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DateTime(3)		       User Contributed Perl Documentation		      DateTime(3)

NAME
       DateTime - A date and time object

VERSION
       version 1.04

SYNOPSIS
	 use DateTime;

	 $dt = DateTime->new(
	     year	=> 1964,
	     month	=> 10,
	     day	=> 16,
	     hour	=> 16,
	     minute	=> 12,
	     second	=> 47,
	     nanosecond => 500000000,
	     time_zone	=> 'Asia/Taipei',
	 );

	 $dt = DateTime->from_epoch( epoch => $epoch );
	 $dt = DateTime->now; # same as ( epoch => time() )

	 $year	 = $dt->year;
	 $month  = $dt->month;		# 1-12

	 $day	 = $dt->day;		# 1-31

	 $dow	 = $dt->day_of_week;	# 1-7 (Monday is 1)

	 $hour	 = $dt->hour;		# 0-23
	 $minute = $dt->minute; 	# 0-59

	 $second = $dt->second; 	# 0-61 (leap seconds!)

	 $doy	 = $dt->day_of_year;	# 1-366 (leap years)

	 $doq	 = $dt->day_of_quarter; # 1..

	 $qtr	 = $dt->quarter;	# 1-4

	 # all of the start-at-1 methods above have corresponding start-at-0
	 # methods, such as $dt->day_of_month_0, $dt->month_0 and so on

	 $ymd	 = $dt->ymd;	       # 2002-12-06
	 $ymd	 = $dt->ymd('/');      # 2002/12/06

	 $mdy	 = $dt->mdy;	       # 12-06-2002
	 $mdy	 = $dt->mdy('/');      # 12/06/2002

	 $dmy	 = $dt->dmy;	       # 06-12-2002
	 $dmy	 = $dt->dmy('/');      # 06/12/2002

	 $hms	 = $dt->hms;	       # 14:02:29
	 $hms	 = $dt->hms('!');      # 14!02!29

	 $is_leap  = $dt->is_leap_year;

	 # these are localizable, see Locales section
	 $month_name  = $dt->month_name; # January, February, ...
	 $month_abbr  = $dt->month_abbr; # Jan, Feb, ...
	 $day_name    = $dt->day_name;	 # Monday, Tuesday, ...
	 $day_abbr    = $dt->day_abbr;	 # Mon, Tue, ...

	 # May not work for all possible datetime, see the docs on this
	 # method for more details.
	 $epoch_time  = $dt->epoch;

	 $dt2 = $dt + $duration_object;

	 $dt3 = $dt - $duration_object;

	 $duration_object = $dt - $dt2;

	 $dt->set( year => 1882 );

	 $dt->set_time_zone( 'America/Chicago' );

	 $dt->set_formatter( $formatter );

DESCRIPTION
       DateTime is a class for the representation of date/time combinations, and is part of the
       Perl DateTime project. For details on this project please see <http://datetime.perl.org/>.
       The DateTime site has a FAQ which may help answer many "how do I do X?" questions. The FAQ
       is at <http://datetime.perl.org/wiki/datetime/page/FAQ>.

       It represents the Gregorian calendar, extended backwards in time before its creation (in
       1582). This is sometimes known as the "proleptic Gregorian calendar". In this calendar,
       the first day of the calendar (the epoch), is the first day of year 1, which corresponds
       to the date which was (incorrectly) believed to be the birth of Jesus Christ.

       The calendar represented does have a year 0, and in that way differs from how dates are
       often written using "BCE/CE" or "BC/AD".

       For infinite datetimes, please see the DateTime::Infinite module.

USAGE
   0-based Versus 1-based Numbers
       The DateTime.pm module follows a simple consistent logic for determining whether or not a
       given number is 0-based or 1-based.

       Month, day of month, day of week, and day of year are 1-based. Any method that is 1-based
       also has an equivalent 0-based method ending in "_0". So for example, this class provides
       both "day_of_week()" and "day_of_week_0()" methods.

       The "day_of_week_0()" method still treats Monday as the first day of the week.

       All time-related numbers such as hour, minute, and second are 0-based.

       Years are neither, as they can be both positive or negative, unlike any other datetime
       component. There is a year 0.

       There is no "quarter_0()" method.

   Error Handling
       Some errors may cause this module to die with an error string. This can only happen when
       calling constructor methods, methods that change the object, such as "set()", or methods
       that take parameters.  Methods that retrieve information about the object, such as
       "year()" or "epoch()", will never die.

   Locales
       All the object methods which return names or abbreviations return data based on a locale.
       This is done by setting the locale when constructing a DateTime object. There is also a
       "DefaultLocale()" class method which may be used to set the default locale for all
       DateTime objects created. If this is not set, then "en_US" is used.

   Floating DateTimes
       The default time zone for new DateTime objects, except where stated otherwise, is the
       "floating" time zone. This concept comes from the iCal standard. A floating datetime is
       one which is not anchored to any particular time zone. In addition, floating datetimes do
       not include leap seconds, since we cannot apply them without knowing the datetime's time
       zone.

       The results of date math and comparison between a floating datetime and one with a real
       time zone are not really valid, because one includes leap seconds and the other does not.
       Similarly, the results of datetime math between two floating datetimes and two datetimes
       with time zones are not really comparable.

       If you are planning to use any objects with a real time zone, it is strongly recommended
       that you do not mix these with floating datetimes.

   Math
       If you are going to be using doing date math, please read the section "How DateTime Math
       Works".

   Time Zone Warnings
       Determining the local time zone for a system can be slow. If $ENV{TZ} is not set, it may
       involve reading a number of files in /etc or elsewhere. If you know that the local time
       zone won't change while your code is running, and you need to make many objects for the
       local time zone, it is strongly recommended that you retrieve the local time zone once and
       cache it:

	 our $App::LocalTZ = DateTime::TimeZone->new( name => 'local' );

	 ... # then everywhere else

	 my $dt = DateTime->new( ..., time_zone => $App::LocalTZ );

       DateTime itself does not do this internally because local time zones can change, and
       there's no good way to determine if it's changed without doing all the work to look it up.

       Do not try to use named time zones (like "America/Chicago") with dates very far in the
       future (thousands of years). The current implementation of "DateTime::TimeZone" will use a
       huge amount of memory calculating all the DST changes from now until the future date. Use
       UTC or the floating time zone and you will be safe.

METHODS
       DateTime provide many methods. The documentation breaks them down into groups based on
       what they do (constructor, accessors, modifiers, etc.).

   Constructors
       All constructors can die when invalid parameters are given.

       DateTime->new( ... )

       This class method accepts parameters for each date and time component: "year", "month",
       "day", "hour", "minute", "second", "nanosecond".  It also accepts "locale", "time_zone",
       and "formatter" parameters.

	 my $dt = DateTime->new(
	     year	=> 1966,
	     month	=> 10,
	     day	=> 25,
	     hour	=> 7,
	     minute	=> 15,
	     second	=> 47,
	     nanosecond => 500000000,
	     time_zone	=> 'America/Chicago',
	 );

       DateTime validates the "month", "day", "hour", "minute", and "second", and "nanosecond"
       parameters. The valid values for these parameters are:

       o       month

	       An integer from 1-12.

       o       day

	       An integer from 1-31, and it must be within the valid range of days for the
	       specified month.

       o       hour

	       An integer from 0-23.

       o       minute

	       An integer from 0-59.

       o       second

	       An integer from 0-61 (to allow for leap seconds). Values of 60 or 61 are only
	       allowed when they match actual leap seconds.

       o       nanosecond

	       An integer >= 0. If this number is greater than 1 billion, it will be normalized
	       into the second value for the DateTime object.

       Invalid parameter types (like an array reference) will cause the constructor to die.

       The value for seconds may be from 0 to 61, to account for leap seconds. If you give a
       value greater than 59, DateTime does check to see that it really matches a valid leap
       second.

       All of the parameters are optional except for "year". The "month" and "day" parameters
       both default to 1, while the "hour", "minute", "second", and "nanosecond" parameters all
       default to 0.

       The "locale" parameter should be a string matching one of the valid locales, or a
       "DateTime::Locale" object. See the DateTime::Locale documentation for details.

       The time_zone parameter can be either a scalar or a "DateTime::TimeZone" object. A string
       will simply be passed to the "DateTime::TimeZone->new" method as its "name" parameter.
       This string may be an Olson DB time zone name ("America/Chicago"), an offset string
       ("+0630"), or the words "floating" or "local". See the "DateTime::TimeZone" documentation
       for more details.

       The default time zone is "floating".

       The "formatter" can be either a scalar or an object, but the class specified by the scalar
       or the object must implement a "format_datetime()" method.

       Parsing Dates

       This module does not parse dates! That means there is no constructor to which you can pass
       things like "March 3, 1970 12:34".

       Instead, take a look at the various "DateTime::Format::*" modules on CPAN. These parse all
       sorts of different date formats, and you're bound to find something that can handle your
       particular needs.

       Ambiguous Local Times

       Because of Daylight Saving Time, it is possible to specify a local time that is ambiguous.
       For example, in the US in 2003, the transition from to saving to standard time occurred on
       October 26, at 02:00:00 local time. The local clock changed from 01:59:59 (saving time) to
       01:00:00 (standard time). This means that the hour from 01:00:00 through 01:59:59 actually
       occurs twice, though the UTC time continues to move forward.

       If you specify an ambiguous time, then the latest UTC time is always used, in effect
       always choosing standard time. In this case, you can simply subtract an hour to the object
       in order to move to saving time, for example:

	 # This object represent 01:30:00 standard time
	 my $dt = DateTime->new(
	     year      => 2003,
	     month     => 10,
	     day       => 26,
	     hour      => 1,
	     minute    => 30,
	     second    => 0,
	     time_zone => 'America/Chicago',
	 );

	 print $dt->hms;  # prints 01:30:00

	 # Now the object represent 01:30:00 saving time
	 $dt->subtract( hours => 1 );

	 print $dt->hms;  # still prints 01:30:00

       Alternately, you could create the object with the UTC time zone, and then call the
       "set_time_zone()" method to change the time zone. This is a good way to ensure that the
       time is not ambiguous.

       Invalid Local Times

       Another problem introduced by Daylight Saving Time is that certain local times just do not
       exist. For example, in the US in 2003, the transition from standard to saving time
       occurred on April 6, at the change to 2:00:00 local time. The local clock changes from
       01:59:59 (standard time) to 03:00:00 (saving time). This means that there is no 02:00:00
       through 02:59:59 on April 6!

       Attempting to create an invalid time currently causes a fatal error.  This may change in
       future version of this module.

       DateTime->from_epoch( epoch => $epoch, ... )

       This class method can be used to construct a new DateTime object from an epoch time
       instead of components. Just as with the "new()" method, it accepts "time_zone", "locale",
       and "formatter" parameters.

       If the epoch value is not an integer, the part after the decimal will be converted to
       nanoseconds. This is done in order to be compatible with "Time::HiRes". If the floating
       portion extends past 9 decimal places, it will be truncated to nine, so that 1.1234567891
       will become 1 second and 123,456,789 nanoseconds.

       By default, the returned object will be in the UTC time zone.

       DateTime->now( ... )

       This class method is equivalent to calling "from_epoch()" with the value returned from
       Perl's "time()" function. Just as with the "new()" method, it accepts "time_zone" and
       "locale" parameters.

       By default, the returned object will be in the UTC time zone.

       DateTime->today( ... )

       This class method is equivalent to:

	 DateTime->now(@_)->truncate( to => 'day' );

       DateTime->from_object( object => $object, ... )

       This class method can be used to construct a new DateTime object from any object that
       implements the "utc_rd_values()" method. All "DateTime::Calendar" modules must implement
       this method in order to provide cross-calendar compatibility. This method accepts a
       "locale" and "formatter" parameter

       If the object passed to this method has a "time_zone()" method, that is used to set the
       time zone of the newly created "DateTime.pm" object.

       Otherwise, the returned object will be in the floating time zone.

       DateTime->last_day_of_month( ... )

       This constructor takes the same arguments as can be given to the "new()" method, except
       for "day". Additionally, both "year" and "month" are required.

       DateTime->from_day_of_year( ... )

       This constructor takes the same arguments as can be given to the "new()" method, except
       that it does not accept a "month" or "day" argument. Instead, it requires both "year" and
       "day_of_year". The day of year must be between 1 and 366, and 366 is only allowed for leap
       years.

       $dt->clone()

       This object method returns a new object that is replica of the object upon which the
       method is called.

   "Get" Methods
       This class has many methods for retrieving information about an object.

       $dt->year()

       Returns the year.

       $dt->ce_year()

       Returns the year according to the BCE/CE numbering system. The year before year 1 in this
       system is year -1, aka "1 BCE".

       $dt->era_name()

       Returns the long name of the current era, something like "Before Christ". See the Locales
       section for more details.

       $dt->era_abbr()

       Returns the abbreviated name of the current era, something like "BC".  See the Locales
       section for more details.

       $dt->christian_era()

       Returns a string, either "BC" or "AD", according to the year.

       $dt->secular_era()

       Returns a string, either "BCE" or "CE", according to the year.

       $dt->year_with_era()

       Returns a string containing the year immediately followed by its era abbreviation. The
       year is the absolute value of "ce_year()", so that year 1 is "1AD" and year 0 is "1BC".

       $dt->year_with_christian_era()

       Like "year_with_era()", but uses the christian_era() method to get the era name.

       $dt->year_with_secular_era()

       Like "year_with_era()", but uses the secular_era() method to get the era name.

       $dt->month()

       Returns the month of the year, from 1..12.

       Also available as "$dt->mon()".

       $dt->month_name()

       Returns the name of the current month. See the Locales section for more details.

       $dt->month_abbr()

       Returns the abbreviated name of the current month. See the Locales section for more
       details.

       $dt->day()

       Returns the day of the month, from 1..31.

       Also available as "$dt->mday()" and "$dt->day_of_month()".

       $dt->day_of_week()

       Returns the day of the week as a number, from 1..7, with 1 being Monday and 7 being
       Sunday.

       Also available as "$dt->wday()" and "$dt->dow()".

       $dt->local_day_of_week()

       Returns the day of the week as a number, from 1..7. The day corresponding to 1 will vary
       based on the locale.

       $dt->day_name()

       Returns the name of the current day of the week. See the Locales section for more details.

       $dt->day_abbr()

       Returns the abbreviated name of the current day of the week. See the Locales section for
       more details.

       $dt->day_of_year()

       Returns the day of the year.

       Also available as "$dt->doy()".

       $dt->quarter()

       Returns the quarter of the year, from 1..4.

       $dt->quarter_name()

       Returns the name of the current quarter. See the Locales section for more details.

       $dt->quarter_abbr()

       Returns the abbreviated name of the current quarter. See the Locales section for more
       details.

       $dt->day_of_quarter()

       Returns the day of the quarter.

       Also available as "$dt->doq()".

       $dt->weekday_of_month()

       Returns a number from 1..5 indicating which week day of the month this is. For example,
       June 9, 2003 is the second Monday of the month, and so this method returns 2 for that day.

       $dt->ymd( $optional_separator ), $dt->mdy(...), $dt->dmy(...)

       Each method returns the year, month, and day, in the order indicated by the method name.
       Years are zero-padded to four digits. Months and days are 0-padded to two digits.

       By default, the values are separated by a dash (-), but this can be overridden by passing
       a value to the method.

       The "$dt->ymd()" method is also available as "$dt->date()".

       $dt->hour()

       Returns the hour of the day, from 0..23.

       $dt->hour_1()

       Returns the hour of the day, from 1..24.

       $dt->hour_12()

       Returns the hour of the day, from 1..12.

       $dt->hour_12_0()

       Returns the hour of the day, from 0..11.

       $dt->am_or_pm()

       Returns the appropriate localized abbreviation, depending on the current hour.

       $dt->minute()

       Returns the minute of the hour, from 0..59.

       Also available as "$dt->min()".

       $dt->second()

       Returns the second, from 0..61. The values 60 and 61 are used for leap seconds.

       Also available as "$dt->sec()".

       $dt->fractional_second()

       Returns the second, as a real number from 0.0 until 61.999999999

       The values 60 and 61 are used for leap seconds.

       $dt->millisecond()

       Returns the fractional part of the second as milliseconds (1E-3 seconds).

       Half a second is 500 milliseconds.

       This value will always be rounded down to the nearest integer.

       $dt->microsecond()

       Returns the fractional part of the second as microseconds (1E-6 seconds).

       Half a second is 500_000 microseconds.

       This value will always be rounded down to the nearest integer.

       $dt->nanosecond()

       Returns the fractional part of the second as nanoseconds (1E-9 seconds).

       Half a second is 500_000_000 nanoseconds.

       $dt->hms( $optional_separator )

       Returns the hour, minute, and second, all zero-padded to two digits.  If no separator is
       specified, a colon (:) is used by default.

       Also available as "$dt->time()".

       $dt->datetime()

       This method is equivalent to:

	 $dt->ymd('-') . 'T' . $dt->hms(':')

       Also available as "$dt->iso8601()".

       $dt->is_leap_year()

       This method returns a true or false indicating whether or not the datetime object is in a
       leap year.

       $dt->week()

	($week_year, $week_number) = $dt->week;

       Returns information about the calendar week which contains this datetime object. The
       values returned by this method are also available separately through the week_year and
       week_number methods.

       The first week of the year is defined by ISO as the one which contains the fourth day of
       January, which is equivalent to saying that it's the first week to overlap the new year by
       at least four days.

       Typically the week year will be the same as the year that the object is in, but dates at
       the very beginning of a calendar year often end up in the last week of the prior year, and
       similarly, the final few days of the year may be placed in the first week of the next
       year.

       $dt->week_year()

       Returns the year of the week. See "$dt->week()" for details.

       $dt->week_number()

       Returns the week of the year, from 1..53. See "$dt->week()" for details.

       $dt->week_of_month()

       The week of the month, from 0..5. The first week of the month is the first week that
       contains a Thursday. This is based on the ICU definition of week of month, and correlates
       to the ISO8601 week of year definition. A day in the week before the week with the first
       Thursday will be week 0.

       $dt->jd(), $dt->mjd()

       These return the Julian Day and Modified Julian Day, respectively.  The value returned is
       a floating point number. The fractional portion of the number represents the time portion
       of the datetime.

       $dt->time_zone()

       This returns the "DateTime::TimeZone" object for the datetime object.

       $dt->offset()

       This returns the offset from UTC, in seconds, of the datetime object according to the time
       zone.

       $dt->is_dst()

       Returns a boolean indicating whether or not the datetime object is currently in Daylight
       Saving Time or not.

       $dt->time_zone_long_name()

       This is a shortcut for "$dt->time_zone->name". It's provided so that one can use
       "%{time_zone_long_name}" as a strftime format specifier.

       $dt->time_zone_short_name()

       This method returns the time zone abbreviation for the current time zone, such as "PST" or
       "GMT". These names are not definitive, and should not be used in any application intended
       for general use by users around the world.

       $dt->strftime( $format, ... )

       This method implements functionality similar to the "strftime()" method in C. However, if
       given multiple format strings, then it will return multiple scalars, one for each format
       string.

       See the "strftime Patterns" section for a list of all possible strftime patterns.

       If you give a pattern that doesn't exist, then it is simply treated as text.

       $dt->format_cldr( $format, ... )

       This method implements formatting based on the CLDR date patterns. If given multiple
       format strings, then it will return multiple scalars, one for each format string.

       See the "CLDR Patterns" section for a list of all possible CLDR patterns.

       If you give a pattern that doesn't exist, then it is simply treated as text.

       $dt->epoch()

       Return the UTC epoch value for the datetime object. Internally, this is implemented using
       "Time::Local", which uses the Unix epoch even on machines with a different epoch (such as
       MacOS). Datetimes before the start of the epoch will be returned as a negative number.

       The return value from this method is always an integer.

       Since the epoch does not account for leap seconds, the epoch time for 1972-12-31T23:59:60
       (UTC) is exactly the same as that for 1973-01-01T00:00:00.

       This module uses "Time::Local" to calculate the epoch, which may or may not handle epochs
       before 1904 or after 2038 (depending on the size of your system's integers, and whether or
       not Perl was compiled with 64-bit int support).

       $dt->hires_epoch()

       Returns the epoch as a floating point number. The floating point portion of the value
       represents the nanosecond value of the object.  This method is provided for compatibility
       with the "Time::HiRes" module.

       $dt->is_finite(), $dt->is_infinite()

       These methods allow you to distinguish normal datetime objects from infinite ones.
       Infinite datetime objects are documented in DateTime::Infinite.

       $dt->utc_rd_values()

       Returns the current UTC Rata Die days, seconds, and nanoseconds as a three element list.
       This exists primarily to allow other calendar modules to create objects based on the
       values provided by this object.

       $dt->local_rd_values()

       Returns the current local Rata Die days, seconds, and nanoseconds as a three element list.
       This exists for the benefit of other modules which might want to use this information for
       date math, such as "DateTime::Event::Recurrence".

       $dt->leap_seconds()

       Returns the number of leap seconds that have happened up to the datetime represented by
       the object. For floating datetimes, this always returns 0.

       $dt->utc_rd_as_seconds()

       Returns the current UTC Rata Die days and seconds purely as seconds.  This number ignores
       any fractional seconds stored in the object, as well as leap seconds.

       $dt->locale()

       Returns the current locale object.

       $dt->formatter()

       Returns current formatter object or class. See "Formatters And Stringification" for
       details.

   "Set" Methods
       The remaining methods provided by "DateTime.pm", except where otherwise specified, return
       the object itself, thus making method chaining possible. For example:

	 my $dt = DateTime->now->set_time_zone( 'Australia/Sydney' );

	 my $first = DateTime
		       ->last_day_of_month( year => 2003, month => 3 )
		       ->add( days => 1 )
		       ->subtract( seconds => 1 );

       $dt->set( .. )

       This method can be used to change the local components of a date time, or its locale. This
       method accepts any parameter allowed by the "new()" method except for "time_zone". Time
       zones may be set using the "set_time_zone()" method.

       This method performs parameters validation just as is done in the "new()" method.

       Do not use this method to do date math. Use the "add()" and "subtract()" methods instead.

       $dt->set_year(), $dt->set_month(), etc.

       DateTime has a "set_*" method for every item that can be passed to the constructor:

       o   $dt->set_year()

       o   $dt->set_month()

       o   $dt->set_day()

       o   $dt->set_hour()

       o   $dt->set_minute()

       o   $dt->set_second()

       o   $dt->set_nanosecond()

       o   $dt->set_locale()

       These are shortcuts to calling "set()" with a single key. They all take a single
       parameter.

       $dt->truncate( to => ... )

       This method allows you to reset some of the local time components in the object to their
       "zero" values. The "to" parameter is used to specify which values to truncate, and it may
       be one of "year", "month", "week", "day", "hour", "minute", or "second". For example, if
       "month" is specified, then the local day becomes 1, and the hour, minute, and second all
       become 0.

       If "week" is given, then the datetime is set to the beginning of the week in which it
       occurs, and the time components are all set to 0.

       $dt->set_time_zone( $tz )

       This method accepts either a time zone object or a string that can be passed as the "name"
       parameter to "DateTime::TimeZone->new()".  If the new time zone's offset is different from
       the old time zone, then the local time is adjusted accordingly.

       For example:

	 my $dt = DateTime->new(
	     year      => 2000,
	     month     => 5,
	     day       => 10,
	     hour      => 15,
	     minute    => 15,
	     time_zone => 'America/Los_Angeles',
	 );

	 print $dt->hour; # prints 15

	 $dt->set_time_zone( 'America/Chicago' );

	 print $dt->hour; # prints 17

       If the old time zone was a floating time zone, then no adjustments to the local time are
       made, except to account for leap seconds. If the new time zone is floating, then the UTC
       time is adjusted in order to leave the local time untouched.

       Fans of Tsai Ming-Liang's films will be happy to know that this does work:

	 my $dt = DateTime->now( time_zone => 'Asia/Taipei' );

	 $dt->set_time_zone( 'Europe/Paris' );

       Yes, now we can know "ni3 na4 bian1 ji2dian3?"

       $dt->set_formatter( $formatter )

       Set the formatter for the object. See "Formatters And Stringification" for details.

       You can set this to "undef" to revert to the default formatter.

   Math Methods
       Like the set methods, math related methods always return the object itself, to allow for
       chaining:

	 $dt->add( days => 1 )->subtract( seconds => 1 );

       $dt->duration_class()

       This returns "DateTime::Duration", but exists so that a subclass of "DateTime.pm" can
       provide a different value.

       $dt->add_duration( $duration_object )

       This method adds a "DateTime::Duration" to the current datetime. See the
       DateTime::Duration docs for more details.

       $dt->add( DateTime::Duration->new parameters )

       This method is syntactic sugar around the "add_duration()" method. It simply creates a new
       "DateTime::Duration" object using the parameters given, and then calls the
       "add_duration()" method.

       $dt->subtract_duration( $duration_object )

       When given a "DateTime::Duration" object, this method simply calls "invert()" on that
       object and passes that new duration to the "add_duration" method.

       $dt->subtract( DateTime::Duration->new parameters )

       Like "add()", this is syntactic sugar for the "subtract_duration()" method.

       $dt->subtract_datetime( $datetime )

       This method returns a new "DateTime::Duration" object representing the difference between
       the two dates. The duration is relative to the object from which $datetime is subtracted.
       For example:

	   2003-03-15 00:00:00.00000000
	-  2003-02-15 00:00:00.00000000
	-------------------------------
	= 1 month

       Note that this duration is not an absolute measure of the amount of time between the two
       datetimes, because the length of a month varies, as well as due to the presence of leap
       seconds.

       The returned duration may have deltas for months, days, minutes, seconds, and nanoseconds.

       $dt->delta_md( $datetime )

       $dt->delta_days( $datetime )

       Each of these methods returns a new "DateTime::Duration" object representing some portion
       of the difference between two datetimes.  The "delta_md()" method returns a duration which
       contains only the month and day portions of the duration is represented. The
       "delta_days()" method returns a duration which contains only days.

       The "delta_md" and "delta_days" methods truncate the duration so that any fractional
       portion of a day is ignored. Both of these methods operate on the date portion of a
       datetime only, and so effectively ignore the time zone.

       Unlike the subtraction methods, these methods always return a positive (or zero) duration.

       $dt->delta_ms( $datetime )

       Returns a duration which contains only minutes and seconds. Any day and month differences
       to minutes are converted to minutes and seconds. This method also always return a positive
       (or zero) duration.

       $dt->subtract_datetime_absolute( $datetime )

       This method returns a new "DateTime::Duration" object representing the difference between
       the two dates in seconds and nanoseconds. This is the only way to accurately measure the
       absolute amount of time between two datetimes, since units larger than a second do not
       represent a fixed number of seconds.

   Class Methods
       DateTime->DefaultLocale( $locale )

       This can be used to specify the default locale to be used when creating DateTime objects.
       If unset, then "en_US" is used.

       DateTime->compare( $dt1, $dt2 ), DateTime->compare_ignore_floating( $dt1, $dt2 )

	 $cmp = DateTime->compare( $dt1, $dt2 );

	 $cmp = DateTime->compare_ignore_floating( $dt1, $dt2 );

       Compare two DateTime objects. The semantics are compatible with Perl's "sort()" function;
       it returns -1 if $dt1 < $dt2, 0 if $dt1 == $dt2, 1 if $dt1 > $dt2.

       If one of the two DateTime objects has a floating time zone, it will first be converted to
       the time zone of the other object. This is what you want most of the time, but it can lead
       to inconsistent results when you compare a number of DateTime objects, some of which are
       floating, and some of which are in other time zones.

       If you want to have consistent results (because you want to sort a number of objects, for
       example), you can use the "compare_ignore_floating()" method:

	 @dates = sort { DateTime->compare_ignore_floating($a, $b) } @dates;

       In this case, objects with a floating time zone will be sorted as if they were UTC times.

       Since DateTime objects overload comparison operators, this:

	 @dates = sort @dates;

       is equivalent to this:

	 @dates = sort { DateTime->compare($a, $b) } @dates;

       DateTime objects can be compared to any other calendar class that implements the
       "utc_rd_values()" method.

   How DateTime Math Works
       It's important to have some understanding of how datetime math is implemented in order to
       effectively use this module and "DateTime::Duration".

       Making Things Simple

       If you want to simplify your life and not have to think too hard about the nitty-gritty of
       datetime math, I have several recommendations:

       o   use the floating time zone

	   If you do not care about time zones or leap seconds, use the "floating" timezone:

	     my $dt = DateTime->now( time_zone => 'floating' );

	   Math done on two objects in the floating time zone produces very predictable results.

	   Note that in most cases you will want to start by creating an object in a specific
	   zone and then convert it to the floating time zone. When an object goes from a real
	   zone to the floating zone, the time for the object remains the same.

	   This means that passing the floating zone to a constructor may not do what you want.

	     my $dt = DateTime->now( time_zone => 'floating' );

	   is equivalent to

	     my $dt = DateTime->now( time_zone => 'UTC' )->set_time_zone('floating');

	   This might not be what you wanted. Instead, you may prefer to do this:

	     my $dt = DateTime->now( time_zone => 'local' )->set_time_zone('floating');

       o   use UTC for all calculations

	   If you do care about time zones (particularly DST) or leap seconds, try to use non-UTC
	   time zones for presentation and user input only.  Convert to UTC immediately and
	   convert back to the local time zone for presentation:

	     my $dt = DateTime->new( %user_input, time_zone => $user_tz );
	     $dt->set_time_zone('UTC');

	     # do various operations - store it, retrieve it, add, subtract, etc.

	     $dt->set_time_zone($user_tz);
	     print $dt->datetime;

       o   math on non-UTC time zones

	   If you need to do date math on objects with non-UTC time zones, please read the
	   caveats below carefully. The results "DateTime.pm" produces are predictable and
	   correct, and mostly intuitive, but datetime math gets very ugly when time zones are
	   involved, and there are a few strange corner cases involving subtraction of two
	   datetimes across a DST change.

	   If you can always use the floating or UTC time zones, you can skip ahead to Leap
	   Seconds and Date Math

       o   date vs datetime math

	   If you only care about the date (calendar) portion of a datetime, you should use
	   either "delta_md()" or "delta_days()", not "subtract_datetime()". This will give
	   predictable, unsurprising results, free from DST-related complications.

       o   subtract_datetime() and add_duration()

	   You must convert your datetime objects to the UTC time zone before doing date math if
	   you want to make sure that the following formulas are always true:

	     $dt2 - $dt1 = $dur
	     $dt1 + $dur = $dt2
	     $dt2 - $dur = $dt1

	   Note that using "delta_days" ensures that this formula always works, regardless of the
	   timezone of the objects involved, as does using "subtract_datetime_absolute()". Other
	   methods of subtraction are not always reversible.

       Adding a Duration to a Datetime

       The parts of a duration can be broken down into five parts. These are months, days,
       minutes, seconds, and nanoseconds. Adding one month to a date is different than adding 4
       weeks or 28, 29, 30, or 31 days.  Similarly, due to DST and leap seconds, adding a day can
       be different than adding 86,400 seconds, and adding a minute is not exactly the same as 60
       seconds.

       We cannot convert between these units, except for seconds and nanoseconds, because there
       is no fixed conversion between the two units, because of things like leap seconds, DST
       changes, etc.

       "DateTime.pm" always adds (or subtracts) days, then months, minutes, and then seconds and
       nanoseconds. If there are any boundary overflows, these are normalized at each step. For
       the days and months the local (not UTC) values are used. For minutes and seconds, the
       local values are used. This generally just works.

       This means that adding one month and one day to February 28, 2003 will produce the date
       April 1, 2003, not March 29, 2003.

	 my $dt = DateTime->new( year => 2003, month => 2, day => 28 );

	 $dt->add( months => 1, days => 1 );

	 # 2003-04-01 - the result

       On the other hand, if we add months first, and then separately add days, we end up with
       March 29, 2003:

	 $dt->add( months => 1 )->add( days => 1 );

	 # 2003-03-29

       We see similar strangeness when math crosses a DST boundary:

	 my $dt = DateTime->new(
	     year      => 2003,
	     month     => 4,
	     day       => 5,
	     hour      => 1,
	     minute    => 58,
	     time_zone => "America/Chicago",
	 );

	 $dt->add( days => 1, minutes => 3 );
	 # 2003-04-06 02:01:00

	 $dt->add( minutes => 3 )->add( days => 1 );
	 # 2003-04-06 03:01:00

       Note that if you converted the datetime object to UTC first you would get predictable
       results.

       If you want to know how many seconds a duration object represents, you have to add it to a
       datetime to find out, so you could do:

	my $now = DateTime->now( time_zone => 'UTC' );
	my $later = $now->clone->add_duration($duration);

	my $seconds_dur = $later->subtract_datetime_absolute($now);

       This returns a duration which only contains seconds and nanoseconds.

       If we were add the duration to a different datetime object we might get a different number
       of seconds.

       DateTime::Duration supports three different end-of-month algorithms for adding months.
       This comes into play when an addition results in a day past the end of the month (for
       example, adding one month to January 30).

	# 2010-08-31 + 1 month = 2010-10-01
	$dt->add( months => 1, end_of_month => 'wrap' );

	# 2010-01-30 + 1 month = 2010-02-28
	$dt->add( months => 1, end_of_month => 'limit' );

	# 2010-04-30 + 1 month = 2010-05-31
	$dt->add( months => 1, end_of_month => 'preserve' );

       By default, it uses "wrap" for positive durations and "preserve" for negative durations.
       See DateTime::Duration for a detailed explanation of these algorithms.

       If you need to do lots of work with durations, take a look at Rick Measham's
       "DateTime::Format::Duration" module, which lets you present information from durations in
       many useful ways.

       There are other subtract/delta methods in DateTime.pm to generate different types of
       durations. These methods are "subtract_datetime()", "subtract_datetime_absolute()",
       "delta_md()", "delta_days()", and "delta_ms()".

       Datetime Subtraction

       Date subtraction is done solely based on the two object's local datetimes, with one
       exception to handle DST changes. Also, if the two datetime objects are in different time
       zones, one of them is converted to the other's time zone first before subtraction. This is
       best explained through examples:

       The first of these probably makes the most sense:

	 my $dt1 = DateTime->new(
	     year      => 2003,
	     month     => 5,
	     day       => 6,
	     time_zone => 'America/Chicago',
	 );

	 # not DST

	 my $dt2 = DateTime->new(
	     year      => 2003,
	     month     => 11,
	     day       => 6,
	     time_zone => 'America/Chicago',
	 );

	 # is DST

	 my $dur = $dt2->subtract_datetime($dt1);
	 # 6 months

       Nice and simple.

       This one is a little trickier, but still fairly logical:

	 my $dt1 = DateTime->new(
	     year      => 2003,
	     month     => 4,
	     day       => 5,
	     hour      => 1,
	     minute    => 58,
	     time_zone => "America/Chicago",
	 );

	 # is DST

	 my $dt2 = DateTime->new(
	     year      => 2003,
	     month     => 4,
	     day       => 7,
	     hour      => 2,
	     minute    => 1,
	     time_zone => "America/Chicago",
	 );

	 # not DST

	 my $dur = $dt2->subtract_datetime($dt1);

	 # 2 days and 3 minutes

       Which contradicts the result this one gives, even though they both make sense:

	 my $dt1 = DateTime->new(
	     year      => 2003,
	     month     => 4,
	     day       => 5,
	     hour      => 1,
	     minute    => 58,
	     time_zone => "America/Chicago",
	 );

	 # is DST

	 my $dt2 = DateTime->new(
	     year      => 2003,
	     month     => 4,
	     day       => 6,
	     hour      => 3,
	     minute    => 1,
	     time_zone => "America/Chicago",
	 );

	 # not DST

	 my $dur = $dt2->subtract_datetime($dt1);

	 # 1 day and 3 minutes

       This last example illustrates the "DST" exception mentioned earlier.  The exception
       accounts for the fact 2003-04-06 only lasts 23 hours.

       And finally:

	 my $dt2 = DateTime->new(
	     year      => 2003,
	     month     => 10,
	     day       => 26,
	     hour      => 1,
	     time_zone => 'America/Chicago',
	 );

	 my $dt1 = $dt2->clone->subtract( hours => 1 );

	 my $dur = $dt2->subtract_datetime($dt1);
	 # 60 minutes

       This seems obvious until you realize that subtracting 60 minutes from $dt2 in the above
       example still leaves the clock time at "01:00:00". This time we are accounting for a 25
       hour day.

       Reversibility

       Date math operations are not always reversible. This is because of the way that addition
       operations are ordered. As was discussed earlier, adding 1 day and 3 minutes in one call
       to "add()" is not the same as first adding 3 minutes and 1 day in two separate calls.

       If we take a duration returned from "subtract_datetime()" and then try to add or subtract
       that duration from one of the datetimes we just used, we sometimes get interesting
       results:

	 my $dt1 = DateTime->new(
	     year      => 2003,
	     month     => 4,
	     day       => 5,
	     hour      => 1,
	     minute    => 58,
	     time_zone => "America/Chicago",
	 );

	 my $dt2 = DateTime->new(
	     year      => 2003,
	     month     => 4,
	     day       => 6,
	     hour      => 3,
	     minute    => 1,
	     time_zone => "America/Chicago",
	 );

	 my $dur = $dt2->subtract_datetime($dt1);
	 # 1 day and 3 minutes

	 $dt1->add_duration($dur);
	 # gives us $dt2

	 $dt2->subtract_duration($dur);
	 # gives us 2003-04-05 02:58:00 - 1 hour later than $dt1

       The "subtract_duration()" operation gives us a (perhaps) unexpected answer because it
       first subtracts one day to get 2003-04-05T03:01:00 and then subtracts 3 minutes to get the
       final result.

       If we explicitly reverse the order we can get the original value of $dt1. This can be
       facilitated by "DateTime::Duration"'s "calendar_duration()" and "clock_duration()"
       methods:

	 $dt2->subtract_duration( $dur->clock_duration )
	     ->subtract_duration( $dur->calendar_duration );

       Leap Seconds and Date Math

       The presence of leap seconds can cause even more anomalies in date math. For example, the
       following is a legal datetime:

	 my $dt = DateTime->new(
	     year      => 1972,
	     month     => 12,
	     day       => 31,
	     hour      => 23,
	     minute    => 59,
	     second    => 60,
	     time_zone => 'UTC'
	 );

       If we do the following:

	$dt->add( months => 1 );

       Then the datetime is now "1973-02-01 00:00:00", because there is no 23:59:60 on
       1973-01-31.

       Leap seconds also force us to distinguish between minutes and seconds during date math.
       Given the following datetime:

	 my $dt = DateTime->new(
	     year      => 1972,
	     month     => 12,
	     day       => 31,
	     hour      => 23,
	     minute    => 59,
	     second    => 30,
	     time_zone => 'UTC'
	 );

       we will get different results when adding 1 minute than we get if we add 60 seconds. This
       is because in this case, the last minute of the day, beginning at 23:59:00, actually
       contains 61 seconds.

       Here are the results we get:

	 # 1972-12-31 23:59:30 - our starting datetime

	 $dt->clone->add( minutes => 1 );
	 # 1973-01-01 00:00:30 - one minute later

	 $dt->clone->add( seconds => 60 );
	 # 1973-01-01 00:00:29 - 60 seconds later

	 $dt->clone->add( seconds => 61 );
	 # 1973-01-01 00:00:30 - 61 seconds later

       Local vs. UTC and 24 hours vs. 1 day

       When math crosses a daylight saving boundary, a single day may have more or less than 24
       hours.

       For example, if you do this:

	 my $dt = DateTime->new(
	     year      => 2003,
	     month     => 4,
	     day       => 5,
	     hour      => 2,
	     time_zone => 'America/Chicago',
	 );

	 $dt->add( days => 1 );

       then you will produce an invalid local time, and therefore an exception will be thrown.

       However, this works:

	 my $dt = DateTime->new(
	     year      => 2003,
	     month     => 4,
	     day       => 5,
	     hour      => 2,
	     time_zone => 'America/Chicago',
	 );

	 $dt->add( hours => 24 );

       and produces a datetime with the local time of "03:00".

       If all this makes your head hurt, there is a simple alternative. Just convert your
       datetime object to the "UTC" time zone before doing date math on it, and switch it back to
       the local time zone afterwards.	This avoids the possibility of having date math throw an
       exception, and makes sure that 1 day equals 24 hours. Of course, this may not always be
       desirable, so caveat user!

   Overloading
       This module explicitly overloads the addition (+), subtraction (-), string and numeric
       comparison operators. This means that the following all do sensible things:

	 my $new_dt = $dt + $duration_obj;

	 my $new_dt = $dt - $duration_obj;

	 my $duration_obj = $dt - $new_dt;

	 foreach my $dt ( sort @dts ) { ... }

       Additionally, the fallback parameter is set to true, so other derivable operators (+=, -=,
       etc.) will work properly. Do not expect increment (++) or decrement (--) to do anything
       useful.

       The string comparison operators, "eq" or "ne", will use the string value to compare with
       non-DateTime objects.

       DateTime objects do not have a numeric value, using "==" or "<=>" to compare a DateTime
       object with a non-DateTime object will result in an exception. To safely sort mixed
       DateTime and non-DateTime objects, use "sort { $a cmp $b } @dates".

       The module also overloads stringification using the object's formatter, defaulting to
       "iso8601()" method. See "Formatters And Stringification" for details.

   Formatters And Stringification
       You can optionally specify a "formatter", which is usually a DateTime::Format::*
       object/class, to control the stringification of the DateTime object.

       Any of the constructor methods can accept a formatter argument:

	 my $formatter = DateTime::Format::Strptime->new(...);
	 my $dt = DateTime->new(year => 2004, formatter => $formatter);

       Or, you can set it afterwards:

	 $dt->set_formatter($formatter);
	 $formatter = $dt->formatter();

       Once you set the formatter, the overloaded stringification method will use the formatter.
       If unspecified, the "iso8601()" method is used.

       A formatter can be handy when you know that in your application you want to stringify your
       DateTime objects into a special format all the time, for example to a different language.

       If you provide a formatter class name or object, it must implement a "format_datetime"
       method. This method will be called with just the DateTime object as its argument.

   CLDR Patterns
       The CLDR pattern language is both more powerful and more complex than strftime. Unlike
       strftime patterns, you often have to explicitly escape text that you do not want
       formatted, as the patterns are simply letters without any prefix.

       For example, "yyyy-MM-dd" is a valid CLDR pattern. If you want to include any lower or
       upper case ASCII characters as-is, you can surround them with single quotes ('). If you
       want to include a single quote, you must escape it as two single quotes ('').

	 'Today is ' EEEE
	 'It is now' h 'o''clock' a

       Spaces and any non-letter text will always be passed through as-is.

       Many CLDR patterns which produce numbers will pad the number with leading zeroes depending
       on the length of the format specifier. For example, "h" represents the current hour from
       1-12. If you specify "hh" then the 1-9 will have a leading zero prepended.

       However, CLDR often uses five of a letter to represent the narrow form of a pattern. This
       inconsistency is necessary for backwards compatibility.

       CLDR often distinguishes between the "format" and "stand-alone" forms of a pattern. The
       format pattern is used when the thing in question is being placed into a larger string.
       The stand-alone form is used when displaying that item by itself, for example in a
       calendar.

       It also often provides three sizes for each item, wide (the full name), abbreviated, and
       narrow. The narrow form is often just a single character, for example "T" for "Tuesday",
       and may not be unique.

       CLDR provides a fairly complex system for localizing time zones that we ignore entirely.
       The time zone patterns just use the information provided by "DateTime::TimeZone", and do
       not follow the CLDR spec.

       The output of a CLDR pattern is always localized, when applicable.

       CLDR provides the following patterns:

       o   G{1,3}

	   The abbreviated era (BC, AD).

       o   GGGG

	   The wide era (Before Christ, Anno Domini).

       o   GGGGG

	   The narrow era, if it exists (and it mostly doesn't).

       o   y and y{3,}

	   The year, zero-prefixed as needed. Negative years will start with a "-", and this will
	   be included in the length calculation.

	   In other, words the "yyyyy" pattern will format year -1234 as "-1234", not "-01234".

       o   yy

	   This is a special case. It always produces a two-digit year, so "1976" becomes "76".
	   Negative years will start with a "-", making them one character longer.

       o   Y{1,}

	   The week of the year, from "$dt->week_year()".

       o   u{1,}

	   Same as "y" except that "uu" is not a special case.

       o   Q{1,2}

	   The quarter as a number (1..4).

       o   QQQ

	   The abbreviated format form for the quarter.

       o   QQQQ

	   The wide format form for the quarter.

       o   q{1,2}

	   The quarter as a number (1..4).

       o   qqq

	   The abbreviated stand-alone form for the quarter.

       o   qqqq

	   The wide stand-alone form for the quarter.

       o   M{1,2]

	   The numerical month.

       o   MMM

	   The abbreviated format form for the month.

       o   MMMM

	   The wide format form for the month.

       o   MMMMM

	   The narrow format form for the month.

       o   L{1,2]

	   The numerical month.

       o   LLL

	   The abbreviated stand-alone form for the month.

       o   LLLL

	   The wide stand-alone form for the month.

       o   LLLLL

	   The narrow stand-alone form for the month.

       o   w{1,2}

	   The week of the year, from "$dt->week_number()".

       o   W

	   The week of the month, from "$dt->week_of_month()".

       o   d{1,2}

	   The numeric day of the month.

       o   D{1,3}

	   The numeric day of the year.

       o   F

	   The day of the week in the month, from "$dt->weekday_of_month()".

       o   g{1,}

	   The modified Julian day, from "$dt->mjd()".

       o   E{1,3} and eee

	   The abbreviated format form for the day of the week.

       o   EEEE and eeee

	   The wide format form for the day of the week.

       o   EEEEE and eeeee

	   The narrow format form for the day of the week.

       o   e{1,2}

	   The local numeric day of the week, from 1 to 7. This number depends on what day is
	   considered the first day of the week, which varies by locale. For example, in the US,
	   Sunday is the first day of the week, so this returns 2 for Monday.

       o   c

	   The numeric day of the week from 1 to 7, treating Monday as the first of the week,
	   regardless of locale.

       o   ccc

	   The abbreviated stand-alone form for the day of the week.

       o   cccc

	   The wide stand-alone form for the day of the week.

       o   ccccc

	   The narrow format form for the day of the week.

       o   a

	   The localized form of AM or PM for the time.

       o   h{1,2}

	   The hour from 1-12.

       o   H{1,2}

	   The hour from 0-23.

       o   K{1,2}

	   The hour from 0-11.

       o   k{1,2}

	   The hour from 1-24.

       o   j{1,2}

	   The hour, in 12 or 24 hour form, based on the preferred form for the locale. In other
	   words, this is equivalent to either "h{1,2}" or "H{1,2}".

       o   m{1,2}

	   The minute.

       o   s{1,2}

	   The second.

       o   S{1,}

	   The fractional portion of the seconds, rounded based on the length of the specifier.
	   This returned without a leading decimal point, but may have leading or trailing
	   zeroes.

       o   A{1,}

	   The millisecond of the day, based on the current time. In other words, if it is
	   12:00:00.00, this returns 43200000.

       o   z{1,3}

	   The time zone short name.

       o   zzzz

	   The time zone long name.

       o   Z{1,3}

	   The time zone offset.

       o   ZZZZ

	   The time zone short name and the offset as one string, so something like "CDT-0500".

       o   v{1,3}

	   The time zone short name.

       o   vvvv

	   The time zone long name.

       o   V{1,3}

	   The time zone short name.

       o   VVVV

	   The time zone long name.

   strftime Patterns
       The following patterns are allowed in the format string given to the "$dt->strftime()"
       method:

       o   %a

	   The abbreviated weekday name.

       o   %A

	   The full weekday name.

       o   %b

	   The abbreviated month name.

       o   %B

	   The full month name.

       o   %c

	   The default datetime format for the object's locale.

       o   %C

	   The century number (year/100) as a 2-digit integer.

       o   %d

	   The day of the month as a decimal number (range 01 to 31).

       o   %D

	   Equivalent to %m/%d/%y. This is not a good standard format if you want folks from both
	   the United States and the rest of the world to understand the date!

       o   %e

	   Like %d, the day of the month as a decimal number, but a leading zero is replaced by a
	   space.

       o   %F

	   Equivalent to %Y-%m-%d (the ISO 8601 date format)

       o   %G

	   The ISO 8601 year with century as a decimal number. The 4-digit year corresponding to
	   the ISO week number (see %V). This has the same format and value as %Y, except that if
	   the ISO week number belongs to the previous or next year, that year is used instead.
	   (TZ)

       o   %g

	   Like %G, but without century, i.e., with a 2-digit year (00-99).

       o   %h

	   Equivalent to %b.

       o   %H

	   The hour as a decimal number using a 24-hour clock (range 00 to 23).

       o   %I

	   The hour as a decimal number using a 12-hour clock (range 01 to 12).

       o   %j

	   The day of the year as a decimal number (range 001 to 366).

       o   %k

	   The hour (24-hour clock) as a decimal number (range 0 to 23); single digits are
	   preceded by a blank. (See also %H.)

       o   %l

	   The hour (12-hour clock) as a decimal number (range 1 to 12); single digits are
	   preceded by a blank. (See also %I.)

       o   %m

	   The month as a decimal number (range 01 to 12).

       o   %M

	   The minute as a decimal number (range 00 to 59).

       o   %n

	   A newline character.

       o   %N

	   The fractional seconds digits. Default is 9 digits (nanoseconds).

	     %3N   milliseconds (3 digits)
	     %6N   microseconds (6 digits)
	     %9N   nanoseconds	(9 digits)

	   This value will always be rounded down to the nearest integer.

       o   %p

	   Either `AM' or `PM' according to the given time value, or the corresponding strings
	   for the current locale. Noon is treated as `pm' and midnight as `am'.

       o   %P

	   Like %p but in lowercase: `am' or `pm' or a corresponding string for the current
	   locale.

       o   %r

	   The time in a.m. or p.m. notation. In the POSIX locale this is equivalent to `%I:%M:%S
	   %p'.

       o   %R

	   The time in 24-hour notation (%H:%M). (SU) For a version including the seconds, see %T
	   below.

       o   %s

	   The number of seconds since the epoch.

       o   %S

	   The second as a decimal number (range 00 to 61).

       o   %t

	   A tab character.

       o   %T

	   The time in 24-hour notation (%H:%M:%S).

       o   %u

	   The day of the week as a decimal, range 1 to 7, Monday being 1. See also %w.

       o   %U

	   The week number of the current year as a decimal number, range 00 to 53, starting with
	   the first Sunday as the first day of week 01. See also %V and %W.

       o   %V

	   The ISO 8601:1988 week number of the current year as a decimal number, range 01 to 53,
	   where week 1 is the first week that has at least 4 days in the current year, and with
	   Monday as the first day of the week. See also %U and %W.

       o   %w

	   The day of the week as a decimal, range 0 to 6, Sunday being 0. See also %u.

       o   %W

	   The week number of the current year as a decimal number, range 00 to 53, starting with
	   the first Monday as the first day of week 01.

       o   %x

	   The default date format for the object's locale.

       o   %X

	   The default time format for the object's locale.

       o   %y

	   The year as a decimal number without a century (range 00 to 99).

       o   %Y

	   The year as a decimal number including the century.

       o   %z

	   The time-zone as hour offset from UTC. Required to emit RFC822-conformant dates (using
	   "%a, %d %b %Y %H:%M:%S %z").

       o   %Z

	   The time zone or name or abbreviation.

       o   %%

	   A literal `%' character.

       o   %{method}

	   Any method name may be specified using the format "%{method}" name where "method" is a
	   valid "DateTime.pm" object method.

   DateTime.pm and Storable
       DateTime implements Storable hooks in order to reduce the size of a serialized DateTime
       object.

THE DATETIME PROJECT ECOSYSTEM
       This module is part of a larger ecosystem of modules in the DateTime family.

   DateTime::Set
       The DateTime::Set module represents sets (including recurrences) of datetimes. Many
       modules return sets or recurrences.

   Format Modules
       The various format modules exist to parse and format datetimes. For example,
       DateTime::Format::HTTP parses dates according to the RFC 1123 format:

	 my $datetime
	     = DateTime::Format::HTTP->parse_datetime('Thu Feb	3 17:03:55 GMT 1994');

	 print DateTime::Format::HTTP->format_datetime($datetime);

       Most format modules are suitable for use as a "formatter" with a DateTime object.

       All format modules start with "DateTime::Format::".

   Calendar Modules
       There are a number of modules on CPAN that implement non-Gregorian calendars, such as the
       Chinese, Mayan, and Julian calendars.

       All calendar modules start with "DateTime::Calendar::".

   Event Modules
       There are a number of modules that calculate the dates for events, such as Easter,
       Sunrise, etc.

       All event modules start with "DateTime::Event::".

   Others
       There are many other modules that work with DateTime, including modules in the "DateTimeX"
       namespace, as well as others.

       See the datetime wiki <http://datetime.perl.org> and search.cpan.org
       <http://search.cpan.org/search?query=datetime&mode=dist> for more details.

KNOWN BUGS
       The tests in 20infinite.t seem to fail on some machines, particularly on Win32. This
       appears to be related to Perl's internal handling of IEEE infinity and NaN, and seems to
       be highly platform/compiler/phase of moon dependent.

       If you don't plan to use infinite datetimes you can probably ignore this. This will be
       fixed (perhaps) in future versions.

SUPPORT
       Support for this module is provided via the datetime@perl.org email list. See
       http://datetime.perl.org/wiki/datetime/page/Mailing_List for details.

       Please submit bugs to the CPAN RT system at
       http://rt.cpan.org/NoAuth/Bugs.html?Dist=DateTime or via email at
       bug-datetime@rt.cpan.org.

DONATIONS
       If you'd like to thank me for the work I've done on this module, please consider making a
       "donation" to me via PayPal. I spend a lot of free time creating free software, and would
       appreciate any support you'd care to offer.

       Please note that I am not suggesting that you must do this in order for me to continue
       working on this particular software. I will continue to do so, inasmuch as I have in the
       past, for as long as it interests me.

       Similarly, a donation made in this way will probably not make me work on this software
       much more, unless I get so many donations that I can consider working on free software
       full time, which seems unlikely at best.

       To donate, log into PayPal and send money to autarch@urth.org or use the button on this
       page: <http://www.urth.org/~autarch/fs-donation.html>

SEE ALSO
       datetime@perl.org mailing list

       http://datetime.perl.org/

AUTHOR
       Dave Rolsky <autarch@urth.org>

COPYRIGHT AND LICENSE
       This software is Copyright (c) 2013 by Dave Rolsky.

       This is free software, licensed under:

	 The Artistic License 2.0 (GPL Compatible)

perl v5.16.3				    2014-06-09				      DateTime(3)
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