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<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>本教程(w3big.com)</title> </head> <body> <form action="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>