Why does a url use ://?
makecheck: Technically, not all of them do; "<schema>:" is the common prefix, and everything else depends on the URL type.See: http://www.ietf.org/rfc/rfc1738.txtIn particular, section 3.1, 'The scheme specific data start with a double slash "//" to indicate that it complies with the common Internet scheme syntax.'.  So it is used by URLs that require any of this information: "//<user>:<password>@<host>:<port>/<url-path>".