Emacs MIME Manual

This manual documents the libraries used to compose and display MIME messages.

This is not a manual meant for users; it's a manual directed at people who want to write functions and commands that manipulate MIME elements.

MIME is short for Multipurpose Internet Mail Extensions. This standard is documented in a number of RFCs; mainly RFC2045 (Format of Internet Message Bodies), RFC2046 (Media Types), RFC2047 (Message Header Extensions for Non-ASCII Text), RFC2048 (Registration Procedures), RFC2049 (Conformance Criteria and Examples). It is highly recommended that anyone who intends writing MIME-compliant software read at least RFC2045 and RFC2047.

1. Interface Functions		An abstraction over the basic functions.
2. Basic Functions		Utility and basic parsing functions.
3. Decoding and Viewing		A framework for decoding and viewing.
4. Composing		MML; a language for describing MIME parts.
5. Standards		A summary of RFCs and working documents used.
6. Index		Function and variable index.

1. Interface Functions

The mail-parse library is an abstraction over the actual low-level libraries that are described in the next chapter.

Standards change, and so programs have to change to fit in the new mold. For instance, RFC2045 describes a syntax for the Content-Type header that only allows ASCII characters in the parameter list. RFC2231 expands on RFC2045 syntax to provide a scheme for continuation headers and non-ASCII characters.

The traditional way to deal with this is just to update the library functions to parse the new syntax. However, this is sometimes the wrong thing to do. In some instances it may be vital to be able to understand both the old syntax as well as the new syntax, and if there is only one library, one must choose between the old version of the library and the new version of the library.

The Emacs MIME library takes a different tack. It defines a series of low-level libraries (`rfc2047.el', `rfc2231.el' and so on) that parses strictly according to the corresponding standard. However, normal programs would not use the functions provided by these libraries directly, but instead use the functions provided by the mail-parse library. The functions in this library are just aliases to the corresponding functions in the latest low-level libraries. Using this scheme, programs get a consistent interface they can use, and library developers are free to create write code that handles new standards.

The following functions are defined by this library:

Function: mail-header-parse-content-type string

Parse string, a Content-Type header, and return a content-type list in the following format:

("type/subtype" (attribute1 . value1) (attribute2 . value2) ...)

Here's an example:

(mail-header-parse-content-type "image/gif; name=\"b980912.gif\"") => ("image/gif" (name . "b980912.gif"))

Function: mail-header-parse-content-disposition string

Parse string, a Content-Disposition header, and return a content-type list in the format above.

Function: mail-content-type-get ct attribute

Returns the value of the given attribute from the content-type list ct.

(mail-content-type-get '("image/gif" (name . "b980912.gif")) 'name) => "b980912.gif"

Function: mail-header-encode-parameter param value

Takes a parameter string `param=value' and returns an encoded version of it. This is used for parameters in headers like `Content-Type' and `Content-Disposition'.

Function: mail-header-remove-comments string

Return a comment-free version of string.

(mail-header-remove-comments "Gnus/5.070027 (Pterodactyl Gnus v0.27) (Finnish Landrace)") => "Gnus/5.070027 "

Function: mail-header-remove-whitespace string

Remove linear white space from string. Space inside quoted strings and comments is preserved.

(mail-header-remove-whitespace "image/gif; name=\"Name with spaces\"") => "image/gif;name=\"Name with spaces\""

Function: mail-header-get-comment string

Return the last comment in string.

(mail-header-get-comment "Gnus/5.070027 (Pterodactyl Gnus v0.27) (Finnish Landrace)") => "Finnish Landrace"

Function: mail-header-parse-address string

Parse an address string string and return a list containing the mailbox and the plaintext name.

(mail-header-parse-address "Hrvoje Niksic ") => ("hniksic@srce.hr" . "Hrvoje Niksic")

Function: mail-header-parse-addresses string

Parse string as a list of addresses and return a list of elements like the one described above.

(mail-header-parse-addresses "Hrvoje Niksic , Steinar Bang <sb@metis.no>") => (("hniksic@srce.hr" . "Hrvoje Niksic") ("sb@metis.no" . "Steinar Bang"))

Function: mail-header-parse-date string

Parse a date string and return an Emacs time structure.

Function: mail-narrow-to-head

Narrow the buffer to the header section of the buffer. Point is placed at the beginning of the narrowed buffer.

Function: mail-header-narrow-to-field

Narrow the buffer to the header under point.

Function: mail-encode-encoded-word-region start end

Encode the non-ASCII words in the region startto end. For instance, `Naïve' is encoded as `=?iso-8859-1?q?Na=EFve?='.

Function: mail-encode-encoded-word-buffer

Encode the non-ASCII words in the current buffer. This function is meant to be called with the buffer narrowed to the headers of a message.

Function: mail-encode-encoded-word-string string

Encode the words that need encoding in string, and return the result.

(mail-encode-encoded-word-string "This is naïve, baby") => "This is =?iso-8859-1?q?na=EFve,?= baby"

Function: mail-decode-encoded-word-region start end

Decode the encoded words in the region startto end.

Function: mail-decode-encoded-word-string string

Decode the encoded words in string and return the result.

(mail-decode-encoded-word-string "This is =?iso-8859-1?q?na=EFve,?= baby") => "This is naïve, baby"

Currently, mail-parse is an abstraction over ietf-drums, rfc2047, rfc2045 and rfc2231. These are documented in the subsequent sections.

2. Basic Functions

This chapter describes the basic, ground-level functions for parsing and handling. Covered here is parsing From lines, removing comments from header lines, decoding encoded words, parsing date headers and so on. High-level functionality is dealt with in the next chapter (see section 3. Decoding and Viewing).

2.1 rfc2045		Encoding Content-Type headers.
2.2 rfc2231		Parsing Content-Type headers.
2.3 ietf-drums		Handling mail headers defined by RFC822bis.
2.4 rfc2047		En/decoding encoded words in headers.
2.5 time-date		Functions for parsing dates and manipulating time.
2.6 qp		Quoted-Printable en/decoding.
2.7 base64		Base64 en/decoding.
2.8 binhex		Binhex decoding.
2.9 uudecode		Uuencode decoding.
2.10 rfc1843		Decoding HZ-encoded text.
2.11 mailcap		How parts are displayed is specified by mailcap files

2.1 rfc2045

RFC2045 is the "main" MIME document, and as such, one would imagine that there would be a lot to implement. But there isn't, since most of the implementation details are delegated to the subsequent RFCs.

So `rfc2045.el' has only a single function:

Function: rfc2045-encode-string parameter value

Takes a parameter and a value and returns a `param=value' string. value will be quoted if there are non-safe characters in it.

2.2 rfc2231

RFC2231 defines a syntax for the `Content-Type' and `Content-Disposition' headers. Its snappy name is MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations.

In short, these headers look something like this:

Content-Type: application/x-stuff; title*0*=us-ascii'en'This%20is%20even%20more%20; title*1*=%2A%2A%2Afun%2A%2A%2A%20; title*2="isn't it!"

They usually aren't this bad, though.

The following functions are defined by this library:

Function: rfc2231-parse-string string

Parse a `Content-Type' header string and return a list describing its elements.

(rfc2231-parse-string "application/x-stuff; title*0*=us-ascii'en'This%20is%20even%20more%20; title*1*=%2A%2A%2Afun%2A%2A%2A%20; title*2=\"isn't it!\"") => ("application/x-stuff" (title . "This is even more ***fun*** isn't it!"))

Function: rfc2231-get-value ct attribute

Takes a list ct of the format above and returns the value of the specified attribute.

Function: rfc2231-encode-string parameter value

Encode the string `parameter=value' for inclusion in headers likes `Content-Type' and `Content-Disposition'.

2.3 ietf-drums

drums is an IETF working group that is working on the replacement for RFC822.

The functions provided by this library include:

Function: ietf-drums-remove-comments string

Remove the comments from string and return the result.

Function: ietf-drums-remove-whitespace string

Remove linear white space from string and return the result. Spaces inside quoted strings and comments are left untouched.

Function: ietf-drums-get-comment string

Return the last most comment from string.

Function: ietf-drums-parse-address string

Parse an address string and return a list of the mailbox and the plain text name.

Function: ietf-drums-parse-addresses string

Parse string, containing any number of comma-separated addresses, and return a list of mailbox/plain text pairs.

Function: ietf-drums-parse-date string

Parse the date string and return an Emacs time structure.

Function: ietf-drums-narrow-to-header

Narrow the buffer to the header section of the current buffer.

2.4 rfc2047

RFC2047 (Message Header Extensions for Non-ASCII Text) specifies how non-ASCII text in headers are to be encoded. This is actually rather complicated, so a number of variables are necessary to tweak what this library does.

The following variables are tweakable:

Variable: rfc2047-default-charset

Characters in this charset should not be decoded by this library. This defaults to `iso-8859-1'.

Variable: rfc2047-header-encoding-list

This is an alist of header / encoding-type pairs. Its main purpose is to prevent encoding of certain headers.

The keys can either be header regexps, or t.

The values can be either nil, in which case the header(s) in question won't be encoded, or mime, which means that they will be encoded.

Variable: rfc2047-charset-encoding-alist

RFC2047 specifies two forms of encoding---Q (a Quoted-Printable-like encoding) and B (base64). This alist specifies which charset should use which encoding.

Variable: rfc2047-encoding-function-alist

This is an alist of encoding / function pairs. The encodings are Q, B and nil.

Variable: rfc2047-q-encoding-alist

The Q encoding isn't quite the same for all headers. Some headers allow a narrower range of characters, and that is what this variable is for. It's an alist of header regexps and allowable character ranges.

Variable: rfc2047-encoded-word-regexp

When decoding words, this library looks for matches to this regexp.

Those were the variables, and these are the functions:

Function: rfc2047-narrow-to-field

Narrow the buffer to the header on the current line.

Function: rfc2047-encode-message-header

Should be called narrowed to the header of a message. Encodes according to rfc2047-header-encoding-alist.

Function: rfc2047-encode-region start end

Encodes all encodable words in the region start to end.

Function: rfc2047-encode-string string

Encode string and return the result.

Function: rfc2047-decode-region start end

Decode the encoded words in the region start to end.

Function: rfc2047-decode-string string

Decode string and return the result.

2.5 time-date

While not really a part of the MIME library, it is convenient to document this library here. It deals with parsing `Date' headers and manipulating time. (Not by using tesseracts, though, I'm sorry to say.)

These functions convert between five formats: a date string, an Emacs time structure, a decoded time list, a number of seconds, and a day number.

The functions have quite self-explanatory names, so the following just gives an overview of which functions are available.

(parse-time-string "Sat Sep 12 12:21:54 1998 +0200") => (54 21 12 12 9 1998 6 nil 7200) (date-to-time "Sat Sep 12 12:21:54 1998 +0200") => (13818 19266) (time-to-seconds '(13818 19266)) => 905595714.0 (seconds-to-time 905595714.0) => (13818 19266 0) (time-to-day '(13818 19266)) => 729644 (days-to-time 729644) => (961933 65536) (time-since '(13818 19266)) => (0 430) (time-less-p '(13818 19266) '(13818 19145)) => nil (subtract-time '(13818 19266) '(13818 19145)) => (0 121) (days-between "Sat Sep 12 12:21:54 1998 +0200" "Sat Sep 07 12:21:54 1998 +0200") => 5 (date-leap-year-p 2000) => t (time-to-day-in-year '(13818 19266)) => 255

And finally, we have safe-date-to-time, which does the same as date-to-time, but returns a zero time if the date is syntactically malformed.

2.6 qp

This library deals with decoding and encoding Quoted-Printable text.

Very briefly explained, QP encoding means translating all 8-bit characters (and lots of control characters) into things that look like `=EF'; that is, an equal sign followed by the byte encoded as a hex string. It is defined in RFC 2045.

The following functions are defined by the library:

Command: quoted-printable-decode-region from to &optional coding-system

QP-decode all the encoded text in the region. If coding-system is non-nil, decode bytes into characters with that coding-system. It is probably better not to use coding-system; instead decode into a unibyte buffer, decode that appropriately and then interpret it as multibyte.

Function: quoted-printable-decode-string string &optional coding-system

Return a QP-encoded copy of string. If coding-system is non-nil, decode bytes into characters with that coding-system.

Command: quoted-printable-encode-region from to &optional fold class

QP-encode all the region. If fold is non-nil, fold lines at 76 characters, as required by the RFC. If class is non-nil, translate the characters not matched by that regexp class, which should be in the form expected by skip-chars-forward and should probably not contain literal eight-bit characters. Specifying class makes sense to do extra encoding in header fields.

If variable mm-use-ultra-safe-encoding is defined and non-nil, fold lines unconditionally and encode `From ' and `-' at the start of lines..

Function: quoted-printable-encode-string string

Return a QP-encoded copy of string.

2.7 base64

Base64 is an encoding that encodes three bytes into four characters, thereby increasing the size by about 33%. The alphabet used for encoding is very resistant to mangling during transit. See section `Base 64 Encoding' in The Emacs Lisp Reference Manual.

2.8 binhex

Binhex is an encoding that originated in Macintosh environments. The following function is supplied to deal with these:

Function: binhex-decode-region start end &optional header-only

Decode the encoded text in the region start to end. If header-only is non-nil, only decode the `binhex' header and return the file name.

2.9 uudecode

Uuencoding is probably still the most popular encoding of binaries used on Usenet, although Base64 rules the mail world.

The following function is supplied by this package:

Function: uudecode-decode-region start end &optional file-name

Decode the text in the region start to end. If file-name is non-nil, save the result to file-name.

2.10 rfc1843

RFC1843 deals with mixing Chinese and ASCII characters in messages. In essence, RFC1843 switches between ASCII and Chinese by doing this:

This sentence is in ASCII. The next sentence is in GB.~{<:Ky2;S{#,NpJ)l6HK!#~}Bye.

Simple enough, and widely used in China.

The following functions are available to handle this encoding:

Function: rfc1843-decode-region start end

Decode HZ-encoded text in the region start to end.

Function: rfc1843-decode-string string

Decode the HZ-encoded string and return the result.

2.11 mailcap

As specified by RFC 1524, MIME-aware message handlers parse mailcap files from a default list, which can be overridden by the MAILCAP environment variable. These describe how elements are supposed to be displayed. Here's an example file:

image/*; gimp -8 %s audio/wav; wavplayer %s

This says that all image files should be displayed with gimp, and that WAVE audio files should be played by wavplayer.

The mailcap library parses such files, and provides functions for matching types.

Variable: mailcap-mime-data

This variable is an alist of alists containing backup viewing rules for MIME types. These are overridden by rules for a type found in mailcap files. The outer alist is keyed on the major content-type and the inner alists are keyed on the minor content-type (which can be a regular expression).

For example:

(("application" ("octet-stream" (viewer . mailcap-save-binary-file) (non-viewer . t) (type . "application/octet-stream")) ("plain" (viewer . view-mode) (test fboundp 'view-mode) (type . "text/plain")))

User Option: mailcap-default-mime-data

This variable is the default value of mailcap-mime-data. It exists to allow setting the value using Custom. It is merged with values from mailcap files by mailcap-parse-mailcaps.

Although it is not specified by the RFC, MIME tools normally use a common means of associating file extensions with defualt MIME types in the absence of other information about the type of a file. The information is found in per-user files `~/.mime.types' and system `mime.types' files found in quasi-standard places. Here is an example:

application/x-dvi dvi audio/mpeg mpga mpega mp2 mp3 image/jpeg jpeg jpg jpe

Variable: mailcap-mime-extensions

This variable is an alist MIME types keyed by file extensions. This is overridden by entries found in `mime.types' files.

User Option: mailcap-default-mime-extensions

This variable is the default value of mailcap-mime-extensions. It exists to allow setting the value using Custom. It is merged with values from mailcap files by mailcap-parse-mimetypes.

Interface functions:

Function: mailcap-parse-mailcaps &optional path force

Parse all the mailcap files specified in a path string path and merge them with the values from mailcap-mime-data. Components of path are separated by the path-separator character appropriate for the system. If force is non-nil, the files are re-parsed even if they have been parsed already. If path is omitted, use the value of environment variable MAILCAPS if it is set; otherwise (on GNU and Unix) use the path defined in RFC 1524, plus `/usr/local/etc/mailcap'.

Function: mailcap-parse-mimetypes &optional path force

Parse all the mimetypes specified in a path string path and merge them with the values from mailcap-mime-extensions. Components of path are separated by the path-separator character appropriate for the system. If path is omitted, use the value of environment variable MIMETYPES if set; otherwise use a default path consistent with that used by mailcap-parse-mailcaps. If force is non-nil, the files are re-parsed even if they have been parsed already.

Function: mailcap-mime-info string &optional request

Gets the viewer command for content-type string. nil is returned if none is found. Expects string to be a complete content-type header line.

If request is non-nil it specifies what information to return. If it is nil or the empty string, the viewer (second field of the mailcap entry) will be returned. If it is a string, then the mailcap field corresponding to that string will be returned (`print', `description', whatever). If it is a number, all the information for this viewer is returned. If it is all, then all possible viewers for this type is returned.

Function: mailcap-mime-types

This function returns a list of all the defined media types.

Function: mailcap-extension-to-mime extension

This function returns the content type defined for a file with the given extension.

3. Decoding and Viewing

This chapter deals with decoding and viewing MIME messages on a higher level.

The main idea is to first analyze a MIME article, and then allow other programs to do things based on the list of handles that are returned as a result of this analysis.

3.1 Dissection		Analyzing a MIME message.
3.2 Handles		Handle manipulations.
3.3 Display		Displaying handles.
3.4 Customization		Variables that affect display.
3.5 New Viewers		How to write your own viewers.

3.1 Dissection

The mm-dissect-buffer is the function responsible for dissecting a MIME article. If given a multipart message, it will recursively descend the message, following the structure, and return a tree of MIME handles that describes the structure of the message.

3.2 Handles

A MIME handle is a list that fully describes a MIME component.

The following macros can be used to access elements from the handle argument:

Macro: mm-handle-buffer handle

Return the buffer that holds the contents of the undecoded MIME part.

Macro: mm-handle-type handle

Return the parsed `Content-Type' of the part.

Macro: mm-handle-encoding handle

Return the `Content-Transfer-Encoding' of the part.

Macro: mm-handle-undisplayer handle

Return the function that can be used to remove the displayed part (if it has been displayed).

Macro: mm-handle-set-undisplayer handle function

Set the undisplayer function for the part to function.

Macro: mm-handle-disposition

Return the parsed `Content-Disposition' of the part.

Macro: mm-handle-disposition

Return the description of the part.

Macro: mm-get-content-id id

Returns the handle(s) referred to by id, the `Content-ID' of the part.

3.3 Display

Functions for displaying, removing and saving. In the descriptions below, `the part' means the MIME part represented by the handle argument.

Function: mm-display-part handle &optional no-default

Display the part. Return nil if the part is removed, inline if it is displayed inline or external if it is displayed externally. If no-default is non-nil, the part is not displayed unless the MIME type of handle is defined to be displayed inline or there is an display method defined for it; i.e. no default external method will be used.

Function: mm-remove-part handle

Remove the part if it has been displayed.

Function: mm-inlinable-p handle

Return non-nil if the part can be displayed inline.

Function: mm-automatic-display-p handle

Return non-nil if the user has requested automatic display of the MIME type of the part.

Function: mm-destroy-part handle

Free all the resources used by the part.

Function: mm-save-part handle

Save the part to a file. The user is prompted for a file name to use.

Function: mm-pipe-part handle

Pipe the part through a shell command. The user is prompted for the command to use.

Function: mm-interactively-view-part handle

Prompt for a mailcap method to use to view the part and display it externally using that method.

3.4 Customization

The display of MIME types may be customized with the following options.

User Option: mm-inline-media-tests

This is an alist where the key is a MIME type, the second element is a function to display the part inline (i.e., inside Emacs), and the third element is a form to be evaled to say whether the part can be displayed inline.

This variable specifies whether a part can be displayed inline, and, if so, how to do it. It does not say whether parts are actually displayed inline.

User Option: mm-inlined-types

This, on the other hand, says what types are to be displayed inline, if they satisfy the conditions set by the variable above. It's a list of MIME media types.

User Option: mm-automatic-display

This is a list of types that are to be displayed "automatically", but only if the above variable allows it. That is, only inlinable parts can be displayed automatically.

User Option: mm-attachment-override-types

Some MIME agents create parts that have a content-disposition of `attachment'. This variable allows overriding that disposition and displaying the part inline. (Note that the disposition is only overridden if we are able to, and want to, display the part inline.)

User Option: mm-discouraged-alternatives

List of MIME types that are discouraged when viewing `multipart/alternative'. Viewing agents are supposed to view the last possible part of a message, as that is supposed to be the richest. However, users may prefer other types instead, and this list says what types are most unwanted. If, for instance, `text/html' parts are very unwanted, and `text/richtech' parts are somewhat unwanted, then the value of this variable should be set to:

("text/html" "text/richtext")

User Option: mm-inline-large-images-p

When displaying inline images that are larger than the window, XEmacs does not enable scrolling, which means that you cannot see the whole image. To prevent this, the library tries to determine the image size before displaying it inline, and if it doesn't fit the window, the library will display it externally (e.g. with `ImageMagick' or `xv'). Setting this variable to t disables this check and makes the library display all inline images as inline, regardless of their size.

User Option: mm-inline-override-p

mm-inlined-types may include regular expressions, for example to specify that all `text/.*' parts be displayed inline. If a user prefers to have a type that matches such a regular expression be treated as an attachment, that can be accomplished by setting this variable to a list containing that type. For example assuming mm-inlined-types includes `text/.*', then including `text/html' in this variable will cause `text/html' parts to be treated as attachments.

3.5 New Viewers

Here's an example viewer for displaying `text/enriched' inline:

(defun mm-display-enriched-inline (handle) (let (text) (with-temp-buffer (mm-insert-part handle) (save-window-excursion (enriched-decode (point-min) (point-max)) (setq text (buffer-string)))) (mm-insert-inline handle text)))

We see that the function takes a MIME handle as its parameter. It then goes to a temporary buffer, inserts the text of the part, does some work on the text, stores the result, goes back to the buffer it was called from and inserts the result.

The two important helper functions here are mm-insert-part and mm-insert-inline. The first function inserts the text of the handle in the current buffer. It handles charset and/or content transfer decoding. The second function just inserts whatever text you tell it to insert, but it also sets things up so that the text can be "undisplayed' in a convenient manner.

4. Composing

Creating a MIME message is boring and non-trivial. Therefore, a library called mml has been defined that parses a language called MML (MIME Meta Language) and generates MIME messages.

The main interface function is mml-generate-mime. It will examine the contents of the current (narrowed-to) buffer and return a string containing the MIME message.

4.1 Simple MML Example		An example MML document.
4.2 MML Definition		All valid MML elements.
4.3 Advanced MML Example		Another example MML document.
4.4 Charset Translation		How charsets are mapped from Mule to MIME.
4.5 Conversion		Going from MIME to MML and vice versa.

4.1 Simple MML Example

Here's a simple `multipart/alternative':

<#multipart type=alternative> This is a plain text part. <#part type=text/enriched> <center>This is a centered enriched part</center> <#/multipart>

After running this through mml-generate-mime, we get this:

Content-Type: multipart/alternative; boundary="=-=-=" --=-=-= This is a plain text part. --=-=-= Content-Type: text/enriched <center>This is a centered enriched part</center> --=-=-=--

4.2 MML Definition

The MML language is very simple. It looks a bit like an SGML application, but it's not.

The main concept of MML is the part. Each part can be of a different type or use a different charset. The way to delineate a part is with a `<#part ...>' tag. Multipart parts can be introduced with the `<#multipart ...>' tag. Parts are ended by the `<#/part>' or `<#/multipart>' tags. Parts started with the `<#part ...>' tags are also closed by the next open tag.

There's also the `<#external ...>' tag. These introduce `external/message-body' parts.

Each tag can contain zero or more parameters on the form `parameter=value'. The values may be enclosed in quotation marks, but that's not necessary unless the value contains white space. So `filename=/home/user/#hello$^yes' is perfectly valid.

The following parameters have meaning in MML; parameters that have no meaning are ignored. The MML parameter names are the same as the MIME parameter names; the things in the parentheses say which header it will be used in.

`type'

The MIME type of the part (`Content-Type').

`filename'

Use the contents of the file in the body of the part (`Content-Disposition').

`charset'

The contents of the body of the part are to be encoded in the character set speficied (`Content-Type').

`name'

Might be used to suggest a file name if the part is to be saved to a file (`Content-Type').

`disposition'

Valid values are `inline' and `attachment' (`Content-Disposition').

`encoding'

Valid values are `7bit', `8bit', `quoted-printable' and `base64' (`Content-Transfer-Encoding').

`description'

A description of the part (`Content-Description').

`creation-date'

RFC822 date when the part was created (`Content-Disposition').

`modification-date'

RFC822 date when the part was modified (`Content-Disposition').

`read-date'

RFC822 date when the part was read (`Content-Disposition').

`size'

The size (in octets) of the part (`Content-Disposition').

Parameters for `application/octet-stream':

`type'

Type of the part; informal--meant for human readers (`Content-Type').

Parameters for `message/external-body':

`access-type'

A word indicating the supported access mechanism by which the file may be obtained. Values include `ftp', `anon-ftp', `tftp', `localfile', and `mailserver'. (`Content-Type'.)

`expiration'

The RFC822 date after which the file may no longer be fetched. (`Content-Type'.)

`size'

The size (in octets) of the file. (`Content-Type'.)

`permission'

Valid values are `read' and `read-write' (`Content-Type').

4.3 Advanced MML Example

Here's a complex multipart message. It's a `multipart/mixed' that contains many parts, one of which is a `multipart/alternative'.

<#multipart type=mixed> <#part type=image/jpeg filename=~/rms.jpg disposition=inline> <#multipart type=alternative> This is a plain text part. <#part type=text/enriched name=enriched.txt> <center>This is a centered enriched part</center> <#/multipart> This is a new plain text part. <#part disposition=attachment> This plain text part is an attachment. <#/multipart>

And this is the resulting MIME message:

Content-Type: multipart/mixed; boundary="=-=-=" --=-=-= --=-=-= Content-Type: image/jpeg; filename="~/rms.jpg" Content-Disposition: inline; filename="~/rms.jpg" Content-Transfer-Encoding: base64 /9j/4AAQSkZJRgABAQAAAQABAAD/2wBDAAgGBgcGBQgHBwcJCQgKDBQNDAsLDBkSEw8UHRof Hh0aHBwgJC4nICIsIxwcKDcpLDAxNDQ0Hyc5PTgyPC4zNDL/wAALCAAwADABAREA/8QAHwAA AQUBAQEBAQEAAAAAAAAAAAECAwQFBgcICQoL/8QAtRAAAgEDAwIEAwUFBAQAAAF9AQIDAAQR BRIhMUEGE1FhByJxFDKBkaEII0KxwRVS0fAkM2JyggkKFhcYGRolJicoKSo0NTY3ODk6Q0RF RkdISUpTVFVWV1hZWmNkZWZnaGlqc3R1dnd4eXqDhIWGh4iJipKTlJWWl5iZmqKjpKWmp6ip qrKztLW2t7i5usLDxMXGx8jJytLT1NXW19jZ2uHi4+Tl5ufo6erx8vP09fb3+Pn6/9oACAEB AAA/AO/rifFHjldNuGsrDa0qcSSHkA+gHrXKw+LtWLrMb+RgTyhbr+HSug07xNqV9fQtZrNI AyiaE/NuBPOOOP0rvRNE880KOC8TbXXGCv1FPqjrF4LDR7u5L7SkTFT/ALWOP1xXgTuXfc7E sx6nua6rwp4IvvEM8chCxWxOdzn7wz6V9AaB4S07w9p5itow0rDLSY5Pt9K43xO66P4xs71m 2QXiGCbA4yOVJ9+1aYORkdK434lyNH4ahCnG66VT9Nj15JFbPdX0MS43M4VQf5/yr2vSpLnw 5ZW8dlCZ8KFXjOPX0/mK6rSPEGt3Angu44fNEReHYNvIH3TzXDeKNO8RX+kSX2ouZkicTIOc L+g7E810ulFjpVtv3bwgB3HJyK5L4quY/C9sVxk3ij/xx6850u7t1mtp/wDlpEw3An3Jr3Dw 34gsbWza4nBlhC5LDsaW6+IFgupQyCF3iHH7gA7c9R9ay7zx6t7aX9jHC4smhfBkGCvHGfrm tLQ7hbnRrV1GPkAP1x1/Hr+Ncr8Vzjwrbf8AX6v/AKA9eQRyYlQk8Yx9K6XTNbkgia2ciSIn 7p5Ga9Atte0LTLKO6it4i7dVRFJDcZ4PvXN+JvEMF9bILVGXJLSZ4zkjivRPDaeX4b08HOTC pOffmua+KkbS+GLVUGT9tT/0B68eeIpIFYjB70+OOVXyoOM9+M1eaWeCLzHPyHGO/NVWvJJm jQ8KGH1NfQWhXSXmh2c8eArRLwO3HSv/2Q== --=-=-= Content-Type: multipart/alternative; boundary="==-=-=" --==-=-= This is a plain text part. --==-=-= Content-Type: text/enriched; name="enriched.txt" <center>This is a centered enriched part</center> --==-=-=-- --=-=-= This is a new plain text part. --=-=-= Content-Disposition: attachment This plain text part is an attachment. --=-=-=--

4.4 Charset Translation

During translation from MML to MIME, for each MIME part which has been composed inside Emacs, an appropriate MIME charset has to be chosen.

If you are running a non-Mule Emacs, this process is simple: if the part contains any non-ASCII (8-bit) characters, the MIME charset given by mail-parse-charset (a symbol) is used. (Never set this variable directly, though. If you want to change the default charset, please consult the documentation of the package which you use to process MIME messages. See section `Various Message Variables' in Message Manual, for example.) If there are only ASCII characters, the MIME charset `US-ASCII' is used, of course.

Things are slightly more complicated when running Emacs with Mule support. In this case, a list of the Mule charsets used in the part is obtained, and the corresponding MIME charsets are determined. If this results in a single MIME charset, this is used to encode the part. But if the resulting list of MIME charsets contains more than one element, two things can happen: if it is possible to encode the part via UTF-8, this charset is used. (For this, Emacs must support the utf-8 coding system, and the part must consist entirely of characters which have Unicode counterparts.) If UTF-8 is not available, the part is split into several, so that each one can be encoded with a single MIME charset. The part can only be split at line boundaries, though--if more than one MIME charset is required to encode a single line, it is not possible to encode the part.

4.5 Conversion

A (multipart) MIME message can be converted to MML with the mime-to-mml function. It works on the message in the current buffer, and substitutes MML markup for MIME boundaries. Non-textual parts do not have their contents in the buffer, but instead have the contents in separate buffers that are referred to from the MML tags.

An MML message can be converted back to MIME by the mml-to-mime function.

These functions are in certain senses "lossy"---you will not get back an identical message if you run MIME-TO-MML and then MML-TO-MIME. Not only will trivial things like the order of the headers differ, but the contents of the headers may also be different. For instance, the original message may use base64 encoding on text, while MML-TO-MIME may decide to use quoted-printable encoding, and so on.

In essence, however, these two functions should be the inverse of each other. The resulting contents of the message should remain equivalent, if not identical.

5. Standards

The Emacs MIME library implements handling of various elements according to a (somewhat) large number of RFCs, drafts and standards documents. This chapter lists the relevant ones. They can all be fetched from `http://quimby.gnus.org/notes/'.

RFC822

STD11

Standard for the Format of ARPA Internet Text Messages.

RFC1036

Standard for Interchange of USENET Messages

RFC1524

A User Agent Configuration Mechanism For Multimedia Mail Format Information

RFC2045

Format of Internet Message Bodies

RFC2046

Media Types

RFC2047

Message Header Extensions for Non-ASCII Text

RFC2048

Registration Procedures

RFC2049

Conformance Criteria and Examples

RFC2231

MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations

RFC1843

HZ - A Data Format for Exchanging Files of Arbitrarily Mixed Chinese and ASCII characters

draft-ietf-drums-msg-fmt-05.txt

Draft for the successor of RFC822

RFC2112

The MIME Multipart/Related Content-type

RFC1892

The Multipart/Report Content Type for the Reporting of Mail System Administrative Messages

RFC2183

Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field

6. Index

Table of Contents

1. Interface Functions
2. Basic Functions

2.1 rfc2045
2.2 rfc2231
2.3 ietf-drums
2.4 rfc2047
2.5 time-date
2.6 qp
2.7 base64
2.8 binhex
2.9 uudecode
2.10 rfc1843
2.11 mailcap

3. Decoding and Viewing

3.1 Dissection
3.2 Handles
3.3 Display
3.4 Customization
3.5 New Viewers

4. Composing

4.1 Simple MML Example
4.2 MML Definition
4.3 Advanced MML Example
4.4 Charset Translation
4.5 Conversion

5. Standards
6. Index

Short Table of Contents

1. Interface Functions
2. Basic Functions
3. Decoding and Viewing
4. Composing
5. Standards
6. Index

About this document

• 1. Section One
• 1.1 Subsection One-One
• ...
• 1.2 Subsection One-Two
• 1.2.1 Subsubsection One-Two-One
• 1.2.2 Subsubsection One-Two-Two
• 1.2.3 Subsubsection One-Two-Three     <== Current Position
• 1.2.4 Subsubsection One-Two-Four
• 1.3 Subsection One-Three
• ...
• 1.4 Subsection One-Four