1. A method for configuring flow control among policy groups used in a network device processing a packet stream, the method comprising: (a) providing a configuration interface for configuring a plurality of policy groups for a network device; (b) identifying, by the configuration interface, a first policy of a first policy group, the first policy specifying a rule comprising a first expression; and (c) receiving, via the interface, information identifying a second policy group to be processed based on an evaluation of the rule.