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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html lang=en>
<head>
<title>CSS Backgrounds and Borders Module Level 4</title>
<link href="../default.css" rel=stylesheet type="text/css">
<style type="text/css">
.prod { font-family: inherit; font-size: inherit }
pre.prod { white-space: pre-wrap; margin: 1em 0 1em 2em }
code { font-size: inherit; }
#box-shadow-samples td { background: white; color: black; }
</style>
<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 Backgrounds and Borders Module Level 4</h1>
<h2 class="no-num no-toc" id=longstatus-date>Editor's Draft 1 April 2010</h2>
<dl>
<dt>This version:
<dd><!--<a href="http://www.w3.org/TR/2010/CR-css3-background-20100401">http://www.w3.org/TR/2010/ED-css3-background-20100401</a>-->
<a
href="http://dev.w3.org/csswg/css4-background">http://dev.w3.org/csswg/css3-background</a>
<dt>Latest version:
<dd><a
href="http://www.w3.org/TR/css4-background">http://www.w3.org/TR/css3-background</a>
<dt>Previous versions:
<dd>None
<dt id=editors-list>Editors:
<dd><a href="http://fantasai.inkedblade.net/contact">Elika J. Etemad</a>
(Invited Expert)
<dd><a href="mailto:howcome@opera.com ">Håkon Wium Lie</a> (Opera
Software)
</dl>
<!--begin-copyright-->
<p class=copyright><a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
rel=license>Copyright</a> © 2010 <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>
<p>CSS is a language for describing the rendering of structured <a
href="#document">documents</a> (such as HTML and XML) on screen, on paper,
in speech, etc. This draft contains the features of CSS level 4
relating to borders and backgrounds. It includes and extends the
functionality of CSS level 3 [[!CSS3BACKGROUND]], which builds on CSS
level 2 <a href="#CSS21" rel=biblioentry>[CSS21]<!--{{CSS21}}--></a>.
The main extensions compared to level 3 are <span class=issue>Fill
this in later</span>
<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-background%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-background” in the subject, preferably like this:
“[<!---->css3-background<!---->] <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>The CSS WG maintains an <a
href="http://www.w3.org/Style/CSS/Tracker/products/11">issues list</a> for
this module. A <a href="http://www.w3.org/Style/CSS/Test/">test suite</a>
for CSS Backgrounds and Borders Level 3 will be developed during the
Candidate Recommendation phase.
<h2 class="no-num no-toc" id=contents>Table of contents</h2>
<!--begin-toc-->
<ul class=toc>
<li><a href="#introduction"><span class=secno>1. </span>Introduction</a>
<li><a href="#values"><span class=secno>2. </span>Values</a>
<li><a href="#backgrounds"><span class=secno>3. </span>Background
properties</a>
<li><a href="#borders"><span class=secno>4. </span>Border properties</a>
<li><a href="#clipping-borders"><span class=secno>5. </span>Clipping
borders</a>
<ul class=toc>
<li><a href="#the-border-clip-properties"><span class=secno>5.1.
</span>The ‘<code class=property>border-clip</code>’
properties</a>
</ul>
<li><a href="#definitions"><span class=secno>6. </span>Definitions</a>
<ul class=toc>
<li><a href="#glossary"><span class=secno>6.1. </span>Glossary</a>
<li><a href="#conformance"><span class=secno>6.2. </span>Conformance</a>
<li><a href="#levels"><span class=secno>6.3. </span>Levels</a>
<ul class=toc>
<li><a href="#level-1"><span class=secno>6.3.1. </span>CSS Level 1</a>
<li><a href="#level-2"><span class=secno>6.3.2. </span>CSS Level 2</a>
<li><a href="#level-3"><span class=secno>6.3.3. </span>CSS Level 3</a>
</ul>
<li><a href="#exit"><span class=secno>6.4. </span>CR exit criteria</a>
</ul>
<li><a href="#acknowledgments"><span class=secno>7.
</span>Acknowledgments</a>
<li><a href="#references"><span class=secno>8. </span>References</a>
<ul class=toc>
<li class=no-num><a href="#normative-references">Normative
references</a>
<li class=no-num><a href="#other-references">Other references</a>
</ul>
<li class=no-num><a href="#property-index">Property index</a>
<li class=no-num><a href="#index">Index</a>
</ul>
<!--end-toc-->
<h2 id=introduction><span class=secno>1. </span>Introduction</h2>
<p><em>This section is not normative.</em>
<p>When elements are rendered according to the <a
href="http://www.w3.org/TR/CSS21/box.html">CSS box model</a> <a
href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>, each element
is either not displayed at all, or formatted as one or more rectangular
boxes. Each box has a rectangular content area, a band of padding around
the content, a border around the padding, and a margin outside the border.
(The margin may actually be negative, but margins have no influence on the
background and border.)
<div class=figure>
<p><img alt="Diagram of a typical box, showing the content, padding,
border and margin areas" src=box>
<p class=caption>The various areas and edges of a typical box. (This
diagram is explained in the CSS2.1 Box Model chapter <a href="#CSS21"
rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>.)
</div>
<p>The properties of this module deal with the decoration of the border
area and with the background of the content, padding and border areas.
<p>The relative stacking order of backgrounds, borders, and shadows is
given in this module. For how these layers interact with other rendered
content, see Appendix E “Elaborate description of Stacking Contexts”
in <a href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>.
<h2 id=values><span class=secno>2. </span>Values</h2>
<p>This specification follows the <a
href="http://www.w3.org/TR/CSS21/about.html#property-defs">CSS property
definition conventions</a> from <a href="#CSS21"
rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>.
<p>Value types are defined in CSS Values Level 3 [[!CSS3VALUES]].
<p>All properties defined in this specification also accept the <a
href="http://www.w3.org/TR/CSS21/cascade.html#value-def-inherit">inherit</a>
keyword as their value, but for readability it has not been listed
explicitly.
<h2 id=backgrounds><span class=secno>3. </span>Background properties</h2>
<p>Each box has a background layer that may be fully transparent (the
default), or filled with a color and/or one or more images. The background
properties specify the color and images (‘<code
class=property>background-image</code>’) to use, and how they are
sized, positioned, tiled, etc.
<p>The definitions of these properties are given in [[!CSS3BACKGROUNDS]].
<h2 id=borders><span class=secno>4. </span>Border properties</h2>
<p>The border can either be a predefined style (solid line, double line,
dotted line, pseudo-3D border, etc.) or it can be an image. In the former
case, various properties define the style, color, and thickness of the
border.
<p>The definitions of most of these properties are given in
[[!CSS3BACKGROUNDS]]. Additional properties are defined below.
<h2 id=clipping-borders><span class=secno>5. </span>Clipping borders</h2>
<p>CSS borders traditionally cover an entire border edge. Sometimes,
however, it can be useful to hide some parts of the border.
<h3 id=the-border-clip-properties><span class=secno>5.1. </span>The
‘<code class=property><a
href="#border-clip">border-clip</a></code>’ properties</h3>
<table class=propdef>
<tbody>
<tr>
<td><em>Name:</em>
<td><dfn id=border-clip>border-clip</dfn>, <dfn
id=border-clip-top>border-clip-top</dfn>, <dfn
id=border-clip-right>border-clip-right</dfn>, <dfn
id=border-clip-bottom>border-clip-bottom</dfn>, <dfn
id=border-clip-left>border-clip-left</dfn>
<tr>
<td><em>Value:</em>
<td>normal | [ <length> | <percentage> | <fraction> ]+
<tr>
<td><em>Initial:</em>
<td>normal
<tr>
<td><em>Applies to:</em>
<td>all elements
<tr>
<td><em>Inherited:</em>
<td>no
<tr>
<td><em>Percentages:</em>
<td>refer to width or height of element
<tr>
<td><em>Media:</em>
<td>visual
<tr>
<td><em>Computed value:</em>
<td>‘<code class=css>normal</code>’, or a list consisting of
absolute lengths, or percentages as specified
</table>
<p class=issue>Should these properties be simplified to only accept
<code>normal | [ <length> | <percentage> ] +</code>?
<p>These properties split their respective borders into parts along the
border edge. The first part is visible, the second is invisible, the third
part is visible, etc. Parts can be specified with lengths, percentages, or
fractions (expressed by the ‘<code class=property>fr</code>’
unit, as per <a href="#CSS3GRID"
rel=biblioentry>[CSS3GRID]<!--{{CSS3GRID}}--></a> or its <a
href="http://dev.w3.org/csswg/css3-grid/">editor's edition</a>). The
‘<code class=property>normal</code>’ value means that the
border is not split, but shown normally.
<p>‘<code class=property><a
href="#border-clip">border-clip</a></code>’ is a shorthand property
for the four individual properties.
<p>If the listed parts are shorter than the border, any remaining border is
split proportionally between the specified fractions. If there are no
fractions, the behavior is as if ‘<code class=css>1fr</code>’
had been specified at the end of the list.
<p>If the listed parts are longer than the border, the specified parts will
be shown in full until the end of the border. In this case, all fractions
will be zero.
<p>For horizontal borders, parts are listed from left to right. For
vertical borders, parts are listed from top to bottom.
<p>The exact border parts are determined by laying out the specified border
parts with all fractions initially set to zero. Any remaining border is
split proportionally between the fractions specified.
<div class=example>
<pre>
border-clip: 10px 1fr 10px;
</pre>
<div style="position: relative; width: 250px; height: 150px; background:
white;">
<div style="border: 2px solid black; width: 200px; height: 100px;
position: absolute; top: 20px; left: 20px">
<div style="position: absolute; background: white; left: 15px; top:
-5px; height: 110px; width: 170px"></div>
<div style="position: absolute; background: white; left: -5px; top:
15px; height: 70px; width: 210px"></div>
</div>
</div>
</div>
<div class=example>
<pre>
border-clip-top: 10px 1fr 10px;
border-clip-bottom: 10px 1fr 10px;
border-clip-right: 5px 1fr 5px;
border-clip-left: 5px 1fr 5px;
</pre>
<div style="position: relative; width: 250px; height: 150px; background:
white;">
<div style="border: 2px solid black; width: 200px; height: 100px;
position: absolute; top: 20px; left: 20px">
<div style="position: absolute; background: white; left: 15px; top:
-5px; height: 110px; width: 170px"></div>
<div style="position: absolute; background: white; left: -5px; top: 5px;
height: 90px; width: 210px"></div>
</div>
</div>
</div>
<div class=example>
<p>By making the first part have zero length, the inverse border of the
previous example can easily be created:
<pre>
border-clip-top: 0 10px 1fr 10px;
border-clip-bottom: 0 10px 1fr 10px;
border-clip-right: 0 5px 1fr 5px;
border-clip-left: 0 5px 1fr 5px;
</pre>
<div style="position: relative; width: 250px; height: 150px; background:
white;">
<div style="border: 2px solid black; width: 200px; height: 100px;
position: absolute; top: 20px; left: 20px">
<div style="position: absolute; background: white; left: -5px; top:
-5px; height: 10px; width: 15px"></div>
<div style="position: absolute; background: white; right: -5px; top:
-5px; height: 10px; width: 15px"></div>
<div style="position: absolute; background: white; left: -5px; top:
95px; height: 10px; width: 15px"></div>
<div style="position: absolute; background: white; right: -5px; top:
95px; height: 10px; width: 15px"></div>
</div>
</div>
</div>
<div class=example>
<pre>
border: thin solid black;
border-clip: 0 1fr; /* hide borders */
border-clip-top: 10px 1fr 10px; /* make certain borders visible */
border-clip-bottom: 10px 1fr 10px;
</pre>
<div style="position: relative; width: 250px; height: 150px; background:
white;">
<div style="border: 2px solid black; width: 200px; height: 100px;
position: absolute; top: 20px; left: 20px">
<div style="position: absolute; background: white; left: 15px; top:
-5px; height: 110px; width: 170px"></div>
<div style="position: absolute; background: white; left: -5px; top: 0px;
height: 100px; width: 210px"></div>
</div>
</div>
</div>
<div class=example>
<pre>
border-top: thin solid black;
border-bottom: thin solid black;
border-clip-top: 10px;
border-clip-bottom: 10px;
</pre>
<div style="position: relative; width: 250px; height: 150px; background:
white;">
<div style="border: 2px solid black; width: 200px; height: 100px;
position: absolute; top: 20px; left: 20px">
<div style="position: absolute; background: white; left: 15px; top:
-5px; height: 110px; width: 200px"></div>
<div style="position: absolute; background: white; left: -5px; top: 0px;
height: 100px; width: 210px"></div>
</div>
</div>
</div>
<div class=example>
<pre>
border-top: thin solid black;
border-clip: 10px;
</pre>
<div style="position: relative; width: 250px; height: 150px; background:
white;">
<div style="border: 2px solid black; width: 200px; height: 100px;
position: absolute; top: 20px; left: 20px">
<div style="position: absolute; background: white; left: 15px; top:
-5px; height: 110px; width: 200px"></div>
<div style="position: absolute; background: white; left: -5px; top: 0px;
height: 110px; width: 210px"></div>
</div>
</div>
</div>
<div class=example>
<p>This rendering:
<div style="background: white; padding: 0.2em 0.5em">
<pre style="margin-left: 0">
A sentence consists of words¹.
</pre>
<div style="width: 3em; height: 2px; background: black"></div>
<pre style="margin-left: 0">
¹ Most often.
</pre>
</div>
can be achieved with this style sheet:
<pre>
@footnote {
border-top: thin solid black;
border-clip: 4em;
}
</pre>
</div>
<div class=example>
<pre>
border: 2px solid black;
border-top-parts: repeat(10px 10px);
</pre>
<p>In this example, the repeat pattern is shown five times and there is,
by coincidence, no remaining border.
<div style="position: relative; width: 100px; background: white; padding:
20px">
<div style="border: 2px solid black; height: 40px"></div>
<div style="position: absolute; background: white; width: 10px; height:
2px; top: 20px; left: 30px"></div>
<div style="position: absolute; background: white; width: 10px; height:
2px; top: 20px; left: 50px"></div>
<div style="position: absolute; background: white; width: 10px; height:
2px; top: 20px; left: 70px"></div>
<div style="position: absolute; background: white; width: 10px; height:
2px; top: 20px; left: 90px"></div>
<div style="position: absolute; background: white; width: 10px; height:
2px; top: 20px; left: 110px"></div>
</div>
</div>
<div class=example>
<pre>
border: 2px solid black;
border-top-parts: repeat(10px 10px);
</pre>
<p>In this example, the repeat pattern is shown five times. The box in
this example is slightly wider than the box in the previous example. The
remaining border is taken up by a fraction, as if this code had been
specified:
<pre>
border: 2px solid black;
border-top-parts: repeat(10px 10px) 1fr;
</pre>
<div style="position: relative; width: 105px; background: white; padding:
20px">
<div style="border: 2px solid black; height: 40px"></div>
<div style="position: absolute; background: white; width: 10px; height:
2px; top: 20px; left: 30px"></div>
<div style="position: absolute; background: white; width: 10px; height:
2px; top: 20px; left: 50px"></div>
<div style="position: absolute; background: white; width: 10px; height:
2px; top: 20px; left: 70px"></div>
<div style="position: absolute; background: white; width: 10px; height:
2px; top: 20px; left: 90px"></div>
<div style="position: absolute; background: white; width: 10px; height:
2px; top: 20px; left: 110px"></div>
<div style="position: absolute; background: red; width: 5px; height: 2px;
top: 20px; left: 120px"></div>
</div>
<p>The fragment is shown in red for illustrative purposes; it should be
shown in black by a compliant UA.
</div>
<div class=example>
<pre>
border: 4px solid black;
border-top-parts: 40px 20px 0 1fr repeat(20px 20px) 0 1fr 40px;
</pre>
<p>In this example, there will be a visible 40px border part on each end
of the top border. Inside the 40px border parts, there will be an
invisible border part of at least 20px. Inside these invisible border
parts, there will be visible border parts, each 20px long with 20px
invisible border parts between them.
<div style="position: relative; width: 192px; background: white; padding:
40px">
<div style="border: 4px solid black; height: 40px"></div>
<div style="position: absolute; background: white; width: 20px; height:
4px; top: 40px; left: 80px"></div>
<div style="position: absolute; background: red; width: 6px; height: 4px;
top: 40px; left: 100px"></div>
<div style="position: absolute; background: white; width: 20px; height:
4px; top: 40px; left: 126px"></div>
<div style="position: absolute; background: white; width: 20px; height:
4px; top: 40px; left: 166px"></div>
<div style="position: absolute; background: red; width: 6px; height: 4px;
top: 40px; left: 186px"></div>
</div>
<p>The fragments are shown in red for illustrative purposes; they should
not be visible in compliant UAs.
</div>
<div class=example>
<pre>
border: 4px solid black;
border-top-parts: 40px 20px 0 1fr 20px 20px 0 1fr 40px;
</pre>
<p>In this example, there will be a visible 40px border part on each end
of the top border. Inside the 40px border parts, there will be an
invisible border part of at least 20px. Inside these invisible border
parts, there will be visible border parts, each 20px long with 20px
invisible border parts between them.
<div style="position: relative; width: 192px; background: white; padding:
40px">
<div style="border: 4px solid black; height: 40px"></div>
<div style="position: absolute; background: white; width: 20px; height:
4px; top: 40px; left: 80px"></div>
<div style="position: absolute; background: red; width: 6px; height: 4px;
top: 40px; left: 100px"></div>
<div style="position: absolute; background: white; width: 20px; height:
4px; top: 40px; left: 126px"></div>
<div style="position: absolute; background: white; width: 20px; height:
4px; top: 40px; left: 166px"></div>
<div style="position: absolute; background: red; width: 6px; height: 4px;
top: 40px; left: 186px"></div>
</div>
<p>The fragments are shown in red for illustrative purposes; they should
not be visible in compliant UAs.
</div>
<div class=example>
<pre>
border: 4px solid black;
border-clip-top: 3fr 10px 2fr 10px 1fr 10px 10px 10px 1fr 10px 2fr 10px 3fr;
</pre>
<p>All but one of the visible border parts are represented as fractions in
this example. The length of these border parts will change when the width
of the element changes. Here is one rendering where 1fr ends up being
10px:
<div style="position: relative; width: 190px; background: white; padding:
40px">
<div style="border: 4px solid black; border-top: none; height: 40px"></div>
<div style="position: absolute; background: red; width: 30px; height:
4px; top: 40px; left: 40px"></div>
<div style="position: absolute; background: white; width: 10px; height:
4px; top: 40px; left: 70px"></div>
<div style="position: absolute; background: red; width: 20px; height:
4px; top: 40px; left: 80px"></div>
<div style="position: absolute; background: white; width: 10px; height:
4px; top: 40px; left: 100px"></div>
<div style="position: absolute; background: red; width: 10px; height:
4px; top: 40px; left: 110px"></div>
<div style="position: absolute; background: white; width: 10px; height:
4px; top: 40px; left: 120px"></div>
<div style="position: absolute; background: black; width: 10px; height:
4px; top: 40px; left: 130px"></div>
<div style="position: absolute; background: white; width: 10px; height:
4px; top: 40px; left: 140px"></div>
<div style="position: absolute; background: red; width: 10px; height:
4px; top: 40px; left: 150px"></div>
<div style="position: absolute; background: white; width: 10px; height:
4px; top: 40px; left: 160px"></div>
<div style="position: absolute; background: red; width: 20px; height:
4px; top: 40px; left: 170px"></div>
<div style="position: absolute; background: white; width: 10px; height:
4px; top: 40px; left: 190px"></div>
<div style="position: absolute; background: red; width: 30px; height:
4px; top: 40px; left: 200px"></div>
</div>
<p>Here is another rendering where 1fr ends up being 30px:
<div style="position: relative; width: 440px; background: white; padding:
40px">
<div style="border: 4px solid black; border-top: none; height: 40px"></div>
<div style="position: absolute; background: red; width: 90px; height:
4px; top: 40px; left: 40px"></div>
<div style="position: absolute; background: white; width: 10px; height:
4px; top: 40px; left: 130px"></div>
<div style="position: absolute; background: red; width: 60px; height:
4px; top: 40px; left: 140px"></div>
<div style="position: absolute; background: white; width: 10px; height:
4px; top: 40px; left: 200px"></div>
<div style="position: absolute; background: red; width: 30px; height:
4px; top: 40px; left: 210px"></div>
<div style="position: absolute; background: white; width: 10px; height:
4px; top: 40px; left: 240px"></div>
<div style="position: absolute; background: black; width: 10px; height:
4px; top: 40px; left: 250px"></div>
<div style="position: absolute; background: white; width: 10px; height:
4px; top: 40px; left: 260px"></div>
<div style="position: absolute; background: red; width: 30px; height:
4px; top: 40px; left: 270px"></div>
<div style="position: absolute; background: white; width: 10px; height:
4px; top: 40px; left: 300px"></div>
<div style="position: absolute; background: red; width: 60px; height:
4px; top: 40px; left: 310px"></div>
<div style="position: absolute; background: white; width: 10px; height:
4px; top: 40px; left: 370px"></div>
<div style="position: absolute; background: red; width: 90px; height:
4px; top: 40px; left: 390px"></div>
</div>
<p>The fragments are shown in red for illustrative purposes; they should
be black in compliant UAs.
</div>
<h2 id=definitions><span class=secno>6. </span>Definitions</h2>
<h3 id=glossary><span class=secno>6.1. </span>Glossary</h3>
<p>The following terms and abbreviations are used in this module.
<dl>
<dt><dfn id=ua>UA</dfn>
<dt><dfn id=user-agent>User Agent</dfn>
<dd>
<p>A program that reads and/or writes CSS style sheets on behalf of a
user in either or both of these categories: programs whose purpose is to
render <a href="#document">documents</a> (e.g., browsers) and programs
whose purpose is to create style sheets (e.g., editors). A UA may fall
into both categories. (There are other programs that read or write style
sheets, but this module gives no rules for them.)
<dt><dfn id=document title="document|documents">document</dfn>
<dd>
<p>A tree-structured document with elements and attributes, such as an
SGML or XML document <a href="#XML11"
rel=biblioentry>[XML11]<!--{{XML11}}--></a>.
<dt><dfn id=style-sheet>style sheet</dfn>
<dd>
<p>A <a href="http://www.w3.org/TR/CSS21/conform.html#style-sheet">CSS
style sheet</a>.
</dl>
<h3 id=conformance><span class=secno>6.2. </span>Conformance</h3>
<p>Conformance requirements are expressed with a combination of descriptive
assertions and RFC 2119 terminology. The key words “MUST”, “MUST
NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”,
“SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in the
normative parts of this document are to be interpreted as described in RFC
2119. However, for readability, these words do not appear in all uppercase
letters in this specification. All of the text of this specification is
normative except sections explicitly marked as non-normative, examples,
and notes. <a href="#RFC2119"
rel=biblioentry>[RFC2119]<!--{{!RFC2119}}--></a>
<p>Examples in this specification are introduced with the words “for
example” or are set apart from the normative text with
<code>class="example"</code>, like this:
<div class=example>
<p>This is an example of an informative example.</p>
</div>
<p>Informative notes begin with the word “Note” and are set apart from
the normative text with <code>class="note"</code>, like this:
<p class=note>Note, this is an informative note.
<p>Conformance to CSS Backgrounds and Borders Level 3 is defined for three
classes:
<dl>
<dt><dfn id=style-sheet0 title="style sheet!!as conformance class">style
sheet</dfn>
<dd>A <a href="http://www.w3.org/TR/CSS21/conform.html#style-sheet">CSS
style sheet</a>.
<dt><dfn id=renderer>renderer</dfn>
<dd>A UA that interprets the semantics of a style sheet and renders <a
href="#document">documents</a> that use them.
<dt><dfn id=authoring-tool>authoring tool</dfn>
<dd>A UA that writes a style sheet.
</dl>
<p>A style sheet is conformant to CSS Backgrounds and Borders Level 3 if
all of its declarations that use properties defined in this module have
values that are valid according to the generic CSS grammar and the
individual grammars of each property as given in this module.
<p>A renderer is conformant to CSS Backgrounds and Borders Level 3 if, in
addition to interpreting the style sheet as defined by the appropriate
specifications, it supports all the properties defined by CSS Backgrounds
and Borders Level 3 by parsing them correctly and rendering the document
accordingly. However the inability of a UA to correctly render a document
due to limitations of the device does not make the UA non-conformant. (For
example, a UA is not required to render color on a monochrome monitor.)
<p>An authoring tool is conformant to CSS Backgrounds and Borders Level 3
if it writes syntactically correct style sheets, according to the generic
CSS grammar and the individual grammars of each property in this module.
<h3 id=levels><span class=secno>6.3. </span>Levels</h3>
<p><em>This section is informative.</em> CSS has different levels of
features, each a subset of the other. (See <a href="#CSSBEIJING"
rel=biblioentry>[CSSBEIJING]<!--{{CSSBEIJING}}--></a> for a full
explanation.) The lists below describe which features from this
specification are in each level.
<h4 id=level-1><span class=secno>6.3.1. </span>CSS Level 1</h4>
<ul>
<li>‘<code class=property>background-color</code>’
<li>‘<code class=property>background-image</code>’ only one
image (no layers)
<li>‘<code class=property>background-repeat</code>’: only
‘<code class=property>repeat</code>’ | ‘<code
class=property>repeat-x</code>’ | ‘<code
class=property>repeat-y</code>’ | ‘<code
class=property>no-repeat</code>’
<li>‘<code class=property>background-attachment</code>’: only
‘<code class=property>scroll</code>’ | ‘<code
class=property>fixed</code>’
<li>‘<code class=property>background-position</code>’: only
one or two values allowed
<li>‘<code class=property>background</code>’ shorthand: only
color, image, repeat, attachment and position
<li>‘<code class=property>border-color</code>’ properties
<li>‘<code class=property>border-style</code>’ properties
<li>‘<code class=property>border-width</code>’ properties
<li>‘<code class=property>border-top</code>’, ‘<code
class=property>border-bottom</code>’, ‘<code
class=property>border-right</code>’, ‘<code
class=property>border-left</code>’, and ‘<code
class=property>border</code>’ shorthands
</ul>
<h4 id=level-2><span class=secno>6.3.2. </span>CSS Level 2</h4>
<ul>
<li>‘<code class=property>background-color</code>’
<li>‘<code class=property>background-image</code>’: only one
image (no layers)
<li>‘<code class=property>background-repeat</code>’: only
‘<code class=property>repeat</code>’ | ‘<code
class=property>repeat-x</code>’ | ‘<code
class=property>repeat-y</code>’ | ‘<code
class=property>no-repeat</code>’
<li>‘<code class=property>background-attachment</code>’: only
‘<code class=property>scroll</code>’ | ‘<code
class=property>fixed</code>’
<li>‘<code class=property>background-position</code>’: only
one or two values allowed
<li>‘<code class=property>background</code>’: only color,
image, repeat, attachment and position
<li>‘<code class=property>border-color</code>’ properties
<li>‘<code class=property>border-style</code>’ properties
<li>‘<code class=property>border-width</code>’ properties
<li>‘<code class=property>border-top</code>’, ‘<code
class=property>border-bottom</code>’, ‘<code
class=property>border-right</code>’, ‘<code
class=property>border-left</code>’, and ‘<code
class=property>border</code>’ shorthands
</ul>
<h4 id=level-3><span class=secno>6.3.3. </span>CSS Level 3</h4>
<ul>
<li>All features described in the CSS Backgrounds and Borders Module Level
3
</ul>
<h3 id=exit><span class=secno>6.4. </span>CR exit criteria</h3>
<p>As described in the W3C process document, a <a
href="http://www.w3.org/2005/10/Process-20051014/tr.html#cfi">Candidate
Recommendation</a> (CR) is a specification that W3C recommends for use on
the Web. The next stage is “Recommendation,” when the specification is
sufficiently implemented.
<p>For this specification to be proposed as a W3C Recommendation, the
following conditions shall be met. 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>A minimum of sixth months of the CR period must have elapsed. This is to
ensure that enough time is given for any remaining major errors to be
caught.
<p>Features will be dropped if two or more interoperable implementations
are not found by the end of the CR period.
<p>Features may/will also be dropped if adequate/sufficient (by judgment of
CSS WG) tests have not been produced for those feature(s) by the end of
the CR period.
<h2 id=acknowledgments><span class=secno>7. </span>Acknowledgments</h2>
<h2 id=references><span class=secno>8. </span>References</h2>
<h3 class=no-num id=normative-references>Normative references</h3>
<!--begin-normative-->
<!-- Sorted by label -->
<dl class=bibliography>
<dt style="display: none"><!-- keeps the doc valid if the DL is empty -->