This module defines the abstract session interface in a class named AbstractSession, and two descendants MasterSession and StackedSession.

Sessions are hierarchically stacked into each other just like proxies. All sessions except the master session have a parent session from which child sessions inherit variables. Child sessions are stacked into their master sessions, so stacked sessions can inherit data from the encapsulating proxy instances. (Inheritance is implemented using a simple getattr wrapper.)

Instances of the Session classes store the parameters of the client-side and server-side connections in a session object (for example, the IP addresses and zone of the server and the client, and the username and group memberships of the user when authentication is used). Other components refer to this data when making various policy-based decisions.