rfc2822 April 2001

3.2.1. Primitive Tokens

   The following are primitive tokens referred to elsewhere in this
   standard, but not otherwise defined in [RFC2234].  Some of them will
   not appear anywhere else in the syntax, but they are convenient to
   refer to in other parts of this document.
   Note: The "specials" below are just such an example.  Though the
   specials token does not appear anywhere else in this standard, it is
   useful for implementers who use tools that lexically analyze
   messages.  Each of the characters in specials can be used to indicate
   a tokenization point in lexical analysis.

NO-WS-CTL       =       %d1-8 /         ; US-ASCII control characters
              %d11 /          ;  that do not include the
              %d12 /          ;  carriage return, line feed,
              %d14-31 /       ;  and white space characters
              %d127

text            =       %d1-9 /         ; Characters excluding CR and LF
              %d11 /
              %d12 /
              %d14-127 /
              obs-text

specials        =       "(" / ")" /     ; Special characters used in
              "<" / ">" /     ;  other parts of the syntax
              "[" / "]" /
              ":" / ";" /
              "@" / "\" /
              "," / "." /
              DQUOTE

   No special semantics are attached to these tokens.  They are simply
   single characters.