn> is defined (recursively) as follows:
<ul>
<li>if the element has 'position: fixed', 'position: absolute', a
value of 'float' that is not ''none'' or the element is the root
element, than it has no template ancestor.
<li>else, if the element's parent has a template as its
'display', then that parent is the element's template
ancestor.
<li>else, the element's template ancestor is the same as its
parent's template ancestor.
</ul>
<h2 id=colwidth>Computing the width of the slots</h2>
<p>First, the <dfn title="intrinsic minimum width|intrinsic preferred
width">intrinsic minimum and intrinsic preferred widths</dfn> are
defined as follows:
<ul>
<li><p>A column with a <var><col-width></var> of a given
<var><length></var> has intrinsic minimum and intrinsic
preferred widths both equal to that <var><length></var>.
<li><p>A column with a <var><col-width></var> of '*' has an
infinite intrinsic preferred width. Its intrinsic minimum width is 0.
<li><p>A column with a <var><col-width></var> of
''min-content'' has an intrinsic minimum width and intrinsic
preferred width that are both equal to the largest of the intrinsic
minimum widths of all the slots in that column:
<ul>
<li>The intrinsic minimum width of a “.” is 0.
<li>The intrinsic minimum width of a letter or “@” is 0 if
that slot spans two or more columns; otherwise, it is the
<em>intrinsic minimum</em> width as defined by [[!CSS3BOX]]. For
the purpose of that definition, the slot is considered as a
block with a 'block-flow' of ''tb'' with its contents as its
children. <span class=issue>Should the block progression
direction be a property?</span>
</ul>
<li><p>A column with a <var><col-width></var> of
''max-content'' has an intrinsic minimum width and intrinsic
preferred width that are both equal to the largest of the intrinsic
preferred widths of all the slots in that column:
<ul>
<li>The intrinsic preferred width of a “.” is 0.
<li>The intrinsic preferred width of a letter or “@” is the
intrinsic preferred width as defined by [[!CSS3BOX]]. For the
purpose of that definition, the slot (which may span several
columns) is considered as a block with a 'block-flow' of ''tb''
with its contents as its children. <span class=issue>Should the
block progression direction be a property?</span>
</ul>
<li><p>A column with a <var><col-width></var> of
'minmax(<var>p</var>,<var>q</var>)' has an intrinsic minimum width
equal to <var>p</var> and an intrinsic preferred width equal to
<var>q</var>.
</ul>
<p>Next, the <dfn>layout algorithm</dfn> distinguishes between
elements with and without an a-priori known content width.
<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.
<ul>
<li>
<p>If the element has an a-priori width:
<ul>
<li>If the sum of the <em title="intrinsic minimum
width">intrinsic minimum widths</em> of the columns is larger
than the element's width, each column is set to its
<em>intrinsic minimum width</em> and the contents will overflow
(see 'overflow').
<li>If the sum of the <em title="intrinsic minimum
width">intrinsic minimum widths</em> of the columns is less than
or equal to the element's width, the columns are widened until
the total width is equal to the element's width, as follows: all
columns get the same width, except that no column or span of
columns may be wider than its <em>intrinsic preferred
width.</em> If the columns cannot be widened enough, the
template is left or right aligned in the element's content area,
depending on whether 'direction' is ''ltr'' or ''rtl'',
respectively.
</ul>
<li>
<p>If the element doesn't have an a-priori width:
<ul>
<li>If the sum of the <em title="intrinsic minimum
width">intrinsic minimum widths</em> of the columns is wider
than the <em>initial containing block,</em> each column is set
to its <em>intrinsic minimum width.</em> The element's <em>used
width</em> is the sum of the widths of the columns.
<li>If the sum of the <em title="intrinsic minimum
width">intrinsic minimum widths</em> of the columns is less than
or equal to the width of the <em>initial containing block,</em>
the columns are widened until the total width is equal to the
<em>initial containing block,</em> as follows: all columns get
the same width, except that no column or span of columns may be
wider than its <em>maximum intrinsic width.</em> The element's
<em>used width</em> is the sum of the widths of the columns.
</ul>
</ul>
<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><col-width></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?
<h2 id=rowheight>Computing the height of the slots</h2>
<p>The height of the template is the smallest possible under the
following constraints:
<ol>
<li>Rows with a height set to <var><length></var> have that
height.
<li>No row has a negative height.
<li>All rows with a height set to '*' are the same height.
<li>Every sequence of one or more rows of which at least one has a
height set to ''auto'' is at least as high as every letter or
“@” slot that spans exactly that sequence of rows.
<li>If the computed value of the ele
3811
ment's 'height' is ''auto'',
then every sequence of one or more rows of which at least one has a
height set to '*' is at least as high as every letter or “@” slot
that spans exactly that sequence of rows.
<li>The whole template is at least as high as the computed value of
the element's 'height', unless that value is ''auto'', or unless all
rows have a height set to <var><length></var>.
</ol>