-
Notifications
You must be signed in to change notification settings - Fork 790
Expand file tree
/
Copy pathOverview.src.html
More file actions
885 lines (727 loc) · 32.8 KB
/
Overview.src.html
File metadata and controls
885 lines (727 loc) · 32.8 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
<!DOCTYPE html>
<html lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>CSS Intrinsic & Extrinsic Sizing Module Level 3</title>
<link rel=contents href="#contents">
<link rel=index href="#index">
<link rel="stylesheet" type="text/css" href="../default.css">
<link href="../csslogo.ico" rel="shortcut icon" type="image/x-icon">
<link rel="stylesheet" type="text/css" href="http://www.w3.org/StyleSheets/TR/W3C-[STATUS].css">
</head>
<div class="head">
<!--logo-->
<h1>CSS Intrinsic & Extrinsic Sizing Module Level 3</h1>
<h2 class="no-num no-toc">[LONGSTATUS] [DATE]</h2>
<dl>
<!--
<dt>This version:
<dd><a href="[VERSION]">http://www.w3.org/TR/[YEAR]/ED-css3-sizing-[CDATE]/</a>
-->
<dt>Latest version:
<dd><a href="[LATEST]">http://www.w3.org/TR/css3-sizing/</a>
<dt>Editor's draft:
<dd><a href="http://dev.w3.org/csswg/[SHORTNAME]/">http://dev.w3.org/csswg/[SHORTNAME]/</a>
<dt>Previous Versions:
<dd><a href="http://www.w3.org/TR/2012/WD-css3-sizing-20120927/">http://www.w3.org/TR/2012/WD-css3-sizing-20120927/</a>
<dt>Issue Tracking:</dt>
<dd><a href="https://www.w3.org/Bugs/Public/buglist.cgi?product=CSS&component=Sizing&resolution=---">W3C Bugzilla</a>
<dt>Feedback:</dt>
<dd><a href="http://lists.w3.org/Archives/Public/www-style/">www-style@w3.org</a> with subject line “<kbd>[[SHORTNAME]] <var>… message topic …</var></kbd>”
<dt>Editors:
<dd class="hcard"><a href="http://www.xanthir.com/contact" class="fn url">Tab Atkins Jr.</a>, <span class="org">Google Inc.</span>
<dd class="hcard"><a href="http://fantasai.inkedblade.net/contact" class="fn url">Elika J. Etemad</a>, <span class="org">Mozilla</span>
</dl>
<!--copyright-->
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc" id="abstract">Abstract</h2>
<p>This module extends the CSS sizing properties with keywords
that represent content-based "intrinsic" sizes
and context-based "extrinsic" sizes,
allowing CSS to more easily describe boxes that fit their content
or fit into a particular layout context.
<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.
<h2 class="no-num no-toc" id="status">Status of this document</h2>
<!--status-->
<p>The following features are at risk: …
<h2 class="no-num no-toc" id="contents">
Table of contents</h2>
<!--toc-->
<h2 id="intro">
Introduction</h2>
<p><em>This section is not normative.</em>
<p>
CSS layout has several different concepts of automatic sizing that are used in various layout calculations.
This section defines some more precise terminology
to help connect the layout behaviors of this spec to the calculations used in other modules,
and some new keywords for the 'width' and 'height' properties
to allow authors to assign elements the dimensions resulting from these size calculations.
<h3 id="placement">
Module interactions</h3>
<p>This module extends the 'width', 'height', 'min-width', 'min-height', 'max-width', 'max-height', and 'column-width'
features defined in [[!CSS21]] chapter 10 and in [[!CSS3COL]]
<h3 id="values">
Values</h3>
<p>This specification follows the
<a href="http://www.w3.org/TR/CSS21/about.html#property-defs">CSS property
definition conventions</a> from [[!CSS21]]. Value types not defined in
this specification are defined in CSS Level 2 Revision 1 [[!CSS21]].
Other CSS modules may expand the definitions of these value types: for
example [[CSS3COLOR]], when combined with this module, expands the
definition of the <color> value type as used in this specification.</p>
<p>In addition to the property-specific values listed in their definitions,
all properties defined in this specification also accept the
<a href="http://www.w3.org/TR/CSS21/cascade.html#value-def-inherit">inherit</a>
keyword as their property value. For readability it has not been repeated
explicitly.
<h2 id="terms">
Terminology</h2>
<dl>
<dt><dfn>size</dfn>
<dd>
A one- or two-dimensional measurement:
a <a href="http://www.w3.org/TR/css3-writing-modes/#measure"><i>measure</i></a>
and/or <a href="http://www.w3.org/TR/css3-writing-modes/#extent"><i>extent</i></a>;
alternatively a width and/or height.
<dt><dfn id="definite" title="definite|definite size">definite size</dfn>
<dd>
A size that can be determined without measuring content;
that is, a <var><length></var>,
a size of the <i>initial containing block</i>,
or a <var><percentage></var> that is resolved against a <i>definite</i> size.
Additionally, the size of the <i>containing block</i> of an absolutely positioned element is always <i>definite</i>
with respect to that element.
<dt><dfn id="indefinite" title="indefinite|indefinite size">indefinite size</dfn>
<dd>
A size that is not <i>definite</i>.
An <i>indefinite</i> <i>available size</i> is essentially infinite.
<dt><dfn id="available" title="available|available size|available measure|available extent|available space">available size</dfn>
<dd>
The space into which a box is laid out,
typically either a measurement of its <i>containing block</i>
or an infinite size.
An <i>available size</i> can alternatively be either a
<dfn>min-content constraint</dfn> or
a <dfn>max-content constraint</dfn>.
<!--
<p>
The space <i>available</i> to a box is determined by the formatting context in which it participates.
In block, table, and inline formatting contexts [[!CSS21]],
the <i>available size</i> is infinite in the block-axis dimension.
<span class="issue">What, exactly, is the available size in the inline axis??? What about other formatting models?</span>
-->
<dt><dfn>fill-available fit</dfn>
<dd>
The <i>fill-available fit</i> into a given size
is that size,
minus the element's computed margins (not collapsed, treating ''auto'' as zero),
border, and padding in the given dimension.
<p class='note'>
Note: This is the formula used to calculate widths of non-replaced blocks in normal flow in <a href="http://www.w3.org/TR/CSS21/visudet.html#blockwidth">CSS2.1§10.3.3</a>.
<dt><dfn title="fallback|fallback size">fallback size</dfn>
<dd>
Some sizing algorithms do not work well with an infinite size.
In these cases, the <i>fallback size</i> is used instead.
Unless otherwise specified,
this is the size of the <i>initial containing block</i>.
<dt><dfn>fill-available measure</dfn>
<dd>
Roughly, the <i>measure<i> a box would take
if it filled its <i>available measure</i>.
(See <a href="http://dev.w3.org/csswg/css3-sizing/#extrinsic-sizing">Extrinsic Size Determination</a>.)
<p class='note'>
Note: This is called the <i>available width</i> in <a href="http://www.w3.org/TR/CSS21/visudet.html#float-width">CSS2.1§10.3.5</a>
and computed by the rules in <a href="http://www.w3.org/TR/CSS21/visudet.html#blockwidth">CSS2.1§10.3.3</a>.
<dt><dfn>max-content measure</dfn>
<dd>
Roughly, the narrowest <i>measure</i> a box could take while fitting around its contents
if <em>none</em> of the soft wrap opportunities within the box were taken.
(See <a href="http://dev.w3.org/csswg/css3-sizing/#intrinsic-sizing">Intrinsic Size Determination</a>.)
<p class='note'>
Note: This is called the <i>preferred width</i> in <a href="http://www.w3.org/TR/CSS21/visudet.html#float-width">CSS2.1§10.3.5</a>
and the <i>maximum cell width</i> in <a href="http://www.w3.org/TR/CSS21/tables.html#auto-table-layout">CSS2.1§17.5.2.2</a>.
<dt><dfn>min-content measure</dfn>
<dd>
The narrowest <i>measure</i> a box could take
that doesn't lead to inline-dimension overflow
that could be avoided by choosing a larger <i>measure</i>.
Roughly, the <i>measure</i> that would fit around its contents
if <em>all</em> soft wrap opportunities within the box were taken.
(See <a href="http://dev.w3.org/csswg/css3-sizing/#intrinsic-sizing">Intrinsic Size Determination</a>.)
<p class='note'>
Note: This is called the <i>preferred minimum width</i> in <a href="http://www.w3.org/TR/CSS21/visudet.html#float-width">CSS2.1§10.3.5</a>
and the <i>minimum content width</i> in <a href="http://www.w3.org/TR/CSS21/tables.html#auto-table-layout">CSS2.1§17.5.2.2</a>.
<dt><dfn>fit-content measure</dfn>
<dd>
If the <i>available</i> measure is finite,
equal to <code>min(<i>max-content</i>, max(<i>min-content</i>, <i>fill-available</i>))</code>.
Otherwise, equal to the <i>max-content measure</i>.
<p class='note'>
Note: This is called the <i>shrink-to-fit</i> width in <a href="http://www.w3.org/TR/CSS21/visudet.html#float-width">CSS2.1§10.3.5</a>
and <a href="http://www.w3.org/TR/css3-multicol/#pseudo-algorithm">CSS Multi-column Layout § 3.4</a>.
<dt><dfn>fill-available extent</dfn>
<dd>
Roughly, the <i>extent</i> a box would take
if it filled its <i>available extent</i>.
(See <a href="http://dev.w3.org/csswg/css3-sizing/#intrinsic-sizing">Intrinsic Size Determination</a>.)
<dt><dfn>max-content extent</dfn>
<dd>
Roughly, the <i>extent</i> of the content after layout.
<dt><dfn>min-content extent</dfn>
<dd>
Equivalent to the <i>max-content extent</i>.
<span class="issue">Or should this be the minimum between allowed break points? It might make sense in multi-col contexts to have min-content and max-content extents be different, even if they are the same elsewhere.</span>
<dt><dfn>fit-content extent</dfn>
<dd>
Analogous to the <i>fit-content measure</i>.
<dt><dfn>max-size contribution</dfn>
<dd>
The size that a box contributes to its <i>containing block</i>'s <i>max-content size</i>.
<dt><dfn>min-size contribution</dfn>
<dd>
The size that a box contributes to its <i>containing block</i>'s <i>min-content size</i>.
<dt><dfn>max-size constraint</dfn>
<dd>
A sizing constraint imposed by the box's <i>containing block</i>
that causes it to produce its <i>max-size contribution</i>.
<dt><dfn>min-size constraint</dfn>
<dd>
A sizing constraint imposed by the box's <i>containing block</i>
that causes it to produce its <i>min-size contribution</i>.
</dl>
<h2 id='size-keywords'>
New Sizing Keywords</h2>
<h3 id='width-height-keywords'>
New Keywords for 'width' and 'height'</h3>
<table class="propdef">
<tr>
<th>Properties:
<td>'width', 'min-width', 'max-width', 'height', 'min-height', 'max-height'
<tr>
<th>New Values:
<td>''fill-available'' | ''max-content'' | ''min-content'' | ''fit-content''
<tr>
<th>Initial:
<td>as defined in [[!CSS21]] and [[!CSS3-FLEXBOX]]
<tr>
<th>Applies to:
<td>as defined in [[!CSS21]]
<tr>
<th>Inherited:
<td>as defined in [[!CSS21]]
<tr>
<th>Percentages:
<td>as defined in [[!CSS21]]
<tr>
<th>Media:
<td>as defined in [[!CSS21]]
<tr>
<th>Computed value:
<td>specified value if keyword specified, else as defined in [[!CSS21]]
</table>
<p>There are four types of automatically-determined sizes in CSS (which
are represented in the width and height properties by the keywords
defined above):
<dl>
<dt><dfn>''fill-available''</dfn>
<dd>
Use the <i>fill-available measure</i> or <i>fill-available extent</i>,
as appropriate to the writing mode.
<dt><dfn>''max-content''</dfn>
<dd>
Use the <i>max-content measure</i> or <i>max-content extent</i>,
as appropriate to the writing mode.
<dt><dfn>''min-content''</dfn>
<dd>
Use the <i>min-content measure</i> or <i>min-content extent</i>,
as appropriate to the writing mode.
<dt><dfn>''fit-content''</dfn>
<dd>
Use the <i>fit-content measure</i> or <i>fit-content extent</i>,
as appropriate to the writing mode.
<dt><dfn>''repudiate-floats''</dfn> <span class='issue'>Less stupid name?</span>
<dd>
In the inline axis,
use the larger of the min-content measure,
and the fill-available measure minus the size of any non-descendant floats in the same formatting context.
(This is similar to the behavior of a box that establishes a formatting context next to a float.)
In the block axis,
this is identical to ''auto''.
<p class='issue'>
Does this value work?
Is it needed?
</dl>
<p class="issue">
Right now all of these except ''fill-available'' mean the same thing
for extents. This may or may not be ideal.
<p class='issue'>
If the measure is ''auto'',
we could have min-content extent imply a max-content measure,
and vice versa.
<p class='note'>
Note that percentages resolved against the intrinsic sizes
(''max-content'', ''min-content'', ''fit-content'', ''repudiate-floats'')
will compute to ''auto'',
<a href="http://www.w3.org/TR/CSS21/visudet.html#the-height-property">as defined by CSS 2.1</a>. [[!CSS21]]
<h3 id='the-contain-floats-value'>
Containing Floats</h3>
<table class="propdef">
<tr>
<th>Properties:
<td>'min-width', 'min-height'
<tr>
<th>New Value:
<td>''contain-floats''
<tr>
<th>Initial:
<td>as defined in [[!CSS21]] and [[!CSS3-FLEXBOX]]
<tr>
<th>Applies to:
<td>as defined in [[!CSS21]]
<tr>
<th>Inherited:
<td>as defined in [[!CSS21]]
<tr>
<th>Percentages:
<td>as defined in [[!CSS21]]
<tr>
<th>Media:
<td>as defined in [[!CSS21]]
<tr>
<th>Computed value:
<td>specified value if keyword specified, else as defined in [[!CSS21]]
</table>
<dl>
<dt><dfn>''contain-floats''</dfn>
<dd>
Equivalent to ''min-content''
except that when applied to the extent of a block box
it forces the inner extent to be large enough to contain
the margin boxes of any floats that originate inside the block
and that participate in the same block formatting context as the block's immediate contents.
</dl>
<h3 id='column-sizing'>
Column Sizing Keywords</h3>
<table class="propdef">
<tbody>
<tr>
<th>Property:
<td>'column-width'
</tr>
<tr>
<th>New Values:
<td>''min-content'' | ''max-content'' | ''fill-available'' | ''fit-content''
</tr>
<tr>
<th>Initial:
<td>as defined in [[!CSS3COL]]
</tr>
<tr>
<th>Applies to:
<td>as defined in [[!CSS3COL]]
</tr>
<tr>
<th>Inherited:
<td>as defined in [[!CSS3COL]]
</tr>
<tr>
<th>Percentages:
<td>as defined in [[!CSS3COL]]
</tr>
<tr>
<th>Media:
<td>as defined in [[!CSS3COL]]
</tr>
<tr>
<th>Computed value:
<td>specified value if keyword specified, else as defined in [[!CSS3COL]]
</tr>
</tbody>
</table>
<p>When used as values for <a href="http://www.w3.org/TR/css3-multicol/#cw">'column-width'</a>,
the new keywords specify the optimal column width:
<dl>
<dt>''min-content''
<dd>Specifies the optimal column width as the <i>min-content measure</i>
of the multi-column element's contents.
<dt>''max-content''
<dd>Specifies the optimal column width as the <i>max-content measure</i>
of the multi-column element's contents.
<dt>''fill-available''
<dd>Specifies the optimal column width as the <i>fill-available measure</i>
of the multi-column element.
<dt>''fit-content''
<dd>Specifies the optimal column width as
<code>min(<i>max-content</i>, max(<i>min-content</i>, <i>fill-available</i>))</code>.
</dl>
<h2 id='intrinsic-sizing'>
Intrinsic Size Determination</h2>
<p>
<dfn>Intrinsic sizing</dfn> determines sizes based on the contents of an element,
without regard for its context.
<h3 id='replaced-intrinsic'>
Intrinsic Sizes of Replaced Elements</h3>
<p>
For replaced elements,
the <i>min-content</i> and <i>max-content</i> sizes are equivalent
and correspond to the used size of the replaced element
according to the ''auto'' size calculation in the corresponding dimension.
(See [[!CSS3-IMAGES]].)
<h3 id='inline-intrinsic'>
Intrinsic Sizes of Non-Replaced Inlines</h3>
<p>
The <i>min-content measure</i> of an inline box
is the length of the largest unbreakable sequence of inline content.
The <i>min-measure contribution</i> of an inline box
is its <i>min-content measure</i>,
plus any inline-axis margin, border, and padding
adjacent to that sequence.
<p>
The <i>max-content measure</i> of an inline box
is the length of the largest sequence of inline content
on a single line
when only forced line breaks are taken.
The <i>max-measure contribution</i> of an inline box
is its <i>max-content measure</i>,
plus any inline-axis margin, border, and padding
adjacent to that sequence.
<p>
The <i>min-content extent</i>, <i>max-content extent</i>, <i>min-extent contribution</i>, and <i>max-content contribution</i> of an inline box
are the distance from the head edge of the first line box
to the foot edge of the last line box
on which the inline appears.
<h3 id='block-intrinsic'>
Intrinsic Sizes of Non-Replaced Blocks</h3>
<p>
The <i>min-content measure</i> of a <i>block container box</i>
is the largest <i>min-measure contribution</i>
of its in-flow or floated children.
<p>
The <i>max-content measure</i> of a <i>block container box</i>
is the measure of the box after layout,
if all children are sized under a <i>max-size constraint</i>.
<p>
If the computed measure of a <i>block-level box</i>
is ''min-content'', ''max-content'', or a <i>definite size</i>,
its <i>min-measure contribution</i>
is that size
plus any inline-axis margin, border, and padding.
Otherwise, if the computed measure of the block is ''fit-content'', ''auto'', or ''fill-available'',
its <i>min-measure contribution</i>
is its <i>min-content measure</i>
plus any inline-axis margin, border, and padding.
<p>
If the computed measure of a <i>block-level box</i>
is ''min-content'', ''max-content'', or a <i>definite size</i>,
its <i>max-measure contribution</i>
is that size
plus any inline-axis margin, border, and padding.
Otherwise, if the computed measure of the block is ''fit-content'', ''auto'', or ''fill-available'',
its <i>max-measure contribution</i>
is its <i>max-content measure</i>
plus any inline-axis margin, border, and padding.
<p>
The <i>min-content extent</i> and <i>max-content extent</i> of a <i>block container box</i>
is the content extent as defined
(for horizontal writing modes)
in <a href="http://www.w3.org/TR/CSS21/visudet.html#normal-block">CSS2.1§10.6.3</a>
and <a href="http://www.w3.org/TR/CSS21/tables.html#height-layout">CSS2.1§17.5.3</a>
for elements with ''height: auto'',
and analogously for vertical writing modes.
<p>
The <i>min-extent contribution</i> and <i>max-extent contribution</i> of a <i>block-level box</i>
is the extent of the block after layout,
plus any block-axis margin, border, and padding.
<h3 id='table-intrinsic'>
Intrinsic Sizes in Table Layout</h3>
<p class='issue'>
???
<h3 id="multicol-intrinsic">
Intrinsic Sizes in Multi-column Layout</h3>
<p>
The <i>min-content measure</i> of a multi-column element
with a computed 'column-width' not ''auto''
is the smaller of
its 'column-width'
and the largest <i>min-measure contribution</i> of its contents.
<p>
The <i>min-content measure</i> of a multi-column element
with a computed 'column-width' of ''auto''
is the largest <i>min-measure contribution</i> of its contents
multiplied by its 'column-count'
(treating ''auto'' as ''1'').
<p>
The <i>max-content measure</i> of a multi-column element
with unrestrained column heights
and a computed 'column-count' not ''auto''
is its 'column-count'
multiplied by the larger of
its 'column-width' (treating ''auto'' as 0)
and the largest <i>max-measure contribution</i> of its contents.
<p>
The <i>max-content measure</i> of a multi-column element
with unrestrained column heights
and a computed 'column-count' of ''auto''
is its 'column-width'
multiplied by the number of columns obtained by taking all allowed column breaks [[CSS3-BREAK]].
<!--
The above was decided based on dholbert's example in http://lists.w3.org/Archives/Public/www-style/2012Oct/0017.html .
These definitions make multicols work well in flexbox,
both in 'stretch' and non-'stretch' cases,
without wasted space or needless overflow.
-->
<p>
The <i>max-content measure</i> of a multi-column element
with restrained-height columns (i.e. a specified 'extent' or 'max-extent')
is the <i>measure</i> that would exactly include all of its columns.
It may be approximated by:
<ul>
<li>
Laying out the element with column-spanning elements given 'display: none',
and taking a measure that includes all the columns.
<li>
Laying out all of the column-spanning elements into that resulting measure,
and taking the resulting extent.
<li>
Subtracting that resulting extent from the specified restraint,
laying out the element without column-spanning elements again into this adjusted extent,
and taking the measure of all its columns as its <i>max-content measure</i>.
</ul>
<p>
or by some more accurate method.
<p class='note'>
This approximation can result in some slack,
but avoids overflow in the most common cases,
where the balanced height of the columns above spanning elements are approximately equal.
<p class='note'>
In the common case of no column-spanning elements,
this approximation collapses to simply doing a layout,
and measuring the resulting columns.
<h2 id='extrinsic-sizing'>
Extrinsic Size Determination</h2>
<p>
<dfn>Extrinsic sizing</dfn> determines sizes based on the context of an element,
without regard for its contents.
<p>
The inner <i>fill-availab
7DD6
le measure</i> of a box is…
<ul>
<li>
If the box is the root or is absolutely-positioned, the measure of its containing block, else
<li>
<code>max(<i>min-measure</i>|0, min(<i>max-measure</i>|infinity, <i>measure</i>|<i>fill-available</i>))</code>
where the sizes are inner measures of the element establishing the box's <i>containing block</i>,
and where the first value is used if it is <i>definite</i> and the second value otherwise.
</ul>
<p>
…less the box's inline-axis margins
(after any <a href="http://www.w3.org/TR/CSS21/box.html#collapsing-margins">margin collapsing</a>, and treating ''auto'' margins as zero),
borders, and padding.
<p>
The <i>fill-available extent</i> of a box is defined analogously,
but in the other dimension.
<p class='issue'>
This definition might end up skipping further up the ancestor chain than we'd like in some cases.
<a href="http://lists.w3.org/Archives/Public/www-style/2012Oct/0204.html">Example.</a>
Maybe it should stop at each formatting root, or something similar?
<!--
dddddddd
TTTTTTTTTTTTTTTTTTTTTTThhhhhhh EEEEEEEEEEEEEEEEEEEEEE d::::::d
T:::::::::::::::::::::Th:::::h E::::::::::::::::::::E d::::::d
T:::::::::::::::::::::Th:::::h E::::::::::::::::::::E d::::::d
T:::::TT:::::::TT:::::Th:::::h EE::::::EEEEEEEEE::::E d:::::d
TTTTTT T:::::T TTTTTT h::::h hhhhh eeeeeeeeeeee E:::::E EEEEEEnnnn nnnnnnnn ddddddddd:::::d
T:::::T h::::hh:::::hhh ee::::::::::::ee E:::::E n:::nn::::::::nn dd::::::::::::::d
T:::::T h::::::::::::::hh e::::::eeeee:::::ee E::::::EEEEEEEEEE n::::::::::::::nn d::::::::::::::::d
T:::::T h:::::::hhh::::::h e::::::e e:::::e E:::::::::::::::E nn:::::::::::::::nd:::::::ddddd:::::d
T:::::T h::::::h h::::::he:::::::eeeee::::::e E:::::::::::::::E n:::::nnnn:::::nd::::::d d:::::d
T:::::T h:::::h h:::::he:::::::::::::::::e E::::::EEEEEEEEEE n::::n n::::nd:::::d d:::::d
T:::::T h:::::h h:::::he::::::eeeeeeeeeee E:::::E n::::n n::::nd:::::d d:::::d
T:::::T h:::::h h:::::he:::::::e E:::::E EEEEEE n::::n n::::nd:::::d d:::::d
TT:::::::TT h:::::h h:::::he::::::::e EE::::::EEEEEEEE:::::E n::::n n::::nd::::::ddddd::::::dd
T:::::::::T h:::::h h:::::h e::::::::eeeeeeee E::::::::::::::::::::E n::::n n::::n d:::::::::::::::::d
T:::::::::T h:::::h h:::::h ee:::::::::::::e E::::::::::::::::::::E n::::n n::::n d:::::::::ddd::::d
TTTTTTTTTTT hhhhhhh hhhhhhh eeeeeeeeeeeeee EEEEEEEEEEEEEEEEEEEEEE nnnnnn nnnnnn ddddddddd ddddd
-->
<h2 id="conformance">
Conformance</h2>
<h3 id="conventions">
Document conventions</h3>
<p>Conformance requirements are expressed with a combination of
descriptive assertions and RFC 2119 terminology. The key words “MUST”,
“MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”,
“RECOMMENDED”, “MAY”, and “OPTIONAL” in the normative parts of this
document are to be interpreted as described in RFC 2119.
However, for readability, these words do not appear in all uppercase
letters in this specification.
<p>All of the text of this specification is normative except sections
explicitly marked as non-normative, examples, and notes. [[!RFC2119]]</p>
<p>Examples in this specification are introduced with the words “for example”
or are set apart from the normative text with <code>class="example"</code>,
like this:
<div class="example">
<p>This is an example of an informative example.</p>
</div>
<p>Informative notes begin with the word “Note” and are set apart from the
normative text with <code>class="note"</code>, like this:
<p class="note">Note, this is an informative note.</p>
<h3 id="conformance-classes">
Conformance classes</h3>
<p>Conformance to CSS Intrinsic & Extrinsic Sizing Level 3
is defined for three conformance classes:
<dl>
<dt><dfn title="style sheet!!as conformance class">style sheet</dfn>
<dd>A <a href="http://www.w3.org/TR/CSS21/conform.html#style-sheet">CSS
style sheet</a>.
<dt><dfn>renderer</dfn></dt>
<dd>A <a href="http://www.w3.org/TR/CSS21/conform.html#user-agent">UA</a>
that interprets the semantics of a style sheet and renders
documents that use them.
<dt><dfn id="authoring-tool">authoring tool</dfn></dt>
<dd>A <a href="http://www.w3.org/TR/CSS21/conform.html#user-agent">UA</a>
that writes a style sheet.
</dl>
<p>A style sheet is conformant to CSS Intrinsic & Extrinsic Sizing Level 3
if all of its statements that use syntax defined in this module are valid
according to the generic CSS grammar and the individual grammars of each
feature defined in this module.
<p>A renderer is conformant to CSS Intrinsic & Extrinsic Sizing Level 3
if, in addition to interpreting the style sheet as defined by the
appropriate specifications, it supports all the features defined
by CSS Intrinsic & Extrinsic Sizing Level 3 by parsing them correctly
and rendering the document accordingly. However, the inability of a
UA to correctly render a document due to limitations of the device
does not make the UA non-conformant. (For example, a UA is not
required to render color on a monochrome monitor.)
<p>An authoring tool is conformant to CSS Intrinsic & Extrinsic Sizing Level 3
if it writes style sheets that are syntactically correct according to the
generic CSS grammar and the individual grammars of each feature in
this module, and meet all other conformance requirements of style sheets
as described in this module.
<h3 id="partia
8DEA
l">
Partial implementations</h3>
<p>So that authors can exploit the forward-compatible parsing rules to
assign fallback values, CSS renderers <strong>must</strong>
treat as invalid (and <a href="http://www.w3.org/TR/CSS21/conform.html#ignore">ignore
as appropriate</a>) any at-rules, properties, property values, keywords,
and other syntactic constructs for which they have no usable level of
support. In particular, user agents <strong>must not</strong> selectively
ignore unsupported component values and honor supported values in a single
multi-value property declaration: if any value is considered invalid
(as unsupported values must be), CSS requires that the entire declaration
be ignored.</p>
<h3 id="experimental">
Experimental implementations</h3>
<p>To avoid clashes with future CSS features, the CSS2.1 specification
reserves a <a href="http://www.w3.org/TR/CSS21/syndata.html#vendor-keywords">prefixed
syntax</a> for proprietary and experimental extensions to CSS.
<p>Prior to a specification reaching the Candidate Recommendation stage
in the W3C process, all implementations of a CSS feature are considered
experimental. The CSS Working Group recommends that implementations
use a vendor-prefixed syntax for such features, including those in
W3C Working Drafts. This avoids incompatibilities with future changes
in the draft.
</p>
<h3 id="testing">
Non-experimental implementations</h3>
<p>Once a specification reaches the Candidate Recommendation stage,
non-experimental implementations are possible, and implementors should
release an unprefixed implementation of any CR-level feature they
can demonstrate to be correctly implemented according to spec.
<p>To establish and maintain the interoperability of CSS across
implementations, the CSS Working Group requests that non-experimental
CSS renderers submit an implementation report (and, if necessary, the
testcases used for that implementation report) to the W3C before
releasing an unprefixed implementation of any CSS features. Testcases
submitted to W3C are subject to review and correction by the CSS
Working Group.
<p>Further information on submitting testcases and implementation reports
can be found from on the CSS Working Group's website at
<a href="http://www.w3.org/Style/CSS/Test/">http://www.w3.org/Style/CSS/Test/</a>.
Questions should be directed to the
<a href="http://lists.w3.org/Archives/Public/public-css-testsuite">public-css-testsuite@w3.org</a>
mailing list.
<h3 id="cr-exit-criteria">
CR exit criteria</h3>
<p>
For this specification to be advanced to Proposed Recommendation,
there must be at least two independent, interoperable implementations
of each feature. Each feature may be implemented by a different set of
products, there is no requirement that all features be implemented by
a single product. For the purposes of this criterion, we define the
following terms:
<dl>
<dt>independent <dd>each implementation must be developed by a
different party and cannot share, reuse, or derive from code
used by another qualifying implementation. Sections of code that
have no bearing on the implementation of this specification are
exempt from this requirement.
<dt>interoperable <dd>passing the respective test case(s) in the
official CSS test suite, or, if the implementation is not a Web
browser, an equivalent test. Every relevant test in the test
suite should have an equivalent test created if such a user
agent (UA) is to be used to claim interoperability. In addition
if such a UA is to be used to claim interoperability, then there
must one or more additional UAs which can also pass those
equivalent tests in the same way for the purpose of
interoperability. The equivalent tests must be made publicly
available for the purposes of peer review.
<dt>implementation <dd>a user agent which:
<ol class=inline>
<li>implements the specification.
<li>is available to the general public. The implementation may
be a shipping product or other publicly available version
(i.e., beta version, preview release, or “nightly build”).
Non-shipping product releases must have implemented the
feature(s) for a period of at least one month in order to
demonstrate stability.
<li>is not experimental (i.e., a version specifically designed
to pass the test suite and is not intended for normal usage
going forward).
</ol>
</dl>
<p>The specification will remain Candidate Recommendation for at least
six months.
<h2 class=no-num id="acknowledgments">
Acknowledgments</h2>
<p>Special thanks go to Aaron Gustafson, L. David Baron
for their contributions to this module.
<h2 class=no-num id="references">
References</h2>
<h3 class="no-num" id="normative-references">
Normative references</h3>
<!--normative-->
<h3 class="no-num" id="other-references">
Other references</h3>
<!--informative-->
<h2 class="no-num" id="index">
Index</h2>
<!--index-->
<h2 class="no-num" id="property-index">
Property index</h2>
<!-- properties -->
</body>
</html>
<!-- Keep this comment at the end of the file
Local variables:
mode: sgml
sgml-declaration:"~/SGML/HTML4.decl"
sgml-default-doctype-name:"html"
sgml-minimize-attributes:t
sgml-nofill-elements:("pre" "style" "br")
sgml-live-element-indicator:t
sgml-omittag:nil
sgml-shorttag:nil
sgml-namecase-general:t
sgml-general-insert-case:lower
sgml-always-quote-attributes:t
sgml-indent-step:nil
sgml-indent-data:t
sgml-parent-document:nil
sgml-exposed-tags:nil
sgml-local-catalogs:nil
sgml-local-ecat-files:nil
End:
-->