FuelSystem.vspec:
VariationPoint: #FuelTank
  - CAR   #include CarFuelTank.vspec
  - TRUCK #include TruckFuelTank.vspec
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CarFuelTank.vspec:
TankCapacity:
  datatype: float
  type: attribute
  unit: l
  description: Capacity of the fuel tank in liters.

AbsoluteLevel:
  datatype: float
  type: sensor
  unit: l
  description: Current available fuel in the fuel tank expressed in liters.

RelativeLevel:
  datatype: uint8
  type: sensor
  unit: percent
  min: 0
  max: 100
  description: Level in fuel tank as percent of capacity. 0 = empty. 100 = full.
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TruckFuelTank.vspec:
FuelTanks:
  type: branch
  description: Contains the different fuel tanks.

FuelTanks.MainFuelTank:
  type: branch
  description: The main fuel tank.