css3-conditional/Overview.src.html

Tue, 13 Nov 2012 14:02:00 -0800

author
L. David Baron <dbaron@dbaron.org>
date
Tue, 13 Nov 2012 14:02:00 -0800
changeset 7029
4f68a956be34
parent 6943
d4c52c4a5501
child 7031
0eeeaff20f24
permissions
-rw-r--r--

Fix Tab's grammar by creating a production (general_enclosed) for a piece that occurs three times, fixing the missing parentheses around one of those occurrences, and adding the function token alternative to it for all three occurrences.

     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 rel="stylesheet" type="text/css"
     9         href="http://www.w3.org/StyleSheets/TR/W3C-[STATUS].css">
    10   <script src="http://test.csswg.org/harness/annotate.js#CSS3-CONDITIONAL_DEV" 
    11         type="text/javascript" defer></script>
    12 </head>
    14 <div class="head">
    15 <!--logo-->
    17 <h1>CSS Conditional Rules Module Level 3</h1>
    19 <h2 class="no-num no-toc">[LONGSTATUS] [DATE]</h2>
    20 <dl>
    21   <dt>This version:
    22     <dd><a href="[VERSION]">
    23     http://www.w3.org/TR/[YEAR]/ED-css3-conditional-[CDATE]/</a>
    25   <dt>Latest version:
    26     <dd><a href="http://www.w3.org/TR/[SHORTNAME]/">http://www.w3.org/TR/[SHORTNAME]/</a>
    28   <dt>Editor's draft:
    29     <dd><a href="http://dev.w3.org/csswg/[SHORTNAME]/">http://dev.w3.org/csswg/[SHORTNAME]/</a>
    31   <dt>Previous version:
    32     <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>
    34   <dt>Editors:
    35     <dd class=vcard><a class=fn href="http://dbaron.org/">L. David Baron</a>,
    36       <a class=org href="http://www.mozilla.org/">Mozilla</a>
    38   <dt>Issues list:
    39     <dd>Maintained in document (only editor's draft is current)
    41     <dt>Feedback:
    43     <dd><a
    44      href="http://lists.w3.org/Archives/Public/www-style/">www-style@w3.org</a>
    45      with subject line “<kbd>&#x5b;[SHORTNAME]&#x5d; <var>… message topic
    46      …</var></kbd>”
    48   <dt>Test suite:
    49     <dd><a href="https://test.csswg.org/shepherd/search/spec/css3-conditional/">submitted tests</a>; no built test suite yet
    51 </dl>
    53 <!--copyright-->
    55 <hr title="Separator for header">
    56 </div>
    58 <h2 class="no-num no-toc" id="abstract">Abstract</h2>
    60   <p>CSS is a language for describing the rendering of structured documents
    61   (such as HTML and XML) on screen, on paper,  in speech, etc. This module
    62   contains the features of CSS for conditional processing of parts of
    63   style sheets, conditioned on capabilities of the processor or the
    64   document the style sheet is being applied to.
    65   It includes and extends the functionality of CSS level&nbsp;2 [[!CSS21]],
    66   which builds on CSS level&nbsp;1 [[CSS1]].
    67   The main extensions compared to level&nbsp;2 are
    68   allowing nesting of certain at-rules inside '@media',
    69   and the addition of the '@supports'
    70   rule for conditional processing.
    72 <h2 class="no-num no-toc" id="status">Status of this document</h2>
    74 <!--status-->
    76 <p>The following features are at risk:
    77 <ul>
    78   <li>The inclusion of '@font-face' rules and
    79   '@keyframes' rules as allowed within all of the @-rules in
    80   this specification is at risk, though only because of the relative
    81   rates of advancement of specifications.  If this specification is able
    82   to advance faster than one or both of the specifications defining
    83   those rules, then the inclusion of those rules will move from this
    84   specification to the specification defining those rules.</li>
    86   <li>The addition of support for @-rules inside of conditional grouping
    87   rules is at risk; if interoperable implementations are not found, it
    88   may be removed to advance the other features in this specification to
    89   Proposed Recommendation.</li>
    91   <li>The '@supports' rule is at risk; if interoperable
    92   implementations are not found, it may be removed to advance the other
    93   features in this specification to Proposed Recommendation.</li>
    94 </ul>
    96 <!--
    98   Things to go in level 4:
   100   * Create some way to put these new conditional things on an @import.
   101   * The @document rule (commented out, down below).
   103 -->
   105 <h2 class="no-num no-toc" id="contents">Table of contents</h2>
   107 <!--toc-->
   109 <h2 id="introduction">Introduction</h2>
   111 <h3 id="context">Background</h3>
   113   <p><em>This section is not normative.</em>
   115   <p>[[!CSS21]] defines one type of conditional group rule, the
   116   '@media' rule, and allows only rulesets (not other @-rules)
   117   inside of it.  The '@media' rule provides the ability to
   118   have media-specific style sheets, which is also provided by style
   119   sheet linking features such as '@import' and
   120   <code class="html">&lt;link&gt;</code>.  The restrictions on the contents of
   121   '@media' rules made them less useful; they have forced authors
   122   using CSS features involving @-rules in media-specific style sheets to
   123   use separate style sheets for each medium.</p>
   125   <p>This specification extends the rules for the contents of
   126   conditional group rules to allow other @-rules, which enables authors
   127   to combine CSS features involving @-rules with media specific style
   128   sheets within a single style sheet.</p>
   130   <p>This specification also defines an additional type of conditional
   131   group rule, '@supports', to
   132   address author and user requirements.</p>
   134   <p>The '@supports' rule allows CSS to be conditioned on
   135   implementation support for CSS properties and values.  This rule makes
   136   it much easier for authors to use new CSS features and provide good
   137   fallback for implementations that do not support those features.  This
   138   is particularly important for CSS features that provide new layout
   139   mechanisms, and for other cases where a set of related styles needs to
   140   be conditioned on property support.</p>
   142 <h3 id="placement">Module Interactions</h3>
   144   <p>This module replaces and extends the '@media' rule
   145   feature defined in [[!CSS21]] section <var>7.2.1</var> and
   146   incorporates the modifications previously made non-normatively by
   147   [[!MEDIAQ]] section <var>1</var>.</p>
   149   <p>Its current definition depends on @-rules defined in [[!CSS3-FONTS]]
   150   and [[!CSS3-ANIMATIONS]], but that dependency is only on the
   151   assumption that those modules will advance ahead of this one.  If this
   152   module advances faster, then the dependency will be reversed.</p>
   154 <h3 id="conventions">Document Conventions</h3>
   156   <p>Conformance requirements are expressed with a combination of
   157   descriptive assertions and RFC 2119 terminology. The key words “MUST”,
   158   “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”,
   159   “RECOMMENDED”, “MAY”, and “OPTIONAL” in the normative parts of this
   160   document are to be interpreted as described in RFC 2119.
   161   However, for readability, these words do not appear in all uppercase
   162   letters in this specification.
   164   <p>All of the text of this specification is normative except sections
   165   explicitly marked as non-normative, examples, and notes. [[!RFC2119]]</p>
   167   <p>Examples in this specification are introduced with the words “for example”
   168   or are set apart from the normative text with
   169   <code class="html">class="example"</code>, like this:
   171   <div class="example">
   172     <p>This is an example of an informative example.</p>
   173   </div>
   175   <p>Informative notes begin with the word “Note” and are set apart from the
   176   normative text with <code class="html">class="note"</code>, like this:
   178   <p class="note">Note, this is an informative note.</p>
   180 <h2 id="processing">Processing of conditional group rules</h2>
   182 <p>This specification defines some CSS @-rules, called <dfn>conditional
   183 group rules</dfn>, that associate a condition with a group of other
   184 CSS rules.  These different rules allow testing different types of
   185 conditions, but share common behavior for how their contents are used
   186 when the condition is true and when the condition is false.</p>
   188 <div class="example">
   189 <p>For example, this rule:</p>
   190 <pre>@media print {
   191   #navigation { display: none }
   192 }</pre>
   193 <p>causes a particular CSS rule (making elements with ID "navigation" be
   194 display:none) apply only when the style sheet is used for a print
   195 medium.
   196 </div>
   198 <p>Each conditional group rule has a condition, which at any time
   199 evaluates to true or false.  When the condition is true, CSS processors
   200 <strong>must</strong> apply the rules inside the group rule as though
   201 they were at the group rule's location; when the condition is false, CSS
   202 processors <strong>must not</strong> apply any of rules inside the group
   203 rule.  The current state of the condition does not affect the CSS object
   204 model, in which the contents of the group rule always remain within the
   205 group rule.</p>
   207 <p>This means that when multiple conditional group rules are nested,
   208 a rule inside of both of them applies only when all of the rules'
   209 conditions are true.</p>
   211 <div class="example">For example, with this set of nested rules:
   212 <pre>@media print { // rule (1)
   213   #navigation { display: none }
   214   @media (max-width: 12cm) { // rule (2)
   215     .note { float: none }
   216   }
   217 }</pre>
   218 the condition of the rule marked (1) is true for print media, and the
   219 condition of the rule marked (2) is true when the width of the display
   220 area (which for print media is the page box) is less than or equal to
   221 12cm.  Thus the rule ''#navigation { display: none }'' applies
   222 whenever this style sheet is applied to print media, and the rule
   223 ''.note { float: none }'' is applied only when the style sheet
   224 is applied to print media <em>and</em> the width of the page box is less
   225 than or equal to 12 centimeters.</div>
   227 <p>When the condition for a conditional group rule changes, CSS
   228 processors <strong>must</strong> reflect that the rules now apply or no
   229 longer apply, except for properties whose definitions define effects of
   230 computed values that persist past the lifetime of that value (such as
   231 for some properties in [[CSS3-TRANSITIONS]] and
   232 [[!CSS3-ANIMATIONS]]).</p>
   234 <h2 id="contents-of">Contents of conditional group rules</h2>
   236 <p>The syntax of each conditional group rule consists of some syntax
   237 specific to the type of rule followed by a <dfn>group rule body</dfn>,
   238 which is a block (pair of braces) containing a sequence of rules.</p>
   240 <p>A group rule body is allowed to contain rulesets and any @-rules that
   241 are allowed at the top level of a style sheet before and after a
   242 ruleset.  This means that @-rules that must occur at the beginning of
   243 the style sheet (such as '@charset', '@import',
   244 and '@namespace' rules) are not allowed inside of conditional group
   245 rules.  Conditional group rules can be nested.</p>
   247 <p>In terms of the grammar, this specification defines the following
   248 productions for use in the grammar of conditional group rules:</p>
   250 <pre>nested_statement
   251   : ruleset | media | page | font_face_rule | keyframes_rule |
   252     supports_rule
   253   ;
   255 group_rule_body
   256   : '{' S* nested_statement* '}' S*
   257   ;</pre>
   258 <p>
   259 in which all the productions are defined in that grammar with the
   260 exception of <code>font_face_rule</code> 
   261 defined in [[!CSS3-FONTS]], <code>keyframes_rule</code> defined in
   262 [[!CSS3-ANIMATIONS]], and <code>media</code> and <code>supports_rule</code>
   263 defined in this specification.</p>
   265 <p>In general, future CSS specifications that add new @-rules that are
   266 not forbidden to occur after some other types of rules should modify
   267 this <code>nested_statement</code> production to keep the grammar
   268 accurate.</p>
   270 <p>Style sheets <strong>must not</strong> use rules other than the allowed ones inside
   271 conditional group rules.</p>
   273 <p>CSS processors <strong>must</strong> ignore rules that are not
   274 allowed within a group rule, and <strong>must</strong> handle invalid
   275 rules inside of group rules as described in <a
   276 href="http://www.w3.org/TR/CSS21/syndata.html#parsing-errors">section
   277 4.2 (Rules for handling parsing errors)</a>, <a
   278 href="http://www.w3.org/TR/CSS21/syndata.html#at-rules">section 4.1.5
   279 (At-rules)</a>, and <a
   280 href="http://www.w3.org/TR/CSS21/syndata.html#rule-sets">section 4.1.7
   281 (Rule sets, declaration blocks, and selectors)</a> of [[!CSS21]].</p>
   283 <h2 id="use">Placement of conditional group rules</h2>
   285 <p>Conditional group rules are allowed at the top-level of a style
   286 sheet, and inside other conditional group rules.  CSS processors
   287 <strong>must</strong> process such rules as <a
   288 href="#processing">described above</a>.</p>
   290 <p>Any rules that are not allowed after a ruleset (e.g., ''@charset'',
   291 ''@import'', or ''@namespace'' rules) are also not allowed after a
   292 conditional group rule.  Therefore, style sheets <strong>must
   293 not</strong> place such rules after a conditional group rules, and CSS
   294 processors <strong>must</strong> ignore such rules.</p>
   296 <h2 id="at-media">Media-specific style sheets:  the '@media' rule</h2>
   298 <p>The <dfn>'@media' rule</dfn> is a conditional group rule whose
   299 condition is a media query.  It consists of the at-keyword
   300 '@media' followed by a (possibly empty) media query list (as
   301 defined in [[!MEDIAQ]]), followed by a group rule body.  The condition
   302 of the rule is the result of the media query.</p>
   304 <div class="example">
   305 <p>This '@media' rule:</p>
   306 <pre>@media print, (max-width: 600px) {
   307   #extra_navigation { display: none }
   308 }</pre>
   309 <p>has the condition ''print, (max-width: 600px)'', which is
   310 true for print media and for devices whose width is at most 600px.  When
   311 either of these is true, the condition of the rule is true, and the rule
   312 ''#extra_navigation { display: none }'' is applied.
   313 </div>
   315 <p>In terms of the grammar, this specification extends the
   316 <code>media</code> production in the
   317 <a href="http://www.w3.org/TR/CSS21/grammar.html">Grammar of CSS 2.1</a>
   318 ([[!CSS21]], Appendix G) into:
   319 <pre>media
   320   : MEDIA_SYM S* media_query_list group_rule_body
   321   ;</pre>
   322 <p>where the <code>group_rule_body</code> production is defined in this
   323 specification, the <code>media_query_list</code> production is defined
   324 in [[!MEDIAQ]], and the others are defined in the <a
   325 href="http://www.w3.org/TR/CSS21/grammar.html">Grammar of CSS 2.1</a>
   326 ([[!CSS21]], Appendix G).
   328 <h2 id="at-supports">Feature queries: the '@supports' rule</h2>
   330 <p>The <dfn>'@supports' rule</dfn> is a conditional group
   331 rule whose condition tests whether the user agent supports CSS
   332 property:value pairs.  Authors can use it to write style sheets that use
   333 new features when available but degrade gracefully when those features
   334 are not supported.  CSS has existing mechanisms for graceful
   335 degradation, such as ignoring unsupported properties or values, but
   336 these are not always sufficient when large groups of styles need to be
   337 tied to the support for certain features, as is the case for use of new
   338 layout system features.</p>
   340 <p>The syntax of the condition in the '@supports' rule is
   341 slightly more complicated than for the other conditional group rules
   342 (though has some similarities to media queries) since:</p>
   343 <ul>
   344   <li>negation is needed so that the new-feature styles and the fallback
   345   styles can be separated (within the forward-compatible grammar's rules
   346   for the syntax of @-rules), and not required to override each other</li>
   347   <li>conjunction (and) is needed so that multiple required features can
   348   be tested</li>
   349   <li>disjunction (or) is needed when there are multiple alternative
   350   features for a set of styles, particularly when some of those
   351   alternatives are vendor-prefixed properties or values</li>
   352 </ul>
   354 <p>Therefore, the syntax of the '@supports' rule allows
   355 testing for property:value pairs, and arbitrary conjunctions (and),
   356 disjunctions (or), and negations (not) of them.</p>
   358 <p>This extends the lexical scanner in the
   359 <a href="http://www.w3.org/TR/CSS21/grammar.html">Grammar of CSS 2.1</a>
   360 ([[!CSS21]], Appendix G) by adding:
   361 <pre>
   362 @{S}{U}{P}{P}{O}{R}{T}{S} {return SUPPORTS_SYM;}
   363 {O}{R}                    {return OR;}
   364 </pre>
   366 <p>and the grammar by adding</p>
   368 <pre><dfn>supports_rule</dfn>
   369   : SUPPORTS_SYM S* <i>supports_condition</i> group_rule_body
   370   ;
   372 <dfn>supports_condition</dfn>
   373   : NOT S* general_enclosed |
   374     general_enclosed ( ( AND | OR ) S* general_enclosed )*
   376 <dfn>general_enclosed</dfn>
   377   : ( FUNCTION | '(' ) any+ ')' S*
   378 </pre>
   380 <p>
   381   The <code>any</code> token is taken from <a href="http://www.w3.org/TR/CSS21/syndata.html">CSS 2.1 Syntax and Basic Data Types</a>.
   383 <p>
   384   The above grammar is purposely very loose for forwards-compatibility reasons.
   385   Any ''@supports'' rule that does not parse according to the grammar above is invalid.  
   386   Style sheets <strong>must not</strong> use such a rule and processors <strong>must</strong> ignore such a rule.
   388 <p>
   389   The actual processing model of ''@supports'' is predicated on a more restricted grammar,
   390   composed of functions or parenthesized declarations,
   391   combined together with logical combinators,
   392   as defined by the following productions:
   394 <pre><dfn>supports_condition</dfn>
   395   : supports_negation | supports_conjunction | supports_disjunction |
   396     supports_condition_in_parens
   397   ;
   399 <dfn>supports_condition_in_parens</dfn>
   400   : ( '(' S* supports_condition ')' S* ) | supports_declaration_condition |
   401     supports_function
   402   ;
   404 <dfn>supports_negation</dfn>
   405   : NOT S* supports_condition_in_parens
   406   ;
   408 <dfn>supports_conjunction</dfn>
   409   : supports_condition_in_parens ( AND S* supports_condition_in_parens )+
   410   ;
   412 <dfn>supports_disjunction</dfn>
   413   : supports_condition_in_parens ( OR S* supports_condition_in_parens )+
   414   ;
   416 <dfn>supports_declaration_condition</dfn>
   417   : '(' S* core_declaration ')' S*
   418   ;
   420 <dfn>supports_function</dfn>
   421   : FUNCTION S* [any|unused]* ')'
   422   ;</pre>
   424 <p>in which <code>core_declaration</code> is the production
   425 <code>declaration</code> in the core syntax of CSS defined in <a
   426 href="http://www.w3.org/TR/CSS21/syndata.html#tokenization">section
   427 4.1.1 (Tokenization)</a> of [[!CSS21]],
   428 and the <code>AND</code> and <code>NOT</code> tokens are defined in
   429 the Media Queries specification [[!MEDIAQ]].</p>
   431 <p>Each of these grammar terms is associated with a boolean result, as
   432 follows:</p>
   433 <dl>
   434 <dt>supports_condition</dt>
   435 <dd>
   436   The result is the result of the single child term.
   437 </dd>
   439 <dt>supports_condition_in_parens</dt>
   440 <dd>
   441   The result is the result of the single <code>supports_condition</code>
   442   or <code>supports_declaration_condition</code> child term.
   443 </dd>
   445 <dt>supports_negation</dt>
   446 <dd>
   447   The result is the <em>negation</em> of the result of the
   448   <code>supports_condition_in_parens</code> child term.
   449 </dd>
   451 <dt>supports_conjunction</dt>
   452 <dd>
   453   The result is true if the result of <em>all</em> of the
   454   <code>supports_condition_in_parens</code> child terms is true;
   455   otherwise it is false.
   456 </dd>
   458 <dt>supports_disjunction</dt>
   459 <dd>
   460   The result is true if the result of <em>any</em> of the
   461   <code>supports_condition_in_parens</code> child terms is true;
   462   otherwise it is false.
   463 </dd>
   465 <dt>supports_declaration_condition</dt>
   466 <dd>
   467   The result is whether the CSS processor <a href="#support-definition">supports</a> the declaration
   468   within the parentheses.
   469 </dd>
   471 <dt>supports_function</dt>
   472 <dd>
   473   The result is always false.
   474   <span class="note">Note that future levels may define functions that can evaluate to true.</span>
   475 </dd>
   477 <dt>anything else</dt>
   478 <dd>
   479   If a parenthesized expression does not match the result of one of the grammar productions above,
   480   it must not be treated as invalid,
   481   but rather simply be false for the purpose of support conditions.
   482 </dl>
   484 <p>The condition of the '@supports' rule is the result of the
   485 <code>supports_condition</code> term that is a child of the
   486 <code>supports_rule</code> term.</p>
   488 <div class="example">
   489 <p>For example, the following rule</p>
   490 <pre>@supports ( display: flexbox ) {
   491   body, #navigation, #content { display: flexbox; }
   492   #navigation { background: blue; color: white; }
   493   #article { background: white; color: black; }
   494 }</pre>
   495 <p>applies the rules inside the '@supports' rule only when
   496 ''display: flexbox'' is supported.</p>
   497 </div>
   499 <div class="example">
   500 <p>The following example shows an additional '@supports' rule that can
   501 be used to provide an alternative for when ''display: flexbox'' is not
   502 supported:</p>
   503 <pre>@supports not ( display: flexbox ) {
   504   body { width: 100%; height: 100%; background: white; color: black; }
   505   #navigation { width: 25%; }
   506   #article { width: 75%; }
   507 }</pre>
   508 <p>Note that the 'width' declarations may be harmful to the
   509 flexbox-based layout, so it is important that they be present only in
   510 the non-flexbox styles.</p>
   511 </div>
   513 <div class="example">
   514 <p>The following example checks for support for the 'box-shadow'
   515 property, including checking for support for vendor-prefixed versions of
   516 it.  When the support is present, it specifies both 'box-shadow' (with
   517 the prefixed versions) and 'color' in a way what would cause the text to
   518 become invisible were 'box-shadow' not supported.</p>
   519 <pre>@supports ( box-shadow: 2px 2px 2px black ) or
   520           ( -moz-box-shadow: 2px 2px 2px black ) or
   521           ( -webkit-box-shadow: 2px 2px 2px black ) or
   522           ( -o-box-shadow: 2px 2px 2px black ) {
   523   .outline {
   524     color: white;
   525     -moz-box-shadow: 2px 2px 2px black;
   526     -webkit-box-shadow: 2px 2px 2px black;
   527     -o-box-shadow: 2px 2px 2px black;
   528     box-shadow: 2px 2px 2px black; /* unprefixed last */
   529   }
   530 }</pre></div>
   532 <p>To avoid confusion between ''and'' and ''or'', the syntax requires
   533 that both ''and'' and ''or'' be specified explicitly (rather than, say,
   534 using commas or spaces for one of them).  Likewise, to avoid confusion
   535 caused by precedence rules, the syntax does not allow ''and'', ''or'',
   536 and ''not'' operators to be mixed without a layer of parentheses.</p>
   538 <div class="example">
   539 <p>For example, the following rule is not valid:
   540 <pre class="illegal">@supports (transition-property: color) or
   541           (animation-name: foo) and
   542           (transform: rotate(10deg)) {
   543   // ...
   544 }</pre>
   545 <p>Instead, authors must write one of the following:</p>
   546 <pre>@supports ((transition-property: color) or
   547            (animation-name: foo)) and
   548           (transform: rotate(10deg)) {
   549   // ...
   550 }</pre>
   551 <pre>@supports (transition-property: color) or
   552           ((animation-name: foo) and
   553            (transform: rotate(10deg))) {
   554   // ...
   555 }</pre>
   556 </div>
   558 <p>The declaration being tested must always occur within parentheses,
   559 when it is the only thing in the expression.<p>
   561 <div class="example">
   562 <p>For example, the following rule is not valid:
   563 <pre class="illegal">@supports display: flexbox {
   564   // ...
   565 }</pre>
   566 <p>Instead, authors must write:</p>
   567 <pre>@supports (display: flexbox) {
   568   // ...
   569 }</pre>
   570 </div>
   572 <p>The syntax allows extra parentheses when they are not needed.  This
   573 flexibility is sometimes useful for authors (for example, when
   574 commenting out parts of an expression) and may also be useful for
   575 authoring tools.</p>
   577 <div class="example">
   578 <p>For example, authors may write:</p>
   579 <pre>@supports ((display: flexbox)) {
   580   // ...
   581 }</pre>
   582 </div>
   584 <p>A trailing ''!important'' on a declaration being tested is allowed,
   585 though it won't change the validity of the declaration.
   587 <div class="example">
   588 <p>For example, the following rule is valid:
   589 <pre>@supports (display: flexbox !important) {
   590   // ...
   591 }</pre>
   592 </div>
   594 <h3 id="support-definition">Definition of support</h3>
   596 <p>For forward-compatibility,
   597 <a href="http://www.w3.org/TR/CSS21/syndata.html#declaration">section 4.1.8
   598 (Declarations and properties)</a> of [[!CSS21]]
   599 defines rules for handling invalid properties and values.
   600 CSS processors that
   601 do not implement or partially implement a specification
   602 <strong>must</strong> treat any part of a value that they
   603 do not implement, or
   604 do not have a usable level of support for,
   605 as invalid according to this rule
   606 for handling invalid properties and values,
   607 and therefore <strong>must</strong> discard the declaration as a parse error.</p>
   609 <p>A CSS processor is considered to <dfn id="dfn-support">support</dfn>
   610 a declaration (consisting of a property and value) if it accepts that
   611 declaration (rather than discarding it as a parse error).
   612 If a processor does not implement, with a usable level of support,
   613 the value given,
   614 then it <strong>must not</strong>
   615 accept the declaration or claim support for it.</p>
   617 <p>These rules (and the equivalence between them) allow
   618 authors to use fallback (either in the [[CSS1]] sense of declarations
   619 that are overridden by later declarations or with the new capabilities
   620 provided by the ''@supports'' rule in this specification) that works
   621 correctly for the features implemented.  This applies especially to
   622 compound values; implementations must implement all parts of the value
   623 in order to consider the declaration supported, either inside a ruleset
   624 or in the declaration condition of an ''@supports'' rule.</p>
   626 <!--
   627 <h2 id="at-document">Document queries: the '@document' rule</h2>
   629 <p>The <dfn>'@document' rule</dfn> is a conditional group
   630 rule whose condition depends on the
   631 <a href="#url-of-doc">URL of the document being styled</a>.
   632 This allows style sheets, particularly user style sheets, to have styles
   633 that only apply to a set of pages rather than to all pages using the
   634 style sheet.</p>
   636 <p class="issue">Given that this @-rule is intended primarily for user
   637 style sheets, what should this specification say about its use in author
   638 style sheets?  Should it be forbidden?  Should use instead be
   639 discouraged?  Or should this specification remain neutral on the
   640 topic, since there are valid uses in author style sheets?</p>
   642 <p id="url-of-doc">The <dfn>URL of the document being styled</dfn> is
   643 the URI at which the document is located, excluding any fragment
   644 identifiers.  (This means, for example, that HTTP redirects have been
   645 followed.)  If the styles are being applied inside a complete document
   646 embedded into the presentation of another (e.g., [[HTML5]]&#39;s <code
   647 class="html">iframe</code>, <code class="html">object</code>, or <code
   648 class="html">img</code> elements), the relevant URI is that of the
   649 frame, not of its container.  However, if content from other documents
   650 is mixed in via mechanisms that mix content from one document into
   651 another (e.g., [[SVG11]]&#39;s <code>use</code> element), then the
   652 address of the container document is used.</p>
   654 <p class="note">Note:  In [[HTML5]], this is the
   655 <a href="http://dev.w3.org/html5/spec/dom.html#documents">document's address</a>
   656 of a document in a
   657 <a href="http://dev.w3.org/html5/spec/browsers.html#browsing-context">browsing context</a>.</p>
   659 <div class="issue">What form of normalization is done on URLs and domains
   660 before matching?  In particular, this specification needs to describe:
   661 <ul>
   662 <li>what form is used for the <a href="#url-of-doc">URL of the document
   663 being styled</a> (and what has been normalized in that form)</li>
   664 <li>what normalization (if any) happens to the argument of each of the match
   665 functions before the comparison that they describe and</li>
   666 <li>whether the
   667 comparison algorithm used is string comparison or some other URL
   668 comparison algorithm.</li></ul></div>
   670 <p>The '@document' rule's condition is written as a
   671 comma-separated list of <dfn>URL matching functions</dfn>, and the
   672 condition evaluates to true whenever any one of those functions
   673 evaluates to true.  The following URL matching functions are
   674 permitted:</p>
   676 <dl>
   677   <dt><dfn id="url-exact" title="url()|URL matching functions::exact">&lt;url&gt;</dfn></dt>
   679   <dd>
   680     <p>The 'url()' function is the <dfn>exact url matching
   681     function</dfn>.  It evaluates to true whenever the <a
   682     href="#url-of-doc">URL of the document being styled</a> is exactly
   683     the URL given.</p>
   685     <p class="Note">The 'url()' function, since it is a core syntax
   686     element in CSS, is allowed (subject to different character
   687     limitations and thus escaping requirements) to contain an unquoted
   688     value (in addition to the string values that are allowed as
   689     arguments for all four functions).</p>
   691     <div class="example">
   692       <p>For example, this rule:</p>
   693 <pre>@document url("http://www.w3.org/Style/CSS/") {
   694   #summary { background: yellow; color: black}
   695 }</pre>
   696       <p>styles the <code class="html">summary</code> element on the page
   697       <code>http://www.w3.org/Style/CSS/</code>, but not on any other
   698       pages.</p>
   699     </div>
   700   </dd>
   702   <dt><dfn id="url-prefix" title="url-prefix()|URL matching functions::prefix">url-prefix(&lt;string&gt;)</dfn></dt>
   704   <dd>
   705     <p>The 'url-prefix()' function is the <dfn>url prefix
   706     matching function</dfn>.  It evaluates to true whenever the
   707     <a href="#url-of-doc">URL of the document being styled</a>
   708     has the argument to the function as an
   709     initial substring (which is true when the two strings are equal).
   710     When the argument is the empty string, it evaluates to true for all
   711     documents.</p>
   712     <div class="example">
   713       <p>For example, this rule:</p>
   714 <pre>@document url-prefix("http://www.w3.org/Style/CSS/") {
   715   #summary { background: yellow; color: black}
   716 }</pre>
   717       <p>styles the <code class="html">summary</code> element on the page
   718       <code>http://www.w3.org/Style/CSS/</code> and on the page
   719       <code>http://www.w3.org/Style/CSS/Test</code>, but it does not
   720       affect the page <code>http://www.w3.org/</code> or the page
   721       <code>http://www.example.com/Style/CSS/</code>.</p>
   722     </div>
   723   </dd>
   725   <dt><dfn id="url-domain" title="domain()|URL matching functions::domain">domain(&lt;string&gt;)</dfn></dt>
   727   <dd>
   728     <p>The 'domain()' function is the <dfn>domain
   729     matching function</dfn>.  It evaluates to true whenever
   730     the <a href="#url-of-doc">URL of the document being styled</a>
   731     has a host subcomponent (as defined in [[!URI]])
   732     and that host subcomponent is exactly the argument to the
   733     'domain()' function or a final substring of the host
   734     component is a period (U+002E) immediately followed by the argument
   735     to the 'domain()' function.</p>
   736     <div class="example">
   737       <p>For example, this rule:</p>
   738 <pre>@document domain("w3.org") {
   739   body { font-size: 16px ! important }
   740 }</pre>
   741       <p>changes the font size of the body element for pages such as
   742       <code>http://www.w3.org/Style/CSS/</code> and
   743       <code>http://w3.org/Style/CSS/</code> and
   744       <code>http://lists.w3.org/Archives/Public/www-style/</code>
   745       but it does not affect the page
   746       <code>http://www.example.com/Style/CSS/</code>.</p>
   747     </div>
   748   </dd>
   750   <dt><dfn id="url-regexp" title="regexp()|URL matching functions::regular expression">regexp(&lt;string&gt;)</dfn></dt>
   752   <dd>
   753     <p>The contents of the &lt;string&gt; argument <strong>must</strong>
   754     match the JavaScript <code>Pattern</code> production
   755     ([[!ECMA-262-5.1]], section 15.10.1).  However,
   756     failing to do so is not a CSS syntax error and does not trigger any
   757     error handling for CSS syntax errors.</p>
   759     <p>The ''regexp()'' function evaluates to true whenever the string
   760     argument compiled as a JavaScript regular expression with the
   761     <code>global</code>, <code>ignoreCase</code> and
   762     <code>multiline</code> flags <em>disabled</em>
   763     (see [[!ECMA-262-5.1]], sections 15.10.7.2 through 15.10.7.4)
   764     compiles successfully and the resulting regular expression matches
   765     the entirety of the
   766     <a href="#url-of-doc">URL of the document being styled</a>.</p>
   768     <p class="note">Note that regular expression must match the entire
   769     URL, not just a part of it.</p>
   771     <p class="note">Note that this definition intentionally matches the
   772     behavior of the <a
   773     href="http://dev.w3.org/html5/spec/common-input-element-attributes.html#attr-input-pattern"><code class="html">pattern</code>
   774     attribute</a> on the <code class="html">input</code> element
   775     in [[HTML5]].</p>
   777     <div class="example">
   778       <p>For example, this rule:</p>
   779 <pre>@document regexp("http://www.w3.org/TR/\\d{4}/[^/]*-CSS2-\\d{8}/") {
   780   body { font-size: 20px ! important }
   781 }</pre>
   782       <p>changes the font size of the body element for pages such as
   783       <code>http://www.w3.org/TR/2011/PR-CSS2-20110412/</code>.</p>
   784       <p class="note">Note that the backslashes in the regular
   785       expression require CSS escaping as ''\\''.</p>
   786     </div>
   787   </dd>
   789 </dl>
   791 <p>Implementations <strong>must</strong> treat any unknown URL matching
   792 functions as a syntax error, and thus ignore the '@document' rule.
   793 <span class="issue">Should we instead have more complicated error
   794 handling rules to make forward-compatibility work differently, or is
   795 this rule the best solution for such future expansion anyway?</span></p>
   797 <div class="issue">This syntax doesn't offer any ability to do negations,
   798 which has been requested in <a
   799 href="https://bugzilla.mozilla.org/show_bug.cgi?id=349813">Mozilla bug
   800 349813</a>.  Use cases that people have wanted negations for
   801 include:
   802 <ul>
   803   <li>User style sheets that want a particular rule in general, but know
   804   that that rule does more harm than good on specific sites.</li>
   805   <li>Authors who have a rule that they want to apply to most of their
   806   pages, but wish to make a few exceptions for.</li>
   807 </ul>
   808 </div>
   810 <p>This extends the lexical scanner in the
   811 <a href="http://www.w3.org/TR/CSS21/grammar.html">Grammar of CSS 2.1</a>
   812 ([[!CSS21]], Appendix G) by adding:
   813 <pre>@{D}{O}{C}{U}{M}{E}{N}{T}	{return DOCUMENT_SYM;}</pre>
   814 <p>and the grammar by adding</p>
   815 <pre>document_rule
   816   : DOCUMENT_SYM S+ url_match_fn ( "," S* url_match_fn )* group_rule_body
   817   ;
   819 url_match_fn
   820   : (URI | FUNCTION S* STRING S* ')' ) S*
   821   ;</pre>
   822 -->
   825 <h2 id="apis">APIs</h2>
   827 <h3 id='extentions-to-cssrule-interface'>
   828 Extensions to the <code>CSSRule</code> interface</h3>
   830 <p>The <code>CSSRule</code> interface is extended as follows:
   832 <pre class='idl'>partial interface CSSRule {
   833     const unsigned short SUPPORTS_RULE = 12;
   834     <!--
   835     const unsigned short DOCUMENT_RULE = 13;
   836     -->
   837 }</pre>
   840 <h3 id='the-cssgroupingrule-interface'>
   841 The <code>CSSGroupingRule</code> interface</h3>
   843 <p>The <dfn><code>CSSGroupingRule</code></dfn> interface represents an at-rule that contains other rules nested inside itself.
   845 <pre class='idl'>interface CSSGroupingRule : CSSRule {
   846     readonly attribute CSSRuleList cssRules;
   847     unsigned long insertRule (DOMString rule, unsigned long index);
   848     void deleteRule (unsigned long index);
   849 }</pre>
   851 <dl class='idl-attributes'>
   852   <dt><code>cssRules</code> of type <code>CSSRuleList</code>, readonly
   853   <dd>The <code>cssRules</code> attribute must return a <code>CSSRuleList</code>
   854     object for the list of CSS rules nested inside the grouping rule.
   855 </dl>
   857 <dl class='idl-methods'>
   858   <dt><code>insertRule(DOMString rule, unsigned long index)</code>, returns
   859     <code>unsigned long</code>
   860   <dd>The <code>insertRule</code> operation must insert a CSS rule <var>rule</var>
   861     into the CSS rule list returned by <code>cssRules</code> at <var>index</var>.
   863   <dt><code>deleteRule (unsigned long index)</code>, return <code>void</code>
   864   <dd>The <code>deleteRule</code> operation must remove a CSS rule from the 
   865     CSS rule list returned by <code>cssRules</code> at <var>index</var>.
   866 </dl>
   869 <h3 id="the-cssconditionrule-interface">
   870 The <code>CSSConditionRule</code> interface</h3>
   872 <p>The <dfn><code>CSSConditionRule</code></dfn> interface represents all the "conditional" at-rules,
   873   which consist of a condition and a statement block.
   875 <pre class='idl'>interface CSSConditionRule : CSSGroupingRule {
   876     attribute DOMString conditionText;
   877 }</pre>
   879 <dl class='idl-attributes'>
   881   <dt><code>conditionText</code> of type <code>DOMString</code>
   882   <dd>
   883     <p>The <code>conditionText</code> attribute represents
   884     the condition of the rule.
   885     Since what this condition does
   886     varies between the derived interfaces of <code>CSSConditionRule</code>,
   887     those derived interfaces
   888     may specify different behavior for this attribute
   889     (see, for example, <code>CSSMediaRule</code> below).
   890     In the absence of such rule-specific behavior,
   891     the following rules apply:</p>
   893     <p>The <code>conditionText</code> attribute, on getting, must return
   894     the result of serializing the associated condition.
   896     <p>On setting the <code>conditionText</code> attribute these steps
   897       must be run:
   899     <ol>
   900       <li>Trim the given value of white space.
   901       <li>If the given value matches the grammar of the 
   902         appropriate condition production for the given rule, 
   903         replace the associated CSS condition with the given value.
   904       <li>Otherwise, do nothing.
   905     </ol>
   906 </dl>
   909 <h3 id="the-cssmediarule-interface">
   910 The <code>CSSMediaRule</code> interface</h3>
   912 <p>The <dfn><code>CSSMediaRule</code></dfn> interface represents a ''@media'' rule:
   914 <pre class='idl'>interface CSSMediaRule : CSSConditionRule {
   915     readonly attribute MediaList media;
   916 }</pre>
   918 <dl class='idl-attributes'>
   919   <dt><code>media</code> of type <code>MediaList</code>, readonly
   920   <dd>The <code>media</code> attribute must return a <code>MediaList</code> object
   921     for the list of media queries specified with the ''@media'' rule.
   923   <dt><code>conditionText</code> of type <code>DOMString</code>
   924   <dd>The <code>conditionText</code> attribute (defined on the <code>CSSConditionRule</code> parent rule),
   925     on getting, must return the value of <code>media.mediaText</code> on the rule.
   927     <p>Setting the <code>conditionText</code> attribute
   928       must set the <code>media.mediaText</code> attribute on the rule.
   929 </dl>
   932 <h3 id="the-csssupportsrule-interface">
   933 The <code>CSSSupportsRule</code> interface</h3>
   935 <p>The <dfn><code>CSSSupportsRule</code></dfn> interface represents a ''@supports'' rule.</p>
   937 <pre class='idl'>interface CSSSupportsRule : CSSConditionRule {
   938 }</pre>
   940 <!--
   941 <h3 id="the-cssdocumentrule-interface">
   942 The <code>CSSDocumentRule</code> interface</h3>
   944 <p>The <dfn><code>CSSDocumentRule</code></dfn> interface represents a ''@document'' rule.</p>
   946 <pre class='idl'>interface CSSDocumentRule : CSSConditionRule {
   947 }</pre>
   948 -->
   951 <h3 id='the-css-interface'>
   952 The <code>CSS</code> interface, and the <code title=''>supports()</code> function</h3>
   954 <p>The <dfn id='CSS-interface'><code>CSS</code></dfn> interface holds useful CSS-related functions that do not belong elsewhere.
   956 <pre class='idl'>interface CSS {
   957   boolean supports(DOMString property, DOMString value);
   958   boolean supports(DOMString declaration);
   959 }</pre>
   961 <dl class='idl-methods'>
   962   <dt><code>supports(DOMString property, DOMString value)</code>,
   963     returns <code>boolean</code>
   964   <dt><code>supports(DOMString conditionText)</code>,
   965     returns <code>boolean</code>
   966   <dd>
   967     When the <code title=''>supports()</code> method is invoked with two arguments <var>property</var> and <var>value</var>,
   968     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,
   969     and <var>value</var> would be successfully parsed as a supported value for that property.
   970     Otherwise, it must return <code>false</code>.
   972     <p>
   973       When invoked with a single <var>conditionText</var> argument,
   974       it must return <code>true</code> if <var>conditionText</var>,
   975       when parsed and evaluated as a <code>supports_condition</code>,
   976       would return true.
   977       Otherwise, it must return <code>false</code>.
   978   </dl>
   981 <h2 class=no-num id="grammar">Grammar</h2>
   983 <p>In order to allow these new @-rules in CSS style sheets, this
   984 specification modifies the <code>stylesheet</code> production in the <a
   985 href="http://www.w3.org/TR/CSS21/grammar.html">Appendix G</a> grammar of
   986 [[!CSS21]] by replacing the <code>media</code> production defined in
   987 [[!CSS21]] with the <code>media</code> production defined in this one,
   988 and additionally inserting <code>| supports_rule</code>
   989 alongside <code>ruleset | media | page</code>.</p>
   992 <h2 id="conformance">Conformance</h2>
   994 <h3 id="base-modules">Base Modules</h3>
   996 <p>This specification defines conformance in terms of base modules,
   997 which are modules that this specification builds on top of.  The base
   998 modules of this module are:</p>
  1000 <ul>
  1001 <li>[[!CSS21]]</li>
  1002 </ul>
  1004 <p>All of the conformance requirements of all base modules are
  1005 incorporated as conformance requirements of this module, except where
  1006 overridden by this module.</p>
  1008 <p>Additionally, all conformance requirements related to validity of
  1009 syntax in this module and all of its base modules are to be interpreted
  1010 as though all syntax in all of those modules is valid.</p>
  1012 <div class="example"><p>For example, this means that grammar presented
  1013 in modules other than [[!CSS21]] must obey the requirements that
  1014 [[!CSS21]] defines for the parsing of properties, and that requirements
  1015 for handling invalid syntax in [[!CSS21]] do not treat syntax added by
  1016 other modules as invalid.</p></div>
  1018 <p>Additionally, the set of valid syntax can be increased by the
  1019 conformance of a style sheet or processor to additional modules; use of
  1020 such syntax does not make a style sheet nonconformant and failure to
  1021 treat such syntax as invalid does not make a processor
  1022 nonconformant.</p>
  1024 <h3 id="conformance-classes">Conformance Classes</h3>
  1026   <p>Conformance to the CSS Conditional Rules Module is defined for three
  1027   conformance classes:
  1028   <dl>
  1029     <dt><dfn title="conformance::style sheet" id="conform-style-sheet">style sheet</dfn>
  1030       <dd>A <a href="http://www.w3.org/TR/CSS21/conform.html#style-sheet">CSS
  1031       style sheet</a>.</dd>
  1032     <dt><dfn title="conformance::processor" id="conform-processor">processor</dfn></dt>
  1033       <dd>A tool that reads CSS style sheets:  it may be a renderer or
  1034       <a
  1035       href="http://www.w3.org/TR/CSS21/conform.html#user-agent">user-agent</a>
  1036       that interprets the semantics of a style sheet and renders
  1037       documents that use style sheets, or it may be a validator that
  1038       checks style sheets.</dd>
  1039     <dt><dfn title="conformance::authoring tool" id="conform-authoring-tool">authoring tool</dfn></dt>
  1040       <dd>A tool that writes a style sheet.</dd>
  1041   </dl>
  1043   <p>A style sheet is conformant to the CSS Conditional Rules Module
  1044   if it meets all of the conformance requirements in the module that are
  1045   described as requirements of style sheets.</p>
  1047   <p>A processor is conformant to the CSS Conditional Rules Module if it
  1048   meets all applicable conformance requirements in the module that are
  1049   described as requirements of processors.  In general, all requirements
  1050   are applicable to renderers.  Requirements concerning a part of CSS
  1051   not performed by a processor are not applicable, e.g., requirements
  1052   related to rendering are not applicable to a validator.  The inability
  1053   of a processor to correctly render a document due to limitations of
  1054   the device does not make it non-conformant. (For example, a renderer
  1055   is not required to render color on a monochrome monitor.)</p>
  1057   <p>An authoring tool is conformant to the CSS Conditional Rules Module
  1058   if it writes style sheets that conform to the module and (if it reads
  1059   CSS) it is a conformant processor.</p>
  1061 <h3 id="partial">
  1062 Partial Implementations</h3>
  1064   <p>So that authors can exploit the forward-compatible parsing rules to
  1065   assign fallback values, CSS renderers <strong>must</strong>
  1066   treat as invalid (and <a href="http://www.w3.org/TR/CSS21/conform.html#ignore">ignore
  1067   as appropriate</a>) any at-rules, properties, property values, keywords,
  1068   and other syntactic constructs for which they have no usable level of
  1069   support. In particular, user agents <strong>must not</strong> selectively
  1070   ignore unsupported component values and honor supported values in a single
  1071   multi-value property declaration: if any value is considered invalid
  1072   (as unsupported values must be), CSS requires that the entire declaration
  1073   be ignored.</p>
  1075 <h3 id="experimental">Experimental Implementations</h3>
  1077   <p>To avoid clashes with future CSS features, the CSS specifications
  1078   reserve a <a href="http://www.w3.org/TR/CSS21/syndata.html#vendor-keywords">prefixed
  1079   syntax</a> for proprietary property and value extensions to CSS. The CSS
  1080   Working Group recommends that experimental implementations of features in
  1081   CSS Working Drafts also use vendor-prefixed property or value names. This
  1082   avoids any incompatibilities with future changes in the draft. Once a
  1083   specification reaches the Candidate Recommendation stage, implementors
  1084   should implement the non-prefixed syntax for any feature they consider to
  1085   be correctly implemented according to spec.</p>
  1087 <h3 id="cr-exit-criteria">CR Exit Criteria</h3>
  1089   <p>For this specification to be advanced to Proposed Recommendation,
  1090   there must be at least two independent, interoperable implementations
  1091   of each feature. Each feature may be implemented by a different set of
  1092   products, there is no requirement that all features be implemented by
  1093   a single product. For the purposes of this criterion, we define the
  1094   following terms:
  1096   <dl>
  1097     <dt>independent <dd>each implementation must be developed by a
  1098     different party and cannot share, reuse, or derive from code
  1099     used by another qualifying implementation. Sections of code that
  1100     have no bearing on the implementation of this specification are
  1101     exempt from this requirement.
  1103     <dt>interoperable <dd>passing the respective test case(s) in the
  1104     official CSS test suite, or, if the implementation is not a Web
  1105     browser, an equivalent test. Every relevant test in the test
  1106     suite should have an equivalent test created if such a user
  1107     agent (UA) is to be used to claim interoperability. In addition
  1108     if such a UA is to be used to claim interoperability, then there
  1109     must one or more additional UAs which can also pass those
  1110     equivalent tests in the same way for the purpose of
  1111     interoperability. The equivalent tests must be made publicly
  1112     available for the purposes of peer review.
  1114     <dt>implementation <dd>a user agent which:
  1116     <ol class=inline>
  1117       <li>implements the specification.
  1119       <li>is available to the general public. The implementation may
  1120       be a shipping product or other publicly available version
  1121       (i.e., beta version, preview release, or “nightly build”). 
  1122       Non-shipping product releases must have implemented the
  1123       feature(s) for a period of at least one month in order to
  1124       demonstrate stability.
  1126       <li>is not experimental (i.e., a version specifically designed
  1127       to pass the test suite and is not intended for normal usage
  1128       going forward).
  1129     </ol>
  1130   </dl>
  1132   <p>The specification will remain Candidate Recommendation for at least
  1133   six months.
  1135 <h2 id="changes">
  1136 Changes</h2>
  1138 <p>The following (non-editorial) changes were made to this specification since the
  1139 <a href="http://www.w3.org/TR/2012/WD-css3-conditional-20120911/">11 September 2012 Working Draft</a>:
  1141 <ul>
  1142   <li>Removed ''@document'' rule; it has been deferred to Level 4.
  1143   <li>Allow functional notation in ''@supports'' queries to be valid (to allow for future extensions),
  1144       but treat such notations as always being false.
  1145   <li>Corrected the grammar as follows:
  1146 <pre>
  1147 -  : SUPPORTS_SYM S+ supports_condition group_rule_body
  1148 +  : SUPPORTS_SYM S* supports_condition group_rule_body
  1149 </pre>
  1150 <pre>
  1151 -  : (URI | FUNCTION) S*
  1152 +  : (URI | FUNCTION S* STRING S* ')' ) S*
  1153 </pre>
  1154   <li>Switched "and", "or", and "not" keywords to use appropriate productions rather than literals.
  1155   <li>Clarified definition of support used for interpreting ''@support'' rules
  1156   and its relationship to CSS forwards-compatible parsing rules.
  1157 </ul>
  1159 <h2 class=no-num id="acknowledgments">Acknowledgments</h2>
  1161 <p>
  1162 Thanks to the ideas and feedback from
  1163 Tab Atkins,
  1164 <span lang="tr">Tantek Çelik</span>,
  1165 Alex Danilo,
  1166 Elika Etemad,
  1167 Pascal Germroth,
  1168 <span lang="de">Björn Höhrmann</span>,
  1169 Paul Irish,
  1170 Vitor Menezes,
  1171 Alex Mogilevsky,
  1172 Chris Moschini,
  1173 Simon Sapin,
  1174 Ben Ward,
  1175 Zack Weinberg,
  1176 Estelle Weyl,
  1177 Boris Zbarsky,
  1178 and all the rest of the <a href="http://lists.w3.org/Archives/Public/www-style/">www-style</a> community.
  1180 </p>
  1182 <h2 class=no-num id="references">References</h2>
  1185 <h3 class="no-num" id="normative-references">Normative references</h3>
  1186 <!--normative-->
  1188 <h3 class="no-num" id="other-references">Other references</h3>
  1189 <!--informative-->
  1191 <h2 class="no-num" id="index">Index</h2>
  1192 <!--index-->
  1194 </body>
  1195 </html>
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