-
Notifications
You must be signed in to change notification settings - Fork 792
Expand file tree
/
Copy pathOverview.html
More file actions
2816 lines (2095 loc) · 78.4 KB
/
Overview.html
File metadata and controls
2816 lines (2095 loc) · 78.4 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 PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html lang=en>
<head profile="http://dublincore.org/documents/2008/08/04/dc-html/ ">
<title>CSS Multi-column Layout Module</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 Multi-column Layout Module" name=dcterms.title>
<meta content=text name=dcterms.type>
<meta content=2013-02-07 name=dcterms.issued>
<meta content="Håkon Wium Lie" name=dcterms.creator>
<meta content=W3C name=dcterms.publisher>
<meta content="http://www.w3.org/TR/2013/ED-css3-multicol-20130207/"
name=dcterms.identifier>
<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 type="text/css">
.cols { width: 500px; height: 200px; background: #fff; position: relative; border: solid 5px blue; margin: 0.5em 2em 1em 0; font: bold 14px/19px Arial, sans-serif }
.cols p { padding: 3px; margin: 0 }
.col { position: absolute; left: 0px; top: 0; z-index: 6; width: 170px }
.gap { position: absolute; background: green; width: 5px; bottom: 0px; top: 0px; border: 10px solid yellow; border-top-width: 0; border-bottom-width: 0; }
.rep { position: absolute; top: 45px; background: black; height: 110px; width: 100px; color: white; z-index: 4 }
table.breaks { border-collapse: collapse; margin: 1em 0 }
table.breaks td, table.breaks th { border: thin solid black; padding: 0.1em 0.2em }
div.example:before { width: 9em }
</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 Multi-column Layout Module</h1>
<h2 class="no-num no-toc" id=w3c-working>Editor's Draft 7 February 2013</h2>
<dl>
<dt>This version:
<dd>
<!--<a href="http://www.w3.org/TR/2013/CR-css3-multicol-20130207">http://www.w3.org/TR/2013/ED-css3-multicol-20130207/</a>-->
<a
href="http://dev.w3.org/csswg/css3-multicol/">http://dev.w3.org/csswg/css3-multicol/</a>
<dt>Latest version:
<dd><a href="http://www.w3.org/TR/css3-multicol">
http://www.w3.org/TR/css3-multicol</a>
<dt>Previous version:
<dd><a
href="http://www.w3.org/TR/2009/CR-css3-multicol-20091217/">http://www.w3.org/TR/2009/CR-css3-multicol-20091217/</a>
<dt>Feedback:</dt>
<dd><a href="mailto:www-style@w3.org?subject=%5Bcss-multicol%5D%20feedback"
>www-style@w3.org</a>
with subject line “<kbd>[css-multicol]
<var>… message topic …</var></kbd>”
(<a rel="discussion" href="http://lists.w3.org/Archives/Public/www-style/"
>archives</a>)
<dt>Editors:
<dd>Håkon Wium Lie, Opera Software, howcome@opera.com
</dl>
<!--begin-copyright-->
<p class=copyright><a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
rel=license>Copyright</a> © 2013 <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>This specification describes multi-column layouts in CSS, a style sheet
language for the web. Using functionality described in the specification,
content can be flowed into multiple columns with a gap and a rule between
them.
<h2 class="no-num no-toc" id=status-of-this-document>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=%5Bcss3-multicol%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
“css3-multicol” in the subject, preferably like this:
“[<!---->css3-multicol<!---->] <em>…summary of comment…</em>”
<p>This document was produced by the <a href="/Style/CSS/members">CSS
Working Group</a> (part of the <a href="/Style/">Style Activity</a>).
<p>This document was produced by a group operating under the <a
href="/Consortium/Patent-Policy-20040205/">5 February 2004 W3C Patent
Policy</a>. W3C maintains a <a href="/2004/01/pp-impl/32061/status"
rel=disclosure>public list of any patent disclosures</a> made in
connection with the deliverables of the group; that page also includes
instructions for disclosing a patent. An individual who has actual
knowledge of a patent which the individual believes contains <a
href="/Consortium/Patent-Policy-20040205/#def-essential">Essential
Claim(s)</a> must disclose the information in accordance with <a
href="/Consortium/Patent-Policy-20040205/#sec-Disclosure">section 6 of the
W3C Patent Policy</a>.</p>
<!--end-status-->
<p>This document has been a Working Draft in the CSS Working Group for
several years. Multi-column layouts are traditionally used in print. On
screen, multi-column layouts have been considered experimental, and
implementation and use experience was deemed necessary in order to
proceed. Several implementations have occurred over the past years, and
this specification incorporates useful feedback from implementors as well
as authors and users.
<p>The specification was updated in April 2011 to correct a contradiction
between the text and the pseudo-algorithm in section 3.4. The
pseudo-algorithm was corrected and also made easier to read. The wording
of a few other sections was improved in places, without changes to the
functionality. In January, 2012, some examples and the description of the
‘<a href="#column-fill"><code class=property>column-fill</code></a>’
property was revised.
<p>This document will remain Candidate Recommendation at least until 12 May
2011. See the <a href="#cr-exit-criteria">CR exit criteria.</a>
<h2 class="no-num no-toc" id=table-of-contents><a name=contents>Table of
contents</a></h2>
<!--begin-toc-->
<ul class=toc>
<li><a href="#introduction"><span class=secno>1. </span>Introduction</a>
<li><a href="#the-multi-column-model"><span class=secno>2. </span>The
multi-column model</a>
<li><a href="#the-number-and-width-of-columns"><span class=secno>3.
</span>The number and width of columns</a>
<ul class=toc>
<li><a href="#cw"><span class=secno>3.1. </span>‘<code
class=property>column-width</code>’</a>
<li><a href="#cc"><span class=secno>3.2. </span>‘<code
class=property>column-count</code>’</a>
<li><a href="#columns"><span class=secno>3.3. </span>‘<code
class=property>columns</code>’</a>
<li><a href="#pseudo-algorithm"><span class=secno>3.4.
</span>Pseudo-algorithm</a>
<li><a href="#stacking-context"><span class=secno>3.5. </span>Stacking
context</a>
</ul>
<li><a href="#column-gaps-and-rules"><span class=secno>4. </span>Column
gaps and rules</a>
<ul class=toc>
<li><a href="#column-gap"><span class=secno>4.1. </span>‘<code
class=property>column-gap</code>’</a>
<li><a href="#crc"><span class=secno>4.2. </span>‘<code
class=property>column-rule-color</code>’</a>
<li><a href="#crs"><span class=secno>4.3. </span>‘<code
class=property>column-rule-style</code>’</a>
<li><a href="#crw"><span class=secno>4.4. </span>‘<code
class=property>column-rule-width</code>’</a>
<li><a href="#column-rule"><span class=secno>4.5. </span>‘<code
class=property>column-rule</code>’</a>
</ul>
<li><a href="#column-breaks"><span class=secno>5. </span>Column breaks</a>
<ul class=toc>
<li><a href="#break-before-break-after-break-inside"><span
class=secno>5.1. </span>‘<code class=property>break-before</code>’,
‘<code class=property>break-after</code>’, ‘<code
class=property>break-inside</code>’</a>
</ul>
<li><a href="#spanning-columns"><span class=secno>6. </span>Spanning
columns</a>
<ul class=toc>
<li><a href="#column-span"><span class=secno>6.1. </span>‘<code
class=property>column-span</code>’</a>
</ul>
<li><a href="#filling-columns"><span class=secno>7. </span>Filling
columns</a>
<ul class=toc>
<li><a href="#cf"><span class=secno>7.1. </span>‘<code
class=property>column-fill</code>’</a>
</ul>
<li><a href="#overflow"><span class=secno>8. </span>Overflow</a>
<ul class=toc>
<li><a href="#overflow-inside-multicol-elements"><span class=secno>8.1.
</span>Overflow inside multicol elements</a>
<li><a href="#pagination-and-overflow-outside-multicol"><span
class=secno>8.2. </span>Pagination and overflow outside multicol
elements</a>
</ul>
<li><a href="#conformance"><span class=secno>9. </span>Conformance</a>
<ul class=toc>
<li><a href="#cr-exit-criteria"><span class=secno>9.1. </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=introduction><span class=secno>1. </span>Introduction</h2>
<p>(This section is not normative.)
<p>This module describes multi-column layout in CSS. By using functionality
described in this document, style sheets can declare that the content of
an element is to be laid out in multiple columns.
<p>On the Web, tables have also been used to describe multi-column layouts.
The main benefit of using CSS-based columns is flexibility; content can
flow from one column to another, and the number of columns can vary
depending on the size of the viewport. Removing presentation table markup
from documents allows them to more easily be presented on various output
devices including speech synthesizers and small mobile devices.
<p>Multi-column layouts are easy to describe in CSS. Here is a simple
example:
<div class=example>
<pre>body { column-width: 12em }</pre>
<p>In this example, the <code class=html>body</code> element is set to
have columns at least ‘<code class=css>12em</code>’ wide. The exact
number of columns will depend on the available space.
</div>
<p>The number of columns can also be set explicitly in the style sheet:
<div class=example>
<pre>body { column-count: 2 }</pre>
<p>In this case, the number of columns is fixed and the column widths will
vary depending on the available width.
</div>
<p>The shorthand ‘<a href="#columns0"><code
class=property>columns</code></a>’ property can be used to set either,
or both, properties in one declaration.
<div class=example>
<p>In these examples, the number of columns, the width of columns, and
both the number and width are set, respectively:
<pre>
body { columns: 2 }
body { columns: 12em }
body { columns: 2 12em }
</pre>
<p>However, as described below, setting both the width and number of
columns rarely makes sense.
</div>
<p>Another group of properties introduced in this module describe gaps and
rules between columns.
<div class=example>
<pre>
body {
column-gap: 1em;
column-rule: thin solid black;
}
</pre>
<p>The first declaration in the example above sets the gap between two
adjacent columns to be 1em. Column gaps are similar to padding areas. In
the middle of the gap there will be a rule which is described by the
‘<a href="#column-rule0"><code class=property>column-rule</code></a>’
property.
</div>
<p>The values of the ‘<a href="#column-rule0"><code
class=property>column-rule</code></a>’ property are similar to those of
the CSS border properties. Like ‘<code class=property>border</code>’,
‘<a href="#column-rule0"><code class=property>column-rule</code></a>’
is a shorthand property.
<div class=example>
<p>In this example, the shorthand ‘<a href="#column-rule0"><code
class=property>column-rule</code></a>’ declaration from the above
example has been expanded:
<pre>
body {
column-gap: 1em;
column-rule-width: thin;
column-rule-style: solid;
column-rule-color: black;
}
</pre>
</div>
<p>The ‘<a href="#column-fill"><code
class=property>column-fill</code></a>’ and ‘<a
href="#column-span0"><code class=property>column-span</code></a>’
properties give style sheets a wider range of visual expressions in
multi-column layouts.
<div class=example>
<p>In this example, columns are set to be balanced, i.e., to have
approximately the same length. Also, <code>h2</code> elements are set to
span across all columns.
<pre>
div { column-fill: balance }
h2 { column-span: all }
</pre>
</div>
<p>This specification introduces ten new properties, all of which are used
in the examples above.
<p>To indicate where column breaks should (or should not) appear, new
keyword values are introduced.
<div class=example>
<p>In this example, <code>h1</code> elements will always have a column
break before them, but the formatter will try to avoid column breaks
inside and after the element.
<pre>
h1 {
break-before: column;
break-inside: avoid-column;
break-after: avoid-column;
}
</pre>
<!--<p>The properties and values used in this example are formally defined in [!CSS3PAGE]].--></div>
<p>If all column properties have their initial value, the layout of an
element will be identical to a multi-column layout with only one column.
<h2 id=the-multi-column-model><span class=secno>2. </span>The multi-column
model</h2>
<p>A <dfn id=multi-column-element>multi-column element</dfn> (or
<em>multicol element</em> for short) is an element whose ‘<a
href="#column-width"><code class=property>column-width</code></a>’ or
‘<a href="#column-count"><code class=property>column-count</code></a>’
property is not ‘<code class=css>auto</code>’ and therefore acts as a
container for multi-column layout.
<p>In the traditional CSS box model, the content of an element is flowed
into the content box of the corresponding element. Multi-column layout
introduces a new type of container between the content box and the
content, namely the <dfn id=column-box>column box</dfn> (or
<em>column</em> for short). The content of a multicol element is flowed
into its column boxes.
<p>Column boxes in a multi-column element are arranged into <em>rows</em>.
Like table cells, the column boxes in a row are ordered in the inline
direction of the multicol element. The <em>column width</em> is the length
of the column box in the inline direction. The <em>column height</em> is
the length of the column box in the block direction. All column boxes in a
row have the same column width, and all column boxes in a row have the
same column height. Within each row in the multi-column element, adjacent
column boxes are separated by a <em>column gap</em>, which may contain a
<em>column rule</em>. All column gaps in the same row are equal. All
column rules in the same row are also equal, if they appear; column rules
only appear between columns that both have content.
<p>In the simplest case a multicol element will contain only one row of
columns, and the height of each column will be equivalent to the used
height of the multi-column element's content box. If the multi-column
element is paginated, the height of each row is constrained by the page
and the content continues in a new row of column boxes on the next page; a
column box never splits across pages. The same effect occurs when a <a
href="#spanning-element"><em>spanning element</em></a> divides the
multi-column element: the columns before the spanning element are balanced
and shortened to fit their content. Content after the spanning element
then flows into a new row of column boxes.
<p>It is not possible to set properties/values on column boxes. For
example, the background of a certain column box cannot be set and a column
box has no concept of padding, margin or borders.
<p class=note>Future specifications may add additional functionality. For
example, columns of different widths and different backgrounds may be
supported.
<div class=example>
<p>Column gaps (yellow) and column rules (green) are shown in this sample
rendition of a multi-column element with padding (blue). The blue and
yellow is present for illustrational purposes only. In actual
implementations these areas will be determined by the background.
<div class=cols>
<div class=col style="">
<p> Ab cde fgh i jkl. Mno<br>
pqr stu vw xyz. A bc<br>
def g hij klm nopqrs<br>
tuv wxy z. Abc de fg<br>
hi jklmno. Pqrstu vw<br>
x yz. Abc def ghi jkl.<br>
M nop qrst uv wx yz.<br>
Ab cde fgh i jkl. Mno<br>
pqr stu vw xyz. A bc<br>
def g hij klm nopqrs
</div>
<div class=col style="left: 175px">
<p> tuv wxy z. Abc de fg<br>
hi jklmno. Pqrstu vw<br>
x yz. Abc def ghi jkl.<br>
M nop qrst uv wx yz.<br>
Ab cde fgh i jkl. Mno<br>
pqr stu vw xyz. A bc<br>
def g hij klm nopqrs<br>
tuv wxy z. Abc de fg<br>
hi jklmno. Pqrstu vw<br>
x yz. Abc def ghi jkl.<br>
</div>
<div class=col style="left: 350px">
<p> M nop qrst uv wx yz.<br>
Ab cde fgh i jkl. Mno<br>
pqr stu vw xyz. A bc<br>
def g hij klm nopqrs<br>
tuv wxy z. Abc de fg<br>
hi jklmno. Pqrstu vw<br>
x yz. Abc def ghi jkl.<br>
M nop qrst uv wx yz.<br>
Ab cde fgh i jkl. Mno<br>
Pqr stu vw xyz.
</div>
<div class=gap style="left: 150px"></div>
<div class=gap style="left: 325px"></div>
</div>
<p>To illustrate the effects of the various properties described in this
specification, variations on a sample document will be used. Here is the
source code of the sample document:
<pre class=html>
<html>
<style type="text/css">
div {
column-width: 15em;
column-gap: 2em; /* shown in yellow */
column-rule: 4px solid green;
padding: 5px; /* shown in blue */
}
p { margin: 0; padding: 0 }
img { display: none }
</style>
<body>
<div>
<p>Ab cde fgh i jkl. Mno
pqr stu vw xyz. A bc
<img src=...>
def g hij
...
</div>
</body>
</html>
</pre>
<p>The nonsensical text in the example is the English alphabet which shows
how text flows from one column to another. To simplify the visualization,
the textual content of the different examples vary slightly.
</div>
<p>Column boxes are block container boxes. That is, column boxes behave
like block-level, table cell, and inline-block boxes as per CSS 2.1,
section 10.1, item 2 <a href="#CSS21"
rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>. However, column boxes do not
establish block container boxes for elements with ‘<code
class=css>position: fixed</code>’ or ‘<code class=css>position:
absolute</code>’.
<div class=example>
<p>In this example, the width of the image is set with these rules:
<pre class=css>
img { display: block; width: 100% }
</pre>
<p>Given that the width is calculated relative to the column box, the
image will be as wide as the column box:
<div class=cols>
<p>Ab cde fgh i jkl. Mno<br>
pqr stu vw xyz. A bc<br>
<br>
<br>
<br>
<br>
<br>
<br>
def g hij klm nopqrs<br>
tuv wxy z. Abc de fg<br>
<div class=col style="left: 175px">
<p>hi jklmno. Pqrstu vw<br>
x yz. Abc def ghi jkl.<br>
M nop qrst uv wx yz.<br>
Ab cde fgh i jkl. Mno<br>
pqr stu vw xyz. A bc<br>
def g hij klm nopqrs<br>
tuv wxy z. Abc de fg<br>
hi jklmno. Pqrstu vw<br>
x yz. Abc def ghi jkl.<br>
M nop qrst uv wx yz.<br>
</div>
<div class=col style="left: 350px">
<p> Ab cde fgh i jkl. Mno<br>
pqr stu vw xyz. A bc<br>
def g hij klm nopqrs<br>
tuv wxy z. Abc de fg<br>
hi jklmno. Pqrstu vw<br>
x yz. Abc def ghi jkl.<br>
M nop qrst uv wx yz.<br>
Ab cde fgh i jkl. Mno<br>
pqr stu vw xyz.
</div>
<div class=rep style="width: 150px"></div>
<div class=gap style="left: 150px"></div>
<div class=gap style="left: 325px"></div>
</div>
</div>
<p>Floats that appear inside multi-column layouts are positioned with
regard to the column box where the float appears.
<div class=example>
<p>In this example, this CSS fragment describes the presentation of the
image:
<pre class=css>
img { display: block; float: right }
</pre>
<div class=cols>
<div class=col style="">
<p> Ab cde fgh i jkl. Mno<br>
pqr stu vw xyz. A bc<br>
def g<br>
hij klm<br>
nopq<br>
rs tuv<br>
wxy x<br>
yz. Ab <br>
cde fgh i jkl. Mno<br>
pqr stu vw xyz. A bc
</div>
<div class=col style="left: 175px">
<p> def g hij klm nopqrs<br>
tuv wxy z. Abc de fg<br>
hi jklmno. Pqrstu vw<br>
x yz. Abc def ghi jkl.<br>
M nop qrst uv wx yz.<br>
Ab cde fgh i jkl. Mno<br>
pqr stu vw xyz. A bc<br>
def g hij klm nopqrs<br>
tuv wxy z. Abc de fg<br>
hi jklmno. Pqrstu vw<br>
</div>
<div class=col style="left: 350px">
<p> x yz. Abc def ghi jkl.<br>
M nop qrst uv wx yz.<br>
Ab cde fgh i jkl. Mno<br>
pqr stu vw xyz. A bc<br>
def g hij klm nopqrs<br>
tuv wxy z. Abc de fg<br>
hi jklmno. Pqrstu vw<br>
x yz. Abc def ghi jkl.<br>
M nop qrst uv wx yz.<br>
</div>
<div class=rep style="left: 50px"></div>
<div class=gap style="left: 150px"></div>
<div class=gap style="left: 325px"></div>
</div>
<p>The black box represents the image.
</div>
<p>A multi-column element establishes a new block formatting context, as
per CSS 2.1 section 9.4.1.
<div class=example>
<p>A top margin set on the first child element of a multicol element will
not collapse with the margins of the multicol element.
</div>
<p>Nested multi-column elements are allowed, but there may be
implementation-specific limits.
<h2 id=the-number-and-width-of-columns><span class=secno>3. </span>The
number and width of columns</h2>
<p>Finding the number and width of columns is fundamental when laying out
multi-column content. When the block direction is unconstrained and no
column breaks are added through style sheets, these two properties
determine the outcome:
<ul>
<li>‘<a href="#column-count"><code
class=property>column-count</code></a>’
<li>‘<a href="#column-width"><code
class=property>column-width</code></a>’
</ul>
<p>A third property, ‘<a href="#columns0"><code
class=property>columns</code></a>’, is a shorthand property which sets
both ‘<a href="#column-width"><code
class=property>column-width</code></a>’ and ‘<a
href="#column-count"><code class=property>column-count</code></a>’.
<h3 id=cw><span class=secno>3.1. </span>‘<a href="#column-width"><code
class=property>column-width</code></a>’</h3>
<table class=propdef>
<tbody>
<tr>
<td><em>Name:</em>
<td><dfn id=column-width>column-width</dfn>
<tr>
<td><em>Value:</em>
<td><length> | auto
<tr>
<td><em>Initial:</em>
<td>auto
<tr>
<td><em>Applies to:</em>
<td>non-replaced block-level elements (except table elements), table
cells, and inline-block elements
<tr>
<td><em>Inherited:</em>
<td>no
<tr>
<td><em>Percentages:</em>
<td>N/A
<tr>
<td><em>Media:</em>
<td>visual
<tr>
<td><em>Computed value:</em>
<td>the absolute length, zero or larger
<tr>
<td><em>Animatable:</em>
<td>as <a
href="http://dev.w3.org/csswg/css3-transitions/#animtype-length">length</a>
</table>
<p>This property describes the width of columns in multicol elements.
<dl>
<dt>auto
<dd>means that the column width will be determined by other properties
(e.g., ‘<a href="#column-count"><code
class=property>column-count</code></a>’, if it has a non-auto value).
<dt><length>
<dd>describes the optimal column width. The actual column width may be
wider (to fill the available space), or narrower (only if the available
space is smaller than the specified column width). Specified values must
be greater than 0.
</dl>
<div class=example>
<p>For example, consider this style sheet:
<pre>
div {
width: 100px;
column-width: 45px;
column-gap: 0;
column-rule: none;
}
</pre>
<p>There is room for two 45px wide columns inside the 100px wide element.
In order to fill the available space the actual column width will be
increased to 50px.
</div>
<div class=example>
<p>Also, consider this style sheet:
<pre>
div {
width: 40px;
column-width: 45px;
column-gap: 0;
column-rule: none;
}
</pre>
<p>The available space is smaller than the specified column width and the
actual column width will therefore be decreased.
</div>
<p>To ensure that ‘<a href="#column-width"><code
class=property>column-width</code></a>’ can be used with vertical text,
column width means the length of the line boxes inside the columns.
<p class=note>The reason for making ‘<a href="#column-width"><code
class=property>column-width</code></a>’ somewhat flexible is to achieve
scalable designs that can fit many screen sizes. To set an exact column
width, all length values (in horizontal text these are: ‘<code
class=property>width</code>’, ‘<a href="#column-width"><code
class=property>column-width</code></a>’, ‘<a href="#column-gap0"><code
class=property>column-gap</code></a>’, and ‘<a
href="#column-rule-width"><code
class=property>column-rule-width</code></a>’) must be specified.
<h3 id=cc><span class=secno>3.2. </span>‘<a href="#column-count"><code
class=property>column-count</code></a>’</h3>
<table class=propdef>
<tbody>
<tr>
<td><em>Name:</em>
<td><dfn id=column-count>column-count</dfn>
<tr>
<td><em>Value:</em>
<td><integer> | auto
<tr>
<td><em>Initial:</em>
<td>auto
<tr>
<td><em>Applies to:</em>
<td>non-replaced block-level elements (except table elements), table
cells, and inline-block elements
<tr>
<td><em>Inherited:</em>
<td>no
<tr>
<td><em>Percentages:</em>
<td>N/A
<tr>
<td><em>Media:</em>
<td>visual
<tr>
<td><em>Computed value:</em>
<td>specified value
<tr>
<td><em>Animatable:</em>
<td>as <a
href="http://dev.w3.org/csswg/css3-transitions/#animtype-integer">integer</a>
A835
</table>
<p>This property describes the number of columns of a multicol element.
<dl>
<dt>auto
<dd>means that the number of columns will be determined by other
properties (e.g., ‘<a href="#column-width"><code
class=property>column-width</code></a>’, if it has a non-auto value).
<dt><integer>
<dd>describes the optimal number of columns into which the content of the
element will be flowed. Values must be greater than 0. If both ‘<a
href="#column-width"><code class=property>column-width</code></a>’ and
‘<a href="#column-count"><code
class=property>column-count</code></a>’ have non-auto values, the
integer value describes the maximum number of columns.
</dl>
<div class=example>
<p>Example:
<pre>body { column-count: 3 }</pre>
</div>
<h3 id=columns><span class=secno>3.3. </span>‘<a href="#columns0"><code
class=property>columns</code></a>’</h3>
<table class=propdef>
<tbody>
<tr>
<td><em>Name:</em>
<td><dfn id=columns0>columns</dfn>
<tr>
<td><em>Value:</em>
<td><a href="#cw"><‘<code
class=property>column-width</code>’></a> || <a
href="#cc"><‘<code class=property>column-count</code>’></a>
<tr>
<td><em>Initial:</em>
<td>see individual properties
<tr>
<td><em>Applies to:</em>
<td>non-replaced block-level elements (except table elements), table
cells, and inline-block elements
<tr>
<td><em>Inherited:</em>
<td>no
<tr>
<td><em>Percentages:</em>
<td>N/A
<tr>
<td><em>Media:</em>
<td>visual
<tr>
<td><em>Computed value:</em>
<td>see individual properties
<tr>
<td><em>Animatable:</em>
<td>see individual properties
</table>
<p>This is a shorthand property for setting ‘<a
href="#column-width"><code class=property>column-width</code></a>’ and
‘<a href="#column-count"><code
class=property>column-count</code></a>’. Omitted values are set to their
initial values.
<div class=example>
<p>Here are some valid declarations using the ‘<a href="#columns0"><code
class=property>columns</code></a>’ property:
<pre>
columns: 12em; /* column-width: 12em; column-count: auto */
columns: auto 12em; /* column-width: 12em; column-count: auto */
columns: 2; /* column-width: auto; column-count: 2 */
columns: 2 auto; /* column-width: auto; column-count: 2 */
columns: auto; /* column-width: auto; column-count: auto */
columns: auto auto; /* column-width: auto; column-count: auto */
</pre>
</div>
<h3 id=pseudo-algorithm><span class=secno>3.4. </span>Pseudo-algorithm</h3>
<p>The pseudo-algorithm below determines the used values for ‘<a
href="#column-count"><code class=property>column-count</code></a>’ (N)
and ‘<a href="#column-width"><code
class=property>column-width</code></a>’ (W). There are two other
variables in the pseudo-algorithm:
<ul>
<li><code>available-width</code>: if the used width of the multi-column
element has not been determined when the ‘<a href="#column-count"><code
class=property>column-count</code></a>’ and ‘<a
href="#column-width"><code class=property>column-width</code></a>’ must
be determined (e.g., if it is floating with a ‘<code
class=property>width</code>’ of ‘<code class=property>auto</code>’
as per CSS 2.1 section 10.3.5) this variable is <code>unknown</code>,
otherwise it is the same as the used width of the multi-column element.
In vertical text, the used height replaces used width in this
calculation.
<li><code>shrink-to-fit</code>: this variable represents the result of a
<em>shrink-to-fit</em> computation. CSS does not define the exact
algorithm.
</ul>
<p>Two assumptions are being made by the pseudo-algorithm:
<ul>
<li>that the block direction is unconstrained
<li>that no column breaks are added through style sheets
</ul>
<p>The <code>floor()</code> function rounds a number to the next smaller
integer. <!--
<pre>
(01) if ((column-width = auto) and (column-count = auto)) or
(02) ((available-width = unknown) and (column-count = auto)) then
(03) exit; /* no columns */
(04) fi
(05)
(06) if (available-width = unknown) and (column-count != auto) and (column-width != auto) then
(07) N := column-count;
(08) W := column-width;
(09) exit;
(10) fi
(11)
(12) if (available-width = unknown) then
(13) available-width := shrink-to-fit;
(14) fi
(15)
(16) if (column-width = auto) then
(18) N := column-count;
(19) W := max(0, (available-width - ((N - 1) * column-gap))/N);