Wed, 10 Aug 2011 23:44:59 +0000
Generic Datatype Reorganization Part IV: Other Dimension Types
Also, remove various normative bits that are wrong, such as angle normalization.
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30 <h1 id=css3-template>CSS3 Values and Units</h1>
32 <h2 class="no-num no-toc" id=longstatus-date>Editor's Draft 10 August 2011</h2>
34 <dl>
35 <dt>This version:
37 <dd><a
38 href="http://www.w3.org/TR/2011/ED-css3-values-20110810/">http://www.w3.org/TR/2011/ED-css3-values-20110810/</a>
40 <dt>Latest version:
42 <dd><a
43 href="http://www.w3.org/TR/css3-values">http://www.w3.org/TR/css3-values</a>
45 <dt>Previous version:
47 <dd><a
48 href="http://www.w3.org/TR/2005/WD-css3-values-20050726">http://www.w3.org/TR/2005/WD-css3-values-20050726</a>
50 <dt>Editors:
52 <dd>Håkon Wium Lie, Opera Software <howcome@opera.com>
54 <dd>Tab Atkins, Google
56 <dd>Elika J. Etemad, Invited Expert
57 </dl>
58 <!--begin-copyright-->
59 <p class=copyright><a
60 href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
61 rel=license>Copyright</a> © 2011 <a
62 href="http://www.w3.org/"><acronym title="World Wide Web
63 Consortium">W3C</acronym></a><sup>®</sup> (<a
64 href="http://www.csail.mit.edu/"><acronym title="Massachusetts Institute
65 of Technology">MIT</acronym></a>, <a href="http://www.ercim.eu/"><acronym
66 title="European Research Consortium for Informatics and
67 Mathematics">ERCIM</acronym></a>, <a
68 href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. W3C <a
69 href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
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73 href="http://www.w3.org/Consortium/Legal/copyright-documents">document
74 use</a> rules apply.</p>
75 <!--end-copyright-->
76 <hr title="Separator for header">
77 </div>
79 <h2 class="no-num no-toc" id=abstract>Abstract</h2>
81 <p>This CSS3 module describes the various values and units that CSS
82 properties accept. Also, it describes how values are computed from
83 "specified" through "computed" and "used" into "actual" values. The main
84 purpose of this module is to define common values and units in one
85 specification which can be referred to by other modules. As such, it does
86 not make sense to claim conformance with this module alone.
88 <h2 class="no-num no-toc" id=status>Status of this document</h2>
89 <!--begin-status-->
91 <p>This is a public copy of the editors' draft. It is provided for
92 discussion only and may change at any moment. Its publication here does
93 not imply endorsement of its contents by W3C. Don't cite this document
94 other than as work in progress.
96 <p>The (<a
97 href="http://lists.w3.org/Archives/Public/www-style/">archived</a>) public
98 mailing list <a
99 href="mailto:www-style@w3.org?Subject=%5Bcss3-values%5D%20PUT%20SUBJECT%20HERE">
100 www-style@w3.org</a> (see <a
101 href="http://www.w3.org/Mail/Request">instructions</a>) is preferred for
102 discussion of this specification. When sending e-mail, please put the text
103 “css3-values” in the subject, preferably like this:
104 “[<!---->css3-values<!---->] <em>…summary of
105 comment…</em>”
107 <p>This document was produced by the <a href="/Style/CSS/members">CSS
108 Working Group</a> (part of the <a href="/Style/">Style Activity</a>).
110 <p>This document was produced by a group operating under the <a
111 href="/Consortium/Patent-Policy-20040205/">5 February 2004 W3C Patent
112 Policy</a>. W3C maintains a <a href="/2004/01/pp-impl/32061/status"
113 rel=disclosure>public list of any patent disclosures</a> made in
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119 href="/Consortium/Patent-Policy-20040205/#sec-Disclosure">section 6 of the
120 W3C Patent Policy</a>.</p>
121 <!--end-status-->
123 <p>All features described in this specification that also exist in CSS 2.1
124 <a href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a> are intended
125 to be backwards compatible. In case of conflict between this draft and
126 CSS 2.1 <a href="#CSS21"
127 rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>, CSS 2.1 probably
128 represents the intention of the CSS WG better than this draft (other than
129 on values and units that are new to CSS3).
131 <p>This is a draft of a <a href="http://www.w3.org/TR/css3-roadmap/">module
132 of CSS level 3</a>. It will probably be bundled with some other modules
133 before it becomes a <a href="http://www.w3.org/TR/#About">W3C
134 Recommendation</a>.
136 <h2 class="no-num no-toc" id=contents>Table of contents</h2>
137 <!--begin-toc-->
139 <ul class=toc>
140 <li><a href="#introduction"><span class=secno>1. </span>Introduction</a>
141 <ul class=toc>
142 <li><a href="#placement"><span class=secno>1.1. </span> Module
143 Interactions</a>
144 </ul>
146 <li><a href="#value-defs"><span class=secno>2. </span> Value Definition
147 Syntax</a>
148 <ul class=toc>
149 <li><a href="#component-types"><span class=secno>2.1. </span> Component
150 value types</a>
152 <li><a href="#component-combinators"><span class=secno>2.2. </span>
153 Component value combinators</a>
155 <li><a href="#component-multipliers"><span class=secno>2.3. </span>
156 Component value multipliers</a>
158 <li><a href="#component-whitespace"><span class=secno>2.4. </span>
159 Component values and white space</a>
161 <li><a href="#value-examples"><span class=secno>2.5. </span> Property
162 value examples</a>
163 </ul>
165 <li><a href="#syntax-and-terminology"><span class=secno>3. </span>Syntax
166 and terminology</a>
167 <ul class=toc>
168 <li><a href="#strings"><span class=secno>3.1. </span>Strings</a>
170 <li><a href="#functional-notation"><span class=secno>3.2.
171 </span>Functional notation</a>
172 </ul>
174 <li><a href="#idents"><span class=secno>4. </span> Keywords and
175 Identifiers</a>
176 <ul class=toc>
177 <li><a href="#keywords"><span class=secno>4.1. </span> Pre-defined
178 Keywords</a>
179 <ul class=toc>
180 <li><a href="#initial-inherit"><span class=secno>4.1.1. </span> The
181 ‘<code class=css>initial</code>’ and ‘<code
182 class=css>inherit</code>’ keywords</a>
183 </ul>
185 <li><a href="#identifiers"><span class=secno>4.2. </span> User-defined
186 Identifiers: the ‘<code
187 class=css><identifier></code>’ type</a>
188 </ul>
190 <li><a href="#numeric-types"><span class=secno>5. </span> Numeric Data
191 Types</a>
192 <ul class=toc>
193 <li><a href="#integers"><span class=secno>5.1. </span> Integers: the
194 ‘<code class=css><integer></code>’ type</a>
196 <li><a href="#numbers"><span class=secno>5.2. </span> Numbers: the
197 ‘<code class=css><number></code>’ type</a>
199 <li><a href="#percentages"><span class=secno>5.3. </span> Percentages:
200 the ‘<code class=css><percentage></code>’ type</a>
201 </ul>
203 <li><a href="#lengths"><span class=secno>6. </span> Distance Units: the
204 ‘<code class=css><length></code>’ type</a>
205 <ul class=toc>
206 <li><a href="#relative-lengths"><span class=secno>6.1. </span> Relative
207 lengths</a>
208 <ul class=toc>
209 <li><a href="#font-relative-lengths"><span class=secno>6.1.1. </span>
210 Font-relative lengths: the ‘<code class=css>em</code>’,
211 ‘<code class=css>ex</code>’, ‘<code
212 class=css>ch</code>’, ‘<code class=css>rem</code>’
213 units</a>
215 <li><a href="#viewport-relative-lengths"><span class=secno>6.1.2.
216 </span> Viewport-relative lengths: the ‘<code
217 class=css>vw</code>’, ‘<code class=css>vh</code>’,
218 ‘<code class=css>vm</code>’ units</a>
219 </ul>
221 <li><a href="#absolute-lengths"><span class=secno>6.2. </span> Absolute
222 lengths: the ‘<code class=css>cm</code>’, ‘<code
223 class=css>mm</code>’, ‘<code class=css>in</code>’,
224 ‘<code class=css>pt</code>’, ‘<code
225 class=css>pc</code>’, ‘<code class=css>px</code>’
226 units </a>
227 </ul>
229 <li><a href="#other-units"><span class=secno>7. </span> Other Units</a>
230 <ul class=toc>
231 <li><a href="#angles"><span class=secno>7.1. </span> Angles: the
232 ‘<code class=css><angle></code>’ type and
233 ‘<code class=css>deg</code>’, ‘<code
234 class=css>grad</code>’, ‘<code class=css>rad</code>’,
235 ‘<code class=css>turn</code>’ units</a>
237 <li><a href="#time"><span class=secno>7.2. </span> Times: the
238 ‘<code class=css><time></code>’ type and ‘<code
239 class=css>s</code>’, ‘<code class=css>ms</code>’
240 units</a>
242 <li><a href="#frequencies-the-ltfrequencygt-type-and-h"><span
243 class=secno>7.3. </span>Frequencies: the ‘<code
244 class=css><frequency></code>’ type and ‘<code
245 class=css>Hz</code>’, ‘<code class=css>kHz</code>’
246 units</a>
247 <ul class=toc>
248 <li><a href="#the-calc-min-and-max-functions"><span class=secno>7.3.1.
249 </span>The ‘<code class=property>calc</code>’,
250 ‘<code class=property>min</code>’ and ‘<code
251 class=property>max</code>’ functions</a>
252 </ul>
254 <li><a href="#ltstringgt"><span class=secno>7.4.
255 </span><string></a>
257 <li><a href="#ltcolorgt"><span class=secno>7.5. </span><color></a>
260 <li><a href="#ltattrgt"><span class=secno>7.6. </span><attr></a>
262 <li><a href="#uris"><span class=secno>7.7. </span><url></a>
264 <li><a href="#ltimagegt"><span class=secno>7.8. </span><image></a>
267 <li><a href="#ltfractiongt"><span class=secno>7.9.
268 </span><fraction></a>
269 <ul class=toc>
270 <li><a href="#the-fr-unit"><span class=secno>7.9.1. </span>The
271 ‘<code class=property>fr</code>’ unit</a>
272 </ul>
274 <li><a href="#ltgridgt"><span class=secno>7.10. </span><grid></a>
275 <ul class=toc>
276 <li><a href="#the-gr-unit"><span class=secno>7.10.1. </span>The
277 ‘<code class=property>gr</code>’ unit</a>
278 </ul>
279 </ul>
281 <li><a href="#specified-computed-used-and-actual-value"><span
282 class=secno>8. </span>Specified, computed, used, and actual values</a>
283 <ul class=toc>
284 <li><a href="#finding-the-specified-value"><span class=secno>8.1.
285 </span>Finding the specified value</a>
287 <li><a href="#finding-the-computed-value"><span class=secno>8.2.
288 </span>Finding the computed value</a>
290 <li><a href="#finding-the-used-value"><span class=secno>8.3.
291 </span>Finding the used value</a>
293 <li><a href="#finding-the-actual-value"><span class=secno>8.4.
294 </span>Finding the actual value</a>
295 </ul>
297 <li class=no-num><a href="#acknowledgments">Acknowledgments</a>
299 <li class=no-num><a href="#references">References</a>
300 <ul class=toc>
301 <li class=no-num><a href="#normative-references">Normative
302 references</a>
304 <li class=no-num><a href="#other-references">Other references</a>
305 </ul>
307 <li class=no-num><a href="#index">Index</a>
308 </ul>
309 <!--end-toc-->
311 <h2 id=introduction><span class=secno>1. </span>Introduction</h2>
313 <p>The value definition field of each CSS property can contain keywords,
314 data types (which appear between ‘<code class=css><</code>’
315 and ‘<code class=css>></code>’), and information on how they
316 can be combined. Generic data types (<a
317 href="#length-value"><code><length></code></a> being the most widely
318 used) that can be used by many properties are described in this
319 specification, while more specific data types (e.g.,
320 <code><border-width></code>) are described in the corresponding
321 modules. </code>
323 <h3 id=placement><span class=secno>1.1. </span> Module Interactions</h3>
325 <p>This module replaces and extends the data type definitions in <a
326 href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a> sections <a
327 href="http://www.w3.org/TR/CSS21/about.html#value-defs">1.4.2.1</a>, <a
328 href="http://www.w3.org/TR/CSS21/syndata.html#values">4.3</a>, and <a
329 href="http://www.w3.org/TR/CSS21/aural.html#aural-intro">A.2</a>.
331 <h2 id=value-defs><span class=secno>2. </span> Value Definition Syntax</h2>
333 <p>The syntax described here is used to define the set of valid values for
334 CSS properties. A property value can have one or more components.
336 <h3 id=component-types><span class=secno>2.1. </span> Component value types</h3>
338 <p>Component value types are designated in several ways:
340 <ol>
341 <li><a href="#keyword">keyword</a> values (such as ‘<code
342 class=css>auto</code>’, ‘<code class=css>disc</code>’,
343 etc.), which appear literally, without quotes (e.g. <code>auto</code>)
345 <li>basic data types, which appear between ‘<code
346 class=css><</code>’ and ‘<code
347 class=css>></code>’ (e.g., <a
348 href="#length-value"><code><length></code></a>, <a
349 href="#percentage-value"><code><percentage></code></a>, etc.).
351 <li>types that have the same range of values as a property bearing the
352 same name (e.g., <code><'border-width'></code>
353 <code><'background-attachment'></code>, etc.). In this case, the
354 type name is the property name (complete with quotes) between the
355 brackets. Such a type does <em>not</em> include the value ‘<code
356 class=property>inherit</code>’.
358 <li>non-terminals that do not share the same name as a property. In this
359 case, the non-terminal name appears between ‘<code
360 class=css><</code>’ and ‘<code
361 class=css>></code>’, as in <code><spacing></code>. Notice
362 the distinction between <code><border-width></code> and
363 <code><'border-width'></code>: the latter is defined as the value
364 of the ‘<code class=property>border-width</code>’ property,
365 the former requires an explicit expansion elsewhere. The definition of a
366 non-terminal is located near its first appearance in the specification.
367 </ol>
369 <p>Some property value definitions also include the slash (/) and/or the
370 comma (,) as literals. These represent their corresponding tokens.
372 <p>All CSS properties also accept the keyword values ‘<code
373 class=css>inherit</code>’ and ‘<code
374 class=css>initial</code>’ as their property value, but for
375 readability these are not listed explicitly in the property value syntax
376 definitions. These keywords cannot be combined with other component values
377 in same declaration; such a declaration is invalid. For example,
378 ‘<code class=css>background: url(corner.png) no-repeat,
379 inherit;</code>’ is invalid.
381 <h3 id=component-combinators><span class=secno>2.2. </span> Component value
382 combinators</h3>
384 <p>Component values can be arranged into property values as follows:
386 <ul>
387 <li>Several juxtaposed words mean that all of them must occur, in the
388 given order.
390 <li>A double ampersand (&&) separates two or more components, all of which
391 must occur, in any order.
393 <li>A double bar (||) separates two or more options: one or more of them
394 must occur, in any order.
396 <li>A bar (|) separates two or more alternatives: exactly one of them must
397 occur.
399 <li>Brackets ([ ]) are for grouping.
400 </ul>
402 <p>Juxtaposition is stronger than the double ampersand, the double
403 ampersand is stronger than the double bar, and the double bar is stronger
404 than the bar. Thus, the following lines are equivalent:
406 <pre>
407 <!----> a b | c || d && e f
408 <!---->[ a b ] | [ c || [ d && [ e f ]]]</pre>
410 <h3 id=component-multipliers><span class=secno>2.3. </span> Component value
411 multipliers</h3>
413 <p>Every type, keyword, or bracketed group may be followed by one of the
414 following modifiers:
416 <ul>
417 <li>An asterisk (*) indicates that the preceding type, word, or group
418 occurs zero or more times.
420 <li>A plus (+) indicates that the preceding type, word, or group occurs
421 one or more times.
423 <li>A question mark (?) indicates that the preceding type, word, or group
424 is optional.
426 <li>A pair of numbers in curly braces ({<var>A</var>,<var>B</var>})
427 indicates that the preceding type, word, or group occurs at least
428 <var>A</var> and at most <var>B</var> times.
430 <li>A hash mark (#) indicates that the preceding type, word, or group
431 occurs one or more times, separated by comma tokens.
432 </ul>
434 <h3 id=component-whitespace><span class=secno>2.4. </span> Component values
435 and white space</h3>
437 <p>Component values are specified in terms of tokens, as described in <a
438 href="http://www.w3.org/TR/CSS21/syndata.html#tokenization">Chapter 4</a>
439 of <a href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>. As the
440 grammar allows spaces between tokens in the components of the
441 <code>value</code> production, spaces may appear between tokens in
442 property values.
444 <p class=note>Note: In many cases, spaces will in fact be <em>required</em>
445 between tokens in order to distinguish them from each other. For example,
446 the value ‘<code class=css>1em2em</code>’ would be parsed as a
447 single <code>DIMEN</code> token with the number ‘<code
448 class=css>1</code>’ and the identifier ‘<code
449 class=css>em2em</code>’, which is an invalid unit. In this case, a
450 space would be required before the ‘<code class=css>2</code>’
451 to get this parsed as the two lengths ‘<code
452 class=css>1em</code>’ and ‘<code class=css>2em</code>’.
454 <h3 id=value-examples><span class=secno>2.5. </span> Property value
455 examples</h3>
457 <p>Below are some examples of properties with their corresponding value
458 definition fields
460 <div class=example>
461 <table class=data id=propvalues>
462 <thead>
463 <tr>
464 <th>Property
466 <th>Value definition field
468 <th>Example value
470 <tbody>
471 <tr>
472 <td>‘<code class=property>orphans</code>’
474 <td><integer>
476 <td>‘<code class=css>3</code>’
478 <tr>
479 <td>‘<code class=property>text-align</code>’
481 <td>left | right | center | justify
483 <td>‘<code class=css>center</code>’
485 <tr>
486 <td>‘<code class=property>padding-top</code>’
488 <td><length> | <percentage>
490 <td>‘<code class=css>5%</code>’
492 <tr>
493 <td>‘<code class=property>outline-color</code>’
495 <td><color> | invert
497 <td>‘<code class=css>#fefefe</code>’
499 <tr>
500 <td>‘<code class=property>text-decoration</code>’
502 <td>none | underline || overline || line-through || blink
504 <td>‘<code class=css>overline underline</code>’
506 <tr>
507 <td>‘<code class=property>font-family</code>’
509 <td><family-name>#
511 <td>‘<code class=css>"Gill Sans", Futura,
512 sans-serif</code>’
514 <tr>
515 <td>‘<code class=property>border-width</code>’
517 <td>[ <length> | thick | medium | thin ]{1,4}
519 <td>‘<code class=css>2px medium 4px</code>’
521 <tr>
522 <td>‘<code class=property>text-shadow</code>’
524 <td>[ inset? && [ <length>{2,4} && <color>? ] ]# | none
526 <td>‘<code class=css>3px 3px rgba(50%, 50%, 50%, 50%),
527 lemonchiffon 0 0 4px inset</code>’
529 <tr>
530 <td>‘<code class=property>voice-pitch</code>’
532 <td>
533 <pre class=value><frequency> && absolute |
534 <!-- -->[[x-low | low | medium | high | x-high] ||
535 <!-- --> [<frequency> | <semitones> | <percentage>]]</pre>
537 <td>‘<code class=css>-2st x-low</code>’
538 </table>
539 </div>
541 <h2 id=syntax-and-terminology><span class=secno>3. </span>Syntax and
542 terminology</h2>
544 <p>The generic data types described in the next sections use some common
545 syntactic building blocks and terms that are described in this section.
547 <h3 id=strings><span class=secno>3.1. </span>Strings</h3>
549 <p>A <dfn id=string>string</dfn> is a sequence of characters enclosed by
550 double quotes or single quotes. Double quotes cannot occur inside double
551 quotes, unless escaped (as ‘<code class=css>\"</code>’ or as
552 ‘<code class=css>\22</code>’). Analogously for single quotes
553 ("\‘<code class=css>" or "\27").<!--"--> </code>
555 <div class=example>
556 <pre>
557 content: "this is a ’string'.";
558 content: "this is a \"string\".";
559 content: ‘<code class=css>this is a "string".</code>’;
560 content: ‘<code class=css>this is a \</code>’string\‘<code class=css>.</code>’;
561 </pre>
562 </div>
564 <p>A string cannot directly contain a <span class=index
565 id=newline>newline</span>. To include a newline in a string, use the
566 escape "\A" (hexadecimal A is the line feed character in Unicode (U+000A),
567 but represents the generic notion of "newline" in CSS). See the <span
568 class=property>‘<code class=property>content</code>’</span>
569 property for an example.
571 <p>It is possible to break strings over several lines, for aesthetic or
572 other reasons, but in such a case the newline itself has to be escaped
573 with a backslash (\). The newline is subsequently removed from the string.
574 For instance, the following two selectors are exactly the same:
576 <div class=example>
577 <p style="display:none">Example(s):</p>
579 <pre>
580 a[title="a not s\
581 o very long title"] {/*...*/}
582 a[title="a not so very long title"] {/*...*/}
583 </pre>
584 </div>
586 <h3 id=functional-notation><span class=secno>3.2. </span>Functional
587 notation</h3>
589 <p>Some values use a <dfn id=functional-notation0>functional notation</dfn>
590 to type values and to and lump values together. The syntax starts with the
591 name of the function followed by a left parenthesis followed by optional
592 whitespace followed by the argument(s) to the functions followed by
593 optional whitespace followed by a right parenthesis. If a function takes
594 more than one argument, the arguments are separated by a comma
595 (‘<code class=css>,</code>’) with optional whitespace before
596 and after the comma.
598 <div class=example> background: url(http://www.example.org/image); color:
599 rgb(100, 200, 50 );</div>
601 <p>Some properties accept space- or comma-separated lists of values. A
602 value that is composed of several values with spaces or commas between
603 them, is called a <dfn id=compound-value>compound value</dfn>. A value
604 that is not a compound value is a <dfn id=simple-value>simple value</dfn>.
607 <h2 id=idents><span class=secno>4. </span> Keywords and Identifiers</h2>
609 <p>An <dfn id=identifier>identifier</dfn> is a sequence of characters
610 conforming to the <code>IDENT</code> token in the <a
611 href="http://www.w3.org/TR/CSS21/syndata.html#tokenization">grammar</a>.
612 <a href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a> Identifiers
613 cannot be quoted; otherwise they would be interpreted as a string.
615 <h3 id=keywords><span class=secno>4.1. </span> Pre-defined Keywords</h3>
617 <p>In the value definition fields, keywords with a pre-defined meaning
618 appear literally. Keywords are CSS <i>identifiers</i> and are interpreted
619 case-insensitively within the ASCII range (i.e., [a-z] and [A-Z] are
620 equivalent).
622 <div class=example>
623 <p>For example, here is the value definition for the ‘<code
624 class=property>border-collapse</code>’ property:</p>
626 <pre>Value: collapse | separate</pre>
628 <p>And here is an example of its use:</p>
630 <pre>table { border-collapse: separate }</pre>
631 </div>
633 <h4 id=initial-inherit><span class=secno>4.1.1. </span> The ‘<code
634 class=css>initial</code>’ and ‘<code
635 class=css>inherit</code>’ keywords</h4>
637 <p>As defined <a href="#component-types">above</a>, all properties accept
638 the ‘<code class=css>initial</code>’ and ‘<code
639 class=css>inherit</code>’ keywords, which represent value concepts
640 common to all CSS properties.
642 <p>The <dfn id=inherit>‘<code class=css>inherit</code>’</dfn>
643 keyword is <a
644 href="http://www.w3.org/TR/CSS21/cascade.html#value-def-inherit">defined</a>
645 in <a href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>.
647 <p>The <dfn id=initial>‘<code class=css>initial</code>’</dfn>
648 keyword represents the value that is designated as the property's initial
649 value. <a href="#CSS3CASCADE"
650 rel=biblioentry>[CSS3CASCADE]<!--{{CSS3CASCADE}}--></a>
652 <p class=issue>Should these keywords affect the specified or computed
653 value? See <a
654 href="http://lists.w3.org/Archives/Public/www-style/2011Jan/0075.html">various</a>
655 <a
656 href="http://lists.w3.org/Archives/Public/www-style/2011May/0402.html">issues</a>.
659 <p class=issue>Would it be useful to have a ‘<code
660 class=property>default</code>’ value, defined to be equivalent to <a
661 class=css href="#inherit">‘<code
662 class=property>inherit</code>’</a> for properties that are inherited
663 by default and equivalent to <a class=css href="#initial">‘<code
664 class=property>initial</code>’</a> for properties that are not
665 inherited by default? This might be easier for authors to use than <a
666 class=css href="#initial">‘<code
667 class=property>initial</code>’</a> and <a class=css
668 href="#inherit">‘<code class=property>inherit</code>’</a>
669 since it wouldn't require thinking about whether a property is inherited
670 by default or not (which isn't obvious for some properties, such as
671 text-decoration and visibility).
673 <h3 id=identifiers><span class=secno>4.2. </span> User-defined Identifiers:
674 the ‘<a href="#identifier-value"><code
675 class=css><identifier></code></a>’ type</h3>
677 <p>Some properties accept arbitrary user-defined identifiers as a component
678 value. This generic data type is denoted by <dfn
679 id=identifier-value><code><identifier></code></dfn>, and represents
680 any valid CSS <a href="#identifier"><i>identifier</i></a> that does not
681 otherwise appear as a pre-defined keyword in that property's value
682 definition. Such identifiers are fully case-sensitive, even in the ASCII
683 range (e.g. ‘<code class=css>example</code>’ and ‘<code
684 class=css>EXAMPLE</code>’ are two different, unrelated user-defined
685 identifiers).
687 <h2 id=numeric-types><span class=secno>5. </span> Numeric Data Types</h2>
689 <h3 id=integers><span class=secno>5.1. </span> Integers: the ‘<a
690 href="#integer-value"><code class=css><integer></code></a>’
691 type</h3>
693 <p>Integer values are denoted by <dfn
694 id=integer-value><code><integer></code></dfn>. An <dfn
695 id=integer>integer</dfn> is one or more decimal digits ‘<code
696 class=css>0</code>’ through ‘<code class=css>9</code>’
697 and corresponds to a subset of the <a
698 href="#number"><code>NUMBER</code></a> token in the <a
699 href="http://www.w3.org/TR/CSS21/syndata.html#tokenization">grammar</a>.
700 Integers may be immediately preceded by ‘<code
701 class=css>-</code>’ or ‘<code class=css>+</code>’ to
702 indicate the sign.
704 <p>Properties may restrict the integer value to some range. If the value is
705 outside the allowed range, the declaration is invalid and must be <a
706 href="http://www.w3.org/TR/CSS21/conform.html#ignore">ignored</a>.
708 <h3 id=numbers><span class=secno>5.2. </span> Numbers: the ‘<a
709 href="#number-value"><code class=css><number></code></a>’ type</h3>
711 <p>Number values are denoted by <dfn
712 id=number-value><code><number></code></dfn>. A <dfn
713 id=number>number</dfn> is either an <a href="#integer"><i>integer</i></a>,
714 or zero or more decimal digits followed by a dot (.) followed by one or
715 more decimal digits. It corresponds to the <a
716 href="#number"><code>NUMBER</code></a> token in the <a
717 href="http://www.w3.org/TR/CSS21/syndata.html#tokenization">grammar</a>.
718 Like integers, numbers may also be immediately preceded by ‘<code
719 class=css>-</code>’ or ‘<code class=css>+</code>’ to
720 indicate the sign.
722 <p>Properties may restrict the number value to some range. If the value is
723 outside the allowed range, the declaration is invalid and must be <a
724 href="http://www.w3.org/TR/CSS21/conform.html#ignore">ignored</a>.
726 <h3 id=percentages><span class=secno>5.3. </span> Percentages: the
727 ‘<a href="#percentage-value"><code
728 class=css><percentage></code></a>’ type</h3>
730 <p>A percentage value is denoted by <dfn
731 id=percentage-value><code><percentage></code></dfn>, consists of a
732 <a href="#number-value"><i><number></i></a> immediately followed by
733 a percent sign ‘<code class=css>%</code>’. It corresponds to
734 the <code>PERCENTAGE</code> token in the <a
735 href="http://www.w3.org/TR/CSS21/syndata.html#tokenization">grammar</a>.
737 <p>Percentage values are always relative to another value, for example a
738 length. Each property that allows percentages also defines the value to
739 which the percentage refers. The value may be that of another property for
740 the same element, a property for an ancestor element, or a value of the
741 formatting context (e.g., the width of a <i>containing block</i>). When a
742 percentage value is set for a property of the <i>root</i> element and the
743 percentage is defined as referring to the inherited value of some
744 property, the resultant value is the percentage times the <i>initial
745 value</i> of that property.
747 <p>Properties may restrict the percentage value to some range. If the value
748 is outside the allowed range, the declaration is invalid and must be <a
749 href="http://www.w3.org/TR/CSS21/conform.html#ignore">ignored</a>.
751 <h2 id=lengths><span class=secno>6. </span> Distance Units: the ‘<a
752 href="#length-value"><code class=css><length></code></a>’ type</h2>
754 <p>Lengths refer to distance measurements and are denoted by <dfn
755 id=length-value><code><length></code></dfn> in the property
756 definitions. A length is a <a href="#dimension"><i>dimension</i></a>. A
757 zero length may be represented instead as the <a
758 href="#number-value"><code><number></code></a> ‘<code
759 class=css>0</code>’. (In other words, for zero lengths the unit
760 identifier is optional.)
762 <p> A <dfn id=dimension>dimension</dfn> is a <a
763 href="#number"><i>number</i></a> immediately followed by a unit
764 identifier. It corresponds to the <a
765 href="#dimension"><code>DIMENSION</code></a> token in the <a
766 href="http://www.w3.org/TR/CSS21/syndata.html#tokenization">grammar</a>.
767 <a href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a> Like
768 keywords, unit identifiers are case-insensitive within the ASCII range.
770 <p>Properties may restrict the length value to some range. If the value is
771 outside the allowed range, the declaration is invalid and must be <a
772 href="http://www.w3.org/TR/CSS21/conform.html#ignore">ignored</a>.
774 <p>While some properties allow negative length values, this may complicate
775 the formatting and there may be implementation-specific limits. If a
776 negative length value is allowed but cannot be supported, it must be
777 converted to the nearest value that can be supported.
779 <p>In cases where the <a href="#used-value">used</a> length cannot be
780 supported, user agents must approximate it in the <a
781 href="#actual-value">actual</a> value.
783 <p>There are two types of length units: relative and absolute.
785 <h3 id=relative-lengths><span class=secno>6.1. </span> Relative lengths</h3>
787 <p><dfn id=relative-length-units title="relative length">Relative length
788 units</dfn> specify a length relative to another length. Style sheets that
789 use relative units can more easily scale from one output environment to
790 another.
792 <p>The relative units are:
794 <table class=data>
795 <caption>Informative Summary of Relative Units</caption>
797 <thead>
798 <tr>
799 <th>unit
801 <th>relative to
803 <tbody>
804 <tr>
805 <td>‘<a href="#em-unit"><code class=css>em</code></a>’
807 <td>font size of the element
809 <tr>
810 <td>‘<a href="#ex-unit"><code class=css>ex</code></a>’
812 <td><i>x-height</i> of the element's font
814 <tr>
815 <td>‘<a href="#ch-unit"><code class=css>ch</code></a>’
817 <td>width of the "0" glyph in the element's font
819 <tr>
820 <td>‘<a href="#rem-unit"><code class=css>rem</code></a>’
822 <td>font size of the root element
824 <tr>
825 <td>‘<a href="#vw-unit"><code class=css>vw</code></a>’
827 <td>viewport's width
829 <tr>
830 <td>‘<a href="#vh-unit"><code class=css>vh</code></a>’
832 <td>viewport's height
834 <tr>
835 <td>‘<a href="#vm-unit"><code class=css>vm</code></a>’
837 <td>minimum of the viewport's height and width
838 </table>
840 <p>Child elements do not inherit the relative values as specified for their
841 parent; they inherit the <a href="#computed-value">computed values</a>.
843 <h4 id=font-relative-lengths><span class=secno>6.1.1. </span> Font-relative
844 lengths: the ‘<a href="#em-unit"><code
845 class=css>em</code></a>’, ‘<a href="#ex-unit"><code
846 class=css>ex</code></a>’, ‘<a href="#ch-unit"><code
847 class=css>ch</code></a>’, ‘<a href="#rem-unit"><code
848 class=css>rem</code></a>’ units</h4>
850 <p>Aside from ‘<a href="#rem-unit"><code
851 class=css>rem</code></a>’ (which refers to the font-size of the root
852 element), the font-relative lengths refer to the computed font metrics of
853 the element on which they are used. The exception is when they occur in
854 the value of the ‘<code class=property>font-size</code>’
855 property itself, in which case they refer to the font metrics of the
856 parent element (or the font metrics corresponding to the initial values of
857 the ‘<code class=property>font</code>’ property, if the
858 element has no parent).
860 <dl>
861 <dt><dfn id=em-unit title=em>em unit</dfn>
863 <dd>
864 <p>Equal to the computed value of the ‘<code
865 class=property>font-size</code>’ property of the element on which
866 it is used.
868 <div class=example>
869 <p>The rule:</p>
871 <pre>h1 { line-height: 1.2em }</pre>
873 <p>means that the line height of <code>h1</code> elements will be 20%
874 greater than the font size of <code>h1</code> element. On the other
875 hand:
877 <pre>h1 { font-size: 1.2em }</pre>
879 <p>means that the font size of <code>h1</code> elements will be 20%
880 greater than the font size inherited by <code>h1</code> elements.</p>
881 </div>
883 <dt><dfn id=ex-unit title=ex>ex unit</dfn>
885 <dd>
886 <p>Equal to the font's x-height. The x-height is so called because it is
887 often equal to the height of the lowercase "x". However, an ‘<a
888 href="#ex-unit"><code class=css>ex</code></a>’ is defined even for
889 fonts that do not contain an "x".
891 <p>The x-height of a font can be found in different ways. Some fonts
892 contain reliable metrics for the x-height. If reliable font metrics are
893 not available, UAs may determine the x-height from the height of a
894 lowercase glyph. One possible heuristic is to look at how far the glyph
895 for the lowercase "o" extends below the baseline, and subtract that
896 value from the top of its bounding box. In the cases where it is
897 impossible or impractical to determine the x-height, a value of 0.5em
898 must be assumed.
900 <dt><dfn id=ch-unit title=ch>ch unit</dfn>
902 <dd>
903 <p>Equal to the advance measure of the "0" (ZERO, U+0030) glyph found in
904 the font used to render it.
906 <dt><dfn id=rem-unit title=rem>rem unit</dfn>
908 <dd>
909 <p>Equal to the computed value of ‘<code
910 class=property>font-size</code>’ on the root element.
912 <p>When specified on the ‘<code
913 class=property>font-size</code>’ property of the root element, the
914 ‘<a href="#rem-unit"><code class=css>rem</code></a>’ units
915 refer to the property's <em>initial value</em>.</p>
916 </dl>
918 <h4 id=viewport-relative-lengths><span class=secno>6.1.2. </span>
919 Viewport-relative lengths: the ‘<a href="#vw-unit"><code
920 class=css>vw</code></a>’, ‘<a href="#vh-unit"><code
921 class=css>vh</code></a>’, ‘<a href="#vm-unit"><code
922 class=css>vm</code></a>’ units</h4>
924 <p>The viewport-relative lengths are relative to the size of the initial
925 containing block. When the height or width of the viewport is changed,
926 they are scaled proportionally.
928 <dl>
929 <dt><dfn id=vw-unit title=vw>vw unit</dfn>
931 <dd>Equal to 1/100th of the width of the initial containing block.
932 <div class=example>
933 <p>In the example below, if the width of the viewport is 200mm, the font
934 size of <code>h1</code> elements will be 16mm (i.e.
935 (8×200mm)/100).
937 <pre>h1 { font-size: 8vw }</pre>
938 </div>
940 <dt><dfn id=vh-unit title=vh>vh unit</dfn>
942 <dd>Equal to 1/100th of the height of the initial containing block.
944 <dt><dfn id=vm-unit title=vm>vm unit</dfn>
946 <dd>Equal to the smaller of ‘<a href="#vw-unit"><code
947 class=css>vw</code></a>’ or ‘<a href="#vh-unit"><code
948 class=css>vh</code></a>’.
949 <p class=issue>Do we need this now that we have the min() function?
950 </dl>
952 <h3 id=absolute-lengths><span class=secno>6.2. </span> Absolute lengths:
953 the ‘<code class=css>cm</code>’, ‘<code
954 class=css>mm</code>’, ‘<code class=css>in</code>’,
955 ‘<code class=css>pt</code>’, ‘<code
956 class=css>pc</code>’, ‘<code class=css>px</code>’ units</h3>
958 <p>The <dfn id=absolute-length-units>absolute length units</dfn> are fixed
959 in relation to each other and anchored to some physical measurement. They
960 are mainly useful when the output environment is known. The absolute units
961 consist of the physical units (in, cm, mm, pt, pc) and the px unit:
963 <table class=data>
964 <thead>
965 <tr>
966 <th>unit
968 <th>definition
970 <tbody>
971 <tr>
972 <td>‘<code class=css>cm</code>’
974 <td>centimeters
976 <tr>
977 <td>‘<code class=css>mm</code>’
979 <td>millimeters
981 <tr>
982 <td>‘<code class=css>in</code>’
984 <td>inches; 1in is equal to 2.54cm
986 <tr>
987 <td>‘<code class=css>px</code>’
989 <td>pixels; 1px is equal to 1/96th of 1in
991 <tr>
992 <td>‘<code class=css>pt</code>’
994 <td>points; 1pt is equal to 1/72nd of 1in
996 <tr>
997 <td>‘<code class=css>pc</code>’
999 <td>picas; 1pc is equal to 12pt
1000 </table>
1002 <pre class=example>
1003 h1 { margin: 0.5in } /* inches */
1004 h2 { line-height: 3cm } /* centimeters */
1005 h3 { word-spacing: 4mm } /* millimeters */
1006 h4 { font-size: 12pt } /* points */
1007 h4 { font-size: 1pc } /* picas */
1008 p { font-size: 12px } /* px */</pre>
1010 <p>For a CSS device, these dimensions are either anchored (i) by relating
1011 the physical units to their physical measurements, or (ii) by relating the
1012 pixel unit to the <a href="#reference-pixel"><i>reference pixel</i></a>.
1013 For print media and similar high-resolution devices, the anchor unit
1014 should be one of the standard physical units (inches, centimeters, etc).
1015 For lower-resolution devices, and devices with unusual viewing distances,
1016 it is recommended instead that the anchor unit be the pixel unit. For such
1017 devices it is recommended that the pixel unit refer to the whole number of
1018 device pixels that best approximates the reference pixel.
1020 <p class=note>Note that if the anchor unit is the pixel unit, the physical
1021 units might not match their physical measurements. Alternatively if the
1022 anchor unit is a physical unit, the pixel unit might not map to a whole
1023 number of device pixels.
1025 <p class=note>Note that this definition of the pixel unit and the physical
1026 units differs from previous versions of CSS. In particular, in previous
1027 versions of CSS the pixel unit and the physical units were not related by
1028 a fixed ratio: the physical units were always tied to their physical
1029 measurements while the pixel unit would vary to most closely match the
1030 reference pixel. (This change was made because too much existing content
1031 relies on the assumption of 96dpi, and breaking that assumption breaks the
1032 content.)
1034 <p>The <dfn id=reference-pixel>reference pixel</dfn> is the visual angle of
1035 one pixel on a device with a pixel density of 96dpi and a distance from
1036 the reader of an arm's length. For a nominal arm's length of 28 inches,
1037 the visual angle is therefore about 0.0213 degrees. For reading at arm's
1038 length, 1px thus corresponds to about 0.26 mm (1/96 inch).
1040 <p>The image below illustrates the effect of viewing distance on the size
1041 of a reference pixel: a reading distance of 71 cm (28 inches)
1042 results in a reference pixel of 0.26 mm, while a reading distance of
1043 3.5 m (12 feet) results in a reference pixel of 1.3 mm.
1045 <div class=figure>
1046 <p><img alt="This diagram illustrates how the definition of a pixel
1047 depends on the users distance from the viewing surface (paper or screen).
1048 The image depicts the user looking at two planes, one 28 inches (71 cm)
1049 from the user, the second 140 inches (3.5 m) from the user. An expanding
1050 cone is projected from the user's eye onto each plane. Where the cone
1051 strikes the first plane, the projected pixel is 0.26 mm high. Where the
1052 cone strikes the second plane, the projected pixel is 1.4 mm high."
1053 src=pixel1.png>
1055 <p class=caption>Showing that pixels must become larger if the viewing
1056 distance increases
1057 </div>
1059 <p>This second image illustrates the effect of a device's resolution on the
1060 pixel unit: an area of 1px by 1px is covered by a single dot in a
1061 low-resolution device (e.g. a typical computer display), while the same
1062 area is covered by 16 dots in a higher resolution device (such as a
1063 printer).
1065 <div class=figure>
1066 <p><img alt="This diagram illustrates the relationship between the
1067 reference pixel and device pixels (called "dots" below). The
1068 image depicts a high resolution (large dot density) laser printer output
1069 on the left and a low resolution monitor screen on the right. For the
1070 laser printer, one square reference pixel is implemented by 16 dots. For
1071 the monitor screen, one square reference pixel is implemented by a single
1072 dot." src=pixel2.png>
1074 <p class=caption>Showing that more device pixels (dots) are needed to
1075 cover a 1px by 1px area on a high-resolution device than on a low-res one
1077 </div>
1079 <h2 id=other-units><span class=secno>7. </span> Other Units</h2>
1081 <h3 id=angles><span class=secno>7.1. </span> Angles: the ‘<a
1082 href="#angle-value"><code class=css><angle></code></a>’ type
1083 and ‘<a href="#deg"><code class=css>deg</code></a>’, ‘<a
1084 href="#grad"><code class=css>grad</code></a>’, ‘<a
1085 href="#rad"><code class=css>rad</code></a>’, ‘<a
1086 href="#turn"><code class=css>turn</code></a>’ units</h3>
1088 <p>Angle values are <i>dimensions</i> denoted by <dfn
1089 id=angle-value><angle></dfn>. The angle unit identifiers are:
1091 <dl>
1092 <dt><dfn id=deg title=deg>deg</dfn>
1094 <dd>Degrees. There are 360 degrees in a full circle.
1096 <dt><dfn id=grad title=grad>grad</dfn>
1098 <dd>Gradians. There are 400 gradians in a full circle.
1100 <dt><dfn id=rad title=rad>rad</dfn>
1102 <dd>Radians. There are 2π radians in a full circle. <span
1103 class=issue>Who is going to use this anyway?</span>
1105 <dt><dfn id=turn title=turn>turn</dfn>
1107 <dd>Turns. There is 1 turn in a full circle.
1108 </dl>
1110 <p>For example, a right angle is ‘<code class=css>90deg</code>’
1111 or ‘<code class=css>100grad</code>’ or ‘<code
1112 class=css>0.25turn</code>’ or approximately ‘<code
1113 class=css>1.570796326794897rad</code>’.
1115 <h3 id=time><span class=secno>7.2. </span> Times: the ‘<a
1116 href="#time-value"><code class=css><time></code></a>’ type and
1117 ‘<a href="#s"><code class=css>s</code></a>’, ‘<a
1118 href="#ms"><code class=css>ms</code></a>’ units</h3>
1120 <p>Time values are <i>dimensions</i> denoted by <dfn
1121 id=time-value><time></dfn>. The time unit identifiers are:
1123 <dl>
1124 <dt><dfn id=s title=s>s</dfn>
1126 <dd>Seconds.
1128 <dt><dfn id=ms title=ms>ms</dfn>
1130 <dd>Milliseconds. There are 1000 milliseconds in a second.
1131 </dl>
1133 <p>Properties may restrict the time value to some range. If the value is
1134 outside the allowed range, the declaration is invalid and must be <a
1135 href="http://www.w3.org/TR/CSS21/conform.html#ignore">ignored</a>.
1137 <h3 id=frequencies-the-ltfrequencygt-type-and-h><span class=secno>7.3.
1138 </span>Frequencies: the ‘<a href="#frequency-value"><code
1139 class=css><frequency></code></a>’ type and ‘<a
1140 href="#hz"><code class=css>Hz</code></a>’, ‘<a
1141 href="#khz"><code class=css>kHz</code></a>’ units</h3>
1143 <p>Frequency values are <i>dimensions</i> denoted by <dfn
1144 id=frequency-value><frequency></dfn>. The frequency unit identifiers
1145 are:
1147 <dl>
1148 <dt><dfn id=hz title=Hz>Hz</dfn>
1150 <dd>Hertz. It represents the number of occurrences per second.
1152 <dt><dfn id=khz title=kHz>kHz</dfn>
1154 <dd>KiloHertz. A kiloHertz is 1000 Hertz.
1155 <p>For example, when representing sound pitches, 200Hz (or 200hz) is a
1156 bass sound, and 6kHz (or 6khz) is a treble sound.</p>
1158 <h4 id=the-calc-min-and-max-functions><span class=secno>7.3.1. </span>The
1159 ‘<a href="#calc"><code class=property>calc</code></a>’,
1160 ‘<a href="#min"><code class=property>min</code></a>’ and
1161 ‘<a href="#max"><code class=property>max</code></a>’
1162 functions</h4>
1164 <p>The <dfn id=calc>calc()</dfn>, <dfn id=min>min()</dfn>, and <dfn
1165 id=max>max()</dfn> functions can be used wherever length, frequency,
1166 angle, time, or number values are allowed.
1168 <div class=example>
1169 <pre>
1170 section {
1171 float: left;
1172 margin: 1em; border: solid 1px;
1173 width: calc(100%/3 - 2*1em - 2*1px);
1174 }
1175 </pre>
1176 </div>
1178 <div class=example>
1179 <pre>
1180 p {
1181 margin: calc(1rem - 2px) calc(1rem - 1px);
1182 }
1183 </pre>
1184 </div>
1186 <div class=example>
1187 <pre>
1188 p { font-size: min(10px, 3em) }
1189 blockquote { font-size: max(30px, 3em) }
1190 </pre>
1191 </div>
1193 <div class=example>
1194 <pre>
1195 .box { width: min(10% + 20px, 300px) }
1196 </pre>
1197 </div>
1199 <p>The expression language of these functions is described by the grammar
1200 and prose below.
1202 <pre>
1203 S : calc | min | max;
1204 calc : "calc(" S* sum ")" S*;
1205 min : "min(" S* sum [ "," S* sum ]* ")" S*;
1206 max : "max(" S* sum [ "," S* sum ]* ")" S*;
1207 sum : product [ [ "+" | "-" ] S* product ]*;
1208 product : unit [ [ "*" | "/" | "mod" ] S* unit ]*;
1209 unit : ["+"|"-"]? [ NUMBER S* | DIMENSION S* | PERCENTAGE S* |
1210 min | max | "(" S* sum ")" S* ];
1211 </pre>
1213 <p>The context of the expression imposes a target type, which is one of
1214 length, frequency, angle, time, or number. NUMBER tokens are of type
1215 number. DIMENSION tokens have types of their units (‘<code
1216 class=property>cm</code>’ is length, ‘<a href="#deg"><code
1217 class=property>deg</code></a>’ is angle etc.); any DIMENSION whose
1218 type does not match the target type is not allowed and must be a parse
1219 error. If percentages are accepted in that context and convertible to
1220 the target type, a PERCENTAGE token in the expression has the target
1221 type; otherwise percentages are not allowed and must be a parse error.
1223 <p>To make expressions simpler, operators have restrictions on the types
1224 they accept. At each operator, the types of the left and right side have
1225 to be checked for these restrictions. If compatible, they return roughly
1226 as follows (the following ignores precedence rules on the operators for
1227 simplicity):
1229 <ol>
1230 <li>At ",", "+", "-":<br>
1231 check: both sides have the same type<br>
1232 return: that type
1234 <li>At "*":<br>
1235 check: at least one side is "number" <br>
1236 return: the type of the other side
1238 <li>At "/":<br>
1239 check: right side is "number"<br>
1240 return: the type of the left side
1241 </ol>
1243 <p>Division by zero is a parse error.
1245 <p>The value resulting from an expression must be clamped to the range
1246 allowed in the target context.
1248 <div class=example> These two are equivalentequivalent to ‘<code
1249 class=css>width: 0px</code>’ since widths smaller than 0px are not
1250 allowed.
1251 <pre>
1252 width: calc(5px - 10px);
1253 width: 0px;
1254 </pre>
1255 </div>
1257 <p>Given the complexities of ‘<code
1258 class=property>width</code>’ and ‘<code
1259 class=property>height</code>’ on table cells and table elements,
1260 calc() expressions for ‘<code class=property>width</code>’
1261 and ‘<code class=property>height</code>’ on table columns,
1262 table column groups, table rows, table row groups, and table cells in
1263 both auto and fixed layout tables are treated as if ‘<code
1264 class=property>auto</code>’ had been specified.
1266 <h3 id=ltstringgt><span class=secno>7.4. </span><string></h3>
1268 <p>Strings are denoted by <dfn id=ltstringgt0><string></dfn> in the
1269 value definitions.
1271 <h3 id=ltcolorgt><span class=secno>7.5. </span><color></h3>
1273 <p><em>This section is not normative. The CSS3 Color module <a
1274 href="#CSS3COLOR" rel=biblioentry>[CSS3COLOR]<!--{{!CSS3COLOR}}--></a>
1275 defines the CSS3 color values.</em>
1277 <p>Color values are denoted by <dfn id=ltcolorgt0><color></dfn> in
1278 the value definitions.
1280 <p>A <dfn id=color>color</dfn> value can either be a keyword, a numerical
1281 specification in a functional notation, or a numerical RGB specification
1282 in a hexadecimal notation. The hexadecimal notation is special shorthand
1283 format that allows compact color descriptions.
1285 <div class=example>
1286 <pre>
1287 em { color: #F00 }
1288 span.issue { color: red }
1289 * { color: hsl(120, 75%, 75%) }
1290 </pre>
1291 </div>
1293 <h3 id=ltattrgt><span class=secno>7.6. </span><attr></h3>
1295 <p class=issue>Describe the feature fully here, not just a delta from CSS
1296 21.
1298 <p class=issue>When attr is set on a pseudo-element, it should apply to
1299 the originating element
1301 <p>In CSS2.1 <a href="#CSS21"
1302 rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>, the ‘<code
1303 class=css>attr()</code>’ expression always returns a string. In
1304 CSS3, the ‘<code class=css>attr()</code>’ expression can
1305 return many different types. The new syntax for the attr() expression
1306 is:
1308 <pre>
1309 'attr(' ident [ ',' <type> [ ',' <value> ]? ]? ')'
1310 </pre>
1312 <p>The first argument represents the attribute name. The value of the
1313 attribute with that name on the element whose computed values are being
1314 computed is used as the value of the expression, according to the rules
1315 given below.
1317 <p>The first argument accepts an optional namespace prefix to identify
1318 the namespace of the attribute. The namespace prefix and the attribute
1319 name is separated by ‘<code class=css>|</code>’, with no
1320 whitespace before or after the separator <a href="#CSS3NAMESPACE"
1321 rel=biblioentry>[CSS3NAMESPACE]<!--{{CSS3NAMESPACE}}--></a>.
1323 <p>The second argument (which is optional but must be present if the
1324 third argument is present) is a <type> and tells the UA how to
1325 interpret the attribute value. It may be one of the values from the list
1326 below.
1328 <p>The third argument (which is optional) is a CSS value which must be
1329 valid where the attr() expression is placed. If it is not valid, then
1330 the whole attr() expression is invalid.
1332 <p>If the attribute named by the first argument is missing, cannot be
1333 parsed, or is invalid for the property, then the value returned by
1334 attr() will be the third argument, or, if the third argument is absent,
1335 will be the value given as the default for the relevant type in the list
1336 below.
1338 <dl>
1339 <dt>string
1341 <dd>The attribute value will be interpreted as the contents of a CSS
1342 string. The default is the empty string.
1344 <dt>color
1346 <dd>The attribute value will be interpreted as a CSS <color> value.
1347 The default is UA dependent but must be the same as the initial value
1348 of the ‘<a href="#color"><code
1349 class=property>color</code></a>’ property.
1351 <dt>url
1353 <dd>The attribute value will be interpreted as the URI part of a
1354 ‘<code class=css>url()</code>’ expression. The default is a
1355 UA-dependent URI defined to point to a non-existent document with a
1356 generic error condition. (i.e. it shouldn't be an FTP URI that causes a
1357 DNS error, or an HTTP URI that results in a 404, it should be a
1358 nondescript error condition.)
1360 <dt>integer
1362 <dd>The attribute value will be interpreted as a CSS integer. The
1363 default is 0. The default should also be used if the property in
1364 question only accepts integers within a certain range and the attribute
1365 is out of range.
1367 <dt>number
1369 <dd>The attribute value will be interpreted as a CSS number. The default
1370 is 0.0. The default should also be used if the property in question
1371 only accepts numbers within a certain range and the attribute is out of
1372 range.
1374 <dt>length, angle, time, frequency
1376 <dd>The attribute value will be interpreted as a CSS length, angle, time
1377 or frequency (respectively), and the unit identifier (if any) will
1378 appear in the attribute value. The default is 0. The default should
1379 also be used if the property in question only accepts values within a
1380 certain range (e.g. positive lengths or angles from 0 to 90deg) and the
1381 attribute is out of range (e.g. a negative length or 180deg).
1383 <dt>em, ex, px, gr, rem, vw, vh, vm, mm, cm, in, pt, pc, deg, grad, rad,
1384 ms, s, Hz, kHz, %
1386 <dd>The attribute value will be interpreted as a float, with the given
1387 type suffixed as a unit. The default is 0 in the relevant units.
1388 </dl>
1390 <p class=issue>Should there also be a "keyword" type to, e.g., support
1391 ‘<code class=css>float: attr(align)</code>’</p>
1393 <p>If the <type> is missing, ‘<a href="#string"><code
1394 class=property>string</code></a>’ is implied.
1396 <p class=issue>Ideally, it shouldn't be necessary to specify the type if
1397 it is obvious. For example, this should be valid: "<tt>background-image:
1398 attr(href);</tt>". This could be described as: <q>If the property only
1399 accepts one type of value (aside from ‘<code
1400 class=property>inherit</code>’ and ‘<code
1401 class=property>initial</code>’), that type is implied</q>.
1403 <p>The attr() form is only valid if the type given (or implied, if it is
1404 missing) is valid for the property. For example, all of the following
1405 are invalid and would cause a parse-time error (and thus cause the
1406 relevant declaration, in this case all of them, to be ignored):
1408 <div class="illegal example">
1409 <p style="display:none">Illegal Examples:
1411 <pre>
1412 content: attr(title, color); /* 'content' doesn't accept colors */
1414 content: attr(end-of-quote, string, inherit) close-quote; /* the
1415 'inherit' value is not allowed there, since the result would be
1416 'inherit close-quote', which is invalid. */
1418 margin: attr(vertical, length) attr(horizontal, deg); /* deg
1419 units are not valid at that point */
1420 <!--
1421 font: attr(weight, integer) attr(size, length)/attr(height,
1422 integer) attr(family, string); /* invalid because
1423 <'font-weight'>s are not integers, but identifiers. */
1424 -->
1425 color: attr(color); /* 'color' doesn't accept strings */
1426 </pre>
1427 </div>
1429 <p>The attr() expression cannot return everything, for example it cannot
1430 do counters, named strings, quotes, or values such as ‘<code
1431 class=property>auto</code>’, ‘<code
1432 class=property>nowrap</code>’, or ‘<code
1433 class=property>baseline</code>’. This is intentional, as the
1434 intent of the ‘<code class=css>attr()</code>’ expression is
1435 not to make it possible to describe a presentational language's
1436 formatting using CSS, but to enable CSS to take semantic data into
1437 account.
1439 <p>Note that the default value need not be of the type given. For
1440 instance, if the type required of the attribute by the author is
1441 ‘<code class=property>px</code>’, the default could still be
1442 ‘<code class=css>5em</code>’.
1444 <div class=example>
1445 <p>Examples:
1447 <pre>
1448 <stock>
1449 <wood length="12"/>
1450 <wood length="5"/>
1451 <metal length="19"/>
1452 <wood length="4"/>
1453 </stock>
1455 stock::before {
1456 display: block;
1457 content: "To scale, the lengths of materials in stock are:";
1458 }
1459 stock > * {
1460 display: block;
1461 width: attr(length, em); /* default 0 */
1462 height: 1em;
1463 border: solid thin;
1464 margin: 0.5em;
1465 }
1466 wood {
1467 background: orange url(wood.png);
1468 }
1469 metal {
1470 background: silver url(metal.png);
1471 }
1473 /* this also uses a possible extension to the 'content' property
1474 to handle replaced content and alternatives to unavailable,
1475 corrupted or unsupported content */
1476 img {
1477 content: replaced attr(src, url), attr(alt, string, none);
1478 height: attr(height, px, auto);
1479 width: attr(width, px, auto);
1480 }
1481 </pre>
1482 </div>
1484 <p>The attr() expression cannot currently fall back onto another
1485 attribute. Future versions of CSS may extend attr() in this direction.
1487 <p class=issue>Should ‘<code class=css>attr()</code>’ be
1488 allowed on any property, in any source language? For example, do we
1489 expect UAs to honor this rule for HTML documents?: <tt>P[COLOR] { color:
1490 attr(COLOR, color) }</tt>.
1492 <h3 id=uris><span class=secno>7.7. </span><url></h3>
1494 <p><dfn id=urls title="Uniform Resource Locator (URL)|URL (Uniform
1495 Resource Locator)">URLs</dfn> (Uniform Resource Locators, see <a
1496 href="#RFC1738" rel=biblioentry>[RFC1738]<!--{{RFC1738}}--></a> and <a
1497 href="#RFC1808" rel=biblioentry>[RFC1808]<!--{{RFC1808}}--></a>) provide
1498 the address of a resource on the Web. An alternative and more general
1499 term is <dfn id=uris0 title="Resource Identifier (URI)|URI (Uniform
1500 Resource Identifier)">URIs</dfn> (Uniform Resource Identifiers, see
1501 [!URI]). This specification uses the term URI.</p>
1503 <p>For historical reasons, the name of the URI function is "url". The URI
1504 function takes one URI as the argument. The URI may be quoted with
1505 single quote (') or double quote (") characters. If quoted,
1506 the two quote characters must be the same.
1508 <div class=example>
1509 <p style="display:none">Example(s):</p>
1511 <pre>
1512 body { background: url("http://www.example.com/pinkish.gif") }
1513 </pre>
1514 </div>
1516 <div class=example>
1517 <p>An example without quotes:</p>
1519 <pre>
1520 li { list-style: url(http://www.example.com/redball.png) disc }
1521 </pre>
1522 </div>
1524 <p>Parentheses, commas, whitespace characters, single quotes
1525 (‘<code class=css>) and double quotes ("<!--"-->) appearing in a
1526 URI must be escaped with a backslash: </code>’\(‘<code
1527 class=css>, </code>’\)‘<code class=css>,
1528 </code>’\,‘<code class=css>.</code></p>
1530 <p>Depending on the type of URI, it might also be possible to write the
1531 above characters as URI-escapes (where "(" = %28, ")" = %29, etc.) as
1532 described in [!URI].</p>
1534 <p>In order to create modular style sheets that are not dependent on the
1535 absolute location of a resource, authors should use relative URIs.
1536 Relative URIs (as defined in <a href="#RFC1808"
1537 rel=biblioentry>[RFC1808]<!--{{RFC1808}}--></a>) are resolved to full
1538 URIs using a base URI. RFC 1808, section 3, defines the
1539 normative algorithm for this process. For CSS style sheets, the base URI
1540 is that of the style sheet, not that of the source document.</p>
1542 <div class=example>
1543 <p>For example, suppose the following rule:</p>
1545 <pre>
1546 body { background: url("yellow") }
1547 </pre>
1549 <p>is located in a style sheet designated by the URI:</p>
1551 <pre>
1552 http://www.example.org/style/basic.css
1553 </pre>
1555 <p>The background of the source document’s BODY will be tiled with
1556 whatever image is described by the resource designated by the URI</p>
1558 <pre>
1559 http://www.example.org/style/yellow
1560 </pre>
1561 </div>
1563 <p>User agents may vary in how they handle URIs that designate
1564 unavailable or inapplicable resources.</p>
1566 <h3 id=ltimagegt><span class=secno>7.8. </span><image></h3>
1568 <p>TBD. <!--
1569 <h4>The 'counter' function</h4>
1571 <p><dfn title="<counter>, definition of">Counters</dfn> are denoted by
1572 identifiers (see the <span class="property">'counter-increment'</span> and
1573 <span class="property">'counter-reset'</span> properties). To refer to the
1574 value of a counter, the notation <dfn>'counter(<identifier>)'</dfn> or
1575 <dfn>'counter(<identifier>, <list-style-type>)'</dfn> is used.
1576 The default style is 'decimal'.</p>
1578 <p>To refer to a sequence of nested counters of the same name, the notation
1579 is 'counters(<identifier>, <string>)' or
1580 'counters(<identifier>, <string>, <list-style-type>)'. See
1581 "Nested counters and scope" [add ref] in the chapter on generated content
1582 [add ref].</p>
1584 <p>In CSS2.1, the values of counters can only be referred to from the <span
1585 class="property">'content'</span> property. Note that 'none' is a possible
1586 <list-style-type>: 'counter(x, none)' yields an empty string.</p>
1588 <div class="example">
1589 <p style="display:none">Example(s):</p>
1591 <p>Here is a style sheet that numbers paragraphs (P) for each chapter (H1).
1592 The paragraphs are numbered with roman numerals, followed by a period and a
1593 space:</p>
1595 <pre>
1596 p { counter-increment: par-num }
1597 h1 { counter-reset: par-num }
1598 p:before { content: counter(par-num, upper-roman) ". " }
1599 </pre>
1600 </div>
1601 -->
1604 <h3 id=ltfractiongt><span class=secno>7.9. </span><fraction></h3>
1606 <p>Some properties accept a series of length values that, in sum, should
1607 add up to a certain length. To take up any remaining space, fractions
1608 can be used.
1610 <h4 id=the-fr-unit><span class=secno>7.9.1. </span>The ‘<code
1611 class=property>fr</code>’ unit</h4>
1613 <p>The <dfn id=fr title="fr (unit)">fr</dfn> unit is used to distribute
1614 any remaining space in a series of length values. If multiple fractions
1615 are specified, they take up space proportionally to their numeric value.
1618 <div class=example>
1619 <pre>
1620 border-parts: 10px 1fr 10px;
1621 border-parts: 10px 1fr 10px 1fr 10px;
1622 border-parts: 10px 2fr 10px 2fr 10px;
1623 </pre>
1624 </div>
1626 <p>The ‘<code class=css>fr</code>’ unit can only be used in
1627 combination with regular length units.
1629 <h3 id=ltgridgt><span class=secno>7.10. </span><grid></h3>
1631 <p>A grid is a set of invisible vertical and horizontal lines that can be
1632 used to align content. In CSS3, a grid lines can be established
1633 implicitly or explicitly <a href="#CSS3COL"
1634 rel=biblioentry>[CSS3COL]<!--{{!CSS3COL}}--></a> <a href="#CSS3GRID"
1635 rel=biblioentry>[CSS3GRID]<!--{{!CSS3GRID}}--></a>. In any case, the
1636 distance between grid lines can be referred to by the ‘<code
1637 class=css>gr</code>’ unit.
1639 <h4 id=the-gr-unit><span class=secno>7.10.1. </span>The ‘<code
1640 class=property>gr</code>’ unit</h4>
1642 <p>The <dfn id=gr title="gr (unit)">gr</dfn> unit is used to position
1643 elements in relation to grid lines.
1645 <div class=example>
1646 <pre>
1647 img {
1648 float: top left multicol;
1649 float-offset: 2gr;
1650 width: 1gr }
1651 }
1652 </pre>
1653 </div>
1655 <p>Grid lines can be laid out in uneven patterns. Therefore, the
1656 ‘<code class=css>gr</code>’ unit is not linear.
1658 <div class=example>
1659 <p>For example, "2gr" is not necessarily twice as long as "1gr".
1660 </div>
1661 <!--
1663 <h3>Special cases</h3>
1665 <p>Two common types of values fall outside the types
1666 described above: the value for font families and the hexadecimal color
1667 notation.
1669 <h4>Font families</h4>
1671 <p>The <span class="property">'font'</span>
1672 and <span class="property">'font-family'</span> properties accept a
1673 comma-separated list of font families. Font families can either be the
1674 name of a certain font, or it can be one of
1675 five <em class="index">generic font families</em>: 'serif',
1676 'sans-serif', 'cursive','fantasy', and 'monospace'. Font family names
1677 are like strings, except that the quotes around them may be omitted.
1678 If quoting is omitted, any white space characters before and after the
1679 font name are ignored and any sequence of white space characters
1680 inside the font name is converted to a single space. Font family names
1681 that happen to be the same as a keyword value (e.g. 'initial',
1682 'inherit', 'default', 'serif', 'sans-serif', 'monospace', 'fantasy',
1683 and 'cursive') must be quoted to prevent confusion with the keywords
1684 with the same names. UAs must not consider these keywords as matching
1685 the ''<family-name>'' type.
1687 <p>Generic font family names are keywords and must not be quoted.
1689 <div class="example">
1690 <pre>body { font-family: "Helvetica", "Univers", "Arial", sans-serif }</pre>
1691 </div>
1692 -->
1694 <h2 id=specified-computed-used-and-actual-value><span class=secno>8.
1695 </span>Specified, computed, used, and actual values</h2>
1697 <p>The final value of a CSS3 property for a given element is the result
1698 of a four-step calculation. First, cascading and inheritance yields the
1699 <a href="#specified-value"><em>specified value</em></a> <a
1700 href="#CSS3CASCADE"
1701 rel=biblioentry>[CSS3CASCADE]<!--{{!CSS3CASCADE}}--></a>. Second,
1702 relative values are computed into absolute values as far as possible
1703 without formatting the document, thereby yielding the <a
1704 href="#computed-value"><em>computed value</em></a>. The computed value
1705 is transformed into the <a href="#used-value"><em>used value</em></a> in
1706 the formatting process. Finally, the computed value is transformed to
1707 the <a href="#actual-value"><em>actual value</em></a> based on
1708 constraints in the user agent.</p>
1710 <h3 id=finding-the-specified-value><span class=secno>8.1. </span>Finding
1711 the <dfn id=specified-value>specified value</dfn></h3>
1713 <p>The <a href="#specified-value"><em>specified value</em></a> is the
1714 output of the cascading and inheritance process <a href="#CSS3CASCADE"
1715 rel=biblioentry>[CSS3CASCADE]<!--{{!CSS3CASCADE}}--></a>.
1717 <h3 id=finding-the-computed-value><span class=secno>8.2. </span>Finding
1718 the <dfn id=computed-value>computed value</dfn></h3>
1720 <p>Specified values may be absolute (i.e., they are not specified
1721 relative to another value, as in ‘<code
1722 class=property>red</code>’ or ‘<code
1723 class=css>2mm</code>’) or relative (i.e., they are specified
1724 relative to another value, as in ‘<code
1725 class=property>auto</code>’, ‘<code
1726 class=css>2em</code>’). For absolute values, no processing is
1727 needed to find the computed value.</p>
1729 <p>For relative values, on the other hand, computation is necessary to
1730 find the computed values: percentages must be multiplied by a reference
1731 value (each property defines which value that is), values with relative
1732 units (em, ex, px) must be made absolute by multiplying with the
1733 appropriate font or pixel size, ‘<code
1734 class=property>auto</code>’ values must be computed by the
1735 formulas given with each property, certain keywords (e.g., ‘<code
1736 class=property>smaller</code>’, ‘<code
1737 class=property>bolder</code>’) must be replaced according to their
1738 definitions. See example (f), (g) and (h) in the table below.</p>
1740 <p>Also, relative URIs are computed into absolute URIs at this stage. The
1741 computed value of invalid and absolute URIs is the same as the specified
1742 value.
1744 <h3 id=finding-the-used-value><span class=secno>8.3. </span>Finding the
1745 <dfn id=used-value>used value</dfn></h3>
1747 <p>Computed values are processed as far as possible without formatting
1748 the document. Some values, however, can only be determined when the
1749 document is being laid out. For example, if the width of an element is
1750 set to be a certain percentage of its containing block, the width cannot
1751 be determined until the width of the containing block has been
1752 determined. The used value is the result of taking the computed value
1753 and resolving any remaining dependencies into an absolute value.
1755 <h3 id=finding-the-actual-value><span class=secno>8.4. </span>Finding the
1756 <dfn id=actual-value>actual value</dfn></h3>
1758 <p>A used value is in principle ready to be used, but a user agent may
1759 not be able to make use of the value in a given environment. For
1760 example, a user agent may only be able to render borders with integer
1761 pixel widths and may therefore have to approximate the computed width.
1762 Also, the font size of an element may need adjustment based on the
1763 availability of fonts or the value of the ‘<code
1764 class=property>font-size-adjust</code>’ property. The actual value
1765 is the computed value after adjustments have been made.
1767 <p>By probing the actual values of elements, much can be learned about
1768 how the document is laid out. However, not all information is recorded
1769 in the actual values. For example, the actual value of the ‘<code
1770 class=property>page-break-after</code>’ property does not reflect
1771 whether there is a page break or not after the element. Similarly, the
1772 actual value of ‘<code class=property>orphans</code>’ does
1773 not reflect how many orphan lines there is in a certain element. See
1774 examples (j) and (k) in the table below.
1776 <table>
1777 <tbody>
1778 <tr>
1779 <th>Example
1781 <th>Winning declaration
1783 <th>Property</th>
1784 <!-- <th>Cascaded value</th> -->
1786 <th>Specified value
1788 <th>Computed value
1790 <th>Used value
1792 <th>Actual value
1794 <tr>
1795 <td>a
1797 <td><tt class=declaration>text-align: left</tt>
1799 <td>text-align</td>
1800 <!-- <td>left</td>-->
1802 <td>left
1804 <td>left
1806 <td>left
1808 <td>left
1810 <tr>
1811 <td>b
1813 <td><tt class=declaration>border-width: inherit</tt>
1815 <td>border-top-width, border-right-width, border-bottom-width,
1816 border-left-width</td>
1817 <!-- <td>inherit</td> -->
1819 <td class=say>4.2px
1821 <td>4.2px
1823 <td>4.2px
1825 <td>4px
1827 <tr>
1828 <td>c
1830 <td>(no winning declaration)
1832 <td>width</td>
1833 <!-- <td>(no specified value)</td>-->
1835 <td>auto (initial value)
1837 <td>auto
1839 <td>120px
1841 <td>120px
1843 <tr>
1844 <td>d
1846 <td><tt class=declaration>list-style-position: inherit</tt>
1848 <td>list-style-position</td>
1849 <!-- <td>inherit</td> -->
1851 <td class=say>inside
1853 <td>inside
1855 <td>inside
1857 <td>inside
1859 <tr>
1860 <td>e
1862 <td><tt class=declaration>list-style-position: initial</tt>
1864 <td>list-style-position</td>
1865 <!-- <td>initial</td>-->
1867 <td>outside (initial value)
1869 <td>outside
1871 <td>outside
1873 <td>outside
1875 <tr>
1876 <td>f
1878 <td><tt class=declaration>font-size: 1.2em</tt>
1880 <td>font-size</td>
1881 <!-- <td>1.2em</td>-->
1883 <td>1.2em
1885 <td class=say>14.1px
1887 <td>14.1px
1889 <td>14px
1891 <tr>
1892 <td>g
1894 <td><tt class=declaration>width: 80%</tt>
1896 <td>width</td>
1897 <!-- <td>80%</td>-->
1899 <td>80%
1901 <td>80%
1903 <td class=say>354.2px
1905 <td>354px
1907 <tr>
1908 <td>h
1910 <td><tt class=declaration>width: auto</tt>
1912 <td>width</td>
1913 <!-- <td>auto</td>-->
1915 <td>auto
1917 <td>auto
1919 <td class=say>134px
1921 <td>134px
1923 <tr>
1924 <td>i
1926 <td><tt class=declaration>height: auto</tt>
1928 <td>height</td>
1929 <!-- <td>auto</td>-->
1931 <td>auto
1933 <td>auto
1935 <td class=say>176px
1937 <td>176px
1939 <tr>
1940 <td>j
1942 <td>(no winning declaration)
1944 <td>page-break-after</td>
1945 <!-- <td>(no specified value)</td>-->
1947 <td>auto (initial value)
1949 <td>auto
1951 <td>auto
1953 <td>auto
1955 <tr>
1956 <td>k
1958 <td><tt class=declaration>orphans: 3</tt>
1960 <td>orphans</td>
1961 <!-- <td>3</td>-->
1963 <td>3
1965 <td>3
1967 <td>3
1969 <td>3
1970 </table>
1972 <h2 class=no-num id=acknowledgments>Acknowledgments</h2>
1974 <p>Comments and suggestions from Giovanni Campagna, Christoph Päper,
1975 Keith Rarick, Alex Mogilevsky, Ian Hickson, David Baron, Edward
1976 Welbourne, Boris Zbarsky, Björn Höhrmann and Michael Day
1977 improved this module. <!--
1979 Ian's proposal:
1980 http://lists.w3.org/Archives/Member/w3c-css-wg/2002OctDec/0141.html
1981 David's proposal
1982 http://lists.w3.org/Archives/Member/w3c-css-wg/2002OctDec/0191.html
1984 -->
1987 <h2 class=no-num id=references>References</h2>
1989 <h3 class=no-num id=normative-references>Normative references</h3>
1990 <!--begin-normative--> <!-- Sorted by label -->
1991 <dl class=bibliography>
1992 <dt style="display:
1993 none"><!-- keeps the doc valid if the DL is empty --> <!---->
1995 <dt id=CSS21>[CSS21]
1997 <dd>Bert Bos; et al. <a
1998 href="http://www.w3.org/TR/2011/REC-CSS2-20110607"><cite>Cascading
1999 Style Sheets Level 2 Revision 1 (CSS 2.1)
2000 Specification.</cite></a> 7 June 2011. W3C Recommendation. URL: <a
2001 href="http://www.w3.org/TR/2011/REC-CSS2-20110607">http://www.w3.org/TR/2011/REC-CSS2-20110607</a>
2002 </dd>
2003 <!---->
2005 <dt id=CSS3CASCADE>[CSS3CASCADE]
2007 <dd>Håkon Wium Lie. <a
2008 href="http://www.w3.org/TR/2005/WD-css3-cascade-20051215"><cite>CSS3
2009 module: Cascading and inheritance.</cite></a> 15 December 2005. W3C
2010 Working Draft. (Work in progress.) URL: <a
2011 href="http://www.w3.org/TR/2005/WD-css3-cascade-20051215">http://www.w3.org/TR/2005/WD-css3-cascade-20051215</a>
2012 </dd>
2013 <!---->
2015 <dt id=CSS3COL>[CSS3COL]
2017 <dd>Håkon Wium Lie. <a
2018 href="http://www.w3.org/TR/2011/CR-css3-multicol-20110412"><cite>CSS
2019 Multi-column Layout Module.</cite></a> 12 April 2011. W3C Candidate
2020 Recommendation. (Work in progress.) URL: <a
2021 href="http://www.w3.org/TR/2011/CR-css3-multicol-20110412">http://www.w3.org/TR/2011/CR-css3-multicol-20110412</a>
2022 </dd>
2023 <!---->
2025 <dt id=CSS3COLOR>[CSS3COLOR]
2027 <dd>Tantek Çelik; Chris Lilley; L. David Baron. <a
2028 href="http://www.w3.org/TR/2011/REC-css3-color-20110607"><cite>CSS
2029 Color Module Level 3.</cite></a> 7 June 2011. W3C Recommendation. URL:
2030 <a
2031 href="http://www.w3.org/TR/2011/REC-css3-color-20110607">http://www.w3.org/TR/2011/REC-css3-color-20110607</a>
2032 </dd>
2033 <!---->
2035 <dt id=CSS3GRID>[CSS3GRID]
2037 <dd>Alex Mogilevsky; Markus Mielke. <a
2038 href="http://www.w3.org/TR/2007/WD-css3-grid-20070905"><cite>CSS Grid
2039 Positioning Module Level 3.</cite></a> 5 September 2007. W3C
2040 Working Draft. (Work in progress.) URL: <a
2041 href="http://www.w3.org/TR/2007/WD-css3-grid-20070905">http://www.w3.org/TR/2007/WD-css3-grid-20070905</a>
2042 </dd>
2043 <!---->
2044 </dl>
2045 <!--end-normative-->
2046 <h3 class=no-num id=other-references>Other references</h3>
2047 <!--begin-informative--> <!-- Sorted by label -->
2048 <dl class=bibliography>
2049 <dt style="display:
2050 none"><!-- keeps the doc valid if the DL is empty --> <!---->
2052 <dt id=CSS3CASCADE>[CSS3CASCADE]
2054 <dd>Håkon Wium Lie. <a
2055 href="http://www.w3.org/TR/2005/WD-css3-cascade-20051215"><cite>CSS3
2056 module: Cascading and inheritance.</cite></a> 15 December 2005. W3C
2057 Working Draft. (Work in progress.) URL: <a
2058 href="http://www.w3.org/TR/2005/WD-css3-cascade-20051215">http://www.w3.org/TR/2005/WD-css3-cascade-20051215</a>
2059 </dd>
2060 <!---->
2062 <dt id=CSS3NAMESPACE>[CSS3NAMESPACE]
2064 <dd>Elika J. Etemad; Anne van Kesteren. <a
2065 href="http://www.w3.org/TR/2008/CR-css3-namespace-20080523/"><cite>CSS
2066 Namespaces Module.</cite></a> 23 May 2008. W3C Candidate
2067 Recommendation. (Work in progress.) URL: <a
2068 href="http://www.w3.org/TR/2008/CR-css3-namespace-20080523/">http://www.w3.org/TR/2008/CR-css3-namespace-20080523/</a>
2069 </dd>
2070 <!---->
2072 <dt id=RFC1738>[RFC1738]
2074 <dd>T. Berners-Lee; L. Masinter; M. McCahill. <a
2075 href="http://www.ietf.org/rfc/rfc1738.txt"><cite>Uniform Resource
2076 Locators (URL).</cite></a> December 1994. Internet RFC 1738. URL: <a
2077 href="http://www.ietf.org/rfc/rfc1738.txt">http://www.ietf.org/rfc/rfc1738.txt</a>
2078 </dd>
2079 <!---->
2081 <dt id=RFC1808>[RFC1808]
2083 <dd>R. Fielding. <a
2084 href="http://www.ietf.org/rfc/rfc1808.txt"><cite>Relative Uniform
2085 Resource Locators.</cite></a> June 1995. Internet RFC 1808. (Obsoleted
2086 by RFC 3986) URL: <a
2087 href="http://www.ietf.org/rfc/rfc1808.txt">http://www.ietf.org/rfc/rfc1808.txt</a>
2088 </dd>
2089 <!---->
2090 </dl>
2091 <!--end-informative-->
2092 <h2 class=no-num id=index>Index</h2>
2093 <!--begin-index-->
2094 <ul class=indexlist>
2095 <li>absolute length units, <a href="#absolute-length-units"
2096 title="absolute length units"><strong>6.2.</strong></a>
2098 <li>actual value, <a href="#actual-value" title="actual
2099 value"><strong>8.4.</strong></a>
2101 <li><angle>, <a href="#angle-value"
2102 title="<angle>"><strong>7.1.</strong></a>
2104 <li>calc(), <a href="#calc" title="calc()"><strong>7.3.1.</strong></a>
2106 <li>ch, <a href="#ch-unit" title=ch><strong>6.1.1.</strong></a>
2108 <li>color, <a href="#color" title=color><strong>7.5.</strong></a>
2110 <li><color>, <a href="#ltcolorgt0"
2111 title="<color>"><strong>7.5.</strong></a>
2113 <li>compound value, <a href="#compound-value" title="compound
2114 value"><strong>3.2.</strong></a>
2116 <li>computed value, <a href="#computed-value" title="computed
2117 value"><strong>8.2.</strong></a>
2119 <li>deg, <a href="#deg" title=deg><strong>7.1.</strong></a>
2121 <li>dimension, <a href="#dimension"
2122 title=dimension><strong>6.</strong></a>
2124 <li>em, <a href="#em-unit" title=em><strong>6.1.1.</strong></a>
2126 <li>ex, <a href="#ex-unit" title=ex><strong>6.1.1.</strong></a>
2128 <li><frequency>, <a href="#frequency-value"
2129 title="<frequency>"><strong>7.3.</strong></a>
2131 <li>fr (unit), <a href="#fr" title="fr
2132 (unit)"><strong>7.9.1.</strong></a>
2134 <li>functional notation, <a href="#functional-notation0"
2135 title="functional notation"><strong>3.2.</strong></a>
2137 <li>grad, <a href="#grad" title=grad><strong>7.1.</strong></a>
2139 <li>gr (unit), <a href="#gr" title="gr
2140 (unit)"><strong>7.10.1.</strong></a>
2142 <li>Hz, <a href="#hz" title=Hz><strong>7.3.</strong></a>
2144 <li>identifier, <a href="#identifier"
2145 title=identifier><strong>4.</strong></a>
2147 <li><a href="#identifier-value"><code><identifier></code></a>, <a
2148 href="#identifier-value"
2149 title="<identifier>"><strong>4.2.</strong></a>
2151 <li>‘<code class=css>inherit</code>’, <a href="#inherit"
2152 title="''inherit''"><strong>4.1.1.</strong></a>
2154 <li>‘<code class=css>initial</code>’, <a href="#initial"
2155 title="''initial''"><strong>4.1.1.</strong></a>
2157 <li>integer, <a href="#integer" title=integer><strong>5.1.</strong></a>
2159 <li><a href="#integer-value"><code><integer></code></a>, <a
2160 href="#integer-value" title="<integer>"><strong>5.1.</strong></a>
2163 <li>kHz, <a href="#khz" title=kHz><strong>7.3.</strong></a>
2165 <li><a href="#length-value"><code><length></code></a>, <a
2166 href="#length-value" title="<length>"><strong>6.</strong></a>
2168 <li>max(), <a href="#max" title="max()"><strong>7.3.1.</strong></a>
2170 <li>min(), <a href="#min" title="min()"><strong>7.3.1.</strong></a>
2172 <li>ms, <a href="#ms" title=ms><strong>7.2.</strong></a>
2174 <li>newline, <a href="#newline" title=newline>3.1.</a>
2176 <li>number, <a href="#number" title=number><strong>5.2.</strong></a>
2178 <li><a href="#number-value"><code><number></code></a>, <a
2179 href="#number-value" title="<number>"><strong>5.2.</strong></a>
2181 <li><a href="#percentage-value"><code><percentage></code></a>, <a
2182 href="#percentage-value"
2183 title="<percentage>"><strong>5.3.</strong></a>
2185 <li>rad, <a href="#rad" title=rad><strong>7.1.</strong></a>
2187 <li>reference pixel, <a href="#reference-pixel" title="reference
2188 pixel"><strong>6.2.</strong></a>
2190 <li>relative length, <a href="#relative-length-units" title="relative
2191 length"><strong>6.1.</strong></a>
2193 <li>rem, <a href="#rem-unit" title=rem><strong>6.1.1.</strong></a>
2195 <li>Resource Identifier (URI), <a href="#uris0" title="Resource
2196 Identifier (URI)"><strong>7.7.</strong></a>
2198 <li>s, <a href="#s" title=s><strong>7.2.</strong></a>
2200 <li>simple value, <a href="#simple-value" title="simple
2201 value"><strong>3.2.</strong></a>
2203 <li>specified value, <a href="#specified-value" title="specified
2204 value"><strong>8.1.</strong></a>
2206 <li>string, <a href="#string" title=string><strong>3.1.</strong></a>
2208 <li><string>, <a href="#ltstringgt0"
2209 title="<string>"><strong>7.4.</strong></a>
2211 <li><time>, <a href="#time-value"
2212 title="<time>"><strong>7.2.</strong></a>
2214 <li>turn, <a href="#turn" title=turn><strong>7.1.</strong></a>
2216 <li>Uniform Resource Locator (URL), <a href="#urls" title="Uniform
2217 Resource Locator (URL)"><strong>7.7.</strong></a>
2219 <li>URI (Uniform Resource Identifier), <a href="#uris0" title="URI
2220 (Uniform Resource Identifier)"><strong>7.7.</strong></a>
2222 <li>URL (Uniform Resource Locator), <a href="#urls" title="URL (Uniform
2223 Resource Locator)"><strong>7.7.</strong></a>
2225 <li>used value, <a href="#used-value" title="used
2226 value"><strong>8.3.</strong></a>
2228 <li>vh, <a href="#vh-unit" title=vh><strong>6.1.2.</strong></a>
2230 <li>vm, <a href="#vm-unit" title=vm><strong>6.1.2.</strong></a>
2232 <li>vw, <a href="#vw-unit" title=vw><strong>6.1.2.</strong></a>
2233 </ul>
2234 <!--end-index-->
2235 </dl>