I have an xhtml 1.1 DOCTYPE declaration that is shown in red and gives a big ugly red square for my code inspection. Particularly the DTD URL is shown in red. Hovering the mouse over it gives me the message, "URI is not registered (Settings | IDE Settings | Resources)." I went to Settings -> IDE Settings -> Resources and added the URI -> local file (which I downloaded) link. But it's still showing in red.
How do I fix this?