<!DOCTYPE html> <html> <head> <meta content="width=device-width initial-scale=1.0 minimum-scale=1.0 maximum-scale=1.0 user-scalable=no" name="viewport"> <meta charset="UTF-8"> <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/4.1.1/css/bootstrap.css"> <style> </style> <script> </script> </head> <body> <div class="alert alert-primary"> 正規表現で入力チェック( required は必須入力 ) </div> <form method="post"> ユーザーID: <input required type="text" name="userid" pattern="[0-9]+"> <input type="submit" name="send" value="ログイン"> </form> </body> </html>