W3C

CSS3 module: Multi-column layout

W3C Working Draft 30 June 2009

This version:
http://www.w3.org/TR/2009/WD-css3-multicol-20090630/
Latest version:
http://www.w3.org/TR/css3-multicol
Previous version:
http://www.w3.org/TR/2007/WD-css3-multicol-20070606/
Editors:
Håkon Wium Lie, Opera Software, howcome@opera.com

Abstract

This module describes multi-column layout in CSS. It builds on the CSS3 Box model module and adds functionality to flow the content of an element into multiple columns.

Status of this document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.

Publication as a Working Draft does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

The (archived) public mailing list www-style@w3.org (see instructions) is preferred for discussion of this specification. When sending e-mail, please put the text “css3-multicol” in the subject, preferably like this: “[css3-multicol] …summary of comment…

This document was produced by the CSS Working Group (part of the Style Activity).

This document was produced by a group operating under the 5 February 2004 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 has been a Working Draft in the CSS Working Group for several years. Multi-column layouts are traditionally used in print. On screen, multi-column layouts have been considered experimental, and implementation and use experience was deemed necessary in order to proceed. Several implementations have occurred over the past years, and this draft incorporates useful feedback from implementors as well as authors and users.

This document is in Last Call. The Last Call period ends on 1 October 2009.

Table of contents

1 Introduction

(This section is not normative.)

This module describes multi-column layout in CSS. By using functionality described in this document, style sheets can declare that the content of an element is to be laid out in multiple columns.

On the Web, tables have also been used to describe multi-column layouts. The main benefit of using CSS-based columns is flexibility; content can flow from one column to another, and the number of columns can vary depending on the size of the viewport. Removing presentation table markup from documents allows them to more easily be presented on various output devices including speech synthesizers and small mobile devices.

Multi-column layouts are easy to describe in CSS. Here is a simple example:

body { column-width: 12em }

In this example, the body element is set to have columns at least ‘12em’ wide. The exact number of columns will depend on the available space.

The number of columns can also be set explicitly in the style sheet:

body { column-count: 2 }

In this case, the number of columns is fixed and the column widths will vary depending on the available width.

The shorthand ‘columns’ property can be used to set either, or both, properties in one declaration.

In this example, but the number and widths of columns is set:

body { columns: 2 }
body { columns: 12em }
body { columns: 2 12em }

Setting both properties rarely makes sense, as described below.

Another group of properties introduced in this module describe gaps and rules between columns.

body { 
  column-gap: 1em;
  column-rule: thin solid black;
}

The first declaration in the example above sets the gap between two adjacent columns to be 1em. Column gaps are similar to padding areas. In the middle of the gap there will be a rule which is described by the ‘column-rule’ property.

The values of the ‘column-rule’ property are similar to those of the CSS border properties. Like ‘border’, ‘column-rule’ is also a compound property.

In this example, the shorthand ‘column-rule’ declaration from the above example has been expanded:

body { 
  column-gap: 1em;
  column-rule-width: thin;
  column-rule-style: solid;
  column-rule-color: black;
}

A third group of properties indicate where column breaks should occur:

In this example, h1 elements will always have a column break before them, while column breaks are avoided after h2 elements.

h1 { column-break-before: always }
h2 { column-break-after: avoid }

Finally, ‘column-fill’ and ‘column-span’ give style sheets a wider range of visual expressions in multi-column layouts.

In this example, columns are set to be balanced, i.e., to have approximately the same length. Also, h2 elements are set to span across all columns.

div { column-fill: balance }
h2 { column-span: all }

This specification introduces twelve new properties, all of which are used in the examples above.

If all column properties have their initial value, the layout of an element will be identical to a multi-column layout with only one column.

2 The multi-column model

A multi-column element (or multicol element for short) is an element whose ‘column-width’ or ‘column-count’ property is not ‘auto’ and therefore acts as a container for multi-column layout.

In the traditional CSS box model, the content of an element is flowed into the content box of the corresponding element. Multi-column layout introduces a new type of container between the content box and the content, namely the column box (or column for short). The content of a multicol element is flowed into its column boxes.

Column boxes in a multi-column element are arranged into rows. Like table cells, the column boxes in a row are ordered in the inline direction of the multicol element. The column width is the length of the column box in the inline direction. The column height is the length of the column box in the block direction. All column boxes in a multi-column element have the same column width, and all column boxes in a row have the same column height. Within each row in the multi-column element, adjacent column boxes are separated by a column gap, which may contain a column rule. All column gaps and column rules in the same row are equal.

In the simplest case a multicol element will contain only one row of columns, and the height of each column will be equivalent to the used height of the multi-column element's content box. If the multi-column element is paginated, then the height of each row is constrained by the page, and the content continues in a new row of column boxes on the next page; a column box never splits across pages. The same effect occurs when a spanning element divides the multi-column element: the columns before the spanning element are balanced and shortened to fit their content. Content after the spanning element then flows into a new row of column boxes.

It is not possible to set properties/values on column boxes. For example, the background of a certain column box cannot be set and a column box has no concept of padding, margin or borders.

Future specifications may add additional functionality. For example, columns of different widths and different backgrounds may be supported.

Column gaps (yellow) and column rules (green) are shown in this sample rendition of a multi-column element with padding (blue). The blue and yellow is present for illustrational purposes only. In actual implementations these ares will be determined by the background.

Ab cde fgh i jkl. Mno
pqr stu vw xyz. A bc
def g hij klm nopqrs
tuv wxy z. Abc de fg
hi jklmno. Pqrstu vw
x yz. Abc def ghi jkl.
M nop qrst uv wx yz.
Ab cde fgh i jkl. Mno
pqr stu vw xyz. A bc
def g hij klm nopqrs

tuv wxy z. Abc de fg
hi jklmno. Pqrstu vw
x yz. Abc def ghi jkl.
M nop qrst uv wx yz.
Ab cde fgh i jkl. Mno
pqr stu vw xyz. A bc
def g hij klm nopqrs
tuv wxy z. Abc de fg
hi jklmno. Pqrstu vw
x yz. Abc def ghi jkl.

M nop qrst uv wx yz.
Ab cde fgh i jkl. Mno
pqr stu vw xyz. A bc
def g hij klm nopqrs
tuv wxy z. Abc de fg
hi jklmno. Pqrstu vw
x yz. Abc def ghi jkl.
M nop qrst uv wx yz.
Ab cde fgh i jkl. Mno
Pqr stu vw xyz.

To illustrate the effects of the various properties described in this specification, variations on a sample document will be used. Here is the source code of the sample document:

<html>
<style>
div {
  column-width: 15em;
  column-gap: 2em;   /* shown in yellow */            
  column-rule: 4px solid green;
  padding: 5px;      /* shown in blue */
}
img { display: none }
</style>
<body>
<div>
Ab cde fgh i jkl. Mno
pqr stu vw xyz. A bc
<img src=...>
def g hij
...
</div>
</body>
</html>

The nonsensical text in the example is the English alphabet which shows how text flows from one column to another. To simplify the visualization, the textual content of the different examples vary slightly.

Column boxes act as the containing block for their content. That is, column boxes behave like block-level, table cell, and inline-block boxes as per CSS 2.1, section 10.1, item 2 [CSS21]. However, column boxes do not establish containing blocks for elements with ‘position: fixed’ or ‘position: absolute’. Percentage values that are calculated relative to the containing block height are calculated based on the multicol element's height, not the column box's height.

In this example, the width of the image is set with these rules:

img { display: block; width: 100% }

Given that the width is calculated relative to the column box, the image will be as wide as the column box:

Ab cde fgh i jkl. Mno
pqr stu vw xyz. A bc






def g hij klm nopqrs
tuv wxy z. Abc de fg

hi jklmno. Pqrstu vw
x yz. Abc def ghi jkl.
M nop qrst uv wx yz.
Ab cde fgh i jkl. Mno
pqr stu vw xyz. A bc
def g hij klm nopqrs
tuv wxy z. Abc de fg
hi jklmno. Pqrstu vw
x yz. Abc def ghi jkl.
M nop qrst uv wx yz.

Ab cde fgh i jkl. Mno
pqr stu vw xyz. A bc
def g hij klm nopqrs
tuv wxy z. Abc de fg
hi jklmno. Pqrstu vw
x yz. Abc def ghi jkl.
M nop qrst uv wx yz.
Ab cde fgh i jkl. Mno
pqr stu vw xyz.

Floats that appear inside multi-column layouts are positioned with regard to the column box where the float appears.

In this example, this CSS fragment describes the presentation of the image:

img { display: block; float: right }

Ab cde fgh i jkl. Mno
pqr stu vw xyz. A bc
def g
hij klm
nopq
rs tuv
wxy x
yz. Ab
cde fgh i jkl. Mno
pqr stu vw xyz. A bc

def g hij klm nopqrs
tuv wxy z. Abc de fg
hi jklmno. Pqrstu vw
x yz. Abc def ghi jkl.
M nop qrst uv wx yz.
Ab cde fgh i jkl. Mno
pqr stu vw xyz. A bc
def g hij klm nopqrs
tuv wxy z. Abc de fg
hi jklmno. Pqrstu vw

x yz. Abc def ghi jkl.
M nop qrst uv wx yz.
Ab cde fgh i jkl. Mno
pqr stu vw xyz. A bc
def g hij klm nopqrs
tuv wxy z. Abc de fg
hi jklmno. Pqrstu vw
x yz. Abc def ghi jkl.
M nop qrst uv wx yz.

The black box represents the image.

A multi-column element establishes a new block formatting context, as per CSS 2.1 section 9.4.1.

Nested multi-column elements are allowed, but there may be implementation-specific limits.

3 The number and width of columns

Finding the number and width of columns is fundamental when laying out multi-column content. When the block direction is unconstrained and no column breaks are added through style sheets, these two properties determine the outcome:

A third property, ‘columns’, is a shorthand property which sets both ‘column-width’ and ‘column-count’.

3.1 column-width

Name: column-width
Value: <length> | auto
Initial: auto
Applies to: non-replaced block-level elements (except table elements), table cells, and inline-block elements
Inherited: no
Percentages: N/A
Media: visual
Computed value: the absolute length

This property describes the width of columns in multicol elements.

auto
means that the column width will be determined by other properties (e.g., ‘column-count’, if it has a non-auto value).
<length>
describes the optimal column width. The actual column width may be wider (to fill the available space), or narrower (only if the available space is smaller than the specified column width). Values must be greater than 0.

For example, consider this style sheet:

div {
  width: 100px;
  column-width: 45px;
  column-gap: 0;
  column-rule: none;
}

There is room for two 45px wide columns inside the 100px wide element. In order to fill the available space the actual column width will be increased to 50px.

Also, consider this style sheet:

div {
  width: 40px;
  column-width: 45px;
  column-gap: 0;
  column-rule: none;
}

The available space is smaller than the specified column width and the actual column width will therefore be decreased.

To ensure that ‘column-width’ can be used with vertical text, column width means the length of the line boxes inside the columns.

The reason for making ‘column-width’ somewhat flexible is to achieve scalable designs that can fit many screen sizes. To set an exact column width, all length values (in horizontal text these are: ‘width’, ‘column-width’, column-gap', and ‘column-rule-width’) must be specified.

3.2 column-count

Name: column-count
Value: <integer> | auto
Initial: auto
Applies to: non-replaced block-level elements (except table elements), table cells, and inline-block elements
Inherited: no
Percentages: N/A
Media: visual
Computed value: specified value

This property describes the number of columns of a multicol element.

auto
means that the number of columns will be determined by other properties (e.g., ‘column-width’, if it has a non-auto value).
<integer>
describes the optimal number of columns into which the content of the element will be flowed. Values must be greater than 0. If both ‘column-width’ and ‘column-count’ have non-auto values, the integer value describes the maximum number of columns.

Example:

body { column-count: 3 }

3.3 columns

Name: columns
Value: <‘column-width’> || <‘column-count’>
Initial: see individual properties
Applies to: non-replaced block-level elements (except table elements), table cells, and inline-block elements
Inherited: no
Percentages: N/A
Media: visual
Computed value: see individual properties

This is a shorthand property for setting ‘column-width’ and ‘column-count’. Omitted values are set to their initial values.

Here are some valid declarations using the ‘columns’ property:

columns: 12em;      /* column-width: 12em; column-count: auto */
columns: auto 12em; /* column-width: 12em; column-count: auto */
columns: 2;         /* column-width: auto; column-count: 2 */
columns: 2 auto;    /* column-width: auto; column-count: 2 */
columns: auto;      /* column-width: auto; column-count: auto */
columns: auto auto; /* column-width: auto; column-count: auto */

3.4 Pseudo-algorithm

The pseudo-algorithm below determines the used values for ‘column-count’ (N) and ‘column-width’ (W). There are two other variables in the pseudo-algorithm:

Two assumptions are being made by the pseudo-algorithm:

The floor() function rounds a number to the next smaller integer.

(01)  if ((column-width = auto) and (column-count = auto)) or
(02)     ((available-width = unknown) and (column-count = auto)) then
(03)    exit; /* no columns */
(04)  fi
(05)  
(06)  if (available-width = unknown) and (column-count != auto) and (column-width != auto) then
(07)    N := column-count;
(08)    W := column-width;
(09)    exit;
(10)  fi
(11)  
(12)  if (available-width = unknown) then
(13)    available-width := shrink-to-fit;
(14)  fi
(15)  
(16)  if (column-width = auto) then
(17)    if ((column-count - 1) * column-gap < available-width) then
(18)      N := column-count;
(19)      W := (available-width - ((N - 1) * column-gap))/N;
(20)    elsif (column-gap >= available-width) then
(21)      N := 1;
(22)      W := available-width;
(23)    else
(24)      N := floor(available-width/column-gap);
(25)      W := (available-width - ((N - 1) * column-gap))/N;
(26)    fi
(27)  elsif (column-count = auto) then
(28)    if (column-width >= available-width) then
(29)      N := 1
(30)      W := available-width;
(31)    else
(32)      N := floor((available-width + column-gap) / (column-width + column-gap));
(33)      W := ((available-width + column-gap) / N) - column-gap;
(34)    fi
(35)  elsif (column-width >= available-width) then
(36)    N := 1
(37)    W := available-width;
(38)  else
(39)    N := floor((available-width + column-gap) / (column-width + column-gap));
(40)    W := ((available-width + column-gap) / N) - column-gap;
(41)  fi

In paged media, user agents may perform this calculation on a per-page basis.

Note that, in most cases, only one of ‘column-width’ and ‘column-count’ affect the layout. If ‘column-width’ has a value other than ‘auto’, ‘column-count’ will be ignored. The only case when both ‘column-width’ and ‘column-count’ can affect the layout is for element where the width of the element has not been determined. This can, e.g., be the case for table cells and floats.

3.5 Stacking context

All column boxes in a multi-column element are in the same stacking context and the drawing order of their contents is as specified in CSS 2.1.

4 Column gaps and rules

Column gaps and rules are placed between columns of the same multi-column element. The length of the column gaps and column rules is equal to the length of the columns. Column gaps take up space. That is, column gaps will push apart content in adjacent columns (within the same multi-column element).

A column rule is placed in the middle of the column gap. Column rules do not take up space. That is, the presence or thickness of a column rule will not alter the placement of anything else. If a column rule is wider than its gap, the column rule will overlap adjacent column boxes. Column rules are painted just above the background of the multicol element. This allows child elements with ‘z-index’ values to be on top of column rules. Column rules are only drawn between columns that have content.

4.1 column-gap

Name: column-gap
Value: <length> | normal
Initial: normal
Applies to: multicol elements
Inherited: no
Percentages: N/A
Media: visual
Computed value: absolute length or ‘normal

The column-gap property sets the gap between columns. If there is a column rule between columns, it will appear in the middle of the gap.

The ‘normal’ value is UA-specific. A value of ‘1em’ is suggested.

Column gaps cannot be negative.

4.2 column-rule-color

Name: column-rule-color
Value: <color>
Initial: currentColor
Applies to: multicol elements
Inherited: no
Percentages: N/A
Media: visual
Computed value: the same as the computed value for the ‘color’ property [CSS3COLOR]

This property sets the color of the column rule. The <color> values are defined in [CSS3COLOR].

Conforming user agents are only required to support the subset of color values defined in [CSS21].

4.3 column-rule-style

Name: column-rule-style
Value: <‘border-style’>
Initial: none
Applies to: multicol elements
Inherited: no
Percentages: N/A
Media: visual
Computed value: specified value

The ‘column-rule-style’ property sets the style of the rule between columns of an element. The <border-style> values are defined in [CSS21].

The ‘inset’ keyword value is shown like the ‘ridge’ value. The ‘outset’ value is shown like ‘groove’.

Note that the ‘none’ value forces the computed value of column-rule-width to be ‘0’.

4.4 column-rule-width

Name: column-rule-width
Value: <‘border-width’>
Initial: medium
Applies to: multicol elements
Inherited: no
Percentages: N/A
Media: visual
Computed value: absolute length; ‘0’ if the column rule style is ‘none’ or ‘hidden

This property sets the width of the rule between columns. Negative values are not allowed.

4.5 column-rule

Name: column-rule
Value: <column-rule-width> || <border-style> || [ <color> | transparent ]
Initial: see individual properties
Applies to: multicol elements
Inherited: no
Percentages: N/A
Media: visual
Computed value: see individual properties

This property is a shorthand property for setting ‘column-rule-width’, ‘column-rule-style’, and ‘column-rule-color’ at the same place in the style sheet. Omitted values are set to their initial values.

5 Column breaks

(This section is not normative; the normative desrciption will appear in [CSS3PAGE])

When content is laid out in multiple columns, the user agent must determine where column breaks are placed. The problem of breaking content into columns is similar to breaking content into pages, and the same properties and rules are used for breaking columns.

Three new properties are introduced to allow column breaks to be described in the same properties as page breaks: break-before, break-after, and break-inside. The table below show the mapping from the CSS2 syntax to the CSS3 syntax for the ‘page-break-before’ and the ‘break-before’ properties. The CSS2 syntax will be treated as an alias for the CSS3 syntax.

CSS2 syntax CSS3 syntax Description
page-break-before: auto break-before: auto no forced page-break/column-break before element
page-break-before: right break-before: right forced page-break so that element ends up on top of right page
page-break-before: left break-before: left forced page-break so that element ends up on top of left page
page-break-before: avoid break-before: avoid page-break/column-break avoided before the element
page-break-before: always break-before: always page-break forced before the element
break-before: page page-break forced before the element
break-before: column column-break forced before the element
break-before: avoid-page page-break avoided before the element
break-before: avoid-column column-break avoided before the element

Likewise, ‘page-break-after’ becomes an alias for ‘break-after’.

The mappings from ‘page-break-inside’ to ‘break-inside’ are:

CSS2 syntax CSS3 syntax Description
page-break-inside: auto break-inside: auto no restriction on page-breaks or column-breaks inside element
page-break-inside: avoid break-inside: avoid avoid page-breaks and column-breaks inside element
break-inside: avoid-page page-break avoided inside element, no restriction on column-break
break-inside: avoid-column column-break avoided inside element, no restriction on page-break

The break-* properties will be formally described in CSS3 Paged Media [CSS3PAGE].

In this example, forced column breaks appear before h2 elements and after img elements:

.multicol { colum-width: 8em }
.multicol h2 { break-before: column }
.multicol img { break-after: column }
.multicol p { break-inside: avoid-column }

Margins will be set to zero around natural column breaks, just like for page breaks.

6 Spanning columns

The ‘column-span’ property makes it possible for an element to span across several columns.

6.1 column-span

Name: column-span
Value: 1 | all
Initial: 1
Applies to: static, non-floating elements
Inherited: no
Percentages: N/A
Media: visual
Computed value: as specified

This property describes how many columns an element spans across. Values are:

1
The element does not span multiple columns.
all
The element spans across all columns. Content in the normal flow that appears before the element is automatically balanced across all columns before the element appears.

An element that spans more than one column is called a spanning element.

In this example, an h2 element has been added to the sample document after the first sentence in the fourth alphabet (i.e., after the word "jkl."). This styling applies:

h2 { column-span: all; background: silver } 
img { display: none }

By setting ‘column-span’ to ‘all’, all content that appear before the h2 element is shown before the h2 element.

Ab cde fgh i jkl. Mno
pqr stu vw xyz. A bc


M nop qrst uv wx yz.
Ab cde fgh i jkl. Mno
pqr stu vw xyz. A bc
def g hij klm nopqrs
tuv wxy z. Abc de fg
hi jklmno. Pqrstu vw

def g hij klm nopqrs
tuv wxy z. Abc de fg


x yz. Abc def ghi jkl.
M nop qrst uv wx yz.
Ab cde fgh i jkl. Mno
pqr stu vw xyz. A bc
def g hij klm nopqrs
tuv wxy z. Abc de fg

hi jklmno. Pqrstu vw
x yz. Abc def ghi jkl.


hi jklmno. Pqrstu vw
x yz. Abc def ghi jkl.
M nop qrst uv wx yz.
Ab cde fgh i jkl. Mno
pqr stu vw xyz.

An H2 element

7 Filling columns

There are two strategies for filling columns: columns can either be balanced, or not. If columns are balanced, UAs should minimize the variation in column length. Otherwise, columns are filled sequentially and will therefore end up having different lengths. In any case, the user agent should try to honor the ‘widows’ and ‘orphans’ properties.

Name: column-fill
Value: auto | balance
Initial: balance
Applies to: multi-column elements
Inherited: no
Percentages: N/A
Media: see below
Computed value: as specified

The values are:

balance
Balance content equally between columns, if possible.
auto
Fills columns sequentially.

In continuous media, this property will only be consulted if the length of columns has been constrained. Otherwise, columns will automatically be balanced.

8 Overflow and multicol elements

8.1 Overflow inside multicol elements

Content in the normal flow that extends into column gaps (e.g., long words) is clipped in the middle of the column gap.

Floats that are wider than the column box intrude into neighboring columns.

img { float: left; width: 120% }

In this example, the image is wider than the column and will therefore intrude into the neighboring column. At the bottom of the middle column is a long word that is clipped in the middle of the column gap.

Ab cde fgh i jkl. Mno
pqr stu vw xyz. A bc






def g hij klm nopqrs
tuv wxy z. Abc de fg

hi jklmno. Pqrstu vw
x yz. Abc def ghi jkl.
M nop qrst uvw
x yz. Ab cde fgh
i jkl. Mnopqr stu
vw xyz. A bcdef
ghij klm nopqrs
tuv wxy z. Abc
de fghi jk klmop qrst
uvwxyzabcdefghijklmn

Ab cde fgh i jkl. Mno
pqr stu vw xyz. A bc
def g hij klm nopqrs
tuv wxy z. Abc de fg
hi jklmno. Pqrstu vw
x yz. Abc def ghi jkl.
M nop qrst uv wx yz.
Ab cde fgh i jkl. Mno
pqr stu vw xyz.

img { float: right; width: 120% }

In this example, the image naturally appears in the last column. Due to being floated to the right, the image will intrude into the neighboring column to the left.

Ab cde fgh i jkl. Mno
pqr stu vw xyz. A bc
def g hij klm nopqrs
tuv wxy z. Abc de fg
hi jklmno. Pqrstu vw
x yz. Abc def ghi j
kl. M nop qrst uv wx
yz. Ab cde fgh i jkl
mno pqr stu vw xyz.

Ab cde fgh i jkl. Mno
pqr stu vw xyz. A bc
def g hij klm nop
qrs tuv wxy z.
Rst uvw x yz. Ab
c def ghi jkl m.
Nop qrst uv wx
yz. Ab cdef gh
i jklmno pqr stu vw

xyz. Abc def ghi jkl
mno. Pqr stu vw xyz.






Ab cde fgh ij klm no.

8.2 Overflow outside multicol elements

Content that extend outside column boxes at the edges of the multi-column element is clipped according to the ‘overflow’ property.

A multi-column element can have more columns than it has room for due to:

In paged media, columns that do not fit within the page are moved to the next page.

In continuous media, the columns that do not fit within the multicol element are added in the inline direction.

In this example, the height of the multi-column element has been constrained to a maximum height. Also, the style sheet specifies that overflowing content should be visible:

div { 
  max-height: 5em;
  overflow: visible;
}

As a result, the number of columns is increased.

Ab cde fgh i jkl. Mno
pqr stu vw xyz. A bc
def g hij klm nopqrs
tuv wxy z. Abc de fg
hi jklmno. Pqrstu vw

x yz. Abc def ghi jkl.
M nop qrst uv wx yz.
Ab cde fgh i jkl. Mno
pqr stu vw xyz. A bc
def g hij klm nopqrs

tuv wxy z. Abc de fg
hi jklmno. Pqrstu vw
x yz. Abc def ghi jkl.
M nop qrst uv wx yz.
Ab cde fgh i jkl. Mno

pqr stu vw xyz. A bc
def g hij klm nopqrs
tuv wxy z. Abc de fg
hi jklmno. Pqrstu vw
x yz. Abc def ghi jkl.

In this example, explicit column breaks are generated after paragraphs:

p { 
  column-break-after: always;
}

As a result, the number of columns is increased:

Ab cde fgh i jkl. Mno
pqr stu vw xyz.

Ab cde fgh i jkl. Mno
pqr stu vw xyz. A bc
def g hij klm nopqrs
tuv wxy z.

Ab cde fgh i jkl mno.

Pqr stu vw xyz. A bc
def g hij klm nopqrs
tuv wxy z. Abc de fg
hi jklmno pqr stu v
wx yz.

In this example, explicit column breaks are generated after paragraphs:

p { 
  column-break-after: always;
}

As a result, the number of columns is increased and another page is generated. This would appear on the first page:

Ab cde fgh i jkl. Mno
pqr stu vw xyz.

Ab cde fgh i jkl. Mno
pqr stu vw xyz. A bc
def g hij klm nopqrs
tuv wxy z.

Ab cde fgh i jkl.

This would appear on the second page:

Ab cde fgh i jkl. Mno
pqr stu vw xyz. A bc
def g hij klm nopqrs
tuv wxy z. Abc de fg
hi jklmno.

9 Conformance

Conforming UAs must flow the content of an element into several columns according to this specification.

User agents that support CSS3 Backgrounds and Borders [CSS3BG] must support ‘column-gap-image’; for other UAs this property is optional.

The 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]

Acknowledgments

This document is based on several older proposals and comments on older proposals. Contributors include Sylvain Galineau, Giovanni Campagna, David Hyatt, David Singer, David Woolley, Elika Etemad, Björn Höhrmann, Joost de Valk, Peter-Paul Koch, Till Halbach, Cédric Savarese, Andy Clarke, Robert O'Callahan, Markus Mielke, Alex Mogilevsky, Sergey Genkin, Michael Day, Melinda Grant, Kevin Lawver, David Baron, Bert Bos, Dave Raggett, Chris Wilson, Robert Stevahn, Peter Linss, Chris Lilley, Steve Zilles, Tantek Çelik, Daniel Glazman and Ian Hickson.

References

Normative references

[CSS21]
Bert Bos; et al. Cascading Style Sheets Level 2 Revision 1 (CSS 2.1) Specification. 23 April 2009. W3C Candidate Recommendation. (Work in progress.) URL: http://www.w3.org/TR/2009/CR-CSS2-20090423/
[CSS3BG]
Elika J. Etemad; Bert Bos. CSS Backgrounds and Borders Module Level 3. 10 September 2008. W3C Working Draft. (Work in progress.) URL: http://www.w3.org/TR/2008/WD-css3-background-20080910
[CSS3COLOR]
Chris Lilley; Tantek Çelik; L. David Baron. CSS Color Module Level 3. 21 July 2008. W3C Working Draft. (Work in progress.) URL: http://www.w3.org/TR/2008/WD-css3-color-20080721
[CSS3PAGE]
Melinda Grant; Håkon Wium Lie. CSS3 Module: Paged Media. 10 October 2006. W3C Working Draft. (Work in progress.) URL: http://www.w3.org/TR/2006/WD-css3-page-20061010
[RFC2119]
S. Bradner. Key words for use in RFCs to Indicate Requirement Levels. Internet RFC 2119. URL: http://www.ietf.org/rfc/rfc2119.txt

Other references

Index

Property index

Property Values Initial Applies to Inh. Percentages Media
column-count <integer> | auto auto non-replaced block-level elements (except table elements), table cells, and inline-block elements no N/A visual
column-fill auto | balance balance multi-column elements no N/A see below
column-gap <length> | normal normal multicol elements no N/A visual
column-rule <column-rule-width> || <border-style> || [ <color> | transparent ] see individual properties multicol elements no N/A visual
column-rule-color <color> currentColor multicol elements no N/A visual
column-rule-style <‘border-style’> none multicol elements no N/A visual
column-rule-width <‘border-width’> medium multicol elements no N/A visual
columns <‘column-width’> || <‘column-count’> see individual properties non-replaced block-level elements (except table elements), table cells, and inline-block elements no N/A visual
column-span 1 | all 1 static, non-floating elements no N/A visual
column-width <length> | auto auto non-replaced block-level elements (except table elements), table cells, and inline-block elements no N/A visual