There is an invisible line added to so it is possible to add indicators like MAs to it. It must be turned on in options to be used.
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.
Sorry if I haven't replied to your message yet, I'm a bit backlogged :)