1. A method of flow control among policy groups used in a network device processing a packet stream, the method comprising: (a) identifying, by an appliance, a first policy group to apply to a received packet stream, the first policy group comprising policies; (b) processing, by the appliance, a first policy of the first policy group, the first policy identifying (i) a rule comprising a first object oriented expression to evaluate a portion of a packet, and (ii) an instruction specifying a second policy group to process subsequent to processing at least one policy of the first policy group, the second policy group comprising policies; (c) evaluating, by the appliance, the first object oriented expression of the rule of the first policy; (d) processing, by the appliance in response to the evaluation of the rule, a second policy of the second policy group in accordance with the instruction of the rule of the first policy; (e) processing, by the appliance, a second policy of the first policy group after the second policy of the second policy group is processed; and (f) performing actions identified in the first policy of the first policy group and the second policy of the second policy group.