forked from w3c/csswg-drafts
-
Notifications
You must be signed in to change notification settings - Fork 0
Expand file tree
/
Copy pathOverview.src.html
More file actions
522 lines (402 loc) · 19.8 KB
/
Overview.src.html
File metadata and controls
522 lines (402 loc) · 19.8 KB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
<!DOCTYPE html>
<html lang="en"><head profile="http://www.w3.org/2006/03/hcard">
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>CSS Hierarchies Module Level 3</title>
<link rel="stylesheet" type="text/css" href="../default.css">
<link href="../csslogo.ico" rel="shortcut icon" type="image/x-icon">
<link rel="stylesheet" type="text/css" href="http://www.w3.org/StyleSheets/TR/w3c-unofficial">
<style type="text/css">
/* delete this block when you've cleared out all the .replaceme elements */
.replaceme {
border: solid red;
padding: 0 0.5em;
margin: 0 0.1em;
background: yellow;
color: green;
}
.replaceme:before {
content: "FIXME(";
color: black;
}
.replaceme:after {
content: ")";
color: black;
}
</style>
<style>
pre.idl { border:solid thin; background:#eee; color:#000; padding:0.5em }
pre.idl :link, pre.idl :visited { color:inherit; background:transparent }
</style>
</head>
<body><div class="head">
<!--logo-->
<h1>CSS Hierarchies Module Level 3</h1>
<h2 class="no-num no-toc">Unofficial Proposal Draft [DATE]</h2>
<dl>
<dt>This version:
<!--<dd><a href="[VERSION]">[VERSION]</a>-->
<dd><a href="//dev.w3.org/csswg/css3-hierarchies/">http://dev.w3.org/csswg/css3-hierarchies/</a>
<dt>Latest version:
<!--<dd><a href="[LATEST]">[LATEST]</a>-->
<dd><a href="//www.w3.org/TR/css3-hierarchies/">http://www.w3.org/TR/css3-hierarchies/</a>
<dt>Editor's draft:
<dd><a href="//dev.w3.org/csswg/css3-hierarchies/">http://dev.w3.org/csswg/css3-hierarchies/</a>
<!--
<dt>Previous version:
<dd><a href="http://www.w3.org/PreviousVersionURI">
http://www.w3.org/PreviousVersionURI</a>
-->
<dt>Feedback:</dt>
<dd><a href="mailto:www-style@w3.org?subject=%5Bcss-hierarchies%5D%20feedback"
>www-style@w3.org</a>
with subject line “<kbd>[css-hierarchies]
<var>… message topic …</var></kbd>”
(<a rel="discussion" href="http://lists.w3.org/Archives/Public/www-style/"
>archives</a>)
<dt>Editors:
<dd class="vcard"><span class="fn">Shane Stephens</span>,
<span class="org">Google, Inc.</span>,
<span class="email">shans@google.com</span>
<dd class="vcard">
<a href="http://xanthir.com/contact/" rel=url>
<span class=fn>Tab Atkins Jr.</span>,
</a>
<span class=org>Google, Inc.</span>
</dl>
<!--copyright-->
<hr title="Separator for header">
</div>
<details class=obsolete open>
<summary>Not Ready For Implementation</summary>
<p>
This spec is not yet ready for implementation.
It exists in this repository to record the ideas and promote discussion.
<p>
Before attempting to implement this spec,
please contact the CSSWG at www-style@w3.org.
</details>
<h2 class="no-num no-toc" id="abstract">Abstract</h2>
<p>CSS is a language for describing the rendering of structured documents
(such as HTML and XML) on screen, on paper, in speech, etc. This module
contains the features of CSS level 3 relating to the hierarchical nesting of style rules.
It includes and extends the functionality of CSS level 2 [[!CSS21]],
which builds on CSS level 1 [[CSS1]].
The main extension compared to level 2 is the ability to nest a style rule within another rule,
allowing greater modularisation and readibility of CSS documents.
<h2 class="no-num no-toc" id="status">Status of this document</h2>
<p><strong>This document is purely an Editor's Draft. It has not yet been adopted by the Working Group, and should not be considered to be part of CSS.</strong></p>
<p>The following features are at risk: …
<h2 class="no-num no-toc" id="contents">Table of contents</h2>
<!--toc-->
<h2 id="intro">
Introduction</h2>
<p><em>This section is not normative.</em>
<p>CSS beyond level 2 is a set of modules, divided up to allow the specifications to develop incrementally, along with their implementations. This specification is one of those modules.
<p>This module describes support for nesting a style rule within another style rule, allowing the inner rule's selector to reference the elements matched by the outer rule. This feature allows related styles to be aggregated into a single structure within the CSS document, improving readability and maintainability.
<h3 id="placement">
Module Interactions</h3>
<p>This module introduces new parser rules that extend the [[!CSS21]] parser model. This module introduces new parser rules that extend the [[CSS4SELECTORS]] module.</p>
<h3 id="values">
Values</h3>
<p>This specification does not define any new properties or values.
<h3 id="motivation">
Motivation</h3>
<p>CSS Rules for even moderately complicated web pages include lots of duplication for the purpose of styling related content. For example, here is a portion of the CSS markup for one version of the [[CSS3COLOR]] module:
<div class='example'>
<pre>
table.colortable td {text-align:center }
table.colortable td.c { text-transform:uppercase }
table.colortable td:first-child, table.colortable td:first-child+td { border:1px solid black }
table.colortable th {text-align:center; background:black; color:white }
table.tprofile th.title {background:gray; color:white}
table.tprofile th { width:29%;padding:2px }
table.tprofile td { width:71%;padding:2px }
table.hslexample { background: #808080; padding:1em; margin:0; float:left; }
table.hslexample td,table.hslexample th { font-size:smaller;width:3em }</pre>
</div>
<p>Hierarchies allow the grouping of related style rules, like this:
<div class='example'>
<pre>
table {
&.colortable {
& td {
text-align:center
&.c { text-transform:uppercase }
&:first-child, &:first-child + td { border:1px solid black }
}
& th {text-align:center; background:black; color:white }
&.tprofile {
& th {
width:29%;padding:2px;
&.title {background:gray; color:white}
}
& td { width:71%;padding:2px }
}
&.hslexample {
background: #808080; padding:1em; margin:0; float:left;
& td, & th { font-size:smaller;width:3em }
}
}</pre>
</div>
<p>Besides removing duplication, the grouping of related rules improves the readability and maintainability of the resulting CSS.
<h2 id="nesting-selector">
The & Selector</h2>
<p>This specification provides a mechanism that allows for the nesting of style rules within other style rules. A nested style rule can used anywhere that a declaration can be used.</p>
<p>In order to accomplish nesting, this specification defines a new simple selector called the nesting selector, represented in selectors by the '&' character. All complex selectors in the selector lists of nested style rules must start with the nesting selector. The nesting selector represents the elements matched by the parent style rule's selector list.</p>
<p class='issue'>Introducing the ''&'' character will cause issues with CSS embedded directly in XML, as it's the first character used in CSS syntax that either requires escaping or using CDATA. Do we need to change this?</p>
<div class='example'>
<p>The following example using Hierarchies:
<pre>
div {
& .keyword {color: red;}
&:hover {background-color: rgb(200, 255, 255);}
}</pre>
<p>...produces the same results as the following CSS:
<pre>
div .keyword {color:red;}
div:hover {background-color: rgb(200, 255, 255);}</pre>
</div>
<div class='example'>
<p>The following example using Hierarchies:
<pre>
div, p {
& .keyword, & .constant {color: red;}
}</pre>
<p>...produces the same results as the following CSS:
<pre>
div .keyword, div .constant, p .keyword, p .constant {
color:red;
}</pre>
</div>
<p>Multiple style rules can be embedded within a style rule. Style rules can be embedded arbitrarily deeply. Embedded style rules and properties can both appear in a single declaration block, and in any order.</p>
<div class='example'>
<p>The following example using Hierarchies:
<pre>
div, p {
& .keyword {color: green;}
font-size: 10px;
& .constant {
color: red;
&:hover:after { content: " [" attr(value) "]";}
background-color: green;
}
}</pre>
<p>...produces the same results as the following CSS:
<pre>
div, p {font-size: 10px;}
div .keyword, p .keyword {color: green;}
div .constant, p .constant {color: red; background-color: green;}
div .constant:hover:after, p .constant:hover:after {content: " [" attr(value) "]";}</pre>
</div>
<p class='note'>Note: Though it's unlikely that stylesheets authored with Hierarchies will be useful in legacy user agents, as the nested sections will be ignored by the error-handling rules, authors can minimize the damage caused by error-recovery by always putting properties before nested rules.</p>
<h2 id="Grammar">
Grammar modifications</h2>
<p>This specification alters the CSS Core Grammar and the Selectors grammar.</p>
<h3 id="css-2-grammar">
Core CSS Grammar</h3>
<p>The following modifications are required to the [[!CSS21]] grammar as defined in Section 4.1.1.</p>
<p>The ruleset rule is changed to:</p>
<pre>ruleset : selectors_group? ruleset-body</pre>
<p>The following rules are added:</p>
<pre>
ruleset-body : '{' S* ruleitem? [ ';' S* ruleitem? ]* '}' S*
ruleitem : declaration | nested-ruleset
nested-ruleset : nested-selectors-group ruleset-body</pre>
<h3 id="selectors4-grammar">
Selectors 4 Grammar</h3>
<p>The following modifications are required to the [[!CSS4SELECTORS]] grammar as defined in Section 16.1.</p>
<p>The following rules are added:</p>
<pre>
nested-selectors-group : nested-selector [ COMMA S* nested-selector ]
nested-selector : nested-compound-selector [ combinator compound-selector ]*
nested-compound-selector : NEST [ HASH | class | attrib | pseudo | negation ]*</pre>
<h3 id="selectors4-lexical-scanner">
Selectors 4 Lexical Scanner</h3>
<p>The following modifications are required to the [[!CSS4SELECTORS]] lexical scanner as defined in Section 16.2.</p>
<p>Immediately below:</p>
<pre>"-->" return CDC;</pre>
<p>the following rule is inserted:</p>
<pre>"&" return NEST;</pre>
<h2 id="cssom">
CSS Object Model Modifications</h2>
<p>The following attribute is required to be added to the CSSStyleRule object defined in Section 6.4.3 of [[!CSSOM]]:</p>
<pre class='idl'>
interface CSSStyleRule : CSSRule {
attribute DOMString selectorText;
<ins>readonly attribute DOMString expandedSelectorText;</ins>
<ins>readonly attribute CSSRuleList cssRules;</ins>
readonly attribute CSSStyleDeclaration style;
};</pre>
<p>The <code>cssRules</code> attribute must return a <code>CSSRuleList</code> object for the list of CSS rules specified within the style rule.</p>
<p>The <code>expandedSelectorText</code> attribute must return a <code>DOMString</code> object containing the result of replacing the ''&'' selector in the <code>selectorText</code> attribute with the <code>expandedSelectorText</code> attribute from the parent rule. If the rule has no parent rule, the <code>expandedSelectorText</code> attribute must return a <code>DOMString</code> object containing the same text as the <code>selectorText</code> attribute.</p>
<p class='issue'>The OM here is meant to reflect the OM for ''@media'' rules. In particular, the lack of a link from a rule to its parent matches rules nested in ''@media''. Should we add such a property to both of these?</p>
<h2 id="conformance">
Conformance</h2>
<h3 id="conventions">
Document Conventions</h3>
<p>Conformance requirements are expressed with a combination of
descriptive assertions and RFC 2119 terminology. The key words “MUST”,
“MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”,
“RECOMMENDED”, “MAY”, and “OPTIONAL” in the normative parts of this
document are to be interpreted as described in RFC 2119.
However, for readability, these words do not appear in all uppercase
letters in this specification.
<p>All of the text of this specification is normative except sections
explicitly marked as non-normative, examples, and notes. [[!RFC2119]]</p>
<p>Examples in this specification are introduced with the words “for example”
or are set apart from the normative text with <code>class="example"</code>,
like this:
<div class="example">
<p>This is an example of an informative example.</p>
</div>
<p>Informative notes begin with the word “Note” and are set apart from the
normative text with <code>class="note"</code>, like this:
<p class="note">Note, this is an informative note.</p>
<h3 id="conformance-classes">
Conformance Classes</h3>
<p>Conformance to <var class="replaceme">CSS TEMPLATE Module</var>
is defined for three conformance classes:
<dl>
<dt><dfn title="style sheet!!as conformance class">style sheet</dfn>
</dt><dd>A <a href="http://www.w3.org/TR/CSS21/conform.html#style-sheet">CSS
style sheet</a>.
</dd><dt><dfn>renderer</dfn></dt>
<dd>A <a href="http://www.w3.org/TR/CSS21/conform.html#user-agent">UA</a>
that interprets the semantics of a style sheet and renders
documents that use them.
</dd><dt><dfn id="authoring-tool">authoring tool</dfn></dt>
<dd>A <a href="http://www.w3.org/TR/CSS21/conform.html#user-agent">UA</a>
that writes a style sheet.
</dd></dl>
<p>A style sheet is conformant to <var class="replaceme">CSS TEMPLATE Module</var>
if all of its declarations that use properties defined in this module
have values that are valid according to the generic CSS grammar and the
individual grammars of each property as given in this module.
<p>A renderer is conformant to <var class="replaceme">CSS TEMPLATE Module</var>
if, in addition to interpreting the style sheet as defined by the
appropriate specifications, it supports all the features defined
by <var class="replaceme">CSS TEMPLATE Module</var> by parsing them correctly
and rendering the document accordingly. However, the inability of a
UA to correctly render a document due to limitations of the device
does not make the UA non-conformant. (For example, a UA is not
required to render color on a monochrome monitor.)
<p>An authoring tool is conformant to <var class="replaceme">CSS TEMPLATE Module</var>
if it writes style sheets that are syntactically correct according to the
generic CSS grammar and the individual grammars of each feature in
this module, and meet all other conformance requirements of style sheets
as described in this module.
<h3 id="partial">
Partial Implementations</h3>
<p>So that authors can exploit the forward-compatible parsing rules to
assign fallback values, CSS renderers <strong>must</strong>
treat as invalid (and <a href="http://www.w3.org/TR/CSS21/conform.html#ignore">ignore
as appropriate</a>) any at-rules, properties, property values, keywords,
and other syntactic constructs for which they have no usable level of
support. In particular, user agents <strong>must not</strong> selectively
ignore unsupported component values and honor supported values in a single
multi-value property declaration: if any value is considered invalid
(as unsupported values must be), CSS requires that the entire declaration
be ignored.</p>
<h3 id="experimental">
Experimental Implementations</h3>
<p>To avoid clashes with future CSS features, the CSS2.1 specification
reserves a <a href="http://www.w3.org/TR/CSS21/syndata.html#vendor-keywords">prefixed
syntax</a> for proprietary and experimental extensions to CSS.
<p>Prior to a specification reaching the Candidate Recommendation stage
in the W3C process, all implementations of a CSS feature are considered
experimental. The CSS Working Group recommends that implementations
use a vendor-prefixed syntax for such features, including those in
W3C Working Drafts. This avoids incompatibilities with future changes
in the draft.
</p>
<h3 id="testing">Non-Experimental Implementations</h3>
<p>Once a specification reaches the Candidate Recommendation stage,
non-experimental implementations are possible, and implementors should
release an unprefixed implementation of any CR-level feature they
can demonstrate to be correctly implemented according to spec.
<p>To establish and maintain the interoperability of CSS across
implementations, the CSS Working Group requests that non-experimental
CSS renderers submit an implementation report (and, if necessary, the
testcases used for that implementation report) to the W3C before
releasing an unprefixed implementation of any CSS features. Testcases
submitted to W3C are subject to review and correction by the CSS
Working Group.
<p>Further information on submitting testcases and implementation reports
can be found from on the CSS Working Group's website at
<a href="http://www.w3.org/Style/CSS/Test/">http://www.w3.org/Style/CSS/Test/</a>.
Questions should be directed to the
<a href="http://lists.w3.org/Archives/Public/public-css-testsuite">public-css-testsuite@w3.org</a>
mailing list.
<h3 id="cr-exit-criteria">
CR Exit Criteria</h3>
<p class="issue">[Change or remove the following CR exit criteria if
the spec is not a module, but, e.g., a Note or a profile. This text was <a href="http://www.w3.org/Style/CSS/Tracker/actions/44"> decided on 2008-06-04.</a>]</p>
<p>
For this specification to be advanced to Proposed Recommendation,
there must be at least two independent, interoperable implementations
of each feature. Each feature may be implemented by a different set of
products, there is no requirement that all features be implemented by
a single product. For the purposes of this criterion, we define the
following terms:
<dl>
<dt>independent </dt><dd>each implementation must be developed by a
different party and cannot share, reuse, or derive from code
used by another qualifying implementation. Sections of code that
have no bearing on the implementation of this specification are
exempt from this requirement.
</dd><dt>interoperable </dt><dd>passing the respective test case(s) in the
official CSS test suite, or, if the implementation is not a Web
browser, an equivalent test. Every relevant test in the test
suite should have an equivalent test created if such a user
agent (UA) is to be used to claim interoperability. In addition
if such a UA is to be used to claim interoperability, then there
must one or more additional UAs which can also pass those
equivalent tests in the same way for the purpose of
interoperability. The equivalent tests must be made publicly
available for the purposes of peer review.
</dd><dt>implementation </dt><dd>a user agent which:
<ol class="inline">
<li>implements the specification.
</li><li>is available to the general public. The implementation may
be a shipping product or other publicly available version
(i.e., beta version, preview release, or “nightly build”).
Non-shipping product releases must have implemented the
feature(s) for a period of at least one month in order to
demonstrate stability.
</li><li>is not experimental (i.e., a version specifically designed
to pass the test suite and is not intended for normal usage
going forward).
</li></ol>
</dd></dl>
<p>The specification will remain Candidate Recommendation for at least
six months.
<h2 class="no-num" id="acknowledgments">Acknowledgments</h2>
<p><var class="replaceme">[acknowledgments]</var></p>
<h2 class="no-num" id="references">References</h2>
<h3 class="no-num" id="normative-references">Normative references</h3>
<!--normative-->
<h3 class="no-num" id="other-references">Other references</h3>
<!--informative-->
<h2 class="no-num" id="index">Index</h2>
<!--index-->
<!-- Keep this comment at the end of the file
Local variables:
mode: sgml
sgml-declaration:"~/SGML/HTML4.decl"
sgml-default-doctype-name:"html"
sgml-minimize-attributes:t
sgml-nofill-elements:("pre" "style" "br")
sgml-live-element-indicator:t
sgml-omittag:nil
sgml-shorttag:nil
sgml-namecase-general:t
sgml-general-insert-case:lower
sgml-always-quote-attributes:t
sgml-indent-step:nil
sgml-indent-data:t
sgml-parent-document:nil
sgml-exposed-tags:nil
sgml-local-catalogs:nil
sgml-local-ecat-files:nil
End:
-->