RFC 1049 (rfc1049) - Page 2 of 8
Content-type header field for Internet messages
Alternative Format: Original Text Document
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
