空白
当浏览器遇到两个或两个以上的连续空格时，只将其显示为一个空格。同样，当遇到一次换行时，浏览器也会将其看作一个空格。这一特性称为白色空间折叠。
<!DOCTYPE html>
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<html>
<head>
<title>空白</title>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
</head>
<body>
<div>空白</div>
<p>1 2 3 4 5 6 </p>
<p>1 2 3 4 5 6 </p>
<p>1 2 3 4 5 6 </p>
</body>
</html>