Previous: Appendix C -- A Complex Multipart Example
Next: Appendix E -- IANA Registration Procedures

Appendix D -- Collected Grammar

By itself, however, this grammar is incomplete. It refers to several entities that are defined by RFC 822. Rather than reproduce those definitions here, and risk unintentional differences between the two, this document simply refers the reader to RFC 822 for the remaining definitions. Wherever a term is undefined, it refers to the RFC 822 definition.

   application-subtype := ("octet-stream" *stream-param)
                       / "postscript" / extension-token

   application-type :=  "application" "/" application-subtype

   attribute := token    ; case-insensitive

   atype := "ftp" / "anon-ftp" / "tftp" / "local-file"
                  / "afs" / "mail-server" / extension-token
                  ; Case-insensitive

   audio-type := "audio" "/" ("basic" / extension-token)

   body-part := <"message" as defined in RFC 822,
            with all header fields optional, and with the
            specified delimiter not occurring anywhere in
            the message body, either on a line by itself
            or as a substring anywhere.>

NOTE:

In certain transport enclaves, RFC 822 restrictions such as the one that limits bodies to printable ASCII characters may not be in force. (That is, the transport domains may resemble standard Internet mail transport as specified in RFC821 and assumed by RFC822, but without certain restrictions.) The relaxation of these restrictions should be construed as locally extending the definition of bodies, for example to include octets outside of the ASCII range, as long as these extensions are supported by the transport and adequately documented in the Content-Transfer-Encoding header field. However, in no event are headers (either message headers or body-part headers) allowed to contain anything other than ASCII characters.

   boundary := 0*69<bchars> bcharsnospace

   bchars := bcharsnospace / " "

   bcharsnospace :=    DIGIT / ALPHA / "'" / "(" / ")" / "+"  / "_"
                  / "," / "-" / "." / "/" / ":" / "=" / "?"

   charset := "us-ascii" / "iso-8859-1" / "iso-8859-2"/ "iso-8859-3"
        / "iso-8859-4" / "iso-8859-5" /  "iso-8859-6" / "iso-8859-7"
        / "iso-8859-8" / "iso-8859-9" / extension-token
        ; case insensitive

   close-delimiter := "--" boundary "--" CRLF;Again,no space by "--",

   content  := "Content-Type"  ":" type "/" subtype  *(";" parameter)
             ; case-insensitive matching of type and subtype

   delimiter := "--" boundary CRLF  ;taken from Content-Type field.
                                ; There must be no space
                                ; between "--" and boundary.

   description := "Content-Description" ":" *text

   discard-text := *(*text CRLF)

   encapsulation := delimiter body-part CRLF

   encoding := "Content-Transfer-Encoding" ":" mechanism

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

   extension-token :=  x-token / iana-token

   external-param :=   (";" "access-type" "=" atype)
                  / (";" "expiration" "=" date-time)

                       ; Note that date-time is quoted
                  / (";" "size" "=" 1*DIGIT)
                  / (";"  "permission"  "="  ("read" / "read-write"))
                       ; Permission is case-insensitive
                  / (";" "name" "="  value)
                  / (";" "site" "=" value)
                  / (";" "dir" "=" value)
                  / (";" "mode" "=" value)
                  / (";" "server" "=" value)
                  / (";" "subject" "=" value)
           ;access-type required; others required based on access-type

   iana-token := <a publicly-defined extension token,
             registered with IANA, as specified in
             Appendix E>

   id :=  "Content-ID" ":" msg-id

   image-type := "image" "/" ("gif" / "jpeg" / extension-token)

   mechanism :=     "7bit"    ;  case-insensitive
                  / "quoted-printable"
                  / "base64"
                  / "8bit"
                  / "binary"
                  / x-token

   message-subtype := "rfc822"
                  / "partial" 2#3partial-param
                  / "external-body" 1*external-param
                  / extension-token

   message-type := "message" "/" message-subtype

   multipart-body :=preamble 1*encapsulation close-delimiter epilogue

   multipart-subtype := "mixed" / "parallel" / "digest"
                  / "alternative" / extension-token

   multipart-type := "multipart" "/" multipart-subtype
                  ";" "boundary" "=" boundary

   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>
        ; 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>

Previous: Appendix C -- A Complex Multipart Example
Next: Appendix E -- IANA Registration Procedures