onclick input type submit

**Check this way it will work as you expected**
//main.php
<html>
<head>
<script type="text/javascript">
    function validateMain()
    {
       alert('main'); 
    }
    function validateSub()
    {
        alert('sub'); 
    }
</script>
</head>
<body>  
<form id="main"  onsubmit="return validateMain();">
        <input type="text" name="first" id="first"/>
        <input type="submit" value="Submit Main"/> 
 </form>
 <iframe name="ifr-form" id="ifr-form" src="test.html"></iframe> 
</body>
</html>

//test.html the second form included through iframe

    <!DOCTYPE html>
<html>
    <head>
        <title></title>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    </head>
    <body>
        <div>


 <form id="sub" onclick="return window.top.validateSub();">
        <input type="text" name="first" id="second"/>
        <input type="button" value="Submit Sub" /> 
      </form>

        </div>
    </body>
</html>

Answers

you must check if php and iframe are compatible, as far as i Know I don't think that frames and php gives any output, hope this helps.