csswg-drafts/css3-page/Overview.src.html at c9d23fa61615b7ae082cfb29e1f9d3b28f2dd921 · w3c/csswg-drafts · GitHub

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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html lang="en">
<head>
<title>
CSS Paged Media Module Level 3
</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<link href="../default.css" rel="stylesheet" type="text/css">
<link rel="stylesheet" type="text/css" href="http://www.w3.org/StyleSheets/TR/W3C-ED.css">
<style type="text/css">
  .keyword { font-weight:bold }
  .equation { padding: 2% }
  table.equation {text-align:center}
  td, th { vertical-align: top }
  pre { font-size: 1em; }

  #margin-values { border-collapse: collapse; }
  #margin-values td,
  #margin-values th
  {
                padding: 0.2em;
                border: thin solid black;
  }

  .property-list
  {
                border: 1px solid black;
                padding: .2em;
                margin-top: 2em;
  }

  .property-list td
  {
                border: 1px solid black;
                padding: .1em;
  }

  .editorial
  {
                display: block;
                font-family: arial, helvetica, sans-serif;
      font-size: 80%;
      margin-left: .5in;
      margin-right: 1in ;
      padding: 0.125in;
      background: #FFFFDD ;
  }

  .editorial:after { content: "Ed."}
  .RFC2119
  {
                text-transform: lowercase;
                font-style: italic
  }

  em em.RFC2119
  {
                text-transform: lowercase;
                font-style: normal
  }

  table.page-sizes
  {
                border: thin solid;
                margin-top: 1.5em;
  }
  table.page-sizes td
  {
                border: thin solid;
                padding: .5em;
  }
  table.page-sizes th
  {
                border: thin solid;
                padding: .5em;
                background: #ffffaa;
  }

</style>
</head>
<body>
<div>
<div class="head">
<!--logo-->
<h1>CSS Paged Media Module Level 3</h1>
<h2 class="no-num no-toc" id="w3c-working">[LONGSTATUS] [DATE]</h2>
<dl>
  <dt>This version:</dt>    <dd><a href="http://dev.w3.org/csswg/css3-page/">http://dev.w3.org/csswg/css3-page/</a></dd>
    <!-- <dd><a href="[VERSION]">http://www.w3.org/TR/[YEAR]/WD-[SHORTNAME]-[CDATE]</a></dd> -->
  <dt>Latest version:</dt>    <dd><a href="http://www.w3.org/TR/css3-page">http://www.w3.org/TR/css3-page</a></dd>
  <dt>Previous version:</dt>    <dd><a href="http://www.w3.org/TR/2004/CR-css3-page-20040225/">http://www.w3.org/TR/2004/CR-css3-page-20040225/</a></dd>
  <dt>Editors:</dt>    <dd>Melinda Grant, Hewlett-Packard</dd>
    <dd>H&aring;kon Wium Lie, Opera Software</dd>
    <dd>Elika J. Etemad, Hewlett-Packard</dd>
</dl>

<!--copyright-->

</div>
<hr title="Separator for header">

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

<p>This module describes the page model that partitions a flow into pages. It
builds on the <a href="/TR/CSS21/box.html">Box model module</a> and introduces
and defines the page model and paged media. It adds functionality for
pagination, page margins, page size and orientation, headers and footers,
widows and orphans, and image orientation. Finally it extends generated content
to enable page numbering and running headers / footers.</p>

<!-- "Status of this document" -->

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

<!--status-->

<p>This document contains the <abbr title="Cascading Style Sheets">CSS3</abbr>
Paged Media Module W3C Last Call <a href="/2005/10/Process-20051014/tr.html#RecsWD">Working Draft</a> of [DATE]. The
Last Call period ends on <span class="fudge">TBD</span>.</p>

<p>Relative to the previous Last Call Working Draft, this version incorporates
changes to the formerly named 'fit' and 'fit-position' properties; they are
renamed to 'image-fit' and 'image-position' and redefined to enable additional
use cases. The margin-box sizing algorithm has been reworded to be a bit
simpler, and many miscellaneous clarifications and editorial improvements have
been incorporated.</p>

<p>The 'image-fit' and 'image-position' properties are explicitly identified as at
risk, and may be removed in the next version of the specification.</p>

<p>Expected next revision to this document is another LCWD, driven by the change
in definition of 'image-fit' and 'image-position'.</p>

<p>The <a href="lc2_issues.htm">Disposition of Comments</a>
document contains the current issues list and responses to input received
during this Last Call period.</p>

<h2 class="no-num no-toc" id="contents">Table of Contents</h2><!--begin-toc-->
<!--end-toc-->
<!-- "Introduction" -->
<h2 id="intro">Introduction</h2>

<p>Paged media (e.g., paper, transparencies, photo album pages, pages
displayed on computer screens as printed output simulations) differ from
<a href="/TR/CSS2/media.html#continuous-media-group">continuous media</a>
in that the content of the document is split into one or more discrete
static display surfaces. To handle pages, CSS3 Paged Media describes how:</p>

<ul>
  <li><a href="#page-breaks">page breaks</a> are created and avoided;</li>
  <li>the page properties such as size, orientation, margins, border, and
  padding are specified;</li>
  <li>headers and footers are established within the page margins;</li>
  <li>content such as page counters are placed in the headers and footers; and</li>
  <li>orphans and widows can be controlled.</li>
</ul>

<p>This module defines a <a href="#page-model">page model</a> that specifies how a
document is formatted within a rectangular area, called the <a href="#page-box-page-rule">page box</a>, that has finite width and height. Often,
but not always, the page box has a one-to-one correspondence to the physical
surface onto which the document is ultimately rendered. The CSS3 page model
specifies formatting within the page box, but it is the user agent's
responsibility to transfer the page box to the sheet. Some user agent transfer
possibilities that are not addressed by CSS3 include:</p>
<ul id="complex-usecases">
  <li>Transferring one page box to one sheet (e.g. single-sided printing);</li>
  <li>Transferring two page boxes to the front and back surfaces of the same
  sheet (e.g. double-sided printing);</li>
  <li>Transferring N (small) page boxes to one sheet (called "N-up");</li>
  <li>Transferring one (large) page box to N x M sheets (called "tiling");</li>
  <li>Creating signatures. A <dfn>signature</dfn> is a group of pages printed on
  a sheet, which, when folded and trimmed like a book, appear in their proper
  sequence;</li>
  <li>Printing one document to multiple output trays;</li>
  <li>Generating files containing print instructions.</li>
</ul>

<p>Although CSS3 does not specify how user agents transfer page boxes to sheets,
it does include certain mechanisms for telling user agents about the intended
page sheet <a href="#page-size">size and orientation</a>. In the general case,
CSS3 assumes that one page box will be transferred to one surface of similar
size.</p>


<h2 id="conformance">Conformance</h2>

<p>The keywords "<em class="RFC2119">MUST</em>", "<em class="RFC2119">SHALL</em>",
"<em class="RFC2119">MUST NOT</em>", "<em class="RFC2119">SHALL NOT</em>",
"<em class="RFC2119">REQUIRED</em>", "<em class="RFC2119">SHOULD</em>",
"<em class="RFC2119">SHOULD NOT</em>", "<em class="RFC2119">RECOMMENDED</em>",
"<em class="RFC2119">MAY</em>", and "<em class="RFC2119">OPTIONAL</em>" when
used in this document are to be interpreted as described in <cite>RFC
2119</cite> [[!RFC2119]]. However, for readability, these words do not appear
in all uppercase letters in this specification. All of the text in this
specification is normative except sections explicitly marked as non-normative,
examples, and notes.</p>

<p>Examples in this specification are introduced with the words "for example"
  or are set apart from the normative text with <code>class="example"</code>,
  like this:

<div class="example">
  <p>This is an example of an informative example.</p>
</div>

<p>Informative notes begin with the word "Note" and are set apart from the
  normative text with <code>class="note"</code>, like this:

<p class="note">Note, this is an informative note.</p>

<h2 id="page-box-page-rule">The Page Model</h2>

<p>In the page model, the document is transferred into one or more page boxes. The
<dfn id="page-box">page box</dfn> is a specialized CSS box that maps to
a rectangular print media surface, such as a page of paper. It is roughly
analogous to the viewport. <img src="PageBox.png" style="float: right;" alt=""
height="266" width="267"> As with other <a href="/TR/CSS21/box.html">boxes</a>,
a page box consists of margin, border, padding, and content areas. The containing
block of the page box is the rectangle that coincides with its margin edges.
The content and margin areas of a page box have special functions:</p>

<ul>
  <li>The content area of a page box is called the <dfn id="page-area">page
  area</dfn>. The content of the document is flowed into one or more page boxes.
  The page area acts as a container for all the boxes generated by the root
  element and its descendants that are laid out within a given page box. The
  edges of the page area on the first page establish the rectangle that is the
  initial <a href="/TR/CSS21/visudet.html#containing-block-details">containing block</a>
  of the document.</li>
  <li>The margin area of a page box is divided into 16 <dfn>margin boxes</dfn>.
  Each margin box has its own margin, border, padding and content areas. Margin
  boxes are typically used to display running h
133E
eaders and footers.</li>
</ul>

<p>The properties of a <dfn>page box</dfn> are determined by properties <a href="/TR/CSS21/syndata.html#declaration">declared</a> within the <dfn><a href="#page-context">page context</a></dfn>, which is the <a href="/TR/CSS21/syndata.html#x14">declaration block</a> of the <code>@page</code>
rule. Page boxes differ from other boxes in that the <span class="property">'width'</span> and <span class="property">'height'</span> properties
do not apply to a page box. The size of the page box is specified using the
<span class="property">'size'</span> property in the page context.</p>

<p>Declarations in the page context affect the page box and / or can inherit
to the margin boxes, but they do not apply to or inherit into the
document's content.</p>

<h3 id="page-terms">Page Terminology</h3>

<p>The following terminology and accompanying diagrams help to describe the
page model:</p>

<dl>
  <dt id="page-sheet">Page sheet</dt>
  <dd><img src="PageSheet.png" style="float: right;" alt="The corner of a page sheet with the non-printable area at the edge and printable area inside it"
  height="148" width="194">The page sheet is one surface of the physical
  medium. The illustration to the right shows a representation of the upper-left
  corner of a page sheet.</dd>

  <dt id="printable-area">Printable and non-printable areas</dt>
  <dd>The non-printable area is the area of a page sheet that a physical device such
  as a printer is not capable of marking reliably, usually due to the printer's
  paper handling mechanism. This value is printer dependent and is usually a
  small region along each edge of the page sheet. The printable area is the area
  of page sheet that a printer <em>is</em> capable of marking reliably. The size
  of the printable area is the size of the page sheet reduced by the size of the
  non-printable area. A user agent may not know the dimensions of this area for a
  particular printing device; but when its dimensions are known, user agents
  <em class="RFC2119">MAY</em> adjust the formatting of the document so that
  content falls within the printable area. How this adjustment is accomplished is
  device dependent within the constraints expressed in the sections <a href="#renderingpages">Rendering page boxes that do not fit a page sheet</a> and
  <a href="#content-outside-box">Content outside the page box</a>.</dd>

  <dt id="content-empty">Content-empty page</dt>
  <dd>a page box whose page area contains no printable content other than
  backgrounds and/or borders. A page box whose page area contains generated
  content, or content whose visibility is 'hidden', or invisible content such as
  a zero-width space is not a content-empty page. On the other hand, a page
  containing only a background and/or borders and/or margin-box content
  <em>is</em> a content-empty page.</dd>

  <dt id="page-orientation">Page Orientation</dt>
  <dd>The page orientation is defined by comparing the length of the edges of a
  <a href="#page-box">page box</a>. The page box is a rectangle with two
  perpendicular edges called the long edge and the short edge. The length of the
  long edge is always greater than or equal to the length of the short edge. When
  the page box is square, the two edges are of the same length and either can be
  used as the long edge with the other being the short edge. This specification
  defines page orientations of 'portrait' and 'landscape'.</dd>

  <dt id="portrait">Portrait Orientation</dt>
  <dd>A portrait page's height is greater than or equal to its width. Horizontal
  elements are parallel to the short edge and vertical elements to the long edge.</dd>

  <dt id="landscape">Landscape Orientation</dt>
  <dd>A landscape page's width is greater than or equal to its height. Horizontal
  elements are parallel to the long edge and vertical elements to the short edge.</dd>

  <dt id="duplex-printing">Duplex Printing</dt>
  <dd>Duplex printing prints one page box per side of a page sheet and uses both
  sides of the page sheet. This module provides no ability to specify whether a
  document is duplex printed, but the concept of left and right pages is based on
  the assumption that the document is duplex printed, regardless of whether or
  not it actually is.</dd>

  <dt id="binding-edge">Binding Edge</dt>
  <dd>The binding edge is the edge of the page box that is toward the binding if the
  material is bound. The binding edge often has a larger margin than the opposite
  edge to provide for the space used by the binding. The binding edge can be any
  of the four edges. However, page sheets are customarily bound so that the
  binding edge of page boxes with portrait orientation is vertical. This module
  provides no method to specify the binding edge. In duplex printing, the binding
  edge is on opposite sides of the page box for the left and right pages.</dd>

  <dt id="facing-pages">Facing Pages</dt>
  <dd>Facing pages are two sequential pages such that when the document is duplex
  printed they are on separate sheets of paper. Typically, the earlier page will
  be the back side of one sheet and the later page will be the front side of
  another. They are usually laid out so that the binding edges of facing pages
  are vertical and adjacent when the pages are placed in their normal reading
  orientation.</dd>

  <dt id="left-page">Left Page</dt>
  <dd>A page that would be on the left if it is part of a pair of facing pages as
  typically laid out. Page layouts for documents using a left-to-right page
  progression have the earlier of the facing pages on the left. Rules specific to
  the left page can be specified using the <span class="css">':left'</span> page
  selector.</dd>

  <dt id="right-page">Right Page</dt>
  <dd>A page that would be on the right if it is part of a pair of facing pages as
  typically laid out. Page layouts for documents using a right-to-left page
  progression have the earlier of the facing pages on the right. Rules specific
  to the right page can be specified using the <span class="css">':right'</span>
  page selector.</dd>
</dl>

<h3 id="progression-pagination">Page Progression and Pagination</h3>

<p>CSS distinguishes between left pages and right pages on all documents,
whether they are printed duplex or not. Each left page is followed by a
right page and vice versa. Left and right pages can be styled differently
with the <a href="#left-right-first"><code>:left</code> and <code>:right</code>
pseudo-classes</a>.

<p>Whether the first page of a document is a left page or a right page
depends on the page progression of the document. The <dfn>page progression</dfn>
is the direction in which the printed pages of a document would be sequenced
when laid out side-to-side; <i>e.g.</i>, English typically progresses from
left to right. In documents with with a left-to-right page progression the
first page of the document is a right page, and vice versa.</p>

<p>The page progression direction is determined as follows:</p>

<ul>
  <li>If text is laid out in horizontal lines, the page progression is the
  same as the inline progression.</li>
  <li>If text is laid out in vertical lines, the page progression is the
  same as the block progression.</li>
</ul>

<p>If the UA supports the 'direction' and 'block-progression' properties
from the CSS 3 Text Layout Module [[CSS3TEXTLAYOUT]], it must determine
whether the first page is a left or right page from the values of those
properties on the root element.</p>

<p>To explicitly force a document to begin printing on a left or right page,
authors can <a href="#page-break-before">insert a page break before</a> the
first generated box. The UA must suppress the first (empty) page(s) in this
case (and the <code>:first</code> selector applies to the first printed
page).</p>

<h3 id="page-size">Page size</h3>

<p>People around the world use many different paper sizes. It is a goal of this
specification that web content should be adaptable to a range of different
sizes without having to write a specific style sheet for each paper size.</p>

<p>However, in some situations it is important that a certain page size achieves a
certain style. One way to achieve this goal is to utilize the 'size' property,
which indicates that the document should preferentially be displayed on a
surface of a certain size; another method is to use Media Queries [[MEDIAQ]]
which allow different style sheets to be applied to different page sizes.</p>

<h4 id="page-size-prop">Page size: the 'size' property</h4>
<table class="propdef" summary="definition of the size property">
  <tr>
    <th>Name:
    <td><dfn id="size">size</dfn>
  <tr>
    <th>Value:
    <td>[ &lt;length&gt;{1,2} | auto | &lt;page-size&gt; ] || [ portrait | landscape]
  <tr>
    <th>Initial:
    <td>auto
  <tr>
    <td><em>Applies to:</em>
    <td>page context
  <tr>
    <th>Inherited:
    <td>N/A
  <tr>
    <th>Percentages:
    <td>N/A
  <tr>
    <th>Media:
    <td>paged
  <tr>
    <td><em>Computed value:</em>
    <td>specified value
</table>

<p>This property specifies the size and orientation of the
<a href="#page-box">page box</a>. In the general case, where one
page box is rendered onto one <a href="#page-sheet">page sheet</a>, the
<span class="property">'size'</span> property also indicates the size of the
destination page sheet.</p>

<p>The size of a page box can either be "absolute" (fixed size) or "relative"
(scalable, i.e., fitting available sheet sizes).</p>

<p>The first three values in the table below can be used to create relative page
boxes.</p>

<p>Other values define a fixed-size page box, and thereby indicate the preferred
output media size. When possible, output should be rendered on the media size
indicated. If the specified size is not available, the smallest available
larger size should be used; if not available, the contents of the page box
should be scaled down to fit the largest smaller page sheet available.</p>

<p>If a <code>size</code> property declaration specifies a page size that would
cause that declaration to not apply (e.g. a media query that qualifies it applies
only to a different paper size) then the declaration must be
<a href="http://www.w3.org/TR/CSS21/conform.html#ignore">ignored</a>.
<span class="issue">Is this a reasonable way of dealing with this conflict?</span></p>

<div class="example">
  <p>In the following example
  <pre>
  @page {
    size: 4in 6in;
  }

  @media (max-width: 6in) {
    @page {
      size: letter;
    }
  }
  </pre>
  <p>The second <code>size</code> declaration is ignored, i.e. the specified value
  of the <code>size</code> property is <code>4in 6in</code>.
</div>

<table class="page-sizes">
<tr>
<th>Value</th>
<th>Description</th>
</tr>
<tr>
<td>auto</td>
<td>The page box will be set to a size and orientation chosen by the UA. In the
usual case, the page box size and orientation is chosen to match the target
media sheet.</td>
</tr>
<tr>
<td>landscape</td>
<td>Specifies that the page's content be printed in landscape orientation. The
longer sides of the page box are horizontal. If a <span class="css">'&lt;page-size&gt;'</span> is not specified, the size of the page sheet
is chosen by the UA.</td>
</tr>
<tr>
<td>portrait</td>
<td>Specifies that the page's content be printed in portrait orientation. The
shorter sides of the page box are horizontal. If a <span class="css">'&lt;page-size&gt;'</span> is not specified, the size of the page sheet
is chosen by the UA.</td>
</tr>
<tr>
<td>&lt;length&gt;</td>
<td>The page box will be set to the given absolute dimension(s). If only one length
value is specified, it sets both the width and height of the page box (i.e.,
the box is a square). If two length values are specified, the first establishes
the page box width, and the second the page box height. 
133E
Values in units of
<span class="css">'em'</span> and <span class="css">'ex'</span> refer to the
page context's font.</td>
</tr>
<tr>
<td>&lt;page-size&gt;</td>
<td>A page size can be specified using one of the following media names. This is
the equivalent of specifying the <span class="css">'&lt;page-size&gt;'</span>
using length values. The definition of the the media names comes from
<cite>Media Standardized Names</cite> [[!PWGMSN]].

<dl>

<dt>A5</dt>
<dd>Equivalent to the size of ISO A5 media: 148mm wide and 210 mm high.</dd>

<dt>A4</dt>
<dd>Equivalent to the size of IS0 A4 media: 210 mm wide and 297 mm high.</dd>

<dt>A3</dt>
<dd>Equivalent to the size of ISO A3 media: 297mm wide and 420mm high.</dd>

<dt>B5</dt>
<dd>Equivalent to the size of ISO B5 media: 176mm wide by 250mm high.</dd>

<dt>B4</dt>
<dd>Equivalent to the size of ISO B4 media: 250mm wide by 353mm high.</dd>

<dt>letter</dt>
<dd>Equivalent to the size of North American letter media: 8.5 inches wide and 11
inches high</dd>

<dt>legal</dt>
<dd>Equivalent to the size of North American legal: 8.5 inches wide by 14 inches
high.</dd>

<dt>ledger</dt>
<dd>Equivalent to the size of North American ledger: 11 inches wide by 17 inches
high.</dd>
</dl></td>
</tr>
</table>

<p>The '&lt;page-size&gt;' names can be used in conjunction with 'landscape' or
'portrait' to indicate both size and orientation.</p>

<h4>Some examples:</h4>

<div class="example">
<pre>
@page {
size: A4 landscape;
}
</pre>

<p>The above example sets the width of the page box to be 297mm and the height to
be 210mm. The page box in this example should be rendered on a page sheet size
of 210 mm by 297 mm.</p>
</div>

<div class="example">

<p>In the following example, the outer edges of the page box will align with the
page. The percentage value on the <span class="property">'margin'</span>
property is relative to the page size so if the page sheet dimensions are 210mm
x 297mm (i.e., A4), the margins are 21mm and 29.7mm. Assuming there are no page
borders or padding set in the UA default style sheet, the resulting page area
is 189mm by 367.3mm (210mm-21mm by 297mm-29.7mm).</p>
<pre>
@page {
size: auto;/* auto is the initial value */
margin: 10%;
}
</pre>
</div>

<div class="example">
<pre>
@page {
size: 8.5in 11in;/* width height */
}
</pre>

<p>The above example sets the width of the page box to be 8.5 inches and the
height to be 11 inches. This indicates that the page sheet size should be
8.5"x11" and the orientation 'portrait'.</p>
</div>

<h4 id="page-size-media-query">Media Queries</h4>

<p>This section is informative.</p>

<p>By using Media Queries [[MEDIAQ]], one style sheet can express different
stylistic preferences for different page sizes. Consider this example:</p>

<div class="example" style="font-size: 10pt;">
<pre>
 /* style sheet for "A4" printing */
 @media print and (width: 21cm) and (height: 29.7cm) {
    @page {
       margin: 3cm;
    }
 }

 /* style sheet for "letter" printing */
 @media print and (width: 8.5in) and (height: 11in) {
    @page {
        margin: 1in;
    }
 }
</pre>
</div>

<p>In the example above, "A4" sheets are given a "3cm" page margin, and "letter"
sheets are given a "1in" page margin.</p>

<h4 id="renderingpages">Rendering page boxes that do not fit a page sheet</h4>

<p>If a page box does not match the target page sheet dimensions, the user agent
<em class="RFC2119">MAY</em> choose (in order of preference) to:</p>

<ol>
  <li>Render the page box at the indicated size on a larger page sheet.</li>
  <li>Rotate the page box 90° if this will make the page box fit the page sheet.</li>
  <li>Scale the page box to fit the page sheet. (The aspect ratio of the page box
  <em class="RFC2119">should</em> be preserved.)</li>
  <li>Reformat the page contents, including 'spilling' onto other page sheets.</li>
  <li>Clip overflowed content (least preferred).</li>
</ol>

<p>The user agent <em class="RFC2119">MAY</em> wish to consult the user before
performing these operations.</p>

<h4 id="positioning-page-box">Positioning the page box on the sheet</h4>

<p>When the page box is smaller than the page size, the user agent <em class="RFC2119">SHOULD</em> either:</p>

<ul>
  <li>center the page box on the sheet since this will align double-sided pages
  and avoid accidental loss of information that is printed near the edge of the
  sheet; or</li>
  <li>position the page box in the upper left corner of the page sheet, as this
  may minimize media consumption.</li>
</ul>

<p>The user agent <em class="RFC2119">MAY</em> wish to consult the user in this
regard.</p><!-- "Page selector and page context" -->

<h3 id="page-selector-and-context">Page Selectors and the Page Context</h3>

<p>Authors can specify various aspects of a page box such as the dimensions,
orientation, and margins within an <span class="css">@page</span> rule. An
<span class="css">@page</span> rule consists of the keyword <span class="css">'@page'</span>, an <em class="RFC2119">OPTIONAL</em> page name followed
with no intervening space by an <em class="RFC2119">OPTIONAL</em> page
pseudo-class and a block of declarations (said to be in the <dfn id="page-context">page context</dfn>).</p>

<p>The <em class="RFC2119">OPTIONAL</em> page name and <em class="RFC2119">OPTIONAL</em> page pseudo-class constitute the <dfn id="page-selector">page selector</dfn>. The page selector specifies for which
pages the declarations apply. In CSS3, page selectors <em class="RFC2119">MAY</em> designate the first page of a document, all left pages, all
right pages, or pages with specific names.</p>

<p>Properties declared within the page context apply to the page box.</p>

<p>If an error is encountered during the processing of a declaration block within
a page or a margin context, the <a href="/TR/CSS21/syndata.html#parsing-errors">Rules for handling parsing errors</a>
apply; that is, valid declarations within the block are applied.</p>

<h4 id="syntax-page-selector">Page selector grammar</h4>

<p>The syntax for a page selector is a specialization of the generic at-rule
defined by CSS 2.1. This grammar extends the at-rule syntax to allow nested
at-rules for @media and @page. User agents <em class="RFC2119">MUST</em> adhere
to the following grammar:</p>

<p>See [[!CSS21]], Section 4.1.1 and Appendix G for the expansion of missing
productions:</p>
<p id="specializatons-of-ATKEYWORD">
All new lexical tokens are specializations of the ATKEYWORD lexical token:</p>
<pre class="lexical">
PAGE_SYM              ::= "@page"
TOPLEFTCORNER_SYM     ::= "@top-left-corner"
TOPLEFT_SYM           ::= "@top-left"
TOPCENTER_SYM         ::= "@top-center"
TOPRIGHT_SYM          ::= "@top-right"
TOPRIGHTCORNER_SYM    ::= "@top-right-corner"
BOTTOMLEFTCORNER_SYM  ::= "@bottom-left-corner"
BOTTOMLEFT_SYM        ::= "@bottom-left"
BOTTOMCENTER_SYM      ::= "@bottom-center"
BOTTOMRIGHT_SYM       ::= "@bottom-right"
BOTTOMRIGHTCORNER_SYM ::= "@bottom-right-corner"
LEFTTOP_SYM           ::= "@left-top"
LEFTMIDDLE_SYM        ::= "@left-middle"
LEFTBOTTOM_SYM        ::= "@left-bottom"
RIGHTTOP_SYM          ::= "@right-top"
RIGHTMIDDLE_SYM       ::= "@right-middle"
RIGHTBOTTOM_SYM       ::= "@right-bottom"

<span id="syntax-prod-media">media</span> :
     MEDIA_SYM S* medium [ COMMA S* medium ]* LBRACE S* [ page | ruleset ]* '}' S*
     ;

<span id="syntax-prod-page">page</span> :
     PAGE_SYM S* IDENT? S* pseudo_page? S*
     '{' S* [ margin_box | ruleset ]? [ ';' S* [ margin_box | ruleset ]? ]* '}' S*
     ;

<span id="syntax-prod-pseudo-page">pseudo_page</span> :
     ':' [ "left" | "right" | "first" ]
     ;

<span id="syntax-prod-margin">margin_box</span> :
     margin_sym S* '{' ruleset* '}' S*
     ;

<span id="syntax-prod-margin-sym">margin_sym</span> :
     TOPLEFTCORNER_SYM |
     TOPLEFT_SYM |
     TOPCENTER_SYM |
     TOPRIGHT_SYM |
     TOPRIGHTCORNER_SYM |
     BOTTOMLEFTCORNER_SYM |
     BOTTOMLEFT_SYM |
     BOTTOMCENTER_SYM |
     BOTTOMRIGHT_SYM |
     BOTTOMRIGHTCORNER_SYM |
     LEFTTOP_SYM |
     LEFTMIDDLE_SYM |
     LEFTBOTTOM_SYM |
     RIGHTTOP_SYM |
     RIGHTMIDDLE_SYM |
     RIGHTBOTTOM_SYM
     ;
</pre>
<p id="page-selector-syntax-restrict">
The following restrictions and relaxations are made to the syntax above:</p>

<ul>
  <li>The value 'auto' <em class="RFC2119">must not</em> be used as a page name
  and <em class="RFC2119">MUST</em> be treated as a syntax error.</li>
</ul>

<div class="example">

<p>The following are examples of page selectors (declaration block intentionally
left blank)</p>
<pre>
@page { ... }
@page :left { ... }
@page :right { ... }
@page LandscapeTable { ... }
@page CompanyLetterHead:first { ... } /*  identifier and pseudo page. */
@page:first { ... };
</pre>

<p>The following are examples of margin boxes where the declaration blocks are
intentionally left blank.</p>
<pre>
@page {
 @top-left { ... /* document name */ }
 @bottom-center { ... /* page number */}
}
@page :left { @left-middle { ... /* page number in left margin */ }}
@page :right{ @right-middle { ... /* page number in right margins of right pages */}}

@page :left { @bottom-left-corner { ... /* left page numbers */ }}
@page :right { @bottom-right-corner { ... /* right page numbers */ }}
@page :first { @bottom-left-corner { ... /* empty footer on 1st page */ }
             @bottom-right-corner { ... /* empty footer */ } }
</pre>
</div>

<h4 id="cascading-and-page-context">Cascading in the page context</h4>

<p>Declarations in page and margin contexts <a href="/TR/CSS21/cascade.html">cascade</a> just like declarations in <a href="/TR/CSS21/syndata.html#rule-sets">rule sets</a>.</p>

<p>The specificity of @page rules is computed in a manner analogous to the
computations defined in the <a href="/TR/CSS21/selector.html">Selectors</a>
module:</p>

6D50
<ul>
  <li>if the @page rule has a named page, f=1; else f=0</li>
  <li>if the @page rule has a ':first' pseudo-class, g=1; else g=0</li>
  <li>if the @page rule has a ':left' or ':right' pseudo-class, h=1; else h=0</li>
</ul>

<p>Concatenating the three numbers f-g-h gives the specificity.</p>

<p>Properties that are not explicitly set within the page or margin context take
their initial values and do not inherit from any element.</p>

<div class="example">

<p>Some page specificity calculation examples follow:</p>
<pre>
      @page { } /* f=0 g=0 h=0 -&gt; specificity = 000 */
      @page :left { } /* f=0 g=0 h=1 -&gt; specificity = 001 */
      @page :first { } /* f=0 g=1 h=0 -&gt; specificity = 010 */
      @page artsy { } /* f=1 g=0 h=0 -&gt; specificity = 100 */
      @page artsy:left { } /* f=1 g=0 h=1 -&gt; specificity = 101 */
      @page artsy:first { } /* f=1 g=1 h=0 -&gt; specificity = 110 */
</pre>
</div>

<div class="example">

<p>Consider the following usage example:</p>
<pre>
@page {
margin-left: 3cm;
}

@page :left {
margin-left: 4cm;
}
</pre>

<p>Due to the higher specificity of the pseudo-class selector, the left margin on
left pages will be 4cm and all other pages
(the right-facing pages) will have a left margin of 3cm.</p>
</div>

<div class="example">

<p>In this example, the higher specificity of the green rules wins over the red
rule. Therefore the first page will have blue text in the top-left margin box
and green text in the top-right margin box, while subsequent pages will have
red text in the margin boxes.</p>
<pre>
@page :first {
color: green;

@top-left {
  content: "foo";
  color: blue;
}
@top-right {
  content: "bar";
}
}

@page { color: red;
@top-center {
  content: "Page " counter(page);
  }
}
</pre>
</div>

<div class="example">

<p>Page contexts cascade, so the following stylesheet would style pages with 25
millimeter margins and 14 point type in the margin boxes:</p>
<pre>
@page { margin: 25mm;}
@page { font-size: 14pt;}
</pre>
</div>

<h3 id="page-properties">Page Properties</h3>
<div>

<p>The following properties can be used in the <a href="#page-context">page
context</a> to style the appearance of the page box and margin boxes:</p>

<ul>
  <li><a href="/TR/CSS21/colors.html#background-properties">background properties</a></li>
  <li><a href="/TR/CSS21/box.html#border-properties">border properties</a></li>
  <li><a href="/TR/CSS21/colors.html#propdef-color">color</a></li>
  <li><a href="/TR/CSS21/generate.html#counters">counter-reset, counter-increment</a></li>
  <li><a href="/TR/CSS21/fonts.html">font properties</a></li>
  <li><a href="/TR/CSS21/visudet.html#line-height">line-height</a></li>
  <li><a href="/TR/CSS21/box.html#margin-properties">margin properties</a></li>
  <li><a href="/TR/CSS21/box.html#padding-properties">padding properties</a></li>
  <li><a href="#page-size">size</a></li>
  <li><a href="/TR/CSS21/text.html">text properties</a></li>
  <li><a href="/TR/CSS21/visufx.html#visibility">visibility</a></li>
</ul>

<p>That is, the margin boxes inherit values for inheritable properties from the
page context.</p>

<p>The following properties can be used in the <a href="#margin-at-rule">margin
context</a> to style margin boxes and their content:</p>

<ul>
  <li><a href="/TR/CSS21/colors.html#background-properties">background properties</a>,</li>
  <li><a href="/TR/CSS21/box.html#border-properties">border properties</a>,</li>
  <li><a href="/TR/CSS21/colors.html#propdef-color">color</a>,</li>
  <li><a href="/TR/CSS21/generate.html#content">content</a>,</li>
  <li><a href="/TR/CSS21/fonts.html">font properties</a>,</li>
  <li><a href="/TR/CSS21/visudet.html#the-height-property">height</a>,</li>
  <li><a href="/TR/CSS21/visudet.html#line-height">line-height</a></li>
  <li><a href="/TR/CSS21/box.html#margin-properties">margin properties</a>,</li>
  <li><a href="/TR/CSS21/box.html#padding-properties">padding properties</a>,</li>
  <li><a href="/TR/CSS21/text.html">text properties</a>,</li>
  <li><a href="/TR/CSS21/visufx.html#visibility">visibility</a>,</li>
  <li><a href="/TR/CSS21/visudet.html#the-width-property">width</a></li>
</ul>

<p>A detailed list of properties that <em class="RFC2119">MUST</em> be supported
within page and margin contexts by a conforming implementation can be found in
<a href="#Appendix_A">Appendix A</a>.</p>

<p>Other properties defined by [[!CSS21]] are ignored in these contexts. Behavior
for properties not included in CSS 2.1 and not listed here or in Appendix A is
undefined.</p>
<p class="note">
Note: The intent of leaving other properties undefined is to allow the gradual
addition of appropriate CSS3 properties as they emerge, without having to
update this specification with each addition.</p>

<p>The normal rules for box properties apply with the following exceptions:</p>

<ul>
  <li>Values in units of <span class="css">'em'</span> and <span class="css">'ex'</span> are interpreted relative to their context. The <a href="#page-context">page context</a> has a font associated with it by an explicit
  use of font properties, or from the UA's default style sheet, or from their
  initial values. (When the value is taken from the UA's default style sheet, the
  UA may choose to apply the value of the root element's 'font-family' property.)
  A margin context has a font association via explicit use of font properties
  within the margin context, or via inheritance from the page context.</li>
  <li>Percentage values on the margin and padding properties are relative to the
  dimensions of the containing block. For right and left values, percentages are
  relative to the width of the containing block; for top and bottom values,
  percentages are relative to the height of the containing block.</li>
  <li>The <span class="property">'width'</span> and <span class="property">'height'</span> properties do not apply to the page box.</li>
  <li>The page background covers the entire page box, including the page margins.
    Background images are positioned as for any other box; however if the
    'background-attachment' is 'fixed' then the image is placed relative to the
    page box instead.</li>
</ul>

<p>The page background and borders are painted first. Margin-boxes are painted
over (on top of) the page box. The root element then paints the canvas and the
document contents within the page padding box. <span class="issue">Check this:
should margin boxes be painted over the canvas background?</span></p>

<p>The exact painting order of margin boxes is not specified, however it is
<em class="RFC2119">recommended</em> that when margin boxes overlap, paint
order should place center/middle margin boxes on top of corner margin boxes,
which are in turn painted on top of other boxes. More precisely, in terms of
the algorithm in <a href="http://www.w3.org/TR/CSS21/zindex.html">CSS2.1
Appendix E</a> the exact "tree order" of margin boxes is not defined, but it
is recommended that center/middle boxes be after corner boxes, which should
themselves be after other boxes.</p>

<p>It is <em class="RFC2119">recommended</em> that user agents establish a default
page margin via the user agent stylesheet that includes any non-printable area.
It is further <em class="RFC2119">recommended</em> that authors assume that the
default page area will not include unprintable regions.</p>

<h3 id="left-right-first">Left, right, and first pages</h3>

<p>When printing double-sided documents, left and right pages are often formatted
differently. This can be expressed through CSS pseudo-classes defined in the
<a href="#page-context">page context</a>.</p>

<p>All pages are automatically classified by user agents into either the
<span class="css">':left'</span> or <span class="css">':right'</span>
pseudo-class. The following example creates left and right binding edges using
these pseudo-classes.</p>

<div class="example">
<pre>
@page :left {
margin-left: 3cm;
margin-right: 4cm;
}

@page :right {
margin-left: 4cm;
margin-right: 3cm;
}
</pre>
</div>

<p>If different declarations have been given for left and right pages, the user
agent <em class="RFC2119">MUST</em> honor these declarations even if the user
agent does not transfer the page boxes to left and right sheets (i.e., a
printer that only prints on one side of the medium must nevertheless produce
correctly formatted output).</p>

<p>Authors can also specify style for the first page of a document with the
<span class="css">':first'</span> pseudo-class. Such style rules are applied only
to the first printed page of a document.</p>

<div class="example">
<pre>
@page { margin: 2cm } /* All margins set to 2cm */

@page :first {
margin-top: 10cm /* Top margin on first page 10cm */
}
</pre>
</div>

<div class="example">
<pre>
html {page-break-before: always;}
</pre>

<p>For an XHTML document with a left-to-right page progression, the above style
rule will cause the first page of the document to print on a ':right' page</p>
</div>
<div class="note">

<p><em><strong>Note.</strong> Adding declarations to the <span class="css">':left'</span> or <span class="css">':right'</span> pseudo-class does not
necessarily influence whether the document comes out of the printer double- or
single-sided (which is outside the scope of this specification).</em></p>
</div>
<div class="note">

<p><em><strong>Note.</strong> Future versions of CSS may include other page
pseudo-classes.</em></p>
</div>

<h3 id="content-outside-box">Content outside the page box</h3>

<p>When formatting content in the page model, some content may end up outside the
page box. For example, an element whose <span class="property">'white-space'</span> property has the value <span class="css">'pre'</span> can generate a box that is wider than the page box. Also,
when boxes are positioned absolutely, they may end up in "inconvenient"
locations. For example, images may be placed on the edge of the page box.
Similarly, when boxes use fixed or relative positioning, they can end up
outside of the page box.</p>