A question about the rsi() function

Hello,

I'm trying to convert this function from pinescript to javascript

mf(src) => rsi(sum(volume * (change(src) <= 0 ? 0 : src), n3), sum(volume * (change(src) >= 0 ? 0 : src), n3))

the only issue is that, by looking at the documentation, the rsi(x, y) function can also take series as the x and y arguments (which is the case in the above function), but there is no information on how the result is calculated from those series.

This is the only thing that they say

If x is a series and y is a series then x and y are considered to be 2 calculated MAs for upward and downward changes.

https://www.tradingview.com/pine-script-reference/#fun_rsi

Can someone please help me understand or point me to a resource on how is this calculated?