CSS Generated Content for Paged Media Module

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.

Value Definitions

This specification follows the CSS property definition conventions from [CSS21] using the value definition syntax from [CSS-VALUES-3]. Value types not defined in this specification are defined in CSS Values & Units [CSS-VALUES-3]. Combination with other CSS modules may expand the definitions of these value types.

In addition to the property-specific values listed in their definitions, all properties defined in this specification also accept the CSS-wide keywords as their property value. For readability they have not been repeated explicitly.

1. Running headers and footers

1.1. Named strings

1.1.1. The string-set property

User agents are expected to support this property on all media, including non-visual ones.

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 [CSS-VALUES-3]

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.

<h1>Loomings</h1>

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

<section title="Loomings">

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

1.1.2. The string() function

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.

1.2. Running elements

@page {
  @top { content: element(header); }
}

h1 { position: running(header); }

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.

running() = running( <custom-ident> )

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

@top-center {
  content: element(heading);
  }

p.rh {
  position: running(heading);
  }

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

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

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);
    }
  }

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.

element() = element( <custom-ident> , [ first | start | last | first-except ]? )

2. Footnotes

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.

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

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.

<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>

@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

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.

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

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

2.4.1. Positioning of the footnote area

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

::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

::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.

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

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

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)

@page :nth(2n)

3.2. Page groups

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;
  break-before: page;
}
child { 
  page: B;
  break-before: page;
}

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 */

<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>

div.chapter {
  page: body;
  break-before: page;
}

table.broadside {
  page: broadside;
  break-before: page;
}

4. Leaders (moved)

Now described in [CSS3-CONTENT]

5. Cross-references (moved)

Now described in [CSS3-CONTENT]

6. Bookmarks (moved)

Now described in [CSS3-CONTENT]

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.

Navigation between pages

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 13 May 2014 Working Draft:

• Clarify that bookmark is only created via bookmark-level property. Remove none value from bookmark-label.
• Move the cross references, leaders, and bookmarks sections to the CSS Generated Content Module.

Changes since the 24 September 2013 Editor’s Draft:

• The spec has a new editor.
• All text and examples rewritten.
• Added attr(<identifier>) value to string-set property. This is supported by both Prince and AntennaHouse.
• Added footnote-policy property to control rendering of footnotes in difficult situations.
• Added footnote-display property to allow inline footnotes.
• Removed sidenotes section.
• Removed section on selecting elements within pages and columns
• Removed page-group property, and added optional argument to nth() page pseudo-class to allow selection within page groups.

Changes since the 29 November 2011 Working Draft:

• Page Marks and Bleeds section moved to CSS Paged Media Module Level 3
• CMYK Colors section moved to CSS Colors Level 4.
• Styling Blank Pages section deleted
• Paged Presentations section moved to CSS Overflow Module Level 3.
• Navigation Between Pages moved to WHATWG CSS Books
• Page floats section moved to CSS Page Floats
• First-page pseudo-element section deleted
• Selecting Columns and Pages section deleted
• env() function removed from string-set property
• alignment values of leaders removed
• leader specified to occupy only a single line
• content() value of target-text changed to content(text)
• target-pull() value of content property removed

Differences with the WHATWG CSS Books specification:

• Added attr(<identifier>) value to string-set property. This is supported by both Prince and AntennaHouse.
• CSS Books does not have the footnote-display property.
• CSS Books does not have the footnote-policy property.
• The relationship between the nth() page pseudo-class and the page-group concept is clarified, which may make the page-group property redundant.
• This specification does not redefine the :first page pseudo-selector to select the first page of a page-group.
• This specification does not consider:
  1. Named areas
  2. Selecting elements within pages
  3. The range() page pseudo-class
  4. Selecting columns
  5. Baseline rhythms
  6. Extending the box model
  7. Character substitution
  8. Microtypography

Acknowledgments

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