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<html><head><script>function validateForm() { var x = document.forms["myForm"]["email"].value; var atpos = x.indexOf("@"); var dotpos = x.lastIndexOf("."); if (atpos<1 || dotpos<atpos+2 || dotpos+2>=x.length) { alert("Not a valid e-mail address"); return false; }}</script></head><body><form name="myForm" action="/action_page.php" onsubmit="return validateForm();" method="post"> Email: <input type="text" name="email"> <input type="submit" value="Submit"></form></body></html>