and at most m occurrences of the rule.  n and m are optional
      decimal values with default values of 0 and infinity respectively.

   [rule]
      An element enclosed in square brackets ('[' and ']') is optional,
      and is equivalent to '*1 rule'.

   N rule
      A rule preceded by a decimal number represents exactly N
      occurrences of the rule.  It is equivalent to 'N*N rule'.

2.2.  Basic Rules

   This specification uses a BNF-like grammar defined in terms of
   characters.  Unlike many specifications which define the bytes
   allowed by a protocol, here each literal in the grammar corresponds
   to the character it represents.  How these characters are represented
   in terms of bits and bytes within a system are either system-defined
   or specified in the particular context.  The single exception is the
   rule 'OCTET', defined below.

   The following rules are used throughout this specification to
   describe basic parsing constructs.

      alpha         = lowalpha | hialpha
      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"
      hialpha       = "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"





 
RFC 3875                    CGI Version 1.1                 October 2004


      digit         = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" |
                      "8" | "9"
      alphanum      = alpha | digit
      OCTET         = <any 8-bit byte>
      CHAR          = alpha | digit | separator | "!" | "#" | "$" |
                      "%" | "&" | "'" | "*" | "+" | "-" | "." | "`" |
                      "^" | "_" | "{" | "|" | "}" | "~" | CTL
      CTL           = <any control character>
      SP            = <space character>
      HT            = <horizontal tab character>
      NL            = 
      LWSP          = SP | HT | NL
      separator     = "(" | ")" | "<" | ">" | "@" | "," | ";" | ":" |
                      "\" | <"> | "/" | "[" | "]" | "?" | "=" | "{" |
                      "}" | SP | HT
      token         = 1*<any CHAR except CTLs or separators>
      quoted-string = <"> *qdtext <">
      qdtext        = <any CHAR except <"> and CTLs but including LWSP>
      TEXT          = <any printable character>

   Note that newline (NL) need not be a single control character, but
   can be a sequence of control characters.  A system MAY define TEXT to
   be a larger set of characters than <any CHAR excluding CTLs but
   including LWSP>.

2.3.  URL Encoding

   Some variables and constructs used here are described as being
   'URL-encoded'.  This encoding is described in section 2 of RFC 2396
   [2].  In a URL-encoded string an escape sequence consists of a
   percent character ("%") followed by two hexadecimal digits, where the
   two hexadecimal digits form an octet.  An escape sequence represents
   the graphic character that has the octet as its code within the
   US-ASCII [9] coded character set, if it exists.  Currently there is
   no provision within the URI syntax to identify which character set
   non-ASCII codes represent, so CGI handles this issue on an ad-hoc
   basis.

   Note that some unsafe (reserved) characters may have different
   semantics when encoded.  The definition of which characters are
   unsafe depends on the context; see section 2 of RFC 2396 [2], updated
   by RFC 2732 [7], for an authoritative treatment.  These reserved
   characters are generally used to provide syntactic structure to the
   character string, for example as field separators.  In all cases, the
   string is first processed with regard to any reserved characters
   present, and then the resulting data can be URL-decoded by replacing
   "%" escape sequences by their character values.





 
RFC 3875                    CGI Version 1.1                 October 2004


   To encode a character string, all reserved and forbidden characters
   are replaced by the corresponding "%" escape sequences.  The string