overwrite routines overlay srcwin
on top of dstwin. scrwin and dstwin are not
required to be the same size; only text where the two windows overlap
is copied. The difference is that overlay is non-destructive (blanks
are not copied) whereas overwrite is destructive.
The return values are unspecified.
copywin routine provides a finer granularity of control
overwrite routines. Like in the
prefresh routine, a rectangle is specified in the destination
window, (dminrow, dmincol) and (dmaxrow,
dmaxcol), and the upper-left-corner coordinates of the source
window, (sminrow, smincol). If the argument overlay
#t, then copying is non-destructive, as in overlay.
#t on success or
#f on failure.
indicate that some part of the window would be placed offscreen.