1. A method of configuring a network device to specify flow control among policies used in processing a packet stream, the method comprising: (a) providing a configuration interface for configuring a plurality of policies of a network device, at least one policy of the plurality of policies comprising a policy identifier; and (b) receiving, via the configuration interface, information identifying a first policy of the plurality of policies, the first policy identifying (i) a rule comprising a first expression and (ii) a first action to be taken based on an evaluation of the rule; and (c) receiving, via the configuration interface, information identifying a second policy of the plurality of policies to apply subsequent to the first policy if the rule evaluates to true.