css-conditional/Overview.src.html

Mon, 03 Jun 2013 16:59:41 +0900

author
L. David Baron <dbaron@dbaron.org>
date
Mon, 03 Jun 2013 16:59:41 +0900
changeset 8325
a738b83fd597
parent 8324
6a24538736c9
child 8326
9421e8cccd2e
permissions
-rw-r--r--

[css-conditional] Make the 'box-shadow' example make more sense, since I was thinking more of 'text-shadow' when I wrote it.

Fixes http://lists.w3.org/Archives/Public/www-style/2013Mar/0037.html

dbaron@2974 1 <!DOCTYPE html public '-//W3C//DTD HTML 4.01//EN'
dbaron@2974 2 'http://www.w3.org/TR/html4/strict.dtd'>
dbaron@2974 3 <html lang="en">
dbaron@2974 4 <head profile="http://www.w3.org/2006/03/hcard">
dbaron@2974 5 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
dbaron@2974 6 <title>CSS Conditional Rules Module Level 3</title>
dbaron@2974 7 <link rel="stylesheet" type="text/css" href="../default.css">
jackalmage@7274 8 <link href="../csslogo.ico" rel="shortcut icon" type="image/x-icon">
jackalmage@7274 9 <link rel="stylesheet" type="text/css" href="http://www.w3.org/StyleSheets/TR/W3C-[STATUS].css">
peter@6932 10 <script src="http://test.csswg.org/harness/annotate.js#CSS3-CONDITIONAL_DEV"
fantasai@7042 11 type="text/javascript" defer></script
dbaron@2974 12 </head>
tantek@7538 13 <body class="h-entry">
dbaron@2974 14
dbaron@2974 15 <div class="head">
dbaron@2974 16 <!--logo-->
dbaron@2974 17
tantek@7538 18 <h1 class="p-name">CSS Conditional Rules Module Level 3</h1>
dbaron@2974 19
tantek@7538 20 <h2 class="no-num no-toc">[LONGSTATUS] <span class="dt-updated"><span class="value-title" title="[CDATE]">[DATE]</span></span></h2>
dbaron@2974 21 <dl>
dbaron@2974 22 <dt>This version:
tantek@7538 23 <dd><a class="u-url" href="[VERSION]">
dbaron@7372 24 http://www.w3.org/TR/[YEAR]/ED-css3-conditional-[CDATE]/</a>
dbaron@2974 25
dbaron@2974 26 <dt>Latest version:
dbaron@3241 27 <dd><a href="http://www.w3.org/TR/[SHORTNAME]/">http://www.w3.org/TR/[SHORTNAME]/</a>
dbaron@2974 28
dbaron@3245 29 <dt>Editor's draft:
bert@3404 30 <dd><a href="http://dev.w3.org/csswg/[SHORTNAME]/">http://dev.w3.org/csswg/[SHORTNAME]/</a>
dbaron@7863 31 (<a href="https://dvcs.w3.org/hg/csswg/log/tip/css-conditional/Overview.src.html">change log</a>,
dbaron@7863 32 <a href="https://dvcs.w3.org/hg/csswg/log/tip/css3-conditional/Overview.src.html">older change log</a>)
dbaron@3245 33
dbaron@2974 34 <dt>Previous version:
dbaron@8324 35 <dd><a rel="previous" href="http://www.w3.org/TR/2013/CR-css3-conditional-20130404/">http://www.w3.org/TR/2013/CR-css3-conditional-20130404/</a></dd>
dbaron@2974 36
dbaron@2974 37 <dt>Editors:
tantek@7538 38 <dd class="p-author h-card vcard"><a class="p-name fn u-url url" rel="author" href="http://dbaron.org/">L. David Baron</a>,
tantek@7538 39 <a class="p-org org h-org" href="http://www.mozilla.org/">Mozilla</a>
dbaron@3744 40
dbaron@3744 41 <dt>Issues list:
dbaron@3744 42 <dd>Maintained in document (only editor's draft is current)
dbaron@3744 43
jackalmage@7856 44 <dt>Feedback:</dt>
bert@7907 45 <dd><a href="mailto:www-style@w3.org?subject=%5Bcss3-conditional%5D%20feedback"
jackalmage@7856 46 >www-style@w3.org</a>
bert@7907 47 with subject line &ldquo;<kbd>[css3-conditional]
jackalmage@7856 48 <var>&hellip; message topic &hellip;</var></kbd>&rdquo;
jackalmage@7856 49 (<a rel="discussion" href="http://lists.w3.org/Archives/Public/www-style/"
jackalmage@7856 50 >archives</a>)
dbaron@3744 51
dbaron@3744 52 <dt>Test suite:
dbaron@7733 53 <dd><a href="https://test.csswg.org/shepherd/search/spec/css3-conditional/">submitted tests</a>,
dbaron@7733 54 <a href="https://test.csswg.org/harness/suite/CSS3-CONDITIONAL_DEV/">nightly test suite</a>
dbaron@3744 55
dbaron@2974 56 </dl>
dbaron@2974 57
dbaron@2974 58 <!--copyright-->
dbaron@2974 59
dbaron@2974 60 <hr title="Separator for header">
dbaron@2974 61 </div>
dbaron@2974 62
jackalmage@6617 63 <h2 class="no-num no-toc" id="abstract">Abstract</h2>
dbaron@2974 64
dbaron@2974 65 <p>CSS is a language for describing the rendering of structured documents
tantek@7538 66 (such as HTML and XML) on screen, on paper, in speech, etc.
tantek@7538 67 <span class="p-summary">
tantek@7538 68 This module
dbaron@2974 69 contains the features of CSS for conditional processing of parts of
dbaron@2974 70 style sheets, conditioned on capabilities of the processor or the
dbaron@2974 71 document the style sheet is being applied to.
dbaron@2974 72 It includes and extends the functionality of CSS level&nbsp;2 [[!CSS21]],
dbaron@2974 73 which builds on CSS level&nbsp;1 [[CSS1]].
dbaron@2974 74 The main extensions compared to level&nbsp;2 are
dbaron@2983 75 allowing nesting of certain at-rules inside '@media',
jackalmage@6838 76 and the addition of the '@supports'
jackalmage@6838 77 rule for conditional processing.
tantek@7538 78 </span>
dbaron@2974 79
jackalmage@6617 80 <h2 class="no-num no-toc" id="status">Status of this document</h2>
dbaron@2974 81
dbaron@2974 82 <!--status-->
dbaron@2974 83
bert@7907 84 <p>See the section <a href="#cr-exit-criteria">“CR Exit Criteria”</a>
bert@7907 85 for details on advancing this specification to W3C Recommendation. The
bert@7907 86 specification will remain Candidate Recommendation at least until 2
bert@7907 87 October 2013. A <a
bert@7907 88 href="http://test.csswg.org/suites/css3-conditional/nightly-unstable/report/"
bert@7907 89 >test suite and implementation report</a> are under development.
bert@7907 90
bert@7907 91 <p>See the section <a href="#changes">“Changes”</a> for changes since
bert@7907 92 the last Working Draft.
bert@7907 93
dbaron@2974 94 <p>The following features are at risk:
dbaron@2974 95 <ul>
dbaron@2983 96 <li>The inclusion of '@font-face' rules and
dbaron@2983 97 '@keyframes' rules as allowed within all of the @-rules in
dbaron@2974 98 this specification is at risk, though only because of the relative
dbaron@2974 99 rates of advancement of specifications. If this specification is able
dbaron@2974 100 to advance faster than one or both of the specifications defining
dbaron@2974 101 those rules, then the inclusion of those rules will move from this
dbaron@2974 102 specification to the specification defining those rules.</li>
dbaron@2974 103
dbaron@2974 104 <li>The addition of support for @-rules inside of conditional grouping
dbaron@2974 105 rules is at risk; if interoperable implementations are not found, it
dbaron@2974 106 may be removed to advance the other features in this specification to
dbaron@2974 107 Proposed Recommendation.</li>
dbaron@2974 108
dbaron@2983 109 <li>The '@supports' rule is at risk; if interoperable
dbaron@2974 110 implementations are not found, it may be removed to advance the other
dbaron@2974 111 features in this specification to Proposed Recommendation.</li>
jackalmage@6838 112 </ul>
jackalmage@6837 113
jackalmage@6838 114 <!--
dbaron@2974 115
jackalmage@6838 116 Things to go in level 4:
jackalmage@6838 117
jackalmage@6838 118 * Create some way to put these new conditional things on an @import.
jackalmage@6838 119 * The @document rule (commented out, down below).
jackalmage@6838 120
jackalmage@6838 121 -->
dbaron@2974 122
jackalmage@6617 123 <h2 class="no-num no-toc" id="contents">Table of contents</h2>
dbaron@2974 124
dbaron@2974 125 <!--toc-->
dbaron@2974 126
jackalmage@6617 127 <h2 id="introduction">Introduction</h2>
dbaron@2974 128
jackalmage@6617 129 <h3 id="context">Background</h3>
dbaron@2974 130
dbaron@2974 131 <p><em>This section is not normative.</em>
dbaron@2974 132
dbaron@2974 133 <p>[[!CSS21]] defines one type of conditional group rule, the
dbaron@2983 134 '@media' rule, and allows only rulesets (not other @-rules)
dbaron@2983 135 inside of it. The '@media' rule provides the ability to
dbaron@2974 136 have media-specific style sheets, which is also provided by style
dbaron@2983 137 sheet linking features such as '@import' and
dbaron@2983 138 <code class="html">&lt;link&gt;</code>. The restrictions on the contents of
dbaron@2983 139 '@media' rules made them less useful; they have forced authors
dbaron@2974 140 using CSS features involving @-rules in media-specific style sheets to
dbaron@2974 141 use separate style sheets for each medium.</p>
dbaron@2974 142
dbaron@2974 143 <p>This specification extends the rules for the contents of
dbaron@2974 144 conditional group rules to allow other @-rules, which enables authors
dbaron@2974 145 to combine CSS features involving @-rules with media specific style
dbaron@2974 146 sheets within a single style sheet.</p>
dbaron@2974 147
jackalmage@6838 148 <p>This specification also defines an additional type of conditional
jackalmage@6838 149 group rule, '@supports', to
dbaron@2974 150 address author and user requirements.</p>
dbaron@2974 151
dbaron@2983 152 <p>The '@supports' rule allows CSS to be conditioned on
dbaron@2974 153 implementation support for CSS properties and values. This rule makes
dbaron@2974 154 it much easier for authors to use new CSS features and provide good
dbaron@2974 155 fallback for implementations that do not support those features. This
dbaron@2974 156 is particularly important for CSS features that provide new layout
dbaron@2974 157 mechanisms, and for other cases where a set of related styles needs to
dbaron@2974 158 be conditioned on property support.</p>
dbaron@2974 159
jackalmage@6617 160 <h3 id="placement">Module Interactions</h3>
dbaron@2974 161
dbaron@2983 162 <p>This module replaces and extends the '@media' rule
dbaron@2974 163 feature defined in [[!CSS21]] section <var>7.2.1</var> and
dbaron@2974 164 incorporates the modifications previously made non-normatively by
dbaron@2974 165 [[!MEDIAQ]] section <var>1</var>.</p>
dbaron@2974 166
dbaron@3462 167 <p>Its current definition depends on @-rules defined in [[!CSS3-FONTS]]
dbaron@2974 168 and [[!CSS3-ANIMATIONS]], but that dependency is only on the
dbaron@2974 169 assumption that those modules will advance ahead of this one. If this
dbaron@2974 170 module advances faster, then the dependency will be reversed.</p>
dbaron@2974 171
jackalmage@6617 172 <h3 id="conventions">Document Conventions</h3>
dbaron@2974 173
dbaron@2974 174 <p>Conformance requirements are expressed with a combination of
dbaron@2974 175 descriptive assertions and RFC 2119 terminology. The key words “MUST”,
dbaron@2974 176 “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”,
dbaron@2974 177 “RECOMMENDED”, “MAY”, and “OPTIONAL” in the normative parts of this
dbaron@2974 178 document are to be interpreted as described in RFC 2119.
dbaron@2979 179 However, for readability, these words do not appear in all uppercase
dbaron@2979 180 letters in this specification.
dbaron@2974 181
dbaron@2974 182 <p>All of the text of this specification is normative except sections
dbaron@2974 183 explicitly marked as non-normative, examples, and notes. [[!RFC2119]]</p>
dbaron@2974 184
dbaron@2974 185 <p>Examples in this specification are introduced with the words “for example”
dbaron@2983 186 or are set apart from the normative text with
dbaron@2983 187 <code class="html">class="example"</code>, like this:
dbaron@2974 188
dbaron@2974 189 <div class="example">
dbaron@2974 190 <p>This is an example of an informative example.</p>
dbaron@2974 191 </div>
dbaron@2974 192
dbaron@2974 193 <p>Informative notes begin with the word “Note” and are set apart from the
dbaron@2983 194 normative text with <code class="html">class="note"</code>, like this:
dbaron@2974 195
dbaron@2974 196 <p class="note">Note, this is an informative note.</p>
dbaron@2974 197
jackalmage@6617 198 <h2 id="processing">Processing of conditional group rules</h2>
dbaron@2974 199
dbaron@2974 200 <p>This specification defines some CSS @-rules, called <dfn>conditional
dbaron@2974 201 group rules</dfn>, that associate a condition with a group of other
dbaron@2974 202 CSS rules. These different rules allow testing different types of
dbaron@2974 203 conditions, but share common behavior for how their contents are used
dbaron@2974 204 when the condition is true and when the condition is false.</p>
dbaron@2974 205
dbaron@2974 206 <div class="example">
dbaron@2974 207 <p>For example, this rule:</p>
dbaron@2974 208 <pre>@media print {
dbaron@7381 209 /* hide navigation controls when printing */
dbaron@2974 210 #navigation { display: none }
dbaron@2974 211 }</pre>
dbaron@2974 212 <p>causes a particular CSS rule (making elements with ID "navigation" be
dbaron@2974 213 display:none) apply only when the style sheet is used for a print
jackalmage@6838 214 medium.
dbaron@2974 215 </div>
dbaron@2974 216
dbaron@2974 217 <p>Each conditional group rule has a condition, which at any time
dbaron@2974 218 evaluates to true or false. When the condition is true, CSS processors
dbaron@2979 219 <strong>must</strong> apply the rules inside the group rule as though
dbaron@2979 220 they were at the group rule's location; when the condition is false, CSS
dbaron@3948 221 processors <strong>must not</strong> apply any of rules inside the group
dbaron@2979 222 rule. The current state of the condition does not affect the CSS object
dbaron@2979 223 model, in which the contents of the group rule always remain within the
dbaron@2979 224 group rule.</p>
dbaron@2974 225
dbaron@2974 226 <p>This means that when multiple conditional group rules are nested,
dbaron@2974 227 a rule inside of both of them applies only when all of the rules'
dbaron@2974 228 conditions are true.</p>
dbaron@2974 229
dbaron@2974 230 <div class="example">For example, with this set of nested rules:
dbaron@2974 231 <pre>@media print { // rule (1)
dbaron@7381 232 /* hide navigation controls when printing */
dbaron@2974 233 #navigation { display: none }
dbaron@2974 234 @media (max-width: 12cm) { // rule (2)
dbaron@7381 235 /* keep notes in flow when printing to narrow pages */
dbaron@2974 236 .note { float: none }
dbaron@2974 237 }
dbaron@2974 238 }</pre>
dbaron@2974 239 the condition of the rule marked (1) is true for print media, and the
dbaron@2974 240 condition of the rule marked (2) is true when the width of the display
dbaron@2974 241 area (which for print media is the page box) is less than or equal to
dbaron@2983 242 12cm. Thus the rule ''#navigation { display: none }'' applies
dbaron@2974 243 whenever this style sheet is applied to print media, and the rule
dbaron@2983 244 ''.note { float: none }'' is applied only when the style sheet
dbaron@2974 245 is applied to print media <em>and</em> the width of the page box is less
dbaron@2974 246 than or equal to 12 centimeters.</div>
dbaron@2974 247
dbaron@2979 248 <p>When the condition for a conditional group rule changes, CSS
dbaron@2979 249 processors <strong>must</strong> reflect that the rules now apply or no
dbaron@2979 250 longer apply, except for properties whose definitions define effects of
dbaron@2979 251 computed values that persist past the lifetime of that value (such as
dbaron@2979 252 for some properties in [[CSS3-TRANSITIONS]] and
dbaron@2979 253 [[!CSS3-ANIMATIONS]]).</p>
dbaron@2974 254
jackalmage@6617 255 <h2 id="contents-of">Contents of conditional group rules</h2>
dbaron@2974 256
dbaron@2974 257 <p>The syntax of each conditional group rule consists of some syntax
dbaron@2974 258 specific to the type of rule followed by a <dfn>group rule body</dfn>,
dbaron@2974 259 which is a block (pair of braces) containing a sequence of rules.</p>
dbaron@2974 260
dbaron@2974 261 <p>A group rule body is allowed to contain rulesets and any @-rules that
dbaron@2974 262 are allowed at the top level of a style sheet before and after a
dbaron@2974 263 ruleset. This means that @-rules that must occur at the beginning of
dbaron@3020 264 the style sheet (such as '@charset', '@import',
dbaron@3020 265 and '@namespace' rules) are not allowed inside of conditional group
dbaron@2974 266 rules. Conditional group rules can be nested.</p>
dbaron@2974 267
dbaron@2974 268 <p>In terms of the grammar, this specification defines the following
dbaron@2974 269 productions for use in the grammar of conditional group rules:</p>
dbaron@2974 270
dbaron@7032 271 <pre><dfn>nested_statement</dfn>
dbaron@7032 272 : ruleset | <i>media</i> | page | font_face_rule | keyframes_rule |
dbaron@7032 273 <i>supports_rule</i>
dbaron@2974 274 ;
dbaron@2974 275
dbaron@7032 276 <dfn>group_rule_body</dfn>
dbaron@7032 277 : '{' S* <i>nested_statement</i>* '}' S*
dbaron@2974 278 ;</pre>
bert@3404 279 <p>
dbaron@2974 280 in which all the productions are defined in that grammar with the
jackalmage@6839 281 exception of <code>font_face_rule</code>
dbaron@5294 282 defined in [[!CSS3-FONTS]], <code>keyframes_rule</code> defined in
jackalmage@6838 283 [[!CSS3-ANIMATIONS]], and <code>media</code> and <code>supports_rule</code>
jackalmage@6838 284 defined in this specification.</p>
dbaron@2974 285
dbaron@2974 286 <p>In general, future CSS specifications that add new @-rules that are
dbaron@2974 287 not forbidden to occur after some other types of rules should modify
dbaron@2974 288 this <code>nested_statement</code> production to keep the grammar
dbaron@2974 289 accurate.</p>
dbaron@2974 290
dbaron@2979 291 <p>Style sheets <strong>must not</strong> use rules other than the allowed ones inside
dbaron@2974 292 conditional group rules.</p>
dbaron@2974 293
dbaron@3019 294 <p>CSS processors <strong>must</strong> ignore rules that are not
dbaron@3019 295 allowed within a group rule, and <strong>must</strong> handle invalid
dbaron@3019 296 rules inside of group rules as described in <a
dbaron@3019 297 href="http://www.w3.org/TR/CSS21/syndata.html#parsing-errors">section
dbaron@3019 298 4.2 (Rules for handling parsing errors)</a>, <a
dbaron@3019 299 href="http://www.w3.org/TR/CSS21/syndata.html#at-rules">section 4.1.5
dbaron@3019 300 (At-rules)</a>, and <a
dbaron@3019 301 href="http://www.w3.org/TR/CSS21/syndata.html#rule-sets">section 4.1.7
dbaron@3019 302 (Rule sets, declaration blocks, and selectors)</a> of [[!CSS21]].</p>
dbaron@2974 303
jackalmage@6617 304 <h2 id="use">Placement of conditional group rules</h2>
dbaron@2974 305
dbaron@3019 306 <p>Conditional group rules are allowed at the top-level of a style
dbaron@3019 307 sheet, and inside other conditional group rules. CSS processors
dbaron@3019 308 <strong>must</strong> process such rules as <a
dbaron@3019 309 href="#processing">described above</a>.</p>
dbaron@3019 310
dbaron@3020 311 <p>Any rules that are not allowed after a ruleset (e.g., ''@charset'',
dbaron@3020 312 ''@import'', or ''@namespace'' rules) are also not allowed after a
dbaron@3020 313 conditional group rule. Therefore, style sheets <strong>must
dbaron@3019 314 not</strong> place such rules after a conditional group rules, and CSS
dbaron@3019 315 processors <strong>must</strong> ignore such rules.</p>
dbaron@2974 316
jackalmage@6617 317 <h2 id="at-media">Media-specific style sheets: the '@media' rule</h2>
dbaron@2974 318
dbaron@7862 319 <p>The <dfn id="atmedia-rule">'@media' rule</dfn> is a conditional group rule whose
dbaron@2974 320 condition is a media query. It consists of the at-keyword
jackalmage@6830 321 '@media' followed by a (possibly empty) media query list (as
dbaron@2974 322 defined in [[!MEDIAQ]]), followed by a group rule body. The condition
dbaron@2974 323 of the rule is the result of the media query.</p>
dbaron@2974 324
dbaron@2974 325 <div class="example">
dbaron@2983 326 <p>This '@media' rule:</p>
dbaron@7381 327 <pre>@media screen and (min-width: 35em),
dbaron@7381 328 print and (min-width: 40em) {
dbaron@7381 329 #section_navigation { float: left; width: 10em; }
dbaron@2974 330 }</pre>
dbaron@7381 331 <p>has the condition
dbaron@7381 332 ''screen and (min-width: 35em), print and (min-width: 40em)'',
dbaron@7381 333 which is true for screen displays
dbaron@7381 334 whose viewport is at least 35 times the initial font size
dbaron@7381 335 and for print displays
dbaron@7381 336 whose viewport is at least 40 times the initial font size.
dbaron@7381 337 When either of these is true,
dbaron@7381 338 the condition of the rule is true,
dbaron@7381 339 and the rule
dbaron@7381 340 ''#section_navigation { float: left; width: 10em; }''
dbaron@7381 341 is applied.</p>
dbaron@2974 342 </div>
dbaron@2974 343
dbaron@2974 344 <p>In terms of the grammar, this specification extends the
dbaron@2974 345 <code>media</code> production in the
dbaron@2974 346 <a href="http://www.w3.org/TR/CSS21/grammar.html">Grammar of CSS 2.1</a>
dbaron@2974 347 ([[!CSS21]], Appendix G) into:
dbaron@7032 348 <pre><dfn>media</dfn>
dbaron@7032 349 : MEDIA_SYM S* media_query_list <i>group_rule_body</i>
dbaron@2974 350 ;</pre>
dbaron@2974 351 <p>where the <code>group_rule_body</code> production is defined in this
dbaron@2974 352 specification, the <code>media_query_list</code> production is defined
dbaron@2974 353 in [[!MEDIAQ]], and the others are defined in the <a
dbaron@2974 354 href="http://www.w3.org/TR/CSS21/grammar.html">Grammar of CSS 2.1</a>
dbaron@2974 355 ([[!CSS21]], Appendix G).
dbaron@2974 356
jackalmage@6617 357 <h2 id="at-supports">Feature queries: the '@supports' rule</h2>
dbaron@2974 358
dbaron@7862 359 <p>The <dfn id="atsupports-rule">'@supports' rule</dfn> is a conditional group
dbaron@2974 360 rule whose condition tests whether the user agent supports CSS
dbaron@2974 361 property:value pairs. Authors can use it to write style sheets that use
dbaron@2974 362 new features when available but degrade gracefully when those features
dbaron@2974 363 are not supported. CSS has existing mechanisms for graceful
dbaron@2974 364 degradation, such as ignoring unsupported properties or values, but
dbaron@2974 365 these are not always sufficient when large groups of styles need to be
dbaron@2974 366 tied to the support for certain features, as is the case for use of new
dbaron@2974 367 layout system features.</p>
dbaron@2974 368
dbaron@2983 369 <p>The syntax of the condition in the '@supports' rule is
dbaron@2974 370 slightly more complicated than for the other conditional group rules
dbaron@2974 371 (though has some similarities to media queries) since:</p>
dbaron@2974 372 <ul>
dbaron@2974 373 <li>negation is needed so that the new-feature styles and the fallback
dbaron@2974 374 styles can be separated (within the forward-compatible grammar's rules
dbaron@2974 375 for the syntax of @-rules), and not required to override each other</li>
dbaron@2974 376 <li>conjunction (and) is needed so that multiple required features can
dbaron@2974 377 be tested</li>
dbaron@2974 378 <li>disjunction (or) is needed when there are multiple alternative
dbaron@2974 379 features for a set of styles, particularly when some of those
dbaron@2974 380 alternatives are vendor-prefixed properties or values</li>
dbaron@2974 381 </ul>
dbaron@2974 382
dbaron@2983 383 <p>Therefore, the syntax of the '@supports' rule allows
dbaron@2974 384 testing for property:value pairs, and arbitrary conjunctions (and),
dbaron@2974 385 disjunctions (or), and negations (not) of them.</p>
dbaron@2974 386
dbaron@2974 387 <p>This extends the lexical scanner in the
dbaron@2974 388 <a href="http://www.w3.org/TR/CSS21/grammar.html">Grammar of CSS 2.1</a>
dbaron@2974 389 ([[!CSS21]], Appendix G) by adding:
jackalmage@6832 390 <pre>
dbaron@7393 391 @{S}{U}{P}{P}{O}{R}{T}{S} {return <dfn>SUPPORTS_SYM</dfn>;}
dbaron@7393 392 {O}{R} {return <dfn>OR</dfn>;}
jackalmage@6832 393 </pre>
jackalmage@6943 394
dbaron@7393 395 <p>This then extends the grammar in the
dbaron@7393 396 <a href="http://www.w3.org/TR/CSS21/grammar.html">Grammar of CSS 2.1</a>,
dbaron@7393 397 using the lexical scanner there, with the additions of
dbaron@7393 398 <code><a href="http://www.w3.org/TR/css3-mediaqueries/#syntax">AND</a></code> and
dbaron@7393 399 <code><a href="http://www.w3.org/TR/css3-mediaqueries/#syntax">NOT</a></code>
dbaron@7393 400 tokens defined in the Media Queries specification [[!MEDIAQ]]
dbaron@7393 401 and the <code>OR</code> and <code>SUPPORTS_SYM</code> tokens defined above,
dbaron@7393 402 and with
dbaron@7393 403 <code><a href="http://www.w3.org/TR/CSS21/syndata.html#tokenization">declaration</a></code>,
dbaron@7393 404 <code><a href="http://www.w3.org/TR/CSS21/syndata.html#tokenization">any</a></code>,
dbaron@7393 405 and <code><a href="http://www.w3.org/TR/CSS21/syndata.html#tokenization">unused</a></code>
dbaron@7393 406 productions
dbaron@7393 407 and the <code><a href="http://www.w3.org/TR/CSS21/syndata.html#tokenization">FUNCTION</a></code> token
dbaron@7393 408 taken from the core syntax of CSS defined in
dbaron@7393 409 <a href="http://www.w3.org/TR/CSS21/syndata.html#tokenization">section 4.1.1 (Tokenization)</a> of [[!CSS21]],
dbaron@7393 410 by adding:</p>
jackalmage@6943 411
jackalmage@6315 412 <pre><dfn>supports_rule</dfn>
dbaron@7393 413 : <i>SUPPORTS_SYM</i> <a href="http://www.w3.org/TR/CSS21/grammar.html#scanner"><i>S</i></a>* <i>supports_condition</i> <a href="http://www.w3.org/TR/CSS21/grammar.html#scanner"><i>S</i></a>* <i>group_rule_body</i>
dbaron@2974 414 ;
dbaron@2974 415
jackalmage@6315 416 <dfn>supports_condition</dfn>
dbaron@7032 417 : <i>supports_negation</i> | <i>supports_conjunction</i> | <i>supports_disjunction</i> |
dbaron@7032 418 <i>supports_condition_in_parens</i>
dbaron@3957 419 ;
dbaron@3957 420
jackalmage@6315 421 <dfn>supports_condition_in_parens</dfn>
dbaron@7393 422 : ( '(' <a href="http://www.w3.org/TR/CSS21/grammar.html#scanner"><i>S</i></a>* <i>supports_condition</i> <a href="http://www.w3.org/TR/CSS21/grammar.html#scanner"><i>S</i></a>* ')' ) | <i>supports_declaration_condition</i> |
dbaron@7032 423 <i>general_enclosed</i>
dbaron@2974 424 ;
dbaron@2974 425
jackalmage@6315 426 <dfn>supports_negation</dfn>
dbaron@7393 427 : <a href="http://www.w3.org/TR/css3-mediaqueries/#syntax"><i>NOT</i></a> <a href="http://www.w3.org/TR/CSS21/grammar.html#scanner"><i>S</i></a>+ <i>supports_condition_in_parens</i>
dbaron@2974 428 ;
dbaron@2974 429
jackalmage@6315 430 <dfn>supports_conjunction</dfn>
dbaron@7393 431 : <i>supports_condition_in_parens</i> ( <a href="http://www.w3.org/TR/CSS21/grammar.html#scanner"><i>S</i></a>+ <a href="http://www.w3.org/TR/css3-mediaqueries/#syntax"><i>AND</i></a> <a href="http://www.w3.org/TR/CSS21/grammar.html#scanner"><i>S</i></a>+ <i>supports_condition_in_parens</i> )+
dbaron@2974 432 ;
dbaron@2974 433
jackalmage@6315 434 <dfn>supports_disjunction</dfn>
dbaron@7393 435 : <i>supports_condition_in_parens</i> ( <a href="http://www.w3.org/TR/CSS21/grammar.html#scanner"><i>S</i></a>+ <i>OR</i> <a href="http://www.w3.org/TR/CSS21/grammar.html#scanner"><i>S</i></a>+ <i>supports_condition_in_parens</i> )+
dbaron@2974 436 ;
dbaron@2974 437
jackalmage@6315 438 <dfn>supports_declaration_condition</dfn>
dbaron@7393 439 : '(' <a href="http://www.w3.org/TR/CSS21/grammar.html#scanner"><i>S</i></a>* <a href="http://www.w3.org/TR/CSS21/syndata.html#tokenization"><i>declaration</i></a> ')'
jackalmage@6943 440 ;
jackalmage@6943 441
dbaron@7031 442 <dfn>general_enclosed</dfn>
dbaron@7393 443 : ( <a href="http://www.w3.org/TR/CSS21/syndata.html#tokenization"><i>FUNCTION</i></a> | '(' ) ( <a href="http://www.w3.org/TR/CSS21/syndata.html#tokenization"><i>any</i></a> | <a href="http://www.w3.org/TR/CSS21/syndata.html#tokenization"><i>unused</i></a> )* ')'
dbaron@7373 444 ;
dbaron@7031 445 </pre>
jackalmage@6943 446
dbaron@7031 447 <p>
dbaron@7038 448 Implementations <strong>must</strong> parse ''@supports'' rules
dbaron@7038 449 based on the above grammar,
dbaron@7038 450 and when interpreting the above grammar,
dbaron@7038 451 <strong>must</strong> match the production before an <code>|</code> operator
dbaron@7038 452 in preference to the one after it.
dbaron@7038 453 </p>
dbaron@7038 454
dbaron@7038 455 <p>
dbaron@7031 456 The above grammar is purposely very loose for forwards-compatibility reasons,
dbaron@7031 457 since the <code>general_enclosed</code> production
dbaron@7031 458 allows for substantial future extensibility.
dbaron@7033 459 Any ''@supports'' rule that does not parse according to the grammar above
dbaron@7033 460 (that is, a rule that does not match this loose grammar
dbaron@7393 461 which includes the <code>general_enclosed</code> production)
dbaron@7033 462 is invalid.
dbaron@7031 463 Style sheets <strong>must not</strong> use such a rule and
dbaron@7031 464 processors <strong>must</strong> ignore such a rule (including all of its contents).
dbaron@7031 465
dbaron@3021 466 <p>Each of these grammar terms is associated with a boolean result, as
dbaron@3021 467 follows:</p>
dbaron@2974 468 <dl>
dbaron@2974 469 <dt>supports_condition</dt>
dbaron@2974 470 <dd>
dbaron@3021 471 The result is the result of the single child term.
dbaron@2974 472 </dd>
dbaron@2974 473
dbaron@3957 474 <dt>supports_condition_in_parens</dt>
dbaron@3957 475 <dd>
dbaron@3957 476 The result is the result of the single <code>supports_condition</code>
dbaron@3957 477 or <code>supports_declaration_condition</code> child term.
dbaron@3957 478 </dd>
dbaron@3957 479
dbaron@2974 480 <dt>supports_negation</dt>
dbaron@2974 481 <dd>
dbaron@3021 482 The result is the <em>negation</em> of the result of the
dbaron@3021 483 <code>supports_condition_in_parens</code> child term.
dbaron@2974 484 </dd>
dbaron@2974 485
dbaron@2974 486 <dt>supports_conjunction</dt>
dbaron@2974 487 <dd>
dbaron@3021 488 The result is true if the result of <em>all</em> of the
dbaron@3021 489 <code>supports_condition_in_parens</code> child terms is true;
dbaron@3021 490 otherwise it is false.
dbaron@2974 491 </dd>
dbaron@2974 492
dbaron@2974 493 <dt>supports_disjunction</dt>
dbaron@2974 494 <dd>
dbaron@3021 495 The result is true if the result of <em>any</em> of the
dbaron@3021 496 <code>supports_condition_in_parens</code> child terms is true;
dbaron@3021 497 otherwise it is false.
dbaron@2974 498 </dd>
dbaron@2974 499
dbaron@2974 500 <dt>supports_declaration_condition</dt>
dbaron@2974 501 <dd>
jackalmage@6943 502 The result is whether the CSS processor <a href="#support-definition">supports</a> the declaration
fantasai@6845 503 within the parentheses.
jackalmage@6943 504 </dd>
jackalmage@6943 505
dbaron@7031 506 <dt>general_enclosed</dt>
jackalmage@6943 507 <dd>
jackalmage@6943 508 The result is always false.
dbaron@7031 509 Additionally, style sheets <strong>must not</strong>
dbaron@7031 510 write ''@supports'' rules
dbaron@7031 511 that match this grammar production.
dbaron@7031 512 (In other words, this production exists only for future extensibility,
dbaron@7031 513 and is not part of the description of a valid style sheet
dbaron@7031 514 in this level of the specification.)
dbaron@7031 515 <span class="note">Note that future levels may define functions
dbaron@7031 516 or other parenthesized expressions that can evaluate to true.</span>
dbaron@2974 517 </dd>
fantasai@7034 518 </dl>
jackalmage@6943 519
dbaron@3021 520 <p>The condition of the '@supports' rule is the result of the
dbaron@3021 521 <code>supports_condition</code> term that is a child of the
dbaron@3021 522 <code>supports_rule</code> term.</p>
dbaron@2974 523
dbaron@2982 524 <div class="example">
dbaron@2982 525 <p>For example, the following rule</p>
dbaron@2982 526 <pre>@supports ( display: flexbox ) {
dbaron@2982 527 body, #navigation, #content { display: flexbox; }
dbaron@2982 528 #navigation { background: blue; color: white; }
dbaron@2982 529 #article { background: white; color: black; }
dbaron@2982 530 }</pre>
dbaron@2983 531 <p>applies the rules inside the '@supports' rule only when
dbaron@2983 532 ''display: flexbox'' is supported.</p>
dbaron@2982 533 </div>
dbaron@2974 534
dbaron@2982 535 <div class="example">
dbaron@2982 536 <p>The following example shows an additional '@supports' rule that can
dbaron@2982 537 be used to provide an alternative for when ''display: flexbox'' is not
dbaron@2982 538 supported:</p>
dbaron@2982 539 <pre>@supports not ( display: flexbox ) {
dbaron@2982 540 body { width: 100%; height: 100%; background: white; color: black; }
dbaron@2982 541 #navigation { width: 25%; }
dbaron@2982 542 #article { width: 75%; }
dbaron@2974 543 }</pre>
dbaron@2982 544 <p>Note that the 'width' declarations may be harmful to the
dbaron@2982 545 flexbox-based layout, so it is important that they be present only in
dbaron@2982 546 the non-flexbox styles.</p>
dbaron@2982 547 </div>
dbaron@2974 548
dbaron@2982 549 <div class="example">
dbaron@2982 550 <p>The following example checks for support for the 'box-shadow'
dbaron@2982 551 property, including checking for support for vendor-prefixed versions of
dbaron@2982 552 it. When the support is present, it specifies both 'box-shadow' (with
dbaron@8325 553 the prefixed versions) and 'border' in a way what would cause the box to
dbaron@2982 554 become invisible were 'box-shadow' not supported.</p>
dbaron@8325 555 <pre>.outline {
dbaron@8325 556 border: 1px solid black;
dbaron@8325 557 padding: 1px;
dbaron@8325 558 }
dbaron@8325 559 @supports ( box-shadow: 0 0 2px black inset ) or
dbaron@8325 560 ( -moz-box-shadow: 0 0 2px black inset ) or
dbaron@8325 561 ( -webkit-box-shadow: 0 0 2px black inset ) or
dbaron@8325 562 ( -o-box-shadow: 0 0 2px black inset ) {
dbaron@2982 563 .outline {
dbaron@8325 564 -moz-box-shadow: 0 0 2px black inset;
dbaron@8325 565 -webkit-box-shadow: 0 0 2px black inset;
dbaron@8325 566 -o-box-shadow: 0 0 2px black inset;
dbaron@8325 567 box-shadow: 0 0 2px black inset; /* unprefixed last */
dbaron@8325 568 /* override the rule above the @supports rule */
dbaron@8325 569 border: none;
dbaron@8325 570 padding: 2px;
dbaron@2982 571 }
dbaron@2982 572 }</pre></div>
dbaron@2974 573
dbaron@2984 574 <p>To avoid confusion between ''and'' and ''or'', the syntax requires
dbaron@2984 575 that both ''and'' and ''or'' be specified explicitly (rather than, say,
dbaron@2984 576 using commas or spaces for one of them). Likewise, to avoid confusion
dbaron@2984 577 caused by precedence rules, the syntax does not allow ''and'', ''or'',
dbaron@2984 578 and ''not'' operators to be mixed without a layer of parentheses.</p>
dbaron@2974 579
dbaron@2984 580 <div class="example">
dbaron@2984 581 <p>For example, the following rule is not valid:
dbaron@3959 582 <pre class="illegal">@supports (transition-property: color) or
dbaron@2984 583 (animation-name: foo) and
dbaron@2984 584 (transform: rotate(10deg)) {
dbaron@2984 585 // ...
dbaron@2984 586 }</pre>
dbaron@2984 587 <p>Instead, authors must write one of the following:</p>
dbaron@2984 588 <pre>@supports ((transition-property: color) or
dbaron@2984 589 (animation-name: foo)) and
dbaron@2984 590 (transform: rotate(10deg)) {
dbaron@2984 591 // ...
dbaron@2984 592 }</pre>
dbaron@2984 593 <pre>@supports (transition-property: color) or
dbaron@3430 594 ((animation-name: foo) and
dbaron@2984 595 (transform: rotate(10deg))) {
dbaron@2984 596 // ...
dbaron@2984 597 }</pre>
dbaron@2984 598 </div>
dbaron@2974 599
dbaron@7374 600 <p>Furthermore, whitespace is required after a ''not'' and on both
dbaron@7374 601 sides of an ''and'' or ''or''.</p>
dbaron@7374 602
dbaron@3957 603 <p>The declaration being tested must always occur within parentheses,
dbaron@3957 604 when it is the only thing in the expression.<p>
dbaron@3957 605
dbaron@3957 606 <div class="example">
dbaron@3957 607 <p>For example, the following rule is not valid:
dbaron@3959 608 <pre class="illegal">@supports display: flexbox {
dbaron@3957 609 // ...
dbaron@3957 610 }</pre>
dbaron@3957 611 <p>Instead, authors must write:</p>
dbaron@3957 612 <pre>@supports (display: flexbox) {
dbaron@3957 613 // ...
dbaron@3957 614 }</pre>
dbaron@3957 615 </div>
dbaron@3957 616
dbaron@3957 617 <p>The syntax allows extra parentheses when they are not needed. This
dbaron@3957 618 flexibility is sometimes useful for authors (for example, when
dbaron@3957 619 commenting out parts of an expression) and may also be useful for
dbaron@3957 620 authoring tools.</p>
dbaron@3957 621
dbaron@3957 622 <div class="example">
dbaron@3957 623 <p>For example, authors may write:</p>
dbaron@3957 624 <pre>@supports ((display: flexbox)) {
dbaron@3957 625 // ...
dbaron@3957 626 }</pre>
dbaron@3957 627 </div>
dbaron@3957 628
jackalmage@6793 629 <p>A trailing ''!important'' on a declaration being tested is allowed,
jackalmage@6793 630 though it won't change the validity of the declaration.
jackalmage@6793 631
jackalmage@6793 632 <div class="example">
jackalmage@6793 633 <p>For example, the following rule is valid:
jackalmage@6793 634 <pre>@supports (display: flexbox !important) {
jackalmage@6793 635 // ...
jackalmage@6793 636 }</pre>
jackalmage@6793 637 </div>
dbaron@6306 638
jackalmage@6617 639 <h3 id="support-definition">Definition of support</h3>
dbaron@3021 640
dbaron@6741 641 <p>For forward-compatibility,
dbaron@6741 642 <a href="http://www.w3.org/TR/CSS21/syndata.html#declaration">section 4.1.8
dbaron@6741 643 (Declarations and properties)</a> of [[!CSS21]]
dbaron@6741 644 defines rules for handling invalid properties and values.
dbaron@6741 645 CSS processors that
dbaron@6741 646 do not implement or partially implement a specification
dbaron@6741 647 <strong>must</strong> treat any part of a value that they
dbaron@6741 648 do not implement, or
dbaron@6741 649 do not have a usable level of support for,
dbaron@6741 650 as invalid according to this rule
dbaron@6741 651 for handling invalid properties and values,
dbaron@6741 652 and therefore <strong>must</strong> discard the declaration as a parse error.</p>
dbaron@6741 653
jackalmage@6617 654 <p>A CSS processor is considered to <dfn id="dfn-support">support</dfn>
dbaron@6741 655 a declaration (consisting of a property and value) if it accepts that
dbaron@6741 656 declaration (rather than discarding it as a parse error).
dbaron@6741 657 If a processor does not implement, with a usable level of support,
dbaron@6741 658 the value given,
dbaron@6741 659 then it <strong>must not</strong>
dbaron@6741 660 accept the declaration or claim support for it.</p>
dbaron@3021 661
dbaron@7382 662 <p class="note">Note that properties or values
dbaron@7382 663 whose support is effectively disabled by user preferences
dbaron@7382 664 are still considered as supported by this definition.
dbaron@7382 665 For example, if a user has enabled a high-contrast mode
dbaron@7382 666 that causes colors to be overridden,
dbaron@7382 667 the CSS processor is still considered to support the 'color' property
dbaron@7382 668 even though declarations of the 'color' property may have no effect.
dbaron@7382 669 On the other hand, a developer-facing preference
dbaron@7382 670 whose purpose is to enable or disable support for an experimental CSS feature
dbaron@7382 671 does affect this definition of support.</p>
dbaron@7382 672
dbaron@6742 673 <p>These rules (and the equivalence between them) allow
dbaron@3021 674 authors to use fallback (either in the [[CSS1]] sense of declarations
dbaron@3021 675 that are overridden by later declarations or with the new capabilities
dbaron@3021 676 provided by the ''@supports'' rule in this specification) that works
dbaron@3021 677 correctly for the features implemented. This applies especially to
dbaron@3021 678 compound values; implementations must implement all parts of the value
dbaron@3021 679 in order to consider the declaration supported, either inside a ruleset
dbaron@3021 680 or in the declaration condition of an ''@supports'' rule.</p>
dbaron@3021 681
jackalmage@6838 682 <!--
jackalmage@6617 683 <h2 id="at-document">Document queries: the '@document' rule</h2>
dbaron@2974 684
dbaron@2983 685 <p>The <dfn>'@document' rule</dfn> is a conditional group
dbaron@3027 686 rule whose condition depends on the
dbaron@3027 687 <a href="#url-of-doc">URL of the document being styled</a>.
dbaron@2974 688 This allows style sheets, particularly user style sheets, to have styles
dbaron@2974 689 that only apply to a set of pages rather than to all pages using the
dbaron@2974 690 style sheet.</p>
dbaron@2974 691
dbaron@2974 692 <p class="issue">Given that this @-rule is intended primarily for user
dbaron@2974 693 style sheets, what should this specification say about its use in author
dbaron@2974 694 style sheets? Should it be forbidden? Should use instead be
dbaron@2974 695 discouraged? Or should this specification remain neutral on the
dbaron@2986 696 topic, since there are valid uses in author style sheets?</p>
dbaron@2974 697
jackalmage@6617 698 <p id="url-of-doc">The <dfn>URL of the document being styled</dfn> is
dbaron@3027 699 the URI at which the document is located, excluding any fragment
dbaron@3027 700 identifiers. (This means, for example, that HTTP redirects have been
dbaron@3027 701 followed.) If the styles are being applied inside a complete document
dbaron@3246 702 embedded into the presentation of another (e.g., [[HTML5]]&#39;s <code
dbaron@3027 703 class="html">iframe</code>, <code class="html">object</code>, or <code
dbaron@3027 704 class="html">img</code> elements), the relevant URI is that of the
dbaron@3027 705 frame, not of its container. However, if content from other documents
dbaron@3027 706 is mixed in via mechanisms that mix content from one document into
dbaron@3246 707 another (e.g., [[SVG11]]&#39;s <code>use</code> element), then the
dbaron@3027 708 address of the container document is used.</p>
dbaron@3027 709
dbaron@3027 710 <p class="note">Note: In [[HTML5]], this is the
fantasai@6697 711 <a href="http://dev.w3.org/html5/spec/dom.html#documents">document's address</a>
dbaron@3027 712 of a document in a
dbaron@3027 713 <a href="http://dev.w3.org/html5/spec/browsers.html#browsing-context">browsing context</a>.</p>
dbaron@3027 714
dbaron@3240 715 <div class="issue">What form of normalization is done on URLs and domains
dbaron@3240 716 before matching? In particular, this specification needs to describe:
dbaron@3240 717 <ul>
dbaron@3240 718 <li>what form is used for the <a href="#url-of-doc">URL of the document
dbaron@3240 719 being styled</a> (and what has been normalized in that form)</li>
dbaron@3240 720 <li>what normalization (if any) happens to the argument of each of the match
dbaron@3240 721 functions before the comparison that they describe and</li>
dbaron@3240 722 <li>whether the
dbaron@3240 723 comparison algorithm used is string comparison or some other URL
dbaron@3240 724 comparison algorithm.</li></ul></div>
dbaron@3027 725
dbaron@2983 726 <p>The '@document' rule's condition is written as a
dbaron@2974 727 comma-separated list of <dfn>URL matching functions</dfn>, and the
dbaron@2974 728 condition evaluates to true whenever any one of those functions
dbaron@2974 729 evaluates to true. The following URL matching functions are
dbaron@2974 730 permitted:</p>
dbaron@2974 731
dbaron@2974 732 <dl>
jackalmage@6617 733 <dt><dfn id="url-exact" title="url()|URL matching functions::exact">&lt;url&gt;</dfn></dt>
dbaron@2974 734
dbaron@2974 735 <dd>
dbaron@2983 736 <p>The 'url()' function is the <dfn>exact url matching
dbaron@3027 737 function</dfn>. It evaluates to true whenever the <a
dbaron@3027 738 href="#url-of-doc">URL of the document being styled</a> is exactly
dbaron@3027 739 the URL given.</p>
dbaron@2974 740
dbaron@2983 741 <p class="Note">The 'url()' function, since it is a core syntax
dbaron@2974 742 element in CSS, is allowed (subject to different character
dbaron@2974 743 limitations and thus escaping requirements) to contain an unquoted
dbaron@2974 744 value (in addition to the string values that are allowed as
dbaron@2974 745 arguments for all four functions).</p>
dbaron@2974 746
dbaron@2974 747 <div class="example">
dbaron@2974 748 <p>For example, this rule:</p>
dbaron@2974 749 <pre>@document url("http://www.w3.org/Style/CSS/") {
dbaron@2974 750 #summary { background: yellow; color: black}
dbaron@2974 751 }</pre>
dbaron@2983 752 <p>styles the <code class="html">summary</code> element on the page
dbaron@2974 753 <code>http://www.w3.org/Style/CSS/</code>, but not on any other
dbaron@2974 754 pages.</p>
dbaron@2974 755 </div>
dbaron@2974 756 </dd>
dbaron@2974 757
jackalmage@6617 758 <dt><dfn id="url-prefix" title="url-prefix()|URL matching functions::prefix">url-prefix(&lt;string&gt;)</dfn></dt>
dbaron@2974 759
dbaron@2974 760 <dd>
dbaron@2983 761 <p>The 'url-prefix()' function is the <dfn>url prefix
dbaron@3027 762 matching function</dfn>. It evaluates to true whenever the
dbaron@3027 763 <a href="#url-of-doc">URL of the document being styled</a>
dbaron@3027 764 has the argument to the function as an
dbaron@2974 765 initial substring (which is true when the two strings are equal).
dbaron@2974 766 When the argument is the empty string, it evaluates to true for all
dbaron@2974 767 documents.</p>
dbaron@2974 768 <div class="example">
dbaron@2974 769 <p>For example, this rule:</p>
dbaron@2974 770 <pre>@document url-prefix("http://www.w3.org/Style/CSS/") {
dbaron@2974 771 #summary { background: yellow; color: black}
dbaron@2974 772 }</pre>
dbaron@2983 773 <p>styles the <code class="html">summary</code> element on the page
dbaron@2974 774 <code>http://www.w3.org/Style/CSS/</code> and on the page
dbaron@2974 775 <code>http://www.w3.org/Style/CSS/Test</code>, but it does not
dbaron@2974 776 affect the page <code>http://www.w3.org/</code> or the page
dbaron@2974 777 <code>http://www.example.com/Style/CSS/</code>.</p>
dbaron@2974 778 </div>
dbaron@2974 779 </dd>
dbaron@2974 780
jackalmage@6617 781 <dt><dfn id="url-domain" title="domain()|URL matching functions::domain">domain(&lt;string&gt;)</dfn></dt>
dbaron@2974 782
dbaron@2974 783 <dd>
dbaron@2983 784 <p>The 'domain()' function is the <dfn>domain
dbaron@2974 785 matching function</dfn>. It evaluates to true whenever
dbaron@3027 786 the <a href="#url-of-doc">URL of the document being styled</a>
dbaron@3027 787 has a host subcomponent (as defined in [[!URI]])
dbaron@2974 788 and that host subcomponent is exactly the argument to the
dbaron@2983 789 'domain()' function or a final substring of the host
dbaron@2974 790 component is a period (U+002E) immediately followed by the argument
dbaron@2983 791 to the 'domain()' function.</p>
dbaron@2974 792 <div class="example">
dbaron@2974 793 <p>For example, this rule:</p>
dbaron@2974 794 <pre>@document domain("w3.org") {
dbaron@2974 795 body { font-size: 16px ! important }
dbaron@2974 796 }</pre>
dbaron@2974 797 <p>changes the font size of the body element for pages such as
dbaron@2974 798 <code>http://www.w3.org/Style/CSS/</code> and
dbaron@2974 799 <code>http://w3.org/Style/CSS/</code> and
dbaron@2974 800 <code>http://lists.w3.org/Archives/Public/www-style/</code>
dbaron@2974 801 but it does not affect the page
dbaron@2974 802 <code>http://www.example.com/Style/CSS/</code>.</p>
dbaron@2974 803 </div>
dbaron@2974 804 </dd>
dbaron@2974 805
jackalmage@6617 806 <dt><dfn id="url-regexp" title="regexp()|URL matching functions::regular expression">regexp(&lt;string&gt;)</dfn></dt>
dbaron@2974 807
dbaron@2974 808 <dd>
dbaron@2986 809 <p>The contents of the &lt;string&gt; argument <strong>must</strong>
dbaron@3068 810 match the JavaScript <code>Pattern</code> production
dbaron@3068 811 ([[!ECMA-262-5.1]], section 15.10.1). However,
dbaron@2986 812 failing to do so is not a CSS syntax error and does not trigger any
dbaron@2986 813 error handling for CSS syntax errors.</p>
dbaron@2986 814
dbaron@2986 815 <p>The ''regexp()'' function evaluates to true whenever the string
dbaron@2986 816 argument compiled as a JavaScript regular expression with the
dbaron@2986 817 <code>global</code>, <code>ignoreCase</code> and
dbaron@2986 818 <code>multiline</code> flags <em>disabled</em>
dbaron@3068 819 (see [[!ECMA-262-5.1]], sections 15.10.7.2 through 15.10.7.4)
dbaron@2986 820 compiles successfully and the resulting regular expression matches
dbaron@3027 821 the entirety of the
dbaron@3027 822 <a href="#url-of-doc">URL of the document being styled</a>.</p>
dbaron@2986 823
dbaron@2986 824 <p class="note">Note that regular expression must match the entire
dbaron@2986 825 URL, not just a part of it.</p>
dbaron@2974 826
dbaron@3018 827 <p class="note">Note that this definition intentionally matches the
dbaron@3018 828 behavior of the <a
dbaron@2983 829 href="http://dev.w3.org/html5/spec/common-input-element-attributes.html#attr-input-pattern"><code class="html">pattern</code>
dbaron@2983 830 attribute</a> on the <code class="html">input</code> element
dbaron@2983 831 in [[HTML5]].</p>
dbaron@2986 832
dbaron@2986 833 <div class="example">
dbaron@2986 834 <p>For example, this rule:</p>
dbaron@2986 835 <pre>@document regexp("http://www.w3.org/TR/\\d{4}/[^/]*-CSS2-\\d{8}/") {
dbaron@2986 836 body { font-size: 20px ! important }
dbaron@2986 837 }</pre>
dbaron@2986 838 <p>changes the font size of the body element for pages such as
dbaron@2986 839 <code>http://www.w3.org/TR/2011/PR-CSS2-20110412/</code>.</p>
dbaron@2986 840 <p class="note">Note that the backslashes in the regular
dbaron@2986 841 expression require CSS escaping as ''\\''.</p>
dbaron@2986 842 </div>
dbaron@2974 843 </dd>
dbaron@2974 844
dbaron@2974 845 </dl>
dbaron@2974 846
dbaron@2979 847 <p>Implementations <strong>must</strong> treat any unknown URL matching
dbaron@3045 848 functions as a syntax error, and thus ignore the '@document' rule.
dbaron@3045 849 <span class="issue">Should we instead have more complicated error
dbaron@3045 850 handling rules to make forward-compatibility work differently, or is
dbaron@3045 851 this rule the best solution for such future expansion anyway?</span></p>
dbaron@2974 852
dbaron@5293 853 <div class="issue">This syntax doesn't offer any ability to do negations,
dbaron@5293 854 which has been requested in <a
jackalmage@6617 855 href="https://bugzilla.mozilla.org/show_bug.cgi?id=349813">Mozilla bug
dbaron@5293 856 349813</a>. Use cases that people have wanted negations for
dbaron@5293 857 include:
dbaron@5293 858 <ul>
dbaron@5293 859 <li>User style sheets that want a particular rule in general, but know
dbaron@5293 860 that that rule does more harm than good on specific sites.</li>
dbaron@5293 861 <li>Authors who have a rule that they want to apply to most of their
dbaron@5293 862 pages, but wish to make a few exceptions for.</li>
dbaron@5293 863 </ul>
dbaron@5293 864 </div>
dbaron@5293 865
dbaron@2974 866 <p>This extends the lexical scanner in the
dbaron@2974 867 <a href="http://www.w3.org/TR/CSS21/grammar.html">Grammar of CSS 2.1</a>
dbaron@2974 868 ([[!CSS21]], Appendix G) by adding:
dbaron@2974 869 <pre>@{D}{O}{C}{U}{M}{E}{N}{T} {return DOCUMENT_SYM;}</pre>
dbaron@2974 870 <p>and the grammar by adding</p>
dbaron@7032 871 <pre><dfn>document_rule</dfn>
dbaron@7032 872 : DOCUMENT_SYM S+ <i>url_match_fn</i> ( "," S* <i>url_match_fn</i> )* <i>group_rule_body</i>
dbaron@2974 873 ;
dbaron@2974 874
dbaron@7032 875 <dfn>url_match_fn</dfn>
dbaron@6740 876 : (URI | FUNCTION S* STRING S* ')' ) S*
dbaron@2974 877 ;</pre>
jackalmage@6838 878 -->
jackalmage@6838 879
dbaron@2974 880
jackalmage@6617 881 <h2 id="apis">APIs</h2>
dbaron@3416 882
jackalmage@6617 883 <h3 id='extentions-to-cssrule-interface'>
jackalmage@6315 884 Extensions to the <code>CSSRule</code> interface</h3>
dbaron@3416 885
jackalmage@6315 886 <p>The <code>CSSRule</code> interface is extended as follows:
jackalmage@6315 887
jackalmage@6315 888 <pre class='idl'>partial interface CSSRule {
jackalmage@6315 889 const unsigned short SUPPORTS_RULE = 12;
jackalmage@6838 890 <!--
jackalmage@6315 891 const unsigned short DOCUMENT_RULE = 13;
jackalmage@6838 892 -->
jackalmage@6315 893 }</pre>
jackalmage@6315 894
jackalmage@6315 895
jackalmage@6655 896 <h3 id='the-cssgroupingrule-interface'>
jackalmage@6655 897 The <code>CSSGroupingRule</code> interface</h3>
jackalmage@6655 898
jackalmage@6655 899 <p>The <dfn><code>CSSGroupingRule</code></dfn> interface represents an at-rule that contains other rules nested inside itself.
jackalmage@6655 900
jackalmage@6655 901 <pre class='idl'>interface CSSGroupingRule : CSSRule {
dbaron@7102 902 readonly attribute <a href="http://www.w3.org/TR/DOM-Level-2-Style/css.html#CSS-CSSRuleList">CSSRuleList</a> cssRules;
jackalmage@6655 903 unsigned long insertRule (DOMString rule, unsigned long index);
jackalmage@6655 904 void deleteRule (unsigned long index);
jackalmage@6655 905 }</pre>
jackalmage@6655 906
jackalmage@6655 907 <dl class='idl-attributes'>
dbaron@7102 908 <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
jackalmage@6655 909 <dd>The <code>cssRules</code> attribute must return a <code>CSSRuleList</code>
jackalmage@6655 910 object for the list of CSS rules nested inside the grouping rule.
jackalmage@6655 911 </dl>
jackalmage@6655 912
jackalmage@6655 913 <dl class='idl-methods'>
jackalmage@6655 914 <dt><code>insertRule(DOMString rule, unsigned long index)</code>, returns
jackalmage@6655 915 <code>unsigned long</code>
dbaron@7104 916 <dd>
dbaron@7104 917 The <code>insertRule</code> operation must
dbaron@7104 918 insert a CSS rule <var>rule</var>
dbaron@7104 919 into the CSS rule list returned by <code>cssRules</code>,
dbaron@7104 920 such that the inserted rule will be at position <var>index</var>,
dbaron@7104 921 and any rules previously at <var>index</var> or higher
dbaron@7104 922 will increase their index by one.
dbaron@7104 923 It must throw INDEX_SIZE_ERR
dbaron@7104 924 if index is greater than <code>cssRules.length</code>.
dbaron@7104 925 It must throw SYNTAX_ERR
dbaron@7104 926 if the rule has a syntax error and is unparseable;
dbaron@7104 927 this does not include syntax errors handled by error handling rules
dbaron@7412 928 for constructs inside of the rule,
dbaron@7412 929 but this does include cases where the string given
dbaron@7412 930 does not parse into a single CSS rule (such as when the string is empty)
dbaron@7412 931 or where there is anything other than whitespace or comments
dbaron@7412 932 after that single CSS rule.
dbaron@7104 933 It must throw HIERARCHY_REQUEST_ERR
dbaron@7104 934 if the rule cannot be inserted at the location specified,
dbaron@7104 935 for example, if an ''@import'' rule is inserted inside a group rule.
dbaron@7104 936
dbaron@7412 937 <p>The return value is the <var>index</var> parameter.
jackalmage@6655 938
jackalmage@6655 939 <dt><code>deleteRule (unsigned long index)</code>, return <code>void</code>
dbaron@7104 940 <dd>
dbaron@7104 941 The <code>deleteRule</code> operation must
dbaron@7104 942 remove a CSS rule from
dbaron@7104 943 the CSS rule list returned by <code>cssRules</code> at <var>index</var>.
dbaron@7104 944 It must throw INDEX_SIZE_ERR
dbaron@7104 945 if index is greater than or equal to <code>cssRules.length</code>.
jackalmage@6655 946 </dl>
jackalmage@6655 947
jackalmage@6655 948
jackalmage@6618 949 <h3 id="the-cssconditionrule-interface">
jackalmage@6618 950 The <code>CSSConditionRule</code> interface</h3>
jackalmage@6315 951
jackalmage@6620 952 <p>The <dfn><code>CSSConditionRule</code></dfn> interface represents all the "conditional" at-rules,
jackalmage@6620 953 which consist of a condition and a statement block.
dbaron@6323 954
jackalmage@6655 955 <pre class='idl'>interface CSSConditionRule : CSSGroupingRule {
dbaron@6324 956 attribute DOMString conditionText;
jackalmage@6315 957 }</pre>
jackalmage@6315 958
jackalmage@6315 959 <dl class='idl-attributes'>
dbaron@6732 960
jackalmage@6619 961 <dt><code>conditionText</code> of type <code>DOMString</code>
dbaron@6732 962 <dd>
dbaron@6732 963 <p>The <code>conditionText</code> attribute represents
dbaron@6732 964 the condition of the rule.
dbaron@6732 965 Since what this condition does
dbaron@6732 966 varies between the derived interfaces of <code>CSSConditionRule</code>,
dbaron@6732 967 those derived interfaces
dbaron@6732 968 may specify different behavior for this attribute
dbaron@6732 969 (see, for example, <code>CSSMediaRule</code> below).
dbaron@6732 970 In the absence of such rule-specific behavior,
dbaron@6732 971 the following rules apply:</p>
dbaron@6732 972
dbaron@6732 973 <p>The <code>conditionText</code> attribute, on getting, must return
jackalmage@6618 974 the result of serializing the associated condition.
jackalmage@6315 975
dbaron@6324 976 <p>On setting the <code>conditionText</code> attribute these steps
jackalmage@6315 977 must be run:
jackalmage@6315 978
jackalmage@6315 979 <ol>
jackalmage@6315 980 <li>Trim the given value of white space.
jackalmage@6315 981 <li>If the given value matches the grammar of the
jackalmage@6618 982 appropriate condition production for the given rule,
jackalmage@6618 983 replace the associated CSS condition with the given value.
jackalmage@6315 984 <li>Otherwise, do nothing.
jackalmage@6315 985 </ol>
jackalmage@6315 986 </dl>
jackalmage@6315 987
jackalmage@6618 988
jackalmage@6618 989 <h3 id="the-cssmediarule-interface">
jackalmage@6618 990 The <code>CSSMediaRule</code> interface</h3>
jackalmage@6618 991
jackalmage@6618 992 <p>The <dfn><code>CSSMediaRule</code></dfn> interface represents a ''@media'' rule:
jackalmage@6618 993
jackalmage@6618 994 <pre class='idl'>interface CSSMediaRule : CSSConditionRule {
dbaron@7102 995 readonly attribute <a href="http://www.w3.org/TR/DOM-Level-2-Style/stylesheets.html#StyleSheets-MediaList">MediaList</a> media;
jackalmage@6618 996 }</pre>
jackalmage@6618 997
jackalmage@6618 998 <dl class='idl-attributes'>
dbaron@7102 999 <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
jackalmage@6618 1000 <dd>The <code>media</code> attribute must return a <code>MediaList</code> object
jackalmage@6618 1001 for the list of media queries specified with the ''@media'' rule.
jackalmage@6618 1002
dbaron@7387 1003 <dt><code>conditionText</code> of type <code>DOMString</code> (CSSMediaRule-specific definition for attribute on CSSConditionRule)
jackalmage@6618 1004 <dd>The <code>conditionText</code> attribute (defined on the <code>CSSConditionRule</code> parent rule),
jackalmage@6618 1005 on getting, must return the value of <code>media.mediaText</code> on the rule.
jackalmage@6618 1006
jackalmage@6621 1007 <p>Setting the <code>conditionText</code> attribute
jackalmage@6621 1008 must set the <code>media.mediaText</code> attribute on the rule.
jackalmage@6621 1009 </dl>
jackalmage@6618 1010
jackalmage@6618 1011
jackalmage@6618 1012 <h3 id="the-csssupportsrule-interface">
jackalmage@6618 1013 The <code>CSSSupportsRule</code> interface</h3>
jackalmage@6618 1014
jackalmage@6618 1015 <p>The <dfn><code>CSSSupportsRule</code></dfn> interface represents a ''@supports'' rule.</p>
jackalmage@6618 1016
jackalmage@6621 1017 <pre class='idl'>interface CSSSupportsRule : CSSConditionRule {
jackalmage@6618 1018 }</pre>
jackalmage@6618 1019
dbaron@7387 1020 <dl class='idl-attributes'>
dbaron@7387 1021 <dt><code>conditionText</code> of type <code>DOMString</code> (CSSSupportsRule-specific definition for attribute on CSSConditionRule)
dbaron@7387 1022 <dd>The <code>conditionText</code> attribute (defined on the <code>CSSConditionRule</code> parent rule),
dbaron@7387 1023 on getting, must return the condition that was specified,
dbaron@7387 1024 without any logical simplifications,
dbaron@7387 1025 so that the returned condition will evaluate to the same result
dbaron@7387 1026 as the specified condition
dbaron@7387 1027 in any conformant implementation of this specification
dbaron@7387 1028 (including implementations that implement future extensions
dbaron@7387 1029 allowed by the <i>general_enclosed</i> exensibility mechanism in this specification).
dbaron@7387 1030 In other words,
dbaron@7387 1031 token stream simplifications are allowed
dbaron@7387 1032 (such as reducing whitespace to a single space
dbaron@7387 1033 or omitting it in cases where it is known to be optional),
dbaron@7392 1034 but logical simplifications (such as removal of unneeded parentheses,
dbaron@7392 1035 or simplification based on evaluating results) are not allowed.
dbaron@7387 1036
dbaron@7387 1037 </dl>
dbaron@7387 1038
jackalmage@6838 1039 <!--
jackalmage@6618 1040 <h3 id="the-cssdocumentrule-interface">
jackalmage@6618 1041 The <code>CSSDocumentRule</code> interface</h3>
jackalmage@6618 1042
jackalmage@6618 1043 <p>The <dfn><code>CSSDocumentRule</code></dfn> interface represents a ''@document'' rule.</p>
jackalmage@6618 1044
jackalmage@6621 1045 <pre class='idl'>interface CSSDocumentRule : CSSConditionRule {
jackalmage@6618 1046 }</pre>
jackalmage@6838 1047 -->
jackalmage@6315 1048
jackalmage@6315 1049
jackalmage@6620 1050 <h3 id='the-css-interface'>
jackalmage@6620 1051 The <code>CSS</code> interface, and the <code title=''>supports()</code> function</h3>
jackalmage@6315 1052
jackalmage@6620 1053 <p>The <dfn id='CSS-interface'><code>CSS</code></dfn> interface holds useful CSS-related functions that do not belong elsewhere.
jackalmage@6315 1054
jackalmage@6620 1055 <pre class='idl'>interface CSS {
dbaron@7043 1056 static boolean supports(DOMString property, DOMString value);
dbaron@7105 1057 static boolean supports(DOMString conditionText);
jackalmage@6620 1058 }</pre>
jackalmage@6620 1059
jackalmage@6620 1060 <dl class='idl-methods'>
jackalmage@6620 1061 <dt><code>supports(DOMString property, DOMString value)</code>,
jackalmage@6620 1062 returns <code>boolean</code>
jackalmage@6625 1063 <dt><code>supports(DOMString conditionText)</code>,
jackalmage@6620 1064 returns <code>boolean</code>
jackalmage@6620 1065 <dd>
jackalmage@6620 1066 When the <code title=''>supports()</code> method is invoked with two arguments <var>property</var> and <var>value</var>,
jackalmage@6620 1067 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,
jackalmage@6620 1068 and <var>value</var> would be successfully parsed as a supported value for that property.
dbaron@7390 1069 (Literal match means that no CSS escape processing is performed,
dbaron@7390 1070 and leading and trailing whitespace are not stripped,
dbaron@7390 1071 so any leading whitespace, trailing whitespace,
dbaron@7390 1072 or CSS escapes equivalent to the name of a property
dbaron@7390 1073 would cause the method to return <code>false</code>.)
jackalmage@6620 1074 Otherwise, it must return <code>false</code>.
jackalmage@6620 1075
jackalmage@6620 1076 <p>
jackalmage@6625 1077 When invoked with a single <var>conditionText</var> argument,
jackalmage@6625 1078 it must return <code>true</code> if <var>conditionText</var>,
jackalmage@6625 1079 when parsed and evaluated as a <code>supports_condition</code>,
jackalmage@6625 1080 would return true.
jackalmage@6620 1081 Otherwise, it must return <code>false</code>.
jackalmage@6620 1082 </dl>
jackalmage@6620 1083
dbaron@3417 1084
fantasai@6831 1085 <h2 class=no-num id="grammar">Grammar</h2>
fantasai@6831 1086
fantasai@6831 1087 <p>In order to allow these new @-rules in CSS style sheets, this
fantasai@6831 1088 specification modifies the <code>stylesheet</code> production in the <a
fantasai@6831 1089 href="http://www.w3.org/TR/CSS21/grammar.html">Appendix G</a> grammar of
fantasai@6831 1090 [[!CSS21]] by replacing the <code>media</code> production defined in
fantasai@6831 1091 [[!CSS21]] with the <code>media</code> production defined in this one,
jackalmage@6838 1092 and additionally inserting <code>| supports_rule</code>
fantasai@6831 1093 alongside <code>ruleset | media | page</code>.</p>
fantasai@6831 1094
fantasai@6831 1095
jackalmage@6617 1096 <h2 id="conformance">Conformance</h2>
dbaron@2974 1097
jackalmage@6617 1098 <h3 id="base-modules">Base Modules</h3>
dbaron@3022 1099
dbaron@3022 1100 <p>This specification defines conformance in terms of base modules,
dbaron@3022 1101 which are modules that this specification builds on top of. The base
dbaron@3022 1102 modules of this module are:</p>
dbaron@3022 1103
dbaron@3022 1104 <ul>
dbaron@3022 1105 <li>[[!CSS21]]</li>
dbaron@3022 1106 </ul>
dbaron@3022 1107
dbaron@3022 1108 <p>All of the conformance requirements of all base modules are
dbaron@3022 1109 incorporated as conformance requirements of this module, except where
dbaron@3022 1110 overridden by this module.</p>
dbaron@3022 1111
dbaron@3022 1112 <p>Additionally, all conformance requirements related to validity of
dbaron@3022 1113 syntax in this module and all of its base modules are to be interpreted
dbaron@3022 1114 as though all syntax in all of those modules is valid.</p>
dbaron@3022 1115
dbaron@3022 1116 <div class="example"><p>For example, this means that grammar presented
dbaron@3022 1117 in modules other than [[!CSS21]] must obey the requirements that
dbaron@3022 1118 [[!CSS21]] defines for the parsing of properties, and that requirements
dbaron@3022 1119 for handling invalid syntax in [[!CSS21]] do not treat syntax added by
dbaron@3022 1120 other modules as invalid.</p></div>
dbaron@3022 1121
dbaron@3022 1122 <p>Additionally, the set of valid syntax can be increased by the
dbaron@3022 1123 conformance of a style sheet or processor to additional modules; use of
dbaron@3022 1124 such syntax does not make a style sheet nonconformant and failure to
dbaron@3022 1125 treat such syntax as invalid does not make a processor
dbaron@3022 1126 nonconformant.</p>
dbaron@3022 1127
jackalmage@6617 1128 <h3 id="conformance-classes">Conformance Classes</h3>
dbaron@2974 1129
dbaron@2974 1130 <p>Conformance to the CSS Conditional Rules Module is defined for three
dbaron@2974 1131 conformance classes:
dbaron@2974 1132 <dl>
jackalmage@6617 1133 <dt><dfn title="conformance::style sheet" id="conform-style-sheet">style sheet</dfn>
dbaron@2974 1134 <dd>A <a href="http://www.w3.org/TR/CSS21/conform.html#style-sheet">CSS
dbaron@3022 1135 style sheet</a>.</dd>
jackalmage@6617 1136 <dt><dfn title="conformance::processor" id="conform-processor">processor</dfn></dt>
dbaron@3022 1137 <dd>A tool that reads CSS style sheets: it may be a renderer or
dbaron@3022 1138 <a
dbaron@3022 1139 href="http://www.w3.org/TR/CSS21/conform.html#user-agent">user-agent</a>
dbaron@2974 1140 that interprets the semantics of a style sheet and renders
dbaron@3022 1141 documents that use style sheets, or it may be a validator that
dbaron@3022 1142 checks style sheets.</dd>
jackalmage@6617 1143 <dt><dfn title="conformance::authoring tool" id="conform-authoring-tool">authoring tool</dfn></dt>
dbaron@3022 1144 <dd>A tool that writes a style sheet.</dd>
dbaron@2974 1145 </dl>
dbaron@3022 1146
dbaron@3022 1147 <p>A style sheet is conformant to the CSS Conditional Rules Module
dbaron@3022 1148 if it meets all of the conformance requirements in the module that are
dbaron@3022 1149 described as requirements of style sheets.</p>
dbaron@3022 1150
dbaron@3022 1151 <p>A processor is conformant to the CSS Conditional Rules Module if it
dbaron@3022 1152 meets all applicable conformance requirements in the module that are
dbaron@3022 1153 described as requirements of processors. In general, all requirements
dbaron@3022 1154 are applicable to renderers. Requirements concerning a part of CSS
dbaron@3022 1155 not performed by a processor are not applicable, e.g., requirements
dbaron@3022 1156 related to rendering are not applicable to a validator. The inability
dbaron@3022 1157 of a processor to correctly render a document due to limitations of
dbaron@3022 1158 the device does not make it non-conformant. (For example, a renderer
dbaron@3022 1159 is not required to render color on a monochrome monitor.)</p>
dbaron@3022 1160
dbaron@3022 1161 <p>An authoring tool is conformant to the CSS Conditional Rules Module
dbaron@3022 1162 if it writes style sheets that conform to the module and (if it reads
dbaron@3022 1163 CSS) it is a conformant processor.</p>
dbaron@2974 1164
jackalmage@6617 1165 <h3 id="partial">
dbaron@2974 1166 Partial Implementations</h3>
dbaron@2974 1167
dbaron@2974 1168 <p>So that authors can exploit the forward-compatible parsing rules to
dbaron@2974 1169 assign fallback values, CSS renderers <strong>must</strong>
dbaron@2974 1170 treat as invalid (and <a href="http://www.w3.org/TR/CSS21/conform.html#ignore">ignore
dbaron@2974 1171 as appropriate</a>) any at-rules, properties, property values, keywords,
dbaron@2974 1172 and other syntactic constructs for which they have no usable level of
dbaron@2974 1173 support. In particular, user agents <strong>must not</strong> selectively
dbaron@2974 1174 ignore unsupported component values and honor supported values in a single
dbaron@2974 1175 multi-value property declaration: if any value is considered invalid
dbaron@2974 1176 (as unsupported values must be), CSS requires that the entire declaration
dbaron@2974 1177 be ignored.</p>
dbaron@2974 1178
jackalmage@6617 1179 <h3 id="experimental">Experimental Implementations</h3>
dbaron@2974 1180
dbaron@2974 1181 <p>To avoid clashes with future CSS features, the CSS specifications
dbaron@2974 1182 reserve a <a href="http://www.w3.org/TR/CSS21/syndata.html#vendor-keywords">prefixed
dbaron@2974 1183 syntax</a> for proprietary property and value extensions to CSS. The CSS
dbaron@2974 1184 Working Group recommends that experimental implementations of features in
dbaron@2974 1185 CSS Working Drafts also use vendor-prefixed property or value names. This
dbaron@2974 1186 avoids any incompatibilities with future changes in the draft. Once a
dbaron@2974 1187 specification reaches the Candidate Recommendation stage, implementors
dbaron@2974 1188 should implement the non-prefixed syntax for any feature they consider to
dbaron@2974 1189 be correctly implemented according to spec.</p>
dbaron@2974 1190
jackalmage@6617 1191 <h3 id="cr-exit-criteria">CR Exit Criteria</h3>
dbaron@2974 1192
dbaron@3244 1193 <p>For this specification to be advanced to Proposed Recommendation,
dbaron@2974 1194 there must be at least two independent, interoperable implementations
dbaron@2974 1195 of each feature. Each feature may be implemented by a different set of
dbaron@2974 1196 products, there is no requirement that all features be implemented by
dbaron@2974 1197 a single product. For the purposes of this criterion, we define the
dbaron@2974 1198 following terms:
dbaron@2974 1199
dbaron@2974 1200 <dl>
dbaron@2974 1201 <dt>independent <dd>each implementation must be developed by a
dbaron@2974 1202 different party and cannot share, reuse, or derive from code
dbaron@2974 1203 used by another qualifying implementation. Sections of code that
dbaron@2974 1204 have no bearing on the implementation of this specification are
dbaron@2974 1205 exempt from this requirement.
dbaron@2974 1206
dbaron@2974 1207 <dt>interoperable <dd>passing the respective test case(s) in the
dbaron@2974 1208 official CSS test suite, or, if the implementation is not a Web
dbaron@2974 1209 browser, an equivalent test. Every relevant test in the test
dbaron@2974 1210 suite should have an equivalent test created if such a user
dbaron@2974 1211 agent (UA) is to be used to claim interoperability. In addition
dbaron@2974 1212 if such a UA is to be used to claim interoperability, then there
dbaron@2974 1213 must one or more additional UAs which can also pass those
dbaron@2974 1214 equivalent tests in the same way for the purpose of
dbaron@2974 1215 interoperability. The equivalent tests must be made publicly
dbaron@2974 1216 available for the purposes of peer review.
dbaron@2974 1217
dbaron@2974 1218 <dt>implementation <dd>a user agent which:
dbaron@2974 1219
dbaron@2974 1220 <ol class=inline>
dbaron@2974 1221 <li>implements the specification.
dbaron@2974 1222
dbaron@2974 1223 <li>is available to the general public. The implementation may
dbaron@2974 1224 be a shipping product or other publicly available version
dbaron@2974 1225 (i.e., beta version, preview release, or “nightly build”).
dbaron@2974 1226 Non-shipping product releases must have implemented the
dbaron@2974 1227 feature(s) for a period of at least one month in order to
dbaron@2974 1228 demonstrate stability.
dbaron@2974 1229
dbaron@2974 1230 <li>is not experimental (i.e., a version specifically designed
dbaron@2974 1231 to pass the test suite and is not intended for normal usage
dbaron@2974 1232 going forward).
dbaron@2974 1233 </ol>
dbaron@2974 1234 </dl>
dbaron@2974 1235
dbaron@2974 1236 <p>The specification will remain Candidate Recommendation for at least
dbaron@2974 1237 six months.
dbaron@2974 1238
fantasai@6831 1239 <h2 id="changes">
fantasai@6831 1240 Changes</h2>
dbaron@2974 1241
fantasai@6831 1242 <p>The following (non-editorial) changes were made to this specification since the
dbaron@7734 1243 <a href="http://www.w3.org/TR/2012/WD-css3-conditional-20121213/">13 December 2012 Working Draft</a>:
fantasai@6831 1244
fantasai@6831 1245 <ul>
dbaron@7734 1246 <li>Require whitespace around ''and'' and ''or'' and after ''not''.
dbaron@7734 1247 <li>Add note explaining that user preferences that effectively disable a property (e.g., high-contrast mode disabling colors) do not effect the definition of support.
dbaron@7734 1248 <li>Describe requirements for conditionText getter on CSSSupportsRule.
dbaron@7734 1249 <li>Clarify the definition of "literal match" in CSS.supports().
dbaron@7734 1250 <li>Specify behavior of CSSGroupingRule.insertRule when given an empty string or more than one syntactically valid rule.
fantasai@6831 1251 </ul>
dbaron@2974 1252
jackalmage@6617 1253 <h2 class=no-num id="acknowledgments">Acknowledgments</h2>
dbaron@2974 1254
dbaron@2974 1255 <p>
dbaron@2974 1256 Thanks to the ideas and feedback from
dbaron@3418 1257 Tab Atkins,
dbaron@7389 1258 Arthur Barstow,
dbaron@7389 1259 Ben Callahan,
dbaron@2974 1260 <span lang="tr">Tantek Çelik</span>,
dbaron@3418 1261 Alex Danilo,
dbaron@2974 1262 Elika Etemad,
dbaron@2974 1263 Pascal Germroth,
dbaron@2974 1264 <span lang="de">Björn Höhrmann</span>,
dbaron@3417 1265 Paul Irish,
dbaron@8325 1266 Brad Kemper,
dbaron@7044 1267 <span lang="nl">Anne van Kesteren</span>,
dbaron@3418 1268 Vitor Menezes,
dbaron@2977 1269 Alex Mogilevsky,
dbaron@2974 1270 Chris Moschini,
dbaron@7389 1271 James Nurthen,
dbaron@7389 1272 Simon Pieters,
dbaron@7389 1273 <span lang="fr">Florian Rivoal</span>,
dbaron@7389 1274 <span lang="fr">Simon Sapin</span>,
dbaron@7389 1275 Nicholas Shanks,
dbaron@2974 1276 Ben Ward,
dbaron@2974 1277 Zack Weinberg,
dbaron@3430 1278 Estelle Weyl,
dbaron@2974 1279 Boris Zbarsky,
dbaron@2974 1280 and all the rest of the <a href="http://lists.w3.org/Archives/Public/www-style/">www-style</a> community.
dbaron@2974 1281
dbaron@2974 1282 </p>
dbaron@2974 1283
jackalmage@6617 1284 <h2 class=no-num id="references">References</h2>
dbaron@2974 1285
dbaron@2974 1286
jackalmage@6617 1287 <h3 class="no-num" id="normative-references">Normative references</h3>
dbaron@2974 1288 <!--normative-->
dbaron@2974 1289
jackalmage@6617 1290 <h3 class="no-num" id="other-references">Other references</h3>
dbaron@2974 1291 <!--informative-->
dbaron@2974 1292
jackalmage@6617 1293 <h2 class="no-num" id="index">Index</h2>
dbaron@2974 1294 <!--index-->
dbaron@2974 1295
dbaron@2974 1296 </body>
dbaron@2974 1297 </html>
dbaron@2974 1298 <!-- Keep this comment at the end of the file
dbaron@2974 1299 Local variables:
dbaron@2974 1300 mode: sgml
dbaron@2974 1301 sgml-declaration:"~/SGML/HTML4.decl"
dbaron@2974 1302 sgml-default-doctype-name:"html"
dbaron@2974 1303 sgml-minimize-attributes:t
dbaron@2974 1304 sgml-nofill-elements:("pre" "style" "br")
dbaron@2974 1305 sgml-live-element-indicator:t
dbaron@2974 1306 sgml-omittag:nil
dbaron@2974 1307 sgml-shorttag:nil
dbaron@2974 1308 sgml-namecase-general:t
dbaron@2974 1309 sgml-general-insert-case:lower
dbaron@2974 1310 sgml-always-quote-attributes:t
dbaron@2974 1311 sgml-indent-step:nil
dbaron@2974 1312 sgml-indent-data:t
dbaron@2974 1313 sgml-parent-document:nil
dbaron@2974 1314 sgml-exposed-tags:nil
dbaron@2974 1315 sgml-local-catalogs:nil
dbaron@2974 1316 sgml-local-ecat-files:nil
dbaron@2974 1317 End:
dbaron@2974 1318 -->
dbaron@2974 1319

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