On this screen you can choose between PHP 4.x.x or PHP 5.x.x encoding. Your choice should be easy when you know what version of PHP is installed on the server where you plan to run your scripts. You can also create two different versions of your scripts if you have clients who may have a preference for a particular version of PHP.
NOTE: Scripts encoded for PHP 4.x.x will not be able to run under PHP 5.x.x and vice versa.