For example, the constant Zend_Date::HOUR can be used in the ways shown below. When working with days of the week, calendar dates, hours, minutes, seconds, and any other date parts that are expressed differently when in different parts of the world, the object's timezone will automatically be used to compute the correct value, even though the internal timestamp is the same for the same moment in time, regardless of the user's physical location in the world. Regardless of the units involved, output must be expressed either as GMT or UTC or localized to a locale. The example output below reflects localization to Europe/GMT+1 hour (e.g. Germany, Austria, France).

Operations Involving Zend_Date::HOUR

Method	Description	Original date	Result
get(Zend_Date::HOUR)	Output of the hour	2009-02-13T14:53:27+01:00	14
set(12, Zend_Date::HOUR)	Set new hour	2009-02-13T14:53:27+01:00	2009-02-13T12:53:27+01:00
add(12, Zend_Date::HOUR)	Add hours	2009-02-13T14:53:27+01:00	2009-02-14T02:53:27+01:00
sub(12, Zend_Date::HOUR)	Subtract hours	2009-02-13T14:53:27+01:00	2009-02-13T02:53:27+01:00
compare(12, Zend_Date::HOUR)	Compare hour, returns 0, 1 or -1	2009-02-13T14:53:27+01:00	1 (if object > argument)
copy(Zend_Date::HOUR)	Copies only the hour part	2009-02-13T14:53:27+01:00	1970-01-01T14:00:00+01:00
equals(14, Zend_Date::HOUR)	Compares the hour, returns TRUE or FALSE	2009-02-13T14:53:27+01:00	TRUE
isEarlier(12, Zend_Date::HOUR)	Compares the hour, returns TRUE or FALSE	2009-02-13T14:53:27+01:00	TRUE
isLater(12, Zend_Date::HOUR)	Compares the hour, returns TRUE or FALSE	2009-02-13T14:53:27+01:00	FALSE

Each part of a date or time has a unique constant in Zend_Date. All constants supported by Zend_Date are listed below.

Day Constants

Constant	Description	Date	Result
Zend_Date::DAY	Day (as number, two digits)	2009-02-13T14:53:27+01:00	13
Zend_Date::DAY_SHORT	Day (as number, one or two digits)	2009-02-06T14:53:27+01:00	6
Zend_Date::WEEKDAY	Weekday (Name of the day, localized, complete)	2009-02-13T14:53:27+01:00	Friday
Zend_Date::WEEKDAY_SHORT	Weekday (Name of the day, localized, abbreviated, two to four chars)	2009-02-13T14:53:27+01:00	Fri for Friday
Zend_Date::WEEKDAY_NAME	Weekday (Name of the day, localized, abbreviated, one or two chars)	2009-02-13T14:53:27+01:00	Fr for Friday
Zend_Date::WEEKDAY_NARROW	Weekday (Name of the day, localized, abbreviated, one char)	2009-02-13T14:53:27+01:00	F for Friday
Zend_Date::WEEKDAY_DIGIT	Weekday (0 = Sunday, 6 = Saturday)	2009-02-13T14:53:27+01:00	5 for Friday
Zend_Date::WEEKDAY_8601	Weekday according to ISO 8601 (1 = Monday, 7 = Sunday)	2009-02-13T14:53:27+01:00	5 for Friday
Zend_Date::DAY_OF_YEAR	Day (as a number, one or two digits)	2009-02-13T14:53:27+01:00	43
Zend_Date::DAY_SUFFIX	English addendum for the day (st, nd, rd, th)	2009-02-13T14:53:27+01:00	th

Week Constants

Constant	Description	Date	Result
Zend_Date::WEEK	Week (as number, 1-53)	2009-02-13T14:53:27+01:00	8

Month Constants

Constant	Description	Date	Result
Zend_Date::MONTH_NAME	Month (Name of the month, localized, complete)	2009-02-13T14:53:27+01:00	February
Zend_Date::MONTH_NAME_SHORT	Month (Name of the month, localized, abbreviated, two to four chars)	2009-02-13T14:53:27+01:00	Feb
Zend_Date::MONTH_NAME_NARROW	Month (Name of the month, localized, abbreviated, one or two chars)	2009-02-13T14:53:27+01:00	F
Zend_Date::MONTH	Month (Number of the month, two digits)	2009-02-13T14:53:27+01:00	02
Zend_Date::MONTH_SHORT	Month (Number of the month, one or two digits)	2009-02-13T14:53:27+01:00	2
Zend_Date::MONTH_DAYS	Number of days for this month (number)	2009-02-13T14:53:27+01:00	28

Year Constants

Constant	Description	Date	Result
Zend_Date::YEAR	Year (number)	2009-02-13T14:53:27+01:00	2009
Zend_Date::YEAR_8601	Year according to ISO 8601 (number)	2009-02-13T14:53:27+01:00	2009
Zend_Date::YEAR_SHORT	Year (number, two digits)	2009-02-13T14:53:27+01:00	09
Zend_Date::YEAR_SHORT_8601	Year according to ISO 8601 (number, two digits)	2009-02-13T14:53:27+01:00	09
Zend_Date::LEAPYEAR	Is the year a leap year? (TRUE or FALSE)	2009-02-13T14:53:27+01:00	FALSE

Time Constants

Constant	Description	Date	Result
Zend_Date::HOUR	Hour (00-23, two digits)	2009-02-13T14:53:27+01:00	14
Zend_Date::HOUR_SHORT	Hour (0-23, one or two digits)	2009-02-13T14:53:27+01:00	14
Zend_Date::HOUR_SHORT_AM	Hour (1-12, one or two digits)	2009-02-13T14:53:27+01:00	2
Zend_Date::HOUR_AM	Hour (01-12, two digits)	2009-02-13T14:53:27+01:00	02
Zend_Date::MINUTE	Minute (00-59, two digits)	2009-02-13T14:53:27+01:00	53
Zend_Date::MINUTE_SHORT	Minute (0-59, one or two digits)	2009-02-13T14:03:27+01:00	3
Zend_Date::SECOND	Second (00-59, two digits)	2009-02-13T14:53:27+01:00	27
Zend_Date::SECOND_SHORT	Second (0-59, one or two digits)	2009-02-13T14:53:07+01:00	7
Zend_Date::MILLISECOND	Millisecond (theoretically infinite)	2009-02-06T14:53:27.20546	20546
Zend_Date::MERIDIEM	Time of day (forenoon or afternoon)	2009-02-13T14:53:27+01:00	afternoon
Zend_Date::SWATCH	Swatch Internet Time	2009-02-13T14:53:27+01:00	620

Timezone Constants

Constant	Description	Date	Result
Zend_Date::TIMEZONE	Name der time zone (string, abbreviated)	2009-02-13T14:53:27+01:00	CET
Zend_Date::TIMEZONE_NAME	Name of the time zone (string, complete)	2009-02-13T14:53:27+01:00	Europe/Paris
Zend_Date::TIMEZONE_SECS	Difference of the time zone to GMT in seconds (integer)	2009-02-13T14:53:27+01:00	3600 (seconds to GMT)
Zend_Date::GMT_DIFF	Difference to GMT in seconds (string)	2009-02-13T14:53:27+01:00	+0100
Zend_Date::GMT_DIFF_SEP	Difference to GMT in seconds (string, separated)	2009-02-13T14:53:27+01:00	+01:00
Zend_Date::DAYLIGHT	Summer time or Winter time? (TRUE or FALSE)	2009-02-13T14:53:27+01:00	FALSE

Date Format Constants (formats include timezone)

Constant	Description	Date	Result
Zend_Date::ISO_8601	Date according to ISO 8601 (string, complete)	2009-02-13T14:53:27+01:00	2009-02-13T14:53:27+01:00
Zend_Date::RFC_2822	Date according to RFC 2822 (string)	2009-02-13T14:53:27+01:00	Fri, 13 Feb 2009 14:53:27 +0100
Zend_Date::TIMESTAMP	» Unix time (seconds since 1.1.1970, mixed)	2009-02-13T14:53:27+01:00	1234533207
Zend_Date::ATOM	Date according to ATOM (string)	2009-02-13T14:53:27+01:00	2009-02-13T14:53:27+01:00
Zend_Date::COOKIE	Date for Cookies (string, for Cookies)	2009-02-13T14:53:27+01:00	Friday, 13-Feb-09 14:53:27 Europe/Paris
Zend_Date::RFC_822	Date according to RFC 822 (string)	2009-02-13T14:53:27+01:00	Fri, 13 Feb 09 14:53:27 +0100
Zend_Date::RFC_850	Date according to RFC 850 (string)	2009-02-13T14:53:27+01:00	Friday, 13-Feb-09 14:53:27 Europe/Paris
Zend_Date::RFC_1036	Date according to RFC 1036 (string)	2009-02-13T14:53:27+01:00	Fri, 13 Feb 09 14:53:27 +0100
Zend_Date::RFC_1123	Date according to RFC 1123 (string)	2009-02-13T14:53:27+01:00	Fri, 13 Feb 2009 14:53:27 +0100
Zend_Date::RSS	Date for RSS Feeds (string)	2009-02-13T14:53:27+01:00	Fri, 13 Feb 2009 14:53:27 +0100
Zend_Date::W3C	Date for HTML or HTTP according to W3C (string)	2009-02-13T14:53:27+01:00	2009-02-13T14:53:27+01:00

Especially note Zend_Date::DATES, since this format specifier has a unique property within Zend_Date as an input format specifier. When used as an input format for $part, this constant provides the most flexible acceptance of a variety of similar date formats. Heuristics are used to automatically extract dates from an input string and then "fix" simple errors in dates (if any), such as swapping of years, months, and days, when possible.

Date and Time Formats (format varies by locale)

Constant	Description	Date	Result
Zend_Date::ERA	Epoch (string, localized, abbreviated)	2009-02-13T14:53:27+01:00	AD (anno Domini)
Zend_Date::ERA_NAME	Epoch (string, localized, complete)	2009-02-13T14:53:27+01:00	anno domini (anno Domini)
Zend_Date::DATES	Standard date (string, localized, default value).	2009-02-13T14:53:27+01:00	13.02.2009
Zend_Date::DATE_FULL	Complete date (string, localized, complete)	2009-02-13T14:53:27+01:00	Friday, 13. February 2009
Zend_Date::DATE_LONG	Long date (string, localized, long)	2009-02-13T14:53:27+01:00	13. February 2009
Zend_Date::DATE_MEDIUM	Normal date (string, localized, normal)	2009-02-13T14:53:27+01:00	13.02.2009
Zend_Date::DATE_SHORT	Abbreviated Date (string, localized, abbreviated)	2009-02-13T14:53:27+01:00	13.02.09
Zend_Date::TIMES	Standard time (string, localized, default value)	2009-02-13T14:53:27+01:00	14:53:27
Zend_Date::TIME_FULL	Complete time (string, localized, complete)	2009-02-13T14:53:27+01:00	14:53 Uhr CET
Zend_Date::TIME_LONG	Long time (string, localized, Long)	2009-02-13T14:53:27+01:00	14:53:27 CET
Zend_Date::TIME_MEDIUM	Normal time (string, localized, normal)	2009-02-13T14:53:27+01:00	14:53:27
Zend_Date::TIME_SHORT	Abbreviated time (string, localized, abbreviated)	2009-02-13T14:53:27+01:00	14:53
Zend_Date::DATETIME	Standard date with time (string, localized, default value).	2009-02-13T14:53:27+01:00	13.02.2009 14:53:27
Zend_Date::DATETIME_FULL	Complete date with time (string, localized, complete)	2009-02-13T14:53:27+01:00	Friday, 13. February 2009 14:53 Uhr CET
Zend_Date::DATETIME_LONG	Long date with time (string, localized, long)	2009-02-13T14:53:27+01:00	13. February 2009 14:53:27 CET
Zend_Date::DATETIME_MEDIUM	Normal date with time (string, localized, normal)	2009-02-13T14:53:27+01:00	13.02.2009 14:53:27
Zend_Date::DATETIME_SHORT	Abbreviated date with time (string, localized, abbreviated)	2009-02-13T14:53:27+01:00	13.02.09 14:53

If you need a date format not shown above, then use a self-defined format composed from the ISO format token specifiers below. The following examples illustrate the usage of constants from the table below to create self-defined ISO formats. The format length is unlimited. Also, multiple usage of format constants is allowed.

The accepted format specifiers can be changed from ISO Format to PHP's date format if you are more comfortable with it. However, not all formats defined in the ISO norm are supported with PHP's date format specifiers. Use the Zend_Date::setOptions(array('format_type' => 'php')) method to switch Zend_Date methods from supporting ISO format specifiers to PHP date() type specifiers (see Self-Defined OUTPUT Formats Using PHP's date() Format Specifiers below).

Constants for ISO 8601 Date Output

Constant	Description	Corresponds best to	Result
G	Epoch, localized, abbreviated	Zend_Date::ERA	AD
GG	Epoch, localized, abbreviated	Zend_Date::ERA	AD
GGG	Epoch, localized, abbreviated	Zend_Date::ERA	AD
GGGG	Epoch, localized, complete	Zend_Date::ERA_NAME	anno domini
GGGGG	Epoch, localized, abbreviated	Zend_Date::ERA	a
y	Year, at least one digit	Zend_Date::YEAR	9
yy	Year, at least two digit	Zend_Date::YEAR_SHORT	09
yyy	Year, at least three digit	Zend_Date::YEAR	2009
yyyy	Year, at least four digit	Zend_Date::YEAR	2009
yyyyy	Year, at least five digit	Zend_Date::YEAR	02009
Y	Year according to ISO 8601, at least one digit	Zend_Date::YEAR_8601	9
YY	Year according to ISO 8601, at least two digit	Zend_Date::YEAR_SHORT_8601	09
YYY	Year according to ISO 8601, at least three digit	Zend_Date::YEAR_8601	2009
YYYY	Year according to ISO 8601, at least four digit	Zend_Date::YEAR_8601	2009
YYYYY	Year according to ISO 8601, at least five digit	Zend_Date::YEAR_8601	02009
M	Month, one or two digit	Zend_Date::MONTH_SHORT	2
MM	Month, two digit	Zend_Date::MONTH	02
MMM	Month, localized, abbreviated	Zend_Date::MONTH_NAME_SHORT	Feb
MMMM	Month, localized, complete	Zend_Date::MONTH_NAME	February
MMMMM	Month, localized, abbreviated, one digit	Zend_Date::MONTH_NAME_NARROW	F
w	Week, one or two digit	Zend_Date::WEEK	5
ww	Week, two digit	Zend_Date::WEEK	05
d	Day of the month, one or two digit	Zend_Date::DAY_SHORT	9
dd	Day of the month, two digit	Zend_Date::DAY	09
D	Day of the year, one, two or three digit	Zend_Date::DAY_OF_YEAR	7
DD	Day of the year, two or three digit	Zend_Date::DAY_OF_YEAR	07
DDD	Day of the year, three digit	Zend_Date::DAY_OF_YEAR	007
E	Day of the week, localized, abbreviated, one char	Zend_Date::WEEKDAY_NARROW	M
EE	Day of the week, localized, abbreviated, two or more chars	Zend_Date::WEEKDAY_NAME	Mo
EEE	Day of the week, localized, abbreviated, three chars	Zend_Date::WEEKDAY_SHORT	Mon
EEEE	Day of the week, localized, complete	Zend_Date::WEEKDAY	Monday
EEEEE	Day of the week, localized, abbreviated, one digit	Zend_Date::WEEKDAY_NARROW	M
e	Number of the day, one digit	Zend_Date::WEEKDAY_DIGIT	4
ee	Number of the day, two digit	Zend_Date::WEEKDAY_NARROW	04
a	Time of day, localized	Zend_Date::MERIDIEM	vorm.
h	Hour, (1-12), one or two digit	Zend_Date::HOUR_SHORT_AM	2
hh	Hour, (01-12), two digit	Zend_Date::HOUR_AM	02
H	Hour, (0-23), one or two digit	Zend_Date::HOUR_SHORT	2
HH	Hour, (00-23), two digit	Zend_Date::HOUR	02
m	Minute, (0-59), one or two digit	Zend_Date::MINUTE_SHORT	2
mm	Minute, (00-59), two digit	Zend_Date::MINUTE	02
s	Second, (0-59), one or two digit	Zend_Date::SECOND_SHORT	2
ss	Second, (00-59), two digit	Zend_Date::SECOND	02
S	Millisecond	Zend_Date::MILLISECOND	20536
z	Time zone, localized, abbreviated	Zend_Date::TIMEZONE	CET
zz	Time zone, localized, abbreviated	Zend_Date::TIMEZONE	CET
zzz	Time zone, localized, abbreviated	Zend_Date::TIMEZONE	CET
zzzz	Time zone, localized, complete	Zend_Date::TIMEZONE_NAME	Europe/Paris
Z	Difference of time zone	Zend_Date::GMT_DIFF	+0100
ZZ	Difference of time zone	Zend_Date::GMT_DIFF	+0100
ZZZ	Difference of time zone	Zend_Date::GMT_DIFF	+0100
ZZZZ	Difference of time zone, separated	Zend_Date::GMT_DIFF_SEP	+01:00
A	Milliseconds from the actual day	Zend_Date::MILLISECOND	20563

Note: Note that the default ISO format differs from PHP's format which can be irritating if you have not used in previous. Especially the format specifiers for Year and Minute are often not used in the intended way.
For year there are two specifiers available which are often mistaken. The Y specifier for the ISO year and the y specifier for the real year. The difference is small but significant. Y calculates the ISO year, which is often used for calendar formats. See for example the 31. December 2007. The real year is 2007, but it is the first day of the first week in the week 1 of the year 2008. So, if you are using 'dd.MM.yyyy' you will get '31.December.2007' but if you use 'dd.MM.YYYY' you will get '31.December.2008'. As you see this is no bug but a expected behaviour depending on the used specifiers.
For minute the difference is not so big. ISO uses the specifier m for the minute, unlike PHP which uses i. So if you are getting no minute in your format check if you have used the right specifier.

If you are more comfortable with PHP's date format specifier than with ISO format specifiers, then you can use the Zend_Date::setOptions(array('format_type' => 'php')) method to switch Zend_Date methods from supporting ISO format specifiers to PHP date() type specifiers. Afterwards, all format parameters must be given with » PHP's date() format specifiers. The PHP date format lacks some of the formats supported by the ISO Format, and vice-versa. If you are not already comfortable with it, then use the standard ISO format instead. Also, if you have legacy code using PHP's date format, then either manually convert it to the ISO format using Zend_Locale_Format::convertPhpToIsoFormat(), or use setOptions(). The following examples illustrate the usage of constants from the table below to create self-defined formats.

The following table shows the list of PHP date format specifiers with their equivalent Zend_Date constants and CLDR and ISO equivalent format specifiers. In most cases, when the CLDR and ISO format does not have an equivalent format specifier, the PHP format specifier is not altered by Zend_Locale_Format::convertPhpToIsoFormat(), and the Zend_Date methods then recognize these "peculiar" PHP format specifiers, even when in the default "ISO" format mode.

Constants for PHP Date Output

Constant	Description	Corresponds best to	closest CLDR equivalent	Result
d	Day of the month, two digit	Zend_Date::DAY	dd	09
D	Day of the week, localized, abbreviated, three digit	Zend_Date::WEEKDAY_SHORT	EEE	Mon
j	Day of the month, one or two digit	Zend_Date::DAY_SHORT	d	9
l (lowercase L)	Day of the week, localized, complete	Zend_Date::WEEKDAY	EEEE	Monday
N	Number of the weekday, one digit	Zend_Date::WEEKDAY_8601	e	4
S	English suffixes for day of month, two chars	no equivalent	no equivalent	st
w	Number of the weekday, 0=sunday, 6=saturday	Zend_Date::WEEKDAY_DIGIT	no equivalent	4
z	Day of the year, one, two or three digit	Zend_Date::DAY_OF_YEAR	D	7
W	Week, one or two digit	Zend_Date::WEEK	w	5
F	Month, localized, complete	Zend_Date::MONTH_NAME	MMMM	February
m	Month, two digit	Zend_Date::MONTH	MM	02
M	Month, localized, abbreviated	Zend_Date::MONTH_NAME_SHORT	MMM	Feb
n	Month, one or two digit	Zend_Date::MONTH_SHORT	M	2
t	Number of days per month, one or two digits	Zend_Date::MONTH_DAYS	no equivalent	30
L	Leapyear, boolean	Zend_Date::LEAPYEAR	no equivalent	TRUE
o	Year according to ISO 8601, at least four digit	Zend_Date::YEAR_8601	YYYY	2009
Y	Year, at least four digit	Zend_Date::YEAR	yyyy	2009
y	Year, at least two digit	Zend_Date::YEAR_SHORT	yy	09
a	Time of day, localized	Zend_Date::MERIDIEM	a (sort of, but likely to be uppercase)	vorm.
A	Time of day, localized	Zend_Date::MERIDIEM	a (sort of, but no guarantee that the format is uppercase)	VORM.
B	Swatch internet time	Zend_Date::SWATCH	no equivalent	1463
g	Hour, (1-12), one or two digit	Zend_Date::HOUR_SHORT_AM	h	2
G	Hour, (0-23), one or two digit	Zend_Date::HOUR_SHORT	H	2
h	Hour, (01-12), two digit	Zend_Date::HOUR_AM	hh	02
H	Hour, (00-23), two digit	Zend_Date::HOUR	HH	02
i	Minute, (00-59), two digit	Zend_Date::MINUTE	mm	02
s	Second, (00-59), two digit	Zend_Date::SECOND	ss	02
e	Time zone, localized, complete	Zend_Date::TIMEZONE_NAME	zzzz	Europe/Paris
I	Daylight	Zend_Date::DAYLIGHT	no equivalent	1
O	Difference of time zone	Zend_Date::GMT_DIFF	Z or ZZ or ZZZ	+0100
P	Difference of time zone, separated	Zend_Date::GMT_DIFF_SEP	ZZZZ	+01:00
T	Time zone, localized, abbreviated	Zend_Date::TIMEZONE	z or zz or zzz	CET
Z	Time zone offset in seconds	Zend_Date::TIMEZONE_SECS	no equivalent	3600
c	Standard Iso format output	Zend_Date::ISO_8601	no equivalent	2004-02-13T15:19:21+00:00
r	Standard Rfc 2822 format output	Zend_Date::RFC_2822	no equivalent	Thu, 21 Dec 2000 16:01:07 +0200
U	Unix timestamp	Zend_Date::TIMESTAMP	no equivalent	15275422364