Note that these are not hyperlinks; these URIs are used for identification. This is a machine-readable way to say “this is HTML”. In particular, software does not usually need to fetch these resources, and certainly does not need to fetch the same one over and over!

A URI is an identifier.A URL is an identifier that tells you how to get to it.

Every URL is a URI; Every URN is a URI; URI and URL are NOT interchangeable – a URL is a URI, but a URI is not always a URL; URLs always contain an access mechanism.