-
Notifications
You must be signed in to change notification settings - Fork 790
Expand file tree
/
Copy pathOverview.bs
More file actions
1182 lines (982 loc) · 38.5 KB
/
Overview.bs
File metadata and controls
1182 lines (982 loc) · 38.5 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
<h1>CSS Text Module Level 4</h1>
<pre class='metadata'>
Shortname: css-text
Level: 4
Status: ED
Work Status: Exploring
Group: csswg
ED: http://dev.w3.org/csswg/css-text-4/
Editor: fantasai, Invited Expert, http://fantasai.inkedblade.net/contact
Editor: Koji Ishii, Invited Expert, kojiishi@gluesoft.co.jp
Editor: Alan Stearns, Adobe Systems, stearns@adobe.com
Abstract: This module defines properties for text manipulation and specifies their processing model. It covers line breaking, justification and alignment, white space handling, and text transformation.
Ignored terms: segment break, segment breaks
</pre>
<h2 id="intro">
Introduction</h2>
Issue: Add final level 3 content
<h2 id="transforming">
Transforming Text</h2>
Issue: Add final level 3 content
<h2 id="white-space-processing">
White Space Processing</h2>
Issue: Add final level 3 tab-size and processing det
77FB
ails
<h3 id="white-space-collapsing">
White Space Collapsing: the 'text-space-collapse' property</h3>
<p class="issue">This section is still under discussion and may change in future drafts.</p>
<pre class="propdef">
Name: text-space-collapse
Value: collapse | discard | preserve | preserve-breaks | preserve-spaces
Initial: collapse
Applies to: all elements
Inherited: yes
Percentages: n/a
Computed value: as specified
Media: visual
</pre>
<p class="issue">Need a property name</p>
This property declares whether and how
<a href="#white-space-processing">white space</a> inside the element is
collapsed. Values have the following meanings, which must be interpreted
according to the white space processing rules:
<dl dfn-for=text-space-collapse dfn-type=value>
<dt><dfn>collapse</dfn>
<dd>
This value directs user agents to collapse sequences of white space
into a single character
(or <a href="http://www.w3.org/TR/css-text/#line-break-transform">in some cases</a>, no character).
<dt><dfn>preserve</dfn>
<dd>
This value prevents user agents
from collapsing sequences of white space.
<a>Segment breaks</a> are preserved as forced line breaks.
<dt><dfn>preserve-breaks</dfn>
<dd>
This value collapses white space as for ''collapse'', but preserves
<a>segment breaks</a> as forced line breaks.
<dt><dfn>preserve-spaces</dfn>
<dd>
This value prevents user agents
from collapsing sequences of white space,
and converts tabs and <a>segment breaks</a> to spaces.
(This value is intended to match the behavior
of <code>xml:space="preserve"</code> in SVG.)
<dt><dfn>discard</dfn>
<dd>
This value directs user agents to “discard”
all white space in the element.
Issue: Does this preserve line break opportunities or no? Do we need a "hide" value?
</dl>
<div class="example">
The following style rules implement MathML's white space processing:
<pre>
@namespace m "http://www.w3.org/1998/Math/MathML";
m|* {
text-space-collapse: discard;
}
m|mi, m|mn, m|mo, m|ms, m|mtext {
text-space-collapse: trim-inner;
}
</pre>
</div>
<p class="issue">This section is still under discussion and may change in future drafts.</p>
<h3 id="white-space-trim">
White Space Trimming: the 'text-space-trim' property</h3>
<pre class="propdef">
Name: text-space-trim
Value: none | trim-inner || discard-before || discard-after
Initial: collapse
Applies to: all elements
Inherited: no
Percentages: n/a
Computed value: as specified
Media: visual
</pre>
This property allows authors to specify trimming behavior
at the beginning and end of a box.
Values have the following meanings,
which must be interpreted according to the white space processing rules:
<dl dfn-for=text-space-trim dfn-type=value>
<dt><dfn>trim-inner</dfn>
<dd>
For block containers this value directs UAs to discard all whitespace
at the beginning of the element up to and including the last <a>segment break</a>
before the first non-white-space character in the element as well as
to discard all white space at the end of the element starting with the
first <a>segment break</a> after the last non-white-space character in the element.
For other elements this value directs UAs to discard all whitespace
at the beginning and end of the element.
<dt><dfn>discard-before</dfn>
<dd>
This value directs the UA to collapse all collapsible whitespace
immediately before the start of the element.
<dt><dfn>discard-after</dfn>
<dd>
This value directs the UA to collapse all collapsible whitespace
immediately after the end of the element.
</dl>
<div class="example">
<p>The following style rules render DT elements as a comma-separated list:
<pre>
93CD
;
dt { display: inline; }
dt + dt:before { content: ", "; text-space-collapse: discard-before; }
</pre>
</div>
<h2 id="line-breaking">
Line Breaking and Word Boundaries</h2>
Issue: Add final level 3 content
<h2 id="wrapping">
Text Wrapping</h2>
Text wrapping is controlled by the 'text-wrap',
'wrap-before',
'wrap-after',
'wrap-inside',
and overflow-wrap properties:
Issue: Add final level 3 overflow-wrap
<h3 id="text-wrap">
Text Wrap Settings: the 'text-wrap' property</h3>
<pre class="propdef">
Name: text-wrap
Value: normal | nowrap | balance
Initial: normal
Applies to: all elements
Inherited: yes
Percentages: n/a
Computed value: as specified
Media: visual
</pre>
This property specifies the mode for text wrapping.
Possible values:
<dl dfn-for=text-wrap dfn-type=value>
<dt><dfn>normal</dfn>
<dd>
Lines may break at allowed break points,
as determined by the line-breaking rules in effect.
Line breaking behavior defined
for the WJ, ZW, and GL line-breaking classes
in [[!UAX14]] must be honored.
<dt><dfn>nowrap</dfn>
<dd>
Lines may not break; text that does not fit within the block container
overflows it.
<dt><dfn>balance</dfn>
<dd>
Same as ''text-wrap/normal'' for inline-level elements.
For block-level elements that
contain line boxes as direct children,
line breaks are chosen to balance
the <a>inline-size</a> those line boxes consume,
if better balance than ''text-wrap/normal'' is possible.
This must not change the number of line boxes
the block would contain
if 'text-wrap' were set to ''text-wrap/normal''.
For balancing purposes,
the <a>inline-size</a> to consider includes
any length taken up
by floats that shorten the line box.
The <a>inline-size</a> to consider comes before
any adjustments for justification.
Line boxes are balanced when the standard deviation
from the average <a>inline-size</a> consumed
is reduced over the block
(including lines that end in a forced break).
The exact algorithm is UA-defined.
UAs may treat this value as ''text-wrap/normal'' if there are more than ten lines to balance.
</dl>
Regardless of the 'text-wrap' value,
lines always break at forced breaks:
for all values,
line-breaking behavior defined
for the BK, CR, LF, CM NL, and SG line breaking classes
in [[!UAX14]] must be honored.
UAs that allow breaks at punctuation other than spaces
should prioritize breakpoints.
For example,
if breaks after slashes have a lower priority than spaces,
the sequence “check /etc”
will never break between the ‘/’ and the ‘e’.
The UA may use the width of the containing block,
the text's language,
and other factors in assigning priorities.
As long as care is taken to avoid such awkward breaks,
allowing breaks at appropriate punctuation other than spaces
is recommended,
as it results in more even-looking margins,
particularly in narrow measures.
<!-- add a sample prioritization algorithm -->
<h3 id="wrap-before">
Inline breaks between boxes: the 'wrap-before'/'wrap-after' properties</h3>
<pre class="propdef">
Name: wrap-before, wrap-after
Value: auto | avoid | avoid-line | avoid-flex | line | flex
Initial: auto
Applies to: <a>inline-level</a> boxes and <a>flex items</a>
Inherited: no
Percentages: n/a
Computed value: as specified
Media: visual
</pre>
These properties specify modifications to break opportunities
in line breaking (and <a>flex line</a> breaking [[CSS3-FLEXBOX]]).
Possible values:
<dl dfn-for="wrap-before, wrap-after" dfn-type=value>
<dt><dfn>auto</dfn>
<dd>
Lines may break at allowed break points
before and after the box,
as determined by the line-breaking rules in effect.
<dt><dfn>avoid</dfn>
<dd>
Line breaking is suppressed immediately before/after the box:
the UA may only break there
if there are no other valid break points
in the line.
If the text breaks,
line-breaking restrictions are honored as for
''wrap-before/auto''.
<dt><dfn>avoid-line</dfn>
<dd>
Same as ''wrap-before/avoid'',
but only for line breaks.
<dt><dfn>avoid-flex</dfn>
<dd>
Same as ''wrap-before/avoid'',
but only for flex line breaks.
<dt><dfn>line</dfn>
<dd>
Force a line break immediately before/after the box
if box is an <a>inline-level</a> box.
<dt><dfn>flex</dfn>
<dd>
Force a <a>flex line</a> break immediately before/after the box
if the box is a <a>flex item</a>
in a <a href="http://www.w3.org/TR/css-flexbox-1/#multi_line">multi-line flex container</a>.
</dl>
Forced line breaks on <a>inline-level</a> boxes propagate upward
through any parent <a>inline boxes</a>
the same way forced breaks on <a>block-level</a> boxes propagate upward
through any parent <a>block boxes</a>
in the same <a>fragmentation context</a>.
[[!CSS3-BREAK]]
<h3 id="wrap-inside">
Line breaks within boxes: the 'wrap-inside' property</h3>
<pre class="propdef">
Name: wrap-inside
Value: auto | avoid
Initial: auto
Applies to: <a>inline boxes</a>
Inherited: no
Percentages: n/a
Computed value: as specified
Media: visual
</pre>
<dl dfn-for=wrap-inside dfn-type=value>
<dt><dfn>auto</dfn>
<dd>
Lines may break at allowed break points
within the box,
as determined by the line-breaking rules in effect.
<dt><dfn>avoid</dfn>
<dd>
Line breaking is suppressed within the box:
the UA may only break within the box
if there are no other valid break points in the line.
If the text breaks,
line-breaking restrictions are honored as for
''wrap-inside/auto''.
If boxes with ''wrap-inside/avoid'' are nested
and the UA must break within these boxes,
a break in an outer box must be used
before a break within an inner box may be used.
</dl>
<h4 id="example-avoid">
Example of using 'wrap-inside: avoid' in presenting a footer</h4>
<div class="example">
The priority of breakpoints can be set
to reflect the intended grouping of text.
Given the rules
<pre>
footer { wrap-inside: avoid; }
venue { wrap-inside: avoid; }
date { wrap-inside: avoid; }
place { wrap-inside: avoid; }
</pre>
and the following markup:
<pre>
<footer>
<venue>27th Internationalization and Unicode Conference</venue>
&#8226; <date>April 7, 2005</date> &#8226;
<place>Berlin, Germany</place>
</footer>
</pre>
In a narrow window the footer could be broken as
<pre>
27th Internationalization and Unicode Conference •
April 7, 2005 • Berlin, Germany
</pre>
or in a narrower window as
<pre>
27th Internationalization and Unicode
Conference • April 7, 2005 •
Berlin, Germany
</pre>
but not as
<pre>
27th Internationalization and Unicode Conference • April
7, 2005 • Berlin, Germany
</pre>
</div>
<h2 id="last-line-limits">
Last Line Minimum Length</h2>
<div class="issue">
See <a href="http://www.w3.org/mid/0BD85DFF-A147-44EF-B18A-FF03C3D67EF0@verou.me">thread</a>.
Issue is about requiring a minimum length for lines.
Common measures seem to be
<ul>
<li>At least as long as the text-indent.
<li>At least X characters.
<li>Percentage-based.
</ul>
Suggestion for value space is ''match-indent | <<length>> | <<percentage>>''
(with ''Xch'' given as an example to make that use case clear).
Alternately <<integer>> could actually count the characters.
It's unclear how this would interact with text balancing (above);
one earlier proposal had them be the same property
(with ''100%'' meaning full balancing).
People have requested word-based limits, but since this is really
dependent on the length of the word, character-based is better.
</div>
<h2 id="white-space-property">
Shorthand for White Space and Wrapping: the 'white-space' property</h2>
Issue: Diff needs to have the shorthand details
<h2 id="hyphenation">
Breaking Within Words</h2>
Issue: Add final level 3 content
<h3 id="hyphenate-character">
Hyphens: the 'hyphenate-character' property</h3>
<pre class="propdef">
Name: hyphenate-character
Value: auto | <string>
Initial: auto
Applies to: all elements
Inherited: yes
Percentages: n/a
Computed value: as specified
Media: visual
</pre>
This property specifies strings that are shown between parts of
hyphenated words. The <dfn for=hyphenate-character>auto</dfn> value means that the user agent should
find an appropriate value, preferably from the same source as the
hyphenation dictionary. If a string is specified, it appears at
the end of the line before a hyphenation break.
<div class="example">
In Latin scripts, the hyphen character (U+2010) is often used to
indicate that a word has been split. Normally, it will not be
necessary to set it explicitly. However, this can easily be done:
<pre>
article { hyphenate-character: "\2010" }
</pre>
</div>
<p class="note">
Both hyphens triggered by automatic hyphenation and
hyphens triggered by soft hyphens are rendered according to
'hyphenate-character'.
<h3 id="hyphenate-size-limits">
Hyphenation Size Limit: the 'hyphenate-limit-zone' property</h3>
<pre class="propdef">
Name: hyphenate-limit-zone
Value: <percentage> | <length>
Initial: 0
Applies to: block containers
Inherited: yes
Percentages: refers to width of the line box
Computed value: as specified
Media: visual
</pre>
<p class="issue">Is 'hyphenate-limit-zone' a good name? Comments/suggestions?
This property specifies the maximum amount of unfilled space (before
justification) that may be left in the line box before hyphenation is
triggered to pull part of a word from the next line back up into the
current line.
<h3 id="hyphenate-char-limits">
Hyphenation Character Limits: the 'hyphenate-limit-chars' property</h3>
<pre class="propdef">
Name: hyphenate-limit-chars
Value: [ auto | <<integer>> ]{1,3}
Initial: auto
Applies to: all elements
Inherited: yes
Percentages: n/a
Computed value: as specified
Media: visual
</pre>
This property specifies the minimum number of characters in a
hyphenated word. If the word does not meet the required minimum
number of characters in the word / before the hyphen / after the
hyphen, then the word must not be hyphenated. Nonspacing combining
marks (<span class="issue">Unicode class</span>) and intra-word
punctuation (Unicode classes P*) do not count towards the minimum.
If three values are specified, the first value is the required
minimum for the total characters in a word, the second value is
the minimum for characters before the hyphenation point, and
the third value is the minimum for characters after the hyphenation
point. If the third value is missing, it is the same as the second.
If the second value is missing,
then it is ''hyphenate-limit-chars/auto''.
The ''hyphenate-limit-chars/auto''
value means that the UA chooses a value that adapts to the current
layout.
<p class="note">Unless the UA is able to calculate a better value, it
is suggested that ''hyphenate-limit-chars/auto'' means 2 for before and after, and 5 for
the word total.
<div class="example">
In the example below, the minimum size of a hyphenated word is
left to the UA (which means it may vary depending on the language,
the length of the line, or other factors), but the minimum number
of characters before and after the hyphenation point is set to 3.
<pre>
p { hyphenate-limit-chars: auto 3; }
</pre>
</div>
<h3 id="hyphenate-line-limits">
Hyphenation Line Limits: the 'hyphenate-limit-lines' and 'hyphenate-limit-last' properties</h3>
<pre class="propdef">
Name: hyphenate-limit-lines
Value: no-limit | <integer>
Initial: no-limit
Applies to: block containers
Inherited: yes
Percentages: n/a
Computed value: as specified
Media: visual
</pre>
This property indicates the maximum number of successive hyphenated
lines in an element. The ''no-limit'' value means that there is no limit.
In some cases, user agents may not be able to honor the specified value.
(See overflow-wrap.) It is not defined whether hyphenation introduced by
such emergency breaking influences nearby hyphenation points.
<pre class="propdef">
Name: hyphenate-limit-last
Value: none | always | column | page | spread
Initial: none
Applies to: block containers
Inherited: yes
Percentages: n/a
Computed value: as specified
Media: visual
</pre>
This property indicates hyphenation behavior at the end of elements,
column, pages and spreads. A spread is a set of two pages that are
visible to the reader at the same time. Values are:
<dl dfn-for=hyphenate-limit-lines dfn-type=value>
<dt><dfn>none</dfn>
<dd>
No restrictions imposed.
<dt><dfn>always</dfn>
<dd>
The last full line of the element, or the last line before any
column, page, or spread break inside the element should not be
hyphenated.
<dt><dfn>column</dfn>
<dd>
The last line before any column, page, or spread break inside
the element should not be hyphenated.
<dt><dfn>page</dfn>
<dd>
The last line before page or spread break inside the element
should not be hyphenated.
<dt><dfn>spread</dfn>
<dd>
The last line before any spread break inside the element should
not be hyphenated.
</dl>
<div class=example>
<pre>
p { hyphenate-limit-last: always }
div.chapter { hyphenate-limit-last: spread }
</pre>
</div>
<div class=example>
A paragraph may be formatted like this when 'hyphenate-limit-last: none' is set:
<pre>
This is just a
simple example
to show Antarc-
tica.
</pre>
With 'hyphenate-limit-last: always' one would get:
<pre>
This is just a
simple example
to show
Antarctica.
</pre>
</div>
<h2 id="alignment">
Alignment and Justification</h2>
Issue: Add final level 3 content
Add this value to text-align
<dl dfn-for=text-align dfn-type=value>
<dt><dfn><string></dfn></dt>
<dd>
The string must be a single character; otherwise the declaration must
be <a href="http://www.w3.org/TR/CSS21/conform.html#ignore">ignored</a>.
When applied to a table cell, specifies the <dfn>alignment character</dfn>
around which the cell's contents will align. See
<a href="#character-alignment">below</a> for further details and
how this value combines with keywords.
</dl>
<h3 id="character-alignment">
Character-based Alignment in a Table Column</h3>
When multiple cells in a column have an alignment character specified,
the alignment character of each such cell in the column is centered along
a single column-parallel axis and the rest of the text in the column
shifted accordingly. (Note that the strings do not have to be the same
for each cell, although they usually are.)
<div class="example">
The following style sheet:
<pre>
TD { text-align: "." center }
</pre>
will cause the column of dollar figures in the following HTML table:
<pre class="html-example">
<TABLE>
<COL width="40">
<TR> <TH>Long distance calls
<TR> <TD> $1.30
<TR> <TD> $2.50
<TR> <TD> $10.80
<TR> <TD> $111.01
<TR> <TD> $85.
<TR> <TD> N/A
<TR> <TD> $.05
<TR> <TD> $.06
</TABLE>
</pre>
to align along the decimal point. The table might be rendered as
follows:
<pre>
+---------------------+
| Long distance calls |
+---------------------+
| $11.30 |
| $22.50 |
| $0.80 |
| $200567.01 |
| $85. |
| N/A |
| $.05 |
| $.06 |
+---------------------+
</pre>
</div>
A keyword value may be specified in conjunction with the <string>
value; if it is not given, it defaults to ''text-align/right''. This value is used:
<ul>
<li>
when character-based alignment is applied to boxes that are not table
cells.
<li>
when the text wraps to multiple lines (at unforced break points).
<li>
when a character-aligned cell spans more than one column. In this
case the keyword alignment value is used to determine which column's
axis to align with: the leftmost column for ''text-align/left'', the rightmost
column for ''text-align/right'' and ''text-align/center'', the startmost column for ''text-align/start'',
the endmost column for ''text-align/end''.
<li>
when the column is wide enough that the character alignment alone does
not determine the positions of its character-aligned contents. In this
case the keyword alignment of the first cell in the column with a
specified alignment character is used to slide the position of the
character-aligned contents to match the keyword alignment insofar as
possible without changing the width of the column.
For ''text-align/center'', the UA may center
the aligned contents using its extremes, center the alignment axis
itself (insofar as possible), or optically center the aligned contents
some other way (such as by taking a weighted average of the extent of
the cells' contents to either side of the axis).
</ul>
<p class="note">
Right alignment is used by default for character-based
alignment because numbering systems are almost all left-to-right even
in right-to-left writing systems, and the primary use case of
character-based alignment is for numerical alignment.
</p>
If the alignment character appears more than once in the text, the first
instance is used for alignment. If the alignment character does not appear
in a cell at all, the string is aligned as if the alignment character had
been inserted at the end of its contents.
Character-based alignment occurs before table cell width computation so
that auto width computations can leave enough space for alignment.
Whether column-spanning cells participate in the alignment prior to
or after width computation is undefined.
If width constraints on the cell contents prevent full alignment
throughout the column, the resulting alignment is undefined.
<h2 id="spacing">
Spacing</h2>
Issue: Add final level 3 word-spacing, letter-spacing
<h3 id="text-spacing-property">
Character Class Spacing: the 'text-spacing' property</h3>
<table class="propdef">
<tr>
<th>Name:
<td><dfn>text-spacing</dfn>
<tr>
<th>Value:
<td>normal | none |
[ trim-start | space-start ] ||
[ trim-end | space-end | allow-end ] ||
[ trim-adjacent | space-adjacent ] ||
no-compress ||
ideograph-alpha ||
ideograph-numeric ||
punctuation
<tr>
<th>Initial:
<td>normal
<tr>
<th>Applies to:
<td>block containers
<tr>
<th>Inherited:
<td>yes
<tr>
<th>Percentages:
<td>N/A
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>specified value
</table>
This property controls spacing between adjacent characters
on the same line within the same inline formatting context
using a set of character-class-based rules.
Such spacing can either be created between or trimmed from the affected glyphs.
Values are defined as follows:
<dl dfn-for=text-spacing dfn-type=value>
<dt><dfn>normal</dfn>
<dd>
Specifies the baseline behavior,
equivalent to ''space-start allow-end trim-adjacent''.
<dt><dfn>none</dfn>
<dd>
Turns off all text-spacing features.
All fullwidth characters are set with full-width glyphs.
<dt><dfn>ideograph-alpha</dfn>
<dd>
Creates 1/4em extra spacing between runs of
<a>ideographs</a> and <a>non-ideographic letters</a>.
Note: A commonly used algorithm for determining this behavior is specified in [[JLREQ]].
<dt><dfn>ideograph-numeric</dfn>
<dd>
Creates 1/4em extra spacing between runs of
<a>ideographs</a> and <a>non-ideographic numerals</a> glyphs.
Note: A commonly used algorithm for determining this behavior is specified in [[JLREQ]].
<dt><dfn>punctuation</dfn>
<dd>
Creates extra non-breaking spacing around punctuation as required by language-specific typographic conventions.
In this level, if the element's content language is French,
narrow no-break space (U+202F) and no-break space (U+00A0) is inserted
where required by <a href="http://unicode.org/udhr/n/notes_fra.html">French typographic guidelines</a>.
Otherwise this value has no effect.
However future specifications may add automatic spacing behavior for other languages.
<dt><dfn>space-start</dfn>
<dd>
Set <a>fullwidth opening punctuation</a> with full-width glyphs (spaced)
at the start of each line.
<dt><dfn>trim-start</dfn>
<dd>
Set <a>fullwidth opening punctuation</a> with half-width glyphs (flush)
at the start of each line.
<dt><dfn>allow-end</dfn>
<dd>
Set <a>fullwidth closing punctuation</a> with half-width glyphs (flush)
at the end of each line
if it does not otherwise fit prior to justification;
otherwise set the punctuation with full-width glyphs.
<dt><dfn>space-end</dfn>
<dd>
Set <a>fullwidth opening punctuation</a> with full-width glyphs (spaced)
at the start of each line.
<dt><dfn>trim-end</dfn>
<dd>
Set <a>fullwidth closing punctuation</a> with half-width glyphs (flush)
at the end of each line.
<dt><dfn>space-adjacent</dfn>
<dd>
Set <a>fullwidth opening punctuation</a> with full-width glyphs (spaced)
when not at the start of the line.
Set <a>fullwidth closing punctuation</a> with full-width glyphs (spaced)
when not at the end of the line.
<dt><dfn>trim-adjacent</dfn>
<dd>
Collapse spacing between punctuation glyphs
<a href="#fullwidth-collapsing">as described below</a>.
<dt><dfn>no-compress</dfn>
<dd>
Justification may not compress text-spacing.
(If this value is not specified, the justification process may reduce autospacing
except when the spacing is at the start or end of the line.)
Note: An example of compression rules is given for Japanese
in 3.8 Line Adjustment in [[JLREQ]].
</dl>
This property is additive with the 'word-spacing' and 'letter-spacing' properties.
That is, the amount of spacing contributed by the 'letter-spacing' setting (if any)
is added to the spacing created by 'text-spacing'.
The same applies to 'word-spacing'.
At element boundaries, the amount of extra spacing introduced between characters
is determined by and rendered within the innermost element that contains the boundary.
If the extra spacing is applied to a particular glyph,
then the spacing is determined by the innermost element containing that glyph.
Note: Values other than ''text-spacing/normal'', ''text-spacing/none'', ''trim-start'', ''trim-end'', and ''space-end''
are at-risk and may be dropped from this level of CSS.
They are defined here currently to help work out a complete design of this feature.
Support for this property is <em>optional</em>.
It is strongly recommended for UAs that wish to support CJK typography.
Issue: It was requested to add a value for doubling the space after periods.
<h4 id="fullwidth-collapsing">
Fullwidth Punctuation Collapsing</h4>
Typically, fullwidth characters have glyphs with the same advance width
as a standard Han character (e.g. 水 U+6C34).
However, many fullwidth punctuation glyphs only take up part of the fullwidth design space.
Thus such punctuation are not always set fullwidth.
Several values of 'text-spacing' allow the author to control
when such characters are set half-width (typically half the width of an ideograph)
and when they are set full-width.
In order to set the text as specified, the UA will need to either
<ul>
<li>
trim (kern) the blank half of the glyphs,
if they are given full-width and must be set half-width, or
<li>
add space to the glyphs,
if they are given half-width must be set full-width.
</ul>
Some fonts use proportional glyphs for fullwidth punctuation characters.
For such proportional glyphs, the given advance width is considered
simultaneously full-width and half-width: no space is added or removed.
<p class="note">
The advance width of a standard Han character
can be determined either from font metrics
such as the OpenType <code>ideo</code> and <code>idtp</code> baselines for the opposite writing mode,
or by taking the advance width of a Han character such as 水 U+6C34.
(The opposite writing mode must be used because some fonts are compressed
so that the characters are not square.)
More information on OpenType metrics can be found
<a href="http://www.microsoft.com/typography/otspec/baselinetags.htm#ideoembox">in the OpenType spec</a>.
Note that if 水 U+6C34, 卜 U+535C, and 一 U+4E00 do not all have the same advance width,
the font has proportional ideographs
and the fullwidth advance width cannot be reliably determined by measuring glyphs.
Unless 'text-spacing' is set to ''space-adjacent'' or ''text-spacing/none''
(or the font has proportional fullwidth punctuation glyphs),
the UA must collapse the space typically associated with such full width glyphs
as follows:
<ul>
<li>
Set <a>fullwidth opening punctuation</a> half-width if the previous character is
a <a>fullwidth opening punctuation</a>,
<a>fullwidth middle dot punctuation</a>,
or ideographic space (U+3000).
Else set it full-width.
<li>
Set <a>fullwidth closing punctuation</a> half-width if the next character is
a <a>fullwidth closing punctuation</a>,
<a>fullwidth middle dot punctuation</a>,
or ideographic space (U+3000).
Else set it full-width.
<li>
Set <a>fullwidth closing punctuation</a> followed by <a>fullwidth opening punctuation</a>
each at "3/4-width", i.e. halfway between full-width and half-width.
</ul>
<div class="example">
The following example table lists the punctuation pairs
affected by adjancent-pairs trimming.
It uses halfwidth equivalents to approximate the trimming effect.
<table class="data">
<caption>Demonstration of adjacent-pairs punctuation trimming</caption>
<thead>
<tr><th>Combination
<th>Sample Pair
<th>Looks Like
<tbody>
<tr><td scope=row>Opening—Opening
<td><tt lang="ja" class="char">〔</tt>+<tt lang="ja" class="char">（</tt>
<td><tt lang="ja" class="char">〔</tt><tt lang="ja" class="char half-r">(</tt>
<tr><td scope=row>Middle Dot—Opening
<td><tt lang="ja" class="char">・</tt>+<tt lang="ja" class="char">（</tt>
<td><tt lang="ja" class="char">・</tt><tt lang="ja" class="char">(</tt>
<tr><td scope=row>Closing—Opening
<td><tt lang="ja" class="char">〕</tt>+<tt lang="ja" class="char">（</tt>
<td><tt lang="ja" class="char">)<span class="quarter">　</span></tt><tt lang="ja" class="char"><span class="quarter">　</span>(</tt>
<tr><td scope=row>Ideographic Space—Opening
<td><tt lang="ja" class="char"> </tt>+<tt lang="ja" class="char">（</tt>
<td><tt lang="ja" class="char"> </tt><tt lang="ja" class="char">(</tt>
<tr><td scope=row>Closing—Closing
<td><tt lang="ja" class="char">）</tt>+<tt lang="ja" class="char">〕</tt>
<td><tt lang="ja" class="char">)</tt><tt lang="ja" class="char">〕</tt>
<tr><td scope=row>Closing—Middle Dot
<td><tt lang="ja" class="char">）</tt>+<tt lang="ja" class="char">・</tt>
<td><tt lang="ja" class="char">)</tt><tt lang="ja" class="char">・</tt>
<tr><td scope=row>Closing—Ideographic Space
<td><tt lang="ja" class="char">）</tt>+<tt lang="ja" class="char"> </tt>
<td><tt lang="ja" class="char">)</tt><tt lang="ja" class="char"> </tt>
</table>
</div>