代码示例：（标识：cssref_default_pre）
<!DOCTYPE html>
<html>
<head>
<style>
/* 默认的 CSS 值 */
pre {
display: block;
font-family: monospace;
white-space: pre;
margin: 1em 0;
}
</style>
</head>
<body>
<p>默认情况下，pre 元素会这样显示：</p>
<pre>
Text in a pre element
is displayed in a fixed-width
font, and it preserves
both spaces and
line breaks
</pre>
<p>自定义的 pre 元素（更改 white-space）：</p>
<pre style="white-space:nowrap;">
Text in a pre element
is displayed in a fixed-width
font, and it preserves
both spaces and
line breaks
</pre>
</body>
</html>
