CSS Overflow Module Level 3

Editor’s Draft,

More details about this document
This version:
https://drafts.csswg.org/css-overflow-3/
Latest published version:
https://www.w3.org/TR/css-overflow-3/
Previous Versions:
Feedback:
CSSWG Issues Repository
Inline In Spec
Editors:
Elika J. Etemad / fantasai (Apple)
Florian Rivoal (On behalf of Bloomberg)
Former Editor:
L. David Baron (Mozilla)
Suggest an Edit for this Spec:
GitHub Editor

Abstract

This module contains the features of CSS relating to scrollable overflow handling in visual media. This level is focused on completing a precise specification for the existing overflow features, including the overflow property and its longhands; and the text-overflow property. A few additional features introduced in support of [CSS-CONTAIN-1] and [CSS-CONTAIN-2] are also defined: overflow: clip and the overflow-clip-margin property.

CSS is a language for describing the rendering of structured documents (such as HTML and XML) on screen, on paper, etc.

Status of this document

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.

Please send feedback by filing issues in GitHub (preferred), including the spec code “css-overflow” in the title, like this: “[css-overflow] …summary of comment…”. All issues and comments are archived. Alternately, feedback can be sent to the (archived) public mailing list www-style@w3.org.

This document is governed by the 03 November 2023 W3C Process Document.

The description of overflow and its longhands is considered significantly more complete and correct than previous working drafts or than [CSS2], but a few questions and issues remain open. ''overflow: clip' and overflow-clip-margin are rather new, and lack implementation experience. text-overflow is stable, is unchanged form its earlier definition in [CSS-UI-3]. While not yet fully validated by implementation experience, the design of line-clamp and its longhands is considered roughly complete. Earlier versions of this specification included experimental new ideas for handling overflow by creating new boxes using fragmentation. These ideas are not abandoned; they are merely deferred until Level 4. Work will resume on fragmented overflow once this level stabilizes completed.

The following features are at-risk, and may be dropped during the CR period:

“At-risk” is a W3C Process term-of-art, and does not necessarily imply that the feature is in danger of being dropped or delayed. It means that the WG believes the feature may have difficulty being interoperably implemented in a timely manner, and marking it as such allows the WG to drop the feature if necessary when transitioning to the Proposed Rec stage, without having to publish a new Candidate Rec without the feature first.

1. Introduction

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 [CSS2] 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 clip value, and defines overflow handling more fully.

[Something something max-lines.]

Note: This specification also reproduces the definition of the text-overflow property previously defined in [CSS-UI-3], with no addition or modification, in order to present text-overflow and block-ellipsis together.

1.1. Value Definitions

This specification follows the CSS property definition conventions from [CSS2] using the value definition syntax from [CSS-VALUES-3]. Value types not defined in this specification are defined in CSS Values & Units [CSS-VALUES-3]. Combination with other CSS modules may expand the definitions of these value types.

In addition to the property-specific values listed in their definitions, all properties defined in this specification also accept the CSS-wide keywords as their property value. For readability they have not been repeated explicitly.

1.2. Module Interactions

This module replaces (supersedes) and extends features defined in [CSS2] section 11.1 Overflow and clipping and [CSS-UI-3] section 5.2. Overflow Ellipsis: the text-overflow property.

2. Overflow Concepts and Terminology

CSS uses the term overflow to describe the contents of a box that extend outside one of that box’s edges (i.e., its content edge, padding edge, border edge, or margin edge). 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 containing block chain includes the box.

In most cases, overflow can be computed for any box from the bounds and properties of that box itself, plus the overflow 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:

2.1. Ink Overflow

The ink overflow 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 scrollable overflow area, such as box shadows, border images, text decoration, overhanging glyphs (with negative side bearings, or with ascenders/descenders extending outside the em box), outlines, 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 ink overflow is undefined.

The ink overflow area is the non-rectangular area occupied by the ink overflow of a box and its contents, and the ink overflow rectangle is the minimal rectangle whose axes are aligned to the box’s axes and that contains the ink overflow area. Note that the ink overflow rectangle is a rectangle in the box’s coordinate system, but might be non-rectangular in other coordinate systems due to transforms. [CSS3-TRANSFORMS]

Any overflow of replaced content is always ink overflow (as opposed to scrollable overflow).

2.2. Scrollable Overflow

The scrollable overflow 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 scrollable overflow area is the non-rectangular region occupied by the scrollable overflow, and the scrollable overflow rectangle is the minimal rectangle whose axes are aligned to the box’s axes and that contains the scrollable overflow area.

The scrollable overflow area is the union of:

Additionally, 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 any content in the negative scrollable overflow region (thereby behaving as if they had no scrollable overflow on the wrong side of the scroll origin).

Note: The scrollable overflow rectangle 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.

2.3. Scrolling Overflow

A box’s overflow can be visible or clipped. CSS also allows a box to be a scroll container that allows clipped parts of its scrollable overflow area to be scrolled into view. The visual “viewport” of a scroll container (through which the scrollable overflow area can be viewed) coincides with its padding box, and is called the scrollport. A box’s nearest scrollport is the scrollport of its nearest scroll container ancestor.

Scrolling operations can be initiated by the user (for example, by manipulating a scrollbar, swiping a touchscreen, or using keyboard controls) or by script (for example, by the scrollIntoView() or focus() APIs). The initial position of the scrollable overflow rectangle within the scrollport before any scrolling operations take effect is the initial scroll position. The initial scroll position is typically dependent on the scroll container’s writing mode, and, unless otherwise specified, coincides with its scroll origin position. However, the align-content and justify-content properties [CSS-ALIGN-3] can be used to change the initial scroll position, see CSS Box Alignment 3 § 5.3 Overflow and Scroll Positions.

A scroll position is a particular alignment of the scrollable overflow rectangle within its scrollport. It is associated with a scroll offset which is its distance from the scroll origin.

The scroll origin is the anchor coordinate of the scrollable overflow rectangle, from which the scrollable overflow rectangle expands. Unless otherwise specified, it is the block-start inline-start corner of the scrollable overflow rectangle. (For example, in a flex container it is the main-start cross-start corner.) The area beyond the scroll origin in either axis is considered the negative scrollable overflow region: content rendered here is not accessible to the reader, see § 2.2 Scrollable Overflow. A scroll container is said to be scrolled to its scroll origin when its scroll origin coincides with the corresponding corner of its scrollport. This scroll position, the scroll origin position, usually, but not always, coincides with the initial scroll position.

For example, the align-content and justify-content properties [CSS-ALIGN-3] and scroll snapping [CSS-SCROLL-SNAP-1] can change the initial scroll position away from the scroll origin position.

Check whether things like baseline alignment depend on the initial scroll position or the scroll origin position.

This doesn’t define a coordinate system for scroll offsets. Whether they increase downward/rightward, block/inline-axis endward, or away from the scroll origin is not defined. Should each API define its coordinate model?

The root viewport, which scrolls the page canvas, uses the principal writing mode for determining its scroll origin and initial scroll position.

Note: In the case where a scroll container (or one of its ancestors) is the target of a graphical transform, the UA might need to take this transform into account when mapping user inputs to scrolling operations. For instance, on a touch screen where the user scrolls by directly dragging the content, the transform would be expected to be taken into account to match the direction of scrolling to the gesture. On the other hand, other user inputs (such as the Page Down key, or a 1D scroll wheel) might be more naturally interpreted ignoring the transform. Choosing the appropriate behavior for each scrolling mechanism is the responsibility of the UA.

3. Scrolling and Clipping Overflow

3.1. Managing Overflow: the overflow-x, overflow-y, and overflow properties

These properties specify whether a box’s overflow is clipped, and if so, whether it is a scroll container.

Name: overflow-x, overflow-y, overflow-block, overflow-inline
Value: visible | hidden | clip | scroll | auto
Initial: visible
Applies to: block containers [CSS2], flex containers [CSS3-FLEXBOX], grid containers [CSS3-GRID-LAYOUT]
Inherited: no
Percentages: N/A
Computed value: usually specified value, but see text
Canonical order: per grammar
Animation type: discrete
Logical property group: overflow

The overflow-x property specifies the handling of overflow in the horizontal axis (i.e., overflow from the left and right sides of the box), and the overflow-y property specifies the handling of overflow in the vertical axis (i.e., overflow from the top and bottom sides of the box).

The overflow-block and overflow-inline properties likewise specify the handling of overflow in the block and inline axis, respectively

These four properties form a logical property group together with the overflow shorthand, and interact as defined in CSS Logical Properties 1 § 4 Flow-Relative Box Model Properties.

Name: overflow
Value: <'overflow-block'>{1,2}
Initial: visible
Applies to: block containers [CSS2], flex containers [CSS3-FLEXBOX], and grid containers [CSS3-GRID-LAYOUT]
Inherited: no
Percentages: N/A
Computed value: see individual properties
Animation type: discrete
Canonical order: per grammar

The overflow property is a shorthand property that sets the specified values of overflow-x and overflow-y in that order. If the second value is omitted, it is copied from the first.

Values have the following meanings:

visible
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 scroll container.
hidden
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 programmatically, for example using the mechanisms defined in [CSSOM-VIEW], and the box is therefore still a scroll container.
clip
This value indicates that the box’s content is clipped to its overflow clip edge 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 scroll container.

Unlike hidden, this value does not cause the element to establish a new formatting context.

Note: Authors who also want the box to establish a formatting context may use display: flow-root together with overflow: clip.

scroll
This value indicates that the content is clipped to the padding box, but can be scrolled into view (and therefore the box is a scroll container). 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.
auto
Like scroll when the box has scrollable overflow; like 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.

The visible/clip values of overflow compute to auto/hidden (respectively) if one of overflow-x or overflow-y is neither visible nor clip.

If the computed value of overflow on a block box is neither visible nor clip nor a combination thereof, it establishes an independent formatting context for its contents.

User agents must also support the overlay keyword as a legacy value alias of auto.

3.1.1. Interaction of visibility and overflow

If the computed value of the visibility property is hidden (or collapse when it has the same effect as hidden), and overflow is either scroll or auto, then:

3.1.2. Interaction of border-radius and overflow

As mentioned in CSS Backgrounds 3 § 4.3 Corner Clipping, the clipping region established by overflow can be rounded:

3.1.3. Overflow in Print and Other Static Media

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) { … } to adjust layout such that all relevant content is simultaneously visible.

On scroll containers in non-interactive media with an overflow value of auto or scroll (but not hidden) UAs may display an indication of any scrollable overflow, such as by displaying scrollbars or an ellipsis.

Note: Not all paged media is non-interactive: for example, e-book readers paginate content, but are interactive.

3.2. Expanding Clipping Bounds: the overflow-clip-margin property

Name: overflow-clip-margin
Value: <visual-box> || <length [0,∞]>
Initial: 0px
Applies to: boxes to which overflow applies
Inherited: no
Percentages: n/a
Computed value: the computed <length> and a <visual-box> keyword
Canonical order: per grammar
Animation type: per computed value if the <visual-box> values match; otherwise discrete

This property defines the overflow clip edge of the box, i.e. precisely how far outside its bounds the box’s content is allowed to paint before being clipped by effects (such as overflow: clip, above) that are defined to clip to the box’s overflow clip edge.

Values are defined as follows:

<visual-box>

Specifies the box edge to use as the overflow clip edge origin, i.e. when the specified offset is zero.

If omitted, defaults to padding-box.

<length [0,∞]>

The specified offset dictates how much the overflow clip edge is expanded from the specified box edge Negative values are invalid. Defaults to zero if omitted.

The overflow clip edge is shaped in the corners exactly the same way as an outer box-shadow with a spread radius of the same cumulative offset from the box’s border edge. See CSS Backgrounds 3 § 4.2 Corner Shaping and CSS Backgrounds 3 § 6.1.1 Shadow Shape, Spread, and Knockout, noting in particular the formula for outsets beyond the border edge.

Note: This property has no effect on boxes with overflow: hidden or overflow: scroll, which are not defined to use the overflow clip edge.

3.3. Overflow Viewport Propagation

UAs must apply the overflow-* values set on the root element to the viewport when the root element’s display value is not none. However, when the root element is an [HTML] html element (including XML syntax for HTML) whose overflow value is visible (in both axes), and that element has as a child a body element whose display value is also not none, 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 visible.

Note: Using containment on the HTML html or body elements disables this special handling of the HTML body element. See the CSS Containment 1 § 2 Strong Containment: the contain property for details.

Note: overflow: hidden on the root element might not clip everything outside the Initial Containing Block if the ICB is smaller than the viewport, which can happen on mobile.

If visible is applied to the viewport, it must be interpreted as auto. If clip is applied to the viewport, it must be interpreted as hidden.

3.4. Smooth Scrolling: the scroll-behavior Property

Name: scroll-behavior
Value: auto | smooth
Initial: auto
Applies to: scroll containers
Inherited: no
Percentages: n/a
Computed value: specified value
Canonical order: per grammar
Animation type: not animatable

The scroll-behavior property specifies the scrolling behavior for a scroll container, when scrolling happens due to navigation, scrolling APIs [CSSOM-VIEW], or scroll snapping operations not initiated by the user [CSS-SCROLL-SNAP-1]. Any other scrolls, e.g. those that are performed by the user, are not affected by this property. When this property is specified on the root element, it applies to the viewport instead.

Note: The scroll-behavior property of the HTML body element is not propagated to the viewport.

auto
The scroll container is scrolled in an instant fashion.
smooth
The scroll container is scrolled in a smooth fashion using a user-agent-defined timing function over a user-agent-defined period of time. User agents should follow platform conventions, if any.

User agents may ignore this property.

4. Scrollbars and Layout

4.1. Scrollbar Contributions to Sizing

When reserving space for a scrollbar placed at the edge of an element’s box, the reserved space is inserted between the inner border edge and the outer padding edge. For the purpose of the background positioning area and background painting area however, this reserved space is considered to be part of the padding box.

In the following document fragment, both an absolutely-positioned element and a background image are positioned to the top right of the box.
<style>
  article {
    background: top right no-repeat url(circle.png);
    position: relative;
    overflow: auto; }
  aside { position: absolute; top: 0; right: 0; }
</style>
<article>
  <aside>×</aside>
</article>

If no scrollbars are present on <article>, they will both coincide in the top right padding edge corner. However, if scrollbars are present then <aside> will be completely visible, on the right padding-box edge adjacent to the scrollbars; whereas the background image will be tucked underneath the scrollbars, in the top right corner of the scrollbar-extended background positioning area.

When the box is intrinsically sized, this reserved space is added to the size of its contents. It is otherwise subtracted from space allotted to the content area. To the extent that the presence of scrollbars can affect sizing, UAs must start with the assumption that no scrollbars are needed, and recalculate sizes if it turns out they are.

In the following document fragment, the outer <article> has height: auto, but max-height: 5em. The inner <section> has large margins and would normally just fit:
...
    article { overflow: auto; max-height: 5em;  width: max-content; }
    section { margin: 2em; line-height: 1 }
...
<article>
  <section>
    This section has big margins.
  </section>
</article>

If we assumed that <article> needed scrollbars, then the height of <section>, including the single line of text and twice 2em of margins, adds up to 5em plus a scrollbar. Since that is greater than 5em, the maximum allowed height, it seems we made the right assumption and d1 indeed needs scrollbars.

However, we should have started by assuming that no scrollbars are needed. In that case the content height of <article> is exactly the maximum height of 5em, proving that the assumption was correct and <article> indeed should not have scrollbars.

4.2. Reserving space for the scrollbar: the scrollbar-gutter property

The space between the inner border edge and the outer padding edge which user agents may reserve to display the scrollbar is called the scrollbar gutter.

The scrollbar-gutter property gives control to the author over the presence of scrollbar gutters separately from the ability to control the presence of scrollbars provided by the overflow property.

Name: scrollbar-gutter
Value: auto | stable && both-edges?
Initial: auto
Applies to: scroll containers
Inherited: no
Percentages: n/a
Computed value: specified keyword(s)
Canonical order: per grammar
Animation type: discrete

This property affects the presence of scrollbar gutters placed at the inline start edge or inline end edge of the box.

The presence of a scrollbar gutter at the block start edge and block end edge of the box cannot be controlled in this level, and is determined the same way as the presence of scrollbar gutters placed at the inline start edge or inline end edge of the box when scrollbar-gutter is auto.

Scrollbars which by default are placed over the content box and do not cause scrollbar gutters to be created are called overlay scrollbars. Such scrollbars are usually partially transparent, revealing the content behind them if any. Their appearance and size may vary based on whether and how the user is interacting with them.

Scrollbars which are always placed in a scrollbar gutter, consuming space when present, are called classic scrollbars. Such scrollbars are usually opaque.

Whether classic scrollbars or overlay scrollbars are used, the appearance and size of the scrollbar, and whether scrollbars appear on the start or end edge of the box, is UA defined.

Note: Which side a scrollbar appears on may depend on operating system conventions, bidirectionality, or other ergonomic considerations.

In the case of classic scrollbars, the width of the scrollbar gutter, if present (see below), is the same as the width of the scrollbar. In the case of overlay scrollbars, no scrollbar gutter is present.

Note: There are known use cases that could be addressed by enabling scrollbar gutters for overlay scrollbars, but no satisfactory design has been agreed to so far. This could be addressed by future extensions of this property. See CSS Overflow 4 § B Possible extensions for scrollbar-gutter.

The values of this property have the following meaning:

auto
Classic scrollbars consume space by creating a scrollbar gutter when overflow is scroll, or when overflow is auto and the box is overflowing. Overlay scrollbars do not consume space.
stable
The scrollbar gutter is present for classic scrollbars when overflow is hidden, scroll, or auto, regardless of whether the box is actually overflowing. Overlay scrollbars do not consume space.

Note: This does not change whether the scrollbar itself is visible, only the presence of a gutter is affected.

both-edges
If a scrollbar gutter would be present on one of the inline start edge or the inline end edge of the box, another scrollbar gutter must be present on the opposite edge as well.

When the scrollbar gutter is present but the scrollbar is not, or the scrollbar is transparent or otherwise does not fully obscure the scrollbar gutter, the background of the scrollbar gutter must be painted as an extension of the padding.

As for the overflow property, when scrollbar-gutter is set on the root element, the user agent must apply it to the viewport instead, and the used value on the root element itself is scrollbar-gutter: auto. However, unlike the overflow property, the user agent must not propagate scrollbar-gutter from the HTML body element.

Note: The following table summarizes the interaction of overflow and scrollbar-gutter showing in which case space is reserved for a classic scrollbar’s scrollbar gutter.
Should a classic scrollbar’s scrollbar gutter be present?
overflow scrollbar-gutter Overflowing Not overflowing
scroll auto yes yes
stable yes yes
auto auto yes
stable yes yes
hidden auto
stable yes yes
visible, clip auto
stable

5. Automatic Ellipses

5.1. Overflow Ellipsis: the text-overflow property

Name: text-overflow
Value: clip | ellipsis
Initial: clip
Applies to: block containers
Inherited: no
Percentages: N/A
Computed value: specified keyword
Canonical order: per grammar
Animation type: discrete

This property specifies rendering when inline content overflows its end line box edge in the inline progression direction of its block container element ("the block") that has overflow other than visible.

Text can overflow for example when it is prevented from wrapping (e.g. due to white-space: nowrap or a single word is too long to fit). Values have the following meanings:

clip
Clip inline content that overflows its block container element. Characters may be only partially rendered.
ellipsis
Render an ellipsis character (U+2026) to represent clipped inline content. Implementations may substitute a more language, script, or writing-mode appropriate ellipsis character, or three dots "..." if the ellipsis character is unavailable.

The term "character" is used in this property definition for better readability and means "grapheme cluster" [UAX29] for implementation purposes.

For the ellipsis value implementations must hide characters and atomic inline-level elements at the end edge of the line as necessary to fit the ellipsis, and place the ellipsis immediately adjacent to the end edge of the remaining inline content. The first character or atomic inline-level element on a line must be clipped rather than ellipsed.

Bidi ellipsis examples

These examples demonstrate which characters get hidden to make room for the ellipsis in a bidi situation: those visually at the end edge of the line.

Sample CSS:

div {
  font-family: monospace;
  white-space: pre;
  overflow: hidden;
  width: 9ch;
  text-overflow: ellipsis;
}

Sample HTML fragments, renderings, and your browser:

HTML Reference rendering Your Browser
<div>שלום 123456</div>
123456 ם…
שלום 123456
<div dir=rtl>שלום 123456</div>
…456 שלום
שלום 123456

ellipsing details

user interaction with ellipsis

Example(s):

text-overflow examples

These examples demonstrate setting the text-overflow of a block container element that has text which overflows its dimensions:

sample CSS for a div:

div {
  font-family:Helvetica,sans-serif; line-height:1.1;
  width:3.1em; padding:.2em; border:solid .1em black; margin:1em 0;
}

sample HTML fragments, renderings, and your browser:

HTML sample rendering your browser
<div>
CSS IS AWESOME, YES
</div>
First, a box with text drawing outside of it.
CSS IS AWESOME, YES
<div style="text-overflow:clip; overflow:hidden">
CSS IS AWESOME, YES
</div>
Second, a similar box with the text clipped outside the box.
CSS IS AWESOME, YES
<div style="text-overflow:ellipsis; overflow:hidden">
CSS IS AWESOME, YES
</div>
Third, a similar box with an ellipsis representing the clipped text.
CSS IS AWESOME, YES
<div style="text-overflow:ellipsis; overflow:hidden">
NESTED
 <p>PARAGRAPH</p>
WON’T ELLIPSE.
</div>
Fourth, a box with a nested paragraph demonstrating anonymous block boxes equivalency and non-inheritance into a nested element.
NESTED

PARAGRAPH

WON’T ELLIPSE.

Note: the side of the line that the ellipsis is placed depends on the direction of the block. E.g. an overflow hidden right-to-left (direction: rtl) block clips inline content on the left side, thus would place a text-overflow ellipsis on the left to represent that clipped content.

ellipsis interaction with scrolling interfaces

This section applies to elements with text-overflow other than text-overflow:clip (non-clip text-overflow) and overflow:scroll.

When an element with non-clip text-overflow has overflow of scroll in the inline progression dimension of the text, and the browser provides a mechanism for scrolling (e.g. a scrollbar on the element, or a touch interface to swipe-scroll, etc.), there are additional implementation details that provide a better user experience:

When an element is scrolled (e.g. by the user, DOM manipulation), more of the element’s content is shown. The value of text-overflow should not affect whether more of the element’s content is shown or not. If a non-clip text-overflow is set, then as more content is scrolled into view, implementations should show whatever additional content fits, only truncating content which would otherwise be clipped (or is necessary to make room for the ellipsis/string), until the element is scrolled far enough to display the edge of the content at which point that content should be displayed rather than an ellipsis/string.

This example uses text-overflow on an element with overflow scroll to demonstrate the above described behavior.

sample CSS:

div.crawlbar {
  text-overflow: ellipsis;
  height: 2em;
  overflow: scroll;
  white-space: nowrap;
  width: 15em;
  border:1em solid black;
}

sample HTML fragment:

<div class="crawlbar">
CSS is awesome, especially when you can scroll
to see extra text instead of just
having it overlap other text by default.
</div>

demonstration of sample CSS and HTML:

CSS is awesome, especially when you can scroll to see extra text instead of just having it overlap other text by default.

While the content is being scrolled, implementations may adjust their rendering of ellipses (e.g. align to the box edge rather than line edge).

Appendix A. Privacy Considerations

This specification introduces no new privacy concerns.

Appendix B. Security Considerations

This specification introduces no new security concerns.

Appendix C. Changes

This appendix is informative.

Changes from the 2021-12-02 Working Draft

Changes from the 2020-06-03 Working Draft

Changes from the 2018-07-31 Working Draft

Changes Prior to the 2018-07-31 Working Draft

Changes predating the publication of the 2018-07-31 Working Draft can be found in the following change logs:

Acknowledgments

Thanks especially to the feedback from Rossen Atanassov, Bert Bos, Tantek Çelik, John Daggett, Daniel Glazman, Vincent Hardy, Håkon Wium Lie, Peter Linss, Robert O’Callahan, Florian Rivoal, Alan Stearns, Steve Zilles, and all the rest of the www-style community.

Conformance

Document conventions

Conformance requirements are expressed with a combination of descriptive assertions and RFC 2119 terminology. The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in the normative parts of this document are to be interpreted as described in RFC 2119. However, for readability, these words do not appear in all uppercase letters in this specification.

All of the text of this specification is normative except sections explicitly marked as non-normative, examples, and notes. [RFC2119]

Examples in this specification are introduced with the words “for example” or are set apart from the normative text with class="example", like this:

This is an example of an informative example.

Informative notes begin with the word “Note” and are set apart from the normative text with class="note", like this:

Note, this is an informative note.

Advisements are normative sections styled to evoke special attention and are set apart from other normative text with <strong class="advisement">, like this: UAs MUST provide an accessible alternative.

Tests

Tests relating to the content of this specification may be documented in “Tests” blocks like this one. Any such block is non-normative.


Conformance classes

Conformance to this specification is defined for three conformance classes:

style sheet
A CSS style sheet.
renderer
A UA that interprets the semantics of a style sheet and renders documents that use them.
authoring tool
A UA that writes a style sheet.

A style sheet is conformant to this specification if all of its statements that use syntax defined in this module are valid according to the generic CSS grammar and the individual grammars of each feature defined in this module.

A renderer is conformant to this specification if, in addition to interpreting the style sheet as defined by the appropriate specifications, it supports all the features defined by this specification by parsing them correctly and rendering the document accordingly. However, the inability of a UA to correctly render a document due to limitations of the device does not make the UA non-conformant. (For example, a UA is not required to render color on a monochrome monitor.)

An authoring tool is conformant to this specification if it writes style sheets that are syntactically correct according to the generic CSS grammar and the individual grammars of each feature in this module, and meet all other conformance requirements of style sheets as described in this module.

Partial implementations

So that authors can exploit the forward-compatible parsing rules to assign fallback values, CSS renderers must treat as invalid (and ignore as appropriate) any at-rules, properties, property values, keywords, and other syntactic constructs for which they have no usable level of support. In particular, user agents must not selectively ignore unsupported component values and honor supported values in a single multi-value property declaration: if any value is considered invalid (as unsupported values must be), CSS requires that the entire declaration be ignored.

Implementations of Unstable and Proprietary Features

To avoid clashes with future stable CSS features, the CSSWG recommends following best practices for the implementation of unstable features and proprietary extensions to CSS.

Non-experimental implementations

Once a specification reaches the Candidate Recommendation stage, non-experimental implementations are possible, and implementors should release an unprefixed implementation of any CR-level feature they can demonstrate to be correctly implemented according to spec.

To establish and maintain the interoperability of CSS across implementations, the CSS Working Group requests that non-experimental CSS renderers submit an implementation report (and, if necessary, the testcases used for that implementation report) to the W3C before releasing an unprefixed implementation of any CSS features. Testcases submitted to W3C are subject to review and correction by the CSS Working Group.

Further information on submitting testcases and implementation reports can be found from on the CSS Working Group’s website at http://www.w3.org/Style/CSS/Test/. Questions should be directed to the public-css-testsuite@w3.org mailing list.

Index

Terms defined by this specification

Terms defined by reference

References

Normative References

[CSS-ALIGN-3]
Elika Etemad; Tab Atkins Jr.. CSS Box Alignment Module Level 3. URL: https://drafts.csswg.org/css-align/
[CSS-BACKGROUNDS-3]
Elika Etemad; Brad Kemper. CSS Backgrounds and Borders Module Level 3. URL: https://drafts.csswg.org/css-backgrounds/
[CSS-BOX-4]
Elika Etemad. CSS Box Model Module Level 4. URL: https://drafts.csswg.org/css-box-4/
[CSS-BREAK-4]
Rossen Atanassov; Elika Etemad. CSS Fragmentation Module Level 4. URL: https://drafts.csswg.org/css-break-4/
[CSS-CASCADE-5]
Elika Etemad; Miriam Suzanne; Tab Atkins Jr.. CSS Cascading and Inheritance Level 5. URL: https://drafts.csswg.org/css-cascade-5/
[CSS-CONTAIN-2]
Tab Atkins Jr.; Florian Rivoal; Vladimir Levin. CSS Containment Module Level 2. URL: https://drafts.csswg.org/css-contain-2/
[CSS-DISPLAY-3]
Elika Etemad; Tab Atkins Jr.. CSS Display Module Level 3. URL: https://drafts.csswg.org/css-display/
[CSS-DISPLAY-4]
CSS Display Module Level 4. Editor's Draft. URL: https://drafts.csswg.org/css-display-4/
[CSS-GRID-2]
Tab Atkins Jr.; Elika Etemad; Rossen Atanassov. CSS Grid Layout Module Level 2. URL: https://drafts.csswg.org/css-grid-2/
[CSS-INLINE-3]
Dave Cramer; Elika Etemad. CSS Inline Layout Module Level 3. URL: https://drafts.csswg.org/css-inline-3/
[CSS-LOGICAL-1]
Rossen Atanassov; Elika Etemad. CSS Logical Properties and Values Level 1. URL: https://drafts.csswg.org/css-logical-1/
[CSS-MASKING-1]
Dirk Schulze; Brian Birtles; Tab Atkins Jr.. CSS Masking Module Level 1. URL: https://drafts.fxtf.org/css-masking-1/
[CSS-OVERFLOW-4]
David Baron; Florian Rivoal; Elika Etemad. CSS Overflow Module Level 4. URL: https://drafts.csswg.org/css-overflow-4/
[CSS-PSEUDO-4]
Daniel Glazman; Elika Etemad; Alan Stearns. CSS Pseudo-Elements Module Level 4. URL: https://drafts.csswg.org/css-pseudo-4/
[CSS-SCROLL-SNAP-1]
Matt Rakow; et al. CSS Scroll Snap Module Level 1. URL: https://drafts.csswg.org/css-scroll-snap-1/
[CSS-TEXT-DECOR-4]
Elika Etemad; Koji Ishii. CSS Text Decoration Module Level 4. URL: https://drafts.csswg.org/css-text-decor-4/
[CSS-TRANSFORMS-2]
Tab Atkins Jr.; et al. CSS Transforms Module Level 2. URL: https://drafts.csswg.org/css-transforms-2/
[CSS-UI-3]
Tantek Çelik; Florian Rivoal. CSS Basic User Interface Module Level 3 (CSS3 UI). URL: https://drafts.csswg.org/css-ui-3/
[CSS-VALUES-3]
Tab Atkins Jr.; Elika Etemad. CSS Values and Units Module Level 3. URL: https://drafts.csswg.org/css-values-3/
[CSS-VALUES-4]
Tab Atkins Jr.; Elika Etemad. CSS Values and Units Module Level 4. URL: https://drafts.csswg.org/css-values-4/
[CSS-WRITING-MODES-4]
Elika Etemad; Koji Ishii. CSS Writing Modes Level 4. URL: https://drafts.csswg.org/css-writing-modes-4/
[CSS2]
Bert Bos; et al. Cascading Style Sheets Level 2 Revision 1 (CSS 2.1) Specification. URL: https://drafts.csswg.org/css2/
[CSS3-FLEXBOX]
Tab Atkins Jr.; et al. CSS Flexible Box Layout Module Level 1. URL: https://drafts.csswg.org/css-flexbox-1/
[CSS3-GRID-LAYOUT]
Tab Atkins Jr.; et al. CSS Grid Layout Module Level 1. URL: https://drafts.csswg.org/css-grid/
[CSS3-TRANSFORMS]
Simon Fraser; et al. CSS Transforms Module Level 1. URL: https://drafts.csswg.org/css-transforms/
[CSS4BACKGROUND]
Bert Bos; Elika J. Etemad; Lea Verou. CSS Backgrounds and Borders Module Level 4. Proposal for a CSS module. URL: https://drafts.csswg.org/css-backgrounds-4/
[CSSOM-VIEW]
Simon Pieters. CSSOM View Module. URL: https://drafts.csswg.org/cssom-view/
[EPUB-33]
Ivan Herman; Matt Garrish; Dave Cramer. EPUB 3.3. URL: https://w3c.github.io/epub-specs/epub33/core/
[HTML]
Anne van Kesteren; et al. HTML Standard. Living Standard. URL: https://html.spec.whatwg.org/multipage/
[RFC2119]
S. Bradner. Key words for use in RFCs to Indicate Requirement Levels. March 1997. Best Current Practice. URL: https://datatracker.ietf.org/doc/html/rfc2119
[UAX29]
Josh Hadley. Unicode Text Segmentation. 16 August 2023. Unicode Standard Annex #29. URL: https://www.unicode.org/reports/tr29/tr29-43.html

Informative References

[CSS-CONTAIN-1]
Tab Atkins Jr.; Florian Rivoal. CSS Containment Module Level 1. URL: https://drafts.csswg.org/css-contain-1/
[CSS-SIZING-3]
Tab Atkins Jr.; Elika Etemad. CSS Box Sizing Module Level 3. URL: https://drafts.csswg.org/css-sizing-3/
[CSS-TEXT-3]
Elika Etemad; Koji Ishii; Florian Rivoal. CSS Text Module Level 3. URL: https://drafts.csswg.org/css-text-3/
[CSS-WRITING-MODES-3]
Elika Etemad; Koji Ishii. CSS Writing Modes Level 3. URL: https://drafts.csswg.org/css-writing-modes-3/
[CSS1]
Håkon Wium Lie; Bert Bos. Cascading Style Sheets, level 1. 13 September 2018. REC. URL: https://www.w3.org/TR/CSS1/
[MEDIAQUERIES-5]
Dean Jackson; et al. Media Queries Level 5. URL: https://drafts.csswg.org/mediaqueries-5/

Property Index

Name Value Initial Applies to Inh. %ages Anim­ation type Canonical order Com­puted value Logical property group
overflow <'overflow-block'>{1,2} visible block containers [CSS2], flex containers [CSS3-FLEXBOX], and grid containers [CSS3-GRID-LAYOUT] no N/A discrete per grammar see individual properties
overflow-block visible | hidden | clip | scroll | auto visible block containers [CSS2], flex containers [CSS3-FLEXBOX], grid containers [CSS3-GRID-LAYOUT] no N/A discrete per grammar usually specified value, but see text overflow
overflow-clip-margin <visual-box> || <length [0,∞]> 0px boxes to which overflow applies no n/a per computed value if the <visual-box> values match; otherwise discrete per grammar the computed <length> and a <visual-box> keyword
overflow-inline visible | hidden | clip | scroll | auto visible block containers [CSS2], flex containers [CSS3-FLEXBOX], grid containers [CSS3-GRID-LAYOUT] no N/A discrete per grammar usually specified value, but see text overflow
overflow-x visible | hidden | clip | scroll | auto visible block containers [CSS2], flex containers [CSS3-FLEXBOX], grid containers [CSS3-GRID-LAYOUT] no N/A discrete per grammar usually specified value, but see text overflow
overflow-y visible | hidden | clip | scroll | auto visible block containers [CSS2], flex containers [CSS3-FLEXBOX], grid containers [CSS3-GRID-LAYOUT] no N/A discrete per grammar usually specified value, but see text overflow
scroll-behavior auto | smooth auto scroll containers no n/a not animatable per grammar specified value
scrollbar-gutter auto | stable && both-edges? auto scroll containers no n/a discrete per grammar specified keyword(s)
text-overflow clip | ellipsis clip block containers no N/A discrete per grammar specified keyword

Issues Index

Is this description of handling transforms sufficiently accurate?
This needs further testing and investigation; is therefore deferred in this draft.
Need to evaluate what should/should not clip scrollable overflow. [Issue #8607]
Check whether things like baseline alignment depend on the initial scroll position or the scroll origin position.
This doesn’t define a coordinate system for scroll offsets. Whether they increase downward/rightward, block/inline-axis endward, or away from the scroll origin is not defined. Should each API define its coordinate model?
MDN

overflow-block

In only one current engine.

Firefox69+SafariNoneChromeNone
Opera?EdgeNone
Edge (Legacy)?IENone
Firefox for Android?iOS Safari?Chrome for Android?Android WebView?Samsung Internet?Opera Mobile?

overflow-inline

In only one current engine.

Firefox69+SafariNoneChromeNone
Opera?EdgeNone
Edge (Legacy)?IENone
Firefox for Android?iOS Safari?Chrome for Android?Android WebView?Samsung Internet?Opera Mobile?
MDN

overflow-clip-margin

In no current engines.

FirefoxNoneSafariNoneChromeNone
Opera?EdgeNone
Edge (Legacy)?IENone
Firefox for Android?iOS Safari?Chrome for Android?Android WebView?Samsung Internet?Opera Mobile?
MDN

overflow-x

In all current engines.

Firefox3.5+Safari3+Chrome1+
Opera9.5+Edge79+
Edge (Legacy)12+IE5+
Firefox for Android?iOS Safari1+Chrome for Android?Android WebView?Samsung Internet?Opera Mobile?

overflow-y

In all current engines.

Firefox3.5+Safari3+Chrome1+
Opera9.5+Edge79+
Edge (Legacy)12+IE5+
Firefox for Android?iOS Safari1+Chrome for Android?Android WebView?Samsung Internet?Opera Mobile?
MDN

overflow

In all current engines.

Firefox1+Safari1+Chrome1+
Opera7+Edge79+
Edge (Legacy)12+IE4+
Firefox for Android4+iOS Safari?Chrome for Android?Android WebView37+Samsung Internet?Opera Mobile?

overflow_value

In all current engines.

Firefox1+Safari1+Chrome1+
Opera7+Edge79+
Edge (Legacy)12+IE4+
Firefox for Android?iOS Safari?Chrome for Android?Android WebView37+Samsung Internet?Opera Mobile?
MDN

scroll-behavior

In all current engines.

Firefox36+Safari15.4+Chrome61+
Opera?Edge79+
Edge (Legacy)?IENone
Firefox for Android?iOS Safari?Chrome for Android?Android WebView?Samsung Internet?Opera Mobile?
MDN

scrollbar-gutter

Firefox97+SafariNoneChrome94+
Opera?Edge94+
Edge (Legacy)?IENone
Firefox for Android?iOS Safari?Chrome for Android?Android WebView?Samsung Internet?Opera Mobile?
MDN

text-overflow

In all current engines.

Firefox7+Safari1.3+Chrome1+
Opera11+Edge79+
Edge (Legacy)12+IE6+
Firefox for Android?iOS Safari?Chrome for Android?Android WebView37+Samsung Internet?Opera Mobile11+
CanIUse

Support:Android Browser123+Baidu Browser13.52+Blackberry BrowserNoneChrome61+Chrome for Android123+Edge79+Firefox36+Firefox for Android124+IENoneIE MobileNoneKaiOS Browser3.0+Opera48+Opera MiniNoneOpera Mobile80+QQ Browser14.9+Safari15.4+Safari on iOS15.4+Samsung Internet8.2+UC Browser for Android15.5+

Source: caniuse.com as of 2024-04-12

CanIUse

Support:Android Browser2.1+Baidu Browser13.52+Blackberry Browser7+Chrome4+Chrome for Android123+Edge12+Firefox7+Firefox for Android124+IE6+IE Mobile10+KaiOS Browser2.5+Opera11+Opera MiniAllOpera Mobile12.1+QQ Browser14.9+Safari3.1+Safari on iOS3.2+Samsung Internet4+UC Browser for Android15.5+

Source: caniuse.com as of 2024-04-12