CSS Generated Content for Paged Media Module

Editor’s Draft, 7 August 2014

This version:
http://dev.w3.org/csswg/css-gcpm/
Previous Versions:
https://dvcs.w3.org/hg/csswg/raw-file/6a5c44d11c2b/css-gcpm/Overview.html
http://www.w3.org/TR/2011/WD-css3-gcpm-20111129/
Feedback:
www-style@w3.org with subject line “[css-gcpm] … message topic …”(archives)
Test Suite:
http://test.csswg.org/suites/css-gcpm-3_dev/nightly-unstable/
Editor:
(Hachette Livre)
Former Editor:
Håkon Wium Lie (Opera Software)
Issue Tracking:
W3C Bugzilla

Abstract

Books and other paged media often use special techniques to display information. Content may be moved to or generated for special areas of the page, such as running heads or footnotes. Generated content within pages, such as tab leaders or cross-references, helps readers navigate within and between pages.

CSS is a language for describing the rendering of structured documents (such as HTML and XML) on screen, on paper, in speech, 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.

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 “css-gcpm” in the subject, preferably like this: “[css-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.

Table of Contents

Introduction

Paged media have many special requirements for the display of document content, which have evolved over the long history of printed books. Running headers and footers function as aids to navigation. Notes may appear at the bottom of the page, as footnotes. The properties of pages themselves may change based on their content or position in the document. Leaders visually connect related content. Cross-references may require generated text. Some paged media formats such as PDF use bookmarks for navigation.

This module defines new properties and values, so that authors may bring these techniques to paged media.

1 Running headers and footers

[CSS3PAGE] describes the sixteen page margin boxes which can be used for running headers and footers, but does not describe a mechanism for inserting content in those boxes. This module provides two methods for for doing so. Named strings copy text for reuse in margin boxes. Running elements move elements (complete with style and structure) from the document to margin boxes.

1.1 Named strings

The string-set property copies the text content of an element into a named string, which functions as a variable. The text content of this named string can be retrieved using the string() function. Since these variables may change on a given page, an optional second value for the string() function allows authors to choose which value on a page is used.

1.1.1 The string-set property

Name:string-set
Value:[[ <custom-ident> <content-list>] [, <custom-ident> <content-list>]* ] | none
Initial:none
Applies to:all elements, but not pseudo-elements
Inherited:no
Media:all
Computed value:specified value
Percentages:N/A

The string-set property contains one or more pairs, each consisting of an custom identifier (the name of the named string) followed by a content-list describing how to construct the value of the named string.

content-list expands to one or more of the following values, in any order.

content-list = [ <string> | <counter()> | <counters()> | <content()> | attr(<identifier>) ]+
<string>
A string, as defined in [CSS21]
<counter()>
A counter() function, as described in [CSS21].
<counters()>
A counters() function, as described in [CSS21].
content()
The content() function, described below.
attr(<identifier>)
Returns the string value of the attribute <identifier>, as defined in [CSS3VAL]
1.1.1.1 The content() function
content() = content([text | before | after | first-letter ])

How do we define the default value for this function?

text
The string value of the element, determined as if white-space: normal had been set. This is the default value
before
The string value of the ::before pseudo-element, determined as if white-space: normal had been set.
after
The string value of the ::after pseudo-element, determined as if white-space: normal had been set.
first-letter
The first letter of the element, as defined for the ::first-letter pseudo-element

The content values of named strings are assigned at the point when the content box of the element is first created (or would have been created if the element’s display value is none). The entry value for a page is the assignment in effect at the end of the previous page. The exit value for a page is the assignment in effect at the end of the current page.

Whenever the value of the element changes, the value of the named string(s) is updated. User agents must be able to recall many values of the named string, as the string() function can return past, current, or future values of the assignment.

HTML:

<h1>Loomings</h1>

CSS:

h1::before { content: 'Chapter ' counter(chapter); }
h1 { string-set: header content(before) ':' content(text); }
h1::after { content: '.'; }

The value of the named string “header” will be “Chapter 1: Loomings”.

HTML:
<section title="Loomings">

CSS:

section { string-set: header attr(title) }

The value of the “header” string will be “Loomings”.

1.1.2 The string() function

The string() function is used to copy the value of a named string to the document, via the content property. This function requires one argument, the name of the named string. Since the value of a named string may change several times on a page (as new instances of the element defining the string appear) an optional second argument indicates which value of the named string should be used.
string() = string( <custom-ident> [ , [ first | start | last | first-except] ]? )

The second argument of the string() function is one of the following keywords:

first
The value of the first assignment on the page is used. If there is no assignment on the page, the entry value is used. first is the default value.
start
If the element is the first element on the page, the value of the first assignment is used. Otherwise the entry value is used. The entry value may be empty if the element hasn’t yet appeared.
last
The exit value of the named string is used.
first-except
This is identical to first, except that the empty string is used on the page where the value is assigned.

CSS:
@page {
   size: 15cm 10cm;
   margin: 1.5cm;
   
   @top-left {
   content: "first: " string(heading, first); 
   }
   @top-center {
   content: "start: " string(heading, start); 
   }
    @top-right {
    content: "last: " string(heading, last); 
   }
  }
  
h2 { string-set: heading content() }

The following figures show the first, start, and last assignments of the “heading” string on various pages.

The start value is empty, as the string had not yet been set at the start of the page.
Since the page starts with an h2, the start value is the value of that head.
Since there’s not an h2 at the top of this page, the start value is the exit value of the previous page.

1.2 Running elements

Many headers and footers cannot be represented only by unformatted text. A book title serving as a running head may contain an italic word, for example. A mechanism is needed to move or copy elements into margin boxes. To do this, we add the running() value to the position property, and the element() value to the content property.
@page {
  @top { content: element(header); }
}

h1 { position: running(header); }

In this example, the h1 element is placed in the @top margin box, complete with formatting and any descendant elements. It does not display in the normal document flow.

1.2.1 The running() value

position: running(custom-ident) removes the element (and associated ::before and ::after pseudo-elements) from the normal flow, and makes it available to place in a page margin box using element(). The element inherits from its original position in the document, but does not display there.

Name:position
New values:running()
Media:paged
running() = string( <custom-ident> )

HTML:

<p class="rh"><i>Miranda v. Arizona</i> in Context</p>
<h2><i>Miranda v. Arizona</i> in Context</h2>

CSS:

@top-center {
  content: element(heading); 
  }
  
p.rh { 
  position: running(heading); 
  }

p.rh::before { 
  content: counter(page) ' / '; 
  }

running header using running elements

Running element in page margin box

The element value() can only be used in page margin boxes. And it cannot be combined with other possible values for the content property.

This idea would be much more useful if we could also copy (rather than just move) elements. That would avoid the duplication of HTML in the example above.

Bert Bos has proposed an alternative syntax, which allows both moving and copying elements into running heads. In the example below, h2 elements appear in their normal place in the document, but are also copied into running heads.

h2 {
display: block;
running: chapter;
font-size: 18pt;
font-weight: bold;
}

h2:running {
display: inline;
font-size: 11pt;
font-weight: normal;
font-variant: small-caps;
letter-spacing: 1pt;
}

@page {
  @top-center {
    content: element(chapter);
    }
  }
Name:running
Value:<custom-ident>
Initial:none
Applies to:elements
Inherited:no
Media:all
Computed value:specified value
Percentages:N/A

1.2.2 The element() value

The element() value of the content property places an element (which has been removed from the normal flow via running()) in a page margin box. Whenever the value of the element changes, the value of element() is updated.

Just as with string(), element() takes an optional keyword to describe which value should be used in the case of multiple assignments on a page. User agents must be able to recall many values, as element() can return past, current, or future values of the assignment.

Name:content
New values:element()
Media:paged
element() = string( <custom-ident> [ , [ first | start | last | first-except] ]? )

2 Footnotes

Ancillary content may be moved to the bottom or side of a page. A footnote is created when such content moves to the bottom of the page, leaving a reference indicator.

2.1 Terminology

Footnotes are complex objects (see the footnote section at [dpub-latinreq]), so it will be helpful to define some terms before proceeding.

page with footnotes

Footnote terminology

footnote element
The element containing the content of the footnote, which will be removed from the flow and displayed as a footnote.
footnote marker (also known as footnote number)
A number or symbol adjacent to the footnote body, identifying the particular footnote. The footnote marker should use the same number or symbol as the corresponding footnote call, although the marker may contain additional punctuation.
footnote body
The footnote marker is placed before the footnote element, and together they represent the footnote body, which will be placed in the footnote area.
footnote call (also known as footnote reference)
A number or symbol, found in the main text, which points to the footnote body.
footnote area
The page area used to display footnotes.
footnote rule (also known as footnote separator)
A horizontal rule is often used to separate the footnote area from the rest of the page. The separator (and the entire footnote area) cannot be rendered on a page with no footnotes.

2.2 Creating footnotes

An element becomes a footnote by applying float: footnote to that element. This triggers the following actions:
  1. The footnote element is removed from the flow, and a ::footnote-call pseudo-element is inserted in its place, which serves as a reference to the footnote.
  2. A ::footnote-marker pseudo-element, identifying the footnote, is placed at the beginning of the footnote element. Together this is the footnote body.
  3. The footnote counter is incremented.
  4. The footnote body is placed in the footnote area at the bottom of the page. Footnote elements from a given page are placed in the footnote area of that page in document order.
HTML:
<p>Though the body was erect, the head was thrown back so that the closed eyes were pointed towards the needle of the tell-tale that swung from a beam in the ceiling.<span class="footnote">The cabin-compass is called the tell-tale, because without going to the compass at the helm, the Captain, while below, can inform himself of the course of the ship.</span></p>

CSS:

@page {
  @footnote {
    float: bottom;
  }
}

span.footnote { float: footnote; }

Why is float:bottom used with the footnote area? Floating footnotes to the footnote area, and then floating the footnote area itself, seems overly complex, given that implementations don’t allow the footnote area to float anywhere else. Note that some implementations do allow the footnote area to be absolutely positioned.

2.3 Types of footnotes

The following new value of the float property creates a footnote element:
Name:float
New values:footnote
Media:paged
footnote
each footnote element is placed in the footnote area of the page

The footnote-display property determines whether a footnote is displayed as a block element or inline element.

Name:footnote-display
Value:block | inline | compact
Initial:block
Applies to:elements
Inherited:no
Media:paged
Computed value:specified value
Percentages:N/A
block
The footnote element is placed in the footnote area as a block element
inline
The footnote element is placed in the footnote area as an inline element
compact
The user agent determines whether a given footnote element is placed as a block element or an inline element. If two or more footnotes could fit on the same line in the footnote area, they should be placed inline.

2.4 The footnote area

A page area that can be used to display footnotes is described in the page context using an @footnote rule. This rule defines a box that, if used, will contain all the footnote elements that appear on that page.

How would one describe this in the grammar of CSS3-Page?

2.4.1 Positioning of the footnote area

The bottom margin edge of the footnote area is positioned so that it touches the bottom of the page area. The footnote area can only contain footnotes.

How do footnotes work in multi-column text? Prince uses float: prince-column-footnote to create a footnote at the bottom of a column rather than the bottom of a page.

Implementations that support footnotes generally support page floats like float: bottom. Page floats should end up above the footnote area. How might this be specified?

2.4.2 Size of the footnote area

The max-height property on the footnote area limits the size of this area, unless the page contains only footnotes (as may happen on the last page of a document).

Since it is undesirable for a page to consist only of footnotes, user agents may set a default max-height value on the footnote area.

2.5 The Footnote Counter

The footnote counter is a predefined counter associated with the footnote element. Its value is the number or symbol used to identify the footnote. This value is used in both the footnote call and the footnote marker. It should be incremented for each footnote.

2.5.1 Values of the footnote counter

The footnote counter, like other counters, may use any counter style. Footnotes often use a sequence of symbols.

::footnote-call { content: counter(footnote, symbols('*', '†', '‡', '§')); }

::footnote-marker { content: counter(footnote, symbols('*', '†', '‡', '§')) '. '; }

2.5.2 Resetting the footnote counter

The footnote counter may be reset on each page.

@page {
  counter-reset: footnote;
  @footnote { … }
}

Note that the value of the footnote counter should depend on the position of the footnote element in the document tree, not where it is eventually placed. A footnote element may sometimes be placed on the page after the footnote call, but the same counter value must be used for both.

2.6 The footnote-call pseudo-element

A ::footnote-call pseudo-element is inserted in place of the footnote element when the latter is removed from the flow. By default, the content of this pseudo-element is the value of the footnote counter, styled as a superscripted number.
::footnote-call {
content: counter(footnote);
vertical-align: baseline;
font-size: 100%;
line-height: inherit;
font-variant-position: super;
}

2.7 The footnote-marker pseudo-element

The ::footnote-marker pseudo-element represents the footnote element’s marker, the number or symbol that identifies each footnote. This pseudo-element behaves like a ::marker pseudo-element, as defined in [CSS3LIST]. It is placed at the beginning of the superior parent’s content, and is inline by default. The ::footnote-marker can be styled just as other ::marker elements can be. The default style should include list-style-position: inside.
::footnote-marker {
content: counter(footnote);
}

::footnote-marker::after {
content: '. ';
}

2.8 Rendering footnotes and footnote policy

Rendering footnotes can be complex. If a footnote falls near the bottom of the page, there may not be enough room on the page for the footnote body. The footnote-policy property allows authors some influence over the rendering of difficult pages.

Name:footnote-policy
Value:auto | line | block
Initial:auto
Applies to:elements
Inherited:no
Media:paged
Computed value:specified value
Percentages:N/A
auto
The user agent chooses how to render footnotes, and may place the footnote body on a later page than the footnote reference. A footnote body must never be placed on a page before the footnote reference.
line
If a given footnote body cannot be placed on the current page due to lack of space, the user agent introduces a forced page break at the start of the line containing the footnote reference, so that both the reference and the footnote body fall on the next page. Note that the user agent must honor widow and orphan settings when doing this, and so may need to insert the page break on an earlier line.
block
As with line, except a forced page break is introduced before the paragraph that contains the footnote.

We need an algorithm for laying out footnotes

2.9 Future directions

The next level will include sidenotes, column footnotes, and multiple footnote areas.

3 Selecting Pages

A paginated document consists of a sequence of pages. [[CSS3PAGE]] defines page selectors, which allow the selection of the first page of the document, left and right pages, and blank pages. Here we extend the idea of page selectors to enable the selection of arbitrary document pages.

3.1 Page Selectors

The nth() page pseudo-class allows the selection of arbitrary document pages. This pseudo-class takes an argument of the form An + B as defined in [CSS3SYN]. When applied to the default @page rule, nth() selects the document page whose index matches the argument.
nth() = ( An+B [of <custom-ident>]?)

nth() is not related to the page counter, which may reset and use various numbering schemes.

When the nth() selector is applied to a named page, and that named page is part of a page-group (see below), it selects the nth page in the page group.

@page :nth(1)

This selects the first page of the document.

@page :nth(2n)
This selects all even document pages.

3.2 Page groups

Many paginated documents have a repeating structure, consisting of many chapters, sections, or articles. The first page of each subdivision often requires special treatment, but [CSS3PAGE] doesn’t define a way to select the first page of each chapter (as distinct from the first page of the entire document).

When the page property is applied to an element that also has a forced break property applied, a page group is created. The page group is the collection of all pages created by an instance of that element. When a new instance of the element is rendered, a new page group is started.

A page may be part of several page groups, as a given page group may have ancestors or descendants that are part of another page group.

CSS:
div { page: A }
child { page: B }
A page may be part of several page groups.
Note that page 5 can be selected in three ways:
@page :nth(5 of A) /* will select 5th page of every <div> */
@page :nth(1 of B) /* will select first page of every <child> */
@page :nth(5)   /* will select 5th page of document */

Consider the following HTML:

<div class="chapter">
<h1>Chapter One</h1>
<p>some text</p>
<table class="broadside">
...
</table>
...
</div>
<div class="chapter">
<h1>Chapter Two</h1>
<p>some text</p>
...
<table class="broadside">
...
</table>
...
</div>

And CSS:

div.Chapter { 
page: body;
}

div.broadside {
page: broadside;
}

In this case, each chapter will form a separate page group. @page:nth(3 of body) will select the third page of each chapter, even if that page happens to use the “broadside” named page. @page:nth(1) will select only the first page of the document, as will @page:first.

4 Leaders

A leader, sometimes known as a tab leader or a dot leader, is a repeating pattern used to visually connect content across horizontal spaces. They are most commonly used in tables of contents, between titles and page numbers. The leader() function, as a value for the content property, is used to create leaders in CSS. This function takes a string (the leader string), which describes the repeating pattern for the leader.
Name:content
New values:leader()
Media:paged
leader() = leader( [dotted | solid | space] | <string>);

Three keywords are shorthand values for common strings:

dotted
leader('. ')
solid
leader(_)
space
leader(' ')
<string>
ol.toc a::after {
  content: leader('.') target-counter(attr(href), page);
}

<h1>Table of Contents</h1>
<ol class="toc">
<li><a href="#chapter1">Loomings</a></li>
<li><a href="#chapter2">The Carpet-Bag</a></li>
<li><a href="#chapter3">The Spouter-Inn</a></li>
</ol>

This might result in:
Table of Contents

1. Loomings.....................1
2. The Carpet-Bag...............9
3. The Spouter-Inn.............13

Do leaders depend on the assumption that the content after the leader is right-aligned (end-aligned)?

4.1 Rendering leaders

Consider a line which contains the content before the leader (the “before content”), the leader, and the content after the leader (the “after content”). Leaders obey the following rules:
  1. The leader string must appear in full at least once.
  2. The leader should be as long as possible
  3. Visible characters in leaders should vertically align with each other when possible.
  4. Line break characters in the leader string must be ignored.
  5. White space in the leader string follows normal CSS rules.
  6. A leader only appears between the start content and the end content.
  7. A leader only appears on a single line, even if the before content and after content are on different lines.
  8. A leader can’t be the only thing on a line.

4.1.1 Procedure for rendering leaders

  1. Lay out the before content, until reaching the line where the before content ends.
    BBBBBBBBBB
    BBB
    
  2. The leader string consists of one or more glyphs, and is thus an inline box. A leader is a row of these boxes, drawn from the end edge to the start edge, where only those boxes not overlaid by the before or after content. On this line, draw the leader string, starting from the end edge, repeating as many times as possible until reaching the start edge.
    BBBBBBBBBB
    ..........
    
  3. Draw the before and after content on top of the leader. If any part of the before or after content overlaps a glyph in a leader string box, that glyph is not displayed.
    BBBBBBBBBB
    BBB....AAA
    
  4. If one full copy of the leader string is not visible:
    BBBBBBB
    BBBBBBA
    
    Insert a line break before the after content, draw the leader on the next line, and draw the end content on top
    BBBBBBB
    BBBBBB
    ......A
    

drawing leaders
Procedure for drawing leaders
drawing leaders
Procedure for drawing leaders when the content doesn’t fit on a single line

5 Cross-references

Many documents contain internal references: Three new values for the content property are used to automatically create these types of cross-references: target-counter(), target-counters(), and target-text(). Each of these displays information obtained from the target end of a link.

5.1 The target-counter() function

The target-counter() function retrieves the value of the innermost counter with a given name. The required arguments are the url of the target and the name of the counter. An optional counter-style argument can be used to format the result.

These functions only take a fragment URL which points to a location in the current document. If there’s no fragment, if the ID referenced isn’t there, or if the URL points to an outside document, the user agent must treat that as an error.

target-counter() = target-counter( <url> , <custom-ident> [ , <counter-style> ]? )
HTML:
…which will be discussed on page <a href="#chapter4_sec2"></a>.

CSS:

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

Result:

…which will be discussed on page 137.

Page numbers in tables of contents can be generated automatically:

HTML:

<nav>
  <ol>
    <li class="frontmatter"><a href="#pref_01">Preface</a></li>
    <li class="frontmatter"><a href="#intr_01">Introduction</a></li>
    <li class="bodymatter"><a href="#chap_01">Chapter One</a></li>
  </ol>
</nav>

CSS:

.frontmatter a::after { content: leader('.') target-counter(attr(href url), page, lower-roman) }
.bodymatter a::after { content: leader('.') target-counter(attr(href url), page, decimal) }

Result:

Preface.............vii
Introduction.........xi
Chapter One...........1

5.2 The target-counters() function

This functions fetches the value of all counters of a given name from the end of a link, and formats them by inserting a given string between the value of each nested counter.
target-counters() = target-counter( <url> , <custom-ident> , <string> [ , <counter-style> ]? )
I have not found a compelling example for target-counters() yet.

5.3 target-text

The target-text() function retrieves the text value of the element referred to by the URL. An optional second argument specifies what content is retrieved, using the same values as the string-set property above.
target-text() = target-counter( <url> [ , [ content | before | after | first-letter] ]? )

A simpler syntax has been proposed by fantasai: http://lists.w3.org/Archives/Public/www-style/2012Feb/0745.html

…which will be discussed <a href="#chapter_h1_1">later</a>.

a::after { content: ", in the chapter entitled " target-text(attr(href url)) }

Result: …which will be discussed later, in the chapter entitled Loomings.

6 Bookmarks

Some document formats, most notably PDF, allow the use of bookmarks as an aid to navigation. Bookmarks provide a hierarchy of links to document elements, as well as text to label the links. A bookmark has three properties: bookmark-level, bookmark-label, and bookmark-state.

A bookmark references a point in the document, which we define to the be the intersection of the before edge and the start edge of the first box or box fragment generated by the element. When a user activates a bookmark, the user agent must bring that reference point to the user’s attention, by moving to that page, scrolling (as defined in CSSOM View), or some other mechanism.

6.1 bookmark-level

The bookmark-level property determines if a bookmark is created, and at what level. If this property is absent, or has value none, no bookmark should be generated, regardless of the values of bookmark-label or bookmark-state.

Name:bookmark-level
Value:none | <integer>
Initial:none
Applies to:all elements
Inherited:no
Media:visual
Computed value:specified value
Percentages:N/A
<integer>
defines the level of the bookmark, with the highest level being 1 (negative and zero values are invalid).
none
no bookmark is generated.
section h1 { bookmark-level: 1; }
section section h1 { bookmark-level: 2; }
section section section h1 { bookmark-level: 3; }

6.2 bookmark-label

Name:bookmark-label
Value:<content-list>
Initial:content(text)
Applies to:all elements
Inherited:no
Media:visual
Computed value:specified value
Percentages:N/A
<content-list>
<content-list> is defined above, in the section on the string-set property. The value of <content-list> becomes the text content of the bookmark label.
HTML:
<h1>Loomings</h1>

CSS:

h1 { 
bookmark-label: content(text);
bookmark-level: 1;
}

The bookmark label will be “Loomings”.

6.3 bookmark-state

Bookmarks typically toggle open and closed, with the open state displaying the next level of bookmarks.
Name:bookmark-state
Value:open | closed
Initial:open
Applies to:block-level elements
Inherited:no
Media:visual
Computed value:specified value
Percentages:N/A
open
The bookmarks of the nearest descendants of an element with a bookmark-state of open will be displayed.
closed
any bookmarks of descendant elements are not initially displayed.

Appendix A: Where Are They Now?

Many sections which were in the 29 November 2011 Working Draft have been moved to other specifications. Here are some notes on where things have moved.

Page marks and bleed area

This section has been moved to CSS Paged Media Module Level 3.

CMYK colors

This section has been moved to CSS Color Module Level 4.

Styling blank pages

This section has been moved to CSS Paged Media Module Level 3

Paged presentations

This section has been moved to CSS Overflow Module Level 3.

This is discussed in WHATWG CSS Books.

Page floats

This section has been moved to CSS Page Floats.

Selecting columns and pages

A brief mention of selecting columns is found in WHATWG CSS Books.

Appendix B: Default UA Stylesheet

This appendix is informative, and is to help UA developers to implement a default stylesheet for HTML, but UA developers are free to ignore or modify as appropriate.

@page {
  counter-reset: footnote;
  @footnote {
    counter-increment: footnote;
    float: bottom;
    column-span: all;
    height: auto;
  }
}

::footnote-marker {
  content: counter(footnote);
  list-style-position: inside;
}

::footnote-marker::after {
  content: '. ';
}

::footnote-call {
  content: counter(footnote);
  vertical-align: super;
  font-size: 65%;
}

@supports ( font-variant-position: super ) {
  ::footnote-call {
    content: counter(footnote);
    vertical-align: baseline;
    font-size: 100%;
    line-height: inherit;
    font-variant-position: super;
  }
}

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

Appendix C: Changes

Changes since the 24 September 2013 Editor’s Draft are:

In addition to the above changes, many other changes have been made since the 29 November 2011 Working Draft:

Differences with the WHATWG CSS Books specification:

Acknowledgments

This work would not be possible without the immense contributions of Håkon Wium Lie.

Chris Lilley, Elika J. Etemad, Alan Stearns, L. David Baron, Bert Bos, [$your_name, ", " ]+ and Liam Quin have provided valuable feedback.

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.

Conformance classes

Conformance to this specification is defined for three conformance classes:

style sheet
A CSS style sheet.
renderer
A UA that interprets the semantics of a style sheet and renders documents that use them.
authoring tool
A UA that writes a style sheet.

A style sheet is conformant to this specification if all of its statements that use syntax defined in this module are valid according to the generic CSS grammar and the individual grammars of each feature defined in this module.

A renderer is conformant to this specification if, in addition to interpreting the style sheet as defined by the appropriate specifications, it supports all the features defined by this specification by parsing them correctly and rendering the document accordingly. However, the inability of a UA to correctly render a document due to limitations of the device does not make the UA non-conformant. (For example, a UA is not required to render color on a monochrome monitor.)

An authoring tool is conformant to this specification if it writes style sheets that are syntactically correct according to the generic CSS grammar and the individual grammars of each feature in this module, and meet all other conformance requirements of style sheets as described in this module.

Partial implementations

So that authors can exploit the forward-compatible parsing rules to assign fallback values, CSS renderers must treat as invalid (and ignore as appropriate) any at-rules, properties, property values, keywords, and other syntactic constructs for which they have no usable level of support. In particular, user agents must not selectively ignore unsupported component values and honor supported values in a single multi-value property declaration: if any value is considered invalid (as unsupported values must be), CSS requires that the entire declaration be ignored.

Experimental implementations

To avoid clashes with future CSS features, the CSS2.1 specification reserves a prefixed syntax for proprietary and experimental extensions to CSS.

Prior to a specification reaching the Candidate Recommendation stage in the W3C process, all implementations of a CSS feature are considered experimental. The CSS Working Group recommends that implementations use a vendor-prefixed syntax for such features, including those in W3C Working Drafts. This avoids incompatibilities with future changes in the draft.

Non-experimental implementations

Once a specification reaches the Candidate Recommendation stage, non-experimental implementations are possible, and implementors should release an unprefixed implementation of any CR-level feature they can demonstrate to be correctly implemented according to spec.

To establish and maintain the interoperability of CSS across implementations, the CSS Working Group requests that non-experimental CSS renderers submit an implementation report (and, if necessary, the testcases used for that implementation report) to the W3C before releasing an unprefixed implementation of any CSS features. Testcases submitted to W3C are subject to review and correction by the CSS Working Group.

Further information on submitting testcases and implementation reports can be found from on the CSS Working Group’s website at http://www.w3.org/Style/CSS/Test/. Questions should be directed to the public-css-testsuite@w3.org mailing list.

References

Normative References

[RFC2119]
S. Bradner. Key words for use in RFCs to Indicate Requirement Levels. URL: http://www.ietf.org/rfc/rfc2119.txt

Informative References

[CSS21]
Bert Bos; et al. Cascading Style Sheets Level 2 Revision 1 (CSS 2.1) Specification. 7 June 2011. W3C Recommendation. URL: http://www.w3.org/TR/2011/REC-CSS2-20110607
[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
[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/
[CSS3SYN]
Tab Atkins Jr.; Simon Sapin. CSS Syntax Module. 5 November 2013. W3C Working Draft. (Work in progress.) URL: http://www.w3.org/TR/2013/WD-css-syntax-3-20131105/
[CSS3VAL]
Håkon Wium Lie; Tab Atkins; Elika J. Etemad. CSS Values and Units Module Level 3. 30 July 2013. W3C Candidate Recommendation. (Work in progress.) URL: http://www.w3.org/TR/2013/CR-css3-values-20130730/

Index

Property index

NameValueInitialApplies toInh.%agesMediaComputed value
string-set[[ <custom-ident> <content-list>] [, <custom-ident> <content-list>]* ] | nonenoneall elements, but not pseudo-elementsnoN/Aallspecified value
running<custom-ident>noneelementsnoN/Aallspecified value
footnote-displayblock | inline | compactblockelementsnoN/Apagedspecified value
footnote-policyauto | line | blockautoelementsnoN/Apagedspecified value
bookmark-levelnone | <integer>noneall elementsnoN/Avisualspecified value
bookmark-label<content-list>content(text)all elementsnoN/Avisualspecified value
bookmark-stateopen | closedopenblock-level elementsnoN/Avisualspecified value

Issues Index

How do we define the default value for this function?

This idea would be much more useful if we could also copy (rather than just move) elements. That would avoid the duplication of HTML in the example above.

Bert Bos has proposed an alternative syntax, which allows both moving and copying elements into running heads. In the example below, h2 elements appear in their normal place in the document, but are also copied into running heads.

h2 {
display: block;
running: chapter;
font-size: 18pt;
font-weight: bold;
}

h2:running {
display: inline;
font-size: 11pt;
font-weight: normal;
font-variant: small-caps;
letter-spacing: 1pt;
}

@page {
  @top-center {
    content: element(chapter);
    }
  }
Name:running
Value:<custom-ident>
Initial:none
Applies to:elements
Inherited:no
Media:all
Computed value:specified value
Percentages:N/A
Why is float:bottom used with the footnote area? Floating footnotes to the footnote area, and then floating the footnote area itself, seems overly complex, given that implementations don’t allow the footnote area to float anywhere else. Note that some implementations do allow the footnote area to be absolutely positioned.
How would one describe this in the grammar of CSS3-Page?
How do footnotes work in multi-column text? Prince uses float: prince-column-footnote to create a footnote at the bottom of a column rather than the bottom of a page.
Implementations that support footnotes generally support page floats like float: bottom. Page floats should end up above the footnote area. How might this be specified?
We need an algorithm for laying out footnotes
Do leaders depend on the assumption that the content after the leader is right-aligned (end-aligned)?
A simpler syntax has been proposed by fantasai: http://lists.w3.org/Archives/Public/www-style/2012Feb/0745.html