Fox VVC or "Variable Valve Control" adds support during high-velocity impacts while leaving the overall shock tune supple for the best of both world. Additionally, the assembly also has a low speed compression adjuster for fine tuning forces from the rider's input. This component comes as part of the Grip2 featured on Factory and Performance-Elite series forks but can be purchased separately and added to Performance series dampers. At less than half the cost of a Grip2 damper, this upgrade has one of the greatest smiles-per-dollar for your OEM fox fork when in comes to maximizing control and tunability.
Please note the assembly doesn't come with the low speed and high speed compression knob. They're purchased separately and can be found here.