break-before

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句法
Page break aliases
形式定义
形式句法
范例
规范
浏览器兼容性
相关话题

break-before CSS property sets how page, column, or region breaks should behave before a generated box. If there is no generated box, the property is ignored.

/* Generic break values */
break-before: auto;
break-before: avoid;
break-before: always;
break-before: all;
/* Page break values */
break-before: avoid-page;
break-before: page;
break-before: left;
break-before: right;
break-before: recto;
break-before: verso;
/* Column break values */
break-before: avoid-column;
break-before: column;
/* Region break values */
break-before: avoid-region;
break-before: region;
/* Global values */
break-before: inherit;
break-before: initial;
break-before: unset;

Each possible break point (in other words, each element boundary) is affected by three properties: the break-after value of the previous element, the break-before value of the next element, and the break-inside value of the containing element.

To determine if a break must be done, the following rules are applied:

If any of the three concerned values is a forced break value ( always , left , right , page , column ，或 region ), it has precedence. If more than one of them are such a break, the one of the element that appears the latest in the flow is taken (i.e., the break-before value has precedence over the break-after value, which itself has precedence over the break-inside value).
If any of the three concerned values is an avoid break value ( avoid , avoid-page , avoid-region ，或 avoid-column ), no such break will be applied at that point.

Once forced breaks have been applied, soft breaks may be added if needed, but not on element boundaries that resolve in a corresponding avoid 值。

句法

break-before property is specified as one of the keyword values from the list below.

值

Generic break values

auto
avoid
always
all

Page break values

avoid-page
page
left
right
recto
verso

Column break values

avoid-column
column

Region break values

avoid-region
region

Page break aliases

For compatibility reasons, the legacy page-break-before property should be treated by browsers as an alias of break-before . This ensures that sites using page-break-before continue to work as designed. A subset of values should be aliased as follows:

page-break-before	break-before
`auto`	`auto`
`left`	`left`
`right`	`right`
`avoid`	`avoid`
`always`	`page`

always value of page-break-* was implemented by browsers as a page break, and not as a column break. Therefore the aliasing is to page , rather than the always value in the Level 4 spec.

形式定义

初始值	`auto`
适用于	block-level elements
继承	no
计算值	如指定
动画类型	discrete

形式句法

auto | avoid | always | all | avoid-page | page | left | right | recto | verso | avoid-column | column | avoid-region | region

范例

Breaking into neat columns

In the following example we have a container that contains an <h1> spanning all columns (achieved using column-span: all ) and a series of <h2> s and paragraphs laid out in multiple columns using column-width: 200px .

By default, the subheadings and paragraphs were laid out rather messily because the headings were not in a uniform place. However, we used break-before: column on the <h2> elements to force a column break before each one, meaning that you end up with an <h2> neatly at the top of each column.

HTML

<article>
  <h1>Main heading</h1>
  <h2>Subheading</h2>
  <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nulla vitae fringilla mauris. Quisque commodo eget nisi sed pretium. Mauris luctus nec lacus in ultricies. Mauris vitae hendrerit arcu, ac scelerisque lacus. Aliquam lobortis in lacus sit amet posuere. Fusce iaculis urna id neque dapibus, eu lacinia lectus dictum.</p>
  <h2>Subheading</h2>
  <p>Praesent condimentum dui dui, sit amet rutrum diam tincidunt eu. Cras suscipit porta leo sit amet rutrum. Sed vehicula ornare tincidunt. Curabitur a ipsum ac diam mattis volutpat ac ut elit. Nullam luctus justo non vestibulum gravida. Morbi metus libero, pharetra non porttitor a, molestie nec nisi.</p>
  <h2>Subheading</h2>
  <p>Vivamus eleifend metus vitae neque placerat, eget interdum elit mattis. Donec eu vulputate nibh. Ut turpis leo, malesuada quis nisl nec, volutpat egestas tellus.
  <h2>Subheading</h2>
  <p>In finibus viverra enim vel suscipit. Quisque consequat velit eu orci malesuada, ut interdum tortor molestie. Proin sed pellentesque augue. Nam risus justo, faucibus non porta a, congue vel massa. Cras luctus lacus nisl, sed tincidunt velit pharetra ac. Duis suscipit faucibus dui sed ultricies.</p>
</article>

CSS

html {
  font-family: helvetica, arial, sans-serif;
}
h1 {
  font-size: 3rem;
  letter-spacing: 2px;
  column-span: all;
}
h2 {
  font-size: 1.2rem;
  color: red;
  letter-spacing: 1px;
  break-before: column;
}
p {
  line-height: 1.5;
}
article {
  column-width: 200px;
  gap: 20px;
}

结果

规范

规范	状态	注释
CSS Fragmentation Module Level 3 The definition of 'break-before' in that specification.	候选推荐	添加 `recto` and `verso` keywords. Changes the media type of this property from `paged` to `visual` . Defines the breaking algorithm with different kinds of breaks.
CSS Regions Module Level 1 The definition of 'break-before' in that specification.	工作草案	Extends the property to handle region breaks. Adds the `avoid-region` and `region` keywords.
CSS Multi-column Layout Module The definition of 'break-before' in that specification.	工作草案	Initial definition. Extends the CSS 2.1 `page-break-before` property to handle both page and column breaks.

浏览器兼容性

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.

Support in multi-column layout

更新 GitHub 上的兼容性数据

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
Supported in Multi-column Layout	Chrome 完整支持 50	Edge 完整支持 12	Firefox 完整支持 65	IE 完整支持 10	Opera 完整支持 37 完整支持 37 不支持 11.1 — 12.1	Safari 不支持 No	WebView Android 完整支持 50	Chrome Android 完整支持 50	Firefox Android 完整支持 65	Opera Android 完整支持 37 完整支持 37 不支持 11.1 — 12.1	Safari iOS 不支持 No	Samsung Internet Android 完整支持 5.0
`always` Experimental	Chrome 不支持 No	Edge 不支持 No	Firefox 不支持 No	IE 不支持 No	Opera 不支持 No	Safari 不支持 No	WebView Android 不支持 No	Chrome Android 不支持 No	Firefox Android 不支持 No	Opera Android 不支持 No	Safari iOS 不支持 No	Samsung Internet Android 不支持 No
`avoid-column`	Chrome 不支持 No	Edge 不支持 12 — 79	Firefox 不支持 No	IE 完整支持 10	Opera 不支持 No	Safari 不支持 No	WebView Android 不支持 No	Chrome Android 不支持 No	Firefox Android 不支持 No	Opera Android 不支持 No	Safari iOS 不支持 No	Samsung Internet Android 不支持 No
`column`	Chrome 完整支持 51	Edge 完整支持 12	Firefox 不支持 No	IE 完整支持 10	Opera 完整支持 38	Safari 不支持 No	WebView Android 完整支持 51	Chrome Android 完整支持 51	Firefox Android 不支持 No	Opera Android 完整支持 41	Safari iOS 不支持 No	Samsung Internet Android 完整支持 5.0

图例

完整支持
不支持
实验。期望将来行为有所改变。

Support in paged media