RFC 1049 (rfc1049) - Page 2 of 8

Content-type header field for Internet messages

RFC 1049                   Mail Content Type                  March 1988


   document with embedded TROFF formatting commands.  A more
   sophisticated example would be a message body encoded in a Page
   Description Language (PDL) such as Postscript.  In both cases, simply
   mapping the ASCII characters to the screen or printer in the usual
   fashion will not render the document image intended by the sender; an
   additional processing step is required to produce an image of the
   message text on a display device or a piece of paper.

   In both of these examples, the message body contains only the legal
   character set, but the content has a structure which produces some
   desirable result after appropriate processing by the recipient.  If a
   message header field could be used to indicate the structuring
   technique used in the message body, then a sophisticated mail system
   could use such a field to automatically invoke the appropriate
   processing of the message body.  For example, a header field which
   indicated that the message body was encoded using Postscript could be
   used to direct a mail system running under Sun Microsystem's NEWS
   window manager to process the Postscript to produce the appropriate
   page image on the screen.

   Private header fields (beginning with "X-") are already being used by
   some systems to affect such a result (e.g., the Andrew Message System
   developed at Carnegie Mellon University).  However, the widespread
   use of such techniques will require general agreement on the name and
   allowed parameter values for a header field to be used for this
   purpose.

   We propose that a new header field, "Content-type:"  be recognized as
   the standard field for indicating the structure of the message body.
   The contents of the "Content-Type:"  field are parameters which
   specify what type of structure is used in the message body.

   Note that we are not proposing that the message body contain anything
   other than ASCII characters as specified in RFC-822.  Whatever
   structuring is contained in the message body must be represented
   using only the allowed ASCII characters.  Thus, this proposal should
   have no impact on existing mailers, only on mail reading systems.

   At the same time, this restriction eliminates the use of more general
   structuring techniques such as Abstract Syntax Notation, (CCITT
   Recommendation X.409) as used in the X.400 messaging standard, which
   are octet-oriented.

   This is not the first proposal for structuring message bodies.
   RFC-767 discusses a proposed technique for structuring multi-media
   mail messages.  We are also aware that many users already employ mail
   to send TROFF, SCRIBE, TEX, Postscript or other structured
   information.  Such postprocessing as is required must be invoked



Sirbu