emacs/man/emacs-xtra.texi

\input texinfo    @c -*-texinfo-*-
@comment %**start of header
@setfilename ../info/emacs-xtra
@settitle Specialized Emacs Features
@syncodeindex fn cp
@syncodeindex vr cp
@syncodeindex ky cp
@comment %**end of header

@copying
This manual describes specialized features of Emacs.

Copyright (C) 2004, 2005 Free Software Foundation, Inc.

@quotation
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.2 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with the Front-Cover texts being ``A GNU
Manual'', and with the Back-Cover Texts as in (a) below.  A copy of the
license is included in the section entitled ``GNU Free Documentation
License'' in the Emacs manual.

(a) The FSF's Back-Cover Text is: ``You have freedom to copy and modify
this GNU Manual, like GNU software.  Copies published by the Free
Software Foundation raise funds for GNU development.''

This document is part of a collection distributed under the GNU Free
Documentation License.  If you want to distribute this document
separately from the collection, you can do so by adding a copy of the
license to the document, as described in section 6 of the license.
@end quotation
@end copying

@dircategory Emacs
@direntry
* Emacs-Xtra: (emacs-xtra).    Specialized Emacs features.
@end direntry

@titlepage
@title Specialized Emacs Features
@page
@vskip 0pt plus 1filll
@insertcopying
@end titlepage

@contents

@ifnottex
@node Top
@top Specialized Emacs Features

@insertcopying

@end ifnottex

@menu
* Introduction::                  What documentation belongs here?
* Autorevert::                    Auto Reverting non-file buffers.
* Subdir switches::               Subdirectory switches in Dired.
* Advanced Calendar/Diary Usage:: Advanced Calendar/Diary customization.
* Index::
@end menu

@node Introduction
@unnumbered Introduction

This manual contains detailed information about various features that
are too specialized to be included in the Emacs manual.  It is
intended to be readable by anyone having a basic knowledge of Emacs.
However, certain sections may be intended for a more specialized
audience, such as Elisp authors.  This should be clearly pointed out
at the beginning of these sections.

This manual is intended as a complement, rather than an alternative,
to other ways to gain a more detailed knowledge of Emacs than the
Emacs manual can provide, such as browsing packages using @kbd{C-h p},
accessing mode documentation using @kbd{C-h m} and browsing user
options using Custom.  Also, certain packages, or collections of
related features, have their own manuals.  The present manual is
mainly intended to be a collection of smaller specialized features,
too small to get their own manual.

Sections intended specifically for Elisp programmers can follow the
style of the Elisp manual.  Other sections should follow the style of
the Emacs manual.

@node Autorevert
@chapter Auto Reverting non-file Buffers

Normally Global Auto Revert Mode only reverts file buffers.  There are
two ways to auto-revert certain non-file buffers: enabling Auto Revert
Mode in those buffers (using @kbd{M-x auto-revert-mode}) and setting
@code{global-auto-revert-non-file-buffers} to @code{t}.  The latter
enables Auto Reverting for all types of buffers for which it is
implemented, that is, for the types of buffers listed in the menu
below.

Like file buffers, non-file buffers should normally not revert while
you are working on them, or while they contain information that might
get lost after reverting.  Therefore, they do not revert if they are
``modified''.  This can get tricky, because deciding when a non-file
buffer should be marked modified is usually more difficult than for
file buffers.

Another tricky detail is that, for efficiency reasons, Auto Revert
often does not try to detect all possible changes in the buffer, only
changes that are ``major'' or easy to detect.  Hence, enabling
auto-reverting for a non-file buffer does not always guarantee that
all information in the buffer is up to date and does not necessarily
make manual reverts useless.

At the other extreme, certain buffers automatically auto-revert every
@code{auto-revert-interval} seconds.  (This currently only applies to
the Buffer Menu.)  In this case, Auto Revert does not print any
messages while reverting, even when @code{auto-revert-verbose} is
non-@code{nil}.

The details depend on the particular types of buffers and are
explained in the corresponding sections.

@menu
* Auto Reverting the Buffer Menu::
* Auto Reverting Dired::
* Supporting additional buffers::
@end menu

@node Auto Reverting the Buffer Menu
@section Auto Reverting the Buffer Menu

If auto-reverting of non-file buffers is enabled, the Buffer Menu
automatically reverts every @code{auto-revert-interval} seconds,
whether there is a need for it or not.  (It would probably take longer
to check whether there is a need than to actually revert.)

If the Buffer Menu inappropriately gets marked modified, just revert
it manually using @kbd{g} and auto-reverting will resume.  However, if
you marked certain buffers to get deleted or to be displayed, you have
to be careful, because reverting erases all marks.  The fact that
adding marks sets the buffer's modified flag prevents Auto Revert from
automatically erasing the marks.

@node Auto Reverting Dired
@section Auto Reverting Dired buffers

Auto-reverting Dired buffers currently works on GNU or Unix style
operating systems.  It may not work satisfactorily on some other
systems.

Dired buffers only auto-revert when the file list of the buffer's main
directory changes.  They do not auto-revert when information about a
particular file changes or when inserted subdirectories change.  To be
sure that @emph{all} listed information is up to date, you have to
manually revert using @kbd{g}, @emph{even} if auto-reverting is
enabled in the Dired buffer.  Sometimes, you might get the impression
that modifying or saving files listed in the main directory actually
does cause auto-reverting.  This is because making changes to a file,
or saving it, very often causes changes in the directory itself, for
instance, through backup files or auto-save files.  However, this is
not guaranteed.

If the Dired buffer is marked modified and there are no changes you
want to protect, then most of the time you can make auto-reverting
resume by manually reverting the buffer using @kbd{g}.  There is one
exception.  If you flag or mark files, you can safely revert the
buffer.  This will not erase the flags or marks (unless the marked
file has been deleted, of course).  However, the buffer will stay
modified, even after reverting, and auto-reverting will not resume.
This is because, if you flag or mark files, you may be working on the
buffer and you might not want the buffer to change without warning.
If you want auto-reverting to resume in the presence of marks and
flags, mark the buffer non-modified using @kbd{M-~}.  However, adding,
deleting or changing marks or flags will mark it modified again.

Remote Dired buffers are not auto-reverted.  Neither are Dired buffers
for which you used shell wildcards or file arguments to list only some
of the files.  @samp{*Find*} and @samp{*Locate*} buffers do not
auto-revert either.

@node Supporting additional buffers
@section Adding Support for Auto-Reverting additional Buffers.

This section is intended for Elisp programmers who would like to add
support for auto-reverting new types of buffers.

To support auto-reverting the buffer must first of all have a
@code{revert-buffer-function}.  @xref{Definition of
revert-buffer-function,, Reverting, elisp, the Emacs Lisp Reference Manual}.

In addition, it @emph{must} have a @code{buffer-stale-function}.

@defvar buffer-stale-function
The value of this variable is a function to check whether a non-file
buffer needs reverting.  This should be a function with one optional
argument @var{noconfirm}.  The function should return non-@code{nil}
if the buffer should be reverted.  The buffer is current when this
function is called.

While this function is mainly intended for use in auto-reverting, it
could be used for other purposes as well.  For instance, if
auto-reverting is not enabled, it could be used to warn the user that
the buffer needs reverting.  The idea behind the @var{noconfirm}
argument is that it should be @code{t} if the buffer is going to be
reverted without asking the user and @code{nil} if the function is
just going to be used to warn the user that the buffer is out of date.
In particular, for use in auto-reverting, @var{noconfirm} is @code{t}.
If the function is only going to be used for auto-reverting, you can
ignore the @var{noconfirm} argument.

If you just want to automatically auto-revert every
@code{auto-revert-interval} seconds, use:

@example
(set (make-local-variable 'buffer-stale-function)
     #'(lambda (&optional noconfirm) 'fast))
@end example

@noindent
in the buffer's mode function.

The special return value @samp{fast} tells the caller that the need
for reverting was not checked, but that reverting the buffer is fast.
It also tells Auto Revert not to print any revert messages, even if
@code{auto-revert-verbose} is non-@code{nil}.  This is important, as
getting revert messages every @code{auto-revert-interval} seconds can
be very annoying.  The information provided by this return value could
also be useful if the function is consulted for purposes other than
auto-reverting.
@end defvar

Once the buffer has a @code{revert-buffer-function} and a
@code{buffer-stale-function}, several problems usually remain.

The buffer will only auto-revert if it is marked unmodified.  Hence,
you will have to make sure that various functions mark the buffer
modified if and only if either the buffer contains information that
might be lost by reverting or there is reason to believe that the user
might be inconvenienced by auto-reverting, because he is actively
working on the buffer.  The user can always override this by manually
adjusting the modified status of the buffer.  To support this, calling
the @code{revert-buffer-function} on a buffer that is marked
unmodified should always keep the buffer marked unmodified.

It is important to assure that point does not continuously jump around
as a consequence of auto-reverting.  Of course, moving point might be
inevitable if the buffer radically changes.

You should make sure that the @code{revert-buffer-function} does not
print messages that unnecessarily duplicate Auto Revert's own messages
if @code{auto-revert-verbose} is @code{t} and effectively override a
@code{nil} value for @code{auto-revert-verbose}.  Hence, adapting a
mode for auto-reverting often involves getting rid of such messages.
This is especially important for buffers that automatically
auto-revert every @code{auto-revert-interval} seconds.

Also, you may want to update the documentation string of
@code{global-auto-revert-non-file-buffers}.

@ifinfo
Finally, you should add a node to this chapter's menu.  This node
@end ifinfo
@ifnotinfo
Finally, you should add a section to this chapter.  This section
@end ifnotinfo
should at the very least make clear whether enabling auto-reverting
for the buffer reliably assures that all information in the buffer is
completely up to date (or will be after @code{auto-revert-interval}
seconds).

@node Subdir switches
@chapter Subdirectory Switches in Dired

You can insert subdirectories with specified @code{ls} switches in
Dired buffers, using @kbd{C-u i}.  You can change the @code{ls}
switches of an already inserted subdirectory using @kbd{C-u l}.

In Emacs versions 22.1 and later, Dired remembers the switches, so
that reverting the buffer will not change them back to the main
directory's switches.  Deleting a subdirectory forgets about its
switches.

Using @code{dired-undo} (usually bound to @kbd{C-_} and @kbd{C-x u})
to reinsert or delete subdirectories, that were inserted with explicit
switches, can bypass Dired's machinery for remembering (or forgetting)
switches.  Deleting a subdirectory using @code{dired-undo} does not
forget its switches.  When later reinserted using @kbd{i}, it will be
reinserted using its old switches.  Using @code{dired-undo} to
reinsert a subdirectory that was deleted using the regular
Dired commands (not @code{dired-undo}) will originally insert it with
its old switches.  However, reverting the buffer will relist it using
the buffer's default switches.  If any of this yields problems, you
can easily correct the situation using @kbd{C-u i} or @kbd{C-u l}.

Dired does not remember the @code{R} switch.  Inserting a subdirectory
with switches that include the @code{R} switch is equivalent with
inserting each of its subdirectories using all remaining switches.
For instance, updating or killing a subdirectory that was inserted
with the @code{R} switch will not update or kill its subdirectories.

The buffer's default switches do not affect subdirectories that were
inserted using explicitly specified switches.  In particular,
commands such as @kbd{s}, that change the buffer's switches do not
affect such subdirectories.  (They do affect subdirectories without
explicitly assigned switches, however.)

You can make Dired forget about all subdirectory switches and relist
all subdirectories with the buffer's default switches using
@kbd{M-x dired-reset-subdir-switches}.  This also reverts the Dired buffer.


@c Moved here from the Emacs Lisp Reference Manual, 2005-03-26.
@node Advanced Calendar/Diary Usage
@chapter Customizing the Calendar and Diary

  There are many customizations that you can use to make the calendar and
diary suit your personal tastes.

@menu
* Calendar Customizing::   Defaults you can set.
* Holiday Customizing::    Defining your own holidays.
* Date Display Format::    Changing the format.
* Time Display Format::    Changing the format.
* Daylight Savings::       Changing the default.
* Diary Customizing::      Defaults you can set.
* Hebrew/Islamic Entries:: How to obtain them.
* Fancy Diary Display::    Enhancing the diary display, sorting entries,
                             using included diary files.
* Sexp Diary Entries::     Fancy things you can do.
@end menu

@node Calendar Customizing
@section Customizing the Calendar
@vindex calendar-holiday-marker
@vindex diary-entry-marker
  The variable @code{calendar-holiday-marker} specifies how to mark a
date as being a holiday.  Its value may be a single-character string
to insert next to the date, or a face name to use for displaying the
date.  Likewise, the variable @code{diary-entry-marker} specifies how
to mark a date that has diary entries.  The calendar creates faces
named @code{holiday-face} and @code{diary-face} for these purposes;
those symbols are the default values of these variables.

@vindex calendar-load-hook
  The variable @code{calendar-load-hook} is a normal hook run when the
calendar package is first loaded (before actually starting to display
the calendar).

@vindex initial-calendar-window-hook
  Starting the calendar runs the normal hook
@code{initial-calendar-window-hook}.  Recomputation of the calendar
display does not run this hook.  But if you leave the calendar with the
@kbd{q} command and reenter it, the hook runs again.@refill

@vindex today-visible-calendar-hook
  The variable @code{today-visible-calendar-hook} is a normal hook run
after the calendar buffer has been prepared with the calendar when the
current date is visible in the window.  One use of this hook is to
replace today's date with asterisks; to do that, use the hook function
@code{calendar-star-date}.

@findex calendar-star-date
@example
(add-hook 'today-visible-calendar-hook 'calendar-star-date)
@end example

@noindent
Another standard hook function marks the current date, either by
changing its face or by adding an asterisk.  Here's how to use it:

@findex calendar-mark-today
@example
(add-hook 'today-visible-calendar-hook 'calendar-mark-today)
@end example

@noindent
@vindex calendar-today-marker
The variable @code{calendar-today-marker} specifies how to mark
today's date.  Its value should be a single-character string to insert
next to the date or a face name to use for displaying the date.  A
face named @code{calendar-today-face} is provided for this purpose;
that symbol is the default for this variable.

@vindex today-invisible-calendar-hook
@noindent
  A similar normal hook, @code{today-invisible-calendar-hook} is run if
the current date is @emph{not} visible in the window.

@vindex calendar-move-hook
  Each of the calendar cursor motion commands runs the hook
@code{calendar-move-hook} after it moves the cursor.

@node Holiday Customizing
@section Customizing the Holidays

@vindex calendar-holidays
@vindex christian-holidays
@vindex hebrew-holidays
@vindex islamic-holidays
  Emacs knows about holidays defined by entries on one of several lists.
You can customize these lists of holidays to your own needs, adding or
deleting holidays.  The lists of holidays that Emacs uses are for
general holidays (@code{general-holidays}), local holidays
(@code{local-holidays}), Christian holidays (@code{christian-holidays}),
Hebrew (Jewish) holidays (@code{hebrew-holidays}), Islamic (Muslim)
holidays (@code{islamic-holidays}), and other holidays
(@code{other-holidays}).

@vindex general-holidays
  The general holidays are, by default, holidays common throughout the
United States.  To eliminate these holidays, set @code{general-holidays}
to @code{nil}.

@vindex local-holidays
  There are no default local holidays (but sites may supply some).  You
can set the variable @code{local-holidays} to any list of holidays, as
described below.

@vindex all-christian-calendar-holidays
@vindex all-hebrew-calendar-holidays
@vindex all-islamic-calendar-holidays
  By default, Emacs does not include all the holidays of the religions
that it knows, only those commonly found in secular calendars.  For a
more extensive collection of religious holidays, you can set any (or
all) of the variables @code{all-christian-calendar-holidays},
@code{all-hebrew-calendar-holidays}, or
@code{all-islamic-calendar-holidays} to @code{t}.  If you want to
eliminate the religious holidays, set any or all of the corresponding
variables @code{christian-holidays}, @code{hebrew-holidays}, and
@code{islamic-holidays} to @code{nil}.@refill

@vindex other-holidays
  You can set the variable @code{other-holidays} to any list of
holidays.  This list, normally empty, is intended for individual use.

@cindex holiday forms
  Each of the lists (@code{general-holidays}, @code{local-holidays},
@code{christian-holidays}, @code{hebrew-holidays},
@code{islamic-holidays}, and @code{other-holidays}) is a list of
@dfn{holiday forms}, each holiday form describing a holiday (or
sometimes a list of holidays).

  Here is a table of the possible kinds of holiday form.  Day numbers
and month numbers count starting from 1, but ``dayname'' numbers
count Sunday as 0.  The element @var{string} is always the
name of the holiday, as a string.

@table @code
@item (holiday-fixed @var{month} @var{day} @var{string})
A fixed date on the Gregorian calendar.

@item (holiday-float @var{month} @var{dayname} @var{k} @var{string})
The @var{k}th @var{dayname} in @var{month} on the Gregorian calendar
(@var{dayname}=0 for Sunday, and so on); negative @var{k} means count back
from the end of the month.

@item (holiday-hebrew @var{month} @var{day} @var{string})
A fixed date on the Hebrew calendar.

@item (holiday-islamic @var{month} @var{day} @var{string})
A fixed date on the Islamic calendar.

@item (holiday-julian @var{month} @var{day} @var{string})
A fixed date on the Julian calendar.

@item (holiday-sexp @var{sexp} @var{string})
A date calculated by the Lisp expression @var{sexp}.  The expression
should use the variable @code{year} to compute and return the date of a
holiday, or @code{nil} if the holiday doesn't happen this year.  The
value of @var{sexp} must represent the date as a list of the form
@code{(@var{month} @var{day} @var{year})}.

@item (if @var{condition} @var{holiday-form})
A holiday that happens only if @var{condition} is true.

@item (@var{function} @r{[}@var{args}@r{]})
A list of dates calculated by the function @var{function}, called with
arguments @var{args}.
@end table

  For example, suppose you want to add Bastille Day, celebrated in
France on July 14.  You can do this as follows:

@smallexample
(setq other-holidays '((holiday-fixed 7 14 "Bastille Day")))
@end smallexample

@noindent
The holiday form @code{(holiday-fixed 7 14 "Bastille Day")} specifies the
fourteenth day of the seventh month (July).

  Many holidays occur on a specific day of the week, at a specific time
of month.  Here is a holiday form describing Hurricane Supplication Day,
celebrated in the Virgin Islands on the fourth Monday in August:

@smallexample
(holiday-float 8 1 4 "Hurricane Supplication Day")
@end smallexample

@noindent
Here the 8 specifies August, the 1 specifies Monday (Sunday is 0,
Tuesday is 2, and so on), and the 4 specifies the fourth occurrence in
the month (1 specifies the first occurrence, 2 the second occurrence,
@minus{}1 the last occurrence, @minus{}2 the second-to-last occurrence, and
so on).

  You can specify holidays that occur on fixed days of the Hebrew,
Islamic, and Julian calendars too.  For example,

@smallexample
(setq other-holidays
      '((holiday-hebrew 10 2 "Last day of Hanukkah")
        (holiday-islamic 3 12 "Mohammed's Birthday")
        (holiday-julian 4 2 "Jefferson's Birthday")))
@end smallexample

@noindent
adds the last day of Hanukkah (since the Hebrew months are numbered with
1 starting from Nisan), the Islamic feast celebrating Mohammed's
birthday (since the Islamic months are numbered from 1 starting with
Muharram), and Thomas Jefferson's birthday, which is 2 April 1743 on the
Julian calendar.

  To include a holiday conditionally, use either Emacs Lisp's @code{if} or the
@code{holiday-sexp} form.  For example, American presidential elections
occur on the first Tuesday after the first Monday in November of years
divisible by 4:

@smallexample
(holiday-sexp '(if (= 0 (% year 4))
                   (calendar-gregorian-from-absolute
                    (1+ (calendar-dayname-on-or-before
                          1 (+ 6 (calendar-absolute-from-gregorian
                                  (list 11 1 year)))))))
              "US Presidential Election")
@end smallexample

@noindent
or

@smallexample
(if (= 0 (% displayed-year 4))
    (fixed 11
           (extract-calendar-day
             (calendar-gregorian-from-absolute
               (1+ (calendar-dayname-on-or-before
                     1 (+ 6 (calendar-absolute-from-gregorian
                              (list 11 1 displayed-year)))))))
           "US Presidential Election"))
@end smallexample

  Some holidays just don't fit into any of these forms because special
calculations are involved in their determination.  In such cases you
must write a Lisp function to do the calculation.  To include eclipses,
for example, add @code{(eclipses)} to @code{other-holidays}
and write an Emacs Lisp function @code{eclipses} that returns a
(possibly empty) list of the relevant Gregorian dates among the range
visible in the calendar window, with descriptive strings, like this:

@smallexample
(((6 27 1991) "Lunar Eclipse") ((7 11 1991) "Solar Eclipse") ... )
@end smallexample

@node Date Display Format
@section Date Display Format
@vindex calendar-date-display-form

  You can customize the manner of displaying dates in the diary, in mode
lines, and in messages by setting @code{calendar-date-display-form}.
This variable holds a list of expressions that can involve the variables
@code{month}, @code{day}, and @code{year}, which are all numbers in
string form, and @code{monthname} and @code{dayname}, which are both
alphabetic strings.  In the American style, the default value of this
list is as follows:

@smallexample
((if dayname (concat dayname ", ")) monthname " " day ", " year)
@end smallexample

@noindent
while in the European style this value is the default:

@smallexample
((if dayname (concat dayname ", ")) day " " monthname " " year)
@end smallexample

@noindent
The ISO standard date representation is this:

@smallexample
(year "-" month "-" day)
@end smallexample

@noindent
This specifies a typical American format:

@smallexample
(month "/" day "/" (substring year -2))
@end smallexample

@node Time Display Format
@section Time Display Format
@vindex calendar-time-display-form

  The calendar and diary by default display times of day in the
conventional American style with the hours from 1 through 12, minutes,
and either @samp{am} or @samp{pm}.  If you prefer the European style,
also known in the US as military, in which the hours go from 00 to 23,
you can alter the variable @code{calendar-time-display-form}.  This
variable is a list of expressions that can involve the variables
@code{12-hours}, @code{24-hours}, and @code{minutes}, which are all
numbers in string form, and @code{am-pm} and @code{time-zone}, which are
both alphabetic strings.  The default value of
@code{calendar-time-display-form} is as follows:

@smallexample
(12-hours ":" minutes am-pm
          (if time-zone " (") time-zone (if time-zone ")"))
@end smallexample

@noindent
Here is a value that provides European style times:

@smallexample
(24-hours ":" minutes
          (if time-zone " (") time-zone (if time-zone ")"))
@end smallexample

@node Daylight Savings
@section Daylight Savings Time
@cindex daylight savings time

  Emacs understands the difference between standard time and daylight
savings time---the times given for sunrise, sunset, solstices,
equinoxes, and the phases of the moon take that into account.  The rules
for daylight savings time vary from place to place and have also varied
historically from year to year.  To do the job properly, Emacs needs to
know which rules to use.

  Some operating systems keep track of the rules that apply to the place
where you are; on these systems, Emacs gets the information it needs
from the system automatically.  If some or all of this information is
missing, Emacs fills in the gaps with the rules currently used in
Cambridge, Massachusetts, which is the center of GNU's world.


@vindex calendar-daylight-savings-starts
@vindex calendar-daylight-savings-ends
  If the default choice of rules is not appropriate for your location,
you can tell Emacs the rules to use by setting the variables
@code{calendar-daylight-savings-starts} and
@code{calendar-daylight-savings-ends}.  Their values should be Lisp
expressions that refer to the variable @code{year}, and evaluate to the
Gregorian date on which daylight savings time starts or (respectively)
ends, in the form of a list @code{(@var{month} @var{day} @var{year})}.
The values should be @code{nil} if your area does not use daylight
savings time.

  Emacs uses these expressions to determine the start and end dates of
daylight savings time as holidays and for correcting times of day in the
solar and lunar calculations.

  The values for Cambridge, Massachusetts are as follows:

@example
@group
(calendar-nth-named-day 1 0 4 year)
(calendar-nth-named-day -1 0 10 year)
@end group
@end example

@noindent
i.e., the first 0th day (Sunday) of the fourth month (April) in
the year specified by @code{year}, and the last Sunday of the tenth month
(October) of that year.  If daylight savings time were
changed to start on October 1, you would set
@code{calendar-daylight-savings-starts} to this:

@example
(list 10 1 year)
@end example

  For a more complex example, suppose daylight savings time begins on
the first of Nisan on the Hebrew calendar.  You should set
@code{calendar-daylight-savings-starts} to this value:

@example
(calendar-gregorian-from-absolute
  (calendar-absolute-from-hebrew
    (list 1 1 (+ year 3760))))
@end example

@noindent
because Nisan is the first month in the Hebrew calendar and the Hebrew
year differs from the Gregorian year by 3760 at Nisan.

  If there is no daylight savings time at your location, or if you want
all times in standard time, set @code{calendar-daylight-savings-starts}
and @code{calendar-daylight-savings-ends} to @code{nil}.

@vindex calendar-daylight-time-offset
  The variable @code{calendar-daylight-time-offset} specifies the
difference between daylight savings time and standard time, measured in
minutes.  The value for Cambridge is 60.

@vindex calendar-daylight-savings-starts-time
@vindex calendar-daylight-savings-ends-time
  The variable @code{calendar-daylight-savings-starts-time} and the
variable @code{calendar-daylight-savings-ends-time} specify the number
of minutes after midnight local time when the transition to and from
daylight savings time should occur.  For Cambridge, both variables'
values are 120.

@node Diary Customizing
@section Customizing the Diary

@vindex holidays-in-diary-buffer
  Ordinarily, the mode line of the diary buffer window indicates any
holidays that fall on the date of the diary entries.  The process of
checking for holidays can take several seconds, so including holiday
information delays the display of the diary buffer noticeably.  If you'd
prefer to have a faster display of the diary buffer but without the
holiday information, set the variable @code{holidays-in-diary-buffer} to
@code{nil}.@refill

@vindex number-of-diary-entries
  The variable @code{number-of-diary-entries} controls the number of
days of diary entries to be displayed at one time.  It affects the
initial display when @code{view-diary-entries-initially} is @code{t}, as
well as the command @kbd{M-x diary}.  For example, the default value is
1, which says to display only the current day's diary entries.  If the
value is 2, both the current day's and the next day's entries are
displayed.  The value can also be a vector of seven elements: for
example, if the value is @code{[0 2 2 2 2 4 1]} then no diary entries
appear on Sunday, the current date's and the next day's diary entries
appear Monday through Thursday, Friday through Monday's entries appear
on Friday, while on Saturday only that day's entries appear.

@vindex print-diary-entries-hook
@findex print-diary-entries
  The variable @code{print-diary-entries-hook} is a normal hook run
after preparation of a temporary buffer containing just the diary
entries currently visible in the diary buffer.  (The other, irrelevant
diary entries are really absent from the temporary buffer; in the diary
buffer, they are merely hidden.)  The default value of this hook does
the printing with the command @code{lpr-buffer}.  If you want to use a
different command to do the printing, just change the value of this
hook.  Other uses might include, for example, rearranging the lines into
order by day and time.

@vindex diary-date-forms
  You can customize the form of dates in your diary file, if neither the
standard American nor European styles suits your needs, by setting the
variable @code{diary-date-forms}.  This variable is a list of patterns
for recognizing a date.  Each date pattern is a list whose elements may
be regular expressions (@pxref{Regular Expressions,,, elisp, the Emacs
Lisp Reference Manual}) or the symbols @code{month}, @code{day},
@code{year}, @code{monthname}, and @code{dayname}.  All these elements
serve as patterns that match certain kinds of text in the diary file.
In order for the date pattern, as a whole, to match, all of its elements
must match consecutively.

  A regular expression in a date pattern matches in its usual fashion,
using the standard syntax table altered so that @samp{*} is a word
constituent.

  The symbols @code{month}, @code{day}, @code{year}, @code{monthname},
and @code{dayname} match the month number, day number, year number,
month name, and day name of the date being considered.  The symbols that
match numbers allow leading zeros; those that match names allow
three-letter abbreviations and capitalization.  All the symbols can
match @samp{*}; since @samp{*} in a diary entry means ``any day'', ``any
month'', and so on, it should match regardless of the date being
considered.

  The default value of @code{diary-date-forms} in the American style is
this:

@example
((month "/" day "[^/0-9]")
 (month "/" day "/" year "[^0-9]")
 (monthname " *" day "[^,0-9]")
 (monthname " *" day ", *" year "[^0-9]")
 (dayname "\\W"))
@end example

  The date patterns in the list must be @emph{mutually exclusive} and
must not match any portion of the diary entry itself, just the date and
one character of whitespace.  If, to be mutually exclusive, the pattern
must match a portion of the diary entry text---beyond the whitespace
that ends the date---then the first element of the date pattern
@emph{must} be @code{backup}.  This causes the date recognizer to back
up to the beginning of the current word of the diary entry, after
finishing the match.  Even if you use @code{backup}, the date pattern
must absolutely not match more than a portion of the first word of the
diary entry.  The default value of @code{diary-date-forms} in the
European style is this list:

@example
((day "/" month "[^/0-9]")
 (day "/" month "/" year "[^0-9]")
 (backup day " *" monthname "\\W+\\<[^*0-9]")
 (day " *" monthname " *" year "[^0-9]")
 (dayname "\\W"))
@end example

@noindent
Notice the use of @code{backup} in the third pattern, because it needs
to match part of a word beyond the date itself to distinguish it from
the fourth pattern.

@node Hebrew/Islamic Entries
@section Hebrew- and Islamic-Date Diary Entries

  Your diary file can have entries based on Hebrew or Islamic dates, as
well as entries based on the world-standard Gregorian calendar.
However, because recognition of such entries is time-consuming and most
people don't use them, you must explicitly enable their use.  If you
want the diary to recognize Hebrew-date diary entries, for example,
you must do this:

@vindex nongregorian-diary-listing-hook
@vindex nongregorian-diary-marking-hook
@findex list-hebrew-diary-entries
@findex mark-hebrew-diary-entries
@smallexample
(add-hook 'nongregorian-diary-listing-hook 'list-hebrew-diary-entries)
(add-hook 'nongregorian-diary-marking-hook 'mark-hebrew-diary-entries)
@end smallexample

@noindent
If you want Islamic-date entries, do this:

@findex list-islamic-diary-entries
@findex mark-islamic-diary-entries
@smallexample
(add-hook 'nongregorian-diary-listing-hook 'list-islamic-diary-entries)
(add-hook 'nongregorian-diary-marking-hook 'mark-islamic-diary-entries)
@end smallexample

  Hebrew- and Islamic-date diary entries have the same formats as
Gregorian-date diary entries, except that @samp{H} precedes a Hebrew
date and @samp{I} precedes an Islamic date.  Moreover, because the
Hebrew and Islamic month names are not uniquely specified by the first
three letters, you may not abbreviate them.  For example, a diary entry
for the Hebrew date Heshvan 25 could look like this:

@smallexample
HHeshvan 25 Happy Hebrew birthday!
@end smallexample

@noindent
and would appear in the diary for any date that corresponds to Heshvan 25
on the Hebrew calendar.  And here is an Islamic-date diary entry that matches
Dhu al-Qada 25:

@smallexample
IDhu al-Qada 25 Happy Islamic birthday!
@end smallexample

  As with Gregorian-date diary entries, Hebrew- and Islamic-date entries
are nonmarking if they are preceded with an ampersand (@samp{&}).

  Here is a table of commands used in the calendar to create diary entries
that match the selected date and other dates that are similar in the Hebrew
or Islamic calendar:

@table @kbd
@item i h d
Add a diary entry for the Hebrew date corresponding to the selected date
(@code{insert-hebrew-diary-entry}).
@item i h m
Add a diary entry for the day of the Hebrew month corresponding to the
selected date (@code{insert-monthly-hebrew-diary-entry}).  This diary
entry matches any date that has the same Hebrew day-within-month as the
selected date.
@item i h y
Add a diary entry for the day of the Hebrew year corresponding to the
selected date (@code{insert-yearly-hebrew-diary-entry}).  This diary
entry matches any date which has the same Hebrew month and day-within-month
as the selected date.
@item i i d
Add a diary entry for the Islamic date corresponding to the selected date
(@code{insert-islamic-diary-entry}).
@item i i m
Add a diary entry for the day of the Islamic month corresponding to the
selected date (@code{insert-monthly-islamic-diary-entry}).
@item i i y
Add a diary entry for the day of the Islamic year corresponding to the
selected date (@code{insert-yearly-islamic-diary-entry}).
@end table

@findex insert-hebrew-diary-entry
@findex insert-monthly-hebrew-diary-entry
@findex insert-yearly-hebrew-diary-entry
@findex insert-islamic-diary-entry
@findex insert-monthly-islamic-diary-entry
@findex insert-yearly-islamic-diary-entry
  These commands work much like the corresponding commands for ordinary
diary entries: they apply to the date that point is on in the calendar
window, and what they do is insert just the date portion of a diary entry
at the end of your diary file.  You must then insert the rest of the
diary entry.

@node Fancy Diary Display
@section Fancy Diary Display
@vindex diary-display-hook
@findex simple-diary-display

  Diary display works by preparing the diary buffer and then running the
hook @code{diary-display-hook}.  The default value of this hook
(@code{simple-diary-display}) hides the irrelevant diary entries and
then displays the buffer.  However, if you specify the hook as follows,

@cindex diary buffer
@findex fancy-diary-display
@example
(add-hook 'diary-display-hook 'fancy-diary-display)
@end example

@noindent
this enables fancy diary display.  It displays diary entries and
holidays by copying them into a special buffer that exists only for the
sake of display.  Copying to a separate buffer provides an opportunity
to change the displayed text to make it prettier---for example, to sort
the entries by the dates they apply to.

  As with simple diary display, you can print a hard copy of the buffer
with @code{print-diary-entries}.  To print a hard copy of a day-by-day
diary for a week, position point on Sunday of that week, type
@kbd{7 d}, and then do @kbd{M-x print-diary-entries}.  As usual, the
inclusion of the holidays slows down the display slightly; you can speed
things up by setting the variable @code{holidays-in-diary-buffer} to
@code{nil}.

@vindex diary-list-include-blanks
  Ordinarily, the fancy diary buffer does not show days for which there are
no diary entries, even if that day is a holiday.  If you want such days to be
shown in the fancy diary buffer, set the variable
@code{diary-list-include-blanks} to @code{t}.@refill

@cindex sorting diary entries
  If you use the fancy diary display, you can use the normal hook
@code{list-diary-entries-hook} to sort each day's diary entries by their
time of day.  Here's how:

@findex sort-diary-entries
@example
(add-hook 'list-diary-entries-hook 'sort-diary-entries t)
@end example

@noindent
For each day, this sorts diary entries that begin with a recognizable
time of day according to their times.  Diary entries without times come
first within each day.

  Fancy diary display also has the ability to process included diary
files.  This permits a group of people to share a diary file for events
that apply to all of them.  Lines in the diary file of this form:

@smallexample
#include "@var{filename}"
@end smallexample

@noindent
includes the diary entries from the file @var{filename} in the fancy
diary buffer.  The include mechanism is recursive, so that included files
can include other files, and so on; you must be careful not to have a
cycle of inclusions, of course.  Here is how to enable the include
facility:

@vindex list-diary-entries-hook
@vindex mark-diary-entries-hook
@findex include-other-diary-files
@findex mark-included-diary-files
@smallexample
(add-hook 'list-diary-entries-hook 'include-other-diary-files)
(add-hook 'mark-diary-entries-hook 'mark-included-diary-files)
@end smallexample

The include mechanism works only with the fancy diary display, because
ordinary diary display shows the entries directly from your diary file.

@node Sexp Diary Entries
@section Sexp Entries and the Fancy Diary Display
@cindex sexp diary entries

  Sexp diary entries allow you to do more than just have complicated
conditions under which a diary entry applies.  If you use the fancy
diary display, sexp entries can generate the text of the entry depending
on the date itself.  For example, an anniversary diary entry can insert
the number of years since the anniversary date into the text of the
diary entry.  Thus the @samp{%d} in this dairy entry:

@findex diary-anniversary
@smallexample
%%(diary-anniversary 10 31 1948) Arthur's birthday (%d years old)
@end smallexample

@noindent
gets replaced by the age, so on October 31, 1990 the entry appears in
the fancy diary buffer like this:

@smallexample
Arthur's birthday (42 years old)
@end smallexample

@noindent
If the diary file instead contains this entry:

@smallexample
%%(diary-anniversary 10 31 1948) Arthur's %d%s birthday
@end smallexample

@noindent
the entry in the fancy diary buffer for October 31, 1990 appears like this:

@smallexample
Arthur's 42nd birthday
@end smallexample

  Similarly, cyclic diary entries can interpolate the number of repetitions
that have occurred:

@findex diary-cyclic
@smallexample
%%(diary-cyclic 50 1 1 1990) Renew medication (%d%s time)
@end smallexample

@noindent
looks like this:

@smallexample
Renew medication (5th time)
@end smallexample

@noindent
in the fancy diary display on September 8, 1990.

  There is an early reminder diary sexp that includes its entry in the
diary not only on the date of occurrence, but also on earlier dates.
For example, if you want a reminder a week before your anniversary, you
can use

@findex diary-remind
@smallexample
%%(diary-remind '(diary-anniversary 12 22 1968) 7) Ed's anniversary
@end smallexample

@noindent
and the fancy diary will show
@smallexample
Ed's anniversary
@end smallexample
@noindent
both on December 15 and on December 22.

@findex diary-date
  The function @code{diary-date} applies to dates described by a month,
day, year combination, each of which can be an integer, a list of
integers, or @code{t}. The value @code{t} means all values.  For
example,

@smallexample
%%(diary-date '(10 11 12) 22 t) Rake leaves
@end smallexample

@noindent
causes the fancy diary to show

@smallexample
Rake leaves
@end smallexample

@noindent
on October 22, November 22, and December 22 of every year.

@findex diary-float
  The function @code{diary-float} allows you to describe diary entries
that apply to dates like the third Friday of November, or the last
Tuesday in April.  The parameters are the @var{month}, @var{dayname},
and an index @var{n}. The entry appears on the @var{n}th @var{dayname}
of @var{month}, where @var{dayname}=0 means Sunday, 1 means Monday, and
so on.  If @var{n} is negative it counts backward from the end of
@var{month}.  The value of @var{month} can be a list of months, a single
month, or @code{t} to specify all months.  You can also use an optional
parameter @var{day} to specify the @var{n}th @var{dayname} of
@var{month} on or after/before @var{day}; the value of @var{day} defaults
to 1 if @var{n} is positive and to the last day of @var{month} if
@var{n} is negative.  For example,

@smallexample
%%(diary-float t 1 -1) Pay rent
@end smallexample

@noindent
causes the fancy diary to show

@smallexample
Pay rent
@end smallexample

@noindent
on the last Monday of every month.

  The generality of sexp diary entries lets you specify any diary
entry that you can describe algorithmically.  A sexp diary entry
contains an expression that computes whether the entry applies to any
given date.  If its value is non-@code{nil}, the entry applies to that
date; otherwise, it does not.  The expression can use the variable
@code{date} to find the date being considered; its value is a list
(@var{month} @var{day} @var{year}) that refers to the Gregorian
calendar.

  The sexp diary entry applies to a date when the expression's value
is non-@code{nil}, but some values have more specific meanings.  If
the value is a string, that string is a description of the event which
occurs on that date.  The value can also have the form
@code{(@var{mark} . @var{string})}; then @var{mark} specifies how to
mark the date in the calendar, and @var{string} is the description of
the event.  If @var{mark} is a single-character string, that character
appears next to the date in the calendar.  If @var{mark} is a face
name, the date is displayed in that face.  If @var{mark} is
@code{nil}, that specifies no particular highlighting for the date.

  Suppose you get paid on the 21st of the month if it is a weekday, and
on the Friday before if the 21st is on a weekend.  Here is how to write
a sexp diary entry that matches those dates:

@smallexample
&%%(let ((dayname (calendar-day-of-week date))
         (day (car (cdr date))))
      (or (and (= day 21) (memq dayname '(1 2 3 4 5)))
          (and (memq day '(19 20)) (= dayname 5)))
         ) Pay check deposited
@end smallexample

  The following sexp diary entries take advantage of the ability (in the fancy
diary display) to concoct diary entries whose text varies based on the date:

@findex diary-sunrise-sunset
@findex diary-phases-of-moon
@findex diary-day-of-year
@findex diary-iso-date
@findex diary-julian-date
@findex diary-astro-day-number
@findex diary-hebrew-date
@findex diary-islamic-date
@findex diary-french-date
@findex diary-mayan-date
@table @code
@item %%(diary-sunrise-sunset)
Make a diary entry for the local times of today's sunrise and sunset.
@item %%(diary-phases-of-moon)
Make a diary entry for the phases (quarters) of the moon.
@item %%(diary-day-of-year)
Make a diary entry with today's day number in the current year and the number
of days remaining in the current year.
@item %%(diary-iso-date)
Make a diary entry with today's equivalent ISO commercial date.
@item %%(diary-julian-date)
Make a diary entry with today's equivalent date on the Julian calendar.
@item %%(diary-astro-day-number)
Make a diary entry with today's equivalent astronomical (Julian) day number.
@item %%(diary-hebrew-date)
Make a diary entry with today's equivalent date on the Hebrew calendar.
@item %%(diary-islamic-date)
Make a diary entry with today's equivalent date on the Islamic calendar.
@item %%(diary-french-date)
Make a diary entry with today's equivalent date on the French Revolutionary
calendar.
@item %%(diary-mayan-date)
Make a diary entry with today's equivalent date on the Mayan calendar.
@end table

@noindent
Thus including the diary entry

@example
&%%(diary-hebrew-date)
@end example

@noindent
causes every day's diary display to contain the equivalent date on the
Hebrew calendar, if you are using the fancy diary display.  (With simple
diary display, the line @samp{&%%(diary-hebrew-date)} appears in the
diary for any date, but does nothing particularly useful.)

  These functions can be used to construct sexp diary entries based on
the Hebrew calendar in certain standard ways:

@cindex rosh hodesh
@findex diary-rosh-hodesh
@cindex parasha, weekly
@findex diary-parasha
@cindex candle lighting times
@findex diary-sabbath-candles
@cindex omer count
@findex diary-omer
@cindex yahrzeits
@findex diary-yahrzeit
@table @code
@item %%(diary-rosh-hodesh)
Make a diary entry that tells the occurrence and ritual announcement of each
new Hebrew month.
@item %%(diary-parasha)
Make a Saturday diary entry that tells the weekly synagogue scripture reading.
@item %%(diary-sabbath-candles)
Make a Friday diary entry that tells the @emph{local time} of Sabbath
candle lighting.
@item %%(diary-omer)
Make a diary entry that gives the omer count, when appropriate.
@item %%(diary-yahrzeit @var{month} @var{day} @var{year}) @var{name}
Make a diary entry marking the anniversary of a date of death.  The date
is the @emph{Gregorian} (civil) date of death.  The diary entry appears
on the proper Hebrew calendar anniversary and on the day before.  (In
the European style, the order of the parameters is changed to @var{day},
@var{month}, @var{year}.)
@end table

  All the functions documented above take an optional argument
@var{mark} which specifies how to mark the date in the calendar display.
If one of these functions decides that it applies to a certain date,
it returns a value that contains @var{mark}.


@node Index
@unnumbered Index

@printindex cp

@bye

@ignore
   arch-tag: 75c33f13-32c6-41b6-9537-847a312e2e49
@end ignore