<!DOCTYPE html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题</title>
</head>
<body>
<input type="checkbox" ><br/><!-- false -->
<input type="checkbox" checked=""><br/><!-- 以下都是true -->
<input type="checkbox" checked=""><br/>
<input type="checkbox" checked="checked"><br/>
<input type="checkbox" checked=checked><br/>
</body>
</html>
