RFC 1522 (rfc1522) - Page 3 of 10

MIME (Multipurpose Internet Mail Extensions) Part Two: Message Header Extensions for Non-ASCII Text

RFC 1522                     MIME Part Two                September 1993


      consistency with STD 11, RFC 822.  However, implementors are
      warned that the character set name must be spelled "US-ASCII" in
      MIME message and body part headers.

2. Syntax of encoded-words

   An "encoded-word" is defined by the following ABNF grammar.  The
   notation of RFC 822 is used, with the exception that white space
   characters MAY NOT appear between components of an encoded-word.

   encoded-word = "=?" charset "?" encoding "?" encoded-text "?="

   charset = token    ; see section 3

   encoding = token   ; see section 4

   token = 1*

   especials = "(" / ")" / "" / "@" / "," / ";" / ":" / "
                / "/" / "[" / "]" / "?" / "." / "="

   encoded-text = 1*
                     ; (but see "Use of encoded-words in message
                     ; headers", section 5)

   Both "encoding" and "charset" names are case-independent.  Thus the
   charset name "ISO-8859-1" is equivalent to "iso-8859-1", and the
   encoding named "Q" may be spelled either "Q" or "q".

   An encoded-word may not be more than 75 characters long, including
   charset, encoding, encoded-text, and delimiters.  If it is desirable
   to encode more text than will fit in an encoded-word of 75
   characters, multiple encoded-words (separated by CRLF SPACE) may be
   used.

   While there is no limit to the length of a multiple-line header
   field, each line of a header field that contains one or more
   encoded-words is limited to 76 characters.

   The length restrictions are included not only to ease
   interoperability through internetwork mail gateways, but also to
   impose a limit on the amount of lookahead a header parser must employ
   (while looking for a final ?= delimiter) before it can decide whether
   a token is an encoded-word or something else.

   The characters which may appear in encoded-text are further
   restricted by the rules in section 5.



Moore