Question regarding Bandpass Filter Harmonic


I have a question on the BandpassFilter found in TOS, specifically on the use of a Harmonic in the inputs. This input is noted twice in the code block as (Length/Harmonic).
What I'm trying to learn, is the Harmonic a function or some type of reserve word that contains additional code not visible? The word Harmonic has unique applications as it relates to the overall codes behavior. Otherwise, you could just replace Harmonic with whatever and set it as an input to select a number value. But I'm sure there's code behind the word Harmonic and that's what I'm trying to find. Any guidance is appreciated.
Nope. Harmonic is not a magic word. It is not function.
It is just the name that this script gives that input.
Feel free to change it to christmas or anything else.
The input needs a name and you can call it anything you wish.

In this script that input is being used as an amplifier. It defaults to 1; so it isn't doing anything at the default.
# TD Ameritrade IP Company, Inc. (c) 2019-2023

declare lower;

input length = 20;
input bandwidth = 0.1;
input harmonic = 1;

def beta1 = Cos(2 * Double.Pi / (length / harmonic));
def gamma1 = Cos(bandwidth * 2 * Double.Pi / (length / harmonic));
def alpha1 = 1 / gamma1 - Sqrt(1 / Sqr(gamma1) - 1);
def bandpass = if IsNaN(close + close[2]) then 0 else (1 - alpha1) * (close - close[2]) / 2 + beta1 * (1 + alpha1) * bandpass[1] - alpha1 * bandpass[2];

plot BandpassFilter = bandpass;
plot ZeroLine = 0;


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