This specification describes multi-column layouts in CSS, a style sheet language for the web. Using functionality described in the specification, content can be flowed into multiple columns with a gap and a rule between them.
This is a delta specification over CSS Multi-column Level 1.
Once the level 1 specification is final,
its content will be integrated into this specification,
which will then replace it.
Until then, CSS Multi-column Level 2 only contains additions and extensions to level 1
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-multicol” in the title, like this:
“[css-multicol] …summary of comment…”.
All issues and comments are archived.
Alternately, feedback can be sent to the (archived) public mailing list www-style@w3.org.
The ::column pseudo-element
represents the individual columns
in a multi-column container.
It only exists on multi-column containers.
A multi-column container has as many ::column pseudo-elements
as it has columns.
They cannot be individually addressed;
any styles applied to a multicol’s ::column pseudo-elements
apply to all of them on that element.
Each ::column has the same size and position
as its corresponding column:
the same size as the column’s available space in the inline axis and the container’s content box in the block axis.
(It does not cover the gaps/rules between columns.)
::column pseudo-elements are treated as children of their multi-column container,
without any contents.
They do not wrap the contents of the column,
just fill the same space.
The ::column pseudo-element accepts only a very limited set of properties:
Additionally, a ::column pseudo-element can have a ::scroll-marker pseudo-element of its own,
as ::column::scroll-marker.
(Other pseudo-elements do not exist on ::column.)
Such ::scroll-marker pseudo-elements
inherit from the ::column pseudo-element’s superior parent,
rather than the ::column itself.
Note: This list of properties and pseudo-elements that work on ::column will likely be expanded in the future,
as we develop more features
that could usefully care about the position of a column
without caring about the contents.
The previous level of this specification defined how
the user agent must determine where column breaks are placed
when content is laid out in multiple columns.
The [CSS3-BREAK] module has since been introduced
to define how to break the content across pages,
columns, or CSS Regions,
and supersedes the column break section of [CSS3-MULTICOL].
This specification defers to [CSS3-BREAK] on this topic.
The column-span property makes it possible for an element to span across several columns.
This specification adds <integer> to the values available in the previous level.
The element spans the specified number of columns.
Values must be greater than 0.
If the specified integer value is equal to,
or larger than the number of columns in the multicol element,
the number of columns spanned will be the same as if column-span: all had been specified.
This definition is insufficient.
Does column-span: 1 count as column-span: none,
or does it create a spanner (which is a BFC)?
Which columns does it span?
How does that affect height calculations, and interact with column-fill
auto
The number of columns spanned by the element
depends on its min-contentouter size in the inline direction of the multi-column container.
If it is smaller than the used value of column-width,
this is the same as if column-span: none had been specified.
Otherwise, the number of columns spanned is the smallest positive integer n for which n × column-width + (n - 1) × column-gap is larger than the min-contentouter size.
If this would be larger than the number of columns,
the number of columns spanned will be the same as if column-span: all had been specified.
If column-span: 1 does not do the same as column-span: none,
should this behave as column-span: 1 or as column-span: none when the element is small enough?
Add final content from previous level
possibly with adjustments to account for <integer> values
9.2. Pagination and overflow outside multicol elements
Add final content from previous level
Acknowledgments
This document builds upon Håkon Wium Lie’s work in [CSS3-MULTICOL],
and is based on several older proposals and comments on older proposals.
Contributors include:
Add final level 1 contributor list
Privacy and Security Considerations
Delta spec lol
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:
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
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.
If column-span: 1 does not do the same as column-span: none,
should this behave as column-span: 1 or as column-span: none when the element is small enough? ↵
Add final content from previous level
possibly with adjustments to account for <integer> values ↵
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