Fuel System return type with PWM pump

I've met many cars , like Toyota landcruiser with a fuel system return type and has a vacuum assist regulator,  but it had also PWM pump and fuel rail pressure sensor ! 

Can any one tell me , how the pressure is being regulated ? 

Is it by the mechanical rail regulatregulator controlling the pump speed ! 

 

Is there a specific year of Land Cruiser you're thinking of? Which engine code, specifically? That'd help me in researching the answer.