grammar RFC3987
  rule IRI
    scheme ':' ihier_part ( '?' iquery )? ( '#' ifragment )?
  end

  rule ihier_part
    '//' iauthority ipath_abempty / ipath_absolute / ipath_rootless / ipath_empty
  end

  rule IRI_reference
    IRI / irelative_ref
  end

  rule absolute_IRI
    scheme ':' ihier_part ( '?' iquery )?
  end

  rule irelative_ref
    irelative_part ( '?' iquery )? ( '#' ifragment )?
  end

  rule irelative_part
    '//' iauthority ipath_abempty / ipath_absolute / ipath_noscheme / ipath_empty
  end

  rule iauthority
    ( iuserinfo '@' )? ihost ( ':' port )?
  end

  rule iuserinfo
    ( iunreserved / pct_encoded / sub_delims / ':' )*
  end

  rule ihost
    IP_literal / IPv4address / ireg_name
  end

  rule ireg_name
    ( iunreserved / pct_encoded / sub_delims )*
  end

  rule ipath
      ipath_abempty   # begins with '/' or is empty
    / ipath_absolute  # begins with '/' but not '//'
    / ipath_noscheme  # begins with a non-colon segment
    / ipath_rootless  # begins with a segment
    / ipath_empty     # zero characters
  end

  rule ipath_abempty
    ( '/' isegment)*
  end

  rule ipath_absolute
    '/' ( isegment_nz ( '/' isegment )* )?
  end

  rule ipath_noscheme
    isegment_nz_nc ( '/' isegment)*
  end

  rule ipath_rootless
    isegment_nz ( '/' isegment )*
  end

  rule ipath_empty
    ''
  end

  rule isegment
    ( ipchar )*
  end

  rule isegment_nz
    ( ipchar )+
  end

  rule isegment_nz_nc
    ( iunreserved / pct_encoded / sub_delims / '@' )+ # non-zero-length segment without any colon ':'
  end

  rule pct_encoded
    '%' HEXDIG HEXDIG
  end

  rule ipchar
    iunreserved / pct_encoded / sub_delims / ':' / '@'
  end

  rule iquery
    ( ipchar iprivate '/' '?' )*
  end

  rule ifragment
    ( ipchar '/' '?' )*
  end

  rule iunreserved
    ALPHA / DIGIT / '-' / '.' / '_' / '~' / ucschar
  end

  rule ucschar
      [\u000A0-\u0D7FF] / [\u0F900-\u0FDCF] / [\u0FDF0-\u0FFEF]
    / [\u10000-\u1FFFD] / [\u20000-\u2FFFD] / [\u30000-\u3FFFD]
    / [\u40000-\u4FFFD] / [\u50000-\u5FFFD] / [\u60000-\u6FFFD]
    / [\u70000-\u7FFFD] / [\u80000-\u8FFFD] / [\u90000-\u9FFFD]
    / [\uA0000-\uAFFFD] / [\uB0000-\uBFFFD] / [\uC0000-\uCFFFD]
    #/ [\uD0000-\uDFFFD] / [\uE1000-\uEFFFD]
    / [\uE1000-\uEFFFD]
  end

  rule iprivate
    [\uE000-\uF8FF] / [\uF0000-\uFFFFD] / [\u100000-\u10FFFD]
  end

  rule scheme
    ALPHA ( ALPHA / DIGIT / "+" / "-" / "." )*
  end

  rule port
    DIGIT*
  end

  rule IP_literal
    "[" ( IPv6address / IPvFuture  ) "]"
  end

  rule IPvFuture
    "v" HEXDIG+ "." ( unreserved / sub_delims / ":" )+
  end

  rule IPv6address
                                    ( h16 ":" ) 6..6 ls32
    /                          "::" ( h16 ":" ) 5..5 ls32
    / [                  h16 ] "::" ( h16 ":" ) 4..4 ls32
    / [ ( h16 ":" ) 1..1 h16 ] "::" ( h16 ":" ) 3..3 ls32
    / [ ( h16 ":" ) 2..2 h16 ] "::" ( h16 ":" ) 2..2 ls32
    / [ ( h16 ":" ) 3..3 h16 ] "::"   h16 ":"        ls32
    / [ ( h16 ":" ) 4..4 h16 ] "::"                  ls32
    / [ ( h16 ":" ) 5..5 h16 ] "::"                  h16
    / [ ( h16 ":" ) 6..6 h16 ] "::"
  end

  rule h16
    HEXDIG 4..4
  end

  rule ls32
    ( h16 ":" h16 ) / IPv4address
  end

  rule IPv4address
    dec_octet "." dec_octet "." dec_octet "." dec_octet
  end

  rule dec_octet
      DIGIT                 # 0-9
    / ['0x30'-'0x39'] DIGIT     # 10-99
    / "1" DIGIT 2..2        # 100-199
    / "2" ['0x30'-'0x34'] DIGIT # 200-249
    / "25" ['0x30'-'0x35']      # 250-255
  end

  rule pct_encoded
    "%" HEXDIG HEXDIG
  end

  rule unreserved
    ALPHA / DIGIT / "-" / "." / "_" / "~"
  end

  rule reserved
    gen_delims / sub_delims
  end

  rule gen_delims
    ":" / "/" / "?" / "#" / "[" / "]" / "@"
  end

  rule sub_delims
     '!' / '$' / '&' / "'" / '(' / ')' / '*' / '+' / ',' / ';' / '='
  end

  rule ALPHA
    [a-zA-Z]
  end

  rule DIGIT
    [0-9]
  end

  rule HEXDIG
    [0-9A-F]
  end

end