# HG changeset patch
# User markus schnalke <meillo@marmaro.de>
# Date 1340620646 -7200
# Node ID 92cbd3fa1c40dde5f9a4ed024135ea8226115c37
# Parent  4a1f5ec6220ddadc6630add9419623ece59366a3
Wrote text about displaying mime messages.

diff -r 4a1f5ec6220d -r 92cbd3fa1c40 discussion.roff
--- a/discussion.roff	Mon Jun 25 10:07:33 2012 +0200
+++ b/discussion.roff	Mon Jun 25 12:37:26 2012 +0200
@@ -2241,7 +2241,134 @@
 
 .U3 "Showing MIME Messages
 .P
-FIXME
+The program
+.Pn mhshow
+had been written to display MIME messages.
+It implemented the conceptional view of the MIME RFCs.
+Nmh's
+.Pn mhshow
+handled each MIME part independently, presenting them separately
+to the user.
+This does not match today's understanding of email attachments,
+where displaying a message is seen to be a single, integrated operation.
+Today, email messages are expected to consist of a main text part
+plus possibly attachments.
+They are not any more seen to be arbitrary MIME hierarchies with
+information on how to display the individual parts.
+I adjusted
+.Pn mhshow 's
+behavior to the modern view on the topic.
+.P
+Note that this section completely ignores the original
+.Pn show
+program, because it was not capable to display MIME messages
+and is no longer part of mmh.
+Although
+.Pn mhshow
+was renamed to
+.Pn show
+in mmh, this section uses the name
+.Pn mhshow ,
+in order to avoid confusion.
+.P
+In mmh, the basic idea is that
+.Pn mhshow
+should display a message in one single pager session.
+Therefore,
+.Pn mhshow
+invokes a pager session for all its output,
+whenever it prints to a terminal.
+.Ci a4197ea6ffc5c1550e8b52d5a654bcaaaee04a4e
+In consequence,
+.Pn mhl
+does no more invoke a pager.
+.Ci 0e46503be3c855bddaeae3843e1b659279c35d70
+With
+.Pn mhshow
+replacing the original
+.Pn show ,
+output from
+.Pn mhl
+does not go to the terminal directly, but through
+.Pn mhshow .
+Hence,
+.Pn mhl
+does not need to invoke a pager.
+The one and only job of
+.Pn mhl
+is to format messages or parts of them.
+The only place in mmh, where a pager is invoked is
+.Pn mhshow .
+.P
+.Pe mhshow-show-*
+profile entries can be used to display MIME parts in a specific way.
+For instance, PDF and Postscript files could be converted to plain text
+to display them in the terminal.
+In mmh, the displaying of MIME parts will always be done serially.
+The request to display the MIME type `multipart/parallel' in parallel
+is ignored.
+It is simply treated as `multipart/mixed'.
+.Ci d0581ba306a7299113a346f9b4c46ce97bc4cef6
+This could already be requested with the, now removed,
+.Sw -serialonly
+switch of
+.Pn mhshow .
+As MIME parts are always processed exclusively , i.e. serially,
+the `%e' escape in
+.Pe mhshow-show-*
+profile entries became useless and was thus removed.
+.Ci a20d405db09b7ccca74d3e8c57550883da49e1ae
+.P
+In the intended setup, only text content would be displayed.
+Non-text content would be converted to text by appropriate
+.Pe mhshow-show-*
+profile entries before, if possible and wanted.
+All output would be displayed in a single pager session.
+Other kinds of attachments are ignored.
+With
+.Pe mhshow-show-*
+profile entries for them, they can be displayed serially along
+the message.
+For parallel display, the attachments need to be stored to disk first.
+.P
+To display text content in foreign charsets, they need to be converted
+to the native charset.
+Therefore,
+.Pe mhshow-charset-*
+profile entries used to be needed.
+In mmh, the convertion is done automatically by piping the text through
+the
+.Pn iconv
+command, if necessary.
+.Ci 2433122c20baccb10b70b49c04c6b0497b5b3b60
+Custom
+.Pe mhshow-show-*
+rules for textual content might need a
+.Cl "iconv -f %c %f |
+prefix to have the text converted to the native charset.
+.P
+Although the convertion of foreign charsets to the native one
+has improved, it is not consistent enough.
+Further work needs to be done and
+the basic concepts in this field need to be re-thought.
+Though, the default setup of mmh displays message in foreign charsets
+correctly without the need to configure anything.
+
+
+.ig
+
+.P
+mhshow/mhstore: Removed support for retrieving message/external-body parts.
+These tools won't download the contents automatically anymore. Instead,
+they print the information needed to get the contents. If someone should
+really receive one of those rare message/external-body messages, he can
+do the job manually. We save nearly a thousand lines of code. That's worth
+it!
+(The profile entry `nmh-access-ftp' and sbr/ruserpass.c for reading
+~/.netrc are gone now.)
+.Ci 55e1d8c654ee0f7c45b9361ce34617983b454c32
+
+..