Example of a URI that isn't a URL?

uri, url, web-standards

Solution

Example stolen from here (where there is also a description of the differences):

URL     http://www.pierobon.org/iis/review1.htm
URN     www.pierobon.org/iis/review1.htm#one
URI     http://www.pierobon.org/iis/review1.htm.html#one

Problem

It's been explained to me numerous times that all URLs are URIs but not all URIs are URLs. Can anyone give an example of something that is a URI but is not a URL?

Original source