xxxxxxxxxx<html><head> <meta charset="utf-8"> <title>W3Cschool(w3cschool.cn)</title> </head><body><form action="/statics/demosource/demo-form.php"> Username: <input type="text" name="usrname" required> <input type="submit"></form><p><strong>注意：</strong> Internet Explorer 9及更早IE版本，或Safari不支持input标签的 required 属性。</p></body></html>