Can be denominated in either US dollars or the number of coins traded.
Can be displayed as stacked or an index that shows the percentage market share each contract has.
In the settings you can exclude any contract so that it only shows the individual and total of the markets you're interested in.
"Linear" or "inverse" refers to the type of perpetual swap contract it is.
Inverse contracts use coin margin, so in this case BTC .
Linear contracts use some type of dollar equivalent margin like USDT for example.
The margin is always specified for the linear contracts.
It's public and free for anyone to use.
People who use my dYdX exchange ref link get access for free: https://dydx.exchange/r/UOMLANHG
In true TradingView spirit, the author of this script has published it open-source, so traders can understand and verify it. Cheers to the author! You may use it for free, but reuse of this code in a publication is governed by House Rules. You can favorite it to use it on a chart.