The DATE_
constants are defined since PHP 5.1.1 and they offer standard
date representations, which can be used along with the date format functions
(like date()).
Following constants exists since PHP 5.1.2 and specify a format returned by functions date_sunrise() and date_sunset().
SUNFUNCS_RET_TIMESTAMP
(int)
SUNFUNCS_RET_STRING
(int)
SUNFUNCS_RET_DOUBLE
(int)