+use anything but Gnus to read the @code{nnmh} articles, you do not
+have to set this variable to @code{t}. The default is @code{nil}.
+@end table
+
+
+@node Maildir
+@subsubsection Maildir
+@cindex nnmaildir
+@cindex maildir
+
+@code{nnmaildir} stores mail in the maildir format, with each maildir
+corresponding to a group in Gnus. This format is documented here:
+@uref{http://cr.yp.to/proto/maildir.html} and here:
+@uref{http://www.qmail.org/man/man5/maildir.html}. @code{nnmaildir}
+also stores extra information in the @file{.nnmaildir/} directory
+within a maildir.
+
+Maildir format was designed to allow concurrent deliveries and
+reading, without needing locks. With other back ends, you would have
+your mail delivered to a spool of some kind, and then you would
+configure Gnus to split mail from that spool into your groups. You
+can still do that with @code{nnmaildir}, but the more common
+configuration is to have your mail delivered directly to the maildirs
+that appear as group in Gnus.
+
+@code{nnmaildir} is designed to be perfectly reliable: @kbd{C-g} will
+never corrupt its data in memory, and @code{SIGKILL} will never
+corrupt its data in the filesystem.
+
+@code{nnmaildir} stores article marks and @acronym{NOV} data in each
+maildir. So you can copy a whole maildir from one Gnus setup to
+another, and you will keep your marks.
+
+Virtual server settings:
+
+@table @code
+@item directory
+For each of your @code{nnmaildir} servers (it's very unlikely that
+you'd need more than one), you need to create a directory and populate
+it with maildirs or symlinks to maildirs (and nothing else; do not
+choose a directory already used for other purposes). Each maildir
+will be represented in Gnus as a newsgroup on that server; the
+filename of the symlink will be the name of the group. Any filenames
+in the directory starting with @samp{.} are ignored. The directory is
+scanned when you first start Gnus, and each time you type @kbd{g} in
+the group buffer; if any maildirs have been removed or added,
+@code{nnmaildir} notices at these times.
+
+The value of the @code{directory} parameter should be a Lisp form
+which is processed by @code{eval} and @code{expand-file-name} to get
+the path of the directory for this server. The form is @code{eval}ed
+only when the server is opened; the resulting string is used until the
+server is closed. (If you don't know about forms and @code{eval},
+don't worry---a simple string will work.) This parameter is not
+optional; you must specify it. I don't recommend using
+@code{"~/Mail"} or a subdirectory of it; several other parts of Gnus
+use that directory by default for various things, and may get confused
+if @code{nnmaildir} uses it too. @code{"~/.nnmaildir"} is a typical
+value.
+
+@item target-prefix
+This should be a Lisp form which is processed by @code{eval} and
+@code{expand-file-name}. The form is @code{eval}ed only when the
+server is opened; the resulting string is used until the server is
+closed.
+
+When you create a group on an @code{nnmaildir} server, the maildir is
+created with @code{target-prefix} prepended to its name, and a symlink
+pointing to that maildir is created, named with the plain group name.
+So if @code{directory} is @code{"~/.nnmaildir"} and
+@code{target-prefix} is @code{"../maildirs/"}, then when you create
+the group @code{foo}, @code{nnmaildir} will create
+@file{~/.nnmaildir/../maildirs/foo} as a maildir, and will create
+@file{~/.nnmaildir/foo} as a symlink pointing to
+@file{../maildirs/foo}.
+
+You can set @code{target-prefix} to a string without any slashes to
+create both maildirs and symlinks in the same @code{directory}; in
+this case, any maildirs found in @code{directory} whose names start
+with @code{target-prefix} will not be listed as groups (but the
+symlinks pointing to them will be).
+
+As a special case, if @code{target-prefix} is @code{""} (the default),
+then when you create a group, the maildir will be created in
+@code{directory} without a corresponding symlink. Beware that you
+cannot use @code{gnus-group-delete-group} on such groups without the
+@code{force} argument.
+
+@item directory-files
+This should be a function with the same interface as
+@code{directory-files} (such as @code{directory-files} itself). It is
+used to scan the server's @code{directory} for maildirs. This
+parameter is optional; the default is
+@code{nnheader-directory-files-safe} if
+@code{nnheader-directory-files-is-safe} is @code{nil}, and
+@code{directory-files} otherwise.
+(@code{nnheader-directory-files-is-safe} is checked only once when the
+server is opened; if you want to check it each time the directory is
+scanned, you'll have to provide your own function that does that.)
+
+@item get-new-mail
+If non-@code{nil}, then after scanning for new mail in the group
+maildirs themselves as usual, this server will also incorporate mail
+the conventional Gnus way, from @code{mail-sources} according to
+@code{nnmail-split-methods} or @code{nnmail-split-fancy}. The default
+value is @code{nil}.
+
+Do @emph{not} use the same maildir both in @code{mail-sources} and as
+an @code{nnmaildir} group. The results might happen to be useful, but
+that would be by chance, not by design, and the results might be
+different in the future. If your split rules create new groups,
+remember to supply a @code{create-directory} server parameter.
+@end table
+
+@subsubsection Group parameters
+
+@code{nnmaildir} uses several group parameters. It's safe to ignore
+all this; the default behavior for @code{nnmaildir} is the same as the
+default behavior for other mail back ends: articles are deleted after
+one week, etc. Except for the expiry parameters, all this
+functionality is unique to @code{nnmaildir}, so you can ignore it if
+you're just trying to duplicate the behavior you already have with
+another back end.
+
+If the value of any of these parameters is a vector, the first element
+is evaluated as a Lisp form and the result is used, rather than the
+original value. If the value is not a vector, the value itself is
+evaluated as a Lisp form. (This is why these parameters use names
+different from those of other, similar parameters supported by other
+back ends: they have different, though similar, meanings.) (For
+numbers, strings, @code{nil}, and @code{t}, you can ignore the
+@code{eval} business again; for other values, remember to use an extra
+quote and wrap the value in a vector when appropriate.)
+
+@table @code
+@item expire-age
+An integer specifying the minimum age, in seconds, of an article
+before it will be expired, or the symbol @code{never} to specify that
+articles should never be expired. If this parameter is not set,
+@code{nnmaildir} falls back to the usual
+@code{nnmail-expiry-wait}(@code{-function}) variables (overrideable by
+the @code{expiry-wait}(@code{-function}) group parameters. If you
+wanted a value of 3 days, you could use something like @code{[(* 3 24
+60 60)]}; @code{nnmaildir} will evaluate the form and use the result.
+An article's age is measured starting from the article file's
+modification time. Normally, this is the same as the article's
+delivery time, but editing an article makes it younger. Moving an
+article (other than via expiry) may also make an article younger.
+
+@item expire-group
+If this is set to a string such as a full Gnus group name, like
+@example
+"backend+server.address.string:group.name"
+@end example
+and if it is not the name of the same group that the parameter belongs
+to, then articles will be moved to the specified group during expiry
+before being deleted. @emph{If this is set to an @code{nnmaildir}
+group, the article will be just as old in the destination group as it
+was in the source group.} So be careful with @code{expire-age} in the
+destination group. If this is set to the name of the same group that
+the parameter belongs to, then the article is not expired at all. If
+you use the vector form, the first element is evaluated once for each
+article. So that form can refer to
+@code{nnmaildir-article-file-name}, etc., to decide where to put the
+article. @emph{If this parameter is not set, @code{nnmaildir} does
+not fall back to the @code{expiry-target} group parameter or the
+@code{nnmail-expiry-target} variable.}
+
+@item read-only
+If this is set to @code{t}, @code{nnmaildir} will treat the articles
+in this maildir as read-only. This means: articles are not renamed
+from @file{new/} into @file{cur/}; articles are only found in
+@file{new/}, not @file{cur/}; articles are never deleted; articles
+cannot be edited. @file{new/} is expected to be a symlink to the
+@file{new/} directory of another maildir---e.g., a system-wide mailbox
+containing a mailing list of common interest. Everything in the
+maildir outside @file{new/} is @emph{not} treated as read-only, so for
+a shared mailbox, you do still need to set up your own maildir (or
+have write permission to the shared mailbox); your maildir just won't
+contain extra copies of the articles.
+
+@item directory-files
+A function with the same interface as @code{directory-files}. It is
+used to scan the directories in the maildir corresponding to this
+group to find articles. The default is the function specified by the
+server's @code{directory-files} parameter.
+
+@item distrust-Lines:
+If non-@code{nil}, @code{nnmaildir} will always count the lines of an
+article, rather than use the @code{Lines:} header field. If
+@code{nil}, the header field will be used if present.
+
+@item always-marks
+A list of mark symbols, such as @code{['(read expire)]}. Whenever
+Gnus asks @code{nnmaildir} for article marks, @code{nnmaildir} will
+say that all articles have these marks, regardless of whether the
+marks stored in the filesystem say so. This is a proof-of-concept
+feature that will probably be removed eventually; it ought to be done
+in Gnus proper, or abandoned if it's not worthwhile.
+
+@item never-marks
+A list of mark symbols, such as @code{['(tick expire)]}. Whenever
+Gnus asks @code{nnmaildir} for article marks, @code{nnmaildir} will
+say that no articles have these marks, regardless of whether the marks
+stored in the filesystem say so. @code{never-marks} overrides
+@code{always-marks}. This is a proof-of-concept feature that will
+probably be removed eventually; it ought to be done in Gnus proper, or
+abandoned if it's not worthwhile.
+
+@item nov-cache-size
+An integer specifying the size of the @acronym{NOV} memory cache. To
+speed things up, @code{nnmaildir} keeps @acronym{NOV} data in memory
+for a limited number of articles in each group. (This is probably not
+worthwhile, and will probably be removed in the future.) This
+parameter's value is noticed only the first time a group is seen after
+the server is opened---i.e., when you first start Gnus, typically.
+The @acronym{NOV} cache is never resized until the server is closed
+and reopened. The default is an estimate of the number of articles
+that would be displayed in the summary buffer: a count of articles
+that are either marked with @code{tick} or not marked with
+@code{read}, plus a little extra.