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 INI_PERDIR  therefore it may not be set using
 ini_set() . However, the
 display_errors directive is
 INI_ALL  therefore it may be set anywhere,
 including with ini_set() .
 
INI_USER 
 (int )
 INI_PERDIR 
 (int )
 INI_SYSTEM 
 (int )
 INI_ALL 
 (int )