<!DOCTYPE html>
<html>
<head>
<title>Wikitechy form attribute</title>
</head>
<body>
<form action="form.html" id="form_1" onsubmit="alert('Submitted!');return false;">
Firstname:<input type="text" name="fname"> <br>
<input type="submit" value="Submit">
</form>
<p>Lastname:<input type="text" name="lname" form="form_1">
</p>
</body>
</html>
<html>
<head>
<title>Wikitechy form attribute</title>
</head>
<body>
<form action="form.html" id="form_1" onsubmit="alert('Submitted!');return false;">
Firstname:<input type="text" name="fname"> <br>
<input type="submit" value="Submit">
</form>
<p>Lastname:<input type="text" name="lname" form="form_1">
</p>
</body>
</html>
Result