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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 rel="stylesheet" type="text/css" href="../default.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 rel="stylesheet" type="text/css"
href="http://www.w3.org/StyleSheets/TR/W3C-WD.css">
</head>
<body>
<div class="head">
<!--logo-->
<h1>CSS Backgrounds and Borders Module Level 4</h1>
<h2 class="no-num no-toc">[LONGSTATUS] [DATE]</h2>
<dl>
<dt>This version:
<dd><!--<a href="http://www.w3.org/TR/[YEAR]/CR-[SHORTNAME]-[CDATE]">[VERSION]</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">[LATEST]</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>
<!--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
<span>documents</span> (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
[[CSS21]]. 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>
<!--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>
<!--toc-->
<h2 id="introduction">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> [[!CSS21]],
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 src="box" alt="Diagram of a typical box, showing the
content, padding, border and margin areas">
<p class="caption">The various areas and edges of a typical box.
(This diagram is explained in the CSS2.1 Box Model chapter [[!CSS21]].)
</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 [[!CSS21]].
<h2 id="values">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 [[!CSS21]].</p>
<p>Value types are defined in CSS Values Level 3 [[!CSS3VALUES]].</p>
<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">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 ('background-image') to use,
and how they are sized, positioned, tiled, etc.
<p>The definitions of these properties are given in [[!CSS3BACKGROUNDS]].
</p>
<h2 id="borders">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.</p>
<h2>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>The 'border-clip' properties</h3>
<table class=propdef>
<tr>
<td><em>Name:</em>
<td><dfn>border-clip</dfn>, <dfn>border-clip-top</dfn>, <dfn>border-clip-right</dfn>, <dfn>border-clip-bottom</dfn>, <dfn>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</span>
<tr>
<td><em>Media:</em>
<td>visual
<tr>
<td><em>Computed value:</em>
<td>''normal'', 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 'fr' unit, as per
[[CSS3GRID]] or its <a href="http://dev.w3.org/csswg/css3-grid/">editor's
edition</a>). The 'normal' value means
that the border is not split, but shown normally.
<p>'border-clip' 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 ''1fr'' 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">Definitions</h2>
<h3 id="glossary">Glossary</h3>
<p>The following terms and abbreviations are used in this
module.
<dl>
<dt><dfn>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 <span>documents</span> (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 title="document|documents">document</dfn>
<dd>
<p>A tree-structured document with elements and attributes, such as an
SGML or XML document [[XML11]].
<dt><dfn>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>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. [[!RFC2119]]</p>
<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>
<p>Conformance to CSS Backgrounds and Borders Level 3 is defined
for three classes:
<dl>
<dt><dfn 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>renderer</dfn></dt>
<dd>A UA that interprets the semantics of a style sheet and renders
<span>documents</span> that use them.
<dt><dfn id="authoring-tool">authoring tool</dfn></dt>
<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">Levels</h3>
<p><em>This section is informative.</em> CSS has different levels of
features, each a subset of the other. (See [[CSSBEIJING]] for a full
explanation.) The lists below describe which features from this
specification are in each level.
<h4 id="level-1">CSS Level 1</h4>
<ul>
<li>'background-color'
<li>'background-image' only one image (no layers)
<li>'background-repeat': only 'repeat' | 'repeat-x' | 'repeat-y' | 'no-repeat'
<li>'background-attachment': only 'scroll' | 'fixed'
<li>'background-position': only one or two values allowed
<li>'background' shorthand: only color, image, repeat, attachment and position
<li>'border-color' properties
<li>'border-style' properties
<li>'border-width' properties
<li>'border-top', 'border-bottom', 'border-right', 'border-left', and 'border' shorthands
</ul>
<h4 id="level-2">CSS Level 2</h4>
<ul>
<li>'background-color'
<li>'background-image': only one image (no layers)
<li>'background-repeat': only 'repeat' | 'repeat-x' | 'repeat-y' | 'no-repeat'
<li>'background-attachment': only 'scroll' | 'fixed'
<li>'background-position': only one or two values allowed
<li>'background': only color, image, repeat, attachment and position
<li>'border-color' properties
<li>'border-style' properties
<li>'border-width' properties
<li>'border-top', 'border-bottom', 'border-right', 'border-left', and 'border' shorthands
</ul>
<h4 id="level-3">CSS Level 3</h4>
<ul>
<li>All features described in the CSS Backgrounds and Borders Module Level 3
</ul>
<h3 id="exit">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">Acknowledgments</h2>
<h2>References</h2>
<h3 class="no-num">Normative references</h3>
<!--normative-->
<h3 class="no-num">Other references</h3>
<!--informative-->
<h2 class="no-num">Property index</h2>
<!-- properties -->
<h2 class="no-num" id="index">Index</h2>
<!--index-->
</body>
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