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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="../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;
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color: black;
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max-width: 50em;
padding: 2em 1em 2em 70px;
}
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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>
<meta content="Bikeshed 1.0.0" name="generator">
<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>
<style>/* http://prismjs.com/download.html?themes=prism&languages=clike */
/**
* prism.js default theme for JavaScript, CSS and HTML
* Based on dabblet (http://dabblet.com)
* @author Lea Verou
*/
code[class*="language-"],
pre[class*="language-"] {
color: black;
text-shadow: 0 1px white;
font-family: Consolas, Monaco, 'Andale Mono', monospace;
direction: ltr;
text-align: left;
white-space: pre;
word-spacing: normal;
word-break: normal;
line-height: 1.5;
-moz-tab-size: 4;
-o-tab-size: 4;
tab-size: 4;
-webkit-hyphens: none;
-moz-hyphens: none;
-ms-hyphens: none;
hyphens: none;
}
pre[class*="language-"]::-moz-selection, pre[class*="language-"] ::-moz-selection,
code[class*="language-"]::-moz-selection, code[class*="language-"] ::-moz-selection {
text-shadow: none;
background: #b3d4fc;
}
pre[class*="language-"]::selection, pre[class*="language-"] ::selection,
code[class*="language-"]::selection, code[class*="language-"] ::selection {
text-shadow: none;
background: #b3d4fc;
}
@media print {
code[class*="language-"],
pre[class*="language-"] {
text-shadow: none;
}
}
/* Code blocks */
pre[class*="language-"] {
padding: 1em;
margin: .5em 0;
overflow: auto;
}
:not(pre) > code[class*="language-"],
pre[class*="language-"] {
background: #f5f2f0;
}
/* Inline code */
:not(pre) > code[class*="language-"] {
padding: .1em;
border-radius: .3em;
}
.token.comment,
.token.prolog,
.token.doctype,
.token.cdata {
color: slategray;
}
.token.punctuation {
color: #999;
}
.namespace {
opacity: .7;
}
.token.property,
.token.tag,
.token.boolean,
.token.number,
.token.constant,
.token.symbol,
.token.deleted {
color: #905;
}
.token.selector,
.token.attr-name,
.token.string,
.token.char,
.token.builtin,
.token.inserted {
color: #690;
}
.token.operator,
.token.entity,
.token.url,
.language-css .token.string,
.style .token.string {
color: #a67f59;
background: hsla(0, 0%, 100%, .5);
}
.token.atrule,
.token.attr-value,
.token.keyword {
color: #07a;
}
.token.function {
color: #DD4A68;
}
.token.regex,
.token.important,
.token.variable {
color: #e90;
}
.token.important {
font-weight: bold;
}
.token.entity {
cursor: help;
}
</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 Overflow Module Level 3</h1>
<h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="content">Editor’s Draft,
<time class="dt-updated" datetime="2015-04-30">30 April 2015</time></span></h2>
<div data-fill-with="spec-metadata">
<dl>
<dt>This version:
<dd><a class="u-url" href="http://dev.w3.org/csswg/css-overflow/">http://dev.w3.org/csswg/css-overflow/</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>Previous Versions:
<dd><a href="http://www.w3.org/TR/2013/WD-css-overflow-3-20130418/" rel="previous">http://www.w3.org/TR/2013/WD-css-overflow-3-20130418/</a>
<dt>Feedback:
<dd><span><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>)</span>
<dt>Issue Tracking:
<dd><a href="#issues-index">Inline In Spec</a>
<dt class="editor">Editors:
<dd class="editor p-author h-card vcard"><a class="p-name fn u-url url" href="http://dbaron.org/">L. David Baron</a> (<span class="p-org org">Mozilla</span>)
<dd class="editor p-author h-card vcard"><a class="p-name fn u-url url" href="http://florian.rivoal.net">Florian Rivoal</a> (<span class="p-org org">Invited Expert</span>) <a class="u-email email" href="mailto:florian@rivoal.net">florian@rivoal.net</a>
<dt>Change Log:
<dd><span><a href="https://hg.csswg.org/drafts/log/tip/css-overflow/Overview.bs">from 27 January 2015 to the present</a></span>
<dd><span><a href="https://hg.csswg.org/drafts/log/tip/css-overflow/Overview.src.html">from 28 March 2013 to 27 January 2015</a></span>
<dd><span><a href="https://hg.csswg.org/drafts/log/tip/css3-overflow/Overview.src.html">from 31 July 2012 to 27 March 2013</a></span>
</dl>
</div>
<div data-fill-with="warning"></div>
<p class="copyright" data-fill-with="copyright"><a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a> © 2015 <a href="http://www.w3.org/"><abbr title="World Wide Web Consortium">W3C</abbr></a><sup>®</sup> (<a href="http://www.csail.mit.edu/"><abbr title="Massachusetts Institute of Technology">MIT</abbr></a>, <a href="http://www.ercim.eu/"><abbr title="European Research Consortium for Informatics and Mathematics">ERCIM</abbr></a>, <a href="http://www.keio.ac.jp/">Keio</a>, <a href="http://ev.buaa.edu.cn/">Beihang</a>). W3C <a href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>, <a href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a> and <a href="http://www.w3.org/Consortium/Legal/copyright-documents">document use</a> rules apply.
</p>
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc no-ref heading settled" id="abstract"><span class="content">Abstract</span></h2>
<div class="p-summary" data-fill-with="abstract">
<p>This module contains the features of CSS relating to 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.</p>
<a href="http://www.w3.org/TR/CSS/">CSS</a> is a language for describing the rendering of structured documents
(such as HTML and XML)
on screen, on paper, in speech, etc.</div>
<h2 class="no-num no-toc no-ref heading settled" id="status"><span class="content">Status of this document</span></h2>
<div data-fill-with="status">
<p>
This is a public copy of the editors’ draft.
It is provided for discussion only and may change at any moment.
Its publication here does not imply endorsement of its contents by W3C.
Don’t cite this document other than as work in progress.
</p>
<p>
The (<a href="http://lists.w3.org/Archives/Public/www-style/">archived</a>) public mailing list
<a href="mailto:www-style@w3.org?Subject=%5Bcss-overflow%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” in the subject,
preferably like this:
“[css-overflow] <em>…summary of comment…</em>”
</p>
<p>
This document was produced by the <a href="http://www.w3.org/Style/CSS/members">CSS Working Group</a>
(part of the <a href="http://www.w3.org/Style/">Style Activity</a>).
</p>
<p>
This document was produced by a group operating under
the <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/">5 February 2004 W3C Patent Policy</a>.
W3C maintains a <a href="http://www.w3.org/2004/01/pp-impl/32061/status" rel="disclosure">public list of any patent disclosures</a>
made in connection with the deliverables of the group;
that page also includes instructions for disclosing a patent.
An individual who has actual knowledge of a patent which the individual believes contains <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">Essential Claim(s)</a>
must disclose the information in accordance with <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">section 6 of the W3C Patent Policy</a>.
</p>
<p>
This document is governed by the <a href="http://www.w3.org/2014/Process-20140801/" id="w3c_process_revision">1 August 2014 W3C Process Document</a>.
</p>
<p>
</p></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="#intro"><span class="secno">1</span> <span class="content">
Introduction</span></a>
<li><a href="#overflow-concepts"><span class="secno">2</span> <span class="content">Types of overflow</span></a>
<ul class="toc">
<li><a href="#ink-overflow"><span class="secno">2.1</span> <span class="content">Ink overflow</span></a>
<li><a href="#scrollable-overflow"><span class="secno">2.2</span> <span class="content">Scrollable overflow</span></a>
<li><a href="#border-box-overflow"><span class="secno">2.3</span> <span class="content">Border box overflow</span></a>
</ul>
<li><a href="#overflow-properties"><span class="secno">3</span> <span class="content">Overflow properties</span></a>
<li><a href="#fragmentation"><span class="secno">4</span> <span class="content">Fragmentation of overflow</span></a>
<li><a href="#paginated-overflow"><span class="secno">5</span> <span class="content">Paginated overflow</span></a>
<li><a href="#fragment-overflow"><span class="secno">6</span> <span class="content">Fragment overflow</span></a>
<ul class="toc">
<li><a href="#fragment-styling"><span class="secno">6.1</span> <span class="content">Fragment styling</span></a>
<ul class="toc">
<li><a href="#fragment-pseudo-element"><span class="secno">6.1.1</span> <span class="content">The ::nth-fragment() pseudo-element</span></a>
<li><a href="#style-of-fragments"><span class="secno">6.1.2</span> <span class="content">Styling of fragments</span></a>
<li><a href="#style-in-fragments"><span class="secno">6.1.3</span> <span class="content">Styling inside fragments</span></a>
</ul>
<li><a href="#max-lines"><span class="secno">6.2</span> <span class="content">The <span class="property">max-lines</span> property</span></a>
</ul>
<li><a href="#static-media"><span class="secno">7</span> <span class="content">Overflow in static media</span></a>
<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="#index"><span class="secno"></span> <span class="content">Index</span></a>
<ul class="toc">
<li><a href="#index-defined-here"><span class="secno"></span> <span class="content">Terms defined by this specification</span></a>
<li><a href="#index-defined-elsewhere"><span class="secno"></span> <span class="content">Terms defined by reference</span></a>
</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="#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>
<p>
</p>
<h2 class="heading settled" data-level="1" id="intro"><span class="secno">1. </span><span class="content">
Introduction</span><a class="self-link" href="#intro"></a></h2>
<p>
In CSS Level 1 <a data-link-type="bi
E8EB
blio" href="#biblio-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>
<p>
CSS Level 2 <a data-link-type="biblio" href="#biblio-css21">[CSS21]</a> introduced the <a class="property" data-link-type="propdesc" href="#propdef-overflow">overflow</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>
<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>
<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>
<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>
<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 data-link-type="biblio" href="#biblio-css3-break">[CSS3-BREAK]</a>.
</p>
<h2 class="heading settled" data-level="2" id="overflow-concepts"><span class="secno">2. </span><span class="content">Types of overflow</span><a class="self-link" href="#overflow-concepts"></a></h2>
<p>
CSS uses the term <dfn data-dfn-type="dfn" data-noexport="" id="overflow">overflow<a class="self-link" href="#overflow"></a></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" id="issue-18c1c008"><a class="self-link" href="#issue-18c1c008"></a>undefined term?</span>
includes the box.
</p>
<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 <a class="css" data-link-type="propdesc" href="http://dev.w3.org/csswg/css-transforms-1/#propdef-transform-style">transform-style: preserve-3d</a> <a data-link-type="biblio" href="#biblio-css3-transforms">[CSS3-TRANSFORMS]</a> is used on
some of the children, their descendants with
<a class="css" data-link-type="propdesc" href="http://dev.w3.org/csswg/css-transforms-1/#propdef-transform-style">transform-style: preserve-3d</a> must also be examined.
</p>
<h3 class="heading settled" data-level="2.1" id="ink-overflow"><span class="secno">2.1. </span><span class="content">Ink overflow</span><a class="self-link" href="#ink-overflow"></a></h3>
<p>
The <dfn data-dfn-type="dfn" data-noexport="" id="ink-overflow0">ink overflow<a class="self-link" href="#ink-overflow0"></a></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>
<p>
Since some effects in CSS (for example, the blurs in
<a class="property" data-link-type="propdesc" href="http://dev.w3.org/csswg/css-text-decor-3/#propdef-text-shadow">text-shadow</a> <a data-link-type="biblio" href="#biblio-css3text">[CSS3TEXT]</a> and <a class="property" data-link-type="propdesc" href="http://dev.w3.org/csswg/css-backgrounds-3/#box-shadow">box-shadow</a> <a data-link-type="biblio" href="#biblio-css3bg">[CSS3BG]</a>)
do not define what visual extent they cover, the extent
of the <a data-link-type="dfn" href="#ink-overflow0">ink overflow</a> is undefined.
</p>
<p class="issue" id="issue-1baddb1e"><a class="self-link" href="#issue-1baddb1e"></a>
Should we try to define it at all and just leave pieces undefined?
</p>
<p>
The <dfn data-dfn-type="dfn" data-noexport="" id="ink-overflow-region">ink overflow region<a class="self-link" href="#ink-overflow-region"></a></dfn> is the non-rectangular region
occupied by the <a data-link-type="dfn" href="#ink-overflow0">ink overflow</a>, and the
<dfn data-dfn-type="dfn" data-noexport="" id="ink-overflow-rectangle">ink overflow rectangle<a class="self-link" href="#ink-overflow-rectangle"></a></dfn> is
the minimal rectangle whose axis is aligned to the box’s axes
and contains the <a data-link-type="dfn" href="#ink-overflow-region">ink overflow region</a>.
Note that the <a data-link-type="dfn" href="#ink-overflow-rectangle">ink overflow rectangle</a> is a rectangle
in the box’s coordinate system, but might be non-rectangular
in other coordinate systems due to transforms <a data-link-type="biblio" href="#biblio-css3-transforms">[CSS3-TRANSFORMS]</a>.
</p>
<h3 class="heading settled" data-level="2.2" id="scrollable-overflow"><span class="secno">2.2. </span><span class="content">Scrollable overflow</span><a class="self-link" href="#scrollable-overflow"></a></h3>
<p>
The <dfn data-dfn-type="dfn" data-noexport="" id="scrollable-overflow0">scrollable overflow<a class="self-link" href="#scrollable-overflow0"></a></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>
<p class="issue" id="issue-6b232bb5"><a class="self-link" href="#issue-6b232bb5"></a>
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 data-link-type="biblio" href="#biblio-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>
<p>
Given the following definitions
<span class="issue" id="issue-101a26b2"><a class="self-link" href="#issue-101a26b2"></a>which belong in <a data-link-type="biblio" href="#biblio-css3-transforms">[CSS3-TRANSFORMS]</a></span>:
</p>
<dl>
<dt><dfn data-dfn-type="dfn" data-noexport="" id="3d_preserving-child">3d-preserving child<a class="self-link" href="#3d_preserving-child"></a></dfn>
<dd>
A child box B of a containing block C is a 3d-preserving
child if it has <a class="css" data-link-type="propdesc" href="http://dev.w3.org/csswg/css-transforms-1/#propdef-transform-style">transform-style: preserve-3d</a>
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 data-link-type="biblio" href="#biblio-css3-transforms">[CSS3-TRANSFORMS]</a>.
<dt><dfn data-dfn-type="dfn" data-noexport="" id="non_3d_preserving-child">non-3d-preserving child<a class="self-link" href="#non_3d_preserving-child"></a></dfn>
<dd>
A child C of a box P is a non-3d-preserving-child if
it is not a <a data-link-type="dfn" href="#3d_preserving-child">3d-preserving child</a>.
<dt><dfn data-dfn-type="dfn" data-noexport="" id="3d_preserving-descendant">3d-preserving descendant<a class="self-link" href="#3d_preserving-descendant"></a></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 data-link-type="dfn" href="#3d_preserving-child">3d-preserving child</a> boxes.
</dl>
<p>The scrollable overflow of a box is the union of the following things,
all adjusted for transforms <span class="issue" id="issue-1b139c15"><a class="self-link" href="#issue-1b139c15"></a>undefined concept!</span> into the box’s coordinate space:</p>
<ul>
<li>
for the box and all of its <a data-link-type="dfn" href="#3d_preserving-descendant">3d-preserving descendant</a> boxes:
<ul>
<li>the box’s own padding edge (for the box itself) or border edge (for <a data-link-type="dfn" href="#3d_preserving-descendant">3d-preserving descendant</a> boxes)
<li>the bounds <span class="issue" id="issue-2d1dc4f9"><a class="self-link" href="#issue-2d1dc4f9"></a>undefined term!</span> of any text directly in the box
<li><span class="issue" id="issue-75780f3f"><a class="self-link" href="#issue-75780f3f"></a>MORE HERE!</span>
</ul>
<li>
for all the <a data-link-type="dfn" href="#non_3d_preserving-child">non-3d-preserving child</a> boxes of the
box and its <a data-link-type="dfn" href="#3d_preserving-descendant">3d-preserving desc
22D5
endant</a> boxes,
the scrollable overflow of the box
</ul>
<p class="issue" id="issue-e889eac0"><a class="self-link" href="#issue-e889eac0"></a>
I wrote this definition off the top of my head,
so it can’t possibly be right.
It’s missing tons of pieces!
</p>
<p class="issue" id="issue-521d48c7"><a class="self-link" href="#issue-521d48c7"></a>
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>
<p>
The <dfn data-dfn-type="dfn" data-noexport="" id="scrollable-overflow-region">scrollable overflow region<a class="self-link" href="#scrollable-overflow-region"></a></dfn> is the non-rectangular region
occupied by the <a data-link-type="dfn" href="#scrollable-overflow0">scrollable overflow</a>, and the
<dfn data-dfn-type="dfn" data-noexport="" id="scrollable-overflow-rectangle">scrollable overflow rectangle<a class="self-link" href="#scrollable-overflow-rectangle"></a></dfn> is
the minimal rectangle whose axis is aligned to the box’s axes
and contains the <a data-link-type="dfn" href="#scrollable-overflow-region">scrollable overflow region</a>.
Note that the <a data-link-type="dfn" href="#scrollable-overflow-rectangle">scrollable overflow rectangle</a> is a rectangle
in the box’s coordinate system, but might be non-rectangular
in other coordinate systems due to transforms <a data-link-type="biblio" href="#biblio-css3-transforms">[CSS3-TRANSFORMS]</a>.
</p>
<h3 class="heading settled" data-level="2.3" id="border-box-overflow"><span class="secno">2.3. </span><span class="content">Border box overflow</span><a class="self-link" href="#border-box-overflow"></a></h3>
<p class="issue" id="issue-3930f393"><a class="self-link" href="#issue-3930f393"></a>
This concept has been proposed for some uses, such as for
determining what the <a class="property" data-link-type="propdesc" href="http://dev.w3.org/csswg/css-ui-3/#propdef-outline">outline</a> 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>
<p>
The <dfn data-dfn-type="dfn" data-noexport="" id="border_box-overflow">border-box overflow<a class="self-link" href="#border_box-overflow"></a></dfn> of a box is the
union of the box’s border edge and the border edges of
the box’s descendants.</p>
<p></p>
<p class="issue" id="issue-42ea3c29"><a class="self-link" href="#issue-42ea3c29"></a>
If needed, define more formally, as for scrollable overflow above.
(Maybe even share the definitions in an appropriate way!)
</p>
<p>
The <dfn data-dfn-type="dfn" data-noexport="" id="border_box-overflow-region">border-box overflow region<a class="self-link" href="#border_box-overflow-region"></a></dfn> is the non-rectangular region
occupied by the <a data-link-type="dfn" href="#border_box-overflow">border-box overflow</a>, and the
<dfn data-dfn-type="dfn" data-noexport="" id="border_box-overflow-rectangle">border-box overflow rectangle<a class="self-link" href="#border_box-overflow-rectangle"></a></dfn> is
the minimal rectangle whose axis is aligned to the box’s axes
and contains the <a data-link-type="dfn" href="#border_box-overflow-region">border-box overflow region</a>.
Note that the <a data-link-type="dfn" href="#border_box-overflow-rectangle">border-box overflow rectangle</a> is a rectangle
in the box’s coordinate system, but might be non-rectangular
in other coordinate systems due to transforms <a data-link-type="biblio" href="#biblio-css3-transforms">[CSS3-TRANSFORMS]</a>.
</p>
<h2 class="heading settled" data-level="3" id="overflow-properties"><span class="secno">3. </span><span class="content">Overflow properties</span><a class="self-link" href="#overflow-properties"></a></h2>
<p>
The <a class="property" data-link-type="propdesc" href="#propdef-overflow-x">overflow-x</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 class="property" data-link-type="propdesc" href="#propdef-overflow-y">overflow-y</a> property specifies the handling
of overflow in the vertical direction
(i.e., overflow from the top and bottom sides of the box)
</p>
<table class="definition propdef" data-link-for-hint="overflow-x">
<tbody>
<tr>
<th>Name:
<td><dfn class="css" data-dfn-type="property" data-export="" id="propdef-overflow-x">overflow-x<a class="self-link" href="#propdef-overflow-x"></a></dfn>, <dfn class="css" data-dfn-type="property" data-export="" id="propdef-overflow-y">overflow-y<a class="self-link" href="#propdef-overflow-y"></a></dfn>
<tr class="value">
<th>Value:
<td class="prod"><a class="css" data-link-type="maybe" href="#valdef-overflow-visible">visible</a> <a data-link-type="grammar" href="http://dev.w3.org/csswg/css-values-3/#comb-one">|</a> <a class="css" data-link-type="maybe" href="#valdef-overflow-hidden">hidden</a> <a data-link-type="grammar" href="http://dev.w3.org/csswg/css-values-3/#comb-one">|</a> <a class="css" data-link-type="maybe" href="#valdef-overflow-clip">clip</a> <a data-link-type="grammar" href="http://dev.w3.org/csswg/css-values-3/#comb-one">|</a> <a class="css" data-link-type="maybe" href="#valdef-overflow-scroll">scroll</a> <a data-link-type="grammar" href="http://dev.w3.org/csswg/css-values-3/#comb-one">|</a> <a class="css" data-link-type="maybe" href="#valdef-overflow-auto">auto</a>
<tr>
<th>Initial:
<td><a class="css" data-link-type="maybe" href="#valdef-overflow-visible">visible</a>
<tr>
<th>Applies to:
<td>block containers <a data-link-type="biblio" href="#biblio-css21">[CSS21]</a>, flex containers <a data-link-type="biblio" href="#biblio-css3-flexbox">[CSS3-FLEXBOX]</a>, and grid containers <a data-link-type="biblio" href="#biblio-css3-grid-layout">[CSS3-GRID-LAYOUT]</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 class="property" data-link-type="propdesc" href="#propdef-overflow">overflow</a> property is a shorthand property
that sets the specified values of both <a class="property" data-link-type="propdesc" href="#propdef-overflow-x">overflow-x</a> and <a class="property" data-link-type="propdesc" href="#propdef-overflow-y">overflow-y</a>
to the value specified for <a class="property" data-link-type="propdesc" href="#propdef-overflow">overflow</a>.
</p>
<table class="definition propdef" data-link-for-hint="overflow">
<tbody>
<tr>
<th>Name:
<td><dfn class="css" data-dfn-type="property" data-export="" id="propdef-overflow">overflow<a class="self-link" href="#propdef-overflow"></a></dfn>
<tr class="value">
<th>Value:
<td class="prod"><a class="css" data-link-type="maybe" href="#valdef-overflow-visible">visible</a> <a data-link-type="grammar" href="http://dev.w3.org/csswg/css-values-3/#comb-one">|</a> <a class="css" data-link-type="maybe" href="#valdef-overflow-hidden">hidden</a> <a data-link-type="grammar" href="http://dev.w3.org/csswg/css-values-3/#comb-one">|</a> <a class="css" data-link-type="maybe" href="#valdef-overflow-clip">clip</a> <a data-link-type="grammar" href="http://dev.w3.org/csswg/css-values-3/#comb-one">|</a> <a class="css" data-link-type="maybe" href="#valdef-overflow-scroll">scroll</a> <a data-link-type="grammar" href="http://dev.w3.org/csswg/css-values-3/#comb-one">|</a> <a class="css" data-link-type="maybe" href="#valdef-overflow-auto">auto</a>
<tr>
<th>Initial:
<td>see individual properties
<tr>
<th>Applies to:
<td>block containers <a data-link-type="biblio" href="#biblio-css21">[CSS21]</a>, flex containers <a data-link-type="bibli
6855
o" href="#biblio-css3-flexbox">[CSS3-FLEXBOX]</a>, and grid containers <a data-link-type="biblio" href="#biblio-css3-grid-layout">[CSS3-GRID-LAYOUT]</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>
<div id="overflow-computed-values">
<p>The computed values of <a class="property" data-link-type="propdesc" href="#propdef-overflow-x">overflow-x</a> and <a class="property" data-link-type="propdesc" href="#propdef-overflow-y">overflow-y</a>
are determined from the cascaded values <a data-link-type="biblio" href="#biblio-css3cascade">[CSS3CASCADE]</a>
based on the following rules:</p>
<ol>
<li>
If one cascaded values is <a class="css" data-link-type="maybe" href="#valdef-overflow-visible">visible</a>
and the other is not,
then computed values are the cascaded values
with <a class="css" data-link-type="maybe" href="#valdef-overflow-visible">visible</a> changed to <a class="css" data-link-type="maybe" href="#valdef-overflow-auto">auto</a>.
<li>
Otherwise, the computed values are as specified.
</ol>
</div>
<p>The values of these properties are:</p>
<dl>
<dt><dfn class="css" data-dfn-for="overflow, overflow-x, overflow-y" data-dfn-type="value" data-export="" id="valdef-overflow-visible">visible<a class="self-link" href="#valdef-overflow-visible"></a></dfn>
<dd>
There is no special handling of overflow, that is, it
may be rendered outside the block container.
<dt><dfn class="css" data-dfn-for="overflow, overflow-x, overflow-y" data-dfn-type="value" data-export="" id="valdef-overflow-hidden">hidden<a class="self-link" href="#valdef-overflow-hidden"></a></dfn>
<dd>This value indicates that
the content is clipped and that no scrolling user interface should be provided by the UA
to view the content outside the clipping region.
However, the content may still be scrolled programatically,
for example using the mechanisms defined in <a data-link-type="biblio" href="#biblio-cssom-view">[CSSOM-VIEW]</a>.
<dt><dfn class="css" data-dfn-for="overflow, overflow-x, overflow-y" data-dfn-type="value" data-export="" id="valdef-overflow-clip">clip<a class="self-link" href="#valdef-overflow-clip"></a></dfn>
<dd>Like <a class="css" data-link-type="maybe" href="#valdef-overflow-hidden">hidden</a>,
this value indicates that
the content is clipped
and that no scrolling user interface should be provided by the UA
to view the content outside the clipping region.
In addition, unlike <a class="css" data-link-type="propdesc" href="#propdef-overflow">overflow: hidden</a>
which still allows programmatic scrolling,
<a class="css" data-link-type="propdesc" href="#propdef-overflow">overflow: clip</a> forbids scrolling entirely,
through any mechanism.
<p class="issue" id="issue-a9ea8890"><a class="self-link" href="#issue-a9ea8890"></a>Mozilla implements -moz-hidden-unscrollable,
which is similar to <a class="css" data-link-type="maybe" href="#valdef-overflow-clip">clip</a>,
except that it does not cause the element to establish a BFC.
Should we match that?</p>
<dt><dfn class="css" data-dfn-for="overflow, overflow-x, overflow-y" data-dfn-type="value" data-export="" id="valdef-overflow-scroll">scroll<a class="self-link" href="#valdef-overflow-scroll"></a></dfn>
<dd>This value indicates that the content is clipped
and that if the user agent uses a scrolling mechanism
that is visible on the screen (such as a scroll bar or a panner),
that mechanism should be displayed for a box
whether or not any of its content is clipped.
This avoids any problem with scrollbars appearing
and disappearing in a dynamic environment.
When this value is specified and the target medium is <a class="css" data-link-type="maybe" href="http://dev.w3.org/csswg/mediaqueries-4/#valdef-media-print">print</a>,
overflowing content may be printed.
<dt><dfn class="css" data-dfn-for="overflow, overflow-x, overflow-y" data-dfn-type="value" data-export="" id="valdef-overflow-auto">auto<a class="self-link" href="#valdef-overflow-auto"></a></dfn>
<dd>The behavior of the <a class="css" data-link-type="maybe" href="#valdef-overflow-auto">auto</a> value is user agent-dependent,
but should cause a scrolling mechanism to be provided for overflowing boxes.
</dl>
<p>Even if <a class="property" data-link-type="propdesc" href="#propdef-overflow">overflow</a> is set to <a class="css" data-link-type="maybe" href="#valdef-overflow-visible">visible</a>,
content may be clipped to a UA’s document window by the native operating environment.</p>
<p>If the computed value of <a class="property" data-link-type="propdesc" href="#propdef-overflow">overflow</a> is not <a class="css" data-link-type="maybe" href="#valdef-overflow-visible">visible</a>,
the element creates a block formatting context.</p>
<p>UAs must apply the <a class="property" data-link-type="propdesc" href="#propdef-overflow">overflow</a> property
set on the root element to the viewport.
HTML UAs must instead apply the ‘overflow’ property
from the <code><a data-link-type="element" href="https://html.spec.whatwg.org/#the-body-element">body</a></code> element to the viewport
if the value on the root element is <a class="css" data-link-type="maybe" href="#valdef-overflow-visible">visible</a>.
The <a class="css" data-link-type="maybe" href="#valdef-overflow-visible">visible</a> value when used for the viewport
must be interpreted as <a class="css" data-link-type="maybe" href="#valdef-overflow-auto">auto</a>.
The element from which the value is propagated
must have a used value for <a class="property" data-link-type="propdesc" href="#propdef-overflow">overflow</a> of <a class="css" data-link-type="maybe" href="#valdef-overflow-visible">visible</a>.</p>
<p>In the case of a scrollbar being placed on an edge of the element’s box,
it should be inserted between the inner border edge
and the outer padding edge.
Any space taken up by the scrollbars should be
taken out of (subtracted from the dimensions of)
the containing block formed by the element with the scrollbars.</p>
<p class="issue" id="issue-402eb70c"><a class="self-link" href="#issue-402eb70c"></a>import examples from <a data-link-type="biblio" href="#biblio-css3-box">[CSS3-BOX]</a>.</p>
<p class="issue" id="issue-c318b1c1"><a class="self-link" href="#issue-c318b1c1"></a>
Explain which directions allow scrolling and which don’t,
as a function of <a class="property" data-link-type="propdesc" href="http://dev.w3.org/csswg/css-writing-modes-3/#propdef-direction">direction</a>
(including propagation of <a class="property" data-link-type="propdesc" href="http://dev.w3.org/csswg/css-writing-modes-3/#propdef-direction">direction</a> to the ICB).
</p>
<p class="issue" id="issue-52e2a181"><a class="self-link" href="#issue-52e2a181"></a>
<a data-link-type="biblio" href="#biblio-css3-marquee">[CSS3-MARQUEE]</a> describes an <a class="property" data-link-type="propdesc" href="http://www.w3.org/TR/2008/CR-css3-marquee-20081205/#the-overflow-style">overflow-style</a> property,
but it has not picked up implementation experience
that the working group is aware of.
Should this document treat <a class="property" data-link-type="propdesc" href="http://www.w3.org/TR/2008/CR-css3-marquee-20081205/#the-overflow-style">overflow-style</a> as a defunct proposal,
or should this document describe the <a class="property" data-link-type="propdesc" href="http://www.w3.org/TR/2008/CR-css3-marquee-20081205/#the-overflow-style">overflow-style</a> property
and attempt to revive it,
despite that implementations have implemented
<a class="property" data-link-type="propdesc" href="#propdef-overflow-x">overflow-x</a> and <a class="property" data-link-type="propdesc" href="#propdef-overflow-y">overflow-y</a> instead?
</p>
<h2 class="heading settled" data-level="4" id="fragmentation"><span class="secno">4. </span><span class="content">Fragmentation of overflow</span><a class="self-link" href="#fragmentation"></a></h2>
<p>The <a class="property" data-link-type="propdesc" href="#propdef-continue">continue</a> property gives authors the ability
to request that content that does not fit inside an element
be fragmented (in the sense of <a data-link-type="biblio" href="#biblio-css3-break">[CSS3-BREAK]</a>),
and provides alternatives
for where the remaining content should continue.</p>
<p>Notably, this property explains traditional pagination,
and extends it further.</p>