The constants below are always available as part of the PHP core.
CASE_LOWER
(integer)
CASE_LOWER is used with
array_change_key_case() and is used to convert array
keys to lower case. This is also the default case for
array_change_key_case().
CASE_UPPER
(integer)
CASE_UPPER is used with
array_change_key_case() and is used to convert array
keys to upper case.
Sorting order flags:
SORT_ASC
(integer)
SORT_ASC is used with
array_multisort() to sort in ascending order.
SORT_DESC
(integer)
SORT_DESC is used with
array_multisort() to sort in descending order.
Sorting type flags: used by various sort functions
SORT_REGULAR
(integer)
SORT_REGULAR is used to compare items normally.
SORT_NUMERIC
(integer)
SORT_NUMERIC is used to compare items numerically.
SORT_STRING
(integer)
SORT_STRING is used to compare items as strings.
SORT_LOCALE_STRING
(integer)
SORT_LOCALE_STRING is used to compare items as
strings, based on the current locale. Added in PHP 5.0.2.
SORT_NATURAL
(integer)
SORT_NATURAL is used to compare items as
strings using "natural ordering" like natsort(). Added in PHP 5.4.0.
SORT_FLAG_CASE
(integer)
SORT_FLAG_CASE can be combined
(bitwise OR) with
SORT_STRING or
SORT_NATURAL to sort strings case-insensitively. Added in PHP 5.4.0.
Filter flags:
ARRAY_FILTER_USE_KEY
(integer)
ARRAY_FILTER_USE_KEY is used with
array_filter() to pass each key as the first argument to the given callback function.
Added in PHP 5.6.0.
ARRAY_FILTER_USE_BOTH
(integer)
ARRAY_FILTER_USE_BOTH is used with
array_filter() to pass both value and key to the given callback function.
Added in PHP 5.6.0.