Although the mechanisms specified  in  this  Draft  are  all
          described  in prose, most are also described formally in the
          modified BNF notation of RFC 822.  Implementors will need to
          be  familiar  with  this  notation  to fully understand this
          specification, and are referred to RFC 822  for  a  complete
          explanation  of  the modified BNF notation.  Here is a brief
          illustrative example:

               sentence  = clause *( punct clause ) "."
               punct     = ":" / ";"
               clause    = 1*word [ "(" clause ")" / "," 1*word ]
               word      = <any English word>

          This defines a sentence as some clauses separated by  puncts
          and  ended  by  a period, a punct as a colon or semicolon, a
          clause as at least one <word> optionally followed by  either
          a  parenthesized  clause  or  a  comma and at least one more
          <word>, and a <word> as (informally) any English  word.   <>
          are  used to enclose names when (and only when) distinguish-
          ing them from surrounding text is useful.  The full form  of
          the  repetition  notation  is <m>"*"<n><thing>, denoting <m>
          through <n> repetitions of <thing>; <m>  defaults  to  zero,
          <n>  to  infinity, and the "*" and <n> can be omitted if <m>
          and <n> are equal, so 1*word is one or more  words,  1*5word
          is one through five words, and 2word is exactly two words.

          The  character  "\"  is not special in any way in this nota-
          tion.

          This Draft is intended  to  be  self-contained;  all  syntax
          rules  used in it are defined within it, and a rule with the
          same name as one found in MAIL does not necessarily have the
          same  definition.   The lexical layer of MAIL is NOT, repeat
          NOT, used in this  Draft,  and  its  presence  must  not  be
          assumed;  notably,  this  Draft  spells out all places where
          white space is permitted/required and all places where  con-
          structs resembling MAIL comments can occur.

               NOTE:  News  parsers  historically  have been much
               less permissive than MAIL parsers.