It's dealing with configuration options in php.ini,may be i think so!
You can see php manual,there is List of php.ini directives!
each option has a definition of changable,which can be set in scripts or php.ini or .htaccess file.
Definition of PHP_INI_* constants
Constant Value Meaning
PHP_INI_USER 1 Entry can be set in user scripts or in Windows registry
PHP_INI_PERDIR 2 Entry can be set in php.ini, .htaccess or httpd.conf
PHP_INI_SYSTEM 4 Entry can be set in php.ini or httpd.conf
PHP_INI_ALL 7 Entry can be set anywhere
so,you can find "short_open_tag":
short_open_tag "1" PHP_INI_PERDIR
that's to say,you must set it in php.ini, .htaccess or httpd.conf;
set in .htaccess:
php_flag short_open_tag on
and you can check that your option is on or off:
<?php
echo ini_get("short_open_tag"); // if on return 1,or return 0
?>