<!-- H5 快捷键 ！+tab 键 -->
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<title>Document</title>
</head>
<body>
</body>
</html>
<!-- xhtml快捷键 html:xt + tab 键 -->
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html;charset=UTF-8">
<title>Document</title>
</head>
<body>
</body>
</html>
<!-- 两者区别：1.文档声明 编码声明不一
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