css3-multicol/Overview.src.html@34298d3d5627
css3-multicol/Overview.src.html
Thu, 07 Feb 2013 22:43:19 -0800
- author
- L. David Baron <dbaron@dbaron.org>
- date
- Thu, 07 Feb 2013 22:43:19 -0800
- changeset 7398
- 34298d3d5627
- parent 6240
- c685227b6e8a
- permissions
- -rw-r--r--
[css3-multicol] Add "Animatable:" lines to propdef tables.
This is as resolved in Tucson face-to-face at
2013-02-04 11:40:47 -0700, and edited by me per discussion starting at
2013-02-05 11:11:38 -0700.
1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
2 <html lang="en">
3 <head>
4 <title>CSS Multi-column Layout Module</title>
6 <link rel="stylesheet" type="text/css" href="../default.css">
8 <link href="http://www.w3.org/StyleSheets/TR/W3C-[STATUS].css" rel=stylesheet type="text/css">
10 <style type="text/css">
11 .cols { width: 500px; height: 200px; background: #fff; position: relative; border: solid 5px blue; margin: 0.5em 2em 1em 0; font: bold 14px/19px Arial, sans-serif }
12 .cols p { padding: 3px; margin: 0 }
13 .col { position: absolute; left: 0px; top: 0; z-index: 6; width: 170px }
14 .gap { position: absolute; background: green; width: 5px; bottom: 0px; top: 0px; border: 10px solid yellow; border-top-width: 0; border-bottom-width: 0; }
15 .rep { position: absolute; top: 45px; background: black; height: 110px; width: 100px; color: white; z-index: 4 }
17 table.breaks { border-collapse: collapse; margin: 1em 0 }
18 table.breaks td, table.breaks th { border: thin solid black; padding: 0.1em 0.2em }
20 div.example:before { width: 9em }
21 </style>
23 </head>
24 <body>
26 <div class="head">
28 <!--logo-->
31 <h1>CSS Multi-column Layout Module</h1>
33 <h2 class="no-num no-toc" id="w3c-working">[LONGSTATUS] [DATE]</h2>
35 <dl>
36 <dt>This version:</dt>
37 <dd>
38 <!--<a href="http://www.w3.org/TR/[YEAR]/CR-[SHORTNAME]-[CDATE]">[VERSION]</a>-->
39 <a href="http://dev.w3.org/csswg/css3-multicol/">http://dev.w3.org/csswg/css3-multicol/</a>
41 <dt>Latest version:
43 <dd><a href="http://www.w3.org/TR/css3-multicol">
44 http://www.w3.org/TR/css3-multicol</a>
46 <dt>Previous version:
48 <dd><a href="http://www.w3.org/TR/2009/CR-css3-multicol-20091217/">http://www.w3.org/TR/2009/CR-css3-multicol-20091217/</a>
50 <dt>Editors:
52 <dd>Håkon Wium Lie, Opera Software, howcome@opera.com
53 </dl>
55 <!--begin-copyright-->
56 <p>[If you keep the <!--comment-->, the copyright will be included
57 here automatically]</p>
58 <!--end-copyright-->
60 <hr title="Separator for header">
61 </div>
64 <h2 class="no-num no-toc" id=abstract>Abstract</h2>
66 <p>This specification describes multi-column layouts in CSS, a style
67 sheet language for the web. Using functionality described in the
68 specification, content can be flowed into multiple columns with a gap
69 and a rule between them.
71 <h2 class="no-num no-toc">Status of this document</h2>
73 <!--begin-status-->
74 <p>[If you keep the <!--comment-->, the status boilerplate will be
75 included here automatically.]</p>
76 <!--end-status-->
78 <p>This document has been a Working Draft in the CSS Working Group for
79 several years. Multi-column layouts are traditionally used in print.
80 On screen, multi-column layouts have been considered experimental, and
81 implementation and use experience was deemed necessary in order to
82 proceed. Several implementations have occurred over the past years, and
83 this specification incorporates useful feedback from implementors as well as
84 authors and users.
86 <p>The specification was updated in April 2011 to correct a
87 contradiction between the text and the pseudo-algorithm in
88 section 3.4. The pseudo-algorithm was corrected and also made
89 easier to read. The wording of a few other sections was improved in
90 places, without changes to the functionality. In January, 2012, some
91 examples and the description of the 'column-fill' property was
92 revised.
94 <p>This document will remain Candidate Recommendation at least until
95 12 May 2011. See the <a href="#cr-exit-criteria">CR exit
96 criteria.</a>
99 <h2 class="no-num no-toc"><a name="contents">Table of contents</a></h2>
101 <!--begin-toc-->
102 <p>[If you keep the <!--comment--> the table of contents will be
103 included here automatically.]</p>
104 <!--end-toc-->
107 <h2>Introduction</h2>
109 <p>(This section is not normative.)
111 <p>This module describes multi-column layout in CSS. By using
112 functionality described in this document, style sheets can declare
113 that the content of an element is to be laid out in multiple
114 columns.
116 <p>On the Web, tables have also been used to describe multi-column
117 layouts. The main benefit of using CSS-based columns is flexibility;
118 content can flow from one column to another, and the number of columns
119 can vary depending on the size of the viewport. Removing presentation
120 table markup from documents allows them to more easily be presented on
121 various output devices including speech synthesizers and small mobile
122 devices.
124 <p>Multi-column layouts are easy to describe in CSS. Here is a simple example:
126 <div class=example>
127 <pre>body { column-width: 12em }</pre>
129 <p>In this example, the <code class=html>body</code> element is
130 set to have columns at least ''12em'' wide. The exact number of
131 columns will depend on the available space.
133 </div>
135 <p>The number of columns can also be set explicitly in the style sheet:
137 <div class=example>
138 <pre>body { column-count: 2 }</pre>
140 <p>In this case, the number of columns is fixed and the column widths
141 will vary depending on the available width.
143 </div>
145 <p>The shorthand 'columns' property can be used to set either,
146 or both, properties in one declaration.
148 <div class=example>
150 <p>In these examples, the number of columns, the width of columns, and
151 both the number and width are set, respectively:
153 <pre>
154 body { columns: 2 }
155 body { columns: 12em }
156 body { columns: 2 12em }
157 </pre>
159 <p>However, as described below, setting both the width and number of
160 columns rarely makes sense.
162 </div>
164 <p>Another group of properties introduced in this module describe
165 gaps and rules between columns.
167 <div class=example>
168 <pre>
169 body {
170 column-gap: 1em;
171 column-rule: thin solid black;
172 }
173 </pre>
175 <p>The first declaration in the example above sets the gap between two
176 adjacent columns to be 1em. Column gaps are similar to padding areas.
177 In the middle of the gap there will be a rule which is described by
178 the 'column-rule' property.
179 </div>
181 <p>The values of the 'column-rule' property are similar to those of
182 the CSS border properties. Like 'border', 'column-rule' is a
183 shorthand property.
185 <div class=example>
186 <p>In this example, the shorthand 'column-rule' declaration from the
187 above example has been expanded:
189 <pre>
190 body {
191 column-gap: 1em;
192 column-rule-width: thin;
193 column-rule-style: solid;
194 column-rule-color: black;
195 }
196 </pre>
197 </div>
200 <p>The 'column-fill' and 'column-span' properties give style sheets a
201 wider range of visual expressions in multi-column layouts.
203 <div class=example>
204 <p>In this example, columns are set to be balanced, i.e., to have
205 approximately the same length. Also, <code>h2</code> elements are set
206 to span across all columns.
208 <pre>
209 div { column-fill: balance }
210 h2 { column-span: all }
211 </pre>
212 </div>
214 <p>This specification introduces ten new properties, all of which
215 are used in the examples above.
217 <p>To indicate where column breaks should (or should not) appear, new
218 keyword values are introduced.
220 <div class=example>
222 <p>In this example, <code>h1</code> elements will always have a column
223 break before them, but the formatter will try to avoid column breaks
224 inside and after the element.
226 <pre>
227 h1 {
228 break-before: column;
229 break-inside: avoid-column;
230 break-after: avoid-column;
231 }
232 </pre>
234 <!--<p>The properties and values used in this example are formally defined in [!CSS3PAGE]].-->
236 </div>
238 <p>If all column properties have their initial value, the layout of
239 an element will be identical to a multi-column layout with only one
240 column.
242 <h2>The multi-column model</h2>
244 <p>A <dfn>multi-column element</dfn> (or <em>multicol element</em>
245 for short) is an element whose 'column-width' or 'column-count'
246 property is not ''auto'' and therefore acts as a container for
247 multi-column layout.
249 <p>In the traditional CSS box model, the content of an element is
250 flowed into the content box of the corresponding element. Multi-column
251 layout introduces a new type of container between the content box and
252 the content, namely the <dfn>column box</dfn> (or <em>column</em> for
253 short). The content of a multicol element is flowed into its column
254 boxes.
256 <p>Column boxes in a multi-column element are arranged
257 into <em>rows</em>. Like table cells, the column boxes in a row are
258 ordered in the inline direction of the multicol element. The
259 <em>column width</em> is the length of the column box in the inline
260 direction. The <em>column height</em> is the length of the column box
261 in the block direction. All column boxes in a row have the same column width, and all
262 column boxes in a row have the same column height. Within each row in the multi-column element,
263 adjacent column boxes are separated by a <em>column gap</em>, which
264 may contain a <em>column rule</em>. All column gaps in the same row
265 are equal. All column rules in the same row are also equal, if they
266 appear; column rules only appear between columns that both have
267 content.
269 <p>In the simplest case a multicol element will contain only one row
270 of columns, and the height of each column will be equivalent to the
271 used height of the multi-column element's content box. If the
272 multi-column element is paginated, the height of each row is
273 constrained by the page and the content continues in a new row of
274 column boxes on the next page; a column box never splits across pages.
275 The same effect occurs when a <em>spanning element</em> divides the
276 multi-column element: the columns before the spanning element are
277 balanced and shortened to fit their content. Content after the
278 spanning element then flows into a new row of column boxes.
280 <p>It is not possible to set properties/values on column boxes. For
281 example, the background of a certain column box cannot be set and a
282 column box has no concept of padding, margin or borders.
284 <p class="note">Future specifications may add additional
285 functionality. For example, columns of different widths and different
286 backgrounds may be supported.</p>
289 <div class="example">
291 <p>Column gaps (yellow) and column rules (green) are shown in this
292 sample rendition of a multi-column element with padding (blue). The
293 blue and yellow is present for illustrational purposes only. In actual
294 implementations these areas will be determined by the background.
296 <div class=cols>
298 <div class="col" style="">
300 <p>
301 Ab cde fgh i jkl. Mno<br>
302 pqr stu vw xyz. A bc<br>
303 def g hij klm nopqrs<br>
304 tuv wxy z. Abc de fg<br>
305 hi jklmno. Pqrstu vw<br>
306 x yz. Abc def ghi jkl.<br>
307 M nop qrst uv wx yz.<br>
309 Ab cde fgh i jkl. Mno<br>
310 pqr stu vw xyz. A bc<br>
311 def g hij klm nopqrs
313 </div>
315 <div class="col" style="left: 175px">
316 <p>
317 tuv wxy z. Abc de fg<br>
318 hi jklmno. Pqrstu vw<br>
319 x yz. Abc def ghi jkl.<br>
320 M nop qrst uv wx yz.<br>
322 Ab cde fgh i jkl. Mno<br>
323 pqr stu vw xyz. A bc<br>
324 def g hij klm nopqrs<br>
325 tuv wxy z. Abc de fg<br>
326 hi jklmno. Pqrstu vw<br>
327 x yz. Abc def ghi jkl.<br>
330 </div>
333 <div class="col" style="left: 350px">
334 <p>
335 M nop qrst uv wx yz.<br>
337 Ab cde fgh i jkl. Mno<br>
338 pqr stu vw xyz. A bc<br>
339 def g hij klm nopqrs<br>
340 tuv wxy z. Abc de fg<br>
341 hi jklmno. Pqrstu vw<br>
342 x yz. Abc def ghi jkl.<br>
344 M nop qrst uv wx yz.<br>
345 Ab cde fgh i jkl. Mno<br>
346 Pqr stu vw xyz.
347 </div>
349 <div class=gap style="left: 150px"></div>
350 <div class=gap style="left: 325px"></div>
351 </div>
353 <p>To illustrate the effects of the various properties described in
354 this specification, variations on a sample document will be used. Here
355 is the source code of the sample document:
357 <pre class="html">
358 <html>
359 <style type="text/css">
360 div {
361 column-width: 15em;
362 column-gap: 2em; /* shown in yellow */
363 column-rule: 4px solid green;
364 padding: 5px; /* shown in blue */
365 }
366 p { margin: 0; padding: 0 }
367 img { display: none }
368 </style>
369 <body>
370 <div>
371 <p>Ab cde fgh i jkl. Mno
372 pqr stu vw xyz. A bc
373 <img src=...>
374 def g hij
375 ...
376 </div>
377 </body>
378 </html>
379 </pre>
381 <p>The nonsensical text in the example is the English alphabet which
382 shows how text flows from one column to another. To simplify the
383 visualization, the textual content of the different examples vary
384 slightly.
385 </div>
388 <p>Column boxes are block container boxes. That
389 is, column boxes behave like block-level, table cell, and inline-block
390 boxes as per CSS 2.1, section 10.1, item 2 [[!CSS21]]. However, column
391 boxes do not establish block container boxes for elements with ''position:
392 fixed'' or ''position: absolute''.
395 <div class=example>
397 <p>In this example, the width of the image is set with these rules:
399 <pre class=css>
400 img { display: block; width: 100% }
401 </pre>
403 <p>Given that the width is calculated relative to the column box, the
404 image will be as wide as the column box:
406 <div class=cols>
408 <p>Ab cde fgh i jkl. Mno<br>
409 pqr stu vw xyz. A bc<br>
411 <br><br><br><br><br><br>
413 def g hij klm nopqrs<br>
414 tuv wxy z. Abc de fg<br>
418 <div class="col" style="left: 175px">
419 <p>hi jklmno. Pqrstu vw<br>
420 x yz. Abc def ghi jkl.<br>
421 M nop qrst uv wx yz.<br>
423 Ab cde fgh i jkl. Mno<br>
424 pqr stu vw xyz. A bc<br>
425 def g hij klm nopqrs<br>
426 tuv wxy z. Abc de fg<br>
427 hi jklmno. Pqrstu vw<br>
428 x yz. Abc def ghi jkl.<br>
429 M nop qrst uv wx yz.<br>
431 </div>
433 <div class="col" style="left: 350px">
434 <p>
435 Ab cde fgh i jkl. Mno<br>
436 pqr stu vw xyz. A bc<br>
437 def g hij klm nopqrs<br>
438 tuv wxy z. Abc de fg<br>
439 hi jklmno. Pqrstu vw<br>
440 x yz. Abc def ghi jkl.<br>
442 M nop qrst uv wx yz.<br>
444 Ab cde fgh i jkl. Mno<br>
445 pqr stu vw xyz.
447 </div>
450 <div class=rep style="width: 150px"></div>
451 <div class=gap style="left: 150px"></div>
452 <div class=gap style="left: 325px"></div>
453 </div>
455 </div>
458 <p>Floats that appear inside multi-column layouts are positioned with
459 regard to the column box where the float appears.
461 <div class="example">
463 <p>In this example, this CSS fragment describes the presentation of the image:
465 <pre class="css">
466 img { display: block; float: right }
467 </pre>
469 <div class=cols>
471 <div class="col" style="">
473 <p>
474 Ab cde fgh i jkl. Mno<br>
475 pqr stu vw xyz. A bc<br>
476 def g<br>
477 hij klm<br>
478 nopq<br>
479 rs tuv<br>
480 wxy x<br>
481 yz. Ab <br>
482 cde fgh i jkl. Mno<br>
483 pqr stu vw xyz. A bc
485 </div>
487 <div class="col" style="left: 175px">
488 <p>
489 def g hij klm nopqrs<br>
490 tuv wxy z. Abc de fg<br>
491 hi jklmno. Pqrstu vw<br>
492 x yz. Abc def ghi jkl.<br>
493 M nop qrst uv wx yz.<br>
495 Ab cde fgh i jkl. Mno<br>
496 pqr stu vw xyz. A bc<br>
497 def g hij klm nopqrs<br>
498 tuv wxy z. Abc de fg<br>
499 hi jklmno. Pqrstu vw<br>
503 </div>
506 <div class="col" style="left: 350px">
507 <p>
508 x yz. Abc def ghi jkl.<br>
509 M nop qrst uv wx yz.<br>
511 Ab cde fgh i jkl. Mno<br>
512 pqr stu vw xyz. A bc<br>
513 def g hij klm nopqrs<br>
514 tuv wxy z. Abc de fg<br>
515 hi jklmno. Pqrstu vw<br>
516 x yz. Abc def ghi jkl.<br>
518 M nop qrst uv wx yz.<br>
520 </div>
522 <div class=rep style="left: 50px"></div>
524 <div class=gap style="left: 150px"></div>
525 <div class=gap style="left: 325px"></div>
526 </div>
528 <p>The black box represents the image.
530 </div>
532 <p>A multi-column element establishes a new block formatting context,
533 as per CSS 2.1 section 9.4.1.
535 <div class="example">
536 <p>A top margin set on the first child element of a multicol element will not collapse with the margins of the multicol element.
537 </div>
539 <p>Nested multi-column elements are allowed, but there may be
540 implementation-specific limits.
543 <h2>The number and width of columns</h2>
545 <p>Finding the number and width of columns is fundamental when
546 laying out multi-column content. When the block direction
547 is unconstrained and no column breaks are added through style sheets,
548 these two properties determine the outcome:
550 <ul>
551 <li>'column-count'
552 <li>'column-width'
553 </ul>
555 <p>A third property, 'columns', is a shorthand property which sets both
556 'column-width' and 'column-count'.
559 <h3 id='cw'>'column-width'</h3>
561 <table class=propdef>
562 <tr>
563 <td><em>Name:</em>
564 <td><dfn>column-width</dfn>
565 <tr>
566 <td><em>Value:</em>
567 <td><length> | auto
568 <tr>
569 <td><em>Initial:</em>
570 <td>auto
571 <tr>
572 <td><em>Applies to:</em>
573 <td>non-replaced block-level elements (except table elements), table cells, and inline-block elements
574 <tr>
575 <td><em>Inherited:</em>
576 <td>no
577 <tr>
578 <td><em>Percentages:</em>
579 <td>N/A
580 <tr>
581 <td><em>Media:</em>
582 <td>visual
583 <tr>
584 <td><em>Computed value:</em>
585 <td>the absolute length, zero or larger
586 <tr>
587 <td><em>Animatable:</em>
588 <td>as <a href="http://dev.w3.org/csswg/css3-transitions/#animtype-length">length</a>
589 </table>
591 <p>This property describes the width of columns in multicol elements.
593 <dl>
595 <dt>auto
597 <dd>means that the column width will be determined by other properties
598 (e.g., 'column-count', if it has a non-auto value).
600 <dt><length>
602 <dd>describes the optimal column width. The actual column width may be
603 wider (to fill the available space), or narrower (only if the
604 available space is smaller than the specified column width). Specified values
605 must be greater than 0.
607 </dl>
611 <div class=example>
612 <p>For example, consider this style sheet:</p>
613 <pre>
614 div {
615 width: 100px;
616 column-width: 45px;
617 column-gap: 0;
618 column-rule: none;
619 }
620 </pre>
622 <p>There is room for two 45px wide columns inside the 100px wide element. In
623 order to fill the available space the actual column width will be
624 increased to 50px.</p>
626 </div>
628 <div class=example>
629 <p>Also, consider this style sheet:</p>
631 <pre>
632 div {
633 width: 40px;
634 column-width: 45px;
635 column-gap: 0;
636 column-rule: none;
637 }
638 </pre>
640 <p>The available space is smaller than the specified column width and
641 the actual column width will therefore be decreased.</p>
643 </div>
645 <p>To ensure that 'column-width' can be used with vertical text,
646 column width means the length of the line boxes inside the columns.
648 <p class=note>The reason for making 'column-width' somewhat flexible
649 is to achieve scalable designs that can fit many screen sizes. To set
650 an exact column width, all length values (in horizontal text these
651 are: 'width', 'column-width', 'column-gap', and 'column-rule-width')
652 must be specified.</p>
655 <h3 id='cc'>'column-count'</h3>
657 <table class=propdef>
658 <tr>
659 <td><em>Name:</em>
660 <td><dfn>column-count</dfn>
661 <tr>
662 <td><em>Value:</em>
663 <td><integer> | auto
664 <tr>
665 <td><em>Initial:</em>
666 <td>auto
667 <tr>
668 <td><em>Applies to:</em>
669 <td>non-replaced block-level elements (except table elements), table cells, and inline-block elements
670 <tr>
671 <td><em>Inherited:</em>
672 <td>no
673 <tr>
674 <td><em>Percentages:</em>
675 <td>N/A
676 <tr>
677 <td><em>Media:</em>
678 <td>visual
679 <tr>
680 <td><em>Computed value:</em>
681 <td>specified value
682 <tr>
683 <td><em>Animatable:</em>
684 <td>as <a href="http://dev.w3.org/csswg/css3-transitions/#animtype-integer">integer</a>
685 </table>
687 <p>This property describes the number of columns of a multicol element.
689 <dl>
691 <dt>auto
693 <dd>means that the number of columns will be determined by other properties
694 (e.g., 'column-width', if it has a non-auto value).
696 <dt><integer>
698 <dd>describes the optimal number of columns into which the content of
699 the element will be flowed. Values must be greater than 0. If both
700 'column-width' and 'column-count' have non-auto values, the integer
701 value describes the maximum number of columns.
703 </dl>
706 <div class=example>
707 <p>Example:</p>
708 <pre>body { column-count: 3 }</pre>
709 </div>
712 <h3>'columns'</h3>
714 <table class=propdef>
715 <tr>
716 <td><em>Name:</em>
717 <td><dfn>columns</dfn>
718 <tr>
719 <td><em>Value:</em>
720 <td><a href='#cw'><'column-width'></a> || <a href='#cc'><'column-count'></a>
721 <tr>
722 <td><em>Initial:</em>
723 <td>see individual properties
724 <tr>
725 <td><em>Applies to:</em>
726 <td>non-replaced block-level elements (except table elements), table cells, and inline-block elements
727 <tr>
728 <td><em>Inherited:</em>
729 <td>no
730 <tr>
731 <td><em>Percentages:</em>
732 <td>N/A
733 <tr>
734 <td><em>Media:</em>
735 <td>visual
736 <tr>
737 <td><em>Computed value:</em>
738 <td>see individual properties
739 <tr>
740 <td><em>Animatable:</em>
741 <td>see individual properties
742 </table>
744 <p>This is a shorthand property for setting 'column-width' and
745 'column-count'. Omitted values are set to their initial values.
747 <div class="example">
748 <p>Here are some valid declarations using the 'columns' property:
749 <pre>
750 columns: 12em; /* column-width: 12em; column-count: auto */
751 columns: auto 12em; /* column-width: 12em; column-count: auto */
752 columns: 2; /* column-width: auto; column-count: 2 */
753 columns: 2 auto; /* column-width: auto; column-count: 2 */
754 columns: auto; /* column-width: auto; column-count: auto */
755 columns: auto auto; /* column-width: auto; column-count: auto */
756 </pre>
757 </div>
759 <h3>Pseudo-algorithm</h3>
761 <P>The pseudo-algorithm below determines the used values for
762 'column-count' (N) and 'column-width' (W). There are two other
763 variables in the pseudo-algorithm:
765 <ul>
767 <li><code>available-width</code>: if the used width of the
768 multi-column element has not been determined when the 'column-count'
769 and 'column-width' must be determined (e.g., if it is floating with a
770 'width' of 'auto' as per CSS 2.1 section 10.3.5) this variable is
771 <code>unknown</code>, otherwise it is the same as the used width of
772 the multi-column element. In vertical text, the used height replaces used width in this calculation.
774 <li><code>shrink-to-fit</code>: this variable represents the result of
775 a <em>shrink-to-fit</em> computation. CSS does not define the exact
776 algorithm.
778 </ul>
780 <p>Two assumptions are being made by the pseudo-algorithm:
782 <ul>
783 <li>that the block direction is unconstrained
784 <li>that no column breaks are added through style sheets
785 </ul>
787 <p>The <code>floor()</code> function rounds a number to the next smaller integer.
789 <!--
790 <pre>
791 (01) if ((column-width = auto) and (column-count = auto)) or
792 (02) ((available-width = unknown) and (column-count = auto)) then
793 (03) exit; /* no columns */
794 (04) fi
795 (05)
796 (06) if (available-width = unknown) and (column-count != auto) and (column-width != auto) then
797 (07) N := column-count;
798 (08) W := column-width;
799 (09) exit;
800 (10) fi
801 (11)
802 (12) if (available-width = unknown) then
803 (13) available-width := shrink-to-fit;
804 (14) fi
805 (15)
806 (16) if (column-width = auto) then
807 (18) N := column-count;
808 (19) W := max(0, (available-width - ((N - 1) * column-gap))/N);
809 (27) elsif (column-count = auto) then
810 (28) if (column-width >= available-width) then
811 (29) N := 1
812 (30) W := available-width;
813 (31) else
814 (32) N := floor((available-width + column-gap) / (column-width + column-gap));
815 (33) W := ((available-width + column-gap) / N) - column-gap;
816 (34) fi
817 (35) elsif (column-width >= available-width) then
818 (36) N := 1
819 (37) W := available-width;
820 (38) else
821 (39) N := min(column-count, floor((available-width + column-gap) / (column-width + column-gap)))
822 (40) W := ((available-width + column-gap) / N) - column-gap;
823 (41) fi
824 </pre>
826 <p><span class=issue>Alternative encoding of pseudo-algorithm:
827 -->
829 <pre>
830 (01) if ((column-width = auto) and (column-count = auto)) then
831 (02) exit; /* not a multicol element */
833 (03) if ((available-width = unknown) and (column-count = auto)) then
834 (04) exit; /* no columns */
836 (05) if (available-width = unknown) and (column-count != auto) and (column-width != auto) then
837 (06) N := column-count;
838 (07) W := column-width;
839 (08) exit;
841 (09) if (available-width = unknown) then
842 (10) available-width := shrink-to-fit;
844 (11) if (column-width = auto) and (column-count != auto) then
845 (12) N := column-count;
846 (13) W := max(0, (available-width - ((N - 1) * column-gap)) / N);
847 (14) exit;
849 (15) if (column-width != auto) and (column-count = auto) then
850 (16) N := max(1, floor((available-width + column-gap) / (column-width + column-gap)));
851 (17) W := ((available-width + column-gap) / N) - column-gap;
852 (18) exit;
854 (19) if (column-width != auto) and (column-count != auto) then
855 (20) N := min(column-count, floor((available-width + column-gap) / (column-width + column-gap)))
856 (21) N := max(1, N);
857 (22) W := ((available-width + column-gap) / N) - column-gap;
858 (23) exit
859 </pre>
862 <p>In paged media, user agents may perform this calculation on a
863 per-page basis.
865 <p class=note>Note that, in most cases, only one of 'column-width' and
866 'column-count' affect the layout. If 'column-width' has a value other
867 than ''auto'', 'column-count' indicates the maximum number of columns.
868 However, both 'column-width' and 'column-count' are honored when the
869 width of the element has not been determined. This can, e.g., be the
870 case for table cells and floats.
874 <h3>Stacking context</h3>
876 <p>All column boxes in a multi-column element are in the same stacking
877 context and the drawing order of their contents is as specified in
878 CSS 2.1. Column boxes do not establish new stacking contexts.
881 <h2>Column gaps and rules</h2>
883 <p>Column gaps and rules are placed between columns in the same
884 multicol element. The length of the column gaps and column rules
885 is equal to the length of the columns. Column gaps take up space. That
886 is, column gaps will push apart content in adjacent columns (within
887 the same multicol element).
889 <p>A column rule is drawn in the middle of the column gap with the
890 endpoints at opposing content edges of the multicol element. Column
891 rules do not take up space. That is, the presence or thickness of a
892 column rule will not alter the placement of anything else. If a column
893 rule is wider than its gap, the adjacent column boxes will overlap the
894 rule, and the rule may possibly extend outside the box of the multicol
895 element. Column rules are painted just above the background of the
896 multicol element. Column rules are only drawn between two columns that
897 both have content.
899 <h3>'column-gap'</h3>
901 <table class=propdef>
902 <tr>
903 <td><em>Name:</em>
904 <td><dfn>column-gap</dfn>
905 <tr>
906 <td><em>Value:</em>
907 <td><length> | normal
908 <tr>
909 <td><em>Initial:</em>
910 <td>normal
911 <tr>
912 <td><em>Applies to:</em>
913 <td>multicol elements
914 <tr>
915 <td><em>Inherited:</em>
916 <td>no
917 <tr>
918 <td><em>Percentages:</em>
919 <td>N/A
920 <tr>
921 <td><em>Media:</em>
922 <td>visual
923 <tr>
924 <td><em>Computed value:</em>
925 <td>absolute length or 'normal'
926 <tr>
927 <td><em>Animatable:</em>
928 <td>as <a href="http://dev.w3.org/csswg/css3-transitions/#animtype-length">length</a>
929 </table>
932 <p>The 'column-gap' property sets the gap between columns. If there is
933 a column rule between columns, it will appear in the middle of the
934 gap.
936 <p>The ''normal'' value is UA-specific. A value of ''1em'' is suggested.
938 <p>Column gaps cannot be negative.
940 <h3 id='crc'>'column-rule-color'</h3>
942 <table class=propdef>
943 <tr>
944 <td><em>Name:</em>
945 <td><dfn>column-rule-color</dfn>
946 <tr>
947 <td><em>Value:</em>
948 <td><color>
949 <tr>
950 <td><em>Initial:</em>
951 <td><a href="http://www.w3.org/TR/css3-color/#currentcolor">currentColor</a>
952 <!-- <td>same as for 'color' property [[!CSS21]]-->
953 <tr>
954 <td><em>Applies to:</em>
955 <td>multicol elements
956 <tr>
957 <td><em>Inherited:</em>
958 <td>no
959 <tr>
960 <td><em>Percentages:</em>
961 <td>N/A
962 <tr>
963 <td><em>Media:</em>
964 <td>visual
965 <tr>
966 <td><em>Computed value:</em>
967 <td>the same as the computed value for the 'color' property [[!CSS21]]
968 <tr>
969 <td><em>Animatable:</em>
970 <td>as <a href="http://dev.w3.org/csswg/css3-transitions/#animtype-color">color</a>
971 </table>
973 <p>This property sets the color of the column rule. The <color>
974 values are defined in [[!CSS21]].
976 <h3 id='crs'>'column-rule-style'</h3>
978 <table class=propdef>
979 <tr>
980 <td><em>Name:</em>
981 <td><dfn>column-rule-style</dfn>
982 <tr>
983 <td><em>Value:</em>
984 <td><a href="http://www.w3.org/TR/CSS2/tables.html#table-border-styles"><border-style></a>
986 <!--http://www.w3.org/TR/CSS21/box.html#value-def-border-style-->
988 <tr>
989 <td><em>Initial:</em>
990 <td>none
991 <tr>
992 <td><em>Applies to:</em>
993 <td>multicol elements
994 <tr>
995 <td><em>Inherited:</em>
996 <td>no
997 <tr>
998 <td><em>Percentages:</em>
999 <td>N/A
1000 <tr>
1001 <td><em>Media:</em>
1002 <td>visual
1003 <tr>
1004 <td><em>Computed value:</em>
1005 <td>specified value
1006 <tr>
1007 <td><em>Animatable:</em>
1008 <td>no
1009 </table>
1011 <p>The 'column-rule-style' property sets the style of the rule between columns of an element. The <border-style> values are defined in [[!CSS21]] and the values are interpreted as in the <a href="http://www.w3.org/TR/CSS2/tables.html#collapsing-borders">the collapsing border model</a>.
1013 <p>The 'none' value forces the computed value of <span class="property">'column-rule-width'</span> to be '0'.
1016 <h3 id='crw'>'column-rule-width'</h3>
1018 <table class=propdef>
1019 <tr>
1020 <td><em>Name:</em>
1021 <td><dfn>column-rule-width</dfn>
1022 <tr>
1023 <td><em>Value:</em>
1024 <td><a href="http://www.w3.org/TR/CSS21/box.html#value-def-border-width"><border-width></a>
1025 <tr>
1026 <td><em>Initial:</em>
1027 <td>medium
1028 <tr>
1029 <td><em>Applies to:</em>
1030 <td>multicol elements
1031 <tr>
1032 <td><em>Inherited:</em>
1033 <td>no
1034 <tr>
1035 <td><em>Percentages:</em>
1036 <td>N/A
1037 <tr>
1038 <td><em>Media:</em>
1039 <td>visual
1040 <tr>
1041 <td><em>Computed value:</em>
1042 <td>absolute length; '0' if the column rule style is 'none' or 'hidden'
1043 <tr>
1044 <td><em>Animatable:</em>
1045 <td>as <a href="http://dev.w3.org/csswg/css3-transitions/#animtype-length">length</a>
1046 </table>
1048 <p>This property sets the width of the rule between columns. Negative values are not allowed.
1051 <h3>'column-rule'</h3>
1053 <table class=propdef>
1054 <tr>
1055 <td><em>Name:</em>
1056 <td><dfn>column-rule</dfn>
1057 <tr>
1058 <td><em>Value:</em>
1059 <td><a href='#crw'><'column-rule-width'></a> || <a href='#crs'><'column-rule-style'></a> || [ <a href='#crc'><'column-rule-color'></a> | transparent ]
1060 <tr>
1061 <td><em>Initial:</em>
1062 <td>see individual properties
1063 <tr>
1064 <td><em>Applies to:</em>
1065 <td>multicol elements
1066 <tr>
1067 <td><em>Inherited:</em>
1068 <td>no
1069 <tr>
1070 <td><em>Percentages:</em>
1071 <td>N/A
1072 <tr>
1073 <td><em>Media:</em>
1074 <td>visual
1075 <tr>
1076 <td><em>Computed value:</em>
1077 <td>see individual properties
1078 <tr>
1079 <td><em>Animatable:</em>
1080 <td>see individual properties
1081 </table>
1083 <p>This property is a shorthand for setting
1084 'column-rule-width', 'column-rule-style', and 'column-rule-color' at
1085 the same place in the style sheet. Omitted values are set to their
1086 initial values.
1088 <div class=example>
1090 <p>In this example, the column rule and the column gap have the same
1091 width. Therefore, they will occupy exactly the same space.
1093 <pre>
1094 body {
1095 column-gap: 1em;
1096 column-rule-width: 1em;
1097 column-rule-style: solid;
1098 column-rule-color: black;
1099 }
1100 </pre>
1101 </div>
1104 <div class=example>
1105 <p>If a tall image is moved to a column on the next page to find room
1106 for it, its natural column may be left empty. If so, the column is is
1107 still considered to have content for the purpose of deciding if the
1108 column rule should be drawn.
1109 </div>
1113 <h2>Column breaks</h2>
1115 <p>When content is laid out in multiple columns, the user agent must
1116 determine where column breaks are placed. The problem of breaking
1117 content into columns is similar to breaking content into pages, which
1118 is described in CSS 2.1, section 13.3.3 [[!CSS21]].
1120 <p>Three new properties are introduced to allow column breaks to be
1121 described in the same properties as page breaks: 'break-before',
1122 'break-after', and 'break-inside'. These properties take the same
1123 values as 'page-break-before', 'page-break-after', and
1124 'page-break-inside' [[!CSS21]]. In addition, some new keyword values
1125 are added.
1128 <h3>'break-before', 'break-after', 'break-inside'</h3>
1130 <table class=propdef>
1131 <tr>
1132 <td><em>Name:</em>
1133 <td><dfn>break-before</dfn>
1134 <tr>
1135 <td><em>Value:</em>
1136 <td>auto | always | avoid | left | right | page | column | avoid-page | avoid-column
1137 <tr>
1138 <td><em>Initial:</em>
1139 <td>auto
1140 <tr>
1141 <td><em>Applies to:</em>
1142 <td>block-level elements
1143 <tr>
1144 <td><em>Inherited:</em>
1145 <td>no
1146 <tr>
1147 <td><em>Percentages:</em>
1148 <td>N/A
1149 <tr>
1150 <td><em>Media:</em>
1151 <td>paged
1152 <tr>
1153 <td><em>Computed value:</em>
1154 <td>specified value
1155 <tr>
1156 <td><em>Animatable:</em>
1157 <td>no
1158 </table>
1160 <table class=propdef>
1161 <tr>
1162 <td><em>Name:</em>
1163 <td><dfn>break-after</dfn>
1164 <tr>
1165 <td><em>Value:</em>
1166 <td>auto | always | avoid | left | right | page | column | avoid-page | avoid-column
1167 <tr>
1168 <td><em>Initial:</em>
1169 <td>auto
1170 <tr>
1171 <td><em>Applies to:</em>
1172 <td>block-level elements
1173 <tr>
1174 <td><em>Inherited:</em>
1175 <td>no
1176 <tr>
1177 <td><em>Percentages:</em>
1178 <td>N/A
1179 <tr>
1180 <td><em>Media:</em>
1181 <td>paged
1182 <tr>
1183 <td><em>Computed value:</em>
1184 <td>specified value
1185 <tr>
1186 <td><em>Animatable:</em>
1187 <td>no
1188 </table>
1192 <table class=propdef>
1193 <tr>
1194 <td><em>Name:</em>
1195 <td><dfn>break-inside</dfn>
1196 <tr>
1197 <td><em>Value:</em>
1198 <td>auto | avoid | avoid-page | avoid-column
1199 <tr>
1200 <td><em>Initial:</em>
1201 <td>auto
1202 <tr>
1203 <td><em>Applies to:</em>
1204 <td>block-level elements
1205 <tr>
1206 <td><em>Inherited:</em>
1207 <td>no
1208 <tr>
1209 <td><em>Percentages:</em>
1210 <td>N/A
1211 <tr>
1212 <td><em>Media:</em>
1213 <td>paged
1214 <tr>
1215 <td><em>Computed value:</em>
1216 <td>specified value
1217 <tr>
1218 <td><em>Animatable:</em>
1219 <td>no
1220 </table>
1223 <p>These properties describe page/column break behavior before/after/inside the generated box. These values are normatively defined in [[!CSS21]]:
1225 <dl>
1226 <dt>auto
1227 <dd>Neither force nor forbid a page/column break before (after, inside) the generated box.
1228 <dt>always
1229 <dd>Always force a page break before (after) the generated box.
1230 <dt>avoid
1231 <dd>Avoid a page/column break before (after, inside) the generated box.
1232 <dt>left
1233 <dd>Force one or two page breaks before (after) the generated box so that the next page is formatted as a left page.
1234 <dt>right
1235 <dd>Force one or two page breaks before (after) the generated box so that the next page is formatted as a right page.
1236 </dl>
1238 <p>This specification adds the following new values:
1240 <dl>
1241 <dt>page
1242 <dd>Always force a page break before (after) the generated box.
1243 <dt>column
1244 <dd>Always force a column break before (after) the generated box.
1245 <dt>avoid-page
1246 <dd>Avoid a page break before (after, inside) the generated box.
1247 <dt>avoid-column
1248 <dd>Avoid a column break before (after, inside) the generated box.
1249 </dl>
1251 <p>When a page or column break splits a box, the box's margins,
1252 borders, and padding have no visual effect where the split occurs.
1253 However, the margin immediately after a forced page/column break will
1254 be preserved. A forced page/column break is a break that does not occur
1255 naturally.
1257 <p class=note>In the future, new properties may describe alternate
1258 ways to handle margins, borders and padding around page/column breaks.
1260 <div class="example">
1262 <p>In this example, forced column breaks appear before <code>h2</code>
1263 elements and after <code>img</code> elements:
1265 <pre>
1266 .multicol { column-width: 8em }
1267 .multicol h2 { break-before: column; margin-top: 2em }
1268 .multicol img { break-after: column }
1269 </pre>
1271 <p>The top margin of <code>h2</code> elements will be preserved since the column break is forced.
1273 </div>
1275 <div class="example">
1277 <p>In this example, the formatter will try avoid column breaks inside <code>p</code> elements:
1279 <pre>
1280 p { break-inside: avoid-column }
1281 </pre>
1282 </div>
1286 <h2>Spanning columns</h2>
1288 <p>The 'column-span' property makes it possible for an element to span
1289 across several columns.
1292 <h3>'column-span'</h3>
1294 <table class=propdef>
1295 <tr>
1296 <td><em>Name:</em>
1297 <td><dfn>column-span</dfn>
1298 <tr>
1299 <td><em>Value:</em>
1300 <td>none | all
1301 <tr>
1302 <td><em>Initial:</em>
1303 <td>none
1304 <tr>
1305 <td><em>Applies to:</em>
1306 <td>in-flow block-level elements
1307 <tr>
1308 <td><em>Inherited:</em>
1309 <td>no
1310 <tr>
1311 <td><em>Percentages:</em>
1312 <td>N/A
1313 <tr>
1314 <td><em>Media:</em>
1315 <td>visual
1316 <tr>
1317 <td><em>Computed value:</em>
1318 <td>specified value
1319 <tr>
1320 <td><em>Animatable:</em>
1321 <td>no
1322 </table>
1324 <p>This property describes how many columns an element spans across. Values are:
1326 <dl>
1328 <dt>none
1330 <dd>The element does not span multiple columns.
1332 <dt>all
1334 <dd>The element spans across all columns of the nearest multicol
1335 ancestor in the same block formatting context. The element spans
1336 across all columns. Content in the normal flow that appears before the
1337 element is automatically balanced across all columns before the
1338 element appears. The element establishes a new block formatting
1339 context.
1341 </dl>
1343 <p>An element that spans more than one column is called a
1344 <dfn>spanning element</dfn> and the box it creates is called a <dfn>spanner</dfn>.
1346 <!--
1347 <p>This property has no effect on elements that do not fit entirely
1348 within the multicol element. Also, if a setting on this property pushes the
1349 element outside a multicol element, this property will have no effect.
1350 -->
1352 <div class="example">
1354 <p>In this example, an <code>h2</code> element has been added to the
1355 sample document after the sixth sentence (i.e., after the word "jkl."). This styling applies:
1357 <pre class="css">
1358 h2 { column-span: all; background: silver }
1359 img { display: none }
1360 </pre>
1362 <p>By setting 'column-span' to ''all'', all content that appear before
1363 the <code>h2</code> element is shown before the <code>h2</code>
1364 element.
1366 <div class=cols>
1368 <p>Ab cde fgh i jkl. Mno<br>
1369 pqr stu vw xyz. A bc<br>
1371 <br><br>
1373 M nop qrst uv wx yz.<br>
1374 Ab cde fgh i jkl. Mno<br>
1375 pqr stu vw xyz. A bc<br>
1376 def g hij klm nopqrs<br>
1377 tuv wxy z. Abc de fg<br>
1378 hi jklmno. Pqrstu vw<br>
1382 <div class="col" style="left: 175px">
1383 <p>def g hij klm nopqrs<br>
1384 tuv wxy z. Abc de fg<br>
1385 <br><br>
1386 x yz. Abc def ghi jkl.<br>
1387 M nop qrst uv wx yz.<br>
1388 Ab cde fgh i jkl. Mno<br>
1389 pqr stu vw xyz. A bc<br>
1390 def g hij klm nopqrs<br>
1391 tuv wxy z. Abc de fg<br>
1394 </div>
1396 <div class="col" style="left: 350px">
1397 <p>
1398 hi jklmno. Pqrstu vw<br>
1399 x yz. Abc def ghi jkl.<br>
1400 <br><br>
1401 hi jklmno. Pqrstu vw<br>
1402 x yz. Abc def ghi jkl.<br>
1403 M nop qrst uv wx yz.<br>
1404 Ab cde fgh i jkl. Mno<br>
1405 pqr stu vw xyz.
1407 </div>
1410 <div class=rep style="width: 490px; height: 20px; background: silver; font-size: 1.5em; padding: 5px">An H2 element</div>
1411 <div class=gap style="left: 150px"></div>
1412 <div class=gap style="left: 325px"></div>
1413 </div>
1414 </div>
1417 <p>A spanning element takes up more space than the element would take
1418 up otherwise. When space is limited, it may be impossible to find room
1419 for the spanning element. In these cases, user agents may treat the
1420 element as if 'none' had been specified on this property.
1422 <div class="example">
1424 <p>In this example, the
1425 H2 element appears later in the content, and the height of the
1426 multicol element is constrained. Therefore, the H2 element appears in
1427 the overflow and there is not room to make the element spanning.
1428 As a result, the element appears as if 'column-span: none' was
1429 specified.
1431 <div class=cols style="height: 100px">
1433 <div class="col" style="">
1434 <p>
1435 Ab cde fgh i jkl. Mno<br>
1436 pqr stu vw xyz. A bc<br>
1437 def g hij klm nopqrs<br>
1438 tuv wxy z. Abc de fg<br>
1439 hi jklmno. Pqrstu vw<br>
1440 </div>
1442 <div class="col" style="left: 175px">
1443 <p>
1444 x yz. Abc def ghi jkl.<br>
1445 M nop qrst uv wx yz.<br>
1446 Ab cde fgh i jkl. Mno<br>
1447 pqr stu vw xyz. A bc<br>
1448 def g hij klm nopqrs
1449 </div>
1451 <div class="col" style="left: 350px">
1452 <p>
1453 tuv wxy z. Abc de fg<br>
1454 hi jklmno. Pqrstu vw<br>
1455 x yz. Abc def ghi jkl.<br>
1456 M nop qrst uv wx yz.<br>
1457 Ab cde fgh i jkl. Mno<br>
1458 </div>
1460 <div class="col" style="left: 525px">
1461 <p>pqr stu vw xyz.
1462 <div class=rep style="width: 140px; height: 40px; background: silver; font-size: 1.5em; padding: 5px; margin: 0; position: static">An H2 element</div>
1463 A bc def g hij klm
1464 </div>
1467 <div class="col" style="left: 700px">
1468 nopqrs tuv wxy z.
1469 </div>
1472 <div class=gap style="left: 150px"></div>
1473 <div class=gap style="left: 325px"></div>
1474 <div class=gap style="left: 500px"></div>
1475 <div class=gap style="left: 675px"></div>
1477 </div>
1479 </div>
1484 <div class="example">
1486 <p>This example is similar to the previous example, except that the H2 element appears naturally in the last column. Still, there is not enough room to make the element spanning.
1488 <div class=cols style="height: 100px">
1490 <div class="col" style="">
1491 <p>
1492 Ab cde fgh i jkl. Mno<br>
1493 pqr stu vw xyz. A bc<br>
1494 def g hij klm nopqrs<br>
1495 tuv wxy z. Abc de fg<br>
1496 hi jklmno. Pqrstu vw<br>
1497 </div>
1499 <div class="col" style="left: 175px">
1500 <p>
1501 x yz. Abc def ghi jkl.<br>
1502 M nop qrst uv wx yz.<br>
1503 Ab cde fgh i jkl. Mno<br>
1504 pqr stu vw xyz. A bc<br>
1505 def g hij klm nopqrs
1506 </div>
1508 <div class="col" style="left: 350px">
1509 <p>
1510 tuv wxy z. Abc de fg<br>
1511 hi jklmno.
1512 <div class=rep style="width: 140px; height: 40px; background: silver; font-size: 1.5em; padding: 5px; margin: 0; position: static">An H2 element</div>
1513 </div>
1515 <div class="col" style="left: 525px">
1516 <p>A bc def g hij klm<br>
1517 nop w rstu vw xyz.
1518 </div>
1521 <div class=gap style="left: 150px"></div>
1522 <div class=gap style="left: 325px"></div>
1523 <div class=gap style="left: 500px"></div>
1525 </div>
1527 </div>
1530 <div class="example">
1532 <p>In paged media spanning elements are honored on all pages. In this example, the first three paragraphs have column breaks after them. An spanning <code>H2</code> element appears after the fourth paragraph. This would appear on the first page:
1534 <div class=cols style="height: 80px; border-bottom: none">
1536 <div class="col" style="">
1538 <p>
1539 Ab cde fgh i jkl. Mno<br>
1540 pqr stu vw xyz.
1541 </div>
1543 <div class="col" style="left: 175px">
1544 <p>
1545 Ab cde fgh i jkl. Mno<br>
1546 pqr stu vw xyz. A bc<br>
1547 def g hij klm nopqrs<br>
1548 tuv wxy z.
1549 </div>
1551 <div class="col" style="left: 350px">
1552 <p>
1553 Ab cde fgh i jkl mno.<br>
1554 Pq rstu vwxyz.
1555 </div>
1558 <div class=gap style="left: 150px"></div>
1559 <div class=gap style="left: 325px"></div>
1560 </div>
1562 <p>This would appear on the second page:
1564 <div class=cols style="height: 200px; border-top: none">
1567 <p>Ab cde fgh i jkl. Mno<br>
1568 pqr stu vw xyz. A bc<br>
1570 <br><br>
1572 M nop qrst uv wx yz.<br>
1573 Ab cde fgh i jkl. Mno<br>
1574 pqr stu vw xyz. A bc<br>
1575 def g hij klm nopqrs<br>
1576 tuv wxy z. Abc de fg<br>
1577 hi jklmno. Pqrstu vw<br>
1581 <div class="col" style="left: 175px">
1582 <p>def g hij klm nopqrs<br>
1583 tuv wxy z. Abc de fg<br>
1584 <br><br>
1585 x yz. Abc def ghi jkl.<br>
1586 M nop qrst uv wx yz.<br>
1587 Ab cde fgh i jkl. Mno<br>
1588 pqr stu vw xyz. A bc<br>
1589 def g hij klm nopqrs<br>
1590 tuv wxy z. Abc de fg<br>
1593 </div>
1595 <div class="col" style="left: 350px">
1596 <p>
1597 hi jklmno. Pqrstu vw<br>
1598 x yz. Abc def ghi jkl.<br>
1599 <br><br>
1600 hi jklmno. Pqrstu vw<br>
1601 x yz. Abc def ghi jkl.<br>
1602 M nop qrst uv wx yz.<br>
1603 Ab cde fgh i jkl. Mno<br>
1604 pqr stu vw xyz.
1606 </div>
1609 <div class=rep style="width: 490px; height: 20px; background: silver; font-size: 1.5em; padding: 5px">An H2 element</div>
1610 <div class=gap style="left: 150px"></div>
1611 <div class=gap style="left: 325px"></div>
1612 </div>
1613 </div>
1618 <h2>Filling columns</h2>
1620 <p>There are two strategies for filling columns: columns can either be
1621 balanced, or not. If columns are balanced, user agents should try to
1622 fill all columns in a row so that the columns appear to have the same
1623 amount of content, while also trying to minimize the overflow content.
1624 If columns are not balanced, they are filled sequentially; some
1625 columns may end up partially filled, or with no content at all. In any
1626 case, user agents must honor forced page breaks and should try to
1627 honor 'widows', 'orphans' and other properties that may affect column
1628 lengths.
1630 <h3 id='cf'>'column-fill'</h3>
1632 <table class=propdef>
1633 <tr>
1634 <td><em>Name:</em>
1635 <td><dfn>column-fill</dfn>
1636 <tr>
1637 <td><em>Value:</em>
1638 <td>auto | balance
1639 <tr>
1640 <td><em>Initial:</em>
1641 <td>balance
1642 <tr>
1643 <td><em>Applies to:</em>
1644 <td>multicol elements
1645 <tr>
1646 <td><em>Inherited:</em>
1647 <td>no
1648 <tr>
1649 <td><em>Percentages:</em>
1650 <td>N/A
1651 <tr>
1652 <td><em>Media:</em>
1653 <td>see below
1654 <tr>
1655 <td><em>Computed value:</em>
1656 <td>specified value
1657 <tr>
1658 <td><em>Animatable:</em>
1659 <td>no
1660 </table>
1662 <p>The values are:
1664 <dl>
1665 <dt>balance
1666 <dd>Balance content equally between columns, if possible.
1667 <dt>auto
1668 <dd>Fills columns sequentially.
1669 </dl>
1671 <!--
1672 <p>In continuous media, this property will only be consulted if the
1673 length of columns has been constrained. Otherwise, columns will
1674 automatically be balanced.
1675 -->
1677 <p>In continuous media, this property does not have any effect in
1678 overflow columns (see below).
1680 <!--
1681 <p>In paged media, this property will only have
1682 effect on the last page the multicol element appears on.
1683 -->
1685 <h2>Overflow</h2>
1687 <h3>Overflow inside multicol elements</h3>
1689 <p>Content in the normal flow that extends into column gaps (e.g.,
1690 long words or images) is clipped in the middle of the column gap.
1692 <div class=example>
1694 <p>In this example, the black image is wider than the column, and is
1695 therefore clipped.
1697 <div class=cols>
1698 <p>Lorem ipsum dolor<br>sit amet. Nam at jus.
1699 <br><br><br><br><br><br><br>
1700 Sed imp er di et ris.<br>Cur abi tur et sapen.
1702 <div style="position: absolute; left: 175px; top: 0; z-index: 6;">
1703 <p>Lorem ipsum dolor<br>sit amet. Nam at jus.<br>
1704 Sed imp er di et ris.<br>Cur abi tur et sapen.<br>
1705 Vivamus a metus.<br> Aenean at risus<br> pharetra ante
1706 luctu<br> feugiat quis enim.<br> Cum sociis natoque<br>
1707 penatibus et magni.</div>
1709 <div style="position: absolute; left: 350px; top: 0; z-index: 6;">
1710 <p>Lorem ipsum dolor<br>sit amet. Nam at jus.<br>
1711 Sed imp er di et ris.<br>Cur abi tur et sapen.<br>
1712 Vivamus a metus.<br> Aenean at risus<br> pharetra ante
1713 luctu<br> feugiat quis enim.<br> Cum sociis natoque<br>
1714 penatibus et magni.</div>
1716 <div class=rep style="width: 163px"></div>
1717 <div class=gap style="left: 150px"></div>
1718 <div class=gap style="left: 325px"></div>
1719 </div>
1721 </div>
1724 <h3>Pagination and overflow outside multicol elements</h3>
1726 <p>Content and column rules that extend outside column boxes at
1727 the edges of the multi-column element are clipped according to the
1728 'overflow' property.
1730 <p>A multicol element can have more columns than it has room for due to:
1732 <ul>
1734 <li>a declaration that constrains the column height (e.g., using
1735 'height' or 'max-height'). In this case, additional column boxes
1736 are created in the inline direction
1738 <li>the size of the page. In this case, additional column boxes are
1739 moved to the next page(s).
1741 <li>explicit column breaks. In this case, additional column boxes are
1742 created in the inline direction for continuous media, and
1743 additional column boxes are moved to the next page(s) for paged
1744 media.
1746 </ul>
1748 <p>Columns that appear outside the multicol element in continuous media
1749 are called <dfn>overflow columns</dfn>.
1751 <div class="example">
1753 <p>In this example, the height of the multi-column element has been
1754 constrained to a maximum height. Also, the style sheet specifies that
1755 overflowing content should be visible:
1757 <pre class=css>
1758 div {
1759 max-height: 5em;
1760 overflow: visible;
1761 }
1762 </pre>
1764 <p>As a result, the number of columns is increased.
1766 <div class=cols style="height: 100px">
1768 <div class="col" style="">
1770 <p>
1771 Ab cde fgh i jkl. Mno<br>
1772 pqr stu vw xyz. A bc<br>
1773 def g hij klm nopqrs<br>
1774 tuv wxy z. Abc de fg<br>
1775 hi jklmno. Pqrstu vw<br>
1776 </div>
1778 <div class="col" style="left: 175px">
1779 <p>
1780 x yz. Abc def ghi jkl.<br>
1781 M nop qrst uv wx yz.<br>
1782 Ab cde fgh i jkl. Mno<br>
1783 pqr stu vw xyz. A bc<br>
1784 def g hij klm nopqrs
1785 </div>
1787 <div class="col" style="left: 350px">
1788 <p>
1789 tuv wxy z. Abc de fg<br>
1790 hi jklmno. Pqrstu vw<br>
1791 x yz. Abc def ghi jkl.<br>
1792 M nop qrst uv wx yz.<br>
1793 Ab cde fgh i jkl. Mno<br>
1794 </div>
1796 <div class="col" style="left: 525px">
1797 <p>
1798 pqr stu vw xyz. A bc<br>
1799 def g hij klm nopqrs<br>
1800 tuv wxy z. Abc de fg<br>
1801 hi jklmno. Pqrstu vw<br>
1802 x yz. Abc def ghi jkl.<br>
1803 </div>
1805 <div class=gap style="left: 150px"></div>
1806 <div class=gap style="left: 325px"></div>
1807 <div class=gap style="left: 500px"></div>
1808 </div>
1810 </div>
1812 <div class="example">
1814 <p>In paged media, the overflow content goes into column on subsequent pages. Given the same content as in the previous example and a page box that only has room for five lines of formatted text, this would appear on the first page:
1816 <div class=cols style="height: 100px; border-bottom: none">
1818 <div class="col" style="">
1820 <p>
1821 Ab cde fgh i jkl. Mno<br>
1822 pqr stu vw xyz. A bc<br>
1823 def g hij klm nopqrs<br>
1824 tuv wxy z. Abc de fg<br>
1825 hi jklmno. Pqrstu vw<br>
1826 </div>
1828 <div class="col" style="left: 175px">
1829 <p>
1830 x yz. Abc def ghi jkl.<br>
1831 M nop qrst uv wx yz.<br>
1832 Ab cde fgh i jkl. Mno<br>
1833 pqr stu vw xyz. A bc<br>
1834 def g hij klm nopqrs
1835 </div>
1837 <div class="col" style="left: 350px">
1838 <p>
1839 tuv wxy z. Abc de fg<br>
1840 hi jklmno. Pqrstu vw<br>
1841 x yz. Abc def ghi jkl.<br>
1842 M nop qrst uv wx yz.<br>
1843 Ab cde fgh i jkl. Mno<br>
1844 </div>
1847 <div class=gap style="left: 150px"></div>
1848 <div class=gap style="left: 325px"></div>
1849 </div>
1851 <p>Assuming column balancing, this would appear on the second page:
1853 <div class=cols style="height: 45px; border-top: none">
1855 <div class="col" style="">
1857 <p>
1858 pqr stu vw xyz. A bc<br>
1859 def g hij klm nopqrs<br>
1860 </div>
1862 <div class="col" style="left: 175px">
1863 <p>
1864 tuv wxy z. Abc de fg<br>
1865 hi jklmno. Pqrstu vw<br>
1866 </div>
1868 <div class="col" style="left: 350px">
1869 <p>
1870 x yz. Abc def ghi jkl.<br>
1871 </div>
1874 <div class=gap style="left: 150px"></div>
1875 <div class=gap style="left: 325px"></div>
1876 </div>
1879 </div>
1882 <div class="example">
1884 <p>In this example, explicit column breaks are generated after paragraphs:
1886 <pre class=css>
1887 p {
1888 break-after: column;
1889 }
1890 </pre>
1892 <p>As a result, the number of columns increases and the extra columns
1893 are added in the inline direction:
1895 <div class=cols style="height: 100px">
1897 <div class="col" style="">
1899 <p>
1900 Ab cde fgh i jkl. Mno<br>
1901 pqr stu vw xyz.
1902 </div>
1904 <div class="col" style="left: 175px">
1905 <p>
1906 Ab cde fgh i jkl. Mno<br>
1907 pqr stu vw xyz. A bc<br>
1908 def g hij klm nopqrs<br>
1909 tuv wxyz. Abc defghi<br>
1910 jklmno pqrstu vwxyz.
1911 </div>
1913 <div class="col" style="left: 350px">
1914 <p>
1915 Ab cde fgh i jkl mno.<br>
1916 </div>
1918 <div class="col" style="left: 525px">
1919 <p>
1920 Pqr stu vw xyz. A bc<br>
1921 def g hij klm nopqrs<br>
1922 tuv wxy z.
1923 </div>
1925 <div class=gap style="left: 150px"></div>
1926 <div class=gap style="left: 325px"></div>
1927 <div class=gap style="left: 500px"></div>
1928 </div>
1930 </div>
1933 <div class="example">
1935 <p>In paged media, extra columns are shown on the next page. Given the
1936 same code as the previous example, the last paragraph appears on the second page. This would appear on the first page:
1938 <div class=cols style="height: 100px; border-bottom: none">
1940 <div class="col" style="">
1942 <p>
1943 Ab cde fgh i jkl. Mno<br>
1944 pqr stu vw xyz.
1945 </div>
1947 <div class="col" style="left: 175px">
1948 <p>
1949 Ab cde fgh i jkl. Mno<br>
1950 pqr stu vw xyz. A bc<br>
1951 def g hij klm nopqrs<br>
1952 tuv wxyz. Abc defghi<br>
1953 jklmno pqrstu vwxyz.
1954 </div>
1956 <div class="col" style="left: 350px">
1957 <p>
1958 Ab cde fgh i jkl mno.<br>
1959 </div>
1962 <div class=gap style="left: 150px"></div>
1963 <div class=gap style="left: 325px"></div>
1964 </div>
1966 <p>This would appear on the second page:
1968 <div class=cols style="height: 23px; border-top: none">
1970 <div class="col" style="">
1971 <p>
1972 Pqr stu vw xyz. A bc
1973 </div>
1975 <div class="col" style="left: 175px">
1976 <p>
1977 def g hij klm nopqrs
1978 </div>
1980 <div class="col" style="left: 350px">
1981 <p>
1982 tuv wxy z.
1983 </div>
1986 <div class=gap style="left: 150px"></div>
1987 <div class=gap style="left: 325px"></div>
1988 </div>
1990 Due to column balancing, the last paragraph is split across three columns.
1992 </div>
2000 <h2>Conformance</h2>
2002 <p>Conforming UAs must flow the content of an element into several
2003 columns according to this specification.
2005 <p>The conformance requirements are expressed with a combination of
2006 descriptive assertions and RFC 2119 terminology. The key words "MUST",
2007 "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT",
2008 "RECOMMENDED", "MAY", and "OPTIONAL" in the normative parts of this
2009 document are to be interpreted as described in RFC 2119.
2010 However, for readability, these words do not appear in all uppercase
2011 letters in this specification. All of the text of this specification is
2012 normative except sections explicitly marked as non-normative, examples,
2013 and notes. [[!RFC2119]]</p>
2016 <h3 id=cr-exit-criteria>CR exit criteria</h3>
2018 <p>As described in the W3C process document, a <a
2019 href="http://www.w3.org/2005/10/Process-20051014/tr.html#cfi">Candidate
2020 Recommendation</a> (CR) is a specification that W3C recommends for use
2021 on the Web. The next stage is <em>Recommendation</em>, when the
2022 specification is sufficiently implemented.
2024 <p>For this specification to be proposed as a W3C Recommendation, the
2025 following conditions shall be met. There must be at least two
2026 independent, interoperable implementations of each feature. Each
2027 feature may be implemented by a different set of products, there is no
2028 requirement that all features be implemented by a single product. For
2029 the purposes of this criterion, we define the following terms:
2031 <dl>
2032 <dt>independent <dd>each implementation must be developed by a
2033 different party and cannot share, reuse, or derive from code
2034 used by another qualifying implementation. Sections of code that
2035 have no bearing on the implementation of this specification are
2036 exempt from this requirement.
2038 <dt>interoperable <dd>passing the respective test case(s) in the
2039 official CSS test suite, or, if the implementation is not a Web
2040 browser, an equivalent test. Every relevant test in the test
2041 suite should have an equivalent test created if such a user
2042 agent (UA) is to be used to claim interoperability. In addition
2043 if such a UA is to be used to claim interoperability, then there
2044 must one or more additional UAs which can also pass those
2045 equivalent tests in the same way for the purpose of
2046 interoperability. The equivalent tests must be made publicly
2047 available for the purposes of peer review.
2049 <dt>implementation <dd>a user agent which:
2051 <ol class="inline">
2052 <li>implements the specification.
2054 <li>is available to the general public. The implementation may
2055 be a shipping product or other publicly available version
2056 (i.e., beta version, preview release, or <em>nightly build</em>).
2057 Non-shipping product releases must have implemented the
2058 feature(s) for a period of at least one month in order to
2059 demonstrate stability.
2061 <li>is not experimental (i.e., a version specifically designed
2062 to pass the test suite and is not intended for normal usage
2063 going forward).
2064 </ol>
2065 </dl>
2067 <p>A minimum of sixth months of the CR period must have elapsed. This
2068 is to ensure that enough time is given for any remaining major errors
2069 to be caught.
2071 <p>Features will be dropped if two or more interoperable
2072 implementations are not found by the end of the CR period.
2074 <p>Features may/will also be dropped if adequate/sufficient (by
2075 judgment of CSS WG) tests have not been produced for those feature(s)
2076 by the end of the CR period.
2081 <h2 class=no-num id=acknowledgments>Acknowledgments</h2>
2083 <p>This document is based on several older proposals and comments on
2084 older proposals. Contributors include
2086 Øyvind Stenhaug,
2087 Sylvain Galineau,
2088 Giovanni Campagna,
2089 David Hyatt,
2090 David Singer,
2091 David Woolley,
2092 Elika Etemad,
2093 Björn Höhrmann,
2094 Joost de Valk,
2095 Peter-Paul Koch,
2096 Shelby Moore,
2097 Till Halbach,
2098 Cédric Savarese,
2099 Andy Clarke,
2100 Robert O'Callahan,
2101 Markus Mielke,
2102 Alex Mogilevsky,
2103 Sergey Genkin,
2104 Michael Day,
2105 Melinda Grant,
2106 Kevin Lawver,
2107 Anton Prowse,
2108 L. David Baron,
2109 Bert Bos,
2110 Dave Raggett,
2111 Chris Wilson,
2112 Robert Stevahn,
2113 Peter Linss,
2114 Chris Lilley,
2115 Steve Zilles,
2116 Tantek Çelik,
2117 Daniel Glazman and
2118 Ian Hickson.</p>
2121 <h2 class=no-num id=references>References</h2>
2124 <h3 class="no-num" id="normative-references">Normative references</h3>
2125 <!--begin-normative-->
2127 <p>[Here will be inserted the file "normative.inc"]</p>
2128 <!--end-normative-->
2130 <h3 class="no-num" id="other-references">Other references</h3>
2131 <!--begin-informative-->
2134 <p>[Here will be inserted the file "informative.inc"]</p>
2135 <!--end-informative-->
2138 <h2 class="no-num" id="index">Index</h2>
2139 <!--index-->
2142 <h2 class="no-num" id="property-index">Property index</h2>
2143 <!-- properties -->
2144 </body>
2145 </html>
2146 <!-- Keep this comment at the end of the file
2147 Local variables:
2148 mode: sgml
2149 sgml-declaration:"~/SGML/HTML4.decl"
2150 sgml-default-doctype-name:"html"
2151 sgml-minimize-attributes:t
2152 sgml-nofill-elements:("pre" "style" "br")
2153 sgml-live-element-indicator:t
2154 sgml-omittag:nil
2155 sgml-shorttag:nil
2156 sgml-namecase-general:t
2157 sgml-general-insert-case:lower
2158 sgml-always-quote-attributes:t
2159 sgml-indent-step:nil
2160 sgml-indent-data:t
2161 sgml-parent-document:nil
2162 sgml-exposed-tags:nil
2163 sgml-local-catalogs:nil
2164 sgml-local-ecat-files:nil
2165 End:
2166 -->
