rfc1049.txt

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RFC 1049                   Mail Content Type                  March 1988


3. The Content-type Header Field

   Whatever structuring technique is specified by the Content-type
   field, it must be known precisely to both the sender and the
   recipient of the message in order for the message to be properly
   interpreted.  In general, this means that the allowed parameter
   values for the Content-type:  field must identify a well-defined,
   standardized, document structuring technique.  We do not preclude,
   however, the use of a Content-type:  parameter value to specify a
   private structuring technique known only to the sender and the
   recipient.

   More precisely, we propose that the Content-type:  header field
   consist of up to four parameter values.  The first, or type parameter
   names the structuring technique; the second, optional, parameter is a
   version number, ver-num, which indicates a particular version or
   revision of the standardized structuring technique.  The third
   parameter is a resource reference, resource-ref, which may indicate a
   standard database of information to be used in interpreting the
   structured document.  The last parameter is a comment.

   In the Extended Backus Naur Form of RFC-822, we have:

   Content-Type:= type [";" ver-num [";" 1#resource-ref]] [comment]

3.1. Type Values

   Initially, the type parameter would be limited to the following set
   of values:

   type:=           "POSTSCRIPT"/"SCRIBE"/"SGML"/"TEX"/"TROFF"/
                    "DVI"/"X-"atom

   These values are not case sensitive.  POSTSCRIPT, Postscript, and
   POStscriPT are all equivalent.

   POSTSCRIPT      Indicates the enclosed document consists of
                   information encoded using the Postscript Page
                   Definition Language developed by Adobe Systems,
                   Inc. [1]

   SCRIBE          Indicates the document contains embedded formatting
                   information according to the syntax used by the
                   Scribe document formatting language distributed by
                   the Unilogic Corporation. [6]

   SGML            Indicates the document contains structuring
                   information to according the rules specified for



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RFC 1049                   Mail Content Type                  March 1988


                   the Standard Generalized Markup Language, IS 8879,
                   as published by the International Organization for
                   Standardization. [3] Documents structured according
                   to the ISO DIS 8613--Office Docment Architecture and
                   Interchange Format--may also be encoded using SGML
                   syntax.

   TEX             Indicates the document contains embedded formatting
                   information according to the syntax of the TEX
                   document production language. [4]

   TROFF           Indicates the document contains embedded formatting
                   information according to the syntax specified for the
                   TROFF formatting package developed by AT&T Bell
                   Laboratories. [5]

   DVI             Indicates the document contains information according
                   to the device independent file format produced by
                   TROFF or TEX.

   "X-"atom        Any type value beginning with the characters "X-" is
                   a private value.

3.2. Version Number

   Since standard structuring techniques in fact evolve over time, we
   leave room for specifying a version number for the content type.
   Valid values will depend upon the type parameter.

   ver-num:=      local-part

     In particular, we have the following valid values:

     For type=POSTSCRIPT

   ver-num:= "1.0"/"2.0"/"null"

     For type=SCRIBE

   ver-num:= "3"/"4"/"5"/"null"

     For type=SGML

   ver-num:="IS.8879.1986"/"null"

3.3. Resource Reference

   resource-ref:=  local-part



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RFC 1049                   Mail Content Type                  March 1988


   As Apple has demonstrated with their implementation of the
   Laserwriter, a very general document structuring technique can be
   made more efficient by defining a set of macros or other similar
   resources to be used in interpreting any transmitted stream.  The
   Macintosh transmits a LaserPrep file to the Laserwriter containing
   font and macro definitions which can be called upon by subsequent
   documents.  The result is that documents as sent to the Laserwriter
   are considerably more compact than if they had to include the
   LaserPrep file each time.  The Resource Reference parameter allows
   specification of a well known resource, such as a LaserPrep file,
   which should be used by the receiving system when processing the
   message.

   Resource references could also include macro packages for use with
   TEX or references to preprocessors such as eqn and tbl for use with
   troff.  Allowed values will vary according to the type parameter.

     In particular, we propose the following values:

     For type = POSTSCRIPT

   resource-ref:=  "laserprep2.9"/"laserprep3.0"/"laserprep3.1"/
                   "laserprep4.0"/local-part

     For type = TROFF

   resource-ref:=  "eqn"/"tbl"/"me"/local-part

3.4. Comment

   The comment field can be any additional comment text the user
   desires.  Comments are enclosed in parentheses as specified in
   RFC-822.

4. Conclusion

   A standardized Content-type field allows mail reading systems to
   automatically identify the type of a structured message body and to
   process it for display accordingly.  The strcutured message body must
   still conform to the RFC-822 requirements concerning allowable
   characters.  A mail reading system need not take any specific action
   upon receiving a message with valid Content-Type header field.  The
   ability to recognize this field and invoke the appropriate display
   process accordingly will, however, improve the readability of
   messages, and allow the exchange of messages containing mathematical
   symbols, or foreign language characters.





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RFC 1049                   Mail Content Type                  March 1988


   In the near term, the major use of a Content-Type:  header field is
   likely to be for designating the message body as containing a Page
   Definition Language representation such as Postscript.

   Additional type values shall be registered with Internet Assigned
   Numbers Coordinator at USC-ISI.  Please contact:

                   Joyce K. Reynolds
                   USC Information Sciences Institute
                   4676 Admiralty Way
                   Marina del Rey, CA  90292-6695

                   213-822-1511    [e-mail]

                                REFERENCES

   1.  Adobe Systems, Inc.  Postscript Language Reference Manual.
       Addison-Wesley, Reading, Mass., 1985.

   2.  Crocker, David H.  RFC-822:  Standard for the Format of ARPA
       Internet Text Messages.  Network Information Center,
       August 13, 1982.

   3.  ISO TC97/SC18.  Standard Generalized Markup Language.
       Tech. Rept. DIS 8879, ISO, 1986.

   4.  Knuth, Donald E.  The TEXbook.  Addison-Wesley, Reading, Mass.,
       1984.

   5.  Ossanna, Joseph F. NROFF/TROFF User's Manual.  Bell
       Laboratories, Murray Hill, New Jersey, 1976.  Computing Science
       Technical Report No.54.

   6.  Unilogic.  SCRIBE Document Production Software.  Unilogic, 1985.
       Fourth Edition.
















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