These modes determine when and where a PHP directive may or may not be set, and each directive within the manual refers to one of these modes. For example, some settings may be set within a PHP script using ini_set(), whereas others may require php.ini or httpd.conf.
For example, the output_buffering setting is PHP_INI_PERDIR therefore it may not be set using ini_set(). However, the display_errors directive is PHP_INI_ALL therefore it may be set anywhere, including with ini_set().
|PHP_INI_USER||Entry can be set in user scripts (like with ini_set()) or in the Windows registry|
|PHP_INI_PERDIR||Entry can be set in php.ini, .htaccess or httpd.conf|
|PHP_INI_SYSTEM||Entry can be set in php.ini or httpd.conf|
|PHP_INI_ALL||Entry can be set anywhere|