Use it with Fundamental functions to state that a mark price needs to be returned. Note that for non-Forex symbols, this price type is only supported on intraday charts with time interval not greater than 15 days.
input priceType = PriceType.MARK;
plot MarkPrice = close(priceType = priceType);
By default, this script returns the close of mark price of the currently selected symbol, with the price type customizable via input parameters.