ignored.  These descriptions are used informally and do not define
   the syntax requirements.

   The second convention is a BNF-like grammar, used to define the
   formal URI syntax.  The grammar is that of [RFC822], except that "|"
   is used to designate alternatives.  Briefly, rules are separated from
   definitions by an equal "=", indentation is used to continue a rule
   definition over more than one line, literals are quoted with "",
   parentheses "(" and ")" are used to group elements, optional elements
   are enclosed in "[" and "]" brackets, and elements may be preceded
   with * to designate n or more repetitions of the following
   element; n defaults to 0.

   Unlike many specifications that use a BNF-like grammar to define the
   bytes (octets) allowed by a protocol, the URI grammar is defined in
   terms of characters.  Each literal in the grammar corresponds to the
   character it represents, rather than to the octet encoding of that
   character in any particular coded character set.  How a URI is
   represented in terms of bits and bytes on the wire is dependent upon
   the character encoding of the protocol used to transport it, or the
   charset of the document which contains it.

   The following definitions are common to many elements:

      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"





 
RFC 2396                   URI Generic Syntax                August 1998


      digit    = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" |
                 "8" | "9"

      alphanum = alpha | digit

   The complete URI syntax is collected in Appendix A.

2. URI Characters and Escape Sequences

   URI consist of a restricted set of characters, primarily chosen to
   aid transcribability and usability both in computer systems and in
   non-computer communications. Characters used conventionally as
   delimiters around URI were excluded.  The restricted set of
   characters consists of digits, letters, and a few graphic symbols
   were chosen from those common to most of the character encodings and
   input facilities available to Internet users.

      uric          = reserved | unreserved | escaped

   Within a URI, characters are either used as delimiters, or to
   represent strings of data (octets) within the delimited portions.
   Octets are either represented directly by a character (using the US-
   ASCII character for that octet [ASCII]) or by an escape encoding.
   This representation is elaborated below.

2.1 URI and non-ASCII characters

   The relationship between URI and characters has been a source of
   confusion for characters that are not part of US-ASCII. To describe
   the relationship, it is useful to distinguish between a "character"
   (as a distinguishable semantic entity) and an "octet" (an 8-bit
   byte). There are two mappings, one from URI characters to octets, and
   a second from octets to original characters:

   URI character sequence->octet sequence->original character sequence

   A URI is represented as a sequence of characters, not as a sequence
   of octets. That is because URI might be "transported" by means that
   are not through a computer network, e.g., printed on paper, read over
   the radio, etc.

   A URI scheme may define a mapping from URI characters to octets;
   whether this is done depends on the scheme. Commonly, within a
   delimited component of a URI, a sequence of characters may be used to
   represent a sequence of octets. For example, the character "a"
   represents the octet 97 (decimal), while the character sequence "%",
   "0", "a" represents the octet 10 (decimal).





 
RFC 2396                   URI Generic Syntax                August 1998


   There is a second translation for some resources: the sequence of
   octets defined by a component of the URI is subsequently used to