scheme: // user:pass @ host:port        /some/path   ?a=multi&part=query #fragment
  http: // foo:P4s$  @ example.com:8080 /also/a/path ?id=1&task=2        #some_ref

• If the // is absent, then the URI is considered non-hierarchical, and the interpretation of all data after the scheme: is left up to the handling client. In practice, most clients follow the conventions used for hierarchical URIs.
• The //, @, #, and ? are separators. Thus, for example, http://example.com&foo=bar@167772161/ actually points to 10.0.0.1 (in decimal format), with example.com&foo=bar being interpreted as a username to be used for any prospective authentication!
• According to the relevant RFC, the host must be either a valid domain name or canonical IPv4 or (bracket enclosed) IPv6 address. However, most parsing libraries will accept decimal, octal, hexadecimal, and even mixed-format IP addresses!
• While the query string is typical represented as a series of &-delimited key/value pairs, this is actually an arbitrary string whose interpretation is left up to the server.
• The fragment is also an arbitrary string, but whose interpretation is left up to the client (and is not supposed to be sent to the server).