The "afsaddress" is left in as historical note, but is not a url
   production.

  prefixedurl            u r l : url

  url                    httpaddress | ftpaddress | newsaddress |
                         nntpaddress | prosperoaddress | telnetaddress
                         | gopheraddress | waisaddress |
                         mailtoaddress  | midaddress | cidaddress

  scheme                 ialpha

  httpaddress            h t t p :   / / hostport [  / path ] [ ?
                         search ]

  ftpaddress             f t p : / / login / path [  ftptype ]

  afsaddress             a f s : / / cellname / path

  newsaddress            n e w s : groupart

  nntpaddress            n n t p : group /  digits

  midaddress             m i d  :  addr-spec

  cidaddress             c i d : content-identifier

  mailtoaddress          m a i l t o : xalphas @ hostname

  waisaddress            waisindex | waisdoc

  waisindex              w a i s : / / hostport / database [ ? search
                         ]

  waisdoc                w a i s : / / hostport / database / wtype  /
                         wpath

  wpath                  digits = path ;  [ wpath ]

  groupart               * | group | article

  group                  ialpha [ . group ]




 
RFC 1630                      URIs in WWW                      June 1994



  article                xalphas @ host

  database               xalphas

  wtype                  xalphas

  prosperoaddress        prosperolink

  prosperolink           p r o s p e r o : / / hostport / hsoname [ %
                         0 0 version [ attributes ] ]

  hsoname                path

  version                digits

  attributes             attribute [ attributes ]

  attribute              alphanums

  telnetaddress          t e l n e t : / / login

  gopheraddress          g o p h e r : / / hostport [/ gtype  [
                         gcommand ] ]

  login                  [ user [ : password ] @ ] hostport

  hostport               host [ : port ]

  host                   hostname | hostnumber

  ftptype                A formcode | E formcode | I | L digits

  formcode               N | T | C

  cellname               hostname

  hostname               ialpha [  .  hostname ]

  hostnumber             digits . digits . digits . digits

  port                   digits

  gcommand               path

  path                   void |  segment  [  / path ]

  segment                xpalphas