overlay(destwin, [sminrow, smincol, dminrow, dmincol, dmaxrow, dmaxcol])
Overlay the window on top of destwin.
The windows need not be the same size, only the overlapping region
is copied. This copy is non-destructive, which means that the
current background character does not overwrite the old contents of
destwin.
To get fine-grained control over the copied region, the second form
of overlay() can be used. sminrow and smincol are the upper-left
coordinates of the source window, and the other variables mark
a rectangle in the destination window.