Removing the boundary line for plot "fillrange"

The following code produces a line at the bottom limit of the fill range. My question is simply, “how can i remove that line”?

`plot(x, bottom, fillrange = top, fillalpha = 0.15, c = 1, label = "Confidence")`

I found that the following works:

`plot(x, bottom, fillrange = top, fillalpha = 0.15, c = 1, label = "Confidence range", linealpha = 0)`