URI-reference = [ absoluteURI | relativeURI ] [ "#" fragment ]
absoluteURI   = scheme ":" ( hier_part | opaque_part )
relativeURI   = ( net_path | abs_path | rel_path ) [ "?" query ]

hier_part     = ( net_path | abs_path ) [ "?" query ]
opaque_part   = uric_no_slash *uric

uric_no_slash = unreserved | escaped | ";" | "?" | ":" | "@" |
                "&" | "=" | "+" | "$" | ","

net_path      = "//" authority [ abs_path ]
abs_path      = "/"  path_segments
rel_path      = rel_segment [ abs_path ]

rel_segment   = 1*( unreserved | escaped |
                    ";" | "@" | "&" | "=" | "+" | "$" | "," )

scheme        = alpha *( alpha | digit | "+" | "-" | "." )

authority     = server | reg_name

reg_name      = 1*( unreserved | escaped | "$" | "," |
                    ";" | ":" | "@" | "&" | "=" | "+" )

server        = [ [ userinfo "@" ] hostport ]
userinfo      = *( unreserved | escaped |
                   ";" | ":" | "&" | "=" | "+" | "$" | "," )

hostport      = host [ ":" port ]
host          = hostname | IPv4address
hostname      = *( domainlabel "." ) toplabel [ "." ]
domainlabel   = alphanum | alphanum *( alphanum | "-" ) alphanum
toplabel      = alpha | alpha *( alphanum | "-" ) alphanum
IPv4address   = 1*digit "." 1*digit "." 1*digit "." 1*digit
port          = *digit

path          = [ abs_path | opaque_part ]
path_segments = segment *( "/" segment )
segment       = *pchar *( ";" param )
param         = *pchar
pchar         = unreserved | escaped |
                ":" | "@" | "&" | "=" | "+" | "$" | ","

query         = *uric

fragment      = *uric

uric          = reserved | unreserved | escaped
reserved      = ";" | "/" | "?" | ":" | "@" | "&" | "=" | "+" |
                "$" | ","
unreserved    = alphanum | mark
mark          = "-" | "_" | "." | "!" | "~" | "*" | "'" |
                "(" | ")"

escaped       = "%" hex hex
hex           = digit | "A" | "B" | "C" | "D" | "E" | "F" |
                        "a" | "b" | "c" | "d" | "e" | "f"

alphanum      = alpha | digit
alpha         = lowalpha | upalpha

lowalpha = "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" | "i" |
           "j" | "k" | "l" | "m" | "n" | "o" | "p" | "q" | "r" |
           "s" | "t" | "u" | "v" | "w" | "x" | "y" | "z"
upalpha  = "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" | "I" |
           "J" | "K" | "L" | "M" | "N" | "O" | "P" | "Q" | "R" |
           "S" | "T" | "U" | "V" | "W" | "X" | "Y" | "Z"
digit    = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" |
           "8" | "9"