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<!DOCTYPE html><html lang=en><head>
<meta content="text/html; charset=utf-8" http-equiv=Content-Type>
<title>CSS Generated Content for Paged Media Module Level 4</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>
</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 Generated Content for Paged Media Module Level 4</h1>
<h2 class="no-num no-toc no-ref heading settled" id=subtitle><span class=content>Editor’s Draft,
<span class=dt-updated><span class=value-title title=20141206>6 December 2014</span></span></span></h2>
<div data-fill-with=spec-metadata><dl><dt>This version:<dd><a class=u-url href=http://dev.w3.org/csswg/css-gcpm-4/>http://dev.w3.org/csswg/css-gcpm-4/</a><dt>Feedback:<dd><span><a href="mailto:www-style@w3.org?subject=%5Bcss-gcpm-4%5D%20feedback">www-style@w3.org</a> with subject line “<kbd>[css-gcpm-4] <var>… message topic …</var></kbd>” (<a href=http://lists.w3.org/Archives/Public/www-style/ rel=discussion>archives</a>)</span><dt>Issue Tracking:<dd><a href=#issues-index>Inline In Spec</a><dd><span><a href="https://www.w3.org/Bugs/Public/enter_bug.cgi?product=CSS&component=Generated%20Content%20for%20Paged%20Media">W3C Bugzilla</a></span><dt class=editor>Editors:<dd class=editor><div class="p-author h-card vcard"><a class="p-name fn u-email email" href=mailto:dauwhe@gmail.com>Dave Cramer</a> (<span class="p-org org">Hachette Livre</span>)</div><dd class=editor><div class="p-author h-card vcard"><a class="p-name fn u-email email" href=mailto:daniel.glazman@disruptive-innovations.com>Daniel Glazman</a> (<span class="p-org org">Disruptive Innovations</span>)</div></dl></div>
<div data-fill-with=warning><details class=annoying-warning open>
<summary>Not Ready For Implementation</summary>
<p>
This spec is not yet ready for implementation.
It exists in this repository to record the ideas and promote discussion.
<p>
Before attempting to implement this spec,
please contact the CSSWG at www-style@w3.org.
</details>
</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" id=abstract><span class=content>Abstract</span></h2>
<div class=p-summary data-fill-with=abstract><p>Level 4 of GCPM proposes a region-based approach to footnotes and running heads.</p>
<a href=http://www.w3.org/TR/CSS/>CSS</a> is a l
F803
anguage for describing the rendering of structured documents
(such as HTML and XML)
on screen, on paper, in speech, etc.</div>
<h2 class="no-num no-toc no-ref heading settled" id=status><span class=content>Status of this document</span></h2>
<div data-fill-with=status><p>
This is a public copy of the editors’ draft.
It is provided for discussion only and may change at any moment.
Its publication here does not imply endorsement of its contents by W3C.
Don’t cite this document other than as work in progress.
<p>
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-gcpm-4%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-gcpm-4” in the subject,
preferably like this:
“[css-gcpm-4] <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>.
<p>
This document is governed by the <a href=http://www.w3.org/2014/Process-20140801/>1 August 2014 W3C Process Document</a>.
</div>
<div data-fill-with=at-risk></div>
<h2 class="no-num no-toc no-ref heading settled" id=contents><span class=content>Table of Contents</span></h2>
<div data-fill-with=table-of-contents role=navigation><ul class=toc role=directory><li><a href=#introduction><span class=secno></span> <span class=content>
Introduction
</span></a><li><a href=#running-headers-and-footers><span class=secno>1</span> <span class=content>
Running headers and footers
</span></a><ul class=toc><li><a href=#copy-into-heading><span class=secno>1.1</span> <span class=content>Copying a flow: the <span class=property data-link-type=propdesc title=copy-into>copy-into</span> property</span></a><li><a href=#flow-persist-heading><span class=secno>1.2</span> <span class=content>Choosing among multiple values on a page</span></a><ul class=toc><li><a href=#page-selector-pseudo-classes><span class=secno>1.2.1</span> <span class=content>Page selector pseudo-classes</span></a></ul></ul><li><a href=#page-area-head><span class=secno>2</span> <span class=content>Creating Page Areas</span></a><li><a href=#footnotes><span class=secno>3</span> <span class=content>
Footnotes
</span></a><ul class=toc><li><a href=#footnote-terms><span class=secno>3.1</span> <span class=content>Terminology</span></a><li><a href=#footnotes-as-regions><span class=secno>3.2</span> <span class=content>Footnotes as Regions</span></a></ul><li><a href=#acknowledgments><span class=secno></span> <span class=content>
Acknowledgments
</span></a><li><a href=#conformance><span class=secno></span> <span class=content>
Conformance</span></a><ul class=toc><li><a href=#conventions><span class=secno></span> <span class=content>
Document conventions</span></a><li><a href=#conformance-classes><span class=secno></span> <span class=content>
Conformance classes</span></a><li><a href=#partial><span class=secno></span> <span class=content>
Partial implementations</span></a><li><a href=#experimental><span class=secno></span> <span class=content>
Experimental implementations</span></a><li><a href=#testing><span class=secno></span> <span class=content>
Non-experimental implementations</span></a></ul><li><a href=#references><span class=secno></span> <span class=content>References</span></a><ul class=toc><li><a href=#normative><span class=secno></span> <span class=content>Normative References</span></a><li><a href=#informative><span class=secno></span> <span class=content>Informative References</span></a></ul><li><a href=#index><span class=secno></span> <span class=content>Index</span></a><li><a href=#property-index><span class=secno></span> <span class=content>Property Index</span></a><li><a href=#issues-index><span class=secno></span> <span class=content>Issues Index</span></a></ul></div>
<main>
<h2 class="no-num heading settled" id=introduction><span class=content>
Introduction
</span></h2>
<p>There have been many proposals for using CSS to move document content, often motivated by the desire for magazine- or book-style layout of footnotes, running heads, pull quotes, sidebars, and so on. <a data-biblio-type=informative data-link-type=biblio href=#biblio-css3gcpm title=CSS3GCPM>[CSS3GCPM]</a> used float: footnote and position: running(). The now-abandoned <a data-biblio-type=informative data-link-type=biblio href=#biblio-css3gencon title=CSS3GENCON>[CSS3GENCON]</a> Working Draft used content: footnote. PrinceXML (and older GCPM drafts) has content: flow() and flow: static(). WHATWG CSS Books has flow: area().</p>
<p>This module proposes a unified approach to paginated layout based on <a data-biblio-type=informative data-link-type=biblio href=#biblio-css3-regions title=CSS3-REGIONS>[CSS3-REGIONS]</a> and <a data-biblio-type=informative data-link-type=biblio href=#biblio-css3-page-template title=CSS3-PAGE-TEMPLATE>[CSS3-PAGE-TEMPLATE]</a>. Additional properties will be introduced as necessary.</p>
<h2 class="heading settled" data-level=1 id=running-headers-and-footers><span class=secno>1. </span><span class=content>
Running headers and footers
</span><a class=self-link href=#running-headers-and-footers></a></h2>
<a data-biblio-type=informative data-link-type=biblio href=#biblio-css3page title=CSS3PAGE>[CSS3PAGE]</a> describes the sixteen page margin boxes which can be used for running headers and footers, but does not describe a mechanism for inserting content in those boxes.
<p><a data-biblio-type=informative data-link-type=biblio href=#biblio-css3gcpm title=CSS3GCPM>[CSS3GCPM]</a> provides for copying the string values of elements into the existing page margin boxes.</p>
<p>The existing mechanisms do not cover many use cases.</p>
<h3 class="heading settled" data-level=1.1 id=copy-into-heading><span class=secno>1.1. </span><span class=content>Copying a flow: the <a class=property data-link-type=propdesc href=#propdef-copy-into>copy-into</a> property</span><a class=self-link href=#copy-into-heading></a></h3>
<p>Headers often contain document content, and it is desirable to both display that content normally (for example, as an <code>h1</code>) and to use the content in a running head. <a data-biblio-type=informative data-link-type=biblio href=#biblio-css3-regions title=CSS3-REGIONS>[CSS3-REGIONS]</a> allows for an element to be moved to a <span class=css>named flow</span>, but doesn’t allow for using the same content in two ways. The <a class=property data-link-type=propdesc href=#propdef-copy-into>copy-into</a> property allows an element to be copied into a content fragment which can then be placed with the <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css-content-3/#propdef-content>content</a> property.</p>
<p class=note role=note>Use cases for running heads can be found in <span data-biblio-type=informative data-link-type=biblio title=LATINREQ>[LATINREQ]</span> http://w3c.github.io/dpub-pagination/#content</p>
<table class="definition propdef"><tr><th>Name:<td><dfn class=css data-dfn-type=property data-export="" id=propdef-copy-into>copy-into<a class=self-link href=#propdef-copy-into></a></dfn><tr><th>Value:<td class=prod>none <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> [ [ <custom-ident> <content-level>] [<a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-comma>,</a> <custom-ident> <content-level>]<a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#mult-zero-plus>*</a> ]<a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#mult-opt>?</a><tr><th>Initial:<td>none<tr><th>Applies to:<td>all elements and pseudo-elements, but not ::first-line or ::first-letter.<tr><th>Inherited:<td>no<tr><th>Percentages:<td>n/a<tr><th>Media:<td>visual<tr><th>Computed value:<td>as specified<tr><th>Animatable:<td>no</table>
<p>The <a class=property data-link-type=propdesc href=#propdef-copy-into>copy-into</a> property contains one or more pairs, each consisting of a custom identifier followed by a content-level keyword describing how to construct the value of the named content fragment.</p>
<p><span class=css>content-level</span> expands to the following values:</p>
<pre class=prod><dfn data-dfn-type=dfn data-noexport="" id=content-list>content-list<a class=self-link href=#content-list></a></dfn> = element <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> content <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> text <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> attr(<identifier>) <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> counter() <a data-link-for="" data-link-type=grammar href=http://dev.w3.org/csswg/css-values-3/#comb-one>|</a> counters()
</pre>
<dl>
<dt>element</dt>
<dd>the entire element is copied into the named content fragment</dd>
<dt>contents</dt>
<dd>only the element’s contents are copied into the named content fragment. This is the default if <span class=css>content-level</span> is not specified.</dd>
<dt>text</dt>
<dd>only the element’s text (including normally collapsed white space) is copied into the named content fragment.</dd>
</dl>
<div class=example>
<pre>h1 {
copy-into: chapter-title element;
font-size: 1.5em;
}
@page {
@top-center {
content: chapter-title '.';
font-size: .9em;
font-variant: small-caps;
}
}
</pre>
</div>
<h3 class="heading settled" data-level=1.2 id=flow-persist-heading><span class=secno>1.2. </span><span class=content>Choosing among multiple values on a page</span><a class=self-link href=#flow-persist-heading></a></h3>
<h4 class="heading settled" data-level=1.2.1 id=page-selector-pseudo-classes><span class=secno>1.2.1. </span><span class=content>Page selector pseudo-classes</span><a class=self-link href=#page-selector-pseudo-classes></a></h4>
<p>By default, the content fragment name would be global, as the named flow is with <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css-regions-1/#propdef-flow-into>flow-into</a>. But if one of the following pseudo-classes are used on the subject of the selector, then the name is locally scoped to just the page the element is on.</p>
<dl>
<dt><dfn class=css data-dfn-type=selector data-export="" id=selectordef-nth-of-pagen>:nth-of-page(n)<a class=self-link href=#selectordef-nth-of-pagen></a></dfn></dt>
<dd>The element is the nth matched element on the page.</dd>
<dt><dfn class=css data-dfn-type=selector data-export="" id=selectordef-first-of-page>:first-of-page<a class=self-link href=#selectordef-first-of-page></a></dfn></dt>
<dd>Same as :nth-of-page(n), but where n = 1 (it is the first matched element on the page).</dd>
<dt><dfn class=css data-dfn-type=selector data-export="" id=selectordef-last-of-page>:last-of-page<a class=self-link href=#selectordef-last-of-page></a></dfn></dt>
<dd>The element is the last matched element on the page.</dd>
<dt><dfn class=css data-dfn-type=selector data-export="" id=selectordef-start-of-page>:start-of-page<a class=self-link href=#selectordef-start-of-page></a></dfn></dt>
<dd>The element is the first matched element on the page, and neither it nor its ancestors have any previous siblings that appear on the page.</dd>
</dl>
<div class=example>
<p>HTML:</p>
<pre><h1>The Voyage of the <i>Beagle</i></h1>
</pre>
<p>CSS:</p>
<pre>h1::before {
content: 'Chapter 'counter(chapterNumber);
}
h1:first-of-page {
copy-into: headerP1 counter(chapter), headerP2;
}
h1::after {
content: '.' copy-into: headerP3;
}
@top-center {
content: headerP1 ": " headerP2 headerP3;
}
</pre>
<p>The value of the named string “headerP1” will be “Chapter 1”, and the value of the named string “headerP2” will be “Voyage of the <i>Beagle</i>”. headerP2 will include the italic tags around "Beagle", because the <code>content-type</code> defaults to <span class=css data-link-for=copy-into>contents</span>, not <span class=css data-link-for=copy-into>text</span>. The value of the named string “headerP3” will be “.”. The top-center content will be “Chapter 1: The Voyage of the <i>Horizon</i>.”</p>
</div>
<div class=example>
HTML:
<pre><section title="Loomings">
</pre>
<p>CSS:</p>
<pre>section:first-of-page { copy-into: header attr(title) }
</pre>
<p>The value of the “header” string will be “Loomings”, assuming that section intersected with the page.</p>
</div>
<div class=example>
CSS:
<pre>@page {
size: 15cm 10cm;
margin: 1.5cm;
@top-left {
content: "first: " heading1;
}
@top-center {
content: "start: " heading2;
}
@top-right {
content: "last: " heading3;
}
}
h2:first-of-page { copy-into: heading1 }
h2:start-of-page { copy-into: heading2 }
h2:last-of-page { copy-into: heading3 }
</pre>
<p>The following figures show the first, start, and last assignments of the “heading” string on various pages.</p>
<figure>
<img alt="" src=images/using-strings-1.jpg width=480>
<figcaption>The <code>start</code> value is empty, as the string had not yet been set at the start of the page.</figcaption>
</figure>
<figure>
<img alt="" src=images/using-strings-2.jpg width=480>
<figcaption>Since the page starts with an h2, the <code>start</code> value is the value of that head.</figcaption>
</figure>
<figure>
<img alt="" src=images/using-strings-3.jpg width=480>
<figcaption>Since there’s not an h2 at the top of this page, the <code>start</code> value is the exit value of the previous page.</figcaption>
</figure>
</div>
<h2 class="heading settled" data-level=2 id=page-area-head><span class=secno>2. </span><span class=content>Creating Page Areas</span><a class=self-link href=#page-area-head></a></h2>
<p><a data-biblio-type=informative data-link-type=biblio href=#biblio-css3-page-template title=CSS3-PAGE-TEMPLATE>[CSS3-PAGE-TEMPLATE]</a> introduces @template and @slot rules. We propose to allow the use of @slot in the @page context, to allow greater flexibility than the page margin boxes in <a data-biblio-type=informative data-link-type=biblio href=#biblio-css3page title=CSS3PAGE>[CSS3PAGE]</a>. These slots can also be used for sidenotes, pull quotes, footnotes, and many other document features.</p>
<div class=example>
<pre>@page body {
@slot center-header {
top: 0px;
left: 1em;
right: 1em;
height: 2em;
flow-from: header;
flow-persist: persist;
wrap-flow: clear;
}
}
</pre>
</div>
<p class=issue id=issue-de25de6c><a class=self-link href=#issue-de25de6c></a>Is there a need for both @page and @template?</p>
<h2 class="heading settled" data-level=3 id=footnotes><span class=secno>3. </span><span class=content>
Footnotes
</span><a class=self-link href=#footnotes></a></h2>
Ancillary content may be moved to the bottom or side of a page. A footnote is created when such content moves to the bottom of the page, leaving a reference indicator.
<h3 class="heading settled" data-level=3.1 id=footnote-terms><span class=secno>3.1. </span><span class=content>Terminology</span><a class=self-link href=#footnote-terms></a></h3>
<p>Footnotes are complex objects, so it will be helpful to define some terms before proceeding.</p>
<figure>
<p><img alt="page with footnotes" src=images/footnote-diagram.001.jpg width=480></p>
<figcaption>Footnote terminology</figcaption>
</figure>
<dl>
<dt>footnote element</dt>
<dd>The element containing the content of the footnote, which will be removed from the flow and displayed as a footnote.</dd>
<dt>footnote marker (also known as footnote number)</dt>
<dd>A number or symbol adjacent to the footnote body, identifying the particular footnote. The footnote marker should use the same number or symbol as the corresponding footnote call, although the marker may contain additional punctuation.</dd>
<dt>footnote body</dt>
<dd>The footnote marker is placed before the footnote element, and together they represent the footnote body, which will be placed in the footnote area.</dd>
<dt>footnote call (also known as footnote reference)</dt>
<dd>A number or symbol, found in the main text, which points to the footnote body.</dd>
<dt>footnote area</dt>
<dd>The page area used to display footnotes.</dd>
<dt>footnote rule (also known as footnote separator)</dt>
<dd>A horizontal rule is often used to separate the footnote area from the rest of the page. The separator (and the entire footnote area) cannot be rendered on a page with no footnotes.</dd>
</dl>
<h3 class="heading settled" data-level=3.2 id=footnotes-as-regions><span class=secno>3.2. </span><span class=content>Footnotes as Regions</span><a class=self-link href=#footnotes-as-regions></a></h3>
<div class=example>
HTML:
<pre style="word-wrap: break-word; white-space: pre-wrap;"><p>Though the body was erect, the head was thrown back so that the closed eyes were pointed towards the needle of the tell-tale that swung from a beam in the ceiling..<span class="reference"><span class="footnote">The cabin-compass is called the tell-tale, because without going to the compass at the helm, the Captain, while below, can inform himself of the course of the ship.</span></span></p>
</pre>
<p>CSS:</p>
<pre>span.footnote {
flow-into: footnote;
flow-policy: copy;
display: block;
}
span.footnote::before {
content: counter(footnote) '. ';
}
span.reference::before {
content: counter(footnote);
font-variant-position: super;
}
@page {
@slot footnote {
flow-from: footnote;
required-flow: footnote;
position: absolute;
left: 54pt;
bottom: 0pt;
width: 352pt;
height: auto;
border-top: .25pt solid black;
vertical-align: bottom;
wrap-flow: clear;
}
}
</pre>
</div>
<p class=issue id=issue-5b376f66><a class=self-link href=#issue-5b376f66></a>The above HTML contains two nested spans for the footnote, as CSS has no mechanism to leave a reference object where something was removed from the flow.</p>
<p class=issue id=issue-76510f61><a class=self-link href=#issue-76510f61></a>Would it be possible to specify <code>flow-into: none</code> on <code>span.footnote::after</code>? <a data-biblio-type=informative data-link-type=biblio href=#biblio-css3-regions title=CSS3-REGIONS>[CSS3-REGIONS]</a> forbids the flow-into property on pseudo-elements, but should that be changed?</p>
<div class=example>
Inline footnote
<pre>span.footnote {
flow-into: footnote;
display: inline;
}
</pre>
</div>
<h2 class="no-num heading settled" id=acknowledgments><span class=content>
Acknowledgments
</span><a class=self-link href=#acknowledgments></a></h2>
<p>Tab Atkins, Jr., Brak Kemper, Håkon Wium Lie, Liam Quin, Peter Sorotokin, Alan Stearns</p>
</main>
<h2 class="no-ref no-num heading settled" id=conformance><span class=content>
Conformance</span><a class=self-link href=#conformance></a></h2>
<h3 class="no-ref heading settled" id=conventions><span class=content>
Document conventions</span><a class=self-link href=#conventions></a></h3>
<p>Conformance requirements are expressed with a combination of
descriptive assertions and RFC 2119 terminology. The key words "MUST",
"MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT",
"RECOMMENDED", "MAY", and "OPTIONAL" in the normative parts of this
document are to be interpreted as described in RFC 2119.
However, for readability, these words do not appear in all uppercase
letters in this specification.
<p>All of the text of this specification is normative except sections
explicitly marked as non-normative, examples, and notes. <a data-biblio-type=normative data-link-type=biblio href=#biblio-rfc2119 title=RFC2119>[RFC2119]</a></p>
<p>Examples in this specification are introduced with the words "for example"
or are set apart from the normative text with <code>class="example"</code>,
like this:
<div class=example>
<p>This is an example of an informative example.</p>
</div>
<p>Informative notes begin with the word "Note" and are set apart from the
normative text with <code>class="note"</code>, like this:
<p class=note role=note>Note, this is an informative note.</p>
<p>Advisements are normative sections styled to evoke special attention and are
set apart from other normative text with <code><strong class="advisement"></code>, like
this:
<strong class=advisement>
UAs MUST provide an accessible alternative.
</strong>
<h3 class="no-ref heading settled" id=conformance-classes><span class=content>
Conformance classes</span><a class=self-link href=#conformance-classes></a></h3>
<p>Conformance to this specification
is defined for three conformance classes:
<dl>
<dt>style sheet
<dd>A <a href=http://www.w3.org/TR/CSS21/conform.html#style-sheet>CSS
style sheet</a>.
<dt>renderer
<dd>A <a href=http://www.w3.org/TR/CSS21/conform.html#user-agent>UA</a>
that interprets the semantics of a style sheet and renders
documents that use them.
<dt>authoring tool
<dd>A <a href=http://www.w3.org/TR/CSS21/conform.html#user-agent>UA</a>
that writes a style sheet.
</dl>
<p>A style sheet is conformant to this specification
if all of its statements that use syntax defined in this module are valid
according to the generic CSS grammar and the individual grammars of each
feature defined in this module.
<p>A renderer is conformant to this specification
if, in addition to interpreting the style sheet as defined by the
appropriate specifications, it supports all the features defined
by this specification by parsing them correctly
and rendering the document accordingly. However, the inability of a
UA to correctly render a document due to limitations of the device
does not make the UA non-conformant. (For example, a UA is not
required to render color on a monochrome monitor.)
<p>An authoring tool is conformant to this specification
if it writes style sheets that are syntactically correct according to the
generic CSS grammar and the individual grammars of each feature in
this module, and meet all other conformance requirements of style sheets
as described in this module.
<h3 class="no-ref heading settled" id=partial><span class=content>
Partial implementations</span><a class=self-link href=#partial></a></h3>
<p>So that authors can exploit the forward-compatible parsing rules to
assign fallback values, CSS renderers <strong>must</strong>
treat as invalid (and <a href=http://www.w3.org/TR/CSS21/conform.html#ignore>ignore
as appropriate</a>) any at-rules, properties, property values, keywords,
and other syntactic constructs for which they have no usable level of
support. In particular, user agents <strong>must not</strong>
13C5
; selectively
ignore unsupported component values and honor supported values in a single
multi-value property declaration: if any value is considered invalid
(as unsupported values must be), CSS requires that the entire declaration
be ignored.</p>
<h3 class="no-ref heading settled" id=experimental><span class=content>
Experimental implementations</span><a class=self-link href=#experimental></a></h3>
<p>To avoid clashes with future CSS features, the CSS2.1 specification
reserves a <a href=http://www.w3.org/TR/CSS21/syndata.html#vendor-keywords>prefixed
syntax</a> for proprietary and experimental extensions to CSS.
<p>Prior to a specification reaching the Candidate Recommendation stage
in the W3C process, all implementations of a CSS feature are considered
experimental. The CSS Working Group recommends that implementations
use a vendor-prefixed syntax for such features, including those in
W3C Working Drafts. This avoids incompatibilities with future changes
in the draft.
</p>
<h3 class="no-ref heading settled" id=testing><span class=content>
Non-experimental implementations</span><a class=self-link href=#testing></a></h3>
<p>Once a specification reaches the Candidate Recommendation stage,
non-experimental implementations are possible, and implementors should
release an unprefixed implementation of any CR-level feature they
can demonstrate to be correctly implemented according to spec.
<p>To establish and maintain the interoperability of CSS across
implementations, the CSS Working Group requests that non-experimental
CSS renderers submit an implementation report (and, if necessary, the
testcases used for that implementation report) to the W3C before
releasing an unprefixed implementation of any CSS features. Testcases
submitted to W3C are subject to review and correction by the CSS
Working Group.
<p>Further information on submitting testcases and implementation reports
can be found from on the CSS Working Group’s website at
<a href=http://www.w3.org/Style/CSS/Test/>http://www.w3.org/Style/CSS/Test/</a>.
Questions should be directed to the
<a href=http://lists.w3.org/Archives/Public/public-css-testsuite>public-css-testsuite@w3.org</a>
mailing list.
<h2 class="no-num heading settled" id=references><span class=content>References</span><a class=self-link href=#references></a></h2><h3 class="no-num heading settled" id=normative><span class=content>Normative References</span><a class=self-link href=#normative></a></h3><dl><dt id=biblio-rfc2119 title=rfc2119><a class=self-link href=#biblio-rfc2119></a>[rfc2119]<dd>S. Bradner. <a href=https://tools.ietf.org/html/rfc2119>Key words for use in RFCs to Indicate Requirement Levels</a>. March 1997. Best Current Practice. URL: <a href=https://tools.ietf.org/html/rfc2119>https://tools.ietf.org/html/rfc2119</a></dl><h3 class="no-num heading settled" id=informative><span class=content>Informative References</span><a class=self-link href=#informative></a></h3><dl><dt id=biblio-css3-page-template title=CSS3-PAGE-TEMPLATE><a class=self-link href=#biblio-css3-page-template></a>[CSS3-PAGE-TEMPLATE]<dd>Alan Stearns. <a href=http://dev.w3.org/csswg/css3-page-template/>CSS Pagination Templates Module Level 3</a>. Proposal for a CSS module. (Retrieved 4 April 2012) URL: <a href=http://dev.w3.org/csswg/css3-page-template/>http://dev.w3.org/csswg/css3-page-template/</a><dt id=biblio-css3-regions title=CSS3-REGIONS><a class=self-link href=#biblio-css3-regions></a>[CSS3-REGIONS]<dd>Vincent Hardy; Rossen Atanassov; Alan Stearns. <a href=http://www.w3.org/TR/2013/WD-css3-regions-20130528/>CSS Regions Module Level 1</a>. 28 May 2013. W3C Working Draft. (Work in progress.) URL: <a href=http://www.w3.org/TR/2013/WD-css3-regions-20130528/>http://www.w3.org/TR/2013/WD-css3-regions-20130528/</a><dt id=biblio-css3gcpm title=CSS3GCPM><a class=self-link href=#biblio-css3gcpm></a>[CSS3GCPM]<dd>Håkon Wium Lie. <a href=http://www.w3.org/TR/2011/WD-css3-gcpm-20111129/>CSS Generated Content for Paged Media Module</a>. 29 November 2011. W3C Working Draft. (Work in progress.) URL: <a href=http://www.w3.org/TR/2011/WD-css3-gcpm-20111129/>http://www.w3.org/TR/2011/WD-css3-gcpm-20111129/</a><dt id=biblio-css3gencon title=CSS3GENCON><a class=self-link href=#biblio-css3gencon></a>[CSS3GENCON]<dd>Ian Hickson. <a href=http://www.w3.org/TR/2003/WD-css3-content-20030514>CSS3 Generated and Replaced Content Module</a>. 14 May 2003. W3C Working Draft. (Work in progress.) URL: <a href=http://www.w3.org/TR/2003/WD-css3-content-20030514>http://www.w3.org/TR/2003/WD-css3-content-20030514</a><dt id=biblio-css3page title=CSS3PAGE><a class=self-link href=#biblio-css3page></a>[CSS3PAGE]<dd>Melinda Grant; et al. <a href=http://www.w3.org/TR/2013/WD-css3-page-20130314/>CSS Paged Media Module Level 3</a>. 14 March 2013. W3C Working Draft. (Work in progress.) URL: <a href=http://www.w3.org/TR/2013/WD-css3-page-20130314/>http://www.w3.org/TR/2013/WD-css3-page-20130314/</a></dl><h2 class="no-num heading settled" id=index><span class=content>Index</span><a class=self-link href=#index></a></h2><ul class=indexlist><li>content-list, <a href=#content-list title="section 1.1">1.1</a><li>copy-into, <a href=#propdef-copy-into title="section 1.1">1.1</a><li>:first-of-page, <a href=#selectordef-first-of-page title="section 1.2.1">1.2.1</a><li>:last-of-page, <a href=#selectordef-last-of-page title="section 1.2.1">1.2.1</a><li>:nth-of-page(n), <a href=#selectordef-nth-of-pagen title="section 1.2.1">1.2.1</a><li>:start-of-page, <a href=#selectordef-start-of-page title="section 1.2.1">1.2.1</a></ul><h2 class="no-num heading settled" id=property-index><span class=content>Property Index</span><a class=self-link href=#property-index></a></h2><table class="proptable data"><thead><tr><th scope=col>Name<th scope=col>Value<th scope=col>Initial<th scope=col>Applies to<th scope=col>Inh.<th scope=col>%ages<th scope=col>Media<th scope=col>Animatable<th scope=col>Computed value<tbody><tr><th scope=row><a class=css data-link-type=property href=#propdef-copy-into>copy-into</a><td>none | [ [ <custom-ident> <content-level>] [, <custom-ident> <content-level>]* ]?<td>none<td>all elements and pseudo-elements, but not ::first-line or ::first-letter.<td>no<td>n/a<td>visual<td>no<td>as specified</table><h2 class="no-num heading settled" id=issues-index><span class=content>Issues Index</span><a class=self-link href=#issues-index></a></h2><div style=counter-reset:issue><div class=issue>Is there a need for both @page and @template?<a href=#issue-de25de6c> ↵ </a></div><div class=issue>The above HTML contains two nested spans for the footnote, as CSS has no mechanism to leave a reference object where something was removed from the flow.<a href=#issue-5b376f66> ↵ </a></div><div class=issue>Would it be possible to specify <code>flow-into: none</code> on <code>span.footnote::after</code>? <a data-biblio-type=informative data-link-type=biblio href=#biblio-css3-regions title=CSS3-REGIONS>[CSS3-REGIONS]</a> forbids the flow-into property on pseudo-elements, but should that be changed?<a href=#issue-76510f61> ↵ </a></div></div>