3 @setfilename emacs-mime
4 @settitle Emacs MIME Manual
10 * Emacs MIME: (emacs-mime). The MIME de/composition library.
15 @setchapternewpage odd
19 This file documents the Emacs MIME interface functionality.
21 Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003
22 Free Software Foundation, Inc.
24 Permission is granted to copy, distribute and/or modify this document
25 under the terms of the GNU Free Documentation License, Version 1.1 or
26 any later version published by the Free Software Foundation; with no
27 Invariant Sections, with the Front-Cover texts being ``A GNU
28 Manual'', and with the Back-Cover Texts as in (a) below. A copy of the
29 license is included in the section entitled ``GNU Free Documentation
30 License'' in the Emacs manual.
32 (a) The FSF's Back-Cover Text is: ``You have freedom to copy and modify
33 this GNU Manual, like GNU software. Copies published by the Free
34 Software Foundation raise funds for GNU development.''
36 This document is part of a collection distributed under the GNU Free
37 Documentation License. If you want to distribute this document
38 separately from the collection, you can do so by adding a copy of the
39 license to the document, as described in section 6 of the license.
45 @title Emacs MIME Manual
47 @author by Lars Magne Ingebrigtsen
50 @vskip 0pt plus 1filll
51 Copyright @copyright{} 1998, 1999, 2000, 2001, 2002, 2003 Free Software
54 Permission is granted to copy, distribute and/or modify this document
55 under the terms of the GNU Free Documentation License, Version 1.1 or
56 any later version published by the Free Software Foundation; with the
57 Invariant Sections being none, with the Front-Cover texts being ``A GNU
58 Manual'', and with the Back-Cover Texts as in (a) below. A copy of the
59 license is included in the section entitled ``GNU Free Documentation
60 License'' in the Emacs manual.
62 (a) The FSF's Back-Cover Text is: ``You have freedom to copy and modify
63 this GNU Manual, like GNU software. Copies published by the Free
64 Software Foundation raise funds for GNU development.''
66 This document is part of a collection distributed under the GNU Free
67 Documentation License. If you want to distribute this document
68 separately from the collection, you can do so by adding a copy of the
69 license to the document, as described in section 6 of the license.
78 This manual documents the libraries used to compose and display
79 @acronym{MIME} messages.
81 This manual is directed at users who want to modify the behaviour of
82 the @acronym{MIME} encoding/decoding process or want a more detailed
83 picture of how the Emacs @acronym{MIME} library works, and people who want
84 to write functions and commands that manipulate @acronym{MIME} elements.
86 @acronym{MIME} is short for @dfn{Multipurpose Internet Mail Extensions}.
87 This standard is documented in a number of RFCs; mainly RFC2045 (Format
88 of Internet Message Bodies), RFC2046 (Media Types), RFC2047 (Message
89 Header Extensions for Non-@acronym{ASCII} Text), RFC2048 (Registration
90 Procedures), RFC2049 (Conformance Criteria and Examples). It is highly
91 recommended that anyone who intends writing @acronym{MIME}-compliant software
92 read at least RFC2045 and RFC2047.
95 * Decoding and Viewing:: A framework for decoding and viewing.
96 * Composing:: @acronym{MML}; a language for describing @acronym{MIME} parts.
97 * Interface Functions:: An abstraction over the basic functions.
98 * Basic Functions:: Utility and basic parsing functions.
99 * Standards:: A summary of RFCs and working documents used.
100 * Index:: Function and variable index.
104 @node Decoding and Viewing
105 @chapter Decoding and Viewing
107 This chapter deals with decoding and viewing @acronym{MIME} messages on a
110 The main idea is to first analyze a @acronym{MIME} article, and then allow
111 other programs to do things based on the list of @dfn{handles} that are
112 returned as a result of this analysis.
115 * Dissection:: Analyzing a @acronym{MIME} message.
116 * Non-MIME:: Analyzing a non-@acronym{MIME} message.
117 * Handles:: Handle manipulations.
118 * Display:: Displaying handles.
119 * Display Customization:: Variables that affect display.
120 * Files and Directories:: Saving and naming attachments.
121 * New Viewers:: How to write your own viewers.
128 The @code{mm-dissect-buffer} is the function responsible for dissecting
129 a @acronym{MIME} article. If given a multipart message, it will recursively
130 descend the message, following the structure, and return a tree of
131 @acronym{MIME} handles that describes the structure of the message.
135 @vindex mm-uu-configure-list
137 Gnus also understands some non-@acronym{MIME} attachments, such as
138 postscript, uuencode, binhex, yenc, shar, forward, gnatsweb, pgp,
139 diff. Each of these features can be disabled by add an item into
140 @code{mm-uu-configure-list}. For example,
144 (add-to-list 'mm-uu-configure-list '(pgp-signed . disabled))
170 Non-@acronym{MIME} forwarded message.
178 @acronym{PGP} signed clear text.
181 @findex pgp-encrypted
182 @acronym{PGP} encrypted clear text.
186 @acronym{PGP} public keys.
189 @findex emacs-sources
190 @vindex mm-uu-emacs-sources-regexp
191 Emacs source code. This item works only in the groups matching
192 @code{mm-uu-emacs-sources-regexp}.
196 @vindex mm-uu-diff-groups-regexp
197 Patches. This is intended for groups where diffs of committed files
198 are automatically sent to. It only works in groups matching
199 @code{mm-uu-diff-groups-regexp}.
206 A @acronym{MIME} handle is a list that fully describes a @acronym{MIME}
209 The following macros can be used to access elements in a handle:
212 @item mm-handle-buffer
213 @findex mm-handle-buffer
214 Return the buffer that holds the contents of the undecoded @acronym{MIME}
218 @findex mm-handle-type
219 Return the parsed @code{Content-Type} of the part.
221 @item mm-handle-encoding
222 @findex mm-handle-encoding
223 Return the @code{Content-Transfer-Encoding} of the part.
225 @item mm-handle-undisplayer
226 @findex mm-handle-undisplayer
227 Return the object that can be used to remove the displayed part (if it
230 @item mm-handle-set-undisplayer
231 @findex mm-handle-set-undisplayer
232 Set the undisplayer object.
234 @item mm-handle-disposition
235 @findex mm-handle-disposition
236 Return the parsed @code{Content-Disposition} of the part.
238 @item mm-handle-disposition
239 @findex mm-handle-disposition
240 Return the description of the part.
242 @item mm-get-content-id
243 Returns the handle(s) referred to by @code{Content-ID}.
251 Functions for displaying, removing and saving.
254 @item mm-display-part
255 @findex mm-display-part
259 @findex mm-remove-part
260 Remove the part (if it has been displayed).
263 @findex mm-inlinable-p
264 Say whether a @acronym{MIME} type can be displayed inline.
266 @item mm-automatic-display-p
267 @findex mm-automatic-display-p
268 Say whether a @acronym{MIME} type should be displayed automatically.
270 @item mm-destroy-part
271 @findex mm-destroy-part
272 Free all resources occupied by a part.
276 Offer to save the part in a file.
280 Offer to pipe the part to some process.
282 @item mm-interactively-view-part
283 @findex mm-interactively-view-part
284 Prompt for a mailcap method to use to view the part.
289 @node Display Customization
290 @section Display Customization
294 @item mm-inline-media-tests
295 @vindex mm-inline-media-tests
296 This is an alist where the key is a @acronym{MIME} type, the second element
297 is a function to display the part @dfn{inline} (i.e., inside Emacs), and
298 the third element is a form to be @code{eval}ed to say whether the part
299 can be displayed inline.
301 This variable specifies whether a part @emph{can} be displayed inline,
302 and, if so, how to do it. It does not say whether parts are
303 @emph{actually} displayed inline.
305 @item mm-inlined-types
306 @vindex mm-inlined-types
307 This, on the other hand, says what types are to be displayed inline, if
308 they satisfy the conditions set by the variable above. It's a list of
309 @acronym{MIME} media types.
311 @item mm-automatic-display
312 @vindex mm-automatic-display
313 This is a list of types that are to be displayed ``automatically'', but
314 only if the above variable allows it. That is, only inlinable parts can
315 be displayed automatically.
317 @item mm-automatic-external-display
318 @vindex mm-automatic-external-display
319 This is a list of types that will be displayed automatically in an
322 @item mm-keep-viewer-alive-types
323 @vindex mm-keep-viewer-alive-types
324 This is a list of media types for which the external viewer will not
325 be killed when selecting a different article.
327 @item mm-attachment-override-types
328 @vindex mm-attachment-override-types
329 Some @acronym{MIME} agents create parts that have a content-disposition of
330 @samp{attachment}. This variable allows overriding that disposition and
331 displaying the part inline. (Note that the disposition is only
332 overridden if we are able to, and want to, display the part inline.)
334 @item mm-discouraged-alternatives
335 @vindex mm-discouraged-alternatives
336 List of @acronym{MIME} types that are discouraged when viewing
337 @samp{multipart/alternative}. Viewing agents are supposed to view the
338 last possible part of a message, as that is supposed to be the richest.
339 However, users may prefer other types instead, and this list says what
340 types are most unwanted. If, for instance, @samp{text/html} parts are
341 very unwanted, and @samp{text/richtext} parts are somewhat unwanted,
342 you could say something like:
345 (setq mm-discouraged-alternatives
346 '("text/html" "text/richtext")
348 (remove "text/html" mm-automatic-display))
351 @item mm-inline-large-images
352 @vindex mm-inline-large-images
353 When displaying inline images that are larger than the window, XEmacs
354 does not enable scrolling, which means that you cannot see the whole
355 image. To prevent this, the library tries to determine the image size
356 before displaying it inline, and if it doesn't fit the window, the
357 library will display it externally (e.g. with @samp{ImageMagick} or
358 @samp{xv}). Setting this variable to @code{t} disables this check and
359 makes the library display all inline images as inline, regardless of
362 @item mm-inline-override-types
363 @vindex mm-inline-override-types
364 @code{mm-inlined-types} may include regular expressions, for example to
365 specify that all @samp{text/.*} parts be displayed inline. If a user
366 prefers to have a type that matches such a regular expression be treated
367 as an attachment, that can be accomplished by setting this variable to a
368 list containing that type. For example assuming @code{mm-inlined-types}
369 includes @samp{text/.*}, then including @samp{text/html} in this
370 variable will cause @samp{text/html} parts to be treated as attachments.
372 @item mm-text-html-renderer
373 @vindex mm-text-html-renderer
374 This selects the function used to render @acronym{HTML}. The predefined
375 renderers are selected by the symbols @code{w3},
376 @code{w3m}@footnote{See @uref{http://emacs-w3m.namazu.org/} for more
377 information about emacs-w3m}, @code{links}, @code{lynx},
378 @code{w3m-standalone} or @code{html2text}. If @code{nil} use an
379 external viewer. You can also specify a function, which will be
380 called with a @acronym{MIME} handle as the argument.
382 @item mm-inline-text-html-with-images
383 @vindex mm-inline-text-html-with-images
384 Some @acronym{HTML} mails might have the trick of spammers using
385 @samp{<img>} tags. It is likely to be intended to verify whether you
386 have read the mail. You can prevent your personal informations from
387 leaking by setting this option to @code{nil} (which is the default).
388 It is currently ignored by Emacs/w3. For emacs-w3m, you may use the
389 command @kbd{t} on the image anchor to show an image even if it is
390 @code{nil}.@footnote{The command @kbd{T} will load all images. If you
391 have set the option @code{w3m-key-binding} to @code{info}, use @kbd{i}
394 @item mm-w3m-safe-url-regexp
395 @vindex mm-w3m-safe-url-regexp
396 A regular expression that matches safe URL names, i.e. URLs that are
397 unlikely to leak personal information when rendering @acronym{HTML}
398 email (the default value is @samp{\\`cid:}). If @code{nil} consider
401 @item mm-inline-text-html-with-w3m-keymap
402 @vindex mm-inline-text-html-with-w3m-keymap
403 You can use emacs-w3m command keys in the inlined text/html part by
404 setting this option to non-@code{nil}. The default value is @code{t}.
406 @item mm-external-terminal-program
407 @vindex mm-external-terminal-program
408 The program used to start an external terminal.
412 @node Files and Directories
413 @section Files and Directories
417 @item mm-default-directory
418 @vindex mm-default-directory
419 The default directory for saving attachments. If @code{nil} use
420 @code{default-directory}.
422 @item mm-tmp-directory
423 @vindex mm-tmp-directory
424 Directory for storing temporary files.
426 @item mm-file-name-rewrite-functions
427 @vindex mm-file-name-rewrite-functions
428 A list of functions used for rewriting file names of @acronym{MIME}
429 parts. Each function is applied successively to the file name.
430 Ready-made functions include
433 @item mm-file-name-delete-control
434 @findex mm-file-name-delete-control
435 Delete all control characters.
437 @item mm-file-name-delete-gotchas
438 @findex mm-file-name-delete-gotchas
439 Delete characters that could have unintended consequences when used
440 with flawed shell scripts, i.e. @samp{|}, @samp{>} and @samp{<}; and
441 @samp{-}, @samp{.} as the first character.
443 @item mm-file-name-delete-whitespace
444 @findex mm-file-name-delete-whitespace
445 Remove all whitespace.
447 @item mm-file-name-trim-whitespace
448 @findex mm-file-name-trim-whitespace
449 Remove leading and trailing whitespace.
451 @item mm-file-name-collapse-whitespace
452 @findex mm-file-name-collapse-whitespace
453 Collapse multiple whitespace characters.
455 @item mm-file-name-replace-whitespace
456 @findex mm-file-name-replace-whitespace
457 @vindex mm-file-name-replace-whitespace
458 Replace whitespace with underscores. Set the variable
459 @code{mm-file-name-replace-whitespace} to any other string if you do
460 not like underscores.
463 The standard Emacs functions @code{capitalize}, @code{downcase},
464 @code{upcase} and @code{upcase-initials} might also prove useful.
466 @item mm-path-name-rewrite-functions
467 @vindex mm-path-name-rewrite-functions
468 List of functions used for rewriting the full file names of @acronym{MIME}
469 parts. This is used when viewing parts externally, and is meant for
470 transforming the absolute name so that non-compliant programs can find
471 the file where it's saved.
478 Here's an example viewer for displaying @code{text/enriched} inline:
481 (defun mm-display-enriched-inline (handle)
484 (mm-insert-part handle)
485 (save-window-excursion
486 (enriched-decode (point-min) (point-max))
487 (setq text (buffer-string))))
488 (mm-insert-inline handle text)))
491 We see that the function takes a @acronym{MIME} handle as its parameter. It
492 then goes to a temporary buffer, inserts the text of the part, does some
493 work on the text, stores the result, goes back to the buffer it was
494 called from and inserts the result.
496 The two important helper functions here are @code{mm-insert-part} and
497 @code{mm-insert-inline}. The first function inserts the text of the
498 handle in the current buffer. It handles charset and/or content
499 transfer decoding. The second function just inserts whatever text you
500 tell it to insert, but it also sets things up so that the text can be
501 ``undisplayed'' in a convenient manner.
507 @cindex MIME Composing
509 @cindex MIME Meta Language
511 Creating a @acronym{MIME} message is boring and non-trivial. Therefore,
512 a library called @code{mml} has been defined that parses a language
513 called @acronym{MML} (@acronym{MIME} Meta Language) and generates
514 @acronym{MIME} messages.
516 @findex mml-generate-mime
517 The main interface function is @code{mml-generate-mime}. It will
518 examine the contents of the current (narrowed-to) buffer and return a
519 string containing the @acronym{MIME} message.
522 * Simple MML Example:: An example @acronym{MML} document.
523 * MML Definition:: All valid @acronym{MML} elements.
524 * Advanced MML Example:: Another example @acronym{MML} document.
525 * Encoding Customization:: Variables that affect encoding.
526 * Charset Translation:: How charsets are mapped from @sc{mule} to @acronym{MIME}.
527 * Conversion:: Going from @acronym{MIME} to @acronym{MML} and vice versa.
528 * Flowed text:: Soft and hard newlines.
532 @node Simple MML Example
533 @section Simple MML Example
535 Here's a simple @samp{multipart/alternative}:
538 <#multipart type=alternative>
539 This is a plain text part.
540 <#part type=text/enriched>
541 <center>This is a centered enriched part</center>
545 After running this through @code{mml-generate-mime}, we get this:
548 Content-Type: multipart/alternative; boundary="=-=-="
554 This is a plain text part.
557 Content-Type: text/enriched
560 <center>This is a centered enriched part</center>
567 @section MML Definition
569 The @acronym{MML} language is very simple. It looks a bit like an SGML
570 application, but it's not.
572 The main concept of @acronym{MML} is the @dfn{part}. Each part can be of a
573 different type or use a different charset. The way to delineate a part
574 is with a @samp{<#part ...>} tag. Multipart parts can be introduced
575 with the @samp{<#multipart ...>} tag. Parts are ended by the
576 @samp{<#/part>} or @samp{<#/multipart>} tags. Parts started with the
577 @samp{<#part ...>} tags are also closed by the next open tag.
579 There's also the @samp{<#external ...>} tag. These introduce
580 @samp{external/message-body} parts.
582 Each tag can contain zero or more parameters on the form
583 @samp{parameter=value}. The values may be enclosed in quotation marks,
584 but that's not necessary unless the value contains white space. So
585 @samp{filename=/home/user/#hello$^yes} is perfectly valid.
587 The following parameters have meaning in @acronym{MML}; parameters that have no
588 meaning are ignored. The @acronym{MML} parameter names are the same as the
589 @acronym{MIME} parameter names; the things in the parentheses say which
590 header it will be used in.
594 The @acronym{MIME} type of the part (@code{Content-Type}).
597 Use the contents of the file in the body of the part
598 (@code{Content-Disposition}).
601 The contents of the body of the part are to be encoded in the character
602 set specified (@code{Content-Type}). @xref{Charset Translation}.
605 Might be used to suggest a file name if the part is to be saved
606 to a file (@code{Content-Type}).
609 Valid values are @samp{inline} and @samp{attachment}
610 (@code{Content-Disposition}).
613 Valid values are @samp{7bit}, @samp{8bit}, @samp{quoted-printable} and
614 @samp{base64} (@code{Content-Transfer-Encoding}). @xref{Charset
618 A description of the part (@code{Content-Description}).
621 RFC822 date when the part was created (@code{Content-Disposition}).
623 @item modification-date
624 RFC822 date when the part was modified (@code{Content-Disposition}).
627 RFC822 date when the part was read (@code{Content-Disposition}).
630 Who to encrypt/sign the part to. This field is used to override any
631 auto-detection based on the To/CC headers.
634 Identity used to sign the part. This field is used to override the
638 The size (in octets) of the part (@code{Content-Disposition}).
641 What technology to sign this @acronym{MML} part with (@code{smime}, @code{pgp}
645 What technology to encrypt this @acronym{MML} part with (@code{smime},
646 @code{pgp} or @code{pgpmime})
650 Parameters for @samp{text/plain}:
654 Formatting parameter for the text, valid values include @samp{fixed}
655 (the default) and @samp{flowed}. Normally you do not specify this
656 manually, since it requires the textual body to be formatted in a
657 special way described in RFC 2646. @xref{Flowed text}.
660 Parameters for @samp{application/octet-stream}:
664 Type of the part; informal---meant for human readers
665 (@code{Content-Type}).
668 Parameters for @samp{message/external-body}:
672 A word indicating the supported access mechanism by which the file may
673 be obtained. Values include @samp{ftp}, @samp{anon-ftp}, @samp{tftp},
674 @samp{localfile}, and @samp{mailserver}. (@code{Content-Type}.)
677 The RFC822 date after which the file may no longer be fetched.
678 (@code{Content-Type}.)
681 The size (in octets) of the file. (@code{Content-Type}.)
684 Valid values are @samp{read} and @samp{read-write}
685 (@code{Content-Type}).
689 Parameters for @samp{sign=smime}:
694 File containing key and certificate for signer.
698 Parameters for @samp{encrypt=smime}:
703 File containing certificate for recipient.
708 @node Advanced MML Example
709 @section Advanced MML Example
711 Here's a complex multipart message. It's a @samp{multipart/mixed} that
712 contains many parts, one of which is a @samp{multipart/alternative}.
715 <#multipart type=mixed>
716 <#part type=image/jpeg filename=~/rms.jpg disposition=inline>
717 <#multipart type=alternative>
718 This is a plain text part.
719 <#part type=text/enriched name=enriched.txt>
720 <center>This is a centered enriched part</center>
722 This is a new plain text part.
723 <#part disposition=attachment>
724 This plain text part is an attachment.
728 And this is the resulting @acronym{MIME} message:
731 Content-Type: multipart/mixed; boundary="=-=-="
739 Content-Type: image/jpeg;
741 Content-Disposition: inline;
743 Content-Transfer-Encoding: base64
745 /9j/4AAQSkZJRgABAQAAAQABAAD/2wBDAAgGBgcGBQgHBwcJCQgKDBQNDAsLDBkSEw8UHRof
746 Hh0aHBwgJC4nICIsIxwcKDcpLDAxNDQ0Hyc5PTgyPC4zNDL/wAALCAAwADABAREA/8QAHwAA
747 AQUBAQEBAQEAAAAAAAAAAAECAwQFBgcICQoL/8QAtRAAAgEDAwIEAwUFBAQAAAF9AQIDAAQR
748 BRIhMUEGE1FhByJxFDKBkaEII0KxwRVS0fAkM2JyggkKFhcYGRolJicoKSo0NTY3ODk6Q0RF
749 RkdISUpTVFVWV1hZWmNkZWZnaGlqc3R1dnd4eXqDhIWGh4iJipKTlJWWl5iZmqKjpKWmp6ip
750 qrKztLW2t7i5usLDxMXGx8jJytLT1NXW19jZ2uHi4+Tl5ufo6erx8vP09fb3+Pn6/9oACAEB
751 AAA/AO/rifFHjldNuGsrDa0qcSSHkA+gHrXKw+LtWLrMb+RgTyhbr+HSug07xNqV9fQtZrNI
752 AyiaE/NuBPOOOP0rvRNE880KOC8TbXXGCv1FPqjrF4LDR7u5L7SkTFT/ALWOP1xXgTuXfc7E
753 sx6nua6rwp4IvvEM8chCxWxOdzn7wz6V9AaB4S07w9p5itow0rDLSY5Pt9K43xO66P4xs71m
754 2QXiGCbA4yOVJ9+1aYORkdK434lyNH4ahCnG66VT9Nj15JFbPdX0MS43M4VQf5/yr2vSpLnw
755 5ZW8dlCZ8KFXjOPX0/mK6rSPEGt3Angu44fNEReHYNvIH3TzXDeKNO8RX+kSX2ouZkicTIOc
756 L+g7E810ulFjpVtv3bwgB3HJyK5L4quY/C9sVxk3ij/xx6850u7t1mtp/wDlpEw3An3Jr3Dw
757 34gsbWza4nBlhC5LDsaW6+IFgupQyCF3iHH7gA7c9R9ay7zx6t7aX9jHC4smhfBkGCvHGfrm
758 tLQ7hbnRrV1GPkAP1x1/Hr+Ncr8Vzjwrbf8AX6v/AKA9eQRyYlQk8Yx9K6XTNbkgia2ciSIn
759 7p5Ga9Atte0LTLKO6it4i7dVRFJDcZ4PvXN+JvEMF9bILVGXJLSZ4zkjivRPDaeX4b08HOTC
760 pOffmua+KkbS+GLVUGT9tT/0B68eeIpIFYjB70+OOVXyoOM9+M1eaWeCLzHPyHGO/NVWvJJm
761 jQ8KGH1NfQWhXSXmh2c8eArRLwO3HSv/2Q==
764 Content-Type: multipart/alternative; boundary="==-=-="
770 This is a plain text part.
773 Content-Type: text/enriched;
777 <center>This is a centered enriched part</center>
783 This is a new plain text part.
786 Content-Disposition: attachment
789 This plain text part is an attachment.
794 @node Encoding Customization
795 @section Encoding Customization
799 @item mm-body-charset-encoding-alist
800 @vindex mm-body-charset-encoding-alist
801 Mapping from @acronym{MIME} charset to encoding to use. This variable is
802 usually used except, e.g., when other requirements force a specific
803 encoding (digitally signed messages require 7bit encodings). The
807 ((iso-2022-jp . 7bit)
808 (iso-2022-jp-2 . 7bit)
814 As an example, if you do not want to have ISO-8859-1 characters
815 quoted-printable encoded, you may add @code{(iso-8859-1 . 8bit)} to
816 this variable. You can override this setting on a per-message basis
817 by using the @code{encoding} @acronym{MML} tag (@pxref{MML Definition}).
819 @item mm-coding-system-priorities
820 @vindex mm-coding-system-priorities
821 Prioritize coding systems to use for outgoing messages. The default
822 is @code{nil}, which means to use the defaults in Emacs. It is a list of
823 coding system symbols (aliases of coding systems does not work, use
824 @kbd{M-x describe-coding-system} to make sure you are not specifying
825 an alias in this variable). For example, if you have configured Emacs
826 to prefer UTF-8, but wish that outgoing messages should be sent in
827 ISO-8859-1 if possible, you can set this variable to
828 @code{(iso-latin-1)}. You can override this setting on a per-message
829 basis by using the @code{charset} @acronym{MML} tag (@pxref{MML Definition}).
831 @item mm-content-transfer-encoding-defaults
832 @vindex mm-content-transfer-encoding-defaults
833 Mapping from @acronym{MIME} types to encoding to use. This variable is usually
834 used except, e.g., when other requirements force a safer encoding
835 (digitally signed messages require 7bit encoding). Besides the normal
836 @acronym{MIME} encodings, @code{qp-or-base64} may be used to indicate that for
837 each case the most efficient of quoted-printable and base64 should be
838 used. You can override this setting on a per-message basis by using
839 the @code{encoding} @acronym{MML} tag (@pxref{MML Definition}).
841 @item mm-use-ultra-safe-encoding
842 @vindex mm-use-ultra-safe-encoding
843 When this is non-@code{nil}, it means that textual parts are encoded as
844 quoted-printable if they contain lines longer than 76 characters or
845 starting with "From " in the body. Non-7bit encodings (8bit, binary)
846 are generally disallowed. This reduce the probability that a non-8bit
847 clean MTA or MDA changes the message. This should never be set
848 directly, but bound by other functions when necessary (e.g., when
849 encoding messages that are to be digitally signed).
853 @node Charset Translation
854 @section Charset Translation
857 During translation from @acronym{MML} to @acronym{MIME}, for each
858 @acronym{MIME} part which has been composed inside Emacs, an appropriate
859 charset has to be chosen.
861 @vindex mail-parse-charset
862 If you are running a non-@sc{mule} Emacs, this process is simple: If the
863 part contains any non-@acronym{ASCII} (8-bit) characters, the @acronym{MIME} charset
864 given by @code{mail-parse-charset} (a symbol) is used. (Never set this
865 variable directly, though. If you want to change the default charset,
866 please consult the documentation of the package which you use to process
867 @acronym{MIME} messages.
868 @xref{Various Message Variables, , Various Message Variables, message,
869 Message Manual}, for example.)
870 If there are only @acronym{ASCII} characters, the @acronym{MIME} charset US-ASCII is
876 @vindex mm-mime-mule-charset-alist
877 Things are slightly more complicated when running Emacs with @sc{mule}
878 support. In this case, a list of the @sc{mule} charsets used in the
879 part is obtained, and the @sc{mule} charsets are translated to @acronym{MIME}
880 charsets by consulting the variable @code{mm-mime-mule-charset-alist}.
881 If this results in a single @acronym{MIME} charset, this is used to encode
882 the part. But if the resulting list of @acronym{MIME} charsets contains more
883 than one element, two things can happen: If it is possible to encode the
884 part via UTF-8, this charset is used. (For this, Emacs must support
885 the @code{utf-8} coding system, and the part must consist entirely of
886 characters which have Unicode counterparts.) If UTF-8 is not available
887 for some reason, the part is split into several ones, so that each one
888 can be encoded with a single @acronym{MIME} charset. The part can only be
889 split at line boundaries, though---if more than one @acronym{MIME} charset is
890 required to encode a single line, it is not possible to encode the part.
892 When running Emacs with @sc{mule} support, the preferences for which
893 coding system to use is inherited from Emacs itself. This means that
894 if Emacs is set up to prefer UTF-8, it will be used when encoding
895 messages. You can modify this by altering the
896 @code{mm-coding-system-priorities} variable though (@pxref{Encoding
899 The charset to be used can be overridden by setting the @code{charset}
900 @acronym{MML} tag (@pxref{MML Definition}) when composing the message.
902 The encoding of characters (quoted-printable, 8bit etc) is orthogonal
903 to the discussion here, and is controlled by the variables
904 @code{mm-body-charset-encoding-alist} and
905 @code{mm-content-transfer-encoding-defaults} (@pxref{Encoding
912 A (multipart) @acronym{MIME} message can be converted to @acronym{MML}
913 with the @code{mime-to-mml} function. It works on the message in the
914 current buffer, and substitutes @acronym{MML} markup for @acronym{MIME}
915 boundaries. Non-textual parts do not have their contents in the buffer,
916 but instead have the contents in separate buffers that are referred to
917 from the @acronym{MML} tags.
920 An @acronym{MML} message can be converted back to @acronym{MIME} by the
921 @code{mml-to-mime} function.
923 These functions are in certain senses ``lossy''---you will not get back
924 an identical message if you run @code{mime-to-mml} and then
925 @code{mml-to-mime}. Not only will trivial things like the order of the
926 headers differ, but the contents of the headers may also be different.
927 For instance, the original message may use base64 encoding on text,
928 while @code{mml-to-mime} may decide to use quoted-printable encoding, and
931 In essence, however, these two functions should be the inverse of each
932 other. The resulting contents of the message should remain equivalent,
938 @cindex format=flowed
940 The Emacs @acronym{MIME} library will respect the @code{use-hard-newlines}
941 variable (@pxref{Hard and Soft Newlines, ,Hard and Soft Newlines,
942 emacs, Emacs Manual}) when encoding a message, and the
943 ``format=flowed'' Content-Type parameter when decoding a message.
945 On encoding text, regardless of @code{use-hard-newlines}, lines
946 terminated by soft newline characters are filled together and wrapped
947 after the column decided by @code{fill-flowed-encode-column}.
948 Quotation marks (matching @samp{^>* ?}) are respected. The variable
949 controls how the text will look in a client that does not support
950 flowed text, the default is to wrap after 66 characters. If hard
951 newline characters are not present in the buffer, no flow encoding
954 On decoding flowed text, lines with soft newline characters are filled
955 together and wrapped after the column decided by
956 @code{fill-flowed-display-column}. The default is to wrap after
962 @node Interface Functions
963 @chapter Interface Functions
964 @cindex interface functions
967 The @code{mail-parse} library is an abstraction over the actual
968 low-level libraries that are described in the next chapter.
970 Standards change, and so programs have to change to fit in the new
971 mold. For instance, RFC2045 describes a syntax for the
972 @code{Content-Type} header that only allows @acronym{ASCII} characters in the
973 parameter list. RFC2231 expands on RFC2045 syntax to provide a scheme
974 for continuation headers and non-@acronym{ASCII} characters.
976 The traditional way to deal with this is just to update the library
977 functions to parse the new syntax. However, this is sometimes the wrong
978 thing to do. In some instances it may be vital to be able to understand
979 both the old syntax as well as the new syntax, and if there is only one
980 library, one must choose between the old version of the library and the
981 new version of the library.
983 The Emacs @acronym{MIME} library takes a different tack. It defines a
984 series of low-level libraries (@file{rfc2047.el}, @file{rfc2231.el}
985 and so on) that parses strictly according to the corresponding
986 standard. However, normal programs would not use the functions
987 provided by these libraries directly, but instead use the functions
988 provided by the @code{mail-parse} library. The functions in this
989 library are just aliases to the corresponding functions in the latest
990 low-level libraries. Using this scheme, programs get a consistent
991 interface they can use, and library developers are free to create
992 write code that handles new standards.
994 The following functions are defined by this library:
997 @item mail-header-parse-content-type
998 @findex mail-header-parse-content-type
999 Parse a @code{Content-Type} header and return a list on the following
1004 (attribute1 . value1)
1005 (attribute2 . value2)
1012 (mail-header-parse-content-type
1013 "image/gif; name=\"b980912.gif\"")
1014 @result{} ("image/gif" (name . "b980912.gif"))
1017 @item mail-header-parse-content-disposition
1018 @findex mail-header-parse-content-disposition
1019 Parse a @code{Content-Disposition} header and return a list on the same
1020 format as the function above.
1022 @item mail-content-type-get
1023 @findex mail-content-type-get
1024 Takes two parameters---a list on the format above, and an attribute.
1025 Returns the value of the attribute.
1028 (mail-content-type-get
1029 '("image/gif" (name . "b980912.gif")) 'name)
1030 @result{} "b980912.gif"
1033 @item mail-header-encode-parameter
1034 @findex mail-header-encode-parameter
1035 Takes a parameter string and returns an encoded version of the string.
1036 This is used for parameters in headers like @code{Content-Type} and
1037 @code{Content-Disposition}.
1039 @item mail-header-remove-comments
1040 @findex mail-header-remove-comments
1041 Return a comment-free version of a header.
1044 (mail-header-remove-comments
1045 "Gnus/5.070027 (Pterodactyl Gnus v0.27) (Finnish Landrace)")
1046 @result{} "Gnus/5.070027 "
1049 @item mail-header-remove-whitespace
1050 @findex mail-header-remove-whitespace
1051 Remove linear white space from a header. Space inside quoted strings
1052 and comments is preserved.
1055 (mail-header-remove-whitespace
1056 "image/gif; name=\"Name with spaces\"")
1057 @result{} "image/gif;name=\"Name with spaces\""
1060 @item mail-header-get-comment
1061 @findex mail-header-get-comment
1062 Return the last comment in a header.
1065 (mail-header-get-comment
1066 "Gnus/5.070027 (Pterodactyl Gnus v0.27) (Finnish Landrace)")
1067 @result{} "Finnish Landrace"
1070 @item mail-header-parse-address
1071 @findex mail-header-parse-address
1072 Parse an address and return a list containing the mailbox and the
1076 (mail-header-parse-address
1077 "Hrvoje Niksic <hniksic@@srce.hr>")
1078 @result{} ("hniksic@@srce.hr" . "Hrvoje Niksic")
1081 @item mail-header-parse-addresses
1082 @findex mail-header-parse-addresses
1083 Parse a string with list of addresses and return a list of elements like
1084 the one described above.
1087 (mail-header-parse-addresses
1088 "Hrvoje Niksic <hniksic@@srce.hr>, Steinar Bang <sb@@metis.no>")
1089 @result{} (("hniksic@@srce.hr" . "Hrvoje Niksic")
1090 ("sb@@metis.no" . "Steinar Bang"))
1093 @item mail-header-parse-date
1094 @findex mail-header-parse-date
1095 Parse a date string and return an Emacs time structure.
1097 @item mail-narrow-to-head
1098 @findex mail-narrow-to-head
1099 Narrow the buffer to the header section of the buffer. Point is placed
1100 at the beginning of the narrowed buffer.
1102 @item mail-header-narrow-to-field
1103 @findex mail-header-narrow-to-field
1104 Narrow the buffer to the header under point. Understands continuation
1107 @item mail-header-fold-field
1108 @findex mail-header-fold-field
1109 Fold the header under point.
1111 @item mail-header-unfold-field
1112 @findex mail-header-unfold-field
1113 Unfold the header under point.
1115 @item mail-header-field-value
1116 @findex mail-header-field-value
1117 Return the value of the field under point.
1119 @item mail-encode-encoded-word-region
1120 @findex mail-encode-encoded-word-region
1121 Encode the non-@acronym{ASCII} words in the region. For instance,
1122 @samp{Naïve} is encoded as @samp{=?iso-8859-1?q?Na=EFve?=}.
1124 @item mail-encode-encoded-word-buffer
1125 @findex mail-encode-encoded-word-buffer
1126 Encode the non-@acronym{ASCII} words in the current buffer. This function is
1127 meant to be called narrowed to the headers of a message.
1129 @item mail-encode-encoded-word-string
1130 @findex mail-encode-encoded-word-string
1131 Encode the words that need encoding in a string, and return the result.
1134 (mail-encode-encoded-word-string
1135 "This is naïve, baby")
1136 @result{} "This is =?iso-8859-1?q?na=EFve,?= baby"
1139 @item mail-decode-encoded-word-region
1140 @findex mail-decode-encoded-word-region
1141 Decode the encoded words in the region.
1143 @item mail-decode-encoded-word-string
1144 @findex mail-decode-encoded-word-string
1145 Decode the encoded words in the string and return the result.
1148 (mail-decode-encoded-word-string
1149 "This is =?iso-8859-1?q?na=EFve,?= baby")
1150 @result{} "This is naïve, baby"
1155 Currently, @code{mail-parse} is an abstraction over @code{ietf-drums},
1156 @code{rfc2047}, @code{rfc2045} and @code{rfc2231}. These are documented
1157 in the subsequent sections.
1161 @node Basic Functions
1162 @chapter Basic Functions
1164 This chapter describes the basic, ground-level functions for parsing and
1165 handling. Covered here is parsing @code{From} lines, removing comments
1166 from header lines, decoding encoded words, parsing date headers and so
1167 on. High-level functionality is dealt with in the next chapter
1168 (@pxref{Decoding and Viewing}).
1171 * rfc2045:: Encoding @code{Content-Type} headers.
1172 * rfc2231:: Parsing @code{Content-Type} headers.
1173 * ietf-drums:: Handling mail headers defined by RFC822bis.
1174 * rfc2047:: En/decoding encoded words in headers.
1175 * time-date:: Functions for parsing dates and manipulating time.
1176 * qp:: Quoted-Printable en/decoding.
1177 * base64:: Base64 en/decoding.
1178 * binhex:: Binhex decoding.
1179 * uudecode:: Uuencode decoding.
1180 * yenc:: Yenc decoding.
1181 * rfc1843:: Decoding HZ-encoded text.
1182 * mailcap:: How parts are displayed is specified by the @file{.mailcap} file
1189 RFC2045 is the ``main'' @acronym{MIME} document, and as such, one would
1190 imagine that there would be a lot to implement. But there isn't, since
1191 most of the implementation details are delegated to the subsequent
1194 So @file{rfc2045.el} has only a single function:
1197 @item rfc2045-encode-string
1198 @findex rfc2045-encode-string
1199 Takes a parameter and a value and returns a @samp{PARAM=VALUE} string.
1200 @var{value} will be quoted if there are non-safe characters in it.
1207 RFC2231 defines a syntax for the @code{Content-Type} and
1208 @code{Content-Disposition} headers. Its snappy name is @dfn{MIME
1209 Parameter Value and Encoded Word Extensions: Character Sets, Languages,
1212 In short, these headers look something like this:
1215 Content-Type: application/x-stuff;
1216 title*0*=us-ascii'en'This%20is%20even%20more%20;
1217 title*1*=%2A%2A%2Afun%2A%2A%2A%20;
1221 They usually aren't this bad, though.
1223 The following functions are defined by this library:
1226 @item rfc2231-parse-string
1227 @findex rfc2231-parse-string
1228 Parse a @code{Content-Type} header and return a list describing its
1232 (rfc2231-parse-string
1233 "application/x-stuff;
1234 title*0*=us-ascii'en'This%20is%20even%20more%20;
1235 title*1*=%2A%2A%2Afun%2A%2A%2A%20;
1236 title*2=\"isn't it!\"")
1237 @result{} ("application/x-stuff"
1238 (title . "This is even more ***fun*** isn't it!"))
1241 @item rfc2231-get-value
1242 @findex rfc2231-get-value
1243 Takes one of the lists on the format above and returns
1244 the value of the specified attribute.
1246 @item rfc2231-encode-string
1247 @findex rfc2231-encode-string
1248 Encode a parameter in headers likes @code{Content-Type} and
1249 @code{Content-Disposition}.
1257 @dfn{drums} is an IETF working group that is working on the replacement
1260 The functions provided by this library include:
1263 @item ietf-drums-remove-comments
1264 @findex ietf-drums-remove-comments
1265 Remove the comments from the argument and return the results.
1267 @item ietf-drums-remove-whitespace
1268 @findex ietf-drums-remove-whitespace
1269 Remove linear white space from the string and return the results.
1270 Spaces inside quoted strings and comments are left untouched.
1272 @item ietf-drums-get-comment
1273 @findex ietf-drums-get-comment
1274 Return the last most comment from the string.
1276 @item ietf-drums-parse-address
1277 @findex ietf-drums-parse-address
1278 Parse an address string and return a list that contains the mailbox and
1279 the plain text name.
1281 @item ietf-drums-parse-addresses
1282 @findex ietf-drums-parse-addresses
1283 Parse a string that contains any number of comma-separated addresses and
1284 return a list that contains mailbox/plain text pairs.
1286 @item ietf-drums-parse-date
1287 @findex ietf-drums-parse-date
1288 Parse a date string and return an Emacs time structure.
1290 @item ietf-drums-narrow-to-header
1291 @findex ietf-drums-narrow-to-header
1292 Narrow the buffer to the header section of the current buffer.
1300 RFC2047 (Message Header Extensions for Non-@acronym{ASCII} Text) specifies how
1301 non-@acronym{ASCII} text in headers are to be encoded. This is actually rather
1302 complicated, so a number of variables are necessary to tweak what this
1305 The following variables are tweakable:
1308 @item rfc2047-default-charset
1309 @vindex rfc2047-default-charset
1310 Characters in this charset should not be decoded by this library.
1311 This defaults to @code{iso-8859-1}.
1313 @item rfc2047-header-encoding-alist
1314 @vindex rfc2047-header-encoding-alist
1315 This is an alist of header / encoding-type pairs. Its main purpose is
1316 to prevent encoding of certain headers.
1318 The keys can either be header regexps, or @code{t}.
1320 The values can be either @code{nil}, in which case the header(s) in
1321 question won't be encoded, or @code{mime}, which means that they will be
1324 @item rfc2047-charset-encoding-alist
1325 @vindex rfc2047-charset-encoding-alist
1326 RFC2047 specifies two forms of encoding---@code{Q} (a
1327 Quoted-Printable-like encoding) and @code{B} (base64). This alist
1328 specifies which charset should use which encoding.
1330 @item rfc2047-encoding-function-alist
1331 @vindex rfc2047-encoding-function-alist
1332 This is an alist of encoding / function pairs. The encodings are
1333 @code{Q}, @code{B} and @code{nil}.
1335 @item rfc2047-q-encoding-alist
1336 @vindex rfc2047-q-encoding-alist
1337 The @code{Q} encoding isn't quite the same for all headers. Some
1338 headers allow a narrower range of characters, and that is what this
1339 variable is for. It's an alist of header regexps / allowable character
1342 @item rfc2047-encoded-word-regexp
1343 @vindex rfc2047-encoded-word-regexp
1344 When decoding words, this library looks for matches to this regexp.
1348 Those were the variables, and these are this functions:
1351 @item rfc2047-narrow-to-field
1352 @findex rfc2047-narrow-to-field
1353 Narrow the buffer to the header on the current line.
1355 @item rfc2047-encode-message-header
1356 @findex rfc2047-encode-message-header
1357 Should be called narrowed to the header of a message. Encodes according
1358 to @code{rfc2047-header-encoding-alist}.
1360 @item rfc2047-encode-region
1361 @findex rfc2047-encode-region
1362 Encodes all encodable words in the region specified.
1364 @item rfc2047-encode-string
1365 @findex rfc2047-encode-string
1366 Encode a string and return the results.
1368 @item rfc2047-decode-region
1369 @findex rfc2047-decode-region
1370 Decode the encoded words in the region.
1372 @item rfc2047-decode-string
1373 @findex rfc2047-decode-string
1374 Decode a string and return the results.
1382 While not really a part of the @acronym{MIME} library, it is convenient to
1383 document this library here. It deals with parsing @code{Date} headers
1384 and manipulating time. (Not by using tesseracts, though, I'm sorry to
1387 These functions convert between five formats: A date string, an Emacs
1388 time structure, a decoded time list, a second number, and a day number.
1390 Here's a bunch of time/date/second/day examples:
1393 (parse-time-string "Sat Sep 12 12:21:54 1998 +0200")
1394 @result{} (54 21 12 12 9 1998 6 nil 7200)
1396 (date-to-time "Sat Sep 12 12:21:54 1998 +0200")
1397 @result{} (13818 19266)
1399 (time-to-seconds '(13818 19266))
1400 @result{} 905595714.0
1402 (seconds-to-time 905595714.0)
1403 @result{} (13818 19266 0)
1405 (time-to-days '(13818 19266))
1408 (days-to-time 729644)
1409 @result{} (961933 65536)
1411 (time-since '(13818 19266))
1414 (time-less-p '(13818 19266) '(13818 19145))
1417 (subtract-time '(13818 19266) '(13818 19145))
1420 (days-between "Sat Sep 12 12:21:54 1998 +0200"
1421 "Sat Sep 07 12:21:54 1998 +0200")
1424 (date-leap-year-p 2000)
1427 (time-to-day-in-year '(13818 19266))
1430 (time-to-number-of-days
1432 (date-to-time "Mon, 01 Jan 2001 02:22:26 GMT")))
1433 @result{} 4.146122685185185
1436 And finally, we have @code{safe-date-to-time}, which does the same as
1437 @code{date-to-time}, but returns a zero time if the date is
1438 syntactically malformed.
1440 The five data representations used are the following:
1444 An RFC822 (or similar) date string. For instance: @code{"Sat Sep 12
1445 12:21:54 1998 +0200"}.
1448 An internal Emacs time. For instance: @code{(13818 26466)}.
1451 A floating point representation of the internal Emacs time. For
1452 instance: @code{905595714.0}.
1455 An integer number representing the number of days since 00000101. For
1456 instance: @code{729644}.
1459 A list of decoded time. For instance: @code{(54 21 12 12 9 1998 6 t
1463 All the examples above represent the same moment.
1465 These are the functions available:
1469 Take a date and return a time.
1471 @item time-to-seconds
1472 Take a time and return seconds.
1474 @item seconds-to-time
1475 Take seconds and return a time.
1478 Take a time and return days.
1481 Take days and return a time.
1484 Take a date and return days.
1486 @item time-to-number-of-days
1487 Take a time and return the number of days that represents.
1489 @item safe-date-to-time
1490 Take a date and return a time. If the date is not syntactically valid,
1491 return a ``zero'' date.
1494 Take two times and say whether the first time is less (i. e., earlier)
1495 than the second time.
1498 Take a time and return a time saying how long it was since that time.
1501 Take two times and subtract the second from the first. I. e., return
1502 the time between the two times.
1505 Take two days and return the number of days between those two days.
1507 @item date-leap-year-p
1508 Take a year number and say whether it's a leap year.
1510 @item time-to-day-in-year
1511 Take a time and return the day number within the year that the time is
1520 This library deals with decoding and encoding Quoted-Printable text.
1522 Very briefly explained, qp encoding means translating all 8-bit
1523 characters (and lots of control characters) into things that look like
1524 @samp{=EF}; that is, an equal sign followed by the byte encoded as a hex
1527 The following functions are defined by the library:
1530 @item quoted-printable-decode-region
1531 @findex quoted-printable-decode-region
1532 QP-decode all the encoded text in the specified region.
1534 @item quoted-printable-decode-string
1535 @findex quoted-printable-decode-string
1536 Decode the QP-encoded text in a string and return the results.
1538 @item quoted-printable-encode-region
1539 @findex quoted-printable-encode-region
1540 QP-encode all the encodable characters in the specified region. The third
1541 optional parameter @var{fold} specifies whether to fold long lines.
1542 (Long here means 72.)
1544 @item quoted-printable-encode-string
1545 @findex quoted-printable-encode-string
1546 QP-encode all the encodable characters in a string and return the
1556 Base64 is an encoding that encodes three bytes into four characters,
1557 thereby increasing the size by about 33%. The alphabet used for
1558 encoding is very resistant to mangling during transit.
1560 The following functions are defined by this library:
1563 @item base64-encode-region
1564 @findex base64-encode-region
1565 base64 encode the selected region. Return the length of the encoded
1566 text. Optional third argument @var{no-line-break} means do not break
1567 long lines into shorter lines.
1569 @item base64-encode-string
1570 @findex base64-encode-string
1571 base64 encode a string and return the result.
1573 @item base64-decode-region
1574 @findex base64-decode-region
1575 base64 decode the selected region. Return the length of the decoded
1576 text. If the region can't be decoded, return @code{nil} and don't
1579 @item base64-decode-string
1580 @findex base64-decode-string
1581 base64 decode a string and return the result. If the string can't be
1582 decoded, @code{nil} is returned.
1593 @code{binhex} is an encoding that originated in Macintosh environments.
1594 The following function is supplied to deal with these:
1597 @item binhex-decode-region
1598 @findex binhex-decode-region
1599 Decode the encoded text in the region. If given a third parameter, only
1600 decode the @code{binhex} header and return the filename.
1609 @code{uuencode} is probably still the most popular encoding of binaries
1610 used on Usenet, although @code{base64} rules the mail world.
1612 The following function is supplied by this package:
1615 @item uudecode-decode-region
1616 @findex uudecode-decode-region
1617 Decode the text in the region.
1625 @code{yenc} is used for encoding binaries on Usenet. The following
1626 function is supplied by this package:
1629 @item yenc-decode-region
1630 @findex yenc-decode-region
1631 Decode the encoded text in the region.
1642 RFC1843 deals with mixing Chinese and @acronym{ASCII} characters in messages. In
1643 essence, RFC1843 switches between @acronym{ASCII} and Chinese by doing this:
1646 This sentence is in @acronym{ASCII}.
1647 The next sentence is in GB.~@{<:Ky2;S@{#,NpJ)l6HK!#~@}Bye.
1650 Simple enough, and widely used in China.
1652 The following functions are available to handle this encoding:
1655 @item rfc1843-decode-region
1656 Decode HZ-encoded text in the region.
1658 @item rfc1843-decode-string
1659 Decode a HZ-encoded string and return the result.
1667 The @file{~/.mailcap} file is parsed by most @acronym{MIME}-aware message
1668 handlers and describes how elements are supposed to be displayed.
1669 Here's an example file:
1673 audio/wav; wavplayer %s
1674 application/msword; catdoc %s ; copiousoutput ; nametemplate=%s.doc
1677 This says that all image files should be displayed with @code{gimp},
1678 that WAVE audio files should be played by @code{wavplayer}, and that
1679 MS-WORD files should be inlined by @code{catdoc}.
1681 The @code{mailcap} library parses this file, and provides functions for
1685 @item mailcap-mime-data
1686 @vindex mailcap-mime-data
1687 This variable is an alist of alists containing backup viewing rules.
1691 Interface functions:
1694 @item mailcap-parse-mailcaps
1695 @findex mailcap-parse-mailcaps
1696 Parse the @file{~/.mailcap} file.
1698 @item mailcap-mime-info
1699 Takes a @acronym{MIME} type as its argument and returns the matching viewer.
1709 The Emacs @acronym{MIME} library implements handling of various elements
1710 according to a (somewhat) large number of RFCs, drafts and standards
1711 documents. This chapter lists the relevant ones. They can all be
1712 fetched from @uref{http://quimby.gnus.org/notes/}.
1717 Standard for the Format of ARPA Internet Text Messages.
1720 Standard for Interchange of USENET Messages
1723 Format of Internet Message Bodies
1729 Message Header Extensions for Non-@acronym{ASCII} Text
1732 Registration Procedures
1735 Conformance Criteria and Examples
1738 @acronym{MIME} Parameter Value and Encoded Word Extensions: Character Sets,
1739 Languages, and Continuations
1742 HZ - A Data Format for Exchanging Files of Arbitrarily Mixed Chinese and
1743 @acronym{ASCII} characters
1745 @item draft-ietf-drums-msg-fmt-05.txt
1746 Draft for the successor of RFC822
1749 The @acronym{MIME} Multipart/Related Content-type
1752 The Multipart/Report Content Type for the Reporting of Mail System
1753 Administrative Messages
1756 Communicating Presentation Information in Internet Messages: The
1757 Content-Disposition Header Field
1760 Documentation of the text/plain format parameter for flowed text.
1776 @c coding: iso-8859-1