-
Notifications
You must be signed in to change notification settings - Fork 790
Expand file tree
/
Copy pathOverview.src.html
More file actions
2899 lines (2412 loc) · 116 KB
/
Overview.src.html
File metadata and controls
2899 lines (2412 loc) · 116 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">
<html lang="en">
<head>
<title>Selectors Level 4</title>
<link href="default.css" type="text/css" rel="stylesheet">
<style type="text/css">
.tprofile td, th { vertical-align: baseline; padding: 0 0.5em; }
.tprofile th { text-align: right; }
</style>
<link href="http://www.w3.org/StyleSheets/TR/W3C-WD.css" type="text/css" rel="stylesheet">
</head>
<body>
<div class="head">
<!--logo-->
<h1 id=title>Selectors Level 4</h1>
<h2 class=
A0B2
"no-num no-toc">[LONGSTATUS] [DATE]</h2>
<dl>
<dt>This version:
<!--
<dd><a href="[VERSION]">
http://www.w3.org/TR/[YEAR]/WD-[SHORTNAME]-[CDATE]/</a>
<dt>Editor's draft:
-->
<dd><a href="http://dev.w3.org/csswg/selectors4/">
http://dev.w3.org/csswg/selectors4/</a>
<dt>Latest version of Selectors Level 4:
<dd><a href="http://www.w3.org/TR/selectors4/">
http://www.w3.org/TR/selectors4/</a>
<dt>Latest Selectors specification:
<dd><a href="http://www.w3.org/TR/selectors/">
http://www.w3.org/TR/selectors/</a>
<dt>Previous version:
<dd><a href="http://www.w3.org/TR/2011/WD-selectors4-20110929/">
http://www.w3.org/TR/2011/WD-selectors4-20110929/</a>
<dt>Editors:
<dd class="vcard"><a class="url fn" href="http://fantasai.inkedblade.net/contact">Elika J. Etemad</a> (Mozilla)
<dt>Previous Editors:
<dd class="vcard"><a lang="tr" class="url fn" href="http://www.tantek.com/">Tantek Çelik</a> (Microsoft)
<dd class="vcard"><span class="fn">Daniel Glazman</span> (Disruptive Innovations SARL)</dd>
<dd class="vcard"><span class="fn">Ian Hickson</span> (Opera Softare ASA)
<dd class="vcard"><span class="fn">Peter Linss</span> (Netscape/AOL)
<dd class="vcard"><span class="fn">John Williams</span> (Quark, Inc.)
</dl>
<!--copyright-->
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc" id=abstract>
Abstract</h2>
<p><em>Selectors</em> are patterns that match against elements in a
tree, and as such form one of several technologies that can be used
to select nodes in an XML document. Selectors have been optimized for
use with HTML and XML, and are designed to be usable in
performance-critical code. They are a core component of
<abbr title="Cascading Style Sheets">CSS</abbr> (Cascading
Style Sheets), which uses Selectors to bind style properties to
elements in the document.</p>
<p>Selectors Level 4 describes the selectors that already exist in
[[!SELECT]], and further introduces new selectors for CSS and
other languages that may need them.</p>
<h2 class="no-num no-toc" id=status>Status of this Document</h2>
<!--status-->
<p><strong>This module is an early-stage Working Draft. If you are
looking for a stable Selectors specification, use
<a href="http://www.w3.org/TR/css3-selectors/">Selectors 3</a>.</strong>
Read the <a href="http://www.w3.org/TR/CSS/">CSS Snapshot</a> for
an overview of the CSS development process.
See the <a href="#overview">Selectors Overview</a> for a summary of
additions to level 3.
<p>This is the first public Working Draft of this new specification.
<h2 class="no-num no-toc" id="contents">Table of Contents</h2>
<!--toc-->
<h2 id=context>
Introduction</h2>
<p><em>This section is not normative.</em>
<p>Selectors define the following function for elements in a tree structure:</p>
<pre>expression ∗ element → boolean</pre>
<p>That is, given an element and a selector, this specification
defines whether that element matches the selector.</p>
<p>These expressions can also be used, for instance, to select a set
of elements, or a single element from a set of elements, by
evaluating the expression across all the elements in a
subtree. <abbr title="Simple Tree Transformation
Sheets">STTS</abbr> (Simple Tree Transformation Sheets), a
language for transforming XML trees, uses this mechanism. [[STTS3]]</p>
<p>Selectors Levels 1, 2, and 3 are defined as the subsets of selector
functionality defined in the <a href="http://www.w3.org/TR/REC-CSS1">CSS1</a>,
<a href="http://www.w3.org/TR/CSS21/">CSS2.1</a>, and
<a href="http://www.w3.org/TR/css3-selectors/">Selectors Level 3</a>
specifications, respectively. This module defines Selectors Level 4.
<h3 id="placement">Module Interactions</h3>
<p>This module replaces the definitions for, and extends the set of
selectors defined for CSS
in [[SELECT]] and [[CSS21]].
<p>Pseudo-element selectors, which define abstract elements in a
rendering tree, are not part of this specification: their generic syntax
is described here, but, due to their close integration with the rendering
model and irrelevance to other uses such as DOM queries, they will be
defined in other modules.
<h2 id=overview>
Selectors Overview</h2>
<p><em>This section is non-normative, as it merely summarizes the
following sections.</em></p>
<p>A Selector represents a structure. This structure can be used as a
condition (e.g. in a CSS rule) that determines which elements a
selector matches in the document tree, or as a flat description of the
HTML or XML fragment corresponding to that structure.</p>
<p>Selectors may range from simple element names to rich contextual
representations.</p>
<p>The following table summarizes the Selector syntax:</p>
<table class="data">
<col class="pattern">
<col class="meaning">
<col class="section">
<col class="level">
<thead>
<tr>
<th>Pattern
<th>Meaning
<th>Section
<th>Level
<tbody>
<tr>
<td><code>*</code>
<td>any element
<td><a href="#universal-selector">Universal selector</a>
<td>2
<tr>
<td><code>E</code>
<td>an element of type E
<td><a href="#type-selectors">Type selector</a>
<td>1
<tbody>
<tr>
<td><code>E:not(<var>s</var>)</code>
<td>an E element that does not match simple selector <var>s</var>
<td><a href="#negation">Negation pseudo-class</a>
<td>3
<tr>
<td><code>E:not(<var>s1</var>, <var>s2</var>)</code>
<td>an E element that does not match either compound selector <var>s1</var>
or compound selector <var>s2</var>
<td><a href="#negation">Negation pseudo-class</a>
<td>4
<tr>
<td><code>E:matches(<var>s1</var>, <var>s2</var>)</code>
<td>an E element that matches compound selector <var>s1</var>
and/or compound selector <var>s2</var>
<td><a href="#matches">Matches-any pseudo-class</a>
<td>4
<tbody>
<tr>
<td><code>E.warning</code>
<td>an E element belonging to the class <code>warning</code>
(the document language specifies how class is determined).
<td><a href="#class-html">Class selectors</a>
<td>1
<tr>
<td><code>E#myid</code>
<td>an E element with ID equal to <code>myid</code>.
<td><a href="#id-selectors">ID selectors</a>
<td>1
<tr>
<td><code>E[foo]</code>
<td>an E element with a <code>foo</code> attribute
<td><a href="#attribute-selectors">Attribute selectors</a>
<td>2
<tr>
<td><code>E[foo="bar"]</code>
<td>an E element whose <code>foo</code> attribute value is
exactly equal to <code>bar</code>
<td><a href="#attribute-selectors">Attribute selectors</a>
<td>2
<tr>
<td><code>E[foo="bar" i]</code>
<td>an E element whose <code>foo</code> attribute value is
exactly equal to any (ASCII-range) case-permutation of <code>bar</code>
<td><a href="#attribute-case">Attribute selectors: Case-sensitivity</a>
<td>4
<tr>
<td><code>E[foo~="bar"]</code>
<td>an E element whose <code>foo</code> attribute value is
a list of whitespace-separated values, one of which is
exactly equal to <code>bar</code>
<td><a href="#attribute-selectors">Attribute selectors</a>
<td>2
<tr>
<td><code>E[foo^="bar"]</code>
<td>an E element whose <code>foo</code> attribute value
begins exactly with the string "bar"
<td><a href="#attribute-selectors">Attribute selectors</a>
<td>3
<tr>
<td><code>E[foo$="bar"]</code>
<td>an E element whose <code>foo</code> attribute value
ends exactly with the string <code>bar</code>
<td><a href="#attribute-selectors">Attribute selectors</a>
<td>3
<tr>
<td><code>E[foo*="bar"]</code>
<td>an E element whose <code>foo</code> attribute value
contains the substring <code>bar</code>
<td><a href="#attribute-selectors">Attribute selectors</a>
<td>3
<tr>
<td><code>E[foo|="en"]</code>
<td>an E element whose <code>foo</code> attribute value is
a hyphen-separated list of values beginning with <code>en</code>
<td><a href="#attribute-selectors">Attribute selectors</a>
<td>2
<tbody>
<tr>
<td><code>E:dir(ltr)</code>
<td>an element of type E in with left-to-right directionality
(the document language specifies how directionality is determined)
<td><a href="#dir-pseudo">The :dir() pseudo-class</a>
<td>2
<tr>
<td><code>E:lang(fr)</code>
<td>an element of type E in language "fr" (the document
language specifies how language is determined)
<td><a href="#lang-pseudo">The :lang() pseudo-class</a>
<td>2
<tbody>
<tr>
<td><code>E:any-link</code>
<td>an E element being the source anchor of a hyperlink
<td><a href="#any-link-pseudo">The hyperlink pseudo-class</a>
<td>1
<tr>
<td><code>E:link</code>
<td>an E element being the source anchor of a hyperlink
of which the target is not yet visited
<td><a href="#link">The link history pseudo-classes</a>
<td>1
<tr>
<td><code>E:visited</code>
<td>an E element being the source anchor of a hyperlink
of which the target is already visited
<td><a href="#link">The link history pseudo-classes</a>
<td>1
<tr>
<td><code>E:local-link</code>
<td>an E element being the source anchor of a hyperlink
of which the target is the current document
<td><a href="#local-pseudo">The local link pseudo-class</a>
<td>4
<tr>
<td><code>E:local-link(0)</code>
<td>an E element being the source anchor of a hyperlink
of which the target is within the current domain
<td><a href="#local-pseudo">The local link pseudo-class</a>
<td>4
<tr>
<td><code>E:target</code>
<td>an E element being the target of the referring URI
<td><a href="#target-pseudo">The target pseudo-class</a>
<td>3
<tr>
<td><code>E:scope</code>
<td>an E element being a designated contextual reference element
<td><a href="#scope-pseudo">The scope pseudo-class</a>
<td>3
<tbody>
<tr>
<td><code>E:current</code>
<td>an E element that is currently presented in a time-dimensional canvas
<td><a href="#time-pseudos">Time-dimensional Pseudo-classes</a>
<td>4
<tr>
<td><code>E:current(<var>s</var>)</code>
<td>an E element that is the deepest <code>:current</code> element that
matches selector <var>s</var>
<td><a href="#time-pseudos">Time-dimensional Pseudo-classes</a>
<td>4
<tr>
<td><code>E:past</code>
<td>an E element that is in the past in a time-dimensional canvas
<td><a href="#time-pseudos">Time-dimensional Pseudo-classes</a>
<td>4
<tr>
<td><code>E:future</code>
<td>an E element that is in the future in a time-dimensional canvas
<td><a href="#time-pseudos">Time-dimensional Pseudo-classes</a>
<td>4
<tbody>
<tr>
<td><code>E:active</code>
<td>an E element that is in an activated state
<td><a href="#useraction-pseudos">The user action pseudo-classes</a>
<td>1
<tr>
<td><code>E:hover</code>
<td>an E element that is under the cursor,
or that has a descendant under the cursor
<td><a href="#useraction-pseudos">The user action pseudo-classes</a>
<td>2
<tr>
<td><code>E:focus</code>
<td>an E element that has user input focus
<td><a href="#useraction-pseudos">The user action pseudo-classes</a>
<td>2
<tr>
<td><code>E:enabled<br>E:disabled</code>
<td>a user interface element E that is enabled or disabled, respectively
<td><a href="#enableddisabled">The :enabled and :disabled pseudo-classes</a>
<td>3
<tr>
<td><code>E:checked</code>
<td>a user interface element E that is checked/selected
(for instance a radio-button or checkbox)
<td><a href="#checked">The selected-option pseudo-class</a>
<td>3
<tr>
<td><code>E:indeterminate</code>
<td>a user interface element E that is in an
indeterminate state (neither checked nor unchecked)
<td><a href="#indeterminate">The indeterminate-value pseudo-class</a>
<td>4
<tr>
<td><code>E:default</code>
<td>a user interface element E that
<td><a href="#default-pseudo">The default option pseudo-class :default</a>
<td>3-UI/4
<tr>
<td><code>E:in-range</code><br><code>E:out-of-range</code>
<td>a user interface element E that
<td><a href="#range-pseudos">The validity pseudo-classes</a>
<td>3-UI/4
<tr>
<td><code>E:required</code><br><code>E:optional</code>
<td>a user interface element E that
<td><a href="#opt-pseudos">The optionality pseudo-classes</a>
<td>3-UI/4
<tr>
<td><code>E:read-only</code><br><code>E:read-write</code>
<td>a user interface element E that
<td><a href="#rw-pseudos">The mutability pseudo-classes</a>
<td>3-UI/4
<tbody>
<tr>
<td><code>E:root</code>
<td>an E element, root of the document
<td><a href="#structural-pseudos">Structural pseudo-classes</a>
<td>3
<tr>
<td><code>E:empty</code>
<td>an E element that has no children (not even text nodes)
<td><a href="#structural-pseudos">Structural pseudo-classes</a>
<td>3
<tr>
<td><code>E:first-child</code>
<td>an E element, first child of its parent
<td><a href="#structural-pseudos">Structural pseudo-classes</a>
<td>2
<tr>
<td><code>E:nth-child(<var>n</var>)</code>
<td>an E element, the <var>n</var>-th child of its parent
<td><a href="#structural-pseudos">Structural pseudo-classes</a>
<td>3
<tr>
<td><code>E:last-child</code>
<td>an E element, last child of its parent
<td><a href="#structural-pseudos">Structural pseudo-classes</a>
<td>3
<tr>
<td><code>E:nth-last-child(<var>n</var>)</code>
<td>an E element, the <var>n</var>-th child of its parent,
counting from the last one
<td><a href="#structural-pseudos">Structural pseudo-classes</a>
<td>3
<tr>
<td><code>E:only-child</code>
<td>an E element, only child of its parent
<td><a href="#structural-pseudos">Structural pseudo-classes</a>
<td>3
<tr>
<td><code>E:first-of-type</code>
<td>an E element, first sibling of its type
<td><a href="#structural-pseudos">Structural pseudo-classes</a>
<td>3
<tr>
<td><code>E:nth-of-type(<var>n</var>)</code>
<td>an E element, the <var>n</var>-th sibling of its type
<td><a href="#structural-pseudos">Structural pseudo-classes</a>
<td>3
<tr>
<td><code>E:last-of-type</code>
<td>an E element, last sibling of its type
<td><a href="#structural-pseudos">Structural pseudo-classes</a>
<td>3
<tr>
<td><code>E:nth-last-of-type(<var>n</var>)</code>
<td>an E element, the <var>n</var>-th sibling of its type,
counting from the last one
<td><a href="#structural-pseudos">Structural pseudo-classes</a>
<td>3
<tr>
<td><code>E:only-of-type</code>
<td>an E element, only sibling of its type
<td><a href="#structural-pseudos">Structural pseudo-classes</a>
<td>3
<tr>
<td><code>E:nth-match(<var>n</var> of <var>selector</var>)</code>
<td>an E element, the <var>n</var>-th sibling matching <var>selector</var>
<td><a href="#structural-pseudos">Structural pseudo-classes</a>
<td>4
<tr>
<td><code>E:nth-match(<var>n</var> of <var>selector</var>)</code>
<td>an E element, the <var>n</var>-th sibling matching <var>selector</var>
<td><a href="#structural-pseudos">Structural pseudo-classes</a>
<td>4
<tbody>
<tr>
<td><code>E:column(<var>selector</var>)</code>
<td>an E element that represents a cell in a grid/table
belonging to a column represented by an element that matches
<var>selector</var>
<td><a href="#table-pseudos">Grid-Structural pseudo-classes</a>
<td>4
<tr>
<td><code>E:nth-column(<var>n</var>)</code>
<td>an E element that represents a cell belonging to the
<var>n</var>th column in a grid/table
<td><a href="#table-pseudos">Grid-Structural pseudo-classes</a>
<td>4
<tr>
<td><code>E:nth-last-column(<var>n</var>)</code>
<td>an E element that represents a cell belonging to the
<var>n</var>th column in a grid/table, counting from the last one
<td><a href="#table-pseudos">Grid-Structural pseudo-classes</a>
<td>4
<tbody>
<tr>
<td><code>E F</code>
<td>an F element descendant of an E element
<td><a href="#descendant-combinators">Descendant combinator</a>
<td>1
<tr>
<td><code>E > F</code>
<td>an F element child of an E element
<td><a href="#child-combinators">Child combinator</a>
<td>2
<tr>
<td><code>E + F</code>
<td>an F element immediately preceded by an E element
<td><a href="#adjacent-sibling-combinators">Adjacent sibling combinator</a>
<td>2
<tr>
<td><code>E ~ F</code>
<td>an F element preceded by an E element
<td><a href="#general-sibling-combinators">General sibling combinator</a>
<td>3
<tr>
<td><code>E /foo/ F</code>
<td>an F element ID-referenced by an E element's <code>foo</code> attribute
<td><a href="#idref-combinators">Reference combinator</a>
<td>4
<tr>
<td><code>$E > F</code>
<td>an E element parent of an F element
<td><a href="#subject">Determining the subject of a selector</a> +
<a href="#child-combinators">Child combinator</a>
<td>4
</tbody></table>
<p>The meaning of each selector is derived from the table above by
prepending "matches" to the contents of each cell in the "Meaning"
column.</p>
<p class="note">Some Level 4 selectors (noted above as "3-UI") were
introduced in [[CSS3UI]].
<h2 id=syntax>
Selector Syntax and Structure</h2>
<h3 id=structure>
Structure and Terminology</h3>
<p>The term <dfn id=selector>selector</dfn> can refer to a <i>simple selector</i>,
<i>compound selector</i>, <i>complex selector</i>, or <i>selector list</i>.
<p>A <dfn id=complex>complex selector</dfn> is a chain of one
or more <a href="#compound">compound selectors</a>
separated by <a href="#combinators">combinators</a>.</p>
<p>A <dfn id=compound>compound selector</dfn>
is a chain of <a href="#simple">simple selectors</a>
that are not separated by a <a href="#combinators">combinator</a>. It
always begins with a <a href="#type-selectors">type selector</a> or a
(possibly implied) <a href="#universal-selector">universal selector</a>.
No other type selector or universal selector is allowed in the sequence.</p>
<p>A <dfn id=simple><a
href="#simple">simple selector</a></dfn> is either a <a
href="#type-selectors">type selector</a>, <a
href="#universal-selector">universal selector</a>, <a
href="#attribute-selectors">attribute selector</a>, <a
href="#class-html">class selector</a>, <a
href="#id-selectors">ID selector</a>, or <a
href="#pseudo-classes">pseudo-class</a>.</p>
<p><dfn id=combinator>Combinators</dfn> are punctuation that represent a particular
kind of relationship between the compound selectors on either side.
Combinators in Selectors level 4 include: whitespace, "greater-than
sign" (U+003E, <code>></code>), "plus sign" (U+002B,
<code>+</code>) and "tilde" (U+007E, <code>~</code>).
<a href="#whitespace">White space</a> may appear between a combinator
and the simple selectors around it.</p>
<p>An empty selector, containing no compound selector, is an
<a href="#invalid">invalid selector</a>.</p>
<h3 id=subject>
Determining the Subject of a Selector</h3>
<p>The elements of a document tree that are represented by a selector
are the <dfn>subjects</dfn> of the selector.
<p>By default, the subjects of a selector are the elements represented
by the last compound selector in the selector. Thus a selector consisting
of a single compound selector represents any element satisfying its
requirements. Prepending another compound selector and a combinator
to a sequence imposes additional matching constraints, so the subjects of
the selector are always a subset of the elements represented by the last
compound selector.</p>
<p>The subject of the selector can be explicitly identified by prepending
a dollar sign ($) to one of the compound selectors in a selector.
Although the element structure that the selector represents is the same
with or without the dollar sign, indicating the subject in this way
can change which compound selector represents the subject in that structure.
<div class="example">
<p>For example, the following selector represents a list item <code>LI</code>
unique child of an ordered list <code>OL</code>:
<pre>OL > LI:only-child</pre>
<p>However the following one represents an ordered list <code>OL</code>
having a unique child, that child being a <code>LI</code>:
<pre>$OL > LI:only-child</pre>
<p>The structures represented by these two selectors are the same, but the
subjects of the selectors are not.
</div>
<h3 id=pseudo-classes>
Pseudo-classes</h3>
<p>The pseudo-class concept is introduced to permit selection based on
information that lies outside of the document tree or that cannot be
expressed using the other simple selectors.</p>
<p>A pseudo-class always consists of a "colon"
(<code>:</code>) followed by the name of the pseudo-class and, for
functional pseudo-classes, by a value between parentheses.
White space is optionally allowed between the parentheses and the
argument, but not between the pseudo-class name and the parentheses.</p>
<p>Pseudo-classes are allowed in all compound selectors
contained in a selector. Pseudo-classes are allowed anywhere in a
compound selector after the leading type selector or
(possibly omitted) universal selector. Pseudo-class names are
case-insensitive. Some pseudo-classes are mutually exclusive (such
that a compound selector containing them, while valid, will never
match anything), while others can apply simultaneously to the same
element. Pseudo-classes may be dynamic, in the sense that an element
can acquire or lose a pseudo-class while a user interacts with the
document.</p>
<p>Dynamic pseudo-classes classify elements on characteristics other
than their name, attributes, or content, in principle characteristics
that cannot be deduced from the document tree.</p>
<p>Dynamic pseudo-classes do not appear in the document source or
document tree.</p>
<h3 id=pseudo-elements>Pseudo-elements</h3>
<p>Pseudo-elements create abstractions about the document tree beyond
those specified by the document language. For instance, document
languages do not offer mechanisms to access the first letter or first
line of an element's content. Pseudo-elements allow authors to refer
to this otherwise inaccessible information. Pseudo-elements may also
provide authors a way to refer to content that does not exist in the
source document (e.g., the <code>::before</code> and
<code>::after</code> pseudo-elements give access to generated
content in CSS [[CSS21]]).</p>
<p>A pseudo-element is made of two colons (<code>::</code>) followed
by the name of the pseudo-element.</p>
<p>This <code>::</code> notation was chosen in order to establish a
discrimination between pseudo-classes (which subclass existing elements)
and pseudo-elements (which are elements not represented in the document
tree). However, for compatibility with existing style sheets, user
agents must also accept the previous one-colon notation for
pseudo-elements introduced in CSS levels 1 and 2 (namely,
<code>:first-line</code>, <code>:first-letter</code>,
<code>:before</code> and <code>:after</code>). This compatibility
notation is not allowed any other pseudo-elements.</p>
<p>Only one pseudo-element may appear per selector, and only if the
subject of the selector is the last compound selector in the selector.
If present the pseudo-element must appear after the compound selector
that represents the <a href="#subject">subjects</a> of the selector.
<p class="note">A future version of this specification may allow
multiple pseudo-elements per selector.</p>
<p>Syntactically, a pseudo-element may be followed by any combination
of the <a href="#useraction-pseudos">user action pseudo-classes</a>.
Whether these pseudo-classes can match on the pseudo-element depends
on the pseudo-class and pseudo-element's definition: unless
otherwise-specified, none of these pseudo-classes will match on the
pseudo-element.
<div class="example">
<p>For example, the <code>:hover</code> pseudo-class specifies that it
can apply to any pseudo-element, i.e. <code>::first-line:hover</code>
will match when the first line is hovered.
However, since neither <code>:focus</code> nor <code>::first-line</code>
define that <code>:focus</code> can apply to <code>::first-line</code>,
the selector <code>::first-line:focus</code> will never match anything.
</div>
<h3 id=case-sensitive>
Characters and case sensitivity</h3>
<p>All Selectors syntax is case-insensitive within the ASCII range
(i.e. [a-z] and [A-Z] are equivalent), except for parts that are
not under the control of Selectors. The case sensitivity of document
language element names, attribute names, and attribute values in
selectors depends on the document language. For example, in HTML,
element names are case-insensitive, but in XML, they are
case-sensitive. Case sensitivity of namespace prefixes is defined in
[[!CSS3NAMESPACE]].</p>
<p><dfn id=whitespace>White space</dfn> in Selectors consists of the
characters SPACE (U+0020), TAB (U+0009), LINE FEED (U+000A),
CARRIAGE RETURN (U+000D), and FORM FEED (U+000C) can occur in whitespace.
Other space-like characters, such as EM SPACE (U+2003) and
IDEOGRAPHIC SPACE (U+3000), are never part of white space.
<p>Characters in Selectors can be escaped with a backslash according
to the same <a href="http://www.w3.org/TR/CSS21/syndata.html#characters">escaping
rules</a> as CSS. [[!CSS21]].</p>
<h3 id="namespaces">
Namespaces</h3>
<p>Certain selectors support namespace prefixes. The
mechanism by which namespace prefixes are <dfn id=nsdecl>declared</dfn> should
be specified by the language that uses Selectors. If the language does
not specify a namespace prefix declaration mechanism, then no prefixes
are declared. In CSS, namespace prefixes are declared with the
<a href="http://www.w3.org/TR/css3-namespace/#declaration"><code>@namespace</code></a>
rule. [[!CSS3NAMESPACE]]</p>
<h3 id=invalid>
Invalid Selectors and Error Handling</h3>
<p>Invalidity is caused by a parsing error, e.g. an unrecognized token or a token
which is not allowed at the current parsing point.
<p>User agents must observe the rules for handling parsing errors:
<ul>
<li>a simple selector containing an <a href="#namespaces">undeclared namespace prefix</a> is invalid</li>
<li>a selector containing an invalid simple selector, an invalid combinator
or an invalid token is invalid. </li>
<li>a selector list containing an invalid selector is invalid.</li>
</ul>
<p>An invalid selector represents nothing.
<p class="issue">It's been <a href="http://lists.w3.org/Archives/Public/www-style/2010Nov/0203.html">requested</a>
that the last rule be dropped in favor of Media Queries-style error-handling.</p>
<h2 id=logical-combination>
Logical Combinations</h2>
<h3 id=grouping>
Selector Lists</h3>
<p>A comma-separated list of selectors represents the union of all
elements selected by each of the individual selectors in the
<dfn>selector list</dfn>.
(A comma is U+002C.) For example, in CSS when several selectors share
the same declarations, they may be grouped into a comma-separated
list. White space may appear before and/or after the comma.</p>
<div class="example">
<p>CSS example:</p>
<p>In this example, we condense three rules with identical
declarations into one. Thus,</p>
<pre>h1 { font-family: sans-serif }
h2 { font-family: sans-serif }
h3 { font-family: sans-serif }</pre>
<p>is equivalent to:</p>
<pre>h1, h2, h3 { font-family: sans-serif }</pre>
</div>
<p><strong>Warning</strong>: the equivalence is true in this example
because all the selectors are valid selectors. If just one of these
selectors were invalid, the entire group of selectors would be
invalid. This would invalidate the rule for all three heading
elements, whereas in the former case only one of the three individual
heading rules would be invalidated.</p>
<div class="example">
<p>Invalid CSS example:</p>
<pre>h1 { font-family: sans-serif }
h2..foo { font-family: sans-serif }
h3 { font-family: sans-serif }</pre>
<p>is not equivalent to:</p>
<pre>h1, h2..foo, h3 { font-family: sans-serif }</pre>
<p>because the above selector (<code>h1, h2..foo, h3</code>)
is entirely invalid and the entire style rule is dropped. (When
the selectors are not grouped, only the rule for <code>h2..foo</code>
is dropped.)</p>
</div>
<h3 id=matches>
The Matches-Any Pseudo-class: '':matches()''</h3>
<p>The matches-any pseudo-class, <code>:matches(<var>X</var>)</code>,
is a functional notation taking a <a href="#grouping">selector list</a>
as its argument. It represents an element that is represented by its argument.
<p>In Selectors Level 4, only <a href="#compound">compound selectors</a>
are allowed within <code>:matches()</code>:
<a href="#combinator">combinators</a> are not allowed. Additionally,
<code>:matches()</code> may not be nested within itself or within
<code>:not()</code>: <code>:matches(:matches(...))</code> and
<code>:not(:matches(...))</code> are invalid.</p>
<p>Pseudo-elements cannot be represented by the matches-any pseudo-class;
they are not valid within <code>:matches()</code>.
<p>Default namespace declarations do not affect the subject of any selector
within a matches-any pseudo-class unless the argument is an explicit
universal selector or a type selector.</p>
<div class="example">
<p>For example, following selector matches any element that is being
hovered or focused, regardless of its namespace. In particular, it
is not limited to only matching elements in the default namespace
that are being hovered or focused.</p>
<pre>*|*:matches(:hover, :focus)</pre>
<p>The following selector, however, represents only hovered or focused
elements that are in the default namespace, because it uses an explicit
universal selector within the <code>:matches()</code> notation:</p>
<pre>*|*:matches(*:hover, *:focus)</pre>
</div>
<h3 id=negation>
The Negation Pseudo-class: '':not()''</h3>
<p>The negation pseudo-class, <code>:not(<var>X</var>)</code>, is a
functional notation taking a <a href="#grouping">selector list</a>
as an argument. It represents an element that is not represented
by its argument.
<p>In Selectors Level 4, only <a href="#compound">compound selectors</a>
are allowed within <code>:matches()</code>:
<a href="#combinator">combinators</a> are not allowed. Additionally,
negations may not be nested within itself or within <code>:matches()</code>:
<code>:not(:not(...))</code> and <code>:matches(:not(...))</code> are invalid.
<p>Pseudo-elements cannot be represented by the negation pseudo-class;
they are not valid within <code>:not()</code>.
<div class="example">
<p>For example, the following selector matches all <code>button</code>
elements in an HTML document that are not disabled.</p>
<pre>button:not([DISABLED])</pre>
<p>The following selector represents all but <code>FOO</code>
elements.</p>
<pre>*:not(FOO)</pre>
<p>The following compound selector represents all HTML elements
except links.</p>
<pre>html|*:not(:link):not(:visited)</pre>
</div>
<p>Default namespace declarations do not affect the subject of any selector
within a negation pseudo-class unless the argument is an explicit universal
selector or a type selector. (See <a href="#matches"><code>:matches()</code></a>
for examples.</p>
<p class="note"><strong>Note</strong>: the :not() pseudo allows
useless selectors to be written. For instance <code>:not(*|*)</code>,
which represents no element at all, or <code>foo:not(bar)</code>,
which is equivalent to <code>foo</code> but with a higher
specificity.</p>
<h2 id=elemental-selectors>
Elemental selectors</h2>
<h3 id=type-selectors>
Type selector</h3>
<p>A <dfn>type selector</dfn> is the name of a document language
element type written using the syntax of
<a href="http://www.w3.org/TR/css3-namespace/#css-qnames">CSS qualified
names</a> [[!CSS3NAMESPACE]]. A type selector represents
an instance of the element type in the document tree. </p>
<div class="example">
<p>Example:</p>
<p>The following selector represents an <code>h1</code> element in the document tree:</p>
<pre>h1</pre>
</div>
<h4 id=typenmsp>
Type selectors and namespaces</h4>
<p>Type selectors allow an optional namespace component: a namespace
prefix that has been previously <a href="#nsdecl">declared</a> may be
prepended to the element name separated by the namespace separator
"vertical bar" (U+007C, <code>|</code>). (See, e.g., [[XML-NAMES]] for the use of namespaces in
XML.)</p>
<p>The namespace component may be left empty (no prefix before the
namespace separator) to indicate that the selector is only to
represent elements with no namespace.</p>
<p>An asterisk may be used for the namespace prefix, indicating that
the selector represents elements in any namespace (including elements
with no namespace).</p>
<p>Element type selectors that have no namespace component (no
namespace separator) represent elements without regard to the
element's namespace (equivalent to "<code>*|</code>") unless a default
namespace has been <a href="#nsdecl">declared</a> for namespaced selectors (e.g. in CSS, in
the style sheet). If a default namespace has been declared, such
selectors will represent only elements in the default namespace.</p>
<p>A type selector containing a namespace prefix that has not been
previously <a href="#nsdecl">declared</a> for namespaced selectors is
an <a href="#conformance">invalid</a> selector.</p>
<p>In a namespace-aware client, the name part of element type
selectors (the part after the namespace separator, if it is present)
will only match against the <a
href="http://www.w3.org/TR/REC-xml-names/#NT-LocalPart">local part</a>
of the element's <a
href="http://www.w3.org/TR/REC-xml-names/#ns-qualnames">qualified
name</a>.</p>
<p>In summary:</p>
<dl>
<dt><code>ns|E</code></dt>
<dd>elements with name E in namespace ns</dd>
<dt><code>*|E</code></dt>
<dd>elements with name E in any namespace, including those without a
namespace</dd>
<dt><code>|E</code></dt>
<dd>elements with name E without a namespace</dd>
<dt><code>E</code></dt>
<dd>if no default namespace has been <a href="#nsdecl">declared</a> for selectors, this is
equivalent to *|E. Otherwise it is equivalent to ns|E where ns is
the default namespace.</dd>
</dl>
<div class="example">
<p>CSS examples:</p>
<pre>@namespace foo url(http://www.example.com);
foo|h1 { color: blue } /* first rule */
foo|* { color: yellow } /* second rule */
|h1 { color: red } /* ...*/
*|h1 { color: green }
h1 { color: green }</pre>
<p>The first rule (not counting the <code>@namespace</code> at-rule)
will match only <code>h1</code> elements in the
"http://www.example.com" namespace.</p>
<p>The second rule will match all elements in the
"http://www.example.com" namespace.</p>
<p>The third rule will match only <code>h1</code> elements with
no namespace.</p>
<p>The fourth rule will match <code>h1</code> elements in any
namespace (including those without any namespace).</p>
<p>The last rule is equivalent to the fourth rule because no default
namespace has been defined.</p>
</div>
<h3 id=universal-selector>
Universal selector </h3>
<p>The <dfn>universal selector</dfn>, written as a
<a href="http://www.w3.org/TR/css3-namespace/#css-qnames">CSS qualified
name</a> [[!CSS3NAMESPACE]] with an asterisk (<code>*</code>
U+002A) as the local name, represents the qualified name of any element
type. It represents any single element in the document tree in any
namespace (including those without a namespace) if no default
namespace has been specified for selectors. If a default namespace has
been specified, see <a href="#univnmsp">Universal selector and
Namespaces</a> below.</p>
<p>If a universal selector represented by <code>*</code> (i.e. without a
namespace prefix) is not the only component of a <a href="#compound">compound
selector</a> or is immediately followed by a
<a href="#pseudo-elements">pseudo-element</a>, then the <code>*</code> may
be omitted and the universal selector's presence implied.</p>
<div class="example">
<p>Examples:</p>
<ul>
<li><code>*[hreflang|=en]</code> and <code>[hreflang|=en]</code> are equivalent,</li>
<li><code>*.warning</code> and <code>.warning</code> are equivalent,</li>
<li><code>*#myid</code> and <code>#myid</code> are equivalent.</li>
</ul>
</div>
<p class="note"><strong>Note:</strong> it is recommended that the
<code>*</code> not be omitted, because it decreases the potential
confusion between, for example,
<code style="white-space: nowrap">div :first-child</code>
and <code style="white-space: nowrap">div:first-child</code>.
Here, <code style="white-space: nowrap">div *:first-child</code>
is more readable.</p>
<h4 id=univnmsp>
Universal selector and namespaces</h4>
<p>The universal selector allows an optional namespace component. It
is used as follows:</p>
<dl>
<dt><code>ns|*</code></dt>
<dd>all elements in namespace ns</dd>
<dt><code>*|*</code></dt>
<dd>all elements</dd>
<dt><code>|*</code></dt>
<dd>all elements without a namespace</dd>
<dt><code>*</code></dt>
<dd>if no default namespace has been specified, this is equivalent to *|*.
Otherwise it is equivalent to ns|* where ns is the default namespace.</dd>
</dl>
<p>A universal selector containing a namespace prefix that has not
been previously <a href="#nsdecl">declared</a> is an <a
href="#conformance">invalid</a> selector.</p>
<h2 id=attribute-selectors>
Attribute selectors</h2>
<p>Selectors allow the representation of an element's attributes. When
a selector is used as an expression to match against an element,
attribute selectors must be considered to match an element if that
element has an attribute that matches the attribute represented by the
attribute selector.</p>
<h3 id=attribute-representation>
Attribute presence and value selectors</h3>
<p>CSS2 introduced four attribute selectors:</p>