:shade(y-down, y-up[, x-left, x-right])
This shades the area between y-down and y-up that is between x-left and x-right
y-down and y-up may be equations, but the x coordinates must be numbers.
(89) :Shade y-down, y-up, [x-left], [x-right], [pattern], [paternresolution]
Shades the area between y-down and y-up that is between x-left and x-right. Additionally, draws both y-down and y-up. The pattern is determined by pattern and paternresolution
Shades the entire screen, so that the entire screen is black.