The core class

The core class is the one which starts and ends the document rendering.
When the core object is instantiated the registry object is created and some of its properties are initialized:

• db: a db class instance (to execute db statements)
• admin_privilege: system admin privilege value
• admin_view_privilege: system admin view privilege value
• public_view_privilege: system public view privilege
• private_view_privilege: system private view privilege

The 'privilege type' properties are the four base system privileges. Installed modules which doesn't need specific permissions can use these.
The admin_privilege refers to administrative tasks which involve db writing actions. The admin_view privileges refers to administration data view. The public_view_privilege refers to the public content view base permission. The private_view_privilege refers to the private content view base permission (private contents are those limited to logged users).