csswg-drafts/css-template/Overview.html at 97f02b93096dd5ce0ebf596055195157e2f6d952 · xfq/csswg-drafts · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
28
12C0
0
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">

<html lang=en>
 <head
  profile="http://dublincore.org/documents/2008/08/04/dc-html/ http://microformats.org/profile/hcard http://microformats.org/wiki/rel-license">
  <meta content="text/html; charset=utf-8" http-equiv=content-type>
  <title>CSS Grid Template 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 Grid Template Layout Module" name=dcterms.title>
  <meta content=text name=dcterms.type>
  <meta content=2013-05-22 name=dcterms.date>
  <meta content="Bert Bos" name=dcterms.creator>
  <meta content="César Acebal" name=dcterms.creator>
  <meta content=W3C name=dcterms.publisher>
  <meta content="http://dev.w3.org/csswg/css3-layout/"
   name=dcterms.identifier>
  <link href="../default.css" rel=stylesheet type="text/css">
  <style type="text/css">
  /* Just in case an incorrect max-width occurs in default.css */
  body {max-width: none !important}

  .prod { font-family: inherit; font-size: inherit }
  pre.prod { white-space: pre-wrap; margin: 1em 0 1em 2em }
  code { font-size: inherit; }

  .example .visible {border: thin dotted silver}
</style>
  <link href="http://www.w3.org/StyleSheets/TR/W3C-ED.css" rel=stylesheet>

 <body class=h-entry>
  <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 class=p-name>CSS Grid Template Layout Module</h1>

   <h2 class="no-num no-toc" id=longstatus-date-3-august-2004>Editor's Draft
    22 May 2013</h2>

   <dl>
    <dt>This version:

    <dd><a class=u-url
     href="http://dev.w3.org/csswg/css3-layout/">http://dev.w3.org/csswg/css3-layout/</a>

    <dt>Latest version:

    <dd><a
     href="http://www.w3.org/TR/css3-layout/">http://www.w3.org/TR/css3-layout/</a>

    <dt>Previous version:

    <dd><a
     href="http://www.w3.org/TR/2011/WD-css3-layout-20111129/">http://www.w3.org/TR/2011/WD-css3-layout-20111129/</a>

    <dt>Feedback:

    <dd><a
     href="mailto:www-style@w3.org?subject=%5Bcss3-layout%5D%20feedback">www-style@w3.org</a>
     with subject line “[css3-layout] <var>… message topic …</var>”
     (<a href="http://lists.w3.org/Archives/Public/www-style/"
     rel=discussion>archives</a>)

    <dt>Editors:

    <dd class="p-author h-card vcard"><span class="p-name fn">Bert Bos</span>
     (<span class="p-org org h-org">W3C</span>) <a class="u-email email"
     href="mailto:bert@w3.org" rel=author>bert@w3.org</a>

    <dd class="p-author h-card vcard"><span class="p-name fn">César
     Acebal</span> (<span class="p-org org h-org">University of
     Oviedo</span>)
   </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.w
8096
3.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>

  <div class=sidefigure>
   <p><img alt="Image: four elements move to four slots in a template"
    longdesc=diagram.desc src=diagram.png>

   <p class=caption>Above: a typical Web page. Below: the underlying grid
    template.
  </div>

  <p>CSS is a simple, declarative language for creating style sheets that
   specify the rendering of HTML and other structured documents. This module
   defines a typographic grid for CSS. It has features to set up a grid
   template, to flow content into it, and to position overlapping elements on
   a grid.

  <p>The ‘<a href="#grid"><code class=property>grid</code></a>’ property
   sets up a matrix of rows and columns and designates empty areas and areas
   for content (called “slots”). The ‘<a href="#flow0"><code
   class=property>flow</code></a>’ property specifies into which slot an
   element flows. A grid template is like a table in that the various slots
   are aligned in rows and columns and can automatically adapt to each
   other's size, and it is like absolute positioning in that elements can be
   put in arbitrary slots so that the visual order becomes independent of the
   document order.

  <p>The <a href="#slot-pseudo-element.">‘<code
   class=css>::slot()</code>’ pseudo-element</a> allows to style the slots
   (backgrounds, borders, etc.)

  <p>Use ‘<a href="#grid-area"><code class=property>grid-area</code></a>’
   instead of ‘<a href="#flow0"><code class=property>flow</code></a>’ to
   put multiple elements on top of one another in the same slot.

  <p>Grid templates can also be associated with pages in paged media, to
   create page templates.

  <p>Slots can form “chains” to create non-rectangular regions. A chain
   of slots is like a series of pages or columns: content is distributed over
   the slots by breaking it at possible break points (see the ‘<code
   class=css>break-*</code>’ properties from <a href="#CSS3-BREAK"
   rel=biblioentry>[CSS3-BREAK]<!--{{CSS3-BREAK}}--></a>).

  <p>The <a href="#region-based">‘<code class=css>@region</code>’
   rule</a> <a href="#CSS3-REGIONS"
   rel=biblioentry>[CSS3-REGIONS]<!--{{!CSS3-REGIONS}}--></a> allows to
   select (parts of) elements based on whether they fall in a certain slot or
   not, and thus style content differently in different slots (region-based
   styling).
   <!--=================================================================-->

  <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=%5Bcss3-layout%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-layout” in the subject, preferably like this:
   “[<!---->css3-layout<!---->] <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>This draft combines ideas from earlier drafts on Template Layout, Grid
   Positioning <a href="#CSS3GRID"
   rel=biblioentry>[CSS3GRID]<!--{{CSS3GRID}}--></a> and Grid Layout <a
   href="#CSS3-GRID-LAYOUT"
   rel=biblioentry>[CSS3-GRID-LAYOUT]<!--{{CSS3-GRID-LAYOUT}}--></a>.

  <p>Issues on this draft are mentioned in the text itself and/or in the
   on-line Tracker under <a
   href="http://www.w3.org/Style/CSS/Tracker/products/15">“Details on
   Product CSS3 Template Layout.”</a>
   <!--=================================================================-->

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

  <ul class=toc>
   <li><a href="#introduction"><span class=secno>1. </span>Introduction</a>
    <ul class=toc>
     <li><a href="#summary-and-use-cases"><span class=secno>1.1.
      </span>Summary and use cases</a>

     <li><a href="#dependencies"><span class=secno>1.2. </span>Dependencies
      on other modules</a>

     <li><a href="#values"><span class=secno>1.3. </span>Values</a>

     <li><a href="#accessibility"><span class=secno>1.4. </span>A note about
      accessibility</a>
    </ul>

   <li><a href="#declaring-templates"><span class=secno>2. </span>Declaring
    templates</a>
    <ul class=toc>
     <li><a href="#grid-template"><span class=secno>2.1. </span>Declaring a
      template: ‘<code class=property>grid-template</code>’</a>

     <li><a href="#grid-column-sizes"><span class=secno>2.2.
      </span>Specifying the widths of columns: ‘<code
      class=property>grid-columns</code>’</a>

     <li><a href="#grid-row-sizes"><span class=secno>2.3. </span>Specifying
      the height of rows: ‘<code class=property>grid-rows</code>’</a>

     <li><a href="#grid-shorthand"><span class=secno>2.4. </span>The ‘<code
      class=property>grid</code>’ shorthand property</a>

     <li><a href="#default"><span class=secno>2.5. </span>Default slots</a>

     <li><a href="#columns"><span class=secno>2.6. </span>Interaction of
      ‘<code class=property>grid</code>’ and ‘<code
      class=property>columns</code>’</a>

     <li><a href="#slot-sizes"><span class=secno>2.7. </span>Calculating the
      size of the grid</a>
    </ul>

   <li><a href="#positioning"><span class=secno>3. </span>Putting content
    into a grid element</a>
    <ul class=toc>
     <li><a href="#flow"><span class=secno>3.1. </span>Flowing content into
      slots: ‘<code class=property>flow</code>’</a>

     <li><a href="#stacking-elements-on-top-of-a-grid-grid-"><span
      class=secno>3.2. </span>Stacking elements on top of a grid: ‘<code
      class=property>grid-area</code>’ and ‘<code
      class=property>grid-auto</code>’</a>
    </ul>

   <li><a href="#styling-slots"><span class=secno>4. </span>Styling slots</a>

    <ul class=toc>
     <li><a href="#slot-pseudo"><span class=secno>4.1. </span>The ‘<code
      class=css>::slot()</code>’ pseudo-element</a>

     <li><a href="#the-blank-pseudo-element"><span class=secno>4.2.
      </span>The ‘<code class=css>::blank()</code>’ pseudo-element</a>

     <li><a href="#content"><span class=secno>4.3. </span>Slots and the
      ‘<code class=property>content</code>’ property</a>
    </ul>

   <li><a href="#region-based"><span class=secno>5. </span>Styling the
    contents of slots with ‘<code class=css>@region</code>’</a>

   <li><a href="#rendering-of-grid-elements"><span class=secno>6.
    </span>Rendering of grid elements</a>
    <ul class=toc>
     <li><a href="#vertical-alignment"><span class=secno>6.1. </span>Vertical
      alignment of the contents of slots</a>

     <li><a href="#paged"><span class=secno>6.2. </span>Breaking grid
      elements across pages or columns</a>

     <li><a href="#stacking-order"><span class=secno>6.3. </span>Stacking
      order</a>

     <li><a href="#floating-elements-inside-templates"><span class=secno>6.4.
      </span>Floating elements inside templates</a>
    </ul>

   <li><a href="#page-templates"><span class=secno>7. </span>Page-based grid
    templates</a>

   <li><a href="#chains"><span class=secno>8. </span>Chaining slots: the
    ‘<code class=property>chains</code>’ property</a>

   <li><a href="#history"><span class=secno>9. </span>History</a>
    <ul class=toc>
     <li><a href="#developing-a-model-of-declaring-using-st"><span
      class=secno>9.1. </span>Developing a model of declaring, using, styling
      and resizing grids</a>

     <li><a href="#syntax-features-and-levels"><span class=secno>9.2.
      </span>Syntax, features and levels</a>
      <ul class=toc>
       <li><a href="#named-vs-numbered-slots"><span class=secno>9.2.1.
        </span>Named vs numbered slots</a>

       <li><a href="#single-letter-names-vs-identifiers"><span
        class=secno>9.2.2. </span>Single letter names vs identifiers</a>

       <li><a href="#display"><span class=secno>9.2.3. </span>Extend ‘<code
        class=property>display</code>’ or add a grid property</a>

       <li><a href="#combining-columns-and-grids"><span class=secno>9.2.4.
        </span>Combining columns and grids</a>

       <li><a href="#shorthand-vs-single-property"><span class=secno>9.2.5.
        </span>Shorthand vs single property</a>

       <li><a href="#the-number-of-rows-and-columns"><span class=secno>9.2.6.
        </span>The number of rows and columns</a>

       <li><a href="#need-fr"><span class=secno>9.2.7. </span>‘<code
        class=css>*</code>’ vs ‘<code class=css>fr</code>’</a>

       <li><a href="#auto-add"><span class=secno>9.2.8. </span>Automatically
        add rows and columns</a>

       <li><a href="#rectangular-slots-vs-non-rectangular-slo"><span
        class=secno>9.2.9. </span>Rectangular slots vs non-rectangular
        slots</a>

       <li><a href="#chained"><span class=secno>9.2.10. </span>Chained
        slots</a>

       <li><a href="#page-grid"><span class=secno>9.2.11. </span>Page
        grids</a>

       <li><a href="#style-the-slots-pseudo-elements"><span
        class=secno>9.2.12. </span>Style the slots (pseudo-elements)</a>

       <li><a href="#select-after-pseudo"><span class=secno>9.2.13.
        </span>Style the contents of slots (region-based styling)</a>

       <li><a href="#orient-the-grid-with-writing-mode-vs-ori"><span
        class=secno>9.2.14. </span>Orient the grid with writing mode vs
        orient the slots</a>

       <li><a href="#indicating-the-default-slot-vs-at"><span
        class=secno>9.2.15. </span>Indicating the default slot (‘<code
        class=css>*</code>’ vs ‘<code class=css>@</code>’)</a>

       <li><a href="#abspos"><span class=secno>9.2.16. </span>Flowing vs
        absolutely positioning content in a grid</a>

       <li><a href="#use-the-pseudo-class-to-create-additiona"><span
        class=secno>9.2.17. </span>Use the pseudo-class to create additional
        slots</a>

       <li><a href="#names-for-edges"><span class=secno>9.2.18. </span>Names
        for edges</a>

       <li><a href="#position-from-the-right-and-bottom"><span
        class=secno>9.2.19. </span>Position from the right and bottom</a>

       <li><a href="#syntax-features-to-shorten-long-grid-spe"><span
        class=secno>9.2.20. </span>Syntax features to shorten long grid
        specifications</a>

       <li><a href="#fit-content-vs-auto-vshellip"><span class=secno>9.2.21.
        </span>‘<code class=css>fit-content</code>’ vs ‘<code
        class=css>auto</code>’ vs…</a>

       <li><a href="#vert-align"><span class=secno>9.2.22. </span>Vertical
        alignment inside slots</a>

       <li><a href="#horizontal-alignment-inside-slots"><span
        class=secno>9.2.23. </span>Horizontal alignment inside slots</a>

       <li><a href="#auto-margins-on-slots"><span class=secno>9.2.24.
        </span>Auto margins on slots</a>

       <li><a href="#page-floats"><span class=secno>9.2.25. </span>Page
        floats</a>

       <li><a href="#break-properties"><span class=secno>9.2.26.
        </span>Break-* properties</a>

       <li><a href="#next-same"><span class=secno>9.2.27. </span>Automatic
        placement of elements</a>

       <li><a href="#the-names-of-the-properties"><span class=secno>9.2.28.
        </span>The names of the properties</a>
      </ul>
    </ul>

   <li><a href="#conformance"><span class=secno>10. </span>Conformance</a>

   <li><a href="#changes"><span class=secno>11. </span>Changes</a>

   <li class=no-num><a href="#acknowledgments">Acknowledgments</a>

   <li class=no-num><a href="#references">References</a>

   <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><em>(This section is not normative.)</em>

  <h3 id=summary-and-use-cases><span class=secno>1.1. </span>Summary and use
   cases</h3>

  <div class=sidefigure>
   <p><img alt="Image: four elements move to four slots in a template"
    longdesc=diagram.desc src=diagram.png>

   <p class=caption>Above: a typical Web page. Below: the underlying grid
    template. It has four slots, a, b, c and d and the grid template is
    defined by ‘<code class=css>grid: "a a a a a a a" "b c c c c d
    d"</code>’.
  </div>

  <p class=mtb>The styling of a Web page, a form or a graphical user
   interface can roughly be divided into two parts: (1) defining the overall
   “grid” of the page or window and (2) specifying the fonts, indents,
   colors, etc., of the text and other objects. The two are not completely
   separate, of course, because indenting or coloring a text influences the
   perceived grid as well. Nevertheless, when one separates the parts of a
   style that should change when the window gets bigger from the parts that
   stay the same, one often finds that the grid changes (room for a sidebar,
   extra navigation bar, big margins, larger images…), while fonts, colors,
   indents, numbering styles, and many other things don't have to change,
   until the size of the window becomes extreme.

  <p>The properties in this specification associate a layout grid with an
   element. Rather than rendering all descendants of an element in a single
   flow, they give an element multiple flows, called <a
   href="#slot">slots,</a> placed on an invisible grid by means of a
   <span>grid template.</span> The descendants are given a ‘<a
   href="#flow0"><code class=property>flow</code></a>’ property to
   designate the slot into which they flow.

  <p>Because layouts on the Web have to adapt to different window and paper
   sizes, the rows and columns of the grid can be made fixed or flexible in
   size.

  <p class=note>In some typographical traditions, the slots are called
   “<span class=index id=fields
   title="field (of a typographical grid)">fields</span>.” Traditionally,
   also, all columns have the same width, called the “<span class=index
   id=module title="module (of a typographical grid)">module</span>” or
   “<span class=index id=unit
   title="unit (of a typographical grid)">unit</span>,” so that the width
   of a field is always a multiple of the module. This specification does not
   use those terms, because equal-width columns is merely the default in CSS,
   which means the grid does not necessarily have a “module.”

  <p>The typical use cases for these properties include:

  <ul>
   <li>
    <p>Complex Web pages, with multiple navigation bars in fixed positions,
     areas for advertisements, etc.

   <li>
    <p>Complex forms, where the alignment of labels and form fields may be
     easier with the properties of this module than with the properties for
     tables and margins.

   <li>
    <p>GUIs, where buttons, toolbars, labels, icons, etc., are aligned in
     complex ways and have to stay aligned (and not wrap, for example) when
     the window is resized.

   <li>
    <p>Paged displays (e.g., printed media) where each page is divided in
     fixed areas for different kinds of content.

   <li>
    <p>Complex pages with multiple regions, where the style of the text does
     not only depend on the type of element it comes from, but also on the
     region it is displayed in.

   <li>Paged displays with complex running headers and footers, e.g., running
    headers that are in between parts of the page content, rather than at the
    edge of the page.
  </ul>

  <p>Once a grid template has been defined, it can also be used to position
   elements without adding them to a flow, typically for the purpose of
   making them overlap (somewhat similar to absolute positioning). For those
   elements, ‘<a href="#grid-area"><code
   class=property>grid-area</code></a>’, instead of ‘<a
   href="#flow0"><code class=property>flow</code></a>’, specifies the
   position; and ‘<a href="#z-index"><code
   class=property>z-index</code></a>’ determines the stacking order.

  <p>Template-based positioning makes many traditional uses of absolute
   positioning unnecessary. Like absolute positioning, grid templates are
   especially useful for aligning elements that don't have simple
   relationships in the source (parent-child, ancestor-descendant, immediate
   sibling). But in contrast to absolute positioning, the elements are not
   positioned with the help of horizontal and vertical coordinates, but by
   flowing them into a template that is very much like a table: The size and
   alignment of elements are governed implicitly by the rows and columns of
   the template, and can automatically adapt to the overall size of the
   element and to the content in each row and column.

  <div class=example>
   <p>In this example, the four children of an element are assigned to four
    slots (called a, b, c and d) in a 2×2 template. (All mark-up examples in
    this specification are HTML fragments, unless otherwise stated.)

   <div class=sidefigure>
    <p><img alt="Image: sample rendering" longdesc=aapje.desc src=aapje.png>

    <p class=caption>Each element occupies one slot. In this template, all
     slots have the same size.
   </div>

   <pre>
&lt;style type="text/css"&gt;
  dl { grid: "a b"
             "c d" }
  #sym1 { flow: a }
  #lab1 { flow: b }
  #sym2 { flow: c }
  #lab2 { flow: d }
&lt;/style&gt;
&lt;dl&gt;
  &lt;dt id=sym1&gt;A
  &lt;dd id=lab1&gt;A is een aapje
  &lt;dt id=sym2&gt;B
  &lt;dd id=lab2&gt;B is de bakker
&lt;/dl&gt;
</pre>

   <p><a href=ex-aapje.html>Try it out!</a> (Uses a JavaScript emulation in
    browsers that do not implement grid templates natively.)
  </div>

  <div class=example>
   <p>Templates can also help with device-independence. This example uses
    Media Queries <a href="#MEDIAQ"
    rel=biblioentry>[MEDIAQ]<!--{{MEDIAQ}}--></a> to change the overall
    layout of a page from 3-column layout for a wide screen to a 1-column
    layout for a narrow screen. It assumes the page has been marked-up with
    logical sections with IDs.

   <pre>
@media all
{
  body { grid: "a a a"
               "b c d" }
  #head { flow: a }
  #nav { flow: b }
  #adv { flow: c }
  #body { flow: d }
}
@media all and (max-width: 500px)
{
  body { grid: "a"
               "b"
               "c" }
  #head { flow: a }
  #nav { flow: b }
  #adv { display: none }
  #body { flow: c }
}
</pre>
  </div>

  <div class=example>
   <p>The slots in a grid do not overlap, unless with negative margins. Here
    is how the <a
    href="http://www.csszengarden.com/?cssfile=/026/026.css&amp;page=0">
    “zunflower” design</a> of the CSS Zen Garden could be done:

   <pre>
#container {grid: "A B C"}
#container::slot(A) {box-shadow: 0.5em 0.5em 0.5em; z-index: 1}
#container::slot(B) {box-shadow: 0.5em 0.5em 0.5em; margin-left: -2em}
#intro {flow: A}
#supportingText {flow: B}
#linkList {flow: C}
</pre>
  </div>

  <div class=example>
   <p>Template-based positioning borrows some concepts from table layout, in
    particular the idea of aligning elements in rows and columns, so that
    they constrain one another's size. But there are also differences. This
    example shows some of them. Assume this document fragment:

   <pre>
&lt;div class=group>
 &lt;div>aa aa aa aa aa aa&lt;/div>
 &lt;div>bbb&lt;/div>
 &lt;div class=menu>ccccc&lt;/div>
&lt;/div>
</pre>

   <p>We can lay it out as three columns, as the following illustrations
    show. The style sheet would contain the following.

   <pre>
.group {display: table}
.group > div {display: table-cell}
</pre>

   <div class=figure>
    <p><img alt="[Three unequal cells]" longdesc=table1.desc src=table1.png>

    <p class=caption>Example of rendering with a table.
   </div>

   <p>We can also use a template, in which case the style sheet would contain
    this:

   <pre>
.group {grid: "a b c"}
.group > div {flow: a}
.group > div + div {flow: b}
.group > div + div + div {flow: c}
</pre>

   <p>By default, the table is as wide as needed to fit its contents. To make
    sure it is as wide as its containing block, we need to add

   <pre>.group {display: table; width: 100%}</pre>

   <p>That is not needed for the grid template, but, on the other hand, if we
    want the template to fit its contents, we would need to say so:

   <pre>.group {grid: "a b c"; width: auto}</pre>

   <p>(See <a href="#CSS3BOX"
    rel=biblioentry>[CSS3BOX]<!--{{!CSS3BOX}}--></a> for the definition of
    the ‘<a href="#width"><code class=property>width</code></a>’
    property.) The columns of the template are by default all the same size.
    The columns of the table satisfy certain constraints, but the exact size
    is not defined. We can make them all the same by adding a rule (see <a
    href="#CSS3TBL" rel=biblioentry>[CSS3TBL]<!--{{!CSS3TBL}}--></a>):

   <pre>.group {display: table; width: 100%; table-layout: fixed}</pre>

   <div class=figure>
    <p><img alt="[Three equal cells]" longdesc=table2.desc src=table2.png>

    <p class=caption>Example of rendering with equal columns.
   </div>

   <p>In both styles, we can set a column to a certain size:

   <pre>div.menu {width: 3em}</pre>

   <p>resp.,

   <pre>.group {grid: * * 3em  "a b c"}</pre>

   <div class=figure>
    <p><img alt="[Two equal cells, third is 3em wide]" longdesc=table3.desc
     src=table3.png>

    <p class=caption>Example of rendering with a fixed third column and the
     other two columns of equal width.
   </div>

   <p>If there is an unknown number of columns (children of the div.group
    element), the style sheet for the table model will automatically take
    them into account. The style sheet for the template model, however,
    creates a template of exactly three columns and can't handle tables with
    an unknown number of columns. The extra elements will be added into the
    default slot (in this case the ‘<code class=css>a</code>’ slot).

   <p>(However, extra columns or rows <em>will</em> be created if necessary
    to absolutely position elements. See the ‘<a href="#grid-area"><code
    class=property>grid-area</code></a>’ property.)

   <p>In both models, elements can have borders, but only in the table model
    can borders be collapsed, which makes setting borders easier in the table
    model:

   <pre>
.group {display: table; border-collapse: collapse}
.group > div {border: solid}
</pre>

   <p>resp.,

   <pre>
.group > div {border: solid; border-left: none}
.group > div:first-child {border-left: solid}
</pre>

   <p>In the template model, the order of the elements is explicit, and thus
    it is possible to reverse the order of the columns:

   <pre>
.group > div {flow: c}
.group > div + div {flow: b}
.group > div + div + div {flow: a}
</pre>

   <div class=figure>
    <p><img alt="[Different contents for the cells]" longdesc=table4.desc
     src=table4.png>

    <p class=caption>Example of rendering with the contents of the three
     columns reversed: the third element is shown in the first slot and the
     first element in the third slot.
   </div>

   <p>In the table model, the order of the rows and columns is given by the
    document source and thus can't be changed.
  </div>

  <div class=example>
   <p>This example shows a way to move notes to the end of a section.
    “Notes” in this example refers to elements in HTML with a class of
    “note”. A fragment of HTML such as

   <pre>
&lt;div class=section>
  &lt;p>The balubious coster of the fifth secter&lt;span
    class=note> The sixth secter coster is a difter
    manon.&lt;/span> of The Rollow Carpug mentizes a costernica.
  &lt;p>…
&lt;/div>
</pre>

   <p>with this style sheet

   <pre>
div.section {
    grid: "*"
          "F"}
.note {
    flow: F;
    content: counter(note) ".\A0" contents;
    counter-increment: note;
    font-size: smaller}
.note::before {
    content: counter(note);
    vertical-align: super;
    font-size: larger}
</pre>

   <p>results in a rendering similar to this:

   <div class=figure>
    <p><img
     alt="Same text, with the SPAN replaced by “(1)” and its content moved to the end."
     longdesc=footnotes.desc src=footnotes.png>

    <p class=caption>Rendering of a text with footnotes.
   </div>

   <p>The “Generated content for paged media” module <a href="#CSS3GCPM"
    rel=biblioentry>[CSS3GCPM]<!--{{CSS3GCPM}}--></a> is expected to define
    specific features for footnotes that are both easier and more powerful
    than this example.
  </div>

  <div class=example>
   <p>This example shows the use of <a class=index href="#chain."
    id=chained-regions title=chain>chained regions:</a> text from region 1
    continues in region 2, 3 and 4. And it shows how to use pseudo-elements
    to style text in a particular region: text in region 1 is bigger than in
    other regions.

   <div class=figure>
    <p><img alt="Image of a complex, 3-column layout"
     longdesc=regions-intro-rendering.desc src=regions-intro-rendering.png>

    <p class=caption>Example rendering
   </div>

   <p>We assume a document fragment similar to this:

   <pre>
&lt;div id=article>
  &lt;h1>Introduction&lt;/h1>
  &lt;p>&lt;img src="sunset" alt="">
  &lt;p>This is an example…

  &lt;h1>More Details&lt;/h1>
  &lt;p>This illustrates…
  &lt;p>Then, the example…
  &lt;p>Finally, this…
&lt;/div>
</pre>

   <p>The style sheet makes the DIV into a grid element with five regions,
    called A, *, b, c and d. The regions are grouped into two chains: region
    A on its own, and the chain consisting of *, b, c and d.

   <pre>
#article {
  <a class=index href="#grid" id=grid0>grid</a>: "A A c"
        "A A c"
        "* * c"
        "a b c";
  <a
    class=index href="#chains0" id=chains1>chains</a>: * a b c }
</pre>

   <p>The ‘<code class=css>*</code>’ is a special name. It indicates the
    <a href="#default-slot."><em>default slot,</em></a> the slot where
    content goes if it doesn't have an explicit ‘<a href="#flow0"><code
    class=property>flow</code></a>’ property. We could have used a normal
    letter and added an explicit ‘<a href="#flow0"><code
    class=property>flow</code></a>’ property to the children of the DIV,
    but by using * we don't have to. All children thus go into region * (and
    continue in a, b and c as needed). The IMG element goes into region A. We
    assume for simplicity that there is only one IMG element:

   <pre>#article img { flow: A }</pre>

   <p>The text in region * is bolder, larger and a different color than in
    the other regions. Also, an H1 that falls into this region is rendered
    differently from other H1s:

   <pre>
<a class=index href="#atregion" id=atregion0>@region</a> ::slot(*)
{
  * {
    font-weight: bold;
    color: #0C3D5F;
    font-size: larger }
  h1 {
    color: crimson;
    display: run-in }
}
</pre>

   <p>(For brevity, the example doesn't show the style rules to set the color
    and background, to make the text justified, add the left border to the
    second H1, etc.)

   <p>As the image shows, the text of the last paragraph isn't complete and
    presumably continues somewhere else, but that part is outside the scope
    of this example. In paged media, we could attach the grid template to a
    page instead of an element and let the text continue on the next page; we
    could also make slot c into a multi-column element so that the text forms
    additional columns to the right of current image (see <a href="#CSS3GCPM"
    rel=biblioentry>[CSS3GCPM]<!--{{CSS3GCPM}}--></a> for some ideas), or we
    could allow a scrollbar on slot c.
  </div>

  <div class=example>
   <p>This example shows two [three] ways to align the contents of a
    fixed-height paragraph to the bottom of the box:

   <dl>
    <dt>Method 1

    <dd>
     <pre>P {height: 20em; grid: "." "*" fit-content}</pre>

    <dt>Method 2

    <dd>
     <pre>P {height: 20em; grid: "*"}
P::slot(*) {vertical-align: bottom}</pre>

    <dt>[Method 3]

    <dd class=issue>[If <a class=index href="#vertical-align"
     id=vertical-align0>vertical-align</a> is generalized to apply to all
     blocks, rather than only to table cells, margin boxes and slots:]
     <pre>P {height: 20em; vertical-align: bottom}</pre>
   </dl>

   <p>However, the styles differ in case the content is taller than 20 em
    and overflows: the first style has a baseline-aligned content which will
    thus overflow <em>below</em> the element's box; the second example has
    bottom-aligned content, which will thus overflow <em>above</em> the
    element's box.
  </div>

  <div class=example>
   <p>This example (based on a challenge by Andrew Fedoniouk) shows how a
    grid template can be used to display six items in two rows of three.
    Assume the following document:

   <pre>
&lt;p&gt;
  &lt;span&gt;...&lt;/span&gt;
  &lt;span&gt;...&lt;/span&gt;
  &lt;span&gt;...&lt;/span&gt;
  &lt;span&gt;...&lt;/span&gt;
  &lt;span&gt;...&lt;/span&gt;
  &lt;span&gt;...&lt;/span&gt;
&lt;/p&gt;
</pre>

   <p>The simplest way to break this into two lines (or more) is to add a
    hard line break after the third SPAN: ‘<code
    class=css>span:nth-child(3)::after {content: "\A"; white-space:
    pre}</code>’. That works fine, unless the SPANs are inline blocks
    (‘<code class=css>span {display: inline-block}</code>’). Another way
    is to float all SPANs and add a ‘<code class=property>clear</code>’
    property on the fourth: ‘<code class=css>span {float: left}
    span:nth-child(4) {clear: left}</code>’. But if the SPANs have
    different heights or baselines, their vertical alignment will be
    different than if they were on the same line.

   <p>With a grid template, we can say that the P has not one, but two flows,
    a and b, the second one positioned below the first; and then we assign
    the fourth and subsequent SPANs to the “b” flow. (The others
    automatically go into the default, first flow.)

   <pre>
p {grid: "a" "b"}
span:nth-child(n+4) {flow: b}
</pre>

   <p>This almost works. There is just a subtle issue with the spaces between
    the SPANs. We moved the last three SPANs to flow b, but we have no way to
    move the spaces between them. They remain in the default (first) slot.
    (They collapse, as there is nothing left between them, so we don't
    actually see them anymore.) To get spaces between the SPANs in slot b, we
    need to generate new spaces:

   <pre>span:nth-child(n+4)::after {content: " "}</pre>

   <p class=issue>This space handling is not very intuitive. One might expect
    there to be a way to say “select everything from this element onward”
    or maybe a pseudo-element selector for the text between elements. Or a
    new property to specify different ways to handle the anonymous text
    inside a grid element. For the moment, there is no such thing.
    Suggestions are welcome.
  </div>

  <div class=example>
   <p>This example uses a <a href="#page-based-template"><em>page-based
    template</em></a> to create a running header that is not at the top of
    the page, but exactly in the middle. We need to define our own page
    template for this, because the predefined page template of <a
    href="#CSS3PAGE" rel=biblioentry>[CSS3PAGE]<!--{{CSS3PAGE}}--></a> only
    has margin boxes along the edge of the page.

   <pre>
@page {
  grid:
    "top-half"
    "running-header" 3em
    "bottom-half";
  chains: top-half bottom-half
}
::slot(running-header) {
  content: "My Magazine - page " counter(page) " - February 2013";
  text-align: center;
  <a
    class=index href="#vertical-align"
    id=vertical-align1>vertical-align</a>: middle;
  border: solid;
  margin: 1em 0;
}
</pre>

   <div class=figure>
    <p><img alt="Image: Example rendering" longdesc=page.desc src=page.png>

    <p class=caption>An example of a page rendered with the above page
     template. It has the “running header” with the page number right in
     the middle of the page.
   </div>
  </div>
  <!--=================================================================-->

  <h3 id=dependencies><span class=secno>1.2. </span>Dependencies on other
   modules</h3>

  <p>This CSS3 module depends on the following other CSS3 modules:

  <ul>
   <li><cite>CSS 2.1</cite> <a href="#CSS21"
    rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a> – <a
    href="http://www.w3.org/TR/CSS21/visuren.html#block-boxes"><dfn
    id=block-container>block container,</dfn></a> the property <dfn
    id=content0>content,</dfn> and the concept of <dfn
    id=stacking-context.>stacking context.</dfn>

   <li><cite>CSS syntax module</cite> <a href="#CSS3SYN"
    rel=biblioentry>[CSS3SYN]<!--{{!CSS3SYN}}--></a> – <dfn
    id=interactive>interactive</dfn> vs <dfn
    id=non-interactive>non-interactive</dfn> media.

   <li><cite>CSS values and Units module</cite> <a href="#CSS3VAL"
    rel=biblioentry>[CSS3VAL]<!--{{!CSS3VAL}}--></a> – <a
    href="/TR/css3-values#strings"> <dfn
    id=ltstringgt><var>&lt;string&gt;</var></dfn></a> and <a
    href="/TR/css3-values#length-value"> <dfn
    id=ltlengthgt><var>&lt;length&gt;</var></dfn></a>.

   <li><cite>CSS box module</cite> <a href="#CSS3BOX"