csswg-drafts/css2/page.html at 8122ab18f7865675dc17d56b659786b4c03759bf · w3c/csswg-drafts · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html lang="en">

<HEAD>
<TITLE>Paged media</TITLE>
<link rel="stylesheet" href="style/default.css" type="text/css">
<link rel="stylesheet" href="http://www.w3.org/StyleSheets/TR/W3C-CR.css" type="text/css">
<link rel="prev" href="generate.html">
<link rel="next" href="colors.html">
<link rel="contents" href="cover.html#minitoc">
<link rel="CSS-properties" href="propidx.html" title="properties">
<link rel="index" href="indexlist.html" title="index">
<link rel="first" href="cover.html">
</HEAD>

<body>
<div class="navbar">
<p><a href="generate.html">previous</a> &nbsp;
<a href="colors.html">next</a> &nbsp;
<a href="cover.html#minitoc">contents</a> &nbsp;
<a href="propidx.html">properties</a> &nbsp;
<a href="indexlist.html">index</a> &nbsp;
</div>
<hr class="navbar">

<h1>13 <a name="the-page">Paged media</a></h1>
<div class="subtoc">
<p><strong>Contents</strong>
  <ul class="toc">
    <li class="tocline2"><a href="page.html#page-intro" class="tocxref">13.1 Introduction to paged media</a>
    <li class="tocline2"><a href="page.html#page-box" class="tocxref">13.2 Page boxes: the @page rule</a>
    <ul class="toc">
      <li class="tocline3"><a href="page.html#page-margins" class="tocxref">13.2.1 Page margins</a>
      <li class="tocline3"><a href="page.html#page-selectors" class="tocxref">13.2.2 Page selectors: selecting left, right, and first pages</a>
      <li class="tocline3"><a href="page.html#outside-page-box" class="tocxref">13.2.3 Content outside the page box</a>
    </ul>
    <li class="tocline2"><a href="page.html#page-breaks" class="tocxref">13.3 Page breaks</a>
    <ul class="toc">
      <li class="tocline3"><a href="page.html#page-break-props" class="tocxref">13.3.1 Page break properties: <span class="propinst-page-break-before">'page-break-before'</span>, <span class="propinst-page-break-after">'page-break-after'</span>, <span class="propinst-page-break-inside">'page-break-inside'</span></a>
      <li class="tocline3"><a href="page.html#break-inside" class="tocxref">13.3.2 Breaks inside elements: <span class="propinst-orphans">'orphans'</span>, <span class="propinst-widows">'widows'</span></a>
      <li class="tocline3"><a href="page.html#allowed-page-breaks" class="tocxref">13.3.3 Allowed page breaks</a>
      <li class="tocline3"><a href="page.html#forced" class="tocxref">13.3.4 Forced page breaks</a>
      <li class="tocline3"><a href="page.html#best-page-breaks" class="tocxref">13.3.5 "Best" page breaks</a>
    </ul>
    <li class="tocline2"><a href="page.html#page-cascade" class="tocxref">13.4 Cascading in the page context</a>
  </ul>
</div>

<h2>13.1 <a name="page-intro">Introduction to paged media</a></h2>

<p>Paged media (e.g., paper, transparencies, pages that are displayed
on computer screens, etc.) differ from <a
href="./media.html#continuous-media-group">continuous media</a> in
that the content of the document is split into one or more discrete
pages. To handle pages, CSS&nbsp;2.1 describes how page margins are set
on <a href="#page-box">page boxes</a>, and how <a href="#page-breaks">page breaks</a> are declared.

<p>The user agent is responsible for transferring the page boxes of a
document onto the real <a name="x0"><span class="index-def"
title="sheet"><dfn>sheets</dfn></span></a> where the document will
ultimately be rendered (paper, transparency, screen, etc.). There is
often a 1-to-1 relationship between a page box and a sheet, but this
is not always the case. Transfer possibilities include:</P>

<ul>
<li>Transferring one page box to one sheet (e.g., single-sided printing).
<li>Transferring two page boxes to both sides of the same sheet (e.g.,
double-sided printing).
<li>Transferring N (small) page boxes to one sheet (called "n-up").
<li>Transferring one (large) page box to N x M sheets (called "tiling").
<li>Creating signatures. A signature is a group of pages
printed on a sheet, which, when folded and trimmed like a book, appear in their
proper sequence.
<li>Printing one document to several output trays.
<li>Outputting to a file.
</ul>


<h2>13.2 <a name="page-box">Page boxes</a>: the @page rule</h2>

<p>The <a name="x1"><span class="index-def" title="page box"><dfn>page
box</dfn></span></a> is a rectangular region that contains two areas:</p>

<ul>

<li>The <span class="index-def" title="page area"><a
name="page-area"><dfn>page area</dfn></a></span>. The page area
includes the boxes laid out on that page. The edges of the first page
area establish the rectangle that is the initial <a
href="visudet.html#containing-block-details">containing block</a> of
the document.
The canvas background is painted within and covers the page area.


<li>The margin area, which surrounds the page area.
The page margin area is transparent.
</ul>

<p>The size of a page box cannot be specified in CSS 2.1.

<P>Authors can specify the margins of a page box inside an <a name="x3"><span
class="index-def" title="@page">@page</span></a> rule. An @page rule
consists of the keyword "@page", followed by an optional page
selector, followed by a block of declarations. The declarations in an
@page rule are said to be in the <span class="index-def"
title="page-context"><a name="page-context"><dfn>page
context</dfn></a></span>.</p>

<P>The <a name="x5"><span class="index-def" title="page selector"><dfn>page
selector</dfn></span></a> specifies for which pages the declarations
apply. In CSS&nbsp;2.1, page selectors may designate the first page,
all left pages, or all right pages</p>


<h3>13.2.1 <a name="page-margins">Page margins</a></h3>

<P>In CSS&nbsp;2.1, only the <a href="box.html#margin-properties">margin
properties</a> (<a href="box.html#propdef-margin-top" class="noxref"><span class="propinst-margin-top">'margin-top'</span></a>,
<a href="box.html#propdef-margin-right" class="noxref"><span class="propinst-margin-right">'margin-right'</span></a>, <a href="box.html#propdef-margin-bottom" class="noxref"><span
class="propinst-margin-bottom">'margin-bottom'</span></a>, <a href="box.html#propdef-margin-left" class="noxref"><span
class="propinst-margin-left">'margin-left'</span></a>, and <a href="box.html#propdef-margin" class="noxref"><span
class="propinst-margin">'margin'</span></a>) apply within the <a
href="#page-context">page context</a>. The following diagram shows the

<div class="figure">
<P><img src="./images/page-info.png" alt="Illustration of sheet, page
box, margin, and page area."><SPAN class="dlink">&nbsp;&nbsp;&nbsp;<A name="img-page-info" href="images/longdesc/page-info-desc.html" title="Long description illustrating relationship between page box
      and sheet">[D]</A></SPAN></p>
</div>

<div class="example"><P style="display:none">Example(s):</P><P>
Here is a simple example which sets all page margins on all pages:

<pre>
@page {
  margin: 3cm;
}
</pre>
</div>

<p>The <a href="#page-context">page context</a> has no notion of
fonts, so 'em' and 'ex' units are not allowed. Percentage values on
the margin properties are relative to the dimensions of the <a
href="#page-box">page box</a>; for left and right margins, they refer
to the width of the page box while for top and bottom margins, they
refer to the height of the page box. All other units associated with
the respective CSS&nbsp;2.1 properties are allowed.

<P>Due to negative margin values (either on the page box or on
elements) or <a href="visuren.html#absolute-positioning">absolute
positioning</a> content may end up outside the page box, but this
content may be "cut" &mdash; by the user agent, the printer, or ultimately,
the paper cutter.


<h3>13.2.2 <a name="page-selectors">Page selectors: selecting left, right, and first pages</a></H3>

<P>When printing double-sided documents, the <a href="#page-box">page
boxes</a> on left and right pages may be different. This can be
expressed through two CSS pseudo-classes that may be used in page selectors.

<P>All pages are automatically classified by user agents into either
the <a name="x6"><span class="index-def"
title=":left|pseudo-class:::left">:left</span></a> or <a name="x8"><span
class="index-def" title=":right|pseudo-class:::right">:right</span></a>
pseudo-class.

<div class="example"><P style="display:none">Example(s):</P><P>
<PRE>
@page :left {
  margin-left: 4cm;
  margin-right: 3cm;
}

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

<p>If different declarations have been given for left and right pages,
the user agent must honor these declarations even if the user agent
does not transfer the page boxes to left and right sheets (e.g., a
printer that only prints single-sided).

<P>Authors may also specify style for the first page of a document
with the <a name="x10"><span class="index-def"
title=":first|pseudo-class:::first">:first</span></a> pseudo-class:

<div class="example"><P style="display:none">Example(s):</P><P>
<PRE>
@page { margin: 2cm } /* All margins set to 2cm */

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

<P>Properties specified in a :left or :right @page rule override
those specified in an @page rule that has no pseudo-class specified.
Properties specified in a :first @page rule override those specified
in :left or :right @page rules.

<P>Margin declarations on left, right, and first pages may result in
different <a href="#page-area">page area</a> widths. To simplify
implementations, user agents may use a single page area width
on left, right, and first pages. In this case, the page area width
of the first page should be used.


<h3>13.2.3  <a name="outside-page-box">Content outside the page box</a></h3>

<P>When formatting content in the page model, some content may end up
outside the current page box. For example, an element whose <a href="text.html#propdef-white-space" class="noxref"><span
class="propinst-white-space">'white-space'</span></a> property has the
value 'pre' may generate a box that is wider than the page box. As
another example, when boxes are positioned absolutely or relatively,
they may end up in "inconvenient" locations. For example, images may
be placed on the edge of the page box or 100,000 meters below the page
box.

<P>The exact formatting of such elements lies outside the scope of
this specification. However, we recommend that authors and user agents
observe the following general principles concerning content outside
the page box:</p>

<ul>

<li>Content should be allowed slightly beyond the page box to allow
pages to "bleed".

<li>User agents should avoid generating a large number of empty page
boxes to honor the positioning of elements (e.g., you do not want to
print 100 blank pages).

<li>Authors should not position elements in inconvenient locations
just to avoid rendering them.

<li>User agents may handle boxes positioned outside the page box in
several ways, including discarding them or creating page boxes for
them at the end of the document.
</ul>

<H2>13.3 <a name="page-breaks">Page breaks</a></H2>

<P>This section describes page breaks in CSS&nbsp;2.1. Five
properties indicate where the user agent may or should break pages,
and on what page (left or right) the subsequent content should resume.
Each page break ends layout in the current <a href="#page-box">page
box</a> and causes remaining pieces of the <a
href="conform.html#doctree">document tree</a> to be laid out in a new
page box.

<h3>13.3.1 <a name="page-break-props">Page break properties</a>: <a href="page.html#propdef-page-break-before" class="noxref"><span
class="propinst-page-break-before">'page-break-before'</span></a>,
<a href="page.html#propdef-page-break-after" class="noxref"><span class="propinst-page-break-after">'page-break-after'</span></a>,
<a href="page.html#propdef-page-break-inside" class="noxref"><span class="propinst-page-break-inside">'page-break-inside'</span></a>
</h3>

<div class="propdef">
<dl><dt>
<span class="index-def" title="'page-break-before'"><a name="propdef-page-break-before" class="propdef-title"><strong>'page-break-before'</strong></a></span>
<dd>
<table class="propinfo" cellspacing=0 cellpadding=0>
<tr valign=baseline><td><em>Value:</em>&nbsp;&nbsp;<td>auto | always | avoid | left | right | <a href="cascade.html#value-def-inherit" class="noxref"><span class="value-inst-inherit">inherit</span></a>
<tr valign=baseline><td><em>Initial:</em>&nbsp;&nbsp;<td>auto
<tr valign=baseline><td><em>Applies to:</em>&nbsp;&nbsp;<td>block-level elements (but see text)
<tr valign=baseline><td><em>Inherited:</em>&nbsp;&nbsp;<td>no
<tr valign=baseline><td><em>Percentages:</em>&nbsp;&nbsp;<td>N/A
<tr valign=baseline><td><em>Media:</em>&nbsp;&nbsp;<td><a href="media.html#visual-media-group" class="noxref">visual</a>, <a href="media.html#paged-media-group" class="noxref">paged</a>
<tr valign=baseline><td><em>Computed&nbsp;value:</em>&nbsp;&nbsp;<td>as specified
</table>
</dl>
</div>


<div class="propdef">
<dl><dt>
<span class="index-def" title="'page-break-after'"><a name="propdef-page-break-after" class="propdef-title"><strong>'page-break-after'</strong></a></span>
<dd>
<table class="propinfo" cellspacing=0 cellpadding=0>
<tr valign=baseline><td><em>Value:</em>&nbsp;&nbsp;<td>auto | always | avoid | left | right | <a href="cascade.html#value-def-inherit" class="noxref"><span class="value-inst-inherit">inherit</span></a>
<tr valign=baseline><td><em>Initial:</em>&nbsp;&nbsp;<td>auto
<tr valign=baseline><td><em>Applies to:</em>&nbsp;&nbsp;<td>block-level elements (but see text)
<tr valign=baseline><td><em>Inherited:</em>&nbsp;&nbsp;<td>no
<tr valign=baseline><td><em>Percentages:</em>&nbsp;&nbsp;<td>N/A
<tr valign=baseline><td><em>Media:</em>&nbsp;&nbsp;<td><a href="media.html#visual-media-group" class="noxref">visual</a>, <a href="media.html#paged-media-group" class="noxref">paged</a>
<tr valign=baseline><td><em>Computed&nbsp;value:</em>&nbsp;&nbsp;<td>as specified
</table>
</dl>
</div>


<div class="propdef">
<dl><dt>
<span class="index-def" title="'page-break-inside'"><a name="propdef-page-break-inside" class="propdef-title"><strong>'page-break-inside'</strong></a></span>
<dd>
<table class="propinfo" cellspacing=0 cellpadding=0>
<tr valign=baseline><td><em>Value:</em>&nbsp;&nbsp;<td>avoid | auto | <a href="cascade.html#value-def-inherit" class="noxref"><span class="value-inst-inherit">inherit</span></a>
<tr valign=baseline><td><em>Initial:</em>&nbsp;&nbsp;<td>auto
<tr valign=baseline><td><em>Applies to:</em>&nbsp;&nbsp;<td>block-level elements (but see text)
<tr valign=baseline><td><em>Inherited:</em>&nbsp;&nbsp;<td>no
<tr valign=baseline><td><em>Percentages:</em>&nbsp;&nbsp;<td>N/A
<tr valign=baseline><td><em>Media:</em>&nbsp;&nbsp;<td><a href="media.html#visual-media-group" class="noxref">visual</a>, <a href="media.html#paged-media-group" class="noxref">paged</a>
<tr valign=baseline><td><em>Computed&nbsp;value:</em>&nbsp;&nbsp;<td>as specified
</table>
</dl>
</div>


<P>Values for these properties have the following meanings:</p>

<dl>
<dt><strong>auto</strong></dt>
<dd>Neither force nor forbid a page break before (after, inside) the
generated box.
<dt><strong>always</strong></dt>
<dd>Always force a page break before (after) the
generated box.</dd>
<dt><strong>avoid</strong></dt>
<dd>Avoid a page break before (after, inside) the generated box.
<dt><strong>left</strong></dt>
<dd>
Force one or two page breaks before
(after) the generated box
so that the next page is formatted as a left page.</dd>
<dt><strong>right</strong></dt>
<dd>
Force one or two page breaks before (after) the generated
box so that the next page is formatted as a right page.</dd>
</dl>

<p>Whether the first page of a document is :left or :right depends on
the major writing direction of the document. A conforming user agent
may interpret the values 'left' and 'right' as 'always'.

<p>A potential page break location is typically under the influence
of the parent element's <a href="page.html#propdef-page-break-inside" class="noxref"><span
class="propinst-page-break-inside">'page-break-inside'</span></a>
property, the <a href="page.html#propdef-page-break-after" class="noxref"><span
class="propinst-page-break-after">'page-break-after'</span></a> property
of the preceding element, and the <a href="page.html#propdef-page-break-before" class="noxref"><span
class="propinst-page-break-before">'page-break-before'</span></a> property
of the following element.  When these properties have values other
than 'auto', the values 'always', 'left', and 'right' take precedence
over 'avoid'.

<p>User Agents must apply these properties to block-level elements
in the normal flow of the root element. User agents may also apply
these properties to other elements, e.g., 'table-row' elements.

<p>When a page break splits a box, the box's margins, borders, and
padding have no visual effect where the split occurs.


<h3>13.3.2 <a name="break-inside">Breaks inside elements</a>: <a href="page.html#propdef-orphans" class="noxref"><span
class="propinst-orphans">'orphans'</span></a>, <a href="page.html#propdef-widows" class="noxref"><span
class="propinst-widows">'widows'</span></a></h3>

<div class="propdef">
<dl><dt>
<span class="index-def" title="'orphans'"><a name="propdef-orphans" class="propdef-title"><strong>'orphans'</strong></a></span>
<dd>
<table class="propinfo" cellspacing=0 cellpadding=0>
<tr valign=baseline><td><em>Value:</em>&nbsp;&nbsp;<td><a href="syndata.html#value-def-integer" class="noxref"><span class="value-inst-integer">&lt;integer&gt;</span></a> | <a href="cascade.html#value-def-inherit" class="noxref"><span class="value-inst-inherit">inherit</span></a>
<tr valign=baseline><td><em>Initial:</em>&nbsp;&nbsp;<td>2
<tr valign=baseline><td><em>Applies to:</em>&nbsp;&nbsp;<td>block-level elements
<tr valign=baseline><td><em>Inherited:</em>&nbsp;&nbsp;<td>yes
<tr valign=baseline><td><em>Percentages:</em>&nbsp;&nbsp;<td>N/A
<tr valign=baseline><td><em>Media:</em>&nbsp;&nbsp;<td><a href="media.html#visual-media-group" class="noxref">visual</a>, <a href="media.html#paged-media-group" class="noxref">paged</a>
<tr valign=baseline><td><em>Computed&nbsp;value:</em>&nbsp;&nbsp;<td>as specified
</table>
</dl>
</div>


<div class="propdef">
<dl><dt>
<span class="index-def" title="'widows'"><a name="propdef-widows" class="propdef-title"><strong>'widows'</strong></a></span>
<dd>
<table class="propinfo" cellspacing=0 cellpadding=0>
<tr valign=baseline><td><em>Value:</em>&nbsp;&nbsp;<td><a href="syndata.html#value-def-integer" class="noxref"><span class="value-inst-integer">&lt;integer&gt;</span></a> | <a href="cascade.html#value-def-inherit" class="noxref"><span class="value-inst-inherit">inherit</span></a>
<tr valign=baseline><td><em>Initial:</em>&nbsp;&nbsp;<td>2
<tr valign=baseline><td><em>Applies to:</em>&nbsp;&nbsp;<td>block-level elements
<tr valign=baseline><td><em>Inherited:</em>&nbsp;&nbsp;<td>yes
<tr valign=baseline><td><em>Percentages:</em>&nbsp;&nbsp;<td>N/A
<tr valign=baseline><td><em>Media:</em>&nbsp;&nbsp;<td><a href="media.html#visual-media-group" class="noxref">visual</a>, <a href="media.html#paged-media-group" class="noxref">paged</a>
<tr valign=baseline><td><em>Computed&nbsp;value:</em>&nbsp;&nbsp;<td>as specified
</table>
</dl>
</div>


<P>The <a href="page.html#propdef-orphans" class="noxref"><span class="propinst-orphans">'orphans'</span></a> property
specifies the minimum number of lines in a block element that must be left
at the bottom of a page. The <a href="page.html#propdef-widows" class="noxref"><span class="propinst-widows">'widows'</span></a> property specifies the minimum
number of lines in a block element that must be left at the top of a page.
Examples of how they are used to control page breaks are given below.

<p>Only positive values are allowed.

<P>For information about paragraph formatting, please consult the
section on <a href="visuren.html#line-box">line boxes</a>.

<h3>13.3.3 <a name="allowed-page-breaks">Allowed page breaks</a></h3>

<p>In the normal flow, page breaks can occur at the following places:</p>

<ol>
<li>
In the vertical margin between block boxes. When an unforced page
break occurs here, the <a href="cascade.html#used-value">used
values</a> of the relevant <a href="box.html#propdef-margin-top" class="noxref"><span
class="propinst-margin-top">'margin-top'</span></a> and <a href="box.html#propdef-margin-bottom" class="noxref"><span
class="propinst-margin-bottom">'margin-bottom'</span></a> properties are
set to '0'. When a forced page break occurs here, the used value of
the relevant <a href="box.html#propdef-margin-bottom" class="noxref"><span
class="propinst-margin-bottom">'margin-bottom'</span></a> property is set
to '0'; the relevant <a href="box.html#propdef-margin-top" class="noxref"><span
class="propinst-margin-top">'margin-top'</span></a> used value may either
be set to '0' or retained.

<li>Between <a href="visuren.html#line-box">line boxes</a>
inside a <a href="visuren.html#block-box">block</a> box.

<li>Between the content edge of a block box and the outer edges of its
child content (margin edges of block-level children or line box edges
for inline-level children) if there is a (non-zero) gap between them.
</ol>

<p class=note>Note: It is expected that CSS3 will specify that the
relevant 'margin-top' applies (i.e., is not set to '0') after a forced
page break.


<p>These breaks are subject to the following rules:

<ul>
<li><strong>Rule A:</strong> Breaking at (1) is allowed only if the <a href="page.html#propdef-page-break-after" class="noxref"><span
class="propinst-page-break-after">'page-break-after'</span></a> and <a href="page.html#propdef-page-break-before" class="noxref"><span
class="propinst-page-break-before">'page-break-before'</span></a> properties of all
the elements generating boxes that
meet at this margin allow it, which is when at least
one of them has the value 'always', 'left', or 'right', or when all of them are
'auto'.

<li><strong>Rule B:</strong> However, if all of them are 'auto' and
a common ancestor of all the elements has a <a href="page.html#propdef-page-break-inside" class="noxref"><span
class="propinst-page-break-inside">'page-break-inside'</span></a> value of
'avoid', then breaking here is not allowed.

<li>
<strong>Rule C:</strong> Breaking at (2) is allowed only if the number of <a
href="visuren.html#line-box">line boxes</a> between the
break and the start of the enclosing block box is
the value of <a href="page.html#propdef-orphans" class="noxref"><span
class="propinst-orphans">'orphans'</span></a> or more, and the number of
line boxes between the break and the end of the box is
the value of <a href="page.html#propdef-widows" class="noxref"><span class="propinst-widows">'widows'</span></a> or more.

<li><strong>Rule D:</strong> In addition, breaking at (2) or (3) is
allowed only if the <a href="page.html#propdef-page-break-inside" class="noxref"><span
class="propinst-page-break-inside">'page-break-inside'</span></a> property
of the element and all its ancestors is 'auto'.
</ul>

<p>If the above does not provide enough break points to keep content
from overflowing the page boxes, then rules A, B and D are dropped in
order to find additional breakpoints.

<p>If that still does not lead to sufficient break points, rule
C is dropped as well, to find still more break points.


<h3>13.3.4 <a name="forced">Forced page breaks</a></h3>

<p>A page break <em>must</em> occur at (1) if, among the <a href="page.html#propdef-page-break-after" class="noxref"><span
class="propinst-page-break-after">'page-break-after'</span></a> and <a href="page.html#propdef-page-break-before" class="noxref"><span
class="propinst-page-break-before">'page-break-before'</span></a>
properties of all the elements generating boxes that meet at this
margin, there is at least one with the value 'always', 'left', or
'right'.

<h3>13.3.5 <a name="best-page-breaks">"Best" page breaks</a></h3>

<p>CSS&nbsp;2.1 does <em>not</em> define which of a set of allowed page breaks
must be used; CSS&nbsp;2.1 does not forbid a user agent from breaking at every
possible break point, or not to break at all. But CSS&nbsp;2.1 does recommend
that user agents observe the following heuristics (while recognizing
that they are sometimes contradictory):</p>

<ul>
<li>Break as few times as possible.
<li>Make all pages that do not end with a forced break appear to have about
the same height.
<li>Avoid breaking inside a replaced element.
</ul>

<div class="example"><P style="display:none">Example(s):</P><P>
Suppose, for example, that the style sheet
contains 'orphans: 4', 'widows: 2', and
there are 20 lines (<a href="visuren.html#line-box">line boxes</a>)
available at the bottom of the current page:</p>

<ul>

<li>If a paragraph at the end of the current page contains 20 lines or fewer,
it should be placed on the current page.

<li>If the paragraph contains 21 or 22 lines, the second part of the
paragraph must not violate the <a href="page.html#propdef-widows" class="noxref"><span
class="propinst-widows">'widows'</span></a> constraint, and so the
second part must contain exactly two lines

<li>If the paragraph contains 23 lines or more, the first part should
contain 20 lines and the second part the remaining lines.

</ul>

<P>Now suppose that <a href="page.html#propdef-orphans" class="noxref"><span class="propinst-orphans">'orphans'</span></a> is
'10',
<a href="page.html#propdef-widows" class="noxref"><span class="propinst-widows">'widows'</span></a> is '20',
and there are 8 lines available at the bottom of the current page:</p>

<ul>

<li>If a paragraph at the end of the current page contains 8 lines or
fewer, it should be placed on the current page.

<li>If the paragraph contains 9 lines or more, it cannot be split
(that would violate the orphan constraint), so it should move
as a block to the next page.
</ul>
</div>

<h2>13.4 <a name="page-cascade">Cascading in the page context</a></H2>

<P>Declarations in the <a href="#page-context">page context</a> obey
the <a href="cascade.html">cascade</a> just like normal CSS
declarations.

<div class="example"><P style="display:none">Example(s):</P><P>
Consider the following example:

<PRE>
@page {
  margin-left: 3cm;
}

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

<P>Due to the <a href="cascade.html#cascading-order">higher
specificity</a> of the pseudo-class selector, the left margin on left
pages will be '4cm' and all other pages (i.e., the right pages) will
have a left margin of '3cm'.
</div>
<hr class="navbar">

<div class="navbar">
<p><a href="generate.html">previous</a> &nbsp;
<a href="colors.html">next</a> &nbsp;
<a href="cover.html#minitoc">contents</a> &nbsp;
<a href="propidx.html">properties</a> &nbsp;
<a href="indexlist.html">index</a> &nbsp;
</div>
</body>
</html>