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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html lang=en>
<head
profile="http://www.w3.org/2006/03/hcard http://microformats.org/wiki/rel-license">
<title>CSS Template Layout Module</title>
<link href="../default.css" rel=stylesheet type="text/css">
<link href="http://www.w3.org/StyleSheets/TR/W3C-ED.css" rel=stylesheet
type="text/css">
<body>
<div class=head> <!--begin-logo-->
<p><a href="http://www.w3.org/"><img alt=W3C height=48
src="http://www.w3.org/Icons/w3c_home" width=72></a> <!--end-logo-->
<h1>CSS Template Layout Module</h1>
<h2 class="no-num no-toc" id=longstatus-date-3-august-2004>Editor's Draft
5 November 2011</h2>
<dl>
<dt>This version:
<dd><a href="http://www.w3.org/TR/2011/ED-css3-layout-20111105/">
http://www.w3.org/TR/2011/ED-css3-layout-20111105</a>
<dt>Latest version:
<dd><a href="http://www.w3.org/TR/css3-layout">
http://www.w3.org/TR/css3-layout</a>
<dt>Previous version:
<dd><a href="http://www.w3.org/TR/2009/WD-css3-layout-20090402">
http://www.w3.org/TR/2009/WD-css3-layout-20090402</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">bert@w3.org</a>
<dd class=vcard><span class=fn>César Acebal</span> (<span
class=org>University of Oviedo</span>)
</dl>
<!--begin-copyright-->
<p class=copyright><a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
rel=license>Copyright</a> © 2011 <a
href="http://www.w3.org/"><acronym
title="World Wide Web Consortium">W3C</acronym></a><sup>®</sup> (<a
href="http://www.csail.mit.edu/"><acronym
title="Massachusetts Institute of Technology">MIT</acronym></a>, <a
href="http://www.ercim.eu/"><acronym
title="European Research Consortium for Informatics and Mathematics">ERCIM</acronym></a>,
<a href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. W3C <a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
<a
href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a>
and <a
href="http://www.w3.org/Consortium/Legal/copyright-documents">document
use</a> rules apply.</p>
<!--end-copyright-->
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc" id=abstract>Abstract</h2>
<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>A grid with four slots defined by ‘<code
class=css>display: "aaaaaaa" "bccccdd"</code>’.
</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 ‘<a href="#slot"><code class=css>::slot</code></a>’
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>
<!--begin-status-->
<p>This is a public copy of the editors' draft. It is provided for
discussion only and may change at any moment. Its publication here does
not imply endorsement of its contents by W3C. Don't cite this document
other than as work in progress.
<p>The (<a
href="http://lists.w3.org/Archives/Public/www-style/">archived</a>) public
mailing list <a
href="mailto:www-style@w3.org?Subject=%5Bcss3-layout%5D%20PUT%20SUBJECT%20HERE">
www-style@w3.org</a> (see <a
href="http://www.w3.org/Mail/Request">instructions</a>) is preferred for
discussion of this specification. When sending e-mail, please put the text
“css3-layout” in the subject, preferably like this:
“[<!---->css3-layout<!---->] <em>…summary of
comment…</em>”
<p>This document was produced by the <a href="/Style/CSS/members">CSS
Working Group</a> (part of the <a href="/Style/">Style Activity</a>).
<p>This document was produced by a group operating under the <a
href="/Consortium/Patent-Policy-20040205/">5 February 2004 W3C Patent
Policy</a>. W3C maintains a <a href="/2004/01/pp-impl/32061/status"
rel=disclosure>public list of any patent disclosures</a> made in
connection with the deliverables of the group; that page also includes
instructions for disclosing a patent. An individual who has actual
knowledge of a patent which the individual believes contains <a
href="/Consortium/Patent-Policy-20040205/#def-essential">Essential
Claim(s)</a> must disclose the information in accordance with <a
href="/Consortium/Patent-Policy-20040205/#sec-Disclosure">section 6 of the
W3C Patent Policy</a>.</p>
<!--end-status-->
<p>This draft is related to the drafts about positoning with grid units
(‘<code class=property>fr</code>’), creating and naming grids
and regions <a href="#CSS3-GRID-LAYOUT"
rel=biblioentry>[CSS3-GRID-LAYOUT]<!--{{CSS3-GRID-LAYOUT}}--></a>,
flexible <abbr title="Graphical User Interfaces">GUIs</abbr> <a
href="#CSS3-FLEXBOX"
rel=biblioentry>[CSS3-FLEXBOX]<!--{{CSS3-FLEXBOX}}--></a>, and tables <a
href="#CSS3TBL" rel=biblioentry>[CSS3TBL]<!--{{!CSS3TBL}}--></a>. 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>
<!--begin-toc-->
<ul class=toc>
<li><a href="#dependencies"><span class=secno>1. </span>Dependencies on
other modules</a>
<li><a href="#introduction"><span class=secno>2. </span>Introduction</a>
<li><a href="#features-out-of-scope"><span class=secno>3. </span>Features
out of scope</a>
<ul class=toc>
<li><a href="#repeating-templates"><span class=secno>3.1.
</span>Repeating templates</a>
<li><a href="#non-rectangular-shapes-and-wrap-arounds"><span
class=secno>3.2. </span>Non-rectangular shapes and wrap-arounds</a>
</ul>
<li><a href="#declaring-templates-the-display-property"><span
class=secno>4. </span>Declaring templates: the ‘<code
class=property>display</code>’ property</a>
<li><a href="#colwidth"><span class=secno>5. </span>Computing the width of
the slots</a>
<li><a href="#rowheight"><span class=secno>6. </span>Computing the height
of the slots</a>
<li><a href="#position"><span class=secno>7. </span>Flowing content into
the template: the ‘<code class=property>position</code>’
property</a>
<li><a href="#slot-pseudo"><span class=secno>8. </span>The ‘<code
class=css>::slot()</code>’ pseudo-element</a>
<li><a href="#vertical-alignment"><span class=secno>9. </span>Vertical
alignment</a>
<li><a href="#paged"><span class=secno>10. </span>Page-based templates and
other templates in paged media</a>
<li><a href="#stacking-order"><span class=secno>11. </span>Stacking
order</a>
<li><a href="#floating-elements-inside-templates"><span class=secno>12.
</span>Floating elements inside templates</a>
<li><a href="#gr-unit"><span class=secno>13. </span>Definition of the
‘<code class=css>fr</code>’ unit in a template element</a>
<li><a href="#chains"><span class=secno>14. </span>Chaining slots: the
‘<code class=property>chains</code>’ property</a>
<li><a href="#breaking-content-between-slots-in-a-chai"><span
class=secno>15. </span>Breaking content between slots in a chain</a>
<li><a href="#cr-exit-criteria"><span class=secno>16. </span>CR exit
criteria</a>
<li><a href="#history"><span class=secno>17. </span>History</a>
<li><a href="#changes"><span class=secno>18. </span>Changes</a>
<li class=no-num><a href="#acknowledgments">Acknowledgments</a>
<li class=no-num><a href="#references">References</a>
<li class=no-num><a href="#index">Index</a>
</ul>
<!--end-toc-->
<h2 id=dependencies><span class=secno>1. </span>Dependencies on other
modules</h2>
<p>This CSS3 module depends on the following other CSS3 modules:
<ul>
<li><cite>CSS syntax module</cite> <a href="#CSS3SYN"
rel=biblioentry>[CSS3SYN]<!--{{!CSS3SYN}}--></a> – <dfn
id=interactive>interactive</dfn> vs <dfn
id=non-interactive>non-interactive</dfn> media.
<li><cite>CSS values and Units module</cite> <a href="#CSS3VAL"
rel=biblioentry>[CSS3VAL]<!--{{!CSS3VAL}}--></a> – <a
href="/TR/css3-values#strings"> <dfn
id=ltstringgt><var><string></var></dfn></a> and <a
href="/TR/css3-values#ltlengthgt"> <dfn
id=ltlengthgt><var><length></var></dfn></a>.
<li><cite>CSS box module</cite> <a href="#CSS3BOX"
rel=biblioentry>[CSS3BOX]<!--{{!CSS3BOX}}--></a> – properties <dfn
id=width>width</dfn>, <dfn id=height>height</dfn>, <dfn
id=float>float</dfn>, <dfn id=display>display</dfn> and <dfn
id=overflow>overflow</dfn>
<li><cite>CSS text layout</cite> <a href="#CSS3TEXTLAYOUT"
rel=biblioentry>[CSS3TEXTLAYOUT]<!--{{!CSS3TEXTLAYOUT}}--></a> –
properties <dfn id=direction>direction</dfn> and <dfn
id=block-flow>block-flow</dfn>
<li><cite>CSS positioning</cite> <a href="#CSS3POS"
rel=biblioentry>[CSS3POS]<!--{{!CSS3POS}}--></a> – property <dfn
id=z-index>z-index</dfn>
<li><cite>CSS paged media</cite> <a href="#CSS3PAGE"
rel=biblioentry>[CSS3PAGE]<!--{{!CSS3PAGE}}--></a> – properties
<dfn id=page-break-before>page-break-before</dfn>, <dfn
id=page-break-after>page-break-after</dfn> and <dfn id=page>page</dfn>;
<a href="/TR/css3-page#page-area0"><dfn id=page-area>page area</dfn></a>
(in particular its width & height).
<li><cite>CSS background and borders</cite> <a href="#CSS3BG"
rel=biblioentry>[CSS3BG]<!--{{!CSS3BG}}--></a> – property <dfn
id=background>background</dfn> <span class=issue>and <dfn
id=box-shadow>box-shadow</dfn>?</span>
<li><cite>CSS tables</cite> <a href="#CSS3TBL"
rel=biblioentry>[CSS3TBL]<!--{{!CSS3TBL}}--></a> – property <dfn
id=vertical-align>vertical-align</dfn>. <span class=issue>[or Box
Module?]</span>
<li><cite>CSS Multi-column Layout Module</cite> <a href="#CSS3COL"
rel=biblioentry>[CSS3COL]<!--{{!CSS3COL}}--></a> – properties <dfn
id=break-before>break-before</dfn>, <dfn id=break-after>break-after</dfn>
and <dfn id=break-inside>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 ‘<code
class=css>::slot()</code>’ pseudo-element”</a>).
<p>It has non-normative (informative) references to the following other
CSS3 modules:
<ul>
<li><cite>Selectors</cite> <a href="#SELECT"
rel=biblioentry>[SELECT]<!--{{SELECT}}--></a>
</ul>
<p>See <a
href="http://www.w3.org/TR/CSS21/about.html#property-defs">section 1.4.2
of CSS level 2</a> <a href="#CSS21"
rel=biblioentry>[CSS21]<!--{{CSS21}}--></a> for the grammar and other
notations that this specification uses in property definitions.
<h2 id=introduction><span class=secno>2. </span>Introduction</h2>
<p><em>(This section is not normative.)</em>
<div class=sidefigure>
<p><img alt="Image: four elements move to four slots in a template"
longdesc=diagram.desc src=diagram.png>
<p class=caption>Four 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 ‘<a href="#position0"><code
class=property>position</code></a>’ property, which specifies in
this case into which slot of the template the element goes. The template
itself is specified on the ‘<a href="#display"><code
class=property>display</code></a>’ property of some ancestor of the
elements to remap.
<div class=example>
<p>In this example, the four children of an element are assigned to four
slots (called a, b, c and d) in a 2×2 template. (All mark-up examples in
this specification are HTML fragments, unless otherwise stated.)
<div class=sidefigure>
<p><img alt="Image: sample rendering" longdesc=aapje.desc src=aapje.png>
<p class=caption>Each element occupies one slot. In this template, all
slots have the same size.
</div>
<pre>
<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 <a href="#MEDIAQ"
rel=biblioentry>[MEDIAQ]<!--{{MEDIAQ}}--></a> to change the overall
layout of a page from 3-column layout for a wide screen to a 1-column
layout for a narrow screen. It assumes the page has been marked-up with
logical sections with IDs.
<pre>
@media all
{
body { 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 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 {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 <a href="#CSS3BOX"
rel=biblioentry>[CSS3BOX]<!--{{!CSS3BOX}}--></a> for the definition of
the ‘<a href="#width"><code class=property>width</code></a>’
property.) The columns of the template are by default all the same size.
The columns of the table satisfy certain constraints, but the exact size
is not defined. We can make them all the same by adding a rule (see <a
href="#CSS3TBL" rel=biblioentry>[CSS3TBL]<!--{{!CSS3TBL}}--></a>):
<pre>.group {display: table; width: 100%; table-layout: fixed}</pre>
<div class=figure>
<p><img alt="[Three equal cells]" longdesc=table2.desc src=table2.png>
<p class=caption>Example of rendering with equal columns.
</div>
<p>In both styles, we can set a column to a certain size:
<pre>div.menu {width: 3em}</pre>
<p>resp.,
<pre>.group {display: "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 ‘<code class=css>a</code>’
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 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>
<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
alt="Same text, with the SPAN replaced by “(1)” and its content moved to the end."
longdesc=footnotes.desc src=footnotes.png>
<p class=caption>Rendering of a text with footnotes.
</div>
</div>
<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 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>
<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(@) {
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.)
</div>
<h2 id=features-out-of-scope><span class=secno>3. </span>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 id=repeating-templates><span class=secno>3.1. </span>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 id=non-rectangular-shapes-and-wrap-arounds><span class=secno>3.2.
</span>Non-rectangular shapes and wrap-arounds</h3>
<p>This specification allows to chain multiple slots togother to form
complex shapes, but each of the slots is itself still rectangular.
<p>Another module, <cite>CSS exclusions and shapes</cite> <a
href="#CSS3-EXCLUSIONS"
rel=biblioentry>[CSS3-EXCLUSIONS]<!--{{CSS3-EXCLUSIONS}}--></a>, is
expected to allow floating elements to have non-rectangular shapes and
allow positioned elements to cause wrap-around.
<h2 id=declaring-templates-the-display-property><span class=secno>4.
</span>Declaring templates: the ‘<a href="#display"><code
class=property>display</code></a>’ 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., ‘<code
class=css>display: -my-product "aa" "bc"</code>’ or ‘<code
class=css>display: -my-product("aa" "bc")</code>’.
<table class=propdef-extra>
<tbody>
<tr>
<td><em>Name:</em>
<td>‘<a href="#display"><code
class=property>display</code></a>’
<tr>
<td><em>New value:</em>
<td><a href="#ltdisplay-typegt0"><var><display-type></var></a>? &&
[ [ <a href="#ltstringgt"><var><string></var></a> [ / <a
href="#ltrow-heightgt"><var><row-height></var></a> ]? ]+ ] <a
href="#ltcol-widthgt"><var><col-width></var></a>*
<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 id=template.>template.</dfn>
<p>An element with such a ‘<a href="#display"><code
class=property>display</code></a>’ 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 id=ltdisplay-typegt><var><display-type></var></dfn> is
one of the following keywords. An omitted keyword is equivalent to
‘<code class=css>block</code>’.
<pre class=prod><dfn
id=ltdisplay-typegt0><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>‘<code class=css>inline</code>’
<dt>‘<code class=css>inline-block</code>’
<dt>‘<code class=css>inline-table</code>’
<dd>These three values are equivalent. The element is an
<em>inline-level</em> element.
<dt>‘<code class=css>list-item</code>’
<dd>The element is formatted as a list item. If the element has the value
‘<code class=css>inside</code>’ for its ‘<code
class=property>list-style-position</code>’, that ‘<code
class=css>inside</code>’ is treated as if it were ‘<code
class=css>outside</code>’.
<dt>‘<code class=css>block</code>’
<dt>‘<code class=css>table</code>’
<dd>These two values are equivalent.
<dt>‘<code class=css>table-row-group</code>’
<dt>‘<code class=css>table-header-group</code>’
<dt>‘<code class=css>table-footer-group</code>’
<dd>This creates a principal block-level box that is the template, with
around it an anonymous ‘<code class=css>table-row</code>’ 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>
<a href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>.
<dt>‘<code class=css>table-row</code>’
<dd>This creates a principal block-level box that is the template and
around it a ‘<code class=css>table-row</code>’ 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>
<a href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>.
<dt>‘<code class=css>table-column-group</code>’
<dt>‘<code class=css>table-column</code>’
<dd>The template is ignored and the element is treated as an element of
the indicated type.
<dt>‘<code class=css>table-cell</code>’
<dd>The element is a table cell with a template.
<dt>‘<code class=css>table-caption</code>’
<dd>The element is a table caption with a template.
<dt>‘<code class=css>none</code>’
<dd>The template is ignored and the element is treated as for ‘<code
class=css>display: none</code>’.
</dl>
<p class=issue>Future display types added in other modules?
<p class=note>Note that ‘<a href="#display"><code
class=property>display</code></a>’ is extended to apply to ‘<a
href="#page"><code class=css>@page</code></a>’ rules as well and
that it has a different default there, viz., ‘<code
class=css>"@"</code>’. 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 <a href="#ltlettergt"><var><letter></var></a> 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 id=slot>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 id=ltrow-heightgt><var><row-height></var></dfn> sets the
height of the preceding row. The default is ‘<code
class=css>auto</code>’. The values can be as follows:
<dl>
<dt><a href="#ltlengthgt"><var><length></var></a>
<dd>An explicit height for that row. Negative values make the template
illegal. If the length is expressed in ‘<code
class=css>gr</code>’ units, these refer to the inherited grid, not
the grid defined by the template itself (see <a
href="#gr-unit">“Definition of the ‘<code
class=css>gr</code>’ 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 id=ltcol-widthgt><var><col-width></var></dfn> sets the
width of a column. If there are more <a
href="#ltcol-widthgt"><var><col-width></var></a>s then columns, the
last ones are ignored. If there are fewer, the missing ones are assumed to
be ‘<code class=css>*</code>’. Each <a
href="#ltcol-widthgt"><var><col-width></var></a> can be one of the
following:
<dl>
<dt><a href="#ltlengthgt"><var><length></var></a>
<dd>An explicit width for that column. Negative values make the template
illegal.
<dt>*
<dd>(asterisk.) All columns with a ‘<code class=css>*</code>’
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 [ <a
href="#ltlengthgt"><var><length></var></a> | 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 ‘<code
class=css>minmax(<var>p</var>,<var>q</var>)</code>’ is treated as
‘<code class=css>minmax(<var>p</var>,<var>p</var>)</code>’.
<dt>fit-content
<dd>Equivalent to ‘<code class=css>minmax(min-content,
max-content)</code>’.
</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 (‘<code class=css>2.5%
97.5%</code>’) introduces an opportunity for errors (e.g.,
‘<code class=css>3% 98%</code>’ causes the template to be
rejected). Abbreviating with numbers,
<pre>display: "ab" * 39*</pre>
<p>(or even just ‘<code class=css>1 39</code>’) is safer. On
the other hand, those 39 identical letters make it immediately clear what
the intention is…
</div>
<p>The orientation of the template is independent of the writing mode
(‘<a href="#direction"><code
class=property>direction</code></a>’ and ‘<a
href="#block-flow"><code class=property>block-flow</code></a>’
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