&reftitle.constants; &extension.constants.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 4.4.0 and 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.

`COUNT_NORMAL` (`integer`)

`COUNT_RECURSIVE` (`integer`)

`EXTR_OVERWRITE` (`integer`)

`EXTR_SKIP` (`integer`)

`EXTR_PREFIX_SAME` (`integer`)

`EXTR_PREFIX_ALL` (`integer`)

`EXTR_PREFIX_INVALID` (`integer`)

`EXTR_PREFIX_IF_EXISTS` (`integer`)

`EXTR_IF_EXISTS` (`integer`)

`EXTR_REFS` (`integer`)