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<!DOCTYPE html>
<html>
<head>
<title>CSS Counter Styles Level 3</title>
<!--
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<link href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright" rel="dcterms.rights">
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<meta content="CSS Counter Styles Level 3" name=dcterms.title>
<meta content=text name=dcterms.type>
<meta content=2013-02-19 name=dcterms.issued>
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type="text/css">
<body>
<div class=head> <!--begin-logo-->
<p><a href="http://www.w3.org/"><img alt=W3C height=48
src="http://www.w3.org/Icons/w3c_home" width=72></a> <!--end-logo-->
<h1>CSS Counter Styles Level 3</h1>
<h2 class="no-num no-toc" id=longstatus-date>Editor's Draft 19 February
2013</h2>
<dl>
<dt>This version:
<dd><!--<a href="http://www.w3.org/TR/2013/ED-css-counter-styles-3-20130219/">http://www.w3.org/TR/2013/WD-css-counter-styles-3-20130219/</a>-->
<a
href="http://dev.w3.org/csswg/css-counter-styles-3/">http://dev.w3.org/csswg/css-counter-styles-3/</a>
133E
<dt>Latest version:
<dd><a
href="http://www.w3.org/TR/css-counter-styles-3/">http://www.w3.org/TR/css-counter-styles-3/</a>
<dt>Editor's Draft:
<dd><a
href="http://dev.w3.org/csswg/css-counter-styles-3/">http://dev.w3.org/csswg/css-counter-styles-3/</a>
<dt>Previous version:
<dd><a
href="http://www.w3.org/TR/2012/WD-css-counter-styles-3-20121009/">http://www.w3.org/TR/2012/WD-css-counter-styles-3-20121009/</a>
<dt>Issue Tracking:
<dd><a
href="https://www.w3.org/Bugs/Public/buglist.cgi?product=CSS&component=Counter%20Styles&resolution=---">Bugzilla</a>
<dt>Feedback:
<dd><a
href="http://lists.w3.org/Archives/Public/www-style/">www-style@w3.org</a>
with subject line “<kbd>[css-counter-styles] <var>… message topic
…</var></kbd>”
<dt>Editor:
<dd class=vcard> <a class=url href="http://xanthir.com/contact/"> <span
class=fn>Tab Atkins Jr.</span>, </a> <span class=org>Google, Inc.</span>
</dl>
<!--begin-copyright-->
<p class=copyright><a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
rel=license>Copyright</a> © 2013 <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>
<!--end-copyright-->
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc" id=abstract> Abstract</h2>
<p> This module introduces the ‘<a href="#at-counter-style"><code
class=css>@counter-style</code></a>’ rule, which allows authors to
define their own custom <i>counter styles</i> for use with CSS list-marker
and generated-content counters <a href="#CSS3LIST"
rel=biblioentry>[CSS3LIST]<!--{{CSS3LIST}}--></a>. It also predefines a
set of common counter styles, including the ones present in CSS2 and
CSS2.1. <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.
<h2 class="no-num no-toc" id=status> Status of this document</h2>
<!--begin-status-->
<p>This is a public copy of the editors' draft. It is provided for
discussion only and may change at any moment. Its publication here does
not imply endorsement of its contents by W3C. Don't cite this document
other than as work in progress.
<p>The (<a
href="http://lists.w3.org/Archives/Public/www-style/">archived</a>) public
mailing list <a
href="mailto:www-style@w3.org?Subject=%5Bcss-counter-styles-3%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-3” in the subject, preferably like this:
“[<!---->css-counter-styles-3<!---->] <em>…summary of
comment…</em>”
<p>This document was produced by the <a href="/Style/CSS/members">CSS
Working Group</a> (part of the <a href="/Style/">Style Activity</a>).
<p>This document was produced by a group operating under the <a
href="/Consortium/Patent-Policy-20040205/">5 February 2004 W3C Patent
Policy</a>. W3C maintains a <a href="/2004/01/pp-impl/32061/status"
rel=disclosure>public list of any patent disclosures</a> made in
connection with the deliverables of the group; that page also includes
instructions for disclosing a patent. An individual who has actual
knowledge of a patent which the individual believes contains <a
href="/Consortium/Patent-Policy-20040205/#def-essential">Essential
Claim(s)</a> must disclose the information in accordance with <a
href="/Consortium/Patent-Policy-20040205/#sec-Disclosure">section 6 of the
W3C Patent Policy</a>.</p>
<!--end-status-->
<p> The following counter styles are at-risk: ‘<a
href="#cjk-decimal"><code class=css>cjk-decimal</code></a>’, ‘<a
href="#hebrew"><code class=css>hebrew</code></a>’, ‘<a
href="#hiragana"><code class=css>hiragana</code></a>’, ‘<a
href="#hiragana-iroha"><code class=css>hiragana-iroha</code></a>’, ‘<a
href="#katakana"><code class=css>katakana</code></a>’, ‘<a
href="#katakana-iroha"><code class=css>katakana-iroha</code></a>’, ‘<a
href="#japanese-informal0"><code
class=css>japanese-informal</code></a>’, ‘<a
href="#japanese-formal0"><code class=css>japanese-formal</code></a>’,
‘<a href="#korean-hangul-formal0"><code
class=css>korean-hangul-formal</code></a>’, ‘<a
href="#korean-hanja-informal0"><code
class=css>korean-hanja-informal</code></a>’, ‘<a
href="#korean-hanja-formal0"><code
class=css>korean-hanja-formal</code></a>’, ‘<a
href="#simp-chinese-informal0"><code
class=css>simp-chinese-informal</code></a>’, ‘<a
href="#simp-chinese-formal0"><code
class=css>simp-chinese-formal</code></a>’, ‘<a
href="#trad-chinese-informal0"><code
class=css>trad-chinese-informal</code></a>’, ‘<a
href="#trad-chinese-formal0"><code
class=css>trad-chinese-formal</code></a>’, and ‘<a
href="#ethiopic-numeric"><code class=css>ethiopic-numeric</code></a>’.
<h2 class="no-num no-toc" id=contents> Table of contents</h2>
<!--begin-toc-->
<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 ‘<code
class=css>@counter-style</code>’ rule</a>
<ul class=toc>
<li><a href="#counter-style-system"><span class=secno>3.1. </span>
Counter algorithms: the ‘<code class=property>system</code>’
descriptor</a>
<ul class=toc>
<li><a href="#cyclic-system"><span class=secno>3.1.1. </span> Cycling
Symbols: the ‘<code class=css>cyclic</code>’ system</a>
<li><a href="#fixed-system"><span class=secno>3.1.2. </span>
Exhaustible Symbols: the ‘<code class=css>fixed</code>’
system</a>
<li><a href="#symbolic-system"><span class=secno>3.1.3. </span>
Repeating Symbols: the ‘<code class=css>symbolic</code>’
system</a>
<li><a href="#alphabetic-system"><span class=secno>3.1.4. </span>
Bijective Numerals: the ‘<code class=css>alphabetic</code>’
system</a>
<li><a href="#numeric-system"><span class=secno>3.1.5. </span>
Positional Numerals: the ‘<code class=css>numeric</code>’
system</a>
<li><a href="#additive-system"><span class=secno>3.1.6. </span>
Accumulating Numerals: the ‘<code class=css>additive</code>’
system</a>
<li><a href="#override-system"><span class=secno>3.1.7. </span>
Tweaking Existing Counter Styles: the ‘<code
class=css>override</code>’ system</a>
</ul>
<li><a href="#counter-style-negative"><span class=secno>3.2. </span>
Formatting negative values: the ‘<code
class=property>negative</code>’ descriptor</a>
<li><a href="#counter-style-prefix"><span class=secno>3.3. </span>
Symbols before the marker: the ‘<code class=property>prefix</code>’
descriptor</a>
<li><a href="#counter-style-suffix"><span class=secno>3.4. </span>
Symbols after the marker: the ‘<code class=property>suffix</code>’
descriptor</a>
<li><a href="#counter-style-range"><span class=secno>3.5. </span>
Limiting the counter scope: the ‘<code class=property>range</code>’
descriptor</a>
<li><a href="#counter-style-width"><span class=secno>3.6. </span>
Zero-Padding and Constant-Width Representations: the ‘<code
class=property>width</code>’ descriptor</a>
<li><a href="#counter-style-fallback"><span class=secno>3.7. </span>
Defining fallback: the ‘<code class=property>fallback</code>’
descriptor</a>
<li><a href="#counter-style-symbols"><span class=secno>3.8. </span>
Marker characters: the ‘<code class=property>symbols</code>’ and
‘<code class=property>additive-symbols</code>’ descriptors</a>
<li><a href="#counter-style-speak-as"><span class=secno>3.9. </span>
Speech Synthesis: the ‘<code class=property>speak-as</code>’
descriptor</a>
</ul>
<li><a href="#symbols-function"><span class=secno>4. </span> Defining
Anonymous Counter Styles: the ‘<code class=css>symbols()</code>’
function</a>
<li><a href="#predefined-counters"><span class=secno>5. </span> Simple
Predefined Counter Styles</a>
<ul class=toc>
<li><a href="#simple-numeric"><span class=secno>5.1. </span> Numeric:
‘<code class=css>decimal</code>’, ‘<code
class=css>decimal-leading-zero</code>’, ‘<code
class=css>cjk-decimal</code>’, ‘<code
class=css>lower-roman</code>’, ‘<code
class=css>upper-roman</code>’, ‘<code class=css>armenian</code>’,
‘<code class=css>georgian</code>’, ‘<code
class=css>hebrew</code>’</a>
<li><a href="#simple-alphabetic"><span class=secno>5.2. </span>
Alphabetic: ‘<code class=css>lower-alpha</code>’, ‘<code
class=css>lower-latin</code>’, ‘<code
class=css>upper-alpha</code>’, ‘<code
class=css>upper-latin</code>’, ‘<code
class=css>lower-greek</code>’, ‘<code class=css>hiragana</code>’,
‘<code class=css>hiragana-iroha</code>’, ‘<code
class=css>katakana</code>’, ‘<code
class=css>katakana-iroha</code>’</a>
<li><a href="#simple-symbolic"><span class=secno>5.3. </span> Symbolic:
‘<code class=css>disc</code>’, ‘<code class=css>circle</code>’,
‘<code class=css>square</code>’, ‘<code
class=css>disclosure-open</code>’, ‘<code
class=css>disclosure-closed</code>’</a>
</ul>
<li><a href="#complex-predefined-counters"><span class=secno>6. </span>
Complex Predefined Counter Styles</a>
<ul class=toc>
<li><a href="#complex-cjk"><span class=secno>6.1. </span> Longhand East
Asian Counter Styles: ‘<code class=css>japanese-informal</code>’,
‘<code class=css>japanese-formal</code>’, ‘<code
class=css>korean-hangul-formal</code>’, ‘<code
class=css>korean-hanja-informal</code>’, ‘<code
class=css>korean-hanja-formal</code>’, ‘<code
class=css>simp-chinese-informal</code>’, ‘<code
class=css>simp-chinese-formal</code>’, ‘<code
class=css>trad-chinese-informal</code>’, ‘<code
class=css>trad-chinese-formal</code>’</a>
<ul class=toc>
<li><a href="#limited-cjk"><span class=secno>6.1.1. </span>
Limited-range Implementation (required)</a>
<li><a href="#extended-cjk"><span class=secno>6.1.2. </span> Extended
Implementation (optional)</a>
</ul>
<li><a href="#ethiopic-numeric-counter-style"><span class=secno>6.2.
</span> Ethiopic Numeric Counter Style: ‘<code
class=css>ethiopic-numeric</code>’</a>
</ul>
<li><a href="#apis"><span class=secno>7. </span>APIs</a>
<ul class=toc>
<li><a href="#extentions-to-cssrule-interface"><span class=secno>7.1.
</span> Extensions to the <code>CSSRule</code> interface</a>
<li><a href="#the-csscounterstylerule-interface"><span class=secno>7.2.
</span> The <code>CSSCounterStyleRule</code> interface</a>
</ul>
<li><a href="#ua-stylesheet"><span class=secno>8. </span> Sample style
sheet for HTML</a>
<li class=no-num><a href="#acknowledgments"> Acknowledgments</a>
<li class=no-num><a href="#conformance"> Conformance</a>
<ul class=toc>
<li class=no-num><a href="#conventions"> Document Conventions</a>
<li class=no-num><a href="#conformance-classes"> Conformance Classes</a>
<li class=no-num><a href="#partial"> Partial Implementations</a>
<li class=no-num><a href="#experimental"> Experimental
Implementations</a>
<li class=no-num><a href="#testing"> Non-Experimental
Implementations</a>
</ul>
<li class=no-num><a href="#references">References</a>
<ul class=toc>
<li class=no-num><a href="#normative-references">Normative
references</a>
<li class=no-num><a href="#other-references">Other references</a>
</ul>
<li class=no-num><a href="#descriptor-index">Descriptor index</a>
<li class=no-num><a href="#index">Index</a>
</ul>
<!--end-toc-->
<hr>
<h2 id=intro><span class=secno>1. </span> Introduction</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> This module introduces the ‘<a href="#at-counter-style"><code
class=css>@counter-style</code></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 ‘<code
class=property>list-style-type</code>’ property or in the <code
title=counter-function>counter()</code> and <code
title=counters-function>counters()</code> functions. It also defines some
additional predefined counter styles, particularly ones which are common
but complicated to represent with ‘<a href="#at-counter-style"><code
class=css>@counter-style</code></a>’.
<h2 id=counter-styles><span class=secno>2. </span> Counter Styles</h2>
<p> A <dfn id=counter-style>counter style</dfn> defines how to convert a
counter value into a string. Counter styles are composed of:
<ul>
<li> a <dfn id=name title=counter-name>name</dfn>, to identify the style
<li> an <dfn id=algorithm title=counter-algorithm>algorithm</dfn> that
transforms counter values into a string representation
<li> a <dfn id=negative-sign title=counter-negative>negative sign</dfn>,
which is prepended or appended to the representation of a negative
counter value
<li> a <dfn id=prefix title=counter-prefix>prefix</dfn>, to prepend to the
representation
<li> a <dfn id=suffix title=counter-suffix>suffix</dfn>, to append to the
representation
<li> a <dfn id=range title=counter-range>range</dfn>, which limits the
values that a counter style handles
<li> a <dfn id=spoken-form title=counter-speak-as>spoken form</dfn>, which
describes how to read out the counter style in a speech synthesizer
<li> and a <dfn id=fallback-style title=counter-fallback>fallback
style</dfn>, 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 id=generate-a-counter-representation
title="generate a counter|generate a counter representation">generate a
counter representation</dfn> using a particular counter style for a
particular counter value, follow these steps:
<ol>
<li> If the counter value is outside the <a href="#range"><i
title=counter-range>range</i></a> of the counter style, exit this
algorithm and instead <a
href="#generate-a-counter-representation"><i>generate a counter
representation</i></a> using the counter style's fallback style and the
same counter value.
<li> Using the counter value and the <a href="#algorithm"><i
title=counter-algorithm>counter algorithm</i></a> for the counter style,
generate an initial representation for the counter value. If the counter
value is negative, instead generate an initial representation using the
absolute value of it.
<li> If the representation uses less symbols than specified in the counter
style's ‘<a href="#descdef-width"><code
class=property>width</code></a>’ descriptor, prepend symbols to the
representation as specified in the ‘<a href="#descdef-width"><code
class=property>width</code></a>’ descriptor.
<li> If the counter value is negative, wrap the representation in the
counter style's <a href="#negative-sign"><i
title=counter-negative>negative sign</i></a> as specified in the ‘<a
href="#descdef-negative"><code class=property>negative</code></a>’
descriptor.
<li> Return the representation.
</ol>
<p class=note> Note that 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 ‘<code class=property>contents</code>’ property for the ‘<code
class=css>::marker</code>’ 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.
<h2 id=the-counter-style-rule><span class=secno>3. </span> Defining Custom
Counter Styles: the ‘<a href="#at-counter-style"><code
class=css>@counter-style</code></a>’ rule</h2>
<p> The <dfn id=at-counter-style>‘<code
class=css>@counter-style</code>’</dfn> rule allows authors to define a
custom <a href="#counter-style"><i>counter style</i></a>. The components
of a <a href="#counter-style"><i>counter style</i></a> are specified by
descriptors in the ‘<a href="#at-counter-style"><code
class=css>@counter-style</code></a>’ rule. The <a href="#algorithm"><i
title=counter-algorithm>algorithm</i></a> is specified implicitly by a
combination of the ‘<a href="#descdef-system"><code
class=css>system</code></a>’, ‘<a href="#descdef-symbols"><code
class=css>symbols</code></a>’, and ‘<a
href="#descdef-additive-symbols"><code
class=css>additive-symbols</code></a>’ properties.
<p> The general form of an ‘<a href="#at-counter-style"><code
class=css>@counter-style</code></a>’ rule is:
<pre>
@counter-style <a
href="#speak-as-counter-style"><i><counter-style-name></i></a> {
[ descriptor: value; ]+
}
</pre>
<p> The <a
href="#speak-as-counter-style"><i><counter-style-name></i></a> must be
be a valid identifier and must not be ‘<a href="#decimal"><code
class=css>decimal</code></a>’ or ‘<code class=css>none</code>’, or
else the rule is invalid. (Note, however, that some names, like ‘<code
class=css>inside</code>’ or ‘<code class=css>initial</code>’, might
conflict with the existing values of properties like ‘<code
class=property>list-style</code>’, and thus won't be usable there.)
<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 ‘<code
class=property>list-style</code>’ set of properties, in the ‘<a
href="#at-counter-style"><code class=css>@counter-style</code></a>’
rule, and in the ‘<code class=css>counter()</code>’ functions.
<p> Each ‘<a href="#at-counter-style"><code
class=css>@counter-style</code></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 href="#at-counter-style"><code
class=css>@counter-style</code></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 href="#at-counter-style"><code
class=css>@counter-style</code></a>’ rule, only the last specified value
is used; all prior values for that descriptor must be ignored.
<p> Defining a ‘<a href="#at-counter-style"><code
class=css>@counter-style</code></a>’ makes it available to the entire
document in which it is included. If multiple ‘<a
href="#at-counter-style"><code class=css>@counter-style</code></a>’
rules are defined with the same name, only one wins, according to standard
cascade rules. ‘<a href="#at-counter-style"><code
class=css>@counter-style</code></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> 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 must be ignored in their entirety; they do not make
the ‘<a href="#at-counter-style"><code
class=css>@counter-style</code></a>’ rule invalid.
<h3 id=counter-style-system><span class=secno>3.1. </span> Counter
algorithms: the ‘<a href="#descdef-system"><code
class=property>system</code></a>’ descriptor</h3>
<table class=descdef>
<tbody>
<tr>
<th>Name:
<td><dfn id=descdef-system>system</dfn>
<tr>
<th>Value:
<td>cyclic | numeric | alphabetic | symbolic | additive | <span
class=nobr>[fixed <integer>?]</span> | <span class=nobr>[ override
<counter-style-name> ]</span>
<tr>
<th>Initial:
<td>symbolic
</table>
<p>The ‘<a href="#descdef-system"><code
class=property>system</code></a>’ descriptor specifies which algorithm
will be used to construct the counter's representation based on the
counter value. For example, ‘<a href="#cyclic"><code
class=css>cyclic</code></a>’ counter styles just cycle through their
symbols repeatedly, while ‘<a href="#speak-as-numeric"><code
class=css>numeric</code></a>’ counter styles interpret their symbols as
digits and build their representation accordingly. The systems are defined
as follows:
<h4 id=cyclic-system><span class=secno>3.1.1. </span> Cycling Symbols: the
‘<a href="#cyclic"><code class=css>cyclic</code></a>’ system</h4>
<p> The <dfn id=cyclic>‘<code class=css>cyclic</code>’</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 href="#counter-symbol"><i>counter
symbol</i></a>), or for cycling through multiple symbols. The first <a
href="#counter-symbol"><i>counter symbol</i></a> is used as the
representation of the value 1, the second <a
href="#counter-symbol"><i>counter symbol</i></a> (if it exists) is used as
the representation of the value 2, etc.
<p> If the system is ‘<a href="#cyclic"><code
class=css>cyclic</code></a>’, the ‘<a href="#descdef-symbols"><code
class=property>symbols</code></a>’ descriptor must contain at least one
<a href="#counter-symbol"><i>counter symbol</i></a>, or else the ‘<a
href="#at-counter-style"><code class=css>@counter-style</code></a>’ rule
is invalid. This system is defined over all counter values.
<div class=example>
<p>A "triangle bullet" counter style can be defined as:
<pre>
@counter-style <dfn id=triangle>triangle</dfn> {
system: cyclic;
symbols: ‣;
suffix: '';
}
</pre>
<p>It will then produce lists that look like:
<pre>
‣ One
‣ Two
‣ Three
</pre>
</div>
<p> If there are <var>N</var> <i>counter symbols</i> and a representation
is being constructed for the integer <var>value</var>, the representation
is the <a href="#counter-symbol"><i>counter symbol</i></a> at index (
(<var>value</var>-1) mod <var>N</var>) of the list of <i>counter
symbols</i> (0-indexed).
<h4 id=fixed-system><span class=secno>3.1.2. </span> Exhaustible Symbols:
the ‘<a href="#fixed"><code class=css>fixed</code></a>’ system</h4>
<p> The <dfn id=fixed>‘<code class=css>fixed</code>’</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> If the system is ‘<a href="#fixed"><code
class=css>fixed</code></a>’, the ‘<a href="#descdef-symbols"><code
class=property>symbols</code></a>’ descriptor must contain at least one
<a href="#counter-symbol"><i>counter symbol</i></a>, or else the ‘<a
href="#at-counter-style"><code class=css>@counter-style</code></a>’ rule
is invalid. This system is defined over counter values in a finite range,
starting with the <a href="#first-symbol-value"><i>first symbol
value</i></a> and having a length equal to the length of the list of
<i>counter symbols</i>.
<p> When this system is specified, it may optionally have an integer
provided after it, which sets the <dfn id=first-symbol-value>first symbol
value</dfn>. If it is omitted, the <a href="#first-symbol-value"><i>first
symbol value</i></a> is 1.
<div class=example>
<p>A "box-corner" counter style can be defined as:
<pre>
@counter-style <dfn id=box-corner>box-corner</dfn> {
system: fixed;
symbols: ◰ ◳ ◲ ◱;
suffix: ':';
}
</pre>
<p>It will then produce lists that look like:
<pre>
◰: One
◳: Two
◲: Three
◱: Four
5: Five
6: Six
</pre>
</div>
<p> The first <a href="#counter-symbol"><i>counter symbol</i></a> is the
representation for the <a href="#first-symbol-value"><i>first symbol
value</i></a>, and subsequent counter values are represented by subsequent
<i>counter symbols</i>. Once the list of <i>counter symbols</i> is
exhausted, further values cannot be represented by this counter style, and
must instead be represented by the fallback counter style.
<h4 id=symbolic-system><span class=secno>3.1.3. </span> Repeating Symbols:
the ‘<a href="#symbolic"><code class=css>symbolic</code></a>’ system</h4>
<p> The ‘<a href="#symbolic"><code class=css>symbolic</code></a>’
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
href="#speak-as-alphabetic"><code class=css>alphabetic</code></a>’
system presents.
<p> If the system is <dfn id=symbolic>‘<code
class=css>symbolic</code>’</dfn>, the ‘<a
href="#descdef-symbols"><code class=property>symbols</code></a>’
descriptor must contain at least one <a href="#counter-symbol"><i>counter
symbol</i></a>, or else the ‘<a href="#at-counter-style"><code
class=css>@counter-style</code></a>’ rule is invalid. This system is
defined only over strictly positive counter values.
<div class=example>
<p>An "footnote" counter style can be defined as:
<pre>
@counter-style <dfn id=footnote>footnote</dfn> {
system: symbolic;
symbols: '*' ⁑ † ‡;
suffix: '';
}
</pre>
<p>It will then produce lists that look like:
<pre>
* One
⁑ Two
† Three
‡ Four
** Five
⁑⁑ Six
</pre>
</div>
<div class=example>
<p> Some style guides mandate a list numbering that looks similar to ‘<a
href="#upper-alpha"><code class=css>upper-alpha</code></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 id=upper-alpha-legal>upper-alpha-legal</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 href="#upper-alpha"><code
class=css>upper-alpha</code></a>’ through the first 27 values, but they
diverge after that, with ‘<a href="#upper-alpha"><code
class=css>upper-alpha</code></a>’ going "AB", "AC", "AD", etc. Starting
at the 53rd value, ‘<a href="#upper-alpha"><code
class=css>upper-alpha</code></a>’ goes "BA", "BB", "BC", etc., while
this style jumps into triple digits with "AAA", "BBB", "CCC", etc.
</div>
<p> To construct the representation, run the following algorithm:
<p> Let <var>N</var> be the length of the list of <i>counter symbols</i>,
<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
href="#counter-symbol"><i>counter symbol</i></a> in the list of <i>counter
symbols</i> (0-indexed).
<ol>
<li>Let the <var>chosen symbol</var> be <code
class=inline>symbol(<var>value</var> mod <var>N</var>)</code>.
<li>Let the <var>representation length</var> be <code class=inline>floor(
(<var>value</var> - 1) / <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> The ‘<a href="#symbolic"><code class=css>symbolic</code></a>’
system will produce representations with sizes that are linear in the
magnitude of the counter value. 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 20 characters long, but they may choose to
instead use the fallback style for representations that would be longer
than 20 characters.
<h4 id=alphabetic-system><span class=secno>3.1.4. </span> Bijective
Numerals: the ‘<a href="#speak-as-alphabetic"><code
class=css>alphabetic</code></a>’ system</h4>
<p> The ‘<a href="#speak-as-alphabetic"><code
class=css>alphabetic</code></a>’ counter system interprets the list of
<i>counter symbols</i> as digits to an <em title="">alphabetic</em>
numbering system, similar to the default ‘<a href="#lower-alpha"><code
class=css>lower-alpha</code></a>’ counter style, which wraps from
‘<code class=property>a</code>’, ‘<code class=property>b</code>’,
‘<code class=property>c</code>’, to ‘<code
class=property>aa</code>’, ‘<code class=property>ab</code>’,
‘<code class=property>ac</code>’. 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 href="#counter-symbol"><i>counter
symbol</i></a> in the list is interpreted as the digit 1, the second as
the digit 2, and so on.
<p> If the system is <dfn id=alphabetic>‘<code
class=css>alphabetic</code>’</dfn>, the ‘<a
href="#descdef-symbols"><code class=property>symbols</code></a>’
descriptor must contain at least two <i>counter symbols</i>, or else the
‘<a href="#at-counter-style"><code
class=css>@counter-style</code></a>’ rule is invalid. This system is
defined only over strictly positive counter values.
<div class=example>
<p>A counter style using go stones can be defined as:
<pre>
@counter-style <dfn id=go>go</dfn> {
system: alphabetic;
symbols: url(white.svg) url(black.svg);
suffix: '';
}
</pre>
<p>It will then produce lists that look like:
<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>This example requires support for SVG images to display
correctly.
</div>
<p> If there are <var>N</var> <i>counter symbols</i>, the representation is
a base <var>N</var> alphabetic number using the <i>counter symbols</i> as
digits. To construct the representation, run the following algorithm:
<p> Let <var>N</var> be the length of the list of <i>counter symbols</i>,
<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
href="#counter-symbol"><i>counter symbol</i></a> in the list of <i>counter
symbols</i> (0-indexed).
<p>While <var>value</var> is not equal to 0:
<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>.
<h4 id=numeric-system><span class=secno>3.1.5. </span> Positional Numerals:
the ‘<a href="#speak-as-numeric"><code class=css>numeric</code></a>’
system</h4>
<p> The <dfn id=numeric>‘<code class=css>numeric</code>’</dfn> counter
system interprets the list of <i>counter symbols</i> as digits to a
"place-value" numbering system, similar to the default ‘<a
href="#decimal"><code class=css>decimal</code></a>’ counter style. The
first <a href="#counter-symbol"><i>counter symbol</i></a> in the list is
interpreted as the digit 0, the second as the digit 1, and so on.
<p> If the system is ‘<a href="#speak-as-numeric"><code
class=css>numeric</code></a>’, the ‘<a href="#descdef-symbols"><code
class=property>symbols</code></a>’ descriptor must contain at least two
<i>counter symbols</i>, or else the ‘<a href="#at-counter-style"><code
class=css>@counter-style</code></a>’ rule is invalid. This system is
defined over all counter values.
<div class=example>
<p>A "trinary" counter style can be defined as:
<pre>
@counter-style <dfn id=trinary>trinary</dfn> {
system: numeric;
symbols: '0' '1' '2';
}
</pre>
<p>It will then produce lists that look like:
<pre>
1. One
2. Two
10. Three
11. Four
12. Five
20. Six
</pre>
</div>
<p> If there are <var>N</var> <i>counter symbols</i>, the representation is
a base <var>N</var> number using the <i>counter symbols</i> as digits. To
construct the representation, run the following algorithm:
<p> Let <var>N</var> be the length of the list of <i>counter symbols</i>,
<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
href="#counter-symbol"><i>counter symbol</i></a> in the list of <i>counter
symbols</i> (0-indexed).
<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 id=additive-system><span class=secno>3.1.6. </span> Accumulating
Numerals: the ‘<a href="#additive"><code
class=css>additive</code></a>’ system</h4>
<p> The <dfn id=additive>‘<code class=css>additive</code>’</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> If the system is ‘<a href="#additive"><code
class=css>additive</code></a>’, the ‘<a
href="#descdef-additive-symbols"><code
class=property>additive-symbols</code></a>’ descriptor must contain at
least one <a href="#additive-tuple"><i>additive tuple</i></a>, or else the
‘<a href="#at-counter-style"><code
class=css>@counter-style</code></a>’ rule is invalid. This system is
nominally defined over all counter values (see algorithm, below, for exact
details).
<div class=example>
<p>A "dice" counter style can be defined as:
<pre>
@counter-style <dfn id=dice>dice</dfn> {
system: additive;
additive-symbols: 6 ⚅, 5 ⚄, 4 ⚃, 3 ⚂, 2 ⚁, 1 ⚀;
suffix: '';
}
</pre>
<p>It will then produce lists that look like:
<pre>
⚀ One
⚁ Two
⚂ Three
...
⚅⚄ Eleven
⚅⚅ Twelve
⚅⚅⚀ Thirteen
</pre>
</div>
<p> To construct the representation, run this algorithm:
<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 <i>additive tuples</i>.
<ol>
<li>If <var>value</var> is initially 0, and there is an <a
href="#additive-tuple"><i>additive tuple</i></a> with a weight of 0,
append that tuple's <a href="#counter-symbol"><i>counter symbol</i></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 href="#additive-tuple"><i>additive tuple</i></a>
from the <var>symbol list</var>. This is the <dfn id=current-tuple
title="current tuple|current tuple's">current tuple</dfn>.
<li>Append the <a href="#current-tuple"><i>current tuple</i></a>'s
<a href="#counter-symbol"><i>counter symbol</i></a> to <var>S</var>
<code>floor( <var>value</var> / <var><a
href="#current-tuple"><i>current tuple's</i></a> weight</var> )</code>
times (this may be 0).
<li>Decrement <var>value</var> by the <var><a
href="#current-tuple"><i>current tuple's</i></a> weight multiplied by
the number of times the <a href="#current-tuple"><i>current
tuple</i></a> was appended to <var>S</var> in the previous step. </var>
</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> The ‘<a href="#additive"><code class=css>additive</code></a>’
system will produce representations with sizes that are linear in the
magnitude of the counter value. 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 20 characters long, but they may choose to
instead use the fallback style for representations that would be longer
than 20 characters.
<h4 id=override-system><span class=secno>3.1.7. </span> Tweaking Existing
Counter Styles: the ‘<a href="#override"><code
class=css>override</code></a>’ system</h4>
<p> The <dfn id=override>‘<code class=css>override</code>’</dfn> system
allows an author to use the <i>algorithm</i> of another counter style, but
alter other aspects, such as the negative sign or the suffix. If a counter
style uses the ‘<a href="#override"><code
class=css>override</code></a>’ system, any unspecified descriptors must
be taken from the overridden counter style specified, rather than taking