Hari,
(PLACEHOLDER."$$<YOUR_INPUT_PARAMETER_CASE_SENSITIVE>$$" => yourStringValues)
if you have more than 1 input parameter, then add them by separating them with 1 comma every time... as I did on my example, I had 2 input parameters
yourStringValues must be comma separates and each of them need to be wrapper in single quotes so If you are passing more than one value you can see what I did on line 18 and also 21. Each of those select intos are for different input parameter values. 18 is for materials, 21 was for locations
makes sense?