Formats universal dates using the same format specifiers as NSDateFormatter. The format is:

%% - A '%' character
%a - Abbreviated weekday name
%A - Full weekday name
%b - Abbreviated month name
%B - Full month name
%c - Shorthand for “%X %x”, the locale format for date and time
%d - Day of the month as a decimal number [01-31]
%e - Same as %d but does not print the leading 0 for days 1 through 9
[unlike strftime[], does not print a leading space]
%F - Milliseconds as a decimal number [000-999]
%H - Hour based on a 24-hour clock as a decimal number [00-23]
%I - Hour based on a 12-hour clock as a decimal number [01-12]
%j - Day of the year as a decimal number [001-366]
%m - Month as a decimal number [01-12]
%M - Minute as a decimal number [00-59]
%p - AM/PM designation for the locale
%S - Second as a decimal number [00-59]
%w - Weekday as a decimal number [0-6], where Sunday is 0
%x - Date using the date representation for the locale, including
the time zone [produces different results from strftime[]]
%X - Time using the time representation for the locale [produces
different results from strftime[]]
%y - Year without century [00-99]
%Y - Year with century [such as 1990]
%Z - Time zone name [such as Pacific Daylight Time;
produces different results from strftime[]]
%z - Time zone offset in hours and minutes from GMT [HHMM]

None of %c, %F, %p, %x, %X, %Z, %z are implemented.