Formula for bollinger bands is as below:
Mid = sma(20)
Top = sma(20) + 2*StdDev(20)
Bottom = sma(20) - 2*StdDev(20)
While standard bollinger bands allow changing standard deviation and length, there is no option to use different moving average.
This indicator allows you to define bollinger bands based on different moving average types which can be selected from input.