-
Notifications
You must be signed in to change notification settings - Fork 708
/
Copy pathOverview.html
2025 lines (1614 loc) · 74.1 KB
/
Overview.html
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 Overflow Module Level 3</title>
<!--
<link href="http://purl.org/dc/terms/" rel="schema.dcterms">
<link href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright" rel="dcterms.rights">
-->
<meta content="CSS Overflow Module Level 3" name=dcterms.title>
<meta content=text name=dcterms.type>
<meta content=2015-01-27 name=dcterms.date>
<meta content="L. David Baron" name=dcterms.creator>
<meta content=W3C name=dcterms.publisher>
<meta content="http://dev.w3.org/csswg/css-overflow-3/"
name=dcterms.identifier>
<link href="#contents" rel=contents>
<link href="#index" rel=index>
<link href="../default.css" rel=stylesheet type="text/css">
<link href="http://www.w3.org/StyleSheets/TR/W3C-ED.css" rel=stylesheet
type="text/css">
<style>
table.source-demo-pair {
width: 100%;
}
.in-cards-demo {
width: 13em;
height: 8em;
padding: 4px;
border: medium solid blue;
margin: 6px;
font: medium/1.3 Times New Roman, Times, serif;
white-space: nowrap;
}
.bouncy-columns-demo {
width: 6em;
height: 10em;
float: left;
margin: 1em;
font: medium/1.25 Times New Roman, Times, serif;
white-space: nowrap;
}
.bouncy-columns-demo.one {
background: aqua; color: black;
transform: rotate(-3deg);
}
.bouncy-columns-demo.two {
background: yellow; color: black;
transform: rotate(3deg);
}
.article-font-inherit-demo {
font: 1em/1.25 Times New Roman, Times, serif;
white-space: nowrap;
}
.article-font-inherit-demo.one {
width: 12em;
font-size: 1.5em;
margin-bottom: 1em;
height: 4em;
}
.article-font-inherit-demo.two {
width: 11em;
margin-left: 5em;
margin-right: 2em;
}
.dark-columns-demo {
width: 6em;
height: 10em;
float: left;
margin-right: 1em;
font: medium/1.25 Times New Roman, Times, serif;
white-space: nowrap;
}
.dark-columns-demo.one {
background: aqua; color: black;
}
.dark-columns-demo.one :link {
color: blue;
}
.dark-columns-demo.one :visited {
color: purple;
}
.dark-columns-demo.two {
background: navy; color: white;
}
.dark-columns-demo.two :link {
color: aqua;
}
.dark-columns-demo.two :visited {
color: fuchsia;
}
.article-max-lines-demo {
font: 1em/1.25 Times New Roman, Times, serif;
white-space: nowrap;
}
.article-max-lines-demo.one::first-letter {
font-size: 2em;
line-height: 0.9;
}
.article-max-lines-demo.one {
font-size: 1.5em;
width: 16em;
}
.article-max-lines-demo.two {
width: 11.5em;
float: left; margin-right: 1em;
}
.article-max-lines-demo.three {
width: 11.5em;
float: left;
}
</style>
<body>
<div class=head> <!--begin-logo-->
<p><a href="http://www.w3.org/"><img alt=W3C height=48
src="http://www.w3.org/Icons/w3c_home" width=72></a> <!--end-logo-->
<h1>CSS Overflow Module Level 3</h1>
<h2 class="no-num no-toc">Editor's Draft 27 January 2015</h2>
<dl>
<dt>This version:
<dd><a
href="http://dev.w3.org/csswg/css-overflow-3/">http://dev.w3.org/csswg/css-overflow-3/</a>
<dt>Latest version:
<dd><a
href="http://www.w3.org/TR/css-overflow-3/">http://www.w3.org/TR/css-overflow-3/</a>
<dt>Editor's draft:
<dd><a
href="http://dev.w3.org/csswg/css-overflow-3/">http://dev.w3.org/csswg/css-overflow-3/</a>
(<a
href="https://dvcs.w3.org/hg/csswg/log/tip/css-overflow/Overview.src.html">change
log</a>, <a
href="https://dvcs.w3.org/hg/csswg/log/tip/css3-overflow/Overview.src.html">older
change log</a>)
<dt>Previous version:
<dd><a
href="http://www.w3.org/TR/2013/WD-css-overflow-3-20130418/">http://www.w3.org/TR/2013/WD-css-overflow-3-20130418/</a>
<dt>Editors:
<dd class="h-card vcard"> <a class="p-name fn u-url url"
href="http://dbaron.org/" rel=author>L. David Baron</a>, <a
class="p-org org" href="http://www.mozilla.org/">Mozilla</a>
<dt>Issue Tracking:
<dd>Maintained in document (only editor's draft is current)
<dt>Feedback:
<dd><a
href="mailto:www-style@w3.org?subject=%5Bcss-overflow%5D%20feedback">www-style@w3.org</a>
with subject line “<kbd>[css-overflow] <var>… message topic
…</var></kbd>” (<a
href="http://lists.w3.org/Archives/Public/www-style/"
rel=discussion>archives</a>)
<dt>Test suite:
<dd>none yet
</dl>
<!--begin-copyright-->
<p class=copyright><a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
rel=license>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>), All Rights Reserved. W3C <a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
<a
href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a>
and <a
href="http://www.w3.org/Consortium/Legal/copyright-documents">document
use</a> rules apply.</p>
<!--end-copyright-->
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc" id=abstract>Abstract</h2>
<p> <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. This module contains the features of CSS
relating to new mechanisms of overflow handling in visual media (e.g.,
screen or paper). In interactive media, it describes features that allow
the overflow from a fixed size container to be handled by pagination
(displaying one page at a time). It also describes features, applying to
all visual media, that allow the contents of an element to be spread
across multiple fragments, allowing the contents to flow across multiple
regions or to have different styles for different fragments.
<h2 class="no-num no-toc" id=status>Status of this document</h2>
<!--begin-status-->
<p>This is a public copy of the editors' draft. It is provided for
discussion only and may change at any moment. Its publication here does
not imply endorsement of its contents by W3C. Don't cite this document
other than as work in progress.
<p>The (<a
href="http://lists.w3.org/Archives/Public/www-style/">archived</a>) public
mailing list <a
href="mailto:www-style@w3.org?Subject=%5Bcss-overflow-3%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-overflow-3” in the subject, preferably like this:
“[<!---->css-overflow-3<!---->] <em>…summary of comment…</em>”
<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>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>
<!--end-status-->
<p>The following features are at risk: …
<h2 class="no-num no-toc" id=contents> Table of contents</h2>
<!--begin-toc-->
<ul class=toc>
<li><a href="#intro"><span class=secno>1. </span> Introduction</a>
<li><a href="#overflow-concepts"><span class=secno>2. </span>Types of
overflow</a>
<ul class=toc>
<li><a href="#ink-overflow"><span class=secno>2.1. </span>Ink
overflow</a>
<li><a href="#scrollable-overflow"><span class=secno>2.2.
</span>Scrollable overflow</a>
<li><a href="#border-box-overflow"><span class=secno>2.3. </span>Border
box overflow</a>
</ul>
<li><a href="#overflow-properties"><span class=secno>3. </span>Overflow
properties</a>
<li><a href="#scrolling-overflow"><span class=secno>4. </span>Scrolling
and hidden overflow</a>
<li><a href="#paginated-overflow"><span class=secno>5. </span>Paginated
overflow</a>
<li><a href="#fragment-overflow"><span class=secno>6. </span>Fragment
overflow</a>
<ul class=toc>
<li><a href="#fragment-styling"><span class=secno>6.1. </span>Fragment
styling</a>
<ul class=toc>
<li><a href="#fragment-pseudo-element"><span class=secno>6.1.1.
</span>The ::nth-fragment() pseudo-element</a>
<li><a href="#style-of-fragments"><span class=secno>6.1.2.
</span>Styling of fragments</a>
<li><a href="#style-in-fragments"><span class=secno>6.1.3.
</span>Styling inside fragments</a>
</ul>
<li><a href="#max-lines"><span class=secno>6.2. </span>The ‘<code
class=property>max-lines</code>’ property</a>
</ul>
<li><a href="#static-media"><span class=secno>7. </span>Overflow in static
media</a>
<li><a href="#conformance"><span class=secno>8. </span> Conformance</a>
<ul class=toc>
<li><a href="#placement"><span class=secno>8.1. </span> Module
interactions</a>
<li><a href="#values"><span class=secno>8.2. </span> Values</a>
<li><a href="#conventions"><span class=secno>8.3. </span> Document
conventions</a>
<li><a href="#conformance-classes"><span class=secno>8.4. </span>
Conformance classes</a>
<li><a href="#partial"><span class=secno>8.5. </span> Partial
implementations</a>
<li><a href="#experimental"><span class=secno>8.6. </span> Experimental
implementations</a>
<li><a href="#testing"><span class=secno>8.7. </span> Non-experimental
implementations</a>
<li><a href="#cr-exit-criteria"><span class=secno>8.8. </span> CR exit
criteria</a>
</ul>
<li class=no-num><a href="#acknowledgments"> Acknowledgments</a>
<li class=no-num><a href="#references"> References</a>
<ul class=toc>
<li class=no-num><a href="#normative-references"> Normative
references</a>
<li class=no-num><a href="#other-references"> Other references</a>
</ul>
<li class=no-num><a href="#index"> Index</a>
<li class=no-num><a href="#property-index"> Property index</a>
</ul>
<!--end-toc-->
<h2 id=intro><span class=secno>1. </span> Introduction</h2>
<p> In CSS Level 1 <a href="#ref-CSS1">[CSS1]<!--{{CSS1}}--></a>, placing
more content than would fit inside an element with a specified size was
generally an authoring error. Doing so caused the content to extend
outside the bounds of the element, which would likely cause that content
to overlap with other elements.
<p> CSS Level 2 <a href="#ref-CSS21">[CSS21]<!--{{CSS21}}--></a> introduced
the ‘<a href="#overflow0"><code class=property>overflow</code></a>’
property, which allows authors to have overflow be handled by scrolling,
which means it is no longer an authoring error. It also allows authors to
specify that overflow is handled by clipping, which makes sense when the
author's intent is that the content not be shown.
<p> However, scrolling is not the only way to present large amounts of
content, and may even not be the optimal way. After all, the codex
replaced the scroll as the common format for large written works because
of its advantages.
<p> This specification introduces a mechanism for Web pages to specify that
an element of a page should handle overflow through pagination rather than
through scrolling.
<p> This specification also extends the concept of overflow in another
direction. Instead of requiring that authors specify a single area into
which the content of an element must flow, this specification allows
authors to specify multiple fragments, each with their own dimensions and
styles, so that the content of the element can flow from one to the next,
using as many as needed to place the content without overflowing.
<p> In both of these cases, implementations must break the content in the
block-progression dimension. Implementations must do this is described in
the CSS Fragmentation Module <a
href="#ref-CSS3-BREAK">[CSS3-BREAK]<!--{{!CSS3-BREAK}}--></a>.
<h2 id=overflow-concepts><span class=secno>2. </span>Types of overflow</h2>
<p> CSS uses the term <dfn id=overflow>overflow</dfn> to describe the
contents of a box that extend outside that one of that box's edges (i.e.,
its <i>content edge</i>, <i>padding edge</i>, <i>border edge</i>, or
<i>margin edge</i>). The overflow might be described as the elements or
features that cause this overflow, the non-rectangular region occupied by
these features, or, more commonly, as the minimal rectangle that bounds
that region. A box's overflow is computed based on the boxes and styles of
the box and of all its descendants whose containing block chain <span
class=issue>undefined term?</span> includes the box.
<p> In most cases, any of these types of overflow can be computed for any
box from the bounds and properties of that box, and from the overflow (of
that type) of each of its children. However, this is not always the case;
for example, when ‘<code class=css>transform-style:
preserve-3d</code>’ <a
href="#ref-CSS3-TRANSFORMS">[CSS3-TRANSFORMS]<!--{{CSS3-TRANSFORMS}}--></a>
is used on some of the children, their descendants with ‘<code
class=css>transform-style: preserve-3d</code>’ must also be examined.
<h3 id=ink-overflow><span class=secno>2.1. </span>Ink overflow</h3>
<p> The <dfn id=ink-overflow0>ink overflow</dfn> of a box is the part of
that box and its contents that creates a visual effect outside of the
box's border box.
<p> Since some effects in CSS (for example, the blurs in ‘<code
class=property>text-shadow</code>’ <a
href="#ref-CSS-TEXT-3">[CSS-TEXT-3]<!--{{CSS-TEXT-3}}--></a> and ‘<code
class=property>box-shadow</code>’ <a
href="#ref-CSS3BG">[CSS3BG]<!--{{CSS3BG}}--></a>) do not define what
visual extent they cover, the extent of the <a
href="#ink-overflow0"><i>ink overflow</i></a> is undefined.
<p class=issue> Should we try to define it at all and just leave pieces
undefined?
<p> The <dfn id=ink-overflow-region>ink overflow region</dfn> is the
non-rectangular region occupied by the <a href="#ink-overflow0"><i>ink
overflow</i></a>, and the <dfn id=ink-overflow-rectangle>ink overflow
rectangle</dfn> is the minimal rectangle whose axis is aligned to the
box's axes and contains the <a href="#ink-overflow-region"><i>ink overflow
region</i></a>. Note that the <a href="#ink-overflow-rectangle"><i>ink
overflow rectangle</i></a> is a rectangle in the box's coordinate system,
but might be non-rectangular in other coordinate systems due to transforms
<a
href="#ref-CSS3-TRANSFORMS">[CSS3-TRANSFORMS]<!--{{CSS3-TRANSFORMS}}--></a>.
<h3 id=scrollable-overflow><span class=secno>2.2. </span>Scrollable
overflow</h3>
<p> The <dfn id=scrollable-overflow0>scrollable overflow</dfn> of a box is
the set of things extending outside of that box's padding edge for which a
scrolling mechanism needs to be provided.
<p class=issue> The following definition should be rewritten to use the
concept of <a
href="http://dev.w3.org/csswg/css-transforms/#3d-rendering-context">3D
rendering context</a> <a
href="#ref-CSS3-TRANSFORMS">[CSS3-TRANSFORMS]<!--{{!CSS3-TRANSFORMS}}--></a>
and related terms, particularly once those concepts stabilize following
changes proposed in the CSS WG meeting on the morning of 2014-01-28.
<p> Given the following definitions <span class=issue>which belong in <a
href="#ref-CSS3-TRANSFORMS">[CSS3-TRANSFORMS]<!--{{CSS3-TRANSFORMS}}--></a></span>:
<dl>
<dt><dfn id=d-preserving-child>3d-preserving child</dfn>
<dd> A child box B of a containing block C is a 3d-preserving child if it
has ‘<code class=css>transform-style: preserve-3d</code>’ and the
user-agent is not required to flatten it based on the <a
href="http://www.w3.org/TR/css3-transforms/#transform-style-property">requirements</a>
in <a
href="#ref-CSS3-TRANSFORMS">[CSS3-TRANSFORMS]<!--{{!CSS3-TRANSFORMS}}--></a>.
<dt><dfn id=non-3d-preserving-child>non-3d-preserving child</dfn>
<dd> A child C of a box P is a non-3d-preserving-child if it is not a <a
href="#d-preserving-child"><i>3d-preserving child</i></a>.
<dt><dfn id=d-preserving-descendant>3d-preserving descendant</dfn>
<dd> Box D is a 3d-preserving descendant of box A if A is an ancestor of
D, and D and all of the boxes (if any) in the containing block chain from
D to A are <a href="#d-preserving-child"><i>3d-preserving child</i></a>
boxes.
</dl>
<p>The scrollable overflow of a box is the union of the following things,
all adjusted for transforms <span class=issue>undefined concept!</span>
into the box's coordinate space:
<ul>
<li> for the box and all of its <a
href="#d-preserving-descendant"><i>3d-preserving descendant</i></a>
boxes:
<ul>
<li>the box's own padding edge (for the box itself) or border edge (for
<a href="#d-preserving-descendant"><i>3d-preserving descendant</i></a>
boxes)
<li>the bounds <span class=issue>undefined term!</span> of any text
directly in the box
<li><span class=issue>MORE HERE!</span>
</ul>
<li> for all the <a href="#non-3d-preserving-child"><i>non-3d-preserving
child</i></a> boxes of the box and its <a
href="#d-preserving-descendant"><i>3d-preserving descendant</i></a>
boxes, the scrollable overflow of the box
</ul>
<p class=issue> I wrote this definition off the top of my head, so it can't
possibly be right. It's missing tons of pieces!
<p class=issue> The handling of preserve-3d subtrees here is probably
wrong; the elements should probably count only towards the overflow of the
element that flattens them.
<p> The <dfn id=scrollable-overflow-region>scrollable overflow region</dfn>
is the non-rectangular region occupied by the <a
href="#scrollable-overflow0"><i>scrollable overflow</i></a>, and the <dfn
id=scrollable-overflow-rectangle>scrollable overflow rectangle</dfn> is
the minimal rectangle whose axis is aligned to the box's axes and contains
the <a href="#scrollable-overflow-region"><i>scrollable overflow
region</i></a>. Note that the <a
href="#scrollable-overflow-rectangle"><i>scrollable overflow
rectangle</i></a> is a rectangle in the box's coordinate system, but might
be non-rectangular in other coordinate systems due to transforms <a
href="#ref-CSS3-TRANSFORMS">[CSS3-TRANSFORMS]<!--{{CSS3-TRANSFORMS}}--></a>.
<h3 id=border-box-overflow><span class=secno>2.3. </span>Border box
overflow</h3>
<p class=issue> This concept has been proposed for some uses, such as for
determining what the ‘<code class=property>outline</code>’ property
goes around, and as the basis of a coordinate system for specifying clips
and masks, but it's not clear if it's needed.
<p> The <dfn id=border-box-overflow0>border-box overflow</dfn> of a box is
the union of the box's border edge and the border edges of the box's
descendants.
<p class=issue> If needed, define more formally, as for scrollable overflow
above. (Maybe even share the definitions in an appropriate way!)
<p> The <dfn id=border-box-overflow-region>border-box overflow region</dfn>
is the non-rectangular region occupied by the <a
href="#border-box-overflow0"><i>border-box overflow</i></a>, and the <dfn
id=border-box-overflow-rectangle>border-box overflow rectangle</dfn> is
the minimal rectangle whose axis is aligned to the box's axes and contains
the <a href="#border-box-overflow-region"><i>border-box overflow
region</i></a>. Note that the <a
href="#border-box-overflow-rectangle"><i>border-box overflow
rectangle</i></a> is a rectangle in the box's coordinate system, but might
be non-rectangular in other coordinate systems due to transforms <a
href="#ref-CSS3-TRANSFORMS">[CSS3-TRANSFORMS]<!--{{CSS3-TRANSFORMS}}--></a>.
<h2 id=overflow-properties><span class=secno>3. </span>Overflow properties</h2>
<p> The ‘<a href="#overflow-x"><code class=css>overflow-x</code></a>’
property specifies the handling of overflow in the horizontal direction
(i.e., overflow from the left and right sides of the box), and the ‘<a
href="#overflow-y"><code class=css>overflow-y</code></a>’ property
specifies the handling of overflow in the vertical direction (i.e.,
overflow from the top and bottom sides of the box)
<table class=propdef>
<tbody>
<tr>
<th>Name:
<td><dfn id=overflow-x>overflow-x</dfn>, <dfn
id=overflow-y>overflow-y</dfn>
<tr>
<th><a href="#values">Value</a>:
<td>visible | hidden | scroll | auto | paged-x | paged-y |
paged-x-controls | paged-y-controls | fragments
<tr>
<th>Initial:
<td>visible
<tr>
<th>Applies to:
<td>block containers <a href="#ref-CSS21">[CSS21]<!--{{!CSS21}}--></a>,
flex containers <a
href="#ref-CSS3-FLEXBOX">[CSS3-FLEXBOX]<!--{{!CSS3-FLEXBOX}}--></a>,
and grid containers <a
href="#ref-CSS-GRID-1">[CSS-GRID-1]<!--{{!CSS-GRID-1}}--></a>
<tr>
<th>Inherited:
<td>no
<tr>
<th>Percentages:
<td>N/A
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>see below
<tr>
<th>Animatable:
<td>no
<tr>
<th>Canonical order:
<td><abbr title="follows order of property value definition">per
grammar</abbr>
</table>
<p> The ‘<a href="#overflow0"><code class=property>overflow</code></a>’
property is a shorthand property that sets the specified values of both
‘<a href="#overflow-x"><code class=property>overflow-x</code></a>’ and
‘<a href="#overflow-y"><code class=property>overflow-y</code></a>’ to
the value specified for ‘<a href="#overflow0"><code
class=property>overflow</code></a>’.
<table class=propdef>
<tbody>
<tr>
<th>Name:
<td><dfn id=overflow0>overflow</dfn>
<tr>
<th><a href="#values">Value</a>:
<td>visible | hidden | scroll | auto | paged-x | paged-y |
paged-x-controls | paged-y-controls | fragments
<tr>
<th>Initial:
<td>see individual properties
<tr>
<th>Applies to:
<td>block containers <a href="#ref-CSS21">[CSS21]<!--{{!CSS21}}--></a>,
flex containers <a
href="#ref-CSS3-FLEXBOX">[CSS3-FLEXBOX]<!--{{!CSS3-FLEXBOX}}--></a>,
and grid containers <a
href="#ref-CSS-GRID-1">[CSS-GRID-1]<!--{{!CSS-GRID-1}}--></a>
<tr>
<th>Inherited:
<td>no
<tr>
<th>Percentages:
<td>N/A
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>see individual properties
<tr>
<th>Animatable:
<td>no
<tr>
<th>Canonical order:
<td><abbr title="follows order of property value definition">per
grammar</abbr>
</table>
<p>The values of these properties are:
<dl>
<dt><dfn id=visible>visible</dfn>
<dd> There is no special handling of overflow, that is, it may be rendered
outside the block container.
<dt><dfn id=hidden>hidden</dfn>
<dt><dfn id=scroll>scroll</dfn>
<dt><dfn id=auto>auto</dfn>
<dd> These values are collectively the <dfn id=scrolling-values>scrolling
values</dfn>; they are defined in the section on <a
href="#scrolling-overflow">scrolling and hidden overflow</a>.
<dt><dfn id=paged-x>paged-x</dfn>
<dt><dfn id=paged-y>paged-y</dfn>
<dt><dfn id=paged-x-controls>paged-x-controls</dfn>
<dt><dfn id=paged-y-controls>paged-y-controls</dfn>
<dt><dfn id=fragments>fragments</dfn>
<dd> These values are collectively the <dfn
id=fragmenting-values>fragmenting values</dfn>; they are defined in the
sections on <a href="#paginated-overflow">paginated overflow</a> and <a
href="#fragment-overflow">fragment overflow</a>.
</dl>
<div id=overflow-computed-values>
<p>The computed values of ‘<a href="#overflow-x"><code
class=property>overflow-x</code></a>’ and ‘<a
href="#overflow-y"><code class=property>overflow-y</code></a>’ are
determined from the cascaded values <a
href="#ref-CSS3CASCADE">[CSS3CASCADE]<!--{{!CSS3CASCADE}}--></a> based on
the following rules:
<ol>
<li> If one or both of the cascaded values are <a
href="#fragmenting-values"><i>fragmenting values</i></a>, then:
<ol>
<li> If one of the cascaded values is one of the <a
href="#fragmenting-values"><i>fragmenting values</i></a> and the other
is not, then the computed values are the same as the cascaded values.
<li> If both of the cascaded values are <a
href="#fragmenting-values"><i>fragmenting values</i></a>, then:
<ol>
<li> for horizontal writing mode <a
href="#ref-CSS-WRITING-MODES-3">[CSS-WRITING-MODES-3]<!--{{!CSS-WRITING-MODES-3}}--></a>,
the computed value for ‘<a href="#overflow-y"><code
class=css>overflow-y</code></a>’ is the cascaded value and the
computed value for ‘<a href="#overflow-x"><code
class=css>overflow-x</code></a>’ is ‘<a href="#hidden"><code
class=css>hidden</code></a>’, or
<li> for vertical writing mode <a
href="#ref-CSS-WRITING-MODES-3">[CSS-WRITING-MODES-3]<!--{{!CSS-WRITING-MODES-3}}--></a>,
the computed value for ‘<a href="#overflow-x"><code
class=css>overflow-x</code></a>’ is the cascaded value and the
computed value for ‘<a href="#overflow-y"><code
class=css>overflow-y</code></a>’ is ‘<a href="#hidden"><code
class=css>hidden</code></a>’.
</ol>
</ol>
<li> Otherwise, if one cascaded values is one of the <a
href="#scrolling-values"><i>scrolling values</i></a> and the other is
‘<a href="#visible"><code class=css>visible</code></a>’, then
computed values are the cascaded values with ‘<a href="#visible"><code
class=css>visible</code></a>’ changed to ‘<a href="#auto"><code
class=css>auto</code></a>’.
<li> Otherwise, the computed values are as specified.
</ol>
</div>
<p class=issue> Are all 4 of the ‘<code class=css>paged-*</code>’
values really needed?
<p> When the <a href="#fragmenting-values"><i>fragmenting values</i></a>
are used, the overflow from the fragments themselves treats the
fragmenting value as ‘<a href="#hidden"><code
class=css>hidden</code></a>’. <span class=issue>Is this the right
behavior?</span> <span class=issue>Give example.</span>
<p class=issue> <a
href="#ref-CSS3-MARQUEE">[CSS3-MARQUEE]<!--{{CSS3-MARQUEE}}--></a>
describes an ‘<code class=property>overflow-style</code>’ property,
but it has not picked up implementation experience that the working group
is aware of. Should this document treat ‘<code
class=property>overflow-style</code>’ as a defunct proposal, or should
this document describe the ‘<code
class=property>overflow-style</code>’ property and attempt to revive it,
despite that implementations have implemented ‘<a
href="#overflow-x"><code class=property>overflow-x</code></a>’ and ‘<a
href="#overflow-y"><code class=property>overflow-y</code></a>’ instead?
<p class=issue> There are <a
href="http://lists.w3.org/Archives/Public/www-style/2012May/1197.html">discussions</a>
about how overflow, overflow-style, overflow-x and overflow-y should work
and interact with each other. Until consensus on this topic is reached, it
is not completely clear which of these should be used for paged-x |
paged-y | paged-x-controls | paged-y-controls | fragments
<h2 id=scrolling-overflow><span class=secno>4. </span>Scrolling and hidden
overflow</h2>
<p class=issue> Move material from <a
href="#ref-CSS21">[CSS21]<!--{{CSS21}}--></a> and <a
href="#ref-CSS3BOX">[CSS3BOX]<!--{{CSS3BOX}}--></a> here.
<p class=issue> Explain which directions allow scrolling and which don't,
as a function of ‘<code class=property>direction</code>’ (including
propagation of ‘<code class=property>direction</code>’ to the ICB).
<h2 id=paginated-overflow><span class=secno>5. </span>Paginated overflow</h2>
<p class=issue>overflow:paginate or overflow:pages (or paged-x, paged-y,
paged-x-controls, paged-y-controls as <a
href="#ref-CSS3GCPM">[CSS3GCPM]<!--{{CSS3GCPM}}--></a> has?)
<p class=issue>Ability to display N pages at once rather than just one page
at once?
<p class=issue> The current implementation of paginated overflow uses the
‘<a href="#overflow0"><code class=property>overflow</code></a>’/‘<a
href="#overflow-x"><code class=property>overflow-x</code></a>’/‘<a
href="#overflow-y"><code class=property>overflow-y</code></a>’
properties rather than the ‘<code
class=property>overflow-style</code>’ property as proposed in the <a
href="#ref-CSS3GCPM">[CSS3GCPM]<!--{{CSS3GCPM}}--></a> draft (which also
matches the <a
href="#ref-CSS3-MARQUEE">[CSS3-MARQUEE]<!--{{CSS3-MARQUEE}}--></a>
proposal). We should probably switch away from ‘<code
class=property>overflow-style</code>’, but that's not 100% clear.
<h2 id=fragment-overflow><span class=secno>6. </span>Fragment overflow</h2>
<p> This section introduces and defines the meaning of the new ‘<a
href="#fragments"><code class=css>fragments</code></a>’ value of the
‘<a href="#overflow0"><code class=property>overflow</code></a>’
property.
<p> When the computed value of ‘<a href="#overflow0"><code
class=property>overflow</code></a>’ for an element is ‘<a
href="#fragments"><code class=css>fragments</code></a>’, and
implementations would otherwise have created a box for the element, then
implementations must create a sequence of <dfn id=fragment-box>fragment
box</dfn>es for that element. (It is possible for an element with ‘<code
class=css>overflow: fragments</code>’ to generate only one <a
href="#fragment-box"><i>fragment box</i></a>. However, if an element's
computed ‘<a href="#overflow0"><code
class=property>overflow</code></a>’ is not ‘<a href="#fragments"><code
class=css>fragments</code></a>’, then its box is not a <a
href="#fragment-box"><i>fragment box</i></a>.) Every <a
href="#fragment-box"><i>fragment box</i></a> is a fragmentation container,
and any overflow that would cause that fragmentation container to fragment
causes another <a href="#fragment-box"><i>fragment box</i></a> created as
a next sibling of the previous one. <span class=issue>Or is it as though
it's a next sibling of the element? Need to figure out exactly how this
interacts with other box-level fixup.</span> Additionally, if the <a
href="#fragment-box"><i>fragment box</i></a> is also a multi-column box
(as defined in <a href="#ref-CSS3COL">[CSS3COL]<!--{{!CSS3COL}}--></a>
<span class=issue>though it defines <i>multi-column element</i></span>)
any content that would lead to the creation of <i>overflow columns</i> <a
href="#ref-CSS3COL">[CSS3COL]<!--{{!CSS3COL}}--></a> instead is flown into
an additional fragment box. However, fragment boxes may themselves be
broken (due to fragmentation in a fragmentation context outside of them,
such as pages, columns, or other fragment boxes); such breaking leads to
fragments of the same fragment box rather than multiple fragment boxes.
(This matters because fragment boxes may be styled by their index; such
breaking leads to multiple fragments of a fragment box with a single
index. This design choice is so that breaking a fragment box across pages
does not break the association of indices to particular pieces of
content.) <span class=issue>Should a forced break that breaks to an outer
fragmentation context cause a new fragment of a single fragment box or a
new fragment box?</span> <span class=issue>Should we find a term other
than <a href="#fragment-box"><i>fragment box</i></a> here to make this a
little less confusing?</span>
<p class=issue> What if we want to be able to style the pieces of an
element split within another type of fragmentation context? These rules
prevent ever using ‘<code class=css>::nth-fragment()</code>’ for that,
despite that the name seems the most logical name for such a feature.
<div class=example>
<table class=source-demo-pair>
<tbody>
<tr>
<td>
<pre><!DOCTYPE HTML>
<title>Breaking content into
equal-sized cards</title>
<style>
.in-cards {
overflow: fragments;
width: 13em;
height: 8em;
padding: 4px;
border: medium solid blue;
margin: 6px;
font: medium/1.3 Times New
Roman, Times, serif;
}
</style>
<div class="in-cards">
In this example, the text in the div
is broken into a series of cards.
These cards all have the same style.
The presence of enough content to
overflow one of the cards causes
another one to be created. The second
card is created just like it's the
next sibling of the first.
</div></pre>
<td>
<div class=in-cards-demo>In this example, the text in the<br>
div is broken into a series of<br>
cards. These cards all have the<br>
same style. The presence of<br>
enough content to overflow<br>
one of the cards causes another</div>
<div class=in-cards-demo>one to be created. The second<br>
card is created just like it's the<br>
next sibling of the first.</div>
</table>
</div>
<p class=issue> We should specify that ‘<code class=css>overflow:
fragments</code>’ does not apply to at least some table parts, and
perhaps other elements as well. We need to determine exactly which ones.
<p class=issue> This specification needs to say which type of fragmentation
context is created so that it's clear which values of the ‘<code
class=css>break-*</code>’ properties cause breaks within this context.
We probably want ‘<code class=css>break-*: region</code>’ to apply.
<p class=issue> This specification needs a processing model that will apply
in cases where the layout containing the fragments has characteristics
that use the intrinsic size of the fragments to change the amount of space
available for them, such as <a
href="#ref-CSS-GRID-1">[CSS-GRID-1]<!--{{CSS-GRID-1}}--></a>. There has
already been some work on such a processing model in <a
href="#ref-CSS-REGIONS-1">[CSS-REGIONS-1]<!--{{CSS-REGIONS-1}}--></a>, and
the work done on a model there, and the editors of that specification,
should inform what happens in this specification.
<h3 id=fragment-styling><span class=secno>6.1. </span>Fragment styling</h3>
<h4 id=fragment-pseudo-element><span class=secno>6.1.1. </span>The
::nth-fragment() pseudo-element</h4>
<p> The ::nth-fragment() pseudo-element is a pseudo-element that describes
some of the <a href="#fragment-box"><i>fragment box</i></a>es generated by
an element. The argument to the pseudo-element takes the same syntax as
the argument to the :nth-child() pseudo-class defined in <a
href="#ref-SELECT">[SELECT]<!--{{!SELECT}}--></a>, and has the same
meaning except that the number is relative to <a
href="#fragment-box"><i>fragment box</i></a>es generated by the element
instead of siblings of the element.
<p class=note> Selectors that allow addressing fragments by counting from
the end rather than the start are intentionally not provided. Such
selectors would interfere with determining the number of fragments.
<p class=issue> Depending on future discussions, this ‘<code
class=css>::nth-fragment(<var>an+b</var>)</code>’ syntax may be replaced
with the new ‘<code class=css>::fragment:nth(<var>an+b</var>)</code>’
syntax.
<h4 id=style-of-fragments><span class=secno>6.1.2. </span>Styling of
fragments</h4>
<p class=issue> Should this apply to fragment overflow only, or also to
paginated overflow? (If it applies, then stricter property restrictions
would be needed for paginated overflow.)
<p> In the absence of rules with ‘<code
class=css>::nth-fragment()</code>’ pseudo-elements, the computed style
for each <a href="#fragment-box"><i>fragment box</i></a> is the computed
style for the element for which the <a href="#fragment-box"><i>fragment
box</i></a> was created. However, the style for a <a
href="#fragment-box"><i>fragment box</i></a> is also influenced by rules
whose selector's <i>subject</i> <a
href="#ref-SELECT">[SELECT]<!--{{!SELECT}}--></a> has an ‘<code
class=css>::nth-fragment()</code>’ pseudo-element, if the 1-based number
of the <a href="#fragment-box"><i>fragment box</i></a> matches that
‘<code class=css>::nth-fragment()</code>’ pseudo-element and the
selector (excluding the ‘<code class=css>::nth-fragment()</code>’
pseudo-element) matches the element generating the fragments.
<p> When determining the style of the <a href="#fragment-box"><i>fragment
box</i></a>, these rules that match the fragment pseudo-element cascade
together with the rules that match the element, with the fragment
pseudo-element adding the specificity of a pseudo-class to the specificity
calculation. <span class=issue>Does this need to be specified in the
cascading module as well?</span>
<div class=example>
<table class=source-demo-pair>
<tbody>
<tr>
<td>
<pre><!DOCTYPE HTML>
<style>
.bouncy-columns {
overflow: fragments;
width: 6em;
height: 10em;
float: left;
margin: 1em;
font: medium/1.25 Times New