I was looking in the datasheet of an optocoupler that will trigger a triac and they provide a very basic layout and resistor values for the gate resistors and a capacitor across the optocoupler.

I came across another circuit that came out of an existing machine and they had put a very small resistor of 100 ohms from the gate to the MT2 termal which connects to the neutral which rings similar to a 10 ohm resistor connected as a pull down resistor on a mosfet to make sure it turns off.

Is this infact what this is and what would be the correct size of this resistor?

 

Check out Fairchild App note AN-3006.
Max.