Proposal: Extended link capabilities to Wanderlust messages for Orgmode

Below you will find three proposals to extend Orgmode's capabilities
to store links to Wanderlust messages. Wanderlust is a mail user agent
for Emacsen, entirely written in elisp.

For the proposed modifications there is an experimental implementation
in the branch org-wl+ of my personal working copy of the Orgmode
repository on github:

http://github.com/dmj/org-mode/tree/org-wl+

They work with simple folder definitions and I am currently setting up
more complex folder definitions for testing.

As these modifications would require a larger patch to org-wl.el the
necessary paper work is initiated.

1.1 Messages in filter folders
-------------------------------

    A filter folder is a virtual folder that displays messages that
    match a particular filter condition.

* Examples

  - /flag:unread/%Inbox

    Show only unread messages in my default imap account's inbox.

  - /tocc:maus.david@gmail.com/%list.emacs-orgmode.gnu.org

    Show only messages that where sent to me, depending on the To:
    and Cc: header field.

* Problem with current solution

  Currently `org-wl-store-link' includes the filter condition in
  the target folder name. As this is no problem if the filter
  condition refers to properties the message bears on itself
  (i.e. header fields) it causes trouble if the filter condition
  refers to the message's state inside the user agent (i.e. flagged
  unread, important etc.).

  If a link is stored to a message that is displayed in the folder

  /flag:unread/%Inbox

  -- the link breaks as soon as the message in question is read and
  hence cannot be found in this folder.

* Proposed modification

  Introduce a new customization variable
  `org-wl-link-remove-filter'. If set to t, filter conditions are
  removed when storing a link to a message that is displayed in a
  filter folder.


1.2 Messages in shimbun folders
--------------------------------

    A shimbun folder's messages are news items that are scraped out of
    web-pages and presented as messages. A shimbun folder is
    accompanied by a corresponding elisp library that fetches a page
    using w3m, parses it for news items and generates the
    messages. There also exist generic shimbun processors for Atom and
    RSS feeds.

    The source page of a shimbun message is indicated by a Xref header
    field with a web link to the original item.

* Examples

  - @heise.telepolis

    Retrieves news items for the german online magazine "Telepolis"

* Problem with current solution

  A shimbun folder is a virtual folder: The messages that are
  displayed are virtual in the sense that they are transformed news
  items of a webpage. If these items vanish from the page that is
  parsed they are out of reach. When reading RSS and Atom feeds or,
  more general, pages with dynamic content this is expected to
  happen.

  I don't know how many users of Orgmode actually use this folder
  type; I use it to read Atom and RSS feeds and sometimes I'd like
  to store a reference to a web source with an interesting
  article. That is: I don't want a link to the virtual shimbun
  message but a link to the message's source.

* Proposed modification

  Introduce new customization variable
  `org-wl-link-shimbun-to-xref'. If set to t, org-wl does not create
  an Wanderlust link but a regular http-link that points to the url
  of the news item as indicated by the Xref header field with the
  shimbun message's subject as description.


1.3 Link to thread
-------------------

    Sometimes I'd like to store a link not just to a particular message
    but to a whole discussion thread.

* Problem with current solution

  It is currently not possible to store a link to a discussion thread.

* Proposed modification

  This is in the moment the toughest part to implement: Using a
  filter folder whos filter condition limits the messages displayed
  to the thread in question seems the way to go.

  The main problem is how to determine the messages that are part of
  a discussion thread. It is possible to find the message that
  started the thread and create a filter that matches all messages
  that have this message's message-id either in the in-reply-to or
  the references header field.

  /message-id:<parent-id>|in-reply-to:<parent-id>|references:<parent-id>/<folder>

  Alas, for this filter condition to work properly it is assumed
  that the mail user agents of the thread's participants use both
  headers (in-reply-to and references) as described in the specs
  (rfc2822, section 3.6.4). That is: This filter condition won't
  find messages deep in the thread that only use the in-reply-to
  header and hence do not bear a property that links back to the
  message that started the thread.[1]

  The best solution seems to be a patch or extension to Wanderlust
  for a new filter condition that uses Wanderlust's built-in
  capabilities to display threads; as long as such a filter
  condition does not exist using the approach above maybe considered
  "good enough" for referencing a discussion thread.

Regards

 -- David

[1] Something David Abrahams pointed out to me on
http://lists.airs.net/wl-en/archive/200912/msg00067.html

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