forked from w3c/csswg-drafts
-
Notifications
You must be signed in to change notification settings - Fork 0
Expand file tree
/
Copy pathOverview.src.html
More file actions
3932 lines (3555 loc) · 154 KB
/
Overview.src.html
File metadata and controls
3932 lines (3555 loc) · 154 KB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
<!DOCTYPE html public '-//W3C//DTD HTML 4.01//EN'
'http://www.w3.org/TR/html4/strict.dtd'>
<html lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>CSS Text Level 3</title>
<link rel="stylesheet" type="text/css" href="../default.css">
<style type="text/css">
.egbidiwsaA,.egbidiwsbB,.egbidiwsaB,.egbidiwsbC
{ white-space:pre;font-size:80%;font-family:monospace; vertical-align:2px; margin:1px }
.egbidiwsaA { background:lime;padding:2px; }
.egbidiwsbB { border:2px solid blue }
.egbidiwsaB { background:yellow;border:2px dotted white }
.egbidiwsbC { border:2px dotted red }
.char { border: 1px dotted gray; }
.quarter { font-size: 25%; }
tt[lang="ja"] { font-family: "MS Gothic", "Osaka", monospace }
div.figure table {
margin :auto;
}
</style>
<link rel="stylesheet" type="text/css" href="http://www.w3.org/StyleSheets/TR/W3C-ED.css">
</head>
<body>
<div class="head">
<!--logo-->
<h1>CSS Text Level 3</h1>
<h2 class="no-num no-toc">[LONGSTATUS] [DATE]</h2>
<dl>
<dt>This version:</dt>
<dd><a href="http://dev.w3.org/csswg/css3-text/">$Date$ (CVS $Revision$)</a>
<!--
<dd><a href="http://www.w3.org/TR/[YEAR]/WD-css3-text-[CDATE]/">http://www.w3.org/TR/[YEAR]/WD-css3-text-[CDATE]/</a></dd>
-->
<dt>Latest version:</dt>
<dd><a href="http://www.w3.org/TR/css3-text/">http://www.w3.org/TR/css3-text/</a></dd>
<dt>Latest editor's draft:</dt>
<dd><a href="http://dev.w3.org/csswg/css3-text/">http://dev.w3.org/csswg/css3-text/</a></dd>
<dt>Previous version:</dt>
<dd><a
href="http://www.w3.org/TR/2011/WD-css3-text-20110901/">http://www.w3.org/TR/2011/WD-css3-text-20110901/</a></dd>
<dt>Issues List:</dt>
<dd><a href="http://www.w3.org/Style/CSS/Tracker/products/10">http://www.w3.org/Style/CSS/Tracker/products/10</a>
<dt>Discussion:</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:</dt>
<dd><a href="http://fantasai.inkedblade.net/contact">Elika J. Etemad</a> (Mozilla)</dd>
<dd><a href="mailto:kojiishi@gluesoft.co.jp">Koji Ishii</a> (Invited Expert)</dd>
</dl>
<!--begin-copyright-->
<p>[Here will be included the file "../copyright.inc"]</p>
<!--end-copyright-->
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc" id="abstract">Abstract</h2>
<p>This CSS3 module defines properties for text manipulation and
specifies their processing model. It covers line breaking, justification
and alignment, white space handling, text decoration and text
transformation.</p>
<h2 class="no-num no-toc" id="status">Status of This Document</h2>
<p><em>This section describes the status of this document at the time of
its publication. Other documents may supersede this document. A list of
current W3C publications and the latest revision of this technical report
can be found in the <a href="http://www.w3.org/TR/">W3C technical reports
index at http://www.w3.org/TR/.</a></em>
<p>Publication as a Working Draft does not imply endorsement by the W3C
Membership. This is a draft document and may be updated, replaced or
obsoleted by other documents at any time. It is inappropriate to cite this
document as other than work in progress.
<p>This CSS module has been produced as a combined effort of the <a
href="http://www.w3.org/International/Activity">W3C Internationalization Activity</a>,
and the <a href="http://www.w3.org/Style/Activity">Style Activity</a> and is maintained
by the <a href="http://www.w3.org/Style/CSS/members">CSS Working Group</a>. It also
includes contributions made by participants in the <a
href="http://www.w3.org/Style/XSL/Group/">XSL Working Group</a> (<a
href="http://cgi.w3.org/MemberAccess/AccessRequest">members
only</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>
<p><strong>Feedback on this draft should be posted to the
(<a href="http://lists.w3.org/Archives/Public/www-style/">archived</a>)
public mailing list <a href="mailto:www-style@w3.org">www-style@w3.org</a></strong>
(see <a href="http://www.w3.org/Mail/Request">instructions</a>) <strong>with
<kbd>[css3-text]</kbd> in the subject line.</strong>
You are strongly encouraged to complain if you see something stupid
in this draft. The editors will do their best to respond to all feedback.</p>
<p>The following features are at risk and may be cut from the spec during
its CR period if there are no (correct) implementations:</p>
<ul>
<li>the <length> values of the 'tab-size' property
<li>the ''start end'' and ''<string>'' values of 'text-align'
<li>the 'hanging-punctuation' property
<li>the percentage values of 'word-spacing'
<li>the 'text-decoration-skip' property / ''ink'' value
<li><span class="issue">audit draft and add more here</span>
</ul>
<h2 class="no-num no-toc" id="contents">
Table of Contents</h2>
<!--toc-->
<h2 id="intro">
Introduction</h2>
<p>[document here]</p>
<p class="issue">This draft describes features that are specific to certain scripts.
There is an ongoing discussion about where these features belong: in
existing CSS properties, in new CSS properties, or perhaps in other
specifications.
<h3 id="placement">
Module Interactions</h3>
<p>This module replaces and extends the text-level
features defined in [[!CSS21]] chapter 16.
<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.
<h3 id="terms">
Terminology</h3>
<p id="grapheme-cluster">A <dfn>grapheme cluster</dfn> is what
a language user considers to be a character or a basic unit of the
script. The term is described in detail in the Unicode Technical
Report: Text Boundaries [[!UAX29]]. This specification uses the
<em>extended grapheme cluster</em> definition in [[!UAX29]] (not
the <em>legacy grapheme cluster</em> definition). The UA may further
tailor the definition as allowed by Unicode. Within this specification,
the ambiguous term <dfn>character</dfn> is used as a friendlier synonym
for <i>grapheme cluster</i>.
See <a href="http://dev.w3.org/csswg/css3-writing-modes/#character-properties">Characters and Properties</a>
for how to determine the Unicode properties of a character.
<p id="letter">A <dfn>letter</dfn> for the purpose of this specification
is a <i>character</i> belonging to one of the Letter or Number general
categories in Unicode. [[!UAX44]]
<p>The rendering characteristics of a <i>character</i> divided by an
element boundary is undefined: it may be rendered as belonging to
either side of the boundary, or as some approximation of belonging
to both. Authors are forewarned that dividing grapheme clusters by
element boundaries may give inconsistent or undesired results.
<h2 id="transforming">
Transforming Text</h2>
<h3 id="text-transform">
<a name="caps-prop"></a>
Transforming Text: the 'text-transform' property</h3>
<table class="propdef">
<tbody>
<tr>
<th>Name:</th>
<td><dfn>text-transform</dfn></td>
</tr>
<tr>
<th><a href="#values">Value</a>:
<td>none |
[ [ capitalize | uppercase | lowercase ] || full-width || full-size-kana ]
</td>
</tr>
<tr>
<th>Initial:</th>
<td>none</td>
</tr>
<tr>
<th>Applies to:</th>
<td>all elements</td>
</tr>
<tr>
<th>Inherited:</th>
<td>yes</td>
</tr>
<tr>
<th>Percentages:</th>
<td>N/A</td>
</tr>
<tr>
<th>Media:</th>
<td>visual</td>
</tr>
<tr>
<th>Computed value:</th>
<td>as specified</td>
</tr>
</tbody>
</table>
<p>This property transforms text for styling purposes.
Values have the following meanings:</p>
<dl>
<dt><dfn title="text-transform:none">''none''</dfn></dt>
<dd>No effects.</dd>
<dt><dfn title="text-transform:capitalize">''capitalize''</dfn></dt>
<dd>Puts the first <i>letter</i> of each word in titlecase; other characters
are unaffected.</dd>
<dt><dfn title="text-transform:uppercase">''uppercase''</dfn></dt>
<dd>Puts all characters in uppercase.
<dt><dfn title="text-transform:lowercase">''lowercase''</dfn></dt>
<dd>Puts all characters in lowercase.</dd>
<dt><dfn title="text-transform:full-width">''full-width''</dfn></dt>
<dd>Puts all characters in fullwidth form.
If the character does not have a corresponding fullwidth form,
it is left as is.
This value is typically used to typeset Latin characters and digits
like ideographic characters.
<dt><dfn title="text-transform:full-size-kana">''full-size-kana''</dfn></dt>
<dd>Converts all small Kana characters to normal Kana.
This value is typically used for ruby annotation text,
where all small Kana should be drawn as large Kana.
</dl>
<p>The case mapping rules for the character repertoire specified by the
Unicode Standard can be found on the Unicode Consortium Web site
[[!UNICODE]]. The UA must use the full case mappings for Unicode
characters, including any conditional casing rules, as defined in
Default Case Algorithm section. If (and only if) the content language
of the element is, according to the rules of the document language,
known, then any appropriate language-specific rules must be applied
as well.
These minimally include, but are not limited to, the language-specific
rules in Unicode's
<a href="http://www.unicode.org/Public/UNIDATA/SpecialCasing.txt">SpecialCasing.txt</a>.
<div class="example">
<p>For example, in Turkish there are two “i”s, one with
a dot—“İ” and “i”— and one
without—“I” and “ı”. Thus the usual
case mappings between “I” and “i” are
replaced with a different set of mappings to their respective
undotted/dotted counterparts, which do not exist in English. This
mapping must only take effect if the language is known to be Turkish
or Azeri; in other languages, the usual mapping of “I”
and “i” is required. This rule is thus conditionally
defined in Unicode's SpecialCasing.txt file.
</div>
<!--
<div class="example">
<p>An example where the UA may choose to include rules beyond those
in Unicode is Greek. In Greek, if the entire word is in upper case,
accents are dropped or transformed
http://blogs.msdn.com/b/michkap/archive/2006/08/18/706383.aspx
</div>
-->
<p>The definition of "word" used for ''capitalize'' is UA-dependent;
[[!UAX29]] is suggested (but not required) for determining such word
boundaries. Authors should not expect ''capitalize'' to follow
language-specific titlecasing conventions (such as skipping articles
in English).
<p>The definition of fullwidth and halfwidth forms can be found on the
Unicode consortium web site at [[!UAX11]].
The mapping to fullwidth form is defined by taking code points with
the <wide> or the <narrow> tag in their Decomposition_Mapping
in [[!UAX44]]. For the <narrow> tag, the mapping is from the code
point to the decomposition (minus <narrow> tag), and for the
<wide> tag, the mapping is from the decomposition (minus the
<wide> tag) back to the original code point.</p>
<p>The mappings for small Kana to normal Kana are defined in
<a href="#small-kana">Small Kana Mappings</a>.</p>
<p>When multiple values are specified and therefore multiple
transformations need to be applied, they are applied in the following
order:</p>
<ol>
<li>''capitalize'', ''uppercase'', and ''lowercase''</li>
<li>''full-width''</li>
<li>''full-size-kana''</li>
</ol>
<p>Text transformation happens after <a href="#white-space-rules">white
space processing</a>, which means that ''full-width'' transforms
only preserved U+0020 spaces to U+3000.
<div class="example">
<p>The following example converts the ASCII characters in abbreviations
in Japanese to their fullwidth variants so that they lay out and line
break like ideographs:
<pre>abbr:lang(ja) { text-transform: full-width; }</pre>
</div>
<p class="issue">CSS may introduce the ability to create custom mapping
tables for less common text transforms, such as by an ''@text-transform''
rule similar to ''@counter-style'' from [[CSS3LIST]], and this mechanism
may be used to replace ''full-size-kana''.
<h2 id="white-space-processing">
White Space Processing</h2>
<p>The source text of a document often contains formatting that
is not relevant to the final rendering: for example, breaking
the source into segments (lines) for ease of editing or adding
white space characters such as tabs and spaces to indent the
source code. CSS white space processing allows the author to
control interpretation of such formatting: to preserve or
collapse it away when rendering the document. Note that white
space processing in CSS interprets white space characters only
for rendering: it has no effect on the underlying document data.
<p id="segment-normalization">
CSS does not define document segmentation rules. Segments could be
separated by a particular newline seqence (such as a line feed or
CRLF pair), or delimited by some other mechanism, such as the SGML
RECORD-START and RECORD-END tokens.
For CSS processing, each document-defined segment break, CRLF sequence
(U+000D U+000A), carriage return (U+000D), and line feed (U+000A)
in the text is treated as a segment break, which is then interpreted
for rendering as defined below.
<p class="note">Note that the document parser may have not only normalized
segment breaks, but also collapsed other space characters or
otherwise processed white space according to markup rules. Because CSS
processing occurs <em>after</em> the parsing stage, it is not possible
to restore these characters for styling. Therefore, some of the
behavior specified below can be affected by these limitations and
may be user agent dependent.</p>
<p class="note">Note that anonymous inlines consisting entirely of
<i>collapsible</i> white space are removed from the rendering tree.
See [[CSS21]] section
<a href="http://www.w3.org/TR/CSS21/visuren.html#anonymous">9.2.2.1</a></p>
<p>Control characters (Unicode class Cc) other than tab (U+0009), line feed
(U+000A), and carriage return (U+000D)
are ignored for the purpose of rendering.
<h3 id="white-space-collapsing">
White Space Collapsing: the 'text-space-collapse' property</h3>
<table class="propdef">
<tbody>
<tr>
<th>Name:</th>
<td><dfn>text-space-collapse</dfn></td>
</tr>
<tr>
<th><a href="#values">Value</a>:
<td>collapse | preserve | preserve-breaks</td>
</tr>
<tr>
<th>Initial:</th>
<td>collapse</td>
</tr>
<tr>
<th>Applies to:</th>
<td>all elements</td>
</tr>
<tr>
<th>Inherited:</th>
<td>yes</td>
</tr>
<tr>
<th>Percentages:</th>
<td>N/A</td>
</tr>
<tr>
<th>Media:</th>
<td>visual</td>
</tr>
<tr>
<th>Computed value:</th>
<td>specified value</td>
</tr>
</tbody>
</table>
<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 <a href="#white-space-rules">white space processing
rules</a>:</p>
<dl>
<dt><dfn title="white-space:collapse">''collapse''</dfn></dt>
<dd>This value directs user agents to collapse sequences of white space
into a single character (or <a href="#line-break-transform">in some
cases</a>, no character).</dd>
<dt><dfn title="white-space:preserve">''preserve''</dfn></dt>
<dd>This value prevents user agents from collapsing sequences
of white space. Segment breaks such as line feeds and carriage returns
are preserved as forced line breaks.</dd>
<dt><dfn title="white-space:preserve-breaks">''preserve-breaks''</dfn></dt>
<dd>This value collapses consecutive spaces, but renders segment
breaks as forced line breaks.</dd>
</dl>
<p>See <a href="#white-space-processing">White Space Processing Rules</a>
for details on how white space collapses. An informative summary of
''collapse'' is presented below:
<ul>
<li>A sequence of segment breaks and other white space between two
Chinese, Japanese, or Yi characters collapses into nothing.
<li>A zero width space before or after a white space sequence
containing a segment break causes the entire sequence of white space
to collapse into a zero width space.
<li>Otherwise, consecutive white space collapses into a single space.
</ul>
<h3 id="tab-size">
Tab Character Size: the 'tab-size' property</h3>
<table class="propdef">
<tbody>
<tr>
<th>Name:</th>
<td><dfn>tab-size</dfn></td>
</tr>
<tr>
<th><a href="#values">Value</a>:
<td><integer> | <length></td>
</tr>
<tr>
<th>Initial:</th>
<td>8</td>
</tr>
<tr>
<th>Applies to:</th>
<td>block containers</td>
</tr>
<tr>
<th>Inherited:</th>
<td>yes</td>
</tr>
<tr>
<th>Percentages:</th>
<td>N/A</td>
</tr>
<tr>
<th>Media:</th>
<td>visual</td>
</tr>
<tr>
<th>Computed value:</th>
<td>specified value</td>
</tr>
</tbody>
</table>
<p>This property determines the measure of the tab character (U+0009)
when rendered. Integers represent the measure in space characters (U+0020).
Negative integers are not allowed.
<h3 id="white-space-rules">
The White Space Processing Rules</h3>
<p>White space processing affects only spaces (U+0020), tabs (U+0009),
and <a href="#segment-normalization">segment breaks</a>.
<p>For each inline (including anonymous inlines) within an inline
formatting context, white space characters are handled as follows,
ignoring bidi formatting characters as if they were not there:</p>
<ul>
<li id="collapse"><p>If 'text-space-collapse'
is set to ''collapse'' or ''preserve-breaks'', white space characters
are considered <dfn>collapsible</dfn> and are processed by
performing the following steps:</p>
<ol>
<li>All spaces and tabs immediately preceding or following a segment
break are removed.</li>
<li>Segment breaks are transformed for
rendering according to the <a href="#line-break-transform">line
break transformation rules</a>.
</li>
<li>Every tab is converted to a space (U+0020).</li>
<li>Any space immediately following another collapsible space
—even one outside the boundary of the inline containing
the space, provided they are within the same inline formatting
context—is collapsed to have zero advance width. (It is
invisible, but retains its line-breaking opportunity, if any.)</li>
</ol>
</li>
<li><p>If 'text-space-collapse' is set to ''preserve'', any sequence of
spaces is treated as a sequence of non-breaking spaces. However,
a line breaking opportunity exists at the end of the sequence.</p></li>
</ul>
<p>Then, the entire block is rendered. Inlines are laid out, taking bidi
reordering into account, and wrapping as specified by the
'text-wrap' property.</p>
<p>As each line is laid out,</p>
<ol>
<li>A sequence of collapsible spaces at the beginning of a line is
removed.
<li>Each tab is rendered as a horizontal shift that lines up
the start edge of the next glyph with the next tab stop.
Tab stops occur at points that are multiples of the width of a
space (U+0020) rendered in the block's font from the block's
starting content edge. How many spaces is given by the 'tab-size'
property.</li>
<li>A sequence of collapsible spaces at the end of a line is removed.
<li>If spaces or tabs at the end of a line are non-collapsible but
have 'text-wrap' set to 'normal' or 'avoid' the UA may visually
collapse their character advance widths.
</ol>
<p>White space that was not removed or collapsed during the white space
processing steps is called <dfn>preserved</dfn> white space.</p>
<div class="example">
<h4 id="egbidiwscollapse">
Example of bidirectionality with white space collapsing</h4>
<p>Consider the following markup fragment, taking special note of spaces
(with varied backgrounds and borders for emphasis and identification):
</p>
<pre><code><ltr>A<span class="egbidiwsaA"> </span><rtl><span class="egbidiwsbB"> </span>B<span class="egbidiwsaB"> </span></rtl><span class="egbidiwsbC"> </span>C</ltr></code></pre>
<p>where the <code><ltr></code> element represents a left-to-right
embedding and the <code><rtl></code> element represents a
right-to-left embedding. If the 'text-space-collapse' property is set
to ''collapse'', the above processing model would result in the
following:</p>
<ul style="line-height:1.3">
<li>The space before the B (<span class="egbidiwsbB"> </span>)
would collapse with the space after the A (<span
class="egbidiwsaA"> </span>).</li>
<li>The space before the C (<span class="egbidiwsbC"> </span>)
would collapse with the space after the B (<span
class="egbidiwsaB"> </span>).</li>
</ul>
<p>This would leave two spaces, one after the A in the left-to-right
embedding level, and one after the B in the right-to-left embedding
level. This is then ordered according to the Unicode bidirectional
algorithm, with the end result being:</p>
<pre>A<span class="egbidiwsaA"> </span><span class="egbidiwsaB"> </span>BC</pre>
<p>Note that there are two spaces between A and B, and none between B
and C. This is best avoided by putting spaces outside the element
instead of just inside the opening and closing tags and, where
practical, by relying on implicit bidirectionality instead of explicit
embedding levels.</p>
</div>
<h4 id="line-break-transform">
Line Break Transformation Rules</h4>
<p>When 'text-space-collapse' is ''preserve-breaks'', segment breaks are
not <i>collapsible</i> and are transformed into a preserved line feed
(U+000A).
<p>When segment breaks are <i>collapsible</i>, they are
either transformed into a space (U+0020) or removed depending on the
context before and after the break.</p>
<p class="note">Note that the white space processing rules have already
removed any tabs and spaces after the segment break before these checks
take place.</p>
<ul>
<li>If the character immediately before or immediately after the segment
break is the zero-width space character (U+200B), then the break
is removed, leaving behind the zero-width space.
<li>Otherwise, if the East Asian Width property [[!UAX11]] of both
the character before and after the line feed is F, W, or H (not A),
and neither side is Hangul, then the segment break is removed.
<li>Otherwise, the segment break is converted to a space (U+0020).
</ul>
<p class="issue">Comments on how well this would work in practice would
be very much appreciated, particularly from people who work with
Thai and similar scripts.</p>
<h3 id="white-space">
White Space and Text Wrapping Shorthand: the 'white-space' property</h3>
<table class="propdef">
<tbody>
<tr>
<th>Name:</th>
<td><dfn>white-space</dfn></td>
</tr>
<tr>
<th><a href="#values">Value</a>:
<td>normal | pre | nowrap | pre-wrap | pre-line</td>
</tr>
<tr>
<th>Initial:</th>
<td>not defined for shorthand properties</td>
</tr>
<tr>
<th>Applies to:</th>
<td>all elements</td>
</tr>
<tr>
<th>Inherited:</th>
<td>yes</td>
</tr>
<tr>
<th>Percentages:</th>
<td>N/A</td>
</tr>
<tr>
<th>Media:</th>
<td>visual</td>
</tr>
<tr>
<th>Computed value:</th>
<td>see individual properties</td>
</tr>
</tbody>
</table>
<p>The 'white-space' property is a shorthand for the
'text-space-collapse' and 'text-wrap' properties.
Not all combinations are represented.
Values have the following meanings:</p>
<dl>
<dt><dfn title="white-space:normal">''normal''</dfn></dt>
<dd>Sets 'text-space-collapse' to ''collapse'' and
'text-wrap' to ''normal''</dd>
<dt><dfn title="white-space:pre">''pre''</dfn></dt>
<dd>Sets 'text-space-collapse' to ''preserve'' and
'text-wrap' to ''none''</dd>
<dt><dfn title="white-space:nowrap">''nowrap''</dfn></dt>
<dd>Sets 'text-space-collapse' to ''collapse'' and
'text-wrap' to ''none''</dd>
<dt><dfn title="white-space:pre-wrap">''pre-wrap''</dfn></dt>
<dd>Sets 'text-space-collapse' to ''preserve'' and
'text-wrap' to ''normal''</dd>
<dt><dfn title="white-space:pre-line">''pre-line''</dfn></dt>
<dd>Sets 'text-space-collapse' to ''preserve-breaks'' and
'text-wrap' to ''normal''</dd>
</dl>
<p>The following informative table summarizes the behavior of various
'white-space' values:</p>
<table class="data">
<colgroup class="header"></colgroup>
<colgroup span=3></colgroup>
<thead>
<tr>
<th></th>
<th>New Lines</th>
<th>Spaces and Tabs</th>
<th>Text Wrapping</th>
</tr>
</thead>
<tbody>
<tr>
<th>normal</th>
<td>Collapse</td>
<td>Collapse</td>
<td>Wrap</td>
</tr>
<tr>
<th>pre</th>
<td>Preserve</td>
<td>Preserve</td>
<td>No wrap</td>
</tr>
<tr>
<th>nowrap</th>
<td>Collapse</td>
<td>Collapse</td>
<td>No wrap</td>
</tr>
<tr>
<th>pre-wrap</th>
<td>Preserve</td>
<td>Preserve</td>
<td>Wrap</td>
</tr>
<tr>
<th>pre-line</th>
<td>Preserve</td>
<td>Collapse</td>
<td>Wrap</td>
</tbody>
</table>
<h2 id="line-breaking">
Line Breaking and Word Boundaries</h2>
<p>In most writing systems, in the absence of hyphenation a line break occurs
only at word boundaries. Many writing systems use spaces or
punctuation to explicitly separate words, and line break opportunities
can be identified by these characters. Scripts such as Thai, Lao, and
Khmer, however, do not use spaces or punctuation to separate words.
Although the zero width space (U+200B) can be used as an explicit word
delimiter in these scripts, this practice is not common. As a result,
a lexical resource is needed to correctly identify break points in such
texts.
<p>In several other writing systems, (including Chinese, Japanese, Yi,
and sometimes also Korean) a line break opportunity is based on
character boundaries, not word boundaries. In these systems a line can break
anywhere <em>except</em> between certain character combinations.
Additionally the level of strictness in these restrictions can vary
with the typesetting style.</p>
<p>CSS does not fully define where line breaking opportunities occur,
however some controls are provided to distinguish common variations.
For breaking opportunities created by characters that disappear at the
line break (i.e. spaces), properties on the element containing that
character control the line breaking at that opportunity.
For breaking opportunities defined by the boundary between two characters,
the properties on the element containing the boundary control breaking.
<!-- http://lists.w3.org/Archives/Public/www-style/2008Dec/0043.html -->
For break opportunities given by the first or last character of a
box, the break occurs immediately before/after the box (at its margin
edge) rather than breaking the box at its content edge.
<div class="note">
<p>Further information on line breaking conventions can be found in
[[JLREQ]] and [[JIS4051]] for Japanese,
[[ZHMARK]] for Chinese, and
in [[!UAX14]] for all scripts in Unicode.
<!-- The CSS Working Group notes that although UAX 14 contains a wealth of
information about line breaking conventions, a literal implementation
of its algorithm has been found to be inadequate in multiple situations. -->
<p class="issue">Any guidance for appropriate references here would be
much appreciated.
<!-- Additionally, some guidance could be provided on how
to break or not break Southeast Asian in the absence of a dictionary.
(See e.g. <a href="http://lists.w3.org/Archives/Public/www-style/2011Feb/0126.html">notes on Thai</a>.) -->
</div>
<p>Floated and absolutely-positioned elements do not introduce a line
breaking opportunity. The line breaking behavior of a replaced element
is equivalent to that of the Object Replacement Character (U+FFFC).
<h3 id="line-break">
Line Breaking Strictness: the 'line-break' property</h3>
<table class="propdef">
<tbody>
<tr>
<th>Name:</th>
<td><dfn>line-break</dfn></td>
</tr>
<tr>
<th><a href="#values">Value</a>:
<td>auto | loose | normal | strict</td>
</tr>
<tr>
<th>Initial:</th>
<td>auto</td>
</tr>
<tr>
<th>Applies to:</th>
<td>all elements</td>
</tr>
<tr>
<th>Inherited:</th>
<td>yes</td>
</tr>
<tr>
<th>Percentages:</th>
<td>N/A</td>
</tr>
<tr>
<th>Media:</th>
<td>visual</td>
</tr>
<tr>
<th>Computed value:</th>
<td>specified value</td>
</tr>
</tbody>
</table>
<p>This property specifies the strictness of line-breaking rules applied
within an element: particularly how line-breaking interacts with
punctuation. Values have the following meanings:</p>
<dl>
<dt><dfn title="line-break:auto">''auto''</dfn></dt>
<dd>The UA determines the set of line-breaking restrictions to use,
and it may vary the restrictions based on the length of the line; e.g.,
use a less restrictive set of line-break rules for short lines.</dd>
<dt><dfn title="line-break:loose">''loose''</dfn></dt>
<dd>Breaks text using the least restrictive set of line-breaking
rules. Typically used for short lines, such as in newspapers.</dd>
<dt><dfn title="line-break:normal">''normal''</dfn></dt>
<dd>Breaks text using the most common set of line-breaking rules.</dd>
<dt><dfn title="line-break:strict">''strict''</dfn></dt>
<dd>Breaks text using the most stringent set of line-breaking
rules.</dd>
</dl>
<p>CSS distinguishes between three levels of strictness in the rules for
implicit line breaking. The precise set of rules in effect for each
level is up to the UA and should follow language conventions. However,
this specification does recommend that:</p>
<ul>
<li>Following breaks be forbidden in ''strict'' line breaking and
allowed in ''normal'' and ''loose'':
<ul>
<li>breaks before Japanese <a href="#small-kana">small kana</a>
<li>breaks before the Katakana-Hiragana prolonged sound mark:
ー U+30FC
</ul>
If the language is known to be Chinese or Japanese, then additionally:
<ul>
<li>breaks before before hyphens:<br>
‐ U+2010, – U+2013, 〜 U+301C,
゠ U+30A0
</ul>
<li>Following breaks be forbidden in ''normal'' and ''strict'' line
breaking and allowed in ''loose'':
<ul>
<li>breaks before iteration marks:<br>
々 U+3005, 〻 U+303B, ゝ U+309D,
ゞ U+309E, ヽ U+30FD, ヾ U+30FE
<li>breaks between some inseparable characters:<br>
‥ U+2025, … U+2026
</ul>
If the language is known to be Chinese or Japanese, then additionally:
<ul>
<li>breaks before certain centered punctuation marks:<br>
: U+003A, ; U+003B, ・ U+30FB,
： U+FF1A, ； U+FF1B, ･ U+FF65,
! U+0021, ? U+003F, ‼ U+203C,
⁇ U+2047, ⁈ U+2048, ⁉ U+2049,
！ U+FF01, ？ U+FF1F
<li>breaks before postfixes:<br>
% U+0025, ¢ U+00A2, ° U+00B0,
‰ U+2030, ′ U+2032, ″ U+2033,
℃ U+2103, ％ U+FF05, ￠ U+FFE0
<li>breaks after prefixes:<br>
$ U+0024, £ U+00A3, ¥ U+00A5,
€ U+20AC, № U+2116, ＄ U+FF04,
￡ U+FFE1, ￥ U+FFE5
</ul>
</ul>
<p class="note">In CSS3 no distinction is made among the levels of
strictness in non-CJK text: only CJK codepoints are affected, unless
the text is marked as Chinese or Japanese, in which case some additional
common codepoints are affected. However a future level of CSS may add
behaviors affecting non-CJK text.
<p>Support for this property is <em>optional</em>. It is recommended
for UAs that wish to support CJK typography and strongly recommended
for UAs in the Japanese market.</p>
<p class="note">The CSSWG recognizes that in a future edition of the
specification finer control over line breaking may be necessary to
satisfy high-end publishing requirements.
<h3 id="word-break">
Word Breaking Rules: the 'word-break' property</h3>
<table class="propdef">
<tbody>
<tr>
<th>Name:</th>
<td><dfn>word-break</dfn></td>
</tr>
<tr>
<th><a href="#values">Value</a>:
<td>normal | keep-all | break-all</td>
</tr>
<tr>
<th>Initial:</th>
<td>normal</td>
</tr>
<tr>
<th>Applies to:</th>
<td>all elements</td>
</tr>
<tr>
<th>Inherited:</th>
<td>yes</td>
</tr>
<tr>
<th>Percentages:</th>
<td>N/A</td>
</tr>
<tr>
<th>Media:</th>
<td>visual</td>
</tr>
<tr>
<th>Computed value:</th>
<td>specified value</td>
</tr>
</tbody>
</table>
<p>This property specifies line break opportunities within words.
Values have the following meanings:</p>
<dl>
<dt><dfn title="word-break:normal">''normal''</dfn></dt>
<dd>Break lines according to their usual rules.</dd>
<dt><dfn title="word-break:break-all">''break-all''</dfn></dt>
<dd>In addition to normal opportunities, lines may break between any two
letters within words except where forbidden by the 'line-break' property.
Hyphenation is not applied. This option is used mostly in a context where
the text is predominantly using CJK characters with few non-CJK excerpts
and it is desired that the text be better distributed on each line.</dd>
<dt><dfn title="word-break:keep-all">''keep-all''</dfn></dt>
<dd>Lines may break only at <a href="#word-separator">word separators</a>
and other explicit break opportunities. Otherwise this option is
equivalent to ''normal''.
This option is mostly used where the presence of word separator
characters still creates line-breaking opportunities, as in Korean.</dd>
</dl>
<div class="example">
<p>Here's a mixed-script sample text:
<pre>这是一些汉字, and some Latin,<!--
--> و کمی نوشتنن عربی, <!--
-->และตัวอย่างการเขียนภาษาไทย.</pre>
<p>The break-points are determined as follows (indicated by ‘·’):
<dl>
<dt>''word-break: normal''</dt>
<dd>
<pre>这·是·一·些·汉·字,·and·some·Latin,<!--
-->·و·کمی·نوشتنن·عربی·<!--
-->และ·ตัวอย่าง·การเขียน·ภาษาไทย.</.pre>
<dt>''word-break: break-all''</dt>
<dd>
<pre>这·是·一·些·汉·字·a·n·d·s·o·m·e·L·a·t·i·n,<!--
-->·و·ﮐ·ﻤ·ﻰ·ﻧ·ﻮ·ﺷ·ﺘ·ﻦ·ﻋ·ﺮ·ﺑ·ﻰ,·<!--
-->แ·ล·ะ·ตั·ว·อ·ย่·า·ง·ก·า·ร·เ·ขี·ย·น·ภ·า·ษ·า·ไ·ท·ย.</pre>
<dt>''word-break: keep-all''</dt>
<dd>
<pre>这是一些汉字,·and·some·Latin,<!--
-->·و·کمی·نوشتنن·عربی,·<!--
-->และ·ตัวอย่าง·การเขียน·ภาษาไทย.</pre>
</dl>
</div>
<p>When shaping scripts such as Arabic are allowed to break within words
due to ''break-all'', the characters must still be shaped as if the
word were not broken.</p>
<h2 id="hyphenation">Hyphenation</h2>
<p>Hyphenation allows the controlled splitting of words to improve the
layout of paragraphs. CSS Text Level 3 does not define the exact rules
for hyphenation, however UAs are strongly encouraged to optimize their