where  may consist of a user name and, optionally, scheme-
   specific information about how to gain authorization to access the
   server.  The parts "@" and ":" may be omitted.

      server        = [ [ userinfo "@" ] hostport ]

   The user information, if present, is followed by a commercial at-sign
   "@".

      userinfo      = *( unreserved | escaped |
                         ";" | ":" | "&" | "=" | "+" | "$" | "," )

   Some URL schemes use the format "user:password" in the userinfo
   field. This practice is NOT RECOMMENDED, because the passing of
   authentication information in clear text (such as URI) has proven to
   be a security risk in almost every case where it has been used.

   The host is a domain name of a network host, or its IPv4 address as a
   set of four decimal digit groups separated by ".".  Literal IPv6
   addresses are not supported.

      hostport      = host [ ":" port ]
      host          = hostname | IPv4address
      hostname      = *( domainlabel "." ) toplabel [ "." ]
      domainlabel   = alphanum | alphanum *( alphanum | "-" ) alphanum
      toplabel      = alpha | alpha *( alphanum | "-" ) alphanum




 
RFC 2396                   URI Generic Syntax                August 1998


      IPv4address   = 1*digit "." 1*digit "." 1*digit "." 1*digit
      port          = *digit

   Hostnames take the form described in Section 3 of [RFC1034] and
   Section 2.1 of [RFC1123]: a sequence of domain labels separated by
   ".", each domain label starting and ending with an alphanumeric
   character and possibly also containing "-" characters.  The rightmost
   domain label of a fully qualified domain name will never start with a
   digit, thus syntactically distinguishing domain names from IPv4
   addresses, and may be followed by a single "." if it is necessary to
   distinguish between the complete domain name and any local domain.
   To actually be "Uniform" as a resource locator, a URL hostname should
   be a fully qualified domain name.  In practice, however, the host
   component may be a local domain literal.

      Note: A suitable representation for including a literal IPv6
      address as the host part of a URL is desired, but has not yet been
      determined or implemented in practice.

   The port is the network port number for the server.  Most schemes
   designate protocols that have a default port number.  Another port
   number may optionally be supplied, in decimal, separated from the
   host by a colon.  If the port is omitted, the default port number is
   assumed.

3.3. Path Component

   The path component contains data, specific to the authority (or the
   scheme if there is no authority component), identifying the resource
   within the scope of that scheme and authority.

      path          = [ abs_path | opaque_part ]

      path_segments = segment *( "/" segment )
      segment       = *pchar *( ";" param )
      param         = *pchar

      pchar         = unreserved | escaped |
                      ":" | "@" | "&" | "=" | "+" | "$" | ","

   The path may consist of a sequence of path segments separated by a
   single slash "/" character.  Within a path segment, the characters
   "/", ";", "=", and "?" are reserved.  Each path segment may include a
   sequence of parameters, indicated by the semicolon ";" character.
   The parameters are not significant to the parsing of relative
   references.






 
RFC 2396                   URI Generic Syntax                August 1998


3.4. Query Component

   The query component is a string of information to be interpreted by
   the resource.

      query         = *uric

   Within a query component, the characters ";", "/", "?", ":", "@",
   "&", "=", "+", ",", and "$" are reserved.