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<!DOCTYPE html>
<html lang=en>
<head>
<meta content="text/html; charset=utf-8" http-equiv=Content-Type>
<title>CSS Overflow Module Level 3</title>
<!--
<link href="http://purl.org/dc/terms/" rel="schema.dcterms">
<link href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright" rel="dcterms.rights">
-->
<meta content="CSS Overflow Module Level 3" name=dcterms.title>
<meta content=text name=dcterms.type>
<meta content=2014-02-10 name=dcterms.date>
<meta content="L. David Baron" name=dcterms.creator>
<meta content=W3C name=dcterms.publisher>
<meta content="http://dev.w3.org/csswg/css-overflow-3/"
name=dcterms.identifier>
<link href="#contents" rel=contents>
<link href="#index" rel=index>
<link href="../default.css" rel=stylesheet type="text/css">
<link href="http://www.w3.org/StyleSheets/TR/W3C-ED.css" rel=stylesheet
type="text/css">
<style>
table.source-demo-pair {
width: 100%;
}
.in-cards-demo {
width: 13em;
height: 8em;
padding: 4px;
border: medium solid blue;
margin: 6px;
font: medium/1.3 Times New Roman, Times, serif;
white-space: nowrap;
}
.bouncy-columns-demo {
width: 6em;
height: 10em;
float: left;
margin: 1em;
font: medium/1.25 Times New Roman, Times, serif;
white-space: nowrap;
}
.bouncy-columns-demo.one {
background: aqua; color: black;
transform: rotate(-3deg);
}
.bouncy-columns-demo.two {
background: yellow; color: black;
transform: rotate(3deg);
}
.article-font-inherit-demo {
font: 1em/1.25 Times New Roman, Times, serif;
white-space: nowrap;
}
.article-font-inherit-demo.one {
width: 12em;
font-size: 1.5em;
margin-bottom: 1em;
height: 4em;
}
.article-font-inherit-demo.two {
width: 11em;
margin-left: 5em;
margin-right: 2em;
}
.dark-columns-demo {
width: 6em;
height: 10em;
float: left;
margin-right: 1em;
font: medium/1.25 Times New Roman, Times, serif;
white-space: nowrap;
}
.dark-columns-demo.one {
background: aqua; color: black;
}
.dark-columns-demo.one :link {
color: blue;
}
.dark-columns-demo.one :visited {
color: purple;
}
.dark-columns-demo.two {
background: navy; color: white;
}
.dark-columns-demo.two :link {
color: aqua;
}
.dark-columns-demo.two :visited {
color: fuchsia;
}
.article-max-lines-demo {
font: 1em/1.25 Times New Roman, Times, serif;
white-space: nowrap;
}
.article-max-lines-demo.one::first-letter {
font-size: 2em;
line-height: 0.9;
}
.article-max-lines-demo.one {
font-size: 1.5em;
width: 16em;
}
.article-max-lines-demo.two {
width: 11.5em;
float: left; margin-right: 1em;
}
.article-max-lines-demo.three {
width: 11.5em;
float: left;
}
</style>
<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 Overflow Module Level 3</h1>
<h2 class="no-num no-toc">Editor's Draft 10 February 2014</h2>
<dl>
<dt>This version:
<dd><a
href="http://dev.w3.org/csswg/css-overflow-3/">http://dev.w3.org/csswg/css-overflow-3/</a>
<dt>Latest version:
<dd><a
href="http://www.w3.org/TR/css-overflow-3/">http://www.w3.org/TR/css-overflow-3/</a>
<dt>Editor's draft:
<dd><a
href="http://dev.w3.org/csswg/css-overflow-3/">http://dev.w3.org/csswg/css-overflow-3/</a>
(<a
href="https://dvcs.w3.org/hg/csswg/log/tip/css-overflow/Overview.src.html">change
log</a>, <a
href="https://dvcs.w3.org/hg/csswg/log/tip/css3-overflow/Overview.src.html">older
change log</a>)
<dt>Previous version:
<dd><a
href="http://www.w3.org/TR/2013/WD-css-overflow-3-20130418/">http://www.w3.org/TR/2013/WD-css-overflow-3-20130418/</a>
<dt>Editors:
<dd class="h-card vcard"> <a class="p-name fn u-url url"
href="http://dbaron.org/" rel=author>L. David Baron</a>, <a
class="p-org org" href="http://www.mozilla.org/">Mozilla</a>
<dt>Issue Tracking:
<dd>Maintained in document (only editor's draft is current)
<dt>Feedback:
<dd><a
href="mailto:www-style@w3.org?subject=%5Bcss-overflow%5D%20feedback">www-style@w3.org</a>
with subject line “<kbd>[css-overflow] <var>… message topic
…</var></kbd>” (<a
href="http://lists.w3.org/Archives/Public/www-style/"
rel=discussion>archives</a>)
<dt>Test suite:
<dd>none yet
</dl>
<!--begin-copyright-->
<p class=copyright><a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
rel=license>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>
<!--end-copyright-->
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc" id=abstract>Abstract</h2>
<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. This module contains the features of CSS
relating to new mechanisms of overflow handling in visual media (e.g.,
screen or paper). In interactive media, it describes features that allow
the overflow from a fixed size container to be handled by pagination
(displaying one page at a time). It also describes features, applying to
all visual media, that allow the contents of an element to be spread
across multiple fragments, allowing the contents to flow across multiple
regions or to have different styles for different fragments.
<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-overflow-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-overflow-3” in the subject, preferably like this:
“[<!---->css-overflow-3<!---->] <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>
<!--end-status-->
<p>The following features are at risk: …
<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="#overflow-concepts"><span class=secno>2. </span>Types of
overflow</a>
<ul class=toc>
<li><a href="#ink-overflow"><span class=secno>2.1. </span>Ink
overflow</a>
<li><a href="#scrollable-overflow"><span class=secno>2.2.
</span>Scrollable overflow</a>
<li><a href="#border-box-overflow"><span class=secno>2.3. </span>Border
box overflow</a>
</ul>
<li><a href="#overflow-properties"><span class=secno>3. </span>Overflow
properties</a>
<li><a href="#scrolling-overflow"><span class=secno>4. </span>Scrolling
and hidden overflow</a>
<li><a href="#paginated-overflow"><span class=secno>5. </span>Paginated
overflow</a>
<li><a href="#fragment-overflow"><span class=secno>6. </span>Fragment
overflow</a>
<ul class=toc>
<li><a href="#fragment-styling"><span class=secno>6.1. </span>Fragment
styling</a>
<ul class=toc>
<li><a href="#fragment-pseudo-element"><span class=secno>6.1.1.
</span>The ::nth-fragment() pseudo-element</a>
<li><a href="#style-of-fragments"><span class=secno>6.1.2.
</span>Styling of fragments</a>
<li><a href="#style-in-fragments"><span class=secno>6.1.3.
</span>Styling inside fragments</a>
</ul>
<li><a href="#max-lines"><span class=secno>6.2. </span>The ‘<code
class=property>max-lines</code>’ property</a>
</ul>
<li><a href="#static-media"><span class=secno>7. </span>Overflow in static
media</a>
<li><a href="#conformance"><span class=secno>8. </span> Conformance</a>
<ul class=toc>
<li><a href="#placement"><span class=secno>8.1. </span> Module
interactions</a>
<li><a href="#values"><span class=secno>8.2. </span> Values</a>
<li><a href="#conventions"><span class=secno>8.3. </span> Document
conventions</a>
<li><a href="#conformance-classes"><span class=secno>8.4. </span>
Conformance classes</a>
<li><a href="#partial"><span class=secno>8.5. </span> Partial
implementations</a>
<li><a href="#experimental"><span class=secno>8.6. </span> Experimental
implementations</a>
<li><a href="#testing"><span class=secno>8.7. </span> Non-experimental
implementations</a>
<li><a href="#cr-exit-criteria"><span class=secno>8.8. </span> CR exit
criteria</a>
</ul>
<li class=no-num><a href="#acknowledgments"> Acknowledgments</a>
<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="#index"> Index</a>
<li class=no-num><a href="#property-index"> Property index</a>
</ul>
<!--end-toc-->
<h2 id=intro><span class=secno>1. </span> Introduction</h2>
<p> In CSS Level 1 <a href="#ref-CSS1">[CSS1]<!--{{CSS1}}--></a>, placing
more content than would fit inside an element with a specified size was
generally an authoring error. Doing so caused the content to extend
outside the bounds of the element, which would likely cause that content
to overlap with other elements.
<p> CSS Level 2 <a href="#ref-CSS21">[CSS21]<!--{{CSS21}}--></a> introduced
the ‘<a href="#overflow0"><code class=property>overflow</code></a>’
property, which allows authors to have overflow be handled by scrolling,
which means it is no longer an authoring error. It also allows authors to
specify that overflow is handled by clipping, which makes sense when the
author's intent is that the content not be shown.
<p> However, scrolling is not the only way to present large amounts of
content, and may even not be the optimal way. After all, the codex
replaced the scroll as the common format for large written works because
of its advantages.
<p> This specification introduces a mechanism for Web pages to specify that
an element of a page should handle overflow through pagination rather than
through scrolling.
<p> This specification also extends the concept of overflow in another
direction. Instead of requiring that authors specify a single area into
which the content of an element must flow, this specification allows
authors to specify multiple fragments, each with their own dimensions and
styles, so that the content of the element can flow from one to the next,
using as many as needed to place the content without overflowing.
<p> In both of these cases, implementations must break the content in the
block-progression dimension. Implementations must do this is described in
the CSS Fragmentation Module <a
href="#ref-CSS3-BREAK">[CSS3-BREAK]<!--{{!CSS3-BREAK}}--></a>.
<h2 id=overflow-concepts><span class=secno>2. </span>Types of overflow</h2>
<p> CSS uses the term <dfn id=overflow>overflow</dfn> to describe the
contents of a box that extend outside that one of that box's edges (i.e.,
its <i>content edge</i>, <i>padding edge</i>, <i>border edge</i>, or
<i>margin edge</i>). The overflow might be described as the elements or
features that cause this overflow, the non-rectangular region occupied by
these features, or, more commonly, as the minimal rectangle that bounds
that region. A box's overflow is computed based on the boxes and styles of
the box and of all its descendants whose containing block chain <span
class=issue>undefined term?</span> includes the box.
<p> In most cases, any of these types of overflow can be computed for any
box from the bounds and properties of that box, and from the overflow (of
that type) of each of its children. However, this is not always the case;
for example, when ‘<code class=css>transform-style:
preserve-3d</code>’ <a
href="#ref-CSS3-TRANSFORMS">[CSS3-TRANSFORMS]<!--{{CSS3-TRANSFORMS}}--></a>
is used on some of the children, their descendants with ‘<code
class=css>transform-style: preserve-3d</code>’ must also be examined.
<h3 id=ink-overflow><span class=secno>2.1. </span>Ink overflow</h3>
<p> The <dfn id=ink-overflow0>ink overflow</dfn> of a box is the part of
that box and its contents that creates a visual effect outside of the
box's border box.
<p> Since some effects in CSS (for example, the blurs in ‘<code
class=property>text-shadow</code>’ <a
href="#ref-CSS-TEXT-3">[CSS-TEXT-3]<!--{{CSS-TEXT-3}}--></a> and ‘<code
class=property>box-shadow</code>’ <a
href="#ref-CSS3BG">[CSS3BG]<!--{{CSS3BG}}--></a>) do not define what
visual extent they cover, the extent of the <a
href="#ink-overflow0"><i>ink overflow</i></a> is undefined.
<p class=issue> Should we try to define it at all and just leave pieces
undefined?
<p> The <dfn id=ink-overflow-region>ink overflow region</dfn> is the
non-rectangular region occupied by the <a href="#ink-overflow0"><i>ink
overflow</i></a>, and the <dfn id=ink-overflow-rectangle>ink overflow
rectangle</dfn> is the minimal rectangle whose axis is aligned to the
box's axes and contains the <a href="#ink-overflow-region"><i>ink overflow
region</i></a>. Note that the <a href="#ink-overflow-rectangle"><i>ink
overflow rectangle</i></a> is a rectangle in the box's coordinate system,
but might be non-rectangular in other coordinate systems due to transforms
<a
href="#ref-CSS3-TRANSFORMS">[CSS3-TRANSFORMS]<!--{{CSS3-TRANSFORMS}}--></a>.
<h3 id=scrollable-overflow><span class=secno>2.2. </span>Scrollable
overflow</h3>
<p> The <dfn id=scrollable-overflow0>scrollable overflow</dfn> of a box is
the set of things extending outside of that box's padding edge for which a
scrolling mechanism needs to be provided.
<p class=issue> The following definition should be rewritten to use the
concept of <a
href="http://dev.w3.org/csswg/css-transforms/#3d-rendering-context">3D
rendering context</a> <a
href="#ref-CSS3-TRANSFORMS">[CSS3-TRANSFORMS]<!--{{!CSS3-TRANSFORMS}}--></a>
and related terms, particularly once those concepts stabilize following
changes proposed in the CSS WG meeting on the morning of 2014-01-28.
<p> Given the following definitions <span class=issue>which belong in <a
href="#ref-CSS3-TRANSFORMS">[CSS3-TRANSFORMS]<!--{{CSS3-TRANSFORMS}}--></a></span>:
<dl>
<dt><dfn id=d-preserving-child>3d-preserving child</dfn>
<dd> A child box B of a containing block C is a 3d-preserving child if it
has ‘<code class=css>transform-style: preserve-3d</code>’ and the
user-agent is not required to flatten it based on the <a
href="http://www.w3.org/TR/css3-transforms/#transform-style-property">requirements</a>
in <a
href="#ref-CSS3-TRANSFORMS">[CSS3-TRANSFORMS]<!--{{!CSS3-TRANSFORMS}}--></a>.
<dt><dfn id=non-3d-preserving-child>non-3d-preserving child</dfn>
<dd> A child C of a box P is a non-3d-preserving-child if it is not a <a
href="#d-preserving-child"><i>3d-preserving child</i></a>.
<dt><dfn id=d-preserving-descendant>3d-preserving descendant</dfn>
<dd> Box D is a 3d-preserving descendant of box A if A is an ancestor of
D, and D and all of the boxes (if any) in the containing block chain from
D to A are <a href="#d-preserving-child"><i>3d-preserving child</i></a>
boxes.
</dl>
<p>The scrollable overflow of a box is the union of the following things,
all adjusted for transforms <span class=issue>undefined concept!</span>
into the box's coordinate space:
<ul>
<li> for the box and all of its <a
href="#d-preserving-descendant"><i>3d-preserving descendant</i></a>
boxes:
<ul>
<li>the box's own padding edge (for the box itself) or border edge (for
<a href="#d-preserving-descendant"><i>3d-preserving descendant</i></a>
boxes)
<li>the bounds <span class=issue>undefined term!</span> of any text
directly in the box
<li><span class=issue>MORE HERE!</span>
</ul>
<li> for all the <a href="#non-3d-preserving-child"><i>non-3d-preserving
child</i></a> boxes of the box and its <a
href="#d-preserving-descendant"><i>3d-preserving descendant</i></a>
boxes, the scrollable overflow of the box
</ul>
<p class=issue> I wrote this definition off the top of my head, so it can't
possibly be right. It's missing tons of pieces!
<p class=issue> The handling of preserve-3d subtrees here is probably
wrong; the elements should probably count only towards the overflow of the
element that flattens them.
<p> The <dfn id=scrollable-overflow-region>scrollable overflow region</dfn>
is the non-rectangular region occupied by the <a
href="#scrollable-overflow0"><i>scrollable overflow</i></a>, and the <dfn
id=scrollable-overflow-rectangle>scrollable overflow rectangle</dfn> is
the minimal rectangle whose axis is aligned to the box's axes and contains
the <a href="#scrollable-overflow-region"><i>scrollable overflow
region</i></a>. Note that the <a
href="#scrollable-overflow-rectangle"><i>scrollable overflow
rectangle</i></a> is a rectangle in the box's coordinate system, but might
be non-rectangular in other coordinate systems due to transforms <a
href="#ref-CSS3-TRANSFORMS">[CSS3-TRANSFORMS]<!--{{CSS3-TRANSFORMS}}--></a>.
<h3 id=border-box-overflow><span class=secno>2.3. </span>Border box
overflow</h3>
<p class=issue> This concept has been proposed for some uses, such as for
determining what the ‘<code class=property>outline</code>’ property
goes around, and as the basis of a coordinate system for specifying clips
and masks, but it's not clear if it's needed.
<p> The <dfn id=border-box-overflow0>border-box overflow</dfn> of a box is
the union of the box's border edge and the border edges of the box's
descendants.
<p class=issue> If needed, define more formally, as for scrollable overflow
above. (Maybe even share the definitions in an appropriate way!)
<p> The <dfn id=border-box-overflow-region>border-box overflow region</dfn>
is the non-rectangular region occupied by the <a
href="#border-box-overflow0"><i>border-box overflow</i></a>, and the <dfn
id=border-box-overflow-rectangle>border-box overflow rectangle</dfn> is
the minimal rectangle whose axis is aligned to the box's axes and contains
the <a href="#border-box-overflow-region"><i>border-box overflow
region</i></a>. Note that the <a
href="#border-box-overflow-rectangle"><i>border-box overflow
rectangle</i></a> is a rectangle in the box's coordinate system, but might
be non-rectangular in other coordinate systems due to transforms <a
href="#ref-CSS3-TRANSFORMS">[CSS3-TRANSFORMS]<!--{{CSS3-TRANSFORMS}}--></a>.
<h2 id=overflow-properties><span class=secno>3. </span>Overflow properties</h2>
<p> The ‘<a href="#overflow-x"><code class=css>overflow-x</code></a>’
property specifies the handling of overflow in the horizontal direction
(i.e., overflow from the left and right sides of the box), and the ‘<a
href="#overflow-y"><code class=css>overflow-y</code></a>’ property
specifies the handling of overflow in the vertical direction (i.e.,
overflow from the top and bottom sides of the box)
<table class=propdef>
<tbody>
<tr>
<th>Name:
<td><dfn id=overflow-x>overflow-x</dfn>, <dfn
id=overflow-y>overflow-y</dfn>
<tr>
<th><a href="#values">Value</a>:
<td>visible | hidden | scroll | auto | paged-x | paged-y |
paged-x-controls | paged-y-controls | fragments
<tr>
<th>Initial:
<td>visible
<tr>
<th>Applies to:
<td>block containers <a href="#ref-CSS21">[CSS21]<!--{{!CSS21}}--></a>,
flex containers <a
href="#ref-CSS3-FLEXBOX">[CSS3-FLEXBOX]<!--{{!CSS3-FLEXBOX}}--></a>,
and grid containers <a
href="#ref-CSS-GRID-1">[CSS-GRID-1]<!--{{!CSS-GRID-1}}--></a>
<tr>
<th>Inherited:
<td>no
<tr>
<th>Percentages:
<td>N/A
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>see below
<tr>
<th>Animatable:
<td>no
<tr>
<th>Canonical order:
<td><abbr title="follows order of property value definition">per
grammar</abbr>
</table>
<p> The ‘<a href="#overflow0"><code class=property>overflow</code></a>’
property is a shorthand property that sets the specified values of both
‘<a href="#overflow-x"><code class=property>overflow-x</code></a>’ and
‘<a href="#overflow-y"><code class=property>overflow-y</code></a>’ to
the value specified for ‘<a href="#overflow0"><code
class=property>overflow</code></a>’.
<table class=propdef>
<tbody>
<tr>
<th>Name:
<td><dfn id=overflow0>overflow</dfn>
<tr>
<th><a href="#values">Value</a>:
<td>visible | hidden | scroll | auto | paged-x | paged-y |
paged-x-controls | paged-y-controls | fragments
<tr>
<th>Initial:
<td>see individual properties
<tr>
<th>Applies to:
<td>block containers <a href="#ref-CSS21">[CSS21]<!--{{!CSS21}}--></a>,
flex containers <a
href="#ref-CSS3-FLEXBOX">[CSS3-FLEXBOX]<!--{{!CSS3-FLEXBOX}}--></a>,
and grid containers <a
href="#ref-CSS-GRID-1">[CSS-GRID-1]<!--{{!CSS-GRID-1}}--></a>
<tr>
<th>Inherited:
<td>no
<tr>
<th>Percentages:
<td>N/A
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>see individual properties
<tr>
<th>Animatable:
<td>no
<tr>
<th>Canonical order:
<td><abbr title="follows order of property value definition">per
grammar</abbr>
</table>
<p>The values of these properties are:
<dl>
<dt><dfn id=visible>visible</dfn>
<dd> There is no special handling of overflow, that is, it may be rendered
outside the block container.
<dt><dfn id=hidden>hidden</dfn>
<dt><dfn id=scroll>scroll</dfn>
<dt><dfn id=auto>auto</dfn>
<dd> These values are collectively the <dfn id=scrolling-values>scrolling
values</dfn>; they are defined in the section on <a
href="#scrolling-overflow">scrolling and hidden overflow</a>.
<dt><dfn id=paged-x>paged-x</dfn>
<dt><dfn id=paged-y>paged-y</dfn>
<dt><dfn id=paged-x-controls>paged-x-controls</dfn>
<dt><dfn id=paged-y-controls>paged-y-controls</dfn>
<dt><dfn id=fragments>fragments</dfn>
<dd> These values are collectively the <dfn
id=fragmenting-values>fragmenting values</dfn>; they are defined in the
sections on <a href="#paginated-overflow">paginated overflow</a> and <a
href="#fragment-overflow">fragment overflow</a>.
</dl>
<div id=overflow-computed-values>
<p>The computed values of ‘<a href="#overflow-x"><code
class=property>overflow-x</code></a>’ and ‘<a
href="#overflow-y"><code class=property>overflow-y</code></a>’ are
determined from the cascaded values <a
href="#ref-CSS3CASCADE">[CSS3CASCADE]<!--{{!CSS3CASCADE}}--></a> based on
the following rules:
<ol>
<li> If one or both of the cascaded values are <a
href="#fragmenting-values"><i>fragmenting values</i></a>, then:
<ol>
<li> If one of the cascaded values is one of the <a
href="#fragmenting-values"><i>fragmenting values</i></a> and the other
is not, then the computed values are the same as the cascaded values.
<li> If both of the cascaded values are <a
href="#fragmenting-values"><i>fragmenting values</i></a>, then:
<ol>
<li> for horizontal writing mode <a
href="#ref-CSS-WRITING-MODES-3">[CSS-WRITING-MODES-3]<!--{{!CSS-WRITING-MODES-3}}--></a>,
the computed value for ‘<a href="#overflow-y"><code
class=css>overflow-y</code></a>’ is the cascaded value and the
computed value for ‘<a href="#overflow-x"><code
class=css>overflow-x</code></a>’ is ‘<a href="#hidden"><code
class=css>hidden</code></a>’, or
<li> for vertical writing mode <a
href="#ref-CSS-WRITING-MODES-3">[CSS-WRITING-MODES-3]<!--{{!CSS-WRITING-MODES-3}}--></a>,
the computed value for ‘<a href="#overflow-x"><code
class=css>overflow-x</code></a>’ is the cascaded value and the
computed value for ‘<a href="#overflow-y"><code
class=css>overflow-y</code></a>’ is ‘<a href="#hidden"><code
class=css>hidden</code></a>’.
</ol>
</ol>
<li> Otherwise, if one cascaded values is one of the <a
href="#scrolling-values"><i>scrolling values</i></a> and the other is
‘<a href="#visible"><code class=css>visible</code></a>’, then
computed values are the cascaded values with ‘<a href="#visible"><code
class=css>visible</code></a>’ changed to ‘<a href="#hidden"><code
class=css>hidden</code></a>’.
<li> Otherwise, the computed values are as specified.
</ol>
</div>
<p class=issue> Are all 4 of the ‘<code class=css>paged-*</code>’
values really needed?
<p> When the <a href="#fragmenting-values"><i>fragmenting values</i></a>
are used, the overflow from the fragments themselves treats the
fragmenting value as ‘<a href="#hidden"><code
class=css>hidden</code></a>’. <span class=issue>Is this the right
behavior?</span> <span class=issue>Give example.</span>
<p class=issue> <a
href="#ref-CSS3-MARQUEE">[CSS3-MARQUEE]<!--{{CSS3-MARQUEE}}--></a>
describes an ‘<code class=property>overflow-style</code>’ property,
but it has not picked up implementation experience that the working group
is aware of. Should this document treat ‘<code
class=property>overflow-style</code>’ as a defunct proposal, or should
this document describe the ‘<code
class=property>overflow-style</code>’ property and attempt to revive it,
despite that implementations have implemented ‘<a
href="#overflow-x"><code class=property>overflow-x</code></a>’ and ‘<a
href="#overflow-y"><code class=property>overflow-y</code></a>’ instead?
<p class=issue> There are <a
href="http://lists.w3.org/Archives/Public/www-style/2012May/1197.html">discussions</a>
about how overflow, overflow-style, overflow-x and overflow-y should work
and interact with each other. Until consensus on this topic is reached, it
is not completely clear which of these should be used for paged-x |
paged-y | paged-x-controls | paged-y-controls | fragments
<h2 id=scrolling-overflow><span class=secno>4. </span>Scrolling and hidden
overflow</h2>
<p class=issue> Move material from <a
href="#ref-CSS21">[CSS21]<!--{{CSS21}}--></a> and <a
href="#ref-CSS3BOX">[CSS3BOX]<!--{{CSS3BOX}}--></a> here.
<h2 id=paginated-overflow><span class=secno>5. </span>Paginated overflow</h2>
<p class=issue>overflow:paginate or overflow:pages (or paged-x, paged-y,
paged-x-controls, paged-y-controls as <a
href="#ref-CSS3GCPM">[CSS3GCPM]<!--{{CSS3GCPM}}--></a> has?)
<p class=issue>Ability to display N pages at once rather than just one page
at once?
<p class=issue> The current implementation of paginated overflow uses the
‘<a href="#overflow0"><code class=property>overflow</code></a>’/‘<a
href="#overflow-x"><code class=property>overflow-x</code></a>’/‘<a
href="#overflow-y"><code class=property>overflow-y</code></a>’
properties rather than the ‘<code
class=property>overflow-style</code>’ property as proposed in the <a
href="#ref-CSS3GCPM">[CSS3GCPM]<!--{{CSS3GCPM}}--></a> draft (which also
matches the <a
href="#ref-CSS3-MARQUEE">[CSS3-MARQUEE]<!--{{CSS3-MARQUEE}}--></a>
proposal). We should probably switch away from ‘<code
class=property>overflow-style</code>’, but that's not 100% clear.
<h2 id=fragment-overflow><span class=secno>6. </span>Fragment overflow</h2>
<p> This section introduces and defines the meaning of the new ‘<a
href="#fragments"><code class=css>fragments</code></a>’ value of the
‘<a href="#overflow0"><code class=property>overflow</code></a>’
property.
<p> When the computed value of ‘<a href="#overflow0"><code
class=property>overflow</code></a>’ for an element is ‘<a
href="#fragments"><code class=css>fragments</code></a>’, and
implementations would otherwise have created a box for the element, then
implementations must create a sequence of <dfn id=fragment-box>fragment
box</dfn>es for that element. (It is possible for an element with ‘<code
class=css>overflow: fragments</code>’ to generate only one <a
href="#fragment-box"><i>fragment box</i></a>. However, if an element's
computed ‘<a href="#overflow0"><code
class=property>overflow</code></a>’ is not ‘<a href="#fragments"><code
class=css>fragments</code></a>’, then its box is not a <a
href="#fragment-box"><i>fragment box</i></a>.) Every <a
href="#fragment-box"><i>fragment box</i></a> is a fragmentation container,
and any overflow that would cause that fragmentation container to fragment
causes another <a href="#fragment-box"><i>fragment box</i></a> created as
a next sibling of the previous one. <span class=issue>Or is it as though
it's a next sibling of the element? Need to figure out exactly how this
interacts with other box-level fixup.</span> Additionally, if the <a
href="#fragment-box"><i>fragment box</i></a> is also a multi-column box
(as defined in <a href="#ref-CSS3COL">[CSS3COL]<!--{{!CSS3COL}}--></a>
<span class=issue>though it defines <i>multi-column element</i></span>)
any content that would lead to the creation of <i>overflow columns</i> <a
href="#ref-CSS3COL">[CSS3COL]<!--{{!CSS3COL}}--></a> instead is flown into
an additional fragment box. However, fragment boxes may themselves be
broken (due to fragmentation in a fragmentation context outside of them,
such as pages, columns, or other fragment boxes); such breaking leads to
fragments of the same fragment box rather than multiple fragment boxes.
(This matters because fragment boxes may be styled by their index; such
breaking leads to multiple fragments of a fragment box with a single
index. This design choice is so that breaking a fragment box across pages
does not break the association of indices to particular pieces of
content.) <span class=issue>Should a forced break that breaks to an outer
fragmentation context cause a new fragment of a single fragment box or a
new fragment box?</span> <span class=issue>Should we find a term other
than <a href="#fragment-box"><i>fragment box</i></a> here to make this a
little less confusing?</span>
<p class=issue> What if we want to be able to style the pieces of an
element split within another type of fragmentation context? These rules
prevent ever using ‘<code class=css>::nth-fragment()</code>’ for that,
despite that the name seems the most logical name for such a feature.
<div class=example>
<table class=source-demo-pair>
<tbody>
<tr>
<td>
<pre><!DOCTYPE HTML>
<title>Breaking content into
equal-sized cards</title>
<style>
.in-cards {
overflow: fragments;
width: 13em;
height: 8em;
padding: 4px;
border: medium solid blue;
margin: 6px;
font: medium/1.3 Times New
Roman, Times, serif;
}
</style>
<div class="in-cards">
In this example, the text in the div
is broken into a series of cards.
These cards all have the same style.
The presence of enough content to
overflow one of the cards causes
another one to be created. The second
card is created just like it's the
next sibling of the first.
</div></pre>
<td>
<div class=in-cards-demo>In this example, the text in the<br>
div is broken into a series of<br>
cards. These cards all have the<br>
same style. The presence of<br>
enough content to overflow<br>
one of the cards causes another</div>
<div class=in-cards-demo>one to be created. The second<br>
card is created just like it's the<br>
next sibling of the first.</div>
</table>
</div>
<p class=issue> We should specify that ‘<code class=css>overflow:
fragments</code>’ does not apply to at least some table parts, and
perhaps other elements as well. We need to determine exactly which ones.
<p class=issue> This specification needs to say which type of fragmentation
context is created so that it's clear which values of the ‘<code
class=property>break</code>’ property cause breaks within this context.
We probably want ‘<code class=css>break: regions</code>’ to apply.
<p class=issue> This specification needs a processing model that will apply
in cases where the layout containing the fragments has characteristics
that use the intrinsic size of the fragments to change the amount of space
available for them, such as <a
href="#ref-CSS-GRID-1">[CSS-GRID-1]<!--{{CSS-GRID-1}}--></a>. There has
already been some work on such a processing model in <a
href="#ref-CSS3-REGIONS">[CSS3-REGIONS]<!--{{CSS3-REGIONS}}--></a>, and
the work done on a model there, and the editors of that specification,
should inform what happens in this specification.
<h3 id=fragment-styling><span class=secno>6.1. </span>Fragment styling</h3>
<h4 id=fragment-pseudo-element><span class=secno>6.1.1. </span>The
::nth-fragment() pseudo-element</h4>
<p> The ::nth-fragment() pseudo-element is a pseudo-element that describes
some of the <a href="#fragment-box"><i>fragment box</i></a>es generated by
an element. The argument to the pseudo-element takes the same syntax as
the argument to the :nth-child() pseudo-class defined in <a
href="#ref-SELECT">[SELECT]<!--{{!SELECT}}--></a>, and has the same
meaning except that the number is relative to <a
href="#fragment-box"><i>fragment box</i></a>es generated by the element
instead of siblings of the element.
<p class=note> Selectors that allow addressing fragments by counting from
the end rather than the start are intentionally not provided. Such
selectors would interfere with determining the number of fragments.
<p class=issue> Depending on future discussions, this ‘<code
class=css>::nth-fragment(<var>an+b</var>)</code>’ syntax may be replaced
with the new ‘<code class=css>::fragment:nth(<var>an+b</var>)</code>’
syntax.
<h4 id=style-of-fragments><span class=secno>6.1.2. </span>Styling of
fragments</h4>
<p class=issue> Should this apply to fragment overflow only, or also to
paginated overflow? (If it applies, then stricter property restrictions
would be needed for paginated overflow.)
<p> In the absence of rules with ‘<code
class=css>::nth-fragment()</code>’ pseudo-elements, the computed style
for each <a href="#fragment-box"><i>fragment box</i></a> is the computed
style for the element for which the <a href="#fragment-box"><i>fragment
box</i></a> was created. However, the style for a <a
href="#fragment-box"><i>fragment box</i></a> is also influenced by rules
whose selector's <i>subject</i> <a
href="#ref-SELECT">[SELECT]<!--{{!SELECT}}--></a> has an ‘<code
class=css>::nth-fragment()</code>’ pseudo-element, if the 1-based number
of the <a href="#fragment-box"><i>fragment box</i></a> matches that
‘<code class=css>::nth-fragment()</code>’ pseudo-element and the
selector (excluding the ‘<code class=css>::nth-fragment()</code>’
pseudo-element) matches the element generating the fragments.
<p> When determining the style of the <a href="#fragment-box"><i>fragment
box</i></a>, these rules that match the fragment pseudo-element cascade
together with the rules that match the element, with the fragment
pseudo-element adding the specificity of a pseudo-class to the specificity
calculation. <span class=issue>Does this need to be specified in the
cascading module as well?</span>
<div class=example>
<table class=source-demo-pair>
<tbody>
<tr>
<td>
<pre><!DOCTYPE HTML>
<style>
.bouncy-columns {
overflow: fragments;
width: 6em;
height: 10em;
float: left;
margin: 1em;
font: medium/1.25 Times New
Roman, Times, serif;
}
.bouncy-columns::nth-fragment(1) {
background: aqua; color: black;