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 defines the long-standing de-facto overflow-x and overflow-y properties, adds a clip value, introduces an overflow-clip-margin property, and defines overflow handling more fully. It also introduces control over smooth scrolling via scroll-behavior and for reserving space for the scrollbar via scrollbar-gutter.

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.

When applied to 'display: table' elements, the properties defined in this module apply to the table grid box (not the table wrapper box). [CSS2] [CSS-TABLES-3]

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:

• ink overflow
• scrollable overflow

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; or text rendering, where shaping and rasterization can vary by platform) do not precisely define what visual extent they cover, the extent of the ink overflow is undefined, and may vary across UAs.

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. See § 3.3 Calculating the Scrollable Overflow Area for details.

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 scroll container is the nearest scroll container ancestor in the containing block chain. (See § 3 Clipping and Scrolling Overflow for control over whether a box clips or scrolls its overflow.)

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. For example, scroll-initial-target property can be used to change the initial scroll position. [CSS-SCROLL-SNAP-2]

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.) 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.

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?

Unless otherwise adjusted (e.g. by content alignment [css-align-3]), the area beyond the scroll origin in either axis is considered the unreachable scrollable overflow region: content rendered here is not accessible to the reader, see § 2.2 Scrollable Overflow.

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. Clipping and Scrolling Overflow

The properties in this chapter specify whether and where a box’s overflow is clipped; if so, whether it is a scroll container; and if so, in which axis(es) it is allowed to scroll (its scrollable axis(es)), thus which of the following types of scroll container it is:

single-axis scroll container

A scroll container that is scrollable in only one axis.

dual-axis scroll container

A scroll container that is scrollable in both axes.

block-axis scroll container

inline-axis scroll container

x-axis scroll container

y-axis scroll container

A scroll container that is scrollable in the specified axis, regardless of whether it can also scroll in the other axis.

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

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.

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.

hidden

This value indicates that the box’s content is clipped to its overflow clip edge 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].

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.

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 can use display: flow-root together with overflow: clip.

scroll

This value indicates that the content is clipped to the overflow clip edge, but can be scrolled into view.

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 scroll, auto, and hidden values are known as the scrollable values of overflow. They cause the box to be a scroll container and the affected axis to be a scrollable axis. A block box that becomes a scroll container also establishes an independent formatting context.

The visible and clip values are known as the non-scrollable values. However, if the other axis specifies a scrollable value, a specified value of visible computes to auto, enabling scrolling in its axis. If neither axis computes to a scrollable value, the box is not a scroll container. If only one axis computes to a scrollable value (i.e. the other axis is clip), the box is a single-axis scroll container.

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

Note: The overflow properties are expanded to apply to replaced elements in Level 4.

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:

• The user agent must not make any scrolling mechanism visible. To the extent that the scrolling mechanism that would normally be visible in the absence of visibility: hidden affects layout, it continues to do so, but is not painted.

• As would be the case with overflow: hidden, scrolling directly triggered by user interactions is disabled, but programmatic scrolling continues to take effect.

• The lack of interactive direct scrolling is enforced even if the user interacts (e.g. with a mouse scrolling wheel) with a descendent of the visibility: hidden scroll container that is itself set to visibility: visible.

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:

• When overflow-x and overflow-y compute to hidden, scroll, or auto, the clipping region is rounded based on the border radius, adjusted to the padding edge, as described in CSS Backgrounds 3 § 4.2 Corner Shaping.

• When both overflow-x and overflow-y compute to clip, the clipping region is rounded as described in § 3.2 Expanding Clipping Bounds: the overflow-clip-margin property.

• However, when one of overflow-x or overflow-y computes to clip and the other computes to visible, the clipping region is not 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.

3.1.4. 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.

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

This property defines the overflow clip edge of the box, i.e. precisely where 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>

The specified offset dictates how much the overflow clip edge is expanded from the specified box edge. Negative values indicate insets, instead. 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.

If the box is a scroll container:

• the overflow clip edge is clamped to stay within the element’s padding box. (This does not affect the computed or used value of this property.)

• the border-box value ignores any specified offset (and, due to the previous bullet point, effectively acts as padding-box)

Note: This property was previously defined to only affect overflow: clip. It now also affects scroll containers, but only to shrink the clipping edge.

3.3. Calculating the Scrollable Overflow Area

The scrollable overflow area of a box is the union of:

• Its own padding box.
• All line boxes it directly contains.
• The border boxes of all boxes for which it is the containing block and whose border boxes are positioned not wholly within its unreachable scrollable overflow region (if any), accounting for transforms by projecting each box onto the plane of the element that establishes its 3D rendering context. [CSS3-TRANSFORMS]

  Is this description of handling transforms sufficiently accurate?

  Border boxes with zero area do not affect the scrollable overflow area.

• The margin areas of grid item and flex item boxes for which the box establishes a containing block.

  The UA may additionally include the margin areas of other boxes for which the box establishes a containing block; however, the conditions under which such margin areas are included is undefined in this level. This needs further testing and investigation; is therefore deferred in this draft.

• The scrollable overflow rectangles of all of the above boxes (including zero-area boxes), clipped to their overflow clip edge if overflow is not visible or contain applies paint, and accounting for transforms as described above.

  Note: The clip, clip-path, and mask-* properties [CSS-MASKING-1] do not affect the scrollable overflow area. Only effects that clip to the overflow clip edge are taken into account.

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

• Additional padding added to the scrollable overflow rectangle as necessary to enable scroll positions that satisfy the requirements of both place-content: start and place-content: end alignment.

  Note: This padding represents, within the scrollable overflow rectangle, the box’s own padding so that when its content is scrolled to its end, there is padding between the edge of its in-flow (or floated) content and the border edge of the box. It typically ends up being exactly the same size as the box’s own padding, except in a few cases—​such as when an out-of-flow positioned element, or the visible overflow of a descendent, has already increased the size of the scrollable overflow rectangle outside the conceptual “content edge” of the scroll container’s content.

  

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 unreachable scrollable overflow region.

Note: The content-distribution properties can alter the unreachable scrollable overflow region to ensure that a scroll container’s alignment subject is reachable after alignment. [css-align-3]

4. Scrolling Behaviors and Animations

CSS provides several controls over how scrolling behaves when triggered.

• CSS Scroll Snap allows defining "snap positions", which are scroll positions to which the scroll container is biased to land.

• CSS Overscroll Behavior allows controlling what happens when scrolling past the end of the scrollable area.

• scroll-behavior, defined below, controls whether programmatic scrolling animates smoothly or not.

Note: For animating other things in conjunction with scrolling, see [SCROLL-ANIMATIONS-1].

4.1. Smooth Scrolling: the scroll-behavior Property

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.

5. Scrollbars and Layout

5.1. Scrollbar Contributions to Sizing

The space reserved for the scrollbar is located between the padding area and the border area of the scroll container box. However, for the purpose of the background positioning area and background painting area, this reserved space is treated as part of the padding area.

<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>

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.

...
    article { overflow: auto; max-height: 5em;  width: max-content; }
    section { margin: 2em; line-height: 1 }
...
<article>
  <section>
    This section has big margins.
  </section>
</article>

5.2. 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.

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 § A 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.

6. Automatic Ellipses

6.1. Overflow Ellipsis: the text-overflow property

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.

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

ellipsing details

• Ellipsing only affects rendering and must not affect layout nor dispatching of pointer events: The UA should dispatch any pointer event on the ellipsis to the elided element, as if text-overflow had been none.
• The ellipsis is styled and baseline-aligned according to the block.
• Ellipsing occurs after relative positioning and other graphical transformations.
• If there is insufficient space for the ellipsis, then clip the rendering of the ellipsis itself (on the same side that neutral characters on the line would have otherwise been clipped with the text-overflow:clip value).

user interaction with ellipsis

• When the user is interacting with content (e.g. editing, selecting, scrolling), the user agent may treat text-overflow: ellipsis as text-overflow: clip.
• Selecting the ellipsis should select the ellipsed text. If all of the ellipsed text is selected, UAs should show selection of the ellipsis. Behavior of partially-selected ellipsed text is up to the UA.

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

<div>
CSS IS AWESOME, YES
</div>

<div style="text-overflow:clip; overflow:hidden">
CSS IS AWESOME, YES
</div>

<div style="text-overflow:ellipsis; overflow:hidden">
CSS IS AWESOME, YES
</div>

<div style="text-overflow:ellipsis; overflow:hidden">
NESTED
 <p>PARAGRAPH</p>
WON'T ELLIPSE.
</div>

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.

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

<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>

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.

Significant changes since the 7 October 2025 Working Draft:

• Allow combining overflow: clip behavior in one axis with scrolling in the other, to allow single-axis trapping for e.g. sticky positioning. (Issue 12289)

• Clarify which clipping affects limit contributions to the scrollable overflow area of the nearest scroll container. (Issue 8607)

• Clarify application of overflow to tables. (Isue 10881)

Significant changes since the 29 March 2023 Working Draft:

• Define that overflow: hidden is treated as overflow: clip on replaced elements. (Issue 7714)

• Redefine the interaction of overflowing content distribution and scroll containers to not impact layout, but to only affect the extent of the scrollable overflow area. (Issue 4957)

• Defined some more terminology to help other specs connect to concepts in this one.

See also Previous Changes.

Acknowledgments

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