def opacity(opacity)
      if opacity.is_a?(Numeric)
        Kernel.raise ArgumentError, 'opacity must be >= 0 and <= 1.0' if opacity < 0 || opacity > 1.0
      end
      primitive "opacity #{opacity}"
    end
def opacity(opacity)
      if opacity.is_a?(Numeric)
        Kernel.raise ArgumentError, 'opacity must be >= 0 and <= 1.0' if opacity < 0 || opacity > 1.0
      end
      primitive "opacity #{opacity}"
    end
Specify drawing fill and stroke opacities. If the value is a string
 ending with a %, the number will be multiplied by 0.01.