Here is some iframed content:

Source: http://google.com.

Here is the markup:

<iframe src="http://google.com" width="100%" height="400"
longdesc="/acooke/projects/iframes/google-LD.html" 
title="Google home page"></iframe>

And here’s the CSS:

iframe {border:1px solid #CCC;}

Using longdesc is recommended for accessibility, though many visual user agents don’t support it (which is a shame, but that’s not really who it’s for). Long description for google.com