octet := "=" 2(DIGIT / "A" / "B" / "C" / "D" / "E" / "F")
        ; octet must be used for characters > 127, =, SPACE, or
   TAB,
        ; and is recommended for any characters not listed in
        ; Appendix B as "mail-safe".

   padding := "0" / "1" /  "2" /  "3" / "4" / "5" / "6" / "7"

   parameter := attribute "=" value

   partial-param :=     (";" "id" "=" value)
                  /  (";" "number" "=" 1*DIGIT)
                  /  (";" "total" "=" 1*DIGIT)
             ; id & number required;total required for last part

   preamble := discard-text       ;  to  be  ignored upon receipt.

   ptext := octet / <any ASCII character except "=", SPACE,  or TAB>




 
RFC 1521                          MIME                    September 1993


        ; characters not listed as "mail-safe" in Appendix B
        ; are also not recommended.

   quoted-printable := ([*(ptext / SPACE /  TAB)  ptext]  ["="] CRLF)
        ; Maximum line length of 76 characters excluding CRLF

   stream-param :=  (";" "type" "=" value)
                / (";" "padding" "=" padding)

   subtype := token  ; case-insensitive

   text-subtype := "plain" / extension-token

   text-type := "text" "/" text-subtype [";" "charset" "=" charset]

   token  :=  1*<any  (ASCII) CHAR except SPACE, CTLs, or tspecials>

   tspecials :=  "(" / ")" / "<" / ">" / "@"
              /  "," / ";" / ":" / "\" / <">
              /  "/" / "[" / "]" / "?" / "="
             ; Must be in quoted-string,
             ; to use within parameter values


   type :=     "application"     /  "audio"   ; case-insensitive
             / "image"           / "message"
             / "multipart"  / "text"
             / "video"           / extension-token
             ; All values case-insensitive

   value := token / quoted-string

   version := "MIME-Version" ":" 1*DIGIT "." 1*DIGIT

   video-type := "video" "/" ("mpeg" / extension-token)

   x-token := <The two characters "X-" or "x-" followed, with no
              intervening white space, by any token>














 
RFC 1521                          MIME                    September 1993


Appendix E -- IANA Registration Procedures

   MIME has been carefully designed to have extensible mechanisms, and
   it is expected that the set of content-type/subtype pairs and their
   associated parameters will grow significantly with time.  Several
   other MIME fields, notably character set names, access-type
   parameters for the message/external-body type, and possibly even
   Content-Transfer-Encoding values, are likely to have new values
   defined over time.  In order to ensure that the set of such values is
   developed in an orderly, well-specified, and public manner, MIME
   defines a registration process which uses the Internet Assigned
   Numbers Authority (IANA) as a central registry for such values.

   In general, parameters in the content-type header field are used to
   convey supplemental information for various content types, and their
   use is defined when the content-type and subtype are defined.  New
   parameters should not be defined as a way to introduce new
   functionality.