Overview.bs

<pre class="metadata">
Title: CSS Overflow Module Level 3
Status: ED
Work Status: Revising
ED: https://drafts.csswg.org/css-overflow-3/
Shortname: css-overflow
Group: csswg
Level: 3
TR: https://www.w3.org/TR/css-overflow-3/
Previous version: https://www.w3.org/TR/2016/WD-css-overflow-3-20160531/
Previous version: https://www.w3.org/TR/2013/WD-css-overflow-3-20130418/
Editor: L. David Baron, Mozilla https://www.mozilla.org/, https://dbaron.org/, w3cid 15393
Editor: Elika J. Etemad / fantasai, Invited Expert, http://fantasai.inkedblade.net/contact, w3cid 35400
Editor: Florian Rivoal, On behalf of Bloomberg, http://florian.rivoal.net/, w3cid 43241
Abstract: This module contains the features of CSS relating to scrollable overflow handling in visual media.
!Change Log: <a href="https://hg.csswg.org/drafts/log/tip/css-overflow/Overview.bs">from 27 January 2015 to the present</a>
!Change Log: <a href="https://hg.csswg.org/drafts/log/tip/css-overflow/Overview.src.html">from 28 March 2013 to 27 January 2015</a>
!Change Log: <a href="https://hg.csswg.org/drafts/log/tip/css3-overflow/Overview.src.html">from 31 July 2012 to 27 March 2013</a>
Ignored Vars: B, P
Ignored Terms: padding edge, viewport, line box, flex order
At Risk: the 'max-lines' property
Status Text: <strong>This update trims away most of the experimental new ideas
   for handling overflow that were described in the <a href="https://www.w3.org/TR/2013/WD-css-overflow-3-20130418/">previous Working Draft</a>.
   These ideas are not abandoned; they are merely <a href="https://drafts.csswg.org/css-overflow/">deferred until Level 4</a>.</strong>
   Level 3 is focused solely on completing a spec for the existing, shipped 'overflow' features;
   work will resume on fragmented overflow and other fun things once this is completed.
</pre>
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<pre class="link-defaults">
spec:css-transforms-2; type:property; text:transform-style
type: dfn; spec:css-multicol-1; text:overflow column
type: dfn; spec:css-transforms-2; text:3d rendering context
</pre>
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<pre class="anchors">
url: https://www.w3.org/TR/2008/CR-css3-marquee-20081205/#the-overflow-style; type: property; text: overflow-style;
</pre>

<h2 id="intro">
Introduction</h2>

	In CSS Level 1 [[CSS1]], 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.

	CSS Level 2 [[CSS21]] introduced the 'overflow' 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.

	This specification introduces the long-standing de-facto 'overflow-x' and 'overflow-y' properties,
	adds a ''overflow/clip'' value,
	and defines overflow handling more fully.

	[Something something 'max-lines'.]

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<h2 id="overflow-concepts">
Types of Overflow</h2>

	CSS uses the term <dfn export>overflow</dfn> to describe
	the contents of a box
	that extend outside 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 term might be interpreted as
	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 layout and styling of the box itself
	and of all descendants whose <a>containing block chain</a>
	includes the box.

	In most cases, <a>overflow</a>
	can be computed for any box
	from the bounds and properties of that box itself,
	plus the <a>overflow</a>
	of each of its children.
	However, this is not always the case; for example,
	when ''transform-style: preserve-3d'' [[CSS3-TRANSFORMS]] is used on
	some of the children, any of their descendants with
	''transform-style: preserve-3d'' must also be examined.

	There are two different types of overflow,
	which are used for different purposes by the UA:

	<ul>
		<li><a>ink overflow</a>
		<li><a>scrollable overflow</a>
	</ul>

<h3 id="ink">Ink Overflow</h3>

	The <dfn export>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.
	Ink overflow is the overflow of painting effects defined to not affect layout
	or otherwise extend the <a>scrollable overflow region</a>,
	such as <a href="https://www.w3.org/TR/css-backgrounds/#box-shadow">box shadows</a>,
	<a href="">border images</a>,
	<a href="https://www.w3.org/TR/css-text-decor-3/">text decoration</a>,
	overhanging glyphs (with negative side bearings,
	or with ascenders/descenders extending outside the em box),
	<a href="https://www.w3.org/TR/CSS2/ui.html#dynamic-outlines">outlines</a>,
	etc.

	Since some effects in CSS (for example, the blurs in
	'text-shadow' [[CSS-TEXT-3]] and 'box-shadow' [[CSS-BACKGROUNDS-3]],
	which are theoretically infinite)
	do not define what visual extent they cover, the extent
	of the <a>ink overflow</a> is undefined.

	The <dfn export>ink overflow region</dfn> is the non-rectangular area
	occupied by the <a>ink overflow</a>
	of a box and its contents,
	and the <dfn export>ink overflow rectangle</dfn> is
	the minimal rectangle whose axes are aligned to the box's axes
	and that contains the <a>ink overflow region</a>.
	Note that the <a>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. [[CSS3-TRANSFORMS]]


<h3 id="scrollable">
Scrollable Overflow</h3>

	The <dfn export>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.

	The <dfn export>scrollable overflow region</dfn> is the non-rectangular region
	occupied by the <a>scrollable overflow</a>, and the
	<dfn export>scrollable overflow rectangle</dfn> is
	the minimal rectangle whose axes are aligned to the box's axes
	and that contains the <a>scrollable overflow region</a>.

	The <a>scrollable overflow region</a> is the union of:
	<ul>
		<li>
			the box’s own content and padding areas

			<div class=issue>
				There's disagreement on the scrolling model.
				2.1 apparently defined that you scrolled the *content* area;
				the content would overflow the content-box,
				and you would union that overflow with the content box to find the scrollable area.
				In particular, this means that the content would be offset by the start-sides padding,
				but if it overflowed,
				it would go right to the edge on the end sides.
				This is what Firefox and IE do.

				At least some authors (and spec authors)
				instead have the mental model that the padding box is what's scrollable,
				so when you scroll to the end of the overflow,
				there's the right/bottom padding.
				Chrome/WebKit do this for the block axis, at least.
				They're somewhat inconsistent for the inline axis;
				there's something weird about how they handle lineboxes.

				It seems that the block-axis padding is probably web-compatible to honor.
				It's unclear that the inline-axis padding will be.
				Further experimentation is needed.
			</div>


		<li>
			all line boxes directly contained by the box

		<li>
			the border boxes
			of all boxes for which it is the containing block
			and whose border boxes are positioned not wholly outside
			its <a>block-start</a> or <a>inline-start</a> padding edges,
			accounting for transforms by projecting each box onto
			the plane of the element that establishes its <a>3D rendering context</a>.
			[[!CSS3-TRANSFORMS]]

			Issue: Is this description of handling transforms
			sufficiently accurate?

		<li>
			the <a>scrollable overflow regions</a> of all of the above boxes
			(accounting for transforms as described above),
			provided they themselves have ''overflow: visible''
			(i.e. do not themselves trap the overflow)
			and that <a>scrollable overflow</a> is not already clipped
			(e.g. by the 'clip' property or the 'contain' property).

			Note: The 'mask-*' properties [[!CSS-MASKING-1]]
			do not affect the <a>scrollable overflow region</a>.

			Issue: Need to evaluate compat of honoring or ignoring 'clip' and 'clip-path'.

		<li>
			Optionally,
			additional padding on the end-edge sides,
			corresponding to the end-side padding of the <a>scroll container</a>, such that the end edges of its in-flow content
			coincide with the end edges of its content area
			when scrolled to the end.

			Issue(129): It's not yet clear if including the end-side padding in the scrollable layer is Web-compatible, so this clause is under investigation.
			It appears that Chrome and Safari include such padding <a href="https://bug748518.bmoattachments.org/attachment.cgi?id=618078">in the block axis</a>;
			and the behavior in the inline axis is <a href="http://jsbin.com/digadoyohi/1/edit?html,css,output">not</a> <a href="http://jsbin.com/vexahocayi/1/edit?html,css,output">clear</a>.

			<!-- Make sure http://jsbin.com/qececaqilo/edit?html,css,output is clearly defined. -->
	</ul>

	The UA may <em>additionally</em> include
	the margin areas of boxes for which it is the containing block.
	The conditions under which such margin areas are included is undefined in this level.
	<span class="issue">This needs further testing and investigation; is therefore deferred in this draft.</span>
	<!--
	Considerations:
	  * floats
	  * relpos
	  * margins that collapsed through to the edge of the scrollable area
	  * inline-side margins on both blocks and inlines
	Notes:
	  The reasoning for only including border boxes is to minimize the cases
	  in which overflow scrolling is triggered; however once overflow is triggered,
	  excluding margins creates tight, uncomfortable edges
	  because the margin has been effectively truncated.
	Testcase:
		http://software.hixie.ch/utilities/js/live-dom-viewer/?%3C!DOCTYPE%20html%3E%0A%3Cstyle%3E%0A%20%20div%20%7B%20height%3A%2050px%3B%20overflow%3A%20scroll%3B%20border%3A%20solid%3B%20position%3A%20relative%3B%7D%0A%20%20p%20%7B%20margin%3A%2025px%3B%20background%3A%20red%3B%20%7D%0A%20%20q%20%7B%20position%3A%20absolute%3B%20background%3A%20blue%3B%20top%3A%2025px%3B%20margin%3A%2025px%3B%20%7D%0A%3C%2Fstyle%3E%0A%3Cdiv%3E%0A%20%20%3Cp%3ETest%20%3Cq%3ETest2%0A%3C%2Fdiv%3E
	-->

	Note: The <a>scrollable overflow rectangle</a> is always a rectangle
	in the box's own coordinate system, but might be non-rectangular
	in other coordinate systems due to transforms [[CSS3-TRANSFORMS]].
	This means scrollbars can sometimes appear when not actually necessary.

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<h2 id="overflow-properties">
Scrolling and Clipping Overflow: the 'overflow-x', 'overflow-y', and 'overflow' properties</h2>

	These properties specify whether a box’s content
	(including any <a>ink overflow</a>)
	is clipped to its padding edge,
	and if so,
	whether it is a <dfn export>scroll container</dfn>
	that allows the user to scroll clipped parts of its <a>scrollable overflow region</a>
	into view.
	The visual viewport of the <a>scroll container</a>
	(through which the <a>scrollable overflow region</a> can be viewed)
	coincides with its padding box,
	and is called the <dfn export>scrollport</dfn>.

	<pre class=propdef>
		Name: overflow-x, overflow-y
		Value: ''visible'' | ''hidden'' | ''clip'' | ''scroll'' | ''auto''
		Initial: ''visible''
		Applies to: block containers [[!CSS21]], flex containers [[!CSS3-FLEXBOX]], and grid containers [[!CSS3-GRID-LAYOUT]]
		Inherited: no
		Percentages: N/A
		Media: visual
		Computed value: as specified, except with ''visible''/''clip'' computing to ''auto''/''hidden'' (respectively) if one of 'overflow-x' or 'overflow-y' is neither ''visible'' nor ''clip''
		Animatable: no
	</pre>

	The 'overflow-x' property specifies
	the handling of <a>overflow</a> in the horizontal direction
	(i.e., overflow from the left and right sides of the box),
	and the 'overflow-y' property specifies the handling
	of <a>overflow</a> in the vertical direction
	(i.e., overflow from the top and bottom sides of the box).

	<pre class=propdef>
		Name: overflow
		Value: ''visible'' | ''hidden'' | ''clip'' | ''scroll'' | ''auto''
		Initial: see individual properties
		Applies to: block containers [[!CSS21]], flex containers [[!CSS3-FLEXBOX]], and grid containers [[!CSS3-GRID-LAYOUT]]
		Inherited: no
		Percentages: N/A
		Media: visual
		Computed value: see individual properties
		Animatable: no
		Canonical order: <abbr title="follows order of property value definition">per grammar</abbr>
	</pre>

	The 'overflow' property is a shorthand property
	that sets the specified values of both 'overflow-x' and 'overflow-y'
	to the value specified for 'overflow'.

	Values have the following meanings:

	<dl dfn-for="overflow, overflow-x, overflow-y" dfn-type="value">
		<dt><dfn>visible</dfn>
		<dd>
			There is no special handling of overflow, that is,
			the box’s content is rendered outside the box if positioned there.
			The box is not a <a>scroll container</a>.

		<dt><dfn>hidden</dfn>
		<dd>
			This value indicates that
			the box’s content is clipped to its padding box
			and that the UA must not provide any scrolling user interface
			to view the content outside the clipping region,
			nor allow scrolling by direct intervention of the user,
			such as dragging on a touch screen
			or using the scrolling wheel on a mouse.
			However, the content must still be scrollable programatically,
			for example using the mechanisms defined in [[CSSOM-VIEW]],
			and the box is therefore still a <a>scroll container</a>.

		<dt><dfn>clip</dfn>
		<dd>
			Like ''hidden'',
			this value indicates that
			the box’s content is clipped to its padding box
			and that no scrolling user interface should be provided by the UA
			to view the content outside the clipping region.
			In addition, unlike ''overflow: hidden''
			which still allows programmatic scrolling,
			''overflow: clip'' forbids scrolling entirely,
			through any mechanism,
			and therefore the box is not a <a>scroll container</a>.

		<dt><dfn>scroll</dfn>
		<dd>
			This value indicates that
			the content is clipped to the padding box,
			but can be scrolled into view
			(and therefore the box is a <a>scroll container</a>).
			Furthermore, 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
			whether or not any of its content is clipped.
			This avoids any problem with scrollbars appearing
			and disappearing in a dynamic environment.
			When the target medium is ''print'',
			overflowing content may be printed;
			it is not defined where it may be printed.

		<dt><dfn>auto</dfn>
		<dd>
			Like ''overflow/scroll'' when the box has <a>scrollable overflow</a>;
			like ''overflow/hidden'' otherwise.
			Thus, if the user agent uses a scrolling mechanism
			that is visible on the screen (such as a scroll bar or a panner),
			that mechanism will only be displayed
			if there is overflow.
		</dl>

	If the computed value of 'overflow' on a <a>block box</a>
	is not ''overflow/visible'',
	it creates a new <a>block formatting context</a> for its content.


<h3 id="static-media">
Overflow in Print and Other Static Media</h3>

	<p class="advisement">
		Since scrolling is not possible in static media
		(such as print)
		authors should be careful to make content accessible in such media,
		for example by using ''@media print, (update: none) { &hellip; }''
		to adjust layout such that all relevant content
		is simultaneously visible.

	On <a>scroll containers</a> in <a>static media</a>
	with an 'overflow' value of ''overflow/auto'' or ''overflow/scroll''
	(but not ''overflow/hidden'')
	UAs may display an indication of any scrollable overflow,
	such as by displaying scrollbars
	or an ellipsis.

	Note: Not all <a>paged media</a> is <a lt="static media">static</a>;
	for example, e-book readers page content,
	but are <a lt="interactive media">interactive</a>.

<h3 id="scrollbar-layout">
Scrollbars and Layout</h3>

	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.

	Issue: import examples from [[CSS3-BOX]].

<h3 id="scrolling-direction">
Scrolling Origin, Direction, and Restriction</h3>

	The <dfn export>initial scroll position</dfn>,
	that is, the initial position of
	the box’s <a>scrollable overflow region</a>
	with respect to its border box,
	prior to any user or programmatic scrolling that changes it,
	is dependent on the box’s <a>writing mode</a>,
	and is by default the <a>block-start</a>/<a>inline-start</a> edge
	of the box’s <a>padding edge</a>.
	However, the 'align-content' and 'justify-content' properties [[!CSS-ALIGN-3]]
	can be used to change this,
	see [[css-align-3#overflow-scroll-position]].

	Due to Web-compatibility constraints
	(caused by authors exploiting legacy bugs to surreptitiously hide content from visual readers but not search engines and/or speech output),
	UAs must clip the <a>scrollable overflow region</a>
	of <a>scroll containers</a>
	on the <a>block-start</a> and </a>inline-start</a> sides of the box
	(thereby behaving as if they had no <a>scrollable overflow</a> on that side).

	The viewport uses the <a>principal writing mode</a> for these calculations.

<h3 id="overflow-propagation">
Overflow Viewport Propagation</h3>

	UAs must apply the 'overflow-*' values
	set on the root element to the <a>viewport</a>.
	However,
	when the root element is an [[!HTML]] <{html}> element
	(including <a href="https://html.spec.whatwg.org/multipage/introduction.html#html-vs-xhtml">XML syntax for HTML</a>)
	whose 'overflow' value is ''overflow/visible'' (in both axes),
	and that element has a <{body}> element as a child,
	user agents must instead apply the 'overflow-*' values
	of the first such child element to the viewport.
	The element from which the value is propagated must then have
	a used 'overflow' value of ''overflow/visible''.

	If ''overflow/visible'' is applied to the viewport,
	it must be interpreted as ''overflow/auto''.

<h2 id="max-lines">
Limiting Visible Lines: the 'max-lines' property</h2>

	<pre class=propdef>
		Name: max-lines
		Value: none | <<integer>>
		Initial: none
		Applies to: <a>block containers</a> (excluding <a>multi-column containers</a>)
		Inherited: no
		Animatable: as integer
		Percentages: N/A
		Media: visual
		Computed value: specified value
	</pre>

	This property allows limiting the contents of a block container
	to the specified number of lines;
	remaining content is fragmented away
	and neither rendered nor measured.
	Specifically,
	if the value of 'max-lines' is not <dfn for=max-lines type=value>none</dfn>:

	<ul>
		<li>The box becomes a <a>fragmentation container</a>
			that captures <a>region breaks</a>,
			if it is not already.
			[[!CSS-BREAK-3]]

		<li>A <a>region break</a>
			is forced after its <var>N</var>th
			descendant <a>in-flow</a> <a>line box</a>,
			where <var>N</var> is the specified value of 'max-lines'.
			The contents of descendants that are <a>scroll containers</a>
			or that are not <a>block containers</a>
			are skipped over while counting line boxes.

			If fewer than <var>N</var> line boxes exist,
			then 'max-lines' introduces no <a>region break</a>.

		<li>The position of the first forced <a>region break</a>
			(whether imposed by 'max-lines' or by another mechanism,
			such as the 'break-before'/'break-after' properties)
			is treated as the end of the <a>fragmentation container</a>,
			and the rest of the <a>fragmented flow</a> is laid out in
			the next <a>fragmentation container</a> in the <a>fragmentation context</a>.

			If there is no subsequent <a>fragmentation container</a>
			(which is the case if the box became a <a>fragmentation container</a>
			merely as a consequence of applying the 'max-lines' property),
			the rest of the <a>fragmented flow</a> is discarded,
			similar to if it were ''display: none'':
			it is neither rendered,
			nor measured as part of the box’s contents for the purpose of
			finding its <a lt="min-content block size">min-content</a>, <a>max-content</a>, or <a lt="automatic size">automatic</a> <a>block sizes</a>,
			nor does allow user interaction.
			However, since intrinsic sizes are calculated across all <a>fragmentation containers</a>,
			this content <em>is</em> taken into account
			for the purpose of finding the box’s
			<a lt="min-content inline size">min-content</a> and <a>max-content</a> <a>inline sizes</a>
			(see [[css-break-3#varying-size-boxes]]).

			Note: In the case of <a href="https://www.w3.org/TR/css-break-3/#parallel-flows">parallel fragmentation flows</a>,
			content occuring after the <a>fragmentation break</a> in the box tree
			could still be rendered,
			if it is laid out above the position
			representing the end of this <a>fragmentation container</a>.

			<!-- Honoring forced breaks from other sources
			is to handle future use cases,
			such as using 'max-lines' to size the first region
			in a two-region section,
			where the first region is for styling the first N lines of the article
			differently from the rest. -->

	</ul>

	Only positive integers are accepted.
	Zero or negative integers are invalid
	and must cause the declaration to be <a>ignored</a>.

	Note: The 'widows', 'orphans', and 'break-inside' properties
	do not affect the position of the forced <a>region break</a>
	introduced by the 'max-lines' property.


<h2 id="block-ellipsis">
Indicating Block-Axis Overflow: the 'block-overflow' property</h2>

	ISSUE: This section is an unofficial draft, posted here for discussion.
	See <a href="https://github.com/w3c/csswg-drafts/issues/390">issue</a>.

	<pre class=propdef>
		Name: block-overflow
		Value: clip | ellipsis | <<string>>
		Initial: clip
		Applies to: <a>block containers</a>
		Inherited: yes
		Animatable: no
		Percentages: N/A
		Media: visual
		Computed value: specified value
	</pre>

	This property allows inserting content into the last line box
	before a (forced <em>or</em> unforced) <a>region break</a>
	to indicate the continuity of truncated/interrupted content.
	It only affects line boxes contained directly by the <a>block container</a> itself,
	but as it inherits, will have an effect on descendants’ line boxes unless overridden.
	If the box contains no line box immediately preceding a <a>region break</a>,
	then this property has no effect.

	ISSUE: Should this apply to other types of fragmentation breaks (e.g. pages, columns)?

	The inserted content is called the <dfn>block overflow ellipsis</dfn>.
	Values have the following meanings:

	<dl dfn-for="block-overflow" dfn-type=value>
		<dt><dfn>clip</dfn>
		<dd>
			The content is not altered.

		<dt><dfn>ellipsis</dfn>
		<dd>
			Render an ellipsis character (U+2026)--
			or a more typographically-appropriate equivalent--
			as the <a>block overflow ellipsis</a>
			at the end of the affected line box.
			UAs should use the conventions of the
			<a>content language</a>,
			writing system, and
			<a>writing mode</a>
			to determine the most appropriate ellipsis string.

		<dt><dfn><<string>></dfn>
		<dd>
			Render the specified string
			as the <a>block overflow ellipsis</a>
			at the end of the affected line box.
			The UA may truncate this string if it is absurdly long.
	</dl>

	<div class="example">
		In this example, the lead paragraph of each article
		is listed in a shortened menu,
		truncated to fit within 10 lines
		that end with “… (continued on next page)”:

		<xmp highlight=css>
			li {
				max-lines: 5;
				block-overflow: "… (continued on next page)";
			}
			strong {
				display: block;
				text-transform: uppercase;
			}
		</xmp>

		<xmp highlight=markup>
			<li><a href="cheese-is-milk">
				<strong>Cheese is Actually Made of Milk!</strong>
				Investigative reporters at the World Wide Web Press Corps
				have discovered the secret of cheese.
				Tracing through byzantine layers of bureacracy and shadow corporations,
				our crack team of journalists have traced the source of camembert.
			</a></li>
		</xmp>

		Sample rendering:

		<pre class="figure">
			+---------------------------------------+
			| CHEESE IS ACTUALLY MADE OF MILK!      |
			| Investigative reporters at the World  |
			| Wide Web Press Corps have discovered  |
			| the secret of cheese. Tracing through |
			| byzantine…  (continued on next page)  |
			+---------------------------------------+
		</pre>
	</div>

	When 'block-overflow' is not ''block-overflow/clip'',
	the <a>block overflow ellipsis</a> string
	is wrapped in an anonymous inline
	and placed at the end of the line box
	as a direct child of the <a>block container</a>’s <a>root inline box</a>,
	reducing the space in the line box
	available to the other contents of the line.
	This inline is assigned ''unicode-bidi: plaintext''
	and is placed in the line box after the last
	<a>soft wrap opportunity</a> [[!CSS-TEXT-3]]
	that would still allow the entire <a>block overflow ellipsis</a> to fit on the line.
	(This can result in the entire contents of the line box being replaced.)
	For this purpose, <a>soft wrap opportunities</a> added by 'overflow-wrap' are ignored.
	Text <a href="https://www.w3.org/TR/css-text-3/#justification">alignment and justification</a>
	occurs after placement,
	and measures the inserted <a>block overflow ellipsis</a>
	together with the rest of the line’s content.

	If there is no next <a>fragmentation container</a>
	and thus the remainder of the content after the break would be discarded,
	then the UA may visually replace the contents of the line,
	as it does for 'text-overflow'.
	If, however, there is a next <a>fragmentation container</a>
	that would receive subsequent content,
	then the content replaced by the <a>block overflow ellipsis</a>
	must be pushed to the next <a>fragmentation container</a>
	and the <a>block overflow ellipsis</a> inserted and laid out
	exactly as if it were part of the <a>in-flow</a> contents of the line.
	This can result in changes to layout within or impacted by the line.
	The means of breaking any resulting cycles is up to the UA.

	If the <a>block overflow ellipsis</a>
	is too long to fit in the line,
	the result is undefined.
	(The UA may, for example, treat the <a>block overflow ellipsis</a> as an unbreakable string,
	or it may lay out the string across more than one line,
	replacing content in earlier lines as well.)

	The <a>block overflow ellipsis</a> does not capture events:
	pointer events are dispatched to whatever is underneath
	or otherwise visually replaced by it.

	It also has no effect on the intrinsic size of the box:
	its <a lt="min-content size">min-content</a> and <a lt="max-content size">max-content</a> sizes
	are calculated exactly as if 'block-overflow' were ''block-overflow/clip''.

	Note: Future specifications may extend this feature,
	for example by providing an ''::ellipsis'' pseudo-element
	to style the text,
	or by allowing the selection of a child element of the block
	to use as either an inline-level or block-level indicator
	(in which case, it can capture events).


<h2 id=line-clamp>
Setting 'max-lines' and 'block-overflow' together: the 'line-clamp' property</h2>

	<pre class=propdef>
		Name: line-clamp
		Value: none | <<integer>>
		Initial: none
		Applies to: see individual properties
		Inherited: see individual properties
		Animatable: see individual properties
		Percentages: N/A
		Media: visual
		Computed value: see individual properties
	</pre>

	The 'line-clamp' property is a <a>shorthand</a>
	for the 'max-lines' and 'block-overflow' properties.

	<dl dfn-for=line-clamp dfn-type=value>
		<dt><dfn>none</dfn>
		<dd>Sets 'max-lines' to ''max-lines/none''
			and 'block-overflow' to ''block-overflow/clip''.

		<dt><dfn><<integer>></dfn>
		<dd>Sets 'max-lines' to the specified <<integer>>
			and 'block-overflow' to ''block-overflow/ellipsis''.

	</dl>

	For compatibility with legacy content, UAs that support 'line-clamp' must also support <dfn dfn-type=property>-webkit-line-clamp</dfn> as an alias.


Privacy and Security Considerations {#priv-sec}
===============================================

This specification introduces no new privacy or security concerns.

<h2 class=no-num id="acknowledgments">
Acknowledgments</h2>

	<p>
		Thanks especially to the feedback from
		Rossen Atanassov,
		Bert Bos,
		Tantek Çelik,
		John Daggett,
		Daniel Glazman,
		Vincent Hardy,
		H&aring;kon Wium Lie,
		Peter Linss,
		Robert O'Callahan,
		Florian Rivoal,
		Alan Stearns,
		Steve Zilles,
		and all the rest of the
		<a href="http://lists.w3.org/Archives/Public/www-style/">www-style</a> community.