csswg-drafts/mediaqueries-3/Overview.src.html at 703445fded436e8a851696fb642fba66bc3322cb · xfq/csswg-drafts · GitHub

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

<style type="text/css">
    blockquote {
      background: #eef;
      padding: 0.5em;
      margin: 1em 0;
      border: thin solid black; }
    pre { font-family: courier, monospace; font-weight: bold; white-space: pre-wrap }
    .example pre em { font-style: normal }
    span.label { font-style: italic }
</style>

<link rel="stylesheet" href="../default.css">
<link rel="stylesheet" href="http://www.w3.org/StyleSheets/TR/W3C-[STATUS]">

</head>
<body>
<div class="head">

<!--logo-->

<h1 id="media-queries">Media Queries Level 3</h1>

<h2 class="no-num no-toc" id="w3c-working">[LONGSTATUS] [DATE]</h2>

<dl>
<dt>This Version:</dt>

<dd><a href="[VERSION]/">http://www.w3.org/TR/[YEAR]/ED-css3-mediaqueries-[CDATE]/</a></dd>

<dt>Latest Version:</dt>

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

<dt>Latest Editor Version:</dt>

<dd><a href="http://dev.w3.org/csswg/css3-mediaqueries/">http://dev.w3.org/csswg/css3-mediaqueries/</a></dd>

<dt>Previous Version:</dt>

<dd><a href=

<dt>Disposition of Comments:

<dd><a href="http://www.w3.org/Style/2012/MediaQueriesDisposalOfComments.html">http://www.w3.org/Style/2012/MediaQueriesDisposalOfComments.html</a>

<dt>Editors:</dt>

<dd class="vcard"><span class="given-name">Florian</span> <span class="family-name">Rivoal</span> &lt;<span class="email">florianr&nbsp;@opera.com</span>&gt;</dd>

<dt>Previous Editors:</dt>

<dd class="vcard"><a class="url fn n" lang="no" href="http://people.opera.com/howcome/">
<span class="given-name">H&aring;kon</span> <span class="additional-name">Wium</span> <span class="family-name">Lie</span></a> &lt;<span class="email">howcome&nbsp;@opera.com</span>&gt;</dd>

<dd class="vcard"><a class="url fn" lang="tr" href="http://tantek.com/">Tantek &Ccedil;elik</a> &lt;<span class="email">tantek&nbsp;@cs.stanford.edu</span>&gt;</dd>

<dd class="vcard"><span class="given-name">Daniel</span> <span class="family-name">Glazman</span> &lt;<span class="email">daniel.glazman&nbsp;@disruptive-innovations.com</span>&gt;</dd>

<dd class="vcard"><a class="url fn n" lang="nl" href="http://annevankesteren.nl/" hreflang="en">Anne van Kesteren</a>
&lt;<span class="email">annevk@opera.com</span>&gt;</dd>

</dl>


<!--copyright-->

<hr title="Separator for header">
</div>


<h2 class="no-num no-toc" id="abstract">Abstract</h2>

<p>HTML4 and CSS2 currently support media-dependent style sheets
tailored for different <em>media types</em>. For example, a
document may use sans-serif fonts when displayed on a screen and
serif fonts when printed. ''screen'' and ''print'' are two media
types that have been defined. <em>Media queries</em> extend the
functionality of media types by allowing more precise labeling of
style sheets.</p>

<p>A media query consists of a media type and zero or more
expressions that check for the conditions of particular <em>media
features</em>. Among the media features that can be used in media queries
are ''width'', ''height'', and ''color''. By using media queries,
presentations can be tailored to a specific range of output devices without
changing the content itself.</p>

<h2 class="no-num no-toc" id="status">Status of this document</h2>

<!--status-->

<!--
<p>This specification is a <strong>Last Call Working Draft</strong>. All
persons are encouraged to review this document and <strong>send comments
to the <a href="http://lists.w3.org/Archives/Public/www-style/">www-style</a>
mailing list</strong> as described above. The
<strong>deadline for comments</strong> is <strong>21 November 2008</strong>.</p>
-->

<p>For this specification to exit the CR stage, the following
conditions shall be met:</p>

<ol>
  <li><p>There must be at least two interoperable implementations. For
  the purposes of this criterion, we define the following terms:</p>

  <dl>
    <dt>interoperable</dt>

    <dd><p>passing the respective test case(s) in the <a href="http://www.w3.org/Style/CSS/Test/">CSS test suite</a>,
    or, if the implementation is not a Web browser, an equivalent
    test. Every relevant test in the test suite should have an
    equivalent test created if such a user agent (UA) is to be used to claim
    interoperability. In addition if such a UA is to be used to claim
    interoperability, then there must one or more additional UAs which
    can also pass those equivalent tests in the same way for the
    purpose of interoperability. The equivalent tests must be made
    publicly available for the purposes of peer review. </p></dd>

    <dt>implementation</dt>

    <dd><p>a user agent which:</p>

    <ol>
      <li>implements the specification.</li>

      <li>is available (i.e. publicly downloadable or available
      through some other public point of sale mechanism). This is the
      "show me" requirement.</li>

      <li>is shipped, or is a "nightly build" (i.e., a development version
      for the next release), but is not experimental (i.e., a version
      specifically designed to pass the test suite and not intended for
      daily usage going forward).</li></ol></dd></dl></li>

  <li><p>There must be a <a href="http://www.w3.org/Style/CSS/Test/MediaQueries/">Test Suite</a>.</p></li>

  <li><p>A minimum of another four weeks of the CR period must elapse.
    That is, this specification will not exit CR before 24 August 2010.
    When the specification exits CR, an implementation report will be
    published. At this point, no such report exists.</p></li>
  </ol>


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

<!--toc-->


<h2>Background</h2>

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

<p>HTML4 [[HTML401]] and CSS2 [[!CSS21]] currently support media-dependent
style sheets tailored for different media types. For example, a
document may use different style sheets for screen and print. In
HTML4, this can be written as:</p>

<div class="example">
<pre><code>&lt;link rel="stylesheet" type="text/css" media="screen" href="sans-serif.css">
&lt;link rel="stylesheet" type="text/css" media="print" href="serif.css"></code></pre>
</div>

<p>Inside a CSS style sheet, one can declare that sections apply to
certain media types:</p>

<div class="example">
<pre><code>@media screen {
  * { font-family: sans-serif }
}</code></pre>
</div>

<p>The ''print'' and ''screen'' media types are defined in HTML4. The
complete list of media types in HTML4 is: ''aural'', ''braille'',
''handheld'', ''print'', ''projection'', ''screen'', ''tty'', ''tv''. CSS2
defines the same list, deprecates ''aural'' and adds ''embossed'' and
''speech''. Also, ''all'' is used to indicate that the style sheet applies
to all media types.</p>

<p>Media-specific style sheets are supported by several user
agents. The most commonly used feature is to distinguish between
''screen'' and ''print''.</p>

<p>There have been requests for ways to describe in more detail
what type of output devices a style sheet applies to. Fortunately
HTML4 foresaw these requests and defined a forward-compatible
syntax for media types. Here is a quote from <a href=
"http://www.w3.org/TR/1999/REC-html401-19991224/types.html#h-6.13">HTML4,
section 6.13</a>:</p>

<blockquote cite="http://www.w3.org/TR/1999/REC-html401-19991224/types.html#h-6.13">
<p>Future versions of HTML may introduce new values and may allow
parameterized values. To facilitate the introduction of these
extensions, conforming user agents must be able to parse the <a href=
"http://www.w3.org/TR/1999/REC-html401-19991224/present/styles.html#adef-media"><samp>media</samp></a> attribute value as follows:</p>

<ol>
<li>The value is a comma-separated list of entries. For example,

<pre><code>media="screen, 3d-glasses, print and resolution > 90dpi"</code></pre>

<p>is mapped to:</p>

<pre><code>"screen"
"3d-glasses"
"print and resolution > 90dpi"</code></pre>
</li>

<li>Each entry is truncated just before the first character that
isn't a US ASCII letter [a-zA-Z] (Unicode decimal 65-90, 97-122),
digit [0-9] (Unicode hex 30-39), or hyphen (45). In the example,
this gives:

<pre><code>"screen"
"3d-glasses"
"print"</code></pre>
</li>
</ol>
</blockquote>

<p>Media queries, as described in this specification, build on the
mechanism outlined in HTML4. The syntax of media queries fit into the
media type syntax reserved in HTML4. The <code class="html">media</code>
attribute of HTML4 also exists in XHTML and generic XML. The same
syntax can also be used inside in the ''@media'' and ''@import'' rules
of CSS.</p>

<p>However, the parsing rules for media queries are incompatible with those
of HTML4 so that they are consistent with those of media queries used in
CSS.</p>

<p class="note">HTML5 [[HTML5]] (at the moment of writing still work in
progress) references the Media Queries specification directly and thus
updates the rules for HTML.</p>


<h2 id="media0">Media Queries</h2>

<p>A media query consists of a media type and zero or more
<span class="index">expressions</span> that check for the conditions of
particular <span class="index">media features</span>.</p>

<p>Statements regarding media queries in this section assume the
<a href="#syntax">syntax section</a> is followed. Media queries that do not
conform to the syntax are discussed in the
<a href="#error-handling">error handling section</a>. I.e. the syntax takes
precedence over requirements in this section.</p>

<div class="example">
<p>Here is a simple example written in HTML:</p>
<pre><code>&lt;link rel="stylesheet" media="screen and (color)" href="example.css" /></code></pre>

<p>This example expresses that a certain style sheet
(<code>example.css</code>) applies to devices of a certain media type
(''screen'') with certain feature (it must be a color screen).</p>

</div>

<div class="example">
<p>Here the same media query written in an @import-rule in CSS:</p>
<pre><code>@import url(color.css) screen and (color);</code></pre>
</div>

<p>A media query is a logical expression that is either true or
false. A media query is true if the media type of the media query
matches the media type of the device where the user agent is running (as
defined in the "Applies to" line), and all expressions in the media query
are true.</p>

<p>A shorthand syntax is offered for media queries that apply to all
media types; the keyword ''all'' can be left out (along with the
trailing ''and''). I.e. if the media type is not explicitly given it is
''all''.</p>

<div class="example">
<p>I.e. these are identical:</p>
<pre><code>@media all and (min-width:500px) { &hellip; }
@media (min-width:500px) { &hellip; }</code></pre>
<p>As are these:</p>
<pre><code>@media (orientation: portrait) { &hellip; }
@media all and (orientation: portrait) { &hellip; }</code></pre>
</div>

<p>Several media queries can be combined in a media query list. A
comma-separated list of media queries. If one or more of the media queries
in the comma-separated list are true, the whole list is true, and otherwise
false. In the media queries syntax, the comma
expresses a logical OR, while the ''and'' keyword expresses a logical
AND.</p>

<div class="example">

<p>Here is an example of several media queries in a comma-separated
list using the an @media-rule in CSS:</p>

<pre><code>@media <em>screen and (color), projection and (color)</em> { &hellip; }</code></pre>
</div>

<p>If the media query list is empty (i.e. the declaration is the empty
string or consists solely of whitespace) it evaluates to true.</p>

<div class="example">
<p>I.e. these are equivalent:</p>
<pre><code>@media all { &hellip; }
@media { &hellip; }</code></pre>
</div>


<p>The logical NOT can be expressed through the ''not'' keyword. The
presence of the keyword ''not'' at the beginning of the media query negates
the result. I.e., if the media query had been true without the ''not''
keyword it will become false, and vice versa. User agents that only support
media types (as described in HTML4) will not recognize the ''not'' keyword
and the associated style sheet is therefore not applied.</p>

<div class="example">
<pre><code>&lt;link rel="stylesheet" media="<em>not screen and (color)</em>" href="example.css" /&gt;</code></pre>
</div>

<p>The keyword ''only'' can also be used to hide style sheets from
older user agents. User agents must process media queries starting
with ''only'' as if the ''only'' keyword was not present.</p>

<div class="example">
<pre><code>&lt;link rel="stylesheet" media="<em>only screen and (color)</em>" href="example.css" /&gt;</code></pre>
</div>

<p>The media queries syntax can be used with HTML, XHTML, XML [[XMLSTYLE]] and the @import and @media rules of CSS.</p>

<div class="example">
<p>Here is the same example written in HTML, XHTML, XML, @import and @media:</p>

<pre><code>&lt;link rel="stylesheet" media="<em>screen and (color), projection and (color)</em>" rel="stylesheet" href="example.css"></code></pre>
<pre><code>&lt;link rel="stylesheet" media="<em>screen and (color), projection and (color)</em>" rel="stylesheet" href="example.css" /></code></pre>
<pre><code>&lt;?xml-stylesheet media="<em>screen and (color), projection and (color)</em>" rel="stylesheet" href="example.css" ?></code></pre>
<pre><code>@import url(example.css) <em>screen and (color), projection and (color)</em>;</code></pre>
<pre><code>@media <em>screen and (color), projection and (color)</em> { &hellip; }</code></pre>

<p class="note">The [[XMLSTYLE]] specification has not yet been updated to
use media queries in the <code>media</code> pseudo-attribute.</p>

</div>

<p>If a media feature does not apply to the device where the UA is
running, expressions involving the media feature will be false.</p>

<div class="example">
<p>The media feature ''device-aspect-ratio'' only applies to
visual devices. On an aural device, expressions involving
''device-aspect-ratio'' will therefore always be false:</p>

<pre><code>&lt;link rel="stylesheet" media="aural and (device-aspect-ratio: 16/9)" href="example.css" /&gt;</code></pre>
</div>

<p>Expressions will always be false if the unit of measurement does
not apply to the device. </p>

<div class="example">
<p>The ''px'' unit does not apply to ''speech'' devices so the following media query is always false:</p>

<pre><code>&lt;link rel="stylesheet" media="speech and (min-device-width: 800px)" href="example.css" /&gt;</code></pre>

<p>Note that the media queries in this example would have
been true if the keyword ''not'' had been added to the beginning of
the media query.</p>
</div>

<p>To avoid circular dependencies, it is never necessary to apply the
style sheet in order to evaluate expressions. For example, the aspect
ratio of a printed document may be influenced by a style sheet, but
expressions involving ''device-aspect-ratio'' will be based on the
default aspect ratio of the user agent.</p>

<p class=note>User agents are expected, but not required, to
re-evaluate and re-layout the page in response to changes in the user
environment, for example if the device is tilted from landscape to
portrait mode.

<h2>Syntax</h2>

<p>The media query syntax is described in terms of the
<a href="http://www.w3.org/TR/CSS21/grammar.html">CSS2 grammar</a>. As such,
rules not defined here are defined in CSS2. The
<code>media_query_list</code> production defined below replaces the
<code>media_list</code> production from CSS2. [[!CSS21]]</p>

<pre>media_query_list
 : S* [media_query [ ',' S* media_query ]* ]?
 ;
media_query
 : [ONLY | NOT]? S* media_type S* [ AND S* expression ]*
 | expression [ AND S* expression ]*
 ;
media_type
 : IDENT
 ;
expression
 : '(' S* media_feature S* [ ':' S* expr ]? ')' S*
 ;
media_feature
 : IDENT
 ;</pre>

<p>COMMENT tokens, as defined by CSS2, do not occur in the grammar (to keep
it  readable), but any number of these tokens may appear anywhere between
other tokens. [[!CSS21]]</p>

<p>The following new definitions are introduced:</p>

<pre>L  l|\\0{0,4}(4c|6c)(\r\n|[ \t\r\n\f])?|\\l
Y  y|\\0{0,4}(59|79)(\r\n|[ \t\r\n\f])?|\\y</pre>

<p>The following new tokens are introduced:</p>

<pre>{O}{N}{L}{Y}      {return ONLY;}
{N}{O}{T}         {return NOT;}
{A}{N}{D}         {return AND;}
{num}{D}{P}{I}    {return RESOLUTION;}
{num}{D}{P}{C}{M} {return RESOLUTION;}</pre>

<p><code>RESOLUTION</code> is to be added to the CSS2
<code>term</code> production.</p>

<p>CSS style sheets are generally case-insensitive, and this is
also the case for media queries.</p>

<p>In addition to conforming to the syntax, each media query needs to use
media types and media features according to their respective specification
in order to be considered conforming.</p>

<div class="example">
<p>Only the first media query is conforming in the example below because the
"example" media type does not exist.</p>

<pre><code>@media all { body { background:lime } }
@media example { body { background:red } }</code></pre>
</div>

<h3>Error Handling</h3>

<p>For media queries that are not conforming user agents need to follow the
rules described in this section.</p>

<ul>
 <li>
  <p><strong>Unknown media types.</strong> Unknown media types evaluate to
  false. Effectively, they are treated identically to known media types
  that do not match the media type of the device.</p>

  <div class="example">
   <p>The media query "<code>unknown</code>" will evaluate to false, unless
   <code>unknown</code> is actually a supported media type. Similarly,
   "<code>not unknown</code>" will evaluate to true.</p>
  </div>

  <p class="note">Unknown media types are distinct from media types that do
  not actually match the IDENT production. Those fall under the malformed
  media query clause.</p>

 <li>
  <p><strong>Unknown media features.</strong> User agents are to represent a
  media query as "<code>not all</code>" when one of the specified media
  features is not known.</p>

  <div class="example">
   <pre><code>&lt;link rel="stylesheet" media="screen and (max-weight: 3kg) and (color), (color)" href="example.css" /&gt;</code></pre>

   <p>In this example, the first media query will be represented as
   "<code>not all</code>" and evaluate to false and the second media query
   is evaluated as if the first had not been specified, effectively.</p>
  </div>

  <div class="example">
   <pre><code>@media (min-orientation:portrait) { &hellip; }</code></pre>

   <p>Is represented as "<code>not all</code>" because the ''orientation''
   feature does not accept the ''min-'' prefix.</p>
  </div>

 <li>
  <p><strong>Unknown media feature values.</strong> As with unknown media
  features, user agents are to represent a media query as
  "<code>not all</code>" when one of the specified media feature values is
  not known.</p>

  <div class="example">
   <p>The media query <code>(color:20example)</code> specifies an unknown
   value for the ''color'' media feature and is therefore represented as
   "<code>not all</code>".</p>
  </div>

  <div class="example">
   <p>This media query is represented as "<code>not all</code>" because
   negative lengths are not allowed for the ''width'' media feature:</p>

   <pre><code>@media (min-width: -100px) { &hellip; }</code></pre>
  </div>

 <li>
  <p><strong>Malformed media query.</strong> User agents are to handle
  unexpected tokens encountered while parsing a media query by reading until
  the end of the media query, while observing
  <a href="http://www.w3.org/TR/CSS21/syndata.html#block">the rules for
  matching pairs</a> of (), [], {}, "", and &#39;&#39;, and correctly handling
  escapes. Media queries with unexpected tokens are represented as
  "<code>not all</code>". [[!CSS21]]

  <div class="example">
   <pre><code>@media (example, all,), speech { /* only applicable to speech devices */ }
@media &amp;test, screen           { /* only applicable to screen devices */ }</code></pre>
  </div>

  <div class="example">
   <p>The following is an malformed media query because having no space
   between ''and'' and the expression is not allowed. (That is reserved for
   the functional notation syntax.)</p>
   <pre><code>@media all and(color) { &hellip; }</code></pre>
  </div>

  <p>Media queries are expected to follow the error handling rules of the
  host language as well.</p>

  <div class="example">
   <pre><code>@media test;,all { body { background:lime } }</code></pre>

   <p>&hellip; will not apply because the semicolon terminates the
   <code>@media</code> rule in CSS.</p>
  </div>
</ul>

<h2 id="media1">Media features</h2>

<p>Syntactically, media features resemble CSS properties: they have
names and accept certain values. There are, however, several
important differences between properties and media features:</p>

<ul>
<li>Properties are used in <em>declarations</em> to give
information about how to present a document. Media features are
used in <em>expressions</em> to describe requirements of the output
device.</li>

<li>Most media features accept optional ''min-'' or ''max-'' prefixes
to express "greater or equal to" and "smaller or equal to"
constraints. This syntax is used to avoid "&lt;" and "&gt;"
characters which may conflict with HTML and XML. Those media features
that accept prefixes will most often be used with prefixes, but can
also be used alone.</li>

<li>Properties always require a value to form a declaration. Media
features, on the other hand, can also be used without a value. For a media
feature <var>feature</var>, <code>(<var>feature</var>)</code> will evaluate
to true if <code>(<var>feature</var>:<var>x</var>)</code> will evaluate to
true for a value <var>x</var> other than zero or zero followed by a unit
identifier (i.e., other than <code>0</code>, <code>0px</code>,
<code>0em</code>, etc.). Media features that are prefixed by min/max cannot
be used without a value. When a media feature prefixed with min/max is used
without a value it makes the media query malformed.</li>

<li>Properties may accept more complex values, e.g., calculations that
involve several other values. Media features only accept single
values: one keyword, one number, or a number with a unit identifier.
(The only exceptions are the ''aspect-ratio'' and ''device-aspect-ratio''
media features.)

</li>


</ul>

<div class="example">
<p>For example, the ''color'' media feature can form expressions without a
value (''(color)''), or with a value (''(min-color: 1)'').</p>
</div>


<p class="note">This specification defines media features usable with visual and
tactile devices. Similarly, media features can be defined for aural
media types.</p>


<h3 id="width">width</h3>

<div class="media-feature"><span class="label">Value:</span>
&lt;length&gt;<br>
<span class="label">Applies to:</span> visual and tactile media
types<br>
<span class="label">Accepts min/max prefixes:</span> yes<br>
</div>

<p>The ''width'' media feature describes the width of the targeted display
area of the output device. For continuous media, this is the width
of the viewport (as described by CSS2, section 9.1.1 [[!CSS21]]) including
the size of a rendered scroll bar (if any). For paged media, this is the
width of the page box (as described by CSS2, section 13.2 [[!CSS21]]).</p>

<p>A specified &lt;length> cannot be negative.</p>

<div class="example">

<p>For example, this media query expresses that the style sheet is
usable on printed output wider than 25cm:</p>

<pre><code>&lt;link rel="stylesheet" media="print and (min-width: 25cm)" href="http://&hellip;" /></code></pre>
</div>

<div class="example">

<p>This media query expresses that the style sheet is usable on
devices with viewport (the part of the screen/paper where the
document is rendered) widths between 400 and 700 pixels:</p>

<pre><code>@media screen and (min-width: 400px) and (max-width: 700px) { &hellip; }</code></pre>
</div>

<div class="example">

<p>This media query expresses that style sheet is usable on screen
and handheld devices if the width of the viewport is greater than
20em.</p>

<pre><code>@media handheld and (min-width: 20em),
  screen and (min-width: 20em) { &hellip; }</code></pre>

<p>The ''em'' value is relative to the initial value of
‘font-size’.</p>

</div>


<h3 id="height">height</h3>

<div class="media-feature"><span class="label">Value:</span>
&lt;length&gt;<br>
<span class="label">Applies to:</span> visual and tactile media
types<br>
<span class="label">Accepts min/max prefixes:</span> yes<br>
</div>

<p>The ''height'' media feature describes the height of the targeted display
area of the output device. For continuous media, this is the height
of the viewport including the size of a rendered scroll bar (if any). For
paged media, this is the height of the page box.</p>

<p>A specified &lt;length> cannot be negative.</p>

<h3 id="device-width">device-width</h3>

<div class="media-feature"><span class="label">Value:</span> &lt;length&gt;<br>
<span class="label">Applies to:</span> visual and tactile media types<br>
<span class="label">Accepts min/max prefixes:</span> yes<br>
</div>

<p>The ''device-width'' media feature describes the width of the rendering
surface of the output device. For continuous media, this is the width
of the screen. For paged media, this is the width of the page sheet
size.</p>

<p>A specified &lt;length> cannot be negative.</p>

<div class="example">
<pre><code>@media screen and (device-width: 800px) { &hellip; }</code></pre>

<p>In the example above, the style sheet will apply only to screens
that currently displays exactly 800 horizontal pixels. The ''px'' unit is
of the logical kind, as described in the <a href="#units">Units</a>
section.</p>

</div>


<h3 id="device-height">device-height</h3>

<div class="media-feature"><span class="label">Value:</span> &lt;length&gt;<br>
<span class="label">Applies to:</span> visual and tactile media types<br>
<span class="label">Accepts min/max prefixes:</span> yes<br>
</div>

<p>The ''device-height'' media feature describes the height of the rendering
surface of the output device. For continuous media, this is the height
of the screen. For paged media, this is the height of the page sheet
size.</p>

<p>A specified &lt;length> cannot be negative.</p>

<div class="example">
<pre><code>&lt;link rel="stylesheet" media="screen and (device-height: 600px)" /&gt;</code></pre>

<p>In the example above, the style sheet will apply only to screens
that have exactly 600 vertical pixels. Note that the definition of the
''px'' unit is the same as in other parts of CSS.</p>

</div>


<h3>orientation</h3>

<div class="media-feature"><span class="label">Value:</span>
portrait | landscape<br>
<span class="label">Applies to:</span> bitmap media types<br>
<span class="label">Accepts min/max prefixes:</span> no<br>
</div>

<p>The ''orientation'' media feature is ''portrait'' when the value of the
''height'' media feature is greater than or equal to the value of the
''width'' media feature. Otherwise ''orientation'' is ''landscape''.</p>

<div class="example">

<pre><code>@media all and (orientation:portrait) { &hellip; }
@media all and (orientation:landscape) { &hellip; }</code></pre>
</div>


<h3>aspect-ratio</h3>

<div class="media-feature"><span class="label">Value:</span>
&lt;ratio&gt;<br>
<span class="label">Applies to:</span> bitmap media types<br>
<span class="label">Accepts min/max prefixes:</span> yes<br>
</div>

<p>The ''aspect-ratio'' media feature is defined as the ratio of the value
of the ''width'' media feature to the value of the ''height'' media
feature.</p>


<h3>device-aspect-ratio</h3>

<div class="media-feature"><span class="label">Value:</span>
&lt;ratio&gt;<br>
<span class="label">Applies to:</span> bitmap media types<br>
<span class="label">Accepts min/max prefixes:</span> yes<br>
</div>

<p>The ''device-aspect-ratio'' media feature is defined as the ratio of the
value of the ''device-width'' media feature to the value of the
''device-height'' media feature.</p>

<div class="example">

<p>For example, if a screen device with square pixels has 1280 horizontal
pixels and 720 vertical pixels (commonly referred to as "16:9"), the
following Media Queries will all match the device:</p>

<pre><code>@media screen and (device-aspect-ratio: 16/9) { &hellip; }
@media screen and (device-aspect-ratio: 32/18) { &hellip; }
@media screen and (device-aspect-ratio: 1280/720) { &hellip; }
@media screen and (device-aspect-ratio: 2560/1440) { &hellip; }</code></pre>
</div>


<h3 id="color">color</h3>

<div class="media-feature"><span class="label">Value:</span> &lt;integer&gt;<br>
<span class="label">Applies to:</span> visual media types<br>
<span class="label">Accept min/max prefixes:</span> yes<br>
</div>

<p>The ''color'' media feature describes the number of bits per color
component of the output device. If the device is not a color device,
the value is zero.</p>

<p>A specified &lt;integer> cannot be negative.</p>

<div class="example">

<p>For example, these two media queries express that a style sheet
applies to all color devices:</p>

<pre><code>@media all and (color) { &hellip; }
@media all and (min-color: 1) { &hellip; }</code></pre>
</div>

<div class="example">
<p>This media query expresses that a style sheet applies to color
devices with 2 or more bits per color component:</p>

<pre><code>@media all and (min-color: 2) { &hellip; }</code></pre>
</div>

<p>If different color components are represented by
different number of bits, the smallest number is used.</p>

<div class="example">
<p>For instance, if an 8-bit color system represents the red
component with 3 bits, the green component with 3 bits and the blue
component with 2 bits, the ''color'' media feature will have a value
of 2.</p>
</div>

<p>In a device with indexed colors, the minimum number of bits per
color component in the lookup table is used.</p>

<p class="note">The described functionality is only able to describe color
capabilities at a superficial level. If further functionality is
required, RFC2531 [[RFC2531]] provides more specific media features
which may be supported at a later stage.</p>


<h3 id="color-index">color-index</h3>

<div class="media-feature"><span class="label">Value:</span>
&lt;integer&gt;<br>
<span class="label">Applies to:</span> visual media types<br>
<span class="label">Accepts min/max prefixes:</span> yes<br>
</div>

<p>The ''color-index'' media feature describes the number of entries
in the color lookup table of the output device. If the device does not
use a color lookup table, the value is zero.

<p>A specified &lt;integer> cannot be negative.</p>

<div class="example">
<p>For example, here are two ways to express that a style sheet
applies to all color index devices:</p>

<pre><code>@media all and (color-index) { &hellip; }
@media all and (min-color-index: 1) { &hellip; }</code></pre>
</div>


<div class="example">
<p>This media query expresses that a style sheet applies to a color
index device with 256 or more entries:</p>

<pre><code>&lt;?xml-stylesheet media="all and (min-color-index: 256)"
  href="http://www.example.com/&hellip;" ?&gt;</code></pre>
</div>

<h3 id="monochrome">monochrome</h3>

<div class="media-feature"><span class="label">Value:</span>
&lt;integer&gt;<br>
<span class="label">Applies to:</span> visual media types<br>
<span class="label">Accepts min/max prefixes:</span> yes<br>
</div>

<p>The ''monochrome'' media feature describes the number of bits per
pixel in a monochrome frame buffer. If the device is not a
monochrome device, the output device value will be 0.</p>

<p>A specified &lt;integer> cannot be negative.</p>

<div class="example">

<p>For example, here are two ways to express that a style sheet
applies to all monochrome devices:</p>

<pre><code>@media all and (monochrome) { &hellip; }
@media all and (min-monochrome: 1) { &hellip; }</code></pre>
</div>

<div class="example">
<p>Express that a style sheet applies to monochrome
devices with more than 2 bits per pixels:</p>

<pre><code>@media all and (min-monochrome: 2) { &hellip; }</code></pre>
</div>


<div class="example">
<p>Express that there is one style sheet for color pages and another for monochrome:</p>

<pre><code>&lt;link rel="stylesheet" media="print and (color)" href="http://&hellip;" /&gt;
&lt;link rel="stylesheet" media="print and (monochrome)" href="http://&hellip;" /&gt;</code></pre>
</div>

<h3 id="resolution">resolution</h3>

<div class="media-feature"><span class="label">Value:</span>
&lt;resolution&gt;<br>
 <span class="label">Applies to:</span> bitmap media types<br>
<span class="label">Accepts min/max prefixes:</span> yes<br>
</div>

<p>The ''resolution'' media feature describes the resolution of the
output device, i.e. the density of the pixels. When querying devices
with non-square pixels, in ''min-resolution'' queries the least-dense
dimension must be compared to the specified value and in
''max-resolution'' queries the most-dense dimensions must be compared
instead. A ''resolution'' (without a "min-" or "max-" prefix) query
never matches a device with non-square pixels.</p>

<p>For printers, this corresponds to the screening resolution (the
resolution for printing dots of arbitrary color).</p>

<div class="example">

<p>For example, this media query expresses that a style sheet is
usable on devices with resolution greater than 300 dots per
inch:</p>

<pre><code>@media print and (min-resolution: 300dpi) { &hellip; }</code></pre>
</div>


<p>This media query expresses that a style sheet is
usable on devices with resolution greater than 118 dots per
centimeter:</p>

<pre><code>@media print and (min-resolution: 118dpcm) { &hellip; }</code></pre>

</div>


<h3 id="scan">scan</h3>

<div class="media-feature"><span class="label">Value:</span>
progressive | interlace<br>
<span class="label">Applies to:</span> "tv" media types<br>
<span class="label">Accepts min/max prefixes:</span> no<br>
</div>

<p>The ''scan'' media feature describes the scanning process of "tv"
output devices.</p>

<div class="example">

<p>For example, this media query expresses that a style sheet is
usable on tv devices with progressive scanning:</p>

<pre><code>@media tv and (scan: progressive) { &hellip; }</code></pre>
</div>

<h3 id="grid">grid</h3>

<div class="media-feature"><span class="label">Value:</span> &lt;integer&gt;<br>
<span class="label">Applies to:</span> visual and tactile media types<br>
<span class="label">Accepts min/max prefixes:</span> no<br>
</div>

<p>The ''grid'' media feature is used to query whether the output device
is grid or bitmap. If the output device is grid-based (e.g., a "tty"
terminal, or a phone display with only one fixed font), the value will
be 1. Otherwise, the value will be 0.</p>

<p>Only 0 and 1 are valid values. (This includes -0.) Thus everything else
creates a malformed media query.</p>

<div class="example">

<p>Here are two examples:</p>

<pre><code>@media handheld and (grid) and (max-width: 15em) { &hellip; }</code>
<code>@media handheld and (grid) and (device-max-height: 7em) { &hellip; }</code></pre>

</div>


<h2 id="values">Values</h2>

<p>This specification also introduces two new values.</p>

<p>The &lt;ratio> value is a positive (not zero or negative) &lt;integer>
followed by optional whitespace, followed by a solidus ('/'), followed by
optional whitespace, followed by a positive &lt;integer>.</p>

<p>The &lt;resolution> value is a positive &lt;number> immediately followed
by a unit identifier (''dpi'' or ''dpcm'').</p>

<p>Whitespace, &lt;integer>, &lt;number> and other values used by this
specification are the same as in other parts of CSS, normatively defined by
CSS 2.1. [[!CSS21]]</p>


<h2 id="units">Units</h2>

<p>The units used in media queries are the same as in other parts of
CSS. For example, the pixel unit represents CSS pixels and not
physical pixels.</p>

<p>Relative units in media queries are based on the initial value, which means
that units are never based on results of declarations. For example, in HTML,
the ''em'' unit is relative to the initial value of 'font-size'.</p>

<h3>Resolution</h3>

<p>The ''dpi'' and ''dpcm'' units describe the resolution of an output
device, i.e., the density of device pixels. Resolution unit identifiers
are:</p>

<dl>
<dt>dpi</dt>