CSS Generated Content for Paged Media Module

Abstract

This module describes features often used in printed publications. Most of the specified functionality involves some sort of generated content where content from the document is adorned, replicated, or moved in the final presentation of the document. Along with two other CSS3 modules – multi-column layout and paged media – this module offers advanced functionality for presenting structured documents on paged media. Paged media can be printed, or presented on screens.

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.

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-gcpm” in the subject, preferably like this: “[css3-gcpm] …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 WD contains functionality that the CSS WG finds interesting and useful. In general, the earlier a feature appears in this draft, the more stable it is. Significant changes in functionality and syntax must be expected from paged presentations and onwards. Also, functionality described in this module may be moved to other modules. Since the previous WD, this specification has been alinged with existing implemenatation. Some functionality has been removed (e.g., env(), target-pull()), or moved to other modules (the styling of blank pages). Some functionality are used in this draft with the expectation that it will appear in other modules (border-clip). The definition of some properties has changed (e.g., the ‘start’ keyword) or been further clarified based on feedback on www-style.

Table of contents

• Introduction
• 1. Running headers and footers
  • 1.1. Named strings
    • 1.1.1. Setting named strings: the ‘string-set’ property
    • 1.1.2. Using named strings
  • 1.2. Running elements
• 2. Leaders
• 3. Cross-references
  • 3.1. The ‘target-counter’ and ‘target-counters’ values
  • 3.2. The ‘target-text’ value
• 4. Footnotes
  • 4.1. Turning elements into footnotes
  • 4.2. The footnote area
  • 4.3. Footnote calls
  • 4.4. Footnote markers
  • 4.5. Counting footnotes
  • 4.6. Laying out footnotes
• 5. Sidenotes
• 6. Page marks and bleed area
• 7. Bookmarks
  • 7.1. ‘bookmark-level’
  • 7.2. ‘bookmark-label’
  • 7.3. ‘bookmark-state’
• 8. CMYK colors
• 9. Styling blank pages
• 10. Paged presentations
• 11. Spatial layout of pages; @layout
  • 11.1. Page shift effects
• 12. Page floats
  • 12.1. Floating to the top/bottom: top, bottom, snap
  • 12.2. Spanning columns
  • 12.3. Deferring floats: float-defer-column, float-defer-page
    • 12.3.1. ‘float-defer-column’
    • 12.3.2. ‘float-defer-page’
  • 12.4. Clearing page floats
  • 12.5. Floating inside and outside pages
  • 12.6. Wrapping around page floats
  • 12.7. The ‘float-offset’ property
  • 12.8. Overconstrained page floats
• 13. Selecting columns and pages
  • 13.1. Selecting certain named pages
  • 13.2. Selecting elements within pages and columns
  • 13.3. Page groups
• 14. Selecting lines
• 15. Conditional text
• 16. Exclusions
  • 16.1. The ‘clear-side’ property
  • 16.2. Exclusions based on images
  • 16.3. Exclusions based on rendered content
  • 16.4. Exclusions based on shapes
• 17. Regions
• 18. Regions and Exclusions examples
• 19. Conformance
• 20. Appendix A: Default style sheet
• Acknowledgments
• References
  • Normative references
  • Other references
• Index
• Property index

Introduction

(This section is not normative.)

This specification describes features often used in printed publications. Some of the proposed functionality (e.g., the new list style types, and border segments) may also used with other media types. However, this specification is monstly concerned with paged media.

1. Running headers and footers

To aid navigation in printed material, headers and footers are often printed in the page margins. [CSS3PAGE] describes how to place headers and footers on a page, but not how to fetch headers and footers from elements in the document. This specification offers two ways to achieve this. The first mechanism is named strings which copies the text (without style, structure, or replaced content) from one element for later reuse in margin boxes. The second mechanism is running elements which moves elements (with style, structure, and replaced content) into a margin box.

1.1. Named strings

Named strings can be thought of as variables that can hold one string of text each. Named strings are created with the ‘string-set’ property which copies a string of text into the named string. Only text is copied; not style, structure, or replaced content.

h1 { string-set: title content(text) }

@page :right { @top-right { content: string(title) }}

1.1.1. Setting named strings: the ‘string-set’ property

The ‘string-set’ property accepts a comma-separated list of named strings. Each named string is followed by a content list that specifies which text to copy into the named string. Whenever an element with value of ‘string-set’ different from ‘none’ is encountered, the named strings are assigned their respective value.

<content-list> expands to one or more of these values, in any order:

<string>

a string, e.g. "foo"

<counter>

the counter() or counters() function, as per CSS 2.1 section 4.3.5

contents()

The textual content of the element, including the content of its ::before and ::after pseudo-element. The content of the element's descendants, including their respective ::before and ::after pseudo-elements, are included in the returned content.

content(text)

The textual content of the element, not including the content of its ::before and ::after pseudo-element. The content of the element's descendants, including their respective ::before and ::after pseudo-elements, are included in the returned content. This is the default value, so ‘content()’ is equivalent to ‘content(text)’.

content(before)

The textual content of the ::before pseudo-element the content of the element.

content(after)

The textual content of the ::after pseudo-element the content of the element.

content(first-letter)

The first letter of the content of the element. The definition of a letter is the same as for :first-letter pseudo-elements.

env()

This function returns data from the local environment of the user at the time of formatting. The function accepts one of these keywords:

• env(url): returns the URL of the document
• env(date): returns the date on the user's system at the time of formatting
• env(time): returns the time on the user's system at the time of formatting
• env(date-time): returns the date and time on the user's system at the time of formatting

Information about date and time is formatted according to the locale of the user's system.

Or, should there be a way to specify the locale? Or should we simply format all in ISO format (e.g., 2010-03-30)?

On many systems, preformatted strings in the user's locale can be found through the strftime function. The date, time and date-time strings can be found by using the "%x", "%X" and "%c" conversion strings, respectively.

@page {
  @top-right { content: env(url) }
  @bottom-right { content: env(date-time) }
}

Named strings can only hold the result of one assignment; whenever a new assignment is made to a named string, its old value is replaced.

User agents, however, must be able to remember the result of more than one assignment as the ‘string()’ functional value (described below) can refer to different assignments.

The scope of a named string is the page of the element to which the ‘string-set’ property is attached and subsequent pages.

The textual content is processed as if ‘white-space: normal’ had been set.

h2 {
  string-set: header "Chapter " counter(header) ": " content();
  counter-increment: header;
}

<h2>Europa</h2>

h2:before { content: "Chapter " counter(header) }
h2 {
  string-set: header content(before) content(text);
  counter-increment: header }

dt { string-set: index first-letter }

title {
  display: none;
  string-set: tittel content();
}

1.1.2. Using named strings

The content of named strings can be recalled by using the ‘string()’ value on the ‘content’ property. The ‘string()’ value has one required argument, namely the name of the string.

@page { @top-center { content: string(header) }}
@page { @right-middle { content: string(index) }}
@page { @top-left { content: string(entry) }}
h1 { string-set: header "Chapter " counter(chapter) content() }
dt { string-set: index first-letter, entry content() }

If the value of the named string is changed by an element on a certain page, the named string may have several values on that page. In order to specify which of these values should be used, an optional argument is accepted on the ‘string()’ value. This argument can have one of four keywords:

• ‘first’: the value of the first assignment on the page is used. If there is no assignment on the page, the named string's entry value is used. The entry value is the value held by the string at the end of the previous page. ‘first’ is the default value.
• ‘start’: the value of the first assignment on the page is used if the element begins the page or the named string has not been assigned a value. Otherwise, the named string's entry value is used.
• ‘last’: the named string's exit value is used
• ‘first-except’: similar to ‘first’, except on the page where the value was assigned. On that page, the empty string is used.

The assignment is considered to take place on the first page where a content box representing the element occurs. If the element does not have any content boxes (e.g., if ‘display: none’ is set), the assignment is considered to take place on the page where the first content box would have occured if the element had been in the normal flow.

@page { @top-left { content: string(term, first) }}
@page { @top-right { content: string(term, last) }}
@page { @top-center { content: string(index, first) }}
dt { string-set: index content(first-letter), term content(text) }

h2 { string-set: header content() }

<h1>Continents</h1>
...
<h2>Africa</h2>
...
...

...
<h2>Americas</h2>
...
<h2>Asia</h2>
...

...
...
...
...

<h2>Europe</h2>
...
<h2>Oceania</h2>
..

@page { @top-left { content: string(term, start) }}
dt { string-set: term content() }

@page { @top-left { content: string(term, first) }}
@page { @top-right { content: string(term, last) }}
@page { @top-center { content: string(index, first) }}
dt { string-set: index content(first-letter), term content(text) }

@page { @top-center { content: string(chapter, first-except) }}
h1 { string-set: chapter content() }

If the named string referred to in a ‘string()’ value has not been assigned a value, the empty string is used.

1.2. Running elements

Named strings, as described above, can only hold textual content; any style, structure or replaced content associated with the element is ignored. To overcome this limitation, a way of moving elements into running headers and footers is introduced.

Elements that are moved into headers and footers are repeated on several pages; they are said to be running elements. To support running elements, a new value – running() – is introduced on the ‘position’ property. It has one required argument: the name by which the running element can be referred to. A running element is not shown in its natural place; there it is treated as if ‘display: none’ had been set. Instead, the running element may be displayed in a margin box.

Like counters and named strings, the name of a running element is chosen by the style sheet author, and the names have a separate name space. A running element can hold one element, including its pseudo-elements and its descendants. Whenever a new element is assigned to a running element, the old element is lost.

User agents, however, must be able to remember the result of more than one assignment as the ‘element()’ value (described below) can refer to different assignments.

Running elements inherit through their normal place in the structure of the document.

title { position: running(header) }
@page { @top-center {
  content: element(header) }
}

Like the ‘string()’ value, the ‘element()’ value accepts an optional second argument:

‘start’

‘first’

‘last’

‘first-except’

The keywords have the same meaning as for the ‘string()’ value, and the place of the assignments are the same.

The ‘element()’ value cannot be combined with any other values.

<style>
  div.header { display: none }
  @media print {
  div.header {
    display: block;
    position: running(header);
  }
  @page { @top-center { content: element(header, first-except) }}
</style>
...
<div class="header">Introduction</div>
<h1 class="chapter">An introduction</div>

...
<style>
@page { @top-center {
  content: element(header, first) }}
.header { position: running(header) }
.once { font-weight: bold }
</style>
...
<div class="header">Not now</div>
<p>Da di ha di da di ...
  <span class="header once">NOW!</span>
  <span class="header">Not now</span>
  ... da di ha di hum.</p>
...

2. Leaders

A leader is a visual pattern that guides the eye. Typically, leaders are used to visually connect an entry in a list with a corresponding code. For example, there are often leaders between titles and page numbers in a table of contents (TOC). Another example is the phone book where there are leaders between a name and a telephone number.

In CSS3, a leader is composed of series of glyphs through the ‘leader()’ value on the ‘content’ property. The functional notation accepts two values. The first describes the glyph pattern that makes up the leader. These values are allowed:

• leader(dotted)
• leader(solid)
• leader(space)
• leader(<string>)

Using the keyword values is equivalent to setting a string value. The table below shows the equivalents:

User Agents should attempt to align corresponding glyphs from the leader pattern between consecutive lines.

The string inside the parenthesis is called the leader string.

In its simplest form, the ‘content’ property only takes one ‘leader()’ value:

heading::after { content: leader(dotted) }

The leader string must be shown in full at least once and this establishes the minimum length of the leader. To fill the available space, the leader string is repeated as many times as possible in the writing direction. At the end of the leader, a partial string pattern may be shown. White space in the leader string is collapsed according to the values on white-space properties.

These properties influence the appearance of leaders: all font properties, text properties, ‘letter-spacing’, white-space properties, background properties, and ‘color’.

heading::after { content: leader(dotted, align) }
heading::after { content: leader(dotted, start) }
heading::after { content: leader(dotted, end) }
heading::after { content: leader(dotted, center) }
heading::after { content: leader(dotted, string-space) }
heading::after { content: leader(dotted, letter-space) }

In a more complex example, the ‘leader’ value is combined with other values on the ‘content’ property:

ul.toc a::after {
  content: leader(". . . ") target-counter(attr(href url), page);
}

If the content connected by a leader end up on different lines, the leader will be present on all lines. Each leader fragment honors the minimum length of the leader.

<style>
.name::after { content: leader(dotted) }
</style>
<div class="entry">
<span class="name">John Doe</span>
<span class="number">123456789</span>
</div>

John Doe....
...123456789

To determine the length of the leaders, user agents must do the following for each line:

1. Lay out the content with leaders of minimum lengths
2. Determine the empty space left on the line.
3. Distribute the empty space between the leaders on the line. Glyphs must not be shown partially. All leaders on the line should, to the extent possible, have the same length. This may not always be possible as the minimum leader length must be honored.
4. Fill the empty space with the specified leader pattern.

<style>
cite::before { content: leader('  ') }
</style>
<blockquote>
  For a moment, nothing happend. 
  Then, after a second or so, 
  nothing continued to happen.
    <cite>Douglas Adams</cite>
</blockquote>

 |For a moment, nothing happend.  |
 |Then, after a second or so,     |
 |nothing continued to happen.    |
 |                   Douglas Adams|

 |For a moment, nothing happend. Then,    |
 |after a second or so, nothing continued |
 |to happen.                 Douglas Adams|

3. Cross-references

It is common to refer to other parts of a document by way of a section number (e.g., "See section 3.4.1"), a page number (e.g., "See discussion on page 72"), or a string (e.g., "See the chapter on Europe"). Being able to resolve these cross-references automatically saves time and reduces the number of errors.

3.1. The ‘target-counter’ and ‘target-counters’ values

Numerical cross-references are generated by ‘target-counter()’ and ‘target-counters()’ values that fetch the value of a counter at the target end of the link. These functions are similar to the ‘counter()’ and ‘counters()’ functions, except that they fetch counter values from remote elements. ‘target-counter()’ has two required arguments: the url of the link, and the name of a counter. ‘target-counters()’ has three required arguments: the url of the link, the name of a counter, and a separator string. Both functions accepts an optional argument at the end that describes which list style type to use when presenting the resulting number; ‘decimal’ being the default.

a::after { content: "(see page " target-counter(attr(href url), page, decimal) ")" }

a::after { content: "(see section " target-counters(attr(href url), section, ".", decimal) ")" }

3.2. The ‘target-text’ value

Textual cross-references are generated by ‘target-text()’ which fetches the textual content from the target end of the link. Only text is copied; not style, structure, or replaced content. ‘target-text()’ has one required argument: the url of the link. An optional second argument specifies exactly which content is fetched. There are four possible values: ‘content’, ‘before’, ‘after’, ‘first-letter’; these keywords are defined above.

<p>See <a href="#chx">this chapter</a> for an in-depth evaluation.
...
<h2 id="chx">A better way</h2>

h2 { counter-increment: chapter }
a { content: "Chapter " target-counter(attr(href url), chapter)
   ' ("'  target-text(attr(href url), content) '") on page '
   target-counter(attr(href url), page);

4. Footnotes

When an element is turned into a footnote, certain things happen: the element is moved to the footnote area, a footnote call is left behind in its place, a footnote marker is displayed before the element, and the footnote counter is incremented.

A footnote is a note typically placed at the bottom of a page that comments on, or cites, a reference. References to footnotes are marked with a footnote call in the main text which corresponds to a footnote marker in the footnote area. The rendering of footnotes is complex. As far as possible, footnotes try to reuse other parts of CSS. However, due to the typographic traditions of footnotes, some new functionality is required to support footnotes in CSS:

• one new value on the ‘float’ property: ‘footnote’
• one new page area: ‘@footnote’
• two new pseudo-elements: ‘::footnote-call’ and ‘::footnote-marker’
• one predefined counter: ‘footnote’
• one new value on the ‘content’ property: ‘target-pull()’
• border segments (see border-clip)
• super-decimal

<style>
.footnote { float: footnote }
</style>

<p>A sentence consists of words. <span class="footnote">Most often.</span>.

A sentence consists of words. ¹

¹ Most often.

<style>
@media print {
  .footnote {
    float: footnote;
    content: target-pull(attr(href url)) }
  .call { display: none }
}
</style>
...
<p>A sentence consists of words<a class="footnote" href="#words"> [3]</a>.
...
<p id=words><span class="call">[3]</span> Most often.

A sentence consists of words¹.

¹ Most often.

<p>Sorry, <span title="This is, of course, a lie.">we're closing for lunch</span>.

span[title]::after {
  content: attr(title);
  float: footnote;
}

4.1. Turning elements into footnotes

An element with ‘float: footnote’ (called a footnote element) is moved to the footnote area and a footnote-call pseudo-element is put in its original place.

span.footnote {
  float: footnote;
}

Footnote elements are presented inside the footnote area, but they inherit through their normal place in the structure of the document.

@footnote {
  display: inline;
}
span.footnote {
  float: footnote;
}

¹ The first footnote. º The second footnote.

For each new footnote element, the ‘footnote’ counter is automatically incremented.

4.2. The footnote area

All elements with ‘float: footnote’ are moved to the footnote area. The footnote area is described by an @footnote-rule inside the @page-rule. By default, the footnote area appears at the bottom of the page, but it can be positioned in other places.

Should the footnote are be positioned using page floats or (fixed?) absolute positioning? Or both?

@page {
  @footnote {
    float: bottom;
    column-span: all;
    width: 100%;
  }
}

@page {
  @footnote {
    float: bottom;
    width: 100%;
  }
}

@page {
  @footnote {
    float: bottom-corner;
    width: 100%;
  }
}

The content of the footnote area is considered to come before other content which may compete for the same space on the same page.

@page { @footnote { float: bottom page}}
div.figure { float: bottom page }

Potentially, every page has a footnote area. If there are no footnotes on the page, the footnote area will not take up any space. If there are footnotes on a page, the layout of the footnote area will be determined by the properties/values set on it, and by the footnote elements elements inside it.

These properties apply to the footnote area: ‘content’, ‘border’, ‘padding’, ‘margin’, ‘height’, ‘width’, ‘max-height’, ‘max-width’, ‘min-height’, ‘min-width’, the background properties.

@footnote {
  margin-top: 0.5em;
  border-top: thin solid black;
  border-clip: 4em;
  padding-top: 0.5em;
}

4.3. Footnote calls

When an element is moved to the footnote area, a footnote-call is left behind. By default, User Agents must behave as if this code is part of the default style sheet:

::footnote-call {
  content: counter(footnote, super-decimal);
}

The resulting note call is a super-script decimal number.

4.4. Footnote markers

A ::footnote-marker pseudo-element is added to each footnote element, in the same place, and replacing, the ::before pseudo-element. User agents must, by default, show the "footnote" counter in the footnote-marker.

::footnote-call {
  content: counter(footnote, super-decimal);
}
::footnote-marker {
  content: counter(footnote, super-decimal);
}

Marker elements are discussed in more detail in the CSS Lists module [CSS3LIST]. One suggested change to that module is to honor the value of ‘list-style-position’ on the ::footnote-marker pseudo-element itself rather than the corresponding list-item element. Further, one clarification to the horizontal placement of the marker is suggested: the margin box of the marker box is horizontally aligned with the start of the line box.

4.5. Counting footnotes

The "footnote" counter is automatically incremented each time a footnote is generated. That is, the "footnote" counter is incremented by one each time an element with ‘float: footnote’ appears.

The footnote counter can be reset with the ‘counter-reset’ property.

@page { counter-reset: footnote }

Should one also be able to manually increment the "footnote" counter?

4.6. Laying out footnotes

Footnotes must appear as early as possible under the following constraints:

1. A footnote marker may not appear on an earlier page than the footnote call.
2. Footnotes may not appear out of document order.
3. The footnote area is limited in size by ‘max-height’, unless the page contains only footnotes. (E.g., if at the end of the document there are still footnotes unprinted, the User Agent can use the whole page to display footnotes.)
4. If there is a footnote call on a page, the footnote area may not be empty, unless its ‘max-height’ is too small.

5. Sidenotes

Sidenotes are supported the same way as footnotes; only the name and the settings in the default style sheet differentiates the two.

@page :left {
  margin-left: 10em;
  @sidenote { position: fixed; left: -8em; width: 6em }
}
@page :right {
  margin-right: 10em;
  @sidenote { position: fixed; right: -8em; width: 6em }
}
img { float: sidenote }

Should there be a mechanism to create new areas like footnote/sidenote, or are two predefinded areas enough?

6. Page marks and bleed area

The ‘marks’ property from [CSS2] is part of this specification.

This property adds crop and/or cross marks to the document. Crop marks indicate where the page should be cut. Cross marks are used to align sheets.

Crop marks and cross marks are printed outside the page box. To have room to show crop and cross marks, the final pages will have to be somewhat bigger than the page box.

@page { marks: crop cross }

This property specifies the extent of the page bleed area outside the page box. This property only has effect if crop marks are enabled.

7. Bookmarks

Some document formats have the capability to represent bookmarks into the document. These bookmarks can e.g. be used to show an outline or an index of the document. Bookmarks are typically shown outside the document itself, often in a tree-structured and clickable table of contents. To generate bookmarks, these properties are defined: ‘bookmark-level’, ‘bookmark-label’, and ‘bookmark-state’.

7.1. ‘bookmark-level’

This property describes what level a certain bookmark has in a hierarchical bookmark structure. The values are:

none

no bookmark is generated

<integer>

Indicates the level of the bookmark; the highest level is ‘1’, then ‘2’, ‘3’ etc. Zero and negative values are not allowed.

7.2. ‘bookmark-label’

This property specifies the label of the bookmark, i.e., the text that will represent the bookmark in the bookmark structure. This properly will only be consulted if ‘bookmark-level’ is different from ‘none’. The values are:

<content-list>

as defined on the ‘string-set’ property

none

no bookmark is generated

h1 { bookmark-level: 1 }
h2 { bookmark-level: 2 }
h3 { bookmark-level: 3 }
h1, h2, h3 { bookmark-label: content() }

a[href] { bookmark-label: attr(href); bookmark-level: 1 }
a[title] { bookmark-label: attr(title); bookmark-level: 1 }

#frog { bookmark-label: "The green frog"; bookmark-level: 1 }

h1 { bookmark-label: content(before) ": " content(); bookmark-level: 1 }
h1:before { content: "Chapter" }

<h1>Africa</h1>

.bookmark {
   bookmark-label: attr(title);
   bookmark-target: attr(href url);
}
...
<a class="bookmark" title="The green pear" href="#pears"/>

7.3. ‘bookmark-state’

A hierarchy of bookmarks may be shown in an open or closed state. The user will typically be able to toggle the state to navigate in the bookmarks. This property describes the initial state of a bookmark.

* { bookmark-state: closed }
h1, h2 { bookmark-state: open }

8. CMYK colors

Printers do not use RGB colors, they (often) use CMYK: cyan, magenta, yellow and black. The ‘device-cmyk()’ functional value allows style sheets to express device-dependent CMYK colors.

h3 { color: device-cmyk(0.8, 0.5, 0.0, 0.3) }

The values representing the colors are between ‘0’ and ‘1’. Values outside this range are clipped.

It is not expected that screen-centric user agents support CMYK colors and it is therefore important that existing CSS color values can be combined with CMYK colors.

h3 {
  color: red;
  color: device-cmyk(0.5, 0.1, 0.0, 0.2);
}

9. Styling blank pages

10. Paged presentations

Printed publications are paged, while screen-based presentations of web pages are most often presented in a continous manner with a scrollbar on the side. There are reasons to believe that screen-based presentations also could benefit from using paged presentations. There is nothing in web specifications that prevent browsers from adding a page-based mode today. However, most web content is authored and styled with a continous presentation in mind. This could change if it becomes possible to describe paged presentations in style sheets. This section is an attempt to do so.

To support paged presentations, four new values are added to the ‘overflow-style’ property:

paged-x

overflow content is paged, and the pages are laid out along the x axis, in the x axis component of the writing direction

paged-y

overflow content is paged, and the pages are laid out along the y axis, in the the y axis component of the writing direction

paged-x-controls

as ‘paged-x’, but with added UA-specific controls to change pages

paged-y-controls

as ‘paged-y’, but with added UA-specific controls to change pages

  html {
    overflow-style: paged-x;
    height: 100%;
  }

  #content {
    overflow-style: paged-x-controls;
    height: 400px;
  }

A paged container cannot be split over multiple columns.

11. Spatial layout of pages; @layout

In commonly used apps, pages are often laid out spatially so that users can nagivate from one page to another by moving up, down, right or left. To support this feature for web content, a new @-rule is proposed: @layout. The purpose of @layout is to describe how pages are laid out spatially relative to the current document.

Four new properties are allowed inside @layout: nav-up, nav-right, nav-bottom, nav-right.

The name of the properties inside @navigation are borrowed from CSS3 Basic User Interface Module.

The properties accept these values:

go()

the function takes one argument, which refers to the rel attribute of the link element

<link rel=index href="../index.html">
<link rel=previous href=g3.html>
<link rel=next href=g1.html>
...

@layout {
  nav-up: go(index); 
  nav-left: go(previous); 
  nav-right: go(next); 
}

This functionality relies on semantics in HTML and CSS. Other languages may have other other ways to describe such semantics. One possible solution for other languages is "link[rel=index] { nav-up: attr(href) }"

‘back’

The keyword takes the user one step back in the history of browsed pages.

@navigation {
  nav-left: back;
}

url()

The funcation takes one argument: a URL. Relative URLs are relative to the style sheet.

@layout {
  nav-up: url(..);
  nav-down: url(a1.html);
}

url-doc()

The function is identical to url(), except that relative URLs are relative to the document, not to the style sheet.

@layout {
  nav-up: url-doc(..);
  nav-down: url-doc(a1.html);
}

@document url("http://example.com/foo") {
  @layout {
    nav-right: link-rel(next);
  }
}

@document url("http://example.com/bar") {
  @layout {
    nav-up: link-rel(next);
  }
}

11.1. Page shift effects

To describe page shift effects, four new properties inside @navigation are proposed: nav-up-shift, nav-right-shift, nav-down-shift, nav-left-shift. These properties take one of several keyword values:

pan

pans to the new page; this is the initial value

turn

turns the page, like soft book pages do

flip

flips the page, like stiff cardbord

fold

the old page folds, like an accordion

The proposed keyword values are loosely described. Are there better ways to describe transitions?

@navigation {
   nav-up-shift: pan;
   nav-down-shift: flip;
}

12. Page floats

In page-based layouts, images and figures are often displayed at the top or bottom of pages. This specificaton adds new keywords on the ‘float’ property to create page floats. A page float can float inside its natural column/page, or its placement can be deferred to a following column/page with the float-defer properties. Page floats can be set to span several columns, thereby supporting commonly used newspaper layouts. New values on the ‘clear’ property adds further ways of refining layouts with page floats.

Not all multicol elements are constrained by the page box. Therefore, a more accurate term for page floats may be column floats as all of them are constrained by the column box. However, in most cases, page floats seems like a better term.

12.1. Floating to the top/bottom: top, bottom, snap

These new keywords on ‘float’ have been added:

top

The float is floated to the top of the column

bottom

The float is floated to the bottom of the column

snap(<length> <length>? [, top | bottom | near ]?)

Makes the element float to the top or bottom if it naturally appears within a certain distance from the top or bottom. The length value(s) specifies the maxium distance from the top/bottom that an element must be within in order to be floated; one length value specifies the distance from both the top and the bottom, two length values specify the distance from the top and bottom, respectively.

The optional keyword value specifies where the element is floated: top, bottom, or the nearest of the two. The initial value is ‘near’. If ‘near’ is in effect and the element is within the specified distance both from the top and the bottom, bottom wins.

An element is considered to be a float if it has a snap() value, even if the element does not appear within the specified distance. This way, it can be determined whether an element is float or not without laying out the document.

snap

same as snap(2em, near)

These new keywords only apply in paged media; in continous media declarations with these keywords are ignored.

Elements with any of these new keywords are called ‘page floats’. Each page float has a natural column, which is the column where the element would have started to appears it it was not a float. Also, each page float has a natural page, which is the page where the element would have started if the was not a float. Unless other constrained by lack of space or other float-* properties, page floats should appear in their natural column on the natural page.

Float figure to top of natural column:

.figure { float: top }

.figure { float: top; width: 50% }

In this example, a figure naturally appears close to a column break. There is not enough space for the figure in the first column, and it is therefore placed in the second column, leaving white space at the bottom of the first column.

To avoid the white space, the image can be floated to the nearest edge (in the block direction):

.figure { float: snap }

In this example, the figure is already at the nearest edge, so it does not move. However, page floats allow subsequent content to be displayed before the page float and the white space can therefore be filled:

In this example, two figures naturally appear in the text flow:

A typographer would typically try to avoid single lines of text above/below figures, which can be achieved with:

div.figure { float: snap(1.5em) }

The length value specifies the reach of the snap function; in this example the second figure is affected, but not the first.

In this example, two figures naturally appear in the text flow:

To make the figures snap to the nearest edges, this code can be applied:

div.figure { float: snap(2.5em) }

The resultant rendering is:

Float figure to top of the natural column, spanning all columns:

.figure { float: top; column-span: all }

table { float: snap }
table { float: snap(3em) }
table { float: snap(3em, bottom) }
table { float: snap(3em 2em, bottom) }

Do numeric values, to represent line numbers, make sense, like for orphans/widows?

12.2. Spanning columns

The ‘column-span’ property is extended with integer values so that elements can span several columns. 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.

In this example, a commonly used newspaper layout is easily described:

body { columns: 3 }
img.A { column-span: 2; width: 100% }  /* image spans two columns */
.one { column-span: 2 }                /* lead paragraph spans two columns */

Further, the ‘page’ value is added to ‘column-span’ so that the page (and not the column or element) becomes the reference.

footer { float: bottom; column-span: page }

<article>
  ...
  <footer>...<.footer>
</article>

An alternative way to express this would be to add a separate propertye, e.g., float-reference: column | multicol | page

12.3. Deferring floats: float-defer-column, float-defer-page

A page float can be deferred to a following column/page with these new properties:

12.3.1. ‘float-defer-column’

12.3.2. ‘float-defer-page’

These properties specify whether page floats should appear in their natural column/page, or in a following column/page. Values are:

none

the page float appears in the natural column/page

<integer>

A positive integer value indicates that the page float should be displayed in a following column/page. A negative integer value indicates that the page float should be displayed in a following column/page, counted from the last column/page. When counting columns, the starting point is the last column of the multicol element on the natural page. When counting pages, the starting point is the last page of the multicol element.

.figure { float: top }
.figure { float-defer-column: 1 }

Float figure to the top of the next-to-last column:

.figure { float: top; float-defer-column: -1 }

Float figure to top of the last column of the multicol element on the current page:

.figure { float: top; float-defer-column: last }

In combination with ‘column-span’, the figure is floated to the top corner of the multicol element on that page:

.figure { float: top; column-span: 2; float-defer-column: last; width: 100% }

Float figure to the top of the second column, spanning two columns:

.figure { 
  float: top; column-span: 2;
  float-defer-column: 1;
}

Float figure to the top right, leaving one full column:

.figure { 
  float: top; column-span: 2;
  float-defer-column: -1;
}

Given that there are four columnn, the same layout would be achived with this code:

.figure { 
  float: top; column-span: 2;
  float-defer-column: 1;
}

.figure { float: top }
.figure { float-defer-page: -1 }

.figure { float: top }
.figure { float-defer-column: -1 }
.figure { float-defer-page: -1 }

last

The page float should be displayed in the last colum, or on the last page.

Float figure to the top of the last column on the natural page:

.figure { float: top }
.figure { float-defer-column: last }

Float figure to the last column on the last page:

.figure { float: top }
.figure { float-defer-column: last }
.figure { float-defer-page: last }

none

The page floats should appear in their natural column/page, if possible.

Zero is not a legal value.

12.4. Clearing page floats

Page floats may request to not be stacked, or to be the only page float on a page/column through new values on the ‘clear’ property:

top/bottom

The page float requests to be the only page float at the top/bottom of the column. If there is already a page float at the requested position, the page float is moved to the next column which does not have a page float in the requested position.

column

The page float requests to be the only page float in the column. If there is already another page float on the page, the page float is moved to the next page which does not have a page float.

page

The page float requests to be the only page float on the page. If there is already another page float on the page, the page float is moved to the next page which does not have a page float.

In this example, the two figures may appear in the same column:

.figure { float: bottom; clear: none }

<div class=figure></div>
<div class=figure></div>

In this example, the two figures will appear in different columns:

.figure { float: bottom; clear: column }

<div class=figure></div>
<div class=figure></div>

In this example, the two figures may appear at the bottom of the same column due to clearing only at the top:

.figure { float: bottom; clear: top }

<div class=figure></div>
<div class=figure></div>

In this example, the two figures will appear in different columns due to clearing at the bottom:

.figure { float: bottom; clear: bottom }

<div class=figure></div>
<div class=figure></div>

.figure { float: top; float-defer-column: last; clear: page }

<div class=figure></div>
<div class=figure></div>

.figure.one { float: top; clear: top }
.figure.two { float: bottom; clear: bottom }

<div class="figure one"></div>
<div class="figure two"></div>

12.5. Floating inside and outside pages

Two allow content to flow to the inside and outside of a page, these keywords are added to the ‘float’ property:

inside

On a right page, this value is synonymous with ‘left’. On a left page, this value is synonymous with ‘right’.

outside

On a left page, this value is synonymous with ‘left’, On a right page, this value is synonymous with ‘right’.

These new values do not create page floats, the are simply aliases for ‘left’ and ‘right’.

.figure { float: outside }

Should there be a way to combine float: top/bottom with left/right?

Should there be a way to delete page floats that end up lonesome on pages?

12.6. Wrapping around page floats

This property indicates whether other content may wrap around a page float:

none

other content may not wrap around the page float

wrap

other content may wrap around the page float

The ‘intrude’ value only works in combination with one of these keywords: ‘left’/‘right’/‘top’/‘bottom’/‘top-corner’/‘bottom-corner’.

img { float: top; column-span: 2; float-wrap: wrap; width: 120%;  }

12.7. The ‘float-offset’ property

This property pushes a float in opposite direction of the where it has been floated with ‘float’. If one value is specified, it is the horizontal offset. If two values are specified, the first is the horizontal and the second is the vertical offset. If no vertical value has been specified, the vertical offset is set to zero.

This property can only influence a float along an axis it has been floated.

img {
  float: left;
  float-offset: 2em 3em;
}

Negative values are allowed; a negative values will push the float in the same direction as it has been floated with ‘float’

This property may move floats into other column than where they naturally appear.

img {
  float: right;
  float-offset: 5px;
}

Percentage values are computed according to this formula:

  (containing-block-width - float-width) * percentage
  (containing-block-height - float-height) * percentage

Pull quotes are often centered in a column. In this example, the pull quote is floated to the right, and then pushed back into the center.

.pullquote {
  float: right;
  float-offset: 50%; /* 50% centers the box */
}

When negative values are set on this property, the column gap is also part of the calculation:

  ((containing-block-width + 2 * column-gap) - float-width) * percentage

img {
  float: top right;
  float-offset: -50% 3em;  /* 50% centers the box */
  width: 120%;
}

img {
  float: top right;
  float-offset: -80% 2em;
  width: 100%;
}

12.8. Overconstrained page floats

In many cases, the specified values on these properties cannot be honored.

.figure { float: top; float-defer-column: 1000 }

.figure { float: top; float-defer-column: -5 }

p { float: top; float-defer-page: last }

Page floats are processed in the order they appear in the source. However, the visual order of page floats may not ne the same as the source order.

.one { float: top; float-defer-page: last; column-span: all }
.two { float: top; clear: column }

<div class=one></div>
<div class=two></div>

.one { float: top; float-defer-page: last; column-span: all }
.two { float: top; clear: column }

<div class=one></div>
<div class=two></div>

When resolving over-constrained layouts, the order of importance for defined goals are:

1. honor basic multi-column layout (‘columns’, ‘column-span: all’, ‘column-gap’ etc)
2. honor ‘column-span: <integer>’
3. honor ‘clear: top/bottom/pcolumn/page’
4. honor ‘float-defer-page’
5. honor ‘float-defer-column’
6. honor ‘float: top/bottom’
7. display all content (as described by other CSS properties)
8. keep the number of pages to a minimum

13. Selecting columns and pages

13.1. Selecting certain named pages

In CSS2, first, left and right pages can be selected. This specification extends pages selectors:

@page funky:nth(1) { background: pink }
@page funky:nth(2) { background: lime }
article { page: funky }

The grammar of allowed arguments to nth() is the same as the nth-child() pseudo-class.

@page :nth(3n) { background: pink }
@page :nth(3n+1)) { background: lime }
@page :nth(3n+2)) { background: white }

13.2. Selecting elements within pages and columns

The ‘page()’ and ‘column()’ pseudo-element allows the selection of pages, columns, and elements within.

article::column(2n) {     /* select every other column of an article */
  ...
}

article::page(left) {   /* select all left pages in an article */
  background: pink;
} 

article::page(left) p {   /* select all p elements that appear on left pages in an article */
  text-align: left;
} 

It is also possible to place the code inside @page:

@page :left {
  {
    p { text-align: left } 
  }
}

::page(left) p { text-align: left }

Is "left" a pseudo-class or pseudo-element? In @page, ":left" is a pseudo-class. However, when we select elements on left pages, it acts like a pseudo-element.

@page :left {
  background: pink;            /* declaration applies to pages */
  {
    p { text-align: left }     /* declaration applies to elements on page */
  }
  @top-center {
    background: orange;        /* declaration applies to margin box */
    {
      p { text-align: left }   /* declaration applies to elements in margin box */
    }
  }
}

13.3. Page groups

Named pages can appear in sequence, stemming from different elements. A sequnce of named pages with the same name is called a page group. The ‘page-group’ property expresses whether an element starts a new page group or not.

This property determines whether the element starts a new page group or not.

auto

The element only starts a new page group if ‘page’ has a named page different from the the previous element.

start

The element always starts a new page group.

@page funky:first {
  background: pink;
}
article {
  page: funky;
  page-group: start;
}

14. Selecting lines

The ‘first-line’ pseudo-element selects the first formatted line of an element. The ‘first-lines(n)’ pseudo-element selects the first n formatted lines of an element.

  article { columns: 3 }
  img, p.lead:first-lines(3) {
    column-span: 2;
  }

  <article>
    <img>
    <p class=lead>
    <p>...    <p>...    <p>...    <p>...    <p>...
  </article>

15. Conditional text

  a:target-layout(attr(href url), same-page) { content: " on this page" }
  a:target-layout(attr(href url), next-page) { content: " on the next page" }
  a:target-layout(attr(href url), previous-page) { content: " on the previous page" }

16. Exclusions

16.1. The ‘clear-side’ property

This property declares if the side of a float should be cleared of content. Values have the following meaning:

auto

if the float is left-floated, there should be no content to the left; if the float is right-floated, there should be no content to the right !_-

left

there should be no content to the left of the float

right

there should be no content to the left of the float -->

none

there may be content on either side of the float

.pullquote {
  float: left;
  float-offset: 50%;
  clear-side: none;
}

16.2. Exclusions based on images

Exclusions are often based on shapes found in images. In this specification, background image can carry the shape, around which text is wrapped. The new property ‘background-exclude-level’ indicates a level in the alpha channel of the background image(s) that defines the shape.

article {
  padding: 4em;
  columns: 15em;
  background: url(nicecar.jpg);
  background-exclude-level: 0.5;
}
article h1 { column-span: all } /* Bonneville Speedway */

article {
  padding: 4em;
  columns: 6em;
  background: url(nicecar.jpg);
  background-exclude-level: 0.5;
}
article h1 { column-span: all } /* Bonneville Speedway */

Background images can be repeated. Therefore exclusions based on images can be repeated.

article {
  background: repeat-y url(zigzag.png);
  background-exclude-level: 0.5;
}
article h1 {
  column-span: all;
}

16.3. Exclusions based on rendered content

A new property. ‘exclude-level’, is introduced to allow wraps around the rendered content of the element.

#dropcaps {
  font-size: 3em;
  float: left;
  exclude-level: 0.5;
  margin-top: -0.2em;
}
<p><span id="dropcaps">Many</span> instances ...</p>
    <p>The text ....</p>

Define behavior if both ‘exclude-level’ and ‘background-exclude-level’ is set.

Some kind of spacing behavior must be defined; ‘exclude-margin’ may be an option.

Define behavior if both ‘exclude-level’ and ‘background-exclude-level’ is set.

16.4. Exclusions based on shapes

I suggest not having exclusions based in shapes in the first generation of exclusions; we may want to definde shapes for CSS in general (e.g., for borders), so we may want to wait until we have a holistic approach.

article::column(1) {
  content-inside: circle(50%, 50%, 30%);
}

article::column(2) {
  content-outside: polygon(x1, y1, x2, y2, x3, y3, ... xn, yn);
  color: red;
}

article::column(1) {
  content-outside: circle(x, y, z);
}
article::column(2) {
  content-inside: polygon(x1, y1, x2, y2, x3, y3, ... xn, yn);
}

17. Regions

Regions are series of stylable boxes into which content can be poured. Columns are regions that are automatically generated to contain all the content of the the multicol element. By adding selectors for columns, columns can be styled and positioned and thereby escape the rigid patterns that columns naturally live in.

div.chapter::column(3)       /* the 3rd column of the element */
div.chapter::column(2n)      /* all even columns of the element */
div.chapter::column(3+)      /* all columns but the 1st and 2nd */
div.chapter::column(2,2)     /* second column on second page */
div.chapter::column(*,2)     /* all columns on the second page */
div.chapter::column(1,*)     /* the first column on all pages */

To underline the fact that columns are regions, the "region" keyword can be used as a substitute for "column".

div.chapter::region(3)       /* the 3rd region of the element */
div.chapter::region(2n)      /* all even regions of the element */
div.chapter::region(3+)      /* all regions but the 1st and 2nd */
div.chapter::region(2,2)     /* second region on second page */
div.chapter::region(*,2)     /* all regions on the second page */
div.chapter::region(1,*)     /* the first column on all pages */

In this example, the multicol layout is changed so that the image (which appears first in the markup) spans two columns and is floated to the top, thereby escaping its natural column. The first column, which holds the start of the textual content is also floated to the top, spanning two columns, and therefore ends up just under the image. When the first column/region is floated away, the second column will move into its space.

article { columns: 3 }
img { column-span: 2; width: 100%; float: top }
article::region(1) {    /* selects column 1 */
  column-span: 2;
  float: top;
  height: 3em;          /* sets preferred height of region */
}

<article>
  <img ...>
  <p>...  <p>...  <p>...
</article>

div.chapter::region(1) {
  transform: rotate(6.5deg);
}
div.chapter::region(2) {
  transform: rotate(-5.5deg) translate(0, 40px);
}

18. Regions and Exclusions examples

article {
  columns: 15em;
}
article::region(1-3) {
  width: 15em;
  height: 15em;
}
article::region(2-3) {
  margin: 4em 0 0 -4em;
}

article {
  columns: 15em;
}
acticle::region(1-3) {
  height: 15em;
}
acticle::region(2-3) {
  margin: 4em 0 0 -4em;
}
acticle::region(2) {
  z-index: 1;
}

19. Conformance

TBD

20. Appendix A: Default style sheet

@page {
  counter-reset: footnote;
  @footnote {
    counter-increment: footnote;
    float: page bottom;
    width: 100%;
    height: auto;
  }
}

::footnote-call {
  counter-increment: footnote;
  content: counter(footnote, super-decimal);
}
::footnote-marker {
  content: counter(footnote, super-decimal);
}


h1 { bookmark-level: 1 }
h2 { bookmark-level: 2 }
h3 { bookmark-level: 3 }
h4 { bookmark-level: 4 }
h5 { bookmark-level: 5 }
h6 { bookmark-level: 6 }

Add grammar for functions defined in this spec.

Acknowledgments

This document has been improved by Bert Bos, Michael Day, Melinda Grant, David Baron, Markus Mielke, Steve Zilles, Ian Hickson, Elika Etemad, Laurens Holst, Mike Bremford, Allan Sandfeld Jensen, Kelly Miller, Werner Donné, Tarquin (Mark) Wilton-Jones, Michel Fortin, Christian Roth, Brady Duga, Del Merritt, Ladd Van Tol, Tab Atkins Jr., Jacob Grundtvig Refstrup, James Elmore, Ian Tindale, Murakami Shinyu, Paul E. Merrell, Philip Taylor, Brad Kemper, Peter Linss, Daniel Glazman, Tantek Çelik, Florian Rivoal, Alex Mogilevsky, Simon Sapin, Cameron McCormack, Liam R E Quin, Peter Moulder, Morten Stenshorne, Rune Lillesveen, Lars Erik Bolstad, Anton Prowse, Michel Onoff

References

Normative references

[CSS3LIST]

Tab Atkins Jr. CSS Lists and Counters Module Level 3. 24 May 2011. W3C Working Draft. (Work in progress.) URL: http://www.w3.org/TR/2011/WD-css3-lists-20110524

Other references

[CSS2]

Ian Jacobs; et al. Cascading Style Sheets, level 2 (CSS2) Specification. 11 April 2008. W3C Recommendation. URL: http://www.w3.org/TR/2008/REC-CSS2-20080411

[CSS3PAGE]

Melinda Grant; et al. CSS Paged Media Module Level 3. 14 March 2013. W3C Working Draft. (Work in progress.) URL: http://www.w3.org/TR/2013/WD-css3-page-20130314/

Index

• bleed, 6.
• bookmark-label, 7.2.
• bookmark-level, 7.1.
• bookmark-state, 7.3.
• bookmark-target, 7.2.
• clear-side, 16.1.
• float-defer-column, 12.3.1.
• float-defer-page, 12.3.2.
• float-offset, 12.7.
• float-wrap, 12.6.
• marks, 6.
• named strings, 1.
• page-group, 13.3.
• running elements, 1.
• string-set, 1.1.1.

Property index