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<!doctype html><html lang="en">
<head>
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
<title>CSS Backgrounds and Borders Module Level 4</title>
<meta content="width=device-width, initial-scale=1, shrink-to-fit=no" name="viewport">
<meta content="exploring" name="csswg-work-status">
<meta content="ED" name="w3c-status">
<link href="../default.css" rel="stylesheet" type="text/css">
<link href="../csslogo.ico" rel="shortcut icon" type="image/x-icon">
<style>
body {
background-image: url("https://www.w3.org/StyleSheets/TR/logo-ED");
};
</style>
<meta content="Bikeshed 1.0.0" name="generator">
<style>
.dfn-panel {
display: inline-block;
position: absolute;
z-index: 35;
height: auto;
width: -webkit-fit-content;
max-width: 300px;
max-height: 500px;
overflow: auto;
padding: 0.5em 0.75em;
font: small Helvetica Neue, sans-serif, Droid Sans Fallback;
background: #DDDDDD;
color: black;
border: outset 0.2em;
}
.dfn-panel:not(.on) { display: none; }
.dfn-panel * { margin: 0; padding: 0; text-indent: 0; }
.dfn-panel > b { display: block; }
.dfn-panel a { color: black; }
.dfn-panel a:not(:hover) { text-decoration: none !important; border-bottom: none !important; }
.dfn-panel > b + b { margin-top: 0.25em; }
.dfn-panel > span { display: list-item; list-style: inside; }
.dfn-panel.activated {
display: inline-block;
position: fixed;
left: .5em;
bottom: .5em;
margin: 0 auto;
max-width: calc(100vw - 1.5em - .4em - .5em);
max-height: 30vh;
}
.dfn-paneled { cursor: pointer; }
</style>
<body class="h-entry">
<div class="head">
<p data-fill-with="logo"><a class="logo" href="http://www.w3.org/"> <img alt="W3C" height="48" src="https://www.w3.org/StyleSheets/TR/2016/logos/W3C" width="72"> </a> </p>
<h1 class="p-name no-ref" id="title">CSS Backgrounds and Borders Module Level 4</h1>
<h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="content">Editor’s Draft, <time class="dt-updated" datetime="2016-05-10">10 May 2016</time></span></h2>
<div data-fill-with="spec-metadata">
<dl>
<dt>This version:
<dd><a class="u-url" href="https://drafts.csswg.org/css-backgrounds-4/">https://drafts.csswg.org/css-backgrounds-4/</a>
<dt>Latest version:
<dd><a href="https://www.w3.org/TR/css-backgrounds-4/">https://www.w3.org/TR/css-backgrounds-4/</a>
<dt>Feedback:
<dd><span><a href="mailto:www-style@w3.org?subject=%5Bcss-backgrounds%5D%20YOUR%20TOPIC%20HERE">www-style@w3.org</a> with subject line “<kbd>[css-backgrounds] <i data-lt="">… message topic …</i></kbd>” (<a href="http://lists.w3.org/Archives/Public/www-style/" rel="discussion">archives</a>)</span>
<dt>Issue Tracking:
<dd><a href="#issues-index">Inline In Spec</a>
<dt class="editor">Editors:
<dd class="editor p-author h-card vcard"><a class="p-name fn u-email email" href="mailto:bert@w3.org">Bert Bos</a> (<span class="p-org org">W3C</span>)
<dd class="editor p-author h-card vcard"><a class="p-name fn u-url url" href="http://fantasai.inkedblade.net/contact">Elika J. Etemad / fantasai</a> (<span class="p-org org">Invited Expert</span>)
<dd class="editor p-author h-card vcard"><a class="p-name fn u-url url" href="http://lea.verou.me/about/">Lea Verou</a> (<span class="p-org org">Invited Expert</span>)
</dl>
</div>
<div data-fill-with="warning">
<details class="annoying-warning" open="">
<summary>Not Ready For Implementation</summary>
<p> This spec is not yet ready for implementation.
It exists in this repository to record the ideas and promote discussion. </p>
<p> Before attempting to implement this spec,
please contact the CSSWG at www-style@w3.org. </p>
</details>
</div>
<p class="copyright" data-fill-with="copyright"><a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a> © 2016 <a href="http://www.w3.org/"><abbr title="World Wide Web Consortium">W3C</abbr></a><sup>®</sup> (<a href="http://www.csail.mit.edu/"><abbr title="Massachusetts Institute of Technology">MIT</abbr></a>, <a href="http://www.ercim.eu/"><abbr title="European Research Consortium for Informatics and Mathematics">ERCIM</abbr></a>, <a href="http://www.keio.ac.jp/">Keio</a>, <a href="http://ev.buaa.edu.cn/">Beihang</a>). 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>
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc no-ref heading settled" id="abstract"><span class="content">Abstract</span></h2>
<div class="p-summary" data-fill-with="abstract">
<p>This module contains the features of CSS relating to the borders and backgrounds of boxes on the page. It includes and extends the functionality of <a href="https://www.w3.org/TR/css3-background/">CSS Backgrounds and Borders Level 3</a>. <a data-link-type="biblio" href="#biblio-css3bg">[CSS3BG]</a> The main extensions compared to level 3 are shaping (<a class="property" data-link-type="propdesc" href="#propdef-corner-shape">corner-shape</a>) and clipping borders (<a class="property" data-link-type="propdesc" href="#propdef-border-clip">border-clip</a>), logical background positions (<a class="property" data-link-type="propdesc" href="#propdef-background-position">background-position</a>), and the <span class="css">extend</span> ability of <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css2/colors.html#propdef-background-repeat">background-repeat</a>.</p>
<a href="http://www.w3.org/TR/CSS/">CSS</a> is a language for describing the rendering of structured documents
(such as HTML and XML)
on screen, on paper, in speech, etc.
</div>
<h2 class="no-num no-toc no-ref heading settled" id="status"><span class="content">Status of this document</span></h2>
<div data-fill-with="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>
<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=%5Bcss-backgrounds%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 “css-backgrounds” in the subject,
preferably like this:
“[css-backgrounds] <em>…summary of comment…</em>” </p>
<p> This document was produced by the <a href="http://www.w3.org/Style/CSS/members">CSS Working Group</a> (part of the <a href="http://www.w3.org/Style/">Style Activity</a>). </p>
<p> This document was produced by a group operating under
the <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/">5 February 2004 W3C Patent Policy</a>.
W3C maintains a <a href="http://www.w3.org/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="http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">Essential Claim(s)</a> must disclose the information in accordance with <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">section 6 of the W3C Patent Policy</a>. </p>
<p> This document is governed by the <a href="http://www.w3.org/2015/Process-20150901/" id="w3c_process_revision">1 September 2015 W3C Process Document</a>. </p>
<p></p>
</div>
<div data-fill-with="at-risk"></div>
<nav data-fill-with="table-of-contents" id="toc">
<h2 class="no-num no-toc no-ref" id="contents">Table of Contents</h2>
<ol class="toc" role="directory">
<li><a href="#intro"><span class="secno">1</span> <span class="content"> Introduction</span></a>
<li>
<a href="#backgrounds"><span class="secno">2</span> <span class="content"> Backgrounds</span></a>
<ol class="toc">
<li>
<a href="#the-background-position"><span class="secno">2.1</span> <span class="content"> Background Positioning: the <span class="property">background-position</span> shorthand property</span></a>
<ol class="toc">
<li><a href="#background-position-longhands"><span class="secno">2.1.1</span> <span class="content"> Background Positioning Longhands: the <span class="property">background-position-x</span>, <span class="property">background-position-y</span>, <span class="property">background-position-inline</span>, and <span class="property">background-position-block</span> properties</span></a>
</ol>
</ol>
<li>
<a href="#corners"><span class="secno">3</span> <span class="content"> Corners</span></a>
<ol class="toc">
<li><a href="#corner-sizing"><span class="secno">3.1</span> <span class="content"> Corner Sizing: the 'border-radius property</span></a>
<li><a href="#corner-shaping"><span class="secno">3.2</span> <span class="content"> Corner Shaping: the <span class="property">corner-shape</span> property</span></a>
<li><a href="#corners-shorthand"><span class="secno">3.3</span> <span class="content"> Corner Shape and Size: the <span class="property">corners</span> shorthand</span></a>
</ol>
<li>
<a href="#partial-borders"><span class="secno">4</span> <span class="content"> Partial borders</span></a>
<ol class="toc">
<li><a href="#border-limit"><span class="secno">4.1</span> <span class="content"> Partial Borders: the <span class="property">border-limit</span> property</span></a>
<li><a href="#border-clip"><span class="secno">4.2</span> <span class="content"> The <span class="property">border-clip</span> properties</span></a>
</ol>
<li>
<a href="#changes"><span class="secno">5</span> <span class="content"> Changes</span></a>
<ol class="toc">
<li><a href="#level-changes"><span class="secno">5.1</span> <span class="content"> Additions Since Level 3</span></a>
</ol>
<li><a href="#acknowledgments"><span class="secno">6</span> <span class="content">Acknowledgments</span></a>
<li>
<a href="#conformance"><span class="secno"></span> <span class="content"> Conformance</span></a>
<ol class="toc">
<li><a href="#document-conventions"><span class="secno"></span> <span class="content"> Document conventions</span></a>
<li><a href="#conform-classes"><span class="secno"></span> <span class="content"> Conformance classes</span></a>
<li>
<a href="#conform-responsible"><span class="secno"></span> <span class="content"> Requirements for Responsible Implementation of CSS</span></a>
<ol class="toc">
<li><a href="#conform-partial"><span class="secno"></span> <span class="content"> Partial Implementations</span></a>
<li><a href="#conform-future-proofing"><span class="secno"></span> <span class="content"> Implementations of Unstable and Proprietary Features</span></a>
<li><a href="#conform-testing"><span class="secno"></span> <span class="content"> Implementations of CR-level Features</span></a>
</ol>
</ol>
<li>
<a href="#index"><span class="secno"></span> <span class="content">Index</span></a>
<ol class="toc">
<li><a href="#index-defined-here"><span class="secno"></span> <span class="content">Terms defined by this specification</span></a>
<li><a href="#index-defined-elsewhere"><span class="secno"></span> <span class="content">Terms defined by reference</span></a>
</ol>
<li>
<a href="#references"><span class="secno"></span> <span class="content">References</span></a>
<ol class="toc">
<li><a href="#normative"><span class="secno"></span> <span class="content">Normative References</span></a>
<li><a href="#informative"><span class="secno"></span> <span class="content">Informative References</span></a>
</ol>
<li><a href="#property-index"><span class="secno"></span> <span class="content">Property Index</span></a>
<li><a href="#issues-index"><span class="secno"></span> <span class="content">Issues Index</span></a>
</ol>
</nav>
<main>
<h2 class="heading settled" data-level="1" id="intro"><span class="secno">1. </span><span class="content"> Introduction</span><a class="self-link" href="#intro"></a></h2>
<p class="issue" id="issue-648e34a3"><a class="self-link" href="#issue-648e34a3"></a> This module is currently maintained as a diff against Level 3.
We will fold in the text once it’s all formatted up and in CR again,
as this will reduce the effort of keeping them in sync
(source diffs will be accurate in reflecting the differences). </p>
<h2 class="heading settled" data-level="2" id="backgrounds"><span class="secno">2. </span><span class="content"> Backgrounds</span><a class="self-link" href="#backgrounds"></a></h2>
<h3 class="heading settled" data-level="2.1" id="the-background-position"><span class="secno">2.1. </span><span class="content"> Background Positioning: the <a class="property" data-link-type="propdesc" href="#propdef-background-position" id="ref-for-propdef-background-position-1">background-position</a> shorthand property</span><a class="self-link" href="#the-background-position"></a></h3>
<table class="def propdef" data-link-for-hint="background-position">
<tbody>
<tr>
<th>Name:
<td><dfn class="dfn-paneled css" data-dfn-type="property" data-export="" data-lt="background-position" id="propdef-background-position">background-position<span class="dfn-panel" data-deco=""><b><a href="#propdef-background-position">#propdef-background-position</a></b><b>Referenced in:</b><span><a href="#ref-for-propdef-background-position-1">2.1.
Background Positioning: the background-position shorthand property</a></span><span><a href="#ref-for-propdef-background-position-2">5.1.
Additions Since Level 3</a></span></span></dfn>
<tr class="value">
<th>Value:
<td class="prod"><a class="production css" data-link-type="type" href="#typedef-position" id="ref-for-typedef-position-1"><position></a><a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#mult-comma">#</a>
<tr>
<th>Initial:
<td>top left
<tr>
<th>Applies to:
<td>all
<tr>
<th>Inherited:
<td>no
<tr>
<th>Percentages:
<td>refer to size of background positioning area <em>minus</em> size of background image
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>A list, each item consisting of: a pair of offsets and an origin, each offset given as a combination of an absolute length and a percentage
<tr>
<th>Animatable:
<td>no
</table>
<p>See <a data-link-type="biblio" href="#biblio-css3bg">[CSS3BG]</a> for definition.</p>
<p>Where </p>
<pre class="prod"><dfn class="dfn-paneled" data-dfn-type="type" data-export="" data-lt="<position>" id="typedef-position"><var><position></var><span class="dfn-panel" data-deco=""><b><a href="#typedef-position">#typedef-position</a></b><b>Referenced in:</b><span><a href="#ref-for-typedef-position-1">2.1.
Background Positioning: the background-position shorthand property</a></span></span></dfn> = [ [ left <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> center <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> right <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> top <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> bottom <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> start <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> end <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> <var><percentage></var> <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> <var><length></var> ]
<a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a>
[ left <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> center <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> right <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> x-start <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> x-end <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> <var><percentage></var> <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> <var><length></var> ]
[ top <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> center <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> bottom <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> y-start <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> y-end <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> <var><percentage></var> <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> <var><length></var> ]
<a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a>
[ center <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> [ left <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> right <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> x-start <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> x-end ] [ <var><percentage></var> <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> <var><length></var> ]<a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#mult-opt">?</a> ] &&
[ center <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> [ top <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> bottom <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> y-start <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> y-end ] [ <var><percentage></var> <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> <var><length></var> ]<a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#mult-opt">?</a> ]
<a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a>
[ center <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> [ start <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> end ] [ <var><percentage></var> <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> <var><length></var> ]<a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#mult-opt">?</a> ]
[ center <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> [ start <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> end ] [ <var><percentage></var> <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> <var><length></var> ]<a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#mult-opt">?</a> ] ]</pre>
<p>Values have the following meanings:</p>
<dl>
<dt>One value
<dd> If only one value is given,
and that value is <span class="css">start</span> or <span class="css">end</span>,
then the keyword is duplicated;
otherwise the second keyword defaults to <span class="css">center</span>.
The resulting value is treated as a two-component value.
<dt>More than one value
<dd>
If the value contains a <span class="css">start</span> or <span class="css">end</span> keyword,
then the shorthand sets <a class="property" data-link-type="propdesc" href="#propdef-background-position-inline" id="ref-for-propdef-background-position-inline-1">background-position-inline</a> and <a class="property" data-link-type="propdesc" href="#propdef-background-position-block" id="ref-for-propdef-background-position-block-1">background-position-block</a> to the specified values.
Otherwise
the shorthand sets <a class="property" data-link-type="propdesc" href="#propdef-background-position-x" id="ref-for-propdef-background-position-x-1">background-position-x</a> and <a class="property" data-link-type="propdesc" href="#propdef-background-position-y" id="ref-for-propdef-background-position-y-1">background-position-y</a> to the specified values.
<p class="issue" id="issue-e752f96e"><a class="self-link" href="#issue-e752f96e"></a> Specify the value assignment in more detail. Should expand just like Level 3.</p>
</dl>
<p class="issue" id="issue-f4a1aeb0"><a class="self-link" href="#issue-f4a1aeb0"></a> Specify what happens to set of properties that are not set. Maybe they’re just not set?</p>
<h4 class="heading settled" data-level="2.1.1" id="background-position-longhands"><span class="secno">2.1.1. </span><span class="content"> Background Positioning Longhands: the <a class="property" data-link-type="propdesc" href="#propdef-background-position-x" id="ref-for-propdef-background-position-x-2">background-position-x</a>, <a class="property" data-link-type="propdesc" href="#propdef-background-position-y" id="ref-for-propdef-background-position-y-2">background-position-y</a>, <a class="property" data-link-type="propdesc" href="#propdef-background-position-inline" id="ref-for-propdef-background-position-inline-2">background-position-inline</a>, and <a class="property" data-link-type="propdesc" href="#propdef-background-position-block" id="ref-for-propdef-background-position-block-2">background-position-block</a> properties</span><a class="self-link" href="#background-position-longhands"></a></h4>
<p class="issue" id="issue-67389536"><a class="self-link" href="#issue-67389536"></a> This section is still being worked out. The tricky thing is making all the start/end keywords work sanely.</p>
<p class="issue" id="issue-x-y-val-pct-len"><a class="self-link" href="#issue-x-y-val-pct-len"></a>The Value lines below don’t allow <percentage> and <length> values to be specified on their own. This disagrees with existing implementations. </p>
<table class="def propdef" data-link-for-hint="background-position-x">
<tbody>
<tr>
<th>Name:
<td><dfn class="dfn-paneled css" data-dfn-type="property" data-export="" data-lt="background-position-x" id="propdef-background-position-x">background-position-x<span class="dfn-panel" data-deco=""><b><a href="#propdef-background-position-x">#propdef-background-position-x</a></b><b>Referenced in:</b><span><a href="#ref-for-propdef-background-position-x-1">2.1.
Background Positioning: the background-position shorthand property</a></span><span><a href="#ref-for-propdef-background-position-x-2">2.1.1.
Background Positioning Longhands: the background-position-x, background-position-y, background-position-inline, and background-position-block properties</a></span></span></dfn>
<tr class="value">
<th>Value:
<td class="prod">[ center <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> [ left <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> right <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> x-start <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> x-end ]<a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#mult-opt">?</a> [ <var><percentage></var> <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> <var><length></var> ]<a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#mult-opt">?</a> ]<a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#mult-comma">#</a>
<tr>
<th>Initial:
<td>left
<tr>
<th>Applies to:
<td>all
<tr>
<th>Inherited:
<td>no
<tr>
<th>Percentages:
<td>refer to width of background positioning area <em>minus</em> height of background image
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>A list, each item consisting of: an offset given as a combination of an absolute length and a percentage, plus an origin keyword
<tr>
<th>Animatable:
<td>no
</table>
<p>This property specifies the background position’s horizontal component.
An omitted origin keyword is assumed to be <a class="css" data-link-type="maybe" href="#valdef-border-limit-left" id="ref-for-valdef-border-limit-left-1">left</a>.</p>
<table class="def propdef" data-link-for-hint="background-position-y">
<tbody>
<tr>
<th>Name:
<td><dfn class="dfn-paneled css" data-dfn-type="property" data-export="" data-lt="background-position-y" id="propdef-background-position-y">background-position-y<span class="dfn-panel" data-deco=""><b><a href="#propdef-background-position-y">#propdef-background-position-y</a></b><b>Referenced in:</b><span><a href="#ref-for-propdef-background-position-y-1">2.1.
Background Positioning: the background-position shorthand property</a></span><span><a href="#ref-for-propdef-background-position-y-2">2.1.1.
Background Positioning Longhands: the background-position-x, background-position-y, background-position-inline, and background-position-block properties</a></span></span></dfn>
<tr class="value">
<th>Value:
<td class="prod">[ center <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> [ top <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> bottom <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> y-start <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> y-end ]<a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#mult-opt">?</a> [ <var><percentage></var> <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> <var><length></var> ]<a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#mult-opt">?</a> ]<a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#mult-comma">#</a>
<tr>
<th>Initial:
<td>left
<tr>
<th>Applies to:
<td>all
<tr>
<th>Inherited:
<td>no
<tr>
<th>Percentages:
<td>refer to height of background positioning area <em>minus</em> height of background image
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>A list, each item consisting of: an offset given as a combination of an absolute length and a percentage, plus an origin keyword
<tr>
<th>Animatable:
<td>no
</table>
<p>This property specifies the background position’s vertical component.
An omitted origin keyword is assumed to be <a class="css" data-link-type="maybe" href="#valdef-border-limit-top" id="ref-for-valdef-border-limit-top-1">top</a>.</p>
<table class="def propdef" data-link-for-hint="background-position-inline">
<tbody>
<tr>
<th>Name:
<td><dfn class="dfn-paneled css" data-dfn-type="property" data-export="" data-lt="background-position-inline" id="propdef-background-position-inline">background-position-inline<span class="dfn-panel" data-deco=""><b><a href="#propdef-background-position-inline">#propdef-background-position-inline</a></b><b>Referenced in:</b><span><a href="#ref-for-propdef-background-position-inline-1">2.1.
Background Positioning: the background-position shorthand property</a></span><span><a href="#ref-for-propdef-background-position-inline-2">2.1.1.
Background Positioning Longhands: the background-position-x, background-position-y, background-position-inline, and background-position-block properties</a></span></span></dfn>
<tr class="value">
<th>Value:
<td class="prod">[ center <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> [ start <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> end ]<a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#mult-opt">?</a> [ <var><percentage></var> <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> <var><length></var> ]<a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#mult-opt">?</a> ]<a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#mult-comma">#</a>
<tr>
<th>Initial:
<td>not applicable (initial value comes from physical property)
<tr>
<th>Applies to:
<td>all
<tr>
<th>Inherited:
<td>no
<tr>
<th>Percentages:
<td>refer to inline-size of background positioning area <em>minus</em> inline-size of background image
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>A list, each item consisting of: an offset given as a combination of an absolute length and a percentage, plus an origin keyword
<tr>
<th>Animatable:
<td>no
</table>
<p>This property specifies the background position’s inline-axis component.
An omitted origin keyword is assumed to be <a class="css" data-link-type="maybe" href="https://drafts.csswg.org/css-transitions-1/#valdef-steps-start">start</a>.</p>
<table class="def propdef" data-link-for-hint="background-position-block">
<tbody>
<tr>
<th>Name:
<td><dfn class="dfn-paneled css" data-dfn-type="property" data-export="" data-lt="background-position-block" id="propdef-background-position-block">background-position-block<span class="dfn-panel" data-deco=""><b><a href="#propdef-background-position-block">#propdef-background-position-block</a></b><b>Referenced in:</b><span><a href="#ref-for-propdef-background-position-block-1">2.1.
Background Positioning: the background-position shorthand property</a></span><span><a href="#ref-for-propdef-background-position-block-2">2.1.1.
Background Positioning Longhands: the background-position-x, background-position-y, background-position-inline, and background-position-block properties</a></span></span></dfn>
<tr class="value">
<th>Value:
<td class="prod">[ center <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> [ start <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> end ]<a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#mult-opt">?</a> [ <var><percentage></var> <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> <var><length></var> ]<a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#mult-opt">?</a> ]<a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#mult-comma">#</a>
<tr>
<th>Initial:
<td>not applicable (initial value comes from physical property)
<tr>
<th>Applies to:
<td>all
<tr>
<th>Inherited:
<td>no
<tr>
<th>Percentages:
<td>refer to size of background positioning area <em>minus</em> size of background image
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>A list, each item consisting of: an offset given as a combination of an absolute length and a percentage, plus an origin keyword
<tr>
<th>Animatable:
<td>no
</table>
<p>This property specifies the background position’s block-axis component.
An omitted origin keyword is assumed to be <a class="css" data-link-type="maybe" href="https://drafts.csswg.org/css-transitions-1/#valdef-steps-start">start</a>.</p>
<h2 class="heading settled" data-level="3" id="corners"><span class="secno">3. </span><span class="content"> Corners</span><a class="self-link" href="#corners"></a></h2>
<h3 class="heading settled" data-level="3.1" id="corner-sizing"><span class="secno">3.1. </span><span class="content"> Corner Sizing: the 'border-radius property</span><a class="self-link" href="#corner-sizing"></a></h3>
<table class="def propdef" data-link-for-hint="border-radius">
<tbody>
<tr>
<th>Name:
<td><dfn class="dfn-paneled css" data-dfn-type="property" data-export="" data-lt="border-radius" id="propdef-border-radius">border-radius<span class="dfn-panel" data-deco=""><b><a href="#propdef-border-radius">#propdef-border-radius</a></b><b>Referenced in:</b><span><a href="#ref-for-propdef-border-radius-1">3.2.
Corner Shaping: the corner-shape property</a></span><span><a href="#ref-for-propdef-border-radius-2">3.3.
Corner Shape and Size: the corners shorthand</a> <a href="#ref-for-propdef-border-radius-3">(2)</a> <a href="#ref-for-propdef-border-radius-4">(3)</a></span></span></dfn>
<tr class="value">
<th>Value:
<td class="prod">[ <a class="production css" data-link-type="type" href="https://drafts.csswg.org/css-values-3/#length-value"><length></a> <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> <a class="production css" data-link-type="type" href="https://drafts.csswg.org/css-values-3/#percentage-value"><percentage></a> ]<a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#mult-num-range">{1,4}</a> [ / [ <a class="production css" data-link-type="type" href="https://drafts.csswg.org/css-values-3/#length-value"><length></a> <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> <a class="production css" data-link-type="type" href="https://drafts.csswg.org/css-values-3/#percentage-value"><percentage></a> ]<a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#mult-num-range">{1,4}</a> ]<a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#mult-opt">?</a>
<tr>
<th>Initial:
<td>0
<tr>
<th>Applies to:
<td>all elements, except table element when <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css2/tables.html#propdef-border-collapse">border-collapse</a> is <a class="css" data-link-type="maybe" href="https://drafts.csswg.org/css-ruby-1/#valdef-ruby-merge-collapse">collapse</a>
<tr>
<th>Inherited:
<td>no
<tr>
<th>Percentages:
<td>n/a
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>specified value
<tr>
<th>Animatable:
<td>no
<tr>
<th>Canonical order:
<td>n/a
</table>
<p>See <a data-link-type="biblio" href="#biblio-css3bg">[CSS3BG]</a>.</p>
<h3 class="heading settled" data-level="3.2" id="corner-shaping"><span class="secno">3.2. </span><span class="content"> Corner Shaping: the <a class="property" data-link-type="propdesc" href="#propdef-corner-shape" id="ref-for-propdef-corner-shape-1">corner-shape</a> property</span><a class="self-link" href="#corner-shaping"></a></h3>
<table class="def propdef" data-link-for-hint="corner-shape">
<tbody>
<tr>
<th>Name:
<td><dfn class="dfn-paneled css" data-dfn-type="property" data-export="" data-lt="corner-shape" id="propdef-corner-shape">corner-shape<span class="dfn-panel" data-deco=""><b><a href="#propdef-corner-shape">#propdef-corner-shape</a></b><b>Referenced in:</b><span><a href="#ref-for-propdef-corner-shape-1">3.2.
Corner Shaping: the corner-shape property</a> <a href="#ref-for-propdef-corner-shape-2">(2)</a></span><span><a href="#ref-for-propdef-corner-shape-3">3.3.
Corner Shape and Size: the corners shorthand</a> <a href="#ref-for-propdef-corner-shape-4">(2)</a> <a href="#ref-for-propdef-corner-shape-5">(3)</a></span><span><a href="#ref-for-propdef-corner-shape-6">5.1.
Additions Since Level 3</a></span></span></dfn>
<tr class="value">
<th>Value:
<td class="prod">[round <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> bevel <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> scoop <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> notch]<a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#mult-num-range">{1,4}</a>
<tr>
<th>Initial:
<td>round
<tr>
<th>Applies to:
<td>all elements, except table element when <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css2/tables.html#propdef-border-collapse">border-collapse</a> is <a class="css" data-link-type="maybe" href="https://drafts.csswg.org/css-ruby-1/#valdef-ruby-merge-collapse">collapse</a>
<tr>
<th>Inherited:
<td>no
<tr>
<th>Percentages:
<td>n/a
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>specified value
<tr>
<th>Animatable:
<td>no
<tr>
<th>Canonical order:
<td>n/a
</table>
<p>By default, non-zero border-radii define
a quarter-ellipse that rounds the affected corners.
However in some cases, other corner shapes are desired.
The <a class="property" data-link-type="propdesc" href="#propdef-corner-shape" id="ref-for-propdef-corner-shape-2">corner-shape</a> property specifies a reinterpretation of the radii
to define other corner shapes.</p>
<dl>
<dt><dfn class="dfn-paneled css" data-dfn-for="corner-shape" data-dfn-type="value" data-export="" data-lt="round" id="valdef-corner-shape-round"><a class="css" data-link-type="maybe" href="#valdef-corner-shape-round" id="ref-for-valdef-corner-shape-round-1">round</a><span class="dfn-panel" data-deco=""><b><a href="#valdef-corner-shape-round">#valdef-corner-shape-round</a></b><b>Referenced in:</b><span><a href="#ref-for-valdef-corner-shape-round-1">3.2.
Corner Shaping: the corner-shape property</a></span></span></dfn>
<dd>Border radii define a convex elliptical curve at the corner.
<dt><dfn class="dfn-paneled css" data-dfn-for="corner-shape" data-dfn-type="value" data-export="" data-lt="bevel" id="valdef-corner-shape-bevel"><a class="css" data-link-type="maybe" href="#valdef-corner-shape-bevel" id="ref-for-valdef-corner-shape-bevel-1">bevel</a><span class="dfn-panel" data-deco=""><b><a href="#valdef-corner-shape-bevel">#valdef-corner-shape-bevel</a></b><b>Referenced in:</b><span><a href="#ref-for-valdef-corner-shape-bevel-1">3.2.
Corner Shaping: the corner-shape property</a></span></span></dfn>
<dd>Border radii define a diagonal slice at the corner.
<dt><dfn class="dfn-paneled css" data-dfn-for="corner-shape" data-dfn-type="value" data-export="" data-lt="scoop" id="valdef-corner-shape-scoop"><a class="css" data-link-type="maybe" href="#valdef-corner-shape-scoop" id="ref-for-valdef-corner-shape-scoop-1">scoop</a><span class="dfn-panel" data-deco=""><b><a href="#valdef-corner-shape-scoop">#valdef-corner-shape-scoop</a></b><b>Referenced in:</b><span><a href="#ref-for-valdef-corner-shape-scoop-1">3.2.
Corner Shaping: the corner-shape property</a> <a href="#ref-for-valdef-corner-shape-scoop-2">(2)</a></span></span></dfn>
<dd>Border radii define a concave elliptical curve at the corner.
<dt><dfn class="dfn-paneled css" data-dfn-for="corner-shape" data-dfn-type="value" data-export="" data-lt="notch" id="valdef-corner-shape-notch"><a class="css" data-link-type="maybe" href="#valdef-corner-shape-notch" id="ref-for-valdef-corner-shape-notch-1">notch</a><span class="dfn-panel" data-deco=""><b><a href="#valdef-corner-shape-notch">#valdef-corner-shape-notch</a></b><b>Referenced in:</b><span><a href="#ref-for-valdef-corner-shape-notch-1">3.2.
Corner Shaping: the corner-shape property</a> <a href="#ref-for-valdef-corner-shape-notch-2">(2)</a></span></span></dfn>
<dd>Border radii define a concave rectangular notch at the corner.
</dl>
<div class="example" id="example-eb5dcbed">
<a class="self-link" href="#example-eb5dcbed"></a> For example, the following declarations create a right-pointing next button.
<pre>a {
border-radius: 0 2em 2em 0;
corner-shape: bevel;
padding: 0.5em 2em 0.5em 0.5em;
</pre>
<p>As a fallback in UAs that don’t support <a class="property" data-link-type="propdesc" href="#propdef-border-radius" id="ref-for-propdef-border-radius-1">border-radius</a>,
the right side would be rounded rather than pointy.</p>
</div>
<p class="issue" id="issue-7e3f29b5"><a class="self-link" href="#issue-7e3f29b5"></a> For <a class="css" data-link-type="maybe" href="#valdef-corner-shape-scoop" id="ref-for-valdef-corner-shape-scoop-2">scoop</a> and <a class="css" data-link-type="maybe" href="#valdef-corner-shape-notch" id="ref-for-valdef-corner-shape-notch-2">notch</a>, how do the color/style/width transitions work?
Do they transition once in the middle, or alternate to match the topness/sideness of that segment of the border? </p>
<p class="issue" id="issue-cba02f09"><a class="self-link" href="#issue-cba02f09"></a> Add a <a class="css" data-link-type="maybe" href="https://drafts.csswg.org/css-transitions-1/#funcdef-transition-timing-function-cubic-bezier">cubic-bezier()</a> function for random other shapes?
Or some other functions? </p>
<h3 class="heading settled" data-level="3.3" id="corners-shorthand"><span class="secno">3.3. </span><span class="content"> Corner Shape and Size: the <a class="property" data-link-type="propdesc" href="#propdef-corners" id="ref-for-propdef-corners-1">corners</a> shorthand</span><a class="self-link" href="#corners-shorthand"></a></h3>
<table class="def propdef" data-link-for-hint="corners">
<tbody>
<tr>
<th>Name:
<td><dfn class="dfn-paneled css" data-dfn-type="property" data-export="" data-lt="corners" id="propdef-corners">corners<span class="dfn-panel" data-deco=""><b><a href="#propdef-corners">#propdef-corners</a></b><b>Referenced in:</b><span><a href="#ref-for-propdef-corners-1">3.3.
Corner Shape and Size: the corners shorthand</a> <a href="#ref-for-propdef-corners-2">(2)</a> <a href="#ref-for-propdef-corners-3">(3)</a></span></span></dfn>
<tr class="value">
<th>Value:
<td class="prod"><a class="production" data-link-type="propdesc" href="#propdef-corner-shape" id="ref-for-propdef-corner-shape-3"><‘corner-shape’></a> <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-any">||</a> <a class="production" data-link-type="propdesc" href="#propdef-border-radius" id="ref-for-propdef-border-radius-2"><‘border-radius’></a>
<tr>
<th>Initial:
<td>see individual properties
<tr>
<th>Applies to:
<td>see individual properties
<tr>
<th>Inherited:
<td>see individual properties
<tr>
<th>Percentages:
<td>see individual properties
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>see individual properties
<tr>
<th>Animatable:
<td>no
</table>
<p>The <a class="property" data-link-type="propdesc" href="#propdef-corners" id="ref-for-propdef-corners-2">corners</a> shorthand sets <a class="property" data-link-type="propdesc" href="#propdef-corner-shape" id="ref-for-propdef-corner-shape-4">corner-shape</a> and <a class="property" data-link-type="propdesc" href="#propdef-border-radius" id="ref-for-propdef-border-radius-3">border-radius</a> in the same declaration.
If either is omitted, it is reset to its initial value.</p>
<div class="example" id="example-9b886b19">
<a class="self-link" href="#example-9b886b19"></a> For example, the following declaration creates a diamond shape.
<pre>corners: bevel 50%;</pre>
<p>In UAs that don’t support <a class="property" data-link-type="propdesc" href="#propdef-corner-shape" id="ref-for-propdef-corner-shape-5">corner-shape</a>, the declaration is ignored
(falls back to a rectangle).</p>
</div>
<div class="example" id="example-0f55a243">
<a class="self-link" href="#example-0f55a243"></a> In this example, the first declaration creates tabs with vertical sides and rounded corners using <a class="property" data-link-type="propdesc" href="#propdef-border-radius" id="ref-for-propdef-border-radius-4">border-radius</a>,
while the second example makes them trapezoid-shaped in UAs that support <a class="property" data-link-type="propdesc" href="#propdef-corners" id="ref-for-propdef-corners-3">corners</a>.
<pre>border-radius: 0.25em 0.25em 0 0;
corners: bevel 0.25em 0.25em 0 0 / 50% 50% 0 0;
</pre>
</div>
<h2 class="heading settled" data-level="4" id="partial-borders"><span class="secno">4. </span><span class="content"> Partial borders</span><a class="self-link" href="#partial-borders"></a></h2>
<p>CSS borders traditionally cover an entire border edge. Sometimes,
however, it can be useful to hide some parts of the border. </p>
<p class="issue" id="issue-32661c58"><a class="self-link" href="#issue-32661c58"></a> Here are two proposals for doing this:
the second one is from GCPM, the first one is an attempt to recast it more readably.
The names are terrible, known problem, proposals accepted.
There is a problem with conceiving this as clipping:
if you have dotted borders, you want whole dots always, not parts of dots.
So it should be a drawing limit, not a clip. </p>
<h3 class="heading settled" data-level="4.1" id="border-limit"><span class="secno">4.1. </span><span class="content"> Partial Borders: the <a class="property" data-link-type="propdesc" href="#propdef-border-limit" id="ref-for-propdef-border-limit-1">border-limit</a> property</span><a class="self-link" href="#border-limit"></a></h3>
<table class="propdef">
<tbody>
<tr>
<th>Name:
<td><dfn class="dfn-paneled css" data-dfn-type="property" data-export="" data-lt="border-limit" id="propdef-border-limit">border-limit<span class="dfn-panel" data-deco=""><b><a href="#propdef-border-limit">#propdef-border-limit</a></b><b>Referenced in:</b><span><a href="#ref-for-propdef-border-limit-1">4.1.
Partial Borders: the border-limit property</a></span></span></dfn>
<tr>
<th>Value:
<td>all | [ sides | corners ] [ <length> | <percentage> ]?
| [ top | right | bottom | left ] [ <length> | <percentage> ]
<tr>
<th>Initial:
<td>round
<tr>
<th>Applies to:
<td>all elements, except table element when <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css2/tables.html#propdef-border-collapse">border-collapse</a> is <a class="css" data-link-type="maybe" href="https://drafts.csswg.org/css-ruby-1/#valdef-ruby-merge-collapse">collapse</a>
<tr>
<th>Inherited:
<td>no
<tr>
<th>Percentages:
<td>relative to border-box
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>as specified
</table>
<p>By default, the entire border is drawn. However, border rendering can be
limited to only part of a border. The keyword specifies which part, and
the length or percentage specifies how much. </p>
<dl>
<dt><dfn class="dfn-paneled css" data-dfn-for="border-limit" data-dfn-type="value" data-export="" data-lt="sides" id="valdef-border-limit-sides"><a class="css" data-link-type="maybe" href="#valdef-border-limit-sides" id="ref-for-valdef-border-limit-sides-1">sides</a><span class="dfn-panel" data-deco=""><b><a href="#valdef-border-limit-sides">#valdef-border-limit-sides</a></b><b>Referenced in:</b><span><a href="#ref-for-valdef-border-limit-sides-1">4.1.
Partial Borders: the border-limit property</a></span></span></dfn>
<dd>The sides are drawn up to but not including the corners (as defined
by the border radii). A length or percentage is measured from the center
of each side: <span class="css">50%</span> draws the middle 50% of the border; by default the
entire side is drawn.
<dt><dfn class="dfn-paneled css" data-dfn-for="border-limit" data-dfn-type="value" data-export="" data-lt="corners" id="valdef-border-limit-corners"><a class="css" data-link-type="maybe" href="#valdef-border-limit-corners" id="ref-for-valdef-border-limit-corners-1">corners</a><span class="dfn-panel" data-deco=""><b><a href="#valdef-border-limit-corners">#valdef-border-limit-corners</a></b><b>Referenced in:</b><span><a href="#ref-for-valdef-border-limit-corners-1">4.1.
Partial Borders: the border-limit property</a> <a href="#ref-for-valdef-border-limit-corners-2">(2)</a> <a href="#ref-for-valdef-border-limit-corners-3">(3)</a></span></span></dfn>
<dd>The corners are drawn plus the specified distance into the sides if
specified. A length is measured from the closest edge of the corner area.
A percentage is measured from the absolute corner of the border box.
<dt><dfn class="dfn-paneled css" data-dfn-for="border-limit" data-dfn-type="value" data-export="" data-lt="left" id="valdef-border-limit-left"><a class="css" data-link-type="maybe" href="#valdef-border-limit-left" id="ref-for-valdef-border-limit-left-2">left</a><span class="dfn-panel" data-deco=""><b><a href="#valdef-border-limit-left">#valdef-border-limit-left</a></b><b>Referenced in:</b><span><a href="#ref-for-valdef-border-limit-left-1">2.1.1.
Background Positioning Longhands: the background-position-x, background-position-y, background-position-inline, and background-position-block properties</a></span><span><a href="#ref-for-valdef-border-limit-left-2">4.1.
Partial Borders: the border-limit property</a></span></span></dfn>
<dt><dfn class="dfn-paneled css" data-dfn-for="border-limit" data-dfn-type="value" data-export="" data-lt="right" id="valdef-border-limit-right"><a class="css" data-link-type="maybe" href="#valdef-border-limit-right" id="ref-for-valdef-border-limit-right-1">right</a><span class="dfn-panel" data-deco=""><b><a href="#valdef-border-limit-right">#valdef-border-limit-right</a></b><b>Referenced in:</b><span><a href="#ref-for-valdef-border-limit-right-1">4.1.
Partial Borders: the border-limit property</a></span></span></dfn>
<dd>For the left and right (vertical) sides, draws the entire side and
corner. For the top and bottom (horizontal) sides, draws the left/right
portion, as specified. Distances are measured as for <a class="css" data-link-type="maybe" href="#valdef-border-limit-corners" id="ref-for-valdef-border-limit-corners-2">corners</a>.
<dt><dfn class="dfn-paneled css" data-dfn-for="border-limit" data-dfn-type="value" data-export="" data-lt="top" id="valdef-border-limit-top"><a class="css" data-link-type="maybe" href="#valdef-border-limit-top" id="ref-for-valdef-border-limit-top-2">top</a><span class="dfn-panel" data-deco=""><b><a href="#valdef-border-limit-top">#valdef-border-limit-top</a></b><b>Referenced in:</b><span><a href="#ref-for-valdef-border-limit-top-1">2.1.1.
Background Positioning Longhands: the background-position-x, background-position-y, background-position-inline, and background-position-block properties</a></span><span><a href="#ref-for-valdef-border-limit-top-2">4.1.
Partial Borders: the border-limit property</a></span></span></dfn>
<dt><dfn class="dfn-paneled css" data-dfn-for="border-limit" data-dfn-type="value" data-export="" data-lt="bottom" id="valdef-border-limit-bottom"><a class="css" data-link-type="maybe" href="#valdef-border-limit-bottom" id="ref-for-valdef-border-limit-bottom-1">bottom</a><span class="dfn-panel" data-deco=""><b><a href="#valdef-border-limit-bottom">#valdef-border-limit-bottom</a></b><b>Referenced in:</b><span><a href="#ref-for-valdef-border-limit-bottom-1">4.1.
Partial Borders: the border-limit property</a></span></span></dfn>
<dd>For the top and bottom (horizontal) sides, draws the entire side and
corner. For the left and right (vertical) sides, draws the top/bottom
portion, as specified. Distances are measured as for <a class="css" data-link-type="maybe" href="#valdef-border-limit-corners" id="ref-for-valdef-border-limit-corners-3">corners</a>.
</dl>
<div class="example" id="example-211cc22c">
<a class="self-link" href="#example-211cc22c"></a>
<p>The following example draws only the middle 50% of the sides.</p>
<pre>box { border: solid; border-parts: sides 50% }</pre>
<p>The following example draws only the curved parts of the corners.</p>
<pre>box { border: solid; border-radius: 1em 2em; border-parts: corners; }</pre>
<p>The following example draws only the left 4em of the top border.</p>
<pre>box { border-top: solid; border-parts: left 4em; }<p>The following example draws only the first 10px of each corner:</p>
<pre>box { border: solid; border-parts: corners 10px; }</pre> <p>The following example draws the curved part of the corner plus 5px
along ths sides:</p>
<pre>box { border: solid; border-radius: 5px; border-shape: scoop; border-parts: corners 5px; }</pre> <p>The following example draws the curved part of the corner and all of
the side except the middle 40%.</p>
<pre>box { border: solid; border-radius: 5px; border-shape: scoope; border-parts: corners 30%; }</pre> </pre>
</div>
<h3 class="heading settled" data-level="4.2" id="border-clip"><span class="secno">4.2. </span><span class="content"> The <a class="property" data-link-type="propdesc" href="#propdef-border-clip" id="ref-for-propdef-border-clip-1">border-clip</a> properties</span><a class="self-link" href="#border-clip"></a></h3>
<table class="propdef">
<tbody>
<tr>
<th>Name:
<td><dfn class="dfn-paneled css" data-dfn-type="property" data-export="" data-lt="border-clip" id="propdef-border-clip">border-clip<span class="dfn-panel" data-deco=""><b><a href="#propdef-border-clip">#propdef-border-clip</a></b><b>Referenced in:</b><span><a href="#ref-for-propdef-border-clip-1">4.2.
The border-clip properties</a> <a href="#ref-for-propdef-border-clip-2">(2)</a></span></span></dfn>, <dfn class="css" data-dfn-type="property" data-export="" id="propdef-border-clip-top">border-clip-top<a class="self-link" href="#propdef-border-clip-top"></a></dfn>, <dfn class="css" data-dfn-type="property" data-export="" id="propdef-border-clip-right">border-clip-right<a class="self-link" href="#propdef-border-clip-right"></a></dfn>, <dfn class="css" data-dfn-type="property" data-export="" id="propdef-border-clip-bottom">border-clip-bottom<a class="self-link" href="#propdef-border-clip-bottom"></a></dfn>, <dfn class="css" data-dfn-type="property" data-export="" id="propdef-border-clip-left">border-clip-left<a class="self-link" href="#propdef-border-clip-left"></a></dfn>
<tr>
<th>Value:
<td>normal | [ <length> | <percentage> | <fraction> ]+
<tr>
<th>Initial:
<td>normal
<tr>
<th>Applies to:
<td>all elements
<tr>
<th>Inherited:
<td>no
<tr>
<th>Percentages:
<td>refer to length of border-edge side
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td><span class="css">normal</span>, or a list consisting of absolute lengths, or percentages as specified
</table>
<p class="issue" id="issue-14d9ac8f"><a class="self-link" href="#issue-14d9ac8f"></a>Should these properties be simplified to only accept <code>normal | [ <length> | <percentage> ] +</code>? </p>
<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 <span class="css">fr</span> unit, as per <a data-link-type="biblio" href="#biblio-css3grid">[CSS3GRID]</a> or its <a href="https://drafts.csswg.org/css3-grid/">editor’s
edition</a>).
The <span class="css">normal</span> value means
that the border is not split, but shown normally. </p>
<p><a class="property" data-link-type="propdesc" href="#propdef-border-clip" id="ref-for-propdef-border-clip-2">border-clip</a> is a shorthand property for the four individual properties. </p>
<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 <span class="css">1fr</span> had been
specified at the end of the list. </p>
<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>
<p>For horizontal borders, parts are listed from left to right. For
vertical borders, parts are listed from top to bottom. </p>
<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. </p>
<div class="example" id="example-fdd9a140">
<a class="self-link" href="#example-fdd9a140"></a>
<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" id="example-d6a76cbb">
<a class="self-link" href="#example-d6a76cbb"></a>
<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" id="example-48afcd7c">
<a class="self-link" href="#example-48afcd7c"></a>
<p>By making the first part have zero length, the inverse border of
the previous example can easily be created: </p>
<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" id="example-986e1e6e">
<a class="self-link" href="#example-986e1e6e"></a>
<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" id="example-875259c7">
<a class="self-link" href="#example-875259c7"></a>
<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" id="example-396eb432">
<a class="self-link" href="#example-396eb432"></a>
<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" id="example-763dbd88">
<a class="self-link" href="#example-763dbd88"></a>
<p>This rendering: </p>
<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" id="example-9d276605">
<a class="self-link" href="#example-9d276605"></a>
<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. </p>
<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" id="example-fc57d294">
<a class="self-link" href="#example-fc57d294"></a>
<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: </p>
<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. </p>
</div>
<div class="example" id="example-dc7a51f1">
<a class="self-link" href="#example-dc7a51f1"></a>
<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. </p>
<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. </p>
</div>
<div class="example" id="example-a925bbb5">
<a class="self-link" href="#example-a925bbb5"></a>
<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. </p>
<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. </p>
</div>
<div class="example" id="example-4b433205">
<a class="self-link" href="#example-4b433205"></a>
<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: </p>
<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: </p>
<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. </p>
</div>
<h2 class="heading settled" data-level="5" id="changes"><span class="secno">5. </span><span class="content"> Changes</span><a class="self-link" href="#changes"></a></h2>
<h3 class="heading settled" data-level="5.1" id="level-changes"><span class="secno">5.1. </span><span class="content"> Additions Since Level 3</span><a class="self-link" href="#level-changes"></a></h3>
<p class="issue" id="issue-faa8d599"><a class="self-link" href="#issue-faa8d599"></a>Additions are a work in progress... here’s what we’re planning to add. :) </p>
<ul>
<li>logical <a class="property" data-link-type="propdesc" href="#propdef-background-position" id="ref-for-propdef-background-position-2">background-position</a> values (<span class="css">start</span>, <span class="css">end</span>)
<li>the <span class="css">extend</span> keyword of <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css2/colors.html#propdef-background-repeat">background-repeat</a>
<li><a class="property" data-link-type="propdesc" href="#propdef-corner-shape" id="ref-for-propdef-corner-shape-6">corner-shape</a>
<li>multiple borders per element
<li>logical border properties
<li><a href="#partial-borders">Partial Borders</a> (make part of border shorthand as well!)
<li><a href="http://lists.w3.org/Archives/Public/www-style/2012Oct/0314.html">More <span class="css">border-radius</span> shorthands</a> for doing both corners on a side at once.
<li>Splitting horizontal / vertical spread radius for box-shadow, if we can come up with a sane syntax for it.
</ul>
<h2 class="heading settled" data-level="6" id="acknowledgments"><span class="secno">6. </span><span class="content">Acknowledgments</span><a class="self-link" href="#acknowledgments"></a></h2>
<p>In addition to the many contributors to the <a data-link-type="biblio" href="#biblio-css1">[CSS1]</a>, <a data-link-type="biblio" href="#biblio-css21">[CSS21]</a>,
and <a data-link-type="biblio" href="#biblio-css3bg">[CSS3BG]</a> predecessors to this module,
the editors would like to thank
Tab Atkins,
and Håkon Wium Lie
for their suggestions and feedback specifically for this Level 4. </p>
</main>
<h2 class="no-ref no-num heading settled" id="conformance"><span class="content"> Conformance</span><a class="self-link" href="#conformance"></a></h2>
<h3 class="heading settled" id="document-conventions"><span class="content"> Document conventions</span><a class="self-link" href="#document-conventions"></a></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. </p>
<p>All of the text of this specification is normative except sections
explicitly marked as non-normative, examples, and notes. <a data-link-type="biblio" href="#biblio-rfc2119">[RFC2119]</a> </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: </p>
<div class="example" id="example-52448c84">
<a class="self-link" href="#example-52448c84"></a>
<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>
<p class="note" role="note">Note, this is an informative note. </p>
<p>Advisements are normative sections styled to evoke special attention and are
set apart from other normative text with <code><strong class="advisement"></code>, like
this: <strong class="advisement"> UAs MUST provide an accessible alternative. </strong> </p>
<h3 class="heading settled" id="conform-classes"><span class="content"> Conformance classes</span><a class="self-link" href="#conform-classes"></a></h3>
<p>Conformance to this specification
is defined for three conformance classes: </p>
<dl>
<dt>style sheet
<dd>A <a href="http://www.w3.org/TR/CSS2/conform.html#style-sheet">CSS
style sheet</a>.
<dt>renderer
<dd>A <a href="http://www.w3.org/TR/CSS2/conform.html#user-agent">UA</a> that interprets the semantics of a style sheet and renders
documents that use them.
<dt>authoring tool
<dd>A <a href="http://www.w3.org/TR/CSS2/conform.html#user-agent">UA</a> that writes a style sheet.
</dl>
<p>A style sheet is conformant to this specification
if all of its statements that use syntax defined in this module are valid
according to the generic CSS grammar and the individual grammars of each
feature defined in this module. </p>
<p>A renderer is conformant to this specification
if, in addition to interpreting the style sheet as defined by the
appropriate specifications, it supports all the features defined
by this specification 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>
<p>An authoring tool is conformant to this specification
if it writes style sheets that are syntactically correct according to the
generic CSS grammar and the individual grammars of each feature in
this module, and meet all other conformance requirements of style sheets
as described in this module. </p>
<h3 class="heading settled" id="conform-responsible"><span class="content"> Requirements for Responsible Implementation of CSS</span><a class="self-link" href="#conform-responsible"></a></h3>
<p>The following sections define several conformance requirements
for implementing CSS responsibly,
in a way that promotes interoperability in the present and future. </p>
<h4 class="heading settled" id="conform-partial"><span class="content"> Partial Implementations</span><a class="self-link" href="#conform-partial"></a></h4>
<p>So that authors can exploit the forward-compatible parsing rules to assign fallback values, <strong>CSS renderers <em>must</em> treat as invalid
(and <a href="http://www.w3.org/TR/CSS2/conform.html#ignore">ignore as appropriate</a>)
any at-rules, properties, property values, keywords, and other syntactic constructs
for which they have no usable level of support</strong>.
In particular, user agents <em>must not</em> selectively ignore
unsupported property values and honor supported values in a single multi-value property declaration:
if any value is considered invalid (as unsupported values must be),
CSS requires that the entire declaration be ignored. </p>
<h4 class="heading settled" id="conform-future-proofing"><span class="content"> Implementations of Unstable and Proprietary Features</span><a class="self-link" href="#conform-future-proofing"></a></h4>
<p>To avoid clashes with future stable CSS features,
the CSSWG recommends <a href="http://www.w3.org/TR/CSS/#future-proofing">following best practices</a> for the implementation of <a href="http://www.w3.org/TR/CSS/#unstable">unstable</a> features and <a href="http://www.w3.org/TR/CSS/#proprietary-extension">proprietary extensions</a> to CSS. </p>
<h4 class="heading settled" id="conform-testing"><span class="content"> Implementations of CR-level Features</span><a class="self-link" href="#conform-testing"></a></h4>
<p>Once a specification reaches the Candidate Recommendation stage,
implementers should release an <a data-link-type="dfn" href="http://www.w3.org/TR/CSS/#vendor-prefix">unprefixed</a> implementation
of any CR-level feature they can demonstrate
to be correctly implemented according to spec,
and should avoid exposing a prefixed variant of that feature. </p>
<p>To establish and maintain the interoperability of CSS across
implementations, the CSS Working Group requests that non-experimental
CSS renderers submit an implementation report (and, if necessary, the
testcases used for that implementation report) to the W3C before
releasing an unprefixed implementation of any CSS features. Testcases
submitted to W3C are subject to review and correction by the CSS
Working Group. </p>
<p>
Further information on submitting testcases and implementation reports
can be found from on the CSS Working Group’s website at <a href="http://www.w3.org/Style/CSS/Test/">http://www.w3.org/Style/CSS/Test/</a>.
Questions should be directed to the <a href="http://lists.w3.org/Archives/Public/public-css-testsuite">public-css-testsuite@w3.org</a> mailing list.
<script src="https://www.w3.org/scripts/TR/2016/fixup.js"></script>
</p>
<h2 class="no-num no-ref heading settled" id="index"><span class="content">Index</span><a class="self-link" href="#index"></a></h2>
<h3 class="no-num no-ref heading settled" id="index-defined-here"><span class="content">Terms defined by this specification</span><a class="self-link" href="#index-defined-here"></a></h3>
<ul class="index">
<li><a href="#propdef-background-position">background-position</a><span>, in §2.1</span>
<li><a href="#propdef-background-position-block">background-position-block</a><span>, in §2.1.1</span>
<li><a href="#propdef-background-position-inline">background-position-inline</a><span>, in §2.1.1</span>
<li><a href="#propdef-background-position-x">background-position-x</a><span>, in §2.1.1</span>
<li><a href="#propdef-background-position-y">background-position-y</a><span>, in §2.1.1</span>
<li><a href="#valdef-corner-shape-bevel">bevel</a><span>, in §3.2</span>
<li><a href="#propdef-border-clip">border-clip</a><span>, in §4.2</span>
<li><a href="#propdef-border-clip-bottom">border-clip-bottom</a><span>, in §4.2</span>