CSS Containment Module Level 1

CSS Containment Module Level 1
CSS Containment Module Level 1
W3C Recommendation
25 June 2024
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Tab Atkins
Google
Florian Rivoal
On behalf of Bloomberg
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Abstract
This CSS module describes the
contain
property, which indicates that the element’s subtree is independent of the rest of the page. This enables heavy optimizations by user agents when used well.
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 section describes the status of this document at the time of its publication.
A list of current W3C publications
and the latest revision of this technical report
can be found in the
W3C technical reports index at https://www.w3.org/TR/.
This document was published
by the
CSS Working Group
as a W3C Recommendation using the
Recommendation
track
A W3C Recommendation is a specification that, after extensive consensus-building, is endorsed by
W3C
and its Members,
and has commitments from Working Group members to
royalty-free licensing
for implementations.
Please send feedback
by
filing issues in GitHub
(preferred),
including the spec code “css-contain” in the title, like this:
“[css-contain]
…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
This document was produced by a group operating under the
W3C Patent Policy
W3C maintains a
public list of any patent disclosures
made in connection with the deliverables of the group;
that page also includes instructions for disclosing a patent.
An individual who has actual knowledge of a patent which the individual believes
contains
Essential Claim(s)
must disclose the information in accordance with
section 6 of the W3C Patent Policy
This document was published by the CSS Working Group as a Recommendation using the
Recommendation track
W3C recommends the wide deployment of this specification as a standard for the Web.
1.
Introduction
Efficiently rendering a website relies on the user agent being able to detect what parts of the page are being displayed,
which parts might affect the currently-displayed section,
and what can be ignored.
There are various heuristics that can be used to guess when a given sub-tree is independent of the rest of the page in some manner,
but they’re fragile,
so innocuous changes to a page may inadvertently make it fail such heuristic tests,
causing rendering to fall into a slow code path.
There are also many things that would be good to isolate which are difficult or impossible to detect in a heuristic manner.
To alleviate these problems
and allow strong, predictable isolation of a subtree from the rest of the page,
this specification defines a
contain
property.
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.
2.
Strong Containment: the
contain
property
Name:
contain
Value:
none
strict
content
[ size
||
layout
||
paint ]
Initial:
none
Applies to:
See
below
Inherited:
no
Percentages:
n/a
Computed value:
the keyword
none
or one or more of
size
layout
paint
Canonical order:
per grammar
Animation type:
not animatable
User agents are expected to support this property on all media, including non-visual ones.
The
contain
property allows an author to indicate that an element and its contents are,
as much as possible,
independent
of the rest of the document tree.
This allows user agents to utilize much stronger optimizations when rendering a page using
contain
properly,
and allows authors to be confident that their page won’t accidentally fall into a slow code path
due to an innocuous change.
none
This value indicates that the property has no effect.
The element renders as normal,
with no containment effects applied.
strict
This value computes to
size layout paint
and thus turns on all forms of
containment
for the element.
content
This value computes to
layout paint
and thus turns on all forms of
containment
except
size containment
for the element.
Note:
contain: content
is reasonably "safe" to apply widely;
its effects are fairly minor in practice,
and most content won’t run afoul of its restrictions.
However, because it doesn’t apply
size containment
the element can still respond to the size of its contents,
which can cause layout-invalidation to percolate further up the tree than desired.
Use
contain: strict
when possible,
to gain as much containment as you can.
size
The value turns on
size containment
for the element.
This ensures that the
containment box
can be laid out
without needing to examine its descendants.
layout
This value turns on
layout containment
for the element.
This ensures that the
containment box
is
totally opaque
for layout purposes;
nothing outside can affect its internal layout,
and vice versa.
paint
This value turns on
paint containment
for the element.
This ensures that the descendants of the
containment box
don’t display outside its bounds,
so if an element is off-screen or otherwise not visible,
its descendants are also guaranteed to be not visible.
This property generally applies to all elements (including
CSS Pseudo-Elements 4
§ 4.1 Generated Content Pseudo-elements: ::before and ::after
although some types of containment have no effect on some elements,
as detailed in
§ 3 Types of Containment
In addition, in the case of
[SVG2]
the
contain
property only applies to
svg
elements that have an associated CSS layout box.
contain
is useful when used widely on a page,
particularly when a page contains a lot of "widgets" which are all independent.
For example, assume a micropost social network had markup something like this:
body
aside
...
aside
section
h2
Messages
h2
article
Lol, check out this dog: images.example.com/jsK3jkl
article
article
I had a ham sandwich today. #goodtimes
article
article
I have political opinions that you need to hear!
article
section
body
There are probably a
lot
of messages displayed on the site,
but each is independent and won’t affect anything else on the site.
As such, each can be marked with
contain: content
to communicate this to the user agent,
so it can optimize the page and skip a lot of computation for messages that are off-screen.
If the size of each message is known ahead of time,
contain: strict
can be applied to communicate further restrictions.
Additionally, when the
used value
of the
contain
property
on either the HTML
html
or
body
elements
is anything other than
none
propagation of properties
from the
body
element
to the
initial containing block
, the viewport, or the
canvas background
is disabled.
Notably, this affects:
writing-mode
direction
, and
text-orientation
(see
CSS Writing Modes 3
§ 8 The Principal Writing Mode
overflow
and its longhands (see
CSS Overflow 3
§ 3.3 Overflow Viewport Propagation
background
and its longhands (see
CSS Backgrounds 3
§ 2.11.2 The Canvas Background and the HTML Element
Note:
Propagation
to the
initial containing block
, the viewport, or the
canvas background
of properties set on the
html
element itself
is unaffected.
3.
Types of Containment
There are several varieties of
containment
that an element can be subject to,
restricting the effects that its descendants can have on the rest of the page in various ways.
Containment
enables much more powerful optimizations by user agents,
and helps authors compose their page out of functional units,
as it limits how widely a given change can affect a document.
Specification authors introducing new properties or mechanisms
need to consider whether and how the various types of containment
affect what they are introducing,
and include in their specification any effect not described here.
3.1.
Size Containment
Giving an element
size containment
makes its
principal box
size containment box
and has the following effects:
The
intrinsic sizes
of the
size containment box
are determined as if the element had no content,
following the same logic as when
sizing as if empty
Note:
This affects explicit invocations of the
min-content
or
max-content
keywords,
as well as any calculation that depends on these measurement,
such as sizing
grid tracks
into which a size contained item is placed,
or if
fit-content sizing
the containment box’s parent.
Laying out a
size containment box
and its content is conceptually done in two phases:
Sizing as if empty
The
used
width
and
height
of the
containment box
are determined as if performing a normal layout of the box,
except that it is treated as having no content—​not even through pseudo elements such as
::before
::after
, or
::marker
Replaced elements
must be treated as having a
natural
width and height of 0
and no
natural aspect ratio
Note:
Size containment only suppresses the
natural aspect ratio
so properties like
aspect-ratio
which affect that
preferred aspect ratio
directly
are honored.
All CSS properties of the
size containment box
are taken into account
as they would be when performing layout normally.
Other specifications may make specific exemptions.
Note:
Even when the element’s
sizing properties
specify an intrinsic size,
this does not necessarily make the element zero-sized:
properties set on the element itself
continue to be taken into account,
which can cause it to be larger.
Laying out in-place
The
containment box
's content
(including any pseudo-elements)
must then be laid out into
the now fixed-size
containment box
normally.
Note:
Size containment
does not suppress baseline alignment.
See
layout containment
for that.
Size containment boxes
are
monolithic
(See
CSS Fragmentation 3
§ 4.1 Possible Break Points
).
Given the following markup and style, the image would be sized to 100px by 100px,
as the aspect ratio set by the
aspect-ratio
property takes effect.
img
width
100
px
aspect-ratio
contain
size
img
src
"https://www.example.com/300x100.jpg"
If the
aspect-ratio
property had not been declared,
the image would have been 100px by 0px,
as its
natural aspect ratio
is suppressed,
and its
natural height
is treated as 0.
However, giving an element
size containment
has no effect if any of the following are true:
if the element does not generate a
principal box
(as is the case with
display: contents
or
display: none
if its
inner display type
is
table
if its
principal box
is
an
internal table box
if its
principal box
is
an
internal ruby box
or a
non-atomic
inline-level
box
Note:
Internal table boxes,
which do not include table captions,
are excluded,
because the table layout algorithm
does not allow boxes to become smaller than their inflow content.
Sizing a table cell as if it was empty and then laying out its content inside without changing the size
is effectively an undefined operation.
Manually setting the
width
or
height
properties to
cannot make it smaller than its content.
This concern does not apply to table captions,
which are perfectly capable of having a fixed size
that is independent of their content.
3.1.1.
Possible Size-Containment Optimizations
This section is non-normative.
By itself,
size containment
does not offer much optimization opportunity.
Its primary benefit on its own is that tools which want to lay out the
containment box
's contents
based on the
containment box
's size
(such as a JS library implementing the "container query" concept)
can do so without fear of "infinite loops",
where having a child’s size respond to the size of the
containment box
causes the
containment box
's size to change as well,
possibly triggering
further
changes in how the child sizes itself
and possibly thus more changes to the
containment box
's size,
ad infinitum.
When paired with
layout containment
, though,
possible optimizations that can be enabled include (but are not limited to):
When the style or contents of a descendant of the
containment box
is changed,
calculating what part of the DOM tree is "dirtied" and might need to be re-laid out
can stop at the
containment box
When laying out the page,
if the
containment box
is off-screen or obscured,
the layout of its contents (i.e. "
laying out in-place
") can be delayed or done at a lower priority.
3.2.
Layout Containment
Giving an element
layout containment
makes its
principal box
layout containment box
and has the following effects:
The
layout containment box
establishes an independent formatting context
If at least one
fragmentation container
of a
fragmentation context
has
layout containment
or if at least one
fragmentation container
of a
fragmentation context
is a descendant of
layout containment box
and
at least one subsequent
fragmentation container
of the same
fragmentation context
is not a descendant of that same element with layout containment,
then the first
layout containment box
which is either a
fragmentation container
itself
or is an ancestor of a
fragmentation container
must “trap” the remainder of the
fragmented flow
fragmentation
must not continue past the
layout containment
boundary,
and the last
fragmentation container
within the first
layout containment
boundary
is treated as if it is the last
fragmentation container
in its
fragmentation context
If subsequent
fragmentation containers
in the
fragmentation context
are only generated when more content remains in the
fragmented flow
then they are not generated.
If they would exist regardless,
they remain part of the
fragmentation context
but do not receive any content from the
fragmented flow
Note:
At the time of writing, no stable specification is affected by this point.
Only specifications that would enable some (but not all) fragmentation containers of a fragmentation context
to be layout-contained (or descendants of a layout contained element)
are concerned.
This is not the case of
[CSS-PAGE-3]
nor of
[CSS-MULTICOL-1]
This requirement is nonetheless included because
several mechanisms that would make this a possibility have been considered
(e.g.:
[CSS-REGIONS-1]
::nth-fragment()
, a hypothetical selector for individual columns of a multicol…),
and the guarantees that layout containment is intended to offer would not be realized
if such mechanisms did not abide by this rule.
[CSS-REGIONS-1]
has details over how
layout containment
affects
regions.
article
Lorem ipsum…
article
div
id
>div
aside
div
id
>div
div
id
>div
aside
aside
div
id
>div
div
id
>div
aside
div
id
>div
article
flow-into
foo
;}
#a
#b
#c
#d
#e
#f
flow-from
foo
;}
aside
contain
layout
In this
[CSS-REGIONS-1]
example,
content can flow from
#a
to
#b
from
#b
to
#c
However as
#c
is the last fragment container in the first
layout containment box
it traps all the remaining content,
and nothing gets flowed into
#d
#e
, or
#f
If the computed value of the
overflow
property is
either
visible
or
clip
or a combination thereof,
any overflow must be treated as
ink overflow
The
layout containment box
establishes an
absolute positioning containing block
and a
fixed positioning containing block
The
layout containment box
creates a
stacking context
Forced breaks
are allowed within
layout containment boxes
but do not propagate to the parent as otherwise described in
CSS Fragmentation 3
§ 3.1 Breaks Between Boxes: the break-before and break-after properties
Note:
This introduces the previously non-existent possibility that
forced breaks
may occur between a box and its container (See
CSS Fragmentation 3
§ 4.1 Possible Break Points
).
For the purpose of the
vertical-align
property,
or any other property whose effects
need to relate the position of the
layout containment box
's baseline
to something other than its descendants,
the
containment box
is treated as having no baseline.
However, giving an element
layout containment
has no effect if any of the following are true:
if the element does not generate a
principal box
(as is the case with
display: contents
or
display: none
if its
principal box
is
an
internal table box
other than
table-cell
if its
principal box
is
an
internal ruby box
or a
non-atomic
inline-level
box
3.2.1.
Possible Layout-Containment Optimizations
This section is non-normative.
Possible optimizations that can be enabled by
layout containment
include (but are not limited to):
When laying out the page,
the contents of separate
containment boxes
can be laid out in parallel,
as they’re guaranteed not to affect each other.
When laying out the page,
if the
containment box
is off-screen or obscured
and the layout of the visible parts of the screen do not depend on the size of the
containment box
(for example, if the
containment box
is near the end of a block container,
and you’re viewing the beginning of the block container),
the layout of the
containment box
' contents can be delayed or done at a lower priority.
(When paired with
size containment
this optimization can be applied more liberally.)
3.3.
Paint Containment
Giving an element
paint containment
makes its
principal box
paint containment box
and has the following effects:
The contents of the element
including any
ink
or
scrollable overflow
must be clipped to the
padding edge
of the
paint containment box
taking
corner clipping
into account.
This does not include the creation of any mechanism
to access or indicate the presence of the clipped content;
nor does it inhibit the creation of any such mechanism through other properties,
such as
overflow
resize
, or
text-overflow
Note:
The next level of this specification
[CSS-CONTAIN-2]
refines this effect
to apply to the
overflow clip edge
rather than the
padding edge
in order to take the new
overflow-clip-margin
property into account.
For implementations that do not support
overflow-clip-margin
the effect is identical.
Note:
The behavior is described in this paragraph is equivalent to changing
overflow-x: visible
into
overflow-x: clip
and
overflow-y: visible
into
overflow-y: clip
at used value time,
while leaving other values of
overflow-x
and
overflow-y
unchanged.
The
paint containment box
establishes an
absolute positioning containing block
and a
fixed positioning containing block
The
paint containment box
creates a
stacking context
The
paint containment box
establishes an independent formatting context
However, giving an element
paint containment
has no effect if any of the following are true:
if the element does not generate a
principal box
(as is the case with
display: contents
or
display: none
if its
principal box
is
an
internal table box
other than
table-cell
if its
principal box
is
an
internal ruby box
or a
non-atomic
inline-level
box
3.3.1.
Possible Paint-Containment Optimizations
This section is non-normative.
Possible optimizations that can be enabled by
paint containment
include (but are not limited to):
If the
containment box
is off-screen or obscured,
the UA can usually skip trying to paint its contents,
as they’re guaranteed to be off-screen/obscured as well.
Note:
Some paint effects such as the
blur()
filter from
[FILTER-EFFECTS-1]
have non local effects.
The user agent needs to keep track of these,
as it may need to repaint parts of an element with such a filter
when its descendents change,
even if they have
paint containment
and could otherwise be skipped.
Unless the clipped content is made accessible via a separate mechanism
such as the
overflow
resize
, or
text-overflow
properties,
the UA can reserve "canvas" space for the box exactly the box’s size.
(In similar, scrollable, situations, like
overflow: hidden
it’s possible to scroll to the currently-clipped content,
so UAs often predictively overpaint somewhat
so there’s something to see as soon as the scroll happens,
rather than a frame later.)
Because they are guaranteed to be stacking contexts,
scrolling elements can be painted into a single GPU layer.
4.
Privacy Considerations
There are no known privacy impacts of the features in this specification.
5.
Security Considerations
There are no known security impacts of the features in this specification.
Like any other CSS specification, it affects the rendering of the document,
but does not introduce any special ability to present content in a misleading way
that was not previously available through other CSS modules
and that isn’t inherent to the act of formatting the document.
Appendix A. Changes
This appendix is
informative
Changes from the
Recommendation of 25 October 2022
Three proposed corrections were formally incorporated into the normative text:
Proposed Correction 1:
A minor adjustment was made
to the way the computed value of the
contain
property is determined:
the shortcut values (
strict
and
content
),
instead of computing to themselves,
compute to the corresponding keywords.
Given that the effect is identical,
this allows implementations not to store the precise syntax through which this was achieved.
Also, thanks to the shortest-serialization principle,
this makes this unimportant difference non observable via serialization.
Proposed Correction 2:
The description of size containment was somewhat ambiguous,
causing implementers to have some doubts about the precise intended effects
in certain cases.
It was replaced with a more precise description,
in order to clarify what is meant without changing the intended behavior.
Proposed Correction 3:
The CSS Working Group had forgotten to consider the effects of containment
on the HTML
html
and
body
elements,
particularly in consideration of the fact that
for legacy reasons,
some properties can propagate outwards from the
body
element.
The text added addresses this oversight.
An
implementation report
details their implementation in multiple engines.
Earlier Changes
Details about earlier changes to this specification
can be found in
the Changes section of its previous publication
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

, like
this:
UAs MUST provide an accessible alternative.
Conformance classes
Conformance to this specification
is defined for three conformance classes:
style sheet
CSS
style sheet
renderer
UA
that interprets the semantics of a style sheet and renders
documents that use them.
authoring tool
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
Questions should be directed to the
public-css-testsuite@w3.org
mailing list.
Index
Terms defined by this specification
contain
, in § 2
containment
, in § 3
content
, in § 2
Laying out in-place
, in § 3.1
layout
, in § 2
layout containment
, in § 3.2
layout containment box
, in § 3.2
none
, in § 2
paint
, in § 2
paint containment
, in § 3.3
paint containment box
, in § 3.3
size
, in § 2
size containment
, in § 3.1
size containment box
, in § 3.1
Sizing as if empty
, in § 3.1
strict
, in § 2
Terms defined by reference
[CSS-BACKGROUNDS-3]
defines the following terms:
background
canvas background
corner clipping
[CSS-BREAK-3]
defines the following terms:
forced break
fragmentation
fragmentation container
fragmentation context
fragmented flow
monolithic
[CSS-CASCADE-5]
defines the following terms:
used value
[CSS-DISPLAY-3]
defines the following terms:
atomic inline
display
establishes an independent formatting context
initial containing block
inline-level
inner display type
internal ruby box
internal table box
principal box
replaced element
table
table-cell
[CSS-GRID-2]
defines the following terms:
grid track
[CSS-IMAGES-3]
defines the following terms:
natural aspect ratio
natural dimension
natural height
[CSS-OVERFLOW-3]
defines the following terms:
clip
ink overflow
overflow
overflow-x
overflow-y
scrollable overflow
visible
[CSS-OVERFLOW-4]
defines the following terms:
::nth-fragment()
overflow clip edge
overflow-clip-margin
[CSS-POSITION-3]
defines the following terms:
absolute positioning containing block
fixed positioning containing block
[CSS-PSEUDO-4]
defines the following terms:
::after
::before
::marker
[CSS-SIZING-3]
defines the following terms:
fit-content size
height
intrinsic size
max-content
min-content
sizing property
width
[CSS-SIZING-4]
defines the following terms:
aspect-ratio
preferred aspect ratio
[CSS-UI-3]
defines the following terms:
text-overflow
[CSS-UI-4]
defines the following terms:
resize
[CSS-VALUES-4]
defines the following terms:
css-wide keywords
||
[CSS-WRITING-MODES-3]
defines the following terms:
direction
[CSS-WRITING-MODES-4]
defines the following terms:
text-orientation
writing-mode
[CSS2]
defines the following terms:
padding edge
stacking context
vertical-align
[FILTER-EFFECTS-1]
defines the following terms:
blur()
[HTML]
defines the following terms:
body
html
[SVG2]
defines the following terms:
svg
References
Normative References
[CSS-BACKGROUNDS-3]
Elika Etemad; Brad Kemper.
CSS Backgrounds and Borders Module Level 3
. 11 March 2024. CR. URL:
[CSS-BREAK-3]
Rossen Atanassov; Elika Etemad.
CSS Fragmentation Module Level 3
. 4 December 2018. CR. URL:
[CSS-CASCADE-5]
Elika Etemad; Miriam Suzanne; Tab Atkins Jr..
CSS Cascading and Inheritance Level 5
. 13 January 2022. CR. URL:
[CSS-DISPLAY-3]
Elika Etemad; Tab Atkins Jr..
CSS Display Module Level 3
. 30 March 2023. CR. URL:
[CSS-IMAGES-3]
Tab Atkins Jr.; Elika Etemad; Lea Verou.
CSS Images Module Level 3
. 18 December 2023. CR. URL:
[CSS-OVERFLOW-3]
Elika Etemad; Florian Rivoal.
CSS Overflow Module Level 3
. 29 March 2023. WD. URL:
[CSS-POSITION-3]
Elika Etemad; Tab Atkins Jr..
CSS Positioned Layout Module Level 3
. 3 April 2023. WD. URL:
[CSS-PSEUDO-4]
Daniel Glazman; Elika Etemad; Alan Stearns.
CSS Pseudo-Elements Module Level 4
. 30 December 2022. WD. URL:
[CSS-SIZING-3]
Tab Atkins Jr.; Elika Etemad.
CSS Box Sizing Module Level 3
. 17 December 2021. WD. URL:
[CSS-UI-3]
Tantek Çelik; Florian Rivoal.
CSS Basic User Interface Module Level 3 (CSS3 UI)
. 21 June 2018. REC. URL:
[CSS-UI-4]
Florian Rivoal.
CSS Basic User Interface Module Level 4
. 16 March 2021. WD. URL:
[CSS-VALUES-3]
Tab Atkins Jr.; Elika Etemad.
CSS Values and Units Module Level 3
. 22 March 2024. CR. URL:
[CSS-VALUES-4]
Tab Atkins Jr.; Elika Etemad.
CSS Values and Units Module Level 4
. 12 March 2024. WD. URL:
[CSS-WRITING-MODES-3]
Elika Etemad; Koji Ishii.
CSS Writing Modes Level 3
. 10 December 2019. REC. URL:
[CSS-WRITING-MODES-4]
Elika Etemad; Koji Ishii.
CSS Writing Modes Level 4
. 30 July 2019. CR. URL:
[CSS2]
Bert Bos; et al.
Cascading Style Sheets Level 2 Revision 1 (CSS 2.1) Specification
. 7 June 2011. REC. URL:
[HTML]
Anne van Kesteren; et al.
HTML Standard
. Living Standard. URL:
[RFC2119]
S. Bradner.
Key words for use in RFCs to Indicate Requirement Levels
. March 1997. Best Current Practice. URL:
[SVG2]
Amelia Bellamy-Royds; et al.
Scalable Vector Graphics (SVG) 2
. 4 October 2018. CR. URL:
Informative References
[CSS-CONTAIN-2]
Tab Atkins Jr.; Florian Rivoal; Vladimir Levin.
CSS Containment Module Level 2
. 17 September 2022. WD. URL:
[CSS-GRID-2]
Tab Atkins Jr.; Elika Etemad; Rossen Atanassov.
CSS Grid Layout Module Level 2
. 18 December 2020. CR. URL:
[CSS-MULTICOL-1]
Florian Rivoal; Rachel Andrew.
CSS Multi-column Layout Module Level 1
. 16 May 2024. CR. URL:
[CSS-OVERFLOW-4]
David Baron; Florian Rivoal; Elika Etemad.
CSS Overflow Module Level 4
. 21 March 2023. WD. URL:
[CSS-PAGE-3]
Elika Etemad.
CSS Paged Media Module Level 3
. 14 September 2023. WD. URL:
[CSS-REGIONS-1]
Rossen Atanassov; Alan Stearns.
CSS Regions Module Level 1
. 9 October 2014. WD. URL:
[CSS-SIZING-4]
Tab Atkins Jr.; Elika Etemad; Jen Simmons.
CSS Box Sizing Module Level 4
. 20 May 2021. WD. URL:
[FILTER-EFFECTS-1]
Dirk Schulze; Dean Jackson.
Filter Effects Module Level 1
. 18 December 2018. WD. URL:
Property Index
Name
Value
Initial
Applies to
Inh.
%ages
Anim­ation type
Canonical order
Com­puted value
contain
none | strict | content | [ size || layout || paint ]
none
See below
no
n/a
not animatable
per grammar
the keyword none or one or more of size, layout, paint