Hi, these parts of the code where executed:
1) The code in the file:
is executed. You will find several functions inside this class. The functions are named like the event when thei are called. E.g. user_insert us called after a user is inserted, user_update is called when a user is updated etc.
These functions are mostly for validating the input.
2) Then the function user_insert / user_update, etc. in the file /root/ispconfig/scripts/lib/config.lib.php where called. These functions where run with root priveliges and they create the linux user accounts and email configuration.
If you want to make your code available to the iSPConfig project, please make shure that the user is able to switch between the current system user based approach and your mysql based approach by a setting in the isp_server table.