51help TIY
码：
<!DOCTYPE HTML> <html> <body> <form action="http://www.51help.tk/example/html5/demo_form.asp" method="get"> Country code: <input type="text" name="country_code" pattern="[A-z]{3}" title="Three letter country code" /> <input type="submit" /> </form> </body> </html>
查看结果: