break-before

break-before CSS 属性定义页面，列或区域在生成的盒子之前应如何处理中断。如果没有生成的盒子，则忽略该属性。

/* Generic break values */
break-before: auto;
break-before: avoid;

/* Page break values */
break-before: avoid-page;
break-before: page;
break-before: always;
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, or 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, or 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 value.

初始值	`auto`
适用元素	block-level elements
是否是继承属性	否
计算值	as specified
Animation type	discrete

Syntax

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

Values

General break values

auto: Allows, but does not force, any break (page, column, or region) to be inserted right before the principal box.
avoid: Avoids any break (page, column, or region) from being inserted right before the principal box.

Page break values

avoid-page: Avoids any page break right before the principal box.
page: Forces a page break right before the principal box.
always: Forces a page break right before the principal box. (This is an alias of page, and has been kept to facilitate the transition from page-break-after, which is a subset of this property.)
left: Forces one or two page breaks right before the principal box, whichever will make the next page into a left page.
right: Forces one or two page breaks right before the principal box, whichever will make the next page into a right page.
recto 实验性: Forces one or two page breaks right before the principal box, whichever will make the next page into a recto page. (A recto page is a right page in a left-to-right spread or a left page in a right-to-left spread.)
verso 实验性: Forces one or two page breaks right before the principal box, whichever will make the next page into a verso page. (A verso page is a left page in a left-to-right spread or a left right in a right-to-left spread.)

Column break values

avoid-column: Avoids any column break right before the principal box.
column: Forces a column break right before the principal box.

Region break values

avoid-region 实验性: Avoids any region break right before the principal box.
region 实验性: Forces a region break right before the principal box.

Formal syntax

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

Specifications

Specification
CSS Fragmentation Module Level 3 # break-between
CSS Regions Module Level 1 # region-flow-break
CSS Multi-column Layout Module Level 1 # break-before-break-after-break-inside

Browser compatibility

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