The following code would create a two-frame layout in browsers that support frames, while the content of the NOFRAMES element would be create a single window in browsers that do not support frames.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Frameset//EN">
<TITLE>This is top.html</TITLE>
<FRAMESET cols="50%, 50%" title="Our big document">
<FRAME src="main.html" title="Where the content is displayed">
<FRAME src="table_of_contents.html" title="Table of Contents">
<A href="table_of_contents.html">Table of Contents.</A>
<!-- other navigational links that are available in main.html are available here also. -->