usefor-article-07 May 2002

2.4.3.  Syntax copied from other standards

   The following syntactic forms, taken from [RFC 2234] or from [RFC
   2822], are repeated here for convenience only:

      ALPHA         = %x41-5A /          ; A-Z
            %x61-7A            ; a-z
      CR            = %x0D               ; carriage return
      CRLF          = CR LF
      DIGIT         = %x30-39            ; 0-9
      HTAB          = %x09               ; horizontal tab
      LF            = %x0A               ; line feed
      SP            = %x20               ; space
      NO-WS-CTL     = %d1-8 /            ; US-ASCII control characters
            %d11 /             ; which do not include the
            %d12 /             ; carriage return, line feed,
            %d14-31 /          ; and whitespace characters
            %d127
      specials      = "(" / ")" /        ; Special characters used in
            "<" / ">" /        ; other parts of the syntax
            "[" / "]" /
            ":" / ";" /
            "@" / "\" /
            "," / "." /
            DQUOTE
      WSP           = SP / HTAB          ; Whitespace characters
      FWS           = ([*WSP CRLF] 1*WSP); Folding whitespace
      ccontent      = ctext / quoted-pair / comment
      comment       = "(" *([FWS] ccontent) [FWS] ")"
      CFWS          = *([FWS] comment) (([FWS] comment) / FWS )
      DQUOTE        = %d34               ; quote mark
      quoted-pair   = "\" text
      atext         = ALPHA / DIGIT /
            "!" / "#" /        ; Any US-ASCII character except
            "$" / "%" /        ; controls, SP, and specials.
            "&" / "'" /        ; Used for atoms
            "*" / "+" /
            "-" / "/" /
            "=" / "?" /
            "^" / "_" /
            "`" / "{" /
            "|" / "}" /
            "~"
      atom          = [CFWS] 1*atext [CFWS]
      dot-atom      = [CFWS] dot-atom-text [CFWS]
      dot-atom-text = 1*atext *( "." 1*atext )
      qcontent      = qtext / quoted-pair
      quoted-string = [CFWS] DQUOTE
               *( [FWS] qcontent ) [FWS]
               DQUOTE [CFWS]
      word          = atom / quoted-string
      phrase        = 1*word

        NOTE: Following [RFC 2234], literal text included in the syntax
        is to be regarded as case-insensitive.  However, in
        contradistinction to [RFC 2822], the Netnews protocols are
        sensitive to case in some instances (as in newsgroup names, some
        header parameters, etc.). Care has been taken to indicate this
        explicitly where required.

   As in [RFC 2822], where any quoted-pair appears it is to be
   interpreted as its text character alone. That is to say, the "\"
   character that appears as part of a quoted-pair is semantically
   "invisible".

   Again, as in [RFC 2822], strings of characters that include
   characters not syntactically allowed in some particular context may
   be incorporated into a quoted-string by "encapsulating" them between
   quote (DQUOTE, US-ASCII 34) characters, prefixing every quote and
   backslash character (and possibly other characters too) with a "\" so
   as to form a quoted-pair, and possibly introducing folding by
   prefixing some WSP with CRLF.

   The semantic value of a quoted-string (i.e. the result of reversing
   the encapsulation) is a string of characters which includes neither
   the optional CFWS outside of the quote characters, nor the quote
   characters themselves, nor any CRLF contained within any FWS between
   the two quote characters, nor the "\" which introduces any quoted-
   pair.