CloudAttribute.FirstLineName

public string FirstLineName {get;}

cloudAttribute.FirstLineName: str

public partial class CloudSample : Indicator
{
    public override void Calculate(int index)
    {
        Fast[index] = Bars.ClosePrices[index];
        Slow[index] = Bars.OpenPrices[index];
    }
}

def calculate(self, index):
    api.Fast[index] = api.Bars.ClosePrices[index]
    api.Slow[index] = api.Bars.OpenPrices[index]

{
  "AccessRights": "None",
  "IsOverlay": true,
  "LineOutputs": [
    {
      "Name": "Fast",
      "Color": "Green"
    },
    {
      "Name": "Slow",
      "Color": "Red"
    }
  ],
  "Clouds": [
    {
      "FirstLineName": "Fast",
      "SecondLineName": "Slow"
    }
  ]
}