OpenOrderRule tries to delegate if possible the implementation of expand to the OpenOrderExpander (an OpenOrder or SubscriptionItem subclass) if available. This way, it is easy to encapsulate OpenOrder logic in an Item and combine many different Open Order logic in the same site without touching the code of the Open Order class. For example, Payroll simulation will be implemented by creating an EmploymentContractItem (subsclass of SubscriptionItem) for every worker's contract. The EmploymentContractItem generated in the simulation future Parysheer LInes for work which are themselves expanded using the appropriate Paysheet Model, as defined in the career. 

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@26442 20353a03-c40f-0410-a6d1-a30d3c3de9de