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MH-E has the capability to create multimedia messages. It uses the MIME (Multipurpose Internet Mail Extensions) protocol(40) The MIME protocol allows you to incorporate images, sound, video, binary files, and even commands that fetch a file with ‘ftp’ when your recipient reads the message!
If you were to create a multimedia message with plain MH commands, you would
insert mhbuild or mhn directives (henceforth called
MH-style directives into your draft and use the mhbuild
command in nmh or mhn command in MH and GNU mailutils to expand
them. MH-E works in much the same way, although it provides a handful of
commands prefixed with C-c C-m to insert the directives so you don't
need to remember the syntax of them. Remember: you can always add MH-style
directives by hand(41).
In addition to MH-style directives, MH-E also supports MML (MIME Meta
Language) tags(42). The option mh-compose-insertion can be
used to choose between them. By default, this option is set to ‘MML’ if
it is supported since it provides a lot more functionality. This option can
also be set to ‘MH’ if MH-style directives are preferred.
The MH-E MIME commands require a media type for each body part or attachment. For example, a PDF document is of type ‘application/pdf’ and an HTML document is of type ‘text/html’. Some commands fill in the media type for you, whereas others require you to enter one.
In the cases where MH-E can do so, it will determine the media type
automatically. It uses the file command to do this. Failing that,
the Emacs function mailcap-mime-types is used to provide a list from
which to choose. This function usually reads the file
‘/etc/mime.types’.
Whether the media type is chosen automatically, or you choose it from a list, use the type that seems to match best the file that you are including. In the case of binaries, the media type ‘application/x-executable’ can be useful. If you can't find an appropriate media type, use ‘text/plain’ for text messages and ‘application/octet-stream’ for everything else.
You are also sometimes asked for a content description. This is simply an optional brief phrase, in your own words, that describes the object. If you don't care to enter a content description, just press return and none will be included; however, a reader may skip over multimedia fields unless the content description is compelling.
You can also create your own MIME body parts. In the following example, I describe how you can create and edit a ‘text/enriched’ body part to liven up your plain text messages with boldface, underlining, and italics. I include an Emacs function which inserts enriched text tags.
(defvar enriched-text-types '(("b" . "bold") ("i" . "italic")
("u" . "underline")
("s" . "smaller") ("B" . "bigger")
("f" . "fixed")
("c" . "center"))
"Alist of (final-character . tag) choices for add-enriched-text.
Additional types can be found in RFC 1563.")
(defun add-enriched-text (begin end)
"Add enriched text tags around region.
The tag used comes from the list enriched-text-types and is
specified by the last keystroke of the command. When called from Lisp,
arguments are BEGIN and END."
(interactive "r")
;; Set type to the tag indicated by the last keystroke.
(let ((type (cdr (assoc (char-to-string (logior last-input-char ?`))
enriched-text-types))))
(save-restriction ; restores state from narrow-to-region
(narrow-to-region begin end) ; narrow view to region
(goto-char (point-min)) ; move to beginning of text
(insert "<" type ">") ; insert beginning tag
(goto-char (point-max)) ; move to end of text
(insert "</" type ">")))) ; insert terminating tag
Emacs function for entering enriched text
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To use the function add-enriched-text, first add it to
‘~/.emacs’ and create key bindings for it (voir la section Composing).
Then, in your plain text message, set the mark with C-@ or C-<SPC>, type in the text to be highlighted, and type C-c t b. This adds ‘<bold>’ where you set the mark and adds ‘</bold>’ at the location of your cursor, giving you something like: ‘You should be <bold>very</bold>’.
Before sending this message, use C-c C-m C-m
(mh-mml-to-mime)(43) to add MIME header fields. Then replace
‘text/plain’ with ‘text/enriched’ in the ‘Content-Type:’
header field.
You may also be interested in investigating sgml-mode.
Binaries, images, sound, and video can be inserted in your message with the
command C-c C-m C-i (mh-compose-insertion). You are prompted
for the filename containing the object, the media type if it cannot be
determined automatically, and a content description. If you're using
MH-style directives, you will also be prompted for additional attributes.
Mail may be forwarded with MIME using the command C-c C-m C-f
(mh-compose-forward). You are prompted for a content description, the
name of the folder in which the messages to forward are located, and a range
of messages, which defaults to the current message in that
folder. Voir la section Ranges.
You can have your message initiate an ftp transfer when the
recipient reads the message. To do this, use the command C-c C-m C-g
(mh-mh-compose-anon-ftp). You are prompted for the remote host and
filename, the media type, and the content description.
If the remote file is a compressed tar file, you can use C-c C-m C-t
(mh-mh-compose-external-compressed-tar). Then, in addition to
retrieving the file via anonymous ftp as per the command C-c C-m
C-g (mh-mh-compose-anon-ftp), the file will also be uncompressed and
untarred. You are prompted for the remote host and filename and the content
description.
The command C-c C-m C-x (mh-mh-compose-external-type) is a
general utility for referencing external files. In fact, all of the other
commands that insert tags to access external files call this command. You
are prompted for the access type, remote host and filename, and content
type. If you provide a prefix argument, you are also prompted for a content
description, attributes, parameters, and a comment.
When you are finished editing a MIME message, it might look like this:
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MH-E MIME draft
Typically, you send a message with attachments just like any other message (voir la section Sending a Message).
However, you may take a sneak preview of the MIME encoding if you wish
by running the command C-c C-m C-m (mh-mml-to-mime). The
following screen shows the MIME encoding specified by the tags. You can
see why mail user agents are usually built to hide these details from the
user.
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MH-E MIME draft ready to send
This action can be undone by running C-_ (undo).
If you're using MH-style directives, use C-c C-e
(mh-mh-to-mime) instead of C-c C-m C-m. This runs the command
mhbuild (mhn) on the message which expands the
tags(44). This action can be undone by running
C-c C-m C-u (mh-mh-to-mime-undo), which works by reverting to a
backup file. You are prompted to confirm this action, but you can avoid the
confirmation by adding an argument (for example, C-u C-c C-m C-u).
If you wish to pass additional arguments to mhbuild
(mhn) to affect how it builds your message, use the option
mh-mh-to-mime-args. For example, you can build a consistency check
into the message by setting mh-mh-to-mime-args to ‘-check’. The
recipient of your message can then run ‘mhbuild -check’ on the
message—mhbuild (mhn) will complain if the message has
been corrupted on the way. The command C-c C-e only consults this
option when given a prefix argument (as in C-u C-c C-e).
The hook mh-mh-to-mime-hook is called after the message has been
formatted by C-c C-e.
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Ce document a été généré par Eric Reinbold le 27 Octobre 2007 en utilisant texi2html 1.78.