csswg-drafts/css3-gcpm/Overview.html at ed82a9eb3170139c4c10af8ed13963e7cb426245 · w3c/csswg-drafts · GitHub

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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">

<html lang=en>
 <head>
  <title>CSS3 module: Generated Content for Paged Media</title>

  <style type="text/css">
.cols { width: 500px; height: 200px; background: #fff; position: relative; border: solid 10px blue; margin: 0.5em 2em 1em 0; font: bold 14px/19px Arial, sans-serif }
.cols p { padding: 3px; margin: 0 }
.gap { position: absolute; background: black; width: 5px; bottom: 0px; top: 0px; border: 10px solid red; border-top-width: 0; border-bottom-width: 0;  }
.rep { position: absolute; top: 45px; background: #333; height: 110px; width: 100px;  color: white; z-index: 4 }
div.example:before { width: 9em !important }
div.example { padding-top: 0.5em }

table.hyphenate { border-collapse: collapse }
table.hyphenate th {
  text-align: left; white-space: nowrap; border: 1px solid black; padding: 0.2em }
table.hyphenate td {
  border: 1px solid black; padding: 0.2em 0.2em 0.2em 1em; font-size: 0.8em }

table.border, table.border td, table.border th, table.border table {
  border-collapse: collapse;
  border: thin solid black;
  padding: 0.2em;
  vertical-align: top;
}
table.border td + td { white-space: pre }
table.border table { padding: 0; border-collapse: separate; border: none; }
table.border table td { border: thin dotted black; padding: 0.2em; margin: 0.2em  }
table.border .comment { margin-top: 0; white-space: normal; font-style: italic }


</style>
  <!--<link rel="stylesheet" type="text/css" href="default.css">-->
  <link href="http://www.w3.org/TR/css3-gcpm/default.css" rel=stylesheet
  type="text/css">
  <link href="http://www.w3.org/StyleSheets/TR/W3C-ED.css" rel=stylesheet
  type="text/css">

 <body>
  <div class=head> <!--begin-logo-->
   <p><a href="http://www.w3.org/"><img alt=W3C height=48
    src="http://www.w3.org/Icons/w3c_home" width=72></a> <!--end-logo-->

   <h1>CSS3 module: Generated Content for Paged Media</h1>

   <h2 class="no-num no-toc" id=w3c-working>Editor's Draft 28 December 2008</h2>

   <dl>
    <dt>This version:

    <dd><a
     href="http://www.w3.org/TR/2008/ED-css3-gcpm-20081228">http://www.w3.org/TR/2008/ED-css3-gcpm-20081228</a>

    <dt>Latest version:

    <dd><a href="http://www.w3.org/TR/css3-gcpm">
     http://www.w3.org/TR/css3-gcpm</a>

    <dt>Previous version:

    <dd><a href="http://www.w3.org/TR/2007/WD-css3-gcpm-20070205">
     http://www.w3.org/TR/2007/WD-css3-gcpm-20070205</a>

    <dt>Editor:

    <dd>H&aring;kon Wium Lie, Opera Software, howcome@opera.com
   </dl>
   <!--begin-copyright-->
   <p class=copyright><a
    href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
    rel=license>Copyright</a> &copy; 2008 <a
    href="http://www.w3.org/"><acronym title="World Wide Web
    Consortium">W3C</acronym></a><sup>&reg;</sup> (<a
    href="http://www.csail.mit.edu/"><acronym title="Massachusetts Institute
    of Technology">MIT</acronym></a>, <a
    href="http://www.ercim.org/"><acronym title="European Research Consortium
    for Informatics and Mathematics">ERCIM</acronym></a>, <a
    href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. W3C <a
    href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
    <a
    href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a>
    and <a
    href="http://www.w3.org/Consortium/Legal/copyright-documents">document
    use</a> rules apply.</p>
   <!--end-copyright-->
   <hr title="Separator for header">
  </div>

  <h2 class="no-num no-toc" id=abstract>Abstract</h2>

  <p>This module describes features often used in printed publications. In
   particular, this specification describes how CSS style sheets can express
   running headers and footers, leaders, cross-references, footnotes, named
   flows, hyphenation, new counter styles, character substitution, image
   resolution, page floats, advanced multi-column layout, conditional
   content, crop and cross marks, bookmarks, CMYK colors, continuation
   markers, change bars, line numbers, named page lists, and generated lists.
   Most of this functionality involves some sort of generated content where
   content from the document is adorned, replicated, or moved in the
   presentation of the document. Along with two other CSS3 modules &ndash;
   multi-column layout and paged media &ndash; this module offers advanced
   functionality for presenting structured documents on paged media. This
   specification only applies to the &lsquo;<code
   class=property>print</code>&rsquo; media type.

  <h2 class="no-num no-toc" id=status>Status of this document</h2>
  <!--begin-status-->

  <p>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.

  <p>The (<a
   href="http://lists.w3.org/Archives/Public/www-style/">archived</a>) public
   mailing list <a href="mailto:www-style@w3.org">www-style@w3.org</a> (see
   <a href="http://www.w3.org/Mail/Request">instructions</a>) is preferred
   for discussion of this specification. When sending e-mail, please put the
   text &#8220;css3-gcpm&#8221; in the subject, preferably like this:
   &#8220;[<!---->css3-gcpm<!---->] <em>&hellip;summary of
   comment&hellip;</em>&#8221;

  <p>This document was produced by the <a href="/Style/CSS/members">CSS
   Working Group</a> (part of the <a href="/Style/">Style Activity</a>).

  <p>This document was produced by a group operating under the <a
   href="/Consortium/Patent-Policy-20040205/">5 February 2004 W3C Patent
   Policy</a>. W3C maintains a <a href="/2004/01/pp-impl/32061/status"
   rel=disclosure>public list of any patent disclosures</a> 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 <a
   href="/Consortium/Patent-Policy-20040205/#def-essential">Essential
   Claim(s)</a> must disclose the information in accordance with <a
   href="/Consortium/Patent-Policy-20040205/#sec-Disclosure">section 6 of the
   W3C Patent Policy</a>.</p>
  <!--end-status-->

  <p>This WD describes functionality at various levels of maturity. Some
   features have been part of other WDs in the past and have already been
   implemented. These parts are fairly stable and unlikely to change much.
   Other features are still at the sketching stage. In general, features
   presented earlier in this draft are more mature that those presented later
   in the draft.

  <h2 class="no-num no-toc" id=table><a name=contents>Table of contents</a></h2>
  <!--begin-toc-->

  <ul class=toc>
   <li><a href="#dependencies"><span class=secno>1. </span>Dependencies on
    other modules</a>

   <li><a href="#introduction"><span class=secno>2. </span>Introduction</a>

   <li><a href="#running"><span class=secno>3. </span>Running headers and
    footers</a>
    <ul class=toc>
     <li><a href="#named"><span class=secno>3.1 </span>Named strings</a>
      <ul class=toc>
       <li><a href="#setting"><span class=secno>3.1.1 </span>Setting named
        strings</a>

       <li><a href="#using"><span class=secno>3.1.2 </span>Using named
        strings</a>
      </ul>

     <li><a href="#running0"><span class=secno>3.2 </span>Running
      elements</a>
    </ul>

   <li><a href="#leaders"><span class=secno>4. </span>Leaders</a>

   <li><a href="#cross-references"><span class=secno>5.
    </span>Cross-references</a>
    <ul class=toc>
     <li><a href="#the-target-counter"><span class=secno>5.1 </span>The
      &lsquo;<code class=css>target-counter</code>&rsquo; and &lsquo;<code
      class=css>target-counters</code>&rsquo; values</a>

     <li><a href="#the-target-text"><span class=secno>5.2 </span>The
      &lsquo;<code class=css>target-text</code>&rsquo; value</a>
    </ul>

   <li><a href="#footnotes"><span class=secno>6. </span>Footnotes</a>
    <ul class=toc>
     <li><a href="#turning"><span class=secno>6.1 </span>Turning elements
      into footnotes</a>

     <li><a href="#the-footnote"><span class=secno>6.2 </span>The footnote
      area</a>

     <li><a href="#footnote"><span class=secno>6.3 </span>Footnote calls</a>

     <li><a href="#footnote0"><span class=secno>6.4 </span>Footnote
      markers</a>

     <li><a href="#counting"><span class=secno>6.5 </span>Counting
      footnotes</a>

     <li><a href="#laying"><span class=secno>6.6 </span>Laying out
      footnotes</a>

     <li><a href="#footnote1"><span class=secno>6.7 </span>Footnote magic</a>


     <li><a href="#border"><span class=secno>6.8 </span>Border parts</a>
    </ul>

   <li><a href="#pulling"><span class=secno>7. </span>Pulling elements:
    &lsquo;<code class=css>target-pull()</code>&rsquo;</a>

   <li><a href="#pushing"><span class=secno>8. </span>Pushing elements: named
    flows</a>

   <li><a href="#hyphenation"><span class=secno>9. </span>Hyphenation</a>
    <ul class=toc>
     <li><a href="#hyphenate"><span class=secno>9.1 </span>Hyphenate
      properties</a>
    </ul>

   <li><a href="#new-counter"><span class=secno>10. </span>New counter
    styles</a>
    <ul class=toc>
     <li><a href="#the-super-decimal"><span class=secno>10.1 </span>The
      &lsquo;<code class=css>super-decimal</code>&rsquo; list-style-type</a>

     <li><a href="#named0"><span class=secno>10.2 </span>Named counter
      styles</a>

     <li><a href="#the-symbols"><span class=secno>10.3 </span>The
      &lsquo;<code class=css>symbols()</code>&rsquo; list-style-type</a>
    </ul>

   <li><a href="#character"><span class=secno>11. </span>Character
    substitution</a>

   <li><a href="#image"><span class=secno>12. </span>Image resolution</a>

   <li><a href="#page-marks"><span class=secno>13. </span>Page marks and
    bleed area</a>

   <li><a href="#bookmarks"><span class=secno>14. </span>Bookmarks</a>

   <li><a href="#cmyk-colors"><span class=secno>15. </span>CMYK colors</a>

   <li><a href="#creating"><span class=secno>16. </span>Creating paged
    presentations</a>

   <li><a href="#the-blank"><span class=secno>17. </span>The :blank page
    pseudo-class</a>

   <li><a href="#page-floats"><span class=secno>18. </span>Page floats</a>

   <li><a href="#advanced"><span class=secno>19. </span>Advanced multi-column
    layout</a>
    <ul class=toc>
     <li><a href="#the-float-offset"><span class=secno>19.1 </span>The
      &lsquo;<code class=property>float-offset</code>&rsquo; property</a>
    </ul>

   <li><a href="#continuation"><span class=secno>20. </span>Continuation
    markers</a>

   <li><a href="#change"><span class=secno>21. </span>Change bars</a>

   <li><a href="#line-numbers"><span class=secno>22. </span>Line numbers</a>

   <li><a href="#page-lists"><span class=secno>23. </span>Page lists</a>
    <ul class=toc>
     <li><a href="#the-page"><span class=secno>23.1 </span>The &lsquo;<code
      class=property>page</code>&rsquo; property</a>
    </ul>

   <li><a href="#generated"><span class=secno>24. </span>Generated lists</a>
    <ul class=toc>
     <li><a href="#the-prototype"><span class=secno>24.1 </span>The prototype
      properties</a>

     <li><a href="#toc"><span class=secno>24.2 </span>TOC</a>

     <li><a href="#glossary"><span class=secno>24.3 </span>Glossary</a>

     <li><a href="#index0"><span class=secno>24.4 </span>Index</a>

     <li><a href="#a-more"><span class=secno>24.5 </span>A more complex
      example</a>
    </ul>

   <li><a href="#conformance"><span class=secno>25. </span>Conformance</a>

   <li><a href="#appendix"><span class=secno>26. </span>Appendix A: Default
    style sheet</a>

   <li class=no-num><a href="#acknowledgments">Acknowledgments</a>

   <li class=no-num><a href="#references">References</a>
    <ul class=toc>
     <li class=no-num><a href="#normative-references">Normative
      references</a>

     <li class=no-num><a href="#other-references">Other references</a>
    </ul>

   <li class=no-num><a href="#index">Index</a>

   <li class=no-num><a href="#property-index">Property index</a>
  </ul>
  <!--end-toc-->

  <h2 id=dependencies><span class=secno>1. </span>Dependencies on other
   modules</h2>

  <p>This CSS3 module has normative references to the following other CSS3
   modules:

  <ul>
   <li><a href="#CSS3LIST" rel=biblioentry>[CSS3LIST]<!--{{!CSS3LIST}}--></a>

   <li><a href="#CSS3VAL" rel=biblioentry>[CSS3VAL]<!--{{!CSS3VAL}}--></a>
  </ul>

  <p>This CSS3 module has non-normative references to the following other
   CSS3 modules:

  <ul>
   <li><a href="#CSS3COL" rel=biblioentry>[CSS3COL]<!--{{CSS3COL}}--></a>

   <li><a href="#CSS3PAGE" rel=biblioentry>[CSS3PAGE]<!--{{CSS3PAGE}}--></a>
  </ul>

  <h2 id=introduction><span class=secno>2. </span>Introduction</h2>

  <p>(This section is not normative.)

  <p>This specification describes features often used in printed
   publications. Some of the proposed functionality (e.g., hyphenation, the
   new list style types, and border segments) may also used with other media
   types. However, this specification is only concerned with the &lsquo;<code
   class=property>print</code>&rsquo; media type.

  <h2 id=running><span class=secno>3. </span>Running headers and footers</h2>

  <p>To aid navigation in printed material, headers and footers are often
   printed in the page margins. <a href="#CSS3PAGE"
   rel=biblioentry>[CSS3PAGE]<!--{{CSS3PAGE}}--></a> 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 <dfn id=named1>named strings</dfn>
   which <em>copies</em> the text (without style, structure, or replaced
   content) from one element for later reuse in margin boxes. The second
   mechanism is <dfn id=running1>running elements</dfn> which <em>moves</em>
   elements (with style, structure, and replaced content) into a margin box.

  <h3 id=named><span class=secno>3.1 </span>Named strings</h3>
  <!--
<p>Named strings are discussed both in the CSS3 Generated and Replaced
Content (section 9) and in CSS3 Paged Media (several places). For a
proposed definition of the property, one has to go back to the <a href="http://www.w3.org/1999/06/WD-css3-page-19990623">CSS3 draft from 1999</a>
1999:
-->

  <p>Named strings can be thought of as variables that can hold one string of
   text each. Named strings are created with the &lsquo;<code
   class=property><a href="#string-set">string-set</a></code>&rsquo; property
   which copies a string of text into the named string. Only text is copied;
   not style, structure, or replaced content.

  <div class=example>
   <p>Consider this code:

   <pre>
h1, h2 { string-set: header content() }
</pre>

   <p>Whenever an <code>h1</code> or <code>h2</code> element is encountered,
    its textual content is copied into a named string called <em>header</em>.
    Its content can be retrieved in the &lsquo;<code
    class=property>content</code>&rsquo; property:

   <pre>
@page :right { @top-right { content: string(header) }}
</pre>
  </div>

  <h4 id=setting><span class=secno>3.1.1 </span>Setting named strings</h4>

  <table class=propdef id=name->
   <tbody>
    <tr>
     <td><em>Name:</em>

     <td><dfn id=string-set>string-set</dfn>

    <tr>
     <td><em>Value:</em>

     <td>[[ &lt;identifier> &lt;content-list>] [, &lt;identifier>
      &lt;content-list>]* ] | none

    <tr>
     <td><em>Initial:</em>

     <td>none

    <tr>
     <td><em>Applies to:</em>

     <td>all elements

    <tr>
     <td><em>Inherited:</em>

     <td>no

    <tr>
     <td><em>Percentages:</em>

     <td>N/A

    <tr>
     <td><em>Media:</em>

     <td>all

    <tr>
     <td><em>Computed&nbsp;value:</em>

     <td>as specified value
  </table>

  <p>The &lsquo;<code class=property><a
   href="#string-set">string-set</a></code>&rsquo; 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 &lsquo;<code class=property><a
   href="#string-set">string-set</a></code>&rsquo; different from
   &lsquo;<code class=css>none</code>&rsquo; is encountered, the named
   strings are assigned their respective value.

  <p>For the &lsquo;<code class=property><a
   href="#string-set">string-set</a></code>&rsquo; property,
   &lt;content-list> expands to one or more of these values, in any order:

  <dl>
   <dt>&lt;string&gt;

   <dd>a string, e.g. "foo"

   <dt>&lt;counter&gt;

   <dd>the counter() or counters() function, as per <a
    href="http://www.w3.org/TR/CSS21/syndata.html#counter">CSS 2.1 section
    4.3.5</a>

   <dt>&lt;content&gt;

   <dd>the &lsquo;<code class=css>content()</code>&rsquo; function, which
    accepts an optional argument:
    <dl>
     <dt>&lsquo;<code class=css>content()</code>&rsquo;

     <dd>Without any arguments, the function returns 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.

     <dt>&lsquo;<code class=css>content(before)</code>&rsquo;

     <dd>The function returns the textual content of the ::before
      pseudo-element the content of the element.

     <dt>&lsquo;<code class=css>content(after)</code>&rsquo;

     <dd>The function returns the textual content of the ::after
      pseudo-element the content of the element.

     <dt>&lsquo;<code class=css>content(first-letter)</code>&rsquo;

     <dd>The function returns the first letter of the content of the element.
      The definition of a letter is the same as for :first-letter
      pseudo-elements.
      <p class=note>The expected use for &lsquo;<code
       class=css>content(first-letter)</code>&rsquo; is to create one-letter
       headers, e.g., in dictionaries.</p>
    </dl>
  </dl>
  <!--<p class="issue">Should target-counter() and leader() also be allowed?</p>-->

  <p>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.

  <p class=note>User agents, however, must be able to remember the result of
   more than one assignment as the &lsquo;<code
   class=css>string()</code>&rsquo; functional value (described below) can
   refer to different assignments.

  <p>The scope of a 
6910
named string is the page of the element to which the
   &lsquo;<code class=property><a
   href="#string-set">string-set</a></code>&rsquo; property is attached and
   subsequent pages.

  <p>The name space of named strings is different from other sets of names in
   CSS.

  <p>The &lsquo;<code class=property><a
   href="#string-set">string-set</a></code>&rsquo; property copies text as
   well as white-space into the named string.

  <div class=example>
   <pre>
h1 {
  string-set: header "Chapter " counter(header) ": " content();
  counter-increment: header }
</pre>

   <p>Note that the string called "header" is different from the counter with
    the same name. The above code may result in <em>header</em> being set to
    "Chapter 2: Europa".
  </div>

  <div class=example>
   <p>This example results in the same value being assigned to
    <em>header</em> as in the previous example.

   <pre>
h1:before { content: "Chapter " counter (header) }
h1 {
  string-set: header content(before) content();
  counter-increment: header }
</pre>
  </div>

  <div class=example>
   <pre>
dt { string-set: index content(first-letter) }
</pre>
  </div>

  <h4 id=using><span class=secno>3.1.2 </span>Using named strings</h4>

  <p>The content of named strings can be recalled by using the &lsquo;<code
   class=css>string()</code>&rsquo; value on the &lsquo;<code
   class=property>content</code>&rsquo; property. The &lsquo;<code
   class=css>string()</code>&rsquo; value has one required argument, namely
   the name of the string.

  <div class=example>
   <pre>
@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 content(first-letter), entry content() }
</pre>
  </div>

  <p>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 &lsquo;<code class=css>string()</code>&rsquo; value. This
   argument can have one of four keywords:

  <ul>
   <li>&lsquo;<code class=css>start</code>&rsquo;: the named string's entry
    value for that page is used.

   <li>&lsquo;<code class=css>first</code>&rsquo;: the value of the first
    assignment is used. If there is no assignment on the page, the start
    value is used. &lsquo;<code class=css>first</code>&rsquo; is the default
    value.

   <li>&lsquo;<code class=css>last</code>&rsquo;: the named string's exit
    value for that page is used

   <li>&lsquo;<code class=css>first-except</code>&rsquo;: similar to
    &lsquo;<code class=css>first</code>&rsquo;, except on the page where the
    value was assigned. On that page, the empty string is used.
  </ul>

  <div class=example>
   <p>In this example, the first term on the page will be shown in the top
    left corner and the last term on the page will be shown in the top right
    corner. In top center of the page, the first letter of first term will be
    shown.

   <pre>
@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() }
</pre>
  </div>

  <div class=example>
   <p>In this example, the header in the top center will be blank on pages
    where &lsquo;<code class=css>h1</code>&rsquo; elements appear. On other
    pages, the string of the previous &lsquo;<code class=css>h1</code>&rsquo;
    element will be shown.

   <pre>
@page { @top-center { content: string(chapter, first-except) }}
h1 { string-set: chapter content() }
</pre>
  </div>

  <p>If the named string referred to in a &lsquo;<code
   class=css>string()</code>&rsquo; value has not been assigned a value, the
   empty string is used.

  <h3 id=running0><span class=secno>3.2 </span>Running elements</h3>

  <p>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.

  <p>Elements that are moved into headers and footers are repeated on several
   pages; they are said to be <em><a href="#running1">running
   elements</a></em>. To support running elements, a new value &ndash;
   running() &ndash; is introduced on the &lsquo;<code
   class=property>position</code>&rsquo; 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 &lsquo;<code class=css>display: none</code>&rsquo; had been set.
   Instead, the running element may be displayed in a margin box.

  <p>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.

  <p class=note>User agents, however, must be able to remember the result of
   more than one assignment as the &lsquo;<code
   class=css>element()</code>&rsquo; value (described below) can refer to
   different assignments.

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

  <div class=example>
   <pre>
title { position: running(header) }
@page { @top-center {
  content: element(header) }
}
</pre>
  </div>

  <p>Like the &lsquo;<code class=css>string()</code>&rsquo; value, the
   &lsquo;<code class=css>element()</code>&rsquo; value accepts an optional
   second argument:

  <dl>
   <dt>&lsquo;<code class=css>start</code>&rsquo;

   <dt>&lsquo;<code class=css>first</code>&rsquo;

   <dt>&lsquo;<code class=css>last</code>&rsquo;

   <dt>&lsquo;<code class=css>first-except</code>&rsquo;
  </dl>

  <p>The keywords have the same meaning as for the &lsquo;<code
   class=css>string()</code>&rsquo; value.

  <p>The &lsquo;<code class=css>element()</code>&rsquo; value cannot be
   combined with any other values.

  <div class=example>
   <p>In this example, the header is hidden from view in all media types
    except print. On printed pages, the header is displayed top center on all
    pages, except where h1 elements appear.

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

</pre>
  </div>

  <div class=example>
   <p>This code illustrates how to change the running header on one page in
    the middle of a run of pages:

   <pre>
...
&lt;style>
@page { @top-center {
  content: element(header, first) }}
.header { position: running(header) }
.once { font-weight: bold }
&lt;/style>
...
&lt;div class="header">Not now&lt;/div>
&lt;p>Da di ha di da di ...
  &lt;span class="header once">NOW!&lt;/span>
  &lt;span class="header">Not now&lt;/span>
  ... da di ha di hum.&lt;/p>
...
</pre>
   The header is "Not now" from the outset, due to the "div" element. The
   first "span" element changes it to "<b>NOW!</b>" on the page where the
   "span" element would have appeared. The second "span" element, which would
   have appeared on the same page as the first is not used because the
   &lsquo;<code class=css>first</code>&rsquo; keyword has been specified.
   However, the second "span" element still sets the exit value for "header"
   and this value is used on subsequent pages.</div>

  <h2 id=leaders><span class=secno>4. </span>Leaders</h2>

  <p>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.

  <p>In CSS3, a leader is composed of series of glyphs through the
   &lsquo;<code class=css>leader()</code>&rsquo; value on the &lsquo;<code
   class=property>content</code>&rsquo; property. The functional notation
   accepts one value which describes the glyph pattern that make up the
   leader. These values are allowed:

  <ul>
   <li>leader(dotted)

   <li>leader(solid)

   <li>leader(space)

   <li>leader(&lt;string&gt;)
  </ul>

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

  <table class=border>
   <tbody>
    <tr>
     <th>Keyword

     <th>String

     <th>Unicode characters

    <tr>
     <td>leader(dotted)

     <td>leader(&lsquo;<code class=css>. </code>&rsquo;)

     <td>\002E \0020

    <tr>
     <td>leader(solid)

     <td>leader(&lsquo;<code class=css>_</code>&rsquo;)

     <td>\005F

    <tr>
     <td>leader(space)

     <td>leader(&lsquo;<code class=css> </code>&rsquo;)

     <td>\0020
  </table>

  <p class=issue>Can leaders also be composed of images or SVG? <!--
<p class="issue">Some fonts may not have suitable glyphs for all
patterns. For example, in some Eastern languages, the alignment of the
shape within the glyph may not be optimal for creating leaders.
-->
   <!--<p class="issue">Are the keywords really necessary?</p>-->

  <p>The string inside the parenthesis is called the <em>leader string</em>.

  <p>In its simplest form, the &lsquo;<code
   class=property>content</code>&rsquo; property only takes one &lsquo;<code
   class=css>leader()</code>&rsquo; value:

  <div class=example>
   <pre>
heading::after { content: leader(dotted) }
</pre>
  </div>

  <p>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 leaders is collapsed according to the values on
   white-space properties.
   <!-- <span class="issue">Or, partial strings be avoided?</span> -->
   <!--<p class="issue">Should other properties influence the appearance of leaders?-->


  <p>These properties influence the appearance of leaders: all font
   properties, text properties, &lsquo;<code
   class=property>letter-spacing</code>&rsquo;, white-space properties,
   background properties, and &lsquo;<code
   class=property>color</code>&rsquo;.

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

  <p>In a more complex example, the &lsquo;<code
   class=property>leader</code>&rsquo; value is combined with other values on
   the &lsquo;<code class=property>content</code>&rsquo; property:

  <div class=example>
   <pre>
ul.toc a::after {
  content: leader(". . . ") target-counter(attr(href, url), page);
}
</pre>
  </div>

  <p>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.

  <div class=example>
   <p>Consider this code:

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

   <p>If the name and number end up on different lines (e.g., in a narrow
    column), it may be formatted like this:

   <pre>
John Doe....
...123456789
</pre>
  </div>

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

  <ol>
   <li>Lay out the content with leaders of minimum lengths

   <li>Determine the empty space left on the line.

   <li>Distribute the empty space between the leaders on the line. G
A2B0
lyphs
    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.

   <li>Fill the empty space with the specified leader pattern.
  </ol>

  <div class=example>
   <p>Consider this code:

   <pre>
&lt;style>
cite::before { content: leader('  ') }
&lt;/style>
&lt;blockquote>
  Bla great bla bla world bla bla
  empire bla bla color bla bla
  history bla bla forever.
    &lt;cite>John Johnson&lt;/cite>
&lt;/blockquote>
</pre>

   <p>Depending on the width of the containing block, this may be rendered
    as:

   <pre>
  Bla great bla bla world bla bla
  empire bla bla color bla bla
  history bla bla forever.   John
  Johnson
</pre>

   <p>However, this rendering is preferable:

   <pre>
  Bla great bla bla world bla bla
  empire bla bla color bla bla
  history bla bla forever.
                     John Johnson
</pre>

   <p>To indicate that <q>John Johnson</q> should be kept on one line, this
    rule can be added to the style sheet:

   <pre>
cite { text-wrap: suppress }
</pre>

   <p>Until &lsquo;<code class=property>text-wrap</code>&rsquo; is widely
    supported, this rule can also be used:

   <pre>
cite { white-space: nowrap }
</pre>

   <p>If the containing element is wider, this may be the resultant
    presentation:

   <pre>
  Bla great bla bla world bla bla empire
  bla bla color bla bla history bla bla
  forever.                  John Johnson
</pre>
  </div>

  <h2 id=cross-references><span class=secno>5. </span>Cross-references</h2>

  <p>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.

  <h3 id=the-target-counter><span class=secno>5.1 </span>The &lsquo;<code
   class=css>target-counter</code>&rsquo; and &lsquo;<code
   class=css>target-counters</code>&rsquo; values</h3>

  <p>Numerical cross-references are generated by &lsquo;<code
   class=css>target-counter()</code>&rsquo; and &lsquo;<code
   class=css>target-counters()</code>&rsquo; values that fetch the value of a
   counter at the target end of the link. These functions are similar to the
   &lsquo;<code class=css>counter()</code>&rsquo; and &lsquo;<code
   class=css>counters()</code>&rsquo; functions, except that they fetch
   counter values from remote elements. &lsquo;<code
   class=css>target-counter()</code>&rsquo; has two required arguments: the
   url of the link, and the name of a counter. &lsquo;<code
   class=css>target-counters()</code>&rsquo; 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; &lsquo;<code
   class=css>decimal</code>&rsquo; being the default.

  <div class=example>
   <p>This style sheet specifies that a string like " (see page 72)" is added
    after a link:

   <pre>
a::after { content: "(see page " target-counter(attr(href, url), page, decimal) ")" }
</pre>
  </div>

  <div class=example>
   <p>This style sheet specifies that a string like " (see section 1.3.5)" is
    added after a link:

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

  <h3 id=the-target-text><span class=secno>5.2 </span>The &lsquo;<code
   class=css>target-text</code>&rsquo; value</h3>

  <p>Textual cross-references are generated by &lsquo;<code
   class=css>target-text()</code>&rsquo; which fetches the textual content
   from the target end of the link. Only text is copied; not style,
   structure, or replaced content. &lsquo;<code
   class=css>target-text()</code>&rsquo; has one required argument: the url
   of the link. An optional second argument specifies exactly which content
   is fetched. There are four possible values:

  <dl>
   <dt>&lsquo;<code class=css>content()</code>&rsquo;

   <dd>refers to 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.

   <dt>&lsquo;<code class=css>content(before)</code>&rsquo;

   <dd>refers to the content of the element's ::before pseudo-element. This
    is the default value.

   <dt>&lsquo;<code class=css>content(after)</code>&rsquo;