How can I make a dropdown inside on iframe drop down on top of the other frames

I have the following in my frameset.jsp

</head>

       <iframe width="100%" src="mail_frame.html"></iframe>

       <iframe width="105开发者_StackOverflow中文版px" height="100%" src="sidenav.html" id="leftnav" name="leftnav" ></iframe>

       <iframe height="100%" src="body.htm" id="main" name="main"></iframe>


</html>

How can I make a drop down contained in mail_frame.html drop down and and overlap the other two frames below it?

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You can't. Frame content is contained within the frame and cannot be positioned outside of it.

It could be faked with cross-frame Javascript that triggers displaying the dropdown in another frame, but that is a hack and will result in headaches.

You are probably better off by not using frames, which is easy if you use some kind of server-side script that includes mail_frame.html, sidenav.html and body.html in one page.

It would look something like this in PHP: (you'll have to adjust it a bit for yourself to make it work)

</head>

       <div id="mail_frame"><?php include('mail_frame.html'); ?></div>

       <div id="leftnav"><?php include('sidenav.html'); ?></div>

       <div id="main"><?php include('body.html'); ?></div>

</html>