Index: gnus.texi
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  * Fuzzy Matching::              What's the big fuzz?
  * Thwarting Email Spam::        Simple ways to avoid unsolicited commercial email.
  * Spam Package::                A package for filtering and processing spam.
+ * The Gnus Registry::           A package for tracking messages by Message-ID.
  * Other modes::                 Interaction with other modes.
  * Various Various::             Things that are really various.
  @end menu
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  Save table: (spam-stat-save)
  @end smallexample
  
+ @node The Gnus Registry
+ @section The Gnus Registry
+ 
+ @cindex registry
+ @cindex split
+ @cindex track
+ 
+ The Gnus registry is a package that tracks messages by their
+ Message-ID across all backends.  This allows Gnus users to do several
+ cool things, be the envy of the locals, get free haircuts, and be
+ experts on world issues.  Well, maybe not all of those, but the
+ features are pretty cool.
+ 
+ Although they will be explained in detail shortly, here's a quick list
+ of said features in case your attention span is...  never mind.
+ 
+ @enumerate
+ 
+ @item Split messages to their parent
+ This keeps discussions in the same group.  You can use the subject and
+ the sender in addition to the Message-ID.  Several strategies are
+ available.
+ 
+ @item Store custom flags and keywords
+ The registry can store custom flags and keywords for a message.  For
+ instance, you can mark a message ``To-Do'' this way and the flag will
+ persist whether the message is in the nnimap, nnml, nnmaildir,
+ etc. backends.
+ 
+ @item Store arbitrary data
+ Through a simple ELisp API, the registry can remember any data for a
+ message.  A built-in inverse map, when activated, allows quick lookups
+ of all messages matching a particular set of criteria.
+ 
+ @end enumerate
+ 
+ 
+ @menu
+ * Setup::                       
+ * Fancy splitting to parent::   
+ * Store custom flags and keywords::  
+ * Store arbitrary data::        
+ @end menu
+ 
+ @node Setup
+ @subsection Setup
+ 
+ Fortunately, setting up the Gnus registry is pretty easy:
+ 
+ @lisp
+ (setq gnus-registry-max-entries 2500
+       gnus-registry-use-long-group-names t)
+ 
+ (gnus-registry-initialize)
+ @end lisp
+ 
+ This adds registry saves to Gnus newsrc saves (which happen on exit
+ and when you press @kbd{s} from the @code{*Group*} buffer.  It also
+ adds registry calls to article actions in Gnus (copy, move, etc.)  so
+ it's not easy to undo the initialization.  See
+ @code{gnus-registry-initialize} for the gory details.
+ 
+ Here are other settings used by the author of the registry (understand
+ what they do before you copy them blindly).
+ 
+ @lisp
+ (setq
+  gnus-registry-split-strategy 'majority
+  gnus-registry-ignored-groups '(("nntp" t)
+                                 ("nnrss" t)
+                                 ("spam" t)
+                                 ("train" t))
+  gnus-registry-max-entries 500000
+  gnus-registry-use-long-group-names t
+  gnus-registry-track-extra '(sender subject))
+ @end lisp
+ 
+ They say: keep a lot of messages around, use long group names, track
+ messages by sender and subject (not just parent Message-ID), and when
+ the registry splits incoming mail, use a majority rule to decide where
+ messages should go if there's more than one possibility.  In addition,
+ the registry should ignore messages in groups that match ``nntp'',
+ ``nnrss'', ``spam'', or ``train.''
+ 
+ You are doubtless impressed by all this, but you ask: ``I am a Gnus
+ user, I customize to live.  Give me more.''  Here you go, these are
+ the general settings.
+ 
+ @defvar gnus-registry-unfollowed-groups
+ The groups that will not be followed by
+ @code{gnus-registry-split-fancy-with-parent}.  They will still be
+ remembered by the registry.  This is a list of regular expressions.
+ @end defvar
+ 
+ @defvar gnus-registry-ignored-groups
+ The groups that will not be remembered by the registry.  This is a
+ list of regular expressions, also available through Group/Topic
+ customization (so you can ignore or keep a specific group or a whole
+ topic).
+ @end defvar
+ 
+ @defvar gnus-registry-use-long-group-names
+ Whether the registry will use long group names.  It's recommended to
+ set this to t, although everything works if you don't.  Future
+ functionality will require it.
+ @end defvar
+ 
+ @defvar gnus-registry-max-entries
+ The number (an integer or nil for unlimited) of entries the registry
+ will keep.
+ @end defvar
+ 
+ @defvar gnus-registry-cache-file
+ The file where the registry will be stored between Gnus sessions.
+ @end defvar
+ 
+ @node Fancy splitting to parent
+ @subsection Fancy splitting to parent
+ 
+ Simply put, this lets you put followup e-mail where it belongs.
+ 
+ Every message has a Message-ID, which is unique, and the registry
+ remembers it.  When the message is moved or copied, the registry will
+ notice this and offer the new group as a choice to the splitting
+ strategy.  
+ 
+ When a followup is made, usually it mentions the original message's
+ Message-ID in the headers.  The registry knows this and uses that
+ mention to find the group where the original message lives.  You only
+ have to put a rule like this:
+ 
+ @lisp
+ (setq nnimap-my-split-fancy '(|
+ 
+       ;; split to parent: you need this
+       (: gnus-registry-split-fancy-with-parent)
+ 
+       ;; other rules, as an example
+       (: spam-split)
+       ;; default mailbox
+       "mail")
+ @end lisp
+ 
+ in your fancy split setup.  In addition, you may want to customize the
+ following variables.
+ 
+ @defvar gnus-registry-track-extra
+ This is a list of symbols, so it's best to change it from the
+ Customize interface.  By default it's nil, but you may want to track
+ subject and sender as well when splitting by parent.  It may work
+ for you.  It can be annoying if your mail flow is large and people
+ don't stick to the same groups.
+ @end defvar
+ 
+ @defvar gnus-registry-split-strategy
+ This is a symbol, so it's best to change it from the Customize
+ interface.  By default it's nil, but you may want to set it to
+ @code{'majority} or @code{'first} to split by sender or subject based
+ on the majority of matches or on the first found.
+ @end defvar
+ 
+ @node Store custom flags and keywords
+ @subsection Store custom flags and keywords
+ 
+ The registry lets you set custom flags and keywords per message.  You
+ can use the Gnus->Registry Marks menu or the @kbd{M M x} keyboard
+ shortcuts, where @code{x} is the first letter of the mark's name.
+ 
+ @defvar gnus-registry-marks
+ The custom marks that the registry can use.  You can modify the
+ default list, if you like.  If you do, you'll have to exit Emacs
+ before they take effect (you can also unload the registry and reload
+ it or evaluate the specific macros you'll need, but you probably don't
+ want to bother).  Use the Customize interface to modify the list.
+ 
+ By default this list has the Important, Work, Personal, To-Do, and
+ Later marks.  They all have keyboard shortcuts like @kbd{M M i} for
+ Important, using the first letter.
+ @end defvar
+ 
+ @defun gnus-registry-mark-article
+ Call this function to mark an article with a custom registry mark.  It
+ will offer the available marks for completion.
+ @end defun
+ 
+ @node Store arbitrary data
+ @subsection Store arbitrary data
+ 
+ The registry has a simple API that uses a Message-ID as the key to
+ store arbitrary data (as long as it can be converted to a list for
+ storage).
+ 
+ @defun gnus-registry-store-extra-entry (id key value)
+ Store @code{value} in the extra data key @code{key} for message
+ @code{id}.
+ @end defun
+ 
+ @defun gnus-registry-delete-extra-entry (id key)
+ Delete the extra data key @code{key} for message @code{id}.
+ @end defun
+ 
+ @defun gnus-registry-fetch-extra (id key)
+ Get the extra data key @code{key} for message @code{id}.
+ @end defun
+ 
+ @defvar gnus-registry-extra-entries-precious
+ If any extra entries are previous, their presence will make the
+ registry keep the whole entry forever, even if there are no groups for
+ the Message-ID and if the size limit of the registry is reached.  By
+ default this is just @code{'(marks)} so the custom registry marks are
+ precious.
+ @end defvar
+ 
  @node Other modes
  @section Interaction with other modes