Port to stricter C99

[emacs.git] / doc / emacs / calendar.texi

@c This is part of the Emacs manual.  -*- coding: utf-8 -*-
@c Copyright (C) 1985-1987, 1993-1995, 1997, 2000-2015 Free Software
@c Foundation, Inc.
@c See file emacs.texi for copying conditions.
@node Calendar/Diary
@chapter The Calendar and the Diary
@cindex calendar
@findex calendar

  Emacs provides the functions of a desk calendar, with a diary of
planned or past events.  It also has facilities for managing your
appointments, and keeping track of how much time you spend working on
certain projects.

  To enter the calendar, type @kbd{M-x calendar}; this displays a
three-month calendar centered on the current month, with point on the
current date.  With a numeric argument, as in @kbd{C-u M-x calendar}, it
prompts you for the month and year to be the center of the three-month
calendar.  The calendar uses its own buffer, whose major mode is
Calendar mode.

  @kbd{Mouse-3} in the calendar brings up a menu of operations on a
particular date; @kbd{Mouse-2} brings up a menu of commonly used
calendar features that are independent of any particular date.  To exit
the calendar, type @kbd{q}.

@iftex
  This chapter describes the basic calendar features.
For more advanced topics,
@pxref{Advanced Calendar/Diary Usage,,, emacs-xtra, Specialized Emacs Features}.
@end iftex

@menu
* Calendar Motion::     Moving through the calendar; selecting a date.
* Scroll Calendar::     Bringing earlier or later months onto the screen.
* Counting Days::       How many days are there between two dates?
* General Calendar::    Exiting or recomputing the calendar.
* Writing Calendar Files:: Writing calendars to files of various formats.
* Holidays::            Displaying dates of holidays.
* Sunrise/Sunset::      Displaying local times of sunrise and sunset.
* Lunar Phases::        Displaying phases of the moon.
* Other Calendars::     Converting dates to other calendar systems.
* Diary::               Displaying events from your diary.
* Appointments::        Reminders when it's time to do something.
* Importing Diary::     Converting diary events to/from other formats.
* Daylight Saving::     How to specify when daylight saving time is active.
* Time Intervals::      Keeping track of time intervals.
@ifnottex
* Advanced Calendar/Diary Usage:: Advanced Calendar/Diary customization.
@end ifnottex
@end menu

@node Calendar Motion
@section Movement in the Calendar

@cindex moving inside the calendar
  Calendar mode provides commands to move through the calendar in
logical units of time such as days, weeks, months, and years.  If you
move outside the three months originally displayed, the calendar
display ``scrolls'' automatically through time to make the selected
date visible.  Moving to a date lets you view its holidays or diary
entries, or convert it to other calendars; moving by long time periods
is also useful simply to scroll the calendar.

@menu
* Calendar Unit Motion::      Moving by days, weeks, months, and years.
* Move to Beginning or End::  Moving to start/end of weeks, months, and years.
* Specified Dates::           Moving to the current date or another
                                specific date.
@end menu

@node Calendar Unit Motion
@subsection Motion by Standard Lengths of Time

  The commands for movement in the calendar buffer parallel the
commands for movement in text.  You can move forward and backward by
days, weeks, months, and years.

@table @kbd
@item C-f
Move point one day forward (@code{calendar-forward-day}).
@item C-b
Move point one day backward (@code{calendar-backward-day}).
@item C-n
Move point one week forward (@code{calendar-forward-week}).
@item C-p
Move point one week backward (@code{calendar-backward-week}).
@item M-@}
Move point one month forward (@code{calendar-forward-month}).
@item M-@{
Move point one month backward (@code{calendar-backward-month}).
@item C-x ]
Move point one year forward (@code{calendar-forward-year}).
@item C-x [
Move point one year backward (@code{calendar-backward-year}).
@end table

@kindex C-f @r{(Calendar mode)}
@findex calendar-forward-day
@kindex C-b @r{(Calendar mode)}
@findex calendar-backward-day
@kindex C-n @r{(Calendar mode)}
@findex calendar-forward-week
@kindex C-p @r{(Calendar mode)}
@findex calendar-backward-week
  The day and week commands are natural analogues of the usual Emacs
commands for moving by characters and by lines.  Just as @kbd{C-n}
usually moves to the same column in the following line, in Calendar
mode it moves to the same day in the following week.  And @kbd{C-p}
moves to the same day in the previous week.

  The arrow keys are equivalent to @kbd{C-f}, @kbd{C-b}, @kbd{C-n} and
@kbd{C-p}, just as they normally are in other modes.

@kindex M-@} @r{(Calendar mode)}
@findex calendar-forward-month
@kindex M-@{ @r{(Calendar mode)}
@findex calendar-backward-month
@kindex C-x ] @r{(Calendar mode)}
@findex calendar-forward-year
@kindex C-x [ @r{(Calendar mode)}
@findex calendar-forward-year
  The commands for motion by months and years work like those for
weeks, but move a larger distance.  The month commands @kbd{M-@}} and
@kbd{M-@{} move forward or backward by an entire month.  The year
commands @kbd{C-x ]} and @w{@kbd{C-x [}} move forward or backward a
whole year.

  The easiest way to remember these commands is to consider months and
years analogous to paragraphs and pages of text, respectively.  But
the commands themselves are not quite analogous.  The ordinary Emacs
paragraph commands move to the beginning or end of a paragraph,
whereas these month and year commands move by an entire month or an
entire year, keeping the same date within the month or year.

  All these commands accept a numeric argument as a repeat count.
For convenience, the digit keys and the minus sign specify numeric
arguments in Calendar mode even without the Meta modifier.  For example,
@kbd{100 C-f} moves point 100 days forward from its present location.

@node Move to Beginning or End
@subsection Beginning or End of Week, Month or Year

  A week (or month, or year) is not just a quantity of days; we think of
weeks (months, years) as starting on particular dates.  So Calendar mode
provides commands to move to the start or end of a week, month or year:

@table @kbd
@kindex C-a @r{(Calendar mode)}
@findex calendar-beginning-of-week
@item C-a
Move point to start of week (@code{calendar-beginning-of-week}).
@kindex C-e @r{(Calendar mode)}
@findex calendar-end-of-week
@item C-e
Move point to end of week (@code{calendar-end-of-week}).
@kindex M-a @r{(Calendar mode)}
@findex calendar-beginning-of-month
@item M-a
Move point to start of month (@code{calendar-beginning-of-month}).
@kindex M-e @r{(Calendar mode)}
@findex calendar-end-of-month
@item M-e
Move point to end of month (@code{calendar-end-of-month}).
@kindex M-< @r{(Calendar mode)}
@findex calendar-beginning-of-year
@item M-<
Move point to start of year (@code{calendar-beginning-of-year}).
@kindex M-> @r{(Calendar mode)}
@findex calendar-end-of-year
@item M->
Move point to end of year (@code{calendar-end-of-year}).
@end table

  These commands also take numeric arguments as repeat counts, with the
repeat count indicating how many weeks, months, or years to move
backward or forward.

@vindex calendar-week-start-day
@cindex weeks, which day they start on
@cindex calendar, first day of week
  By default, weeks begin on Sunday.  To make them begin on Monday
instead, set the variable @code{calendar-week-start-day} to 1.

@node Specified Dates
@subsection Specified Dates

  Calendar mode provides commands for moving to a particular date
specified in various ways.

@table @kbd
@item g d
Move point to specified date (@code{calendar-goto-date}).
@item g D
Move point to specified day of year (@code{calendar-goto-day-of-year}).
@item g w
Move point to specified week of year (@code{calendar-iso-goto-week}).
@item o
Center calendar around specified month (@code{calendar-other-month}).
@item .
Move point to today's date (@code{calendar-goto-today}).
@end table

@kindex g d @r{(Calendar mode)}
@findex calendar-goto-date
  @kbd{g d} (@code{calendar-goto-date}) prompts for a year, a month, and a day
of the month, and then moves to that date.  Because the calendar includes all
dates from the beginning of the current era, you must type the year in its
entirety; that is, type @samp{2010}, not @samp{10}.

@kindex g D @r{(Calendar mode)}
@findex calendar-goto-day-of-year
@kindex g w @r{(Calendar mode)}
@findex calendar-iso-goto-week
  @kbd{g D} (@code{calendar-goto-day-of-year}) prompts for a year and
day number, and moves to that date.  Negative day numbers count
backward from the end of the year.  @kbd{g w}
(@code{calendar-iso-goto-week}) prompts for a year and week number,
and moves to that week.

@kindex o @r{(Calendar mode)}
@findex calendar-other-month
  @kbd{o} (@code{calendar-other-month}) prompts for a month and year,
then centers the three-month calendar around that month.

@kindex . @r{(Calendar mode)}
@findex calendar-goto-today
  You can return to today's date with @kbd{.}@:
(@code{calendar-goto-today}).

@node Scroll Calendar
@section Scrolling in the Calendar

@cindex scrolling in the calendar
  The calendar display scrolls automatically through time when you
move out of the visible portion.  You can also scroll it manually.
Imagine that the calendar window contains a long strip of paper with
the months on it.  Scrolling the calendar means moving the strip
horizontally, so that new months become visible in the window.

@table @kbd
@item >
Scroll calendar one month forward (@code{calendar-scroll-left}).
@item <
Scroll calendar one month backward (@code{calendar-scroll-right}).
@item C-v
@itemx @key{next}
Scroll forward by three months (@code{calendar-scroll-left-three-months}).
@item M-v
@itemx @key{prior}
Scroll backward by three months (@code{calendar-scroll-right-three-months}).
@end table

@kindex > @r{(Calendar mode)}
@findex calendar-scroll-left
@kindex < @r{(Calendar mode)}
@findex calendar-scroll-right
  The most basic calendar scroll commands scroll by one month at a
time.  This means that there are two months of overlap between the
display before the command and the display after.  @kbd{>} scrolls the
calendar contents one month forward in time.  @kbd{<} scrolls the
contents one month backwards in time.

@kindex C-v @r{(Calendar mode)}
@findex calendar-scroll-left-three-months
@kindex M-v @r{(Calendar mode)}
@findex calendar-scroll-right-three-months
  The commands @kbd{C-v} and @kbd{M-v} scroll the calendar by an entire
``screenful''---three months---in analogy with the usual meaning of
these commands.  @kbd{C-v} makes later dates visible and @kbd{M-v} makes
earlier dates visible.  These commands take a numeric argument as a
repeat count; in particular, since @kbd{C-u} multiplies the next command
by four, typing @kbd{C-u C-v} scrolls the calendar forward by a year and
typing @kbd{C-u M-v} scrolls the calendar backward by a year.

  The function keys @key{next} and @key{prior} are equivalent to
@kbd{C-v} and @kbd{M-v}, just as they are in other modes.

@node Counting Days
@section Counting Days

@table @kbd
@item M-=
Display the number of days in the current region
(@code{calendar-count-days-region}).
@end table

@kindex M-= @r{(Calendar mode)}
@findex calendar-count-days-region
  To determine the number of days in a range, set the mark on one
date using @kbd{C-@key{SPC}}, move point to another date, and type @kbd{M-=}
(@code{calendar-count-days-region}).  The numbers of days shown is
@emph{inclusive}; that is, it includes the days specified by mark and
point.

@node General Calendar
@section Miscellaneous Calendar Commands

@table @kbd
@item p d
Display day-in-year (@code{calendar-print-day-of-year}).
@item C-c C-l
Regenerate the calendar window (@code{calendar-redraw}).
@item @key{SPC}
Scroll the next window up (@code{scroll-other-window}).
@item @key{DEL}
@itemx S-@key{SPC}
Scroll the next window down (@code{scroll-other-window-down}).
@item q
Exit from calendar (@code{calendar-exit}).
@end table

@kindex p d @r{(Calendar mode)}
@cindex day of year
@findex calendar-print-day-of-year
  To display the number of days elapsed since the start of the year, or
the number of days remaining in the year, type the @kbd{p d} command
(@code{calendar-print-day-of-year}).  This displays both of those
numbers in the echo area.  The count of days elapsed includes the
selected date.  The count of days remaining does not include that
date.

@kindex C-c C-l @r{(Calendar mode)}
@findex calendar-redraw
  If the calendar window text gets corrupted, type @kbd{C-c C-l}
(@code{calendar-redraw}) to redraw it.  (This can only happen if you use
non-Calendar-mode editing commands.)

@kindex SPC @r{(Calendar mode)}
  In Calendar mode, you can use @key{SPC} (@code{scroll-other-window})
and @key{DEL} (@code{scroll-other-window-down}) to scroll the other
window (if there is one) up or down, respectively.  This is handy when
you display a list of holidays or diary entries in another window.

@kindex q @r{(Calendar mode)}
@findex exit-calendar
@vindex calendar-remove-frame-by-deleting
  To exit from the calendar, type @kbd{q} (@code{calendar-exit}).  This
buries all buffers related to the calendar, selecting other buffers.
(If a frame contains a dedicated calendar window, exiting from the
calendar deletes or iconifies that frame depending on the value of
@code{calendar-remove-frame-by-deleting}.)

@c FIXME this mentions holidays and diary entries, albeit briefly, so
@c should it be moved after those sections?  Or at least xref them.
@node Writing Calendar Files
@section Writing Calendar Files

  You can write calendars and diary entries to HTML and @LaTeX{} files.

@cindex calendar and HTML
  The Calendar HTML commands produce files of HTML code that contain
calendar, holiday, and diary entries.  Each file applies to one month,
and has a name of the format @file{@var{yyyy}-@var{mm}.html}, where
@var{yyyy} and @var{mm} are the four-digit year and two-digit month,
respectively.  The variable @code{cal-html-directory} specifies the
default output directory for the HTML files.  To prevent holidays
from being shown, customize @code{cal-html-holidays}.

@vindex cal-html-css-default
  Diary entries enclosed by @code{<} and @code{>} are interpreted as
HTML tags (for example: this is a diary entry with <font
color=''red''>some red text</font>).  You can change the overall
appearance of the displayed HTML pages (for example, the color of
various page elements, header styles) via a stylesheet @file{cal.css} in
the directory containing the HTML files (see the value of the variable
@code{cal-html-css-default} for relevant style settings).

@kindex t @r{(Calendar mode)}
@table @kbd
@item H m
Generate a one-month calendar (@code{cal-html-cursor-month}).
@item H y
Generate a calendar file for each month of a year, as well as an index
page (@code{cal-html-cursor-year}).  By default, this command writes
files to a @var{yyyy} subdirectory---if this is altered some hyperlinks
between years will not work.
@end table

  If the variable @code{cal-html-print-day-number-flag} is
non-@code{nil}, then the monthly calendars show the day-of-the-year
number.  The variable @code{cal-html-year-index-cols} specifies the
number of columns in the yearly index page.

@cindex calendar and @LaTeX{}
  The Calendar @LaTeX{} commands produce a buffer of @LaTeX{} code that
prints as a calendar.  Depending on the command you use, the printed
calendar covers the day, week, month or year that point is in.

@kindex t @r{(Calendar mode)}
@table @kbd
@item t m
Generate a one-month calendar (@code{cal-tex-cursor-month}).
@item t M
Generate a sideways-printing one-month calendar
(@code{cal-tex-cursor-month-landscape}).
@item t d
Generate a one-day calendar
(@code{cal-tex-cursor-day}).
@item t w 1
Generate a one-page calendar for one week, with hours
(@code{cal-tex-cursor-week}).
@item t w 2
Generate a two-page calendar for one week, with hours
(@code{cal-tex-cursor-week2}).
@item t w 3
Generate an ISO-style calendar for one week, without hours
(@code{cal-tex-cursor-week-iso}).
@item t w 4
Generate a calendar for one Monday-starting week, with hours
(@code{cal-tex-cursor-week-monday}).
@item t w W
Generate a two-page calendar for one week, without hours
(@code{cal-tex-cursor-week2-summary}).
@item t f w
Generate a Filofax-style two-weeks-at-a-glance calendar
(@code{cal-tex-cursor-filofax-2week}).
@item t f W
Generate a Filofax-style one-week-at-a-glance calendar
(@code{cal-tex-cursor-filofax-week}).
@item t y
Generate a calendar for one year
(@code{cal-tex-cursor-year}).
@item t Y
Generate a sideways-printing calendar for one year
(@code{cal-tex-cursor-year-landscape}).
@item t f y
Generate a Filofax-style calendar for one year
(@code{cal-tex-cursor-filofax-year}).
@end table

  Some of these commands print the calendar sideways (in ``landscape
mode''), so it can be wider than it is long.  Some of them use Filofax
paper size (3.75in x 6.75in).  All of these commands accept a prefix
argument, which specifies how many days, weeks, months or years to print
(starting always with the selected one).

  If the variable @code{cal-tex-holidays} is non-@code{nil} (the default),
then the printed calendars show the holidays in @code{calendar-holidays}.
If the variable @code{cal-tex-diary} is non-@code{nil} (the default is
@code{nil}), diary entries are included also (in monthly, filofax, and
iso-week calendars only).  If the variable @code{cal-tex-rules} is
non-@code{nil} (the default is @code{nil}), the calendar displays ruled
pages in styles that have sufficient room.  Consult the documentation of
the individual cal-tex functions to see which calendars support which
features.

  You can use the variable @code{cal-tex-preamble-extra} to insert extra
@LaTeX{} commands in the preamble of the generated document if you need
to.

@node Holidays
@section Holidays
@cindex holidays

  The Emacs calendar knows about many major and minor holidays,
and can display them.  You can add your own holidays to the default list.

@table @kbd
@item Mouse-3 Holidays
@itemx h
Display holidays for the selected date
(@code{calendar-cursor-holidays}).
@item x
Mark holidays in the calendar window (@code{calendar-mark-holidays}).
@item u
Unmark calendar window (@code{calendar-unmark}).
@item a
List all holidays for the displayed three months in another window
(@code{calendar-list-holidays}).
@item M-x holidays
List all holidays for three months around today's date in another
window.
@item M-x list-holidays
List holidays in another window for a specified range of years.
@end table

@kindex h @r{(Calendar mode)}
@findex calendar-cursor-holidays
@vindex calendar-view-holidays-initially-flag
  To see if any holidays fall on a given date, position point on that
date in the calendar window and use the @kbd{h} command.  Alternatively,
click on that date with @kbd{Mouse-3} and then choose @kbd{Holidays}
from the menu that appears.  Either way, this displays the holidays for
that date, in the echo area if they fit there, otherwise in a separate
window.

@kindex x @r{(Calendar mode)}
@findex calendar-mark-holidays
@kindex u @r{(Calendar mode)}
@findex calendar-unmark
@vindex calendar-mark-holidays-flag
  To view the distribution of holidays for all the dates shown in the
calendar, use the @kbd{x} command.  This displays the dates that are
holidays in a different face.
@iftex
@xref{Calendar Customizing,,, emacs-xtra, Specialized Emacs Features}.
@end iftex
@ifnottex
@xref{Calendar Customizing, calendar-holiday-marker}.
@end ifnottex
  The command applies both to the currently visible months and to
other months that subsequently become visible by scrolling.  To turn
marking off and erase the current marks, type @kbd{u}, which also
erases any diary marks (@pxref{Diary}).  If the variable
@code{calendar-mark-holidays-flag} is non-@code{nil}, creating or
updating the calendar marks holidays automatically.

@kindex a @r{(Calendar mode)}
@findex calendar-list-holidays
  To get even more detailed information, use the @kbd{a} command, which
displays a separate buffer containing a list of all holidays in the
current three-month range.  You can use @key{SPC} and @key{DEL} in the
calendar window to scroll that list up and down, respectively.

@findex holidays
  The command @kbd{M-x holidays} displays the list of holidays for the
current month and the preceding and succeeding months; this works even
if you don't have a calendar window.  If the variable
@code{calendar-view-holidays-initially-flag} is non-@code{nil}, creating
the calendar displays holidays in this way.  If you want the list of
holidays centered around a different month, use @kbd{C-u M-x
holidays}, which prompts for the month and year.

  The holidays known to Emacs include United States holidays and the
major Bahá'í, Chinese, Christian, Islamic, and Jewish holidays; also the
solstices and equinoxes.

@findex list-holidays
   The command @kbd{M-x holiday-list} displays the list of holidays for
a range of years.  This function asks you for the starting and stopping
years, and allows you to choose all the holidays or one of several
categories of holidays.  You can use this command even if you don't have
a calendar window.

  The dates used by Emacs for holidays are based on @emph{current
practice}, not historical fact.  For example Veteran's Day began in
1919, but is shown in earlier years.

@node Sunrise/Sunset
@section Times of Sunrise and Sunset
@cindex sunrise and sunset

  Special calendar commands can tell you, to within a minute or two, the
times of sunrise and sunset for any date.

@table @kbd
@item Mouse-3 Sunrise/sunset
@itemx S
Display times of sunrise and sunset for the selected date
(@code{calendar-sunrise-sunset}).
@item M-x sunrise-sunset
Display times of sunrise and sunset for today's date.
@item C-u M-x sunrise-sunset
Display times of sunrise and sunset for a specified date.
@item M-x calendar-sunrise-sunset-month
Display times of sunrise and sunset for the selected month.
@end table

@kindex S @r{(Calendar mode)}
@findex calendar-sunrise-sunset
@findex sunrise-sunset
  Within the calendar, to display the @emph{local times} of sunrise and
sunset in the echo area, move point to the date you want, and type
@kbd{S}.  Alternatively, click @kbd{Mouse-3} on the date, then choose
@samp{Sunrise/sunset} from the menu that appears.  The command @kbd{M-x
sunrise-sunset} is available outside the calendar to display this
information for today's date or a specified date.  To specify a date
other than today, use @kbd{C-u M-x sunrise-sunset}, which prompts for
the year, month, and day.

  You can display the times of sunrise and sunset for any location and
any date with @kbd{C-u C-u M-x sunrise-sunset}.  This asks you for a
longitude, latitude, number of minutes difference from Coordinated
Universal Time, and date, and then tells you the times of sunrise and
sunset for that location on that date.

  Because the times of sunrise and sunset depend on the location on
earth, you need to tell Emacs your latitude, longitude, and location
name before using these commands.  Here is an example of what to set:

@vindex calendar-location-name
@vindex calendar-longitude
@vindex calendar-latitude
@example
(setq calendar-latitude 40.1)
(setq calendar-longitude -88.2)
(setq calendar-location-name "Urbana, IL")
@end example

@noindent
Use one decimal place in the values of @code{calendar-latitude} and
@code{calendar-longitude}.

  Your time zone also affects the local time of sunrise and sunset.
Emacs usually gets time zone information from the operating system, but
if these values are not what you want (or if the operating system does
not supply them), you must set them yourself.  Here is an example:

@vindex calendar-time-zone
@vindex calendar-standard-time-zone-name
@vindex calendar-daylight-time-zone-name
@example
(setq calendar-time-zone -360)
(setq calendar-standard-time-zone-name "CST")
(setq calendar-daylight-time-zone-name "CDT")
@end example

@noindent
The value of @code{calendar-time-zone} is the number of minutes
difference between your local standard time and Coordinated Universal
Time (Greenwich time).  The values of
@code{calendar-standard-time-zone-name} and
@code{calendar-daylight-time-zone-name} are the abbreviations used in
your time zone.  Emacs displays the times of sunrise and sunset
@emph{corrected for daylight saving time}.  @xref{Daylight Saving},
for how daylight saving time is determined.

  As a user, you might find it convenient to set the calendar location
variables for your usual physical location in your @file{.emacs} file.
If you are a system administrator, you may want to set these variables
for all users in a @file{default.el} file.  @xref{Init File}.

@node Lunar Phases
@section Phases of the Moon
@cindex phases of the moon
@cindex moon, phases of

  These calendar commands display the dates and times of the phases of
the moon (new moon, first quarter, full moon, last quarter).  This
feature is useful for debugging problems that ``depend on the phase of
the moon''.

@table @kbd
@item M
Display the dates and times for all the quarters of the moon for the
three-month period shown (@code{calendar-lunar-phases}).
@item M-x lunar-phases
Display dates and times of the quarters of the moon for three months around
today's date.
@end table

@kindex M @r{(Calendar mode)}
@findex calendar-lunar-phases
  Within the calendar, use the @kbd{M} command to display a separate
buffer of the phases of the moon for the current three-month range.  The
dates and times listed are accurate to within a few minutes.

@findex lunar-phases
  Outside the calendar, use the command @kbd{M-x lunar-phases} to
display the list of the phases of the moon for the current month and the
preceding and succeeding months.  For information about a different
month, use @kbd{C-u M-x lunar-phases}, which prompts for the month and
year.

  The dates and times given for the phases of the moon are given in
local time (corrected for daylight saving, when appropriate).
See the discussion in the previous section.  @xref{Sunrise/Sunset}.

@node Other Calendars
@section Conversion To and From Other Calendars

@cindex Gregorian calendar
  The Emacs calendar displayed is @emph{always} the Gregorian calendar,
sometimes called the ``new style'' calendar, which is used in most of
the world today.  However, this calendar did not exist before the
sixteenth century and was not widely used before the eighteenth century;
it did not fully displace the Julian calendar and gain universal
acceptance until the early twentieth century.  The Emacs calendar can
display any month since January, year 1 of the current era, but the
calendar displayed is always the Gregorian, even for a date at which
the Gregorian calendar did not exist.

  While Emacs cannot display other calendars, it can convert dates to
and from several other calendars.

@menu
* Calendar Systems::       The calendars Emacs understands
                             (aside from Gregorian).
* To Other Calendar::      Converting the selected date to various calendars.
* From Other Calendar::    Moving to a date specified in another calendar.
@end menu

@c FIXME perhaps most of the details should be moved to cal-xtra.
@c Just list the major supported systems here?
@node Calendar Systems
@subsection Supported Calendar Systems

@cindex ISO commercial calendar
  The ISO commercial calendar is often used in business.

@cindex Julian calendar
  The Julian calendar, named after Julius Caesar, was the one used in Europe
throughout medieval times, and in many countries up until the nineteenth
century.

@cindex Julian day numbers
@cindex astronomical day numbers
  Astronomers use a simple counting of days elapsed since noon, Monday,
January 1, 4713 B.C. on the Julian calendar.  The number of days elapsed
is called the @dfn{Julian day number} or the @dfn{Astronomical day number}.

@cindex Hebrew calendar
  The Hebrew calendar is used by tradition in the Jewish religion.  The
Emacs calendar program uses the Hebrew calendar to determine the dates
of Jewish holidays.  Hebrew calendar dates begin and end at sunset.

@cindex Islamic calendar
  The Islamic calendar is used in many predominantly Islamic countries.
Emacs uses it to determine the dates of Islamic holidays.  There is no
universal agreement in the Islamic world about the calendar; Emacs uses
a widely accepted version, but the precise dates of Islamic holidays
often depend on proclamation by religious authorities, not on
calculations.  As a consequence, the actual dates of observance can vary
slightly from the dates computed by Emacs.  Islamic calendar dates begin
and end at sunset.

@cindex French Revolutionary calendar
  The French Revolutionary calendar was created by the Jacobins after the 1789
revolution, to represent a more secular and nature-based view of the annual
cycle, and to install a 10-day week in a rationalization measure similar to
the metric system.  The French government officially abandoned this
calendar at the end of 1805.

@cindex Mayan calendar
  The Maya of Central America used three separate, overlapping calendar
systems, the @emph{long count}, the @emph{tzolkin}, and the @emph{haab}.
Emacs knows about all three of these calendars.  Experts dispute the
exact correlation between the Mayan calendar and our calendar; Emacs uses the
Goodman-Martinez-Thompson correlation in its calculations.

@cindex Coptic calendar
@cindex Ethiopic calendar
  The Copts use a calendar based on the ancient Egyptian solar calendar.
Their calendar consists of twelve 30-day months followed by an extra
five-day period.  Once every fourth year they add a leap day to this
extra period to make it six days.  The Ethiopic calendar is identical in
structure, but has different year numbers and month names.

@cindex Persian calendar
  The Persians use a solar calendar based on a design of Omar Khayyam.
Their calendar consists of twelve months of which the first six have 31
days, the next five have 30 days, and the last has 29 in ordinary years
and 30 in leap years.  Leap years occur in a complicated pattern every
four or five years.
The calendar implemented here is the arithmetical Persian calendar
championed by Birashk, based on a 2,820-year cycle.  It differs from
the astronomical Persian calendar, which is based on astronomical
events.  As of this writing the first future discrepancy is projected
to occur on March 20, 2025.  It is currently not clear what the
official calendar of Iran will be at that time.
@c FIXME not so far in the future now.

@cindex Chinese calendar
  The Chinese calendar is a complicated system of lunar months arranged
into solar years.  The years go in cycles of sixty, each year containing
either twelve months in an ordinary year or thirteen months in a leap
year; each month has either 29 or 30 days.  Years, ordinary months, and
days are named by combining one of ten ``celestial stems'' with one of
twelve ``terrestrial branches'' for a total of sixty names that are
repeated in a cycle of sixty.

@cindex Bahá'í calendar
  The Bahá'í calendar system is based on a solar cycle of 19 months with
19 days each.  The four remaining ``intercalary'' days are placed
between the 18th and 19th months.

@node To Other Calendar
@subsection Converting To Other Calendars

  The following commands describe the selected date (the date at point)
in various other calendar systems:

@table @kbd
@kindex p @r{(Calendar mode)}
@findex calendar-print-other-dates
@item Mouse-3  Other calendars
@itemx p o
Display the selected date in various other calendars.
(@code{calendar-print-other-dates}).
@findex calendar-iso-print-date
@item p c
Display ISO commercial calendar equivalent for selected day
(@code{calendar-iso-print-date}).
@findex calendar-julian-print-date
@item p j
Display Julian date for selected day (@code{calendar-julian-print-date}).
@findex calendar-astro-print-day-number
@item p a
Display astronomical (Julian) day number for selected day
(@code{calendar-astro-print-day-number}).
@findex calendar-hebrew-print-date
@item p h
Display Hebrew date for selected day (@code{calendar-hebrew-print-date}).
@findex calendar-islamic-print-date
@item p i
Display Islamic date for selected day (@code{calendar-islamic-print-date}).
@findex calendar-french-print-date
@item p f
Display French Revolutionary date for selected day
(@code{calendar-french-print-date}).
@findex calendar-bahai-print-date
@item p b
Display Bahá'í date for selected day
(@code{calendar-bahai-print-date}).
@findex calendar-chinese-print-date
@item p C
Display Chinese date for selected day
(@code{calendar-chinese-print-date}).
@findex calendar-coptic-print-date
@item p k
Display Coptic date for selected day
(@code{calendar-coptic-print-date}).
@findex calendar-ethiopic-print-date
@item p e
Display Ethiopic date for selected day
(@code{calendar-ethiopic-print-date}).
@findex calendar-persian-print-date
@item p p
Display Persian date for selected day
(@code{calendar-persian-print-date}).
@findex calendar-mayan-print-date
@item p m
Display Mayan date for selected day (@code{calendar-mayan-print-date}).
@end table

  Otherwise, move point to the date you want to convert, then type the
appropriate command starting with @kbd{p} from the table above.  The
prefix @kbd{p} is a mnemonic for ``print'', since Emacs ``prints'' the
equivalent date in the echo area.  @kbd{p o} displays the
date in all forms known to Emacs.  You can also use @kbd{Mouse-3} and
then choose @kbd{Other calendars} from the menu that appears.  This
displays the equivalent forms of the date in all the calendars Emacs
understands, in the form of a menu.  (Choosing an alternative from
this menu doesn't actually do anything---the menu is used only for
display.)

@node From Other Calendar
@subsection Converting From Other Calendars

  You can use the other supported calendars to specify a date to move
to.  This section describes the commands for doing this using calendars
other than Mayan; for the Mayan calendar, see the following section.

@kindex g @var{char} @r{(Calendar mode)}
@findex calendar-iso-goto-date
@findex calendar-iso-goto-week
@findex calendar-julian-goto-date
@findex calendar-astro-goto-day-number
@findex calendar-bahai-goto-date
@findex calendar-hebrew-goto-date
@findex calendar-islamic-goto-date
@findex calendar-french-goto-date
@findex calendar-chinese-goto-date
@findex calendar-persian-goto-date
@findex calendar-coptic-goto-date
@findex calendar-ethiopic-goto-date
@table @kbd
@item g c
Move to a date specified in the ISO commercial calendar
(@code{calendar-iso-goto-date}).
@item g w
Move to a week specified in the ISO commercial calendar
(@code{calendar-iso-goto-week}).
@item g j
Move to a date specified in the Julian calendar
(@code{calendar-julian-goto-date}).
@item g a
Move to a date specified with an astronomical (Julian) day number
(@code{calendar-astro-goto-day-number}).
@item g b
Move to a date specified in the Bahá'í calendar
(@code{calendar-bahai-goto-date}).
@item g h
Move to a date specified in the Hebrew calendar
(@code{calendar-hebrew-goto-date}).
@item g i
Move to a date specified in the Islamic calendar
(@code{calendar-islamic-goto-date}).
@item g f
Move to a date specified in the French Revolutionary calendar
(@code{calendar-french-goto-date}).
@item g C
Move to a date specified in the Chinese calendar
(@code{calendar-chinese-goto-date}).
@item g p
Move to a date specified in the Persian calendar
(@code{calendar-persian-goto-date}).
@item g k
Move to a date specified in the Coptic calendar
(@code{calendar-coptic-goto-date}).
@item g e
Move to a date specified in the Ethiopic calendar
(@code{calendar-ethiopic-goto-date}).
@end table

  These commands ask you for a date on the other calendar, move point
to the Gregorian calendar date equivalent to that date, and display
the other calendar's date in the echo area.  Emacs uses strict
completion (@pxref{Completion Exit}) whenever it asks you to type a
month name, so you don't have to worry about the spelling of Hebrew,
Islamic, or French names.

@c FIXME move?
@findex calendar-hebrew-list-yahrzeits
@cindex yahrzeits
  One common issue concerning the Hebrew calendar is the computation
of the anniversary of a date of death, called a ``yahrzeit''.  The Emacs
calendar includes a facility for such calculations.  If you are in the
calendar, the command @kbd{M-x calendar-hebrew-list-yahrzeits} asks you for
a range of years and then displays a list of the yahrzeit dates for those
years for the date given by point.  If you are not in the calendar,
this command first asks you for the date of death and the range of
years, and then displays the list of yahrzeit dates.

@node Diary
@section The Diary
@cindex diary

  The Emacs diary keeps track of appointments or other events on a daily
basis, in conjunction with the calendar.  To use the diary feature, you
must first create a diary file containing a list of events and
their dates.  Then Emacs can automatically pick out and display the
events for today, for the immediate future, or for any specified
date.

  Although you probably will start by creating a diary manually, Emacs
provides a number of commands to let you view, add, and change diary
entries.

@menu
* Format of Diary File::   Entering events in your diary.
* Displaying the Diary::   Viewing diary entries and associated calendar dates.
* Date Formats::           Various ways you can specify dates.
* Adding to Diary::        Commands to create diary entries.
* Special Diary Entries::  Anniversaries, blocks of dates, cyclic entries, etc.
@end menu

@node Format of Diary File
@subsection The Diary File
@cindex diary file

@vindex diary-file
  Your @dfn{diary file} is a file that records events associated with
particular dates.  The name of the diary file is specified by the
variable @code{diary-file}.  The default is @file{~/.emacs.d/diary},
though for compatibility with older versions Emacs will use
@file{~/diary} if it exists.
@ignore
@c I don't think this is relevant any more.  The utility doesn't seem
@c to be part of the default install on GNU/Linux machines these days.
@c When I tried it with my basic diary file, it just died with an error.
The @code{calendar} utility program supports a subset of the format
allowed by the Emacs diary facilities, so you can use that utility to
view the diary file, with reasonable results aside from the entries it
cannot understand.
@end ignore

  Each entry in the diary file describes one event and consists of one
or more lines.  An entry always begins with a date specification at the
left margin.  The rest of the entry is simply text to describe the
event.  If the entry has more than one line, then the lines after the
first must begin with whitespace to indicate they continue a previous
entry.  Lines that do not begin with valid dates and do not continue a
preceding entry are ignored.  Here's an example:

@example
12/22/2015  Twentieth wedding anniversary!
10/22       Ruth's birthday.
* 21, *:    Payday
Tuesday--weekly meeting with grad students at 10am
         Supowit, Shen, Bitner, and Kapoor to attend.
1/13/89     Friday the thirteenth!!
thu 4pm     squash game with Lloyd.
mar 16      Dad's birthday
April 15, 2016 Income tax due.
* 15        time cards due.
@end example

@noindent
This example uses extra spaces to align the event descriptions of most
of the entries.  Such formatting is purely a matter of taste.

  You can also use a format where the first line of a diary entry
consists only of the date or day name (with no following blanks or
punctuation).  For example:

@example
02/11/2012
      Bill B. visits Princeton today
      2pm Cognitive Studies Committee meeting
      2:30-5:30 Liz at Lawrenceville
      4:00pm Dentist appt
      7:30pm Dinner at George's
      8:00-10:00pm concert
@end example

@noindent
This entry will have a different appearance if you use the simple diary
display
@iftex
(@pxref{Diary Display,,, emacs-xtra, Specialized Emacs Features}).
@end iftex
@ifnottex
(@pxref{Diary Display}).
@end ifnottex
The simple diary display omits the date line at the beginning; only the
continuation lines appear.  This style of entry looks neater when you
display just a single day's entries, but can cause confusion if you ask
for more than one day's entries.

@node Displaying the Diary
@subsection Displaying the Diary

  Once you have created a diary file, you can use the calendar to view
it.  You can also view today's events outside of Calendar mode.  In the
following, key bindings refer to the Calendar buffer.

@table @kbd
@item Mouse-3 Diary
@itemx d
Display all diary entries for the selected date
(@code{diary-view-entries}).
@item s
Display the entire diary file (@code{diary-show-all-entries}).
@item m
Mark all visible dates that have diary entries
(@code{diary-mark-entries}).
@item u
Unmark the calendar window (@code{calendar-unmark}).
@item M-x diary-print-entries
Print hard copy of the diary display as it appears.
@item M-x diary
Display all diary entries for today's date.
@item M-x diary-mail-entries
Mail yourself email reminders about upcoming diary entries.
@end table

@kindex d @r{(Calendar mode)}
@findex diary-view-entries
@vindex calendar-view-diary-initially-flag
  Displaying the diary entries with @kbd{d} shows in a separate buffer
the diary entries for the selected date in the calendar.  The mode line
of the new buffer shows the date of the diary entries.  Holidays are
shown either in the buffer or in the mode line, depending on the display
method you choose
@iftex
(@pxref{Diary Display,,, emacs-xtra, Specialized Emacs Features}).
@end iftex
@ifnottex
(@pxref{Diary Display}).
@end ifnottex
If you specify a numeric argument with @kbd{d}, it shows all the diary
entries for that many successive days.  Thus, @kbd{2 d} displays all the
entries for the selected date and for the following day.

  Another way to display the diary entries for a date is to click
@kbd{Mouse-3} on the date, and then choose @kbd{Diary entries} from
the menu that appears.  If the variable
@code{calendar-view-diary-initially-flag} is non-@code{nil}, creating the
calendar lists the diary entries for the current date (provided the
current date is visible).

@kindex m @r{(Calendar mode)}
@findex diary-mark-entries
@vindex calendar-mark-diary-entries-flag
  To get a broader view of which days are mentioned in the diary, use
the @kbd{m} command.  This marks the dates that have diary entries in
a different face.
@iftex
@xref{Calendar Customizing,,, emacs-xtra, Specialized Emacs Features}.
@end iftex
@ifnottex
@xref{Calendar Customizing, diary-entry-marker}.
@end ifnottex

  This command applies both to the months that are currently visible
and to those that subsequently become visible after scrolling.  To turn
marking off and erase the current marks, type @kbd{u}, which also
turns off holiday marks (@pxref{Holidays}).  If the variable
@code{calendar-mark-diary-entries-flag} is non-@code{nil}, creating or
updating the calendar marks diary dates automatically.

@vindex diary-nonmarking-symbol
  To prevent an individual diary entry from being marked in the
calendar, insert the string that @code{diary-nonmarking-symbol}
specifies (the default is @samp{&}) at the beginning of the entry,
before the date.  This has no effect on display of the entry in the
diary buffer; it only affects marks on dates in the calendar.
Nonmarking entries can be useful for generic entries that would
otherwise mark many different dates.

@kindex s @r{(Calendar mode)}
@findex diary-show-all-entries
  To see the full diary file, rather than just some of the entries, use
the @kbd{s} command.

@findex diary
  The command @kbd{M-x diary} displays the diary entries for the current
date, independently of the calendar display, and optionally for the next
few days as well; the variable @code{diary-number-of-entries} specifies
how many days to include.
@iftex
@xref{Diary Customizing,,, emacs-xtra, Specialized Emacs Features}.
@end iftex
@ifnottex
@xref{Diary Customizing, diary-number-of-entries}.
@end ifnottex

  If you put @code{(diary)} in your @file{.emacs} file, this
automatically displays a window with the day's diary entries when you
start Emacs.

@findex diary-mail-entries
@vindex diary-mail-days
  Some people like to receive email notifications of events in their
diary.  To send such mail to yourself, use the command @kbd{M-x
diary-mail-entries}.  A prefix argument specifies how many days
(starting with today) to check; otherwise, the variable
@code{diary-mail-days} says how many days.

@node Date Formats
@subsection Date Formats

  Here are some sample diary entries, illustrating different ways of
formatting a date.  The examples all show dates in American order
(month, day, year), but Calendar mode supports European order (day,
month, year) and ISO order (year, month, day) as options.

@example
4/20/12  Switch-over to new tabulation system
apr. 25  Start tabulating annual results
4/30  Results for April are due
*/25  Monthly cycle finishes
Friday  Don't leave without backing up files
@end example

  The first entry appears only once, on April 20, 2012.  The second and
third appear every year on the specified dates, and the fourth uses a
wildcard (asterisk) for the month, so it appears on the 25th of every
month.  The final entry appears every week on Friday.

  You can use just numbers to express a date, as in
@samp{@var{month}/@var{day}} or @samp{@var{month}/@var{day}/@var{year}}.
This must be followed by a nondigit.  In the date itself, @var{month}
and @var{day} are numbers of one or two digits.  The optional @var{year}
is also a number, and may be abbreviated to the last two digits; that
is, you can use @samp{11/12/2012} or @samp{11/12/12}.

  Dates can also have the form @samp{@var{monthname} @var{day}} or
@samp{@var{monthname} @var{day}, @var{year}}, where the month's name can
be spelled in full or abbreviated (with or without a period).  The
preferred abbreviations for month and day names can be set using
the variables @code{calendar-abbrev-length},
@code{calendar-month-abbrev-array}, and
@code{calendar-day-abbrev-array}.  The default is to use the first three
letters of a name as its abbreviation.  Case is not significant.

  A date may be @dfn{generic}; that is, partially unspecified.  Then the
entry applies to all dates that match the specification.  If the date
does not contain a year, it is generic and applies to any year.
Alternatively, @var{month}, @var{day}, or @var{year} can be @samp{*};
this matches any month, day, or year, respectively.  Thus, a diary entry
@samp{3/*/*} matches any day in March of any year; so does @samp{march
*}.

@vindex calendar-date-style
@findex calendar-set-date-style
  If you prefer the European style of writing dates (in which the day
comes before the month), or the ISO style (in which the order is year,
month, day), type @kbd{M-x calendar-set-date-style} while in the
calendar, or customize the variable @code{calendar-date-style}.  This
affects how diary dates are interpreted, date display, and the order in
which some commands expect their arguments to be given.

  You can use the name of a day of the week as a generic date which
applies to any date falling on that day of the week.  You can abbreviate
the day of the week as described above, or spell it in full; case is not
significant.

@node Adding to Diary
@subsection Commands to Add to the Diary

  While in the calendar, there are several commands to create diary
entries.  The basic commands are listed here; more sophisticated
commands are in the next section (@pxref{Special Diary Entries}).
Entries can also be based on non-Gregorian calendars.
@iftex
@xref{Non-Gregorian Diary,,, emacs-xtra, Specialized Emacs Features}.
@end iftex
@ifnottex
@xref{Non-Gregorian Diary}.
@end ifnottex

@table @kbd
@item i d
Add a diary entry for the selected date (@code{diary-insert-entry}).
@item i w
Add a diary entry for the selected day of the week (@code{diary-insert-weekly-entry}).
@item i m
Add a diary entry for the selected day of the month (@code{diary-insert-monthly-entry}).
@item i y
Add a diary entry for the selected day of the year (@code{diary-insert-yearly-entry}).
@end table

@kindex i d @r{(Calendar mode)}
@findex diary-insert-entry
  You can make a diary entry for a specific date by selecting that date
in the calendar window and typing the @kbd{i d} command.  This command
displays the end of your diary file in another window and inserts the
date; you can then type the rest of the diary entry.

@kindex i w @r{(Calendar mode)}
@findex diary-insert-weekly-entry
@kindex i m @r{(Calendar mode)}
@findex diary-insert-monthly-entry
@kindex i y @r{(Calendar mode)}
@findex diary-insert-yearly-entry
  If you want to make a diary entry that applies to a specific day of
the week, select that day of the week (any occurrence will do) and type
@kbd{i w}.  This inserts the day-of-week as a generic date; you can then
type the rest of the diary entry.  You can make a monthly diary entry in
the same fashion: select the day of the month, use the @kbd{i m}
command, and type the rest of the entry.  Similarly, you can insert a
yearly diary entry with the @kbd{i y} command.

  All of the above commands make marking diary entries by default.  To
make a nonmarking diary entry, give a prefix argument to the command.
For example, @kbd{C-u i w} makes a nonmarking weekly diary entry.

  When you modify the diary file, be sure to save the file before
exiting Emacs.  Saving the diary file after using any of the above
insertion commands will automatically update the diary marks in the
calendar window, if appropriate.  You can use the command
@code{calendar-redraw} to force an update at any time.

@node Special Diary Entries
@subsection Special Diary Entries

  In addition to entries based on calendar dates, the diary file can
contain @dfn{sexp entries} for regular events such as anniversaries.
These entries are based on Lisp expressions (sexps) that Emacs evaluates
as it scans the diary file.  Instead of a date, a sexp entry contains
@samp{%%} followed by a Lisp expression which must begin and end with
parentheses.  The Lisp expression determines which dates the entry
applies to.

  Calendar mode provides commands to insert certain commonly used
sexp entries:

@table @kbd
@item i a
Add an anniversary diary entry for the selected date
(@code{diary-insert-anniversary-entry}).
@item i b
Add a block diary entry for the current region
(@code{diary-insert-block-entry}).
@item i c
Add a cyclic diary entry starting at the date
(@code{diary-insert-cyclic-entry}).
@end table

@kindex i a @r{(Calendar mode)}
@findex diary-insert-anniversary-entry
  If you want to make a diary entry that applies to the anniversary of a
specific date, move point to that date and use the @kbd{i a} command.
This displays the end of your diary file in another window and inserts
the anniversary description; you can then type the rest of the diary
entry.  The entry looks like this:

@findex diary-anniversary
@example
%%(diary-anniversary 10 31 1988) Arthur's birthday
@end example

@noindent
This entry applies to October 31 in any year after 1988; @samp{10 31
1988} specifies the date.  (If you are using the European or ISO
calendar style, the input order of month, day and year is different.)
The reason this expression requires a beginning year is that advanced
diary functions can use it to calculate the number of elapsed years.

  A @dfn{block} diary entry applies to a specified range of consecutive
dates.  Here is a block diary entry that applies to all dates from June
24, 2012 through July 10, 2012:

@findex diary-block
@example
%%(diary-block 6 24 2012 7 10 2012) Vacation
@end example

@noindent
The @samp{6 24 2012} indicates the starting date and the @samp{7 10 2012}
indicates the stopping date.  (Again, if you are using the European or ISO
calendar style, the input order of month, day and year is different.)

@kindex i b @r{(Calendar mode)}
@findex diary-insert-block-entry
  To insert a block entry, place point and the mark on the two
dates that begin and end the range, and type @kbd{i b}.  This command
displays the end of your diary file in another window and inserts the
block description; you can then type the diary entry.

@kindex i c @r{(Calendar mode)}
@findex diary-insert-cyclic-entry
   @dfn{Cyclic} diary entries repeat after a fixed interval of days.  To
create one, select the starting date and use the @kbd{i c} command.  The
command prompts for the length of interval, then inserts the entry,
which looks like this:

@findex diary-cyclic
@example
%%(diary-cyclic 50 3 1 2012) Renew medication
@end example

@noindent
This entry applies to March 1, 2012 and every 50th day following;
@samp{3 1 2012} specifies the starting date.  (If you are using the
European or ISO calendar style, the input order of month, day and year
is different.)

  All three of these commands make marking diary entries.  To insert a
nonmarking entry, give a prefix argument to the command.  For example,
@kbd{C-u i a} makes a nonmarking anniversary diary entry.

  Marking sexp diary entries in the calendar can be time-consuming,
since every date visible in the calendar window must be individually
checked.  So it's a good idea to make sexp diary entries nonmarking
(with @samp{&}) when possible.

  Another sophisticated kind of sexp entry, a @dfn{floating} diary entry,
specifies a regularly occurring event by offsets specified in days,
weeks, and months.  It is comparable to a crontab entry interpreted by
the @code{cron} utility.  Here is a nonmarking, floating diary entry
that applies to the fourth Thursday in November:

@findex diary-float
@example
&%%(diary-float 11 4 4) American Thanksgiving
@end example

@noindent
The 11 specifies November (the eleventh month), the 4 specifies Thursday
(the fourth day of the week, where Sunday is numbered zero), and the
second 4 specifies the fourth Thursday (1 would mean ``first'', 2 would
mean ``second'', @minus{}2 would mean ``second-to-last'', and so on).
The month can be a single month or a list of months.  Thus you could change
the 11 above to @samp{'(1 2 3)} and have the entry apply to the last
Thursday of January, February, and March.  If the month is @code{t}, the
entry applies to all months of the year.

  Each of the standard sexp diary entries takes an optional parameter
specifying the name of a face or a single-character string to use when
marking the entry in the calendar.  Most generally, sexp diary entries
can perform arbitrary computations to determine when they apply.
@iftex
@xref{Sexp Diary Entries,,, emacs-xtra, Specialized Emacs Features}.
@end iftex
@ifnottex
@xref{Sexp Diary Entries}.
@end ifnottex

@node Appointments
@section Appointments
@cindex appointment notification

@vindex appt-display-format
@vindex appt-audible
@vindex appt-display-mode-line
  If you have a diary entry for an appointment, and that diary entry
begins with a recognizable time of day, Emacs can warn you in advance
that an appointment is pending.  Emacs alerts you
to the appointment by displaying a message in your chosen format, as
specified by the variable @code{appt-display-format}.  If the value of
@code{appt-audible} is non-@code{nil}, the warning includes an audible
reminder.  In addition, if @code{appt-display-mode-line} is
non-@code{nil}, Emacs displays the number of minutes to the
appointment on the mode line.

@vindex appt-display-duration
@vindex appt-disp-window-function
@vindex appt-delete-window-function
  If @code{appt-display-format} has the value @code{window}, then the
variable @code{appt-display-duration} controls how long the reminder
window is visible for; and the variables
@code{appt-disp-window-function} and @code{appt-delete-window-function}
give the names of functions used to create and destroy the window,
respectively.

@findex appt-activate
  To enable appointment notification, type @kbd{M-x appt-activate}.
With a positive argument, it enables notification; with a negative
argument, it disables notification; with no argument, it toggles.
Enabling notification also sets up an appointment list for today from
the diary file, giving all diary entries found with recognizable times
of day, and reminds you just before each of them.

  For example, suppose the diary file contains these lines:

@example
Monday
  9:30am Coffee break
 12:00pm Lunch
@end example

@vindex appt-message-warning-time
@vindex appt-warning-time-regexp
@noindent
Then on Mondays, you will be reminded at around 9:20am about your
coffee break and at around 11:50am about lunch.  The variable
@code{appt-message-warning-time} specifies how many minutes (default 12)
in advance to warn you.  This is a default warning time.  Each
appointment can specify a different warning time by adding a piece
matching @code{appt-warning-time-regexp} (see that variable's
documentation for details).

  You can write times in am/pm style (with @samp{12:00am} standing
for midnight and @samp{12:00pm} standing for noon), or 24-hour
European/military style.  You need not be consistent; your diary file
can have a mixture of the two styles.  Times must be at the beginning of
diary entries if they are to be recognized.

@vindex appt-display-diary
  Emacs updates the appointments list from the diary file
automatically just after midnight.  You can force an update at any
time by re-enabling appointment notification.  Both these actions also
display the day's diary buffer, unless you set
@code{appt-display-diary} to @code{nil}.  The appointments list is
also updated whenever the diary file (or a file it includes; see
@iftex
@ref{Fancy Diary Display,,, emacs-xtra, Specialized Emacs Features})
@end iftex
@ifnottex
@ref{Fancy Diary Display})
@end ifnottex
is saved.

@findex appt-add
@findex appt-delete
@cindex alarm clock
  You can also use the appointment notification facility like an alarm
clock.  The command @kbd{M-x appt-add} adds entries to the appointment
list without affecting your diary file.  You delete entries from the
appointment list with @kbd{M-x appt-delete}.

@node Importing Diary
@section Importing and Exporting Diary Entries

  You can transfer diary entries between Emacs diary files and a
variety of other formats.

@vindex diary-outlook-formats
  You can import diary entries from Outlook-generated appointment
messages.  While viewing such a message in Rmail or Gnus, do @kbd{M-x
diary-from-outlook} to import the entry.  You can make this command
recognize additional appointment message formats by customizing the
variable @code{diary-outlook-formats}.  Other mail clients can set
@code{diary-from-outlook-function} to an appropriate value.

@c FIXME the name of the RFC is hardly very relevant.
@cindex iCalendar support
  The icalendar package allows you to transfer data between your Emacs
diary file and iCalendar files, which are defined in ``RFC
2445---Internet Calendaring and Scheduling Core Object Specification
(iCalendar)'' (as well as the earlier vCalendar format).

@c  Importing works for ``ordinary'' (i.e., non-recurring) events, but
@c (at present) may not work correctly (if at all) for recurring events.
@c Exporting of diary files into iCalendar files should work correctly
@c for most diary entries.  This feature is a work in progress, so the
@c commands may evolve in future.

@findex icalendar-import-buffer
  The command @code{icalendar-import-buffer} extracts
iCalendar data from the current buffer and adds it to your
diary file.  This function is also suitable for automatic extraction of
iCalendar data; for example with the Rmail mail client one could use:

@example
(add-hook 'rmail-show-message-hook 'icalendar-import-buffer)
@end example

@findex icalendar-import-file
  The command @code{icalendar-import-file} imports an iCalendar file
and adds the results to an Emacs diary file.  For example:

@example
(icalendar-import-file "/here/is/calendar.ics"
                       "/there/goes/ical-diary")
@end example

@noindent
You can use an @code{#include} directive to add the import file contents
to the main diary file, if these are different files.
@iftex
@xref{Fancy Diary Display,,, emacs-xtra, Specialized Emacs Features}.
@end iftex
@ifnottex
@xref{Fancy Diary Display}.
@end ifnottex


@findex icalendar-export-file, icalendar-export-region
  Use @code{icalendar-export-file} to interactively export an entire
Emacs diary file to iCalendar format.  To export only a part of a diary
file, mark the relevant area, and call @code{icalendar-export-region}.
In both cases, Emacs appends the result to the target file.

@node Daylight Saving
@section Daylight Saving Time
@cindex daylight saving time

  Emacs understands the difference between standard time and daylight
saving time---the times given for sunrise, sunset, solstices,
equinoxes, and the phases of the moon take that into account.  The rules
for daylight saving 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.

@vindex calendar-daylight-savings-starts
@vindex calendar-daylight-savings-ends
  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.  If the resulting rules are not what you want,
you can tell Emacs the rules to use by setting certain variables:
@code{calendar-daylight-savings-starts} and
@code{calendar-daylight-savings-ends}.

  These values should be Lisp expressions that refer to the variable
@code{year}, and evaluate to the Gregorian date on which daylight
saving 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 saving time.

  Emacs uses these expressions to determine the starting date of
daylight saving time for the holiday list and for correcting times of
day in the solar and lunar calculations.

  The values for Cambridge, Massachusetts are as follows:

@example
(calendar-nth-named-day 2 0 3 year)
(calendar-nth-named-day 1 0 11 year)
@end example

@noindent
That is, the second 0th day (Sunday) of the third month (March) in
the year specified by @code{year}, and the first Sunday of the eleventh month
(November) of that year.  If daylight saving 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

  If there is no daylight saving 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 saving time and standard time, measured in
minutes.  The value for Cambridge, Massachusetts is 60.

@c @vindex calendar-daylight-savings-starts-time  too long!
@vindex calendar-daylight-savings-ends-time
  Finally, the two variables
@code{calendar-daylight-savings-starts-time} and
@code{calendar-daylight-savings-ends-time} specify the number of
minutes after midnight local time when the transition to and from
daylight saving time should occur.  For Cambridge, Massachusetts both
variables' values are 120.

@node Time Intervals
@section Summing Time Intervals
@cindex time intervals, summing
@cindex summing time intervals
@cindex timeclock

  The timeclock package adds up time intervals, so you can (for
instance) keep track of how much time you spend working on particular
projects.

@findex timeclock-in
@findex timeclock-out
@findex timeclock-change
@findex timeclock-workday-remaining
@findex timeclock-when-to-leave
  Use the @kbd{M-x timeclock-in} command when you start working on a
project, and @kbd{M-x timeclock-out} command when you're done.  Each
time you do this, it adds one time interval to the record of the
project.  You can change to working on a different project with @kbd{M-x
timeclock-change}.

  Once you've collected data from a number of time intervals, you can use
@kbd{M-x timeclock-workday-remaining} to see how much time is left to
work today (assuming a typical average of 8 hours a day), and @kbd{M-x
timeclock-when-to-leave} which will calculate when you're ``done''.

@vindex timeclock-modeline-display
@findex timeclock-modeline-display
  If you want Emacs to display the amount of time ``left'' of your
workday in the mode line, either customize the
@code{timeclock-modeline-display} variable and set its value to
@code{t}, or invoke the @kbd{M-x timeclock-modeline-display} command.

@vindex timeclock-ask-before-exiting
  Terminating the current Emacs session might or might not mean that
you have stopped working on the project and, by default, Emacs asks
you.  You can, however, customize the value of the variable
@code{timeclock-ask-before-exiting} to @code{nil} to avoid the question;
then, only an explicit @kbd{M-x timeclock-out} or @kbd{M-x
timeclock-change} will tell Emacs that the current interval is over.

@cindex @file{timelog} file
@vindex timeclock-file
@findex timeclock-reread-log
  The timeclock functions work by accumulating the data in a file
called @file{~/.emacs.d/timelog}.  You can specify a
different name for this file by customizing the variable
@code{timeclock-file}.  If you edit the timeclock file manually, or if
you change the value of any of timeclock's customizable variables, you
should run the command @kbd{M-x timeclock-reread-log} to update the
data in Emacs from the file.

@ifnottex
@include cal-xtra.texi
@end ifnottex