The longdesc attribute points to a page with a long description of the content of a frame:

Edit code and click me	Your Result (Some examples do not work in Google Chrome):
<html> <frameset cols="50%,50%"> <frame src="http://xhtml.co.il/tryit/html/frame_a.htm" longdesc="http://xhtml.co.il/tryit/html/xhtml.txt" /> <frame src="http://xhtml.co.il/tryit/html/frame_b.htm" /> </frameset> </html>
Edit the code above and click to see the result	www.xhtml.co.il - Try it yourself