-
Notifications
You must be signed in to change notification settings - Fork 790
Expand file tree
/
Copy pathOverview.html
More file actions
2420 lines (1680 loc) · 111 KB
/
Overview.html
File metadata and controls
2420 lines (1680 loc) · 111 KB
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
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
<!doctype html>
<html lang="en">
<head>
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
<title>CSS Fragmentation Module Level 3</title>
<meta content="refining" name="csswg-work-status">
<meta content="ED" name="w3c-status">
<link href="../default.css" rel="stylesheet" type="text/css">
<link href="../csslogo.ico" rel="shortcut icon" type="image/x-icon">
<style>
body {
background: url("https://www.w3.org/StyleSheets/TR/logo-ED") top left no-repeat white;
background-attachment: fixed;
color: black;
font-family: sans-serif;
margin: 0 auto;
max-width: 50em;
padding: 2em 1em 2em 70px;
}
:link { color: #00C; background: transparent }
:visited { color: #609; background: transparent }
a[href]:active { color: #C00; background: transparent }
a[href]:hover { background: #ffa }
a[href] img { border-style: none }
h1, h2, h3, h4, h5, h6 { text-align: left }
h1, h2, h3 { color: #005A9C; }
h1 { font: 170% sans-serif }
h2 { font: 140% sans-serif }
h3 { font: 120% sans-serif }
h4 { font: bold 100% sans-serif }
h5 { font: italic 100% sans-serif }
h6 { font: small-caps 100% sans-serif }
.hide { display: none }
div.head { margin-bottom: 1em }
div.head h1 { margin-top: 2em; clear: both }
div.head table { margin-left: 2em; margin-top: 2em }
p.copyright { font-size: small }
p.copyright small { font-size: small }
pre { margin-left: 2em }
dt { font-weight: bold }
ul.toc, ol.toc {
list-style: none;
}
</style>
<meta content="Bikeshed 1.0.0" name="generator">
</head>
<body class="h-entry">
<div class="head">
<p data-fill-with="logo"><a class="logo" href="http://www.w3.org/">
<img alt="W3C" height="48" src="https://www.w3.org/Icons/w3c_home" width="72">
</a>
</p>
<h1 class="p-name no-ref" id="title">CSS Fragmentation Module Level 3</h1>
<h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="content">Editor’s Draft,
<time class="dt-updated" datetime="2015-07-15">15 July 2015</time></span></h2>
<div data-fill-with="spec-metadata">
<dl>
<dt>This version:
<dd><a class="u-url" href="http://dev.w3.org/csswg/css-break/">http://dev.w3.org/csswg/css-break/</a>
<dt>Latest version:
<dd><a href="http://www.w3.org/TR/css-break-3/">http://www.w3.org/TR/css-break-3/</a>
<dt>Previous Versions:
<dd><a href="http://www.w3.org/TR/2015/WD-css3-break-20150129/" rel="previous">http://www.w3.org/TR/2015/WD-css3-break-20150129/</a>
<dt>Feedback:
<dd><span><a href="mailto:www-style@w3.org?subject=%5Bcss-break%5D%20YOUR%20TOPIC%20HERE">www-style@w3.org</a> with subject line “<kbd>[css-break] <var>… message topic …</var></kbd>” (<a href="http://lists.w3.org/Archives/Public/www-style/" rel="discussion">archives</a>)</span>
<dt>Issue Tracking:
<dd><a href="#issues-index">Inline In Spec</a>
<dt class="editor">Editors:
<dd class="editor p-author h-card vcard"><a class="p-name fn u-email email" href="mailto:ratan@microsoft.com<">Rossen Atanassov</a> (<span class="p-org org">Microsoft</span>)
<dd class="editor p-author h-card vcard"><a class="p-name fn u-url url" href="http://fantasai.inkedblade.net/contact">fantasai</a> (<span class="p-org org">Invited Expert</span>)
</dl>
</div>
<div data-fill-with="warning"></div>
<p class="copyright" data-fill-with="copyright"><a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a> © 2015 <a href="http://www.w3.org/"><abbr title="World Wide Web Consortium">W3C</abbr></a><sup>®</sup> (<a href="http://www.csail.mit.edu/"><abbr title="Massachusetts Institute of Technology">MIT</abbr></a>, <a href="http://www.ercim.eu/"><abbr title="European Research Consortium for Informatics and Mathematics">ERCIM</abbr></a>, <a href="http://www.keio.ac.jp/">Keio</a>, <a href="http://ev.buaa.edu.cn/">Beihang</a>). 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>
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc no-ref heading settled" id="abstract"><span class="content">Abstract</span></h2>
<div class="p-summary" data-fill-with="abstract">
<p>This module describes the fragmentation model that partitions a flow into pages, columns, or regions.
It builds on the Page model module and introduces and defines the fragmentation model.
It adds functionality for pagination, breaking variable fragment size and orientation, widows and orphans.</p>
<a href="http://www.w3.org/TR/CSS/">CSS</a> is a language for describing the rendering of structured documents
(such as HTML and XML)
on screen, on paper, in speech, etc.</div>
<h2 class="no-num no-toc no-ref heading settled" id="status"><span class="content">Status of this document</span></h2>
<div data-fill-with="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>
<p>
The (<a href="http://lists.w3.org/Archives/Public/www-style/">archived</a>) public mailing list
<a href="mailto:www-style@w3.org?Subject=%5Bcss-break%5D%20PUT%20SUBJECT%20HERE">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 “css-break” in the subject,
preferably like this:
“[css-break] <em>…summary of comment…</em>”
</p>
<p>
This document was produced by the <a href="http://www.w3.org/Style/CSS/members">CSS Working Group</a>
(part of the <a href="http://www.w3.org/Style/">Style Activity</a>).
</p>
<p>
This document was produced by a group operating under
the <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/">5 February 2004 W3C Patent Policy</a>.
W3C maintains a <a href="http://www.w3.org/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="http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">Essential Claim(s)</a>
must disclose the information in accordance with <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">section 6 of the W3C Patent Policy</a>.
</p>
<p>
This document is governed by the <a href="http://www.w3.org/2014/Process-20140801/" id="w3c_process_revision">1 August 2014 W3C Process Document</a>.
</p>
<p>
</p></div>
<div data-fill-with="at-risk"></div>
<h2 class="no-num no-toc no-ref heading settled" id="contents"><span class="content">Table of Contents</span></h2>
<div data-fill-with="table-of-contents" role="navigation">
<ul class="toc" role="directory">
<li><a href="#intro"><span class="secno">1</span> <span class="content">
Introduction</span></a>
<ul class="toc">
<li><a href="#placement"><span class="secno">1.1</span> <span class="content">
Module Interactions</span></a>
<li><a href="#values"><span class="secno">1.2</span> <span class="content">
Values</span></a>
</ul>
<li><a href="#fragmentation-model"><span class="secno">2</span> <span class="content">
Fragmentation Model and Terminology</span></a>
<ul class="toc">
<li><a href="#parallel-flows"><span class="secno">2.1</span> <span class="content">
Parallel Fragmentation Flows</span></a>
<li><a href="#nested-flows"><span class="secno">2.2</span> <span class="content">
Nested Fragmentation Flows</span></a>
</ul>
<li><a href="#breaking-controls"><span class="secno">3</span> <span class="content">
Controlling Breaks</span></a>
<ul class="toc">
<li><a href="#break-between"><span class="secno">3.1</span> <span class="content">
Breaks Between Boxes: the <span class="property">break-before</span> and <span class="property">break-after</span> properties</span></a>
<ul class="toc">
<li><a href="#generic-break-values"><span class="secno"></span> <span class="content">
Generic Break Values</span></a>
<li><a href="#page-break-values"><span class="secno"></span> <span class="content">
Page Break Values</span></a>
<li><a href="#column-break-values"><span class="secno"></span> <span class="content">
Column Break Values</span></a>
<li><a href="#region-break-values"><span class="secno"></span> <span class="content">
Region Break Values</span></a>
</ul>
<li><a href="#break-within"><span class="secno">3.2</span> <span class="content">
Breaks Within Boxes: the <span class="property">break-inside</span> property</span></a>
<li><a href="#widows-orphans"><span class="secno">3.3</span> <span class="content">
Breaks Between Lines: <span class="property">orphans</span>, <span class="property">widows</span></span></a>
<li><a href="#page-break-properties"><span class="secno">3.4</span> <span class="content">
Page Break Aliases: the <span class="property">page-break-before</span>, <span class="property">page-break-after</span>, and <span class="property">page-break-inside</span> properties</span></a>
</ul>
<li><a href="#breaking-rules"><span class="secno">4</span> <span class="content">
Rules for Breaking</span></a>
<ul class="toc">
<li><a href="#possible-breaks"><span class="secno">4.1</span> <span class="content">
Possible Break Points</span></a>
<li><a href="#break-types"><span class="secno">4.2</span> <span class="content">
Types of Breaks</span></a>
<li><a href="#forced-breaks"><span class="secno">4.3</span> <span class="content">
Forced Breaks</span></a>
<li><a href="#unforced-breaks"><span class="secno">4.4</span> <span class="content">
Unforced Breaks</span></a>
<li><a href="#best-breaks"><span class="secno">4.5</span> <span class="content">
Optimizing Unforced Breaks</span></a>
</ul>
<li><a href="#breaking-boxes"><span class="secno">5</span> <span class="content">
Box Model for Breaking</span></a>
<ul class="toc">
<li><a href="#varying-size-boxes"><span class="secno">5.1</span> <span class="content">
Breaking into Varying-size Fragmentainers</span></a>
<li><a href="#break-margins"><span class="secno">5.2</span> <span class="content">
Adjoining Margins at Breaks</span></a>
<li><a href="#box-splitting"><span class="secno">5.3</span> <span class="content">
Splitting Boxes</span></a>
<li><a href="#break-decoration"><span class="secno">5.4</span> <span class="content">
Fragmented Borders and Backgrounds: the <span class="property">box-decoration-break</span> property</span></a>
<ul class="toc">
<li><a href="#joining-boxes"><span class="secno">5.4.1</span> <span class="content">
Joining Boxes for <span class="css">slice</span></span></a>
</ul>
<li><a href="#transforms"><span class="secno">5.5</span> <span class="content">
Transforms, Positioning, and Pagination</span></a>
</ul>
<li><a href="#changes"><span class="secno"></span> <span class="content">
Changes</span></a>
<li><a href="#acknowledgments"><span class="secno"></span> <span class="content">
Acknowledgments</span></a>
<li><a href="#conformance"><span class="secno"></span> <span class="content">
Conformance</span></a>
<ul class="toc">
<li><a href="#conventions"><span class="secno"></span> <span class="content">
Document conventions</span></a>
<li><a href="#conformance-classes"><span class="secno"></span> <span class="content">
Conformance classes</span></a>
<li><a href="#partial"><span class="secno"></span> <span class="content">
Partial implementations</span></a>
<li><a href="#experimental"><span class="secno"></span> <span class="content">
Experimental implementations</span></a>
<li><a href="#testing"><span class="secno"></span> <span class="content">
Non-experimental implementations</span></a>
</ul>
<li><a href="#index"><span class="secno"></span> <span class="content">Index</span></a>
<ul class="toc">
<li><a href="#index-defined-here"><span class="secno"></span> <span class="content">Terms defined by this specification</span></a>
<li><a href="#index-defined-elsewhere"><span class="secno"></span> <span class="content">Terms defined by reference</span></a>
</ul>
<li><a href="#references"><span class="secno"></span> <span class="content">References</span></a>
<ul class="toc">
<li><a href="#normative"><span class="secno"></span> <span class="content">Normative References</span></a>
<li><a href="#informative"><span class="secno"></span> <span class="content">Informative References</span></a>
</ul>
<li><a href="#property-index"><span class="secno"></span> <span class="content">Property Index</span></a>
<li><a href="#issues-index"><span class="secno"></span> <span class="content">Issues Index</span></a>
</ul></div>
<main>
<h2 class="no-num no-toc heading settled" id="tagline"><span class="content">Breaking the Web, one fragment at a time</span></h2>
<h2 class="heading settled" data-level="1" id="intro"><span class="secno">1. </span><span class="content">
Introduction</span><a class="self-link" href="#intro"></a></h2>
<p><em>This section is not normative.</em></p>
<p>
In paged media (e.g., paper, transparencies, photo album pages, pages
displayed on computer screens as printed output simulations), as
opposed to <a href="http://www.w3.org/TR/CSS2/media.html#continuous-media-group">
continuous media</a>, the content of the document is split into one or
more discrete display surfaces. In order to avoid awkward breaks
(such as halfway through a line of text), the layout engine must be
able to shift around content that would fall across the page break.
This process is called <dfn data-dfn-type="dfn" data-noexport="" id="pagination">pagination<a class="self-link" href="#pagination"></a></dfn>.
</p>
<p>
In CSS, in addition to paged media, certain layout features such as
<a href="http://www.w3.org/TR/css3-regions/">regions</a> <a data-link-type="biblio" href="#biblio-css3-regions">[CSS3-REGIONS]</a>
and <a href="http://www.w3.org/TR/css3-multicol/">multi-column layout</a>
<a data-link-type="biblio" href="#biblio-css3col">[CSS3COL]</a> create a similarly fragmented environment.
The generic term for breaking content across containers is
<a data-link-type="dfn" href="#fragmentation">fragmentation</a>.
This module explains how content breaks across <a data-link-type="dfn" href="#fragmentation-container">fragmentation containers</a> (<a data-link-type="dfn" href="#fragmentainer">fragmentainers</a>)
such as pages and columns and how such breaks can be
<a href="#breaking-controls">controlled by the author</a>.
</p>
<h3 class="heading settled" data-level="1.1" id="placement"><span class="secno">1.1. </span><span class="content">
Module Interactions</span><a class="self-link" href="#placement"></a></h3>
<p>
This module replaces and extends the pagination controls defined in
<a data-link-type="biblio" href="#biblio-css21">[CSS21]</a> <a href="http://www.w3.org/TR/CSS21/page.html#page-breaks">section 13.3</a>
and in <a data-link-type="biblio" href="#biblio-css3page">[CSS3PAGE]</a>.
</p>
<h3 class="heading settled" data-level="1.2" id="values"><span class="secno">1.2. </span><span class="content">
Values</span><a class="self-link" href="#values"></a></h3>
<p>
This specification follows the <a href="http://www.w3.org/TR/CSS21/about.html#property-defs">
CSS property definition conventions</a> from <a data-link-type="biblio" href="#biblio-css21">[CSS21]</a>. Value types not defined
in this specification are defined in CSS Level 2 Revision 1 <a data-link-type="biblio" href="#biblio-css21">[CSS21]</a>. Other CSS
modules may expand the definitions of these value types: for example <a data-link-type="biblio" href="#biblio-css3val">[CSS3VAL]</a>,
when combined with this module, adds the <a class="css" data-link-type="maybe" href="http://dev.w3.org/csswg/css-cascade-4/#valdef-all-initial">initial</a> value
to the properties defined here.</p>
<p>
In addition to the property-specific values listed in their definitions, all properties
defined in this specification also accept the <a href="http://www.w3.org/TR/CSS21/cascade.html#value-def-inherit">
inherit</a> keyword as their property value. For readability it has not been
repeated explicitly.
</p>
<h2 class="heading settled" data-level="2" id="fragmentation-model"><span class="secno">2. </span><span class="content">
Fragmentation Model and Terminology</span><a class="self-link" href="#fragmentation-model"></a></h2>
<dl>
<dt><dfn data-dfn-type="dfn" data-export="" id="fragmentation-container">fragmentation container<a class="self-link" href="#fragmentation-container"></a></dfn> (<dfn data-dfn-type="dfn" data-export="" id="fragmentainer">fragmentainer<a class="self-link" href="#fragmentainer"></a></dfn>)
<dd>
A box—such as a page box, column box, or region—that contains
a portion (or all) of a <a data-link-type="dfn" href="#fragmented-flow">fragmented flow</a>.
Fragmentainers can be pre-defined, or generated as needed.
When breakable content overflows a fragmentainer in the block dimension,
instead of overflowing it breaks into the next container in its
<a data-link-type="dfn" href="#fragmentation-context">fragmentation context</a>.
<dt><dfn data-dfn-type="dfn" data-export="" id="fragmentation-context">fragmentation context<a class="self-link" href="#fragmentation-context"></a></dfn>
<dd>
An ordered series of <a data-link-type="dfn" href="#fragmentainer">fragmentainers</a>,
such as created by a <a href="http://www.w3.org/TR/css3-multicol/">multi-column element</a>,
a chain of <a href="http://www.w3.org/TR/css3-regions">CSS regions</a>,
or a <a href="http://www.w3.org/TR/css3-page/">paged media display</a>.
A given fragmentation context can only have one block flow direction
across all its <a data-link-type="dfn" href="#fragmentainer">fragmentainers</a>.
(Descendants of the <a data-link-type="dfn" href="#fragmentation-root">fragmentation root</a> may have other block flow directions,
but fragmentation proceeds according to the block flow direction applied to the <a data-link-typ
1337
e="dfn" href="#fragmentation-root">fragmentation root</a>.)
<dt><dfn data-dfn-type="dfn" data-export="" id="fragmented-flow">fragmented flow<a class="self-link" href="#fragmented-flow"></a></dfn>
<dd>
A content flow that is being laid out in a <a data-link-type="dfn" href="#fragmentation-context">fragmentation context</a>.
The <a data-link-type="dfn" href="#fragmented-flow">fragmented flow</a> consists of the content of a (possibly anonymous) box
called the <dfn data-dfn-type="dfn" data-export="" id="fragmentation-root">fragmentation root<a class="self-link" href="#fragmentation-root"></a></dfn>.
<dt><dfn data-dfn-type="dfn" data-export="" id="fragmentation-direction">fragmentation direction<a class="self-link" href="#fragmentation-direction"></a></dfn>
<dd>
The block flow direction of the <a data-link-type="dfn" href="#fragmentation-context">fragmentation context</a>,
i.e. the direction in which content is fragmented.
(In this level of CSS, content only fragments in one dimension.)
<dt><dfn data-dfn-type="dfn" data-export="" id="fragmentation">fragmentation<a class="self-link" href="#fragmentation"></a></dfn>
<dd>
The process of splitting a content flow across the <a data-link-type="dfn" href="#fragmentainer">fragmentainers</a>
that form a <a data-link-type="dfn" href="#fragmentation-context">fragmentation context</a>.
<dt><dfn data-dfn-type="dfn" data-export="" id="box-fragment">box fragment<a class="self-link" href="#box-fragment"></a></dfn> or <dfn data-dfn-type="dfn" data-export="" id="fragment">fragment<a class="self-link" href="#fragment"></a></dfn>
<dd>
The portion of a box that belongs to exactly one <a data-link-type="dfn" href="#fragmentainer">fragmentainer</a>.
A box in continuous flow always consists of only one fragment.
A box in a fragmented flow consists of one or more fragments.
<dt><dfn data-dfn-type="dfn" data-export="" id="remaining-fragmentainer-extent">remaining fragmentainer extent<a class="self-link" href="#remaining-fragmentainer-extent"></a></dfn>
<dd>
The remaining <a data-link-type="dfn" href="http://dev.w3.org/csswg/css-writing-modes-3/#block-axis">block-axis</a> space in the <a data-link-type="dfn" href="#fragmentainer">fragmentainer</a> available to a given element,
i.e. between the end of preceding content in <a data-link-type="dfn" href="#fragmentainer">fragmentainer</a>
and the edge of the <a data-link-type="dfn" href="#fragmentainer">fragmentainer</a>.
</dl>
<p>
Each <dfn data-dfn-type="dfn" data-noexport="" id="fragmentation-break">fragmentation break<a class="self-link" href="#fragmentation-break"></a></dfn> (hereafter, <dfn data-dfn-type="dfn" data-noexport="" id="break">break<a class="self-link" href="#break"></a></dfn>)
ends layout of the fragmented box in the current <a data-link-type="dfn" href="#fragmentainer">fragmentainer</a>
and causes the remaining content to be laid out in the next <a data-link-type="dfn" href="#fragmentainer">fragmentainer</a>,
in some cases causing a new <a data-link-type="dfn" href="#fragmentainer">fragmentainer</a> to be generated
to hold the deferred content.
</p>
<p class="note" role="note">
Breaking inline content into lines is another form of fragmentation,
and similarly creates box fragments when it breaks
<a href="http://www.w3.org/TR/CSS21/visuren.html#inline-boxes">inline boxes</a>
across <a href="http://www.w3.org/TR/CSS21/visuren.html#line-box">line boxes</a>.
However, inline breaking is not covered here; see <a data-link-type="biblio" href="#biblio-css21">[CSS21]</a>/<a data-link-type="biblio" href="#biblio-css3text">[CSS3TEXT]</a>.
</p>
<h3 class="heading settled" data-level="2.1" id="parallel-flows"><span class="secno">2.1. </span><span class="content">
Parallel Fragmentation Flows</span><a class="self-link" href="#parallel-flows"></a></h3>
<p>
When multiple flows are laid out parallel to each other,
fragmentation is performed independently in each flow.
For example, if an element is floated,
then a forced break inside the float
will not affect the content wrapping outside the float
(except insofar as it may increase the height of the float).
</p>
<p>
The following are examples of parallel flows
whose contents will fragment independently:
</p>
<ul>
<li>The contents of a float vs. the content wrapping outside the float.
<li>The contents of a float vs. the contents of an adjacent float.
<li>The contents of each table cell in a single table row.
<li>The contents of each grid item in a single grid row.
<li>The contents of each flex item in a flex layout row.
<li>The contents of absolutely-positioned elements
that cover the same range of their containing block’s fragmentation context.
</ul>
<p>
Content overflowing the content edge of a fixed-size box
is considered parallel to the content after the fixed-size box
and follows the normal fragmentation rules.
Although overflowing content doesn’t affect the size of the <a data-link-type="dfn" href="#fragmentation-root">fragmentation root</a> box,
it does increase the length of the <a data-link-type="dfn" href="#fragmented-flow">fragmented flow</a>,
spilling into or generating additional <a data-link-type="dfn" href="#fragmentainer">fragmentainers</a> as necessary.
</p>
<h3 class="heading settled" data-level="2.2" id="nested-flows"><span class="secno">2.2. </span><span class="content">
Nested Fragmentation Flows</span><a class="self-link" href="#nested-flows"></a></h3>
<p>
Breaking a <a data-link-type="dfn" href="#fragmentainer">fragmentainer</a> <var>F</var> effectively splits the <a data-link-type="dfn" href="#fragmentainer">fragmentainer</a>
into two <a data-link-type="dfn" href="#fragmentainer">fragmentainers</a> (<var>F<sub>1</sub></var> and <var>F<sub>2</sub></var>).
The only difference is that,
with regards to the content of <a data-link-type="dfn" href="#fragmentainer">fragmentainer</a> <var>F</var>,
the type of break
between the two pieces <var>F<sub>1</sub></var> and <var>F<sub>2</sub></var>
is the <a href="#break-types">type of break</a> created
by the <a data-link-type="dfn" href="#fragmentation-context">fragmentation context</a> that split <var>F</var>,
not the type of break normally created by <var>F</var>’s own <a data-link-type="dfn" href="#fragmentation-context">fragmentation context</a>.
</p>
<div class="example" id="example-336a11b1"><a class="self-link" href="#example-336a11b1"></a>
For example, if a region box is broken at a page boundary,
then the content of the region will be affected by a page break at that point
(but not by a region break).
</div>
<div class="note" role="note">
Note that when a multi-column element breaks across pages,
it generates a new row of columns on the next page for the rest of its content,
so that a page break within a multi-column element
is always both a page break and a column break.
</div>
<h2 class="heading settled" data-level="3" id="breaking-controls"><span class="secno">3. </span><span class="content">
Controlling Breaks</span><a class="self-link" href="#breaking-controls"></a></h2>
<p>
The following sections explain how breaks are controlled in a <a data-link-type="dfn" href="#fragmented-flow">fragmented flow</a>.
A page/column/region break opportunity between two boxes
is under the influence of
the containing block’s <a class="property" data-link-type="propdesc" href="#propdef-break-inside">break-inside</a> property,
the <a class="property" data-link-type="propdesc" href="#propdef-break-after">break-after</a> property of the preceding element,
and the <a class="property" data-link-type="propdesc" href="#propdef-break-before">break-before</a> property of the following element.
A page/column/region break opportunity between line boxes
is under the influence of
the containing block’s <a class="property" data-link-type="propdesc" href="#propdef-break-inside">break-inside</a>, <a class="property" data-link-type="propdesc" href="#propdef-widows">widows</a>, and <a class="property" data-link-type="propdesc" href="#propdef-orphans">orphans</a> properties.
A fragmentation break can be
allowed, forced, or discouraged depending on the values of these properties.
A forced break overrides any break restrictions acting at that break point.
In the case of forced page breaks, the author can also specify
on which page (<a href="http://www.w3.org/TR/css3-page/#left-right-first">left or right</a>)
the subsequent content should resume.
</p>
<p>
See the section on <a href="#breaking-rules">rules for breaking</a>
for the exact rules on how these properties affect fragmentation.
</p>
<h3 class="heading settled" data-level="3.1" id="break-between"><span class="secno">3.1. </span><span class="content">
Breaks Between Boxes: the <a class="property" data-link-type="propdesc" href="#propdef-break-before">break-before</a> and <a class="property" data-link-type="propdesc" href="#propdef-break-after">break-after</a> properties</span><a class="self-link" href="#break-between"></a></h3>
<table class="propdef">
<tbody>
<tr>
<th>Name:
<td><dfn class="css" data-dfn-type="property" data-export="" id="propdef-break-before">break-before<a class="self-link" href="#propdef-break-before"></a></dfn>, <dfn class="css" data-dfn-type="property" data-export="" id="propdef-break-after">break-after<a class="self-link" href="#propdef-break-after"></a></dfn>
<tr>
<th>Value:
<td>auto | avoid | always | any |
avoid-page | page | left | right | recto | verso |
avoid-column | column | avoid-region | region
<tr>
<th>Initial:
<td>auto
<tr>
<th>Applies to:
<td>block-level elements, table row groups, table rows (but see prose)
<tr>
<th>Inherited:
<td>no
<tr>
<th>Percentages:
<td>N/A
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>specified value
</table>
<p>
These properties specify page/column/region break behavior
before/after the generated box.
The <dfn data-dfn-type="dfn" data-noexport="" id="forced-break-values">forced break values<a class="self-link" href="#forced-break-values"></a></dfn>
<a class="css" data-link-type="maybe" href="#valdef-break-before-always">always</a>, <a class="css" data-link-type="maybe" href="#valdef-break-before-any">any</a>, <a class="css" data-link-type="maybe" href="#valdef-break-before-left">left</a>, <a class="css" data-link-type="maybe" href="#valdef-break-before-right">right</a>, <a class="css" data-link-type="maybe" href="#valdef-break-before-recto">recto</a>, <a class="css" data-link-type="maybe" href="#valdef-break-before-verso">verso</a>, <a class="css" data-link-type="maybe" href="#valdef-break-before-page">page</a>, <a class="css" data-link-type="maybe" href="#valdef-break-before-column">column</a> and <a class="css" data-link-type="maybe" href="#valdef-break-before-region">region</a>
create a <a href="#forced-breaks">forced break</a> in the flow
while the <dfn data-dfn-type="dfn" data-noexport="" id="avoid-break-values">avoid break values<a class="self-link" href="#avoid-break-values"></a></dfn>
<a class="css" data-link-type="maybe" href="#valdef-break-before-avoid">avoid</a>, <a class="css" data-link-type="maybe" href="#valdef-break-before-avoid-page">avoid-page</a>, <a class="css" data-link-type="maybe" href="#valdef-break-before-avoid-column">avoid-column</a> and <a class="css" data-link-type="maybe" href="#valdef-break-before-avoid-region">avoid-region</a>
indicate that content should be kept together.
</p>
<p>
Since breaks are only allowed between siblings,
not between a box and its container (see <a href="#possible-breaks">Possible Break Points</a>),
a <a class="property" data-link-type="propdesc" href="#propdef-break-before">break-before</a> value on a first-child box is propagated to its container.
Likewise a <a class="property" data-link-type="propdesc" href="#propdef-break-after">break-after</a> value on a last-child box is propagated to its container.
(Conflicting values <a href="#forced-breaks">combine</a> as defined below.)
This propagation stops before it breaks through the nearest matching fragmentation context.
</p>
<p>
Values for <a class="property" data-link-type="propdesc" href="#propdef-break-before">break-before</a> and <a class="property" data-link-type="propdesc" href="#propdef-break-after">break-after</a> are defined in the sub-sections below.
User Agents must apply these properties to boxes in the normal flow of the <a data-link-type="dfn" href="#fragmentation-root">fragmentation root</a>.
User agents should also apply these properties to floated boxes
whose containing block is in the normal flow of the root fragmented element.
User agents may also apply these properties to other boxes.
</p>
<h4 class="no-num heading settled" id="generic-break-values"><span class="content">
Generic Break Values</span><a class="self-link" href="#generic-break-values"></a></h4>
<p>
These values have an effect regardless of
the type of fragmented context containing the flow.
</p>
<dl>
<dt><dfn class="css" data-dfn-for="break-before,break-after" data-dfn-type="value" data-export="" id="valdef-break-before-auto">auto<a class="self-link" href="#valdef-break-before-auto"></a></dfn>
<dd>
Neither force nor forbid a break before/after the <a href="http://www.w3.org/TR/CSS21/visuren.html#block-boxes">principal box</a>.
<dt><dfn class="css" data-dfn-for="break-before,break-after" data-dfn-type="value" data-export="" id="valdef-break-before-avoid">avoid<a class="self-link" href="#valdef-break-before-avoid"></a></dfn>
<dd>
Avoid a break before/after the <a href="http://www.w3.org/TR/CSS21/visuren.html#block-boxes">principal box</a>.
<dt><dfn class="css" data-dfn-for="break-before,break-after" data-dfn-type="value" data-export="" id="valdef-break-before-always">always<a class="self-link" href="#valdef-break-before-always"></a></dfn>
<dd>
Always force a break
(of all possible types, through all fragmentation contexts)
before/after the <a href="http://www.w3.org/TR/CSS21/visuren.html#block-boxes">principal box</a>.
<dt><dfn class="css" data-dfn-for="break-before,break-after" data-dfn-type="value" data-export="" id="valdef-break-before-any">any<a class="self-link" href="#valdef-break-before-any"></a></dfn>
<dd>
Force a break of any type, whichever is the type of the deepest fragmentation context,
before/after the <a href="http://www.w3.org/TR/CSS21/visuren.html#block-boxes">principal box</a>.
</dl>
<h4 class="no-num heading settled" id="page-break-values"><span class="content">
Page Break Values</span><a class="self-link" href="#page-break-values"></a></h4>
<p>
These values only have an effect in paginated contexts;
if the flow is not paginated, they have no effect.
</p>
<dl>
<dt><dfn class="css" data-dfn-for="break-before,break-after" data-dfn-type="value" data-export="" id="valdef-break-before-avoid-page">avoid-page<a class="self-link" href="#valdef-break-before-avoid-page"></a></dfn>
<dd>
Avoid a page break before/after the <a href="http://www.w3.org/TR/CSS21/visuren.html#block-boxes">principal box</a>.
<dt><dfn class="css" data-dfn-for="break-before,break-after" data-dfn-type="value" data-export="" id="valdef-break-before-page">page<a class="self-link" href="#valdef-break-before-page"></a></dfn>
<dd>
Always force a page break before/after the <a href="http://www.w3.org/TR/CSS21/visuren.html#block-boxes">principal box</a>.
<dt><dfn class="css" data-dfn-for="break-before,break-after" data-dfn-type="value" data-export="" id="valdef-break-before-left">left<a class="self-link" href="#valdef-break-before-left"></a></dfn>
<dd>
Force one or two page breaks before/after the <a href="http://www.w3.org/TR/CSS21/visuren.html#block-boxes">principal box</a> so that the next page is formatted as a left page.
<dt><dfn class="css" data-dfn-for="break-before,break-after" data-dfn-type="value" data-export="" id="valdef-break-before-right">right<a class="self-link" href="#valdef-break-before-right"></a></dfn>
<dd>
Force one or two page breaks before/after the <a href="http://www.w3.org/TR/CSS21/visuren.html#block-boxes">principal box</a> so that the next page is formatted as a right page.
<dt><dfn class="css" data-dfn-for="break-before,break-after" data-dfn-type="value" data-export="" id="valdef-break-before-recto">recto<a class="self-link" href="#valdef-break-before-recto"></a></dfn>
<dd>
Force one or two page breaks before/after the <a href="http://www.w3.org/TR/CSS21/visuren.html#block-boxes">principal box</a> so that
the next page is formatted as either a left page or a right page,
whichever is second (according to the <a data-link-type="dfn" href="http://dev.w3.org/csswg/css-page-3/#page-progression">page progression</a>) in a page spread.
<dt><dfn class="css" data-dfn-for="break-before,break-after" data-dfn-type="value" data-export="" id="valdef-break-before-verso">verso<a class="self-link" href="#valdef-break-before-verso"></a></dfn>
<dd>
Force one or two page breaks before/after the <a href="http://www.w3.org/TR/CSS21/visuren.html#block-boxes">principal box</a> so that
the next page is formatted as either a left page or a right page,
whichever is first (according to the <a data-link-type="dfn" href="http://dev.w3.org/csswg/css-page-3/#page-progression">page progression</a>) in a page spread.
</dl>
<h4 class="no-num heading settled" id="column-break-values"><span class="content">
Column Break Values</span><a class="self-link" href="#column-break-values"></a></h4>
<p>
These values only have an effect in multi-column contexts;
if the flow is not within a multi-column context, they have no effect.
</p>
<dl>
<dt><dfn class="css" data-dfn-for="break-before,break-after" data-dfn-type="value" data-export="" id="valdef-break-before-avoid-column">avoid-column<a class="self-link" href="#valdef-break-before-avoid-column"></a></dfn>
<dd>
Avoid a column break before/after the <a href="http://www.w3.org/TR/CSS21/visuren.html#block-boxes">principal box</a>.
<dt><dfn class="css" data-dfn-for="break-before,break-after" data-dfn-type="value" data-export="" id="valdef-break-before-column">column<a class="self-link" href="#valdef-break-before-column"></a></dfn>
<dd>
Always force a column break before/after the <a href="http://www.w3.org/TR/CSS21/visuren.html#block-boxes">principal box</a>.
</dl>
<h4 class="no-num heading settled" id="region-break-values"><span class="content">
Region Break Values</span><a class="self-link" href="#region-break-values"></a></h4>
<p>
These values only have an effect in multi-region contexts;
if the flow is not linked across multiple regions, these values have no effect.
</p>
<dl>
<dt><dfn class="css" data-dfn-for="break-before,break-after" data-dfn-type="value" data-export="" id="valdef-break-before-avoid-region">avoid-region<a class="self-link" href="#valdef-break-before-avoid-region"></a></dfn>
<dd>
Avoid a region break before/after the <a href="http://www.w3.org/TR/CSS21/visuren.html#block-boxes">principal box</a>.
<dt><dfn class="css" data-dfn-for="break-before,break-after" data-dfn-type="value" data-export="" id="valdef-break-before-region">region<a class="self-link" href="#valdef-break-before-region"></a></dfn>
<dd>
Always force a region break before/after the <a href="http://www.w3.org/TR/CSS21/visuren.html#block-boxes">principal box</a>.
</dl>
<h3 class="heading settled" data-level="3.2" id="break-within"><span class="secno">3.2. </span><span class="content">
Breaks Within Boxes: the <a class="property" data-link-type="propdesc" href="#propdef-break-inside">break-inside</a> property</span><a class="self-link" href="#break-within"></a></h3>
<table class="propdef">
<tbody>
<tr>
<th>Name:
<td><dfn class="css" data-dfn-type="property" data-export="" id="propdef-break-inside">break-inside<a class="self-link" href="#propdef-break-inside"></a></dfn>
<tr>
<th>Value:
<td>auto | avoid | avoid-page | avoid-column | avoid-region
<tr>
<th>Initial:
<td>auto
<tr>
<th>Applies to:
<td>elements in the normal flow that establish formatting contexts,
or that are block containers, table row groups, or table rows
<tr>
<th>Inherited:
<td>no
<tr>
<th>Percentages:
<td>N/A
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>specified value
</table>
<p>
This property specifies page/column/region break behavior
within the element’s principal box.
Values have the following meanings:
</p>
<dl>
<dt><dfn class="css" data-dfn-for="break-inside,page-break-inside" data-dfn-type="value" data-export="" id="valdef-break-inside-auto">auto<a class="self-link" href="#valdef-break-inside-auto"></a></dfn>
<dd>
Impose no additional breaking constraints within the box.
<dt><dfn class="css" data-dfn-for="break-inside,page-break-inside" data-dfn-type="value" data-export="" id="valdef-break-inside-avoid">avoid<a class="self-link" href="#valdef-break-inside-avoid"></a></dfn>
<dd>
Avoid breaks within the box.
<dt><dfn class="css" data-dfn-for="break-inside,page-break-inside" data-dfn-type="value" data-export="" id="valdef-break-inside-avoid-page">avoid-page<a class="self-link" href="#valdef-break-inside-avoid-page"></a></dfn>
<dd>
Avoid a page break within the box.
<dt><dfn class="css" data-dfn-for="break-inside,page-break-inside" data-dfn-type="value" data-export="" id="valdef-break-inside-avoid-column">avoid-column<a class="self-link" href="#valdef-break-inside-avoid-column"></a></dfn>
<dd>
Avoid a column break within the box.
<dt><dfn class="css" data-dfn-for="break-inside,page-break-inside" data-dfn-type="value" data-export="" id="valdef-break-inside-avoid-region">avoid-region<a class="self-link" href="#valdef-break-inside-avoid-region"></a></dfn>
<dd>
Avoid a region break within the box.
</dl>
<h3 class="heading settled" data-level="3.3" id="widows-orphans"><span class="secno">3.3. </span><span class="content">
Breaks Between Lines: <a class="property" data-link-type="propdesc" href="#propdef-orphans">orphans</a>, <a class="property" data-link-type="propdesc" href="#propdef-widows">widows</a></span><a class="self-link" href="#widows-orphans"></a></h3>
<table class="propdef">
<tbody>
<tr>
<th>Name:
<td><dfn class="css" data-dfn-type="property" data-export="" id="propdef-orphans">orphans<a class="self-link" href="#propdef-orphans"></a></dfn>, <dfn class="css" data-dfn-type="property" data-export="" id="propdef-widows">widows<a class="self-link" href="#propdef-widows"></a></dfn>
<tr>
<th>Value:
<td><integer>
<tr>
<th>Initial:
<td>2
<tr>
<th>Applies to:
<td>block containers
<tr>
<th>Inherited:
<td>yes
<tr>
<th>Percentages:
<td>N/A
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>specified value
</table>
<p>
The <a class="property" data-link-type="propdesc" href="#propdef-orphans">orphans</a> property specifies the minimum number
of line boxes in a block container
that must be left in a <a data-link-type="dfn" href="#fragment">fragment</a> <em>before</em> a fragmentation break.
The <a class="property" data-link-type="propdesc" href="#propdef-widows">widows</a> property specifies the minimum number
of line boxes of a block container
that must be left in a <a data-link-type="dfn" href="#fragment">fragment</a> <em>after</em> a break.
Examples of how they are used to control fragmentation breaks are given
<a href="#widows-orphans-example">below</a>.
</p>
<p>
Only positive integers are allowed as values of <a class="property" data-link-type="propdesc" href="#propdef-orphans">orphans</a> and <a class="property" data-link-type="propdesc" href="#propdef-widows">widows</a>.
Negative values and zero are invalid and must cause the declaration to be
<a href="http://www.w3.org/TR/CSS21/conform.html#ignore">ignored</a>.
</p>
<p>
If a block contains fewer lines than the value of <a class="property" data-link-type="propdesc" href="#propdef-widows">widows</a> or <a class="property" data-link-type="propdesc" href="#propdef-orphans">orphans</a>,
the rule simply becomes that all lines in the block must be kept together.
</p>
<h3 class="heading settled" data-level="3.4" id="page-break-properties"><span class="secno">3.4. </span><span class="content">
Page Break Aliases: the <a class="property" data-link-type="propdesc" href="http://dev.w3.org/csswg/css2/page.html#propdef-page-break-before">page-break-before</a>, <a class="property" data-link-type="propdesc" href="http://dev.w3.org/csswg/css2/page.html#propdef-page-break-after">page-break-after</a>, and <a class="property" data-link-type="propdesc" href="http://dev.w3.org/csswg/css2/page.html#propdef-page-break-inside">page-break-inside</a> properties</span><a class="self-link" href="#page-break-properties"></a></h3>
<p>For compatibility with <a href="http://www.w3.org/TR/CSS21/page.html">CSS Level 2</a>,