I have some small code but I can’t understand, please explain it, thanks:

atr = mult * ta.atr(length) // series float ?
// longStop is a value of float or series float?
longStop = (useClose ? ta.highest(close, length) : ta.highest(length)) - atr
longStopPrev = nz(longStop[1], longStop) // completely don't understand: return of longStop is series??
longStop := close[1] > longStopPrev ? math.max(longStop, longStopPrev) : longStop