what is :media in application layout in .js and .css include tag???

    <%= stylesheet_link_tag "components/jscrollpane/jscrollpane.css", :media=>"screen" %>

	<%= stylesheet_link_tag "components/tipsy/tipsy.css", :media=>"all" %>

what is this :media?

and what is the this “all” and “screen”

if there are more than “screen” and “all” in media tag than explain it also…

thanks

Fahim Babar Patel

Googling for
stylesheet media screen
brings up this as the first link
http://www.w3.org/TR/CSS2/media.html

Colin