cairo:region-union-rectangle (region x y width height)

region -- a cairo:region-t instance
x -- an integer for the x coordinate
y -- an integer for the y coordinate
width -- an integer for the width of the rectangle
height -- an integer for the height of the rectangle

The passed in cairo:region-t instance for the result or nil if an error occured.

Computes the union of region with rectangle and places the result in region.