css3-conditional/Overview.src.html@06244e910e27
css3-conditional/Overview.src.html
Wed, 06 Feb 2013 23:47:11 -0800
- author
- L. David Baron <dbaron@dbaron.org>
- date
- Wed, 06 Feb 2013 23:47:11 -0800
- changeset 7381
- 06244e910e27
- parent 7374
- 34b185ae3bac
- child 7382
- 6e5d9a1539bd
- permissions
- -rw-r--r--
[css3-conditional] Make examples represent slighty better practices.
Addresses issue raised in
http://lists.w3.org/Archives/Public/www-style/2012Dec/0224.html
which is issue 1 in the LCWD disposition of comments.
1 <!DOCTYPE html public '-//W3C//DTD HTML 4.01//EN'
2 'http://www.w3.org/TR/html4/strict.dtd'>
3 <html lang="en">
4 <head profile="http://www.w3.org/2006/03/hcard">
5 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
6 <title>CSS Conditional Rules Module Level 3</title>
7 <link rel="stylesheet" type="text/css" href="../default.css">
8 <link href="../csslogo.ico" rel="shortcut icon" type="image/x-icon">
9 <link rel="stylesheet" type="text/css" href="http://www.w3.org/StyleSheets/TR/W3C-[STATUS].css">
10 <!--
11 <script src="http://test.csswg.org/harness/annotate.js#CSS3-CONDITIONAL_DEV"
12 type="text/javascript" defer></script
13 -->
14 </head>
16 <div class="head">
17 <!--logo-->
19 <h1>CSS Conditional Rules Module Level 3</h1>
21 <h2 class="no-num no-toc">[LONGSTATUS] [DATE]</h2>
22 <dl>
23 <dt>This version:
24 <dd><a href="[VERSION]">
25 http://www.w3.org/TR/[YEAR]/ED-css3-conditional-[CDATE]/</a>
27 <dt>Latest version:
28 <dd><a href="http://www.w3.org/TR/[SHORTNAME]/">http://www.w3.org/TR/[SHORTNAME]/</a>
30 <dt>Editor's draft:
31 <dd><a href="http://dev.w3.org/csswg/[SHORTNAME]/">http://dev.w3.org/csswg/[SHORTNAME]/</a>
33 <dt>Previous version:
34 <dd><a href="http://www.w3.org/TR/2012/WD-css3-conditional-20120911/">http://www.w3.org/TR/2012/WD-css3-conditional-20120911/</a></dd>
36 <dt>Editors:
37 <dd class=vcard><a class=fn href="http://dbaron.org/">L. David Baron</a>,
38 <a class=org href="http://www.mozilla.org/">Mozilla</a>
40 <dt>Issues list:
41 <dd>Maintained in document (only editor's draft is current)
43 <dt>Feedback:
45 <dd><a
46 href="http://lists.w3.org/Archives/Public/www-style/">www-style@w3.org</a>
47 with subject line “<kbd>[[SHORTNAME]] <var>… message topic
48 …</var></kbd>”
50 <dt>Test suite:
51 <dd><a href="https://test.csswg.org/shepherd/search/spec/css3-conditional/">submitted tests</a>; no built test suite yet
53 </dl>
55 <!--copyright-->
57 <hr title="Separator for header">
58 </div>
60 <h2 class="no-num no-toc" id="abstract">Abstract</h2>
62 <p>CSS is a language for describing the rendering of structured documents
63 (such as HTML and XML) on screen, on paper, in speech, etc. This module
64 contains the features of CSS for conditional processing of parts of
65 style sheets, conditioned on capabilities of the processor or the
66 document the style sheet is being applied to.
67 It includes and extends the functionality of CSS level 2 [[!CSS21]],
68 which builds on CSS level 1 [[CSS1]].
69 The main extensions compared to level 2 are
70 allowing nesting of certain at-rules inside '@media',
71 and the addition of the '@supports'
72 rule for conditional processing.
74 <h2 class="no-num no-toc" id="status">Status of this document</h2>
76 <!--status-->
78 <p>The following features are at risk:
79 <ul>
80 <li>The inclusion of '@font-face' rules and
81 '@keyframes' rules as allowed within all of the @-rules in
82 this specification is at risk, though only because of the relative
83 rates of advancement of specifications. If this specification is able
84 to advance faster than one or both of the specifications defining
85 those rules, then the inclusion of those rules will move from this
86 specification to the specification defining those rules.</li>
88 <li>The addition of support for @-rules inside of conditional grouping
89 rules is at risk; if interoperable implementations are not found, it
90 may be removed to advance the other features in this specification to
91 Proposed Recommendation.</li>
93 <li>The '@supports' rule is at risk; if interoperable
94 implementations are not found, it may be removed to advance the other
95 features in this specification to Proposed Recommendation.</li>
96 </ul>
98 <p>This is a <strong>Last Call Working Draft</strong>.
99 The deadline for comments is <strong>10 January 2013</strong>.
101 <!--
103 Things to go in level 4:
105 * Create some way to put these new conditional things on an @import.
106 * The @document rule (commented out, down below).
108 -->
110 <h2 class="no-num no-toc" id="contents">Table of contents</h2>
112 <!--toc-->
114 <h2 id="introduction">Introduction</h2>
116 <h3 id="context">Background</h3>
118 <p><em>This section is not normative.</em>
120 <p>[[!CSS21]] defines one type of conditional group rule, the
121 '@media' rule, and allows only rulesets (not other @-rules)
122 inside of it. The '@media' rule provides the ability to
123 have media-specific style sheets, which is also provided by style
124 sheet linking features such as '@import' and
125 <code class="html"><link></code>. The restrictions on the contents of
126 '@media' rules made them less useful; they have forced authors
127 using CSS features involving @-rules in media-specific style sheets to
128 use separate style sheets for each medium.</p>
130 <p>This specification extends the rules for the contents of
131 conditional group rules to allow other @-rules, which enables authors
132 to combine CSS features involving @-rules with media specific style
133 sheets within a single style sheet.</p>
135 <p>This specification also defines an additional type of conditional
136 group rule, '@supports', to
137 address author and user requirements.</p>
139 <p>The '@supports' rule allows CSS to be conditioned on
140 implementation support for CSS properties and values. This rule makes
141 it much easier for authors to use new CSS features and provide good
142 fallback for implementations that do not support those features. This
143 is particularly important for CSS features that provide new layout
144 mechanisms, and for other cases where a set of related styles needs to
145 be conditioned on property support.</p>
147 <h3 id="placement">Module Interactions</h3>
149 <p>This module replaces and extends the '@media' rule
150 feature defined in [[!CSS21]] section <var>7.2.1</var> and
151 incorporates the modifications previously made non-normatively by
152 [[!MEDIAQ]] section <var>1</var>.</p>
154 <p>Its current definition depends on @-rules defined in [[!CSS3-FONTS]]
155 and [[!CSS3-ANIMATIONS]], but that dependency is only on the
156 assumption that those modules will advance ahead of this one. If this
157 module advances faster, then the dependency will be reversed.</p>
159 <h3 id="conventions">Document Conventions</h3>
161 <p>Conformance requirements are expressed with a combination of
162 descriptive assertions and RFC 2119 terminology. The key words “MUST”,
163 “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”,
164 “RECOMMENDED”, “MAY”, and “OPTIONAL” in the normative parts of this
165 document are to be interpreted as described in RFC 2119.
166 However, for readability, these words do not appear in all uppercase
167 letters in this specification.
169 <p>All of the text of this specification is normative except sections
170 explicitly marked as non-normative, examples, and notes. [[!RFC2119]]</p>
172 <p>Examples in this specification are introduced with the words “for example”
173 or are set apart from the normative text with
174 <code class="html">class="example"</code>, like this:
176 <div class="example">
177 <p>This is an example of an informative example.</p>
178 </div>
180 <p>Informative notes begin with the word “Note” and are set apart from the
181 normative text with <code class="html">class="note"</code>, like this:
183 <p class="note">Note, this is an informative note.</p>
185 <h2 id="processing">Processing of conditional group rules</h2>
187 <p>This specification defines some CSS @-rules, called <dfn>conditional
188 group rules</dfn>, that associate a condition with a group of other
189 CSS rules. These different rules allow testing different types of
190 conditions, but share common behavior for how their contents are used
191 when the condition is true and when the condition is false.</p>
193 <div class="example">
194 <p>For example, this rule:</p>
195 <pre>@media print {
196 /* hide navigation controls when printing */
197 #navigation { display: none }
198 }</pre>
199 <p>causes a particular CSS rule (making elements with ID "navigation" be
200 display:none) apply only when the style sheet is used for a print
201 medium.
202 </div>
204 <p>Each conditional group rule has a condition, which at any time
205 evaluates to true or false. When the condition is true, CSS processors
206 <strong>must</strong> apply the rules inside the group rule as though
207 they were at the group rule's location; when the condition is false, CSS
208 processors <strong>must not</strong> apply any of rules inside the group
209 rule. The current state of the condition does not affect the CSS object
210 model, in which the contents of the group rule always remain within the
211 group rule.</p>
213 <p>This means that when multiple conditional group rules are nested,
214 a rule inside of both of them applies only when all of the rules'
215 conditions are true.</p>
217 <div class="example">For example, with this set of nested rules:
218 <pre>@media print { // rule (1)
219 /* hide navigation controls when printing */
220 #navigation { display: none }
221 @media (max-width: 12cm) { // rule (2)
222 /* keep notes in flow when printing to narrow pages */
223 .note { float: none }
224 }
225 }</pre>
226 the condition of the rule marked (1) is true for print media, and the
227 condition of the rule marked (2) is true when the width of the display
228 area (which for print media is the page box) is less than or equal to
229 12cm. Thus the rule ''#navigation { display: none }'' applies
230 whenever this style sheet is applied to print media, and the rule
231 ''.note { float: none }'' is applied only when the style sheet
232 is applied to print media <em>and</em> the width of the page box is less
233 than or equal to 12 centimeters.</div>
235 <p>When the condition for a conditional group rule changes, CSS
236 processors <strong>must</strong> reflect that the rules now apply or no
237 longer apply, except for properties whose definitions define effects of
238 computed values that persist past the lifetime of that value (such as
239 for some properties in [[CSS3-TRANSITIONS]] and
240 [[!CSS3-ANIMATIONS]]).</p>
242 <h2 id="contents-of">Contents of conditional group rules</h2>
244 <p>The syntax of each conditional group rule consists of some syntax
245 specific to the type of rule followed by a <dfn>group rule body</dfn>,
246 which is a block (pair of braces) containing a sequence of rules.</p>
248 <p>A group rule body is allowed to contain rulesets and any @-rules that
249 are allowed at the top level of a style sheet before and after a
250 ruleset. This means that @-rules that must occur at the beginning of
251 the style sheet (such as '@charset', '@import',
252 and '@namespace' rules) are not allowed inside of conditional group
253 rules. Conditional group rules can be nested.</p>
255 <p>In terms of the grammar, this specification defines the following
256 productions for use in the grammar of conditional group rules:</p>
258 <pre><dfn>nested_statement</dfn>
259 : ruleset | <i>media</i> | page | font_face_rule | keyframes_rule |
260 <i>supports_rule</i>
261 ;
263 <dfn>group_rule_body</dfn>
264 : '{' S* <i>nested_statement</i>* '}' S*
265 ;</pre>
266 <p>
267 in which all the productions are defined in that grammar with the
268 exception of <code>font_face_rule</code>
269 defined in [[!CSS3-FONTS]], <code>keyframes_rule</code> defined in
270 [[!CSS3-ANIMATIONS]], and <code>media</code> and <code>supports_rule</code>
271 defined in this specification.</p>
273 <p>In general, future CSS specifications that add new @-rules that are
274 not forbidden to occur after some other types of rules should modify
275 this <code>nested_statement</code> production to keep the grammar
276 accurate.</p>
278 <p>Style sheets <strong>must not</strong> use rules other than the allowed ones inside
279 conditional group rules.</p>
281 <p>CSS processors <strong>must</strong> ignore rules that are not
282 allowed within a group rule, and <strong>must</strong> handle invalid
283 rules inside of group rules as described in <a
284 href="http://www.w3.org/TR/CSS21/syndata.html#parsing-errors">section
285 4.2 (Rules for handling parsing errors)</a>, <a
286 href="http://www.w3.org/TR/CSS21/syndata.html#at-rules">section 4.1.5
287 (At-rules)</a>, and <a
288 href="http://www.w3.org/TR/CSS21/syndata.html#rule-sets">section 4.1.7
289 (Rule sets, declaration blocks, and selectors)</a> of [[!CSS21]].</p>
291 <h2 id="use">Placement of conditional group rules</h2>
293 <p>Conditional group rules are allowed at the top-level of a style
294 sheet, and inside other conditional group rules. CSS processors
295 <strong>must</strong> process such rules as <a
296 href="#processing">described above</a>.</p>
298 <p>Any rules that are not allowed after a ruleset (e.g., ''@charset'',
299 ''@import'', or ''@namespace'' rules) are also not allowed after a
300 conditional group rule. Therefore, style sheets <strong>must
301 not</strong> place such rules after a conditional group rules, and CSS
302 processors <strong>must</strong> ignore such rules.</p>
304 <h2 id="at-media">Media-specific style sheets: the '@media' rule</h2>
306 <p>The <dfn>'@media' rule</dfn> is a conditional group rule whose
307 condition is a media query. It consists of the at-keyword
308 '@media' followed by a (possibly empty) media query list (as
309 defined in [[!MEDIAQ]]), followed by a group rule body. The condition
310 of the rule is the result of the media query.</p>
312 <div class="example">
313 <p>This '@media' rule:</p>
314 <pre>@media screen and (min-width: 35em),
315 print and (min-width: 40em) {
316 #section_navigation { float: left; width: 10em; }
317 }</pre>
318 <p>has the condition
319 ''screen and (min-width: 35em), print and (min-width: 40em)'',
320 which is true for screen displays
321 whose viewport is at least 35 times the initial font size
322 and for print displays
323 whose viewport is at least 40 times the initial font size.
324 When either of these is true,
325 the condition of the rule is true,
326 and the rule
327 ''#section_navigation { float: left; width: 10em; }''
328 is applied.</p>
329 </div>
331 <p>In terms of the grammar, this specification extends the
332 <code>media</code> production in the
333 <a href="http://www.w3.org/TR/CSS21/grammar.html">Grammar of CSS 2.1</a>
334 ([[!CSS21]], Appendix G) into:
335 <pre><dfn>media</dfn>
336 : MEDIA_SYM S* media_query_list <i>group_rule_body</i>
337 ;</pre>
338 <p>where the <code>group_rule_body</code> production is defined in this
339 specification, the <code>media_query_list</code> production is defined
340 in [[!MEDIAQ]], and the others are defined in the <a
341 href="http://www.w3.org/TR/CSS21/grammar.html">Grammar of CSS 2.1</a>
342 ([[!CSS21]], Appendix G).
344 <h2 id="at-supports">Feature queries: the '@supports' rule</h2>
346 <p>The <dfn>'@supports' rule</dfn> is a conditional group
347 rule whose condition tests whether the user agent supports CSS
348 property:value pairs. Authors can use it to write style sheets that use
349 new features when available but degrade gracefully when those features
350 are not supported. CSS has existing mechanisms for graceful
351 degradation, such as ignoring unsupported properties or values, but
352 these are not always sufficient when large groups of styles need to be
353 tied to the support for certain features, as is the case for use of new
354 layout system features.</p>
356 <p>The syntax of the condition in the '@supports' rule is
357 slightly more complicated than for the other conditional group rules
358 (though has some similarities to media queries) since:</p>
359 <ul>
360 <li>negation is needed so that the new-feature styles and the fallback
361 styles can be separated (within the forward-compatible grammar's rules
362 for the syntax of @-rules), and not required to override each other</li>
363 <li>conjunction (and) is needed so that multiple required features can
364 be tested</li>
365 <li>disjunction (or) is needed when there are multiple alternative
366 features for a set of styles, particularly when some of those
367 alternatives are vendor-prefixed properties or values</li>
368 </ul>
370 <p>Therefore, the syntax of the '@supports' rule allows
371 testing for property:value pairs, and arbitrary conjunctions (and),
372 disjunctions (or), and negations (not) of them.</p>
374 <p>This extends the lexical scanner in the
375 <a href="http://www.w3.org/TR/CSS21/grammar.html">Grammar of CSS 2.1</a>
376 ([[!CSS21]], Appendix G) by adding:
377 <pre>
378 @{S}{U}{P}{P}{O}{R}{T}{S} {return SUPPORTS_SYM;}
379 {O}{R} {return OR;}
380 </pre>
382 <p>and the grammar by adding</p>
384 <pre><dfn>supports_rule</dfn>
385 : SUPPORTS_SYM S* <i>supports_condition</i> S* <i>group_rule_body</i>
386 ;
388 <dfn>supports_condition</dfn>
389 : <i>supports_negation</i> | <i>supports_conjunction</i> | <i>supports_disjunction</i> |
390 <i>supports_condition_in_parens</i>
391 ;
393 <dfn>supports_condition_in_parens</dfn>
394 : ( '(' S* <i>supports_condition</i> S* ')' ) | <i>supports_declaration_condition</i> |
395 <i>general_enclosed</i>
396 ;
398 <dfn>supports_negation</dfn>
399 : NOT S+ <i>supports_condition_in_parens</i>
400 ;
402 <dfn>supports_conjunction</dfn>
403 : <i>supports_condition_in_parens</i> ( S+ AND S+ <i>supports_condition_in_parens</i> )+
404 ;
406 <dfn>supports_disjunction</dfn>
407 : <i>supports_condition_in_parens</i> ( S+ OR S+ <i>supports_condition_in_parens</i> )+
408 ;
410 <dfn>supports_declaration_condition</dfn>
411 : '(' S* declaration ')'
412 ;
414 <dfn>general_enclosed</dfn>
415 : ( FUNCTION | '(' ) ( any | unused )* ')'
416 ;
417 </pre>
419 <p>in which <code>declaration</code>, <code>any</code>, and
420 <code>unused</code> are the productions in the core syntax of CSS
421 defined in <a
422 href="http://www.w3.org/TR/CSS21/syndata.html#tokenization">section
423 4.1.1 (Tokenization)</a> of [[!CSS21]],
424 and the <code>AND</code> and <code>NOT</code> tokens are defined in
425 the Media Queries specification [[!MEDIAQ]].</p>
427 <p>
428 Implementations <strong>must</strong> parse ''@supports'' rules
429 based on the above grammar,
430 and when interpreting the above grammar,
431 <strong>must</strong> match the production before an <code>|</code> operator
432 in preference to the one after it.
433 </p>
435 <p>
436 The above grammar is purposely very loose for forwards-compatibility reasons,
437 since the <code>general_enclosed</code> production
438 allows for substantial future extensibility.
439 Any ''@supports'' rule that does not parse according to the grammar above
440 (that is, a rule that does not match this loose grammar
441 which includes the general_enclosed production)
442 is invalid.
443 Style sheets <strong>must not</strong> use such a rule and
444 processors <strong>must</strong> ignore such a rule (including all of its contents).
446 <p>Each of these grammar terms is associated with a boolean result, as
447 follows:</p>
448 <dl>
449 <dt>supports_condition</dt>
450 <dd>
451 The result is the result of the single child term.
452 </dd>
454 <dt>supports_condition_in_parens</dt>
455 <dd>
456 The result is the result of the single <code>supports_condition</code>
457 or <code>supports_declaration_condition</code> child term.
458 </dd>
460 <dt>supports_negation</dt>
461 <dd>
462 The result is the <em>negation</em> of the result of the
463 <code>supports_condition_in_parens</code> child term.
464 </dd>
466 <dt>supports_conjunction</dt>
467 <dd>
468 The result is true if the result of <em>all</em> of the
469 <code>supports_condition_in_parens</code> child terms is true;
470 otherwise it is false.
471 </dd>
473 <dt>supports_disjunction</dt>
474 <dd>
475 The result is true if the result of <em>any</em> of the
476 <code>supports_condition_in_parens</code> child terms is true;
477 otherwise it is false.
478 </dd>
480 <dt>supports_declaration_condition</dt>
481 <dd>
482 The result is whether the CSS processor <a href="#support-definition">supports</a> the declaration
483 within the parentheses.
484 </dd>
486 <dt>general_enclosed</dt>
487 <dd>
488 The result is always false.
489 Additionally, style sheets <strong>must not</strong>
490 write ''@supports'' rules
491 that match this grammar production.
492 (In other words, this production exists only for future extensibility,
493 and is not part of the description of a valid style sheet
494 in this level of the specification.)
495 <span class="note">Note that future levels may define functions
496 or other parenthesized expressions that can evaluate to true.</span>
497 </dd>
498 </dl>
500 <p>The condition of the '@supports' rule is the result of the
501 <code>supports_condition</code> term that is a child of the
502 <code>supports_rule</code> term.</p>
504 <div class="example">
505 <p>For example, the following rule</p>
506 <pre>@supports ( display: flexbox ) {
507 body, #navigation, #content { display: flexbox; }
508 #navigation { background: blue; color: white; }
509 #article { background: white; color: black; }
510 }</pre>
511 <p>applies the rules inside the '@supports' rule only when
512 ''display: flexbox'' is supported.</p>
513 </div>
515 <div class="example">
516 <p>The following example shows an additional '@supports' rule that can
517 be used to provide an alternative for when ''display: flexbox'' is not
518 supported:</p>
519 <pre>@supports not ( display: flexbox ) {
520 body { width: 100%; height: 100%; background: white; color: black; }
521 #navigation { width: 25%; }
522 #article { width: 75%; }
523 }</pre>
524 <p>Note that the 'width' declarations may be harmful to the
525 flexbox-based layout, so it is important that they be present only in
526 the non-flexbox styles.</p>
527 </div>
529 <div class="example">
530 <p>The following example checks for support for the 'box-shadow'
531 property, including checking for support for vendor-prefixed versions of
532 it. When the support is present, it specifies both 'box-shadow' (with
533 the prefixed versions) and 'color' in a way what would cause the text to
534 become invisible were 'box-shadow' not supported.</p>
535 <pre>@supports ( box-shadow: 2px 2px 2px black ) or
536 ( -moz-box-shadow: 2px 2px 2px black ) or
537 ( -webkit-box-shadow: 2px 2px 2px black ) or
538 ( -o-box-shadow: 2px 2px 2px black ) {
539 .outline {
540 color: white;
541 -moz-box-shadow: 2px 2px 2px black;
542 -webkit-box-shadow: 2px 2px 2px black;
543 -o-box-shadow: 2px 2px 2px black;
544 box-shadow: 2px 2px 2px black; /* unprefixed last */
545 }
546 }</pre></div>
548 <p>To avoid confusion between ''and'' and ''or'', the syntax requires
549 that both ''and'' and ''or'' be specified explicitly (rather than, say,
550 using commas or spaces for one of them). Likewise, to avoid confusion
551 caused by precedence rules, the syntax does not allow ''and'', ''or'',
552 and ''not'' operators to be mixed without a layer of parentheses.</p>
554 <div class="example">
555 <p>For example, the following rule is not valid:
556 <pre class="illegal">@supports (transition-property: color) or
557 (animation-name: foo) and
558 (transform: rotate(10deg)) {
559 // ...
560 }</pre>
561 <p>Instead, authors must write one of the following:</p>
562 <pre>@supports ((transition-property: color) or
563 (animation-name: foo)) and
564 (transform: rotate(10deg)) {
565 // ...
566 }</pre>
567 <pre>@supports (transition-property: color) or
568 ((animation-name: foo) and
569 (transform: rotate(10deg))) {
570 // ...
571 }</pre>
572 </div>
574 <p>Furthermore, whitespace is required after a ''not'' and on both
575 sides of an ''and'' or ''or''.</p>
577 <p>The declaration being tested must always occur within parentheses,
578 when it is the only thing in the expression.<p>
580 <div class="example">
581 <p>For example, the following rule is not valid:
582 <pre class="illegal">@supports display: flexbox {
583 // ...
584 }</pre>
585 <p>Instead, authors must write:</p>
586 <pre>@supports (display: flexbox) {
587 // ...
588 }</pre>
589 </div>
591 <p>The syntax allows extra parentheses when they are not needed. This
592 flexibility is sometimes useful for authors (for example, when
593 commenting out parts of an expression) and may also be useful for
594 authoring tools.</p>
596 <div class="example">
597 <p>For example, authors may write:</p>
598 <pre>@supports ((display: flexbox)) {
599 // ...
600 }</pre>
601 </div>
603 <p>A trailing ''!important'' on a declaration being tested is allowed,
604 though it won't change the validity of the declaration.
606 <div class="example">
607 <p>For example, the following rule is valid:
608 <pre>@supports (display: flexbox !important) {
609 // ...
610 }</pre>
611 </div>
613 <h3 id="support-definition">Definition of support</h3>
615 <p>For forward-compatibility,
616 <a href="http://www.w3.org/TR/CSS21/syndata.html#declaration">section 4.1.8
617 (Declarations and properties)</a> of [[!CSS21]]
618 defines rules for handling invalid properties and values.
619 CSS processors that
620 do not implement or partially implement a specification
621 <strong>must</strong> treat any part of a value that they
622 do not implement, or
623 do not have a usable level of support for,
624 as invalid according to this rule
625 for handling invalid properties and values,
626 and therefore <strong>must</strong> discard the declaration as a parse error.</p>
628 <p>A CSS processor is considered to <dfn id="dfn-support">support</dfn>
629 a declaration (consisting of a property and value) if it accepts that
630 declaration (rather than discarding it as a parse error).
631 If a processor does not implement, with a usable level of support,
632 the value given,
633 then it <strong>must not</strong>
634 accept the declaration or claim support for it.</p>
636 <p>These rules (and the equivalence between them) allow
637 authors to use fallback (either in the [[CSS1]] sense of declarations
638 that are overridden by later declarations or with the new capabilities
639 provided by the ''@supports'' rule in this specification) that works
640 correctly for the features implemented. This applies especially to
641 compound values; implementations must implement all parts of the value
642 in order to consider the declaration supported, either inside a ruleset
643 or in the declaration condition of an ''@supports'' rule.</p>
645 <!--
646 <h2 id="at-document">Document queries: the '@document' rule</h2>
648 <p>The <dfn>'@document' rule</dfn> is a conditional group
649 rule whose condition depends on the
650 <a href="#url-of-doc">URL of the document being styled</a>.
651 This allows style sheets, particularly user style sheets, to have styles
652 that only apply to a set of pages rather than to all pages using the
653 style sheet.</p>
655 <p class="issue">Given that this @-rule is intended primarily for user
656 style sheets, what should this specification say about its use in author
657 style sheets? Should it be forbidden? Should use instead be
658 discouraged? Or should this specification remain neutral on the
659 topic, since there are valid uses in author style sheets?</p>
661 <p id="url-of-doc">The <dfn>URL of the document being styled</dfn> is
662 the URI at which the document is located, excluding any fragment
663 identifiers. (This means, for example, that HTTP redirects have been
664 followed.) If the styles are being applied inside a complete document
665 embedded into the presentation of another (e.g., [[HTML5]]'s <code
666 class="html">iframe</code>, <code class="html">object</code>, or <code
667 class="html">img</code> elements), the relevant URI is that of the
668 frame, not of its container. However, if content from other documents
669 is mixed in via mechanisms that mix content from one document into
670 another (e.g., [[SVG11]]'s <code>use</code> element), then the
671 address of the container document is used.</p>
673 <p class="note">Note: In [[HTML5]], this is the
674 <a href="http://dev.w3.org/html5/spec/dom.html#documents">document's address</a>
675 of a document in a
676 <a href="http://dev.w3.org/html5/spec/browsers.html#browsing-context">browsing context</a>.</p>
678 <div class="issue">What form of normalization is done on URLs and domains
679 before matching? In particular, this specification needs to describe:
680 <ul>
681 <li>what form is used for the <a href="#url-of-doc">URL of the document
682 being styled</a> (and what has been normalized in that form)</li>
683 <li>what normalization (if any) happens to the argument of each of the match
684 functions before the comparison that they describe and</li>
685 <li>whether the
686 comparison algorithm used is string comparison or some other URL
687 comparison algorithm.</li></ul></div>
689 <p>The '@document' rule's condition is written as a
690 comma-separated list of <dfn>URL matching functions</dfn>, and the
691 condition evaluates to true whenever any one of those functions
692 evaluates to true. The following URL matching functions are
693 permitted:</p>
695 <dl>
696 <dt><dfn id="url-exact" title="url()|URL matching functions::exact"><url></dfn></dt>
698 <dd>
699 <p>The 'url()' function is the <dfn>exact url matching
700 function</dfn>. It evaluates to true whenever the <a
701 href="#url-of-doc">URL of the document being styled</a> is exactly
702 the URL given.</p>
704 <p class="Note">The 'url()' function, since it is a core syntax
705 element in CSS, is allowed (subject to different character
706 limitations and thus escaping requirements) to contain an unquoted
707 value (in addition to the string values that are allowed as
708 arguments for all four functions).</p>
710 <div class="example">
711 <p>For example, this rule:</p>
712 <pre>@document url("http://www.w3.org/Style/CSS/") {
713 #summary { background: yellow; color: black}
714 }</pre>
715 <p>styles the <code class="html">summary</code> element on the page
716 <code>http://www.w3.org/Style/CSS/</code>, but not on any other
717 pages.</p>
718 </div>
719 </dd>
721 <dt><dfn id="url-prefix" title="url-prefix()|URL matching functions::prefix">url-prefix(<string>)</dfn></dt>
723 <dd>
724 <p>The 'url-prefix()' function is the <dfn>url prefix
725 matching function</dfn>. It evaluates to true whenever the
726 <a href="#url-of-doc">URL of the document being styled</a>
727 has the argument to the function as an
728 initial substring (which is true when the two strings are equal).
729 When the argument is the empty string, it evaluates to true for all
730 documents.</p>
731 <div class="example">
732 <p>For example, this rule:</p>
733 <pre>@document url-prefix("http://www.w3.org/Style/CSS/") {
734 #summary { background: yellow; color: black}
735 }</pre>
736 <p>styles the <code class="html">summary</code> element on the page
737 <code>http://www.w3.org/Style/CSS/</code> and on the page
738 <code>http://www.w3.org/Style/CSS/Test</code>, but it does not
739 affect the page <code>http://www.w3.org/</code> or the page
740 <code>http://www.example.com/Style/CSS/</code>.</p>
741 </div>
742 </dd>
744 <dt><dfn id="url-domain" title="domain()|URL matching functions::domain">domain(<string>)</dfn></dt>
746 <dd>
747 <p>The 'domain()' function is the <dfn>domain
748 matching function</dfn>. It evaluates to true whenever
749 the <a href="#url-of-doc">URL of the document being styled</a>
750 has a host subcomponent (as defined in [[!URI]])
751 and that host subcomponent is exactly the argument to the
752 'domain()' function or a final substring of the host
753 component is a period (U+002E) immediately followed by the argument
754 to the 'domain()' function.</p>
755 <div class="example">
756 <p>For example, this rule:</p>
757 <pre>@document domain("w3.org") {
758 body { font-size: 16px ! important }
759 }</pre>
760 <p>changes the font size of the body element for pages such as
761 <code>http://www.w3.org/Style/CSS/</code> and
762 <code>http://w3.org/Style/CSS/</code> and
763 <code>http://lists.w3.org/Archives/Public/www-style/</code>
764 but it does not affect the page
765 <code>http://www.example.com/Style/CSS/</code>.</p>
766 </div>
767 </dd>
769 <dt><dfn id="url-regexp" title="regexp()|URL matching functions::regular expression">regexp(<string>)</dfn></dt>
771 <dd>
772 <p>The contents of the <string> argument <strong>must</strong>
773 match the JavaScript <code>Pattern</code> production
774 ([[!ECMA-262-5.1]], section 15.10.1). However,
775 failing to do so is not a CSS syntax error and does not trigger any
776 error handling for CSS syntax errors.</p>
778 <p>The ''regexp()'' function evaluates to true whenever the string
779 argument compiled as a JavaScript regular expression with the
780 <code>global</code>, <code>ignoreCase</code> and
781 <code>multiline</code> flags <em>disabled</em>
782 (see [[!ECMA-262-5.1]], sections 15.10.7.2 through 15.10.7.4)
783 compiles successfully and the resulting regular expression matches
784 the entirety of the
785 <a href="#url-of-doc">URL of the document being styled</a>.</p>
787 <p class="note">Note that regular expression must match the entire
788 URL, not just a part of it.</p>
790 <p class="note">Note that this definition intentionally matches the
791 behavior of the <a
792 href="http://dev.w3.org/html5/spec/common-input-element-attributes.html#attr-input-pattern"><code class="html">pattern</code>
793 attribute</a> on the <code class="html">input</code> element
794 in [[HTML5]].</p>
796 <div class="example">
797 <p>For example, this rule:</p>
798 <pre>@document regexp("http://www.w3.org/TR/\\d{4}/[^/]*-CSS2-\\d{8}/") {
799 body { font-size: 20px ! important }
800 }</pre>
801 <p>changes the font size of the body element for pages such as
802 <code>http://www.w3.org/TR/2011/PR-CSS2-20110412/</code>.</p>
803 <p class="note">Note that the backslashes in the regular
804 expression require CSS escaping as ''\\''.</p>
805 </div>
806 </dd>
808 </dl>
810 <p>Implementations <strong>must</strong> treat any unknown URL matching
811 functions as a syntax error, and thus ignore the '@document' rule.
812 <span class="issue">Should we instead have more complicated error
813 handling rules to make forward-compatibility work differently, or is
814 this rule the best solution for such future expansion anyway?</span></p>
816 <div class="issue">This syntax doesn't offer any ability to do negations,
817 which has been requested in <a
818 href="https://bugzilla.mozilla.org/show_bug.cgi?id=349813">Mozilla bug
819 349813</a>. Use cases that people have wanted negations for
820 include:
821 <ul>
822 <li>User style sheets that want a particular rule in general, but know
823 that that rule does more harm than good on specific sites.</li>
824 <li>Authors who have a rule that they want to apply to most of their
825 pages, but wish to make a few exceptions for.</li>
826 </ul>
827 </div>
829 <p>This extends the lexical scanner in the
830 <a href="http://www.w3.org/TR/CSS21/grammar.html">Grammar of CSS 2.1</a>
831 ([[!CSS21]], Appendix G) by adding:
832 <pre>@{D}{O}{C}{U}{M}{E}{N}{T} {return DOCUMENT_SYM;}</pre>
833 <p>and the grammar by adding</p>
834 <pre><dfn>document_rule</dfn>
835 : DOCUMENT_SYM S+ <i>url_match_fn</i> ( "," S* <i>url_match_fn</i> )* <i>group_rule_body</i>
836 ;
838 <dfn>url_match_fn</dfn>
839 : (URI | FUNCTION S* STRING S* ')' ) S*
840 ;</pre>
841 -->
844 <h2 id="apis">APIs</h2>
846 <h3 id='extentions-to-cssrule-interface'>
847 Extensions to the <code>CSSRule</code> interface</h3>
849 <p>The <code>CSSRule</code> interface is extended as follows:
851 <pre class='idl'>partial interface CSSRule {
852 const unsigned short SUPPORTS_RULE = 12;
853 <!--
854 const unsigned short DOCUMENT_RULE = 13;
855 -->
856 }</pre>
859 <h3 id='the-cssgroupingrule-interface'>
860 The <code>CSSGroupingRule</code> interface</h3>
862 <p>The <dfn><code>CSSGroupingRule</code></dfn> interface represents an at-rule that contains other rules nested inside itself.
864 <pre class='idl'>interface CSSGroupingRule : CSSRule {
865 readonly attribute <a href="http://www.w3.org/TR/DOM-Level-2-Style/css.html#CSS-CSSRuleList">CSSRuleList</a> cssRules;
866 unsigned long insertRule (DOMString rule, unsigned long index);
867 void deleteRule (unsigned long index);
868 }</pre>
870 <dl class='idl-attributes'>
871 <dt><code>cssRules</code> of type <code><a href="http://www.w3.org/TR/DOM-Level-2-Style/css.html#CSS-CSSRuleList">CSSRuleList</a></code>, readonly
872 <dd>The <code>cssRules</code> attribute must return a <code>CSSRuleList</code>
873 object for the list of CSS rules nested inside the grouping rule.
874 </dl>
876 <dl class='idl-methods'>
877 <dt><code>insertRule(DOMString rule, unsigned long index)</code>, returns
878 <code>unsigned long</code>
879 <dd>
880 The <code>insertRule</code> operation must
881 insert a CSS rule <var>rule</var>
882 into the CSS rule list returned by <code>cssRules</code>,
883 such that the inserted rule will be at position <var>index</var>,
884 and any rules previously at <var>index</var> or higher
885 will increase their index by one.
886 It must throw INDEX_SIZE_ERR
887 if index is greater than <code>cssRules.length</code>.
888 It must throw SYNTAX_ERR
889 if the rule has a syntax error and is unparseable;
890 this does not include syntax errors handled by error handling rules
891 for constructs inside of the rule.
892 It must throw HIERARCHY_REQUEST_ERR
893 if the rule cannot be inserted at the location specified,
894 for example, if an ''@import'' rule is inserted inside a group rule.
896 <span class="issue">This needs to specify what to do
897 if <code>rule</code> is the empty string,
898 if it contains more than one CSS rule,
899 or if it contains garbage after a valid rule.</span>
901 <dt><code>deleteRule (unsigned long index)</code>, return <code>void</code>
902 <dd>
903 The <code>deleteRule</code> operation must
904 remove a CSS rule from
905 the CSS rule list returned by <code>cssRules</code> at <var>index</var>.
906 It must throw INDEX_SIZE_ERR
907 if index is greater than or equal to <code>cssRules.length</code>.
908 </dl>
911 <h3 id="the-cssconditionrule-interface">
912 The <code>CSSConditionRule</code> interface</h3>
914 <p>The <dfn><code>CSSConditionRule</code></dfn> interface represents all the "conditional" at-rules,
915 which consist of a condition and a statement block.
917 <pre class='idl'>interface CSSConditionRule : CSSGroupingRule {
918 attribute DOMString conditionText;
919 }</pre>
921 <dl class='idl-attributes'>
923 <dt><code>conditionText</code> of type <code>DOMString</code>
924 <dd>
925 <p>The <code>conditionText</code> attribute represents
926 the condition of the rule.
927 Since what this condition does
928 varies between the derived interfaces of <code>CSSConditionRule</code>,
929 those derived interfaces
930 may specify different behavior for this attribute
931 (see, for example, <code>CSSMediaRule</code> below).
932 In the absence of such rule-specific behavior,
933 the following rules apply:</p>
935 <p>The <code>conditionText</code> attribute, on getting, must return
936 the result of serializing the associated condition.
938 <p>On setting the <code>conditionText</code> attribute these steps
939 must be run:
941 <ol>
942 <li>Trim the given value of white space.
943 <li>If the given value matches the grammar of the
944 appropriate condition production for the given rule,
945 replace the associated CSS condition with the given value.
946 <li>Otherwise, do nothing.
947 </ol>
948 </dl>
951 <h3 id="the-cssmediarule-interface">
952 The <code>CSSMediaRule</code> interface</h3>
954 <p>The <dfn><code>CSSMediaRule</code></dfn> interface represents a ''@media'' rule:
956 <pre class='idl'>interface CSSMediaRule : CSSConditionRule {
957 readonly attribute <a href="http://www.w3.org/TR/DOM-Level-2-Style/stylesheets.html#StyleSheets-MediaList">MediaList</a> media;
958 }</pre>
960 <dl class='idl-attributes'>
961 <dt><code>media</code> of type <code><a href="http://www.w3.org/TR/DOM-Level-2-Style/stylesheets.html#StyleSheets-MediaList">MediaList</a></code>, readonly
962 <dd>The <code>media</code> attribute must return a <code>MediaList</code> object
963 for the list of media queries specified with the ''@media'' rule.
965 <dt><code>conditionText</code> of type <code>DOMString</code>
966 <dd>The <code>conditionText</code> attribute (defined on the <code>CSSConditionRule</code> parent rule),
967 on getting, must return the value of <code>media.mediaText</code> on the rule.
969 <p>Setting the <code>conditionText</code> attribute
970 must set the <code>media.mediaText</code> attribute on the rule.
971 </dl>
974 <h3 id="the-csssupportsrule-interface">
975 The <code>CSSSupportsRule</code> interface</h3>
977 <p>The <dfn><code>CSSSupportsRule</code></dfn> interface represents a ''@supports'' rule.</p>
979 <pre class='idl'>interface CSSSupportsRule : CSSConditionRule {
980 }</pre>
982 <!--
983 <h3 id="the-cssdocumentrule-interface">
984 The <code>CSSDocumentRule</code> interface</h3>
986 <p>The <dfn><code>CSSDocumentRule</code></dfn> interface represents a ''@document'' rule.</p>
988 <pre class='idl'>interface CSSDocumentRule : CSSConditionRule {
989 }</pre>
990 -->
993 <h3 id='the-css-interface'>
994 The <code>CSS</code> interface, and the <code title=''>supports()</code> function</h3>
996 <p>The <dfn id='CSS-interface'><code>CSS</code></dfn> interface holds useful CSS-related functions that do not belong elsewhere.
998 <pre class='idl'>interface CSS {
999 static boolean supports(DOMString property, DOMString value);
1000 static boolean supports(DOMString conditionText);
1001 }</pre>
1003 <dl class='idl-methods'>
1004 <dt><code>supports(DOMString property, DOMString value)</code>,
1005 returns <code>boolean</code>
1006 <dt><code>supports(DOMString conditionText)</code>,
1007 returns <code>boolean</code>
1008 <dd>
1009 When the <code title=''>supports()</code> method is invoked with two arguments <var>property</var> and <var>value</var>,
1010 it must return <code>true</code> if <var>property</var> is a literal match for the name of a CSS property that the UA supports,
1011 and <var>value</var> would be successfully parsed as a supported value for that property.
1012 Otherwise, it must return <code>false</code>.
1014 <p>
1015 When invoked with a single <var>conditionText</var> argument,
1016 it must return <code>true</code> if <var>conditionText</var>,
1017 when parsed and evaluated as a <code>supports_condition</code>,
1018 would return true.
1019 Otherwise, it must return <code>false</code>.
1020 </dl>
1023 <h2 class=no-num id="grammar">Grammar</h2>
1025 <p>In order to allow these new @-rules in CSS style sheets, this
1026 specification modifies the <code>stylesheet</code> production in the <a
1027 href="http://www.w3.org/TR/CSS21/grammar.html">Appendix G</a> grammar of
1028 [[!CSS21]] by replacing the <code>media</code> production defined in
1029 [[!CSS21]] with the <code>media</code> production defined in this one,
1030 and additionally inserting <code>| supports_rule</code>
1031 alongside <code>ruleset | media | page</code>.</p>
1034 <h2 id="conformance">Conformance</h2>
1036 <h3 id="base-modules">Base Modules</h3>
1038 <p>This specification defines conformance in terms of base modules,
1039 which are modules that this specification builds on top of. The base
1040 modules of this module are:</p>
1042 <ul>
1043 <li>[[!CSS21]]</li>
1044 </ul>
1046 <p>All of the conformance requirements of all base modules are
1047 incorporated as conformance requirements of this module, except where
1048 overridden by this module.</p>
1050 <p>Additionally, all conformance requirements related to validity of
1051 syntax in this module and all of its base modules are to be interpreted
1052 as though all syntax in all of those modules is valid.</p>
1054 <div class="example"><p>For example, this means that grammar presented
1055 in modules other than [[!CSS21]] must obey the requirements that
1056 [[!CSS21]] defines for the parsing of properties, and that requirements
1057 for handling invalid syntax in [[!CSS21]] do not treat syntax added by
1058 other modules as invalid.</p></div>
1060 <p>Additionally, the set of valid syntax can be increased by the
1061 conformance of a style sheet or processor to additional modules; use of
1062 such syntax does not make a style sheet nonconformant and failure to
1063 treat such syntax as invalid does not make a processor
1064 nonconformant.</p>
1066 <h3 id="conformance-classes">Conformance Classes</h3>
1068 <p>Conformance to the CSS Conditional Rules Module is defined for three
1069 conformance classes:
1070 <dl>
1071 <dt><dfn title="conformance::style sheet" id="conform-style-sheet">style sheet</dfn>
1072 <dd>A <a href="http://www.w3.org/TR/CSS21/conform.html#style-sheet">CSS
1073 style sheet</a>.</dd>
1074 <dt><dfn title="conformance::processor" id="conform-processor">processor</dfn></dt>
1075 <dd>A tool that reads CSS style sheets: it may be a renderer or
1076 <a
1077 href="http://www.w3.org/TR/CSS21/conform.html#user-agent">user-agent</a>
1078 that interprets the semantics of a style sheet and renders
1079 documents that use style sheets, or it may be a validator that
1080 checks style sheets.</dd>
1081 <dt><dfn title="conformance::authoring tool" id="conform-authoring-tool">authoring tool</dfn></dt>
1082 <dd>A tool that writes a style sheet.</dd>
1083 </dl>
1085 <p>A style sheet is conformant to the CSS Conditional Rules Module
1086 if it meets all of the conformance requirements in the module that are
1087 described as requirements of style sheets.</p>
1089 <p>A processor is conformant to the CSS Conditional Rules Module if it
1090 meets all applicable conformance requirements in the module that are
1091 described as requirements of processors. In general, all requirements
1092 are applicable to renderers. Requirements concerning a part of CSS
1093 not performed by a processor are not applicable, e.g., requirements
1094 related to rendering are not applicable to a validator. The inability
1095 of a processor to correctly render a document due to limitations of
1096 the device does not make it non-conformant. (For example, a renderer
1097 is not required to render color on a monochrome monitor.)</p>
1099 <p>An authoring tool is conformant to the CSS Conditional Rules Module
1100 if it writes style sheets that conform to the module and (if it reads
1101 CSS) it is a conformant processor.</p>
1103 <h3 id="partial">
1104 Partial Implementations</h3>
1106 <p>So that authors can exploit the forward-compatible parsing rules to
1107 assign fallback values, CSS renderers <strong>must</strong>
1108 treat as invalid (and <a href="http://www.w3.org/TR/CSS21/conform.html#ignore">ignore
1109 as appropriate</a>) any at-rules, properties, property values, keywords,
1110 and other syntactic constructs for which they have no usable level of
1111 support. In particular, user agents <strong>must not</strong> selectively
1112 ignore unsupported component values and honor supported values in a single
1113 multi-value property declaration: if any value is considered invalid
1114 (as unsupported values must be), CSS requires that the entire declaration
1115 be ignored.</p>
1117 <h3 id="experimental">Experimental Implementations</h3>
1119 <p>To avoid clashes with future CSS features, the CSS specifications
1120 reserve a <a href="http://www.w3.org/TR/CSS21/syndata.html#vendor-keywords">prefixed
1121 syntax</a> for proprietary property and value extensions to CSS. The CSS
1122 Working Group recommends that experimental implementations of features in
1123 CSS Working Drafts also use vendor-prefixed property or value names. This
1124 avoids any incompatibilities with future changes in the draft. Once a
1125 specification reaches the Candidate Recommendation stage, implementors
1126 should implement the non-prefixed syntax for any feature they consider to
1127 be correctly implemented according to spec.</p>
1129 <h3 id="cr-exit-criteria">CR Exit Criteria</h3>
1131 <p>For this specification to be advanced to Proposed Recommendation,
1132 there must be at least two independent, interoperable implementations
1133 of each feature. Each feature may be implemented by a different set of
1134 products, there is no requirement that all features be implemented by
1135 a single product. For the purposes of this criterion, we define the
1136 following terms:
1138 <dl>
1139 <dt>independent <dd>each implementation must be developed by a
1140 different party and cannot share, reuse, or derive from code
1141 used by another qualifying implementation. Sections of code that
1142 have no bearing on the implementation of this specification are
1143 exempt from this requirement.
1145 <dt>interoperable <dd>passing the respective test case(s) in the
1146 official CSS test suite, or, if the implementation is not a Web
1147 browser, an equivalent test. Every relevant test in the test
1148 suite should have an equivalent test created if such a user
1149 agent (UA) is to be used to claim interoperability. In addition
1150 if such a UA is to be used to claim interoperability, then there
1151 must one or more additional UAs which can also pass those
1152 equivalent tests in the same way for the purpose of
1153 interoperability. The equivalent tests must be made publicly
1154 available for the purposes of peer review.
1156 <dt>implementation <dd>a user agent which:
1158 <ol class=inline>
1159 <li>implements the specification.
1161 <li>is available to the general public. The implementation may
1162 be a shipping product or other publicly available version
1163 (i.e., beta version, preview release, or “nightly build”).
1164 Non-shipping product releases must have implemented the
1165 feature(s) for a period of at least one month in order to
1166 demonstrate stability.
1168 <li>is not experimental (i.e., a version specifically designed
1169 to pass the test suite and is not intended for normal usage
1170 going forward).
1171 </ol>
1172 </dl>
1174 <p>The specification will remain Candidate Recommendation for at least
1175 six months.
1177 <h2 id="changes">
1178 Changes</h2>
1180 <p>The following (non-editorial) changes were made to this specification since the
1181 <a href="http://www.w3.org/TR/2012/WD-css3-conditional-20120911/">11 September 2012 Working Draft</a>:
1183 <ul>
1184 <li>Removed ''@document'' rule; it has been deferred to Level 4.
1185 <li>Allow functional notation in ''@supports'' queries to be valid (to allow for future extensions),
1186 but treat such notations as always being false.
1187 <li>Corrected the grammar as follows:
1188 <pre>
1189 - : SUPPORTS_SYM S+ supports_condition group_rule_body
1190 + : SUPPORTS_SYM S* supports_condition group_rule_body
1191 </pre>
1192 <pre>
1193 - : (URI | FUNCTION) S*
1194 + : (URI | FUNCTION S* STRING S* ')' ) S*
1195 </pre>
1196 <li>Switched "and", "or", and "not" keywords to use appropriate productions rather than literals.
1197 <li>Clarified definition of support used for interpreting ''@support'' rules
1198 and its relationship to CSS forwards-compatible parsing rules.
1199 </ul>
1201 <h2 class=no-num id="acknowledgments">Acknowledgments</h2>
1203 <p>
1204 Thanks to the ideas and feedback from
1205 Tab Atkins,
1206 <span lang="tr">Tantek Çelik</span>,
1207 Alex Danilo,
1208 Elika Etemad,
1209 Pascal Germroth,
1210 <span lang="de">Björn Höhrmann</span>,
1211 Paul Irish,
1212 <span lang="nl">Anne van Kesteren</span>,
1213 Vitor Menezes,
1214 Alex Mogilevsky,
1215 Chris Moschini,
1216 Simon Sapin,
1217 Ben Ward,
1218 Zack Weinberg,
1219 Estelle Weyl,
1220 Boris Zbarsky,
1221 and all the rest of the <a href="http://lists.w3.org/Archives/Public/www-style/">www-style</a> community.
1223 </p>
1225 <h2 class=no-num id="references">References</h2>
1228 <h3 class="no-num" id="normative-references">Normative references</h3>
1229 <!--normative-->
1231 <h3 class="no-num" id="other-references">Other references</h3>
1232 <!--informative-->
1234 <h2 class="no-num" id="index">Index</h2>
1235 <!--index-->
1237 </body>
1238 </html>
1239 <!-- Keep this comment at the end of the file
1240 Local variables:
1241 mode: sgml
1242 sgml-declaration:"~/SGML/HTML4.decl"
1243 sgml-default-doctype-name:"html"
1244 sgml-minimize-attributes:t
1245 sgml-nofill-elements:("pre" "style" "br")
1246 sgml-live-element-indicator:t
1247 sgml-omittag:nil
1248 sgml-shorttag:nil
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1250 sgml-general-insert-case:lower
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1254 sgml-parent-document:nil
1255 sgml-exposed-tags:nil
1256 sgml-local-catalogs:nil
1257 sgml-local-ecat-files:nil
1258 End:
1259 -->
