console 命令行工具 X clear
console
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
</head>
<body>
  <h1>测试是否是闰年</h1>
  <form action="https://www.jikesn.com/demo/php/testif/39-testIf.php" method='post'>
      <input type="text" name='year' placeholder="请输入合法年份">
      <input type="submit" value="测试">
  </form>
</body>
</html>