break-before - CSS: Cascading Style Sheets 编辑

The 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:

1. 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).
2. 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.

Syntax

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

Values

Generic 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.

always 

Forces a page break right after the principal box. The type of this break is that of the immediately-containing fragmentation context. If we are inside a multicol container then it would force a column break, inside paged media (but not inside a multicol container) a page break.

all 

Forces a page break right after the principal box. Breaking through all possible fragmentation contexts. So a break inside a multicol container, which was inside a page container would force a column and page break.

Page break values

avoid-page

Avoids any page break right before the principal box.

page

Forces a page break right before the principal box.

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

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

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

Avoids any region break right before the principal box.

region

Forces a region break right before the principal box.

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:

The 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.

Formal definition

Formal syntax

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

Examples

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;
}

Result

Specifications

Browser compatibility

Support in multi-column layout

BCD tables only load in the browser

Support in paged media

BCD tables only load in the browser

See also

• Multiple-column Layout
• Breaking Boxes With CSS Fragmentation