CSS 分页媒体 - break-before 属性

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CSS break-before 分页媒体属性指定是否应该在元素之前发生分页符。这对于控制打印页面的布局很有用。

可能的值

以下是可以传递给b>break-before 分页媒体属性的一系列可能值

通用换行值

  • auto − 默认值。它将根据可用空间自动在元素之前换页。

  • avoid − 如果需要，它会避免在元素之前换页。

分页符值

  • avoid-page − 它会阻止在元素之前换页。

  • page − 强制在元素之前换页。

  • left − 强制在元素之前换页，以便下一页格式化为左侧页。

  • right − 强制在元素之前换页，以便下一页格式化为右侧页。

栏换行值

  • avoid-column − 避免在元素之前换栏。

  • column − 在元素之前添加栏换行。

应用于

块级元素。

DOM 语法

breakBefore = "auto|avoid|avoid-page|page|left|right|avoid-column|column";

分页符别名

Web 浏览器将旧版 page-break-before 属性视为 break-before 属性的别名。这确保了使用 page-break-before 的网站能够平稳运行。对于 break-before 属性，以下值应相等。

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

以下规则用于确定是否必须进行换行

  • 任何三个相关值（always、left、right、page、column 或 region）中的 强制换行值 优先。如果存在多个分页符属性，我们选择序列中最后出现的那个。序列是 : break-before 优先于 break-after，而 break-after 优先于 break-inside。

  • 如果任何三个相关值是 避免分页符值，例如 avoid、avoid-page、avoid-region 或 avoid-column，则在该位置不会添加分页符。

CSS break-before - auto 值

以下示例演示了（在打印布局中）break-before: auto 属性在打印页面时会自动在部分之前换页 -

<html>
<head>
<style>
   main {
      height: 50px;
      width: 150px;
   }
   section {
      break-before: auto; 
      border: 1px solid black;
      padding: 5px;
      margin: 10px;
   }
   button {
      background-color: violet;
      padding: 5px;
      margin: 10px;
   }
</style>
</head>
<body>
   <p>Click on below button to see the effect when you print the page.</p>
   <button onclick="printPage()">Print Page</button>
   <main>
      <section>
         <h3>Column 1</h3>
         <p>This is a column 1.</p>
      </section>
      <section>
         <h3>Column 2</h3>
         <p>This is a column 2.</p>
      </section>
      <section>
         <h3>Column 3</h3>
         <p>This is a column 3.</p>
      </section>
      <section>
         <h3>Column 4</h3>
         <p>This is a column 4.</p>
      </section>
      <section>
         <h3>Column 5</h3>
         <p>This is a column 5.</p>
      </section>
      <section>
         <h3>Column 6</h3>
         <p>This is a column 6.</p>
      </section>
      <section>
         <h3>Column 7</h3>
         <p>This is a column 7. This section is break automatically based on the available space and content.</p>
      </section>
   </main>
<script>
   function printPage() {
      window.print();
   }
</script>
</body>
</html>

CSS break-before - avoid 值

以下示例演示了（在打印布局中）break-before: avoid 属性在打印页面时会避免在部分之前换页 -

<html>
<head>
<style>
   main {
      height: 50px;
      width: 180px;
   }
   section {
      break-before: avoid; 
      border: 1px solid black;
      padding: 5px;
      margin: 10px;
   }
   button {
      background-color: violet;
      padding: 5px;
      margin: 10px;
   }
</style>
</head>
<body>
   <p>Click on below button to see the effect when you print the page.</p>
   <button onclick="printPage()">Print Page</button>
   <main>
      <section>
         <h3>Column 1</h3>
         <p>This is a column 1.</p>
      </section>
      <section>
         <h3>Column 2</h3>
         <p>This is a column 2.</p>
      </section>
      <section>
         <h3>Column 3</h3>
         <p>This is a column 3.</p>
      </section>
      <section>
         <h3>Column 4</h3>
         <p>This is a column 4.</p>
      </section>
      <section>
         <h3>Column 5</h3>
         <p>This is a column 5.</p>
      </section>
      <section>
         <h3>Column 6</h3>
         <p>This is a column 6.</p>
      </section>
      <section>
         <h3>Column 7</h3>
         <p>This is a column 7.</p>
      </section>

   </main>
<script>
   function printPage() {
      window.print();
   }
</script>
</body>
</html>

CSS break-before - avoid-page 值

以下示例演示了 break-before: avoid-page 属性在打印页面时会避免在元素之前换页 -

<html>
<head>
<style>
   .avoid-break-page {
      break-before: avoid-page; 
   }
   button {
      background-color: violet;
      padding: 5px;
   }
</style>
</head>
<body>
   <p>Click on below button to see the effect when you print the page.</p>
   <button onclick="printPage()">Print Page</button>

   <div><p>This is a paragraph 1. It will be displayed on first page.</p></div>
   <div class="avoid-break-page"><p>This is a paragraph 2. It will be displayed on first page.</p></div>
   <div><p>This is a paragraph 3. It will be displayed on first page.</p></div>
   <div><p>This is a paragraph 4. It will be displayed on first page.</p></div>
   <script>
      function printPage() {
         window.print();
      }
   </script>
</body>
</html>

CSS break-before - page 值

以下示例演示了 break-before: page 属性在打印页面时会换页 -

<html>
<head>
<style>
   .break-page {
      break-before: page; 
   }
   button {
      background-color: violet;
      padding: 5px;
   }
</style>
</head>
<body>
   <p>Click on below button to see the effect when you print the page.</p>
   <button onclick="printPage()">Print Page</button>

   <div><p>This is a paragraph 1. It will be displayed on first page.</p></div>
   <div class="break-page"><p>This is a paragraph 2.After applying the break-before property, this paragraph will be displayed on the second page.</p></div>
   <div><p>This is a paragraph 3. It will be displayed on second page.</p></div>
   <div><p>This is a paragraph 4. It will be displayed on second page.</p></div>
   <script>
      function printPage() {
         window.print();
      }
   </script>
</body>
</html>

CSS break-before - left 值

以下示例演示了 break-before: left 属性在打印页面时会将元素换到左侧的下一页 -

<html>
<head>
<style>
   .page-break-left {
      break-before: left; 
   }
   button {
      background-color: violet;
      padding: 5px;
   }
</style>
</head>
<body>
   <p>Click on below button to see the effect when you print the page.</p>
   <button onclick="printPage()">Print Page</button>

   <div><p>This is a paragraph 1. It will be displayed on first page.</p></div>
   <div><p>This is a paragraph 2. It will be displayed on first page.</p></div>
   <div class="page-break-left"><p>This is a paragraph 3.After applying the break-before: left property, this paragraph will be displayed to the next page on left side when page is printed.</p></div>
   <div><p>This is a paragraph 4. It will be displayed on second page.</p></div>
   <div><p>This is a paragraph 5. It will be displayed on second page.</p></div>
   <script>
      function printPage() {
         window.print();
      }
   </script>
</body>
</html>

CSS break-before - right 值

以下示例演示了 break-before: right 属性在打印页面时会将元素换到右侧的下一页 -

<html>
<head>
<style>
   .page-break-right {
      break-before: right; 
   }
   button {
      background-color: violet;
      padding: 5px;
   }
</style>
</head>
<body>
   <p>Click on below button to see the effect when you print the page.</p>
   <button onclick="printPage()">Print Page</button>

   <div><p>This is a paragraph 1. It will be displayed on first page.</p></div>
   <div><p>This is a paragraph 2. It will be displayed on first page.</p></div>
   <div class="page-break-right"><p>This is a paragraph 3. After applying the break-before: right property, this paragraph will be displayed to the next page on right side when page is printed.</p></div>
   <div><p>This is a paragraph 4. It will be displayed on second page.</p></div>
   <div><p>This is a paragraph 5. It will be displayed on second page.</p></div>
   <script>
      function printPage() {
         window.print();
      }
   </script>
</body>
</html>

CSS break-before - avoid-column 值

以下示例演示了 break-before: avoid-column 属性在打印页面时会避免在每个部分之前换栏 -

<html>
<head>
<style>
   main {
      column-width: 200px;
      column-gap: 10px;
   }
   section {
      width: 200px;
      height: 130px;
      border: 2px solid black;
      margin: 10px;
      padding: 5px;
   }
   .break-column {
      break-before: avoid-column;
   }
   button {
      background-color: violet;
      padding: 5px;
   }
</style>
</head>
<body>
   <p>Click on below button to see the effect when you print the page.</p>
   <button onclick="printPage()">Print Page</button>
   <main>
      <section>
         <h3>Column 1</h3>
         <p>This is a column 1.</p>
      </section>
      <section class="break-column">
         <h3>Column 2</h3>
         <p>This is a column 2.</p>
      </section>
      <section>
         <h3>Column 3</h3>
         <p>This is a column 3.</p>
      </section>
      <section>
         <h3>Column 4</h3>
         <p>This is a column 4.</p>
      </section>
   </main>
   <script>
      function printPage() {
         window.print();
      }
   </script>
</body>
</html>

CSS Break column - column 值

以下示例演示了 break-before: column 属性在打印页面时会在每个部分之前添加栏换行以创建多栏布局 -

<html>
<head>
<style>
   main {
      column-width: 200px;
      column-gap: 10px;
   }
   section {
      width: 200px;
      height: 130px;
      border: 2px solid black;
      margin: 10px;
      padding: 5px;
   }
   .break-column {
      break-before: column;
   }
   button {
      background-color: violet;
      padding: 5px;
   }
</style>
</head>
<body>
   <p>Click on below button to see the effect when you print the page.</p>
   <button onclick="printPage()">Print Page</button>
   <main>
      <section>
         <h3>Column 1</h3>
         <p>This is a column 1.</p>
      </section>
      <section class="break-column">
         <h3>Column 2</h3>
         <p>This is a column 2. After applying break-before: column, this section will be displayed on next column.</p>
      </section>
      <section>
         <h3>Column 3</h3>
         <p>This is a column 3.</p>
      </section>
      <section>
         <h3>Column 4</h3>
         <p>This is a column 4.</p>
      </section>
   </main>
   <script>
      function printPage() {
         window.print();
      }
   </script>
</body>
</html>
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