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<!DOCTYPE html><html lang=en><head>
<meta content="text/html; charset=utf-8" http-equiv=Content-Type>
<title>CSS Counter Styles Level 3</title>
<link href=../default.css rel=stylesheet type=text/css>
<link href=../csslogo.ico rel="shortcut icon" type=image/x-icon>
<style>
body {
background: url("https://www.w3.org/StyleSheets/TR/logo-ED") top left no-repeat white;
background-attachment: fixed;
color: black;
font-family: sans-serif;
margin: 0 auto;
max-width: 50em;
padding: 2em 1em 2em 70px;
}
:link { color: #00C; background: transparent }
:visited { color: #609; background: transparent }
a[href]:active { color: #C00; background: transparent }
a[href]:hover { background: #ffa }
a[href] img { border-style: none }
h1, h2, h3, h4, h5, h6 { text-align: left }
h1, h2, h3 { color: #005A9C; }
h1 { font: 170% sans-serif }
h2 { font: 140% sans-serif }
h3 { font: 120% sans-serif }
h4 { font: bold 100% sans-serif }
h5 { font: italic 100% sans-serif }
h6 { font: small-caps 100% sans-serif }
.hide { display: none }
div.head { margin-bottom: 1em }
div.head h1 { margin-top: 2em; clear: both }
div.head table { margin-left: 2em; margin-top: 2em }
p.copyright { font-size: small }
p.copyright small { font-size: small }
pre { margin-left: 2em }
dt { font-weight: bold }
ul.toc, ol.toc {
list-style: none;
}
</style>
<style>
pre.stylesheet { white-space: pre-wrap; }
code.inline { display: inline-block; }
</style>
</head>
<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/Icons/w3c_home width=72>
</a>
</p>
<h1 class="p-name no-ref" id=title>CSS Counter Styles Level 3</h1>
<h2 class="no-num no-toc no-ref heading settled heading" id=subtitle><span class=content>Editor’s Draft,
<span class=dt-updated><span class=value-title title=20140625>25 June 2014</span></span></span></h2>
<div data-fill-with=spec-metadata><dl>
<dt>Feedback:
<dd><a href="mailto:www-style@w3.org?subject=%5Bcss-counter-styles%5D%20feedback">www-style@w3.org</a>
with subject line
“<kbd>[css-counter-styles] <var>… message topic …</var></kbd>”(<a href=http://lists.w3.org/Archives/Public/www-style/ rel=discussion>archives</a>)
<dt>Issue Tracking:
<dd><a href="https://www.w3.org/Bugs/Public/buglist.cgi?product=CSS&component=Counter%20Styles&resolution=---">Bugzilla</a>
<dt>Previous Versions:
<dd><dd><a href=http://www.w3.org/TR/2012/WD-css-counter-styles-3-20121009/ rel=previous>http://www.w3.org/TR/2012/WD-css-counter-styles-3-20121009/</a>
<dt>Editor:
<dd><dd class="p-author h-card vcard"><a class="p-name fn u-url url" href=http://xanthir.com/contact/>Tab Atkins Jr.</a> (<span class="p-org org">Google</span>)
<dt>Latest version:
<dd><a href=http://w3.org/TR/css-counter-styles-3/>http://w3.org/TR/css-counter-styles-3/</a>
<dt>This version:
<dd><a class=u-url href=http://dev.w3.org/csswg/css-counter-styles/>http://dev.w3.org/csswg/css-counter-styles/</a>
</dl>
</div>
<div data-fill-with=warning></div>
<p class=copyright data-fill-with=copyright><a href=http://www.w3.org/Consortium/Legal/ipr-notice#Copyright>Copyright</a> © 2014 <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>), All Rights Reserved. W3C <a href=http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer>liability</a>, <a href=http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks>trademark</a> and <a href=http://www.w3.org/Consortium/Legal/copyright-documents>document use</a> rules apply.
</p>
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc no-ref heading settled heading" id=abstract><span class=content>Abstract</span></h2>
<p class=p-summary data-fill-with=abstract><p>This module introduces the <a class=css data-link-type=maybe href=#at-ruledef-counter-style title=@counter-style>@counter-style</a> rule, which allows authors to define their own custom counter styles for use with CSS list-marker and generated-content counters <a data-biblio-type=informative data-link-type=biblio href=#biblio-css3list title=biblio-css3list>[CSS3LIST]</a>. It also predefines a set of common counter styles, including the ones present in CSS2 and CSS2.1.</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.</p>
<h2 class="no-num no-toc no-ref heading settled heading" 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>
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-counter-styles%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-counter-styles” in the subject,
preferably like this:
“[css-counter-styles] <em>…summary of comment…</em>”
<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>
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>.</div>
<div data-fill-with=at-risk><p>The following features are at-risk, and may be dropped during the CR period:
<ul><li>the counter styles <a class=css data-link-type=maybe href=#valuedef-cjk-decimal title=cjk-decimal>cjk-decimal</a>, <a class=css data-link-type=maybe href=#valuedef-hebrew title=hebrew>hebrew</a>, <a class=css data-link-type=maybe href=#valuedef-hiragana title=hiragana>hiragana</a>, <a class=css data-link-type=maybe href=#valuedef-hiragana-iroha title=hiragana-iroha>hiragana-iroha</a>, <a class=css data-link-type=maybe href=#valuedef-katakana title=katakana>katakana</a>, <a class=css data-link-type=maybe href=#valuedef-katakana-iroha title=katakana-iroha>katakana-iroha</a>, <a class=css data-link-type=maybe href=#valuedef-japanese-informal title=japanese-informal>japanese-informal</a>, <a class=css data-link-type=maybe href=#valuedef-japanese-formal title=japanese-formal>japanese-formal</a>, <a class=css data-link-type=maybe href=#valuedef-korean-hangul-formal title=korean-hangul-formal>korean-hangul-formal</a>, <a class=css data-link-type=maybe href=#valuedef-korean-hanja-informal title=korean-hanja-informal>korean-hanja-informal</a>, <a class=css data-link-type=maybe href=#valuedef-korean-hanja-formal title=korean-hanja-formal>korean-hanja-formal</a>, <a class=css data-link-type=maybe href=#valuedef-simp-chinese-informal title=simp-chinese-informal>simp-chinese-informal</a>, <a class=css data-link-type=maybe href=#valuedef-simp-chinese-formal title=simp-chinese-formal>simp-chinese-formal</a>, <a class=css data-link-type=maybe href=#valuedef-trad-chinese-informal title=trad-chinese-informal>trad-chinese-informal</a>, <a class=css data-link-type=maybe href=#valuedef-trad-chinese-formal title=trad-chinese-formal>trad-chinese-formal</a>, and <a class=css data-link-type=maybe href=#valuedef-ethiopic-numeric title=ethiopic-numeric>ethiopic-numeric</a>.</ul></div>
<h2 class="no-num no-toc no-ref heading settled heading" id=contents><span class=content>Table of Contents</span></h2>
<div data-fill-with=table-of-contents><ul class=toc>
<li><a href=#intro><span class=secno>1</span> Introduction</a>
<li><a href=#counter-styles><span class=secno>2</span> Counter Styles</a>
<li><a href=#the-counter-style-rule><span class=secno>3</span> Defining Custom Counter Styles: the <span>@counter-style</span> rule</a>
<ul class=toc>
<li><a href=#counter-style-system><span class=secno>3.1</span> Counter algorithms: the <span>system</span> descriptor</a>
<ul class=toc>
<li><a href=#cyclic-system><span class=secno>3.1.1</span> Cycling Symbols: the <span>cyclic</span> system</a>
<li><a href=#fixed-system><span class=secno>3.1.2</span> Exhaustible Symbols: the <span>fixed</span> system</a>
<li><a href=#symbolic-system><span class=secno>3.1.3</span> Repeating Symbols: the <span>symbolic</span> system</a>
<li><a href=#alphabetic-system><span class=secno>3.1.4</span> Bijective Numerals: the <span>alphabetic</span> system</a>
<li><a href=#numeric-system><span class=secno>3.1.5</span> Positional Numerals: the <span>numeric</span> system</a>
<li><a href=#additive-system><span class=secno>3.1.6</span> Accumulating Numerals: the <span>additive</span> system</a>
<li><a href=#extends-system><span class=secno>3.1.7</span> Tweaking Existing Counter Styles: the <span>extends</span> system <span></span></a></ul>
<li><a href=#counter-style-negative><span class=secno>3.2</span> Formatting negative values: the <span>negative</span> descriptor</a>
<li><a href=#counter-style-prefix><span class=secno>3.3</span> Symbols before the marker: the <span>prefix</span> descriptor</a>
<li><a href=#counter-style-suffix><span class=secno>3.4</span> Symbols after the marker: the <span>suffix</span> descriptor</a>
<li><a href=#counter-style-range><span class=secno>3.5</span> Limiting the counter scope: the <span>range</span> descriptor</a>
<li><a href=#counter-style-pad><span class=secno>3.6</span> Zero-Padding and Constant-Width Representations: the <span>pad</span> descriptor</a>
<li><a href=#counter-style-fallback><span class=secno>3.7</span> Defining fallback: the <span>fallback</span> descriptor</a>
<li><a href=#counter-style-symbols><span class=secno>3.8</span> Marker characters: the <span>symbols</span> and <span>additive-symbols</span> descriptors</a>
<li><a href=#counter-style-speak-as><span class=secno>3.9</span> Speech Synthesis: the <span>speak-as</span> descriptor</a></ul>
<li><a href=#symbols-function><span class=secno>4</span> Defining Anonymous Counter Styles: the <span>symbols()</span> function</a>
<li><a href=#extending-css2><span class=secno>5</spa
4A52
n> Extending <span>list-style-type</span>, <span>counter()</span>, and <span>counters()</span></a>
<li><a href=#predefined-counters><span class=secno>6</span> Simple Predefined Counter Styles</a>
<ul class=toc>
<li><a href=#simple-numeric><span class=secno>6.1</span> Numeric: <span>decimal</span>, <span>decimal-leading-zero</span>, <span>cjk-decimal</span>, <span>lower-roman</span>, <span>upper-roman</span>, <span>armenian</span>, <span>georgian</span>, <span>hebrew</span></a>
<li><a href=#simple-alphabetic><span class=secno>6.2</span> Alphabetic: <span>lower-alpha</span>, <span>lower-latin</span>, <span>upper-alpha</span>, <span>upper-latin</span>, <span>lower-greek</span>, <span>hiragana</span>, <span>hiragana-iroha</span>, <span>katakana</span>, <span>katakana-iroha</span></a>
<li><a href=#simple-symbolic><span class=secno>6.3</span> Symbolic: <span>disc</span>, <span>circle</span>, <span>square</span>, <span>disclosure-open</span>, <span>disclosure-closed</span></a></ul>
<li><a href=#complex-predefined-counters><span class=secno>7</span> Complex Predefined Counter Styles</a>
<ul class=toc>
<li><a href=#complex-cjk><span class=secno>7.1</span> Longhand East Asian Counter Styles: <span>japanese-informal</span>, <span>japanese-formal</span>, <span>korean-hangul-formal</span>, <span>korean-hanja-informal</span>, <span>korean-hanja-formal</span>, <span>simp-chinese-informal</span>, <span>simp-chinese-formal</span>, <span>trad-chinese-informal</span>, <span>trad-chinese-formal</span></a>
<ul class=toc>
<li><a href=#limited-cjk><span class=secno>7.1.1</span> Limited-range Implementation (required)</a></ul>
<li><a href=#ethiopic-numeric-counter-style><span class=secno>7.2</span> Ethiopic Numeric Counter Style: <span>ethiopic-numeric</span></a></ul>
<li><a href=#additional-predefined><span class=secno>8</span> Additional Predefined Counter Styles</a>
<li><a href=#apis><span class=secno>9</span> APIs</a>
<ul class=toc>
<li><a href=#extentions-to-cssrule-interface><span class=secno>9.1</span> Extensions to the <code>CSSRule</code> interface</a>
<li><a href=#the-csscounterstylerule-interface><span class=secno>9.2</span> The <code>CSSCounterStyleRule</code> interface</a></ul>
<li><a href=#ua-stylesheet><span class=secno>10</span> Sample style sheet for HTML</a>
<li><a href=#changes><span class=secno></span> Changes since the July 2013 Working Draft</a>
<li><a href=#acknowledgments><span class=secno></span> Acknowledgments</a>
<li><a href=#conformance><span class=secno></span> Conformance</a>
<ul class=toc>
<li><a href=#conventions><span class=secno></span> Document conventions</a>
<li><a href=#conformance-classes><span class=secno></span> Conformance classes</a>
<li><a href=#partial><span class=secno></span> Partial implementations</a>
<li><a href=#experimental><span class=secno></span> Experimental implementations</a>
<li><a href=#testing><span class=secno></span> Non-experimental implementations</a></ul>
<li><a href=#references><span class=secno></span> References</a>
<ul class=toc>
<li><a href=#normative><span class=secno></span> Normative References</a>
<li><a href=#informative><span class=secno></span> Informative References</a></ul>
<li><a href=#index><span class=secno></span> Index</a>
<li><a href=#property-index><span class=secno></span> Property index</a>
<ul class=toc>
<li><a href=#counter-style-descriptor-table><span class=secno></span> <span>@counter-style</span> Descriptors</a></ul>
<li><a href=#issues-index><span class=secno></span> Issues Index</a></ul></div>
<h2 class="heading settled heading" data-level=1 id=intro><span class=secno>1 </span><span class=content>
Introduction</span><a class=self-link href=#intro></a></h2>
<p>CSS 1 defined a handful of useful counter styles based on the styles that HTML traditionally allowed on ordered and unordered lists.
While this was expanded slightly by CSS2.1,
it doesn’t address the needs of worldwide typography.</p>
<p>This module introduces the <a class=css data-link-type=maybe href=#at-ruledef-counter-style title=@counter-style>@counter-style</a> rule which allows CSS to address this in an open-ended manner,
by allowing the author to define their own counter styles.
These styles can then be used in the <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css-lists-3/#propdef-list-style-type title=list-style-type>list-style-type</a> property
or in the <a class=css data-link-type=maybe href=http://dev.w3.org/csswg/css-lists-3/#funcdef-counter title=counter()>counter()</a> and <a class=css data-link-type=maybe href=http://dev.w3.org/csswg/css-lists-3/#funcdef-counters title=counters()>counters()</a> functions.
It also defines some additional predefined counter styles,
particularly ones which are common but complicated to represent with <a class=css data-link-type=maybe href=#at-ruledef-counter-style title=@counter-style>@counter-style</a>.</p>
<h2 class="heading settled heading" data-level=2 id=counter-styles><span class=secno>2 </span><span class=content>
Counter Styles</span><a class=self-link href=#counter-styles></a></h2>
<p>A <dfn data-dfn-type=dfn data-export="" id=counter-style>counter style<a class=self-link href=#counter-style></a></dfn> defines how to convert a counter value into a string.
Counter styles are composed of:</p>
<ul>
<li>
a name,
to identify the style
<li>
an algorithm,
which transforms integer counter values into a basic string representation
<li>
a negative sign,
which is prepended or appended to the representation of a negative counter value.
<li>
a prefix,
to prepend to the representation
<li>
a suffix
to append to the representation
<li>
a range,
which limits the values that a counter style handles
<li>
a spoken form,
which describes how to read out the counter style in a speech synthesizer
<li>
and a fallback style,
to render the representation with when the counter value is outside the counter style’s range
or the counter style otherwise can’t render the counter value
</ul>
<p>When asked to <dfn data-dfn-type=dfn data-export="" id=generate-a-counter title="generate a counter|generate a counter representation">generate a counter representation<a class=self-link href=#generate-a-counter></a></dfn>
using a particular counter style for a particular counter value,
follow these steps:</p>
<ol>
<li>
If the counter style is unknown,
exit this algorithm and instead <a data-link-type=dfn href=#generate-a-counter title="generate a counter representation">generate a counter representation</a>
using the <a class=css data-link-type=maybe href=#valuedef-decimal title=decimal>decimal</a> style and the same counter value.
<li>
If the counter value is outside the <a class=property data-link-type=propdesc href=#descdef-range title=range>range</a> of the counter style,
exit this algorithm and instead <a data-link-type=dfn href=#generate-a-counter title="generate a counter representation">generate a counter representation</a>
using the counter style’s fallback style and the same counter value.
<li>
Using the counter value and the counter algorithm for the counter style,
generate an <dfn data-dfn-type=dfn data-noexport="" id=initial-representation-for-the-counter-value>initial representation for the counter value<a class=self-link href=#initial-representation-for-the-counter-value></a></dfn>.
If the counter value is negative
and the counter style <a data-link-type=dfn href=#use-a-negative-sign title="uses a negative sign">uses a negative sign</a>,
instead generate an initial representation using the absolute value of the counter value.
<li>
If the representation uses less symbols than specified in the counter style’s <a class=property data-link-type=propdesc href=#descdef-pad title=pad>pad</a> descriptor,
prepend symbols to the representation as specified in the <a class=property data-link-type=propdesc href=#descdef-pad title=pad>pad</a> descriptor.
<li>
If the counter value is negative
and the counter style <a data-link-type=dfn href=#use-a-negative-sign title="uses a negative sign">uses a negative sign</a>,
wrap the representation in the counter style’s negative sign
as specified in the <a class=property data-link-type=propdesc href=#descdef-negative title=negative>negative</a> descriptor.
<li>
Return the representation.
</ol>
<p class=note>Note: the prefix and suffix don’t play a part in this algorithm.
This is intentional;
the prefix and suffix aren’t part of the string returned by the counter() or counters() functions.
Instead, the prefix and suffix are added by the algorithm that constructs the value of the <a class=css-code data-link-spec=css-ui-3 data-link-type=property href=http://dev.w3.org/csswg/css-ui-3/#content title=content>content</a> property
for the <a class=css data-link-type=maybe href=http://dev.w3.org/csswg/css-lists-3/#selectordef-marker title=::marker>::marker</a> pseudo-element.
This also implies that the prefix and suffix always come from the specified counter-style,
even if the actual representation is constructed by a fallback style.</p>
<p>Some values of <a class=property data-link-type=propdesc href=#descdef-system title=system>system</a> (<a class=css data-link-type=maybe href=#valuedef-symbolic title=symbolic>symbolic</a>, <a class=css data-link-type=maybe href=#valuedef-additive title=additive>additive</a>)
and some descriptors (<a class=property data-link-type=propdesc href=#descdef-pad title=pad>pad</a>)
can generate representations with size linear to an author-supplied number.
This can potentially be abused to generate excessively large representations
and consume undue amounts of the user’s memory or even hang their browser.
User agents must support representations at least 60 Unicode codepoints long,
but they may choose to instead use the fallback style for representations that would be longer than 60 codepoints.</p>
<h2 class="heading settled heading" data-level=3 id=the-counter-style-rule><span class=secno>3 </span><span class=content>
Defining Custom Counter Styles: the <a class=css data-link-type=maybe href=#at-ruledef-counter-style title=@counter-style>@counter-style</a> rule</span><a class=self-link href=#the-counter-style-rule></a></h2>
<p>The <dfn class=css-code data-dfn-type=at-rule data-export="" id=at-ruledef-counter-style>@counter-style<a class=self-link href=#at-ruledef-counter-style></a></dfn> rule allows authors to define a custom <a data-link-type=dfn href=#counter-style title="counter style">counter style</a>.
The components of a <a data-link-type=dfn href=#counter-style title="counter style">counter style</a> are specified by descriptors in the <a class=css data-link-type=maybe href=#at-ruledef-counter-style title=@counter-style>@counter-style</a> rule.
The algorithm is specified implicitly by a combination of the <span class=css data-link-type=maybe title=system>system</span>, <span class=css data-link-type=maybe title=symbols>symbols</span>, and <span class=css data-link-type=maybe title=additive-symbols>additive-symbols</span> properties.</p>
<p>The general form of an <a class=css data-link-type=maybe href=#at-ruledef-counter-style title=@counter-style>@counter-style</a> rule is:</p>
<pre>@counter-style <a class="production css-code" data-link-type=type href=#typedef-counter-style-name title="<counter-style-name>"><counter-style-name></a> { <a class="production css-code" data-link-type=type href=http://dev.w3.org/csswg/css-syntax-3/#typedef-declaration-list title="<declaration-list>"><declaration-list></a> }</pre>
<p>where <dfn class=css-code data-dfn-type=type data-export="" id=typedef-counter-style-name><counter-style-name><a class=self-link href=#typedef-counter-style-name></a></dfn> is a <a class="production css-code" data-link-type=type href=http://dev.w3.org/csswg/css-values-3/#identifier-value title="<custom-ident>"><custom-ident></a>.</p>
<p>If a counter style’s name is an <a data-link-type=dfn href=http://dev.w3.org/csswg/css-syntax-3/#ascii-case-insensitive title="ascii case-insensitive">ASCII case-insensitive</a> match for "decimal" or "none",
the <a class=css data-link-type=maybe href=#at-ruledef-counter-style title=@counter-style>@counter-style</a> rule is invalid.</p>
<p class=note>Note: Note that <a class="production css-code" data-link-type=type href=http://dev.w3.org/csswg/css-values-3/#identifier-value title="<custom-ident>"><custom-ident></a> also automatically excludes the <a data-link-spec=css-values data-link-type=dfn href=http://dev.w3.org/csswg/css-values-3/#css-wide-keywords title="css-wide keywords">CSS-wide keywords</a>.
In addition, some names, like <span class=css data-link-type=maybe title=inside>inside</span>,
are valid as counter style names,
but conflict with the existing values of properties like <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css-lists-3/#propdef-list-style title=list-style>list-style</a>,
and so won’t be usable there.</p>
<p>Counter style names are case-sensitive.
However, the names defined in this specification are ASCII lower-cased on parse
wherever they are used as counter styles, e.g.
in the <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css-lists-3/#propdef-list-style title=list-style>list-style</a> set of properties,
in the <a class=css data-link-type=maybe href=#at-ruledef-counter-style title=@counter-style>@counter-style</a> rule,
and in the <a class=css data-link-type=maybe href=http://dev.w3.org/csswg/css-lists-3/#funcdef-counter title=counter()>counter()</a> functions.</p>
<p>Each <a class=css data-link-type=maybe href=#at-ruledef-counter-style title=@counter-style>@counter-style</a> rule specifies a value for every counter-style descriptor,
either implicitly or explicitly.
Those not given explicit value in the rule take the initial value listed with each descriptor in this specification.
These descriptors apply solely within the context of the <a class=css data-link-type=maybe href=#at-ruledef-counter-style title=@counter-style>@counter-style</a> rule in which they are defined,
and do not apply to document language elements.
There is no notion of which elements the descriptors apply to or whether the values are inherited by child elements.
When a given descriptor occurs multiple times in a given <a class=css data-link-type=maybe href=#at-ruledef-counter-style title=@counter-style>@counter-style</a> rule,
only the last specified value is used;
all prior values for that descriptor must be ignored.</p>
<p>Defining a <a class=css data-link-type=maybe href=#at-ruledef-counter-style title=@counter-style>@counter-style</a> makes it available to the entire document in which it is included.
If multiple <a class=css data-link-type=maybe href=#at-ruledef-counter-style title=@counter-style>@counter-style</a> rules are defined with the same name,
only one wins,
according to standard cascade rules.
<a class=css data-link-type=maybe href=#at-ruledef-counter-style title=@counter-style>@counter-style</a> rules cascade "atomically":
if one replaces another of the same name,
it replaces it <em>entirely</em>,
rather than just replacing the specific descriptors it specifies.</p>
<p class=note>Note: Note that even the predefined counter styles can be overridden;
the UA stylesheet occurs before any other stylesheets,
so the predefined ones always lose in the cascade.</p>
<p>This at-rule conforms with the forward-compatible parsing requirement of CSS;
conformant parsers that don’t understand these rules will ignore them without error.
Any descriptors that are not recognized or implemented by a given user agent,
or whose value does not match the grammars given here or in a future version of this specification,
must be ignored in their entirety;
they do not make the <a class=css data-link-type=maybe href=#at-ruledef-counter-style title=@counter-style>@counter-style</a> rule invalid.</p>
<h3 class="heading settled heading" data-level=3.1 id=counter-style-system><span class=secno>3.1 </span><span class=content>
Counter algorithms: the <a class=property data-link-type=propdesc href=#descdef-system title=system>system</a> descriptor</span><a class=self-link href=#counter-style-system></a></h3>
<table class="definition descdef" data-dfn-for=@counter-style><tr><th>Name:<td><dfn class=css-code data-dfn-for=@counter-style data-dfn-type=descriptor data-export="" id=descdef-system>system<a class=self-link href=#descdef-system></a></dfn><tr><th>For:<td><a class=css-code data-link-type=at-rule href=#at-ruledef-counter-style title=@counter-style>@counter-style</a><tr><th>Value:<td class=prod>cyclic <a class=prod-punc data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one title=|>|</a> numeric <a class=prod-punc data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one title=|>|</a> alphabetic <a class=prod-punc data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one title=|>|</a> symbolic <a class=prod-punc data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one title=|>|</a> additive <a class=prod-punc data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one title=|>|</a> <span class=nobr>[fixed <a class="production css-code" data-link-type=type href=http://dev.w3.org/csswg/css-syntax-3/#typedef-integer title="<integer>"><integer></a><a class=prod-punc data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#mult-opt title=?>?</a>]</span> <a class=prod-pun
4A52
c data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one title=|>|</a> <span class=nobr>[ override <a class="production css-code" data-link-type=type href=#typedef-counter-style-name title="<counter-style-name>"><counter-style-name></a> ]</span><tr><th>Initial:<td>symbolic</table>
<p>The <a class=property data-link-type=propdesc href=#descdef-system title=system>system</a> descriptor specifies which algorithm will be used to construct
the counter’s representation based on the counter value. For example,
<a class=css data-link-type=maybe href=#valuedef-cyclic title=cyclic>cyclic</a> counter styles just cycle through their symbols repeatedly,
while <a class=css-code data-link-for=system data-link-type=value href=#valuedef-numeric title=numeric>numeric</a> counter styles interpret their symbols as digits and
build their representation accordingly. The systems are defined as follows:</p>
<h4 class="heading settled heading" data-level=3.1.1 id=cyclic-system><span class=secno>3.1.1 </span><span class=content>
Cycling Symbols: the <a class=css data-link-type=maybe href=#valuedef-cyclic title=cyclic>cyclic</a> system</span><a class=self-link href=#cyclic-system></a></h4>
<p>The <dfn class=css-code data-dfn-for=@counter-style/system data-dfn-type=value data-export="" id=valuedef-cyclic>cyclic<a class=self-link href=#valuedef-cyclic></a></dfn> counter system cycles repeatedly through its provided symbols,
looping back to the beginning when it reaches the end of the list.
It can be used for simple bullets
(just provide a single <a data-link-type=dfn href=#counter-symbol title="counter symbol">counter symbol</a>),
or for cycling through multiple symbols.
The first <a data-link-type=dfn href=#counter-symbol title="counter symbol">counter symbol</a> is used as the representation of the value 1,
the second <a data-link-type=dfn href=#counter-symbol title="counter symbol">counter symbol</a> (if it exists) is used as the representation of the value 2, etc.</p>
<p>If the system is <a class=css data-link-type=maybe href=#valuedef-cyclic title=cyclic>cyclic</a>,
the <a class=property data-link-type=propdesc href=#descdef-symbols title=symbols>symbols</a> descriptor must contain at least one <a data-link-type=dfn href=#counter-symbol title="counter symbol">counter symbol</a>,
or else the <a class=css data-link-type=maybe href=#at-ruledef-counter-style title=@counter-style>@counter-style</a> rule is invalid.
This system is defined over all counter values.</p>
<div class=example>
A "triangle bullet" counter style can be defined as:
<pre>@counter-style <dfn data-dfn-type=dfn data-noexport="" id=triangle>triangle<a class=self-link href=#triangle></a></dfn> {
system: cyclic;
symbols: ‣;
suffix: " ";
}
</pre>
<p>It will then produce lists that look like:</p>
<pre>‣ One
‣ Two
‣ Three
</pre>
</div>
<p>If there are <var>N</var> <a data-link-type=dfn href=#counter-symbol title="counter symbols">counter symbols</a>
and a representation is being constructed for the integer <var>value</var>,
the representation is the <a data-link-type=dfn href=#counter-symbol title="counter symbol">counter symbol</a>
at index ( (<var>value</var>-1) mod <var>N</var>)
of the list of <a data-link-type=dfn href=#counter-symbol title="counter symbols">counter symbols</a> (0-indexed).</p>
<h4 class="heading settled heading" data-level=3.1.2 id=fixed-system><span class=secno>3.1.2 </span><span class=content>
Exhaustible Symbols: the <a class=css data-link-type=maybe href=#valuedef-fixed title=fixed>fixed</a> system</span><a class=self-link href=#fixed-system></a></h4>
<p>The <dfn class=css-code data-dfn-for=@counter-style/system data-dfn-type=value data-export="" id=valuedef-fixed>fixed<a class=self-link href=#valuedef-fixed></a></dfn> counter system runs through its list of counter symbols once,
then falls back.
It is useful for representing counter styles that only have a finite number of representations.
For example, Unicode defines several limited-length runs of special characters meant for lists,
such as circled digits.</p>
<p>If the system is <a class=css data-link-type=maybe href=#valuedef-fixed title=fixed>fixed</a>,
the <a class=property data-link-type=propdesc href=#descdef-symbols title=symbols>symbols</a> descriptor must contain at least one <a data-link-type=dfn href=#counter-symbol title="counter symbol">counter symbol</a>,
or else the <a class=css data-link-type=maybe href=#at-ruledef-counter-style title=@counter-style>@counter-style</a> rule is invalid.
This system is defined over counter values in a finite range,
starting with the <a data-link-type=dfn href=#first-symbol-value title="first symbol value">first symbol value</a> and having a length equal to the length of the list of <a data-link-type=dfn href=#counter-symbol title="counter symbols">counter symbols</a>.</p>
<p>When this system is specified,
it may optionally have an integer provided after it,
which sets the <dfn data-dfn-type=dfn data-export="" id=first-symbol-value>first symbol value<a class=self-link href=#first-symbol-value></a></dfn>.
If it is omitted, the <a data-link-type=dfn href=#first-symbol-value title="first symbol value">first symbol value</a> is 1.</p>
<div class=example>
A "box-corner" counter style can be defined as:
<pre>@counter-style <dfn data-dfn-type=dfn data-noexport="" id=box-corner>box-corner<a class=self-link href=#box-corner></a></dfn> {
system: fixed;
symbols: ◰ ◳ ◲ ◱;
suffix: ': ';
}
</pre>
<p>It will then produce lists that look like:</p>
<pre>◰: One
◳: Two
◲: Three
◱: Four
5: Five
6: Six
</pre>
</div>
<p>The first <a data-link-type=dfn href=#counter-symbol title="counter symbol">counter symbol</a> is the representation for the <a data-link-type=dfn href=#first-symbol-value title="first symbol value">first symbol value</a>,
and subsequent counter values are represented by subsequent <a data-link-type=dfn href=#counter-symbol title="counter symbols">counter symbols</a>.
Once the list of <a data-link-type=dfn href=#counter-symbol title="counter symbols">counter symbols</a> is exhausted,
further values cannot be represented by this counter style,
and must instead be represented by the fallback counter style.</p>
<h4 class="heading settled heading" data-level=3.1.3 id=symbolic-system><span class=secno>3.1.3 </span><span class=content>
Repeating Symbols: the <a class=css data-link-type=maybe href=#valuedef-symbolic title=symbolic>symbolic</a> system</span><a class=self-link href=#symbolic-system></a></h4>
<p>The <dfn class=css-code data-dfn-for=system data-dfn-type=value data-export="" id=valuedef-symbolic>symbolic<a class=self-link href=#valuedef-symbolic></a></dfn> counter system cycles repeatedly through its provided symbols,
doubling, tripling, etc. the symbols on each successive pass through the list.
For example, if the original symbols were "*" and "†",
then on the second pass they would instead be "**" and "††",
while on the third they would be "***"and "†††", etc.
It can be used for footnote-style markers,
and is also sometimes used for alphabetic-style lists for a slightly different presentation than what the <a class=css-code data-link-for=system data-link-type=value href=#valuedef-alphabetic title=alphabetic>alphabetic</a> system presents.</p>
<p>If the system is <a class=css data-link-type=maybe href=#valuedef-symbolic title=symbolic>symbolic</a>,
the <a class=property data-link-type=propdesc href=#descdef-symbols title=symbols>symbols</a> descriptor must contain at least one <a data-link-type=dfn href=#counter-symbol title="counter symbol">counter symbol</a>,
or else the <a class=css data-link-type=maybe href=#at-ruledef-counter-style title=@counter-style>@counter-style</a> rule is invalid.
This system is defined only over strictly positive counter values.</p>
<div class=example>
An "footnote" counter style can be defined as:
<pre>@counter-style <dfn data-dfn-type=dfn data-noexport="" id=footnote>footnote<a class=self-link href=#footnote></a></dfn> {
system: symbolic;
symbols: '*' ⁑ † ‡;
suffix: " ";
}
</pre>
<p>It will then produce lists that look like:</p>
<pre>* One
⁑ Two
† Three
‡ Four
** Five
⁑⁑ Six
</pre>
</div>
<div class=example>
Some style guides mandate a list numbering that looks similar to <a class=css data-link-type=maybe href=#valuedef-upper-alpha title=upper-alpha>upper-alpha</a>,
but repeats differently after the first 26 values,
instead going "AA", "BB", "CC", etc.
This can be achieved with the symbolic system:
<pre>@counter-style <dfn data-dfn-type=dfn data-noexport="" id=upper-alpha-legal>upper-alpha-legal<a class=self-link href=#upper-alpha-legal></a></dfn> {
system: symbolic;
symbols: A B C D E F G H I J K L M
N O P Q R S T U V W X Y Z;
}
</pre>
<p>This style is identical to <a class=css data-link-type=maybe href=#valuedef-upper-alpha title=upper-alpha>upper-alpha</a> through the first 27 values,
but they diverge after that, with <a class=css data-link-type=maybe href=#valuedef-upper-alpha title=upper-alpha>upper-alpha</a> going "AB", "AC", "AD", etc.
Starting at the 53rd value, <a class=css data-link-type=maybe href=#valuedef-upper-alpha title=upper-alpha>upper-alpha</a> goes "BA", "BB", "BC", etc.,
while this style jumps into triple digits with "AAA", "BBB", "CCC", etc.</p>
</div>
<p>To construct the representation, run the following algorithm:</p>
<p>Let <var>N</var> be the length of the list of <a data-link-type=dfn href=#counter-symbol title="counter symbols">counter symbols</a>,
<var>value</var> initially be the counter value,
<var>S</var> initially be the empty string,
and <var>symbol(n)</var> be the nth <a data-link-type=dfn href=#counter-symbol title="counter symbol">counter symbol</a> in the list of <a data-link-type=dfn href=#counter-symbol title="counter symbols">counter symbols</a> (0-indexed).</p>
<ol>
<li>Let the <var>chosen symbol</var> be <code class=inline>symbol( (<var>value</var> - 1) mod <var>N</var>)</code>.
<li>Let the <var>representation length</var> be <code class=inline>ceil( <var>value</var> / <var>N</var> )</code>.
<li>Append the <var>chosen symbol</var> to <var>S</var> a number of times equal to the <var>representation length</var>.
</ol>
<p>Finally, return <var>S</var>.</p>
<h4 class="heading settled heading" data-level=3.1.4 id=alphabetic-system><span class=secno>3.1.4 </span><span class=content>
Bijective Numerals: the <a class=css data-link-type=maybe href=#valuedef-alphabetic title=alphabetic>alphabetic</a> system</span><a class=self-link href=#alphabetic-system></a></h4>
<p>The <dfn class=css-code data-dfn-for=@counter-style/system data-dfn-type=value data-export="" id=valuedef-alphabetic>alphabetic<a class=self-link href=#valuedef-alphabetic></a></dfn> counter system interprets the list of <a data-link-type=dfn href=#counter-symbol title="counter symbols">counter symbols</a> as digits to an <em>alphabetic</em> numbering system,
similar to the default <a class=css data-link-type=maybe href=#valuedef-lower-alpha title=lower-alpha>lower-alpha</a> counter style,
which wraps from "a", "b", "c", to "aa", "ab", "ac".
Alphabetic numbering systems do not contain a digit representing 0;
so the first value when a new digit is added is composed solely of the first digit.
Alphabetic numbering systems are commonly used for lists,
and also appear in many spreadsheet programs to number columns.
The first <a data-link-type=dfn href=#counter-symbol title="counter symbol">counter symbol</a> in the list is interpreted as the digit 1,
the second as the digit 2,
and so on.</p>
<p>If the system is <a class=css-code data-link-for=system data-link-type=value href=#valuedef-alphabetic title=alphabetic>alphabetic</a>,
the <a class=property data-link-type=propdesc href=#descdef-symbols title=symbols>symbols</a> descriptor must contain at least two <a data-link-type=dfn href=#counter-symbol title="counter symbols">counter symbols</a>,
or else the <a class=css data-link-type=maybe href=#at-ruledef-counter-style title=@counter-style>@counter-style</a> rule is invalid.
This system is defined only over strictly positive counter values.</p>
<div class=example>
A counter style using go stones can be defined as:
<pre>@counter-style <dfn data-dfn-type=dfn data-noexport="" id=go>go<a class=self-link href=#go></a></dfn> {
system: alphabetic;
symbols: url(white.svg) url(black.svg);
suffix: " ";
}
</pre>
<p>It will then produce lists that look like:</p>
<div class=alphabetic-example>
<span><img alt="" src=images/white.svg></span> One<br>
<span><img alt="" src=images/black.svg></span> Two<br>
<span><img alt="" src=images/white.svg><img alt="" src=images/white.svg></span> Three<br>
<span><img alt="" src=images/white.svg><img alt="" src=images/black.svg></span> Four<br>
<span><img alt="" src=images/black.svg><img alt="" src=images/white.svg></span> Five<br>
<span><img alt="" src=images/black.svg><img alt="" src=images/black.svg></span> Six<br>
<span><img alt="" src=images/white.svg><img alt="" src=images/white.svg><img alt="" src=images/white.svg></span> Seven
</div>
<p class=note>Note: This example requires support for SVG images to display correctly.</p>
</div>
<p>If there are <var>N</var> <a data-link-type=dfn href=#counter-symbol title="counter symbols">counter symbols</a>,
the representation is a base <var>N</var> alphabetic number using the <a data-link-type=dfn href=#counter-symbol title="counter symbols">counter symbols</a> as digits.
To construct the representation, run the following algorithm:</p>
<p>Let <var>N</var> be the length of the list of <a data-link-type=dfn href=#counter-symbol title="counter symbols">counter symbols</a>,
<var>value</var> initially be the counter value,
<var>S</var> initially be the empty string,
and <var>symbol(n)</var> be the nth <a data-link-type=dfn href=#counter-symbol title="counter symbol">counter symbol</a> in the list of <a data-link-type=dfn href=#counter-symbol title="counter symbols">counter symbols</a> (0-indexed).</p>
<p>While <var>value</var> is not equal to 0:</p>
<ol>
<li>Set <var>value</var> to <code><var>value</var> - 1</code>.
<li>Prepend <var>symbol( <var>value</var> mod <var>N</var> )</var>
to <var>S</var>.
<li>Set <var>value</var> to <code>floor( <var>value</var> / <var>N</var> )</code>.
</ol>
<p>Finally, return <var>S</var>.</p>
<h4 class="heading settled heading" data-level=3.1.5 id=numeric-system><span class=secno>3.1.5 </span><span class=content>
Positional Numerals: the <a class=css data-link-type=maybe href=#valuedef-numeric title=numeric>numeric</a> system</span><a class=self-link href=#numeric-system></a></h4>
<p>The <dfn class=css-code data-dfn-for=@counter-style/system data-dfn-type=value data-export="" id=valuedef-numeric>numeric<a class=self-link href=#valuedef-numeric></a></dfn> counter system interprets the list of <a data-link-type=dfn href=#counter-symbol title="counter symbols">counter symbols</a>
as digits to a "place-value" numbering system,
similar to the default <a class=css data-link-type=maybe href=#valuedef-decimal title=decimal>decimal</a> counter style.
The first <a data-link-type=dfn href=#counter-symbol title="counter symbol">counter symbol</a> in the list is interpreted as the digit 0,
the second as the digit 1,
and so on.</p>
<p>If the system is <a class=css-code data-link-for=system data-link-type=value href=#valuedef-numeric title=numeric>numeric</a>,
the <a class=property data-link-type=propdesc href=#descdef-symbols title=symbols>symbols</a> descriptor must contain at least two <a data-link-type=dfn href=#counter-symbol title="counter symbols">counter symbols</a>,
or else the <a class=css data-link-type=maybe href=#at-ruledef-counter-style title=@counter-style>@counter-style</a> rule is invalid.
This system is defined over all counter values.</p>
<div class=example>
A "trinary" counter style can be defined as:
<pre>@counter-style <dfn data-dfn-type=dfn data-noexport="" id=trinary>trinary<a class=self-link href=#trinary></a></dfn> {
system: numeric;
symbols: '0' '1' '2';
}
</pre>
<p>It will then produce lists that look like:</p>
<pre>1. One
2. Two
10. Three
11. Four
12. Five
20. Six
</pre>
</div>
<p>If there are <var>N</var> <a data-link-type=dfn href=#counter-symbol title="counter symbols">counter symbols</a>,
the representation is a base <var>N</var> number using the <a data-link-type=dfn href=#counter-symbol title="counter symbols">counter symbols</a> as digits.
To construct the representation, run the following algorithm:</p>
<p>Let <var>N</var> be the length of the list of <a data-link-type=dfn href=#counter-symbol title="counter symbols">counter symbols</a>,
<var>value</var> initially be the counter value,
<var>S</var> initially be the empty string,
and <var>symbol(n)</var> be the nth <a data-link-type=dfn href=#counter-symbol title="counter symbol">counter symbol</a> in the list of <a data-link-type=dfn href=#counter-symbol title="counter symbols">counter symbols</a> (0-indexed).</p>
<ol>
<li>If <var>value</var> is 0, append <var>symbol(0)</var> to
<var>S</var> and return <var>S</var>.
<li>While <var>value</var> is not equal to 0:
<ol>
<li>Prepend <var>symbol( <var>value</var> mod <var>N</var> )</var>
to <var>S</var>.
<li>Set <var>value</var> to <code>floor( <var>value</var> / <var>N</var> )</code>.
</ol>
<li>Return <var>S</var>.
</ol>
<h4 class="heading settled heading" data-level=3.1.6 id=additive-system><span class=secno>3.1.6 </span><span class=content>
Accumulating Numerals: the <a class=css data-link-type=maybe href=#valuedef-additive title=additive>additive</a> system</span><a class=self-link href=#additive-system></a></h4>
<p>The <dfn class=css-code data-dfn-for=@counter-style/system data-dfn-type=value data-export="" id=valuedef-additive>additive<a class=self-link href=#valuedef-additive></a></dfn> counter system is used to represent "sign-value" numbering systems,
which, rather than using reusing digits in different positions to change their value,
define additional digits with much larger values,
so that the value of the number can be obtained by adding all the digits together.
This is used in Roman numerals
and other numbering systems around the world.</p>
<p>If the system is <a class=css data-link-type=maybe href=#valuedef-additive title=additive>additive</a>,
the <a class=property data-link-type=propdesc href=#descdef-additive-symbols title=additive-symbols>additive-symbols</a> descriptor must contain at least one <a data-link-type=dfn href=#additive-tuple title="additive tuple">additive tuple</a>,
or else the <a class=css data-link-type=maybe href=#at-ruledef-counter-style title=@counter-style>@counter-style</a> rule is invalid.
This system is nominally defined over all counter values
(see algorithm, below, for exact details).</p>
<div class=example>
A "dice" counter style can be defined as:
<pre>@counter-style <dfn data-dfn-type=dfn data-noexport="" id=dice>dice<a class=self-link href=#dice></a></dfn> {
system: additive;
additive-symbols: 6 ⚅, 5 ⚄, 4 ⚃, 3 ⚂, 2 ⚁, 1 ⚀;
suffix: " ";
}
</pre>
<p>It will then produce lists that look like:</p>
<pre>⚀ One
⚁ Two
⚂ Three
...
⚅⚄ Eleven
⚅⚅ Twelve
⚅⚅⚀ Thirteen
</pre>
</div>
<p>To construct the representation, run this algorithm:</p>
<p>Let <var>value</var> initially be the counter value,
<var>S</var> initially be the empty string,
and <var>symbol list</var> initially be the list of <a data-link-type=dfn href=#additive-tuple title="additive tuples">additive tuples</a>.</p>
<ol>
<li>If <var>value</var> is initially 0, and there is an <a data-link-type=dfn href=#additive-tuple title="additive tuple">additive tuple</a> with a weight of 0, append that tuple’s <a data-link-type=dfn href=#counter-symbol title="counter symbol">counter symbol</a> to S and return S.
<li>While <var>value</var> is greater than 0 and there are elements left in the <var>symbol list</var>:
<ol>
<li>Pop the first <a data-link-type=dfn href=#additive-tuple title="additive tuple">additive tuple</a> from the <var>symbol list</var>.
This is the <dfn data-dfn-type=dfn data-noexport="" id=current-tuple>current tuple<a class=self-link href=#current-tuple></a></dfn>.
<li>Append the <a data-link-type=dfn href=#current-tuple title="current tuple">current tuple</a>’s <a data-link-type=dfn href=#counter-symbol title="counter symbol">counter symbol</a> to <var>S</var>
<code>floor( <var>value</var> / <var><a data-link-type=dfn href=#current-tuple title="current tuple">current tuple</a>’s weight</var> )</code>
times (this may be 0).
<li>Decrement <var>value</var> by the <var><a data-link-type=dfn href=#current-tuple title="current tuple">current tuple</a>’s</var> weight multiplied
by the number of times the <a data-link-type=dfn href=#current-tuple title="current tuple">current tuple</a> was appended to <var>S</var>
in the previous step.
</ol>
<li>If the loop ended because <var>value</var> is 0, return S. Otherwise, the given counter value cannot be represented by this counter style, and must instead be represented by the fallback counter style.
</ol>
<p class=note>Note: All of the predefined additive <a class=css data-link-type=maybe href=#at-ruledef-counter-style title=@counter-style>@counter-style</a> rules in this specification
produce representations for every value in their range,
but it’s possible to produce values for <span class=css data-link-type=maybe title=additive-symbols>additive-symbols</span> that will fail to find a representation
with the algorithm defined above,
even though theoretically a representation could be found.
For example, if a <a class=css data-link-type=maybe href=#at-ruledef-counter-style title=@counter-style>@counter-style</a> was defined with <a class=css data-link-type=propdesc href=#descdef-additive-symbols title=additive-symbols>additive-symbols: 3 "a", 2 "b";</a>,
the algorithm defined above will fail to find a representation for a counter value of 4,
even though theoretically a "bb" representation would work.
While unfortunate, this is required to maintain the property that the algorithm runs in linear time
relative to the size of the counter value.</p>
<h4 class="heading settled heading" data-level=3.1.7 id=extends-system><span class=secno>3.1.7 </span><span class=content>
Tweaking Existing Counter Styles: the <a class=css data-link-type=maybe href=#valuedef-extends title=extends>extends</a> system
<span id=override-system></span></span><a class=self-link href=#extends-system></a></h4>
<p>The <dfn class=css-code data-dfn-for=@counter-style/system data-dfn-type=value data-export="" id=valuedef-extends>extends<a class=self-link href=#valuedef-extends></a></dfn> system allows an author to use the algorithm of another counter style,
but alter other aspects,
such as the negative sign or the suffix.
If a counter style uses the <a class=css data-link-type=maybe href=#valuedef-extends title=extends>extends</a> system,
any unspecified descriptors must be taken from the extended counter style specified,
rather than taking their initial values.</p>
<p>If a @counter-style uses the <a class=css data-link-type=maybe href=#valuedef-extends title=extends>extends</a> system,
it must not contain a <a class=property data-link-type=propdesc href=#descdef-symbols title=symbols>symbols</a> or <a class=property data-link-type=propdesc href=#descdef-additive-symbols title=additive-symbols>additive-symbols</a> descriptor,
or else the <a class=css data-link-type=maybe href=#at-ruledef-counter-style title=@counter-style>@counter-style</a> rule is invalid.</p>
<p>If the specified counter style name isn’t the name of any currently-defined counter style,
it must be treated as if it was extending the <a class=css data-link-type=maybe href=#valuedef-decimal title=decimal>decimal</a> counter style.
If one or more <a class=css data-link-type=maybe href=#at-ruledef-counter-style title=@counter-style>@counter-style</a> rules form a cycle with their <a class=css data-link-type=maybe href=#valuedef-extends title=extends>extends</a> values,
all of the counter styles participating in the cycle
must be treated as if they were extending the <a class=css data-link-type=maybe href=#valuedef-decimal title=decimal>decimal</a> counter style instead.</p>
<div class=example>
For example, if you wanted
4148
a counter style that was identical to decimal,
but used a parenthesis rather than a period after it, like:
<pre>1) first item
2) second item
3) third item
</pre>
<p>Rather than writing up an entirely new counter style,
this can be done by just extending <a class=css data-link-type=maybe href=#valuedef-decimal title=decimal>decimal</a>:</p>
<pre class=css>@counter-style decimal-paren {
system: extends decimal;
suffix: ") ";
}
</pre>
</div>
<h3 class="heading settled heading" data-level=3.2 id=counter-style-negative><span class=secno>3.2 </span><span class=content>
Formatting negative values: the <a class=property data-link-type=propdesc href=#descdef-negative title=negative>negative</a> descriptor</span><a class=self-link href=#counter-style-negative></a></h3>
<table class="definition descdef" data-dfn-for=@counter-style><tr><th>Name:<td><dfn class=css-code data-dfn-for=@counter-style data-dfn-type=descriptor data-export="" id=descdef-negative>negative<a class=self-link href=#descdef-negative></a></dfn><tr><th>For:<td><a class=css-code data-link-type=at-rule href=#at-ruledef-counter-style title=@counter-style>@counter-style</a><tr><th>Value:<td class=prod><a class="production css-code" data-link-type=type href=#typedef-symbol title="<symbol>"><symbol></a> <a class="production css-code" data-link-type=type href=#typedef-symbol title="<symbol>"><symbol></a><a class=prod-punc data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#mult-opt title=?>?</a><tr><th>Initial:<td>"\2D" ("-" hyphen-minus)</table>
<p>The <a class=property data-link-type=propdesc href=#descdef-negative title=negative>negative</a> descriptor defines how to alter the representation when
the counter value is negative.</p>
<p>The first <a class="production css-code" data-link-type=type href=#typedef-symbol title="<symbol>"><symbol></a> in the value is prepended to the representation when the
counter value is negative. The second <a class="production css-code" data-link-type=type href=#typedef-symbol title="<symbol>"><symbol></a>, if specified, is appended
to the representation when the counter value is negative.</p>
<div class=example>
For example, specifying <a class=css data-link-type=propdesc href=#descdef-negative title=negative>negative: "(" ")";</a> will make negative
values be wrapped in parentheses, which is sometimes used in financial
contexts, like "(2) (1) 0 1 2 3...".
</div>
<p>Not all <a class=property data-link-type=propdesc href=#descdef-system title=system>system</a> values use a negative sign.
In particular, a counter style <dfn data-dfn-type=dfn data-export="" id=use-a-negative-sign title="use a negative sign|uses a negative sign">uses a negative sign<a class=self-link href=#use-a-negative-sign></a></dfn>
is one where its <a class=property data-link-type=propdesc href=#descdef-system title=system>system</a> value is
<a class=css data-link-type=maybe href=#valuedef-symbolic title=symbolic>symbolic</a>,
<a class=css data-link-for=system data-link-type=maybe href=#valuedef-alphabetic title=alphabetic>alphabetic</a>,
<a class=css data-link-for=system data-link-type=maybe href=#valuedef-numeric title=numeric>numeric</a>,
<a class=css data-link-type=maybe href=#valuedef-additive title=additive>additive</a>,
or <span class=css data-link-type=maybe title=override>override</span> if the overridden counter style itself <a data-link-type=dfn href=#use-a-negative-sign title="uses a negative sign">uses a negative sign</a>.
If a counter style does not <a data-link-type=dfn href=#use-a-negative-sign title="use a negative sign">use a negative sign</a>,
it ignores the negative sign when <a data-link-type=dfn href=#generate-a-counter title="generate a counter representation">generating a counter representation</a>.</p>
<h3 class="heading settled heading" data-level=3.3 id=counter-style-prefix><span class=secno>3.3 </span><span class=content>
Symbols before the marker: the <a class=property data-link-type=propdesc href=#descdef-prefix title=prefix>prefix</a> descriptor</span><a class=self-link href=#counter-style-prefix></a></h3>
<table class="definition descdef" data-dfn-for=@counter-style><tr><th>Name:<td><dfn class=css-code data-dfn-for=@counter-style data-dfn-type=descriptor data-export="" id=descdef-prefix>prefix<a class=self-link href=#descdef-prefix></a></dfn><tr><th>For:<td><a class=css-code data-link-type=at-rule href=#at-ruledef-counter-style title=@counter-style>@counter-style</a><tr><th>Value:<td class=prod><a class="production css-code" data-link-type=type href=#typedef-symbol title="<symbol>"><symbol></a><tr><th>Initial:<td>"" (the empty string)</table>
<p>The <a class=property data-link-type=propdesc href=#descdef-prefix title=prefix>prefix</a> descriptor specifies a <a class="production css-code" data-link-type=type href=#typedef-symbol title="<symbol>"><symbol></a> that is prepended to the
marker representation. Prefixes are only added by the algorithm for constructing
the default contents of the <a class=css data-link-type=maybe href=http://dev.w3.org/csswg/css-lists-3/#selectordef-marker title=::marker>::marker</a> pseudo-element; the prefix is not
added automatically when the counter() or counters() functions are used.
Prefixes come before any negative sign.</p>
<h3 class="heading settled heading" data-level=3.4 id=counter-style-suffix><span class=secno>3.4 </span><span class=content>
Symbols after the marker: the <a class=property data-link-type=propdesc href=#descdef-suffix title=suffix>suffix</a> descriptor</span><a class=self-link href=#counter-style-suffix></a></h3>
<table class="definition descdef" data-dfn-for=@counter-style><tr><th>Name:<td><dfn class=css-code data-dfn-for=@counter-style data-dfn-type=descriptor data-export="" id=descdef-suffix>suffix<a class=self-link href=#descdef-suffix></a></dfn><tr><th>For:<td><a class=css-code data-link-type=at-rule href=#at-ruledef-counter-style title=@counter-style>@counter-style</a><tr><th>Value:<td class=prod><a class="production css-code" data-link-type=type href=#typedef-symbol title="<symbol>"><symbol></a><tr><th>Initial:<td>"\2E\20" ("." full stop followed by a space)</table>
<p>The <a class=property data-link-type=propdesc href=#descdef-suffix title=suffix>suffix</a> descriptor specifies a <a class="production css-code" data-link-type=type href=#typedef-symbol title="<symbol>"><symbol></a> that is appended to the
marker representation. Suffixes are only added by the algorithm for constructing
the default contents of the <a class=css data-link-type=maybe href=http://dev.w3.org/csswg/css-lists-3/#selectordef-marker title=::marker>::marker</a> pseudo-element; the suffix is not
added automatically when the counter() or counters() functions are used.
Suffixes are added to the representation after negative signs.</p>
<h3 class="heading settled heading" data-level=3.5 id=counter-style-range><span class=secno>3.5 </span><span class=content>
Limiting the counter scope: the <a class=property data-link-type=propdesc href=#descdef-range title=range>range</a> descriptor</span><a class=self-link href=#counter-style-range></a></h3>
<table class="definition descdef" data-dfn-for=@counter-style><tr><th>Name:<td><dfn class=css-code data-dfn-for=@counter-style data-dfn-type=descriptor data-export="" id=descdef-range>range<a class=self-link href=#descdef-range></a></dfn><tr><th>For:<td><a class=css-code data-link-type=at-rule href=#at-ruledef-counter-style title=@counter-style>@counter-style</a><tr><th>Value:<td class=prod>[ [ <a class="production css-code" data-link-type=type href=http://dev.w3.org/csswg/css-syntax-3/#typedef-integer title="<integer>"><integer></a> <a class=prod-punc data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one title=|>|</a> infinite ]{2} ]<a class=prod-punc data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#mult-comma title=#>#</a> <a class=prod-punc data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one title=|>|</a> auto<tr><th>Initial:<td>auto</table>
<p>The <a class=property data-link-type=propdesc href=#descdef-range title=range>range</a> descriptor defines the ranges over which the counter style is defined.
If a counter style is used to represent a counter value outside of its ranges,
the counter style instead drops down to its fallback counter style.</p>
<dl data-dfn-for=@counter-style/range>
<dt><dfn class=css-code data-dfn-for=@counter-style/range data-dfn-type=value data-export="" id=valuedef-auto0>auto<a class=self-link href=#valuedef-auto0></a></dfn>
<dd>
The range depends on the counter system:
<ul>
<li>
For <a class=css data-link-type=maybe href=#valuedef-cyclic title=cyclic>cyclic</a>, <a class=css-code data-link-for=system data-link-type=value href=#valuedef-numeric title=numeric>numeric</a>, and <a class=css data-link-type=maybe href=#valuedef-fixed title=fixed>fixed</a> systems,
the range is negative infinity to positive infinity.
<li>
For <a class=css-code data-link-for=system data-link-type=value href=#valuedef-alphabetic title=alphabetic>alphabetic</a> and <a class=css data-link-type=maybe href=#valuedef-symbolic title=symbolic>symbolic</a> systems,
the range is 1 to positive infinity.
<li>
For <a class=css data-link-type=maybe href=#valuedef-additive title=additive>additive</a> systems,
the range is 0 to positive infinity.
<li>
For <span class=css data-link-type=maybe title=override>override</span> systems,
the range is whatever <a class=css data-link-for=range data-link-type=maybe href=#valuedef-auto0 title=auto>auto</a> would produce for the overridden system;
if overriding a complex predefined style (<a data-section="" href=#complex-predefined-counters>§7
Complex Predefined Counter Styles</a>),
the range is the style’s defined range.
</ul>
<dt>[ [ <a class="production css-code" data-link-type=type href=http://dev.w3.org/csswg/css-syntax-3/#typedef-integer title="<integer>"><integer></a> | infinite ]{2} ]#
<dd>
This defines a comma-separated list of ranges.
For each individual range,
the first value is the lower bound
and the second value is the upper bound.
This range is inclusive - it contains both the lower and upper bound numbers.
If <span class=css data-link-type=maybe title=infinite>infinite</span> is used as the first value in a range,
it represents negative infinity;
if used as the second value,
it represents positive infinity.
The range of the counter style is the union of all the ranges defined in the list.
<p>If the lower bound of any range is higher than the upper bound,
the entire descriptor is invalid and must be ignored.</p>
</dl>
<p>Implementations must support ranges with a lower bound of at least -2<sup>15</sup>
and an upper bound of at least 2<sup>15</sup>-1
(the range of a signed 2-byte int).
They may support higher ranges.
If any specified bound is outside of the implementation’s supported bounds,
it must be treated as the closest bound that the implementation does support.</p>
<h3 class="heading settled heading" data-level=3.6 id=counter-style-pad><span class=secno>3.6 </span><span class=content>
Zero-Padding and Constant-Width Representations: the <a class=property data-link-type=propdesc href=#descdef-pad title=pad>pad</a> descriptor</span><a class=self-link href=#counter-style-pad></a></h3>
<table class="definition descdef" data-dfn-for=@counter-style><tr><th>Name:<td><dfn class=css-code data-dfn-for=@counter-style data-dfn-type=descriptor data-export="" id=descdef-pad>pad<a class=self-link href=#descdef-pad></a></dfn><tr><th>For:<td><a class=css-code data-link-type=at-rule href=#at-ruledef-counter-style title=@counter-style>@counter-style</a><tr><th>Value:<td class=prod><a class="production css-code" data-link-type=type href=http://dev.w3.org/csswg/css-syntax-3/#typedef-integer title="<integer>"><integer></a> <a class=prod-punc data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-all title=&&>&&</a> <a class="production css-code" data-link-type=type href=#typedef-symbol title="<symbol>"><symbol></a><tr><th>Initial:<td>0 ""</table>
<p>The <a class=property data-link-type=propdesc href=#descdef-pad title=pad>pad</a> descriptor allows an author to specify a "fixed-width" counter style,
where representations shorter than the pad value are padded with a particular <a class="production css-code" data-link-type=type href=#typedef-symbol title="<symbol>"><symbol></a>.
Representations larger than the specified pad value are constructed as normal.</p>
<dl>
<dt><a class="production css-code" data-link-type=type href=http://dev.w3.org/csswg/css-syntax-3/#typedef-integer title="<integer>"><integer></a> && <a class="production css-code" data-link-type=type href=#typedef-symbol title="<symbol>"><symbol></a>
<dd>
The <a class="production css-code" data-link-type=type href=http://dev.w3.org/csswg/css-synta
8CEA
x-3/#typedef-integer title="<integer>"><integer></a> specifies a minimum length that all counter representations must reach.
<p>Let <var>difference</var> be the provided <a class="production css-code" data-link-type=type href=http://dev.w3.org/csswg/css-syntax-3/#typedef-integer title="<integer>"><integer></a>
minus the number of <a data-link-type=dfn href=http://dev.w3.org/csswg/css-text-3/#grapheme-cluster title="grapheme clusters">grapheme clusters</a> in the <a data-link-type=dfn href=#initial-representation-for-the-counter-value title="initial representation for the counter value">initial representation for the counter value</a>.
<span class=note>(Note that, per the algorithm to <a data-link-type=dfn href=#generate-a-counter title="generate a counter representation">generate a counter representation</a>,
this occurs before adding prefixes/suffixes/negatives.)</span>
If the counter value is negative
and the counter style <a data-link-type=dfn href=#use-a-negative-sign title="uses a negative sign">uses a negative sign</a>,
further reduce <var>difference</var>
by the number of <a data-link-type=dfn href=http://dev.w3.org/csswg/css-text-3/#grapheme-cluster title="grapheme clusters">grapheme clusters</a> in the counter style’s <a class=property data-link-type=propdesc href=#descdef-negative title=negative>negative</a> descriptor’s <a class="production css-code" data-link-type=type href=#typedef-symbol title="<symbol>"><symbol></a>(s).</p>
<p>If <var>difference</var> is greater than zero,
prepend <var>difference</var> copies of the specified <a class="production css-code" data-link-type=type href=#typedef-symbol title="<symbol>"><symbol></a> to the representation.</p>
<p>The <a class="production css-code" data-link-type=type href=http://dev.w3.org/csswg/css-syntax-3/#typedef-integer title="<integer>"><integer></a> must be non-negative.
A negative value is a syntax error.</p>
</dl>
<div class=example>
The most common example of "fixed-width" numbering is zero-padded decimal numbering.
If an author knows that the numbers used will be less than a thousand, for example,
it can be zero-padded with a simple <a class=css data-link-type=propdesc href=#descdef-pad title=pad>pad: 3 "0";</a> descriptor,
ensuring that all of the representations are 3 digits wide.
<p>This will cause, for example,
1 to be represented as "001",
20 to be represented as "020",
300 to be represented as "300",
4000 to be represented as "4000",
and -5 to be represented as "-05".</p>
</div>
<p class=note>Note: The <a class=property data-link-type=propdesc href=#descdef-pad title=pad>pad</a> descriptor counts the number of <a data-link-type=dfn href=http://dev.w3.org/csswg/css-text-3/#grapheme-cluster title="grapheme clusters">grapheme clusters</a> in the representation,
but pads it with <a class="production css-code" data-link-type=type href=#typedef-symbol title="<symbol>"><symbol></a>s.
If the specified <a class=property data-link-type=propdesc href=#descdef-pad title=pad>pad</a> <a class="production css-code" data-link-type=type href=#typedef-symbol title="<symbol>"><symbol></a> is multi-character,
this will likely not have the desired effect.
Unfortunately, there’s no way to use the number of <a data-link-type=dfn href=http://dev.w3.org/csswg/css-text-3/#grapheme-cluster title="grapheme clusters">grapheme clusters</a> in the <a class=property data-link-type=propdesc href=#descdef-pad title=pad>pad</a> <a class="production css-code" data-link-type=type href=#typedef-symbol title="<symbol>"><symbol></a>
without violating useful constraints.
It is recommended that authors only specify <a class="production css-code" data-link-type=type href=#typedef-symbol title="<symbol>"><symbol></a>s of a single <a data-link-type=dfn href=http://dev.w3.org/csswg/css-text-3/#grapheme-cluster title="grapheme cluster">grapheme cluster</a>
in the <a class=property data-link-type=propdesc href=#descdef-pad title=pad>pad</a> descriptor.</p>
<h3 class="heading settled heading" data-level=3.7 id=counter-style-fallback><span class=secno>3.7 </span><span class=content>
Defining fallback: the <a class=property data-link-type=propdesc href=#descdef-fallback title=fallback>fallback</a> descriptor</span><a class=self-link href=#counter-style-fallback></a></h3>
<table class="definition descdef" data-dfn-for=@counter-style><tr><th>Name:<td><dfn class=css-code data-dfn-for=@counter-style data-dfn-type=descriptor data-export="" id=descdef-fallback>fallback<a class=self-link href=#descdef-fallback></a></dfn><tr><th>For:<td><a class=css-code data-link-type=at-rule href=#at-ruledef-counter-style title=@counter-style>@counter-style</a><tr><th>Value:<td class=prod><a class="production css-code" data-link-type=type href=#typedef-counter-style-name title="<counter-style-name>"><counter-style-name></a><tr><th>Initial:<td>decimal</table>
<p>The <a class=property data-link-type=propdesc href=#descdef-fallback title=fallback>fallback</a> descriptor specifies a fallback counter style to be used
when the current counter style can’t create a representation for a given
counter value. For example, if a counter style defined with a range of 1-10
is asked to represent a counter value of 11, the counter value’s representation
is instead constructed with the fallback counter style (or possibly the
fallback style’s fallback style, if the fallback style can’t represent that
value, etc.).</p>
<p>If the value of the <a class=property data-link-type=propdesc href=#descdef-fallback title=fallback>fallback</a> descriptor isn’t the name of any
currently-defined counter style, the used value of the <a class=property data-link-type=propdesc href=#descdef-fallback title=fallback>fallback</a> descriptor
is <a class=css data-link-type=maybe href=#valuedef-decimal title=decimal>decimal</a> instead. Similarly, while following fallbacks to find
a counter style that can render the given counter value, if a loop in the
specified fallbacks is detected, the <a class=css data-link-type=maybe href=#valuedef-decimal title=decimal>decimal</a> style must be used instead.</p>
<p class=note>Note that it is not necessarily an error to specify fallback
loops. For example, if an author desires a counter style with significantly
different representations for even and odd counter values, they may find it
easiest to define one style that can only represent odd values and one that
can only represent even values, and specify each as the fallback for the
other one. Though the fallback graph is circular, at no point do you encounter
a loop while following these fallbacks - every counter value is represented
by one or the other counter style.
<h3 class="heading settled heading" data-level=3.8 id=counter-style-symbols><span class=secno>3.8 </span><span class=content>
Marker characters: the <a class=property data-link-type=propdesc href=#descdef-symbols title=symbols>symbols</a> and <a class=property data-link-type=propdesc href=#descdef-additive-symbols title=additive-symbols>additive-symbols</a> descriptors</span><a class=self-link href=#counter-style-symbols></a></h3>
<table class="definition descdef" data-dfn-for=@counter-style><tr><th>Name:<td><dfn class=css-code data-dfn-for=@counter-style data-dfn-type=descriptor data-export="" id=descdef-symbols>symbols<a class=self-link href=#descdef-symbols></a></dfn><tr><th>For:<td><a class=css-code data-link-type=at-rule href=#at-ruledef-counter-style title=@counter-style>@counter-style</a><tr><th>Value:<td class=prod><a class="production css-code" data-link-type=type href=#typedef-symbol title="<symbol>"><symbol></a><a class=prod-punc data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#mult-one-plus title=+>+</a><tr><th>Initial:<td>n/a</table>
<table class="definition descdef" data-dfn-for=@counter-style><tr><th>Name:<td><dfn class=css-code data-dfn-for=@counter-style data-dfn-type=descriptor data-export="" id=descdef-additive-symbols>additive-symbols<a class=self-link href=#descdef-additive-symbols></a></dfn><tr><th>For:<td><a class=css-code data-link-type=at-rule href=#at-ruledef-counter-style title=@counter-style>@counter-style</a><tr><th>Value:<td class=prod>[ <a class="production css-code" data-link-type=type href=http://dev.w3.org/csswg/css-syntax-3/#typedef-integer title="<integer>"><integer></a> <a class=prod-punc data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-all title=&&>&&</a> <a class="production css-code" data-link-type=type href=#typedef-symbol title="<symbol>"><symbol></a> ]<a class=prod-punc data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#mult-comma title=#>#</a><tr><th>Initial:<td>n/a</table>