Howto ? Local/Master Value

Hi all, I m note a great php config hacker. But I notice thing that i doesnt have to notice before :) In my phpinfo i notice 2 column ; Local Value & Master Value http://www.dealgates.com/phpinfo.php So you can make several config judging from the current account ? I dont found anything about that ... How several configs are maintained in a mutual web server ? Surely one php.ini for all and some little hacks on vhosts config ? like here : http://www.php.net/features.safe-mode You can a vhost.conf file. <Directory /vhosts/domain.com/httpdocs/> php_admin_value safe_mode 0 php_admin_value open_basedir "/" </Directory> Explain me ? Thanks.