RFC 1522 (rfc1522) - Page 2 of 10

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

RFC 1522                     MIME Part Two                September 1993


   specification.

   While it is unfortunate that these programs do not correctly
   interpret RFC 822 headers, to "break" these programs would cause
   severe operational problems for the Internet mail system.  The
   extensions described in this memo therefore do not rely on little-
   used features of RFC 822.

   Instead, certain sequences of "ordinary" printable ASCII characters
   (known as "encoded-words") are reserved for use as encoded data.  The
   syntax of encoded-words is such that they are unlikely to
   "accidentally" appear as normal text in message headers.
   Furthermore, the characters used in encoded-words are restricted to
   those which do not have special meanings in the context in which the
   encoded-word appears.

   Generally, an "encoded-word" is a sequence of printable ASCII
   characters that begins with "=?", ends with "?=", and has two "?"s in
   between.  It specifies a character set and an encoding method, and
   also includes the original text encoded as graphic ASCII characters,
   according to the rules for that encoding method.

   A mail composer that implements this specification will provide a
   means of inputting non-ASCII text in header fields, but will
   translate these fields (or appropriate portions of these fields) into
   encoded-words before inserting them into the message header.

   A mail reader that implements this specification will recognize
   encoded-words when they appear in certain portions of the message
   header.  Instead of displaying the encoded-word "as is", it will
   reverse the encoding and display the original text in the designated
   character set.

   NOTES

      This memo relies heavily on notation and terms defined STD 11, RFC
      822 and RFC 1521.  In particular, the syntax for the ABNF used in
      this memo is defined in STD 11, RFC 822, as well as many of the
      terms used in the grammar for the header extensions defined here.
      Successful implementation of this protocol extension requires
      careful attention to the details of both STD 11, RFC 822 and RFC
      1521.

      When the term "ASCII" appears in this memo, it refers to the "7-
      Bit American Standard Code for Information Interchange", ANSI
      X3.4-1986.  The MIME charset name for this character set is "US-
      ASCII".  When not specifically referring to the MIME charset name,
      this document uses the term "ASCII", both for brevity and for



Moore