@section Format specs

Format specs in dateutils are similar to posix' strftime().

However, due to a broader range of supported calendars dateutils must
employ different rules.

Date specs:
@verbatim
  %a  The abbreviated weekday name
  %A  The full weekday name
  %_a The weekday name shortened to a single character (MTWRFAS)
  %b  The abbreviated month name
  %B  The full month name
  %_b The month name shortened to a single character (FGHJKMNQUVXZ)
  %c  The count of the weekday within the month (range 00 to 05)
  %C  The count of the weekday within the year (range 00 to 53)
  %d  The day of the month, 2 digits (range 00 to 31)
  %D  The day of the year, 3 digits (range 000 to 366)
  %F  Equivalent to %Y-%m-%d (ymd's canonical format)
  %j  Equivalent to %D
  %m  The month in the current calendar (range 00 to 19)
  %Q  The quarter of the year (range Q1 to Q4)
  %q  The number of the quarter (range 01 to 04)
  %s  The number of seconds since the Epoch.
  %u  The weekday as number (range 01 to 07, Sunday being 07)
  %U  The week count, first day of week is Sun (range 00 to 53)
  %V  The ISO week count, first day of week is Mon (range 01 to 53)
  %w  The weekday as number (range 00 to 06, Sunday being 00)
  %W  The week count, first day of week is Mon (range 00 to 53)
  %y  The year without a century (range 00 to 99)
  %Y  The year including the century
  %Z  The zone offset in hours and minutes (HH:MM) with
      a preceding sign (+ for offsets east of UTC, - for offsets
      west of UTC)

  %Od The day as roman numerals
  %Om The month as roman numerals
  %Oy The two digit year as roman numerals
  %OY The year including the century as roman numerals

  %rs In time systems whose Epoch is different from the unix Epoch, this
      selects the number of seconds since then.
  %rY In calendars with years that don't coincide with the Gregorian
      years, this selects the calendar's year.

  %dth  The day of the month as an ordinal number, 1st, 2nd, 3rd, etc.
  %mth  The month of the year as an ordinal number, 1st, 2nd, 3rd, etc.

  %db The business day of the month (since last month's ultimo)
  %dB Number of business days until this month's ultimo
@end verbatim

Time specs:
@verbatim
  %H  The hour of the day using a 24h clock, 2 digits (range 00 to 23)
  %I  The hour of the day using a 12h clock, 2 digits (range 01 to 12)
  %M  The minute (range 00 to 59)
  %N  The nanoseconds (range 000000000 to 999999999)
  %p  The string AM or PM, noon is PM and midnight is AM.
  %P  Like %p but in lowercase
  %S  The second (range 00 to 60, 60 is for leap seconds)
  %T  Equivalent to %H:%M:%S
@end verbatim

General specs:
@verbatim
  %n  A newline character
  %t  A tab character
  %%  A literal % character
@end verbatim

Modifiers:
@verbatim
  %O  Modifier to turn decimal numbers into Roman numerals
  %r  Modifier to turn units into real units
  th  Suffix, read and print ordinal numbers
  b   Suffix, treat days as business days
@end verbatim

By design dates before 1601-01-01 are not supported.

For conformity here is a list of calendar designators and their
corresponding format string:
@verbatim
  ymd     %Y-%m-%d
  ymcw    %Y-%m-%c-%w
  ywd     %rY-W%V-%u
  bizda   %Y-%m-%db
  lilian     n/a
  ldn        n/a
  julian     n/a
  jdn        n/a
@end verbatim

These designators can be used as output format string, moreover,
@code{lilian}/@code{ldn} and @code{julian}/@code{jdn} can also be used
as input format string.
